3,110 research outputs found
Hybrid deterministic and stochastic approach for efficient atomistic simulations at long time scales
We propose a hybrid deterministic and stochastic approach to achieve extended
time scales in atomistic simulations that combines the strengths of molecular
dynamics (MD) and Monte Carlo (MC) simulations in an easy-to-implement way. The
method exploits the rare event nature of the dynamics similar to most current
accelerated MD approaches but goes beyond them by providing, without any
further computational overhead, (a) rapid thermalization between infrequent
events, thereby minimizing spurious correlations, and (b) control over accuracy
of time-scale correction, while still providing similar or higher boosts in
computational efficiency. We present two applications of the method: (a)
Vacancy-mediated diffusion in Fe yields correct diffusivities over a wide range
of temperatures and (b) source-controlled plasticity and deformation behavior
in Au nanopillars at realistic strain rates (10^4/s and lower), with excellent
agreement with previous theoretical predictions and in situ high-resolution
transmission electron microscopy observations. The method gives several
orders-of-magnitude improvements in computational efficiency relative to
standard MD and good scalability with the size of the system.Comment: 4 pages, 2 figures. Corrected logarithm base in figures 2 and
RESOLVING CONFLICT AND BUSINESS ANTHROPOLOGY
Disagreements and conflicts are natural, not abnormal. Various methods of dealing with such struggles exist. Although the standard tools of negotiation and decision making are useful, alternative techniques (such as mediation, arbitration, and litigation) are sometimes needed. In addition, processes of indigenous conflict resolution (that embrace local traditions) have a potential role, especially within small-scale, rural, and/or ethnically distinct communities. Business anthropologists have unique skills for facilitating conflict resolution in many situations
ETHNOGRAPHY: NATURALISTIC RESEARCH AND BUSINESS ANTHROPOLOGY
Ethnographies provide complicated pictures of social behavior. The goal is to understand people on their own terms. Topics can range from full cultural profiles to the study of relatively distinct patterns of behavior (such as product consumption, workplace patterns, and so forth). Although many âscientificâ researchers feel that naturalistic methods such as ethnography are not adequately rigorous, they possess the potential to deal with culturally distinctive populations as well as viewing social actors within a real-life context
BUSINESS ANTHROPOLOGY, ANOMIE, AND DYSFUNCTION: TRANSCENDING THE TYRANNY OF THE MAJORITY
The impact of economic development upon ethnic and cultural diversity is discussed with reference to the concept of anomie in which socially acceptable goals can no longer be achieved in socially acceptable ways. Specific responses to anomie are explored with reference to the âtyranny of the majorityâ, in which peopleâs needs are denied after being outvoted. Strategies such as the âconcurrent majorityâ can help the ethnic minorities protect their rights and heritage. Business anthropologists have an important role in this regard
Cluster expansion Monte Carlo study of phase stability of vanadium nitrides
Phase stability of stable and metastable vanadium nitrides is studied using density functional theory (DFT) based total-energy calculations combined with cluster expansion Monte Carlo simulation and supercell methods. We have computed the formation enthalpy of the various stable and metastable vanadium nitride phases considering the available structural models and found that the formation enthalpies of the different phases decrease in the same order as they appear in the experimental aging sequence. DFT calculations are known to show stoichiometric V2N to be polymorphic in Ï”-Fe_2N and ζ-Fe2_N structures within a few meV and VN to be more stable in WC(B_h) phase than in the experimentally observed NaCl(B1) structure. As these nitrides are known to be generally nonstoichiometric due to presence of nitrogen vacancies, we used cluster expansion and supercell methods for examining the effect of nitrogen vacancies on the phase stability. It is found that nitrogen vacancies, represented by â», stabilize Ï”-Fe_2N phase of V_2N_(1âxâ»x) and NaCl(B1) phase of VN_(1âxâ»x) compared to ζ-Fe_2N and WC(B_h) phases respectively, rendering the computed phase stability scenario to be in agreement with experiments. Analysis of supercell calculated electronic density of states (DOS) of VN_(1âxâ»x) with varying x, shows that the nitrogen vacancies increase the DOS at Fermi level in WC phase, whereas they decrease the DOS in NaCl phase. And this serves as the mechanism of enhancement of the stability of the NaCl phase. Monte Carlo simulations were used for computing the finite temperature formation enthalpies of these phases as a function of nitrogen-vacancy concentration and found close agreement for NaCl(B1) phase of VN_(1âxâ»x) for which measured values are available
Transcending Differences and Celebrating Achievements: Folklore as a Conduit of Understanding
Collaboration
Method for locating low-energy solutions within DFT+U
