Search

Your search keyword '"David Harker"' showing total 89 results
Start Over Author "David Harker"
89 results on '"David Harker"'

1. Diverse Organic-Mineral Associations in Jezero Crater, Mars

Author

Sunanda Sharma, Ryan D. Roppel, Ashley E. Murphy, Luther W. Beegle, Rohit Bhartia, Andrew Steele, Joseph Razzell Hollis, Sandra Siljeström, Francis M. McCubbin, Sanford A. Asher, William J. Abbey, Abigail C. Allwood, Eve L. Berger, Benjamin L. Bleefeld, Aaron S. Burton, Sergei V. Bykov, Emily L. Cardarelli, Pamela G. Conrad, Andrea Corpolongo, Andrew D. Czaja, Lauren P. DeFlores, Kenneth Edgett, Kenneth A. Farley, Teresa Fornaro, Allison C. Fox, Marc D. Fries, David Harker, Keyron Hickman-Lewis, Joshua Huggett, Samara Imbeah, Ryan S. Jakubek, Linda C. Kah, Carina Lee, Yang Liu, Angela Magee, Michelle Minitti, Kelsey R. Moore, Alyssa Pascuzzo, Carolina Rodriguez Sanchez-Vahamonde, Eva L. Scheller, Svetlana Shkolyar, Kathryn M. Stack, Kim Steadman, Michael Tuite, Kyle Uckert, Alyssa Werynski, Roger C. Wiens, Amy J. Williams, Katherine Winchell, Megan R. Kennedy, and Anastasia Yanchilina

Subjects
Lunar and Planetary Science and Exploration, Geosciences (General)
Abstract

The presence and distribution of preserved organic matter on the surface of Mars can provide key information about the Martian carbon cycle and the potential of the planet to host life throughout its history. Several types of organic molecules have been previously detected in Martian meteorites1 and at Gale crater, Mars. Evaluating the diversity and detectability of organic matter elsewhere on Mars is important for understanding the extent and diversity of Martian surface processes and the potential availability of carbon sources1,5,6. Here we report the detection of Raman and fluorescence spectra consistent with several species of aromatic organic molecules in the Máaz and Séítah formations within the Crater Floor sequences of Jezero crater, Mars. We report specific fluorescence-mineral associations consistent with many classes of organic molecules occurring in different spatial patterns within these compositionally distinct formations, potentially indicating different fates of carbon across environments. Our findings suggest there may be a diversity of aromatic molecules prevalent on the Martian surface, and these materials persist despite exposure to surface conditions. These potential organic molecules are largely found within minerals linked to aqueous processes, indicating that these processes may have had a key role in organic synthesis, transport or preservation.

Published
2023
Full Text
View/download PDF

2. Geological, Multispectral, and Meteorological Imaging Results from the Mars 2020 Perseverance Rover in Jezero Crater

Author

James F. Bell, III, Justin N. Maki, Sanna Alwmark, Bethany L. Ehlmann, Sarah A. Fagents, John P. Grotzinger, Sanjeev Gupta, Alexander Hayes, Ken E. Herkenhoff, Briony H. N. Horgan, Jeffrey R. Johnson, Kjartan B. Kinch, Mark T. Lemmon, Morten B. Madsen, Jorge I. Núñez, Gerhard Paar, Melissa Rice, James W. Rice, Jr, Nicole Schmitz, Robert Sullivan, Alicia Vaughan, Mike J. Wolff, Andreas Bechtold, Tanja Bosak, Louise E. Duflot, Alberto G. Fairén, Brad Garczynski, Ralf Jaumann, Marco Merusi, Chase Million, Eleni Ravanis, David L. Shuster, Justin Simon, Michael St. Clair, Christian Tate, Sebastian Walter, Benjamin Weiss, Alyssa M. Bailey, Tanguy Bertrand, Olivier Beyssac, Adrian J. Brown, Piluca Caballo-Perucha, Michael A. Caplinger, Christy M. Caudill, Francesca Cary, Ernest Cisneros, Edward Cloutis, Nathan Cluff, Paul Corlies, Kelsie Crawford, Sabrina Curtis, Robert Deen, Darian Dixon, Christopher Donaldson, Megan Barrington, Michelle Ficht, Stephanie Fleron, Michael Hansen, David Harker, Rachel Howson, Joshua Huggett, Samantha Jacob, Elsa Jensen, Ole B Jensen, Mohini Jodhpurkar, Jonathan Joseph, Christian Juarez, Linda C Kah, Oak Kanine, Jessica Kristensen, Tex Kubacki, Kristiana Lapo, Angela Magee, Michael Maimone, Greg L Mehall, Laura Mehall, Jess Mollerup, Daniel Viúdez-Moreiras, Kristen Paris, Kathryn E Powell, Frank Preusker, Jon Proton, Corrine Rojas, Danny Sallurday, Kim Saxton, Eva Scheller, Christina H Seeger, Mason Starr, Nathan Stein, Nathalie Turenne, Jason Van Beek, Andrew G Winhold, and Rachel Yingling

Subjects
Lunar and Planetary Science and Exploration
Abstract

Perseverance’s Mastcam-Z instrument provides high-resolution stereo and multispectral images with a unique combination of spatial resolution, spatial coverage, and wavelength coverage along the rover’s traverse in Jezero crater, Mars. Images reveal rocks consistent with an igneous (including volcanic and/or volcaniclastic) and/or impactite origin and limited aqueous alteration, including polygonally fractured rocks with weathered coatings; massive boulder-forming bedrock consisting of mafic silicates, ferric oxides, and/or iron-bearing alteration minerals; and coarsely layered outcrops dominated by olivine. Pyroxene dominates the iron-bearing mineralogy in the fine-grained regolith, while olivine dominates the coarse-grained regolith. Solar and atmospheric imaging observations show significant intra- and intersol variations in dust optical depth and water ice clouds, as well as unique examples of boundary layer vortex action from both natural (dust devil) and Ingenuity helicopter–induced dust lifting. High-resolution stereo imaging also provides geologic context for rover operations, other instrument observations, and sample selection, characterization, and confirmation.

Published
2022
Full Text
View/download PDF

3. Data from Blocking Monocytic Myeloid-Derived Suppressor Cell Function via Anti-DC-HIL/GPNMB Antibody Restores the In Vitro Integrity of T Cells from Cancer Patients

Author

Kiyoshi Ariizumi, Ponciano D. Cruz, Farshid Araghizadeh, Purva Gopal, David Harker, Vijay Ramani, Yutaka Horiuchi, Saad Khan, Barbara Haley, John Mansour, Kevin Courtney, Udit Verma, Yull Arriaga, Muhammad Beg, Jin-Sung Chung, and Masato Kobayashi

Abstract

Purpose:Blocking the function of myeloid-derived suppressor cells (MDSC) is an attractive approach for cancer immunotherapy. Having shown DC-HIL/GPNMB to be the T-cell-inhibitory receptor mediating the suppressor function of MDSCs, we evaluated the potential of anti-DC-HIL mAb as an MDSC-targeting cancer treatment.Experimental Design:Patients with metastatic cancer (n = 198) were analyzed by flow cytometry for DC-HIL or PDL1 expression on blood CD14+HLA-DRno/lo MDSCs. Their suppressor function was assessed by in vitro coculture with autologous T cells, and the ability of anti-DC-HIL or anti-PDL1 mAb to reverse such function was determined. Tumor expression of these receptors was examined histologically, and the antitumor activity of the mAb was evaluated by attenuated growth of colon cancers in mice.Results:Patients with metastatic cancer had high blood levels of DC-HIL+ MDSCs compared with healthy controls. Anti-DC-HIL mAb reversed the in vitro function in ∼80% of cancer patients tested, particularly for colon cancer. Despite very low expression on blood MDSCs, anti-PDL1 mAb was as effective as anti-DC-HIL mAb in reversing MDSC function, a paradoxical phenomenon we found to be due to upregulated expression of PDL1 by T-cell-derived IFNγ in cocultures. DC-HIL is not expressed by colorectal cancer cells but by CD14+ cells infiltrating the tumor. Finally, anti-DC-HIL mAb attenuated growth of preestablished colon tumors by reducing MDSCs and increasing IFNγ-secreting T cells in the tumor microenvironment, with similar outcomes to anti-PDL1 mAb.Conclusions:Blocking DC-HIL function is a potentially useful treatment for at least colorectal cancer with high blood levels of DC-HIL+ MDSCs.See related commentary by Colombo, p. 453

Published
2023

4. Supplementary Table S1 -S5 from Blocking Monocytic Myeloid-Derived Suppressor Cell Function via Anti-DC-HIL/GPNMB Antibody Restores the In Vitro Integrity of T Cells from Cancer Patients

Author

Kiyoshi Ariizumi, Ponciano D. Cruz, Farshid Araghizadeh, Purva Gopal, David Harker, Vijay Ramani, Yutaka Horiuchi, Saad Khan, Barbara Haley, John Mansour, Kevin Courtney, Udit Verma, Yull Arriaga, Muhammad Beg, Jin-Sung Chung, and Masato Kobayashi

Abstract

Supplementary Table S1. Summary of MDSC analysis of metastatic cancer patents. aAll cancer patients are diagnosed as stage III or IV. Supplementary Table S2. Correlation of variables and expansion of DC-HIL+ MDSCs among colorectal cancer patients. Supplementary Table S3. % DC-HIL+ MDSC/PBMC in subgroups with vs. without radiotherapy. Supplementary Table S4. Reversing effects of anti-DC-HIL vs. anti-PDL1 mAb on MDSC suppressor function between two different treatments. Supplementary Table S5. DC-HIL and PDL1 expression in colorectal cancer tissues.

