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First-principles study of crystallographic slip modes in ω-Zr.
We use first-principles density functional theory to study the preferred modes of slip in the high-pressure ω phase of Zr. The generalized stacking fault energy surfaces associated with shearing on nine distinct crystallographic slip modes in the hexagonal ω-Zr crystal are calculated, from which characteristics such as ideal shear stress, the dislocation Burgers vector, and possible accompanying atomic shuffles, are extracted. Comparison of energy barriers and ideal shear stresses suggests that the favorable modes are prismatic 〈c〉, prismatic-II [Formula: see text] and pyramidal-II 〈c + a〉, which are distinct from the ground state hexagonal close packed α phase of Zr. Operation of these three modes can accommodate any deformation state. The relative preferences among the identified slip modes are examined using a mean-field crystal plasticity model and comparing the calculated deformation texture with the measurement. Knowledge of the basic crystallographic modes of slip is critical to understanding and analyzing the plastic deformation behavior of ω-Zr or mixed α-ω phase-Zr
Properties of Phase transitions of a Higher Order
The following is a thermodynamic analysis of a III order (and some aspects of
a IV order) phase transition. Such a transition can occur in a superconductor
if the normal state is a diamagnet. The equation for a phase boundary in an H-T
(H is the magnetic field, T, the temperature) plane is derived. by considering
two possible forms of the gradient energy, it is possible to construct a field
theory which describes a III or a IV order transition and permits a study of
thermal fluctuations and inhomogeneous order parameters.Comment: 13 pages, revtex, no figure
Connections between conjectures of Alon-Tarsi, Hadamard-Howe, and integrals over the special unitary group
We show the Alon-Tarsi conjecture on Latin squares is equivalent to a very
special case of a conjecture made independently by Hadamard and Howe, and to
the non-vanishing of some interesting integrals over SU(n). Our investigations
were motivated by geometric complexity theory.Comment: 7 page
A performance model of speculative prefetching in distributed information systems
Previous studies in speculative prefetching focus on building and evaluating access models for the purpose of access prediction. This paper investigates a complementary area which has been largely ignored, that of performance modelling. We use improvement in access time as the performance metric, for which we derive a formula in terms of resource parameters (time available and time required for prefetching) and speculative parameters (probabilities for next access). The performance maximization problem is expressed as a stretch knapsack problem. We develop an algorithm to maximize the improvement in access time by solving the stretch knapsack problem, using theoretically proven apparatus to reduce the search space. Integration between speculative prefetching and caching is also investigated, albeit under the assumption of equal item sizes
A distributed directory scheme for information access in mobile computers
In this paper, we discuss the design aspects of a dynamic distributed directory scheme (DDS) to facilitate efficient and transparent access to information files in mobile environments. The proposed directory interface enables users of mobile computers to view a distributed file system on a network of computers as a globally shared file system. In order to counter some of the limitations of wireless communications, we propose improvised invalidation schemes that avoid false sharing and ensure uninterrupted usage under disconnected and low bandwidth conditions
Can re-entrance be observed in force induced transitions?
A large conformational change in the reaction co-ordinate and the role of the
solvent in the formation of base-pairing are combined to settle a long standing
issue {\it i.e.} prediction of re-entrance in the force induced transition of
DNA. A direct way to observe the re-entrance, i.e a strand goes to the closed
state from the open state and again to the open state with temperature, appears
difficult to be achieved in the laboratory. An experimental protocol (in direct
way) in the constant force ensemble is being proposed for the first time that
will enable the observation of the re-entrance behavior in the
force-temperature plane. Our exact results for small oligonucleotide that forms
a hairpin structure provide the evidence that re-entrance can be observed.Comment: 12 pages and 5 figures (RevTex4). Accepted in Europhys Lett. (2009
Electron-hole coexistence in disordered graphene probed by high-field magneto-transport
We report on magneto-transport measurement in disordered graphene under
pulsed magnetic field of up to 57T. For large electron or hole doping, the
system displays the expected anomalous Integer Quantum Hall Effect (IQHE)
specific to graphene up to filling factor . In the close vicinity of the
charge neutrality point, the system breaks up into co-existing puddles of holes
and electrons, leading to a vanishing Hall and finite longitudinal resistance
with no hint of divergence at very high magnetic field. Large resistance
fluctuations are observed near the Dirac point. They are interpreted as the the
natural consequence of the presence of electron and hole puddles. The magnetic
field at which the amplitude of the fluctuations are the largest is directly
linked to the mean size of the puddles
Parallel matrix inversion techniques
In this paper, we present techniques for inverting sparse, symmetric and positive definite matrices on parallel and distributed computers. We propose two algorithms, one for SIMD implementation and the other for MIMD implementation. These algorithms are modified versions of Gaussian elimination and they take into account the sparseness of the matrix. Our algorithms perform better than the general parallel Gaussian elimination algorithm. In order to demonstrate the usefulness of our technique, we implemented the snake problem using our sparse matrix algorithm. Our studies reveal that the proposed sparse matrix inversion algorithm significantly reduces the time taken for obtaining the solution of the snake problem. In this paper, we present the results of our experimental work
Laminate comprising fibers embedded in cured amine terminated bis-imide
Amine terminated bisaspartimides are prepared by a Michael type reaction of an aromatic bismaleimide and an aromatic diamine in an aprotic solvent. These bisaspartimides are thermally polymerized to yield tough, resinous polymers crosslinked through -NH- groups. Such polymers are useful in applications requiring materials with resistance to change at elevated temperatures
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