597 research outputs found
Resonant instabilities mediated by drag and electrostatic interactions in laboratory and astrophysical dusty plasmas
Dusty plasmas are known to support a diverse range of instabilities,
including both generalizations of standard plasma instabilities and ones caused
by effects specific to dusty systems. It has been recently demonstrated that a
novel broad class of streaming instabilities, termed resonant drag
instabilities (RDIs), can be attributed to a particular resonance phenomenon
caused by defective eigenvalues of the linearized dust/fluid system. In this
work, it is demonstrated that this resonance phenomenon is not unique to RDIs
and can be used as a framework to understand a wider range of instabilities,
termed resonant instabilities. Particular attention is given to the filamentary
ionization instability seen in laboratory dusty plasmas and to the two-stream
instability. It is shown that, due to the commonalities in underlying physics
between the dust-ion-acoustic two-stream instability and the acoustic RDI,
these instabilities should be relevant in strongly overlapping regimes in
astrophysical dusty plasmas. It is proposed that a similar overlap in the
experimental accessibility of these modes (and of the filamentary instability)
allows for the possibility of experimental investigation of complex and
astrophysically relevant instability dynamics.Comment: 18 pages, 15 figure
EUV Debris Mitigation using Magnetic Nulls
Next generation EUV sources for photolithography use light produced by
laser-produced plasmas (LPP) from ablated tin droplets. A major challenge for
extending the lifetime of these devices is mitigating damage caused by
deposition of tin debris on the sensitive collection mirror. Especially
difficult to stop are high energy (up to 10 keV) highly charged tin ions
created in the plasma. Existing solutions include the use of stopping gas,
electric fields, and magnetic fields. One common configuration consists of a
magnetic field perpendicular to the EUV emission direction, but such a system
can result in ion populations that are trapped rather than removed. We
investigate a previously unconsidered mitigation geometry consisting of a
magnetic null by performing full-orbit integration of the ion trajectories in
an EUV system with realistic dimensions, and optimize the coil locations for
the null configuration. The magnetic null prevents a fraction of ions from
hitting the mirror comparable to that of the perpendicular field, but does not
trap any ions due to the chaotic nature of ion trajectories that pass close to
the null. This technology can potentially improve LPP-based EUV
photolithography system efficiency and lifetime, and may allow for a different,
more efficient formulation of buffer gas
A Local Computation Approximation Scheme to Maximum Matching
We present a polylogarithmic local computation matching algorithm which
guarantees a (1-\eps)-approximation to the maximum matching in graphs of
bounded degree.Comment: Appears in Approx 201
Why do some people search for their files much more than others? A preliminary study
Purpose: Previous research has repeatedly shown that people only search for files in a small minority of cases when they do not remember the file's location. The current study aimed to examine whether there is a group of hyper-searchers who search significantly more than others. Based on previous neurocognitive studies, this study aims to hypothesize that if such a group exists, they will have superior verbal memory and reduced visuospatial memory. Design/methodology/approach: In total, 65 participants completed a questionnaire estimating their search percentages, as well as reporting demographic data. Verbal memory was measured using the Wechsler logical memory test, and visuospatial memory was assessed using an online card memory game. Findings: Hyper-searchers were defined as participants with search percentage of over one standard deviation (SD) above the mean. The average search percentage of the seven participants who met this criterion was 51% (SDÂ =Â 14%), over five times more than the other participants (MÂ =Â 10%, SDÂ =Â 9%). Similar results were obtained by re-analyzing data from four previous papers (NÂ =Â 1,252). The results further confirmed the hypothesis that hyper-searchers have significantly better verbal memory than other participants, possibly making searching easier and more successful for them. Lastly, the search percentage was positively predicted by verbal memory scores and negatively predicted by visuospatial memory scores. Explanations and future research are discussed. Originality/value: This preliminary study is the first to introduce the concept of hyper-searchers, demonstrate its existence and study its causes
Slow fluctuations in enhanced Raman scattering and surface roughness relaxation
We propose an explanation for the recently measured slow fluctuations and
``blinking'' in the surface enhanced Raman scattering (SERS) spectrum of single
molecules adsorbed on a silver colloidal particle. We suggest that these
fluctuations may be related to the dynamic relaxation of the surface roughness
on the nanometer scale and show that there are two classes of roughness with
qualitatively different dynamics. The predictions agree with measurements of
surface roughness relaxation. Using a theoretical model for the kinetics of
surface roughness relaxation in the presence of charges and optical electrical
fields, we predict that the high-frequency electromagnetic field increases both
the effective surface tension and the surface diffusion constant and thus
accelerates the surface smoothing kinetics and time scale of the Raman
fluctuations in manner that is linear with the laser power intensity, while the
