3,427 research outputs found
Tensionless strings: physical Fock space and higher spin fields
I study the physical Fock space of the tensionless string theory with
perimeter action, exploring its new gauge symmetry algebra. The cancellation of
conformal anomaly requires the space-time to be 13-dimensional. All particles
are massless and there are no tachyon states in the spectrum. The zero mode
conformal operator defines the levels of the physical Fock space. All levels
can be classified by the highest Casimir operator W of the little group E(11)
for massless particles in 11-dimensions. The ground state is infinitely
degenerated and contains massless gauge fields of arbitrary large integer spin,
realizing the irreducible representations of E(11) of fixed helicity. The
excitation levels realize CSR representations of little group E(11) with an
infinite number of helicities. After inspection of the first excitation level,
which, as I prove, is a physical null state, I conjecture that all excitation
levels are physical null states. In this theory the tensor field of the second
rank does not play any distinctive role and therefore one can suggest that in
this model there is no gravity.Comment: 22 pages, Latex, references adde
Variational approach to probabilistic finite elements
Probabilistic finite element method (PFEM), synthesizing the power of finite element methods with second-moment techniques, are formulated for various classes of problems in structural and solid mechanics. Time-invariant random materials, geometric properties, and loads are incorporated in terms of their fundamental statistics viz. second-moments. Analogous to the discretization of the displacement field in finite element methods, the random fields are also discretized. Preserving the conceptual simplicity, the response moments are calculated with minimal computations. By incorporating certain computational techniques, these methods are shown to be capable of handling large systems with many sources of uncertainties. By construction, these methods are applicable when the scale of randomness is not very large and when the probabilistic density functions have decaying tails. The accuracy and efficiency of these methods, along with their limitations, are demonstrated by various applications. Results obtained are compared with those of Monte Carlo simulation and it is shown that good accuracy can be obtained for both linear and nonlinear problems. The methods are amenable to implementation in deterministic FEM based computer codes
Demonstration of a 1/4 cycle phase shift in the radiation-induced oscillatory-magnetoresistance in GaAs/AlGaAs devices
We examine the phase and the period of the radiation-induced
oscillatory-magnetoresistance in GaAs/AlGaAs devices utilizing in-situ magnetic
field calibration by Electron Spin Resonance of DiPhenyl-Picryl-Hydrazal. The
results confirm a -independent 1/4 cycle phase shift with respect to the condition for , and they also suggest a small
( 2%) reduction in the effective mass ratio, , with respect
to the standard value for GaAs/AlGaAs devices.Comment: 4 pages, 4 color figure
Progesterone Signaling Mechanisms in Brain and Behavior
Steroid hormone, progesterone, modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and behavior. These neuronal effects are mediated primarily by intracellular progestin receptors (PRs) in the steroid-sensitive neurons, resulting in transcription-dependent genomic actions (classical mechanism). In addition to progesterone, intracellular PRs can also be activated in a “ligand-independent” manner by neurotransmitters, peptide growth factors, cyclic nucleotides, and neurosteroids. Recent studies indicate that rapid, non-classical progesterone actions involving cytoplasmic kinase signaling and/or extranuclear PRs can result in both transcription-independent and transcription-dependent actions. Cross-talk between extranuclear and classical intracellular signaling pathways promotes progesterone-dependent behavior in mammals. This review focuses on the mechanisms by which progesterone-initiated signaling mechanisms converge with PRs in the brain to modulate reproductive behavior in female rodents
Reliable Synchronization Primitives for Java
Java is an architecture-independent, object-oriented language designed to facilitate code-sharing across the Internet in general, via the Web in particular. Java is multithreaded, providing thread creation and synchronization constructs based on generalized monitors. Although these primitives are appropriate for many windowing applications, they are not necessarily well-suited for the larger class of multithreaded programs that occur as part of distributed systems. We demonstrate how the Java primitives, in conjunction with the object-oriented aspects of the language, can be used to implement a collection of other traditional synchronization paradigms. These paradigms are formally specified, their implementations are rigorously verified, and their use is illustrated with several examples
Radiation induced zero-resistance states in GaAs/AlGaAs heterostructures: Voltage-current characteristics and intensity dependence at the resistance minima
High mobility two-dimensional electron systems exhibit vanishing resistance
over broad magnetic field intervals upon excitation with microwaves, with a
characteristic reduction of the resistance with increasing radiation intensity
at the resistance minima. Here, we report experimental results examining the
voltage - current characteristics, and the resistance at the minima vs. the
microwave power. The findings indicate that a non-linear V-I curve in the
absence of microwave excitation becomes linearized under irradiation, unlike
expectations, and they suggest a similarity between the roles of the radiation
intensity and the inverse temperature.Comment: 3 color figures; publishe
Polarization immunity of magnetoresistivity response under Microwave excitation
We analyze theoretically the dependence of the microwave polarization sate
and sense on the magnetoresistivity response of two-dimensional electron
systems. Linear and circular polarization have been considered with different
senses and directions. We discuss the polarization dependence of the
longitudinal magnetoresistivity and propose an explanation for the
experimentally observed polarization immunity, i.e., resistivity oscillations
and zero resistance state regions are unaffected by the sense of circular
polarization or by the direction of microwave electric field.Comment: 4 pages and 1 figur
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