bluuebunny/crossref_metadata_2025 huggingface dataset:
WELL-FORMED SET REPRESENTATIONS OF SOLIDS
Authors: SHAPIRO VADIM
Published: May 2003

All point Membership Classification (PMC) algorithms on solids constructed using regularized set operations require representing and computing neighborhoods of a point with respect to the represented solid. Such computations involve some of the more sensitive and difficult algorithms in solid modeling. We establish the necessary and sufficient conditions under which set-theoretic constructions are well-formed so that PMC amounts to evaluating a ternary logic expression and does not require any neighborhood computations. We demonstrate well-formedness of any monotone set expression whose primitives form a simple arrangement in Ed, and of common representations for polyhedral objects constructed using 'decreasing convex hull' algorithms. Well-formed representations exist for every solid but not for every fixed collection of primitives. We also give a necessary and sufficient test for existence of such representations. Identifying and eliminating neighborhood computations whenever possible should lead to simpler, more efficient, and robust geometric algorithms that are also more suitable for hardware implementation. Finally, well-formed set representations can be trivially translated into representations of solids by real-valued implicit functions.
IMMOBILIZING A SHAPE
Authors: CZYZOWICZ JUREK , STOJMENOVIC IVAN , URRUTIA JORGE
Published: May 2003

Let shape P be any simply-connected set in the plane, bounded by a Jordan curve, that is not a circular disk. We say that a set of points I on the boundary of P immobilize the shape if any rigid motion of P in the plane causes at least one point of I to penetrate the interior of P. We prove that four points always suffice to immobilize any shape. For a large class of shapes, which includes polygons without parallel edges, three points are sufficient to immobilize. An O(n log  n) algorithm is given that finds a set 3 points that immobilize a given polygon without parallel edges. The algorithm becomes linear for convex polygons. Some results are generalized for d-dimensional polytopes, where 2d points are always sufficient and sometimes necessary to immobilize.
THE OBJECT COMPLEXITY MODEL FOR HIDDEN-SURFACE REMOVAL
Authors: GROVE EDWARD F. , MURALI T. M. , VITTER JEFFREY SCOTT
Published: May 2003

We define a new model of complexity, called object complexity, for measuring the performance of hidden-surface removal algorithms. This model is more appropriate for predicting the performance of these algorithms on current graphics rendering systems than the standard measure of scene complexity used in computational geometry.

We also consider the problem of determining the set of visible windows in scenes consisting of n axis-parallel windows in ℝ3. We present an algorithm that runs in optimal Θ(n log  n) time. The algorithm solves in the object complexity model the same problem that Bern3 addressed in the scene complexity model.
ON PIERCING SETS OF AXIS-PARALLEL RECTANGLES AND RINGS
Authors: SEGAL MICHAEL
Published: May 2003

We consider the p-piercing problem for axis-parallel rectangles. We are given a collection of axis-parallel rectangles in the plane and wish to determine whether there exists a set of p points whose union intersects all the given rectangles. We present efficient algorithms for finding a piercing set (i.e, a set of p points as above) for values of p=1,2,3,4,5. The result for 4 and 5-piercing improves an existing result of O(n  log 3 n) and O(n  log 4 n) to O(n  log  n) time. The result for 5-piercing can be applied find an O(n  log 2 n) time algorithm for planar rectilinear 5-center problem, in which we are given a set S of n points in the pane, and wish to find 5 axis-parallel congruent squares of smallest possible size whose union covers S. We improve the existing algorithm for general (but fixed) p to O(np-4 log  n) running time, and we also extend our algorithms to higher dimensional space. We also consider the problem of piercing a set of rectangular rings.
SKEW VORONOI DIAGRAMS
Authors: AICHHOLZER OSWIN , AURENHAMMER FRANZ , CHEN DANNY Z. , LEE D. T. , PAPADOPOULOU EVANTHIA
Published: May 2003

On a tilted plane T in three-space, skew distances are defined as the Euclidean distance plus a multiple of the signed difference in height. Skew distances may model realistic environments more closely than the Euclidean distance. Voronoi diagrams and related problems under this kind of distances are investigated. A relationship to convex distance functions and to Euclidean Voronoi diagrams for planar circles is shown, and is exploited for a geometric analysisis and a plane-sweep construction of Voronoi diagrams on T. An output-sensitive algorithm running in time O(n  log  h) is developed, where n and h are the numbers of sites and non-empty Voronoi regions, respectively. The all nearest neighbors problem for skew distances, which has certain features different from its Euclidean counterpart, is solved in O(n  log  n) time.
3-PIERCING OF d-DIMENSIONAL BOXES AND HOMOTHETIC TRIANGLES
Authors: ASSA EYAL , KATZ MATTHEW J.
Published: May 2003

In the p-piercing problem, a set [Formula: see text] of nd-dimensional objects is given, and one has to compute a piercing set for [Formula: see text] of size p, if such a set exists. We consider several instances of the 3-piercing problem that admit linear or almost linear solutions: (i) If [Formula: see text] consists of axis-parallel boxes in ℛd, then a piercing triplet for [Formula: see text] can be found (if such a triplet exists) in O(n log  n) time, for 3 ≤ d ≤ 5, and in [Formula: see text] time, for d ≥ 6. Based on the solutions for 3 ≤ d ≤ 5, efficient solutions are obtained to the corresponding 3-center problem — Given a set [Formula: see text] of n points of ℛd, compute the smallest edge length λ such that [Formula: see text] can be covered by the union of three axis-parallel cubes of edge length λ. (ii) If [Formula: see text] consists of homothetic triangles in the plane, or of 4-oriented trapezoids in the plane, then a piercing triplet can be found in O(n log  n) time.
ON HAMILTONIAN TRIANGULATIONS IN SIMPLE POLYGONS
Authors: NARASIMHAN GIRI
Published: May 2003

