bluuebunny/crossref_metadata_2025 huggingface dataset:
APPROXIMATION ALGORITHM FOR MULTIPLE-TOOL MILLING
Authors: ARYA SUNIL , CHENG SIU-WING , MOUNT DAVID M.
Published: May 2003

Milling is the mechanical process of removing material from a piece of stock through the use of a rapidly spinning circular milling tool in order to form some desired geometric shape. An important problem in computer-aided design and manufacturing is the automated generation of efficient milling plans for computerized numerically controlled (CNC) milling machines. Among the most common milling problems is simple 2-dimensional pocket milling: cut a given 2-dimensional region down to some constant depth using a given set of milling tools. Most of the research in this area has focused on generating such milling plans assuming that the machine has a tool of a single size. Since modern CNC milling machines typically have access to a number of milling tools of various sizes and the ability to change tools automatically, this raises the important optimization problem of generating efficient milling plans that take advantage of this capability to reduce the total milling time. We consider the following multiple-tool milling problem: Given a region in the plane and a set of tools of different sizes, determine how to mill the desired region with minimum cost. The problem is known to be NP-hard even when restricted to the case of a single tool. In this paper, we present a polynomial-time approximation algorithm for the multiple-tool milling problem. The running time and approximation ratio of our algorithm depend on the simple cover complexity (introduced by Mitchell, Mount, and Suri) of the milling region.
ON CONNECTING RED AND BLUE RECTILINEAR POLYGONAL OBSTACLES WITH NONINTERSECTING MONOTONE RECTILINEAR PATHS
Authors: ATALLAH MIKHAIL J. , CHEN DANNY Z.
Published: May 2003

We present efficient algorithms for the problems of matching red and blue disjoint geometric obstacles in the plane and connecting the matched obstacle pairs with mutually nonintersecting paths that have useful geometric properties. We first consider matching n red and n blue disjoint rectilinear rectangles and connecting the n matched rectangle pairs with nonintersecting monotone rectilinear paths; each such path consists of O(n) segments and is not allowed to touch any rectangle other than the matched pair that it is linking. Based on a numbering scheme for certain geometric objects and on several useful geometric observations, we develop an O(n log n) time, O(n) space algorithm that produces a desired matching for rectilinear rectangles. If an explicit printing of all the n paths is required, then our algorithm takes O(n log n+λ) time and O(n) space, where λ is the total size of the desired output. We then extend these matching algorithms to other classes of red/blue polygonal obstacles. The numbering scheme also finds applications to other problems.
LOWER BOUNDS FOR STREETS AND GENERALIZED STREETS
Authors: LÓPEZ-ORTIZ ALEJANDRO , SCHUIERER SVEN
Published: May 2003

We present lower bounds for on-line searching problems in two special classes of simple polygons called streets and generalized streets. In streets we assume that the location of the target is known to the robot in advance and prove a lower bound of [Formula: see text] on the competitive ratio of any deterministic search strategy—which can be shown to be tight.

For generalized streets we show that if the location of the target is not known, then there is a class of orthogonal generalized streets for which the competitive ratio of any search strategy is at least [Formula: see text] in the L2-metric—again matching the competitive ratio of the best known algorithm. We also show that if the location of the target is known, then the competitive ratio for searching in generalized streets in the L1-metric is at least 9 which is tight as well.

The former result is based on a lower bound on the average competitive ratio of searching on the real line if an upper bound of D to the target is given. We show that in this case the average competitive ratio is at least 9-O(1/ log D).
DECOMPOSITION AND PARALLELIZATION TECHNIQUES FOR ENUMERATING THE FACETS OF COMBINATORIAL POLYTOPES
Authors: CHRISTOF THOMAS , REINELT GERHARD
Published: May 2003

A convex polytope can either be described as convex hull of vertices or as solution set of a finite number of linear inequalities and equations. Whereas both representations are equivalent from a theoretical point of view, they are not when optimization problems over the polytope have to be solved. It is a challenging task to convert one description into the other. In this paper we address the efficient computation of the facet structure of several polytopes associated with combinatorial optimization problems. New results are presented which are of interest for theoretical investigations as well as for practical optimization.
POLYGON CONTAINMENT AND TRANSLATIONAL IN-HAUSDORFF-DISTANCE BETWEEN SEGMENT SETS ARE 3SUM-HARD
Authors: BAREQUET GILL , HAR-PELED SARIEL
Published: May 2003

The 3SUM problem represents a class of problems conjectured to require Ω(n2) time to solve, where n is the size of the input. Given two polygons P and Q in the plane, we show that some variants of the decision problem, whether there exists a transformation of P that makes it contained in Q, are 3SUM-hard. In the first variant P and Q are any simple polygons and the allowed transformations are translations only; in the second and third variants both polygons are convex and we allow either rotations only or any rigid motion. We also show that finding the translation in the plane that minimizes the Hausdorff distance between two segment sets is 3SUM-hard.
COMPUTING AN ALMOST MINIMUM SET OF SPANNING LINE SEGMENTS OF A POLYHEDRON
Authors: WANG JIAYE , LIU DING YUAN , WANG WENPING
Published: May 2003

