54,908 research outputs found
Supersymmetry and the Anomalous Anomalous Magnetic Moment of the Muon
The recently reported measurement of the muon's anomalous magnetic moment
differs from the standard model prediction by 2.6 standard deviations. We
examine the implications of this discrepancy for supersymmetry. Deviations of
the reported magnitude are generic in supersymmetric theories. Based on the new
result, we derive model-independent upper bounds on the masses of observable
supersymmetric particles. We also examine several model frameworks. The sign of
the reported deviation is as predicted in many simple models, but disfavors
anomaly-mediated supersymmetry breaking.Comment: 4 pages, 4 figures, version to appear in Phys. Rev. Let
Low Voltage Nanoelectromechanical Switches Based on Silicon Carbide Nanowires
We report experimental demonstrations of electrostatically actuated, contact-mode nanoelectromechanical switches based on very thin silicon carbide (SiC) nanowires (NWs). These NWs are lithographically patterned from a 50 nm thick SiC layer heteroepitaxially grown on single-crystal silicon (Si). Several generic designs of in-plane electrostatic SiC NW switches have been realized, with NW widths as small as ~20 nm and lateral switching gaps as narrow as ~10 nm. Very low switch-on voltages are obtained, from a few volts down to ~1 V level. Two-terminal, contact-mode “hot” switching with high on/off ratios (>10^2 or 10^3) has been demonstrated repeatedly for many devices. We find enhanced switching performance in bare SiC NWs, with lifetimes exceeding those based on metallized SiC NWs
Experimentally realizable control fields in quantum Lyapunov control
As a hybrid of techniques from open-loop and feedback control, Lyapunov
control has the advantage that it is free from the measurement-induced
decoherence but it includes the system's instantaneous message in the control
loop. Often, the Lyapunov control is confronted with time delay in the control
fields and difficulty in practical implementations of the control. In this
paper, we study the effect of time-delay on the Lyapunov control, and explore
the possibility of replacing the control field with a pulse train or a
bang-bang signal. The efficiency of the Lyapunov control is also presented
through examining the convergence time of the controlled system. These results
suggest that the Lyapunov control is robust gainst time delay, easy to realize
and effective for high-dimensional quantum systems
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Experimental study on transcritical Rankine cycle (TRC) using CO2/R134a mixtures with various composition ratios for waste heat recovery from diesel engines
A carbon dioxide (CO2) based mixture was investigated as a promising solution to improve system performance and expand the condensation temperature range of a CO2 transcritical Rankine cycle (C-TRC). An experimental study of TRC using CO2/R134a mixtures was performed to recover waste heat of engine coolant and exhaust gas from a heavy-duty diesel engine. The main purpose of this study was to investigate experimentally the effect of the composition ratio of CO2/R134a mixtures on system performance. Four CO2/R134a mixtures with mass composition ratios of 0.85/0.15, 0.7/0.3, 0.6/0.4 and 0.4/0.6 were selected. The high temperature working fluid was expanded through an expansion valve and then no power was produced. Thus, current research focused on the analysis of measured operating parameters and heat exchanger performance. Heat transfer coefficients of various heat exchangers using supercritical CO2/R134a mixtures were provided and discussed. These data may provide useful reference for cycle optimization and heat exchanger design in application of CO2 mixtures. Finally, the potential of power output was estimated numerically. Assuming an expander efficiency of 0.7, the maximum estimations of net power output using CO2/R134a (0.85/0.15), CO2/R134a (0.7/0.3), CO2/R134a (0.6/0.4) and CO2/R134a (0.4/0.6) are 5.07 kW, 5.45 kW, 5.30 kW, and 4.41 kW, respectively. Along with the increase of R134a composition, the estimation of net power output, thermal efficiency and exergy efficiency increased at first and then decreased. CO2/R134a (0.7/0.3) achieved the maximum net power output at a high expansion inlet pressure, while CO2/R134a (0.6/0.4) behaves better at low pressure
Superstructure-induced splitting of Dirac cones in silicene
Atomic scale engineering of two-dimensional materials could create devices
with rich physical and chemical properties. External periodic potentials can
enable the manipulation of the electronic band structures of materials. A
prototypical system is 3x3-silicene/Ag(111), which has substrate-induced
periodic modulations. Recent angle-resolved photoemission spectroscopy
measurements revealed six Dirac cone pairs at the Brillouin zone boundary of
Ag(111), but their origin remains unclear [Proc. Natl. Acad. Sci. USA 113,
14656 (2016)]. We used linear dichroism angle-resolved photoemission
spectroscopy, the tight-binding model, and first-principles calculations to
reveal that these Dirac cones mainly derive from the original cones at the K
(K') points of free-standing silicene. The Dirac cones of free-standing
silicene are split by external periodic potentials that originate from the
substrate-overlayer interaction. Our results not only confirm the origin of the
Dirac cones in the 3x3-silicene/Ag(111) system, but also provide a powerful
route to manipulate the electronic structures of two-dimensional materials.Comment: 6 pages, 3 figure
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