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Chemically fueled autonomous molecular machines are catalysis-driven systems governed by Brownian information ratchet mechanisms. One fundamental principle behind their operation is kinetic asymmetry, which quantifies the directionality of molecular motors. However, it is difficult for synthetic chemists to apply this concept to molecular design because kinetic asymmetry is usually introduced in abstract mathematical terms involving experimentally inaccessible parameters. Furthermore, two seemingly contradictory mechanisms have been proposed for chemically driven autonomous molecular machines: Brownian ratchet and power stroke mechanisms. This Perspective addresses both these issues, providing accessible and experimentally useful design principles for catalysis-driven molecular machinery. We relate kinetic asymmetry to the Curtin-Hammett principle using a synthetic rotary motor and a kinesin walker as illustrative examples. Our approach describes these molecular motors in terms of the Brownian ratchet mechanism but pinpoints both chemical gating and power strokes as tunable design elements that can affect kinetic asymmetry. We explain why this approach to kinetic asymmetry is consistent with previous ones and outline conditions where power strokes can be useful design elements. Finally, we discuss the role of information, a concept used with different meanings in the literature. We hope that this Perspective will be accessible to a broad range of chemists, clarifying the parameters that can be usefully controlled in the design and synthesis of molecular machines and related systems. It may also aid a more comprehensive and interdisciplinary understanding of biomolecular machinery.

Ediacaran cap dolostone atop Marinoan glacial deposits contains complex sedimentary structures with extremely negative δ13Ccarb values in close association with oscillations in palaeoclimatic and oceanographic proxy records. However, the precise geological, geochronological and geochemical context of the cap dolostone is not clarified, which hampers us from correctly interpreting the extremely negative δ13Ccarb values and their causal relationships with the Snowball Earth hypothesis. In this study, we conducted detailed in situ geochronological and geochemical analyses on the calcite within the cap dolostone from the Ediacaran Doushantuo Formation in South China in order to define its formation and relationship to the Snowball Earth hypothesis. Petrographic observations show that formation of dolomite pre-dates precipitation of calcite and pyrite, which pre-dates quartz cementation in the basal cap carbonate. Calcite cement within the cap dolostone yielded a U–Pb age of 636.5 ± 7.4/17.8 Ma (2σ, MSWD = 1.6, n = 36/40), which is within uncertainty of a published dolomite U–Pb age of 632 ± 17 Ma (recalculated as 629.3 ± 16.7/22.9 Ma). These age constraints negate the possibility that the calcite cement was formed by late Ediacaran or Cambrian hydrothermal activity. The rare earth element distribution patterns suggest a dominant seawater origin overprinted by subsequent early Ediacaran hydrothermal activity. The combined age, petrographic and geochemical data suggest oxidization of methane clathrates in response to complicated interplay between eustasy and isostatic rebound and hydrothermal fluids.

U-Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method, with potential applications to a vast array of geological issues. Accurate LA-ICP-MS calcite U-Pb dating requires matrix-matched RMs for the correction of instrumental mass bias of Pb/U ratios. Several materials are currently being used as RMs, including WC-1, Duff Brown Tank, ASH-15, JT, and AHX-1A. In this study, we will give a brief introduction of LA-ICP-MS lab at IGGCAS for carbonate U-Pb dating. Meanwhile we further characterized two calcite reference materials for micro-beam U-Pb geochronology and and C, O isotope ratio measurements. LA-ICP-MS multiple spot analyses (> 400) at different regions of materials reveal that calcite TLM and LSJ07 are homogeneous for the U-Pb age with 220.72 +/-0.98 Ma and 26.54+/-0.41 Ma respectively. SIMS multiple spot analyses (> 100) reveals calcite TLM is homogeneous for the O isotope ratio at mm special resolution. MAT 253 gives a bulk result of δ18O =-14.20 ‰. LA-MC-ICP-MS multiple spot analyses (> 200) reveals calcite TLM and LSJ07 are homogeneous for the C and O isotope ratio at mm special resolution. MAT 253 gives bulk results of δ13C =-1.53 ‰ andδ13C =-0.33 ‰ for TLM and LSJ07 respectively. These two materials represent a useful addition to the currently distributed WC-1, Duff Brown Tank, ASH-15, JT, and AHX-1A for micro-analytical techniques of U-Pb geochronology and C, O isotope ratio measurements.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of calcite has been an emerging research direction in recent years that has been widely applied to various disciplines, such as dating of brittle deformation, biological biomineralization, oceanic crust alteration, and hydrocarbon migration. The method has the advantage of quickly locating regions of relatively high uranium content and radiogenic lead that avoids the time-consuming procedures traditionally required for isotope dilution methods. Herein, we show how this method is successfully applied to dating of diagenesis and hydrothermal activity in Precambrian-Phanerozoic sedimentary rocks, but with a note of caution that the susceptibility of the calcite U-Pb isotope system to fluid activities means interpretation of calcite U-Pb data and selection of calcite standard should be cautioned. We demonstrate the following case studies: LA-ICP-MS calcite U-Pb geochronology has aided in defining the Mesoproterozoic-Neoproterozoic boundary (ca. 1010 Ma) in North China Craton. It also constrains the timing of calcite infillings in the Ediacaran cap carbonate to be ca. 636 Ma, indicating an early diagenetic origin and thus confirming a methane seepage hypothesis. Two episodes of hydrothermal activity (ca. 290 Ma and ca. 250 Ma) have been recognized from the Cambrian carbonate in the Tarim region, which was induced by the Permian Tarim Large Igneous Province (LIP) and Indosinian orogeny, respectively.