A set of spanning line segments (SLS) is a subset of the edges of a finite polyhedron in E 3 such that an arbitrary plane intersects the polyhedron if and only if the plane intersects at least one of the line segments of the SLS. In this paper an algorithm is presented for computing an almost minimum set of spanning line segments for an arbitrary polyhedron [Formula: see text] . When the number of extreme vertices of [Formula: see text] is odd, the computed SLS is minimum; when the number of extreme vertices of [Formula: see text] is even, the size of the computed SLS is at most the minimum size plus one. The algorithm has linear-time complexity for a convex polyhedron, hence is optimal in this case; its time complexity is Θ(m log m) for an arbitrary polyhedron, where m is the number of vertices of the polyhedron.
CONSTRUCTING A STRONGLY CONVEX SUPERHULL OF POINTS
Authors: CHEN WEI , DENG XIAOWEN , WADA KOICHI , KAWAGUCHI KIMIO
Published: May 2003

Let S be a set of n points in the plane and CH(S) be the convex hull of S. We consider the problem of constructing an approximate convex hull which contains CH(S) with strong convexity. An ∊-convex δ-superhull of S is a convex polygon P satisfying the following conditions: (1) P has at most O(n) vertices, (2) P contains CH(S), (3) no vertex of P lies farther than δ outside CH(S), and (4) P remains convex even if its vertices are perturbed by as much as ∊. The parameters ∊ and δ represent the strength of convexity of P and the degree of approximation of P to CH(S), respectively. In this paper, we show that there exists an ∊-convex [Formula: see text]-superhull with at most n vertices for any S and any ∊ ≥ 0 and it can be constructed in O(n log n) time (in O(n) time is S is sorted).
THE L∞ VORONOI DIAGRAM OF SEGMENTS AND VLSI APPLICATIONS
Authors: PAPADOPOULOU EVANTHA , LEE D. T.
Published: May 2003

In this paper we address the L∞ Voronoi diagram of polygonal objects and present application in VLSI layout and manufacturing. We show that L∞ Voronoi diagram of polygonal objects consists of straight line segments and thus it is much simpler to compute than its Euclidean counterpart; the degree of the computation is significantly lower. Moreover, it has a natural interpretation. In applications where Euclidean precision is not essential the L∞ Voronoi diagram can provide a better alternative. Using the L∞ Voronoi diagram of polygons we address the problem of calculating the critical area for shorts in a VLSI layout. The critical area computation is the main computational bottleneck in VLSI yield prediction.
SEARCHING A POLYGONAL REGION FROM THE BOUNDARY
Authors: SUZUKI ICHIRO , TAZOE YUICHI , YAMASHITA MASAFUMI , KAMEDA TIKO
Published: May 2003

Polygon search is the problem of finding mobile intruders who move unpredictably in a polygonal region, using one or more mobile searchers. Different levels of vision are assumed to model the ability of the searchers. In this paper we mainly consider a special case of this problem, termed boundary search, in which a single searcher has to find the intruders from the boundary of the region. Our main result is that a single searcher whose vision is limited to the ray of a single flashlight is just as capable as a single searcher having a light bulb that gives 360° vision, that is, any polygon that can be searched by the latter from the boundary can also be searched by the former from the boundary. The proof of the equivalence uses another new result, termed Monotonic Extension Theorem, together with a two-dimensional diagram called the planar boundary visibility map that represents the status of the search as a function of time. We partially settle a long-standing conjecture on the equivalence of the abilities of two types of searchers, one having two flashlights and the other having full 360° vision, for the general (non-boundary) polygon search problem.
THE SHUFFLING BUFFER
Authors: DEVILLERS OLIVIER , GUIGUE PHILIPPE
Published: May 2003

The complexity of randomized incremental algorithms is analyzed with the assumption of a random order of the input. To guarantee this hypothesis, the n data have to be known in advance in order to be mixed what contradicts with the on-line nature of the algorithm. We present the shuffling buffer technique to introduce sufficient randomness to guarantee an improvement on the worst case complexity by knowing only k data in advance. Typically, an algorithm with O(n2) worst-case complexity and O(n) or O(n log n) randomized complexity has an [Formula: see text] complexity for the shuffling buffer. We illustrate this with binary search trees, the number of Delaunay triangles or the number of trapezoids in a trapezoidal map created during an incremental construction.
COMPUTATIONAL GEOMETRY COLUMN 42
Authors: MITCHELL JOSEPH S. B. , O'ROURKE JOSEPH
Published: May 2003

A compendium of thirty previously published open problems in computational geometry is presented.
FURTHEST SITE ABSTRACT VORONOI DIAGRAMS
Authors: MEHLHORN KURT , MEISER STEFAN , RASCH RONALD
Published: May 2003

Voronoi diagrams were introduced by R. Klein as a unifying approach to Voronoi diagrams. In this paper we study furthest site abstract Voronoi diagrams and give a unified mathematical and algorithmic treatment for them. In particular, we show that furthest site abstract Voronoi diagrams are trees, have linear size, and that, given a set of n sites, the furthest site abstract Voronoi diagram can be computed by a randomized algorithm in expected time O(n log n).
ON GEOMETRIC PATH QUERY PROBLEMS
Authors: CHEN DANNY Z. , DAESCU OVIDIU , KLENK KEVIN S.
Published: May 2003

In this paper, we study several geometric path query problems. Given a scene of disjoint polygonal obstacles with totally n vertices in the plane, we construct efficient data structures that enable fast reporting of an "optimal" obstacle-avoiding path (or its length, cost, directions, etc) between two arbitrary query points s and t that are given in an on-line fashion. We consider geometric paths under several optimality criteria: L m length, number of edges (called links), monotonicity with respect to a certain direction, and some combinations of length and links. Our methods are centered around the notion of gateways, a small number of easily identified points in the plane that control the paths we seek. We give efficient solutions for several special cases based upon new geometric observations. We also present solutions for the general cases based upon the computation of the minimum size visibility polygon for query points.
TERRAIN DECOMPOSITION AND LAYERED MANUFACTURING
Authors: FEKETE SÁNDOR P. , MITCHELL JOSEPH S. B.
Published: May 2003

