Type IIA Orientifold Limit of M-Theory on Compact Joyce 8-Manifold of Spin(7)-Holonomy

We show that M-theory compactified on a compact Joyce 8-manifold of $Spin(7)$-holonomy, which yields an effective theory in $D = 3$ with $\N$ = 1 supersymmetry, admits at some special points in it moduli space a description in terms of type IIA theory on an orientifold of compact Joyce 7-manifold of $G_2$-holonomy. We find the evidence in favour of this duality by computing the massless spectra on both M-thory side and type IIA side. For the latter, we compute the massless spectra by going to the orbifold limit of the Joyce 7-manifold.Comment: 26 pages, 2 eps figures, Latex file, two references and one footnote added, corrected some typo

Supersymmetric Boost on Intersecting D-branes

We study the effect of the Born-Infeld electric field on the supersymmetric configuration of various composite D-branes. We show that the generic values of the electric field do not affect the supersymmetry but, as it approaches $1/2\pi\alpha'$ keeping the magnetic field finite, various combinations of the magnetic fields allow up to 8 supersymmetries. We also explore the unbroken supersymmetries for two intersecting D-strings which are in uniform or relative motion. For a finite uniform Lorentz boost, 16 supersymmetries are guaranteed only when they are parallel. For an infinite one, 8 supersymmetries are preserved only when both the D-strings are oriented to the forward or backward direction of the boost. Under a finite relative boost, 8 supersymmetries are preserved only when the intersecting angle is less than $\pi/2$ and the intersecting point moves at the speed of light. As for an infinite relative boost, 8 supersymmetries are preserved regardless of the values of the intersecting angle.Comment: 27 pages using REVTeX4, 7 figure

Multi-resolution texture classification based on local image orientation

The aim of this paper is to evaluate quantitatively the discriminative power of the image orientation in the texture classification process. In this regard, we have evaluated the performance of two texture classification schemes where the image orientation is extracted using the partial derivatives of the Gaussian function. Since the texture descriptors are dependent on the observation scale, in this study the main emphasis is placed on the implementation of multi-resolution texture analysis schemes. The experimental results were obtained when the analysed texture descriptors were applied to standard texture databases

Catalytic conversion of methanol to larger organic molecules over crystalline forsterite: laboratory study and astrophysical implications

Laboratory catalytic reactions of methanol over heated crystalline silicates (forsterite) lead to the formation of gas-phase olefinic and polycyclic aromatic hydrocarbon (PAH) molecules, and are of potential importance in astrophysical environments including hot molecular cores, protoplanetary disks and shocks. In our experiments the methanol reagent, together with intermediate and product gas-phase molecular species were detected using time-of-flight mass-spectrometry (TOF-MS). A solid deposited on the crystalline forsterite surface was examined subsequently using high-resolution transmission electron microscopy and thermal gravimetric techniques and found to comprise amorphous and graphitic carbon. The chemical players in this work – gas-phase methanol, crystalline silicates and PAHs, have been identified spectroscopically in a range of astrophysical environments including young and evolved stars, protoplanetary disks, comets, captured dust particles and meteorites. It is envisaged that reactions on bare dust grains as studied here both experimentally and theoretically through DFT calculations, can have implications for chemical transformations and conversions, in forming PAH molecules and potentially in the synthesis of prebiotic molecules

Impacts of environmental factors and human disturbance on composition of roadside vegetation in Xishuangbanna National Nature Reserve of Southwest China

AbstractVegetation-disturbance-environment relationships in Xishuangbanna Nature Reserve (XNR) was examined using multivariate analysis to understand the impacts of environmental factors and human disturbance on vegetation along the highway corridor. The results show that native forests were the best habitat for protected/endangered species and native species. The exotic plants Eupatorium odoratum and Eupatorium adenophora were found primarily in secondary forests and their presence was positively associated with altitude and soil potassium concentrations. The distribution of two protected plants, Phoebe nanmu and Pometia tomentosa, was negatively associated with road disturbance. Understanding the complex effects of environmental factors and human disturbance is key for developing conservation and restoration strategies for roadside plant ecosystems

Null Brane Intersections

We study pairs of planar D-branes intersecting on null hypersurfaces, and other related configurations. These are supersymmetric and have finite energy density. They provide open-string analogues of the parabolic orbifold and null-fluxbrane backgrounds for closed superstrings. We derive the spectrum of open strings, showing in particular that if the D-branes are shifted in a spectator dimension so that they do not intersect, the open strings joining them have no asymptotic states. As a result, a single non-BPS excitation can in this case catalyze a condensation of massless modes, changing significantly the underlying supersymmetric vacuum state. We argue that a similar phenomenon can modify the null cosmological singularity of the time-dependent orbifolds. This is a stringy mechanism, distinct from black-hole formation and other strong gravitational instabilities, and one that should dominate at weak string coupling. A by-product of our analysis is a new understanding of the appearance of 1/4 BPS threshold bound states, at special points in the moduli space of toroidally-compactified type-II string theory.Comment: Tex file, uses harvmac, 24 pages with 5 figures. Corrected typos and added references. Final version to appear in JHE

