2,517 research outputs found
Role of Sterile Neutrino Warm Dark Matter in Rhenium and Tritium Beta Decays
Sterile neutrinos with mass in the range of one to a few keV are important as
extensions of the Standard Model of particle physics and are serious dark
matter (DM) candidates. This DM mass scale (warm DM) is in agreement with both
cosmological and galactic observations. We study the role of a keV sterile
neutrino through its mixing with a light active neutrino in Rhenium 187 and
Tritium beta decays. We pinpoint the energy spectrum of the beta particle, 0 <
T_e < (Q_{beta} - m_s), as the region where a sterile neutrino could be
detected and where its mass m_s could be measured. This energy region is at
least 1 keV away rom the region suitable to measure the mass of the light
active neutrino, located near the endpoint Q_{beta} . The emission of a keV
sterile neutrino in a beta decay could show up as a small kink in the spectrum
of the emitted beta particle. With this in view, we perform a careful
calculation of the Rhenium and Tritium beta spectra and estimate the size of
this perturbation by means of the dimensionless ratio R of the sterile neutrino
to the active neutrino contributions. We comment on the possibility of
searching for sterile neutrino signatures in two experiments which are
currently running at present, MARE and KATRIN, focused on the Rhenium 187 and
Tritium beta decays respectively.Comment: 16 pages, 10 figures. Version to appear in Nucl. Phys. B. Results and
conclusions unchange
Gamma rays from microquasars Cygnus X-1 and Cygnus X-3
Gamma-ray observations of microquasars at high and very-high energies can
provide valuable information of the acceleration processes inside the jets, the
jet-environment interaction and the disk-jet coupling. Two high-mass
microquasars have been deeply studied to shed light on these aspects: Cygnus
X-1 and Cygnus X-3. Both systems display the canonical hard and soft X-ray
spectral states of black hole transients, where the radiation is dominated by
non-thermal emission from the corona and jets and by thermal emission from the
disk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeV
using 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. A
hint of orbital flux modulation was also found, as the source is only detected
in phases around the compact object superior conjunction. We conclude that the
high-energy gamma-ray emission from Cygnus X-1 is most likely associated with
jets and its detection allow us to constrain the production site. Moreover, we
include in the discussion the final results of a MAGIC long-term campaign on
Cygnus X-1 that reaches almost 100 hr of observations at different X-ray
states. On the other hand, during summer 2016, Cygnus X-3 underwent a flaring
activity period in radio and high-energy gamma rays, similar to the one that
led to its detection in the high-energy regime in 2009. MAGIC performed
comprehensive follow-up observations for a total of about 70 hr. We discuss our
results in a multi-wavelength context.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Present and future of surface-enhanced Raman scattering
The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article
Nuevo rumbo estratégico y reestructuración: el caso NH Hotel Group
[EN] This article seeks to analyze the change in direction of NH Hotel Group, which, as a
consequence of the transformations in its strategic environment and the economic crisis, found
it needed to face the future by implementing a strategic plan and restructuring its business
portfolio. The document sets out the phases it followed in the implementation of the plan and
shows the positive evolution it has experienced, analyzing the company¿s historical evolution
through a study of secondary sources. We conclude that the NH Hotel Group case supports
the affirmation that the definition and execution of an appropriate strategic plan helps improve
company results, with flexibility being equally important in the implementation in order to adapt
to possible changes in the environment[ES] El presente artículo busca analizar el cambio de rumbo de NH Hotel Group que, como consecuencia de las transformaciones producidas en su entorno competitivo y la crisis económica, se encontró en la necesidad de afrontar el futuro implantando un plan estratégico y reestructurando su cartera de negocio. El documento expone las fases que siguió en la implantación de dicho plan y presenta la evolución positiva que ha experimentado, analizando la evolución histórica de la compañía a través de un estudio de fuentes secundarias. Concluimos que el caso de NH Hotel Group apoya la afirmación de que la definición y ejecución de un adecuado plan estratégico ayuda a mejorar los resultados empresariales, siendo igualmente importante la flexibilidad en la implantación para adaptarse a posibles cambios en el entorno.De Diego, E.; Susaeta-Erburu, L.; Pin-Arboledas, JR.; Suárez-Ruz, ME. (2016). New Strategic Direction and Reestructuring. The NH Hotel Group case. UNIVERSIA BUSINESS REVIEW. 52:114-167. doi:10.3232/UBR.2016.V13.N4.03S1141675
Answer Set Programming for Non-Stationary Markov Decision Processes
Non-stationary domains, where unforeseen changes happen, present a challenge
for agents to find an optimal policy for a sequential decision making problem.
