Feed forward rings

Military and other critical (life-threatening/life-saving) systems require performance evaluations from a survivability, reliability, maintainability, and availability (SRMA) perspective. Applying SRMA concepts to commercial token passing ring local area networks (LANs) (e.g., IEEE-802.5, FDDI, SAE-9B) has uncovered several design issues that could impact the utility of these networks in a critical system. This article discloses a new architecture for token passing rings, called “feed forward rings” (FFR), which provides a significant improvement in system survivability, can eliminate “jabber mode” induced ring failures, and provides for passive optical bridging between rings.

The basic “feed forward” concept is that LANs, based on token passing protocols and utilizing multiple, physically separated, fiber optic rings, should have the serial data stream on each ring flowing in the same direction of rotation. This article provides qualitative observations on the performance of current commercial rings and discusses the advantages of several FFR topologies. Implementation issues related to FFRs are also discussed. It is recommended that FFR alternatives to counterrotating rings (CRR) with separated cables be considered for inclusion in LAN standards.     

Network survivability analysis

Advances in fiber optic and local area network (LAN) technologies are providing system designers with many new options for interconnecting computer equipment. A recurring problem for military system designers, who are end-users of a LAN standard, is implementing LANs so that the survivability, reliability, maintainability, and availability (SRMA) of a system is maximized. LAN standards working groups are currently making design decisions about topologies, components, and protocols that directly affect the SRMA of the end-user's system. This article focuses on a new analytic technique, called “network survivability analysis,” that provides the mathematical tools needed to compare the survivability of arbitrary network topologies. For background, several network metrics are described and their limitations for LAN standards development identified. Network survivability is defined, and several token-passing ring case examples are analyzed. The primary strength of network survivability analysis is that it can be used to provide a quantitative comparison among LAN topologies without knowledge of the end-user's equipment, systems, or environments.     

Network survivability analysis

Advances in fiber optic and local area network (LAN) technologies are providing system designers with many new options for interconnecting computer equipment. A recurring problem for military system designers, who are end-users of a LAN standard, is implementing LANs so that the survivability, reliability, maintainability, and availability (SRMA) of a system is maximized. LAN standards working groups are currently making design decisions about topologies, components, and protocols that directly affect the SRMA of the end-user's system. This article focuses on a new analytic technique, called “network survivability analysis,” that provides the mathematical tools needed to compare the survivability of arbitrary network topologies. For background, several network metrics are described and their limitations for LAN standards development identified. Network survivability is defined, and several token-passing ring case examples are analyzed. The primary strength of network survivability analysis is that it can be used to provide a quantitative comparison among LAN topologies without knowledge of the end-user's equipment, systems, or environments.     

A U(1) gauge-Higgs system with a radial degree of freedom

The phase diagram of a lattice U(1) gauge-Higgs model is derived without freezing the Higgs field length. For sufficienly small Higgs self-coupling strength, the “confinement” and “Higgs” phases are separated, in contrast to what is observed in the fixed length model.     

Completeness of “good” Bethe ansatz solutions of a quantum-group-invariant Heisenberg model

The sl_q(2) quantum-group-invariant Heisenberg model with open boundary conditions is investigated by means of the Bethe ansatz. As is well known, quantum groups for q equal to a root of unity possess a finite number of “good” representations with non-zero q-dimension and “bad” ones with vanishing q-dimension. Correspondingly, the state space of an invariant Heisenberg chain decomposes into “good” and “bad” states. A “good” state may be described by a path of only “good” representations. It is shown that the “good” states are given by all “good” Bethe ansatz solutions with roots restricted to the first periodicity strip, i.e. only positive-parity strings (in the language of Takahashi) are allowed. Applying Bethe's string-counting technique completeness of the “good” Bethe states is proven, i.e. the same number of states is found as the number of all restricted paths on the sl_q(2) Bratteli diagram. It is the first time that a “completeness” proof for an anisotropic quantum-invariant reduced Heisenberg model is performed.     

Swendsen-Wang simulation of Ising spins and a precise definition of critical clusters

A recent ultrafast simulation of Ising spins (σ_i = ± 1) utilizes a random + to − flip-over of duly defined decoupled blocks of spins. We show that the random dynamics alone suffices to prove the correspondence of the blocks with “critical clusters” describing thermal (magnetic) fluctuation. (The precise requirement is σ_iσ_i = 1, for a pair of spins inside a block, and σ_iσ_j = 0, for a σ_i inside and σ_j, outside.) The present approach helps to extend the study of critical clusters, and also ultrafast simulation, to the case of nonzero magnetization. Finite critical clusters constitute always a ± symmetric set and are very different (much smaller) than continuous domains of similarly oriented spins.     

The pion velocity at chiral restoration and the vector manifestation

We study the effects of Lorentz non-invariance on the physical pion velocity at the critical temperature T_c in an effective theory of hidden local symmetry (HLS) with the “vector manifestation” fixed point. We match at a “matching scale” Λ_M the axial-vector current correlator in the HLS with the one in the operator product expansion for QCD, and present the matching condition to determine the bare pion velocity. We find that the physical pion velocity, which is found to be one at T=T_c when starting from the Lorentz invariant bare HLS, remains close to one with the Lorentz non-invariance, v_π(T_c)=0.83–0.99. This result is quite similar to the pion velocity in dense matter.     