An n-vertex simple polygon P is said to have a Hamiltonian Triangulation if it has a triangulation whose dual graph contains a hamiltonian path. Such triangulations are useful in fast rendering engines in Computer Graphics. We give a new characterization of polygons with hamiltonian triangulations and use it to devise O(n log  n)-time algorithms to recognize such polygons. We also give efficient algorithms for several related problems.
MIXED SPANNING TREES IN THEORY AND PRACTICE
Authors: RICHARDS DANA , SALOWE JEFFREY S.
Published: May 2003

A mixed spanning tree is a tree that seeks to combine the properties of a minimim weight spanning tree and shortest path tree. We concentrate on the problem for complete Euclidean graphs. A survey of prior algorithms is given and several new algorithms are proposed. New analyses of some known algorithms are provided. All the algorithms are compared empirically and it is shown that the algorithms with the best known performance bounds, perform the worst in practice. Evidence is given to support the hypothesis that the performance depends on the algorithm's use of long edges.
ON COMPUTING TRANSLATIONAL SWEPT VOLUMES
Authors: BAEK NAKHOON , SHIN SUNG-YONG , CHWA KYUNG-YONG
Published: May 2003

A swept volume is a nice tool for solving various types of interference problems. Previous investigations have concentrated on sweeping an object along an arbitrary path that results in complex algorithms. We study the most fundamental motion, which is translation along a linear path. After analyzing the structure of the swept volume, we present an incremental algorithm for constructing a swept volume. Our algorithm takes O(n2α(n)+T c ) time where n is the number of vertices in the original object and T c is the time for handling face cycles. When the object is monotone with respect to the sweeping path, we show that its swept volume can be calculated in O(n) time after O(n log  n+k) time preprocessing, where k is the number of regions in the arrangement of the projected image of the object.
CORRIGENDUM TO "AN INCREMENTAL ALGORITHM FOR CONSTRUCTING SHORTEST WATCHMAN ROUTES"
Authors: TAN XUEHOU , HIRATA TOMIO , INAGAKI YASUYOSHI
Published: May 2003

This corrigendum fixes an error that appears in the previously published papers concerning the watchman route problem. A modification to our incremental watchman route algorithm previously presented in this journal is made, which gives an O(n4) time solution to the watchman route problem.
AUTOMATIC RECONSTRUCTION OF 3D CAD MODELS FROM DIGITAL SCANS
Authors: BERNARDINI FAUSTO , BAJAJ CHANDRAJIT L. , CHEN JINDONG , SCHIKORE DANIEL R.
Published: May 2003

We present an approach for the reconstruction and approximation of 3D CAD models from an unorganized collection of points. Applications include rapid reverse engineering of existing objects for use in a virtual prototyping environment, including computer aided design and manufacturing. Our reconstruction approach is flexible enough to permit interpolation of both smooth surfaces and sharp features, while placing few restrictions on the geometry or topology of the object.

Our algorithm is based on alpha-shapes to compute an initial triangle mesh approximating the surface of the object. A mesh reduction technique is applied to the dense triangle mesh to build a simplified approximation, while retaining important topological and geometric characteristics of the model. The reduced mesh is interpolated with piecewise algebraic surface patches which approximate the original points.

The process is fully automatic, and the reconstruction is guaranteed to be homeomorphic and error bounded with respect to the original model when certain sampling requirements are satisfied. The resulting model is suitable for typical CAD modeling and analysis applications.
COMPLEXITY MEASURES FOR ASSEMBLY SEQUENCES
Authors: GOLDWASSER MICHAEL H. , MOTWANI RAJEEV
Published: May 2003

Our work focuses on various complexity measures for two-handed assembly sequences. For many products, there exist an exponentially large set of valid sequences, and a natural goal is to use automated systems to select wisely from the choices. Although there has been a great deal of algorithmic success for finding feasible assembly sequences, there has been very little success towards optimizing the costs of sequences. We attempt to explain this lack of progress, by proving the inherent difficulty in finding optimal, or even near-optimal, assembly sequences. To begin, we define, "virtual assembly sequencing," a graph-theoretic problem that is a generalization of assembly sequencing, focusing on the combinatorial aspect of the family of feasible assembly sequences while temporarily separating out the specific geometric assumptions inherent to assembly sequencing. We formally prove the hardness of finding even near-optimal sequences for most cost measures ion our generalized framework. As a special case, we prove equally strong inapproximability results for the problem of scheduling with AND/OR precedence constraints. Finally, we re-introduce the geometry, and continue by realizing several of these hardness results in rather simple geometric settings. We are able to show strong inapproximability results, for example using an assembly consisting solely of unit disks in the plane.
A VISIBILITY-BASED PURSUIT-EVASION PROBLEM
Authors: GUIBAS LEONIDAS J. , LATOMBE JEAN-CLAUDE , LAVALLE STEVEN M. , LIN DAVID , MOTWANI RAJEEV
Published: May 2003

This paper addresses the problem of planning the motion of one or more pursuers in a polygonal environment to eventually "see" an evader that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. This problem was first introduced by Suzuki and Yamashita. Our study of this problem is motivated in part by robotics applications, such as surveillance with a mobile robot equipped with a camera that must find a moving target in a cluttered workspace.

