9,949 research outputs found
Standard Model False Vacuum Inflation: Correlating the Tensor-to-Scalar Ratio to the Top Quark and Higgs Boson masses
For a narrow band of values of the top quark and Higgs boson masses, the
Standard Model Higgs potential develops a false minimum at energies of about
GeV, where primordial Inflation could have started in a cold
metastable state. A graceful exit to a radiation-dominated era is provided,
e.g., by scalar-tensor gravity models. We pointed out that if Inflation
happened in this false minimum, the Higgs boson mass has to be in the range
GeV, where ATLAS and CMS subsequently reported excesses of
events. Here we show that for these values of the Higgs boson mass, the
inflationary gravitational wave background has be discovered with a
tensor-to-scalar ratio at hand of future experiments. We suggest that combining
cosmological observations with measurements of the top quark and Higgs boson
masses represents a further test of the hypothesis that the Standard Model
false minimum was the source of Inflation in the Universe.Comment: v1: 4 pages, 2 figures; v2: 5 pages, 2 figures, improvements in the
text; v3: 5 pages, 2 figures, minor improvements in the text, matches PRL
versio
IETS and quantum interference: propensity rules in the presence of an interference feature
Destructive quantum interference in single molecule electronics is an
intriguing phe- nomenon; however, distinguishing quantum interference effects
from generically low transmission is not trivial. In this paper, we discuss how
quantum interference ef- fects in the transmission lead to either low current
or a particular line shape in current-voltage curves, depending on the position
of the interference feature. Sec- ondly, we consider how inelastic electron
tunneling spectroscopy can be used to probe the presence of an interference
feature by identifying vibrational modes that are se- lectively suppressed when
quantum interference effects dominate. That is, we expand the understanding of
propensity rules in inelastic electron tunneling spectroscopy to molecules with
destructive quantum interference.Comment: 19 pages, 6 figure
Micro-doppler-based in-home aided and unaided walking recognition with multiple radar and sonar systems
Published in IET Radar, Sonar and Navigation. Online first 21/06/2016.The potential for using micro-Doppler signatures as a basis for distinguishing between aided and unaided gaits is considered in this study for the purpose of characterising normal elderly gait and assessment of patient recovery. In particular, five different classes of mobility are considered: normal unaided walking, walking with a limp, walking using a cane or tripod, walking with a walker, and using a wheelchair. This presents a challenging classification problem as the differences in micro-Doppler for these activities can be quite slight. Within this context, the performance of four different radar and sonar systems – a 40 kHz sonar, a 5.8 GHz wireless pulsed Doppler radar mote, a 10 GHz X-band continuous wave (CW) radar, and a 24 GHz CW radar – is evaluated using a broad range of features. Performance improvements using feature selection is addressed as well as the impact on performance of sensor placement and potential occlusion due to household objects. Results show that nearly 80% correct classification can be achieved with 10 s observations from the 24 GHz CW radar, whereas 86% performance can be achieved with 5 s observations of sonar
Entanglement Typicality
We provide a summary of both seminal and recent results on typical
entanglement. By typical values of entanglement, we refer here to values of
entanglement quantifiers that (given a reasonable measure on the manifold of
states) appear with arbitrarily high probability for quantum systems of
sufficiently high dimensionality. We work within the Haar measure framework for
discrete quantum variables, where we report on results concerning the average
von Neumann and linear entropies as well as arguments implying the typicality
of such values in the asymptotic limit. We then proceed to discuss the
generation of typical quantum states with random circuitry. Different phases of
entanglement, and the connection between typical entanglement and
thermodynamics are discussed. We also cover approaches to measures on the
non-compact set of Gaussian states of continuous variable quantum systems.Comment: Review paper with two quotes and minimalist figure
Single-molecule Electronics: Cooling Individual Vibrational Modes by the Tunneling Current
Electronic devices composed of single molecules constitute the ultimate limit
in the continued downscaling of electronic components. A key challenge for
single-molecule electronics is to control the temperature of these junctions.