Methane activation over Ag-exchanged ZSM-5 zeolites: A theoretical study

Methane activation catalyzed over Ag-exchanged ZSM-5 zeolites was investigated by using the density functional theory (DFT) with a cluster model. Two different pathways were taken into account in this work: the “alkyl” and the “carbenium” pathways. The activation barriers obtained are 34.09 and 66.63 kcal/mol for the “alkyl” and the “carbenium” pathway, respectively. The calculated results show that the activation barrier of the “alkyl” pathway is smaller than that of “carbenium” pathway. Consequently, the “alkyl” pathway is the preferential reaction pathway. A new mechanism of methane conversion in the presence of ethene was proposed. In the catalytic cycle, the initial step of methane activation proceeds with the “alkyl” pathway and the Ag⁺ cation acts as an acceptor of the methyl group, then ethene reacts with the Ag⁺CH₃⁻ group to form propene. In addition, it is found that the Ag⁺ cations play an important role in the methane activation, compared with the reaction of methane activation over H-ZSM-5.     

Vulnerability in one-dimensional excitable media

Potentially life-threatening cardiac arrhythmias can be iniated with stimuli timed to occur during the “vulnerable window (VW)”. We defined VW as the time interval between the “conditioning” and “test” stimuli following in sequence, during which the test stimulus response propagates in only one direction. We show that the VW is a generic feature of excitable media and describe the relationship between the properties of an excitable medium and the VW. We present asymptotic results that reveal the sensitivity of the VW to both the propagation velocity of the conditioning wavefront and the recovery process parameters. We also have identified a critical length of medium that must be excited in order to reveal vulnerability. Analytical results are in agreement with numerical studies.     

The short-range van Hemmen model in a simple Kikuchi approximation: Comparison with the mean-field model and with spin-glasses

A simple first-order Kikuchi approximation is studied for the short-range (nearest-neighbour) version of the van Hemmen mean-field model originally proposed for spin-glasses. Although the approximation is very similar to the mean-field treatment, the phase diagrams from the two methods are drastically different. Previously reported results are reviewed and extended. The “reentrant” ferromagnetic to “spin-glass” transition found in zero magnetic field persists in small fields. The equilibrium magnetization displays a maximum as a function of temperature in the reentrance region. The characteristic S-shape of the magnetization versus field in the “spin-glass” region and magnetic hysteresis are observed. In addition, some exact results concerning the problem of the lower critical dimension of the short-range model are derived.     

Recursive sampling simulations of 3D gravity coupled to scalar fermions

We study numerically the phase structure of a model of 3D gravity interacting with scalar fermions. We measure the 3D counterpart of the “string” susceptibility exponent as a function of the inverse Newton coupling . We show that there are two phases separated by a critical point around _c2. The numerical results support the hypothesis that the phase structures of 3D and 2D simplicial gravity are qualitatively similar, the inverse Newton coupling in 3D playing the role of the central charge of matter in 2D.     

Acoustic Analyses of Developmental Changes and Emotional Expression in the Preverbal Vocalizations of Infants

The nonverbal vocal utterances of seven normally hearing infants were studied within their first year of life with respect to age- and emotion-related changes. Supported by a multiparametric acoustic analysis it was possible to distinguish one inspiratory and eleven expiratory call types. Most of the call types appeared within the first two months; some emerged in the majority of infants not until the 5th (“laugh”) or 7th month (“babble”). Age-related changes in acoustic structure were found in only 4 call types (“discomfort cry,” “short discomfort cry,” “wail,” “moan”). The acoustic changes were characterized mainly by an increase in harmonic-to-noise ratio and homogeneity of the call, a decrease in frequency range and a downward shift of acoustic energy from higher to lower frequencies. Emotion-related differences were found in the acoustic structure of single call types as well as in the frequency of occurrence of different call types. A change from positive to negative emotional state was accompanied by an increase in call duration, frequency range, and peak frequency (frequency with the highest amplitude within the power spectrum). Negative emotions, in addition, were characterized by a significantly higher rate of “crying,” “hic” and “ingressive vocalizations” than positive emotions, while positive emotions showed a significantly higher rate of “babble,” “laugh,” and “raspberry.”     

Analysis of the critical behaviour of curved regions in equilibrium shapes of in crystals

Crystal shapes near {111} facets have been analyzed on indium crystals in their equilibrium shape. These measurements are compared with two theoretical concepts of the critical behaviour of curved regions: the “Pokrovsky-Talapov transition” and the “mean field theory”. Taking into account, on the one hand, the inaccuracy of the experimental determination of the origin of the curved region and, on the other hand, the “window” of validity of the Pokrovsky-Talapov transition theory, the choice between the two theories is difficult. Nevertheless the analytical expression of the mean field theory reproduces surprisingly well all the points of the experimental profile.     