A few bounds are introduced, and a complete algorithm is presented for computing a successful motion strategy for a single pursuer. For simply-connected free spaces, it is shown that the minimum number of pursuers required is Θ( lg  n). For multiply-connected free spaces, the bound is [Formula: see text] pursuers for a polygon that has n edges and h holes. A set of problems that are solvable by a single pursuer and require a linear number of recontaminations is shown. The complete algorithm searches a finite graph that is constructed on the basis of critical information changes. It has been implemented and computed examples are shown.
COMPUTATIONAL GEOMETRY COLUMN 35
Authors: O'ROURKE JOSEPH
Published: May 2003

The subquadratic algorithm of Kapoor for finding shortest paths on a polyhedron is described.
INTERSECTION PROBLEMS ON SEGMENTS UNDER BOUNDARY UPDATES WITH APPLICATION TO PERSISTENT LISTS
Authors: D'AMORE FABRIZIO , GIACCIO ROBERTO
Published: May 2003

We consider some intersection problems on segments of [Formula: see text] in the partially dynamic setting called boundary update, where updates occur at the boundary of a given region. In particular, we maintain a set S of line segments under (boundary) insertions and deletions, such that, given a line segment ℓ either of fixed slope or originating from a fixed point and given a point p∈S∩ℓ, we can efficiently and orderly report all segments intersecting ℓ; insertions/deletions of segments occur at the boundaries of a vertical infinite slab. We provide practical algorithms requiring [Formula: see text] space, [Formula: see text] time per update and [Formula: see text] time per query, where k is the number of reported segments.

Our results allow both modeling a moving window over a larger data set and answering segment intersection queries at an extra query cost of [Formula: see text]; also, they provide a methodology for designing access methods to temporal databases as well as a new kind of partially persistent lists.
DATA GENERATION FOR GEOMETRIC ALGORITHMS ON NON-UNIFORM DISTRIBUTIONS
Authors: MILLER GARY L. , TALMOR DAFNA , TENG SHANG-HUA
Published: May 2003

We study the geometric properties of point sets that arise in the generation of bounded aspect-ratio meshes and present a constructive formulation to define distributions that allow arbitrary refinements. This formulation can be used to define distributions with one or more singularities, which do not occur in the uniform case but do occur in mesh generation for real-world applications. We give an efficient algorithm for the generation of a point set from these distributions.

This work is in part motivated by the following observation: The Poisson distribution, points placed uniformly and randomly in a fixed dimension, is one of the most commonly used classes of data sets in the experimental evaluation of geometric algorithms and their implementation. However, despite its importance and interest to computational geometry, the Poisson distribution fails to be good test data for triangulation algorithms and software for mesh generation. Consequently, many implemented sequential and parallel algorithms are tuned to work efficiently for the uniform distribution, but fail to be efficient for nonuniform distributions. Even though the focus of our work is on the generation of data for Delaunay-based mesh algorithms, we hope that it will motivate further theoretical investigations on the generation of data for other geometric algorithms and software.
MINIMUM NUMBER OF PIECES IN A CONVEX PARTITION OF A POLYGONAL DOMAIN
Authors: MARTINI H. , SOLTAN V.
Published: May 2003

Let [Formula: see text] be a given nonempty family of directions in the plane. For a multiply connected polygonal domain P with polygonal holes, possibly degenerate, we determine the minimum number of convex polygons into which P is partitioned by linear cuts in the directions from [Formula: see text].
COMPUTATIONAL GEOMETRY COLUMN 36
Authors: O'ROURKE JOSEPH
Published: May 2003

Two results in "computational origami" are illustrated.
THE VLASOV–POISSON SYSTEM WITH STRONG MAGNETIC FIELD IN QUASINEUTRAL REGIME
Authors: GOLSE F. , SAINT-RAYMOND L.
Published: May 2003

Consider the motion of a gas of electrons with a background of ions, subject to the self-consistent electric field and to a constant external magnetic field. As the Debye length and the Larmor radius vanish at the same rate, the asymptotic current density is governed by the 2D1/2 incompressible Euler equation. Establishing limit requires to overcome various difficulties: compactness with respect to the space variable, control of large velocities, oscillations in the time variable. Yet, for particular initial data, the simultaneous gyrokinetic and quasineutral approximation is completely justified.
ON THE RATE OF CONVERGENCE OF APPROXIMATION SCHEMES FOR BELLMAN EQUATIONS ASSOCIATED WITH OPTIMAL STOPPING TIME PROBLEMS
Authors: JAKOBSEN ESPEN ROBSTAD
Published: May 2003

We provide estimates on the rate of convergence for approximation schemes for Bellman equations associated with optimal stopping of controlled diffusion processes. These results extend (and slightly improve) the recent results by Barles & Jakobsen to the more difficult time-dependent case. The added difficulties are due to the presence of boundary conditions (initial conditions!) and the new structure of the equation which is now a parabolic variational inequality. The method presented is purely analytic and rather general and is based on earlier work by Krylov and Barles & Jakobsen. As applications we consider so-called control schemes based on the dynamic programming principle and finite difference methods (though not in the most general case). In the optimal stopping case these methods are similar to the Brennan & Schwartz scheme. A simple observation allows us to obtain the optimal rate 1/2 for the finite difference methods, and this is an improvement over previous results by Krylov and Barles & Jakobsen. Finally, we present an idea that allows us to improve all the above-mentioned results in the linear case. In particular, we are able to handle finite difference methods with variable diffusion coefficients without the reduction of order of convergence observed by Krylov in the nonlinear case.
ABSORPTION-DELAY MODELS OF HEAT TRANSPORT
Authors: SHOWALTER R. E. , VISARRAGA D. B.
Published: May 2003

