3,000 research outputs found
Why does wurtzite form in nanowires of III-V zinc-blende semiconductors?
We develop a nucleation-based model to explain the formation of the wurtzite
(WZ) crystalline phase during the vapor-liquid-solid growth of free-standing
nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires,
nucleation generally occurs at the outer edge of the solid/liquid interface
(the triple phase line) rather than elsewhere at the solid/liquid interface. In
the present case, this entails major differences between ZB and WZ nuclei.
Depending on the pertinent interface energies, WZ nucleation is favored at high
liquid supersaturation. This explains our systematic observation of ZB during
the early stages of nanowire growth.Comment: 4 pages with 4 figures Submitted to Physical Review Letter
An accurate equation of state for the one component plasma in the low coupling regime
An accurate equation of state of the one component plasma is obtained in the
low coupling regime . The accuracy results from a smooth
combination of the well-known hypernetted chain integral equation, Monte Carlo
simulations and asymptotic analytical expressions of the excess internal energy
. In particular, special attention has been brought to describe and take
advantage of finite size effects on Monte Carlo results to get the
thermodynamic limit of . This combined approach reproduces very accurately
the different plasma correlation regimes encountered in this range of values of
. This paper extends to low 's an earlier Monte Carlo
simulation study devoted to strongly coupled systems for ({J.-M. Caillol}, {J. Chem. Phys.} \textbf{111}, 6538 (1999)). Analytical
fits of in the range are provided with a
precision that we claim to be not smaller than . HNC equation and
exact asymptotic expressions are shown to give reliable results for
only in narrow intervals, i.e. and respectively
The Origin of Antarctic Precipitation: A Modeling Approach
Isotope concentrations in polar ice cores have long been used to estimate paleotemperatures. Underlying the use of this "isotope paleothermometer" is the assumption that the relationship between surface temperature and isotope concentration over time at a single geographical point is the same as that observed over space during the present-day climate. The validity of this assumption may in fact be compromised by several factors related to climate change. The specific factor studied in this paper involves the evaporative sources for polar precipitation. Climatic changes in the relative strengths of these sources would imply a need for a recalibration of the paleothermometer. To quantify such changes, we performed two GCM simulations, one of present-day climate and the other of the climate during the Last Glacial Maximum (LGM), roughly 18000 years ago. Evaporative sources of Antarctic precipitation were established using special tracer diagnostics. Results suggest that polar precipitation during the LGM does indeed consist of (relatively) more water from tropical oceans, a direct reflection of the LGM's increased equator-to-pole temperature gradient and its increased sea ice extent, which reduces high latitude evaporation. This result implies that an uncalibrated ice core paleothermometer would produce LGM temperatures that are biased slightly low. Because LGM boundary conditions are still under debate, we performed a third GCM simulation using a modified set of LGM boundary conditions. Using this simulation gives some qualitatively similar results, though the tropical contribution is not quite as high. Uncertainties in the LGM boundary conditions does hamper success in calibrating the paleothermometer
Line shape diagnostics for solid density plasmas produced by ultra intense subpicosecond laser
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87325/2/158_1.pd
Traditional Techniques of oil extraction from Kapok (Ceiba pentandra Gaertn.), Mahogany (Khaya senegalensis) and Neem (Azadirach indica A. Juss.) Seeds from the Far-North Region of cameroon
An investigation was carried out in four localities of the Far-North of Cameroon (Maroua, Mokolo, Kaele and Yagoua in order to improve endogenous methods of oil extraction from kapok (Ceiba pentandra Gaertn.), mahogany (Hhaya Senegalensis) and neem (Azadirachta indica A. Juss.) seed. The questionnaire administered to 75 traditional producers permitted us to note that extraction of oil from kapok is scarce. The traditional extraction processes from these oilseeds vary. But two principal techniques are predominant: the kneading process and the heated paste process. Husking, pounding and extraction make up the bottleneck. The yields are low, averagely six pans (of 1L capacity) are used to obtain one litre of oil. Amelioration of these methods through the introduction of grinders and pressers will not only help reduce strenuousness, but also increase the capacity to treat the yields and oil quality
Knowledge, Attitudes, Practices and Beliefs about Medical Male Circumcision (MMC) among a Sample of Health Care Providers in Haiti
Background
Haiti has the highest number of people living with HIV infection in the Caribbean/Latin America region. Medical male circumcision (MMC) has been recommended to help prevent the spread of HIV. We sought to assess knowledge, attitudes, practices and beliefs about MMC among a sample of health care providers in Haiti.
Methods
A convenience sample of 153 health care providers at the GHESKIO Centers in Haiti responded to an exploratory survey that collected information on several topics relevant to health providers about MMC. Descriptive statistics were calculated for the responses and multivariable logistic regression was conducted to determine opinions of health care providers about the best age to perform MMC on males. Bayesian network analysis and sensitivity analysis were done to identify the minimum level of change required to increase the acceptability of performing MMC at age less than 1 year.
Results
The sample consisted of medical doctors (31.0%), nurses (49.0%), and other health care professionals (20.0%). Approximately 76% showed willingness to offer MMC services if they received training. Seventy-six percent believed that their male patients would accept circumcision, and 59% believed infancy was the best age for MMC. More than 90% of participants said that MMC would reduce STIs. Physicians and nurses who were willing to offer MMC if provided with adequate training were 2.5 (1.15–5.71) times as likely to choose the best age to perform MMC as less than one year. Finally, if the joint probability of choosing “the best age to perform MMC” as one year or older and having the mistaken belief that MMC prevents HIV entirely is reduced by 63% then the probability of finding that performing MMC at less than one year acceptable to health care providers is increased by 35%.
Conclusion
Participants demonstrated high levels of knowledge and positive attitudes towards MMC. Although this study suggests that circumcision is acceptable among certain health providers in Haiti, studies with larger and more representative samples are needed to confirm this finding
Implicit complexity for coinductive data: a characterization of corecurrence
We propose a framework for reasoning about programs that manipulate
coinductive data as well as inductive data. Our approach is based on using
equational programs, which support a seamless combination of computation and
reasoning, and using productivity (fairness) as the fundamental assertion,
rather than bi-simulation. The latter is expressible in terms of the former. As
an application to this framework, we give an implicit characterization of
corecurrence: a function is definable using corecurrence iff its productivity
is provable using coinduction for formulas in which data-predicates do not
occur negatively. This is an analog, albeit in weaker form, of a
characterization of recurrence (i.e. primitive recursion) in [Leivant, Unipolar
induction, TCS 318, 2004].Comment: In Proceedings DICE 2011, arXiv:1201.034
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