Equation of state and phonon frequency calculations of diamond at high pressures

The pressure-volume relationship and the zone-center optical phonon frequency of cubic diamond at pressures up to 600 GPa have been calculated based on Density Functional Theory within the Local Density Approximation and the Generalized Gradient Approximation. Three different approaches, viz. a pseudopotential method applied in the basis of plane waves, an all-electron method relying on Augmented Plane Waves plus Local Orbitals, and an intermediate approach implemented in the basis of Projector Augmented Waves have been used. All these methods and approximations yield consistent results for the pressure derivative of the bulk modulus and the volume dependence of the mode Grueneisen parameter of diamond. The results are at variance with recent precise measurements up to 140 GPa. Possible implications for the experimental pressure determination based on the ruby luminescence method are discussed.Comment: 10 pages, 6 figure

Mechanical Deformation Induced in Si and GaN Under Berkovich Nanoindentation

Details of Berkovich nanoindentation-induced mechanical deformation mechanisms of single-crystal Si(100) and the metal-organic chemical-vapor deposition (MOCVD) derived GaN thin films have been systematic investigated by means of micro-Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM) techniques. The XTEM samples were prepared by using focused ion beam (FIB) milling to accurately position the cross-section of the nanoindented area. The behaviors of the discontinuities displayed in the loading and unloading segments of the load-displacement curves of Si and GaN thin films performed with a Berkovich diamond indenter tip were explained by the observed microstructure features obtained from XTEM analyses. According to the observations of micro-Raman and XTEM, the nanoindentation-induced mechanical deformation is due primarily to the generation and propagation of dislocations gliding along the pyramidal and basal planes specific to the hexagonal structure of GaN thin films rather than by indentation-induced phase transformations displayed in Si

Population distribution and ancestry of the cancer protective MDM2 SNP285 (rs117039649)

The MDM2 promoter SNP285C is located on the SNP309G allele. While SNP309G enhances Sp1 transcription factor binding and MDM2 transcription, SNP285C antagonizes Sp1 binding and reduces the risk of breast-, ovary- and endometrial cancer. Assessing SNP285 and 309 genotypes across 25 different ethnic populations (>10.000 individuals), the incidence of SNP285C was 6-8% across European populations except for Finns (1.2%) and Saami (0.3%). The incidence decreased towards the Middle-East and Eastern Russia, and SNP285C was absent among Han Chinese, Mongolians and African Americans. Interhaplotype variation analyses estimated SNP285C to have originated about 14,700 years ago (95% CI: 8,300 - 33,300). Both this estimate and the geographical distribution suggest SNP285C to have arisen after the separation between Caucasians and modern day East Asians (17,000 - 40,000 years ago). We observed a strong inverse correlation (r = -0.805; p < 0.001) between the percentage of SNP309G alleles harboring SNP285C and the MAF for SNP309G itself across different populations suggesting selection and environmental adaptation with respect to MDM2 expression in recent human evolution. In conclusion, we found SNP285C to be a pan-Caucasian variant. Ethnic variation regarding distribution of SNP285C needs to be taken into account when assessing the impact of MDM2 SNPs on cancer risk

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

FIRST PRINCIPLES CALCULATION OF THE PHONON SPECTRA OF SOLIDS

In this article, a first principles microscopic calculation of Si is presented and compared with results of other methods

Parallel Programming on Amoeba Using Efficient Distributed Shared Memory

Programming using message passing is considered difficult and therefore many researchers have proposed a model based on distributed shared memory (DSM). Currently, there is a trend to weaken the consistency of distributed shared memory. This allows for a good performance but complicates programming of applications. We have designed a new model for distributed shared memory that is efficient and consistent. Our approach is based on efficient low-level communication protocols and on a language that allows us to use implementation techniques that existing DSM systems cannot use effectively. We have implemented our DSM system on top of the Amoeba distributed operating system using its fast remote procedure call and group communication mechanisms. Using this implementation we measured the performance of the basic costs for operations on DSM and of several parallel applications

Comment on "Pseudopotentials that work: From H to Pu"

In this Comment we report on small differences found in the ion-core pseudopotentials of Si between our results and the values tabulated earlier by Bachelet, Hamann, and Schlüter. It is shown that the rounding of the parameters in their tables leads to inaccuracies. For convenience to future users of the Bachelet-Hamann-Schlüter potentials a correct set of reference tables is given.Comment behorende bij 10.1103/PhysRevB.26.4199FWN – Publicaties zonder aanstelling Universiteit Leide