Published
2023

5. Supplementary Fig. S1-S8 from Blocking Monocytic Myeloid-Derived Suppressor Cell Function via Anti-DC-HIL/GPNMB Antibody Restores the In Vitro Integrity of T Cells from Cancer Patients

Author

Kiyoshi Ariizumi, Ponciano D. Cruz, Farshid Araghizadeh, Purva Gopal, David Harker, Vijay Ramani, Yutaka Horiuchi, Saad Khan, Barbara Haley, John Mansour, Kevin Courtney, Udit Verma, Yull Arriaga, Muhammad Beg, Jin-Sung Chung, and Masato Kobayashi

Abstract

Supplementary Fig. S1. Early stages CRC patients expressed very low DC-HIL expression on MDSCs. Supplementary Fig. S2. No effect of anti-CD14 mAb on T cell suppressor function of MDSCs. Supplementary Fig. S3. DC-HILneg MC38 and CT26 mouse colon cancer cell lines exhibit high response to anti-DC-HIL treatment. Supplementary Fig. S4. MDSCs in spleen and draining lymph nodes did not express DC-HIL. Supplementary Fig. S5. Combination treatment of anti-DC-HIL/anti-PDL1 mAb did not produce synergistic anti-tumor effects to MC38 colon cancer. Supplementary Fig. S6. Changes in health conditions of mice treated with anti-DC-HIL mAb. Supplementary Fig. S7. Representative FACS data showing frequency of immune cells in the tumor microenvironment of mice treated with mAb. Supplementary Fig. S8. Blood granulocytic MDSC of CRC patients expressed low-levels of DC-HIL and were not immunosuppressive in ex vivo cultures.

Published
2023

7. Geological, multispectral, and meteorological imaging results from the Mars 2020 Perseverance rover in Jezero crater

Author

James F. Bell, Justin N. Maki, Sanna Alwmark, Bethany L. Ehlmann, Sarah A. Fagents, John P. Grotzinger, Sanjeev Gupta, Alexander Hayes, Ken E. Herkenhoff, Briony H. N. Horgan, Jeffrey R. Johnson, Kjartan B. Kinch, Mark T. Lemmon, Morten B. Madsen, Jorge I. Núñez, Gerhard Paar, Melissa Rice, James W. Rice, Nicole Schmitz, Robert Sullivan, Alicia Vaughan, Mike J. Wolff, Andreas Bechtold, Tanja Bosak, Louise E. Duflot, Alberto G. Fairén, Brad Garczynski, Ralf Jaumann, Marco Merusi, Chase Million, Eleni Ravanis, David L. Shuster, Justin Simon, Michael St. Clair, Christian Tate, Sebastian Walter, Benjamin Weiss, Alyssa M. Bailey, Tanguy Bertrand, Olivier Beyssac, Adrian J. Brown, Piluca Caballo-Perucha, Michael A. Caplinger, Christy M. Caudill, Francesca Cary, Ernest Cisneros, Edward A. Cloutis, Nathan Cluff, Paul Corlies, Kelsie Crawford, Sabrina Curtis, Robert Deen, Darian Dixon, Christopher Donaldson, Megan Barrington, Michelle Ficht, Stephanie Fleron, Michael Hansen, David Harker, Rachel Howson, Joshua Huggett, Samantha Jacob, Elsa Jensen, Ole B. Jensen, Mohini Jodhpurkar, Jonathan Joseph, Christian Juarez, Linda C. Kah, Oak Kanine, Jessica Kristensen, Tex Kubacki, Kristiana Lapo, Angela Magee, Michael Maimone, Greg L. Mehall, Laura Mehall, Jess Mollerup, Daniel Viúdez-Moreiras, Kristen Paris, Kathryn E. Powell, Frank Preusker, Jon Proton, Corrine Rojas, Danny Sallurday, Kim Saxton, Eva Scheller, Christiana H. Seeger, Mason Starr, Nathan Stein, Nathalie Turenne, Jason Van Beek, Andrew G. Winhold, and Rachel Yingling

Subjects
Multidisciplinary, OPTICAL DEPTH, IMAGER, Mastcam-Z, Multispectral, Mars 2020, 500 Naturwissenschaften und Mathematik::520 Astronomie::520 Astronomie und zugeordnete Wissenschaften, CLOUDS, Mars, Geology, Perseverance, WIND, VIKING, Mars 2020 Perseverance rover, Imaging, MARTIAN ATMOSPHERE, results, Jezero crater, SAND, VENTIFACTS, DUST AEROSOL, SYSTEM
Abstract

Perseverance’s Mastcam-Z instrument provides high-resolution stereo and multispectral images with a unique combination of spatial resolution, spatial coverage, and wavelength coverage along the rover’s traverse in Jezero crater, Mars. Images reveal rocks consistent with an igneous (including volcanic and/or volcaniclastic) and/or impactite origin and limited aqueous alteration, including polygonally fractured rocks with weathered coatings; massive boulder-forming bedrock consisting of mafic silicates, ferric oxides, and/or iron-bearing alteration minerals; and coarsely layered outcrops dominated by olivine. Pyroxene dominates the iron-bearing mineralogy in the fine-grained regolith, while olivine dominates the coarse-grained regolith. Solar and atmospheric imaging observations show significant intra- and intersol variations in dust optical depth and water ice clouds, as well as unique examples of boundary layer vortex action from both natural (dust devil) and Ingenuity helicopter–induced dust lifting. High-resolution stereo imaging also provides geologic context for rover operations, other instrument observations, and sample selection, characterization, and confirmation.

Published
2022

8. A succinct primer to philosophy of science

Author

David Harker

Subjects
History, Philosophy of biology, Philosophy of science, History and Philosophy of Science, Philosophy, General Social Sciences, Polity, History general, Philosophy of technology, Classics
Published
2021

9. Blastic plasmacytoid dendritic cell neoplasm in a young patient

Author

Jeffrey N, Li, David, Harker, Travis, Vandergriff, and Arturo, Dominguez

Subjects
Male, Young Adult, Neutropenia, Skin Neoplasms, Treatment Outcome, Hematologic Neoplasms, Sepsis, Antineoplastic Combined Chemotherapy Protocols, Humans, Dendritic Cells, Fournier Gangrene
Abstract

Blastic plasmacytoid dendritic cell neoplasm is a rare hematologic neoplasm originating from plasmacytoid dendritic cell precursors that has an aggressive disease course with typically poor prognosis. Herein, we report a man in his early twenties who presented with rapid onset of violaceous nodules and purpuric papules and macules that began on his chest before spreading to his arms, back, face, scalp, and legs. He also exhibited systemic symptoms including weight loss and night sweats. He was diagnosed with blastic plasmacytoid dendritic cell neoplasm and began treatment with aggressive multidrug therapy. Thus far his treatment has resulted in complete resolution of his cutaneous manifestations.

Published
2021

10. Demarcation and The Created Controversy

Author

David Harker

Subjects
Philosophy of language, Philosophy of mind, Philosophy, Philosophy of science, Demarcation problem, Sociology, Social significance, Epistemology
Abstract

The problem of demarcation continues to attract attention, in part because solutions are perceived to have enormous social significance. The civic motivation, however, I argue is in tension with the heterogeneity of the sciences. Philosophers of science would be better employed reflecting on the features, causes, and consequences, of created, scientific controversies. These arise when relevant experts are in broad agreement about what conclusions can sensibly be drawn from available evidence, but the public perceives an expert community deeply divided and conclusions that are plagued by profound and systemic uncertainty. In the second part of the paper I explore this concept further.

Published
2016

11. How to Split a Theory: Defending Selective Realism and Convergence without Proximity

Author

David Harker

Subjects
Philosophy, History, History and Philosophy of Science, business.industry, Inference, Scientific realism, Convergence (relationship), Artificial intelligence, business, Realism, Epistemology, Mathematics
Abstract

The most influential arguments for scientific realism remain centrally concerned with an inference from scientific success to the approximate truth of successful theories. Recently, however...

Published
2013

12. MYC amplification in angiosarcomas arising in the setting of chronic lymphedema of morbid obesity

Author

David, Harker, Michael, Jennings, Patrick, McDonough, Melissa, Mauskar, Stephanie, Savory, Gregory A, Hosler, and Travis, Vandergriff

Subjects
Proto-Oncogene Proteins c-myc, Skin Neoplasms, Chronic Disease, Hemangiosarcoma, Gene Amplification, Humans, Female, Lymphedema, Middle Aged, In Situ Hybridization, Fluorescence, Obesity, Morbid
Abstract

Angiosarcoma is a malignancy of vascular endothelial cells which may arise secondarily as a complication of lymphedema, including chronic lymphedema of morbid obesity. Amplifications in MYC are frequently present in secondary angiosarcoma (arising in irradiated sites and chronic lymphedema) and less frequently in primary cutaneous angiosarcoma.To describe the presence of MYC amplifications in two cases of cutaneous angiosarcoma secondary to chronic lymphedema of morbid obesity.This study is a case series of two patients with cutaneous angiosarcoma. Clinical data was retrieved from the medical records. Histopathological analysis of the biopsy specimens was performed, including immunohistochemistry, along with fluorescence in situ hybridization.Angiosarcoma arose in the setting of massive chronic lymphedema complicating morbid obesity without other predisposing risk factors. Both cases exhibited epithelioid cell morphology and high-level MYC amplification.We report MYC amplification in two cases of angiosarcoma arising in massive chronic lymphedema of morbid obesity.