A temperature jump in water traveling through a pipe is delayed by the absorption of heat into the pipe wall. The convective transport of heat by the water and the conductive exchange with the interior pipe wall are described by an exact but highly singular micro-model. The limiting form of this parabolic initial-boundary-value problem is a distributed microstructure model, which can successively be better approximated by simpler first- and second-order kinetic models. This model provides a means to validate and calibrate these classical multi-temperature kinetic models which are used to describe the delay.
ON SOLVING STOCHASTIC INITIAL-VALUE DIFFERENTIAL EQUATIONS
Authors: BABUŠKA IVO , LIU KANG-MAN
Published: May 2003

This paper addresses the issues involved in solving systems of linear ODE's with stochastic coefficients and loadings described by the Karhunen–Loeve expansion. The Karhunen–Loeve expansion is used to discretize random functions into a denumerable set of uncorrelated random variables, thus providing us for transforming this problem into an equivalent deterministic one. Perturbation error estimates and a priori error estimates between the exact solution and the finite element solution in the framework of Sobolev space are given. The method of successive approximations for finite element solutions is analyzed.
THE ALLEGRO GRAVITATIONAL WAVE DETECTOR
Authors: MCHUGH M. P. , ALLEN Z. , HAMILTON W. O. , JOHNSON W. W. , SANTOSTASI G.
Published: May 2003

The ALLEGRO gravitational wave detector has been in nearly continuous operation for the past four years with a duty cycle of over 90%. The data is continuously filtered for bursts and has a noise level near 12 mK , or 8×10-22 strain/Hz. An initial data exchange under the IGEC has been completed.
TAMA STATUS REPORT
Authors:   TAMA Collaboration, KANDA NOBUYUKI
Published: May 2003

TAMA 300 m laser interferometric gravitational wave detector operated in August and September 1999. We had total four night operation with best strain sensitivity of 3×10-20. The longest continuous locking is over 7 hours. The calibration of the interferometer sensitivity was archived with 1% accuracy in Δh/h. TAMA Phase-I sensitivity is evaluated as S/N~10 for 10 kpc event.
INITIAL OPERATION OF THE INTERNATIONAL GRAVITATIONAL EVENT COLLABORATION
Authors: PRODI G. A. , MARTINUCCI V. , MEZZENA R. , VINANTE A. , VITALE S. , HENG I. S. , ALLEN Z. A. , HAMILTON W. O. , JOHNSON W. W. , MCHUGH M. P. , SANTOSTASI G. , ASTONE P. , BAGGIO L. , CERDONIO M. , CONTI L. , VISCONTI V. Crivelli , ROCCO E. , BASSAN M. , COCCIA E. , MINENKOV Y. , MODENA I. , MOLETI A. , PIZZELLA G. , BLAIR D. G. , IVANOV E. N. , LOCKE C. R. , TOBAR M. E. , BONALDI H. , FALFERI P. , BONIFAZI P. , TERENZI R. , VISCO M. , CARELLI P. , COSMELLI C. , FRASCA S. , PALLOTTINO G. V. , SALEMI F. , D'ANTONIO S. , FAFONE V. , MARINI A. , MAUCELI E. , MODESTINO G. , RONGA F. , VOTANO L. , FORTINI P. , ORTOLAN A. , VEDOVATO G. , TAFFARELLO L. , ZENDRI J. P.
Published: May 2003

The International Gravitational Event Collaboration, IGEC, is a coordinated effort by research groups operating gravitational wave detectors working towards the detection of millisecond bursts of gravitational waves. Here we report on the current IGEC resonant bar observatory, its data analysis procedures, the main properties of the first exchanged data set. Even though the available data set is not complete, in the years 1997 and 1998 up to four detectors were operating simultaneously. Preliminary results are mentioned.
CALIBRATION, DATA DIAGNOSTIC AND DATA VALIDATION
Authors: MOURS B. , VITALE S.
Published: May 2003

This is a brief introductory overview to papers devoted to key steps in preparing data from Gravitational Wave detectors in view of a confident signal extraction.
NON-GAUSSIAN NOISE IN GRAVITATIONAL WAVE RESONANT DETECTORS: EXPLORER AND NAUTILUS REPORT
Authors: BONIFAZI PAOLO
Published: May 2003

The problem of the non-Gaussian and non-stationary noise in the data of the International Gravitational Wave Event Collaboration (IGEC) is investigated for the two detectors Explorer and Nautilus. We report simple tests that show how part of the IGEC events belong to non-Gaussian and non-stationary noise.
MONITORING AND ADAPTIVE REMOVAL OF THE POWER SUPPLY HARMONICS APPLIED TO THE VIRGO READ-OUT NOISE
Authors: BUSKULIC D. , DEROME L. , FLAMINIO R. , HERMEL R. , LACOTTE J. C. , MARION F. , MASSEROT A. , MASSONNET L. , MOURS B. , MORAND R. , PUPPO P. , VERKINDT D. , YVERT M.
Published: May 2003

The VIRGO signal read-out system is based on a sixteen channels architecture. The system is now installed at the site and the noise of eight of the channels has been measured. The noise at 50 Hz and all its harmonics is coherent with a simultaneous measurement of the power supply. The power supply measurement has been used to remove the 50 Hz line and all its harmonics from the signal read-out noise.
IDENTIFICATION AND MONITORING OF VIOLIN MODES USING THE KARHOUNEN–LOÈVE TRANSFORM
Authors: CELLA GIANCARLO , CHICKARMANE VIJAY , VICERÉ ANDREA
Published: May 2003

The Karhounen–Loève(K-L) transform is used as a method to analyze the simulated thermal noise of a simple suspension system. Added to this noise are impulses which are supposed to mimic the effect of creep events in the suspension wires. The K-L transform allows us to identify the internal modes of the suspension's wires (the so-called violin modes), and then monitor their excitation to look for these impulsive events.
ADAPTIVE FILTERING TECHNIQUES FOR INTERFEROMETRIC DATA PREPARATION: REMOVAL OF LONG-TERM SINUSOIDAL SIGNALS AND OSCILLATORY TRANSIENTS
Authors: CHASSANDE-MOTTIN E. , DHURANDHAR S.
Published: May 2003

