Sergey Volkov

A Web-Based Platform for Publication and Distributed Execution of Computing Applications

Researchers increasingly rely on using web-based systems for accessing and running scientific applications across distributed computing resources. However existing systems lack a number of important features, such as publication and sharing of scientific applications as online services, decoupling of applications from computing resources and providing remote programmatic access. This paper presents Everest, a Web-based platform for researchers supporting publication, execution and composition of applications running across distributed computing resources. Everest addresses the described challenges by relying on modern Web technologies and cloud computing models. It follows the Platform as a Service (PaaS) cloud delivery model by providing all its functionality via remote Web and programming interfaces. Any application added to Everest is automatically published both as a user-facing Web form and a Web service. Another distinct feature of Everest is the ability to attach external computing resources by any user and flexibly use these resources for running applications. The paper provides an overview of the platforms architecture and its main components, describes recent developments, presents results of experimental evaluation of the platform and discusses remaining challenges.

Synthesis, crystal structure and thermal expansion of a novel borate, Ba3Bi2(BO3)4

Abstract Single crystals of novel metastable borate Ba3Bi2(BO3)4, were obtained from melt with stoichiometric composition. The compound is structurally related to the A3Ln2(BO3)4 family of luminescent borates (A = Ca, Sr, Ba; Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb). The crystal structure was solved by direct methods and refined to R = 0.041 (wR = 0.045), orthorhombic, Pnma, a = 7.9508(5), b = 17.399(1), c = 8.9791(5) A˚ , V = 1242.1(1) A˚ 3, Z = 4. The structure contains isolated BO3 triangles linked through Ba2+and Bi3+ cations distributed among three cation sites, M1, M2 and M3. The mixture of the Ba3Bi2(BO3)4 and BaBiBO4 phases in the ~1 : 1 ratio was investigated by means of high-temperature X-ray powder diffraction in air. Ba3Bi2(BO3)4 demonstrates an anisotropic thermal expansion with the following coefficients: aa = 16, ab = 11, ac = 11, aV = 38 x 10-6 K-1 at 25 ºC. The anisotropy increases on heating: aa = 32, ab=-2, ac = 7, aV = 37 x 10-6 K-1 at 700 ºC. The reason for the strong anisotropy of thermal expansion is the preferable orientation of the BO3 triangles.

Crystal structure of new polymorphic modification β-Ca3B2SiO8, β-α phase transition and thermal expansion of α- and β-modifications

Single crystals of the β-Ca3B2SiO8 new monoclinic modification have been obtained by cooling the melt of a stoichiometric composition. The crystal structure has been determined from the single crystal X-ray diffraction data and refined with R = 0.059 (wR = 0.069) in the monoclinic space group P21/m. The thermal behavior of the synthetic borosilicate has been studied. At 472 ± 5°С, a reversible phase transition of the first order occurs, leading to the formation of the orthorhombic α-Ca3B2SiO8 modification. The thermal expansion of α- and β-modifications of Ca3B2SiO8 is anisotropic: (α11 = 15, α22 = 16, α33 =–1, αV = 30 × 10–6°С–1) and α11 = 9, α22 = 28, α33 = 1, αV = 38 × 10–6°C–1, respectively.

Incommensurate modulation and thermal expansion of Sr3B2 + xSi1 − xO8 − x/2 solid solutions

Crystal structures of Sr3B(2 + x)Si(1 - x)O(8 - x/2) solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0βγ)000(0βγ)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P2(1)/n(0βγ). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.

Crystal structures and thermal expansion of Sr1–xBaxBi2B2O7 solid solutions

A series of Sr1–xBaxBi2B2O7 solid solutions (x = 0–1) have been synthesized by crystallization from glass ceramics. The crystal structures of solid solutions at x = 0.65 and x = 1 were solved by direct methods of X-ray diffraction from single crystal data and refined in a reduced cell (

Thermal behavior of borate BaBiBO4

{a_{Ba}}{\kern 1pt} = {a_{Sr}}/\sqrt 3

RietveldToTensor : Program for Processing Powder X-Ray Diffraction Data under Variable Conditions

) relative to SrBi2B2O7 in the same space group P63. Using the Rietveld method, the phase transition range at x = 0.65–0.70 with a reduction of the unit cell has been revealed. As was shown by method of high-temperature powder X-ray diffraction, the solid solutions demonstrated an anisotropic thermal expansion (TE) upon heating in air.

Forms of solid solution ordering upon decreasing temperature

Abstract The low-temperature polymorph β-Ca11B2Si4O22 crystallizes as a monoclinic structure [space group is P21/c, a=14.059(9), b=6.834(5), c=10.597(7) Å, β=100.735(8)°]. The crystal investigated by single-crystal X-ray diffraction was a twin composed of six individuals. The crystal structure is similar to that of mineral spurrite, Ca5(SiO4)2CO3, and can be described as a framework of [CaO5] and [CaO6] polyhedra, the cavities of which are filled with [SiO4] and [BO3] groups. The orientation relationship of twin domains was investigated by electron backscatter diffraction (EBSD). Thermal expansion was studied by high-temperature X-ray powder diffraction. It is slightly anisotropic: α11=10, α22=16, α33=12×10−6°C−1 at 200°C.