Published
2016

15. Creating Scientific Controversies

Author

David Harker

Abstract

For decades, cigarette companies helped to promote the impression that there was no scientific consensus concerning the safety of their product. The appearance of controversy, however, was misleading, designed to confuse the public and to protect industry interests. Created scientific controversies emerge when expert communities are in broad agreement but the public perception is one of profound scientific uncertainty and doubt. In the first book-length analysis of the concept of a created scientific controversy, David Harker explores issues including climate change, Creation science, the anti-vaccine movement and genetically modified crops. Drawing on work in cognitive psychology, social epistemology, critical thinking and philosophy of science, he shows readers how to better understand, evaluate, and respond to the appearance of scientific controversy. His book will be a valuable resource for students of philosophy of science, environmental and health sciences, and social and natural sciences.

Published
2015

17. Defining science and the empiricist approach

Author

David Harker

Subjects
Philosophy of science, Demarcation problem, Scientific method, Philosophy, Falsifiability, Empiricism, Scientific revolution, Epistemology
Published
2015

18. Issues of public health: AIDS, autism and GMOs

Author

David Harker

Subjects
medicine.medical_specialty, Acquired immunodeficiency syndrome (AIDS), Public health, medicine, Autism, Psychology, medicine.disease, Psychiatry
Published
2015

19. Points to remember: Part I

Author

David Harker

Subjects
Value (ethics), Demarcation problem, Scientific progress, media_common.quotation_subject, Certainty, Empiricism, Psychology, Scientific theory, Object (philosophy), Underdetermination, media_common, Epistemology
Abstract

A satisfying solution to the problem of demarcation remains elusive, but, regardless, we shouldn't be content with dismissing any theory, study or method simply because it doesn't fulfil a particular definition. Empiricist attitudes towards the sciences emphasize both observations and certain forms of reasoning, but the basic empiricist picture could easily lead to confusion about how sciences work. Our experiences are not always reliable indicators of how things are. We should be wary of placing too much emphasis on how things appear. Biases in subjective experience can be overcome through improved experimental design. There might be very good reasons for ignoring certain data, but those reasons may not always be immediately apparent to those who lack relevant training and education. Certainty is not something sciences achieve, but absence of certainty is consistent with having lots of compelling evidence for given conclusions. We continue to learn about how past experiences can better predict future events. Scientific methods are themselves appropriate objects of criticism and refinement, and the introduction of new methods may be entirely justifiable. All theories confront anomalies, so anomalies alone can't be adequate reasons to dismiss a theory. Theories are pursued, in part, because they offer the most promise for purposes of furthering our understanding. Kuhn's suggestion that scientists work within something like a paradigm has historical plausibility, but this need not imply strong incommensurability between paradigms. Scientific progress is contingent, shaped in part by what problems scientists choose to engage, what technology becomes available, as well as broader socio-economic and political factors. Nevertheless, such contingencies are quite consistent with scientists achieving substantive results relative to the objectives they set. The arguments from underdetermination and discontinuity within the sciences are each reminders of scientific fallibility. Neither provides compelling reasons to deny particular scientific theories or conclusions that some people may find inconvenient or objectionable. Scientific communities may be a more appropriate object for explaining scientific authority. Sciences are not value free, but the role of values in sciences need not compromise scientific authority. It is appropriate to criticize scientific conclusions, methods and theories, but we should remember that some criticisms may be entirely misguided. Worthwhile criticisms are precise and well-supported.

Published
2015

21. Inherent irrationality: cognitive biases and heuristics

Author

David Harker

Subjects
Confirmation bias, media_common.quotation_subject, Base rate fallacy, Irrationality, Bias blind spot, Heuristics, Psychology, Social heuristics, Cognitive bias, Hindsight bias, Cognitive psychology, media_common
Published
2015

23. Introduction: scientific authority and the created controversy

Author

David Harker

Subjects
Value (ethics), symbols.namesake, Politics, Hawking, Aesthetics, Creation science, Political science, Galileo (satellite navigation), symbols, Junk science, Natural (music), Engineering ethics, Mental image
Abstract

The word science can conjure up for us a variety of ideas and images. It can whisk us back to cluttered classrooms, furnished with tall stools and long benches, Bunsen burners, and glass-doored cupboards stocked with assorted paraphernalia. The word might bring to mind the names and faces of famous scientists: Newton, Faraday, Hawking, Curie, Galileo and Mendel all jostle for attention, but ultimately are crowded out by a mental image of Freud and his cigar, Einstein and his untamed hair, or Darwin and an almost equally untamed beard. Maybe it rouses important scientific concepts, activities or instruments, the atom, star gazing, the test tube or the microscope. Perhaps we imagine a pristine laboratory, a young technician dressed in an immaculate white coat, scrutinizing a vial of blue translucent fluid for reasons unknown. Science is ubiquitous. Its boundaries are fuzzy, its range bewildering. Distinctions have been drawn between different types of science, natural versus social, hard versus soft, historical versus experimental, and so on. Disagreement reigns over whether economics is science, whether anthropology is science, whether history is science. Creation science calls itself science, but many call foul. Politicians have suggested – what sounds thoroughly reasonable – that policy should utilize sound science and eschew junk science . Scientific discoveries are reported in the media; scientific concepts are utilized in novels, film and television. Science is popularized and demonized. It offers explanations of our most commonplace observations, but in terms that are peculiar and hard to comprehend. Scientific developments are integral to some of society's most remarkable achievements, but also some of our most horrifying tragedies. Science is both utterly familiar and an immediate source of controversy and debate. The fact that science occupies an extraordinarily important place within modern society makes it important to think more carefully about what science is. A great deal of scientific research is conducted in service to issues of public safety and perceived public need, is funded by taxpayers, and is overseen at least to some extent by political systems. It is sensible to consider whether the research being pursued is of genuine value, of greater value than research that doesn't get funded, and whether the degree of political oversight is appropriate. The technological fruits of scientific labours often give rise to hard questions about the ethics of warfare, human reproduction, food production, energy development and more.

Published
2015

26. Two arguments for scientific realism unified

Author

David Harker

Subjects
History, History and Philosophy of Science, Unification, Aether, Argument, Interpretation (philosophy), Scientific realism, Sociology, Complement (linguistics), Scientific theory, Realism, Epistemology
Abstract

Inferences from scientific success to the approximate truth of successful theories remain central to the most influential arguments for scientific realism. Challenges to such inferences, however, based on radical discontinuities within the history of science, have motivated a distinctive style of revision to the original argument. Conceding the historical claim, selective realists argue that accompanying even the most revolutionary change is the retention of significant parts of replaced theories, and that a realist attitude towards the systematically retained constituents of our scientific theories can still be defended. Selective realists thereby hope to secure the argument from success against apparent historical counterexamples. Independently of that objective, historical considerations have inspired a further argument for selective realism, where evidence for the retention of parts of theories is itself offered as justification for adopting a realist attitude towards them. Given the nature of these arguments from success and from retention, a reasonable expectation is that they would complement and reinforce one another, but although several theses purport to provide such a synthesis the results are often unconvincing. In this paper I reconsider the realist’s favoured type of scientific success, novel success, offer a revised interpretation of the concept, and argue that a significant consequence of reconfiguring the realist’s argument from success accordingly is a greater potential for its unification with the argument from retention.

