Structural regularities of welded seam between Ti-Tib and vanadium with 12X18H10T interlayer by using electron beam welding

Досліджувалися можливості отримання зварного з'єднання сплавуТі-TiB заустенітної сталлю 12Х18Н10Т шляхом формування проміжного шару в зварному з'єднанні. Для цього на поверхні зразка сплаву Ті-TiB формувався легований прошарок, що містить армуючі волокна TiB і основні легуючі елементи стали 12Х18Н10Т. Було визначено, що такий прошарок одержується застосуванням електронно-променевого зварювання з'єднання сплаву Ті-TiB з ванадієм через фольгу зі сталі 12Х18Н10Т. Було виявлено, що мікроструктура сформованого прошарку сплаву на основі титану іванадію з легуючими добавками має характер металевої матриці, армованої мікроволокнами, склад яких відповідає боріду титану, легованого ванадієм. Було виявлено, що для армуючих боридних мікроволокон в мікроструктур і прошарку сплаву на основі титану і ванадію характерною особливістю є їх значне подрібнення в порівнянні з вихідним сплавом Ті-TiB. Крім того, в цьому прошарку в зоні розпаду первинних борідів титану, ініційованого впливом електронного променя, були виявлені фазові утворення за елементним складом близькі Ti2B. В результаті було зроблено припущення, що прошарок сплаву на основі Ti (63-68 at.%) І V (18-25 at.%) із легуючими добавками (Fe, Cr, Ni, B, C), сформований на поверхні сплаву Ті -TiB, перспективний для використання для електронно-променевого зварювання сталі 12Х18Н10Т зі сплавом Ті-TiB.Possibilities of obtaining and using an intermediate layer for joining of Ti-TiB and austenitic steel 12X18H10T (analog of AISI 321; 1.4541; X10CrNiTi18-10) were studied. An alloyed interlayer with TiB reinforcing fibers and the main alloying elements of 12X18H10T steel was formed on the surface of the Ti-TiB sample. Such interlayer was formed during electron beam welding of Ti-TiB with vanadium using foil made of 12X18H10T steel. The microstructure of the interlayer consists of a metal matrix reinforced with microfibers. It’s composition corresponds to vanadium-alloyed titanium boride. In comparison to the initial Ti-TiB alloy, significant grinding of reinforcing boride microfibers in the interlayer microstructure was observed. Besides, the phase formations close to Ti2B in zone of primary titanium borides decomposition in the interlayer, initiated by electron beam were determined. As a result, application of Ti (63–68 at. %) and V (18–25 at. %) based interlayer with alloying additives (Fe, Cr, Ni, B, C) has great potential for utilization in electron-beam welding of 12Х18Н10Т steel with Ti-TiB alloy.Исследовались возможности получения и использования промежуточной прослойки для выполнения сварного соединения сплава Ті-TiB с аустенитной сталью 12Х18Н10Т (аналоги AISI 321, 1.4541, X10CrNiTi18-10). Для этого на поверхности образца сплава Ті-TiB формировалась легированная прослойка, содержащая армирующие волокна TiB и основные легирующие элементы стали 12Х18Н10Т. Было определено, что такая прослойка получается применением электронно-лучевой сварки соединения сплава Ті-TiB с ванадием через фольгу из стали 12Х18Н10Т. Было выявлено, что микроструктура сформированной прослойки сплава на основе титана и ванадия с легирующими добавками имеет характер металлической матрицы, армированной микроволокнами, состав которых соответствует бориду титана, легированногованадием. Былообнаружено, что для армирующих боридных микроволокон в микроструктуре прослойки сплава на основе титана и ванадия характерной особенностью является их значительно еизмельчение в сравнении с исходным сплавом Ті-TiB. Кроме того, в этой прослойке в зоне распада первичных боридо втитана, инициированного влиянием электронного луча, были обнаружены фазовые образования по элементному составу близкие Ti2B. В результате было сделано предположение, что прослойка сплава на основе Ti (63–68 at. %) и V (18–25 at. %) с легирующими добавками (Fe, Cr, Ni, B, C), сформированная на поверхности сплава Ті-TiB, перспективна для использования для электронно-лучевой сварки стали 12Х18Н10Т со сплавом Ті-TiB

The Expanding Fireball of Nova Delphini 2013

A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages could result from interactions with the companion during the common envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion. Studying the structure of novae during the earliest phases is challenging because of the high spatial resolution needed to measure their small sizes. Here we report near-infrared interferometric measurements of the angular size of Nova Delphini 2013, starting from one day after the explosion and continuing with extensive time coverage during the first 43 days. Changes in the apparent expansion rate can be explained by an explosion model consisting of an optically thick core surrounded by a diffuse envelope. The optical depth of the ejected material changes as it expands. We detect an ellipticity in the light distribution, suggesting a prolate or bipolar structure that develops as early as the second day. Combining the angular expansion rate with radial velocity measurements, we derive a geometric distance to the nova of 4.54 +/- 0.59 kpc from the Sun.Comment: Published in Nature. 32 pages. Final version available at http://www.nature.com/nature/journal/v515/n7526/full/nature13834.htm

