1,349 research outputs found
H.E.S.S. deeper observations on SNR RX J0852.0-4622
Supernova Remnants (SNRs) are believed to be acceleration sites of Galactic
cosmic rays. Therefore, deep studies of these objects are instrumental for an
understanding of the high energy processes in our Galaxy. RX J0852.0-4622, also
known as Vela Junior, is one of the few (4) shell-type SNRs resolved at Very
High Energies (VHE; E > 100 GeV). It is one of the largest known VHE sources (~
1.0 deg radius) and its flux level is comparable to the flux level of the Crab
Nebula in the same energy band. These characteristics allow for a detailed
analysis, shedding further light on the high-energy processes taking place in
the remnant. In this document we present further details on the spatial and
spectral morphology derived with an extended data set. The analysis of the
spectral morphology of the remnant is compatible with a constant power-law
photon index of 2.11 +/- 0.05_stat +/- 0.20_syst from the whole SNR in the
energy range from 0.5 TeV to 7 TeV. The analysis of the spatial morphology
shows an enhanced emission towards the direction of the pulsar PSR J0855-4644,
however as the pulsar is lying on the rim of the SNR, it is difficult to
disentangle both contributions. Therefore, assuming a point source, the upper
limit on the flux of the pulsar wind nebula (PWN) between 1 TeV and 10 TeV, is
estimated to be ~ 2% of the Crab Nebula flux in the same energy range
Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants
The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3 PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy Υ-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte-Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a Υ-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 h of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations wit ο(100) hours of exposure per source
XMM-Newton evidence of shocked ISM in SN 1006: indications of hadronic acceleration
Shock fronts in young supernova remnants are the best candidates for being
sites of cosmic ray acceleration up to a few PeV, though conclusive
experimental evidence is still lacking. Hadron acceleration is expected to
increase the shock compression ratio, providing higher postshock densities, but
X-ray emission from shocked ambient medium has not firmly been detected yet in
remnants where particle acceleration is at work. We exploited the deep
observations of the XMM-Newton Large Program on SN 1006 to verify this
prediction. We performed spatially resolved spectral analysis of a set of
regions covering the southeastern rim of SN 1006. We studied the spatial
distribution of the thermodynamic properties of the ambient medium and
carefully verified the robustness of the result with respect to the analysis
method. We detected the contribution of the shocked ambient medium. We also
found that the postshock density of the interstellar medium significantly
increases in regions where particle acceleration is efficient. Under the
assumption of uniform preshock density, we found that the shock compression
ratio reaches a value of ~6 in regions near the nonthermal limbs. Our results
support the predictions of shock modification theory and indicate that effects
of acceleration of cosmic ray hadrons on the postshock plasma can be observed
in supernova remnants.Comment: Accepted for publication in A&
Exploring the nature of the unidentified VHE gamma-ray source HESS J1507-622
The nature of the first unidentified VHE gamma-ray source with significant
angular offset from the Galactic plane of 3.5 degrees, HESS J1507-622, is
explored. Fermi-LAT data in the high-energy (HE, 100 MeV < E < 100 GeV)
gamma-ray range collected over 34 month are used to describe the spectral
energy distribution (SED) of the source. HESS J1507-622 is detected in the
Fermi energy range and its spectrum is best described by a power law in energy
with Gamma=1.7 +/- 0.1 stat +/- 0.2_sys and integral flux between (0.3-300) GeV
of F = (2.0 +/-0.5_stat +/- 1.0_sys) x 10^-9 cm^-2 s^-1. With the available
data it is not possible to discriminate between a hadronic and a leptonic
scenario for HESS J1507-622. The location and compactness of the source
indicate a considerable physical offset from the Galactic plane for this
object. In case of a multiple-kpc distance, this challenges a pulsar wind
nebula (PWN) origin for HESS J1507-622 since the time of travel for a pulsar
born in the Galactic disk to reach such a location would exceed the inverse
Compton (IC) cooling time of electrons that are energetic enough to produce VHE
gamma-rays. However, an origin of this gamma-ray source connected to a pulsar
that was born off the Galactic plane in the explosion of a hypervelocity star
cannot be excluded. The nature of HESS J1507-622 is still unknown to date, and
a PWN scenario cannot be ruled out in general. On the contrary HESS J1507-622
could be the first discovered representative of a population of spatially
extended VHE gamma-ray emitters with HE gamma-ray counterpart that are located
at considerable offsets from the Galactic plane. Future surveys in the VHE
gamma-ray range are necessary to probe the presence or absence of such a source
population.(abridged)Comment: accepted for publication in A&A, 7 pages, 3 figure
A new calibration guideline for worm and worm-gear rolling testers
The evaluation and calibration of gear testers are considered as a key point to ensure the obtained results in gear metrology. Although ISO TC 60 working group has developed standards in this regard, the fact is that for the time being, there are not specific international standards for gear rolling tests. In this work, a periodical calibration guideline for gear rolling testers, particularly for worm gear transmission, is proposed, allowing the reduction of possible error sources in the measurement process. A series of tasks distributed over time are suggested in this work to maintain the accuracy of the gear rolling test machines
Urban climate multi-scale modelling in Bilbao (Spain): a review
Despite development of cities are including more sustainable aspects (e.g. reduction of energy consumption), urban climate still
needs to be consolidated as an important variable in urban planning. In this sense, the analysis of urban climate requires a multiscale
approach. This work presents a review of the results of the analysis of urban climate in Bilbao (Spain). In the meso-scale,
an Urban Climate Map (UC-Map) is developed using a method based on GIS calculations, specific climatic measurements and
urban climate expert knowledge. All the information is grouped in 5 information layers (building volume, building surface
fraction, urban green areas, ventilation paths and slopes). The final UC-Map presents areas with relative homogeneous climate
variables (i.e. climatopes) that are classified in terms of thermal comfort. Urban planning recommendations are defined. In the