Two tricritical lines from a Ginzburg-Landau expansion: application to the LOFF phase

We study the behavior of the two plane waves configuration in the LOFF phase close to T=0. The study is performed by using a Landau-Ginzburg expansion up to the eighth order in the gap. The general study of the corresponding grand potential shows, under the assumption that the eighth term in the expansion is strictly positive, the existence of two tricritical lines. This allows to understand the existence of a second tricritical point for two antipodal plane waves in the LOFF phase and justifies why the transition becomes second order at zero temperature. The general analysis done in this paper can be applied to other cases.Comment: LaTex file, 15 pages, 6 figure

Non-linear stability in photogravitational non-planar restricted three body problem with oblate smaller primary

We have discussed non-linear stability in photogravitational non-planar restricted three body problem with oblate smaller primary. By photogravitational we mean that both primaries are radiating. We normalised the Hamiltonian using Lie transform as in Coppola and Rand (1989). We transformed the system into Birkhoff's normal form. Lie transforms reduce the system to an equivalent simpler system which is immediately solvable. Applying Arnold's theorem, we have found non-linear stability criteria. We conclude that $L_6$ is stable. We plotted graphs for $(\omega_1, D_2).$ They are rectangular hyperbola.Comment: Accepted for publication in Astrophysics & Space Scienc

Optimization of Residual Stresses in Laser-Mixed WC(Co,Ni) Coatings

A ternary mixture of tungsten carbide (WC), cobalt (Co), and nickel (Ni) powders is prepared to form ceramic-metal composite coatings employed for laser cladding of 40Cr steel. This coating is investigated using the mixture design to evaluate the influence of its ratios on the residual stresses in the clads. The WC/Co/Ni ternary mixture exhibits higher residual stresses than those of the Co/Ni or WC/Ni binary mixtures, except for the WC/Co one. Single WC, Co, or Ni designs illustrate a high sensitivity of residual stresses, cracks pass through the interior of WC particles rather than around them, and the cracks mostly propagate along the eutectic phases at 50%Co–50%WC. A reduced special quartic model in the mixture design exhibits excellent fit, predicted and experimental values of residual stresses for these laser clads are in good agreement.Изготовлена трехкомпонентная смесь порошков карбида вольфрама (WC), кобальта (Со) и никеля (Ni) для получения металлокерамических композиционных покрытий, используемых для плакирования стали 40 Сr. При исследовании покрытия подбирался состав смеси для оценки влияния соотношения ее компонентов на остаточные напряжения в плакировках. Трехкомпонентная смесь WC/Co/Ni имеет более высокие остаточные напряжения, чем двухкомпонентные смеси Co/Ni или WC/Ni, за исключением WC/Co. Однокомпонентные составы WC, Co или Ni обусловливают высокую чувствительность остаточных напряжений, трещины скорее проходят внутри частиц WC, чем вокруг них, рост трещин происходит главным образом вдоль эвтектических фаз для состава 50%Co 50%WC. Приведенная специальная модель четвертого порядка показывает отличное соответствие при подборе состава смеси, хорошо согласуются между собой прогнозируемые и экспериментальные значения остаточных напряжений в лазерных плакировках.Виготовлена трихкомпонентна суміш порошків карбіду вольфраму (WC), кобальту (Со) і нікелю (Ni) для отримання металокерамічних композиційних покриттів, що використовуються для плакованої стали 40 Сг. При дослідженні покриття підбирався склад суміші для оцінки впливу співвідношення її компонентів на залишкові напруження в плакіровкі. Трикомпонентна суміш WC / Co / Ni має більш високі залишкові напруження, ніж двокомпонентні суміші Co / Ni або WC / Ni, за винятком WC / Co. Однокомпонентні склади WC, Co або Ni зумовлюють високу чутливість залишкових напружень, тріщини швидше проходять всередині частинок WC, ніж навколо них, зростання тріщин відбувається головним чином уздовж евтектичних фаз для складу 50% Co-50% WC. Наведена спеціальна модель четвертого порядку показує відмінне відповідність при підборі складу суміші, добре узгоджуються між собою прогнозовані і експериментальні значення залишкових напружень в лазерних плакіровках