bluuebunny/crossref_metadata_2025 huggingface dataset:
NONRECURRENCE PROBLEM IN EVOLUTION OF A HARD-DISK SYSTEM
Authors: SOMSIKOV V. M.
Published: July 2002

The evolution of a hard-disk system has been investigated on the bases of the matrix of pair collision (MPC). With the help of MPC the motion equations of this system have been derived. From the properties of the motion equations it was found that as a result of collisions the integral force acting on any disk subsystem tends to zero. It was found that the magnitude of possible fluctuations in the system is to be defined by the condition t fluct ≤ t kin , where t kin is the characteristic time, which determined by kinetic potential defined relevant point of a phase space. The t fluct time is determined by the probability laws. The analysis of the obtained results testifies that the nature of the nonrecurrence are determined by the fundamental symmetry principles.
CONTROLLING SPATIOTEMPORAL CHAOS IN OPTICAL SYSTEMS
Authors: KAHAN SANDRA , MONTAGNE RAÚL
Published: July 2002

We investigate analytically and numerically a nonfeedback control technique for spatially extended systems. The method is suited for systems where some parameters can be modified. We apply the control scheme to a model used to describe vectorial transverse pattern formation in nonlinear optical systems, the Vector Complex Ginzburg–Landau Equation (VCGLE). Our scheme stabilizes a periodic regime where otherwise a chaotic regime is observed. We confirm by analytical calculation and direct simulation how this scheme, based in the use of a nonlinear diffraction term, stabilizes unstable polarized standing waves and linearly polarized traveling waves in a chaotic scenery.
RTD-BASED CELLULAR NEURAL NETWORKS WITH MULTIPLE STEADY STATES
Authors: ITOH MAKOTO , JULIÁN PEDRO , CHUA LEON O.
Published: July 2002

In this paper, we study the relationship between the standard cellular neural network (CNN) and the resonant tunneling diode (RTD)-based CNN. We investigate the functional and advanced capabilities of a new generation of CNNs that exploit the multiplicity of steady states. We also include in the analysis higher order CNNs. Furthermore, some methods for designing RTD-based CNNs with multiple steady states are presented.
PERIODIC AND APERIODIC STOCHASTIC RESONANCE WITH OUTPUT SIGNAL-TO-NOISE RATIO EXCEEDING THAT AT THE INPUT
Authors: CHAPEAU-BLONDEAU FRANÇOIS
Published: July 2002

Stochastic resonance (SR) is a nonlinear effect whereby a system is able to improve, via noise addition, the detectability of a signal in noise. SR has been demonstrated with different types of systems and signals where in each case, an appropriate detectability measure is shown improvable at the output of the stochastic resonator when noise is added at its input. A complementary issue, important for practical applications of SR, is the possibility of making the signal detectability at the ouput exceed that at the input when noise is added. We demonstrate this possibility, for both periodic and aperiodic SR, with a simple nonlinear system that we show exactly tractable analytically.
DISCRETE WAVELET MODELS FOR IDENTIFICATION AND QUALITATIVE ANALYSIS OF CHAOTIC SYSTEMS
Authors: BILLINGS S. A. , COCA D.
Published: July 2002

This paper develops an original approach for identifying models of chaotic systems directly from noise-corrupted data. The nonlinear functional describing the process is constructed using a new multiresolution model structure implemented with B-spline wavelet and scaling functions. Following an iterative strategy, a sequence of model sets of increasing complexity are postulated and tested until a suitable model is found. An orthogonal-forward-regression routine coupled with model validity tests is used to select parsimonious wavelet models and to measure the quality of the fit. The effectiveness of the identification procedure is demonstrated using both simulated and experimental data. It is shown that the proposed method can produce accurate models which exhibit qualitatively the same dynamical behavior as the observed system and are characterized by dynamical invariants which are very close to those of the original system.
COLOR MAP OF LYAPUNOV EXPONENTS OF INVARIANT SETS
Authors: MONTI MARCO , PARDO WILLIAM B. , WALKENSTEIN JONATHAN A. , ROSA EPAMINONDAS , GREBOGI CELSO
Published: July 2002

The largest Lyapunov exponent of the Lorenz system is used as a measure of chaotic behavior to construct parameter space color maps. Each color in these maps corresponds to different values of the Lyapunov exponent and indicates, in parameter space, the locations of different levels of chaos for the Lorenz system. Practical applications of these maps include moving in parameter space from place to place without leaving a region of specific behavior of the system.
A RECYCLED CHARACTERIZATION OF KNEADING SEQUENCES
Authors: THUNBERG H.
Published: July 2002

