1,406 research outputs found
pDCell: an End-to-End Transport Protocol for Mobile Edge Computing Architectures
Pendiente publicación 2019To deal with increasingly demanding services and the rapid growth
in number of devices and traffic, 5G and beyond mobile networks
need to provide extreme capacity and peak data rates at very low
latencies. Consequently, applications and services need to move
closer to the users into so-called edge data centers. At the same
time, there is a trend to virtualize core and radio access network
functionalities and bring them to edge data centers as well. However,
as is known from conventional data centers, legacy transport
protocols such as TCP are vastly suboptimal in such a setting.
In this work, we present pDCell, a transport design for mobile
edge computing architectures that extends data center transport
approaches to the mobile network domain. Specifically, pDCell
ensures that data traffic from application servers arrives at virtual
radio functions (i.e., C-RAN Central Units) timely to (i) minimize
queuing delays and (ii) to maximize cellular network utilization.
We show that pDCell significantly improves flow completion times
compared to conventional transport protocols like TCP and data
center transport solutions, and is thus an essential component for
future mobile networks.This work is partially supported by the European Research Council
grant ERC CoG 617721, the Ramon y Cajal grant from the Spanish
Ministry of Economy and Competitiveness RYC-2012-10788, by
the European Union H2020-ICT grant 644399 (MONROE), by the
H2020 collaborative Europe/Taiwan research project 5G-CORAL
(grant num. 761586) and the Madrid Regional Government through
the TIGRE5-CM program (S2013/ICE-2919). Further, the work of
Dr. Kogan is partially supported by a grant from the Cisco University
Research Program Fund, an advised fund of Silicon Valley
Community Foundation.No publicad
Reflexiones sobre el campo de la investigación en proyecto arquitectónico
Este trabajo presenta el problema de la investigación en el marco de las maestrías en proyecto arquitectónico y se pregunta, en primer lugar, en qué medida el campo de la investigación en proyecto es homologable al campo de la investigación científica. Tal como señala Ynoub (2020) para el campo del Diseño, existen dos diferencias fundamentales respecto de las ciencias fácticas o empíricas: por un lado, en el tipo de investigación que aquí nos interesa, el objeto de estudio “no constituye un dato a priori a la experiencia” sino que éste “es creado en el acto y por medio de la actividad de Diseño (sea como idea proyectada, sea como objeto construido)” (p.19). Por otro lado, en la medida en que el objeto es imaginado y orientado por fines, implica valores que atienden a lo que “las cosas deben ser, pueden ser o es deseable que sean conforme a dichos fines, fijados por los intereses y perspectivas del Diseño” (p.20). Esta dimensión valorativa vuelve conflictiva la búsqueda de la objetividad inherente a toda investigación científica. Sin embargo, sostenemos que toda investigación en proyecto arquitectónico, debe producir un tipo de conocimiento de impacto teórico disciplinar –“con la pretensión de alcanzar un grado de generalización o transferencia de los conocimientos obtenidos” (Ynoub, 2014, p.125)–.
Una segunda pregunta gira en torno a cómo se construye un problema de investigación en proyecto, es decir, vehiculizable a través del proyecto arquitectónico. Sostenemos que construir el problema de una investigación implica, primero, focalizar o precisar un tema, y segundo, especificarlo o recortarlo. En el caso de la investigación en proyecto, es preciso que el problema haga foco en alguno de los aspectos disciplinares internos: en el producto y/o en el proceso que le diera origen (la proyectación).
La última pregunta indaga en el rol del proyecto y sus técnicas en el abordaje metodológico de este tipo de investigación. Sostenemos que el proyecto se transforma primordialmente en el medio que posibilita el conocimiento, y no en el fin en sí mismo –como podría serlo en la práctica en sí–. De esta manera, el producto de la proyectación no coincide con el producto de la investigación (el conocimiento adquirido). Por otra parte, un momento conflictivo está dado por la identificación entre proyectista e investigador; conflicto al que puede sumarse un segundo aspecto problemático, en caso de coincidir el abordaje metodológico con el propio objeto de estudio (si la investigación hace foco en la proyectación).