Biology operates through autonomous chemically fuelled molecular machinery

Chemical reaction networks that transform out-of-equilibrium 'fuel' to 'waste' are the engines that power the biomolecular machinery of the cell. Inspired by such systems, autonomous artificial molecular machinery is being developed that functions by catalysing the decomposition of chemical fuels, exploiting kinetic asymmetry to harness energy released from the fuel-to-waste reaction to drive non-equilibrium structures and dynamics. Different aspects of chemical fuels profoundly influence their ability to power molecular machines. Here we consider the structure and properties of the fuels that biology has evolved and compare their features with those of the rudimentary synthetic chemical fuels that have so far been used to drive autonomous non-equilibrium molecular-level dynamics. We identify desirable, but context-specific, traits for chemical fuels together with challenges and opportunities for the design and invention of new chemical fuels to power synthetic molecular machinery and other dissipative nanoscale processes.

We report a rotaxane-based information ratchet in which the macrocycle distribution is pumped away from equilibrium using a carbodiimide fuel. A carboxylate group on the axle, nonequidistant between two macrocycle binding sites, efficiently catalyzes the hydration of a carbodiimide fuel to the corresponding urea waste, with >80% of the fuel molecules reacting through the machine-catalyzed pathway. The energy of the reaction is harnessed by kinetic differentiation of the mechanical states of the machine driving the macrocycle to the binding site distal to the catalyst. Steric hindrance between the macrocycle and the fuel slows the reaction of the carboxylate group (to form a barrier to macrocycle movement) in the proximal co-conformer, whereas hydrogen bonding between the macrocycle and the barrier accelerates hydrolysis of the activated ester proximal isomer. The two directionally biased processes reinforce each other’s effect, resulting in a doubly kinetically gated ratchet that achieves 1:18 directionality, an exceptional degree of selectivity for a synthetic chemically fueled molecular motor.

SUMMARYThe incidence of recreational water-associated outbreaks in the United States has significantly increased, driven, at least in part, by outbreaks both caused byCryptosporidiumand associated with treated recreational water venues. Because of the parasite's extreme chlorine tolerance, transmission can occur even in well-maintained treated recreational water venues (e.g. pools) and a focal cryptosporidiosis outbreak can evolve into a community-wide outbreak associated with multiple recreational water venues and settings (e.g. childcare facilities). In August 2004 in Auglaize County, Ohio, multiple cryptosporidiosis cases were identified and anecdotally linked to pool A. Within 5 days of the first case being reported, pool A was hyperchlorinated to achieve 99·9%Cryptosporidiuminactivition. A case-control study was launched to epidemiologically ascertain the outbreak source 11 days later. A total of 150 confirmed and probable cases were identified; the temporal distribution of illness onset was peaked, indicating a point-source exposure. Cryptosporidiosis was significantly associated with swimming in pool A (matched odds ratio 121·7, 95% confidence interval 27·4–∞) but not with another venue or setting. The findings of this investigation suggest that proactive implementation of control measures, when increasedCryptosporidiumtransmission is detected but before an outbreak source is epidemiologically ascertained, might prevent a focal cryptosporidiosis outbreak from evolving into a community-wide outbreak.

