199 research outputs found
Electrical Transport Across an Individual Magnetic Domain Wall in (Ga,Mn)As Microdevices
Recent studies demonstrate that an individual magnetic domain wall (DW) can
be trapped and reproducibly positioned within multiterminal (Ga,Mn)As
microdevices. The electrical resistance obtained from such measurements is
found to be measurably altered by the presence of this single entity. To
elucidate these observations we develop a simple model for the electrical
potential distribution along a multiterminal device in the presence of a single
DW. This is employed to calculate the effect of a single DW upon the
longitudinal and transverse resistance. The model provides very good agreement
with experimental observations, and serves to highlight important deviations
from simple theory. We show that measurements of transverse resistance along
the channel permits establishing the position and the shape of the DW contained
within it. An experimental scheme is developed that enables unambiguous
extraction of the intrinsic DW resistivity. This permits the intrinsic
contribution to be differentiated from resistivities originating from the bulk
and from magnetic anisotropy - effects that are generally manifested as large
backgrounds in the experiments.Comment: Submitted to Physical Review
Multi-decadal trends in global terrestrial evapotranspiration and its components
Evapotranspiration (ET) is the process by which liquid water becomes water vapor and energetically this accounts for much of incoming solar radiation. If this ET did not occur temperatures would be higher, so understanding ET trends is crucial to predict future temperatures. Recent studies have reported prolonged declines in ET in recent decades, although these declines may relate to climate variability. Here, we used a well-validated diagnostic model to estimate daily ET during 1981–2012, and its three components: transpiration from vegetation (Et), direct evaporation from the soil (Es) and vaporization of intercepted rainfall from vegetation (Ei). During this period, ET over land has increased significantly (p < 0.01), caused by increases in Et and Ei, which are partially counteracted by Es decreasing. These contrasting trends are primarily driven by increases in vegetation leaf area index, dominated by greening. The overall increase in Et over land is about twofold of the decrease in Es. These opposing trends are not simulated by most Coupled Model Intercomparison Project phase 5 (CMIP5) models, and highlight the importance of realistically representing vegetation changes in earth system models for predicting future changes in the energy and water cycle
Traffic restrictions during the 2008 Olympic Games reduced urban heat intensity and extent in Beijing
Satellite thermal remote sensing has been utilized to examine the urban heat dynamics in relation to the urban traffic restriction policy. During the 2008 Olympic Games in Beijing, the traffic volume was approximately cut off by half through the road space rationing. Based on daily MODIS satellite thermal observations on the surface temperature, statistical models were developed to analyze the contribution of traffic volume reduction to the urban heat intensity and spatial extent. Our analyses show that cutting off half of the traffic volume has led to a marked decrease in the mean surface temperature by 1.5–2.4 °C and shrinkage of the heat extent by 820 km2 in Beijing. This research suggests that the impact of urban traffic on heat intensity is considerably larger than previously thought, and the management of urban traffic and vehicle fossil fuel use should be included in the future urban heat mitigation plan
Material Properties of GaN in the Context of Electron Devices
AbstractWide bandgap nitride semiconductors have recently attracted a great level of attention owing to their direct bandgaps in the visible to ultraviolet regions of the spectrum as emitters and detectors. However, this material system with its favorable heterojunctions and transport properties began to produce very respectable power levels in microwave amplifiers. If and when the breakdown fields achieved experimentally approaches the predicted values, this material system may also be very attractive for switching power devices. In addition to the premature breakdown, a number of scientific challenges remain including a clear experimental investigation of polarization effects. In this paper, transport properties as pertained to electronic devices and potential switching devices, and polarization effects will be treated
Chiral Surface Plasmon Polaritons on Metallic Nanowires
Chiral surface plasmon polaritons (SPPs) can be generated by linearly
polarized light incident at the end of a nanowire, exciting a coherent
superposition of three specific nanowire waveguide modes. Images of chiral SPPs
on individual nanowires obtained from quantum dot fluorescence excited by the
SPP evanescent field reveal the chirality predicted in our theoretical model.
The handedness and spatial extent of the helical periods of the chiral SPPs
depend on the input polarization angle and nanowire diameter as well as the
dielectric environment. Chirality is preserved in the free-space output wave,
making a metallic nanowire a broad bandwidth subwavelength source of circular
polarized photons.Comment: 4 figure
The emission positions of kHz QPOs and Kerr spacetime influence
Based the Alfven wave oscillation model (AWOM) and relativistic precession
model (RPM) for twin kHz QPOs, we estimate the emission positions of most
detected kHz QPOs to be at r=18+-3 km (R/15km) except Cir X-1 at r = 30\+-5 km
(R/15km). For the proposed Keplerian frequency as an upper limit to kHz QPO,
the spin effects in Kerr Spacetime are discussed, which have about a 5% (2%)
modification for that of the Schwarzchild case for the spin frequency of 1000
(400) Hz.The application to the four typical QPO sources, Cir X-1, Sco X-1, SAX
J1808.4-3658 and XTE 1807-294, is mentioned.Comment: Science China, Physics, Mechanics & Astronomy, 2010, 53, NO.
An Unified Approach To Pseudo Scalar Meson Photoproductions Off Nucleons In The Quark Model
An unified approach to the pseudo scalar meson (, and )
photoproduction off nucleons are presented. It begins with the low energy QCD
Lagrangian, and the resonances in the s- and u- channels are treated in the
framework of the quark model
The duality hypothesis is imposed to limit the number of the t-channel
exchanges. The CGLN amplitudes for each reaction are evaluated, which include
both proton and neutron targets. The important role by the S-wave resonances in
the second resonance region is discussed, it is particularly important for the
and photoproductions.Comment: 31 pages in Latex fil
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