1,371 research outputs found
Photodesorption of CO ice
At the high densities and low temperatures found in star forming regions, all
molecules other than H2 should stick on dust grains on timescales shorter than
the cloud lifetimes. Yet these clouds are detected in the millimeter lines of
gaseous CO. At these temperatures, thermal desorption is negligible and hence a
non-thermal desorption mechanism is necessary to maintain molecules in the gas
phase. Here, the first laboratory study of the photodesorption of pure CO ice
under ultra high vacuum is presented, which gives a desorption rate of 3E-3 CO
molecules per UV (7-10.5 eV) photon at 15 K. This rate is factors of 1E2-1E5
larger than previously estimated and is comparable to estimates of other
non-thermal desorption rates. The experiments constrains the mechanism to a
single photon desorption process of ice surface molecules. The measured
efficiency of this process shows that the role of CO photodesorption in
preventing total removal of molecules in the gas has been underestimated.Comment: 5 pages, 4 figures, accepted by ApJ
Quasilocal Thermodynamics of Kerr and Kerr-anti-de Sitter Spacetimes and the AdS/CFT Correspondence
We consider the quasilocal thermodynamics of rotating black holes in
asymptotically flat and asymptotically anti de Sitter spacetimes. Using the
minimal number of intrinsic boundary counterterms inspired by the AdS/CFT
correspondence, we find that we are able to carry out an analysis of the
thermodynamics of these black holes for virtually all possible values of the
rotation parameter and cosmological constant that leave the quasilocal boundary
well-defined, going well beyond what is possible with background subtraction
methods. Specifically, we compute the quasilocal energy and angular
momentum for arbitrary values of the rotation, mass and cosmological
constant parameters for the 3+1 dimensional Kerr, Kerr-AdS black holes and 2+1
dimensional BTZ black hole. We perform a quasilocal stability analysis and find
phase behavior that is commensurate with previous analyses carried out at
infinity.Comment: Latex, 43 pages, 22 eps figures, several typos corrected, final
version to appear in Phys. Rev.
Gravitational quasinormal modes for Kerr Anti-de Sitter black holes
We investigate the quasinormal modes for gravitational perturbations of
rotating black holes in four dimensional Anti-de Sitter (AdS) spacetime. The
study of the quasinormal frequencies related to these modes is relevant to the
AdS/CFT correspondence. Although results have been obtained for Schwarzschild
and Reissner-Nordstrom AdS black holes, quasinormal frequencies of Kerr-AdS
black holes are computed for the first time. We solve the Teukolsky equations
in AdS spacetime, providing a second order and a Pade approximation for the
angular eigenvalues associated to the Teukolsky angular equation. The
transformation theory and the Regge-Wheeler-Zerilli equations for Kerr-AdS are
obtained.Comment: 20 pages, 13 figures, ReVTe
Improving Phase Change Memory Performance with Data Content Aware Access
A prominent characteristic of write operation in Phase-Change Memory (PCM) is
that its latency and energy are sensitive to the data to be written as well as
the content that is overwritten. We observe that overwriting unknown memory
content can incur significantly higher latency and energy compared to
overwriting known all-zeros or all-ones content. This is because all-zeros or
all-ones content is overwritten by programming the PCM cells only in one
direction, i.e., using either SET or RESET operations, not both. In this paper,
we propose data content aware PCM writes (DATACON), a new mechanism that
reduces the latency and energy of PCM writes by redirecting these requests to
overwrite memory locations containing all-zeros or all-ones. DATACON operates
in three steps. First, it estimates how much a PCM write access would benefit
from overwriting known content (e.g., all-zeros, or all-ones) by
comprehensively considering the number of set bits in the data to be written,
and the energy-latency trade-offs for SET and RESET operations in PCM. Second,
it translates the write address to a physical address within memory that
contains the best type of content to overwrite, and records this translation in
a table for future accesses. We exploit data access locality in workloads to
minimize the address translation overhead. Third, it re-initializes unused
memory locations with known all-zeros or all-ones content in a manner that does
not interfere with regular read and write accesses. DATACON overwrites unknown
content only when it is absolutely necessary to do so. We evaluate DATACON with
workloads from state-of-the-art machine learning applications, SPEC CPU2017,
and NAS Parallel Benchmarks. Results demonstrate that DATACON significantly
improves system performance and memory system energy consumption compared to
the best of performance-oriented state-of-the-art techniques.Comment: 18 pages, 21 figures, accepted at ACM SIGPLAN International Symposium
on Memory Management (ISMM
Kerr de Sitter Spacetimes in Various Dimension and dS/CFT Correspondence
We consider the Kerr-de Sitter (Kerr-dS) black hole in various dimensions.