We propose an adaptive denoising scheme for poorly modeled non-Gaussian features in the gravitational wave interferometric data. Preliminary tests on real data show encouraging results.
THE FOOTPRINTS OF NOISE IN RATIONAL INTERPOLATION
Authors: FOURNIER JEAN-DANIEL , PINDOR MACIEJ
Published: May 2003

The reliability of rational approximations built from noisy data is explored. One considers a rational interpolation f(t) of a function S(t) known only via its, randomly perturbed, values at a finite number of real points. It is found that in the small noise amplitude régime, the zeros and poles of f(t) split into two families: one reflecting the analytic structure of the function S(t); and one made of coalescent zero-pole pairs, most of the time confined in the real and/or complex vicinity of the interpolation interval. This exciting result seems to open the door to the detection of noise and, perhaps, to its subsequent erasure.
DANTE: A PROPOSAL FOR AN INTERACTIVE DATA ANALYSIS TOOL FOR THE VIRGO COLLABORATION
Authors: BIZOUARD M.-A. , ARNAUD N. , BARRAND G. , BARSUGLIA M. , CAVALIER F. , DAVIER M. , HELLO P. , HEUSSE P. , PRADIER T.
Published: May 2003

Dante is an interactive data analysis environment proposed for the VIRGO collaboration. It is based on Open-Scientist, an architecture written in C++ and developed at LAL mainly for the High Energy Physics community. Its modularity and openness guarantees an adaptability to the fast turnover of software technologies. The architecture presents a hierarchical multi-package decomposition in which basic "user" packages (histogramming, fitting, algorithm toolboxes) are independent of facility packages (storage, visualization, command interpreter). The main functionalities of a preliminary implementation of Dante are reviewed.
VEGA, AN ENVIRONMENT FOR GRAVITATIONAL WAVES DATA ANALYSIS
Authors: BUSKULIC D. , DEROME L. , FLAMINIO R. , MARION F. , MASSONET L. , MOURS B. , MORAND R. , VERKINDT D. , YVERT M.
Published: May 2003

A new generation of large scale and complex Gravitational Wave detectors is building up. They will produce big amount of data and will require intensive and specific interactive/batch data analysis. We will present VEGA, a framework for such data analysis, based on ROOT. VEGA uses the Frame format defined as standard by GW groups around the world. Furthermore, new tools are developed in order to facilitate data access and manipulation, as well as interface with existing algorithms. VEGA is currently evaluated by the VIRGO experiment.
SNAG, A TOOLBOX FOR GRAVITATIONAL WAVE DATA ANALYSIS
Authors: FRASCA SERGIO , PALOMBA CRISTIANO , RUFFATO ROBERTO , MAJORANA ETTORE
Published: May 2003

Snag is a MatLab toolbox, developed in the Rome Virgo group, to analyse gravitational data and develop detection methods. It is written using the OOP features of last versions of MatLab programming language and contains a large number of functions, most of which can be accessed by a GUI. Data_Browser is a GUI Snag application to access gravitational antenna sampled data in files.
ABOUT THE DETECTION OF GRAVITATIONAL WAVE BURSTS
Authors: PRADIER T. , ARNAUD N. , BIZOUARD M.-A. , CAVALIER F. , DAVIER M. , HELLO P.
Published: May 2003

Several filtering methods for the detection of gravitational wave bursts in interferometric detectors are presented. These are simple and fast methods which can act as online triggers. All methods are compared to matched filtering with the help of a figure of merit based on the detection of supernovae signals simulated by Zwerger and Müller.
SEARCHING FOR GRAVITATIONAL WAVES FROM INSPIRALING COMPACT BINARIES USING TAMA300 DATA
Authors:   TAMA300 collaboration, TAGOSHI HIDEYUKI , TANAKA TAKAHIRO , KANDA NOBUYUKI , TATSUMI DAISUKE , TELADA SOUICHI , OHASHI MASATAKE
Published: May 2003

We analyzed the 7 hours of continuous data from TAMA300 by using the matched filtering, searching for the gravitational waves from inspiraling compact binaries. For future long-term continuous operation, it is necessary to reduce the computation time. For this purpose, we introduced hierarchical search strategy. We also introduced a χ2-test to avoid the loss of signal due to the non-Gaussian property of noise. In this paper, we report the results from our preliminary analysis.
WORKSHOP ON COINCIDENCE ANALYSIS
Authors: PIZZELLA G.
Published: May 2003

Problems arising when searching for coincidences with multiple gravitational wave detectors are discussed and solutions are proposed. Efficiency for event detection and the timing problem are investigated.
A LIKELIHOOD BASED SCHEME FOR ESTIMATING AND LIMITING RATES IN COINCIDENCE ANALYSIS
Authors: MUKHERJEE SOMA , MOHANTY SOUMYA D.
Published: May 2003

We show how a likelihood based analysis can be used to set upper limits, obtain confidence intervals or make point estimates in a coincidence analysis. This approach is transparent and provides a unified scheme for a wide variety of situations.
BACKGROUND ESTIMATION IN A GRAVITATIONAL WAVE EXPERIMENT
Authors: ASTONE PIA , FRASCA SERGIO , PIZZELLA GUIDO
Published: May 2003

The problem to estimate the background due to accidental coincidences in the search for coincidences in gravitational wave experiments is discussed. The use of delayed coincidences obtained by orderly shifting the event times of one of the two detectors is shown to be the most correct.
NONLINEAR ALGORITHM OF SEARCHING FOR ASTRO-GRAVITY CORRELATIONS
Authors: RUDENKO V. N. , GUSEV A. V.
Published: May 2003