We consider a problem that arises in generating three-dimensional models by methods of layered manufacturing: How does one decompose a given model P into a small number of sub-models each of which is a terrain polyhedron? Terrain polyhedra have a base facet such that, for each point of the polyhedron, the line segment joining the point to its orthogonal projection on the base facet lies within the polyhedron. Terrain polyhedra are exactly the class of polyhedral models for which it is possible to construct the model using layered manufacturing (with layers parallel to the base facet), without the need for constructing "supports" (which must later be removed). In order to maximize the integrity of a prototype, one wants to minimize the number of individual sub-models that are manufactured and then glued together.

We show that it is NP-hard to decide if a three-dimensional model P of genus 0 can be decomposed into k terrain polyhedra. We also prove a two-dimensional version of this theorem, for the case in which P is a polygonal region with holes. Both results still hold if we are restricted to isothetic objects and/or axis-parallel layering directions.
A POINT-PLACEMENT STRATEGY FOR CONFORMING DELAUNAY TETRAHEDRALIZATION
Authors: MURPHY MICHAEL , MOUNT DAVID M. , GABLE CARL W.
Published: May 2003

A strategy is presented to find a set of points that yields a Conforming Delaunay tetrahedralization of a three-dimensional Piecewise-Linear complex (PLC). This algorithm is novel because it imposes no angle restrictions on the input PLC. In the process, an algorithm is described that computes a planar conforming Delaunay triangulation of a Planar Straight-Line Graph (PSLG) such that each triangle has a bounded circumradius, which may be of independent interest.
DECELERATING CAUSAL BULK VISCOUS COSMOLOGICAL MODELS
Authors: HARKO T. , MAK M. K.
Published: May 2003

The dynamics of a causal bulk viscous cosmological fluid filled flat constantly decelerating noninflationary Robertson–Walker spacetime is considered. The matter component of the Universe is assumed to satisfy a linear barotropic equation of state and the state equation of the small temperature Boltzmann gas. The resulting cosmological models satisfy the condition of smallness of the viscous stress. The evolution of the relaxation time, temperature, bulk viscosity coefficient and comoving entropy of the dissipative cosmological fluid are obtained by assuming several bulk viscosity coefficient-relaxation time relations.
THE COSMOLOGICAL GENE PROJECT: CLUSTER ANALYSIS OF THE ATMOSPHERIC FLUCTUATIONS ON ARCMIN-SCALE IMAGING OF THE COSMIC MICROWAVE BACKGROUND
Authors: JØRGENSEN H. E. , KOTOK E. V. , NOVIKOV I. D. , NASELSKY I. P. , NASELSKY P. D. , VASIL'EV E. V. , PARIJSKIJ YU. , TCIBULEV P.
Published: May 2003

We discuss some aspects of the Cosmological Gene Project started at the Special Astrophysical Observatory (Russia) in 1999. The goal of the project is to measure the anisotropy and polarization of the Cosmic Microwave Background (CMB) and investigation of atmospheric fluctuations and foreground on arcmin-scales using the radio-telescope RATAN-600. We develop the cluster analysis of one-dimensional random fields for the application to the RATAN-600 scans. We analyze the specific properties of peak clusterisation in the RATAN-600 scans which to separate the primordial CMB signal from noise.
OSCILLATING UNIVERSE AS EIGENSOLUTIONS OF COSMOLOGICAL SCHRÖDINGER EQUATION
Authors: CAPOZZIELLO S. , FEOLI A. , LAMBIASE G.
Published: May 2003

We propose a cosmological model which could explain, in a very natural way, the apparently periodic structures of the universe, as revealed in a series of recent observations. Our point of view is to reduce the cosmological Friedman–Einstein dynamical system to a sort of Schrödinger equation whose bound eigensolutions are oscillating functions. Taking into account the cosmological expansion, the large scale periodic structure could be easily recovered considering the amplitudes and the correlation lengths of the galaxy clusters.
MOTION OF TEST PARTICLES AROUND GAUGE MONOPOLES OR NEAR COSMIC STRINGS CONSIDERING SEMICLASSICAL GRAVITATIONAL EFFECTS
Authors: CHAKRABORTY SUBENOY , RAHAMAN Md. FAROOK
Published: May 2003

In this paper, we have studied the motion of test particles near cosmic strings as well as around gauge monopoles with semiclassical gravitational effects. In case of cosmic strings, the nature of the trajectory of the test particle has changed due to the semiclassical effects while for gauge monopole the trajectory has no effect due to the semiclassical consideration.
ORBIT DESIGN AND ANALYSIS FOR THE ASTROD MISSION CONCEPT
Authors: WU AN-MING , XU XIAOHUI , NI WEI-TOU
Published: May 2003

The ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) mission concept is to conduct high-precision measurement of relativistic effects, better determination of the orbits of major asteroids and other solar system parameters, improvement in the measurement of [Formula: see text], measurement of solar angular momentum via Lense–Thirring effect, and the detection of low-frequency gravitational waves and solar oscillations in a single mission. It will be realized by placing a fleet of drag-free spacecraft in solar orbits together with an Earth reference system. Two spacecraft launched into separate solar orbits, as a simple implementation, can reach the opposite side of Sun after traveling about 2.5 years. In this paper, we describe the orbit design process for this simple implementation including the two-body model, initial velocity determination, and optimization consideration. Through fine tuning of the initial velocity, we can have the two spacecraft nearly return to the 2.5 years positions at 7.5 years mission time, which means that the ASTROD mission can have a second good chance to observe Shapiro time delay precisely and to measure the solar Lense–Thirring effect if the mission lasts over 7.5 years. We also calculate the light traveling time and the Shapiro time delay.
ON THE UPPER LIMIT FOR SURFACE TEMPERATURE OF A STATIC AND SPHERICAL BODY
Authors: ŞİŞMAN ALTUĜ
Published: May 2003

An upper limit for surface temperature of a static and spherical body in steady state is determined by considering the gravitational temperature drop (GTD). For this aim, a body consisting of black body radiation (BBR) only is considered. Thus, it is assumed that body has minimum mass and minimum GTD. By solving the Oppenheimer–Volkoff equation, density distribution of self-gravitating thermal photon sphere with infinite radius is obtained. Surface temperature is defined as the temperature at distance of R from centre of this photon sphere. By means of the density-temperature relation of BBR, surface temperature is expressed as a function of central temperature and radius R. Variation of surface temperature with central temperature is examined. It is shown that surface temperature has a maximum for a finite value of central temperature. For this maximum, an analytical expression depending on only the radius is obtained. Since a real static and stable body with finite radius has much more mass and much more GTD than their values considered here, obtained maximum constitutes an upper limit for surface temperature of a real body. This limitation on surface temperature also limits the radiative energy lose from a body. It is shown that this limit for radiative energy lose is a constant independently from body radius and central temperature. Variation of the minimum mass with central temperature is also examined. It is seen that the surface temperature and minimum mass approach some limit values, which are less than their maximums, by making damping oscillations when central temperature goes to infinity.
KINKS, ENERGY CONDITIONS AND CLOSED TIMELIKE CURVES
Authors: GONZÁLEZ-DÍAZ PEDRO F.
Published: May 2003

A link between the possibility of extending a geodesically incomplete kinked spacetime to a spacetime which is geodesically complete and the energy conditions is discussed for the case of a cylindrically-symmetric spacetime kink. It is concluded that neither the strong nor the weak energy condition can be satisfied in the four-dimensional example, though the latter condition may survive on the transversal sections of such a spacetime. It is also shown that the matter which propagates quantum-mechanically in a kinked spacetime can always be trapped by closed timelike curves, but signaling connections between that matter and any possible observer can only be made of totally incoherent radiation, so preventing observation of causality violation.
CHARGED DILATONIC BLACK HOLE AND TEST PARTICLES
Authors: CHAKRABORTY SUBENOY
Published: May 2003

We present a detailed analysis of the motion of test particles around a charged dilatonic black hole, using the Hamilton–Jacobi (HJ) formalism. We have considered test particles with various masses, electric charges and dilatonic charges and examine its behavior both in static and nonstatic cases.
CHARGED BLACK HOLE AND TEST PARTICLES
Authors: RAHAMAN FAROOK
Published: May 2003

A detailed analysis of the motion of test particles have been done around changed black hole. The study of the trajectories of the test particles have been done using the Hamilton–Jacobi formalism. We have considered test particles with various masses and electric charges and examine its behaviour both in static and nonstatic cares.
GENERALIZED SCALAR TENSOR THEORY IN FOUR AND HIGHER DIMENSION
Authors: CHAKRABORTY SUBENOY , GHOSH ARABINDA
Published: May 2003

In this paper, we have considered generalized scalar–tensor theory for four-dimensional Bianchi-I model and also for a five-dimensional cosmological model. We have studied both exponential and power law solutions, considering a bulk viscous fluid. To solve the complicated coupled field equations, we have made assumptions among the physical parameters and solutions have been discussed.
EFFECT OF THE THERMAL PRESSURE ON THE DYNAMICAL EVOLUTION OF THE UNIVERSE
Authors: ZHANG TONG-JIE
Published: May 2003

While the pressureless dust assumption has been widely adopted in the standard model of cosmology, a quantitative estimate of the actual contribution of thermal pressure of the baryonic matter and the hot/cold dark matter to the dynamical evolution of the Universe has not yet been made in literature. In this paper we provide a simple scenario of how the solution, e.g. the age of the Universe, is affected by the inclusion of the thermal pressure of the baryon and dark matter particles.
HAMILTONIAN FLUIDS IN A FRW COSMOLOGY
Authors: TRIAY R. , FLICHE H. H. , NOVELLO M. , DE FREITAS L. R.
Published: May 2003

With the ulterior motivation in mind to investigate the contribution of quantum processes on the dynamics of the expansion of the universe, we investigate dissipative cosmological solutions which preserve the isotropy and the homogeneity. For performing such an investigation, we derive a method which enables us to describe a 2D dynamical system by a Hamiltonian formulation. As formal example, an admissible form for the bulk (viscous) pressure is derived.
GRAVITATIONAL LENSING STATISTICAL PROPERTIES IN GENERAL FRW COSMOLOGIES WITH DARK ENERGY COMPONENT(S): ANALYTIC RESULTS
Authors: ZHU ZONG-HONG
Published: May 2003

