668 research outputs found
Novel topological black holes from thermodynamics and deforming horizons
Two novel topological black hole exact solutions with unusual shapes of
horizons in the simplest holographic axions model, the four-dimensional
Einstein-Maxwell-axions theory, are constructed. We draw embedding diagrams in
various situations to display unusual shapes of novel black holes. To
understand their thermodynamics from the quasi-local aspect, we re-derive the
unified first law and the Misner-Sharp mass from the Einstein equations for the
spacetime as a warped product \M2 \times \Mco2. The Ricci scalar \Rhat of
the sub-manifold \Mco2 can be a non-constant. We further improve the
thermodynamics method based on the unified first law. Such a method simplifies
constructing solutions and hints at generalization to higher dimensions.
Moreover, we apply the unified first law to discuss black hole thermodynamics.Comment: 19 pages, 18 figures, Significantly revised: (1) more embedding
diagrams for various shapes, specifically including the shape without
singularity; (2) content about Kodama vector and global monopole solutions
replaced by solving Einstein's equation from given ansatzes; (3) more
tractable text to find the unified first law from Einstein's equatio
A trick for calculating surface gravities of Killing horizons
We propose a trick for calculating the surface gravity of the Killing
horizon, especially for cases of rotating black holes. By choosing nice slices,
the surface gravity and angular momentums can be directly read from relevant
components of the inverse metric. We give several cases to show how to apply
the trick step by step.Comment: 16 pages; no figur
Light Ring behind Wormhole Throat: Geodesics, Images and Shadows
The geodesics of the Ellis-Bronnikov wormhole with two parameters are
studied. The asymmetric wormhole has only one light ring and one innermost
stable circular orbit located on one side of the wormhole throat. Consequently,
certain light rays can be reflected back by the wormhole. Additionally, the
same wormhole can have different appearances on both sides of the throat. We
present novel images of the wormhole with a light ring behind the throat in a
scenario with an accretion disk as the light source and in a backlit wormhole
scenario, which are distinct from the images of other compact objects and have
the potential to be observed.Comment: 26 pages, 14 figures, add reference
A 97 fJ/Conversion Neuron-ADC with Reconfigurable Sampling and Static Power Reduction
A bio-inspired Neuron-ADC with reconfigurable sampling and static power
reduction for biomedical applications is proposed in this work. The Neuron-ADC
leverages level-crossing sampling and a bio-inspired refractory circuit to
compressively converts bio-signal to digital spikes and
information-of-interest. The proposed design can not only avoid dissipating ADC
energy on unnecessary data but also achieve reconfigurable sampling, making it
appropriate for either low power operation or high accuracy conversion when
dealing with various kinds of bio-signals. Moreover, the proposed dynamic
comparator can reduce static power up to 41.1% when tested with a 10 kHz
sinusoidal input. Simulation results of 40 nm CMOS process show that the
Neuron-ADC achieves a maximum ENOB of 6.9 bits with a corresponding FoM of 97
fJ/conversion under 0.6 V supply voltage.Comment: Accepted to 2022 IEEE the 18th Asia Pacific Conference on Circuits
and Systems (APCCAS
Does the Dirac Cone Exist in Silicene on Metal Substrates?
Absence of the Dirac cone due to a strong band hybridization is revealed to
be a common feature for epitaxial silicene on metal substrates according to our
first-principles calculations for silicene on Ir, Cu, Mg, Au, Pt, Al, and Ag
substrates. The destroyed Dirac cone of silicene, however, can be effectively
restored with linear or parabolic dispersion by intercalating alkali metal
atoms between silicene and the metal substrates, offering an opportunity to
study the intriguing properties of silicene without further transfer of
silicene from the metal substrates
Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations
Although many prototype devices based on two-dimensional (2D) MoS2 have been
fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental
nature of 2D MoS2-metal contacts has not been well understood yet. We provide a
comprehensive ab initio study of the interfacial properties of a series of
monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt,
Ni, and Au). A comparison between the calculated and observed Schottky barrier
heights (SBHs) suggests that many-electron effects are strongly suppressed in
channel 2D MoS2 due to a charge transfer. The extensively adopted energy band
calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc
interface. By contrast, an ab initio quantum transport device simulation better
reproduces the observed SBH in the two types of contacts and highlights the
importance of a higher level theoretical approach beyond the energy band
calculation in the interface study. BL MoS2-metal contacts have a reduced SBH
than ML MoS2-metal contacts due to the interlayer coupling and thus have a
higher electron injection efficiency.Comment: 36 pages, 13 figures, 3 table
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