Controlling heating and cooling effects in individual vibrational modes, can in
principle, be utilized to increase stability of single-molecule junctions under
bias, to pump energy into particular vibrational modes to perform
current-induced reactions or to increase the resolution in inelastic electron
tunneling spectroscopy by controlling the life-times of phonons in a molecule
by suppressing absorption and external dissipation processes. Under bias the
current and the molecule exchange energy, which typically results in heating of
the molecule. However, the opposite process is also possible, where energy is
extracted from the molecule by the tunneling current. Designing a molecular
'heat sink' where a particular vibrational mode funnels heat out of the
molecule and into the leads would be very desirable. It is even possible to
imagine how the vibrational energy of the other vibrational modes could be
funneled into the 'cooling mode', given the right molecular design. Previous
efforts to understand heating and cooling mechanisms in single molecule
junctions, have primarily been concerned with small models, where it is unclear
which molecular systems they correspond to. In this paper, our focus is on
suppressing heating and obtaining current-induced cooling in certain
vibrational modes. Strategies for cooling vibrational modes in single-molecule
junctions are presented, together with atomistic calculations based on those
strategies. Cooling and reduced heating are observed for two different cooling
schemes in calculations of atomistic single-molecule junctions.Comment: 18 pages, 6 figure
Reconfigurable Intelligent Surfaces for Energy Efficiency in Wireless Communication
The adoption of a Reconfigurable Intelligent Surface (RIS) for downlink
multi-user communication from a multi-antenna base station is investigated in
this paper. We develop energy-efficient designs for both the transmit power
allocation and the phase shifts of the surface reflecting elements, subject to
individual link budget guarantees for the mobile users. This leads to
non-convex design optimization problems for which to tackle we propose two
computationally affordable approaches, capitalizing on alternating
maximization, gradient descent search, and sequential fractional programming.
Specifically, one algorithm employs gradient descent for obtaining the RIS
phase coefficients, and fractional programming for optimal transmit power
allocation. Instead, the second algorithm employs sequential fractional
programming for the optimization of the RIS phase shifts. In addition, a
realistic power consumption model for RIS-based systems is presented, and the
performance of the proposed methods is analyzed in a realistic outdoor
environment. In particular, our results show that the proposed RIS-based
resource allocation methods are able to provide up to higher energy
efficiency, in comparison with the use of regular multi-antenna
amplify-and-forward relaying.Comment: Accepted by IEEE TWC; additional materials on the topic are included
in the 2018 conference publications at ICASSP
(https://ieeexplore.ieee.org/abstract/document/8461496) and GLOBECOM 2018
(arXiv:1809.05397
Implementation of a Direct-Imaging and FX Correlator for the BEST-2 Array
A new digital backend has been developed for the BEST-2 array at
Radiotelescopi di Medicina, INAF-IRA, Italy which allows concurrent operation
of an FX correlator, and a direct-imaging correlator and beamformer. This
backend serves as a platform for testing some of the spatial Fourier transform
concepts which have been proposed for use in computing correlations on
regularly gridded arrays. While spatial Fourier transform-based beamformers
have been implemented previously, this is to our knowledge, the first time a
direct-imaging correlator has been deployed on a radio astronomy array.
Concurrent observations with the FX and direct-imaging correlator allows for
direct comparison between the two architectures. Additionally, we show the
potential of the direct-imaging correlator for time-domain astronomy, by
passing a subset of beams though a pulsar and transient detection pipeline.
These results provide a timely verification for spatial Fourier transform-based
instruments that are currently in commissioning. These instruments aim to
detect highly-redshifted hydrogen from the Epoch of Reionization and/or to
perform widefield surveys for time-domain studies of the radio sky. We
experimentally show the direct-imaging correlator architecture to be a viable
solution for correlation and beamforming.Comment: 12 pages, 17 figures, 2 tables, Accepted to MNRAS January 24, 2014,
includes appendix diagram
Molecular architecture of human polycomb repressive complex 2.
Polycomb Repressive Complex 2 (PRC2) is essential for gene silencing, establishing transcriptional repression of specific genes by tri-methylating Lysine 27 of histone H3, a process mediated by cofactors such as AEBP2. In spite of its biological importance, little is known about PRC2 architecture and subunit organization. Here, we present the first three-dimensional electron microscopy structure of the human PRC2 complex bound to its cofactor AEBP2. Using a novel internal protein tagging-method, in combination with isotopic chemical cross-linking and mass spectrometry, we have localized all the PRC2 subunits and their functional domains and generated a detailed map of interactions. The position and stabilization effect of AEBP2 suggests an allosteric role of this cofactor in regulating gene silencing. Regions in PRC2 that interact with modified histone tails are localized near the methyltransferase site, suggesting a molecular mechanism for the chromatin-based regulation of PRC2 activity.DOI:http://dx.doi.org/10.7554/eLife.00005.001
No Fermionic Wigs for BPS Attractors in 5 Dimensions
We analyze the fermionic wigging of 1/2-BPS (electric) extremal black hole
attractors in N=2, D=5 ungauged Maxwell-Einstein supergravity theories, by
exploiting anti-Killing spinors supersymmetry transformations. Regardless of
the specific data of the real special geometry of the manifold defining the
scalars of the vector multiplets, and differently from the D=4 case, we find
that there are no corrections for the near--horizon attractor value of the
scalar fields; an analogous result also holds for 1/2-BPS (magnetic) extremal
black string. Thus, the attractor mechanism receives no fermionic corrections
in D=5 (at least in the BPS sector).Comment: 24 pages, LaTeX2
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