640 results on '"Bogdan, F."'
Search Results
152. Experimental determination of reader resolution using PRS patterns and application to media cluster size measurement
- Author
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Valcu, Bogdan F., primary, Wu, Xiao, additional, Albuquerque, Goncalo, additional, Papusoi, Cristian, additional, and Desai, Mrugesh, additional
- Published
- 2017
- Full Text
- View/download PDF
153. VariaSim
- Author
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Bogdan F. Romanescu, Michael E. Bauer, Daniel J. Sorin, and Sule Ozev
- Subjects
Computer architecture ,Computer science ,Hardware_INTEGRATEDCIRCUITS ,Hardware_PERFORMANCEANDRELIABILITY ,General Medicine ,Process variability ,Cmos process ,Hardware_LOGICDESIGN ,Electronic circuit - Abstract
In this paper, we present VariaSim, the publicly available Static Statistical Timing Analysis (SSTA) Tool from Duke University. VariaSim enables researchers to analyze the impact of CMOS process variability on the behavior of circuits and systems.
- Published
- 2007
154. Application of the apparent lattice parameter to determination of the core-shell structure of nanocrystals
- Author
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Ewa Grzanka, Witold Palosz, Bogdan F. Palosz, Stanislaw Gierlotka, and Svetlana Stelmakh
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Condensed matter physics ,business.industry ,Chemistry ,Computer Science::Information Retrieval ,Neutron diffraction ,Stacking ,Bragg's law ,Condensed Matter Physics ,Inorganic Chemistry ,Core shell ,Optics ,Lattice constant ,Nanocrystal ,Lattice (order) ,General Materials Science ,business ,Lattice model (physics) - Abstract
In this review work we discuss applicability of Bragg scattering to examination of nanocrystals. We approximate the structure of nanograins by a commonly accepted core-shell model. We show that, for principal reasons, the Bragg equation is not applicable directly to nanocrystals. We use the Bragg relation through application of the apparent lattice parameter (alp) concept which we use to evaluate quantitatively the core-shell model. We also introduce a new parameter of the structure, Equivalent Cubic Lattice Parameter (EClp), which quantifies deviation of the real (trigonal) lattice from its parent fcc structure due to the lattice deformation (e.g. by the stacking faults). We show examples of an analysis of experimental X-ray and neutron diffraction data based on the alp methodology and on the theoretical patterns calculated for various core-shell models.
- Published
- 2007
155. Asymmetric distribution of metals in theXenopus laevisoocyte: a synchrotron X-ray fluorescence microprobe study
- Author
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Konstantin Ignatyev, Nick Ovsenek, Bogdan F. Gh. Popescu, Zachery R. Belak, and Helen Nichol
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Microprobe ,Polarity in embryogenesis ,Iron ,Xenopus ,chemistry.chemical_element ,Zinc ,Mitochondrial cloud ,Microscopy, Scanning Probe ,Biochemistry ,Selenium ,Xenopus laevis ,Metals, Heavy ,medicine ,Animals ,Molecular Biology ,biology ,Spectrometry, X-Ray Emission ,Cell Biology ,biology.organism_classification ,Oocyte ,Copper ,Crystallography ,medicine.anatomical_structure ,chemistry ,Oocytes ,Biophysics ,Synchrotrons - Abstract
The asymmetric distribution of many components of the Xenopus oocyte, including RNA, proteins, and pigment, provides a framework for cellular specialization during development. During maturation, Xenopus oocytes also acquire metals needed for development, but apart from zinc, little is known about their distribution. Synchrotron X-ray fluorescence microprobe was used to map iron, copper, and zinc and the metalloid selenium in a whole oocyte. Iron, zinc, and copper were asymmetrically distributed in the cytoplasm, while selenium and copper were more abundant in the nucleus. A zone of high copper and zinc was seen in the animal pole cytoplasm. Iron was also concentrated in the animal pole but did not colocalize with zinc, copper, or pigment accumulations. This asymmetry of metal deposition may be important for normal development. Synchrotron X-ray fluorescence microprobe will be a useful tool to examine how metals accumulate and redistribute during fertilization and embryonic development.
- Published
- 2007
156. Neutron diffraction studies of the atomic thermal vibrations in complex materials: application of the Wilson method to examination of micro- and nano-crystalline SiC
- Author
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Witold Palosz, T. Waldek Zerda, Ewa Grzanka, Bogdan F. Palosz, Svitlana Stelmakh, Marcin Wojdyr, Thomas Proffen, and Sven C. Vogel
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Diffraction ,Neutron diffraction ,Crystal structure ,Condensed Matter Physics ,Molecular physics ,Nanocrystalline material ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Microcrystalline ,Nanocrystal ,chemistry ,Silicon carbide ,General Materials Science ,Atomic spacing - Abstract
The Wilson method was applied for determination of the thermal atomic motions in micro- and nano-crystalline SiC. Limitations of application of this method to examination of complex materials with atoms vibrating with more that one amplitude were discussed. It is shown that a unique interpretation of Wilson plots for crystals with more than one type of atoms and weak vibration component(s) requires measurements performed up to a very large diffraction vector Q (>25 Å–1). Atomic vibrations in microcrystalline SiC were evaluated based on the diffractograms calculated for models built assuming different mean square atomic displacements (vibration amplitudes) of the component atoms. For nanocrystalline SiC two different temperature atomic factors which describe vibrations of the atoms in the grain interior (B core) and at its surface (B shell) were determined.
- Published
- 2007
157. Multiple Sclerosis masquerading as Alzheimer type dementia – Clinical, radiological and pathological findings
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W. O. Tobin, Joseph E. Parisi, Julie A. Fields, Kejal Kantarci, MB Bruns, Claudia F. Lucchinetti, Val J. Lowe, Bogdan F. Gh. Popescu, B. F. Boeve, and Istvan Pirko
- Subjects
0301 basic medicine ,Pathology ,medicine.medical_specialty ,Multiple Sclerosis ,Autopsy ,Article ,White matter ,03 medical and health sciences ,Myelin ,0302 clinical medicine ,Alzheimer Disease ,medicine ,Dementia ,Humans ,Pathological ,Myelin Sheath ,Cerebral Cortex ,medicine.diagnostic_test ,business.industry ,Multiple sclerosis ,Magnetic resonance imaging ,medicine.disease ,Magnetic Resonance Imaging ,030104 developmental biology ,medicine.anatomical_structure ,Neurology ,Neurology (clinical) ,Alzheimer's disease ,business ,030217 neurology & neurosurgery - Abstract
Background and objectives: We report a comprehensive clinical, radiological, neuropsychometric and pathological evaluation of a woman with a clinical diagnosis of AD dementia (ADem), but whose autopsy demonstrated widespread demyelination, without Alzheimer disease (AD) pathology. Methods and results: Initial neuropsychometric evaluation suggested amnestic mild cognitive impairment (aMCI). Serial magnetic resonance images (MRI) images demonstrated the rate of increase in her ventricular volume was comparable to that of 46 subjects with aMCI who progressed to ADem, without accumulating white matter disease. Myelin immunohistochemistry at autopsy demonstrated extensive cortical subpial demyelination. Subpial lesions involved the upper cortical layers, and often extended through the entire width of the cortex. Conclusions: Multiple sclerosis (MS) can cause severe cortical dysfunction and mimic ADem. Cortical demyelination is not well detected by standard imaging modalities and may not be detected on autopsy without myelin immunohistochemistry.
