2,584 research outputs found
Linkage of modules over Cohen-Macaulay rings
Inspired by the works in linkage theory of ideals, the concept of sliding
depth of extension modules is defined to prove the Cohen-Macaulyness of linked
module if the base ring is merely Cohen-Macaulay. Some relations between this
new condition and other module-theory conditions such as G-dimension and
sequentially Cohen-Macaulay are established. By the way several already known
theorems in linkage theory are improved or recovered by new approaches.Comment: 12 Page
Effective Mechanical Properties of Multilayer Nano-Heterostructures
Two-dimensional and quasi-two-dimensional materials are important nanostructures because of their exciting electronic, optical, thermal, chemical and mechanical properties. However, a single-layer nanomaterial may not possess a particular property adequately, or multiple desired properties simultaneously. Recently a new trend has emerged to develop nano-heterostructures by assembling multiple monolayers of different nanostructures to achieve various tunable desired properties simultaneously. For example, transition metal dichalcogenides such as MoS2 show promising electronic and piezoelectric properties, but their low mechanical strength is a constraint for practical applications. This barrier can be mitigated by considering graphene-MoS2 heterostructure, as graphene possesses strong mechanical properties. We have developed efficient closed-form expressions for the equivalent elastic properties of such multi-layer hexagonal nano-hetrostructures. Based on these physics-based analytical formulae, mechanical properties are investigated for different heterostructures such as graphene-MoS2, graphene-hBN, graphene-stanene and stanene-MoS2. The proposed formulae will enable efficient characterization of mechanical properties in developing a wide range of application-specific nano-heterostructures
Thermal instability in ionized plasma
We study magnetothermal instability in the ionized plasmas including the
effects of Ohmic, ambipolar and Hall diffusion. Magnetic field in the single
fluid approximation does not allow transverse thermal condensations, however,
non-ideal effects highly diminish the stabilizing role of the magnetic field in
thermally unstable plasmas. Therefore, enhanced growth rate of thermal
condensation modes in the presence of the diffusion mechanisms speed up the
rate of structure formation.Comment: Accepted for publication in Astrophysics & Space Scienc
2D Gravity on with Chern-Simons Corrections
We study 2D Maxwell-dilaton gravity with higher order corrections given by
the Chern-Simons term. The model admits three distinctive vacuum
solutions. By making use of the entropy function formalism we find the entropy
of the solutions which is corrected due to the presence of the Chern-Simons
term. We observe that the form of the correction depends not only on the
coefficient of the Chern-Simons term, but also on the sign of the electric
charge; pointing toward the chiral nature of the dual CFT. Using the asymptotic
symmetry of the theory as well as requiring a consistent picture we can find
the central charge and the level of U(1) current. Upon uplifting the solutions
to three dimensions we get purely geometric solutions which will be either
or warped with an identification.Comment: 15 pages; V2: refs adde
Supergravity Description of the Large N Noncommutative Dipole Field Theories
We consider system of Dp-branes in the presence of a nonzero B field with one
leg along brane worldvolume and the other transverse to it. We study the
corresponding supergravity solutions and show that the worldvolume theories
decouple from gravity for . Therefore these solutions provide dual
description of large N noncommutative dipole field theories. We shall only
consider those systems which preserve 8 supercharges in the branes worldvolume.
We analyze the system of M5-branes and NS5-branes in the presence of nonzero C
field and RR field with one leg along the transverse direction and the others
along the worldvolume of the brane, respectively. This could provide a new
deformation of (2,0) and little string field theories. Finally, we study the
Wilson loops using the dual gravity descriptions.Comment: 24 pages, Latex fil
From Gapped Excitons to Gapless Triplons in One Dimension
Often, exotic phases appear in the phase diagrams between conventional
phases. Their elementary excitations are of particular interest. Here, we
consider the example of the ionic Hubbard model in one dimension. This model is
a band insulator (BI) for weak interaction and a Mott insulator (MI) for strong
interaction. Inbetween, a spontaneously dimerized insulator (SDI) occurs which
is governed by energetically low-lying charge and spin degrees of freedom.
