2,985 research outputs found
THE SPECTROSCOPY OF CRYSTAL DEFECTS - A COMPENDIUM OF DEFECT NOMENCLATURE
The authors bring together tables of current defect nomenclature and a summary of the rules actually practised (rather than idealised schemes) in choosing such labels for signals obtained with a range of spectroscopies. As well as providing a source of reference for the user lost in a maze of labels, the compilation also indicates parallels between similar defect species in very different systems (e.g. ice and quartz), even though the relationships may be far from obvious from the labels. The systems considered are all non-metals, namely ionic crystals (including oxides), silica, semiconductors (e.g. III-V and tetrahedrally coordinated II-VI), valence crystals (e.g. diamond, c-Si, a-Si) and other special hosts like ice and conducting polymers
Experimental studies on the impact properties of water ice
Experimental studies on the impact of ice particles at very low velocity were continued. These measurements have applications in the dynamics of Saturn's rings. Initially data were obtained on the coefficient of restitution for ice spheres of one radius of curvature. The type of measurements were expanded to include restitution data for balls with a variety of surfaces as well as sticking forces between ice particles. Significant improvements were made to this experiment, the most important being the construction of a new apparatus. The new apparatus consists of a smaller version of the disk pendulum and a stainless steel, double-walled cryostat. The apparatus has proved to be a significant improvement over the old one. Measurements can now be made at temperatures near 90 K, comparable to the temperature of the environment of Saturn's rings, and with much greater temperature stability. It was found that a roughened contact surface or the presence of frost can cause a much larger change in the restitution measure than the geometrical effect of the radius of curvature
Resolved Stellar Populations of Super-Metal-Rich Star Clusters in the Bulge of M31
We have applied the MCS image deconvolution algorithm (Magain, Courbin & Sohy
1998) to HST/WFPC2 V, I data of three M31 bulge globular clusters (G170, G177,
and G198) and control fields near each cluster. All three clusters are clearly
detected, with an increase in stellar density with decreasing radius from the
cluster centers; this is the first time that stars have been resolved in bulge
clusters in the inner regions of another galaxy. From the RGB slopes of the
clusters and the difference in I magnitude between the HB and the top of the
RGB, we conclude that these three clusters all have roughly solar metallicity,
in agreement with earlier integrated-light spectroscopic measurements. Our data
support a picture whereby the M31 bulge clusters and field stars were born from
the same metal-rich gas, early in the galaxy formation.Comment: 7 pages, 4 Postscript figures, accepted for publication in A&
Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms
In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is
on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein
modes; yet only for the Eu and Sr systems is there a large dip in the thermal
conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here
we argue that it is the off-center displacement that is crucial for
understanding this unexplained difference in behavior. It enhances the coupling
between the "rattler" motion and the lattice phonons for the Eu and Sr systems,
and turns on/off another scattering mechanism (for 1K < T < 20K) produced by
the presence/absence of off-center sites. The random occupation of different
off-center sites produces a high density of symmetry-breaking defects which
scatters phonons. It may also be important for improving our understanding of
other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened
arguments regarding need for additional phonon scattering mechanis
The impact of two-dimensional elastic disk
The impact of a two-dimensional elastic disk with a wall is numerically
studied. It is clarified that the coefficient of restitution (COR) decreases
with the impact velocity. The result is not consistent with the recent
quasi-static theory of inelastic collisions even for very slow impact. The
abrupt drop of COR is found due to the plastic deformation of the disk, which
is assisted by the initial internal motion.(to be published in J. Phys. Soc.
Jpn.)Comment: 6 Pages,2 figure
Alignments of the Dominant Galaxies in Poor Clusters
We have examined the orientations of brightest cluster galaxies (BCGs) in
poor MKW and AWM clusters and find that, like their counterparts in richer
Abell clusters, poor cluster BCGs exhibit a strong propensity to be aligned
with the principal axes of their host clusters as well as the surrounding
distribution of nearby (< 20/h Mpc) Abell clusters. The processes responsible
for dominant galaxy alignments are therefore independent of cluster richness.
We argue that these alignments most likely arise from anisotropic infall of
material into clusters along large-scale filaments.Comment: 8 pages, 5 figure
Measuring Thread Timing to Assess the Feasibility of Early-bird Message Delivery
Early-bird communication is a communication/computation overlap technique
that combines fine-grained communication with partitioned communication to
improve application run-time. Communication is divided among the compute
threads such that each individual thread can initiate transmission of its
portion of the data as soon as it is complete rather than waiting for all of
the threads. However, the benefit of early-bird communication depends on the
completion timing of the individual threads. In this paper, we measure and
evaluate the potential overlap, the idle time each thread experiences between
finishing their computation and the final thread finishing. These measurements
help us understand whether a given application could benefit from early-bird
communication. We present our technique for gathering this data and evaluate
data collected from three proxy applications: MiniFE, MiniMD, and MiniQMC. To
characterize the behavior of these workloads, we study the thread timings at
both a macro level, i.e., across all threads across all runs of an application,
and a micro level, i.e., within a single process of a single run. We observe
that these applications exhibit significantly different behavior. While MiniFE
and MiniQMC appear to be well-suited for early-bird communication because of
their wider thread distribution and more frequent laggard threads, the behavior
of MiniMD may limit its ability to leverage early-bird communication
- …