- Published
- 2015
158. HAMR recording challenges at high linear densities
- Author
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Bogdan F. Valcu, Michael Alex, G. Bertero, and R. Eaton
- Subjects
Heat-assisted magnetic recording ,Computer science ,Limiting ,Area density ,Engineering physics - Abstract
HAMR technology has experienced big advances in just this last year but hurdles still abound and need to be resolved before HAMR can fulfill its full potential for both lifetime and areal density capability [1,2]. A few of these challenges are directly tied to component optical, thermal and magnetic designs. Specifically, from a media perspective, in-plane grains and grain size distribution are a major concern limiting the linear density capability of the HAMR system. Assuming that high enough thermal gradients are achieved, bit curvature also limits the resolution of the system and needs to be better characterized and addressed. Many of these issues are exclusive of HAMR recording. Thus, they present new challenges but also new opportunities for workarounds and innovation in the magnetic recording industry; something our industry is famous for overcoming.
- Published
- 2015
159. Investigation of relaxation of nanodiamond surface in real and reciprocal spaces
- Author
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Ewa Grzanka, S. Stelmakh, T. W. Zerda, Cristian Pantea, Bogdan F. Palosz, W. Palosz, and Th. Proffen
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Materials science ,Synthetic diamond ,Mechanical Engineering ,Material properties of diamond ,Neutron diffraction ,Mineralogy ,Diamond ,General Chemistry ,engineering.material ,Electronic, Optical and Magnetic Materials ,law.invention ,Reciprocal lattice ,law ,Materials Chemistry ,engineering ,Graphite ,Diamond cubic ,Electrical and Electronic Engineering ,Composite material ,Nanodiamond - Abstract
The structure of a nanodiamond powder with an average grain size of 5 nm was investigated using large-Q neutron diffraction. Both Bragg scattering and PDF analysis were employed. The effect of annealing under vacuum at temperatures up to 1200 °C was studied. The studies lead to a tentative model of nanocrystalline diamond, where the core with a perfect diamond lattice is surrounded by a shell of compressed diamond lattice, and this core–shell structure is enveloped in a non-diamond carbon. The non-diamond envelope of nanograins, a “gas-like” carbon, is stable up to 1000 °C and transforms into a graphite phase (an onion-type structure) at about 1200 °C. The amount of non-crystalline carbon in the powder annealed below 1000 °C is about 10%. In the sample annealed at 1200 °C a graphite-type carbon, with a total of about 15% of sp2 bonds is formed.
- Published
- 2006
160. Neutron diffraction studies of the atomic vibrations of bulk and surface atoms of nanocrystalline SiC
- Author
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Yusheng Zhao, Bogdan F. Palosz, Ewa Grzanka, W. Palosz, and S. Stelmakh
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Diffraction ,Materials science ,Neutron diffraction ,Shell (structure) ,Condensed Matter Physics ,Nanocrystalline material ,Inorganic Chemistry ,Vibration ,Core (optical fiber) ,Amplitude ,Thermal ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Atomic physics - Abstract
Thermal atomic motions of nanocrystalline Sic were characterized by two temperature atomic factors B(sub core), and B(sub shell). With the use of wide angle neutron diffraction data it was shown that at the diffraction vector above 15A(exp -1) the Wilson plots gives directly the temperature factor of the grain interior (B(sub core)). At lower Q values the slope of the Wilson plot provides information on the relative amplitudes of vibrations of the core and shell atoms.
- Published
- 2006
161. Tuning aerosol-assisted vapor phase processing towards low oxygen GaN powders
- Author
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S. Stelmakh, Jerzy F. Janik, Bogdan F. Palosz, Ewa Grzanka, Mariusz Drygaś, and Robert T. Paine
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Materials science ,Nanoparticle ,Mineralogy ,chemistry.chemical_element ,Surfaces and Interfaces ,Chemical vapor deposition ,Condensed Matter Physics ,Microstructure ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Materials Chemistry ,Particle ,Particle size ,Methanol ,Electrical and Electronic Engineering ,Gallium ,Pyrolysis - Abstract
Herein, are reported studies of various experimental conditions aimed at optimizing the Aerosol-Assisted Vapor Phase Synthesis (AAVS) of GaN powders. In general, the process utilizes affordable oxygen-bearing gallium precursors in aqueous/methanol solutions to initially prepare nano-sized GaN x O y powders of spheroidal morphology. Subsequent pyrolysis of the GaN x O y intermediate in a NH 3 atmosphere converts the powders to sub-micron, crystalline GaN powders that usually contain some residual oxygen. The application of appropriate solvents, e.g., methanol, in the aerosol powder generation stage and the use of pyrolysis temperatures in the range 900-1000 °C may improve both the extent of nitridation and, to certain degree, the control over average particle sizes. The characteristics of the AAVS-produced materials are compared with those for bulk GaN powders obtained by direct nitridation of commercial gallium oxide.
- Published
- 2006
162. Diagnostic utility of aquaporin-4 in the analysis of active demyelinating lesions
- Author
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Sean J. Pittock, Caterina Giannini, Stacey L. Clardy, Yong Guo, Joseph E. Parisi, Mark E. Jentoft, Elizabeth A. Shuster, Wolfgang Brück, Claudia F. Lucchinetti, Vanda A. Lennon, Clara D. Boyd, Bruce A. Cohen, Dean M. Wingerchuk, Bogdan F. Gh. Popescu, Imke Metz, Brian G. Weinshenker, and Jonathan L. Carter
- Subjects
Adult ,Male ,Pathology ,medicine.medical_specialty ,Multiple Sclerosis ,Adolescent ,Biopsy ,Demyelinating Autoimmune Diseases, CNS ,Transverse myelitis ,Cohort Studies ,Myelin ,Young Adult ,Demyelinating disease ,Medicine ,Humans ,Child ,Myelin Sheath ,Aged ,Autoantibodies ,Aged, 80 and over ,Aquaporin 4 ,Inflammation ,Neuromyelitis optica ,medicine.diagnostic_test ,business.industry ,Multiple sclerosis ,Neuromyelitis Optica ,Brain ,Middle Aged ,medicine.disease ,Immunohistochemistry ,3. Good health ,medicine.anatomical_structure ,Spinal Cord ,Astrocytes ,Immunoglobulin G ,Female ,sense organs ,Neurology (clinical) ,Differential diagnosis ,business - Abstract
Objective: To assess, in a surgical biopsy cohort of active demyelinating lesions, the diagnostic utility of aquaporin-4 (AQP4) immunohistochemistry in identifying neuromyelitis optica (NMO) or NMO spectrum disorder (NMOSD) and describe pathologic features that should prompt AQP4 immunohistochemical analysis and AQP4–immunoglobulin G (IgG) serologic testing. Methods: This was a neuropathologic cohort study of 20 surgical biopsies (19 patients; 11 cord/9 brain), performed because of diagnostic uncertainty, interpreted as active demyelinating disease and containing 2 or more of the following additional features: tissue vacuolation, granulocytic infiltrates, or astrocyte injury. Results: AQP4 immunoreactivity was lost in 18 biopsies and increased in 2. Immunopathologic features of the AQP4 loss cohort were myelin vacuolation (18), dystrophic astrocytes and granulocytes (17), vascular hyalinization (16), macrophages containing glial fibrillary acid protein (GFAP)–positive debris (14), and Creutzfeldt-Peters cells (0). All 14 cases with available serum tested positive for AQP4-IgG after biopsy. Diagnosis at last follow-up was NMO/NMOSD (15) and longitudinally extensive transverse myelitis (1 each relapsing and single). Immunopathologic features of the AQP4 increased cohort were macrophages containing GFAP-positive debris and granulocytes (2), myelin vacuolation (1), dystrophic astrocytes (1), Creutzfeldt-Peters cells (1), and vascular hyalinization (1). Diagnosis at last follow-up was multiple sclerosis (MS) and both tested AQP4-IgG seronegative after biopsy. Conclusions: AQP4 immunohistochemistry with subsequent AQP4-IgG testing has diagnostic utility in identifying cases of NMO/NMOSD. This study highlights the importance of considering NMOSD in the differential diagnosis of tumefactive brain or spinal cord lesions. AQP4-IgG testing may avert biopsy and avoid ineffective therapies if these patients are erroneously treated for MS.