A general scheme of searching for astro-gravity correlations is considered. Main properties of linear (gaussian) algorithms are briefly summarized. A common description of nonlinear asymptotic algorithms is presented and the physical sense of the quasi-optimal sufficient statistics is clarified.
STOCHASTIC BACKGROUND OF GRAVITATIONAL WAVES
Authors: ASTONE PIA , FERRARI VALERIA , MAGGIORE MICHELE , ROMANO JOSEPH D.
Published: May 2003

The search for a stochastic background of gravitational waves is very interesting, both from a cosmological and astrophysical point of view. We give here a brief summary of the status of theoretical predictions, experimental results and data analysis activities.
ROME ALL-SKY SEARCH FOR PERIODIC SOURCES
Authors: FRASCA SERGIO
Published: May 2003

Optimal methods cannot be applied in the search for periodic gravitational sources, because of the high computing power needed. Some ideas on the hierarchical method based on the Hough transform, proposed by the Rome Virgo group, are presented.
SOME PROBLEMS OF TOPOLOGY CHANGE DESCRIPTION IN THE THEORY OF SPACETIME
Authors: KONSTANTINOV M. YU.
Published: May 2003

The problem of topology change description in gravitation theory is analyzed in details. It is pointed out that in standard four-dimensional theories the topology of space may be considered as a particular case of the boundary conditions (or constraints). Therefore to describe the changes of space or spacetime topology the number of the coordinate maps, the order of their junction and the junction conditions must be converted from the class of constraints or boundary data into the class of dynamical variables. In the framework of four-dimensional theory this problem cannot be solved in its general formulation, while it is possible to describe the changes of three-space topology on the given four-manifold. In the framework of multidimensional theories the space (and spacetime) may be considered as the embedded manifolds. It gives the real possibilities both for the dynamical description of the topology of space or spacetime and for the description of the topology changes of general kind.
STRANGE STARS AND RELATED ASTROPHYSICAL PHENOMENA
Authors: CHENG K. S. , DAI Z. G. , LU T.
Published: May 2003

Some historical remarks concerning the strange stars are briefly discussed. The recent developments in physics and dynamical behavior of strange stars are reviewed. Especially, various observational effects in distinguishing strange stars from neutron stars and related interesting astrophysical phenomena are also discussed.
PRIMORDIAL MAGNETIC FIELDS
Authors: ENQVIST KARI
Published: May 2003

The explanation of the observed galactic magnetic fields may require the existence of a primordial magnetic field. Such a field may arise during the early cosmological phase transitions, or because of other particle physics related phenomena in the very early universe reviewed here. The turbulent evolution of the initial, randomly fluctuating microscopic field to a large-scale macroscopic field can be described in terms of a shell model, which provides an approximation to the complete magnetohydrodynamics. The results indicate that there is an inverse cascade of magnetic energy whereby the coherence of the magnetic field is increased by many orders of magnitude. Cosmological seed fields roughly of the order of 10-20 G at the scale of protogalaxy, as required by the dynamo explanation of galactic magnetic fields, thus seem plausible.
A 3D DYNAMIC MODEL OF VASCULAR TREES
Authors: BEZY-WENDLING J. , BRUNO A.
Published: May 2003

A new vascular model is presented. It is a 3D dynamic and functional model in which the organ growth leads to the development of the vascular tree. The growth is controlled by the simulated cells rhythm of regeneration. Since the function of vessels is the irrigation/drainage of the tissue, their geometry follows mainly from the angiogenesis process and depends on some hemodynamic features, like the pressure (at the entrance and the extremities of the tree) and the total flow rate in the organ. At each step of the development, a cost function related to the total blood volume in the vascular tree is minimized. Simulation results concerning both the growth of an arterial tree and its anatomical and physiological characterization are presented with respect to different adjustments of the model parameters. Local or global vascular modifications appearing in pathology (like local hyper-vascularization, for example) are simulated. Other results like the coupling between an arterial and a venous tree, and like the contrast product propagation in an arterial tree are also illustrated. Future works deal with possible extensions of the model to be used in the generation of CT images, and in the simulation of other pathological processes.
BIRTH, DEATH, STEP SIZE, AND THE SHAPE OF DLA
Authors: VOSS RICHARD F.
Published: May 2003

New large-scale off-lattice simulations of 2d diffusion-limited aggregation (DLA) show a richness of cluster morphology approaching electrochemical, fluid, and dielectric experimental systems. Contrary to common belief, the birth, death, and step size of the random walkers are critical in determining asymptotic cluster shape. Numerical instabilities mimic dense radial growth experiments with outer tip suppression, while enhancement produces single arm dominance.
SCALING BEHAVIOR OF THE DENDRITIC BRANCHES OF THALAMIC NEURONS
Authors: KNIFFKI KLAUS-D. , PAWLAK MATTHIAS , VAHLE-HINZ CHRISTIANE
Published: May 2003

The morphology of Golgi-impregnated thalamic neurons was investigated quantitatively. In particular, it was sought to test whether the dendritic bifurcations can be described by the scaling law (d0)n=(d1)n+(d2)nwith a single value of the diameter exponent n. Here d0 is the diameter of the parent branch, d1 and d2 are the diameters of the two daughter branches. Neurons from two functionally distinct regions were compared: the somatosensory ventrobasal complex (VB) and its nociceptive ventral periphery (VBvp). It is shown that for the neuronal trees studied in both regions, the scaling law was fulfilled. The diameter exponent n, however, was not a constant. It increased from n=1.76 for the 1st order branches to n=3.92 for the 7th order branches of neurons from both regions. These findings suggest that more than one simple intrinsic rule is involved in the neuronal growth process, and it is assumed that the branching ratio d0/d1 is not required to be encoded genetically. Furthermore, the results support the concept of the dendritic trees having a statistically identical topology in neurons of VB and VBvp and thus may be regarded as integrative modules.
FRACTAL ASPECTS OF PROTEIN STRUCTURE AND DYNAMICS
Authors: DEWEY T. GREGORY
Published: May 2003