This work investigates a solution to this problem that combines Markov Decision
Processes (MDP) and Reinforcement Learning (RL) with Answer Set Programming
(ASP) in a method we call ASP(RL). In this method, Answer Set Programming is
used to find the possible trajectories of an MDP, from where Reinforcement
Learning is applied to learn the optimal policy of the problem. Results show
that ASP(RL) is capable of efficiently finding the optimal solution of an MDP
representing non-stationary domains
Variability of the bond and mechanical properties of self-compacting concrete
This main objective of this research is to evaluate the variability of the mechanical properties (compressive strength, modulus of elasticity
and tensile strength) and bond strength of the self-compacting concrete (SCC), with 50 MPa compressive strength at 28 days, varying
the maximum aggregate size and the SCC fluidity. The tests were made in 15 x 30 cm concrete cylinders and in beams standardized by
Rilem-Ceb-Fib (1973). In agreement with the obtained results, can be concluded that the variability of the self-compacting concrete is
small for the modulus of elasticity and for the compressive strength, but the tensile strength presented a significant variability due to the
failure mode. About the bond strength, the variability was small showing that the self-compacting concrete is reliable and possesses great potential for use in the civil construction.Peer ReviewedPostprint (published version
Evidence for non-thermal X-ray emission from the double WR colliding-wind binary Apep
Context: Massive colliding-wind binaries (CWBs) can be non-thermal sources.
The emission produced in their wind-collision region (WCR) encodes information
of both the shocks properties and the relativistic electrons accelerated in
them. The recently discovered system Apep, a unique massive system hosting two
Wolf-Rayet stars, is the most powerful synchrotron radio emitter among the
known CWBs, being an exciting candidate to investigate the non-thermal
processes associated with stellar wind shocks.
Aims: We intend to break the degeneracy between the relativistic particle
population and the magnetic field strength in the WCR of Apep by probing its
hard X-ray spectrum, where inverse-Compton (IC) emission is expected to
dominate.
Methods: We observe Apep with NuSTAR for 60 ks and combine this with a
re-analysis of a deep archival XMM-Newton observation to better constrain the
X-ray spectrum. We use a non-thermal emission model to derive physical
parameters from the results.
Results: We detect hard X-ray emission consistent with a power-law component.
This is compatible with IC emission produced in the WCR for a magnetic field of
100-160 mG and a fraction of ~1.5e-4 of the total wind kinetic power being
converted into relativistic electron acceleration.
Conclusions: This is the first time that the non-thermal emission from a CWB
is detected both in radio and high energies. This allows us to derive the most
robust constraints of the particle acceleration efficiency and magnetic field
intensity in a CWB so far, reducing the typical uncertainty of a few orders of
magnitude to just within a factor of two. This constitutes an important step
forward in our characterisation of the physical properties of CWBs.Comment: 12 pages, 6 figures, accepted for publication in A&
On the conservation of the slow conformational dynamics within the amino acid kinase family: NAGK the paradigm
N-Acetyl-L-Glutamate Kinase (NAGK) is the structural paradigm for examining the catalytic mechanisms and dynamics of amino acid kinase family members. Given that the slow conformational dynamics of the NAGK (at the microseconds time scale or slower) may be rate-limiting, it is of importance to assess the mechanisms of the most cooperative modes of motion intrinsically accessible to this enzyme. Here, we present the results from normal mode analysis using an elastic network model representation, which shows that the conformational mechanisms for substrate binding by NAGK strongly correlate with the intrinsic dynamics of the enzyme in the unbound form. We further analyzed the potential mechanisms of allosteric signalling within NAGK using a Markov model for network communication. Comparative analysis of the dynamics of family members strongly suggests that the low-frequency modes of motion and the associated intramolecular couplings that establish signal transduction are highly conserved among family members, in support of the paradigm sequence→structure→dynamics→function © 2010 Marcos et al
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