309 research outputs found
Sub-GeV Dark Matter Shining at Future MeV Gamma-Ray Telescopes
We propose a novel framework where light (sub-GeV) dark matter (DM) is
detectable with future MeV gamma-ray telescopes without conflicting with Cosmic
Microwave Background (CMB) data. The stable DM particle has a very low
thermal relic abundance due to its large pair-annihilation cross section. The
DM number density is stored in a heavier, meta-stable partner with
suppressed pair-annihilation rates, that does not perturb the CMB, and whose
late-time decays fill the universe with DM
particles. We provide explicit, model-independent realizations for this
framework, and discuss constraints on late-time decays, and thus on parameters
of this setup, from CMB, Big Bang Nucleosynthesis, and Large Scale Structure.Comment: 6 pages, 3 figures, version published in Physical Review Letter
When the Universe Expands Too Fast: Relentless Dark Matter
We consider a modification to the standard cosmological history consisting of
introducing a new species whose energy density red-shifts with the scale
factor like . For , such a red-shift is
faster than radiation, hence the new species dominates the energy budget of the
universe at early times while it is completely negligible at late times. If
equality with the radiation energy density is achieved at low enough
temperatures, dark matter can be produced as a thermal relic during the new
cosmological phase. Dark matter freeze-out then occurs at higher temperatures
compared to the standard case, implying that reproducing the observed abundance
requires significantly larger annihilation rates. Here, we point out a
completely new phenomenon, which we refer to as dark
matter: for large enough , unlike the standard case where annihilation ends
shortly after the departure from thermal equilibrium, dark matter particles
keep annihilating long after leaving chemical equilibrium, with a significant
depletion of the final relic abundance. Relentless annihilation occurs for and for s-wave and p-wave annihilation, respectively, and it
thus occurs in well motivated scenarios such as a quintessence with a kination
phase. We discuss a few microscopic realizations for the new cosmological
component and highlight the phenomenological consequences of our calculations
for dark matter searches.Comment: 14 pages, 9 figure
Dark Matter Inelastic Up-Scattering with the Interstellar Plasma: An Exciting New Source of X-Ray Lines, including at 3.5 keV
We explore the phenomenology of a class of models where the dark matter
particle can inelastically up-scatter to a heavier excited state via
off-diagonal dipolar interactions with the interstellar plasma (gas or free
electrons). The heavier particle then rapidly decays back to the dark matter
particle plus a quasi-monochromatic photon. For the process to occur at
appreciable rates, the mass splitting between the heavier state and the dark
matter must be comparable to, or smaller than, the kinetic energy of particles
in the plasma. As a result, the predicted photon line falls in the soft X-ray
range, or, potentially, at arbitrarily lower energies. We explore experimental
constraints from cosmology and particle physics, and present accurate
calculations of the dark matter thermal relic density and of the flux of
monochromatic X-rays from thermal plasma excitation. We find that the model
provides a natural explanation for the observed 3.5 keV line from clusters of
galaxies and from the Galactic center, and is consistent with null detections
of the line from dwarf galaxies. The unique line shape, which will be resolved
by future observations with the Hitomi (formerly Astro-H) satellite, and the
predicted unique morphology and target-temperature dependence will enable easy
discrimination of this class of models versus other scenarios for the
generation of the 3.5 keV line or of any other unidentified line across the
electromagnetic spectrum.Comment: 16 pages, 9 figures; v2, version published in Physical Review
Direct torque control for dual three-phase induction motor drives
A direct torque control (DTC) strategy for dual three-phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are constant inverter switching frequency, good transient and steady-state performance, and low distortion of machine currents with respect to direct self-control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10-kW DTC dual three-phase induction motor drive prototype
Temperatures evaluation in an integrated motor drive for traction applications
The integrated propulsion motor is a drive designed for an individual self-driven container rail-platform wagon developed in the ldquointegrated standard transport unitrdquo research and development project, supported by the European commission. This paper presents the study of the motor and the converter temperatures at rated and overload working conditions. The problem is afforded by combining the simulation (finite-element method and lumped-parameter models) and the experimental approaches. For this purpose, a dedicated experimental setup has been designed and realized
Малое и среднее предпринимательство: закономерности развития
Представлен анализ уровня развития, достигнутого малыми и средними предприятиями, а также индивидуальными предпринимателями в Российской Федерации. Рассмотрены основные показатели функционирования предпринимательских структур по видам экономической деятельности. Приведены зависимости, показывающие распределение средней численности работников. Показана возможность разработки производственных функций для совокупности малых, средних предприятий и индивидуальных предпринимателей. Сделаны выводы об основных закономерностях развития предпринимательских структур
Combined Layer-by-Layer/Hydrothermal Synthesis of Fe3O4@MIL-100(Fe) for Ofloxacin Adsorption from Environmental Waters
: A simple not solvent and time consuming Fe3O4@MIL-100(Fe), synthesized in the presence of a small amount of magnetite (Fe3O4) nanoparticles (27.3 wt%), is here presented and discussed. Layer-by-layer alone (20 shell), and combined layer-by-layer (5 shell)/reflux or /hydrothermal synthetic procedures were compared. The last approach (Fe3O4@MIL-100_H sample) is suitable (i) to obtain rounded-shaped nanoparticles (200-400 nm diameter) of magnetite core and MIL-100(Fe) shell; (ii) to reduce the solvent and time consumption (the layer-by-layer procedure is applied only 5 times); (iii) to give the highest MIL-100(Fe) amount in the composite (72.7 vs. 18.5 wt% in the layer-by-layer alone); (iv) to obtain a high surface area of 3546 m2 g-1. The MIL-100(Fe) sample was also synthesized and both materials were tested for the absorption of Ofloxacin antibiotic (OFL). Langmuir model well describes OFL adsorption on Fe3O4@MIL-100_H, indicating an even higher adsorption capacity (218 ± 7 mg g-1) with respect to MIL-100 (123 ± 5 mg g-1). Chemisorption regulates the kinetic process on both the composite materials. Fe3O4@MIL-100_H performance was then verified for OFL removal at µg per liter in tap and river waters, and compared with MIL-100. Its relevant and higher adsorption efficiency and the magnetic behavior make it an excellent candidate for environmental depollution
analysis and visualization of natural threats against the security of electricity transmission system
Abstract Electricity is one of the crucial energies of modern society, but it is greatly threatened by various kinds of menaces, especially natural hazards. Although they rarely happen, their occurrence may hugely affect the operation of power system. In this paper, we firstly, according the impact on power systems, classify natural threats into two categories (natural disasters and extreme weather conditions) and several subcategories (geological, hydrological, meteorological and climatological). Then the changes in natural threats to power systems and their trends during recent decades are discussed, along with a review of events that pose natural threats to the power system. Finally, the georeferenced model based on the Italy transmission system for natural threats analysis is presented
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