10,510 research outputs found
Particle-in-cell and weak turbulence simulations of plasma emission
The plasma emission process, which is the mechanism for solar type II and
type III radio bursts phenomena, is studied by means of particle-in-cell and
weak turbulence simulation methods. By plasma emission, it is meant as a loose
description of a series of processes, starting from the solar flare associated
electron beam exciting Langmuir and ion-acoustic turbulence, and subsequent
partial conversion of beam energy into the radiation energy by nonlinear
processes. Particle-in-cell (PIC) simulation is rigorous but the method is
computationally intense, and it is difficult to diagnose the results. Numerical
solution of equations of weak turbulence (WT) theory, termed WT simulation, on
the other hand, is efficient and naturally lends itself to diagnostics since
various terms in the equation can be turned on or off. Nevertheless, WT theory
is based upon a number of assumptions. It is, therefore, desirable to compare
the two methods, which is carried out for the first time in the present paper
with numerical solutions of the complete set of equations of the WT theory and
with two-dimensional electromagnetic PIC simulation. Upon making quantitative
comparisons it is found that WT theory is largely valid, although some
discrepancies are also found. The present study also indicates that it requires
large computational resources in order to accurately simulate the radiation
emission processes, especially for low electron beam speeds. Findings from the
present paper thus imply that both methods may be useful for the study of solar
radio emissions as they are complementary.Comment: 21 pages, 9 figure
What determines social service workers’ wages: A cross-country analysis using a Luxembourg Income Study
The study is aimed at exploring the influencing factor of wages among social service workers (SSWs) through a cross-country analysis. Using Luxembourg Income Study data, two aspects are emphasised: first, the trends and patterns of wage levels among SSWs. Second, the determining factors that influence their low wages at a cross-national level and how those factors are intersectionally intertwined to exacerbate the wage level. Three significant findings are confirmed: a universal gendered wage gap; a more significant wage gap for those on part-time and/or fractured contracts and employed in the private sector; and a substantial association between a higher education and higher wages. Two policy concerns are raised for discussion: first, tackling the gendered wage gap and ensuring more secure employment, and a guaranteed living wage for those employed in the private sector. Second, enhancing the professionalism for empowering their effective choices in the labour market is essential [148 words]
Molecular Gas Content of HI Monsters and Implications to Cold Gas Content Evolution in Galaxies
We present 12CO (J=1-0) observations of a sample of local galaxies
(0.04<z<0.08) with a large neutral hydrogen reservoir, or "HI monsters". The
data were obtained using the Redshift Search Receiver on the FCRAO 14 m
telescope. The sample consists of 20 HI-massive galaxies with M(HI)>3e10Msun
from the ALFALFA survey and 8 LSBs with a comparable M(HI) (>1.5e10Msun). Our
sample selection is purely based on the amount of neutral hydrogen, thereby
providing a chance to study how atomic and molecular gas relate to each other
in these HI-massive systems. We have detected CO in 15 out of 20 ALFALFA
selected galaxies and 4 out of 8 LSBs with molecular gas mass M(H2) of
(1-11)e9Msun. Their total cold gas masses of (2-7e10Msun make them some of the
most gas-massive galaxies identified to date in the Local Universe. Observed
trends associated with HI, H2, and stellar properties of the HI massive
galaxies and the field comparison sample are analyzed in the context of
theoretical models of galaxy cold gas content and evolution, and the importance
of total gas content and improved recipes for handling spatially differentiated
behaviors of disk and halo gas are identified as potential areas of improvement
for the modeling.Comment: 18 pages, 11 figures, 2 tables; Accepted for publication in MNRA
Topology of Luminous Red Galaxies from the Sloan Digital Sky Survey
We present measurements of the genus topology of luminous red galaxies (LRGs)
from the Sloan Digital Sky Survey (SDSS) Data Release 7 catalog, with
unprecedented statistical significance. To estimate the uncertainties in the
measured genus, we construct 81 mock SDSS LRG surveys along the past light cone
from the Horizon Run 3, one of the largest N-body simulations to date that
evolved 7210^3 particles in a 10815 Mpc/h size box. After carefully modeling
and removing all known systematic effects due to finite pixel size, survey
boundary, radial and angular selection functions, shot noise and galaxy
biasing, we find the observed genus amplitude to reach 272 at 22 Mpc/h