Proteins have well-defined three dimensional structures which are dictated by their amino acid sequence. Despite this great specificity, general structural and dynamic properties exist. Scaling relationships for the radius of gyration and surface area of a large data set of proteins are demonstrated in this work. These results show that proteins scale as collapsed polymers. Thermal fluctuations are examined for two different proteins by an analysis of the Debye-Waller factors derived from X-ray crystallographic data. Long-range correlations exist between fluctuations along the backbone. A disordered Ising model is presented which gives similar correlations. To further examine the role of multiple connectivity in protein structures, the vibrational spectrum for an alpha helix (linear chain with H-bonds) is analyzed from recursive relationships derived using a decimation technique.
FRACTAL MODEL OF BLOOD VESSEL SYSTEM
Authors: KALDA JAAN
Published: May 2003

A possible way of modeling of self-similar biological tree-like structures is proposed. Special attention is paid to the blood-vessel system, with elaboration on a model with certain spatial arrangement of the vessels and reasonable dependence of the blood pressure on the vessels diameter, such that the organism has a homogeneous oxygen supply. A model of the lung is also presented, which reproduces a qualitatively right dependence of the average diameter of the tubes on their generation number. The model of the blood-vessel system is based on suitably generalized Scheidegger’s model of rivers. The statistical characteristics of the modified Scheidegger’s model are established.
SIDEBRANCHING IN NOISELESS DIFFUSION-LIMITED AGGREGATION
Authors: KASSNER K.
Published: May 2003

The equivalence between diffusion-limited aggregation (DLA) and growth in a Laplacian field is exploited to construct an algorithm for the simulation of DLA at large finite noise reduction. This algorithm allows performing of the limit towards infinite noise reduction, yielding a feasible prescription for the simulation of the noiseless, i.e., deterministic limit. Contrary to previous expectations as well as explicit predictions from an analytic theory, clusters grown without noise develop sidebranches. An explanation of this result in terms of the outer radius used in DLA simulations is suggested. Various implications, including the question whether or when noise reduction may accelerate the approach to asymptotic behavior, are discussed.
FRACTAL FRAGMENTATION IN REPLICATIVE SYSTEMS
Authors: LANDINI GABRIEL , RIPPIN JOHN W.
Published: May 2003

This paper describes a cell growth model formed by two cell types in which the cells are capable of displacing adjacent populations. Evolution of the model gives rise to patches that are fractally distributed (fractal fragmentation). The fragmentation of the system is not highly sensitive to the relative proportions of the two cell types, and it reveals new insights into fractal pattern formation. It is suggested that the fractal fragmentation is the natural outcome of multiple small perturbations in spatial rearrangement of the cells during multiplication. In addition, the model could prove useful in explaining both the development and spread of clones in a population of cells, and pattern formation in mosaic animal organs, in neither of which active movement of cells is implicit.
DYNAMIC SCALING OF RIVER-SIZE DISTRIBUTION IN THE EXTENDED SCHEIDEGGER'S RIVER NETWORK MODEL
Authors: NAGATANI TAKASHI
Published: May 2003

The scaling behavior of the river-size distribution is investigated in the river network model. The river network model is an extended version of the Scheidegger’s river model to take into account a flow-dependent meandering. It is shown that the river-size distribution ns(t) satisfies the dynamic scaling law ns(t)≈s−τf(s/tz) and the dynamic exponent z is approximately given by the exponent of the area of the drainage basin. The scaling relationship (2−τ)z=1 is found. The dynamic exponent z (or the exponent of the drainage basin) changes continuously from 1.5 (the value of the Scheidegger’s river) to 1.0 (the value of a linear river), with increasing exponent γ of the flow-dependent meandering, and the exponent τ of the river-size distribution changes from 1.33 to 1.0.
DYNAMICAL MODEL FOR VIRUS SPREAD
Authors: CAMELO-NETO G. , COUTINHO S.
Published: May 2003

The steady state properties of the mean density population of infected cells in a viral spread is simulated by a general forest like cellular automaton model with two distinct populations of cells (permissive and resistant ones) and studied in the framework of the mean field approximation. Stochastic dynamical ingredients are introduced into this model to mimic cells regeneration (with probability p) and to consider infection processes by other means than contiguity (with probability f). Simulations are carried out on a L×L square lattice taking into consideration the eighth first neighbors. The mean density population of infected cells (Di) is measured as a function of the regeneration probability p, and analyzed for small values of the ratio f/p and for distinct degrees of cell resistance. The results obtained by a mean field like approach recovers the simulations results. The role of the resistant parameter R (R≥2) on the steady state properties, is investigated and discussed in comparison with the R=1 monocell case which corresponds to the self organized critical forest model. The fractal dimension of the dead cells ulcers contours was also estimated and analyzed as a function of the model parameters.
MASS MULTIFRACTAL CHARACTERIZATION OF BLOOD VESSEL SYSTEMS
Authors: JESTCZEMSKI F. , SERNETZ M.
Published: May 2003

