50,108 research outputs found
Control theory for principled heap sizing
We propose a new, principled approach to adaptive heap sizing based on control theory. We review current state-of-the-art heap sizing mechanisms, as deployed in Jikes RVM and HotSpot. We then formulate heap sizing as a control problem, apply and tune a standard controller algorithm, and evaluate its performance on a set of well-known benchmarks. We find our controller adapts the heap size more responsively than existing mechanisms. This responsiveness allows tighter virtual machine memory footprints while preserving target application throughput, which is ideal for both embedded and utility computing domains. In short, we argue that formal, systematic approaches to memory management should be replacing ad-hoc heuristics as the discipline matures. Control-theoretic heap sizing is one such systematic approach
The Effects of Dissolved Methane upon Liquid Argon Scintillation Light
In this paper we report on measurements of the effects of dissolved methane
upon argon scintillation light. We monitor the light yield from an alpha source
held 20 cm from a cryogenic photomultiplier tube (PMT) assembly as methane is
injected into a high-purity liquid argon volume. We observe significant
suppression of the scintillation light yield by dissolved methane at the 10
part per billion (ppb) level. By examining the late scintillation light time
constant, we determine that this loss is caused by an absorption process and
also see some evidence of methane-induced scintillation quenching at higher
concentrations (50-100 ppb). Using a second PMT assembly we look for visible
re-emission features from the dissolved methane which have been reported in
gas-phase argon methane mixtures, and we find no evidence of visible
re-emission from liquid-phase argon methane mixtures at concentrations between
10 ppb and 0.1%.Comment: 18 pages, 11 figures Updated to match published versio
Occurrence of bovine hydatidosis and evaluation of its risk to humans in traditional communities of Southern Region of Ethiopia
Background: Cystic Echinococcosis/ Hydatid Disease, is an infection caused by the larval stage of the tapeworm Echinococcus granulosus, one of the most widespread parasitic zoonoses.Objective: To determine the occurrence, localization and fertility/sterility rates of hydatid cyst in cattle, to determine the prevalence of adult E. granulosus in dogs and asses the risk for human infection in traditional communities.Methods: Postmortem examination, hydatid cyst characterization, questionnaire survey and dog stool sample examination were carried out.Results: Of the total 320 ruminants examined at backyard slaughtering, 151 (47.2%) were found harboring hydatid cysts. The liver and lungs were the two main infected organs, 34.4% and 52.3%, respectively. The majority of the cysts found were small, 54.3%, and medium, 37.7%. From the total number of cysts found, 70.2% were sterile, while 29.8% were fertile. A questionnaire survey revealed that local people were unaware of the life cycle of E. granulosus and the perpetuation of its life cycle by their cultural and traditional practices. Dogs have intimate contact with humansand other domestic animals, share the same house and also dogs do not have access for veterinary care. Stool samples of 62 dogs were collected and analyzed with a 30% prevalence of taenia infection confirmed to be E. granulosus.Conclusion: Because of the high prevalence of E. granulosus infection in dogs and hydatidosis in cattle as well as common practice of backyard slaughtering, the risk of human infection in traditional communities is suspected to be high and requires immediate attention to study the status of cystic ehinococcosis in the human population of the study area.[Ethiop. J. Health Dev. 2012;26(1):43-48
Evidence for nonlinear diffusive shock acceleration of cosmic-rays in the 2006 outburst of the recurrent nova RS Ophiuchi
Spectroscopic observations of the 2006 outburst of the recurrent nova RS
Ophiuchi at both infrared (IR) and X-ray wavelengths have shown that the blast
wave has decelerated at a higher rate than predicted by the standard
test-particle adiabatic shock-wave model. Here we show that the observed
evolution of the nova remnant can be explained by the diffusive shock
acceleration of particles at the blast wave and the subsequent escape of the
highest energy ions from the shock region. Nonlinear particle acceleration can
also account for the difference of shock velocities deduced from the IR and
X-ray data. The maximum energy that accelerated electrons and protons can have
achieved in few days after outburst is found to be as high as a few TeV. Using
the semi-analytic model of nonlinear diffusive shock acceleration developed by
Berezhko & Ellison, we show that the postshock temperature of the shocked gas
measured with RXTE/PCA and Swift/XRT imply a relatively moderate acceleration
efficiency.Comment: Accepted for publication in ApJ
Radio Emission from a Young Supernova Remnant Interacting with an Interstellar Cloud: MHD Simulation with Relativistic Electrons
We present two-dimensional MHD simulations of the evolution of a young Type
Ia supernova remnant during its interaction with an interstellar cloud of
comparable size at impact. We include for the first time in such simulations
explicit relativistic electron transport, including spectral information using
a simple but effective scheme that follows their acceleration at shocks and
subsequent transport. From this information we also model radio synchrotron
emission, including spectra. The principal conclusions from these experiments
are: 1) Independent of the cloud interaction, the SNR reverse shock can be an
efficient site for particle acceleration in a young SNR. 2) At these early
times the synchrotron spectral index due to electrons accelerated at the
primary shocks should be close to 0.5 unless those shocks are modified by
cosmic-ray pressures. However, interaction with the cloud generates regions of
distinctly steeper spectra, which may complicate interpretation in terms of
global dynamical models for SNR evolution. 3) The internal motions within the
SNR become highly turbulent following the cloud interaction. 4) An initially
uniform interstellar magnetic field is preferentially amplified along the
magnetic equator of the SNR, primarily due to biased amplification by
instabilities. Independent of the external field configuration, there is a net
radial direction to this field inside the SNR. 5) Filamentary radio structures
correlate well with magnetic filaments, while diffuse emission follows the
electron distribution. 6) Interaction with the cloud enhances both the electron
population and the radio emission.Comment: 29 pages of Latex generated text with 6 figures in gif format.
