Angular Extensions Research Articles

Spatial extension of dark subhalos as seen by Fermi -LAT and the implications for WIMP constraints

Spatial extension has been hailed as a "smoking gun" in the gamma-ray search of dark galactic subhalos, which would appear as unidentified sources for gamma-ray telescopes. In this work, we study the sensitivity of the Fermi-LAT to extended subhalos using simulated data based on a realistic sky model. We simulate spatial templates for a set of representative subhalos, whose parameters were derived from our previous work with N-body cosmological simulation data. We find that detecting an extended subhalo and finding an unequivocal signal of angular extension requires, respectively, a flux 2 to 10 times larger than in the case of a point-like source. By studying a large grid of models, where parameters such as the WIMP mass, annihilation channel or subhalo model are varied significantly, we obtain the response of the LAT as a function of the product of annihilation cross section times the J-factor. Indeed, we show that spatial extension can be used as an additional filter to reject subhalos candidates among the pool of unidentified LAT sources, as well as a "smoking gun" for positive identification. For instance, typical angular extensions of a few tenths of degree are expected for the considered scenarios. Finally, we also study the impact of the obtained LAT sensitivity to such extended subhalos on the achievable dark matter constraints, which are a few times less constraining than comparable point-source limits.

Modeling Gamma-Ray SEDs and Angular Extensions of Extreme TeV Blazars from Intergalactic Proton-Initiated Cascades in Contemporary Astrophysical EGMF Models

The intrinsic spectra of some distant blazars known as “extreme TeV blazars” have shown a hint at an anomalous hardening in the TeV energy region. Several extragalactic propagation models have been proposed to explain this possible excess transparency of the Universe to gamma-rays starting from a model which assumes the existence of so-called axion-like particles (ALPs) and the new process of gamma-ALP oscillations. Alternative models suppose that some of the observable gamma-rays are produced in the intergalactic cascades. This work focuses on investigating the spectral and angular features of one of the cascade models, the Intergalactic Hadronic Cascade Model (IHCM) in the contemporary astrophysical models of Extragalactic Magnetic Field (EGMF). For IHCM, EGMF largely determines the deflection of primary cosmic rays and electrons of intergalactic cascades and, thus, is of vital importance. Contemporary Hackstein models are considered in this paper and compared to the model of Dolag. The models assumed are based on simulations of the local part of large-scale structure of the Universe and differ in the assumptions for the seed field. This work provides spectral energy distributions (SEDs) and angular extensions of two extreme TeV blazars, 1ES 0229+200 and 1ES 0414+009. It is demonstrated that observable SEDs inside a typical point spread function of imaging atmospheric Cherenkov telescopes (IACTs) for IHCM would exhibit a characteristic high-energy attenuation compared to the ones obtained in hadronic models that do not consider EGMF, which makes it possible to distinguish among these models. At the same time, the spectra for IHCM models would have longer high energy tails than some available spectra for the ALP models and the universal spectra for the Electromagnetic Cascade Model (ECM). The analysis of the IHCM observable angular extensions shows that the sources would likely be identified by most IACTs not as point sources but rather as extended ones. These spectra could later be compared with future observation data of such instruments as Cherenkov Telescope Array (CTA) and LHAASO.

Analysis of the electrical field in viscosity sensors with torsionally vibrating quartz cylinders

The potential and electric fields in viscosity sensors with torsionally vibrating quartz cylinders are calculated for various sensor geometries by means of analytical solution techniques and a numerical integration method for the Laplace equation. Sensor geometries with electrodes on the surface of the cylinder and offset at a distance from the cylinder are investigated for different angular extensions of the electrodes and dielectric constants of the fluid. It is found that the electric field is more favorable for the excitation of the torsional vibration when the electrodes are located at a distance from the cylinder surface rather than on the cylinder. When the electrodes are on the surface of the cylinder, the direction of the piezoelectrically active component of the electric field is reversed in certain regions near the edges of the cylinder, which hinders the excitation of the torsional vibration. As a result of this analysis, a novel viscosity sensor with line conductor electrodes was developed and validated in our laboratory. Furthermore, this article provides a brief review of the available literature on torsionally vibrating quartz cylinder viscometers.