Applying a systematically controlled version of the continuous unitary
transformations (CUTs) we are able to determine the dispersions of the
elementary charge and spin excitations and of their most relevant bound states
on equal footing. The key idea is to start from an externally dimerized system
using the relative weak interdimer coupling as small expansion parameter which
finally is set to unity to recover the original model.Comment: 18 pages, 10 figure
Modern cemented Furlong hemiarthroplasty: Are dislocations rates better?
BACKGROUND: Dislocation following hip hemiarthroplasty is a major complication with increased mortality and morbidity. Data looking at dislocation following contemporary bipolar stems are lacking in literature. METHODS: Retrospective review of our prospective national hip fracture database over a two-year period. Group 1 comprised of consecutive patients receiving bipolar Furlong prosthesis (N222) while Group 2 was made up of a historical cohort (uncemented; N254). Clinical and radiological records were reviewed to determine dislocation rates, causes and associative factors of dislocations. Data were analysed using SPSS. RESULTS: Following 476 hemiarthroplasties performed during the study period, 12 (2.5%) dislocations were reported (eight in Group 1; four in Group 2). There was no significant difference in dislocation rates (3.6% vs 1.6%) between groups (p = 0.159). Subgroup analysis of Group 1 demonstrated a significant difference in dislocations with Furlong cemented (6%) as compared with Furlong uncemented (0%) hemiarthroplasties (p = 0.024). Following dislocation, death rates increased to 8.3% from 1.7% in both groups. CONCLUSION: There is a statistically significant increase in dislocation rate following use of cemented Furlong prosthesis when compared to similar uncemented prosthesis at the same treatment period. However, when compared to traditional uncemented prosthesis, there is no difference in dislocation rates
New Attractors, Entropy Function and Black Hole Partition Function
By making use of the entropy function formalism we study the generalized
attractor equations in the four dimensional N=2 supergravity in presence of
higher order corrections. This result might be used to understand a possible
ensemble one could associate to an extremal black hole.Comment: 20 pages, latex file, V2: minor corrections, typos corrected, Refs
added, V3: the version appeared in JHE
The potential use of service-oriented infrastructure framework to enable transparent vertical scalability of cloud computing infrastructure
Cloud computing technology has become familiar to most Internet users. Subsequently, there has been an increased growth in the use of cloud computing, including Infrastructure as a Service (IaaS). To ensure that IaaS can easily meet the growing demand, IaaS providers usually increase the capacity of their facilities in a vertical IaaS increase capability and the capacity for local IaaS amenities such as increasing the number of servers, storage and network bandwidth. However, at the same time, horizontal scalability is sometimes not enough and requires additional strategies to ensure that the large number of IaaS service requests can be met. Therefore, strategies requiring horizontal scalability are more complex than the vertical scalability strategies because they involve the interaction of more than one facility at different service centers. To reduce the complexity of the implementation of the horizontal scalability of the IaaS infrastructures, the use of a technology service oriented infrastructure is recommended to ensure that the interaction between two or more different service centers can be done more simply and easily even though it is likely to involve a wide range of communication technologies and different cloud computing management. This is because the service oriented infrastructure acts as a middle man that translates and processes interactions and protocols of different cloud computing infrastructures without the modification of the complex to ensure horizontal scalability can be run easily and smoothly. This paper presents the potential of using a service-oriented infrastructure framework to enable transparent vertical scalability of cloud computing infrastructures by adapting three projects in this research: SLA@SOI consortium, Open Cloud Computing Interface (OCCI), and OpenStack
Orbiting Membranes in M-theory on AdS_7 x S^4 Background
We study classical solutions describing rotating and boosted membranes on
AdS_7 x S^4 background in M-theory. We find the dependence of the energy on the
spin and R-charge of these solutions. In the flat space limit we get E ~
S^{2/3}, while for AdS at leading order E-S grows as S^{1/3}. The membranes on
AdS_4 x S^7 background have briefly been studied as well.Comment: 13 pages, latex, v2: a note and refs. added, some typos correcte
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