- Published
- 2014
163. Structure–redox reactivity relationships in Co1−xZnxFe2O4: the role of stoichiometry.
- Author
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Tatarchuk, Tetiana, Paliychuk, Natalia, Pacia, Michał, Kaspera, Wojciech, Macyk, Wojciech, Kotarba, Andrzej, Bogacz, Bogdan F., Pędziwiatr, Antoni T., Mironyuk, Ivan, Gargula, Renata, Kurzydło, Piotr, and Shyichuk, Alexander
- Subjects
CHEMICAL reactions ,STOICHIOMETRY ,MICROSTRUCTURE - Abstract
Nanostructured Zn-doped cobalt ferrites (Co
1−x Znx Fe2 O4 , where x ranges from 0.0 to 1.0 with a step of 0.1) were studied in order to elucidate the relation between their cationic distribution within the spinel sublattices and catalytic properties. The thermal transformation of the precursors (metal hydroxides) obtained through the hydroxide co-precipitation method was studied by DTA, TGA and FTIR. The thermal behavior of the precursors showed that cobalt ferrite was formed at a lower temperature (376 °C) in comparison to zinc ferrite (478 °C). FTIR analysis revealed vibrational bands around 400 cm−1 and 600 cm−1 related to (MO4 )6− and (MO6 )9− groups, respectively. The cationic distribution was determined from Mössbauer spectra analysis and the results showed that Zn ions occupy the A-sites, while Co and Fe ions are located in the A- and B-sites. The spectra indicate spinel magnetic ordering in samples with x = 0.0…0.5. The increase in Zn content influences the difference in the Pauling electronegativities, distances between magnetic ions (hopping length) and polaron radius of Co1−x Znx Fe2 O4 ferrites, inducing changes in the ionic bond strength for the A- and B-sites. Photoelectrochemical measurements demonstrated that the introduction of Zn2+ into the spinel structure modifies the ability of the materials to reduce O2 . Whereas photoinduced reduction of dioxygen at CoFe2 O4 competes successfully with anodic photocurrent generation (observed as a decrease of photocurrent), for ZnFe2 O4 this process is negligible. The relation between the cationic distribution (analyzed in terms of antistructure modeling) and the catalytic activity of spinel ferrites was demonstrated for the example of the soot combustion process. It was shown that the octahedral cobalt centers exhibit a higher catalytic activity than the tetrahedral ones. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
164. Fabrication and Physical Properties of SiC-GaAs Nano-Composites
- Author
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Dariusz Wasik, Bogdan F. Palosz, Maria Kaminska, Ewa Grzanka, Stanislaw Gierlotka, Andrzej Twardowski, G. Kalisz, Jolanta Borysiuk, and Anna Swiderska-Sroda
- Subjects
Materials science ,Scanning electron microscope ,General Physics and Astronomy ,Condensed Matter Physics ,Microstructure ,Atomic and Molecular Physics, and Optics ,Nanocrystalline material ,Crystallography ,symbols.namesake ,Transmission electron microscopy ,Phase (matter) ,symbols ,Melting point ,General Materials Science ,Composite material ,Raman spectroscopy ,High-resolution transmission electron microscopy ,Diffractometer - Abstract
Nano-composites consisting of primary phase of hard nanocrystalline SiC matrix and the secondary nanocrystalline semiconductor (GaAs) phase were obtained by high-pressure zone infiltration. The synthesis process occurs in three stages: (i) at room temperature the nanopowder of SiC is compacted along with GaAs under high pressure up to 8 GPa, (ii) the temperature is increased above the melting point of GaAs up to 1600 K and, the pores are being filled with liquid, (iii) upon cooling GaAs nanocrystallites grow in the pores. Synthesis of nano-composites was performed using a toroid-type high-pressure apparatus (IHPP of the Polish Academy of Sciences, Warsaw) and six-anvil cubic press (MAX-80 at HASYLAB, Hamburg). X-ray diffraction studies were performed using a laboratory D5000 Siemens diffractometer. Phase composition, grain size, and macrostrains present in the synthesized materials were examined. Microstructure of the composites was characterized using scanning electron microscopy and high resolution transmission electron microscopy. Far-infrared reflectivity measurements were used to determine built-in strain.
- Published
- 2005
165. High-Pressure and -Temperature Sintering of Nanosized Hydroxyapatite Powders
- Author
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Stanislaw Gierlotka, Ulrich Bismayer, Arndt Klocke, Jianmin Shi, and Bogdan F. Palosz
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Mechanical property ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,High pressure ,Sintering ,General Materials Science ,Composite material ,Nanoceramic - Published
- 2005
166. From Dental Enamel to Synthetic Hydroxyapaptite-Metal Composites
- Author
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Jianmin M. Sc Shi, Stanislaw Gierlotka, Arndt Klocke, Bogdan F. Palosz, and Ulrich Bismayer
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Metal ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,visual_art ,Dental enamel ,Composite number ,visual_art.visual_art_medium ,General Materials Science ,Composite material - Published
- 2005
167. Investigation of the Microstructure of SiC-Zn Nanocomposites by Microscopic Methods: SEM, AFM and TEM
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Ewa Grzanka, Svetlana Stelmakh, Anna Swiderska-Sroda, Stanislaw Gierlotka, Christian Lathe, A. Presz, A. Maranda-Niedbala, Bogdan F. Palosz, Nathalie Herlin-Boime, G. Kalisz, J. A. Kozubowski, Laboratoire Francis PERRIN (LFP - URA 2453), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and 3.3 Chemistry and Physics of Earth Materials, 3.0 Geodynamics and Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum
- Subjects
Materials science ,Nanoparticle ,Sintering ,550 - Earth sciences ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Grain size ,Nanocomposites ,0104 chemical sciences ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Micrometre ,High pressure ,Transmission electron microscopy ,General Materials Science ,Crystallite ,Composite material ,0210 nano-technology ,Single crystal - Abstract
SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration process under the pressure of 2-8 GPa and at the temperature of 400_1000oC. SiC nanopowders used in the experiments formed loosely agglomerated chains of single crystal nanoparticles. The dimension of the agglomerates was in the micrometer range, the mean grain size was up to tens of nanometers. Microstructural investigations of the nanocomposites were performed at a different resolution levels using scanning, transmission electron microscopy and atomic force microscopy techniques (SEM, TEM, AFM, respectively). SEM observations indicate a presence of nano-dispersed, uniform (on the micrometer scale) mixture of two phases. TEM observations show that distribution of SiC and Zn nanocrystallites is uniform on the nanometer scale. High-resolution TEM images demonstrate an existence of thin (on the order of tens of Angstroms) Zn layers separating SiC grains. AFM images of the mechanically polished samples show a smooth surface with the roughness on the order of the SiC grain size (10-30 nm). After ion etching of some samples the AFM topographs show surface irregularities: periodically spaced hillocks 50-100 nm in height. The size of the SiC grains remains equal to that of the initial powder crystallites. The size of the Zn grains varies in the range of 20-100 nm depending on the initial SiC grain size and the composite fabrication conditions.
- Published
- 2005
168. Multiscale Computational Study on the Catalytic Mechanism of the Nonmetallo Amidase Maleamate Amidohydrolase (NicF)
- Author
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Ion, Bogdan F., Meister, Paul J., and Gauld, James W.