Finalmente se analizan dos casos –ambos desarrollados a nivel de Plan de Trabajo Final en el marco de la Maestría en Proyecto Arquitectónico (Ma.P.A.) de la Universidad de Buenos Aires– para ejemplificar los distintos modos en que puede construirse el problema y desplegarse una investigación en proyecto.Facultad de Arquitectura y Urbanism
Generalized Random Phase Approximation and Gauge Theories
Mean-field treatments of Yang-Mills theory face the problem of how to treat
the Gauss law constraint. In this paper we try to face this problem by studying
the excited states instead of the ground state. For this purpose we extend the
operator approach to the Random Phase Approximation (RPA) well-known from
nuclear physics and recently also employed in pion physics to general bosonic
theories with a standard kinetic term. We focus especially on conservation
laws, and how they are translated from the full to the approximated theories,
demonstrate that the operator approach has the same spectrum as the RPA derived
from the time-dependent variational principle, and give - for Yang-Mills theory
- a discussion of the moment of inertia connected to the energy contribution of
the zero modes to the RPA ground state energy. We also indicate a line of
thought that might be useful to improve the results of the Random Phase
Approximation.Comment: 66 pages, REVTeX4, uses amsfonts and package longtabl
First-Principles Study for the Anisotropy of Iron-based Superconductors toward Power and Device Applications
Performing the first-principles calculations, we investigate the anisotropy
in the superconducting state of iron-based superconductors to gain an insight
into their potential applications. The anisotropy ratio of the
c-axis penetration depth to the ab-plane one is relatively small in BaFe2As2
and LiFeAs, i.e., , indicating that the transport
applications are promising in these superconductors. On the other hand, in
those having perovskite type blocking layers such as Sr2ScFePO3 we find a very
large value, , comparable to that in strongly
anisotropic high-Tc cuprate Bi2Sr2CaCu2O{8-\delta}. Thus, the intrinsic
Josephson junction stacks are expected to be formed along the c-axis, and novel
Josephson effects due to the multi-gap nature are also suggested in these
superconductors.Comment: 5 pages, 4 figure
Stability and dynamics of free magnetic polarons
The stability and dynamics of a free magnetic polaron are studied by Monte
Carlo simulation of a classical two-dimensional Heisenberg model coupled to a
single electron. We compare our results to the earlier mean-field analysis of
the stability of the polaron, finding qualitative similarity but quantitative
differences. The dynamical simulations give estimates of the temperature
dependence of the polaron diffusion, as well as a crossover to a tunnelling
regime.Comment: 4 pages including 4 .eps figure
Theory of quasi-spherical accretion in X-ray pulsars
A theoretical model for quasi-spherical subsonic accretion onto slowly
rotating magnetized neutron stars is constructed. In this model the accreting
matter subsonically settles down onto the rotating magnetosphere forming an
extended quasi-static shell. This shell mediates the angular momentum removal
from the rotating neutron star magnetosphere during spin-down episodes by
large-scale convective motions. The accretion rate through the shell is
determined by the ability of the plasma to enter the magnetosphere. The
settling regime of accretion can be realized for moderate accretion rates g/s. At higher accretion rates a free-fall
gap above the neutron star magnetosphere appears due to rapid Compton cooling,
and accretion becomes highly non-stationary. From observations of the
spin-up/spin-down rates (the angular rotation frequency derivative , and near the torque reversal)
of X-ray pulsars with known orbital periods, it is possible to determine the
main dimensionless parameters of the model, as well as to estimate the magnetic
field of the neutron star. We illustrate the model by determining these
parameters for three wind-fed X-ray pulsars GX 301-2, Vela X-1, and GX 1+4. The
model explains both the spin-up/spin-down of the pulsar frequency on large
time-scales and the irregular short-term frequency fluctuations, which can
correlate or anti-correlate with the X-ray flux fluctuations in different
systems. It is shown that in real pulsars an almost iso-angular-momentum
rotation law with , due to strongly anisotropic radial
turbulent motions sustained by large-scale convection, is preferred.Comment: 48 pages, 4 figures, accepted for publication in MNRA
Is there a highly magnetized neutron star in GX 301-2?
