Effects of the background radiation on radio pulsar and supernova remnant searches and the birth rates of these objects

In different directions of the Galaxy the Galactic background radio radiation and radiation of complex star formation regions which include large number of OB associations have different influences on radio pulsar (PSR) and supernova remnant (SNR) searches. In this work we analyse the effects of these background radiations on the observations of PSRs at 1400 MHz and SNRs at 1000 MHz. In the interval l=0$^o$$\pm60^o$ the PSRs with flux F$_{1400}$$>$0.2 mJy and the SNRs with surface brightness $\Sigma$$>10^{-21}$ Wm$^{-2}$Hz$^{-1}$sr$^{-1}$ are observable for all values of l and b. All the SNRs with $\Sigma$$>3\times10^{-22}$ Wm$^{-2}$Hz$^{-1}$sr$^{-1}$ can be observed in the interval 60$^o$$<$l$<300^o$. We have examined samples of PSRs and SNRs to estimate the birth rates of these objects in the region up to 3.2 kpc from the Sun and also in the Galaxy. The birth rate of PSRs is about one in 200 years and the birth rate of SNRs is about one in 65 years in our galaxy.Comment: revised versio

Synoptic Sky Surveys and the Diffuse Supernova Neutrino Background: Removing Astrophysical Uncertainties and Revealing Invisible Supernovae

The cumulative (anti)neutrino production from all core-collapse supernovae within our cosmic horizon gives rise to the diffuse supernova neutrino background (DSNB), which is on the verge of detectability. The observed flux depends on supernova physics, but also on the cosmic history of supernova explosions; currently, the cosmic supernova rate introduces a substantial (+/-40%) uncertainty, largely through its absolute normalization. However, a new class of wide-field, repeated-scan (synoptic) optical sky surveys is coming online, and will map the sky in the time domain with unprecedented depth, completeness, and dynamic range. We show that these surveys will obtain the cosmic supernova rate by direct counting, in an unbiased way and with high statistics, and thus will allow for precise predictions of the DSNB. Upcoming sky surveys will substantially reduce the uncertainties in the DSNB source history to an anticipated +/-5% that is dominated by systematics, so that the observed high-energy flux thus will test supernova neutrino physics. The portion of the universe (z < 1) accessible to upcoming sky surveys includes the progenitors of a large fraction (~ 87%) of the expected 10-26 MeV DSNB event rate. We show that precision determination of the (optically detected) cosmic supernova history will also make the DSNB into a strong probe of an extra flux of neutrinos from optically invisible supernovae, which may be unseen either due to unexpected large dust obscuration in host galaxies, or because some core-collapse events proceed directly to black hole formation and fail to give an optical outburst.Comment: 11 pages, 6 figure

Excitonic instability and electric-field-induced phase transition towards a two dimensional exciton condensate

We present an InAs-GaSb-based system in which the electric-field tunability of its 2D energy gap implies a transition towards a thermodynamically stable excitonic condensed phase. Detailed calculations show a 3 meV BCS-like gap appearing in a second-order phase transition with electric field. We find this transition to be very sharp, solely due to exchange interaction, and so, the exciton binding energy is greatly renormalized even at small condensate densities. This density gradually increases with external field, thus enabling the direct probe of the Bose-Einstein to BCS crossover.Comment: LaTex, 11 pages, 3 ps figures, To appear in PR

Technologies for measuring the dynamic parameters of rowing based on strain gauge systems

One of the criteria for the effectiveness of flatwater rowing biomechanics is the interaction of the athlete with the surface of the water by an oar, as well as the effectiveness of transferring the efforts developed by the athlete to the boat for its advancement. The quality of an athlete's move-ments with a paddle in rowing locomotives depends on the level of development of power abilities and can be quantified using strain gauge systems. However, the lack of recommendations describ-ing the specifics of the preparation and use of such systems in training process significantly reduce the degree of their use. The article discusses the technical features and methodological founda-tions of the use of strain gauge systems to measure the efforts of an athlete when interacting with an oar in flatwater kayaking and canoeing. To substantiate the choice of the scheme of loading and securing the paddle when graduating the strain gauge system, as well as the place of its direct attachment to the forearm, the authors carried out mathematical modeling of diagrams of bending moments arising on the paddle in response to external forces, as a result of which three options for the support and orientation of the paddle are presented, depending on the location of key sup-port points. To substantiate the method of attaching the strain gauge system to the forearm, a series of tests with paddle loading was carried out, as a result of which the presence of a linear relationship between the values of the external load and the readings of the strain gauge system was assessed, as well as the repeatability of the recorded data. Based on the results of the as-sessment, recommendations are presented for the practical application of the results of the study in assessing the speed and strength training of rowers on kayaks and canoes.Одним из критериев эффективности биомеханики гребли на плоской воде является взаимодействие спортсмена с поверхностью воды при помощи весла, а также эффективность передачи усилий, развиваемых спортсменом, на лодку для ее продвижения. Качество движений спортсмена с веслом в гребных тренажерах зависит от уровня развития силовых способностей и может быть количественно оценено с помощью тензометрических систем. Однако отсутствие рекомендаций, описывающих специфику подготовки и использования таких систем в тренировочном процессе, существенно снижает степень их использования. В статье рассматриваются технические особенности и методологические основы использования тензометрических систем для измерения усилий спортсмена при взаимодействии с веслом в плавании на плоских байдарках и каноэ. Для обоснования выбора схемы нагружения и закрепления лопатки при градуировке тензометрической системы, а также места ее непосредственного крепления к цевью, авторами было проведено математическое моделирование диаграмм изгибающих моментов, возникающих на лопатке в ответ на воздействие внешних сил, в результате которого были получены три представлены варианты крепления и ориентации лопасти в зависимости от расположения ключевых точек опоры. Для обоснования способа крепления тензометрической системы к предплечью была проведена серия испытаний с лопастной нагрузкой, в результате которых было оценено наличие линейной зависимости между значениями внешней нагрузки и показаниями тензометрической системы, а также повторяемость записанные данные. По результатам оценки представлены рекомендации по практическому применению результатов исследования при оценке скоростно-силовой подготовки гребцов на байдарках и каноэ