VDR independent induction of acid-sphingomyelinase by 1,23(OH)2 D3 in gastric cancer cells: Impact on apoptosis and cell morphology

1 alpha,25-dihydroxyvitamin D3 (1,23(OH)2 D3) is known to play a dual role in cancer, by promoting or inhibiting carcinogenesis via 1,23(OH)2 D3 receptor (VDR) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Fok I polymorphism of VDR may indirectly influence the receptor levels through autoregulation. The involvement of neutral sphingomyelinase in the non-classic VDR-mediated genomic pathway response to 1,23(OH)2 D3 treatment has been reported. Until now no information were reported about Fok I polymorphism of VDR in NCI-N87 human gastric cancer cells and the relation between acid sphingomyelinase and 1,23(OH)2 D3. Herein, we showed that NCI-N87 human gastric cancer cells are homozygous for the Fok I ′C′ allele; resulting in a three amino acid-truncated protein form of the VDR. Surprisingly 1,23(OH)2 D3 treatments strongly down-regulated the expression of VDR whereas acid sphingomyelinase and PTEN expression were upregulated. No changes of neutral sphingomyelinase expression were observed after 1,23(OH)2 D3 treatment, whereas acid sphingomyelinase activity increased. Furthermore 1,23(OH)2 D3 induced over-expression of caspase 8, CDKN2B, MAP3K5, cytochrome C apoptotic genes. Morphological analysis highlighted some very large round or oval cells and small cells with angular or fusiform extensions, confirmed by MIB-1 immunodetection and Hercep test.Taken together our results indicated that the action of 1,23(OH)2 D3 in gastric cancer cells was independent on 1,23(OH)2 D3 receptor and suggested the acid sphingomyelinase as a possible target to induce molecular events.

The spatial coherence of noise fields evoked by continuous source distributions.

In this work, analytic expressions for the spatial coherence of noise fields are derived in the modal domain with the aim of providing a sparse representation. For this purpose, the sound field in a region of interest is expressed in terms of a given pressure distribution on a virtual surrounding cylindrical or spherical surface. According to the Huygens-Fresnel principle, the sound pressure on this surface is represented by a continuous distribution of elementary line or point sources, where orthogonal basis functions characterize the spatial properties. To describe spatially windowed pressure distributions with arbitrary angular extensions, orthogonal basis functions of limited angular support are proposed. As special cases, circular and spherical pressure distributions with uncorrelated source modes of equal power are investigated. It is shown that these distributions result, respectively, in cylindrically isotropic and spherically isotropic, i.e., diffuse noise fields. The analytic expressions derived in this work allow for a prediction of the spatial coherence between arbitrary positions within the region of interest, such that no microphones need to be placed at the actual points of interest. Simulation results are presented to validate the derived relations.

Tomographic-spectral approach for dark matter detection in the cross-correlation between cosmic shear and diffuse γ-ray emission

We recently proposed to cross-correlate the diffuse extragalactic γ-ray background with the gravitational lensing signal of cosmic shear. This represents a novel and promising strategy to search for annihilating or decaying particle dark matter (DM) candidates. In the present work, we demonstrate the potential of a tomographic-spectral approach: measuring the cross-correlation in separate bins of redshift and energy significantly improves the sensitivity to a DM signal. Indeed, the technique proposed here takes advantage of the different scaling of the astrophysical and DM components with redshift and, simultaneously of their different energy spectra and different angular extensions. The sensitivity to a particle DM signal is extremely promising even when the DM-induced emission is quite faint. We first quantify the prospects of detecting DM by cross-correlating the Fermi Large Area Telescope (LAT) diffuse γ-ray background with the cosmic shear expected from the Dark Energy Survey. Under the hypothesis of a significant subhalo boost, such a measurement can deliver a 5σ detection of DM, if the DM particle is lighter than 300 GeV and has a thermal annihilation rate. We then forecast the capability of the European Space Agency Euclid satellite (whose launch is planned for 2020), in combination with an hypothetical future γ-ray detector with slightly improved specifications compared to current telescopes. We predict that the cross-correlation of their data will allow a measurement of the DM mass with an uncertainty of a factor of 1.5–2, even for moderate subhalo boosts, for DM masses up to few hundreds of GeV and thermal annihilation rates.