We present the results of an in-depth study of the long-period X-ray pulsar
GX 301-2. Using archival data of INTEGRAL, RXTE ASM, and CGRO BATSE, we study
the spectral and timing properties of the source. Comparison of our timing
results with previously published work reveals a secular decay of the orbital
period at a rate of \simeq -3.25 \times 10^{-5} d yr^{-1}, which is an order of
magnitude faster than for other known systems. We argue that this is probably
result either of the apsidal motion or of gravitational coupling of the matter
lost by the optical companion with the neutron star, although current
observations do not allow us to distinguish between those possibilities. We
also propose a model to explain the observed long pulse period. We find that a
very strong magnetic field B \sim 10^{14} G can explain the observed pulse
period in the framework of existing models for torques affecting the neutron
star. We show that the apparent contradiction with the magnetic field strength
B_{CRSF} \sim 4 \times 10^{12} G derived from the observed cyclotron line
position may be resolved if the line formation region resides in a tall
accretion column of height \sim 2.5 - 3 R_{NS}. The color temperature measured
from the spectrum suggests that such a column may indeed be present, and our
estimates show that its height is sufficient to explain the observed cyclotron
line position.Comment: 10 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics. Referee comments are implemented
Impaired perceptual learning in a mouse model of Fragile X syndrome is mediated by parvalbumin neuron dysfunction and is reversible.
To uncover the circuit-level alterations that underlie atypical sensory processing associated with autism, we adopted a symptom-to-circuit approach in the Fmr1-knockout (Fmr1-/-) mouse model of Fragile X syndrome. Using a go/no-go task and in vivo two-photon calcium imaging, we find that impaired visual discrimination in Fmr1-/- mice correlates with marked deficits in orientation tuning of principal neurons and with a decrease in the activity of parvalbumin interneurons in primary visual cortex. Restoring visually evoked activity in parvalbumin cells in Fmr1-/- mice with a chemogenetic strategy using designer receptors exclusively activated by designer drugs was sufficient to rescue their behavioral performance. Strikingly, human subjects with Fragile X syndrome exhibit impairments in visual discrimination similar to those in Fmr1-/- mice. These results suggest that manipulating inhibition may help sensory processing in Fragile X syndrome
Bohr's Correspondence Principle and The Area Spectrum of Quantum Black Holes
During the last twenty-five years evidence has been mounting that a
black-hole surface area has a {\it discrete} spectrum. Moreover, it is widely
believed that area eigenvalues are {\it uniformally} spaced. There is, however,
no general agreement on the {\it spacing} of the levels. In this letter we use
Bohr's correspondence principle to provide this missing link. We conclude that
the area spacing of a black-hole is . This is the unique spacing
consistent both with the area-entropy {\it thermodynamic} relation for black
holes, with Boltzmann-Einstein formula in {\it statistical physics} and with
{\it Bohr's correspondence principle}.Comment: 10 page
Fluctuation induced hopping and spin polaron transport
We study the motion of free magnetic polarons in a paramagnetic background of
fluctuating local moments. The polaron can tunnel only to nearby regions of
local moments when these fluctuate into alignment. We propose this fluctuation
induced hopping as a new transport mechanism for the spin polaron. We calculate
the diffusion constant for fluctuation induced hopping from the rate at which
local moments fluctuate into alignment. The electrical resistivity is then
obtained via the Einstein relation. We suggest that the proposed transport
mechanism is relevant in the high temperature phase of the Mn pyrochlore
colossal magneto resistance compounds and Europium hexaboride.Comment: 8 pages, 3 figure
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