371 research outputs found
Использование золошлаковых материалов теплоэнергетики в строительных материалах
The possible trends to improve the building-technical properties of dry ashes characteristics formed as a result of solid fuel combustion at thermal power stations are presented. The results of different fly-ash conditioning technologies application to widen the trends and to increase the volumes of their use in the construction materials and products.Представлены возможные направления улучшения строительно-технических характеристик сухих зол, образующихся при сжигании твердого топлива на тепловых электростанциях. Приведены результаты применения различных технологий кондиционирования свойств золы для расширения направлений и увеличения объемов их использования при производстве строительных материалов и изделий
D-branes on general N=1 backgrounds: superpotentials and D-terms
We study the dynamics governing space-time filling D-branes on Type II flux
backgrounds preserving four-dimensional N=1 supersymmetry. The four-dimensional
superpotentials and D-terms are derived. The analysis is kept on completely
general grounds thanks to the use of recently proposed generalized
calibrations, which also allow one to show the direct link of the
superpotentials and D-terms with BPS domain walls and cosmic strings
respectively. In particular, our D-brane setting reproduces the tension of
D-term strings found from purely four-dimensional analysis. The holomorphicity
of the superpotentials is also studied and a moment map associated to the
D-terms is proposed. Among different examples, we discuss an application to the
study of D7-branes on SU(3)-structure backgrounds, which reproduces and
generalizes some previous results.Comment: 50 pages; v2: table of contents, some clarifications and references
added; v3: typos corrected and references adde
Supersymmetric D-branes and calibrations on general N=1 backgrounds
We study the conditions to have supersymmetric D-branes on general {\cal N}=1
backgrounds with Ramond-Ramond fluxes. These conditions can be written in terms
of the two pure spinors associated to the SU(3)\times SU(3) structure on
T_M\oplus T^\star_M, and can be split into two parts each involving a different
pure spinor. The first involves the integrable pure spinor and requires the
D-brane to wrap a generalised complex submanifold with respect to the
generalised complex structure associated to it. The second contains the
non-integrable pure spinor and is related to the stability of the brane. The
two conditions can be rephrased as a generalised calibration condition for the
brane. The results preserve the generalised mirror symmetry relating the type
IIA and IIB backgrounds considered, giving further evidence for this duality.Comment: 23 pages. Some improvements and clarifications, typos corrected and
references added. v3: Version published in JHE
Influence of blast furnace slag type on physical and mechanical properties of Portland cement
Physical properties, grain, chemical and mineral compositions of blast-furnace slags selected from the dumps of JSC 'EVRAZ Nizhny Tagil metallurgical plant' and PJSC 'Nadezhdinski Metallurgical Plant' were studied. Also, the same parameters of granulated blast-furnace slag of JSC 'Mechel-Materialy' currently used by cement plants in the Ural region as a mineral additive during Portland cement grinding were investigated. By chemical composition all of them are acidic. In contrast to granulated slag which mainly contains the vitreous phase dump slags are well crystallized and mainly contain the minerals okermanite, mervinite and monticellite. Dump slags have a Student's t-criterion of more than 15.0, i.e. they can be used as a mineral additive during Portland cement grinding. The introduction of 20 % of the studied slags reduces the water demand of Portland cement of joint grinding and accelerates the setting of the cement paste, reduces the bending and compression strength compared to the additive-free cement. Slag-containing cements after 7 and 28 days of hardening have similar values of compressive strength: 27.2-29.2 and 41.1-43.0 MPa respectively, they are normally hardening and have a strength class of 42.5. Chemical, physical and mechanical properties of these cements meet the requirements of Russian Standard 31108-2016. © Published under licence by IOP Publishing Ltd
Utilization of final tailings concentration of titano-magnetite ores in Portland cement production
