418 research outputs found
Mechanisms of arsenic clustering in silicon
A model of arsenic clustering in silicon is proposed and analyzed. The main
feature of the proposed model is the assumption that negatively charged arsenic
complexes play a dominant role in the clustering process. To confirm this
assumption, electron density and concentration of impurity atoms incorporated
into the clusters are calculated as functions of the total arsenic
concentration. A number of the negatively charged clusters incorporating a
point defect and one or more arsenic atoms are investigated. It is shown that
for the doubly negatively charged clusters or for clusters incorporating more
than one arsenic atom the electron density reaches a maximum value and then
monotonically and slowly decreases as total arsenic concentration increases. In
the case of doubly negatively charged cluster incorporating two arsenic atoms,
the calculated electron density agrees well with the experimental data.
Agreement with the experiment confirms the conclusion that two arsenic atoms
participate in the cluster formation. Among all present models, the proposed
model of clustering by formation of doubly negatively charged cluster
incorporating two arsenic atoms gives the best fit to the experimental data and
can be used in simulation of high concentration arsenic diffusion.Comment: 13 pages, 4 figures. Revised and shortened version of the paper has
been published in Phys. Rev. B, Vol.74 (3), art. no. 035205 (2006
Simulation of boron diffusion during low-temperature annealing of implanted silicon
Modeling of ion-implanted boron redistribution in silicon crystals during
low-temperature annealing with a small thermal budget has been carried out. It
was shown that formation of "tails"' in the low-concentration region of
impurity profiles occurs due to the long-range migration of boron interstitialsComment: 16 pages, 3 figure
Continuous-Flow Synthesis of Arylthio-Cyclopropyl Carbonyl Compounds
The straightforward, continuous-flow synthesis of cyclopropyl carbaldehydes and ketones has been developed starting from 2-hydroxycyclobutanones and aryl thiols. This acid-catalyzed mediated procedure allows access to the multigram and easily scalable synthesis of cyclopropyl adducts under mild conditions, using reusable Amberlyst-35 as a catalyst. The resins, suitably ground and used for filling steel columns, have been characterized via TGA, ATR, SEM and BET analyses to describe the physical-chemical properties of the packed bed and the continuous-flow system in detail. To highlight the synthetic versatility of the arylthiocyclopropyl carbonyl compounds, a series of selective oxidation reactions have been performed to access sulfoxide and sulfone carbaldehyde cyclopropanes, oxiranes and carboxylic acid derivatives
Insights into the reactivity of 2-hydroxycyclobutanones with thiols corroborated by quantum chemical DFT investigations, NMR and Raman analysis
A general strategy for the synthesis of 2-substituted cyclobutanone sulfides via a tandem Br nsted acid-catalyzed nucleophile addition/ring contraction/C3-C4 ring expansion reaction sequence has been exploited. The procedure led to a wide panel of four-membered cyclic ketones in good to excellent yields and with broad substrate scope. Mechanistic aspects and kinetic parameters were investigated by quantum chemical DFT calculations, allowing us to rationalize the different reactivity of 2-aryl- and 2-alkyl-substituted 2-hydroxycyclobutanones towards thiol nucleophiles in reactions mediated by sulfonic acids. NMR and in situ Raman techniques were employed to better understand the reaction kinetics and parameters that affect the desired outcome
Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution
The larger number of models of asteroid shapes and their rotational states
derived by the lightcurve inversion give us better insight into both the nature
of individual objects and the whole asteroid population. With a larger
statistical sample we can study the physical properties of asteroid
populations, such as main-belt asteroids or individual asteroid families, in
more detail. Shape models can also be used in combination with other types of
observational data (IR, adaptive optics images, stellar occultations), e.g., to
determine sizes and thermal properties. We use all available photometric data
of asteroids to derive their physical models by the lightcurve inversion method
and compare the observed pole latitude distributions of all asteroids with
known convex shape models with the simulated pole latitude distributions. We
used classical dense photometric lightcurves from several sources and
sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff,
Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the
lightcurve inversion method to determine asteroid convex models and their
rotational states. We also extended a simple dynamical model for the spin
evolution of asteroids used in our previous paper. We present 119 new asteroid
models derived from combined dense and sparse-in-time photometry. We discuss
the reliability of asteroid shape models derived only from Catalina Sky Survey