The Impact of Photoelectron Spectroscopy on Surface Chemistry and Catalysis

Objective.—Terminal deoxynucleotidyl transferase (TdT) is a useful marker in the diagnosis of acute lymphoblastic leukemia (ALL) (French-American-British [FAB] L1 and L2) and is most useful in distinguishing ALL from mature B-lymphoid neoplasms, such as Burkitt lymphoma (FAB L3) and other lymphoid malignancies. The frequency of TdT-negative ALL is not known. Here we report 3 TdT-negative ALL cases that met the criteria for T-cell ALL. Design.—We reviewed approximately 200 cases of ALL retrieved from the database at our institution. All cases were evaluated using Wright-Giemsa, myeloperoxidase, butyrate, and TdT staining; immunophenotyped using flow cytometry; and studied using Southern blot analyses for T-cell receptors and immunoglobulin gene rearrangement. Results.—All ALL cases (L1 and L2) were TdT-positive, except for 3 cases that were of early T-cell lineage. None of the 3 cases demonstrated positivity for TdT in immunofluorescence staining with polyclonal antibodies or flow cytometry with monoclonal antibodies. Flow cytometric analysis confirmed a pre–T-cell immunophenotype in all 3 cases. One of the cases showed rearrangement of a T-cell antigen receptor and immunoglobulin heavy chain (JH). A second case showed germline configuration of T-cell receptors, but also showed rearrangement of the JH, despite the expression of T-cell markers only.

/ Land use/land cover classifications for 1973 and 1991, derived from the interpretation of satellite imagery, are quantified on the basis of biophysical land units in a study area in southeastern Australia. Nutrient export potentials are estimated for each land unit based on their composition of land use/land cover classes. Spatial and temporal comparisons are made of the land units based on the calculated pollution hazard indicators to provide an insight into changes in the state of the environment and the regional significance of land use changes. For example, one ecosystem, unique to the study, showed a large increase in pollution hazard over the study period as a manifestation of an 11-fold rise in cleared area and an expansion of cropping activities. The benefits to environmental management in general are discussed.KEY WORDS: Land cover change; Nutrient export; Environmental condition; Pollution hazard; Agricultural pollution; Nonpoint source pollution; Diffuse pollution; Environmental degradation

There has been considerable recent concern over the amount of vegetation clearance and associated environmental degradation risk in the Western Division of New South Wales. An integrated remote sensing/GIS approach was used to provide information required to address this issue. The extent and nature of recent vegetation clearance was quantified to give a basic indication of the prevailing land condition in a study area in the central‐eastern portion of the Western Division. Between 1973 and 1991 there was an increase of 86 per cent in the extent of cleared landscapes. Further interpretation of this indicator with respect to the study period identified spatial and temporal trends critical to understanding the significance of observed environmental change. Change has not been uniform, with environments covering the red‐earth lands fringing the Lachlan River floodplain particularly impacted. The nature of changes was quantified with respect to various land units. The suitability of the approach for ...

Using a combination of continuum modeling, atomistic simulations, and numerical optimization, we estimate the flexural rigidity of a graphene sheet. We consider a rectangular sheet that is initially parallel to a rigid substrate. The sheet interacts with the substrate by van der Waals forces and deflects in response to loading on a pair of opposite edges. To estimate the flexural rigidity, we model the graphene sheet as a continuum and numerically solve an appropriate differential equation for the transverse deflection. This solution depends on the flexural rigidity. We then use an optimization procedure to find the value of the flexural rigidity that minimizes the difference between the numerical solutions and the deflections predicted by atomistic simulations. This procedure predicts a flexural rigidity of 0.26 nNnm=1.62 eV.

A combination of photoelectron and vibrational spectroscopies has established that a high energy formate species generated at a Pb(110)-surface is tilted with respect to the surface normal and decomposes spontaneously through H-bonding interactions with HCOOH(g) at 295 K.

In a combined photoelectron-vibrational spectroscopic study of the chemistry of formic acid interaction with A1(111) surfaces the influence of temperature, surface oxidation and coadsorption with water have been investigated. At the clean surface adsorption at low temperatures leads to deprotonation and on warming to room temperature the major species is formate. On the other hand direct interaction with A1(111) at room temperature leads to more extensive bond cleavage including the formation of chemisorbed oxygen, and carbidic carbon. At the preoxidized A1(111) surface deprotonation is facile at 80 K but there is no evidence for further reaction on warning to room temperature. When formic acid is coadsorbed with water at 295 K, HREEL and XP spectra confirm the formation of surface formate together with hydroxyl and chemisorbed oxygen species.