Mimicking diffuse supernova antineutrinos with the Sun as a source

Measuring the electron antineutrino component of the cosmic diffuse supernova neutrino background (DSNB) is the next ambitious goal for low-energy neutrino astronomy. The largest flux is expected in the lowest accessible energy bin. However, for E < 15 MeV a possible signal can be mimicked by a solar electron antineutrino flux that originates from the usual 8B neutrinos by spin-flavor oscillations. We show that such an interpretation is possible within the allowed range of neutrino electromagnetic transition moments and solar turbulent field strengths and distributions. Therefore, an unambiguous detection of the DSNB requires a significant number of events at E > 15 MeV.Comment: 4 pages, 1 figur

Models of coherent exciton condensation

That excitons in solids might condense into a phase-coherent ground state was proposed about 40 years ago, and has been attracting experimental and theoretical attention ever since. Although experimental confirmation has been hard to come by, the concepts released by this phenomenon have been widely influential. This tutorial review discusses general aspects of the theory of exciton and polariton condensates, focussing on the reasons for coherence in the ground state wavefunction, the BCS to Bose crossover(s) for excitons and for polaritons, and the relationship of the coherent condensates to standard lasers.Comment: 27 pages, 6 figures. Submitted for a special issue of J. Phys. Cond. Matt. associated with the EU network "Photon-mediated phenomena in semiconductor nanostructures

Persistent Spin Currents in Helimagnets

We demonstrate that weak external magnetic fields generate dissipationless spin currents in the ground state of systems with spiral magnetic order. Our conclusions are based on phenomenological considerations and on microscopic mean-field theory calculations for an illustrative toy model. We speculate on possible applications of this effect in spintronic devices.Comment: 9 pages, 6 figures, updated version as published, Journal referenc

The Relation Between the Surface Brightness and the Diameter for Galactic Supernova Remnants

In this work, we have constructed a relation between the surface brightness ($\Sigma$) and diameter (D) of Galactic C- and S-type supernova remnants (SNRs). In order to calibrate the $\Sigma$-D dependence, we have carefully examined some intrinsic (e.g. explosion energy) and extrinsic (e.g. density of the ambient medium) properties of the remnants and, taking into account also the distance values given in the literature, we have adopted distances for some of the SNRs which have relatively more reliable distance values. These calibrator SNRs are all C- and S-type SNRs, i.e. F-type SNRs (and S-type SNR Cas A which has an exceptionally high surface brightness) are excluded. The Sigma-D relation has 2 slopes with a turning point at D=36.5 pc: $\Sigma$(at 1 GHz)=8.4$^{+19.5}_{-6.3}$$\times10^{-12}$ D$^{{-5.99}^{+0.38}_{-0.33}}$ Wm$^{-2}$Hz$^{-1}$ster$^{-1}$ (for $\Sigma$$\le3.7\times10^{-21}$ Wm$^{-2}$Hz$^{-1}$ster$^{-1}$ and D$\ge$36.5 pc) and $\Sigma$(at 1 GHz)=2.7$^{+2.1}_{-1.4}$$\times$ 10$^{-17}$ D$^{{-2.47}^{+0.20}_{-0.16}}$ Wm$^{-2}$Hz$^{-1}$ster$^{-1}$ (for $\Sigma$$>3.7\times10^{-21}$ Wm$^{-2}$Hz$^{-1}$ster$^{-1}$ and D$<$36.5 pc). We discussed the theoretical basis for the $\Sigma$-D dependence and particularly the reasons for the change in slope of the relation were stated. Added to this, we have shown the dependence between the radio luminosity and the diameter which seems to have a slope close to zero up to about D=36.5 pc. We have also adopted distance and diameter values for all of the observed Galactic SNRs by examining all the available distance values presented in the literature together with the distances found from our $\Sigma$-D relation.Comment: 45 pages, 2 figures, accepted for publication in Astronomical and Astrophysical Transaction

Electronic properties and phase transitions in low-dimensional semiconductors

We present the first review of the current state of the literature on electronic properties and phase transitions in TlX and TlMX2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi- and photoconductivity, non-linear effects in their I-V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of TlX and TlMX2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor-metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. Electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed.Comment: 70 pages, 38 figure