Various astronomical observations have been consistently making a strong case for the existence of a component of dark energy with negative pressure in the universe. It is now necessary to take the dark energy component(s) into account in gravitational lensing statistics and other cosmological tests. By using the comoving distance we derive analytic but simple expressions for the optical depth of multiple image, the expected value of image separation and the probability distribution of image separation caused by an assemble of singular isothermal spheres in general FRW cosmological models with dark energy component(s). We also present the kinematical and dynamical properties of these kinds of cosmological models and calculate the age of the universe and the distance measures, which are often used in classical cosmological tests. In some cases we are able to give formulae that are simpler than those found elsewhere in the literature, which could make the cosmological tests for dark energy component(s) more convenient.
LARGE QUANTUM GRAVITY EFFECTS: CYLINDRICAL WAVES IN FOUR DIMENSIONS
Authors: ANGULO MARÍA E. , MENA MARUGÁN GUILLERMO A.
Published: May 2003

Linearly polarized cylindrical waves in four-dimensional vacuum gravity are mathematically equivalent to rotationally symmetric gravity coupled to a Maxwell (or Klein–Gordon) field in three dimensions. The quantization of this latter system was performed by Ashtekar and Pierri in a recent work. Employing that quantization, we obtain here a complete quantum theory which describes the four-dimensional geometry of the Einstein–Rosen waves. In particular, we construct regularized operators to represent the metric. It is shown that the results achieved by Ashtekar about the existence of important quantum gravity effects in the Einstein–Maxwell system at large distances from the symmetry axis continue to be valid from a four-dimensional point of view. The only significant difference is that, in order to admit an approximate classical description in the asymptotic region, states that are coherent in the Maxwell field need not contain a large number of photons anymore. We also analyze the metric fluctuations on the symmetry axis and argue that they are generally relevant for all of the coherent states.
GLOBAL MONOPOLES IN LYRA GEOMETRY
Authors: RAHAMAN F.
Published: May 2003

We present the solutions for the metric outside a monopole resulting from the breaking of a global 0(3) symmetry within the framework of Lyra geometry. We have shown that monopole exerts gravitational force on matter around it.
MODEL INDEPENDENT ACCELERATING UNIVERSE AND THE COSMOLOGICAL COINCIDENCE PROBLEM
Authors: DE LA MACORRA A.
Published: May 2003

We show that the evolution of the quintessence energy density ΩQ is model independent in an accelerating universe. The accelerating behavior has lasted at most 0.5 e-folds of expansion assuming a present day value of ΩQ=2/3. The generic evolution differs from the exact solution by a percentage given by r=2γQ, with γQ=(ρQ+pQ)/ρQ. For a small γQ the evolution remains a good approximation for a long period. Nucleosynthesis bounds on ΩQ suggest that the model independent solution is valid for at least 12 e-folds of expansion which includes then the scale of radiation and matter equality. We can, therefore, establish model independent conditions on the cosmological parameters at some factor scale ai≪a0. Finally, we discuss the relevance of this result to the cosmological coincidence problem.
A COMPARATIVE STUDY OF BONDI-TYPE AND RADIATIVE OUTFLOWS AROUND COMPACT OBJECTS
Authors: CHATTOPADHYAY INDRANIL , CHAKRABARTI SANDIP K.
Published: May 2003

Astrophysical jets are observed to come out with relativistic speed and are extremely collimated. Here we study the effect of momentum deposition by hot photons from the torus like, puffed up inner region of the accretion disc on radial outflows. We calculate the radiative momentum deposition force on the outflows and find that there is a focusing effect. The size of the radiating torus completely determines the location where the radiative force is maximum. We solve the steady state equations of motion of the radial outflow, in Schwarzschild geometry to show that the acceleration achieved is appreciable, when it is compared with Bondi-type outflow. We also show that, the photon momentum deposition force results in bringing the sonic point closer to the black hole thereby resulting in a more energetic outflows as compared to purely thermally driven outflow. Particularly interesting is that in many cases, where bound matters are freed and driven off as outflows after sufficient momentum is deposited.
A GENERALIZED EQUIVALENCE PRINCIPLE
Authors: LYRE HOLGER
Published: May 2003

Gauge field theories may quite generally be defined as describing the coupling of a matter-field to an interaction-field, and they are suitably represented in the mathematical framework of fiber bundles. Their underlying principle is the so-called gauge principle, which is based on the idea of deriving the coupling structure of the fields by satisfying a postulate of local gauge covariance. The gauge principle is generally considered to be sufficient to define the full structure of gauge-field theories. This paper contains a critique of this usual point of view: firstly, by emphazising an intrinsic gauge theoretic conventionalism which crucially restricts the conceptual role of the gauge principle and, secondly, by introducing a new generalized equivalence principle — the identity of inertial and field charge (as generalizations of inertial and gravitational mass) — in order to give a conceptual justification for combining the equations of motion of the matter-fields and the field equations of the interaction-fields.
THE TOPOLOGICAL ORIGIN OF BLACK HOLE ENTROPY
Authors: WU ZHONG CHAO
Published: May 2003

In gravitational thermodynamics, the origin of a black hole's entropy is the topology of its instanton or constrained instanton. We prove that the entropy of an arbitrary nonrotating black hole is one quarter the sum of the products of the Euler characteristics of its horizons with their respective areas. The Gauss–Bonnet-like form of the action is not only crucial for the evaluation, but also for the existence of the entropy. This result covers all previous results on the entropy of a nonrotating black hole with a regular instanton. The argument can be readily extended into the lower or higher dimensional model. The problem of quantum creation of such a black hole is completely resolved.
MAGNETIZED CYLINDRICALLY SYMMETRIC UNIVERSE WITH BULK VISCOSITY
Authors: CHAKRABARTY INDRAJIT , PRADHAN ANIRUDH , SASTE N. N.
Published: May 2003