Multijoint reflexes of the stroke arm: Neural coupling of the elbow and shoulder

The reflex torque responses of the elbow and shoulder to constant velocity angular extensions of the full comfortable range of the spastic elbow were measured in 16 people with unilateral stroke and 6 neurologically intact controls in order to identify the interjoint reflex coupling that occurs after stroke. The resulting responses showed a substantial reflex torque at the elbow and shoulder in subjects with stroke, with 12 of the 16 subjects producing adduction of the shoulder in response to passive extension of the elbow. The presence of simultaneous shoulder flexion torque with elbow flexion torque and with an identical waveform indicated an active role of biarticular elbow/shoulder flexors, such as the biceps. As the biceps muscle produces a shoulder abduction moment, shoulder adduction produced during elbow extension was thought to be associated with neural rather than biomechanical coupling. These results suggest that spasticity in people with stroke is more complex than its traditional perception as a hyperexcitable stretch reflex, and includes potent heteronymous reflex pathways. The reflex coupling observed between the shoulder and elbow should be considered in the diagnosis and clinical management of spasticity. The potential impact of this reflex on the coordination of volitional arm movements will be examined in future studies.

Infrared Mapping of Four Interesting Planetary Nebulae

We present Two Micron All Sky Survey near-infrared (NIR) photometric mapping of the planetary nebulae A30, A78, NGC 7027, and BD +30 3639. It is shown that the NIR envelopes of both NGC 7027 and BD +30 3639 extend to much greater distances than has previously been supposed. It also appears that the dust in NGC 7027 has extinction properties similar to those of interstellar grains, and that the radii of the particles must be reasonably large. An analysis of emission in A78 and A30 shows the infrared indices to be reasonably large and implies grain temperatures Tgr of order ≈950 K. Similarly, the angular extensions of the continua (>18'' and >22'', respectively) suggest that they may arise from very small grains indeed. By contrast, while BD +30 3639 is also characterized by a high-temperature continuum, much of this emission appears to be confined to the core. This may imply that grain heating arises through direct stellar irradiation.

Low-complexity estimation of 2D DOA for coherently distributed sources

We consider the estimation of two-dimensional (azimuth and elevation) direction-of-arrival (DOA) using a pair of uniform circular arrays under a coherently distributed source model. Since the coherently distributed source is characterized by four parameters, the nominal azimuth DOA, angular extension of the azimuth DOA, nominal elevation DOA, and angular extension of the elevation DOA, the computational complexity of the parameter estimation is normally highly demanding. We propose a low-complexity estimation algorithm, called the sequential one-dimensional searching algorithm by concentrating only on the estimation of DOAs. The SOS algorithm has a basis on the eigenstructure between the steering matrix and signal subspace, and utilizes preliminary estimates obtained at a pre-processing stage. The SOS algorithm estimates the DOAs, but not the angular extensions: although the SOS algorithm does not provide estimates of angular extensions, it is useful when the angular extensions are small. Specifically, it is shown from simulation results that the SOS algorithm exhibits as good an estimation performance as the maximum likelihoood method for coherently distributed sources.

A NOTE ON THE VALVE STRUCTURE OF TRICERATIUM HETEROGONUM BARKER & MEAKIN, AN UNUSUAL SPECIES FROM CONSET, BARBADOS

The valve structure of Triceratium heterogonum Barker & Meakin is basically quadrate in which two opposing angles have gently rounded apices while the other two angles are slightly more acute. The valve margin between the angular extensions is concave. Each valve has two types of processes, a single process lying within each angle, those of opposing angles identical. Lying within the broader and more rounded angle is a hyaline tubular structure, directed outwards, and terminating in a cup-like structure; at the other pole a shorter elevation terminating in a thickened hyaline rim. A detailed description of the valve structure and processes is given, comparisons of the tubular structure made with those of other genera and a discussion on relationships with other genera, particularly that with Triceratium sensu stricto, is also given. A new genus Petrochiscus is proposed with T. heterogonum as the generitype.

