Vector Approaches Research Articles

Galanin and galanin receptors in epilepsy

The shift in the balance between the inhibition and the excitation in favor of the latter is a major mechanism of the evolvement of epileptic seizures. On the neurotransmitter level two major players contribute to such misbalance: an inhibitory transmitter gamma-aminobutyric acid, and an excitatory amino acid glutamate. Neuropeptides are powerful modulators of classical neurotransmitters, and thus represent an intriguing tool for restoring the balance between the inhibition and the excitation, through either blocking or activating peptide receptors depending on whether a peptide is pro- or anticonvulsant. Galanin, a 29-amino acid residues neuropeptide which inhibits glutamate release in the hippocampus, is a likely member of the anticonvulsant peptide family. During the past decade growing evidence has been suggesting that galanin is in fact a powerful inhibitor of seizure activity. This review summarizes the state of research of galanin in epilepsy, beginning with the first simple experiments which showed that central injection of galanin agonists inhibited seizures, and that seizures themselves affected galanin signaling in the hippocampus; exploring the impact of active manipulation with the expression of galanin and galanin receptors on seizures, using transgenic animals, antisense and peptide-expressing vector approaches; and concluding with the recent advances in pharmacology, which led to the synthesis of non-peptide galanin receptor agonists with anticonvulsant properties. We also address recently established functions of galanin in seizure-associated neuronal degeneration and neuronal plasticity.

Real wave vectors for dynamic analysis of periodic structures

A modified version of the traditional wave vector computational scheme for the dynamic analysis of long undamped periodic structures is presented. First, the consistency of the complex wave vector mathematical formulation is discussed, placing particular emphasis on the real or complex nature of the resulting characteristic equation from which the natural frequencies are derived. It is shown that the rearrangement in terms of complex waves entering the domain, devised to overcome ill-conditioning arising in the transfer matrix formulation, entails as a side effect an ill-posed problem, as it leads to a complex characteristic equation in a real unknown. Next, the proposed approach is described. It provides for transformation of frequency-dependent real transfer matrices for state vectors to real transfer matrices for wave vectors, thus avoiding an ill-conditioned and ill-posed problem. Finally, applications to mono-coupled and bi-coupled structures are illustrated, aiming at comparing the proposed method with the transfer matrix and complex wave vector approaches.

Theory of Machines and Mechanisms

Theory of Mechanisms by John J. Uicker, Gordon R. Pennock and Joseph E. Shigley, 3rd Edition. Oxford Press, 2003The scholarship of the late Joseph Shigley continues to influence mechanical design education almost a decade after his death in 1994 through the publication of new editions of his books Theory of Machines and Mechanisms (Oxford Press) with Profs. Uicker and Pennock, and his Mechanical Engineering Design (McGraw-Hill) with Prof. Mischke. The Theory of Machines and Mechanisms traces itself to the integration of Prof. Shigley’s Kinematic Analysis of Mechanisms and Dynamic Analysis of Machines into the single book Theory of Machines in 1961. John Uicker worked with Prof. Shigley on the 1995 second edition that included the analysis of spatial mechanisms and robots using vector formulations adapted for numerical computation. For this third edition, Gordon Pennock joins Prof. Uicker to provide an impressive new look to this classic text. The book is divided into three basic parts: kinematics and mechanisms, the design of mechanisms, and dynamics of machines. In the first part, the focus is on the analysis of mechanical movement, and I like the vector and matrix formulation that includes kinematic coefficients because it provides a convenient transition to the analysis of spatial mechanisms and robots. The graphical and complex vector approaches, which are well adapted to the study of planar mechanisms, are carefully presented as well. The second part is a survey of cams, gearing and linkages, and robot kinematics. The third part presents the force analysis, vibration and balancing of a range of machine systems including engines, flywheels, governors and gyroscopes. My primary concern with this book is that machine theory of the past necessarily focused on the velocity, acceleration and forces in a device at one particular configuration, while it is the value of these parameters throughout the movement that is of interest. Prof. Uicker’s Integrated Mechanisms Program (IMP), which dates back to 1964, was among the first software systems for machine simulation, and Prof. Pennock is a leading researcher in robot and spatial linkage analysis. I hope that their future editions move in the direction of showing students how to analyze and simulate the movement of machine systems using the computers that are available to most all engineers. In any case, this book provides an excellent presentation of machine theory with a depth and breadth that can find use in courses ranging from an undergraduate survey of machine theory to an advanced undergraduate or even graduate level course on machine kinematics and dynamics. Practicing engineers will find this book to be a valuable reference on the principles of machine theory.