- Abstract
Maleamate amidohydrolase (NicF) is a key enzyme in vitamin B3metabolism that catalyzes the hydrolysis of maleamate to produce maleic acid and ammonia. Unlike most members from the amidohydrolase superfamily it does not require a metal ion. Here, we use multiscale computational enzymology to investigate the catalytic mechanism, substrate binding, oxyanion hole, and roles of key active site residues of NicF from Bordetella bronchiseptica. In particular, molecular dynamics (MD) simulations, quantum mechanics/molecular mechanics (QM/MM) and QTAIM methods have been applied. The mechanism of the NicF-catalyzed reaction proceeds by a nucleophilic addition–elimination sequence involving the formation of a thioester enzyme intermediate (IC2in stage 1) followed by hydrolysis of the thioester bond to form the products (stage 2). Consequently, the formation of IC2in stage 1 is the rate-limiting step with a barrier of 88.8 kJ·mol–1relative to the reactant complex, RC. Comparisons with related metal-dependent enzymes, particularly the zinc-dependent nicotinamidase from Streptococcus pneumonia(SpNic), have also been made to further illustrate unique features of the present mechanism. Along with −NH– donor groups of the oxyanion hole (i.e., HN–Thr146, HN–Cys150), the active site β-hydroxyl of threonine (HO−βThr146) is concluded to play a role in stabilizing the carbonyl oxygen of maleamate during the mechanism.
- Published
- 2024
- Full Text
- View/download PDF
169. X-ray diffraction studies of thermal properties of the core and surface shell of isolated and sintered SiC nanocrystals
- Author
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Stanislaw Gierlotka, H.-P. Weber, Ewa Grzanka, S. Stelmakh, and Bogdan F. Palosz
- Subjects
Materials science ,Mechanical Engineering ,Metals and Alloys ,Analytical chemistry ,Mineralogy ,Sintering ,Nanocrystalline material ,Thermal expansion ,symbols.namesake ,Nanocrystal ,Mechanics of Materials ,X-ray crystallography ,Materials Chemistry ,symbols ,Crystallite ,Thermal analysis ,Debye model - Abstract
The effect of the presence of surface strains on the apparent lattice parameters (alp) obtained experimentally for nanocrystalline SiC is discussed. The alp values were determined for two kinds of powders with an average crystallite size of 11 nm and related sintered samples. The measurements were done in a wide range of the diffractions vector up to Q = 12 A −1 , allowing for evaluation of the internal pressure in the grains. Based on in situ high-temperature measurements, the thermal expansion coefficient and overall temperature factor B T were evaluated. It is shown that while the thermal expansion coefficient changes very little upon sintering, there is a large difference in the amplitude of the atomic oscillations between powders and sintered SiC reflected in a difference between respective Debye temperatures. It is concluded that the overall thermal properties of nanocrystals are determined by two components: thermal properties of the crystallite surface and its interior. The atoms at the surface vibrate much stronger than those in the bulk, and their behavior is strongly affected by the crystallite’s environment.
- Published
- 2004
170. Powder Precursors for Nanoceramics: Cleaning and Compaction
- Author
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Stanislaw Gierlotka, Svetlana Stelmakh, Anna Swiderska-Sroda, G. Kalisz, Ewa Grzanka, and Bogdan F. Palosz
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Materials science ,Metallurgy ,Compaction ,Diamond ,Porosimetry ,engineering.material ,Condensed Matter Physics ,Ceramic matrix composite ,Atomic and Molecular Physics, and Optics ,Nanocrystalline material ,Outgassing ,Chemical engineering ,engineering ,General Materials Science ,Porosity ,Inert gas - Abstract
Thermal surface purification in an inert gas flow and densification processes of SiC and diamond nanocrystalline powders with specific surface in the range of 60 – 300 m2/g and average grain sizes from 5 to 15 nm in diameter were examined. Termogravimetric Analysis (TGA) linked with mass spectrometry of outgassing products show that surface impurities desorb at up to 450°C. Further heating above 450°C leads to oxidation of the powder surface. Small Angle X-Ray Scattering (SAXS) and gas porosimetry (ASAP) was applied to investigate densification of the nanocrystalline powders. Compaction under 1GPa or higher pressure was found necessary for obtaining the ceramic matrix with porosity in the nanometer range.
- Published
- 2004
171. High pressure x-ray diffraction studies on nanocrystalline materials
- Author
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Stanislaw Gierlotka, S Werner, Bogdan F. Palosz, W. Palosz, S. Stelmakh, Roman Pielaszek, Ulli Bismayer, and Ewa Grzanka
- Subjects
Diffraction ,Bulk modulus ,Crystallography ,Materials science ,Lattice constant ,X-ray crystallography ,Hydrostatic pressure ,General Materials Science ,Composite material ,Condensed Matter Physics ,Nanocrystalline material ,Powder diffraction ,Grain size - Abstract
Application of in situ high pressure powder diffraction technique for examination of specific structural properties of nanocrystals based on the experimental data of SiC nanocrystalline powders of 2 to 30 nrn diameter in diameter is presented. Limitations and capabilities of the experimental techniques themselves and methods of diffraction data elaboration applied to nanocrystals with very small dimensions (< 30 nm) are discussed. It is shown that due to the complex structure, constituting a two-phase, core/surface shell system, no unique lattice parameter value and, consequently, no unique compressibility coefficient can satisfactorily describe the behavior of nanocrystalline powders under pressure. We offer a tentative interpretation of the distribution of macro- and micro-strains in nanoparticles of different grain size.
- Published
- 2004
172. X-Ray Powder Diffraction Study of Atomic Structure of Nanocrystalline SiC and Diamond Materials
- Author
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Stanislaw Gierlotka, Bogdan F. Palosz, Witold Palosz, Roman Pielaszek, Ulrich Bismayer, Svetlana Stelmakh, P. Jóvári, J. Neuefeind, and Ewa Grzanka
- Subjects
Diffraction ,Materials science ,Condensed matter physics ,Mechanical Engineering ,X-ray ,Diamond ,engineering.material ,Condensed Matter Physics ,Nanocrystalline material ,Crystallography ,Lattice constant ,Nanocrystal ,Mechanics of Materials ,Lattice (order) ,engineering ,General Materials Science ,Powder diffraction - Abstract
A considerable fraction of atoms in nanosize particles is at the grain surface (due to the small size of the crystals). We assume that the surface atoms form a separate structural phase relative to the bulk of the grain (the core). Therefore, one set of the lattice parameters characterizing a nanocrystal may be inadequate for a unique description of its structure. An alternative evaluation of diffraction data of nanocparticles, based on the 'apparent lattice parameter' is proposed. Based on this new methodology it is shown that real nano-crystals constitiute a complex, more than a one-uniform-phase structure.
- Published
- 2004
173. Microwave – Hydrothermal Synthesis of Nanocrystalline Pr - Doped Zirconia Powders at Pressures up to 8 MPa
- Author
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A. Opalińska, Bogdan F. Palosz, S. Braccini, Ewa Grzanka, Witold Łojkowski, Tadeusz Chudoba, Gian Carlo Pellacani, Federica Bondioli, Cristina Leonelli, and Anna Maria Ferrari
- Subjects
Materials science ,microwave ,Praseodymium ,nanopowders ,Doping ,chemistry.chemical_element ,Mineralogy ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Nanocrystalline material ,chemistry ,Chemical engineering ,Hydrothermal synthesis ,zirconia ,General Materials Science ,Cubic zirconia ,Microwave - Published
- 2003
174. Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)
- Author
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Stanislaw Gierlotka, Bogdan F. Palosz, Ewa Grzanka, Roman Pielaszek, Svetlana Stelmakh, Ulrich Bismayer, Th. Proffen, H.-P. Weber, and Witold Palosz
- Subjects
Diffraction ,Materials science ,Condensed matter physics ,Bragg's law ,Diamond ,engineering.material ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Grain size ,Nanocrystalline material ,Condensed Matter::Materials Science ,Crystallography ,Lattice constant ,X-ray crystallography ,Physics::Atomic and Molecular Clusters ,engineering ,General Materials Science ,Powder diffraction - Abstract
Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.