Published
2010

29. A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

Author

J. P. Grotzinger, D. Y. Sumner, L. C. Kah, K. Stack, S. Gupta, L. Edgar, D. Rubin, K. Lewis, J. Schieber, N. Mangold, R. Milliken, P. G. Conrad, D. DesMarais, J. Farmer, K. Siebach, F. Calef, J. Hurowitz, S. M. McLennan, D. Ming, D. Vaniman, J. Crisp, A. Vasavada, K. S. Edgett, M. Malin, D. Blake, R. Gellert, P. Mahaffy, R. C. Wiens, S. Maurice, J. A. Grant, S. Wilson, R. C. Anderson, L. Beegle, R. Arvidson, B. Hallet, R. S. Sletten, M. Rice, J. Bell, J. Griffes, B. Ehlmann, R. B. Anderson, T. F. Bristow, W. E. Dietrich, G. Dromart, J. Eigenbrode, A. Fraeman, C. Hardgrove, K. Herkenhoff, L. Jandura, G. Kocurek, S. Lee, L. A. Leshin, R. Leveille, D. Limonadi, J. Maki, S. McCloskey, M. Meyer, M. Minitti, H. Newsom, D. Oehler, A. Okon, M. Palucis, T. Parker, S. Rowland, M. Schmidt, S. Squyres, A. Steele, E. Stolper, R. Summons, A. Treiman, R. Williams, A. Yingst, MSL Science Team, Osku Kemppinen, Nathan Bridges, Jeffrey R. Johnson, David Cremers, Austin Godber, Meenakshi Wadhwa, Danika Wellington, Ian McEwan, Claire Newman, Mark Richardson, Antoine Charpentier, Laurent Peret, Penelope King, Jennifer Blank, Gerald Weigle, Shuai Li, Kevin Robertson, Vivian Sun, Michael Baker, Christopher Edwards, Kenneth Farley, Hayden Miller, Megan Newcombe, Cedric Pilorget, Claude Brunet, Victoria Hipkin, Richard Léveillé, Geneviève Marchand, Pablo Sobrón Sánchez, Laurent Favot, George Cody, Lorenzo Flückiger, David Lees, Ara Nefian, Mildred Martin, Marc Gailhanou, Frances Westall, Guy Israël, Christophe Agard, Julien Baroukh, Christophe Donny, Alain Gaboriaud, Philippe Guillemot, Vivian Lafaille, Eric Lorigny, Alexis Paillet, René Pérez, Muriel Saccoccio, Charles Yana, Carlos Armiens-Aparicio, Javier Caride Rodríguez, Isaías Carrasco Blázquez, Felipe Gómez Gómez, Javier Gómez-Elvira, Sebastian Hettrich, Alain Lepinette Malvitte, Mercedes Marín Jiménez, Jesús Martínez-Frías, Javier Martín-Soler, F. Javier Martín-Torres, Antonio Molina Jurado, Luis Mora-Sotomayor, Guillermo Muñoz Caro, Sara Navarro López, Verónica Peinado-González, Jorge Pla-García, José Antonio Rodriguez Manfredi, Julio José Romeral-Planelló, Sara Alejandra Sans Fuentes, Eduardo Sebastian Martinez, Josefina Torres Redondo, Roser Urqui-O’Callaghan, María-Paz Zorzano Mier, Steve Chipera, Jean-Luc Lacour, Patrick Mauchien, Jean-Baptiste Sirven, Heidi Manning, Alberto Fairén, Alexander Hayes, Jonathan Joseph, Robert Sullivan, Peter Thomas, Audrey Dupont, Angela Lundberg, Noureddine Melikechi, Alissa Mezzacappa, Julia DeMarines, David Grinspoon, Günther Reitz, Benito Prats, Evgeny Atlaskin, Maria Genzer, Ari-Matti Harri, Harri Haukka, Henrik Kahanpää, Janne Kauhanen, Mark Paton, Jouni Polkko, Walter Schmidt, Tero Siili, Cécile Fabre, James Wray, Mary Beth Wilhelm, Franck Poitrasson, Kiran Patel, Stephen Gorevan, Stephen Indyk, Gale Paulsen, David Bish, Brigitte Gondet, Yves Langevin, Claude Geffroy, David Baratoux, Gilles Berger, Alain Cros, Claude d’Uston, Olivier Forni, Olivier Gasnault, Jérémie Lasue, Qiu-Mei Lee, Pierre-Yves Meslin, Etienne Pallier, Yann Parot, Patrick Pinet, Susanne Schröder, Mike Toplis, Éric Lewin, Will Brunner, Ezat Heydari, Cherie Achilles, Brad Sutter, Michel Cabane, David Coscia, Cyril Szopa, François Robert, Violaine Sautter, Stéphane Le Mouélic, Marion Nachon, Arnaud Buch, Fabien Stalport, Patrice Coll, Pascaline François, François Raulin, Samuel Teinturier, James Cameron, Sam Clegg, Agnès Cousin, Dorothea DeLapp, Robert Dingler, Ryan Steele Jackson, Stephen Johnstone, Nina Lanza, Cynthia Little, Tony Nelson, Richard B. Williams, Andrea Jones, Laurel Kirkland, Burt Baker, Bruce Cantor, Michael Caplinger, Scott Davis, Brian Duston, Donald Fay, David Harker, Paul Herrera, Elsa Jensen, Megan R. Kennedy, Gillian Krezoski, Daniel Krysak, Leslie Lipkaman, Elaina McCartney, Sean McNair, Brian Nixon, Liliya Posiolova, Michael Ravine, Andrew Salamon, Lee Saper, Kevin Stoiber, Kimberley Supulver, Jason Van Beek, Tessa Van Beek, Robert Zimdar, Katherine Louise French, Karl Iagnemma, Kristen Miller, Fred Goesmann, Walter Goetz, Stubbe Hviid, Micah Johnson, Matthew Lefavor, Eric Lyness, Elly Breves, M. Darby Dyar, Caleb Fassett, Laurence Edwards, Robert Haberle, Tori Hoehler, Jeff Hollingsworth, Melinda Kahre, Leslie Keely, Christopher McKay, Lora Bleacher, William Brinckerhoff, David Choi, Jason P. Dworkin, Melissa Floyd, Caroline Freissinet, James Garvin, Daniel Glavin, Daniel Harpold, David K. Martin, Amy McAdam, Alexander Pavlov, Eric Raaen, Michael D. Smith, Jennifer Stern, Florence Tan, Melissa Trainer, Arik Posner, Mary Voytek, Andrew Aubrey, Alberto Behar, Diana Blaney, David Brinza, Lance Christensen, Lauren DeFlores, Jason Feldman, Sabrina Feldman, Gregory Flesch, Insoo Jun, Didier Keymeulen, Michael Mischna, John Michael Morookian, Betina Pavri, Marcel Schoppers, Aaron Sengstacken, John J. Simmonds, Nicole Spanovich, Manuel de la Torre Juarez, Christopher R. Webster, Albert Yen, Paul Douglas Archer, Francis Cucinotta, John H. Jones, Richard V. Morris, Paul Niles, Elizabeth Rampe, Thomas Nolan, Martin Fisk, Leon Radziemski, Bruce Barraclough, Steve Bender, Daniel Berman, Eldar Noe Dobrea, Robert Tokar, Timothy Cleghorn, Wesley Huntress, Gérard Manhès, Judy Hudgins, Timothy Olson, Noel Stewart, Philippe Sarrazin, Edward Vicenzi, Mark Bullock, Bent Ehresmann, Victoria Hamilton, Donald Hassler, Joseph Peterson, Scot Rafkin, Cary Zeitlin, Fedor Fedosov, Dmitry Golovin, Natalya Karpushkina, Alexander Kozyrev, Maxim Litvak, Alexey Malakhov, Igor Mitrofanov, Maxim Mokrousov, Sergey Nikiforov, Vasily Prokhorov, Anton Sanin, Vladislav Tretyakov, Alexey Varenikov, Andrey Vostrukhin, Ruslan Kuzmin, Benton Clark, Michael Wolff, Oliver Botta, Darrell Drake, Keri Bean, Mark Lemmon, Susanne P. Schwenzer, Ella Mae Lee, Robert Sucharski, Miguel Ángel de Pablo Hernández, Juan José Blanco Ávalos, Miguel Ramos, Myung-Hee Kim, Charles Malespin, Ianik Plante, Jan-Peter Muller, Rafael Navarro-González, Ryan Ewing, William Boynton, Robert Downs, Mike Fitzgibbon, Karl Harshman, Shaunna Morrison, Onno Kortmann, Amy Williams, Günter Lugmair, Michael A. Wilson, Bruce Jakosky, Tonci Balic-Zunic, Jens Frydenvang, Jaqueline Kløvgaard Jensen, Kjartan Kinch, Asmus Koefoed, Morten Bo Madsen, Susan Louise Svane Stipp, Nick Boyd, John L. Campbell, Glynis Perrett, Irina Pradler, Scott VanBommel, Samantha Jacob, Tobias Owen, Hannu Savijärvi, Eckart Boehm, Stephan Böttcher, Sönke Burmeister, Jingnan Guo, Jan Köhler, César Martín García, Reinhold Mueller-Mellin, Robert Wimmer-Schweingruber, John C. Bridges, Timothy McConnochie, Mehdi Benna, Heather Franz, Hannah Bower, Anna Brunner, Hannah Blau, Thomas Boucher, Marco Carmosino, Sushil Atreya, Harvey Elliott, Douglas Halleaux, Nilton Rennó, Michael Wong, Robert Pepin, Beverley Elliott, John Spray, Lucy Thompson, Suzanne Gordon, Ann Ollila, Joshua Williams, Paulo Vasconcelos, Jennifer Bentz, Kenneth Nealson, Radu Popa, Jeffrey Moersch, Christopher Tate, Mackenzie Day, Raymond Francis, Emily McCullough, Ed Cloutis, Inge Loes ten Kate, Daniel Scholes, Susan Slavney, Thomas Stein, Jennifer Ward, Jeffrey Berger, John E. Moores, Division of Geological and Planetary Sciences [Pasadena], California Institute of Technology (CALTECH), Department of Earth and Planetary Science [UC Berkeley] (EPS), University of California [Berkeley], University of California-University of California, The University of Tennessee [Knoxville], Department of Earth Science and Technology [Imperial College London], Imperial College London, ASU School of Earth and Space Exploration (SESE), Arizona State University [Tempe] (ASU), US Geological Survey [Santa Cruz], United States Geological Survey [Reston] (USGS), Princeton University, Department of Geological Sciences [Bloomington], Indiana University [Bloomington], Indiana University System-Indiana University System, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Department of Geological Sciences [Providence], Brown University, NASA Goddard Space Flight Center (GSFC), NASA Ames Research Center (ARC), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Department of Geosciences [Stony Brook], Stony Brook University [SUNY] (SBU), State University of New York (SUNY)-State University of New York (SUNY), State University of New York (SUNY), NASA Johnson Space Center (JSC), NASA, Planetary Science Institute [Tucson] (PSI), Department of Physics [Guelph], University of Guelph, Space Remote Sensing Group (ISR-2), Los Alamos National Laboratory (LANL), Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Center for Earth and Planetary Studies [Washington] (CEPS), Smithsonian National Air and Space Museum, Smithsonian Institution-Smithsonian Institution, Department of Earth and Space Sciences [Seattle], University of Washington [Seattle], Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Department of Geological Sciences [Austin], Jackson School of Geosciences (JSG), University of Texas at Austin [Austin]-University of Texas at Austin [Austin], Rensselaer Polytechnic Institute (RPI), Canadian Space Agency (CSA), NASA Headquarters, Institute of Meteoritics [Albuquerque] (IOM), The University of New Mexico [Albuquerque], University of Hawaii, Brock University [Canada], Cornell University [New York], Geophysical Laboratory [Carnegie Institution], Carnegie Institution for Science [Washington], Massachusetts Institute of Technology (MIT), Lunar and Planetary Institute [Houston] (LPI), GeoRessources, Centre National de la Recherche Scientifique (CNRS)-Université de Lorraine (UL)-Centre de recherches sur la géologie des matières premières minérales et énergétiques (CREGU)-Institut national des sciences de l'Univers (INSU - CNRS), University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Carnegie Institution for Science, Institut national des sciences de l'Univers (INSU - CNRS)-Centre de recherches sur la géologie des matières premières minérales et énergétiques (CREGU)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), NWO-NSO: The role of perchlorates in the preservation of organic compounds on Mars, and Petrology