SEAD: secure efficient distance vector routing for mobile wireless ad hoc networks

An ad hoc network is a collection of wireless computers (nodes), communicating among themselves over possibly multihop paths, without the help of any infrastructure such as base stations or access points. Although many previous ad hoc network routing protocols have been based in part on distance vector approaches, they have generally assumed a trusted environment. In this paper, we design and evaluate the Secure Efficient Ad hoc Distance vector routing protocol (SEAD), a secure ad hoc network routing protocol based on the design of the Destination-Sequenced Distance-Vector routing protocol. In order to support use with nodes of limited CPU processing capability, and to guard against Denial-of-Service attacks in which an attacker attempts to cause other nodes to consume excess network bandwidth or processing time, we use efficient one-way hash functions and do not use asymmetric cryptographic operations in the protocol. SEAD performs well over the range of scenarios we tested, and is robust against multiple uncoordinated attackers creating incorrect routing state in any other node, even in spite of any active attackers or compromised nodes in the network.

Propagation of MHD waves in a plasma in a sheared magnetic field with straight field lines

The propagation of MHD plasma waves in a sheared magnetic field is investigated. The problem is solved using a simplified model: a cold plasma is inhomogeneous in one direction, and the magnetic field lines are straight. The waves are assumed to travel in the plane perpendicular to the radial coordinate (i.e., the coordinate along which the plasma and magnetic field are inhomogeneous). It is shown that the character of the singularity at the resonance surface is the same as that in a homogeneous magnetic field. It is found that the shear gives rise to the transverse dispersion of Alfven waves, i.e., the dependence of the radial component of the wave vector on the wave frequency. In the presence of shear, Alfven waves are found to propagate across magnetic surfaces. In this case, the transparent region is bounded by two turning points, at one of which, the radial component of the wave vector approaches infinity and, at the other one, it vanishes. At the turning point for magnetosonic waves, the electric and magnetic fields are finite; however, the radial component of the wave vector approaches infinity, rather than vanishes as in the case with a homogeneous field.

Three-dimensional vector radiative transfer in a semi-infinite, Rayleigh scattering medium exposed to spatially varying polarized radiation: generalized reflection matrix

Three-dimensional vector radiative transfer in a semi-infinite medium exposed to spatially varying, polarized radiation is studied. The problem is to determine the generalized reflection matrix for a multiple scattering medium characterized by a 4×4 scattering matrix. A double integral transform is used to convert the three-dimensional vector radiative transfer equation to a one-dimensional form, and a modified Ambarzumian's method is then applied to derive a nonlinear integral equation for the generalized reflection matrix. The spatially varying backscattered radiation for an arbitrarily polarized incident beam can be found from the generalized reflection matrix. For Rayleigh scattering and normal incidence and emergence, the generalized reflection matrix is shown to have five non-zero elements. Benchmark results for these five elements are presented and compared to asymptotic results. When the incident radiation is polarized, the vector approach used in this study correctly predicts three-dimensional behavior, while the scalar approach does not. When the incident radiation is unpolarized, both the vector and scalar approaches predict a two-dimensional distribution of the intensity, but the error in the scalar prediction can be as high as 20%.

Corneal and refractive error astigmatism in Singaporean schoolchildren: a vector-based Javal's rule.

Traditional approaches to Javal's rule do not use data from subjects with oblique astigmatism and have not been used to make predictions about subjects with oblique astigmatism. Vector approaches to analyzing refractive error can circumvent these problems. Subjects were 993 Singaporean schoolchildren. We performed linear regression of refractive error astigmatism on corneal astigmatism, using J0 vectors to describe with-the-rule and against-the-rule astigmatism and J45 vectors to describe oblique astigmatism. We obtained the following statistically significant regression relationships: RJ0 = 0.931 x CJ0 - 0.276 and RJ45 = 0.638 x CJ45 + 0.010, where R and C denote refractive error astigmatism and corneal astigmatism, respectively. Our vector-based Javal's rule gives closer predictions of refractive astigmatism than the original Javal's rule and the simplified Javal's rule and can be applied in cases of corneal oblique astigmatism.