- Published
- 2003
175. Microwave Driven Hydrothermal Synthesis of Zinc Oxide Nanopowders
- Author
-
T. Strachowski, A. Presz, Witold Łojkowski, Ludomir Ślusarski, Ewa Grzanka, and Bogdan F. Palosz
- Subjects
Materials science ,chemistry ,Chemical engineering ,chemistry.chemical_element ,Hydrothermal synthesis ,General Materials Science ,Zinc ,Condensed Matter Physics ,Chemical synthesis ,Atomic and Molecular Physics, and Optics ,Microwave - Published
- 2003
176. Application of X-ray Powder Diffraction to Nano-materials - Determination of the Atomic Structure of Nanocrystals with Relaxed and Strained Surfaces
- Author
-
Witold Lojkowski, Ewa Grzanka, Witold Palosz, Stanislaw Gierlotka, S. Stelmakh, H.-P. Weber, Ulrich Bismayer, Bogdan F. Palosz, J. Neuefeind, and Roman Pielaszek
- Subjects
Diffraction ,Materials science ,Condensed matter physics ,Neutron diffraction ,Physics::Optics ,Crystallography ,Lattice constant ,General Materials Science ,Diffraction topography ,Crystallite ,Selected area diffraction ,Instrumentation ,Powder diffraction ,Electron backscatter diffraction - Abstract
The applicability of standard methods for the evaluation of powder diffraction data of nano-size crystallites is analyzed. Based on theoretical considerations, it is shown that deviations of the structure of small particles from the Bragg approximation on an infinite crystal lattice leads to significant differences in the diffraction patterns, which may lead to an erroneous interpretation of the experimental results. An alternative evaluation of the diffraction data of nano-particles, based on the so-called "apparent lattice parameter", alp , is proposed. Based on this method, it is shown that real nano-crystals constitute a complex, heterogeneous multi-phase structure.
- Published
- 2003
177. Effect of crystallographic orientation on grain size distribution
- Author
-
Yoshio Takahashi, Bogdan F. Valcu, and H. Neal Bertram
- Subjects
Crystallographic point group ,Crystallography ,Materials science ,Ferromagnetism ,Plane (geometry) ,Dispersion (optics) ,Particle-size distribution ,General Physics and Astronomy ,Thin film ,Symmetry (physics) ,Grain size - Abstract
The control of grain size statistics is essential in the manufacture of granular thin films used in high-density recording. In this article transmission electron microscope observations of perpendicular media are shown that indicate larger grain size dispersion than in typical longitudinal media. We explain this result by utilizing a simple Voronoi model that includes the crystallographic symmetry. The higher symmetry of the magnetic layer in perpendicular media increases the grain size dispersion. It is argued that out-of plane dispersion of the vertical axes of grains, important in longitudinal media, further enhances the differences between grain size distributions in these two types of media. The results are confirmed by experimental measurements.
- Published
- 2002
178. Analysis of short and long range atomic order in nanocrystalline diamonds with application of powder diffractometry
- Author
-
H.-P. Weber, S. Stelmakh, Roman Pielaszek, Peter A. Curreri, Ulrich Bismayer, Thomas Proffen, Witold Palosz, Ewa Grzanka, J. Neuefiend, R. VonDreele, and Bogdan F. Palosz
- Subjects
Diffraction ,Materials science ,Condensed matter physics ,Neutron diffraction ,Bragg's law ,Crystal structure ,Condensed Matter Physics ,Nanocrystalline material ,Inorganic Chemistry ,Crystallography ,Lattice constant ,Perfect crystal ,General Materials Science ,Powder diffraction - Abstract
Fundamental limitations, with respect to nanocrystalline materials, of the traditional elaboration of powder diffraction data like the Rietveld method are discussed. A tentative method of the analysis of powder diffraction patterns of nanocrystals based on the examination of the variation of lattice parameters calculated from individual Bragg lines (named the “apparent lattice parameter”, alp) is introduced. We examine the application of our methodology using theoretical diffraction patterns computed for models of nanocrystals with a perfect crystal lattice and for grains with a two-phase, core-shell structure. We use the method for the analysis of X-ray and neutron experimental diffraction data of nanocrystalline diamond powders of 4, 6 and 12 nm in diameter. The effects of an internal pressure and strain at the grain surface are discussed. The results are based on the dependence of the alp values on the diffraction vector Q and on the PDF analysis. It is shown, that the experimental results lend a strong support to the concept of a two-phase structure of nanocrystalline diamond.
- Published
- 2002
179. Generation and Relaxation of Microstrains in GaN Nanocrystals under Extreme Pressures
- Author
-
Stanislaw Gierlotka, Ewa Grzanka, R. Pielaszek, F. Porsch, Ulrich Bismayer, Bogdan F. Palosz, F. Palosz, J.R. Wells, and Jerzy F. Janik
- Subjects
Diffraction ,Stress (mechanics) ,Full width at half maximum ,Materials science ,Relaxation (NMR) ,General Physics and Astronomy ,Bragg's law ,Crystallite ,Composite material ,Grain size ,Nanocrystalline material - Abstract
Nanocrystalline powders of GaN with grain sizes ranging from 2 to 30 nm were examined under high external pressures by in situ diffraction techniques in a diamond anvil cell at DESY (HASYLAB, Station F3). The experiments on densification of pure powders under high pressure were performed without a pressure medium. The mechanism of generation and relaxation of internal strains and their distribution in nanoparticles was deduced from the Bragg reflections recorded in situ under high pressures at room temperature. The microstrain was calculated from the full-width at half-maximum (FWHM) values of the Bragg lines. It was found that microstrains in GaN crystallites are generated and subsequently relaxed by two mechanisms: generation of stacking faults and change of the size and shape of the grains occurring under external stress.
- Published
- 2002
180. Effect of Cr concentration gradient on the intergranular exchange in CoCr(Ta,Pt) thin films
- Author
-
H. Neal Bertram and Bogdan F. Valcu
- Subjects
Magnetization ,Magnetic anisotropy ,Materials science ,Ferromagnetism ,Condensed matter physics ,Exchange interaction ,Metallurgy ,General Physics and Astronomy ,Thermal fluctuations ,Grain boundary ,Intergranular corrosion ,Thin film - Abstract
Intergranular exchange in CoCr-alloy polycrystalline thin films utilized for longitudinal recording media is analyzed in terms of details of their chemical composition. Two neighboring interacting grains are modeled by a linear “atomic” chain extending from the center of one grain to the center of another. The composition at each spin site determines the interspin exchange interaction. Thermal fluctuations are included via mean field theory and they yield spacial variations of the saturation magnetization and the crystal anisotropy that differ from the bulk properties. Equilibrium spin configurations for the linear chain are obtained for different Cr concentrations at the grain boundary and for different temperatures. Chromium segregation at the boundary is confirmed to be the mechanism for grain decoupling. An effective exchange parameter, assuming uniformly magnetized grains like those in large-scale micromagnetic simulations, is determined. This parameter decreases significantly with increasing tempera...
- Published
- 2002
181. [Untitled]
- Author
-
Anna Swiderska-Sroda, Stanislaw Gierlotka, J. A. Kozubowski, E. A. Ekimov, A. M. Naletov, E. L. Gromnitskaya, Witold Lojkowski, and Bogdan F. Palosz
- Subjects
Nanocomposite ,Materials science ,Nanostructured materials ,General Materials Science ,Non oxide ceramics ,Composite material ,Microstructure ,Nanodiamond ,Indentation hardness - Published
- 2002
182. Pulse shape, resolution, and signal-to-noise ratio in perpendicular recording
- Author
-
Thomas Roscamp, H.N. Bertram, and Bogdan F. Valcu
- Subjects
Physics ,Magnetoresistance ,business.industry ,Perpendicular recording ,Scalar potential ,Giant magnetoresistance ,Finite element method ,Electronic, Optical and Magnetic Materials ,Computational physics ,Magnetization ,Optics ,Perpendicular ,Magnetic potential ,Electrical and Electronic Engineering ,business - Abstract
The paper theoretically examines playback characteristics of a giant magnetoresistive (GMR) head for perpendicular recorded magnetization transitions with a soft underlayer. The magnetic scalar potential, calculated numerically by the finite-element method, is fitted to a simple formula involving geometry-dependent parameters. The reciprocity principle leads to the shape of the single pulse signal. For high permeability of the underlayer the pulse has an error function-type dependence on distance. Within this approximation, the paper derives simple formulas for the pulsewidth T/sub 50/, D/sub 50/, and transition-noise-limited signal-to-noise ratio.
