425,104 research outputs found
Generalized Points-to Graphs: A New Abstraction of Memory in the Presence of Pointers
Flow- and context-sensitive points-to analysis is difficult to scale; for
top-down approaches, the problem centers on repeated analysis of the same
procedure; for bottom-up approaches, the abstractions used to represent
procedure summaries have not scaled while preserving precision.
We propose a novel abstraction called the Generalized Points-to Graph (GPG)
which views points-to relations as memory updates and generalizes them using
the counts of indirection levels leaving the unknown pointees implicit. This
allows us to construct GPGs as compact representations of bottom-up procedure
summaries in terms of memory updates and control flow between them. Their
compactness is ensured by the following optimizations: strength reduction
reduces the indirection levels, redundancy elimination removes redundant memory
updates and minimizes control flow (without over-approximating data dependence
between memory updates), and call inlining enhances the opportunities of these
optimizations. We devise novel operations and data flow analyses for these
optimizations.
Our quest for scalability of points-to analysis leads to the following
insight: The real killer of scalability in program analysis is not the amount
of data but the amount of control flow that it may be subjected to in search of
precision. The effectiveness of GPGs lies in the fact that they discard as much
control flow as possible without losing precision (i.e., by preserving data
dependence without over-approximation). This is the reason why the GPGs are
very small even for main procedures that contain the effect of the entire
program. This allows our implementation to scale to 158kLoC for C programs
First principles study of strain/electronic interplay in ZnO; Stress and temperature dependence of the piezoelectric constants
We present a first-principles study of the relationship between stress,
temperature and electronic properties in piezoelectric ZnO. Our method is a
plane wave pseudopotential implementation of density functional theory and
density functional linear response within the local density approximation. We
observe marked changes in the piezoelectric and dielectric constants when the
material is distorted. This stress dependence is the result of strong, bond
length dependent, hybridization between the O and Zn electrons. Our
results indicate that fine tuning of the piezoelectric properties for specific
device applications can be achieved by control of the ZnO lattice constant, for
example by epitaxial growth on an appropriate substrate.Comment: accepted for publication in Phys. Rev.
X-ray detection with Micromegas with background levels below 10 keVcms
Micromegas detectors are an optimum technological choice for the detection of
low energy x-rays. The low background techniques applied to these detectors
yielded remarkable background reductions over the years, being the CAST
experiment beneficiary of these developments. In this document we report on the
latest upgrades towards further background reductions and better understanding
of the detectors' response. The upgrades encompass the readout electronics, a
new detector design and the implementation of a more efficient cosmic muon veto
system. Background levels below 10keVcms have been
obtained at sea level for the first time, demonstrating the feasibility of the
expectations posed by IAXO, the next generation axion helioscope. Some results
obtained with a set of measurements conducted in the x-ray beam of the CAST
Detector Laboratory will be also presented and discussed
Experimental study of local strong parity violation in relativistic nuclear collisions
Parity-odd domains, corresponding to non-trivial topological solutions of the
QCD vacuum, might be created in relativistic heavy ions collisions. These
domains are predicted to lead to charge separation along the system orbital
momentum of the system created in non-central collisions. Three-particle mixed
harmonics azimuthal correlator is a \P even observable but directly sensitive
to the charge separation effect. Using this observable to analyze Au+Au and
Cu+Cu collisions at and 62 GeV, STAR detects a signal
consistent with several of the theoretical expectations. Possible contributions
from effects not related to parity violation are studied with existing event
generators, which fail to describe the data. Future directions in studying the
effect are discussed.Comment: Proceedings, plenary invited talk at Quark Matter 2009 Conference,
Knoxville, Tennessee. One reference added. Final versio
Application of Pulsed Field Gel Electrophoresis to Determine Îł-ray-induced Double-strand Breaks in Yeast Chromosomal Molecules
The frequency of DNA double-strand breaks (dsb) was determined in yeast cells exposed to Îł-rays under anoxic conditions. Genomic DNA of treated cells was separated by pulsed field gel electrophoresis, and two different approaches for the evaluation of the gels were employed: (1) The DNA mass distribution profile obtained by electrophoresis was compared to computed profiles, and the number of DSB per unit length was then derived in terms of a fitting procedure; (2) hybridization of selected chromosomes was performed, and a comparison of the hybridization signals in treated and untreated samples was then used to derive the frequency of dsb
Biophysically motivated efficient estimation of the spatially isotropic R*2 component from a single gradientârecalled echo measurement
Purpose
To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientationâdependent part of R*2 using a single gradientârecalled echo (GRE) measurement.
Methods
The proposed method utilized a temporal secondâorder approximation of the hollowâcylinderâfiber model, in which the parameter describing the linear signal decay corresponded to the orientationâindependent part of R*2. The estimated parameters were compared to the classical, monoâexponential decay model for R*2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R*2, it was compared to the established phenomenological method for separating R*2 into orientationâdependent and âindependent parts.
Results
Using the phenomenological method on the classical signal model, the wellâknown separation of R*2 into orientationâdependent and âindependent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed.
Conclusions
Since the proposed secondâorder model features orientationâdependent and âindependent components at distinct temporal orders, it can be used to remove the orientation dependence of R*2 using only a single GRE measurement
Atmospheric neutrino flux from 3-dimensional simulation
The atmospheric muon and neutrino flux have been simulated using the same
approach which successfully accounted for the recent secondary proton, electron
and positron flux measurements in orbit by the AMS experiment. For the muon
flux, a good agreement is obtained with the CAPRICE and HEAT data for altitudes
ranging from sea level up to about 38 km. The general features of the
calculated atmospheric neutrino flux are reported and discussed. The flux
obtained at the Super-Kamiokande experiment location are reported and compared
with other calculations. For low neutrino energies the flux obtained is
significantly smaller than that used in the data analysis of underground
experiment. The simulation results for the SOUDAN experiment site are also
reported.Comment: 33 pages, 27 figures, 12 tables, final version for Phys. Rev.
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