TARGETING GENE THERAPY FOR TRANSPLANTATION WITH VENOM

TARGETING GENE THERAPY FOR TRANSPLANTATION WITH VENOM

Adeno-associated virus vector-mediated gene transfer to somatic cells in the central nervous system

Publisher Summary This chapter focuses on adeno-associated virus vector-mediated gene transfer to somatic cells in the central nervous system (CNS). The recombinant adeno-associated virus (rAAV) vector system incorporates features that make it a good choice for in vivo research. These features include efficient and long-term gene expression in a broad range of organs that appears to be well tolerated by laboratory animals. The brain is a, particularly good target for viral vector approaches because of the topic maps of neuroanatomical organization. Wild-type AAV infection commonly occurs early in life, and up to 80% of the human population is seropositive for AAV. AAV is a dependovirus requiring a helper virus to complete its life cycle. Apart from gene therapy applications, in vivo rAAV somatic cell gene transfer is likely to be useful for disease modeling. The pathology of Parkinson's disease is characterized by movement disorders concomitant with the degeneration of dopaminergic neurons in the substantia nigra and their axons in the striatum. Alzheimer's disease is, in part, a cholinergic deficit supported by the role of the neurotransmitter acetylcholine in memory function.

Infinite Lifshitz point in incommensurate type-I dielectrics

The phenomenological analysis of the pressure-temperature $(P\ensuremath{-}T)$ phase diagram of ${[\mathrm{N}(\mathrm{C}\mathrm{H}}_{3}{)}_{4}{]}_{2}{\mathrm{CuCl}}_{4}$ (TMATC-Cu) crystals is presented. It is shown that serious disagreement between the experimental results and theory may be removed assuming that the coefficient of the Landau free energy expansion $\ensuremath{\kappa}$ at the gradient term ${(dq/dz)(dq}^{*}/dz)$ changes the sign in the experimental range of pressures. The phase diagram in the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\kappa}$ phase plane is characterized by infinite Lifshitz point (at $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\kappa}}\ensuremath{\infty})$ in which both lines of the phase transitions into the incommensurate phase merge together, whereas the incommensurate wave vector approaches its zero value. The triple point ${(P}_{K}\ensuremath{\approx}55\mathrm{MPa},$ ${T}_{K}\ensuremath{\approx}304\mathrm{K})$ observed in these crystals may be considered as an artificial point, which results from the limitation of experimental resolution. Therefore, even above ${P}_{K}$ there still exist two very close (unresolved) lines of the incommensurate phase transitions.

A comparison of log-linear analysis and contrast vector approaches for modeling fundamental causal structures: A comment on von Eye and Brandtstädter (1998).

A comparison of log-linear analysis and contrast vector approaches for modeling fundamental causal structures: A comment on von Eye and Brandtstädter (1998).

Diagonal stability in the large-scale system approach

Diagonal type Lyapunov functions are ubiquitous in interconnected systems analysis and design, either by the so called vector or scalar Lyapunov function approaches. Clear justification for this phenomenon has not been given in the extensive literature on the field. This paper explains the reasons for this ubiquity, actually justifying the necessity of diagonal stability in this context.

Contribution to parallel and vector computation in multibody dynamics

In spite of the continuous and sustained increase in CPU-time performances of modern computer processors, one notes a real eagerness in the scientific community to investigate both the vector and parallel computational approaches. The goal is obviously to attain high-speed simulation whatever the envisaged numerical treatment may be. The aim of the present contribution is, firstly, to point out the advantage of splitting a multibody system into distinct parts in a `coarse grain level' parallelization context, and secondly, to stress the advisability of vectorizing multibody equations of motion in order to compute them in an adequate computer environment.

On the relation between tensor and vector approaches of nematodynamics

In this paper the relationship between tensorial and vector approaches for elastodynamics is examined in the framework of continuum theory of nematics. It will be elucidated that the Lagrange multipliers are required in the tensorial framework as well as the vector framework to assure equivalence between them. A contraction for the tensorial indices in the the time- dependent Ginzburg-Landau equation will be found eventually to result in the vector form concerned with the Ericksen-Leslie equation without flow dynamics.

Generalized multichannel image-filtering structures

Recent works in multispectral image processing advocate the employment of vector approaches for this class of signals. Vector processing operators that involve the minimization of a suitable error criterion have been proposed and shown appropriate for this task. In this framework, two main classes of vector processing filters have been reported in the literature. Astola et al. (1990) introduce the well-known class of vector median filters (VMF), which are derived as maximum likelihood (ML) estimates from exponential distributions. Trahanias et al. (see ibid., vol.2, no.4, p.528-34, 1993 and vol.5, no.6, p.868-80, 1996) study the processing of color image data using directional information, considering the class of vector directional filters (VDF). We introduce a new filter structure, the directional-distance filters (DDF), which combine both VDF and VMF in a novel way. We show that DDF are robust signal estimators under various noise distributions, they have the property of chromaticity preservation and, finally, compare favorably to other multichannel image processing filters.

