Sharif Digital Repository

The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented for correlation between external pressure and heat transfer coefficient. Acceptable... 

Conformational diseases have been investigated extensively in recent years; as a result, a number of drug candidates have been introduced as amyloid inhibitors; however, no effective therapies have been put forward. RS-0406 with pyridazine as its core chemical structure has so far shown promising results in inhibiting amyloid formation. In the present work, using molecular dynamics, we undertook the investigation of RS-0406 interactions with U-shaped Aβ1−42 and Aβ1−40 pentamers, Aβ1−42 monomers, and double-horseshoe-like Aβ1−42. To set better parameters for the small molecule, experimental and computational log P values were obtained. In addition, an analogue of RS-0406 was also simulated... 

A number of conformational diseases in humans have been associated with protein/peptide fibrillation known as amyloid. Although extensive studies have been conducted in understanding the molecular basis of amyloid formation, a detailed mechanism is still missing. Experimentally, HEWL (hen egg white lysozyme) has been exploited ubiquitously as a model protein for amyloid fibrillation and drug inhibition. However, computational studies investigating fibril formation of HEWL have been a difficult task to perform mainly due to high stability of lysozymes and the absence of crystal structures of HEWL fibril oligomers. In this study, we have examined various conditions of HEWL amyloid formation... 

We consider single field chaotic inflationary models plus a cosine modulation term, as in axion monodromy models, and augment them by a light scalar field with similar cosine coupling. We show that the power spectrum of curvature perturbations of this model is dominated by the one-loop contribution to the inflaton two-point function which is enhanced due to resonant interactions. This allows us to disentangle the scale of the scalar and tensor perturbations and hence, to suppress the ratio of tensor-to-scalar power spectra and alter the expression of the scalar spectral tilt from the simple chaotic models. Thus, our resonating module opens the way to reconcile chaotic models with convex... 

Expanding on [1], we analyze in detail the single field chaotic inflationary models plus a cosine modulation term, augmented by a light scalar field with inflaton dependent oscillatory mass term. We work out in detail the Feynman diagrams and compute one, two and in general estimate higher loop two and three point functions in the in-in formulation. We explicitly establish how the oscillatory mass term can amplify one-loop effects to dominate over the tree as well as the higher loop contributions. The power spectrum of curvature perturbations of this model is hence enhanced compared to the simple single field chaotic model. As a consequence, one can suppress the tensor to scalar ratio r and... 

We consider D3-brane action in the maximally supersymmetric type IIB plane-wave background. Upon fixing the light-cone gauge, we obtain the light-cone Hamiltonian which is manifestly supersymmetric. The 1/2 BPS solutions of this theory (solutions which preserve 16 supercharges) are either of the form of spherical three branes, the giant gravitons, or zero size point like branes. We then construct specific classes of 1/4 BPS solutions of this theory in which static electric field on the brane is turned on. These solutions are deformations about either of the two 1/2 BPS solutions. In particular, we study in some detail 1/4 BPS configurations with electric dipole on the three sphere giant,... 

Near Horizon Extremal Geometries (NHEG) are solutions to gravity theories with SL(2, ℝ) × U(1) N (for some N) symmetry, are smooth geometries and have no event horizon, unlike black holes. Following the ideas by R. M. Wald, we derive laws of NHEG dynamics, the analogs of laws of black hole dynamics for the NHEG. Despite the absence of horizon in the NHEG, one may associate an entropy to the NHEG, as a Noether-Wald conserved charge. We work out "entropy" and "entropy perturbation" laws, which are respectively universal relations between conserved Noether charges corresponding to the NHEG and a system probing the NHEG. Our entropy law is closely related to Sen's entropy function. We also... 

In this paper the tachyonic resonance preheating generated from the bosonic trilinear χ2 interactions in an expanding universe is studied. In λ 4/4 inflationary model the trilinear interaction, in contrast to the four-legs 2χ2, breaks the conformal symmetry explicitly and the resonant source term becomes nonperiodic, making the Floquet theorem inapplicable. We find that the occupation number of the produced χ particles has a nonlinear exponential growth with exponent ∼x3/2, where x is the conformal time. This should be contrasted with preheating from a periodic resonant source arising, for example, from the four-legs 2χ2 interaction, where the occupation number has a linear exponential... 

The general solution of steady-state asymmetric mechanical and thermal stresses of a hollow thick cylinder made of fluid-saturated functionally graded porous piezoelectric materials based on two-dimensional equations of thermoelasticity is considered. The general form of thermal and mechanical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the nonhomogeneous system of partial differential Navier equations, using the complex Fourier series and the power law functions method. The material properties are assumed to depend on the radial and circumferential variables and are expressed as power law functions... 

The analytical solution of steady-state asymmetric thermo-electro-mechanical loads of a hollow thick infinite cylinder made of porous piezoelectric materials (2D-PPMs) based on two-dimensional equations of thermoelasticity is considered. The general form of thermal and mechanical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations using the complex Fourier series and the power-exponential law functions method. The material properties are assumed to depend on the radial and circumferential variable and are expressed as power-exponential law... 