When producing iron ore concentrate at Kachkanarsk integrated mining works 2 types of wastes are formed, namely: final tailings of dry magnetic separation (DMS) and final tailings of wet magnetic separation (WMS). Final tailings of wet magnetic separation (WMS) are pulled off or dumped into disposal area up to 45mln tons annually causing great damages to the environment. These final tailings are finely dispersed materials, their chemical composition is oxides of silicon, aluminium, calcium and iron in general. All this allows to use the wastes under consideration to produce Portland cement clinker replacing clayey and iron components in the raw material mixture completely and limestone partially. The replacement of clay with final tailings of ore enrichment are suitable to manufacture clinker raw material mixture allowing to use two-component raw mix instead of three-component and four-component one thus simplifying the technology of cement production and improving the ecological situation in Sverdlovsk region. The utilization of final tailings for concentration of titano-magnetite ores decreases fuel consumption when burning clinker compared to the traditional compositions. Experimental cement meets all the requirements of the Russian Standard 10178 as to their chemical and physic-mechanical properties and have grade 500. © Published under licence by IOP Publishing Ltd
Deformations of calibrated D-branes in flux generalized complex manifolds
We study massless deformations of generalized calibrated cycles, which
describe, in the language of generalized complex geometry, supersymmetric
D-branes in N=1 supersymmetric compactifications with fluxes. We find that the
deformations are classified by the first cohomology group of a Lie algebroid
canonically associated to the generalized calibrated cycle, seen as a
generalized complex submanifold with respect to the integrable generalized
complex structure of the bulk. We provide examples in the SU(3) structure case
and in a `genuine' generalized complex structure case. We discuss cases of
lifting of massless modes due to world-volume fluxes, background fluxes and a
generalized complex structure that changes type.Comment: 52 pages, added references, added comment on ellipticity in appendix
B, made minor changes according to instructions referee JHE
Determination of the HQET Parameters from the Decay
We combine the resummations for radiative corrections and for the heavy quark
expansion to study the inclusive radiative decay . The
infrared renormalon ambiguity is also taken into account. Including both
theoretical and experimental uncertainties, we determine the allowed domain for
the HQET parameters and centered at GeV and GeV.Comment: IR renormalon ambiguity is include
Mirror symmetry in two steps: A-I-B
We suggest an interpretation of mirror symmetry for toric varieties via an
equivalence of two conformal field theories. The first theory is the twisted
sigma model of a toric variety in the infinite volume limit (the A-model). The
second theory is an intermediate model, which we call the I-model. The
equivalence between the A-model and the I-model is achieved by realizing the
former as a deformation of a linear sigma model with a complex torus as the
target and then applying to it a version of the T-duality. On the other hand,
the I-model is closely related to the twisted Landau-Ginzburg model (the
B-model) that is mirror dual to the A-model. Thus, the mirror symmetry is
realized in two steps, via the I-model. In particular, we obtain a natural
interpretation of the superpotential of the Landau-Ginzburg model as the sum of
terms corresponding to the components of a divisor in the toric variety. We
also relate the cohomology of the supercharges of the I-model to the chiral de
Rham complex and the quantum cohomology of the underlying toric variety.Comment: 50 pages; revised versio
Coisotropic D8-branes and Model-building
Up to now chiral type IIA vacua have been mostly based on intersecting
D6-branes wrapping special Lagrangian 3-cycles on a CY three-fold. We argue
that there are additional BPS D-branes which have so far been neglected, and
which seem to have interesting model-building features. They are coisotropic
D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional
submanifolds of the CY which are trivial in homology, but contain a worldvolume
flux that induces D6-brane charge on them. This induced D6-brane charge not
only renders the D8-brane BPS, but also creates D=4 chirality when two
D8-branes intersect. We discuss in detail the case of a type IIA Z2 x Z2
orientifold, where we provide explicit examples of coisotropic D8-branes. We
study the chiral spectrum, SUSY conditions, and effective field theory of
different systems of D8-branes in this orientifold, and show how the magnetic
fluxes generate a superpotential for untwisted Kahler moduli. Finally, using
both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like
type IIA vacua.Comment: 63 pages, 11 figures. Typos corrected and comments adde
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