532 research outputs found
Self-consistent quantum-kinetic theory for interacting drifting electrons and force-driven phonons in a 1D system
A self-consistent quantum-kinetic model is developed for studying
strong-field nonlinear electron transport interacting with force-driven phonons
within a quantum-wire system. For this model, phonons can be dragged into
motion through strong electron-phonon scattering by fast-moving electrons along
the opposite direction of the DC electric field. Meanwhile, the DC-field
induced charge current of electrons can be either enhanced or reduced by the
same electron-phonon scattering, depending on the relative direction of a DC
field with respect to that of an applied temperature gradient for driving
phonons. By making use of this quantum-kinetic model beyond the relaxation-time
approximation, neither electron nor phonon temperature is required for
describing ultrafast electron-phonon scattering and their correlated transports
in this 1D electronic-lattice system. onsistent quantum-kinetic model is
developed for studying strong-field nonlinear electron transport interacting
with force-driven phonons within a quantum-wire system. For this model, phonons
can be dragged into motion through strong electron-phonon scattering by
fast-moving electrons along the opposite direction of the DC electric field.
Meanwhile, the DC-field induced charge current of electrons can be either
enhanced or reduced by the same electron-phonon scattering, depending on the
relative direction of a DC field with respect to that of an applied temperature
gradient for driving phonons. By making use of this quantum-kinetic model
beyond the relaxation-time approximation, neither electron nor phonon
temperature is required for describing ultrafast electron-phonon scattering and
their correlated transports in this 1D electronic-lattice system
Distribution of the k-regular partition function modulo composite integers M
Let denote the regular partitons of a natural number . In
this paper, we study the behavior of modulo composite integers
which are coprime to . Specially, we prove that for arbitrary regular
partiton function and integer coprime to , there are infinitely
many Ramanujan-type congruences of modulo
Fully Printed High-Frequency Phased-Array Antenna on Flexible Substrate
To address the issues of flexible electronics needed for surface-to-surface, surface-to-orbit, and back-to-Earth communications necessary for manned exploration of the Moon, Mars, and beyond, a room-temperature printing process has been developed to create active, phased-array antennas (PAAs) on a flexible Kapton substrate. Field effect transistors (FETs) based on carbon nanotubes (CNTs), with many unique physical properties, were successfully proven feasible for phased-array antenna systems. The carrier mobility of an individual CNT is estimated to be at least 100,000 sq cm/V(dot)s. The CNT network in solution has carrier mobility as high as 46,770 sq cm/V(dot)s, and has a large current-density carrying capacity of approx. 1,000 mA/sq cm , which corresponds to a high carrying power of over 2,000 mW/ sq cm. Such high carrier mobility, and large current carrying capacity, allows the achievement of high-speed (>100 GHz), high-power, flexible electronic circuits that can be monolithically integrated on NASA s active phasedarray antennas for various applications, such as pressurized rovers, pressurized habitats, and spacesuits, as well as for locating beacon towers for lunar surface navigation, which will likely be performed at S-band and attached to a mobile astronaut. A fully printed 2-bit 2-element phasedarray antenna (PAA) working at 5.6 GHz, incorporating the CNT FETs as phase shifters, is demonstrated. The PAA is printed out at room temperature on 100-mm thick Kapton substrate. Four CNT FETs are printed together with microstrip time delay lines to function as a 2-bit phase shifter. The FET switch exhibits a switching speed of 0.2 ns, and works well for a 5.6-GHz RF signal. The operating frequency is measured to be 5.6 GHz, versus the state-of-the-art flexible FET operating frequency of 52 MHz. The source-drain current density is measured to be over 1,000 mA/sq cm, while the conventional organic FETs, and single carbon nanotube-based FETs, are typically in the mA to mA/sq cm range. The switching voltage used is 1.8 V, while the state-of-the-art flexible FET has a gate voltage around 50 V. The gate voltage can effectively control the source-drain current with an ON-OFF ratio of over 1,000 obtained at a low Vds bias of 1.8 V. The azimuth steering angles of PAA are measured at 0deg, -14.5deg, -30deg, and 48.6deg. The measured far-field patterns agree well with simulation results. The efficiency of the 2-bit 2-element PAA is measured to be 39 percent, including the loss of transmission line, FET switch, and coupling loss of RF probes. With further optimization, the efficiency is expected to be around 50-60 percent
An improvement on the parity of Schur's partition function
We improve S.-C. Chen's result on the parity of Schur's partition function.
Let be the number of Schur's partitions of , i.e., the number of
partitions of into distinct parts congruent to . S.-C. Chen
\cite{MR3959837} shows .
In this paper, we improve Chen's result to $\frac{x}{(\log{x})^{\frac{11}{12}}}
\ll \sharp \{0\le n\le x:A(2n+1)\; \text{is odd}\}\ll
\frac{x}{(\log{x})^{\frac{1}{2}}}.
Surface Plasmonics and Its Applications in Infrared Sensing
Surface plasmonic waves have been extensively researched due to their strong surface confinement. The strong surface confinement allows high absorption in an infrared (IR) detector with a thin active absorption region. The excitation of surface plasmonic resonance (SPR) depends on the metallic structures and the interface materials. This enables engineering of plasmonic-enhanced IR detector properties (e.g. detection wavelength, polarization and angular dependence) by properly designing the plasmonic structures. This chapter first gives a brief review of the surface plasmonic waves, followed by the description of SPR excitation in a metallic two-dimensional (2D) sub-wavelength hole array (2DSHA) structure. The applications of the 2DSHA SPR in IR detector enhancement are then presented with a discussion of the polarization and angular dependence
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