For any infinite sequence E on two symbols one can define two sequences of positive integers S(E) (the splitting times) and T(E) (the cosplitting times), which each describe the self-replicative structure of E. If E is the kneading sequence of a unimodal map, it is known that S(E) and T(E) carry a lot of information on the dynamics, and that they are disjoint. We show the reverse implication: A nonperiodic sequence E is the kneading sequence of some unimodal map if the sequences S(E) and T(E) are disjoint.
SYNCHRONOUS AND ASYNCHRONOUS CHAOS IN COUPLED NEUROMODULES
Authors: PASEMANN FRANK
Published: July 2002

The parametrized time-discrete dynamics of two recurrently coupled neuromodules is studied analytically and by computer simulations. Conditions for the existence of synchronized dynamics are derived and periodic as well as quasiperiodic and chaotic attractors constrained to a synchronization manifold M are observed. Stability properties of the synchronized dynamics is discussed by using Lyapunov exponents parallel and transversal to the synchronization manifold. Simulation results are presented for selected sets of parameters. It is observed that locally stable synchronous dynamics often coexists with asynchronous periodic, quasiperiodic or even chaotic attractors.
ASYMPTOTIC SYNCHRONIZATION IN NETWORKS OF LOCALLY CONNECTED OSCILLATORS
Authors: LABBI ABDERRAHIM , MILANESE RUGGERO , BOSCH HOLGER
Published: July 2002

In this paper, we describe the asymptotic behavior of a network of locally connected oscillators. The main result concerns asymptotic synchronization. The presented study is stated in the framework of neuronal modeling of visual object segmentation using oscillatory correlation. The practical motivations of the synchronization analysis are based on neurophysiological experiments which led to the assumptions that existence of temporal coding schemes in the brain by which neurons, with oscillatory dynamics, coding for the same coherent object synchronize their activities, while neurons coding for different objects oscillate with nonzero phase lags. The oscillator model considered is the FitzHugh–Nagumo neuron model. We restrict our study to the mathematical analysis of a network of such neurons. We firstly show the motivations and suitability of choosing FitzHugh–Nagumo oscillator, mainly for stimulus coding purposes, and then we give sufficient conditions on the coupling parameters which guarantee asymptotic synchronization of oscillators receiving the same external stimulation (input). We have used networks of such oscillators to design a layered architecture for object segmentation in gray-level images. Due to space limitations, description of this architecture and simulation results are briefly referred to by the end of the paper.
SEIFERT UNIONS AND SPACES OF GRAPHS IN S3
Authors: GOMEZ-LARRAÑAGA J. C. , HEIL WOLFGANG H.
Published: July 2002

Let Γ be a non-splittable in S3, not a tree. It is shown that if the space [Formula: see text] of Γ is a Seifert union of solid tori then M is homeomorphic to the space of a tree of Burde-Murasugi links.
REEXAMINING THE UNIVERSALITY OF THE BURKERT PROFILE ON CLUSTER SCALES: DARK MATTER CORES
Authors: XUE YAN-JIE , WU XIANG-PING
Published: July 2002

The Burkert profile is a competing candidate for the analytic approximation of virialized dark halos especially when dark matter particles have a finite cross-section for elastic collisions. In this paper we reexamine its universality in massive systems, using an ensemble of 45 nearby X-ray clusters and 20 distant X-ray/lensing clusters. Despite the fact that this empirical profile turns out a great success on galactic scales and also reproduces approximately the X-ray observed surface brightness profiles of clusters, the dark matter cores of clusters predicted by the Burkert profile are too large to be reconciled with the strong gravitational lensing measurements. Specifically, the typical dark halo cores of clusters represented by the Burkert profile are about 0.2 Mpc, and only a small fraction (~1/4) of clusters can have compact cores smaller than 0.1 Mpc. This will constitute a critical challenge to the Burkert profile as a universal dark matter density law over entire mass ranges.
BLUESHIFTS IN ABSORPTION LINES OF QUASI-STELLAR OBJECTS?
Authors: BASU D.
Published: July 2002

Possibility of misidentification of emission lines of QSOs and thereby missing detection of blueshifts have been suggested and demonstrated in literature. It is shown here that absorption lines observed in the spectra of QSOs may also have been misidentified. Plenty search lines are available at higher wavelengths (red/IR regions) for identification with observed absorption lines, although lines from lower wavelengths (UV/blue regions) are always considered for identification. Re-examination of the published spectra of ten QSOs shows that the observed absorption lines can be interpreted as blueshifted, with same or better accuracy and sometimes more convincingly than redshifts. Objects on the sight line are identified with same emission blueshift as the blueshift of the absorption system of the QSO, the emission spectrum of the QSO itself being of course interpreted as blueshifted as well. It is proposed that the absorbers are probably linked with the QSO either physically or tidally/gravitationally as a result of some ejection mechanism. The observed blueshifts of spectral lines in emission and absorption can be explained in a model comprising of multiple expanding universes.
EXPERIMENTAL HINTS OF GRAVITY IN LARGE EXTRA DIMENSIONS?
Authors: SIGURDSSON STEINN
Published: July 2002