We consider a magnetic cylindrically symmetric universe with two degrees of freedom in the presence of an electrically neutral viscous fluid. The source of the magnetic field is an electric current along the x-axis. The coefficient of bulk viscosity is assumed to be a power function of the mass density. Without assuming any adhoc law, we obtain a cosmological constant as a decreasing function of time which is supported by results from recent supernovae observations.
TIMELIKE AND SPACELIKE RICCI COLLONEATION VECTORS IN STRING COSMOLOGY
Authors: YILMAZ İHSAN
Published: May 2003

In this paper, we study the consequences of the existence of timelike and spacelike Ricci collineation vectors (RCVs) for string cloud in the context of general relativity. Necessary and sufficient conditions are derived for a space-time with string cloud to admit a timelike RCV parallel to ua and a spacelike RCV parallel to xa. Also, some results are obtained.
DISTORTED BLACK HOLES WITH CHARGE
Authors: FAIRHURST STEPHEN , KRISHNAN BADRI
Published: May 2003

We present new solutions to the Einstein–Maxwell equations representing a class of charged distorted black holes. These solutions are static-axisymmetric and are generalizations of the distorted black hole solutions studied by Geroch and Hartle. Physically, they represent a charged black hole distorted by external matter fields. We discuss the zeroth and first law for these black holes. The first law is proved in two different forms, one motivated by the isolated horizon framework and the other using normalizations at infinity.
DETECTION OF IMPULSIVE LIGHT-LIKE SIGNALS IN GENERAL RELATIVITY
Authors: BARRABÈS C. , HOGAN P. A.
Published: May 2003

The principal purpose of this paper is to study the effect of an impulsive light-like signal on neighbouring test particles. Such a signal can in general be unambiguously decomposed into a light-like shell of null matter and an impulsive gravitational wave. Our results are: (a) If there is anisotropic stress in the light-like shell then test particles initially moving in the signal front are displaced out of this 2-surface after encountering the signal; (b) For a light-like shell with no anisotropic stress accompanying a gravitational wave the effect of the signal on test particles moving in the signal front is to displace them relative to each other with the usual distortion due to the gravitational wave diminished by the presence of the light-like shell. An explicit example for a plane-fronted signal is worked out.
STRUCTURE AND PROPERTIES OF NEUTRON STARS IN THE RELATIVISTIC MEAN-FIELD THEORY
Authors: BEDNAREK ILONA , MANKA RYSZARD
Published: May 2003

Properties of rotating neutron stars with the use of relativistic mean-field theory are considered. The performed analysis of neutron star matter is based on the nonlinear Lgrangian density. The presence of nonlinear interaction of vector mesons modifies the density dependence of the ρ field and influences bulk parameters of neutron stars. The observed quasiperiodic X-ray oscillations of low mass X-ray binaries can be used in order to constrain the equation of state of neutron star matter. Having assumed that the maximum frequency of the quasiperiodic oscillations originates at the circular orbit it is possible to estimate masses and radii of neutron stars.
ON THE HBO MECHANISM OF X-RAY NEUTRON STAR
Authors: ZHANG C. M.
Published: May 2003

We ascribe the 15–60 Hz Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the orbiting accreted matter at the boundary of magnetosphere-disk of X-ray neutron star (NS). Considering the relativistic motion mechanism for the kHz QPO, that the radii of the inner disk and magnetosphere-disk of NS are correlated with each other by a factor is assumed. The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The theoretical relations between 15–60 Hz QPO (HBO) frequency and the twin kHz QPOs are similar to the measured empirical formula. Further, the better fitted NS mass by the proposed model is about 1.9 solar masses for the detected LMXBs.
THE CONSISTENT NEWTONIAN LIMIT OF EINSTEIN'S GRAVITY WITH A COSMOLOGICAL CONSTANT
Authors: NOWAKOWSKI MAREK
Published: May 2003

We derive the "exact" Newtonian limit of general relativity with a positive cosmological constant Λ. We point out that in contrast to the case with Λ=0, the presence of a positive Λ in Einsteins's equations enforces, via the condition |Φ|≪1 on the potential Φ, a range ℛ max (Λ)≫r≫ℛ min (Λ), within which the Newtonian limit is valid. It also leads to the existence of a maximum mass, ℳ max (Λ). As a consequence we cannot put the boundary condition for the solution of the Poisson equation at infinity. A boundary condition suitably chosen now at a finite range will then get reflected in the solution of Φ provided the mass distribution is not spherically symmetric.
DAMPING TIME AND STABILITY OF DENSITY FERMION PERTURBATIONS IN THE EXPANDING UNIVERSE
Authors: SIGISMONDI COSTANTINO , FILIPPI SIMONETTA , RUFFINI REMO , SÁNCHEZ LUIS ALBERTO
Published: May 2003

The classic problem of the growth of density perturbations in an expanding Newtonian universe is revisited following the work of Bisnovatyi-Kogan and Zel'dovich. We propose a more general analytical approach: a system of free particles satisfying semidegenerate Fermi–Dirac statistics on the background of an exact expanding solution is examined in the linear approximation. This differs from the corresponding work of Bisnovatyi-Kogan and Zel'dovich where classical particles fulfilling Maxwell–Boltzmann statistics were considered. The solutions of the Boltzmann equation are obtained by the method of characteristics. An expression for the damping time of a decaying solution is discussed and a zone in which free streaming is hampered is found, corresponding to wavelengths less than the Jeans one. In the evolution of the system, due to the decrease of the Jeans length, those perturbations may lead to gravitational collapse. At variance with current opinions, we deduce that perturbations with λ≥λ J Max /1.48 are able to generate structures and the lower limit for substructures mass is M=M J max /(1.48)3≈M J max /3, where M J max is the maximum value of the Jeans mass.
RICCI COLLINEATIONS OF THE BIANCHI TYPES I AND III, AND KANTOWSKI–SACHS SPACETIMES
Authors: CAMCI U. , BAYSAL H. , TARHAN İ. , YILMAZ İ. , YAVUZ İ.
Published: May 2003