Introducing a counterterm, we show that the total action of these spacetimes
are finite. We compute the masses and the angular momenta of Kerr-dS spaces
with one rotational parameter in four, five and seven dimensions. These
conserved charges are also computed for the case of Kerr-dS space with two
rotational parameters in five dimensions. Although the angular momentum density
due to the counterterm is nonzero, it gives a vanishing contribution to the
total angular momentum. We also find that the total angular momentum of the
spacetime is independent of the radius of the boundary for all cases, a fact
that is not true for the total mass of the system.Comment: 11 pages, no figure, reference added, the version to be published in
Phys. Rev. D6
Potential and limitation of internet of things (IOT) application in the automotive industry: An overview
With yearly output exceeding 70 million units, the automotive industry is one of the world's largest manufacturing industries. According to worldwide estimates, the car industry's global revenue was an astounding 3 trillion dollars equating to a combined global GDP of 3.65 percent. The emergence of IoT in the automobile sector has created new opportunities for automakers and purchasers worldwide. With industrial and commercial applications, IoT in the automobile industry has developed into a significant hotspot for a variety of multipurpose applications. From linked automobiles to automated transportation systems, Internet of Things applications have had a significant impact on the worldwide automotive business. The Internet of Things, along with other disruptive technologies, is reshaping the automobile sector as a whole. The evolution of this sector has resulted in the birth of ground-breaking advancements in automobiles, namely linked and autonomous vehicles. Different types of internet of things technology have significant qualities that make them viable candidates as a technology for use in automotive industry. This paper focuses on internet of things latest findings done by previous researcher and describes the operation of the technology. Moreover, this paper also provides insights into some countermeasures against internet of things
Holography for Einstein-Maxwell-dilaton theories from generalized dimensional reduction
We show that a class of Einstein-Maxwell-Dilaton (EMD) theories are related
to higher dimensional AdS-Maxwell gravity via a dimensional reduction over
compact Einstein spaces combined with continuation in the dimension of the
compact space to non-integral values (`generalized dimensional reduction').
This relates (fairly complicated) black hole solutions of EMD theories to
simple black hole/brane solutions of AdS-Maxwell gravity and explains their
properties. The generalized dimensional reduction is used to infer the
holographic dictionary and the hydrodynamic behavior for this class of theories
from those of AdS. As a specific example, we analyze the case of a black brane
carrying a wave whose universal sector is described by gravity coupled to a
Maxwell field and two neutral scalars. At thermal equilibrium and finite
chemical potential the two operators dual to the bulk scalar fields acquire
expectation values characterizing the breaking of conformal and generalized
conformal invariance. We compute holographically the first order transport
coefficients (conductivity, shear and bulk viscosity) for this system.Comment: v2, Important additions: (1) discussion of the entropy current, (2)
postulated zeta/eta bound is generically violated. Some comments and
references added, typos corrected. 50 page
Symbolic analysis of analog circuits containing voltage mirrors
7 páginas, 7 figuras, 2 tablas, 4 imágenes.-- Open Access: This article is distributed under the terms of the Creative Commons Attribution Noncommercial License.The pathological elements voltage mirror (VM) and current mirror (CM) have shown advantages in analog behavioral modeling and circuit synthesis, where many nullor-mirror equivalences have been explored to design and to transform voltage-mode circuits to current-mode ones and viceversa. However, both the VM and CM have not equivalents to perform automatic symbolic circuit analysis. In this manner, we introduce nullor-equivalents for these pathological elements allowing to include parasitics and to perform only symbolic nodal analysis. The nullor-equivalent of the CM is extended to provide multiple-outpus (MO-CM). Finally, two active filters containing VMs, CMs and MO-CMs are analysed to show the usefulness of the models.This work is supported by: UC-MEXUS and
CONACyT under grants CN-09-310 and 48396-Y; by Promep-Mexico under grant UATLX-PTC-088; by Consejeria de Innovacion, Ciencia y Empresa, Junta de Andalucia-Spain TIC-2532; and by the
JAE-Doc program of CSIC co-funded by FSE, Spain.Peer reviewe
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
Quasinormal modes and holographic correlators in a crunching AdS geometry
We calculate frequency space holographic correlators in an asymptotically AdS crunching background, dual to a relevant deformation of the M2-brane CFT placed in de Sitter spacetime. For massless bulk scalars, exploiting the connection to a solvable supersymmetric quantum mechanical problem, we obtain the exact frequency space correlator for the dual operator in the deformed CFT. Controlling the shape of the crunching surface in the Penrose diagram by smoothly dialling the deformation from zero to infinity, we observe that in the large deformation limit the Penrose diagram becomes a `square', and the exact holographic correlators display striking similarities to their counterparts in the BTZ black hole and its higher dimensional generalisations. We numerically determine quasinormal poles for relevant and irrelevant operators, and find an intricate pattern of these in the complex frequency plane. In the case of relevant operators, the deformation parameter has an infinite sequence of critical values, each one characterised by a pair of poles colliding and moving away from the imaginary frequency axis with increasing deformation. In the limit of infinite deformation all scalar operators have identical quasinormal spectra. We compare and contrast our strongly coupled de Sitter QFT results with strongly coupled thermal correlators from AdS black holes
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