Neutrino-driven Type-II supernova explosions and the role of convection

The role of neutrino heating and convection in the explosions of Type-II supernovae is reviewed. The neutrino-driven mechanism of supernova explosions is based upon the fact that high-energetic neutrinos streaming up from the hotter interior must transfer energy to the cooler layers adjacent to the nascent neutron star. While this energy deposition is unavoidable, there is still controversy about the point whether it is able to drive and power a Type-II supernova event or not. To investigate this question one-dimensional hydrodynamical simulations have been performed for the longtime evolution of the collapsed stellar core after the bounce at nuclear matter density and after the associated formation of the supernova shock. In these studies the parameters describing the neutrino emission have been varied and the influence of the temporal contraction of the central part of the nascent neutron star has been tested. A detailed analysis of these models reveals that the possibility to obtain explosions is very sensitive to the physical conditions at and in the protoneutron star and to the properties of the matter accreted into the shock. It critically depends on the neutrino fluxes during the shock revival phase. Yet, above a certain threshold for the neutrino luminosity, stable explosions can be obtained in spherical symmetry. Recently, convection has become a topic which has attracted a lot of attention, partly inspired by the existence of convectively unstable regions in the the post-collapse core, partly by the fact that effects from large-scale mixing processes have been observed in SN 1987A. We repeated our calculations in two dimensions to answer the question whether and which convective processes occur during the early phase of the supernova explosion and to which extent they help the star to explode as a consequence of the neutrino energy deposition. Our results show strong convective processes in the collapsed stellar core in two spatially separate regions. One region of convection lies inside the neutrino sphere and another one is located in the neutrino-heated layer below the shock front. The convective mixing around the neutrino sphere is mainly driven by the negative lepton gradient, which is maintained due to rapid loss of leptons from the semitransparent layers at the neutrino sphere. This is found to considerably speed up the deleptonization of the outer layers of the collapsed stellar core. Even 0.5 seconds after bounce the convective motion is still present in the protoneutron star. Three-dimensional simulations revealed that rising and sinking convective elements have angular sizes between 10 ° and 15 °, which causes corresponding anisotropies of the neutrino emission from the core. The large-scale convective overturn that takes place between the shock and the position of maximum neutrino heating is able to efficiently transport energy from the heated layer into the postshock region. This helps to stabilize the shock revival during the critical phase. The overturn pattern shows downflows of matter in narrow flux tubes and rising bubbles with typical angular extensions of 30 ° to 60 ° (in two dimensions). The material falling towards the neutron star loses lepton number, but readily absorbs energy in the neutrino-heated region, before it rises again. This matter is not accreted onto the protoneutron star. After about 0.4 seconds the turbulent phase outside of the protoneutron star is followed by the spherically symmetrical neutrino-wind phase. The supernova shock is strongly deformed and velocity, density, temperature, and entropy in the postshock region exhibit large-scale variations with a contrast of up to a factor of 3. This must have consequences for the formation and spatial distribution of nucleosynthesis products and might help to explain the dumpiness, anisotropies, envelope and mantle mixing, and large velocities of iron group nuclei which were observed in the ejecta of SN 1987A and other supernovae. Although in this respect of essential importance, convection in the postshock region does not seem to be indispensable to get successful Type-II explosions via the neutrino-heating mechanism, nor do our simulations allow for the conclusion that its presence inevitably makes the mechanism successful and the explosions very energetic. As in spherical symmetry, the explosion energy is very sensitive to the neutrino energy deposition and the size of the neutrino fluxes during a period of several hundred milliseconds after core bounce.

Extension of off-nadir view angles for directional sensor systems

A knowledge-based system called VEG was expanded to infer nadir or any off-nadir reflectance(s) of a vegetation target given any combination of other directional reflectance(s) of the target. VEG determines the best techniques to use in an array of techniques, applies the techniques to the target data, and provides a rigorous estimate of the accuracy of the inference(s). The knowledge-based system, VEG, facilitates the use of diverse knowledge bases to be incorporated into the inference techniques. In this study, VEG used additional information to make more accurate view-angle extension techniques than the traditional techniques that only use spectral data from the unknown target. VEG used spectral data and a normalized difference technique to infer the percentage of ground cover of the unknown target. This estimate of percentage of ground cover of the unknown target along with information on the sun angle were then used to search a historical data base for targets that match the unknown target in these characteristics. This data captured the general shape of the reflectance distribution of the unknown target. This historical information was used to estimate the coefficients of the techniques for the conditions at hand and to test the accuracy of the techniques. The tests used in this study were difficult ones. For example, techniques were tested that make long angular extensions using one, two, or four input view angles to predict an unknown nadir value. Furthermore, a wide variety of unknown targets were tested. The errors (±proportional rms) obtained were on the order of 0.15. In addition techniques were tested that use seven or nine multiple view angles to predict the entire hemispherical reflectance distribution of an unknown target. The accuracy of these tests was relatively good considering the relatively dynamic and noisy nature of directional reflectance distributions. The accuracy of the techniques in this study depends on the smoothness of the historical reflectance distributions and the amount of historical data available that closely matches the unknown target.