Ricci collineations of the Bianchi types I and III, and Kantowski–Sachs spacetimes are classified according to their Ricci collineation vector (RCV) field of the form (i)–(iv) one component of ξa(xb) is nonzero, (v)–(x) two components of ξa(xb) are nonzero, and (xi)–(xiv) three components of ξa(xb) are nonzero. Their relation with isometries of the spacetimes is established. In case (v), when det (Rab)=0, some metrics are found under the time transformation, in which some of these metrics are known, and the other ones new. Finally, the family of contracted Ricci collineations (CRC) are presented.
STRING COSMOLOGY WITH MAGNETIC FIELD IN BIANCHI V MODEL
Authors: CHAKRABORTY NARAYAN CHANDRA , CHAKRABORTY SUBENOY
Published: May 2003

String Cosmology with magnetic field has been studied for Bianchi V space-time model for different directions of the magnetic field and string. For equation of state, we have examined geometric string (Nambu string), Takabayashi string (p-string), string with uniform energy density or barotropic equation of state. Exact analytic solution is possible only in few cases.
HIGHER DIMENSIONAL COSMOLOGICAL MODEL IN LYRA GEOMETRY
Authors: RAHAMAN FAROOK , BERA JAYANTA KUMAR
Published: May 2003

In this paper Kaluza–Klein cosmological model within the framework of Lyra geometry has been discussed. The physical behavior of the model is examined in vacuum and in the presence of perfect fluids.
DOMAIN WALL IN LYRA GEOMETRY
Authors: RAHAMAN FAROOK , CHAKRABORTY SUBENOY , KALAM MEHEDI
Published: May 2003

In this paper we have evaluated solutions for domain wall in Lyra geometry. Solutions are obtained with separable form for the metric coefficients. Finally acceleration due to the domain wall has been analised by studying geodesic equation.
OPTIMIZED DELTA EXPANSION FOR RELATIVISTIC NUCLEAR MODELS: RENORMALIZATION OF VACUUM FLUCTUATIONS
Authors: MENEZES D. P. , PINTO M. B. , KREIN G.
Published: May 2003

We use the optimized linear δ expansion and functional methods to study vacuum contributions in nuclear matter up to the lowest non-trivial order which includes exchange terms. We show that well known results (MFT, RHA and HF) can be easily reproduced when appropriate limits are taken. Neglecting vacuum contributions we explicitly show that the δ expansion goes beyond the traditional loop approximation previously used to study two loop vacuum contributions in nuclear matter. We then evaluate and renormalize vacuum exchange contributions showing that they are numerically very large, as predicted by the ordinary loop approximation.
EFFECT OF NUCLEAR DEFORMATION ON THE ALPHA-DECAY HALF-LIFE OF EVEN-EVEN ALPHA EMITTERS
Authors: DIMARCO A. , DUARTE S. B. , TAVARES O. A. P. , GONÇALVES M. , GARCÍA F. , RODRÍGUEZ O. , GUZMÁN F.
Published: May 2003

Alpha-decay half-life of even-even emitters has been calculated in terms of tunnelling through a quantum mechanical potential barrier. A multipolar expansion of Coulomb potential has been developed taking into account the nuclear quadrupole, hexadecapole, and hexacontatetrapole deformations. We show that using a free-parameter model the calculated half-lives do not vary significantly with higher order multipolarities of the daughter nucleus deformation.
THE NUCLEAR SCALAR POTENTIAL AND THE EMC EFFECT
Authors: ROŻYNEK JACEK
Published: May 2003

Based on the relativistic mean field model of nuclear matter with scalar and vector components, a convolution model of deeply inelastic electron-nucleus scattering has been developed. The influence of the scalar potential changes the nucleon structure function inside the nucleus and ensures agreement with the experiment in the Björken x>0.2. The Sum Rules are discussed. The role of the relativistic scalar and vector nuclear potential in the nucleus is shown.
SIMILARITY ANALYSIS OF NONLINEAR EQUATIONS AND BASES OF FINITE WAVELENGTH SOLITONS
Authors: LUDU A. , STOITCHEVA G. , DRAAYER J. P.
Published: May 2003

We introduce a generalized similarity analysis which grants a qualitative description of the localised solutions of any nonlinear differential equation. This procedure provides relations between amplitude, width, and velocity of the solutions, and it is shown to be useful in analysing nonlinear structures like solitons, dublets, triplets, compact supported solitons and other patterns. We also introduce kink-antikink compact solutions for a nonlinear-nonlinear dispersion equation, and we construct a basis of finite wavelength functions having self-similar properties.
ROTATIONAL-INVARIANT MODEL OF THE STATES WITH Kπ=1+ AND THEIR CONTRIBUTION TO THE SCISSORS MODE
Authors: KULIEV A. A. , AKKAYA R. , ILHAN M. , GULIYEV E. , SALAMOV C. , SELVI S.
Published: May 2003

