10,446 research outputs found
Microscopic Mechanism of the Helix-to-Layer Transformation in Elemental Group VI Solids
We study the conversion of bulk Se and Te, consisting of intertwined a
helices, to structurally very dissimilar, atomically thin two-dimensional (2D)
layers of these elements. Our ab initio calculations reveal that previously
unknown and unusually stable \delta - and \eta-2D allotropes may form in an
intriguing multi-step process that involves a concerted motion of many atoms at
dislocation defects. We identify such a complex reaction path involving
zipper-like motion of such dislocations that initiate structural changes. With
low activation barriers <0.3 eV along the optimum path, the conversion process
may occur at moderate temperatures. We find all one-dimensional (1D) and 2D
chalcogen structures to be semiconducting.Comment: accepted by Nano Letter
Fermions Tunneling from Higher-Dimensional Reissner-Nordstr\"om Black Hole: Semiclassical and Beyond Semiclassical Approximation
Based on semiclassical tunneling method, we focus on charged fermions
tunneling from higher-dimensional Reissner-Nordstr\"{o}m black hole. We first
simplify the Dirac equation by semiclassical approximation, and then a
semiclassical Hamilton-Jacobi equation is obtained. Using the Hamilton-Jacobi
equation, we study the Hawking temperature and fermions tunneling rate at the
event horizon of the higher-dimensional Reissner-Nordstr\"{o}m black hole
spacetime. Finally, the correct entropy is calculation by the method beyond
semiclassical approximation.Comment: 7 page
Glider: A GPU Library Driver for Improved System Security
Legacy device drivers implement both device resource management and
isolation. This results in a large code base with a wide high-level interface
making the driver vulnerable to security attacks. This is particularly
problematic for increasingly popular accelerators like GPUs that have large,
complex drivers. We solve this problem with library drivers, a new driver
architecture. A library driver implements resource management as an untrusted
library in the application process address space, and implements isolation as a
kernel module that is smaller and has a narrower lower-level interface (i.e.,
closer to hardware) than a legacy driver. We articulate a set of device and
platform hardware properties that are required to retrofit a legacy driver into
a library driver. To demonstrate the feasibility and superiority of library
drivers, we present Glider, a library driver implementation for two GPUs of
popular brands, Radeon and Intel. Glider reduces the TCB size and attack
surface by about 35% and 84% respectively for a Radeon HD 6450 GPU and by about
38% and 90% respectively for an Intel Ivy Bridge GPU. Moreover, it incurs no
performance cost. Indeed, Glider outperforms a legacy driver for applications
requiring intensive interactions with the device driver, such as applications
using the OpenGL immediate mode API
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