The effect of an absorptive bottom on the propagation of the coherence function in a shallow-water channel

When a transverse plane wave propagates through a shallow-water channel with random sound-speed fluctuations, the waveforms at different transverse separations no longer correlate perfectly. The associated coherence falls as the in-line propagation distance and the transverse separation increase. In the (lossless) rigid-bottom case, when the waveforms are represented as a summation of normal modes, the multimodal coherence vector obeys a first-order matrix differential equation with in-line propagation distance as the independent variable. The scattering matrix in this differential equation is a function of transverse separation. As the in-line propagation distance approaches infinity, the coherence vector approaches a constant vector times a scalar Dirac delta function centered at zero transverse separation. If the bottom is absorptive rather than rigid, an additional diffusion term appears in the matrix partial differential equation governing the coherence. Diffusion along the transverse separation axis then prevents the creation of a Dirac delta function as the in-line propagation distance increases without limit. This diffusion occurs whenever the imaginary part of the horizontal wave-number component for a particular mode is nonzero. Some graphical outputs depicting the coherence propagation for an absorptive bottom are presented in this paper. [Work supported by ONR Code 321.]

Analytical investigations of horizontal meso-scale momentum equations with Newtonian nudging

This study presents an analytical investigation of the local behaviour of the solution to a mesoscale model with Newtonian nudging when observed winds are time varying. The analysis examines each Fourier component of the time series of observed winds. Unlike the case with a constant observed wind, the nudged wind vector does not asymptotically approach the observed wind. In response to sinusoidal oscillation of the observed wind, the nudged wind vector is always on a half circle connecting the vector ends of the observed and un-nudged modelled winds. When nudging parameter α→0, the nudged wind vector approaches the un-nudged wind; when α→∞, the nudged wind vector approaches the observed wind. For commonly used values of nudging parameter α, the modelled wind field always carries errors.

Fractal volume compression

This research explores the principles, implementation, and optimization of a competitive volume compression system based on fractal image compression. The extension of fractal image compression to volumetric data is trivial in theory. However, the simple addition of a dimension to existing fractal image compression algorithms results in infeasible compression times and noncompetitive volume compression results. This paper extends several fractal image compression enhancements to perform properly and efficiently on volumetric data, and introduces a new 3D edge classification scheme based on principal component analysis. Numerous experiments over the many parameters of fractal volume compression suggest aggressive settings of its system parameters. At this peak efficiency, fractal volume compression surpasses vector quantization and approaches within 1 dB PSNR of the discrete cosine transform. When compared to the DCT, fractal volume compression represents surfaces in volumes exceptionally well at high compression rates, and the artifacts of its compression error appear as noise instead of deceptive smoothing or distracting ringing.

Intensity-dependent absorption and photorefractive properties in cerium-doped BaTiO3 crystals

We report the optical absorption and photorefractive properties of a series of cerium-doped barium titanate crystals. The light-induced absorption and the intensity-dependent two-beam coupling gain coefficient indicate that there are at least two active trap levels in cerium-doped BaTiO3 crystals. The total effective trap density, the Debye screening wave vector, and the intensity-dependent factor increase with cerium-doping concentration as well as the pump beam intensity. The positive light-induced absorption and the negative absorption gain coefficient as the grating wave vector approaches zero indicate that the excitation cross section of shallow traps is larger than that of deep traps. One of these crystals exhibits a two-beam coupling coefficient of 8.06 cm−1 for ordinarily polarized beams, which is the highest ever reported to date. Both electro-optic index grating and absorption grating are contributing to the coupling coefficient. The response time of as-grown cerium-doped BaTiO3 with 15 ppm cerium is 220 ms at an intensity of 800 mW/cm2.

Progress Towards Gene Therapy for the Hemophilias

A variety of vector systems and approaches for transferring the genes for factors VIII and IX are being investigated. This indicates that there is no clearly superior technique that has emerged. However, considerable progress is being made in factor expression in animal models. In addition, as mechanisms of vector biology are elucidated, this facilitates more rational design of vector improvements.