The widely employed DFT+U formalism is known to give rise to many self-consistent yet energetically distinct solutions in correlated systems, which can be highly problematic for reliably predicting the thermodynamic and physical properties of such materials. Here we study this phenomenon in the bulk materials UO_2, CoO, and NiO, and in a CeO_2 surface. We show that the following factors affect which self-consistent solution a DFT+U calculation reaches: (i) the magnitude of U; (ii) initial correlated orbital occupations; (iii) lattice geometry; (iv) whether lattice symmetry is enforced on the charge density; and (v) even electronic mixing parameters. These various solutions may differ in total energy by hundreds of meV per atom, so identifying or approximating the ground state is critical in the DFT+U scheme. We propose an efficient U-ramping method for locating low-energy solutions, which we validate in a range of test cases. We also suggest that this method may be applicable to hybrid functional calculations
Magnetic defects promote ferromagnetism in Zn1-xCoxO
Experimental studies of Zn1-xCoxO as thin films or nanocrystals have found
ferromagnetism and Curie temperatures above room temperature and that p- or
n-type doping of Zn1-xCoxO can change its magnetic state. Bulk Zn1-xCoxO with a
low defect density and x in the range used in experimental thin film studies
exhibits ferromagnetism only at very low temperatures. Therefore defects in
thin film samples or nanocrystals may play an important role in promoting
magnetic interactions between Co ions in Zn1-xCoxO. The electronic structures
of Co substituted for Zn in ZnO, Zn and O vacancies, substituted N and
interstitial Zn in ZnO were calculated using the B3LYP hybrid density
functional in a supercell. The B3LYP functional predicts a band gap of 3.34 eV
for bulk ZnO, close to the experimental value of 3.47 eV. Occupied minority
spin Co 3d levels are at the top of the valence band and unoccupied levels lie
above the conduction band minimum. Majority spin Co 3d levels hybridize
strongly with bulk ZnO states. The neutral O vacancy and interstitial Zn are
deep and shallow donors, respectively. The Zn vacancy is a deep acceptor and
the acceptor level for substituted N is at mid gap. The possibility that p- or
n-type dopants promote exchange coupling of Co ions was investigated by
computing total energies of magnetic states of ZnO supercells containing two Co
ions and an oxygen vacancy, substituted N or interstitial Zn in various charge
states. The neutral N defect and the singly-positively charged O vacancy are
the only defects which strongly promote ferromagnetic exchange coupling of Co
ions at intermediate range.Comment: 9 pages, 11 figure
Beached birds on the Flemish beaches
The history of collecting beached birds along the Flemish coast goes back to 1962. The study aims to determine the oil-rate (the proportion of oiled birds) of the beach washed birds, which is a good tool to determine trends in the chronic pollution of our coastal waters with oil. Since 1992, the Research Institute for Nature and Forest (INBO) is responsible for the Beached Bird Surveys (BBS) and organises systematic counts once a month during October - March.The numbers of beached birds fluctuated a lot over the previous decades, depending on the number of birds wintering along our coast, oil spills and weather conditions. During the winter 2006/2007, 447 beached birds were counted along the Flemish coast, being 0.99 birds km-1, close to the average number of 1.06 birds km-1 since the winter 1991/1992 (numbers of beached birds due to the Tricolor oil spill during the winter 2002/2003 are ignored in this analysis). The highest densities were encountered during February, a general tendency. Auks and gulls were the most numerous last winter, and that was always the case since the winter 1991/1992. A of Uria aalge and Razorbills) last winter will be remembered as the winter with the highest proportion of auks since the winter 1992.Guillemots and Razorbills are especially vulnerable for oil pollution because they spend most of their life swimming at beach were auks. During the first half of the winter, the oil-rate was relatively low, but the second half was characterised by a relatively high score. Recently, OSPAR (the commission for the Protection of Marine Environment of the North-East Atlantic) has recognised the oil-rate among Guillemots as EcoQ, an indicator to evaluate trends in chronic oil pollution of the marine environment. The EcoQ-objective is to force back the oil rate of Guillemots to 10% or less. When examining the changes in the oil-rate of Guillemots that washed ashore our beaches since 1962, three periods are noticeable. Between 1962 and 1990, the oil rate of beached Guillemots was very high (> 95% of all beached Guillemots were fouled). Since 1990, there was a remarkable decline with an average oil-rate of about 60%. Since 2004 the decline continued with an all time lowest score of an oil-rate of âonlyâ 17% last winter. On the other hand, there is no decline in the density of Guillemots found death along the Flemish coast, so possibly a problem in food viability is responsible for the death of many auks since 1990. Diet studies on collected auks will hopefully tell us something why auks wash ashore without any visible reason
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