Subjects
Geologic Sediments, Salinity, Extraterrestrial Environment, Nitrogen, General Science & Technology, Iron, Curiosity rover, Mars, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Astrobiology, MSL Science Team, Exobiology, MSL, Martian, Multidisciplinary, fluvial-lacustrine environments, Biosphere, Water, Phosphorus, Mars Exploration Program, 15. Life on land, Hydrogen-Ion Concentration, Carbon, Oxygen, Planetary science, Bays, 13. Climate action, Rocknest, Sample Analysis at Mars, Sedimentary rock, Oxidation-Reduction, Geology, Sulfur, Hydrogen
Abstract

International audience; The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

Published
2014

30. Mars' surface radiation environment measured with the Mars science laboratory's curiosity rover

Author

Donald M. Hassler, Cary Zeitlin, Robert F. Wimmer-Schweingruber, Bent Ehresmann, Scot Rafkin, Jennifer L. Eigenbrode, David E. Brinza, Gerald Weigle, Stephan Böttcher, Eckart Böhm, Soenke Burmeister, Jingnan Guo, Jan Köhler, Cesar Martin, Guenther Reitz, Francis A. Cucinotta, Myung-Hee Kim, David Grinspoon, Mark A. Bullock, Arik Posner, Javier Gómez-Elvira, Ashwin Vasavada, John P. Grotzinger, MSL Science Team, Osku Kemppinen, David Cremers, James F. Bell, Lauren Edgar, Jack Farmer, Austin Godber, Meenakshi Wadhwa, Danika Wellington, Ian McEwan, Claire Newman, Mark Richardson, Antoine Charpentier, Laurent Peret, Penelope King, Jennifer Blank, Mariek Schmidt, Shuai Li, Ralph Milliken, Kevin Robertson, Vivian Sun, Michael Baker, Christopher Edwards, Bethany Ehlmann, Kenneth Farley, Jennifer Griffes, Hayden Miller, Megan Newcombe, Cedric Pilorget, Melissa Rice, Kirsten Siebach, Katie Stack, Edward Stolper, Claude Brunet, Victoria Hipkin, Richard Léveillé, Geneviève Marchand, Pablo Sobrón Sánchez, Laurent Favot, George Cody, Andrew Steele, Lorenzo Flückiger, David Lees, Ara Nefian, Mildred Martin, Marc Gailhanou, Frances Westall, Guy Israël, Christophe Agard, Julien Baroukh, Christophe Donny, Alain Gaboriaud, Philippe Guillemot, Vivian Lafaille, Eric Lorigny, Alexis Paillet, René Pérez, Muriel Saccoccio, Charles Yana, Carlos Armiens‐Aparicio, Javier Caride Rodríguez, Isaías Carrasco Blázquez, Felipe Gómez Gómez, Sebastian Hettrich, Alain Lepinette Malvitte, Mercedes Marín Jiménez, Jesús Martínez-Frías, Javier Martín-Soler, F. Javier Martín-Torres, Antonio Molina Jurado, Luis Mora-Sotomayor, Guillermo Muñoz Caro, Sara Navarro López, Verónica Peinado-González, Jorge Pla-García, José Antonio Rodriguez Manfredi, Julio José Romeral-Planelló, Sara Alejandra Sans Fuentes, Eduardo Sebastian Martinez, Josefina Torres Redondo, Roser Urqui-O'Callaghan, María-Paz Zorzano Mier, Steve Chipera, Jean-Luc Lacour, Patrick Mauchien, Jean-Baptiste Sirven, Heidi Manning, Alberto Fairén, Alexander Hayes, Jonathan Joseph, Steven Squyres, Robert Sullivan, Peter Thomas, Audrey Dupont, Angela Lundberg, Noureddine Melikechi, Alissa Mezzacappa, Thomas Berger, Daniel Matthia, Benito Prats, Evgeny Atlaskin, Maria Genzer, Ari-Matti Harri, Harri Haukka, Henrik Kahanpää, Janne Kauhanen, Mark Paton, Jouni Polkko, Walter Schmidt, Tero Siili, Cécile Fabre, James Wray, Mary Beth Wilhelm, Franck Poitrasson, Kiran Patel, Stephen Gorevan, Stephen Indyk, Gale Paulsen, Sanjeev Gupta, David Bish, Juergen Schieber, Brigitte Gondet, Yves Langevin, Claude Geffroy, David Baratoux, Gilles Berger, Alain Cros, Claude d’Uston, Olivier Forni, Olivier Gasnault, Jérémie Lasue, Qiu-Mei Lee, Sylvestre Maurice, Pierre-Yves Meslin, Etienne Pallier, Yann Parot, Patrick Pinet, Susanne Schröder, Mike Toplis, Éric Lewin, Will Brunner, Ezat Heydari, Cherie Achilles, Dorothy Oehler, Brad Sutter, Michel Cabane, David Coscia, Cyril Szopa, Gilles Dromart, François Robert, Violaine Sautter, Stéphane Le Mouélic, Nicolas Mangold, Marion Nachon, Arnaud Buch, Fabien Stalport, Patrice Coll, Pascaline François, François Raulin, Samuel Teinturier, James Cameron, Sam Clegg, Agnès Cousin, Dorothea DeLapp, Robert Dingler, Ryan Steele Jackson, Stephen Johnstone, Nina Lanza, Cynthia Little, Tony Nelson, Roger C. Wiens, Richard B. Williams, Andrea Jones, Laurel Kirkland, Allan Treiman, Burt Baker, Bruce Cantor, Michael Caplinger, Scott Davis, Brian Duston, Kenneth Edgett, Donald Fay, Craig Hardgrove, David Harker, Paul Herrera, Elsa Jensen, Megan R. Kennedy, Gillian Krezoski, Daniel Krysak, Leslie Lipkaman, Michael Malin, Elaina McCartney, Sean McNair, Brian Nixon, Liliya Posiolova, Michael Ravine, Andrew Salamon, Lee Saper, Kevin Stoiber, Kimberley Supulver, Jason Van Beek, Tessa Van Beek, Robert Zimdar, Katherine Louise French, Karl Iagnemma, Kristen Miller, Roger Summons, Fred Goesmann, Walter Goetz, Stubbe Hviid, Micah Johnson, Matthew Lefavor, Eric Lyness, Elly Breves, M. Darby Dyar, Caleb Fassett, David F. Blake, Thomas Bristow, David DesMarais, Laurence Edwards, Robert Haberle, Tori Hoehler, Jeff Hollingsworth, Melinda Kahre, Leslie Keely, Christopher McKay, Lora Bleacher, William Brinckerhoff, David Choi, Pamela Conrad, Jason P. Dworkin, Melissa Floyd, Caroline Freissinet, James Garvin, Daniel Glavin, Daniel Harpold, Paul Mahaffy, David K. Martin, Amy McAdam, Alexander Pavlov, Eric Raaen, Michael D. Smith, Jennifer Stern, Florence Tan, Melissa Trainer, Michael Meyer, Mary Voytek, Robert C. Anderson, Andrew Aubrey, Luther W. Beegle, Alberto Behar, Diana Blaney, Fred Calef, Lance Christensen, Joy A. Crisp, Lauren DeFlores, Jason Feldman, Sabrina Feldman, Gregory Flesch, Joel Hurowitz, Insoo Jun, Didier Keymeulen, Justin Maki, Michael Mischna, John Michael Morookian, Timothy Parker, Betina Pavri, Marcel Schoppers, Aaron Sengstacken, John J. Simmonds, Nicole Spanovich, Manuel de la Torre Juarez, Christopher R. Webster, Albert Yen, Paul Douglas Archer, John H. Jones, Douglas Ming, Richard V. Morris, Paul Niles, Elizabeth Rampe, Thomas Nolan, Martin Fisk, Leon Radziemski, Bruce Barraclough, Steve Bender, Daniel Berman, Eldar Noe Dobrea, Robert Tokar, David Vaniman, Rebecca M. E. Williams, Aileen Yingst, Kevin Lewis, Laurie Leshin, Timothy Cleghorn, Wesley Huntress, Gérard Manhès, Judy Hudgins, Timothy Olson, Noel Stewart, Philippe Sarrazin, John Grant, Edward Vicenzi, Sharon A. Wilson, Victoria Hamilton, Joseph Peterson, Fedor Fedosov, Dmitry Golovin, Natalya Karpushkina, Alexander Kozyrev, Maxim Litvak, Alexey Malakhov, Igor Mitrofanov, Maxim Mokrousov, Sergey Nikiforov, Vasily Prokhorov, Anton Sanin, Vladislav Tretyakov, Alexey Varenikov, Andrey Vostrukhin, Ruslan Kuzmin, Benton Clark, Michael Wolff, Scott McLennan, Oliver Botta, Darrell Drake, Keri Bean, Mark Lemmon, Susanne P. Schwenzer, Ryan B. Anderson, Kenneth Herkenhoff, Ella Mae Lee, Robert Sucharski, Miguel Ángel de Pablo Hernández, Juan José Blanco Ávalos, Miguel Ramos, Charles Malespin, Ianik Plante, Jan-Peter Muller, Rafael Navarro-González, Ryan Ewing, William Boynton, Robert Downs, Mike Fitzgibbon, Karl Harshman, Shaunna Morrison, William Dietrich, Onno Kortmann, Marisa Palucis, Dawn Y. Sumner, Amy Williams, Günter Lugmair, Michael A. Wilson, David Rubin, Bruce Jakosky, Tonci Balic-Zunic, Jens Frydenvang, Jaqueline Kløvgaard Jensen, Kjartan Kinch, Asmus Koefoed, Morten Bo Madsen, Susan Louise Svane Stipp, Nick Boyd, John L. Campbell, Ralf Gellert, Glynis Perrett, Irina Pradler, Scott VanBommel, Samantha Jacob, Tobias Owen, Scott Rowland, Hannu Savijärvi, César Martín García, Reinhold Mueller-Mellin, John C. Bridges, Timothy McConnochie, Mehdi Benna, Heather Franz, Hannah Bower, Anna Brunner, Hannah Blau, Thomas Boucher, Marco Carmosino, Sushil Atreya, Harvey Elliott, Douglas Halleaux, Nilton Rennó, Michael Wong, Robert Pepin, Beverley Elliott, John Spray, Lucy Thompson, Suzanne Gordon, Horton Newsom, Ann Ollila, Joshua Williams, Paulo Vasconcelos, Jennifer Bentz, Kenneth Nealson, Radu Popa, Linda C. Kah, Jeffrey Moersch, Christopher Tate, Mackenzie Day, Gary Kocurek, Bernard Hallet, Ronald Sletten, Raymond Francis, Emily McCullough, Ed Cloutis, Inge Loes ten Kate, Raymond Arvidson, Abigail Fraeman, Daniel Scholes, Susan Slavney, Thomas Stein, Jennifer Ward, Jeffrey Berger, John E. Moores, NWO-NSO: The role of perchlorates in the preservation of organic compounds on Mars, Petrology, Southwest Research Institute [Boulder] (SwRI), Kiel University, NASA Goddard Space Flight Center (GSFC), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), German Aerospace Center (DLR), University of Nevada [Reno], Universities Space Research Association (USRA), Denver Museum of Nature and Science, NASA Headquarters, Centro de Astrobiologia [Madrid] (CAB), Instituto Nacional de Técnica Aeroespacial (INTA)-Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), GeoRessources, and Centre National de la Recherche Scientifique (CNRS)-Université de Lorraine (UL)-Centre de recherches sur la géologie des matières premières minérales et énergétiques (CREGU)-Institut national des sciences de l'Univers (INSU - CNRS)