The major techniques presently used for characterising solid surfaces are summarized. These techniques include interactions (or release) of photons, electrons and neutral or charged atoms and molecules, and other miscellaneous methods which may be applied to single crystal surfaces or polycrystalline material

Observing structured parent-child interaction in clinic analogs has been a tradition in child clinical assessment since the 1960s. The clinic analog is designed to re-create important conditions from natural contexts such that dysfunctional parent-child patterns can be observed and modified. To those basic goals, the modern clinician would add diagnosis and treatment evaluation. Three classes of parent-child clinic analogs designed to evaluate preadolescent children with externalizing disorders were reviewed: free play, parent-directed play, and parent-directed chores. Free-play analogs and parent-directed chore analogs were found to have merit, but remain psychometrically underdeveloped. Practitioner reliance on questionnaires and interviews appears likely to continue until observational analogs have attained sufficient psychometric qualities to facilitate routine clinical decisions.

This study defines the specific communications capabilities of U.S. Navy ships and identifies operational problems and technical barriers prohibiting telemedicine on a wide scale. This information is needed so the transmission of medical data can be managed in conformance with shipboard capabilities and contingencies can be developed for the potential degradation of those capabilities. While communications requirements for telemedicine in the civilian sector continue to be defined and implemented on a limited basis, the Department of Defense (DoD) must also supply similar needs in hostile environments.

The purpose of this pilot study is to report a cost comparison of general anesthesia (GA) versus oral conscious sedation (CS) for the treatment of pediatric dental patients.The study sample included 22 children whose parents/guardian selected GA care for their child. Selection criteria limited inclusion to healthy children (ASA I) ages 24-60 m.o. The subjects acted as their own comparison group to an estimation CS model. Models were developed to assess societal costs for treatment under GA and CS. Treatment rendered was equalized using the dental Relative Based Value Units Scale (RBVU).Ordinary Least Squares Regression analysis techniques showed the association of RBVU to the total societal costs of GA and CS to be significant (P0.01) with an adjusted R2 of .64 and .78 respectively. When regression lines were plotted, the intersection represented RBVU level at which societal costs of GA and CS were the same.Under the conditions of this pilot study, it is concluded that CS costs exceed GA costs at a RBVU level of 66.4, which would equate to more than three CS appointments.

The purpose of this study was to evaluate the response of the human primary pulp to the carbon dioxide laser and formocresol for vital pulp therapy.Fifteen healthy children with intact, caries-and-restoration-free, contralateral primary cuspids with at least two-thirds of the roots remaining who were scheduled for orthodontic extraction were randomly assigned to pulpotomy treatment with a carbon dioxide laser or formocresol. The treated teeth were clinically and radiographically evaluated at 28 and 90 days post-treatment prior to extraction. The extracted teeth were evaluated histologically for pulpal response.All teeth were asymptomatic and clinically normal at both observation periods. Internal root resorption was observed in one formocresol and two laser treated teeth. There was a significant inverse correlation between the laser energy applied to the pulp and the degree of inflammation at 28 days (P = .01) but not at 90 days (P = .27).Carbon dioxide laser treatment compared favorably to formocresol for pulpotomy in primary teeth.

The objective of this study was to assess the pattern of permanent teeth present in a self-selected sample of 17 female and 35 male patients with ectodermal dysplasia presenting for treatment with dental implants.Mean age of sample: 18.7 years, age range: 5.9 to 60.9 years. Panoramic radiographs were examined independently by two investigators to determine the permanent teeth present. None of the sample reported extractions of permanent teeth prior to presenting for implants.Permanent teeth most likely to be present, reported as a percentage of the patient sample with that tooth, were: maxillary central incisors (42%), maxillary first molars (41%), mandibular first molars (39%), maxillary canines (22%), mandibular second molars (17%), maxillary second premolars (15%), and mandibular premolars (12%). Comparing dentition by quadrants, mandibular anterior teeth (canines and incisors) were least likely to be present.Results support previous findings that the maxillary central incisors, maxillary first molars, mandibular first molars, and maxillary canines are the most conserved teeth in hypodontia. Successful use of osseointegrated implants in the anterior mandibles of most of these patients suggests that habilitation of the mandible with dental implant-supported prostheses is a reasonable option.