data (IAU code 703) and present 20 such models. By using different values for a
scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in
the dynamical model for the spin evolution and by comparing synthetics and
observed pole-latitude distributions, we were able to constrain the typical
values of the cYORP parameter as between 0.05 and 0.6.Comment: Accepted for publication in A&A, January 15, 201
Formation of Zr I and II lines under non-LTE conditions of stellar atmospheres
The non-local thermodynaic equilibrium (non-LTE) line formation for the two
ions of zirconium is considered through a range of spectral types when the Zr
abundance varies from the solar value down to [Zr/H] = -3. The model atom was
built using 148 energy levels of Zr I, 772 levels of Zr II, and the ground
state of Zr III. It was shown that the main non-LTE mechnism for the minority
species Zr I is ultraviolet overionization. Non-LTE leads to systematically
depleted total absorption in the Zr I lines and positive abundance corrections,
reaching to 0.33 dex for the solar metallicity models. The excited levels of Zr
II are overpopulated relative to their thermodynamic equilibrium populations in
the line formation layers due to radiative pumping from the low-excitation
levels. As a result, the line source function exceeds the Planck function
leading to weakening the Zr II lines and positive non-LTE abundance
corrections. Such corrections grow towards lower metallicity and lower surface
gravity and reach to 0.34 dex for Teff = 5500 K, log g = 2.0, [M/H] = -2. As a
test and first application of the Zr I-Zr II model atom, Zr abundance was
determined for the Sun on the basis of 1D LTE model atmosphere. Lines of Zr I
and Zr II give consistent within the error bars non-LTE abundances, while the
difference in LTE abundances amounts to 0.28 dex. The solar abundance of
zirconium obtained with the MAFAGS solar model atmosphere is log eps(Zr) =
2.63+-0.07.Comment: published in Astron. Letters, 36, 664 (2010); Erratum was submitte
ИССЛЕДОВАНИЕ МЕХАНИЧЕСКИХ СВОЙСТВ ПОЛИИМИДНЫХ ПЛЕНОК ПРИ ВОЗДЕЙСТВИИ ФАКТОРОВ КОСМОСА, ИМИТИРУЕМЫХ ЛАБОРАТОРНО
В работе изучены механические свойства полиимидных пленок типа kapton-H (производства КНР) толщиной 75 мкм в условиях одноосного растяжения при температуре 293 К после воздействия факторов космического пространства - раздельного и совместного облучения протонами и электронами с энергией Е=160кэВ и флюенсом (полным потоком частиц, падающих на образцы) 1016 см-2. Определены предел вынужденной эластичности, предел прочности, суммарная деформация до разрушения и вклады в суммарную деформацию, связанные с упругой деформацией, происходящей на линейной стадии, полной вынужденной эластической и необратимой деформацией, которые вносят свой вклад в общую деформацию образцов на нелинейной стадии. Полная вынужденная эластическая деформация состоит из высокоэластической деформации, обратимой при температуре испытания, и задержанной эластической деформации. После воздействия облучения обнаружено увеличение предела вынужденной эластичности пленок на 5-11%, снижение предела прочности на 10-14% и уменьшение суммарной деформации на 20-28%. Максимальное изменение всех механических характеристик происходит под воздействием облучения протонами. Установлено, что снижение суммарной деформации облученных пленок происходит, в основном, за счет сокращения на 80% вклада необратимой деформации. Вклад полной вынужденной эластической деформации пленки полиимида практически не изменяется после облучения, что имеет важное научное и прикладное значение
Heroes and villains of world history across cultures
© 2015 Hanke et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedEmergent properties of global political culture were examined using data from the World History Survey (WHS) involving 6,902 university students in 37 countries evaluating 40 figures from world history. Multidimensional scaling and factor analysis techniques found only limited forms of universality in evaluations across Western, Catholic/Orthodox, Muslim, and Asian country clusters. The highest consensus across cultures involved scientific innovators, with Einstein having the most positive evaluation overall. Peaceful humanitarians like Mother Theresa and Gandhi followed. There was much less cross-cultural consistency in the evaluation of negative figures, led by Hitler, Osama bin Laden, and Saddam Hussein. After more traditional empirical methods (e.g., factor analysis) failed to identify meaningful cross-cultural patterns, Latent Profile Analysis (LPA) was used to identify four global representational profiles: Secular and Religious Idealists were overwhelmingly prevalent in Christian countries, and Political Realists were common in Muslim and Asian countries. We discuss possible consequences and interpretations of these different representational profiles.This research was supported by grant RG016-P-10 from the Chiang Ching-Kuo Foundation for International Scholarly Exchange (http://www.cckf.org.tw/).
Religion
Culture
Entropy
China
Democracy
Economic histor
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