Subjects
Extraterrestrial Environment, Surface Properties, Mars, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Cosmic ray, Radiation Dosage, Exploration of Mars, Astrobiology, Martian surface, Exobiology, galactic cosmic rays, solar energetic particles, Mars Science Laboratory’s Curiosity rover, Humans, Organic Chemicals, Particle radiation, Martian, Radiation Assessment Detector (RAD), Multidisciplinary, Mars Exploration Program, Space Flight, Radiation assessment detector, 13. Climate action, Health threat from cosmic rays, Deinococcus, Cosmic Radiation
Abstract

International audience; The Radiation Assessment Detector (RAD) on the Mars Science Laboratory's Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the martian surface for similar to 300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars and provide an anchor point with which to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient martian environment.

Published
2014

32. Isotope ratios of H, C, and O in CO2 and H2O of the martian atmosphere

Author

Chris R, Webster, Paul R, Mahaffy, Gregory J, Flesch, Paul B, Niles, John H, Jones, Laurie A, Leshin, Sushil K, Atreya, Jennifer C, Stern, Lance E, Christensen, Tobias, Owen, Heather, Franz, Robert O, Pepin, Andrew, Steele, Cherie, Achilles, Christophe, Agard, José Alexandre, Alves Verdasca, Robert, Anderson, Ryan, Anderson, Doug, Archer, Carlos, Armiens-Aparicio, Ray, Arvidson, Evgeny, Atlaskin, Andrew, Aubrey, Burt, Baker, Michael, Baker, Tonci, Balic-Zunic, David, Baratoux, Julien, Baroukh, Bruce, Barraclough, Keri, Bean, Luther, Beegle, Alberto, Behar, James, Bell, Steve, Bender, Mehdi, Benna, Jennifer, Bentz, Gilles, Berger, Jeff, Berger, Daniel, Berman, David, Bish, David F, Blake, Juan J, Blanco Avalos, Diana, Blaney, Jen, Blank, Hannah, Blau, Lora, Bleacher, Eckart, Boehm, Oliver, Botta, Stephan, Böttcher, Thomas, Boucher, Hannah, Bower, Nick, Boyd, Bill, Boynton, Elly, Breves, John, Bridges, Nathan, Bridges, William, Brinckerhoff, David, Brinza, Thomas, Bristow, Claude, Brunet, Anna, Brunner, Will, Brunner, Arnaud, Buch, Mark, Bullock, Sönke, Burmeister, Michel, Cabane, Fred, Calef, James, Cameron, John, Campbell, Bruce, Cantor, Michael, Caplinger, Javier, Caride Rodríguez, Marco, Carmosino, Isaías, Carrasco Blázquez, Antoine, Charpentier, Steve, Chipera, David, Choi, Benton, Clark, Sam, Clegg, Timothy, Cleghorn, Ed, Cloutis, George, Cody, Patrice, Coll, Pamela, Conrad, David, Coscia, Agnès, Cousin, David, Cremers, Joy, Crisp, Alain, Cros, Frank, Cucinotta, Claude, d'Uston, Scott, Davis, Mackenzie, Day, Manuel, de la Torre Juarez, Lauren, DeFlores, Dorothea, DeLapp, Julia, DeMarines, David, DesMarais, William, Dietrich, Robert, Dingler, Christophe, Donny, Bob, Downs, Darrell, Drake, Gilles, Dromart, Audrey, Dupont, Brian, Duston, Jason, Dworkin, M Darby, Dyar, Lauren, Edgar, Kenneth, Edgett, Christopher, Edwards, Laurence, Edwards, Bethany, Ehlmann, Bent, Ehresmann, Jen, Eigenbrode, Beverley, Elliott, Harvey, Elliott, Ryan, Ewing, Cécile, Fabre, Alberto, Fairén, Ken, Farley, Jack, Farmer, Caleb, Fassett, Laurent, Favot, Donald, Fay, Fedor, Fedosov, Jason, Feldman, Sabrina, Feldman, Marty, Fisk, Mike, Fitzgibbon, Melissa, Floyd, Lorenzo, Flückiger, Olivier, Forni, Abby, Fraeman, Raymond, Francis, Pascaline, François, Caroline, Freissinet, Katherine Louise, French, Jens, Frydenvang, Alain, Gaboriaud, Marc, Gailhanou, James, Garvin, Olivier, Gasnault, Claude, Geffroy, Ralf, Gellert, Maria, Genzer, Daniel, Glavin, Austin, Godber, Fred, Goesmann, Walter, Goetz, Dmitry, Golovin, Felipe, Gómez Gómez, Javier, Gómez-Elvira, Brigitte, Gondet, Suzanne, Gordon, Stephen, Gorevan, John, Grant, Jennifer, Griffes, David, Grinspoon, John, Grotzinger, Philippe, Guillemot, Jingnan, Guo, Sanjeev, Gupta, Scott, Guzewich, Robert, Haberle, Douglas, Halleaux, Bernard, Hallet, Vicky, Hamilton, Craig, Hardgrove, David, Harker, Daniel, Harpold, Ari-Matti, Harri, Karl, Harshman, Donald, Hassler, Harri, Haukka, Alex, Hayes, Ken, Herkenhoff, Paul, Herrera, Sebastian, Hettrich, Ezat, Heydari, Victoria, Hipkin, Tori, Hoehler, Jeff, Hollingsworth, Judy, Hudgins, Wesley, Huntress, Joel, Hurowitz, Stubbe, Hviid, Karl, Iagnemma, Steve, Indyk, Guy, Israël, Ryan, Jackson, Samantha, Jacob, Bruce, Jakosky, Elsa, Jensen, Jaqueline Kløvgaard, Jensen, Jeffrey, Johnson, Micah, Johnson, Steve, Johnstone, Andrea, Jones, Jonathan, Joseph, Insoo, Jun, Linda, Kah, Henrik, Kahanpää, Melinda, Kahre, Natalya, Karpushkina, Wayne, Kasprzak, Janne, Kauhanen, Leslie, Keely, Osku, Kemppinen, Didier, Keymeulen, Myung-Hee, Kim, Kjartan, Kinch, Penny, King, Laurel, Kirkland, Gary, Kocurek, Asmus, Koefoed, Jan, Köhler, Onno, Kortmann, Alexander, Kozyrev, Jill, Krezoski, Daniel, Krysak, Ruslan, Kuzmin, Jean Luc, Lacour, Vivian, Lafaille, Yves, Langevin, Nina, Lanza, Jeremie, Lasue, Stéphane, Le Mouélic, Ella Mae, Lee, Qiu-Mei, Lee, David, Lees, Matthew, Lefavor, Mark, Lemmon, Alain, Lepinette Malvitte, Richard, Léveillé, Éric, Lewin-Carpintier, Kevin, Lewis, Shuai, Li, Leslie, Lipkaman, Cynthia, Little, Maxim, Litvak, Eric, Lorigny, Guenter, Lugmair, Angela, Lundberg, Eric, Lyness, Morten, Madsen, Justin, Maki, Alexey, Malakhov, Charles, Malespin, Michael, Malin, Nicolas, Mangold, Gérard, Manhes, Heidi, Manning, Geneviève, Marchand, Mercedes, Marín Jiménez, César, Martín García, Dave, Martin, Mildred, Martin, Jesús, Martínez-Frías, Javier, Martín-Soler, F Javier, Martín-Torres, Patrick, Mauchien, Sylvestre, Maurice, Amy, McAdam, Elaina, McCartney, Timothy, McConnochie, Emily, McCullough, Ian, McEwan, Christopher, McKay, Scott, McLennan, Sean, McNair, Noureddine, Melikechi, Pierre-Yves, Meslin, Michael, Meyer, Alissa, Mezzacappa, Hayden, Miller, Kristen, Miller, Ralph, Milliken, Douglas, Ming, Michelle, Minitti, Michael, Mischna, Igor, Mitrofanov, Jeff, Moersch, Maxim, Mokrousov, Antonio, Molina Jurado, John, Moores, Luis, Mora-Sotomayor, John Michael, Morookian, Richard, Morris, Shaunna, Morrison, Reinhold, Mueller-Mellin, Jan-Peter, Muller, Guillermo, Muñoz Caro, Marion, Nachon, Sara, Navarro López, Rafael, Navarro-González, Kenneth, Nealson, Ara, Nefian, Tony, Nelson, Megan, Newcombe, Claire, Newman, Horton, Newsom, Sergey, Nikiforov, Brian, Nixon, Eldar, Noe Dobrea, Thomas, Nolan, Dorothy, Oehler, Ann, Ollila, Timothy, Olson, Miguel Ángel, de Pablo Hernández, Alexis, Paillet, Etienne, Pallier, Marisa, Palucis, Timothy, Parker, Yann, Parot, Kiran, Patel, Mark, Paton, Gale, Paulsen, Alex, Pavlov, Betina, Pavri, Verónica, Peinado-González, Laurent, Peret, Rene, Perez, Glynis, Perrett, Joe, Peterson, Cedric, Pilorget, Patrick, Pinet, Jorge, Pla-García, Ianik, Plante, Franck, Poitrasson, Jouni, Polkko, Radu, Popa, Liliya, Posiolova, Arik, Posner, Irina, Pradler, Benito, Prats, Vasily, Prokhorov, Sharon Wilson, Purdy, Eric, Raaen, Leon, Radziemski, Scot, Rafkin, Miguel, Ramos, Elizabeth, Rampe, François, Raulin, Michael, Ravine, Günther, Reitz, Nilton, Rennó, Melissa, Rice, Mark, Richardson, François, Robert, Kevin, Robertson, José Antonio, Rodriguez Manfredi, Julio J, Romeral-Planelló, Scott, Rowland, David, Rubin, Muriel, Saccoccio, Andrew, Salamon, Jennifer, Sandoval, Anton, Sanin, Sara Alejandra, Sans Fuentes, Lee, Saper, Philippe, Sarrazin, Violaine, Sautter, Hannu, Savijärvi, Juergen, Schieber, Mariek, Schmidt, Walter, Schmidt, Daniel, Scholes, Marcel, Schoppers, Susanne, Schröder, Susanne, Schwenzer, Eduardo, Sebastian Martinez, Aaron, Sengstacken, Ruslan, Shterts, Kirsten, Siebach, Tero, Siili, Jeff, Simmonds, Jean-Baptiste, Sirven, Susie, Slavney, Ronald, Sletten, Michael, Smith, Pablo, Sobrón Sánchez, Nicole, Spanovich, John, Spray, Steven, Squyres, Katie, Stack, Fabien, Stalport, Thomas, Stein, Noel, Stewart, Susan Louise Svane, Stipp, Kevin, Stoiber, Ed, Stolper, Bob, Sucharski, Rob, Sullivan, Roger, Summons, Dawn, Sumner, Vivian, Sun, Kimberley, Supulver, Brad, Sutter, Cyril, Szopa, Florence, Tan, Christopher, Tate, Samuel, Teinturier, Inge, ten Kate, Peter, Thomas, Lucy, Thompson, Robert, Tokar, Mike, Toplis, Josefina, Torres Redondo, Melissa, Trainer, Allan, Treiman, Vladislav, Tretyakov, Roser, Urqui-O'Callaghan, Jason, Van Beek, Tessa, Van Beek, Scott, VanBommel, David, Vaniman, Alexey, Varenikov, Ashwin, Vasavada, Paulo, Vasconcelos, Edward, Vicenzi, Andrey, Vostrukhin, Mary, Voytek, Meenakshi, Wadhwa, Jennifer, Ward, Eddie, Weigle, Danika, Wellington, Frances, Westall, Roger Craig, Wiens, Mary Beth, Wilhelm, Amy, Williams, Joshua, Williams, Rebecca, Williams, Richard B, Williams, Mike, Wilson, Robert, Wimmer-Schweingruber, Mike, Wolff, Mike, Wong, James, Wray, Megan, Wu, Charles, Yana, Albert, Yen, Aileen, Yingst, Cary, Zeitlin, Robert, Zimdar, and María-Paz, Zorzano Mier