Effectiveness of Wear Plate at the Saddle Support

A theory is presented to analyze the effectiveness of incorporating a wear plate at the saddle support of a cylindrical pressure vessel. The wear plate can be either welded to the vessel or of loose fitting. The theory is based on a contact stress formulation together with the use of a cylindrical shell bending theory for simply supported cylinder. The effectiveness of the wear plate in reducing the peak circumferential saddle-horn stress is quantified by definition of a stress reduction factor. Parametric data are carried out for the saddle angle of 120 deg. From the study, the optimum thickness of the wear plate for three different angular extensions, are obtained.

Estimates of the Energy Cost of Rifle Carriage in Biathlon Ski Skating

Elite biathletes now ski using skating techniques in place of the more traditional diagonal stride. Because of the more extreme flexion and extension of the trunk with these new techniques, it has become necessary to reevaluate the method of rifle carriage. This paper describes a model which evaluates the incremental mechanical power required to move the additional weight of the rifle through defined angular flexions and extensions of the trunk. By combining this model with actual observations of typical kinematics of trunk flexion, we can generate realistic estimates of the energy cost of rifle carriage. This approach is also used to evaluate the energy consequences of reduced rifle mass and of different rifle carriage strategies while moving with ski skating techniques. These results show that rotational kinetic energy changes are a minor part of the overall energy cost of rifle carriage, and that changes in the horizontal velocity of the rifle are the greatest source of increased cost of transport. The largest reductions in this cost, however, would come from reducing rifle mass because both potential and kinetic energies are affected. Additional but secondary reductions can be obtained by placing the rifle center of mass opposite the lumbosacral joint, thereby reducing horizontal and vertical excursions of the rifle.

Thixotropic behaviour of human finger flexor muscles with accompanying changes in spindle and reflex responses to stretch.

Prompted by previous reports on muscle thixotropy, we have investigated changes in inherent and reflex stiffness of the finger flexor muscles of human subjects at rest, following transient conditioning manoeuvres involving contractions and/or length changes of the finger flexors. The stiffness measurements were combined with electromyographic recordings from forearm and hand muscles and with microneurographic recordings of afferent stretch responses in finger flexor nerve fascicles. Finger flexor stiffness was evaluated by measuring (a) the flexion angle of the metacarpo-phalangeal joints at which the system during rest balanced the force of gravity and (b) the speed and amplitude of angular finger extensions induced by recurrent extension torque pulses of constant strength delivered by a torque motor. In the latter case, extension drifts in the resting position of the fingers were prevented by a weak flexion bias torque holding the fingers in a pre-determined, semiflexed position against a stop-bar. Stiffness changes following passive large amplitude finger flexions and extensions were studied in subjects with nerve blocks or nerve lesions preventing neurally mediated contractions in the forearm and hand muscles. Inherent stiffness was enhanced following transient finger flexions and reduced following transient finger extensions. The after-effects gradually declined during observation periods of several minutes. Similar results were obtained in subjects with intact innervation who succeeded during the pre- and post-conditioning periods in keeping the arm and hand muscles relaxed (i.e. showed no electromyographic activity). In these subjects it was also found that the after-effects were similar for active and passive finger movements and that isometric voluntary finger flexor contractions loosened the system in a way similar to finger extensions. In some subjects electromyographic reflex discharges appeared in the finger flexors in response to the extension test pulses. When elicited by small ramp stretch stimuli of constant amplitude, the stretch reflex responses were found to vary in strength in parallel with the changes in inherent stiffness following the various conditioning manoeuvres. The strength of the multi-unit afferent stretch discharges in the muscle nerve, used as index of muscle spindle stretch sensitivity, varied in parallel with the changes in inherent stiffness. Post-manoeuvre changes in muscle spindle stretch sensitivity were seen also when the spindles were de-efferented by a nerve block proximal to the recording site. The results can be explained in terms of thixotropic behaviour of extra- and intrafusal muscle fibres.(ABSTRACT TRUNCATED AT 400 WORDS)