Recent conjectures suggest the universe may have large extra dimensions, through which gravity propagates. This implies gross departures from Newton's law of gravity at small length scales. Here I consider some implications for particle dynamics on scales comparable to the compactification radius, R c ≲1 mm. During planet formation, coalescence of micron sized dust grains to planetesimals is a rate critical step. Blum et al. (2000) found dust grain aggregates form low fractal dimension structures in microgravity, consistent with high angular momentum coalescence. I consider the effects of non-Newtonian gravity on dust aggregation on scales less than R c and show they naturally coalesce into low-dimensional structures with high specific angular momentum. We infer R c ≈80 microns.
COSMOLOGICAL TERM AS A CORRECTION OF METRIC TENSOR FIELD
Authors: FUKUI TAKAO
Published: July 2002

Models of the universe with a cosmological term which is introduced as a correction of the metric tensor field are studied. By revisiting with these models some of the conventional success, we infer that a model with a linear correction is a favourable candidate for a model of the universe. The cosmological constant and the flatness problems are examined in the model. There might be a possibility to solve the other cosmological problems only with the metric tensor field.
TOTAL REACTION CROSS SECTIONS FOR 100-MeV ALPHA PARTICLES USING SEMI-PENOMENOLOGICAL NUCLEON DENSITY DISTRIBUTION
Authors: AHMAD I. , MADANI J. H.
Published: July 2002

Theoretical study of α total reaction cross-sections for 50 Ti , 52 Cr , 54,58 Fe , and 58,64 Ni nuclei at 100 MeV is presented. Working within the framework of Coulomb modified Glauber model, we calculate α reaction cross-sections in terms of the phenomenological N-α amplitude using the semi-phenomenological nucleon density distribution proposed by Gambhir and Patil [Z. Phys.A324 (1986) 9]. We find that the semi-phenomenological density reproduces the observed behaviour of the reaction cross-sections for the isotopes and isotones quite satisfactorily.
LONG RANGE INTERACTION BETWEEN PROTEIN COMPLEXES IN DNA CONTROLS REPLICATION AND CELL CYCLE PROGRESSION
Authors: MATSSON LEIF
Published: July 2002

A model that controls DNA replication and the cell cycle is derived in terms of manybody physics. It predicts a long range force F(φ) =-(κ/2)φ(1-φ/N) (2-φ/N) in the lattice of pre-replication complexes (pre-RCs) bound by the DNA duplex, φ being the number of pre-RCS, N the threshold number at which replication is initiated, and κ the compressibility modulus in the lattice which behaves like an elastically braced string. Initiation of replication is explained by a switch of sign of F, from attraction (-) and assembly in the G1 phase (0 <φ<N), to repulsion (+) and partial disassembly in the S phase (N<φ<2N), with concomitant release of licensing factors from pre-RCs and prevention of re-replication. Termination of replication is due to a vanishing of F at φ=2N, at which all primed replicons in DNA have been duplicated once, and F(0)=0 corresponds to a resting cell in absence of a driving force at φ=0. The switch of sign of F at φ=N similarly explains the dynamic instability in growing microtubules (MTs), as well as the switch mechanism in the interaction of interleukin-2 (IL2) with its receptor in late G1, at the R-point, after which a T cell proceeds to replication without further exposure to IL2. Shape, slope and scale of the response curves derived agree well with experimental data from dividing T cells and polymerizing MTs, the variable length of which is explained here by a nonlinear dependence of the growth amplitude on the initial concentrations of guanosine-triphosphate (GTP) and tubulin dimers.
A MODEL-INDEPENDENT ANALYSIS OF THE DEMOGRAPHIC IMPACT OF HIV/AIDS IN THE STATE OF SÃO PAULO, BRAZIL
Authors: MASSAD E. , COUTINHO F. A. B. , BURATTINI M. N. , LOPEZ L. F.
Published: July 2002