micro-scale, results extracted from ENVI-met model in four urban spaces show the influence in thermal comfort levels of the
interaction of regional climate conditions with the urban development characteristics of each area and the location inside the
whole city. In both spatial scales, climate modelling should be accompanied by specific measurement campaigns to validate
results.Basque Science, Technology and Innovation Plan under the Project K-Egokitzen
European Community's Seventh Framework Programme under, Project RAMSES - Reconciling Adaptation, Mitigation and Sustainable Development for Citie
Self-adaptive overtemperature protection materials for safety-centric domestic induction heating applications
Security aspects in the household sphere have become a major concern in modern societies. In particular, regardless of the technology used, users increasingly appreciate a protection system to prevent material damage in the case of human errors or distractions during the cooking process. This paper presents a sensorless method for detecting and limiting overtemperature, unique to induction cooktops, based on their specific features, such as automatic pot detection and load power factor estimation. The protection system exploits the change in the load material properties at certain temperatures, the effect of which may be enhanced by arranging a multilayer structure comprising a low Curie temperature alloy and an aluminum layer. The proposed multilayer load exhibits two differentiated states: a normal state, where the cookware is efficiently heated, and a protection state, above the safety temperature, where the power factor abruptly decreases, limiting the overheating and making the state easily detectable by the cooktop. This method of overtemperature self-protection uses the electronics of conventional induction cooktops; therefore, no other sensors or systems are required, reducing its complexity and costs. Simulation and experimental results are provided for several cookware designs, thereby proving the feasibility of this proposal
Analytical Formulation of Copper Loss of Litz Wire with Multiple Levels of Twisting Using Measurable Parameters
Litz wire has been widely utilized in power transformers and inductors as a wire with low copper loss at high-frequency operation. The Litz wire is commonly made of many thin isolated strands twisted in multiple levels. Due to its complicated structure, the copper loss prediction of the Litz wire has been difficult, hindering the design optimization of the Litz wire structure. To overcome this difficulty, preceding studies have investigated the analytical copper loss models of the constituting elements of the Litz wire, i.e., the strands and the bundles of strands. The purpose of this article is to propose an analytical copper loss model of the Litz wire by utilizing these preceding knowledge. The proposed model is formulated only with parameters that can be measured by basic testing instruments. Besides, the proposed model considers the bundle structure of the Litz wire, which affects the local ac current distribution, and the twisting pitch, which causes the inclination of the Litz wire strands. The proposed model was tested by comparing the analytical prediction and experimental measurements of the ac resistance of commercially available Litz wires. As a result, the predicted ac resistance showed good agreement with the measured ac resistance, suggesting the appropriateness of the proposed model. © 1972-2012 IEEE
Design of a multi-point kinematic coupling for a high precision telescopic simultaneous measurement system
This paper covers the design of a new multi-point kinematic coupling specially developed for a high precision multi-telescopic arm measurement system for the volumetric verification of machine tools with linear and/or rotary axes. The multipoint kinematic coupling allows the simultaneous operation of the three telescopic arms that are registered at the same time to a sphere fixed on the machine tool spindle nose. Every coupling provides an accurate multi-point contact to the sphere, avoiding collisions and interferences with the other two multi-point kinematic couplings, and generating repulsion forces among them to ensure the coupling’s fingers interlacing along the machine tool x/y/z travels in the verification process. Simulation presents minimal deformation of the kinematic coupling under load, assuring the precision of the sphere-to-sphere distance meas-urement. Experimental results are provided to show that the multi-point kinematic coupling developed has repeatability values below ±1.2 µm in the application. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Effects of non-uniform interstellar magnetic field on synchrotron X-ray and inverse-Compton gamma-ray morphology of SNRs
Observations of SNRs in X-ray and gamma-ray bands promise to contribute with
important information in our understanding on the nature of galactic cosmic
rays. The analysis of SNRs images collected in different energy bands requires
the support of theoretical modeling of synchrotron and inverse Compton (IC)
emission. We develop a numerical code (REMLIGHT) to synthesize, from MHD
simulations, the synchrotron radio, X-ray and IC gamma-ray emission from SNRs
expanding in non-uniform interstellar medium (ISM) and/or non-uniform
interstellar magnetic field (ISMF). As a first application, the code is used to
investigate the effects of non-uniform ISMF on the SNR morphology in the
non-thermal X-ray and gamma-ray bands. We perform 3D MHD simulations of a
spherical SNR shock expanding through a magnetized ISM with a gradient of
ambient magnetic field strength. The model includes an approximate treatment of
upstream magnetic field amplification and the effect of shock modification due
to back reaction of accelerated cosmic rays. From the simulations, we
synthesize the synchrotron radio, X-ray and IC gamma-ray emission with
REMLIGHT, making different assumptions about the details of acceleration and
injection of relativistic electrons. A gradient of the ambient magnetic field
strength induces asymmetric morphologies in radio, X-ray and gamma-ray bands
independently from the model of electron injection if the gradient has a
component perpendicular to the line-of-sight. The degree of asymmetry of the
remnant morphology depends on the details of the electron injection and
acceleration and is different in the radio, X-ray, and gamma-ray bands. The
non-thermal X-ray morphology is the most sensitive to the gradient, showing the
highest degree of asymmetry. The IC gamma-ray emission is weakly sensitive to
the non-uniform ISMF, the degree of asymmetry of the SNR morphology being the
lowest in this band.Comment: 16 pages, 13 Figures; accepted for publication on A&A. Version with
full resolution images can be found at
http://www.astropa.unipa.it/~orlando/PREPRINTS/sorlando_15505.pd
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