7,474 research outputs found
Electron-dependent thermoelectric properties in Si/Si_(1_x)Ge_(x) heterostructures and Si_(1-x)Ge_(x) alloys from first-principles
Unlike phononic thermal conductivity (which is shown in the literature to be reduced due to alloying and has a nearly constant value over a range of compositional variations), electron-dependent thermoelectric properties are shown here, from first-principles, to vary nonlinearly with composition. Of the Si/Si_(1_x)Ge_(x) systems considered, the maximum thermopower observed, which is 10% higher than that of crystalline Si, is obtained for a Si_(0.875)Ge_(0.125) alloy. Also, heterostructuring is shown to reduce thermopower, electrical conductivity, and electron thermal conductivity. Additionally, neither Lorenz number nor Seebeck coefficient shows oscillations for heterostructures, regardless of electron/hole energies, contradicting the conclusions obtained with miniband approximations
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Intelligent Active Vibration Control for a Flexible Beam System
YesThis paper presents an investigation into the
development of an intelligent active vibration control
(AVC) system. Evolutionary Genetic algorithms (GAs)
and Adaptive Neuro-Fuzzy Inference system (ANFIS)
algorithms are used to develop mechanisms of an AVC
system, where the controller is designed on the basis of
optimal vibration suppression using the plant model. A
simulation platform of a flexible beam system in
transverse vibration using finite difference (FD) method
is considered to demonstrate the capabilities of the AVC
system using GAs and ANFIS. MATLAB GA tool box for
GAs and Fuzzy Logic tool box for ANFIS function are
used for AVC system design. The system is then
implemented, tested and its performance assessed for GAs
and ANFIS based design. Finally a comparative
performance of the algorithm in implementing AVC
system using GAs and ANFIS is presented and discussed
through a set of experiments
Multilayer Layer Graphene Nanoribbon Flash Memory: Analysis of Programming and Erasing Operation
Flash memory based on floating gate transistor is the most widely used memory
technology in modern microelectronic applications. We recently proposed a new
concept of multilayer graphene nanoribbon (MLGNR) and carbon nanotube (CNT)
based floating gate transistor design for future nanoscale flash memory
technology. In this paper, we analyze the tunneling current mechanism in the
proposed graphene-CNT floating gate transistor. We anticipate that the proposed
floating gate transistor would adopt Fowler-Nordheim (FN) tunneling during its
programming and erase operations. In this paper, we have investigated the
mechanism of tunneling current and the factors that would influence this
current and the behavior of the proposed floating gate transistor. The analysis
reveals that FN tunneling is a strong function of the high field induced by the
control gate, and the thicknesses of the control oxide and the tunnel oxide.Comment: in IEEE SOCC, Las Vegas, USA, 201
Strong enhancement of Jc in binary and alloyed in-situ MgB2 wires by a new approach: Cold high pressure densification
Cold high pressure densification (CHPD) is presented as a new way to
substantially enhance the critical current density of in situ MgB2 wires at 4.2
and 20 K at fields between 5 and 14 T. The results on two binary MgB2 wires and
an alloyed wire with 10 wt.% B4C are presented The strongest enhancement was
measured at 20K, where cold densification at 1.85 GPa on a binary Fe/MgB2 wire
raised both Jcpara and Jcperp by more than 300% at 5T, while Birr was enhanced
by 0.7 T. At 4.2K, the enhancement of Jc was smaller, but still reached 53% at
10 T. After applying pressures up to 6.5 GPa, the mass density dm of the
unreacted (B+Mg) mixture inside the filaments reached 96% of the theoretical
density. After reaction under atmospheric pressure, this corresponds to a
highest mass density df in the MgB2 filaments of 73%. After reaction, the
electrical resistance of wires submitted to cold densification was found to
decrease, reflecting an improved connectivity. A quantitative correlation
between filament mass density and the physical properties was established.
Monofilamentary rectangular wires with aspect ratios a/b < 1.25 based on low
energy ball milled powders exhibited very low anisotropy ratios, Gamma =
Jcpara/Jcperp being < 1.4 at 4.2 K and 10T. The present results can be
generalized to alloyed MgB2 wires, as demonstrated on a wire with B4C
additives. Based on the present data, it follows that cold densification has
the potential of further improving the highest Jcpara and Jcperp values
reported so far for in situ MgB2 tapes and wires with SiC and C additives.
Investigations are under work in our laboratory to determine whether the
densification method CHPD can be applied to longer wire or tape lengths.Comment: Submitted to Superconductors Science and Technolog
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