- Published
- 2002
183. [Untitled]
- Author
-
Witold Lojkowski, Bogdan F. Palosz, Stanislaw Gierlotka, A. M. Naletov, E. A. Ekimov, E. L. Gromnitskaya, and J. A. Kozubowski
- Subjects
Materials science ,Nanocomposite ,General Chemical Engineering ,Material properties of diamond ,Composite number ,Metals and Alloys ,Diamond ,Young's modulus ,engineering.material ,Microstructure ,Indentation hardness ,Inorganic Chemistry ,Crystallography ,symbols.namesake ,Volume fraction ,Materials Chemistry ,symbols ,engineering ,Composite material - Abstract
A bulk composite material close in hardness to diamond was fabricated from nanocrystalline diamond and SiC. The mechanical properties and microstructure of the composite were studied. Young's modulus of the composite is found to be notably lower than the one following from the additivity rule, which is attributable to the influence of structural defects present in the interfacial zone between SiC and diamond. SiC consists of nanometer-scale grains near the interface and submicron grains in the “pores.”
- Published
- 2002
184. Experimental determination of reader resolution using PRS patterns and application to media cluster size measurement
- Author
-
Cristian Papusoi, M. Desai, Bogdan F. Valcu, Goncalo Albuquerque, and Xiao Wu
- Subjects
010302 applied physics ,Physics ,business.industry ,Resolution (electron density) ,General Physics and Astronomy ,Function (mathematics) ,01 natural sciences ,Signal ,Noise (electronics) ,lcsh:QC1-999 ,Spectral line ,Magnetic transitions ,Optics ,0103 physical sciences ,Cluster size ,Sensitivity (control systems) ,business ,lcsh:Physics - Abstract
A technique to determine experimentally the reader resolution in magnetic recording by using pseudo-random sequence (PRS) patterns written on the disc is presented. The spectrum of the PRS signal is analyzed to extract simultaneously the width of the magnetic transitions and the reader sensitivity as a function of frequency. When playback spacing is increased, reader sensitivity rolls off faster with frequency, in good quantitative agreement with modeling results involving micromagnetic simulation of the reader. The reader sensitivity is further employed to de-convolve the magnetic cluster size from measured spectra of media noise.
- Published
- 2017
185. P3‐010: MULTIPLE SCLEROSIS MASQUERADING AS ALZHEIMER'S TYPE DEMENTIA: CLINICAL, RADIOLOGICAL, AND PATHOLOGICAL FINDINGS
- Author
-
Val J. Lowe, Bradley F. Boeve, Claudia F. Lucchinetti, Bogdan F. Gh. Popescu, Julie A. Fields, Istvan Pirko, W. Oliver Tobin, and Kejal Kantarci
- Subjects
Pediatrics ,medicine.medical_specialty ,Pathology ,Epidemiology ,business.industry ,Health Policy ,Multiple sclerosis ,medicine.disease ,Alzheimer s type dementia ,Psychiatry and Mental health ,Cellular and Molecular Neuroscience ,Developmental Neuroscience ,Radiological weapon ,medicine ,Neurology (clinical) ,Geriatrics and Gerontology ,business ,Pathological - Published
- 2014
186. Computational investigations on the catalytic mechanism of maleate isomerase: the role of the active site cysteine residues
- Author
-
James W. Gauld, Bogdan F. Ion, and Hisham Dokainish
- Subjects
ONIOM ,cis-trans-Isomerases ,Maleate isomerase ,biology ,Chemistry ,Stereochemistry ,General Physics and Astronomy ,Active site ,Active site cysteine ,Catalysis ,Molecular dynamics ,Nucleophile ,Bacterial Proteins ,Catalytic Domain ,biology.protein ,Quantum Theory ,Cysteine ,Physical and Theoretical Chemistry ,Isomerization ,Biochemistry, Biophysics, and Structural Biology - Abstract
The maleate isomerase (MI) catalysed isomerization of maleate to fumarate has been investigated using a wide range of computational modelling techniques, including small model DFT calculations, QM-cluster approach, quantum mechanical/molecular mechanical approach (QM/MM in the ONIOM formalism) and molecular dynamics simulations. Several fundamental questions regarding the mechanism were answered in detail, such as the activation and stabilization of the catalytic Cys in a rather hydrophobic active site. The two previously proposed mechanisms were considered, where either enediolate or succinyl-Cys intermediate forms. Small model calculations as well as an ONIOM-based approach suggest that an enediolate intermediate is too unstable. Furthermore, the formation of succinyl-Cys intermediate via the nucleophilic attack of Cys76(-) on the substrate C2 (as proposed experimentally) was found to be energetically unfeasible in both QM-cluster and ONIOM approaches. Instead, our results show that Cys194, upon activation via the substrate, acts as a nucleophile and Cys76 acts as an acid/base catalyst, forming a succinyl-Cys intermediate in a concerted fashion. Indeed, the calculated PA of Cys76 is always higher than that of Cys194 before or upon substrate binding in the active site. Furthermore, the mechanism proceeds via multiple steps by substrate rotation around C2-C3 with the assistance of the now negatively charged Cys76, leading to the formation of fumarate. Finally, our calculated barrier is in good agreement with experiment. These findings represent a novel mechanism in the racemase superfamily.
- Published
- 2014
187. Delayed nerve stimulation promotes axon-protective neurofilament phosphorylation, accelerates immune cell clearance and enhances remyelination in vivo in focally demyelinated nerves
- Author
-
Tessa Gordon, Douglas W. Zochodne, Nikki A McLean, Bogdan F. Gh. Popescu, and Valerie M. K. Verge
- Subjects
Male ,Neurofilament ,Stilbamidines ,Intermediate Filaments ,lcsh:Medicine ,03 medical and health sciences ,Myelin ,0302 clinical medicine ,Ranvier's Nodes ,medicine ,Animals ,Axon ,Remyelination ,Nerve Tissue ,Phosphorylation ,Rats, Wistar ,lcsh:Science ,Myelin Sheath ,030304 developmental biology ,Brain-derived neurotrophic factor ,0303 health sciences ,Multidisciplinary ,Node of Ranvier ,Neuronal Plasticity ,Glial fibrillary acidic protein ,biology ,Staining and Labeling ,business.industry ,Brain-Derived Neurotrophic Factor ,Macrophages ,lcsh:R ,Biology and Life Sciences ,Myelin Basic Protein ,Axons ,Electric Stimulation ,Cell biology ,Myelin basic protein ,medicine.anatomical_structure ,nervous system ,Cellular Neuroscience ,Immunology ,biology.protein ,lcsh:Q ,Schwann Cells ,business ,030217 neurology & neurosurgery ,Research Article ,Neuroscience ,Demyelinating Diseases - Abstract
Rapid and efficient axon remyelination aids in restoring strong electrochemical communication with end organs and in preventing axonal degeneration often observed in demyelinating neuropathies. The signals from axons that can trigger more effective remyelination in vivo are still being elucidated. Here we report the remarkable effect of delayed brief electrical nerve stimulation (ES; 1 hour @ 20 Hz 5 days post-demyelination) on ensuing reparative events in a focally demyelinated adult rat peripheral nerve. ES impacted many parameters underlying successful remyelination. It effected increased neurofilament expression and phosphorylation, both implicated in axon protection. ES increased expression of myelin basic protein (MBP) and promoted node of Ranvier re-organization, both of which coincided with the early reappearance of remyelinated axons, effects not observed at the same time points in non-stimulated demyelinated nerves. The improved ES-associated remyelination was accompanied by enhanced clearance of ED-1 positive macrophages and attenuation of glial fibrillary acidic protein expression in accompanying Schwann cells, suggesting a more rapid clearance of myelin debris and return of Schwann cells to a nonreactive myelinating state. These benefits of ES correlated with increased levels of brain derived neurotrophic factor (BDNF) in the acute demyelination zone, a key molecule in the initiation of the myelination program. In conclusion, the tremendous impact of delayed brief nerve stimulation on enhancement of the innate capacity of a focally demyelinated nerve to successfully remyelinate identifies manipulation of this axis as a novel therapeutic target for demyelinating pathologies.