Subjects
Atmosphere, Martian, chemistry.chemical_compound, Multidisciplinary, Meteorite, chemistry, Stable isotope ratio, Sample Analysis at Mars, Carbonate, Mars Exploration Program, Atmosphere of Mars, Astrobiology
Abstract

Mars' Atmosphere from Curiosity The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. Mahaffy et al. (p. 263 ) present volume-mixing ratios of Mars' five major atmospheric constituents (CO 2 , Ar, N 2 , O 2 , and CO) and isotope measurements of 40 Ar/ 36 Ar and C and O in CO 2 , based on data from one of SAM's instruments, obtained between 31 August and 21 November 2012. Webster et al. (p. 260 ) used data from another of SAM's instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO 2 and H 2 O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO 2 and H 2 O were largely established after the period of early atmospheric loss some 4 billion years ago.

Published
2013

33. The half-life of DNA in bone: measuring decay kinetics in 158 dated fossils

Author

James Haile, Charlotte L. Oskam, José Alfredo Samaniego, Matthew J. Collins, R. Paul Scofield, Michael Bunce, Marie L. Hale, Eske Willerslev, Guojie Zhang, Paula F. Campos, Richard N. Holdaway, Morten E. Allentoft, M. Thomas P. Gilbert, and David Harker

Subjects
Mitochondrial DNA, DNA digital data storage, Biology, Real-Time Polymerase Chain Reaction, DNA, Mitochondrial, General Biochemistry, Genetics and Molecular Biology, Bone and Bones, Birds, chemistry.chemical_compound, Animals, Research Articles, General Environmental Science, General Immunology and Microbiology, Models, Genetic, Ecology, Fossils, Radiometric Dating, Temperature, Half-life, General Medicine, Hydrogen-Ion Concentration, Nuclear DNA, Kinetics, Real-time polymerase chain reaction, chemistry, Evolutionary biology, DNA fragmentation, Depurination, General Agricultural and Biological Sciences, DNA, Half-Life, New Zealand
Abstract

Claims of extreme survival of DNA have emphasized the need for reliable models of DNA degradation through time. By analysing mitochondrial DNA (mtDNA) from 158 radiocarbon-dated bones of the extinct New Zealand moa, we confirm empirically a long-hypothesized exponential decay relationship. The average DNA half-life within this geographically constrained fossil assemblage was estimated to be 521 years for a 242 bp mtDNA sequence, corresponding to a per nucleotide fragmentation rate ( k ) of 5.50 × 10 –6 per year. With an effective burial temperature of 13.1°C, the rate is almost 400 times slower than predicted from published kinetic data of in vitro DNA depurination at pH 5. Although best described by an exponential model ( R 2 = 0.39), considerable sample-to-sample variance in DNA preservation could not be accounted for by geologic age. This variation likely derives from differences in taphonomy and bone diagenesis, which have confounded previous, less spatially constrained attempts to study DNA decay kinetics. Lastly, by calculating DNA fragmentation rates on Illumina HiSeq data, we show that nuclear DNA has degraded at least twice as fast as mtDNA. These results provide a baseline for predicting long-term DNA survival in bone.

Published
2012

34. A Likely Explanation: IBE as a Guide to Better (but not more probable) Hypotheses

Author

David Harker

Subjects
Philosophy
Abstract

Several friends of inference to best explanation have claimed in recent work that explanatory virtues, such as consilience, simplicity and increased precision, play an important heuristic role in assigning probabilities to available hypotheses and that it is this role that justifies continued efforts to investigate the scope, nature and epistemic value of the inference rule. In this paper I argue that understanding explanatory virtues as a guide to probability assignments creates a critical dilemma for advocates of IBE that has not previously been made sufficiently explicit and which has significant implications for the prospects of the rule. I conclude that the viability of IBE requires that explanatory virtues be related to a non-probabilistic conception of success.

Published
2011

37. Colored lattices

Author

David Harker

Subjects
Discrete mathematics, Multidisciplinary, Group (mathematics), ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, Permutation group, Type (model theory), Cyclic permutation, Combinatorics, Colored, Physical Sciences: Chemistry, Abelian group, Row, Direct product, Mathematics
Abstract

Combinations of translations and color permutations are derived that leave a periodic array of colored points—a colored lattice—apparently unchanged. It is found that there are three types of colored lattices: ( 1 ) those in which all rows and nets have more than one color, ( 2 ) those in which there are rows with only one color, and ( 3 ) those in which there are both rows and nets with only one color. The color permutation groups of colored lattices are all Abelian. The direct product of three independent cyclic subgroups is required by type 1 , but only two are required by type 2 ; in type 3 the color permutation group consists of the n powers of a cyclic permutation of all n colors present—i.e., the group consists of a single cycle.

Published
1978

38. The three-colored three-dimensional space groups

Author

David Harker

Subjects
Combinatorics, Symmetry operation, Colored, Mirror image, Space group, General Medicine, Trigonal crystal system, Point group, Notation, Three-dimensional space, Mathematics
Abstract

This article contains a table of the groups of combined geometrical and color-permutational symmetry operations that leave a certain kind of three-colored, three-dimensionally periodic object apparently unchanged. The asymmetric units - 'motifs' - of the object are all either geometrically congruent to, or are mirror images of, one another. Each motif has a 'color' representing a scalar quality of some kind, and three different colors of motifs are assumed to occur in the object. Two types of three-colored space groups exist: type I in which all of the geometrical lattice translations leave all the motifs unchanged in color, and type II in which at least one of the geometrical lattice translations requires a permutation of the three colors in order to restore the original appearance. There are 88 three-colored space groups of type I, and 341 of type II. Type I can belong only to the trigonal, hexagonal and cubic systems; type II can belong to any system, except the cubic. A notation for the three-colored, three-dimensional space groups is proposed. It is based on similar principles to those used in the article on colored point groups by Harker [Acta Cryst. (1976), A32, 133-139].