Within the Random-Phase Approximation the method of self-consistent determination of the isoscalar and isovector effective separable interactions restoring a broken symmetry of the deformed mean-field is given. The method allows to treat more rigorously without free parameters the properties of the scissors mode and is used to develop the rotational invariant microscopic model of the states with Kπ=1+. The spurious state separates out and has zero energy. An important consequence of this separation is the fragmentation of the scissors mode and the collectivization of the low-lying 1+ states. In addition to the isoscalar restoring interactions the consideration of the isovector restoring forces in calculations causes the splitting of the states with large B(M1) strength at low energy. The model contains a single parameter of isovector spin-spin interactions and it allows one to describe satisfactorily the fragmentation of the scissors mode and the dependence of the summed B(M1) strength on δ2 and A in deformed nuclei.
PARITY-PROJECTED RESONATING HARTREE-FOCK APPROXIMATION TO THE LIPKIN MODEL
Authors: NISHIYAMA SEIYA , IDO MORIYOSHI , ISHIDA KAZUHIRO
Published: May 2003

An exact eigenstate of the Lipkin-model Hamiltonian has a parity-symmetry. The resonating Hartree-Fock (Res-HF) ground-state wave function however breaks the parity-symmetry. To restore the parity-symmetry, we develop a parity-projected (P-P) Res-HF approximation to the Lipkin model. The P-P Res-HF wave function is superposed by two P-P Slater determinants. Self-consistent calculation is carried out so as to optimize the P-P Res-HF energy functional. A Res-HF ground state with definite parity brings us the ground-state energy much nearer to the exact one than that the Res-HF and explains most of the ground-state correlation energy. We also show behaviour of P-P Res-HF orbital energies and mixing coefficients calculated by the P-P Res-HF approximation and compare them with those calculated by the parity-unprojected Res-HF approximation. From this comparison, we find very interesting relations between them which have never been seen in the parity-unprojected Res-HF calculation.
FIRST-ORDER APPROXIMATION OF THE NUMBER-PROJECTED SO(2N) TAMM-DANCOFF EQUATION AND ITS REDUCTION BY THE SCHUR FUNCTION
Authors: NISHIYAMA SEIYA
Published: May 2003

First-order approximation of the number-projected (NP) SO(2N) Tamm-Dancoff (TD) equation is developed to describe ground and excited states of superconducting fermion systems. We start from an NP Hartree-Bogoliubov (HB) wave function. The NP SO(2N) TD expansion is generated by quasi-particle pair excitations from the degenerate geminals in the number-projected HB wave function. The Schrödinger equation is cast into the NP SO(2N) TD equation by the variation principle. We approximate it up to first order. This approximate equation is reduced to a simpler form by the Schur function of group characters which has a close connection with the soliton theory on the group manifold.
QUANTUM RECOIL AND THE GAMMA-RAY AMPLIFICATION BY STIMULATED EMISSION OF RADIATION FROM POSITRONS CHANNELLING IN AN ACOUSTICALLY EXCITED CRYSTAL
Authors: ZHANG QI-REN
Published: May 2003

The importance of the quantum recoil in the possible gamma-ray amplification by stimulated emission of radiation from positrons channelling in an acoustically excited crystal is emphasized.
ENERGY ANALYSIS OF A NONLINEAR MODEL OF THE NORMAL HUMAN LUNG
Authors: ATHANASIADES A. , GHORBEL F. , CLARK J. W. , NIRANJAN S. C. , OLANSEN J. , ZWISCHENBERGER J. B. , BIDANI A.
Published: May 2003

Despite the existence of respiratory mechanics models in the literature, rarely one finds analytical expressions that predict the work of breathing (WOB) associated with natural breathing maneuvers in non-ventilated subjects. In the present study, we develop relations that explicitly identify WOB, based on a proposed nonlinear model of respiratory mechanics. The model partitions airways resistance into three components (upper, middle and small), includes a collapsible airways segment, a viscoelastic element describing lung tissue dynamics and a static chest wall compliance. The individual contribution of these respiratory components on WOB is identified and analyzed. For instance, according to model predictions, during the forced vital capacity (FVC) maneuver, most of the work is expended against dissipative forces, mainly during expiration. In addition, expiratory dissipative work during FVC is almost equally partitioned among the upper airways and the collapsible airways resistances. The former expends work at the beginning of expiration, the latter at the end of expiration. The contribution of the peripheral airways is small. Our predictions are validated against laboratory data collected from volunteer subjects and using the esophageal catheter balloon technique.
STABILITY OF A 2-DIMENSIONAL NEURAL NETWORK WITH TIME DELAYS
Authors: MA W. , HARA T. , TAKEUCHI Y.
Published: May 2003

A 2-dimensional neural network with time delayed connections between neurons is considered. Based on the construction of Liapunov functionals, we obtain sufficient criteria to ensure local and global asymptotic stability of the equilibrium of the neural network.
GLOBAL STABILITY FOR A PHYTOPLANKTON-NUTRIENT SYSTEM
Authors: PARDO OLIVIER
Published: May 2003

The model proposed by A. H. Taylor et al. [18] is discussed, with a view to determining the global asymptotic stability of the equilibria. The system consists of two autonomous differential equations, modeling the couple Phytoplankton-Nutrient with no delay on the recycling efficiency of nutrient by bacterial decomposition. Two distinct cases, persistence and extinction of phytoplankton are considered. In each case we will state the local and then the global stability of the equilibria by constructing an appropriate Lyapunov function and using the LaSalle's invariance principle. Also, in the case of extinction of phytoplankton we have introduced a supply of nutrient in the system and we have revealed the bloom of phytoplankton, which appears biologically in upwelling conditions.