addition of salt retards the surface relaxation kinetics and increases the time
scale of the fluctuations. These predictions are in qualitative agreement with
the Raman experiments
Evolution of the Schr\"odinger--Newton system for a self--gravitating scalar field
Using numerical techniques, we study the collapse of a scalar field
configuration in the Newtonian limit of the spherically symmetric
Einstein--Klein--Gordon (EKG) system, which results in the so called
Schr\"odinger--Newton (SN) set of equations. We present the numerical code
developed to evolve the SN system and topics related, like equilibrium
configurations and boundary conditions. Also, we analyze the evolution of
different initial configurations and the physical quantities associated to
them. In particular, we readdress the issue of the gravitational cooling
mechanism for Newtonian systems and find that all systems settle down onto a
0--node equilibrium configuration.Comment: RevTex file, 19 pages, 26 eps figures. Minor changes, matches version
to appear in PR
Cauchy-perturbative matching and outer boundary conditions: computational studies
We present results from a new technique which allows extraction of
gravitational radiation information from a generic three-dimensional numerical
relativity code and provides stable outer boundary conditions. In our approach
we match the solution of a Cauchy evolution of the nonlinear Einstein field
equations to a set of one-dimensional linear equations obtained through
perturbation techniques over a curved background. We discuss the validity of
this approach in the case of linear and mildly nonlinear gravitational waves
and show how a numerical module developed for this purpose is able to provide
an accurate and numerically convergent description of the gravitational wave
propagation and a stable numerical evolution.Comment: 20 pages, RevTe
Evaluation of MAGE-1 and MAGE-3 as tumour-specific markers to detect blood dissemination of hepatocellular carcinoma cells
The members of MAGE gene family are highly expressed in human hepatocellular carcinoma (HCC). In the present study, we tested the tumour-specific MAGE-1 and MAGE-3 transcripts in the peripheral blood of HCC patients by nested RTâPCR to detect the circulating tumour cells and evaluate their potential clinical implication. Of 30 HCC patients, the positive rate of MAGE-1 and MAGE-3 transcripts was 43.3% (13 out of 30) and 33.3% (10 out of 30) in PBMC samples, whilst the positive rate was 70% (21 out of 30) and 53.3% (16 out of 30) in the resected HCC tissue samples, respectively. The positivity for at least one MAGE gene transcript was 63.3% (19 out of 30) in PBMC samples of HCC patients and 83.3% (25 out of 30) in the resected HCC tissue samples. MAGE-1 and/or MAGE-3 mRNA were not detected in the PBMC of those patients from whom the resected HCC tissues were MAGE-1 or MAGE-3 mRNA negative, nor in the 25 PBMC samples from healthy donors. The detection of MAGE transcripts in PBMC was correlated with the advanced stages and tumour size of the HCC, being 82.4% (14 out of 17) in tumour stages III and IVa, 56.6% (five out of nine) in stage II, and null (nought out of four) in stage I. The serum α-FP in 33.3% (10 out of 30) of HCC patients was normal or slightly elevated (<40âng mlâ1). However, six of these 10 patients (α-FP <40âng mlâ1) were MAGE-1 and /or MAGE-3 mRNA positive in their PBMC. The follow-up survey of MAGE mRNA in PBMC was performed in 12 patients. Seven patients with persistent MAGE-1 and/or MAGE-3 mRNA positive or from negative turned to positive died because of metastasis and/or recurrence. In striking contrast, all four patients with MAGE-1 and/or MAGE-3 mRNA from positive turned to negative and one patient with persistent MAGE-3 transcript negative are alive after last test. Collectively, detection of MAGE transcripts with follow-up survey in PBMC is a feasible and reliable assay for the early prediction of the relapse and prognosis of the HCC patients
Performance Evaluation of Pseudospectral Ultrasound Simulations on a Cluster of Xeon Phi Accelerators
The rapid development of novel procedures in medical ultrasonics, including treatment planning in therapeutic ultrasound and image reconstruction in photoacoustic tomography, leads to increasing demand for large-scale ultrasound simulations. However, routine execution of such simulations using traditional methods, e.g., finite difference time domain, is expensive and often considered intractable due to the computational and memory requirements. The k-space corrected pseudospectral time domain method used by the k-Wave toolbox allows for significant reductions in spatial and temporal grid resolution. These improvements are achieved at the cost of all-to-all communication, which are inherent to the multi-dimensional fast Fourier transforms. To improve data locality, reduce communication and allow efficient use of accelerators, we recently implemented a domain decomposition technique based on a local Fourier basis.
In this paper, we investigate whether it is feasible to run the distributed k-Wave implementation on the Salomon cluster equipped with 864 Intel Xeon Phi (Knightâs Corner) accelerators. The results show the immaturity of the KNC platform with issues ranging from limited support of Infiniband and LustreFS in Intel MPI on this platform to poor performance of 3D FFTs achieved by Intel MKL on the KNC architecture. Yet, we show that it is possible to achieve strong and weak scaling comparable to CPU-only platforms albeit with the runtime 1.8Ă to 4.3Ă longer. However, the accounting policy for Salomonâs accelerators is far more favorable and thus their employment reduces the computational cost significantly
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