- Published
- 2014
188. Aluminum Nitride Compressibility and Thermal Expansion under Pressure
- Author
-
Stanislaw Gierlotka, Andrzej Gregorczyk, Bogdan F. Palosz, Piotr Biczyk, Ulrich Bismayer, and Ewa Grzanka
- Subjects
Phase transition ,Materials science ,Mechanical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,Sintering ,Nitride ,Condensed Matter Physics ,Thermal expansion ,chemistry ,Mechanics of Materials ,Aluminium ,Compressibility ,General Materials Science ,Composite material - Published
- 2001
189. Distribution of Strain in GaN and SiC Nanocrystals under Extreme Pressures
- Author
-
Ewa Grzanka, Stanislaw Gierlotka, Svetlana Stelmakh, K. Akimow, A. Grzegorczyk, Piotr Biczyk, Ulrich Bismayer, Jerzy F. Janik, Bogdan F. Palosz, and Roman Pielaszek
- Subjects
Materials science ,Nanocrystal ,Strain (chemistry) ,Distribution (number theory) ,Mechanics of Materials ,Mechanical Engineering ,High pressure ,Compressibility ,General Materials Science ,Nanotechnology ,Composite material ,Condensed Matter Physics ,Nanomaterials - Published
- 2001
190. Jitter in a Voronoi Pattern Media-Effect of Grain Size Distribution and Reader Width
- Author
-
Nan-Hsiung Yeh and Bogdan F. Valcu
- Subjects
Particle-size distribution ,Statistical physics ,Electrical and Electronic Engineering ,Computational geometry ,Voronoi diagram ,Signal ,Noise (electronics) ,Randomness ,Grain size ,Electronic, Optical and Magnetic Materials ,Jitter ,Mathematics - Abstract
We calculate jitter of the signal from transitions written on Voronoi-pattern media and played back with readers of varying widths. The expected dependence of jitter on reader width, as predicted by the microtrack model, is verified down to very narrow readers. Decrease in grain size variance results in less jitter. The original Voronoi patterns give a jitter value very close to the microtrack model. However, when the Voronoi patterns are modified such that grain size distribution is reduced, the jitter can be significantly smaller than in the microtrack model. This is due to the reduced randomness in the distribution of grain centers.
- Published
- 2010
191. Pathologic heterogeneity persists in early active multiple sclerosis lesions
- Author
-
Imke, Metz, Stephen D, Weigand, Bogdan F G, Popescu, Josa M, Frischer, Joseph E, Parisi, Yong, Guo, Hans, Lassmann, Wolfgang, Brück, and Claudia F, Lucchinetti
- Subjects
Adult ,Male ,Multiple Sclerosis ,Adolescent ,Middle Aged ,Article ,Cohort Studies ,Young Adult ,Early Diagnosis ,Disease Progression ,Humans ,Female ,Longitudinal Studies ,Aged ,Demyelinating Diseases ,Follow-Up Studies ,Retrospective Studies - Abstract
Multiple sclerosis (MS) lesions demonstrate immunopathological heterogeneity in patterns of demyelination. Previous cross-sectional studies reported immunopatterns of demyelination were identical among multiple active demyelinating lesions from the same individual, but differed between individuals, leading to the hypothesis of intraindividual pathological homogeneity and interindividual heterogeneity. Other groups suggested a time-dependent heterogeneity of lesions. The objective of our present study was to analyze tissue samples collected longitudinally to determine whether patterns of demyelination persist over time within a given patient.Archival tissue samples derived from patients with pathologically confirmed central nervous system inflammatory demyelinating disease who had undergone either diagnostic serial biopsy or biopsy followed by autopsy were analyzed immunohistochemically. The inclusion criteria consisted of the presence of early active demyelinating lesions--required for immunopattern classification--obtained from the same patient at 2 or more time points.Among 1,321 surgical biopsies consistent with MS, 22 cases met the study inclusion criteria. Twenty-one patients (95%) showed a persistence of immunopathological patterns in tissue sampled from different time points. This persistence was demonstrated for all major patterns of demyelination. A single patient showed features suggestive of both pattern II and pattern III on biopsy, but only pattern II among all active lesions examined at autopsy.These findings continue to support the concept of patient-dependent immunopathological heterogeneity in early MS and suggest that the mechanisms and targets of tissue injury may differ among patient subgroups. These observations have potentially significant implications for individualized therapeutic approaches.
- Published
- 2013
192. Effect of high pressures on exchange and hyperfine interactions in rare-earth orthoferrites
- Author
-
A. G. Gavrilyuk, Bogdan F. Palosz, I. A. Troyan, G. N. Stepanov, S. Stel’makh, Igor S. Lyubutin, A. S. Stepin, M. Winzenick, and V. A. Sidorov
- Subjects
Phase transition ,Orthoferrite ,chemistry.chemical_compound ,Materials science ,chemistry ,Condensed matter physics ,Chemical bond ,General Physics and Astronomy ,Diamagnetism ,Crystal structure ,Hyperfine structure ,Néel temperature ,Magnetic field - Abstract
The effect of high pressures P on the Neel temperature TN, the crystal lattice parameters, and the magnitude of the hyperfine magnetic field HSn at a nucleus of a diamagnetic tin atom was studied in pure and tin-doped orthoferrites RFeO3 (R = Nd, Lu). The dependence of these quantities on the geometry of the exchange bonds, specifically, the angle and length of the chemical bond Fe-O-Fe(Sn), was analyzed. It was established that under pressure the angular contribution decreases and the radial contribution increases TN and HSn, the radial contribution being greater than the angular contribution in absolute magnitude. Numerical estimates were obtained for the angular and radial contributions to TN and HSn. In lutecium orthoferrite, at P > 30 GPa anomalies indicating a possible phase transition were observed in the behavior of the lattice parameters and the value of HSn.
- Published
- 2000
193. Evolution of Microstructure of Nanocrystalline SiC under High Pressures
- Author
-
Stanislaw Gierlotka, Bogdan F. Palosz, Dirk Kurtenbach, Ulrich Bismayer, Svetlana Stelmakh, and Roman Pielaszek
- Subjects
Materials science ,Strain (chemistry) ,Mechanics of Materials ,Mechanical Engineering ,visual_art ,Metallurgy ,visual_art.visual_art_medium ,Sintering ,General Materials Science ,Ceramic ,Condensed Matter Physics ,Microstructure ,Nanocrystalline material - Published
- 2000
194. High-pressure high-temperature in situ diffraction studies of nanocrystalline ceramic materials at HASYLAB
- Author
-
Stanislaw Gierlotka, P. Zinn, Ulrich Bismayer, Hans Boysen, Roman Pielaszek, Bogdan F. Palosz, S. Stelmakh, and M. Winzenick
- Subjects
Diffraction ,Materials science ,Mechanical Engineering ,Metals and Alloys ,Bragg's law ,Nanocrystalline material ,Diamond anvil cell ,Crystallography ,Mechanics of Materials ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Grain boundary ,Ceramic ,Composite material ,Pressure gradient ,Powder diffraction - Abstract
High-pressure in situ diffraction studies were performed up to 8 GPa in a cubic anvil cell MAX80 (Station F2.1) and up to 45 GPa in a Diamond Anvil Cell (DAC-Station F3 at HASYLAB, Hamburg). A series of nanocrystals of SiC with grain sizes ranging from 2 nm to several μm were examined in non-hydrostatic conditions by pressing pure powders. A new method of evaluation of powder diffraction data measured at high pressures is presented. This method is based on quantitative evaluation of asymmetry of Bragg reflections where each peak is described as a combination of two reflections of two similar crystallographic phases having different compressibilities. The measured changes of the lattice parameters calculated for split Bragg reflections were used for determination of the pressure gradient which occurs across the grain boundaries in the compressed materials. A model of the strain induced in compacts of pure powders under high pressures is proposed. The model accounts for the presence of two phases: a volume phase corresponds to cores of individual grains which are surrounded by a surface phase which is formed of free surfaces in loose powders and of grain boundaries in solids. Due to extreme hardening of the boundaries under non-hydrostatic pressure conditions, the effective pressure in the interior of the grains is much lower than the applied external pressure. It is suggested that additional ‘hardening’ of the grain boundaries results from the presence of dislocations which are generated at the surface of the grains. The actual gradient of the pressure depends on the size of the grains, and also on the method of synthesis of the materials.