Accepted for publication in the Astrophysical Journal. High resolution
postscript figures can be obtained by anonymous ftp from
ftp://ftp.msi.umn.edu/pub/users/twj/sn
Gluino Contribution to the 3-loop QCD beta function in the Minimal Supersymmetric Standard Model
We deduce the gluino contribution to the three-loop QCD \beta function within
the minimal supersymmetric Standard Model (MSSM) from its standard QCD
expression. The result is a first step in the computation of the full MSSM
three-loop \beta function. In addition, in the case of a light gluino it
provides the strong three-loop SUSY correction to the extrapolation of the
strong coupling constant from the low energy regime to the Z region and up to
the squark threshold.Comment: 11 pages, RevTex, 4 Postscript figur
Magnetic impurities coupled to quantum antiferromagnets in one dimension
Magnetic impurities coupled antiferromagnetically to a one-dimensional
Heisenberg model are studied by numerical diagonalization of chains of finite
clusters. By calculating the binding energy and the correlation function, it is
shown that a local singlet develops around each impurity. This holds true for
systems with a single impurity, with two impurities, and for impurities forming
a lattice. The local character of the singlet is found to be little affected by
the presence of other impurity spins. A small effective interaction is found
between a pair of impurity spins, which oscillates depending on impurity
distances. For impurity lattices, the energy spectrum shows a gap which is
found to be much smaller than the binding energy per impurity if the coupling
constants are small. For larger coupling constants, it increases to the same
order of magnitude as the binding energy, indicating that a local singlet is
broken to create excited states. Impurity lattices with ferromagnetic couplings
are also studied and their connection to the Haldane problem is discussed.Comment: 25 pages, plain TeX, 17 figures available on request, to be publised
in Phys. Rev.
Determination of the Strong Coupling \boldmath{\as} from hadronic Event Shapes and NNLO QCD predictions using JADE Data
Event Shape Data from annihilation into hadrons collected by the
JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used
to determine the strong coupling . QCD predictions complete to
next-to-next-to-leading order (NNLO), alternatively combined with resummed
next-to-leading-log-approximation (NNLO+NLLA) calculations, are used. The
combined value from six different event shape observables at the six JADE
centre-of-mass energies using the NNLO calculations is
= 0.1210 +/- 0.0007(stat.) +/- 0.0021(expt.) +/- 0.0044(had.)
+/- 0.0036(theo.) and with the NNLO+NLLA calculations the combined value is
= 0.1172 +/- 0.0006(stat.) +/- 0.0020(expt.) +/- 0.0035(had.) +/-
0.0030(theo.) . The stability of the NNLO and NNLO+NLLA results with respect to
missing higher order contributions, studied by variations of the
renormalisation scale, is improved compared to previous results obtained with
NLO+NLLA or with NLO predictions only. The observed energy dependence of
agrees with the QCD prediction of asymptotic freedom and excludes
absence of running with 99% confidence level.Comment: 9 pages, EPHJA style, 4 figures, corresponds to published version
with JADE author lis
Kondo effect in coupled quantum dots under magnetic fields
The Kondo effect in coupled quantum dots is investigated theoretically under
magnetic fields. We show that the magnetoconductance (MC) illustrates peak
structures of the Kondo resonant spectra. When the dot-dot tunneling coupling
is smaller than the dot-lead coupling (level broadening), the
Kondo resonant levels appear at the Fermi level (). The Zeeman splitting
of the levels weakens the Kondo effect, which results in a negative MC. When
is larger than , the Kondo resonances form bonding and
anti-bonding levels, located below and above , respectively. We observe a
positive MC since the Zeeman splitting increases the overlap between the levels
at . In the presence of the antiferromagnetic spin coupling between the
dots, the sign of MC can change as a function of the gate voltage.Comment: 6 pages, 3 figure
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