Published
1981

39. Effect of rotational symmetry on colored lattices

Author

David Harker

Subjects
Physics, Combinatorics, Matrix (mathematics), Multidisciplinary, Colored, Physical Sciences: Chemistry, Group (mathematics), Lattice (order), Rotational symmetry, Order (group theory), Coset, Symmetry (geometry)
Abstract

A colored lattice L c has a geometrical lattice L. A subgroup lattice L′ of L and each of its cosets consist of like-colored points, each coset having a different color. The index of L′ in L is given by Δ, the determinant of the matrix ( t jk ) that converts L into L′. This is the order of the factor group {L/L′}, and is also the number n of colors present. The crystal systems—i.e., the combinations of rotational symmetry axes—of L c , L , and L′ are all the same, but L and L′ may have different centerings; this results in 39 combinations of centerings, called here the 39 symmetry types of colored lattices. These types are tabulated here, together with the special forms taken by ( t jk ) and the formulas for Δ. In only 7 of the 39 types can the number of colors be arbitrary; in most types certain numbers of colors are impossible.

Published
1978

41. An X‐Ray Microscope Using Mirrors of Adjustable Curvature

Author

Charlys M. Lucht and David Harker

Subjects
Microscopy, Materials science, Microscope, business.industry, X-Rays, Polishing, Curvature, Radius of curvature (optics), law.invention, Grinding, Surface coating, Optics, law, business, Instrumentation, X-ray microscope
Abstract

An x‐ray microscope is described in which the mirrors are thin optical flats. These flats are mechanically bent to obtain the radius of curvature necessary to focus the image. The adjustable curvature increases the flexibility of the microscope and the ease of focusing the image. The difficulties of grinding and polishing concave cylindrical surfaces are avoided.The degree of smoothness of reflecting surfaces was studied, and the anelastic properties of various mirror materials were investigated to find a material suitable for bending. Highly polished tungsten carbide was found to be an excellent mirror material and does not require an evaporated surface coating of high density metal.The x‐ray microscope promises to be a valuable research instrument.

Published
1951

42. Myelin Membrane Structure As Revealed by X-Ray Diffraction

Author

David Harker

Subjects
Diffraction, Double layer (biology), Electron density, Chemistry, Cell Membrane, Biophysics, Articles, Osmium, Sciatic Nerve, Molecular physics, Crystallography, Reflection (mathematics), X-Ray Diffraction, X-ray crystallography, Turn (geometry), Animals, Anura, Lipid bilayer, Fourier series, Mathematics, Myelin Sheath
Abstract

The present work consists of a new interpretation of the data presented in the article entitled "X-Ray Diffraction of Myelin Membrane. II" by C. K. Akers and D. F. Parsons (1970, Biophys. J.10:116). It will be shown that the projection of the electron density onto the normal to the myelin multilayer derived by these authors is no more consistent with their data than another electron density function, or, perhaps, its negative. (A density function and its negative are related as follows: one of them is a certain density distribution, the other is the same function subtracted from a constant uniform density. Two density functions so related produce identical diffracted intensities.) The Fourier series for the projection of the electron density onto the normal to the myelin multilayer has coefficients +/-[hI(h)](1/2) where I(h) are the intensities of the five orders of reflection; data from which these can be estimated are presented by Akers and Parsons. The sequence of signs found here is + - - + + for the positive density (or - + + - - for the negative one). Quantitative agreement exists between the five X-ray diffraction data of Akers and Parsons and the same intensities calculated from the new model of the myelin structure described here. In this model the myelin double layer, 171 A thick, consists of a central lipid layer 72.4 A thick covered on both surfaces by protein layers 6.9 A thick; these protein layers are covered, in turn, by other lipid layers 42.4 A thick. Minor modifications of this model will no doubt be required to produce agreement between the observed and calculated intensities of the higher order reflections.

Published
1972

43. Relations between Initial and Final Orientations in Rolling and Annealing of Silicon Ferrite

Author

David Harker and B. F. Decker

Subjects
Materials science, Condensed matter physics, Silicon, chemistry, Physics::Instrumentation and Detectors, Annealing (metallurgy), Metallurgy, Final product, General Physics and Astronomy, chemistry.chemical_element
Abstract

An investigation of the effects of rolling and annealing on the orientation of individual grains in silicon ferrite strip yielded results which led to the formulation of a theory for the appearance of the ``magnetic'' orientation in the final processed strip. It is proposed that, in a fine‐grained strip of silicon ferrite, those grains which are already in the ``magnetic'' orientation before rolling will keep that mean orientation during rolling but become more highly strained than other grains, and therefore, they will become the portions of the cold‐rolled strip with highest free energy. In the annealing process these highest energy regions will recrystallize first, becoming lowest energy regions which will be able to consume the now higher energy regions surrounding them. Since these nuclei have the ``magnetic'' orientation, the final product also attains the ``magnetic'' orientation.

Published
1951

45. The crystal structure of decaborane, B10H14

Author

J. S. Kasper, David Harker, and C. M. Lucht

Subjects
Crystal, Diffraction, chemistry.chemical_compound, Crystallography, chemistry, Decaborane, Binding energy, General Earth and Planetary Sciences, Molecule, Sublimation (phase transition), Electron, Crystal structure, General Environmental Science
Abstract

The crystal structure of decaborane has been determined from X-ray diffraction data. Crystals prepared by sublimation at room temperature, or above, show a high degree of polysynthetic twhming, giving rise to diffuseness of reflections for which h and k are odd. In the untwinned condition, the crystal is monoclinie, but pseudo-orthorhombie, and it is convenient to choose the twofold axis in the c direction. The space group is then Ull2/a-C~a. With a0=14-45, b0=20-88 , c 0 -5-68 A.,/? = 90"0 °, the cell contains 8 molecules of B10H14 and the calculated density is 0.96 g.cm. -3. The individual crystals that make up the actual, highly twinned crystalline edifice are so short in the b direction (a few unit translations) that it is convenient ~o consider the system as a partially ordered crystal, the disordered state of which is described by a unit cell one-quarter the size of the

Published
1950

46. THE STRUCTURE OF CRYSTALLINE PROTEINS

Author

David Harker

Subjects
Crystallography, History and Philosophy of Science, Chemistry, General Neuroscience, Structure (category theory), Proteins, General Biochemistry, Genetics and Molecular Biology
Published
1957

48. The Crystal Structure of Hydrazinium Difluoride

Author

David Harker and Marritt L. Kronberg

Subjects
chemistry.chemical_compound, Crystallography, Octahedron, Chemistry, Hydrogen bond, Coordination number, Difluoride, Atom, General Physics and Astronomy, Crystal structure, Physical and Theoretical Chemistry, Fluoride, Ion
Abstract

An x‐ray analysis shows that crystalline hydrazinium difluoride is built upon a rhombohedral unit cell having a0=5.43A, α=38°10′, containing one molecular formula. The positions of the atoms have been determined and correspond to trans‐hydrazinium ions which form linear hydrogen bonds to fluoride ions at the corners of an elongated octahedron. Each fluoride ion forms three hydrogen bonds to different hydrazinium ions, and condenses the octahedra into continuous layers. As a result of the packing of these layers to build up the structure, each nitrogen atom comes in contact with an ``extra'' fluoride ion and thereby assumes a coordination number of 5. Analysis of the N–N and N–H≡F distances of 1.42A and 2.62A, respectively, shows that each atom in the hydrazinium ion bears approximately ¼ of a unit of positive charge. The bearing of the structure of the ion on the adjacent charge rule is discussed. Some of the properties of the ion are interpreted in terms of the structure.

Published
1942

49. Surface Replicas for Use in the Electron Microscope

Author

David Harker and Vincent J. Schaefer

Subjects
Surface (mathematics), Range (particle radiation), Materials science, Micrograph, business.industry, General Physics and Astronomy, law.invention, Solvent, Coated surface, Optics, Interference (communication), law, Vertical direction, Composite material, Electron microscope, business
Abstract

A simple method is described for making replicas of surfaces for study in the electron microscope. The surface to be studied is cleaned and then coated with a very thin slightly wedge‐shaped film of polyvinyl formal having a range in thickness from about 500 to 750A in 2.5 cm. This film is formed by dipping the prepared surface into a 0.5‐percent solution of the resin dissolved in dioxane or ethylene dichloride and permitting the solvent to evaporate while the surface is held in a vertical position. The replica film is removed by placing the coated surface under water and peeling the film from it. A description of this technique is given in detail. A graph is presented which shows the thickness of resin films obtainable from various concentrations of resin in dioxane, and a table gives the interference effects which may be used for determining approximate thicknesses of thin resin films. Several easy procedures are described for checking the thickness of such films. A technique is described for preparing strong films having a thickness of 100A and an area of 3 cm2 when mounted in air. Such films are very useful when working with the electron microscope and several methods are described for mounting specimens on them, including a conditioning treatment—useful in mounting water suspensions—which makes one surface very hydrophilic. Five micrographs show the results obtainable with the techniques described.

Published
1942

50. The Crystal Structure of the Mineral Tetradymite, Bi2Te2S

Author

David Harker

Subjects
Inorganic Chemistry, Crystallography, Mineral, Materials science, engineering, Tetradymite, General Materials Science, Crystal structure, engineering.material, Condensed Matter Physics
Published
1934

Catalog

Books, media, physical & digital resources
See catalog results