- Published
- 1999
195. Second Order Anisotropy in Exchange Spring Systems
- Author
-
Bogdan F. Valcu, Alexander Dobin, and Erol Girt
- Subjects
Magnetization ,Magnetic anisotropy ,Materials science ,Ferromagnetism ,Condensed matter physics ,Demagnetizing field ,Spin valve ,Spring system ,Electrical and Electronic Engineering ,Anisotropy ,Micromagnetics ,Electronic, Optical and Magnetic Materials - Abstract
XCHANGE spring systems have been proposed recently as a possible solution for increasing write-ability of recording media. The structure allows for the reduction of the switching field, significantly more substantial than the reduction expected by averaging the anisotropy fields of the hard and soft layers. The reversal process in case an external field is applied parallel to the easy axis of the hard layer has been described in [2]: a domain wall develops in the soft phase that subsequently propagates through the interface and assists switching the hard phase. Separating the magnetic properties of the soft and hard layers in the structure is essential in the process of developing the media. Films containing only the hard phase can be used to measure the saturation moment and anisotropy field and , for example by employing the torque method. The torque curve—showing how the component of magnetization perpendicular to the field varies with the angle when the sample is rotated in a constant field—has a sinusoid shape and is easily expressed mathematically if we assume that the hard layer behaves as a single spin. By fitting the experimental data an effective anisotropy is determined, to which the demagnetization term equal to must be added to obtain the crystalline Hk. The difficulty of measuring the properties of the soft phase-M and come from the fact its microstructure changes significantly if the soft layer is grown by itself, compared to the case when it is grown on top of the hard layer. Thus we cannot use films composed of the soft layer only, we must measure directly the exchange spring structure. In analyzing the torque curve of the exchange spring, we must take into account the nonuniformity of magnetization orientation. Partial domain walls develop at the boundary of the two phases, due to the difference in anisotropy [3]. The magnetization of the hard/soft layer combination can be modeled theoretically as a one-dimensional chain of spins, extending from the bottom of the hard layer to the top of the soft layer. We deduced analytical formulas for the dependence of spin orientation on the position in the chain, when the sample is rotated in constant
- Published
- 2008
196. Experimental Evidence of Domain Wall Assisted Switching in Composite Media
- Author
-
Bogdan F. Valcu, Thomas P. Nolan, A. Yu. Dobin, Erol Girt, H.J. Richter, and Xiaowei Wu
- Subjects
Condensed Matter::Materials Science ,Magnetic anisotropy ,Magnetization ,Domain wall (magnetism) ,Materials science ,Condensed matter physics ,Remanence ,Electrical and Electronic Engineering ,Coercivity ,Anisotropy ,Magnetocrystalline anisotropy ,Layer (electronics) ,Electronic, Optical and Magnetic Materials - Abstract
We fabricated perpendicular media with decoupled magnetic grains that consist of a low magnetocrystalline anisotropy layer with various thicknesses directly grown on top of a high anisotropy layer. Nonuniform magnetization rotation was confirmed by measuring coercivity and remanent coercivity in these media. The reduction of remanent coercivity with increasing the low anisotropy layer thickness, measured at low temperature, is consistent with micromagnetic calculations. These results suggest domain wall assisted switching in composite media
- Published
- 2007
197. Correlation of Signal and SNR Thermal Decay
- Author
-
Bogdan F. Valcu, Nan-Hsiung Yeh, H.J. Richter, and R. Brockie
- Subjects
Physics ,Linear density ,Magnetometer ,Equalization (audio) ,Perpendicular recording ,Signal ,Electronic, Optical and Magnetic Materials ,law.invention ,Computational physics ,Nuclear magnetic resonance ,Signal-to-noise ratio (imaging) ,law ,Content (measure theory) ,High Energy Physics::Experiment ,Thermal stability ,Electrical and Electronic Engineering - Abstract
Media thermal stability is characterized by using spin-stand tests for both signal and signal-to-noise ratio (SNR) decay. Agreement is shown between vibrating sample magnetometer (VSM) and spin-stand evaluations of the thermal decay rate dependence on linear density. For an equalized system, there is linear correlation between measured SNR and signal decay rates. Equalization to targets with DC content will result in higher decay
- Published
- 2007
198. VSM Simulation of Perpendicular Recording
- Author
-
Bogdan F. Valcu and H.J. Richter
- Subjects
Physics ,Magnetometer ,business.industry ,Perpendicular recording ,Ring (chemistry) ,Magnetic hysteresis ,Square (algebra) ,Electronic, Optical and Magnetic Materials ,law.invention ,Loop (topology) ,Optics ,Nuclear magnetic resonance ,law ,Shielded cable ,Head (vessel) ,Electrical and Electronic Engineering ,business - Abstract
We report simulations of the writing process of isolated transitions with a magnetometer for perpendicular recording. The fields of three different head types, a pole head, a shielded pole head and a ring head were used to study the writing of transitions on two perpendicular media, one with a very square loop and the other one with a shallow loop. It is found that the shielded head records the narrowest transitions, followed by the ring and then by the pole head
- Published
- 2007
199. Easy-Plane Magnetic Anisotropy Induced by Stress-Annealing in Finemet-Type Materials
- Author
-
Bogdan F. Palosz, S. N. Kane, Stanislaw Gierlotka, Henryk K. Lachowicz, and A. Gupta
- Subjects
Magnetic anisotropy ,Materials science ,Amorphous metal ,Magic angle ,Condensed matter physics ,Annealing (metallurgy) ,Ribbon ,Mössbauer spectroscopy ,General Physics and Astronomy ,Anisotropy - Abstract
It is shown that annealing under stress of FINEMET-type metallic glass ribbon (FeCuNbSiB) induces magnetic anisotropy of an easy-plane type (cross-section of the ribbon). This conclusion has been drawn analyzing experimental results obtained by means of Kerr-effect (domain structure) and Mossbauer spectroscopy operating in the so-called "magic angle" configuration which allows us to calculate all three spatial components of magnetiza tion. Additionally, it is also shown that no crystallographic texture is created in the sample after stress-annealing, the feature which would have been an origin of the observed anisotropy. PACS numbers: 75.30.Gw, 75.50.Kj, 75.60.Ch
- Published
- 1998
200. Evolution of Disordering in SiC under High Pressure High Temperature Conditions: In-situ Powder Diffraction Study
- Author
-
M. Aloszyna, Svetlana Stelmakh, Stanislaw Gierlotka, Th. Peun, P. Zinn, D. G. Keil, Bogdan F. Palosz, Roman Pielaszek, and Ulrich Bismayer
- Subjects
In situ ,Crystallography ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,High pressure ,Compressibility ,General Materials Science ,Composite material ,Condensed Matter Physics ,Powder diffraction - Published
- 1998
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