Outer curvature and conformal geometry of an imbedding

The differential geometry of an imbedded (e.g. string or membrane world sheet) surface in a higher-dimensional background is shown to be conveniently describable (except in the null limit case) in terms of what are designated as its first, second, and third fundamental tensors, which will have the respective symmetry properties η_μν = η_(μν) as a trivial algebraic identity, K_μν^ρ = K_(μν)^ρ as the “generalised Weingarten identity”, which is the (Frobenius type) integrability condition for the imbedding, and Ξ_λμν^ρ = Ξ_(λμν)^ρ as a “generalised Codazzi equation”, which depends on the background geometry being flat or of constant curvature, needing replacement by a more complicated expression for a generic value of the background curvature B_κλ^μ_ν. The “generalised Gauss equation” expressing the dependence on this background curvature of the internal curvature tensor R_κλ^μ_ν of the imbedded surface is converted into terms of the first and second fundamental tensors, and it is thereby demonstrated that the vanishing of the (conformally invariant) “conformation tensor”, i.e. the trace free part C_μν^ρ of the second fundamental tensor K_μv^ρ, is a sufficient condition for conformal flatness of the imbedded surface (and thus in particular for the vanishing of its (Weyl type) conformal curvature tensor C_κλ^μ_ν) provided the background is itself conformally flat. In a trio of which the first two members are the generalised Gauss and Codazzi equations, the “third” member is shown to give an expression in terms of C_μν^ρ for the (trace free, conformally invariant) “outer curvature” tensor Ω_κλ^μ_ν whose vanishing is the condition for feasibility of the natural generalisation of the Walker frame transportation ansatz. The vanishing of C_μν^ρ is shown to be sufficient in a conformally flat background for the vanishing also of Ω_κλ^μ_ν.     

Zigzag wall dynamics in uniaxial in-plane magnetic thin films

An unusual right/left zigzag wall propagation in the bias (transverse) and ac fields applied simultaneously is observed. A dynamic model based on the variable coercivity, effective transverse field, transformation of the walls from asymmetric Bloch into asymmetric Néel type (and vice versa) is proposed. Degeneration of two segments of one “zig” (or “zag”) which “sense” differently the transverse field is one of the crucial point of the zigzag dynamics.     

Divisors on elliptic Calabi-Yau 4-folds and the superpotential in F-theory — I

Each smooth elliptic Calabi-Yau 4-fold determines both a three-dimensional physical theory (a compactification of “M-theory”) and a four-dimensional physical theory (using the “F-theory” construction). A key issue in both theories is the calculation of the “superpotential” of the theory, which by a result of Witten is determined by the divisors D on the 4-fold satisfying X( _D = 1. We propose a systematic approach to identify these divisors, and derive some criteria to determine whether a given divisor indeed contributes. We then apply our techniques in explicit examples, in particular, when the base B of the elliptic fibration is a toric variety or a Fano 3-fold.

When B is Fano, we show how divisors contributing to the superpotential are always “exceptional” (in some sense) for the Calabi-Yau 4-fold X. This naturally leads to certain transitions of X, i.e., birational tranformations to a singular model (where the image of D no longer contributes) as well as certain smoothings of the singular model. The singularities which occur are “canonical”, the same type of singularities of a (singular) Weierstrass model. We work out the transitions. If a smoothing exists, then the Hodge numbers change.

We speculate that divisors contributing to the superpotential are always “exceptional” (in some sense) for X, also in M-theory. In fact we show that this is a consequence of the (log)-minimal model algorithm in dimension 4, which is still conjectural in its generality, but it has been worked out in various cases, among which are toric varieties.     

Flux creep through the surface barrier and columnar defects in HTSC

The rate of flux creep over the surface barrier in clean HTSC samples is found. This rate proves to be significantly different for the cases of vortex entry and escape (relaxation “in” and “out”, respectively). Since a flat surface is topologically similar to the artificial columnar defects, their comparison is useful. The vortex creep over the surface is equivalent to that over the cylinder defect of radius r > λ, whereas the radii of real defects obtained so far are of order . We discuss the effect of the smallness of defect radius on the creep process, which results in very small activation energies U at large critical current J_c. The importance of the increase of the defect radius is predicted.     

Discrete gauge symmetry anomalies

It has been recently argued that quantum gravity effects strongly violate all non-gauge symmetries. This would suggest that all low energy discrete symmetries should be gauge symmetries, either continuous or discrete. Acceptable continuous gauge symmetries are constrained by the condition they should be anomaly free. We show here that any discrete gauge symmetry should also obey certain “discrete anomaly cancellation” conditions. These conditions strongly constrains the massles fermion content of the theory and follow from the “parent” cancellation of the usual continuous gauge anomalies. They have interesting applications in model building. As an example we consider the constraints on the Z_N “generalized matter parities” of the supersymmetric standard model. We show that only a few (including the standard R-parity) are “discrete anomaly free” unless the fermion content of the minimal supersymmetric standard model is enlarged.