The blood vessel system as measured on kidney1 and placenta arteries2,3 is known to be a non-homogeneous fractal with a distribution of local dimensions. We interpret this distribution as a mass multifractal property and we have therefore examined the average of the masses Mi(r) and their qth moments within boxes of increasing size r. The centers i of the boxes are randomly distributed on the vessels. The generalized dimensions Dq are introduced by taking the average of (Mi(r)/M0)q-1 over the centers i, according to the probability distribution Mi(r)/M0 (M0: total mass of the cluster). Thus, we have determined Dq by calculating <(Mi(r)/M0)q-1>< centers i> ∝ (r/L)(q-1) Dq (L: diameter of the cluster).
SPREADING OF N DIFFUSING SPECIES WITH DEATH AND BIRTH FEATURES
Authors: HAVLIN S. , BUNDE A. , LARRALDE H. , LEREAH Y. , MEYER M. , TRUNFIO P. , STANLEY H. E.
Published: May 2003

The number of distinct sites visited by a random walker after t steps is of great interest, as it provides a direct measure of the territory covered by a diffusing particle. We review the analytical solution to the problem of calculating SN(t), the mean number of distinct sites visited by N random walkers on a d-dimensional lattice, for d=1, 2, 3 in the limit of large N. There are three distinct time regimes for SN(t). A remarkable transition, for dimension ≥2, in the geometry of the set of visited sites is found. This set initially grows as a disk with a relatively smooth surface until it reaches a certain size, after which the surface becomes increasingly rough. We also review the results for a model for migration and spreading of populations and diseases. The model is based on N diffusing species, where each species has a probability α- of dying (or recovery from a disease) and a probability α+ to give birth (or to infect another species). It is found analytically that when α+ ≈ α- ≠ 0, after a crossover time t× ~ N/2α-, the territory covered by the population is localized around its center of mass while the center of mass diffuses regularly. When α+ > α-, the localization breaks down after a second crossover time and the species diffuse and spread around their center of mass. These results may explain the phenomena of migration and spreading of diseases and population appearing in nature.
GIBBS-THOMSON AND OTHER QUANTITATIVE RELATIONS IN DENDRITIC CRYSTAL GROWTH
Authors: TANAKA A. , YOKOYAMA T.
Published: May 2003

The Gibbs-Thomson relation is well-known in crystal growth. That implies that the temperature of interface is not equal to the melting temperature due to its surface energy. It is, however, a qualitative relation near equilibrium, not clear not only qualitatively but also quantitatively far equilibrium. One of the authors has measured quantitative relation in experimental dendritic, i.e., far equilibrium, crystal growth. We also carried out numerical simulations using Phase Field Model, and obtained new relation. We will discuss this in detail here.
THE ELECTRIC PROPERTIES OF SINTERED CERMET AS A CONTINUUM PERCOLATION MEDIUM
Authors: YOSHIDA KATSUKUNI
Published: May 2003

The percolation process in the sintered Nb-Al2O3 cermet has been investigated by measuring the statistical behavior of the metallic cluster and the critical exponent of the conductivity. The present continuum system has been found to exhibit a percolation character similar to that of the conventional discrete-lattice percolation systems.
VISCOUS FINGERING PATTERNS IN HIGH MOLECULAR WEIGHT POLYMER SOLUTIONS
Authors: KAWAGUCHI MASAMI , MAKINO KYOKO , KATO TADAYA
Published: May 2003

Characteristics of viscous fingering patterns in polymer solutions were investigated by introducing air into a radial Hele-Shaw cell, in which high molecular weight Hydroxypropyl Methyl Cellulose (HPMC) solution was placed. HPMC chains form a chain entanglement easily, which leads to an increase in elasticity. The resulting patterns showed a drastic morphological change from highly branched patterns to tip-splitting patterns to skewering patterns, with an increase in injection pressure. Such a crossover in the fingering patterns could be well correlated with the characteristic quantities of pattern growth, such as the finger width and tip velocity.
SURFACE EXPLOSION IN AUTOCATALYTIC MONOMER-MONOMER REACTIONS
Authors: KOLB M.
Published: May 2003

A lattice model of the A-B type has been introduced recently to describe temporal oscillations and pattern formation for the NO-CO reaction catalyzed by a Pt surface. Under certain experimental conditions one observes the rapid reactional removal of an adsorbed layer upon nucleation — a direct consequence of the autocatalytic nature of the reaction. Here this surface explosion is described by the same model, but now only depending on a single parameter: the initial fraction of A sites. Simulations show that a reactive "cleaning" of the surface is possible for a wide range of A coverages. For low (high) values of the parameter, a transition towards a B (A) poisoned state is observed. Fractal reaction patterns appear in the vicinity of the transition points. Both transitions have large scale characteristics of standard percolation.
PERCOLATIVE TREATMENT OF THE RESTRICTED TRIMOLECULAR REACTION A + 2X ⇌ 3X
Authors: TRETYAKOV A. Yu. , PROVATA A.
Published: May 2003

We indicate the possibility of existence of a percolation-like transition in the behavior of the trimolecular reaction A + 2X ⇌ 3X on a 2-d square lattice, with the initial concentration p of X particles serving as a control parameter. Using a renormalization group approach, we find that the transition value of p falls into the interval 0 ≤ pc < 0.052.
MOTT'S LIKE BEHAVIOR OF ELECTRON TRANSFER REACTIONS
Authors: MALINSKY J. , MOROZOVSKIY A.
Published: May 2003

New model of Long Range Electron Transfer has been suggested to evaluate an electron transfer rate in some structures like proteins. Mott's like behavior has been obtained. It is possible that this description might yield better estimation for an electron rate than one which has been accepted in this field. This phenomenon may bridge proteins and doped semiconductors as far as their conductivity is concerned. Both Franck-Condon factor as well as an electron contribution have been optimized at the same footing. Fit with experimental data is considered to be reasonable. Fractal considerations allow one to account for intervening medium.