24,276 research outputs found
On the Scale-Invariant Distribution of the Diffusion Coefficient for Classical Particles Diffusing in Disordered Media.-
The scaling form of the whole distribution P(D) of the random diffusion
coefficient D(x) in a model of classically diffusing particles is investigated.
The renormalization group approach above the lower critical dimension d=0 is
applied to the distribution P(D) using the n-replica approach. In the annealed
approximation (n=1), the inverse gaussian distribution is found to be the
stable one under rescaling. This identification is made based on symmetry
arguments and subtle relations between this model and that of fluc- tuating
interfaces studied by Wallace and Zia. The renormalization-group flow for the
ratios between consecutive cumulants shows a regime of pure diffusion for small
disorder, in which P(D) goes to delta(D-), and a regime of strong disorder
where the cumulants grow infinitely large and the diffusion process is ill
defined. The boundary between these two regimes is associated with an unstable
fixed-point and a subdiffusive behavior: =Ct**(1-d/2). For the quenched
case (n goes to 0) we find that unphysical operators are generated raisng
doubts on the renormalizability of this model. Implications to other random
systems near their lower critical dimension are discussed.Comment: 21 pages, 1 fig. (not included) Use LaTex twic
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Reversible writing of high-mobility and high-carrier-density doping patterns in two-dimensional van der Waals heterostructures
A key feature of two-dimensional materials is that the sign and concentration of their carriers can be externally controlled with techniques such as electrostatic gating. However, conventional electrostatic gating has limitations, including a maximum carrier density set by the dielectric breakdown, and ionic liquid gating and direct chemical doping also suffer from drawbacks. Here, we show that an electron-beam-induced doping technique can be used to reversibly write high-resolution doping patterns in hexagonal boron nitride-encapsulated graphene and molybdenum disulfide (MoS2) van der Waals heterostructures. The doped MoS2 device exhibits an order of magnitude decrease of subthreshold swing compared with the device before doping, whereas the doped graphene devices demonstrate a previously inaccessible regime of high carrier concentration and high mobility, even at room temperature. We also show that the approach can be used to write high-quality p–n junctions and nanoscale doping patterns, illustrating that the technique can create nanoscale circuitry in van der Waals heterostructures
Direct CP, T and/or CPT violations in the K^0-\bar{K^0} system - Implications of the recent KTeV results on decays -
The recent results on the CP violating parameters Re(e'/e) and \Delta\phi =
\phi_{00}-\phi_{+-} reported by the KTeV Collaboration are analyzed with a view
to constrain CP, T and CPT violations in a decay process. Combining with some
relevant data compiled by the Particle Data Group, we find Re(e_2-e_0) = (0.85
+- 3.11)*10^{-4} and Im(e_2-e_0) = (3.2 +- 0.7)*10^{-4}, where Re(e_I) and
Im(e_I) represent respectively CP/CPT and CP/T violations in decay of K^0 and
\bar{K^0} into a 2\pi state with isospin I.Comment: 7 pages, No figure
The Amplitude in an External Homogeneous Electromagnetic Field
Neutrino-photon interactions in the presence of an external homogeneous
constant electromagnetic field are studied. The amplitude is
calculated in an electromagnetic field of the general type, when the two field
invariants are nonzero.Comment: 7 pages, 1 figur
Radiative Corrections to Electron-Proton Scattering
The radiative corrections to elastic electron-proton scattering are analyzed
in a hadronic model including the finite size of the nucleon. For initial
electron energies above 8 GeV and large scattering angles, the proton vertex
correction in this model increases by at least two percent the overall factor
by which the one-photon exchange (Rosenbluth) cross section must be multiplied.
The contribution of soft photon emission is calculated exactly. Comparison is
made with the generally used expressions previously obtained by Mo and Tsai.
Results are presented for some kinematics at high momentum transfer.Comment: 31 pages, 4 figure
Vehicular fuel composition and atmospheric emissions in South China: Hong Kong, Macau, Guangzhou, and Zhuhai
International audienceVehicular emission is an important source of air pollutants in urban cities in the Pearl River Delta (PRD) region of South China. In order to study the impact of vehicular fuel on air quality, several commonly used fuel samples were collected in four main cities in the PRD region ? Hong Kong, Guangzhou, Macau and Zhuhai, and analyzed for their volatile organic compounds (VOCs) composition. Source profiles of the vehicular fuels used in these cities were constructed and are believed to be the first reported for the PRD region. The C8?C10 hydrocarbons were the main constituents of diesel. Different from diesel, gasoline used in the PRD region was mainly comprised of lighter C4?C7 hydrocarbons, with toluene and i-pentane being the two most abundant species. The benzene content in the Guangzhou and Zhuhai gasoline samples were higher than that in Hong Kong and Macau and exceeded the maximum benzene levels for Mainland China unleaded gasoline. Liquefied Petroleum Gas (LPG) samples were collected only in Hong Kong and were comprised mainly of n-butane, propane and i-butane. Traffic samples indicated that evaporative loss and vehicular combustion were the primary contributors to elevated VOC levels in roadside atmospheres. Significant i-pentane and toluene concentrations were observed in roadside atmospheres in all four cities. Ratio of i-pentane in gasoline samples to that in roadside samples were calculated and this showed that the degree of evaporative loss was higher in Guangzhou and Zhuhai than that in Hong Kong and Macau. We suggest the difference is due to the better maintenance and more new cars in Hong Kong and Macau. From tunnel samples collected in Hong Kong in two different years, we found that the relative amount of propane, i-butane, and n-butane increased between 2001 to 2003, consistent with the 40% increase in LPG fueled vehicles. Propane to butanes ratios were calculated for LPG and tunnels samples, and the comparable ratios illustrated the LPG leakages from LPG fueled vehicles crossing the tunnel
THE SURFACE EMG ACTIVITY OF THE UPPER LIMB MUSCLES IN TABLE TENNIS FOREHAND DRIVES
The purpose of this study was to analyze the 3D kinematics variables and the upper limb muscle surface EMG activity of Taiwan elite table tennis players when they were performing forehand drives after receiving topspin and backspin services. Ten Vicon MX-13 2+cameras (Vicon, Oxford, UK, 250Hz) were used to record the 3D kinematics data and measured the EMG signals of seven upper limb muscles of the players. The results showed that the tactics of the table tennis players performed the forehand drive to receive backspin were both to increase the racket tilt angle in advance and to raise the path angle during the upswing phase. The players exerted greater muscular activity during receiving the backspin forehand drive than receiving topspin forehand drive in the wrist extensor, the biceps and the triceps
Infrared probe of the anomalous magnetotransport of highly oriented pyrolytic graphite in the extreme quantum limit
We present a systematic investigation of the magnetoreflectance of highly
oriented pyrolytic graphite in magnetic field B up to 18 T . From these
measurements, we report the determination of lifetimes tau associated with the
lowest Landau levels in the quantum limit. We find a linear field dependence
for inverse lifetime 1/tau(B) of the lowest Landau levels, which is consistent
with the hypothesis of a three-dimensional (3D) to 1D crossover in an
anisotropic 3D metal in the quantum limit. This enigmatic result uncovers the
origin of the anomalous linear in-plane magnetoresistance observed both in bulk
graphite and recently in mesoscopic graphite samples
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