On the gamma-ray emission of Type Ia Supernovae

A multi-dimension, time-dependent Monte Carlo code is used to compute sample gamma-ray spectra to explore whether unambiguous constraints could be obtained from gamma-ray observations of Type Ia supernovae. Both spherical and aspherical geometries are considered and it is shown that moderate departures from sphericity can produce viewing-angle effects that are at least as significant as those caused by the variation of key parameters in one-dimensional models. Thus gamma-ray data could in principle carry some geometrical information, and caution should be applied when discussing the value of gamma-ray data based only on one-dimensional explosion models. In light of the limited sensitivity of current gamma-ray observatories, the computed theoretical spectra are studied to revisit the issue of whether useful constraints could be obtained for moderately nearby objects. The most useful gamma-ray measurements are likely to be of the light curve and time-dependent hardness ratios, but sensitivity higher than currently available, particularly at relatively hard energies (~2-3 MeV), is desirable.Comment: 10 pages, 8 figures. Accepted by MNRAS. Minor changes to clarify discussion in Section

The Additional Line Component within the Iron K\alpha Profile in MCG-6-30-15: Evidence for Blob Ejection?

The EPIC data of MCG -6-30-15 observed by XMM-Newton were analyzed for the complexities of the iron K-alpha line. Here we report that the additional line component (ALC) at 6.9 keV undoubtedly appears within the broad iron Kalpha; line profile at the high state, whereas it disappears at the low state. These state-dependent behaviors exclude several possible origins and suggest an origin of the ALC in matter being ejected from the vicinity of the black hole. At the low state, the newborn blob ejected from the accretion disk is so Thomson-thick that hard X-rays are blocked from ionizing the old blobs, leading to the disappearance of the ALC. When the blob becomes Thomson-thin as a result of expansion, the hard X-ray will penetrate it and ionize the old ones, emitting the ALC at the high state. The blob ejection is the key to switching the ALC on or off.Comment: 6 pages, 4 Figure

A semianalytical approach to spatial averaging of hydraulic conductivity in heterogeneous aquifers

Numerical models of groundwater flow require hydraulic conductivity values to be assigned to the grid blocks covering the flow domain. However, field-measured conductivities tend to be measured at a different scale (usually smaller) than that of the grid blocks. The present paper describes a novel approach for upscaling field values to block-scale, which combines the rigorous result of small-value perturbation analysis with a plausible generalization of the first-order results to large variance. Also the correlation lengths are assumed to be comparable to block size. Steady-state flow through a block of stochastically heterogeneous medium with constant hydraulic head values at the two opposite sides is analyzed. An upscaling rule and relationship is obtained between the local-scale hydraulic conductivity and the expected mean and variance of block-scale conductivity, where the block size is comparable with the correlation scale of the local conductivity field. The rather simple expressions obtained are validated using data from numerical experiments. Furthermore, a generalized spatial power-averaging method to calculate the block-scale conductivity from values of local-scale conductivity is developed, in which the exponent value is given as a function of the ratios of flow domain dimensions to the respective correlation lengths

Evaluation of the microstructure and mechanical properties of a new modified cast and laser-melted AA7075 alloy

The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy. © 2019 by the authors.Ministry of Science and Higher Education of the Russian FederationThe author (Asmaa M. Khalil) gratefully acknowledges financial support from the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of MISiS (Support project for young research engineers)

Proceedings of the joint Russian-American hydrogeology seminar

Hydrogeology research has been very active in both Russia and the US because of the concerns for migration of radioactive and chemical contaminants in soils and geologic formations, as well as for water problems related to mining and other industrial operations. Russian hydrogeologists have developed various analysis and field testing techniques, sometimes in parallel with US counterparts. These Proceedings come out of a Seminar held to bring together a small group (about 15) of active Russian researchers in geologic flow and transport associated with the disposal of radioactive and chemical wastes either on the soils or through deep injection wells, with a corresponding group (about 25) of American hydrogeologists. The meeting was intentionally kept small to enable informal, detailed and in-depth discussions on hydrogeological issues of common interest. Out of this interaction, the authors hope that, firstly, they will have learned from each other and secondly, that research collaborations will be established where there is the opportunity. This proceedings presents the summaries and viewgraphs from the presentations. What cannot be conveyed here is the warm and cooperative atmosphere of these interactions, both inside and outside the formal sessions, which may well lead to future collaborations

Investigating Students' Experiences with Collaboration Analytics for Remote Group Meetings.