We argue that one can relax the requirements of the non-associative three-algebras recently used in constructing D = 3, = 8 superconformal field theories, and introduce the notion of ''relaxed three-algebras''. We present a specific realization of the relaxed three-algebras in terms of classical Lie algebras with a matrix representation, endowed with a non-associative four-bracket structure which is prescribed to replace the three-brackets of the three-algebras. We show that both the so(4)-based solutions as well as the cases with non-positive definite metric find a uniform description in our setting. We discuss the implications of our four-bracket representation for the D = 3, = 8 and multi... 

In this paper we continue analysis of the Matrix theory describing the DLCQ of type IIB string theory on AdS5×S5 (and/or the plane-wave) background, i.e. the tiny graviton matrix theory (TGMT). We study and classify 1/2, 1/4, and 1/8 BPS solutions of the TGMT which are generically of the form of rotating three-brane giants. These are branes whose shape are deformed three-spheres and hyperboloids. In lack of a classification of such ten-dimensional type IIb supergravity configurations, we focus on the dual N=4 four-dimensional 1/2, 1/4, and one 1/8 BPS operators and show that they are in one-to-one correspondence with the states of the same set of quantum numbers in TGMT. This provides... 

In this paper we consider all consistent extensions of the AdS5 × S5 superalgebra, psu(2,2/4), to incorporate brane charges by introducing both bosonic and fermionic (non)central extensions. We study the Inönü-Wigner contraction of the extended psu(2,2/4) under the Penrose limit to obtain the most general consistent extension of the plane-wave superalgebra and compare these extensions with the possible BPS (flat or spherical) brane configurations in the plane-wave background. We give an explicit realization of some of these extensions in terms of the Tiny Graviton Matrix Theory (TGMT) [14] which is the 0+1 dimensional gauge theory conjectured to describe the DLCQ of strings on the AdS5 × S5... 

We apply the Dirac bracket quantization to open strings attached to branes in the presence of background antisymmetric field and recover an inherent noncommutativity in the internal coordinates of the brane. © 2000 Elsevier Science B.V. All rights reserved  

We construct the NHEG phase space, the classical phase space of Near-Horizon Extremal Geometries with fixed angular momenta and entropy, and with the largest symmetry algebra. We focus on vacuum solutions to d dimensional Einstein gravity. Each element in the phase space is a geometry with SL(2,R)×U(1)d-3 isometries which has vanishing SL(2,R) and constant U(1) charges. We construct an on-shell vanishing symplectic structure, which leads to an infinite set of symplectic symmetries. In four spacetime dimensions, the phase space is unique and the symmetry algebra consists of the familiar Virasoro algebra, while in d> 4 dimensions the symmetry algebra, the NHEG algebra, contains infinitely many... 

Abstract: We construct the classical phase space of geometries in the near-horizon region of vacuum extremal black holes as announced in [arXiv:1503.07861]. Motivated by the uniqueness theorems for such solutions and for perturbations around them, we build a family of metrics depending upon a single periodic function defined on the torus spanned by the U(1) isometry directions. We show that this set of metrics is equipped with a consistent symplectic structure and hence defines a phase space. The phase space forms a representation of an infinite dimensional algebra of so-called symplectic symmetries. The symmetry algebra is an extension of the Virasoro algebra whose central extension is the... 

We extend the analysis of Fareghbal to charged black hole solutions of four-dimensional U(1)4 gauged supergravity which carry three charges. There are two decoupling near-horizon limits, one over the near-Bogomol'nyi-Prasad- Sommerfield (BPS) black hole solution and the other over the near-extremal, but non-BPS geometry. Taking the limit over the 11-dimensional uplift of these black hole solutions, for both of these cases we obtain a geometry which has a piece (conformal) to rotating BTZ×S2. We study the 4D, 11D, and 5D, 3D black hole properties. Moreover, we show that the BTZ×S2 geometry obtained after the near-BPS (near-extremal) limit is also a solution to five-dimensional U(1)3 ungauged... 

In this paper, the general analysis of two-dimensional steady-state thermal and mechanical stresses for a hollow thick infinite cylinder made of Functionally Graded Piezoelectric Materials (2D-FGPMs) is performed and developed. The general form of thermal, mechanical, and electrical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations, using the complex Fourier series and the power law functions method. The material properties are assumed dependent on the radial and circumferential variables and are expressed as power law functions along the... 

In this paper, the general analysis of two-dimensional steady-state thermal and mechanical stresses for a hollow thick infinite cylinder made of Functionally Graded Piezoelectric Materials (2D-FGPMs) is performed and developed. The general form of thermal, mechanical, and electrical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations, using the complex Fourier series and the power law functions method. The material properties are assumed dependent on the radial and circumferential variables and are expressed as power law functions along the... 

We study near-horizon limits of near-extremal charged black hole solutions to five-dimensional U(1) 3 gauged supergravity carrying two charges, extending the recent work of Balasubramanian et al. [1]. We show that there are two near-horizon decoupling limits for the near-extremal black holes, one corresponding to the near-BPS case and the other for the far from BPS case. Both of these limits are only defined on the 10d IIB uplift of the 5d black holes, resulting in a decoupled geometry with a six-dimensional part (conformal to) a rotating BTZ × S 3. We study various aspects of these decoupling limits both from the gravity side and the dual field theory side. For the latter we argue that...