smoothing scale with an uncertainty of 4.2%; the estimated error fully
incorporates cosmic variance. This is the most accurate constraint of the genus
amplitude to date, which significantly improves on our previous results. In
particular, the shape of the genus curve agrees very well with the mean
topology of the SDSS LRG mock surveys in the LCDM universe. However, comparison
with simulations also shows small deviations of the observed genus curve from
the theoretical expectation for Gaussian initial conditions. While these
discrepancies are mainly driven by known systematic effects such as those of
shot noise and redshift-space distortions, they do contain important
cosmological information on the physical effects connected with galaxy
formation, gravitational evolution and primordial non-Gaussianity. We address
here the key role played by systematics on the genus curve, and show how to
accurately correct for their effects to recover the topology of the underlying
matter. In a forthcoming paper, we provide an interpretation of those
deviations in the context of the local model of non-Gaussianity.Comment: 23 pages, 18 figures. APJ Supplement Series 201
Electron Transport in Graphene Nanoribbon Field-Effect Transistor under Bias and Gate Voltages: Isochemical Potential Approach
Zigzag graphene nanoribbon (zGNR) of narrow width has a moderate energy gap in its antiferromagnetic ground state. So far, first-principles electron transport calculations have been performed using nonequilibrium Green function (NEGF) method combined with density functional theory (DFT). However, the commonly practiced bottom-gate control has not been studied computationally due to the need to simulate an electron reservoir that fixes the chemical potential of electrons in the zGNR and electrodes. Here, we present the isochemical potential scheme to describe the top/back-gate effect using external potential. Then, we examine the change in electronic state under the modulation of chemical potential and the subsequent electron transport phenomena in zGNR transistor under substantial top-/back-gate and bias voltages. The gate potential can activate the device states resulting in a boosted current. This gate-controlled current-boosting could be utilized for designing novel zGNR field effect transistors (FETs).ope
Spectral dimensions of hierarchical scale-free networks with shortcuts
The spectral dimension has been widely used to understand transport
properties on regular and fractal lattices. Nevertheless, it has been little
studied for complex networks such as scale-free and small world networks. Here
we study the spectral dimension and the return-to-origin probability of random
walks on hierarchical scale-free networks, which can be either fractals or
non-fractals depending on the weight of shortcuts. Applying the renormalization
group (RG) approach to the Gaussian model, we obtain the spectral dimension
exactly. While the spectral dimension varies between and for the
fractal case, it remains at , independent of the variation of network
structure for the non-fractal case. The crossover behavior between the two
cases is studied through the RG flow analysis. The analytic results are
confirmed by simulation results and their implications for the architecture of
complex systems are discussed.Comment: 10 pages, 3 figure
Optical spectroscopic investigation on the coupling of electronic and magnetic structure in multiferroic hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films
We investigated the effects of temperature and magnetic field on the
electronic structure of hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films
using optical spectroscopy. As the magnetic ordering of the system was
disturbed, a systematic change in the electronic structure was commonly
identified in this series. The optical absorption peak near 1.7 eV showed an
unexpectedly large shift of more than 150 meV from 300 K to 15 K, accompanied
by an anomaly of the shift at the Neel temperature. The magnetic field
dependent measurement clearly revealed a sizable shift of the corresponding
peak when a high magnetic field was applied. Our findings indicated strong
coupling between the magnetic ordering and the electronic structure in the
multiferroic hexagonal RMnO3 compounds.Comment: 16 pages including 4 figure
The versatile terahertz reflection and transmission spectrometer with the location of objects of researches in the horizontal plane
The experimental setup of versatile pulse terahertz reflection and transmission spectrometer and operation concept were described. Using this setup the temporary forms of THz signal reflected from and transmitted through the samples like amino acids, dental tissue and normal were obtained. The possibility of structural determination of powdered media was demonstrated using this method
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