Remote meetings have become the norm for most students learning synchronously at a distance during the ongoing coronavirus pandemic. This has motivated the use of artificial intelligence in education (AIED) solutions to support the teaching and learning practice in these settings. However, the use of such solutions requires new research particularly with regards to the human factors that ultimately shape the future design and implementations. In this paper, we build on the emerging literature on human-centred AIED and explore students’ experiences after interacting with a tool that monitors their collaboration in remote meetings (i.e., using Zoom) during 10 weeks. Using the social translucence framework, we probed into the feedback provided by twenty students regarding the design and implementation requirements of the system after their exposure to the tool in their course. The results revealed valuable insights in terms of visibility (what should be made visible to students via the system), awareness (how can this information increase students’ understanding of collaboration performance), and accountability (to what extent students take responsibility of changing their behaviours based on the system’s feedback); as well as the ethical and privacy aspects related to the use of collaboration analytics tools in remote meetings. This study provides key suggestions for the future design and implementations of AIED systems for remote meetings in educational settings

Testing Comptonizing coronae on a long BeppoSAX observation of the Seyfert 1 galaxy NGC 5548

We test accurate models of Comptonization spectra over the high quality data of the BeppoSAX long look at NGC 5548, allowing for different geometries of the scattering region, different temperatures of the input soft photon field and different viewing angles. We find that the BeppoSAX data are well represented by a plane parallel or hemispherical corona viewed at an inclination angle of 30$^{\circ}$. For both geometries the best fit temperature of the soft photons is close to 15$^{+3}_{-9}$ eV. The corresponding best fit values of the hot plasma temperature and optical depth are $kT_{\rm e}\simeq$ 250--260 keV and $\tau\simeq$ 0.16--0.37 for the slab and hemisphere respectively. These values are substantially different from those derived fitting the data with a power-law + cut off approximation to the Comptonization component (kT_{\rm e}\lta 60 keV, $\tau\simeq$ 2.4). This is due to the fact that accurate Comptonization spectra in anisotropic geometries show "intrinsic" curvature which reduces the necessity of a high energy cut-off. The Comptonization parameter derived for the slab model {is} larger than predicted for a two phase plane parallel corona in energy balance, suggesting that a more ``photon-starved'' geometry is necessary. The spectral softening detected during a flare which occurred in the central part of the observation corresponds to a decrease of the Comptonization parameter, probably associated with an increase of the soft photon luminosity, the {hard} photon luminosity remaining constant.Comment: 36 pages, 9 figures, accepted by Ap

НЕКОТОРЫЕ ОСОБЕННОСТИ УЧЕТА МОРАЛЬНОГО ИЗНОСА ПРИ ВЫБОРЕ ВАРИАНТОВ СТРОИТЕЛЬСТВА, РЕМОНТА ИЛИ РЕКОНСТРУКЦИИ ЗДАНИЙ

In the XXI century moral depreciation concept comprises not only deterioration of outside appearance of construction elements in the course of time but accelerated fashion changes in respect of interior design and rapid increase in technical level for residence buildings. For this reason if average rate of building dilapidation in the buildings of series 1–335, 1–335А and 1–464А constructed in Minsk within the period of 1957–1975 and being operated till 2005–2006 has constituted 25–29 % and their moral depreciation has been equal to more than 40 % then rate of the moral depreciation has significantly increased in the XXI century. Such situation requires execution of special investigations. High operating rates of refinancing have led to the necessity for record keeping of initial expenses and repairability levels because selection of building construction, repair or reconstruction variant depends on these parameters. Repairability classification of main elements of residence buildings and premises has been proposed for regulation of such selection procedure. In this case it is recommended to take into account technological effectiveness of repair and technical service, verifiability, accessibility, easy dismountability, substitutability and interchangeability of construction elements and technical devices. The paper presents nomograms that permit to make easier practical calculations on determination of cost-efficient time period for operation of the element prior to its substitution at various refinancing rates and also for comparison of relative initial expenses according to time service. В XXI в. в понятие морального износа жилья входит не только ухудшение с течением времени внешнего вида строительных элементов, но и ускоренная смена моды на внутренний вид и быстрое повышение технического уровня оборудования жилых помещений. Поэтому, если в зданиях серий 1–335, 1–335А и 1–464А, построенных в Минске с 1957 по 1975 год, при эксплуатации до 2005–2006 гг. cредний уровень физического износа составлял 25–29 %, а моральный износ – более 40 %, то в XXI в. скорость морального износа существенно увеличилась. Эта ситуация требует специальных исследований. Действующие в настоящее время высокие ставки рефинансирования привели к необходимости учета первоначальных затрат и уровней ремонтопригодности, от которых зависит выбор варианта строительства, ремонта или реконструкции зданий. Для упорядочения такого выбора предложена классификация ремонтопригодности основных элементов жилых зданий и помещений. При этом учитываются технологичность ремонта и технического обслуживания, а также контролируемость, доступность, легкосъемность, заменяемость и взаимозаменяемость строительных элементов и технических устройств. В статье приведены номограммы, позволяющие облегчить практические расчеты по определению экономически выгодного промежутка времени эксплуатации элемента перед его заменой на новый при различных ставках рефинансирования, а также для сравнения относительных первоначальных затрат в зависимости от срока службы.

