1,605 research outputs found
The minimal conformal O(N) vector sigma model at d=3
For the minimal O(N) sigma model, which is defined to be generated by the
O(N) scalar auxiliary field alone, all n-point functions, till order 1/N
included, can be expressed by elementary functions without logarithms.
Consequently, the conformal composite fields of m auxiliary fields possess at
the same order such dimensions, which are m times the dimension of the
auxiliary field plus the order of differentiation.Comment: 15 page
Massive Fields of Arbitrary Integer Spin in Symmetrical Einstein Space
We study the propagation of gauge fields with arbitrary integer spins in the
symmetrical Einstein space of any dimensionality. We reduce the problem of
obtaining a gauge-invariant Lagrangian of integer spin fields in such
background to an purely algebraic problem of finding a set of operators with
certain features using the representation of high-spin fields in the form of
some vectors of pseudo-Hilbert space. We consider such construction in the
linear order in the Riemann tensor and scalar curvature and also present an
explicit form of interaction Lagrangians and gauge transformations for massive
particles with spins 1 and 2 in terms of symmetrical tensor fields.Comment: 15 pages, latex, no figures,minor change
Synaptic transmission as a cooperative phenomenon in confined systems
In this review paper, the theory of synaptic transmission (ST) was developed
and discussed. We used the hypothesis of isomorphism between: (a) the
cooperative behavior of mediators --- acetylcholine molecules (ACh) and
cholinoreceptors in a synaptic cleft with binding into mediator-receptor (AChR)
complexes, (b) the critical phenomena in confined binary liquid mixtures. The
systems of two (or three) nonlinear differential equations were proposed to
find the change of concentrations of ACh, AChR complexes, and ferment
acetylcholinesterase. The main findings of our study: the linear size of the
activation zone was evaluated; the process of postsynaptic membrane activation
was described as a cooperative process; different approximations of ACh
synchronous release were examined; stationary states and types of singular
points were studied for the proposed models of ST; the nonlinear kinetic model
with three order parameters demonstrated a strange-attractor behavior.Comment: 12 pages, 1 figur
Optimum pulse shapes for stimulated Raman adiabatic passage
Stimulated Raman adiabatic passage (STIRAP), driven with pulses of optimum
shape and delay has the potential of reaching fidelities high enough to make it
suitable for fault-tolerant quantum information processing. The optimum pulse
shapes are obtained upon reduction of STIRAP to effective two-state systems. We
use the Dykhne-Davis-Pechukas (DDP) method to minimize nonadiabatic transitions
and to maximize the fidelity of STIRAP. This results in a particular relation
between the pulse shapes of the two fields driving the Raman process. The
DDP-optimized version of STIRAP maintains its robustness against variations in
the pulse intensities and durations, the single-photon detuning and possible
losses from the intermediate state.Comment: 8 pages, 6 figures. submitted to Phys. Rev.
Scanning Electron Fractography of Body Centered Cubic (BCC) Metals
Scanning electron fractography is an inherent part of investigations of factors which determine the mechanical properties of materials and their failure. Transition bcc metals show the widest variety of fracture mechanisms under uniaxial tension.
Brittle fracture is affected by cleavage from various defects - stress concentrators.
In brittle-ductile transition, fracture starts by a tough mode but finishes by a brittle one - by cleavage. A fracture mechanism changes after the tough crack has reached some critical length. Mechanisms of subcritical growth are of cleavage with relaxation, inter-granular fracture and dimpled ones.
Dimples are observed in ductile fracture. Cleavage is absent. The dimples are nucleated as a result of both failure of particles and their interfaces and delamination of structure elements.
All varieties of observed fracture surface may be described as a result of actions of the following mechanisms - cleavage, cleavage with relaxation, pore coalescence, brittle intergranular or intercellular fracture.
Fractographical analysis allows one to obtain information not only about the fracture mechanisms but also such characteristics as: fracture toughness, brittle-ductile transition limits, structure transformations preceding fracture
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