The Prosensory Function of Sox2 in the Chicken Inner Ear Relies on the Direct Regulation of Atoh1

The proneural gene Atoh1 is crucial for the development of inner ear hair cells and it requires the function of the transcription factor Sox2 through yet unknown mechanisms. In the present work, we used the chicken embryo and HEK293T cells to explore the regulation of Atoh1 by Sox2. The results show that hair cells derive from Sox2-positive otic progenitors and that Sox2 directly activates Atoh1 through a transcriptional activator function that requires the integrity of Sox2 DNA binding domain. Atoh1 activation depends on Sox transcription factor binding sites (SoxTFBS) present in the Atoh1 3′ enhancer where Sox2 directly binds, as shown by site directed mutagenesis and chromatin immunoprecipitation (ChIP). In the inner ear, Atoh1 enhancer activity is detected in the neurosensory domain and it depends on Sox2. Dominant negative competition (Sox2HMG-Engrailed) and mutation of the SoxTFBS abolish the reporter activity in vivo. Moreover, ChIP assay in isolated otic vesicles shows that Sox2 is bound to the Atoh1 enhancer in vivo. However, besides activating Atoh1, Sox2 also promotes the expression of Atoh1 negative regulators and the temporal profile of Atoh1 activation by Sox2 is transient suggesting that Sox2 triggers an incoherent feed-forward loop. These results provide a mechanism for the prosensory function of Sox2 in the inner ear. We suggest that sensory competence is established early in otic development through the activation of Atoh1 by Sox2, however, hair cell differentiation is prevented until later stages by the parallel activation of negative regulators of Atoh1 function

Land, Environmental Externalities and Tourism Development

In a two sectors dynamic model we analyze the process of tourism development based on the accumulation of capital (building of tourism facilities) and the reallocation of land from traditional activities to the tourism sector. The model incorporates the conflict between occupation of the territory by the tourism facilities, other productive activities and availability of cultural, natural and environmental assets that are valued by residents and visitors. We characterize the process of tourism development in two settings: the socially optimal solution and a situation where the costs of tourism expansion are external to the decision makers, where externalities on residents as well as intraindustry externalities are considered. Regarding the optimal solution, we show that it is optimal to limit tourism expansion before it reaches its maximum capacity even in a context where the economic attractiveness of tourism relative to other productive sectors rise continuously. However, in this context and when all the costs of tourism development are externalities the only limit to tourism quantitative expansion is its maximum capacity determined by the availability of land. Finally, we show that excessive environmental degradation from the future generations' point of view is not a problem of discounting the future but rather a problem of externalities that affects negatively the current and future generations

Optimal Afforestation Contracts with Asymmetric Information on Private Environmental Benefits

We investigate the problem of subsidising afforestation when private information exists with respect to the level of private utility derived from the project. We develop a simple model that allows for an intelligent design of contracts when information is asymmetric. The model involves the Principal and two groups of agents (landowners): a green' group deriving high private utility from the projects and a conventional' group deriving lower utility. Afforestation projects may be produced in different environmental quality, and we distinguish between two cases, a high quality and a low quality project. We find that the optimal set of contracts under asymmetric information involves two different contracts. One in which green landowners are somewhat overcompensated for projects of high quality, and one where conventional landowners are offered contracts including lower quality projects, compared to the symmetric case, but with compensation equal to his indifference payment. It is the ability to reduce quality requirements along with subsidies offered that allows for revelation of the private information. Finally, we discus how the results obtained may be used in the implementation of incentive schemes

SOX2 Co-Occupies Distal Enhancer Elements with Distinct POU Factors in ESCs and NPCs to Specify Cell State

SOX2 is a master regulator of both pluripotent embryonic stem cells (ESCs) and multipotent neural progenitor cells (NPCs); however, we currently lack a detailed understanding of how SOX2 controls these distinct stem cell populations. Here we show by genome-wide analysis that, while SOX2 bound to a distinct set of gene promoters in ESCs and NPCs, the majority of regions coincided with unique distal enhancer elements, important cis-acting regulators of tissue-specific gene expression programs. Notably, SOX2 bound the same consensus DNA motif in both cell types, suggesting that additional factors contribute to target specificity. We found that, similar to its association with OCT4 (Pou5f1) in ESCs, the related POU family member BRN2 (Pou3f2) co-occupied a large set of putative distal enhancers with SOX2 in NPCs. Forced expression of BRN2 in ESCs led to functional recruitment of SOX2 to a subset of NPC-specific targets and to precocious differentiation toward a neural-like state. Further analysis of the bound sequences revealed differences in the distances of SOX and POU peaks in the two cell types and identified motifs for additional transcription factors. Together, these data suggest that SOX2 controls a larger network of genes than previously anticipated through binding of distal enhancers and that transitions in POU partner factors may control tissue-specific transcriptional programs. Our findings have important implications for understanding lineage specification and somatic cell reprogramming, where SOX2, OCT4, and BRN2 have been shown to be key factors