ВЕРОЯТНОСТНАЯ ОЦЕНКА НЕОБХОДИМОСТИ И ВИДА РЕМОНТА ЗДАНИЯ И ЕГО ЭЛЕМЕНТОВ

The existing normative documents consider 100%-wear as an extreme limit for operation of constructional element or structure. While using probabilistic rate of physical wear and determining the necessity in repair 100%-wear is assumed on the basis of physical state of constructional elements and structures that corresponds to minimum allowable reliability level. The paper contains description of a new method for determination of necessity in repair and its type for building and its elements on the basis of probabilistic assessment of their physical wear which is mated with residual reliability. Such method of calculation is carried out by determination of initial and threshold limit values for failure or destruction probabilities and density of probability distribution. According to these values time wear rate is selected and it ensures higher specific growth of failure and destruction probabilities at initial running period of the element operation. Then a planned wear assessment of building elements is carried out on a periodical basis. In the case when the planned rate of probability growth is equal to 0.4–0.5 from the critical value it is necessary to execute a mean current repair and when the probability level reaches value of 0.8 or even more in comparison with a critical one then it is necessary to carry out a capital repair in order to reduce probability value which will be close to the initial one. Such planned assessment of physical wear is made according to regulatory indirect indicators and in the case when intensity of physical wear exceeds the planned level it is necessary to determine strength characteristics of building elements while using instrumental physical methods. Taking into account a relative novelty of probabilistic assessment of necessity in repair and its type for building and its elements during operational period it is recommendable to carry out additional theoretical and statistic investigations in order to include this method in normative technical construction documents. В нынешних нормативных документах 100%-й износ принимается за крайний предел эксплуатации строительного элемента или конструкции. При использовании вероятностной степени физического износа и определении необходимости ремонта за 100% следует принимать физическое состояние строительных элементов и конструкций, соответствующее минимально допустимому уровню надежности. В статье приведено описание нового метода определения необходимости и вида ремонта здания и его элементов на базе вероятностной оценки их физического износа, которая сопрягается с остаточной надежностью. Такой метод расчета производится путем определения начального и предельно-допустимого значений вероятности отказа или разрушения и плотности распределения вероятности, по которым выбирают масштаб износа по времени, обеспечивающий повышенный удельный рост вероятности отказа или разрушения в начальный обкаточный период эксплуатации элемента. Затем периодически проводится плановая оценка износа элементов здания. В случае превышения планового уровня роста вероятности 0,4–0,5 от критического выполняется средний ткущий ремонт, а в случае достижения уровня вероятности 0,8 и более от критического – капитальный ремонт для снижения значения вероятности до близкого к начальному. Текущая плановая оценка физического износа производится по нормативным косвенным признакам, а при превышении интенсивности физического износа планового уровня немедленно переходят к определению прочностных свойств элементов здания приборными физическими методами. Учитывая относительную новизну вероятностной оценки необходимости и вида ремонта здания и его элементов в процессе их эксплуатации, следует выполнить дополнительные теоретические и статистические исследования для включения этого метода в строительную нормативно-техническую документацию