The devastating figures that recently emerged from a demographic study of the impact of HIV/AIDS in some African countries mark the return to the conditions of the XIXth century, when high birth rates were neutralized by equally high death rates. In the State of São Paulo, Brazil, AIDS is the second cause of death among men aged twenty to forty nine years and the first cause of death of women in the same age class. In this work we propose a mathematical treatment to evaluate the impact of AIDS mortality on the age structure of an affected population, namely, that of the state of São Paulo, Brazil. We propose four indicators for the estimation of the impact of AIDS mortality. The first is the age-dependent differences in ten years survival probabilities attributable to AIDS. The second is the difference in the average age of survivors after 10 years of AIDS. The next is the conventional life expectancy at birth for children born in 1996 and with AIDS prevalence assumed at its maximum value and remaining in steady-state afterwards. Finally, we calculate the differences in the life expectancy of individuals considering the effect of AIDS for only ten years. We found that, in the period between 1987 and 1996 the effects were small but very interesting. However, projecting to the future the conditions of 1996, we calculate that the population of the state of São Paulo would lose 3 years in the average life expectancy at birth.
THE ATTRACTING BASINS AND THE ASSESSMENT OF THE TRANSMISSION COEFFICIENTS FOR HIV AND M. TUBERCULOSIS INFECTIONS AMONG WOMEN INMATES
Authors: RAIMUNDO SILVIA MARTORANO , YANG HYUN MO , BASSANEZI RODNEY CARLOS , FERREIRA MARIZETE A. C.
Published: July 2002

It has been observed that in many cases one infection can partially protect against another infection or it may lead to a co-infection. For instance, the interaction between infections with different strains, like dengue and malaria or tuberculosis and lepra, induces cross immunity. On the other hand, individuals infected with HIV are much more susceptible to other infections, for instance, tuberculosis. We propose a compartmental model to describe the transmission of AIDS and tuberculosis in a closed community as an example of one infection activating the other one. When studying the dynamics of the interactions we obtain basins of attraction where one infection prevails over the other one and where both infections coalesce. Furthermore, we are taking into account an adaptation of the model in order to assess the transmission coefficients for HIV and Mycobacterium tuberculosis infections among women inmates.
DEPENDENCE OF FLUX DISTRIBUTION AND SYSTEM COORDINATION ON DYNAMICAL STATES FOR BIOCHEMICAL SYSTEMS WITH MULTIPLE COEXISTING STATES
Authors: LIU JUNLI
Published: July 2002

Flux distribution and system coordination in branched biochemical systems with a source producing multiple coexisting states have been studied both theoretically and numerically. For such systems, flux distribution depends sensitively on the dynamical states and the parameter values of enzymatic kinetics at branching point. Various dynamical states including noise-induced new states can be located by superimposing noisy fluctuations on a branched biochemical system with multiple coexisting states. Once noise induces transitions or new dynamical states, the flux through a specific branch may increase, maintain or decrease, depending on parameter values of enzymatic kinetics at branching point. Furthermore, system coordination can be destroyed by noise-induced dynamical changes. When at least one state cannot be coordinated in the absence of noise, noise-induced transitions may destroy system coordination. When all coexisting states are coordinated in the absence of noise, noise-induced new states may be still able to destroy system coordination. It is revealed that destruction of system coordination is due to the interaction of enzyme saturation and noise-induced dynamical changes. Finally, control of flux distribution and maintenance of system coordination for biochemical systems with multiple coexisting states are discussed.
SYNCHRONIZATION OF CELL DIVISION
Authors: PRESNOV E. V.
Published: July 2002

Most living organisms display many types of biological rhythms. We describe how a growing population of cells may be distributed between age classes or cell types, and define conditions necessary to produce synchronous population development. A probabilistic model describing the changes in cell numbers during proliferation is presented. The model predicts that during cell reproduction with constant parameters any cell population approaches a stationary behavior. According to this model, synchronization of cell growth is possible if there is a uniform parameter set for cell division. This point is illustrated by a set of graphs showing snapshots of model simulations with different parameter sets for transient and stationary behaviors.
TIMING ANALYSIS OF A FAULT-TOLERANT TECHNIQUE SUBJECT TO HARDWARE FAILURES
Authors: GUROV SERGEY V. , UTKIN LEV V. , SHUBINSKY IGOR B.
Published: July 2002

In this paper, we focus on the timing analysis of a fault-tolerance technique when a program is written in the form of several modules. If a hardware failure does occur during the ith module execution, the program must roll back and after restoring, the ith module execution is repeated. All random variables, such as time to hardware failure, replication time, and execution time of modules are arbitrarily distributed. We propose the efficient recurrence algorithms for computing the probability distribution and the mean value of execution time. The asymptotic behavior of the fault-tolerance technique is discussed. We prove that by increasing the number of modules, the mean execution time of a module tends to a defined value. The numerical examples are provided to illustrate and analyze the results. The application examples show that for the large variety of systems there exists an optimal number of modules minimizing the execution time.
TEST STATISTICS FOR SYSTEM DESIGN FAILURE
Authors: MAY JOHN , KUBALL SILKE , HUGHES GORDON
Published: July 2002

A structural model for the estimation of software failure rates is proposed which is based on a partition of the code into components. Systematic failure is assumed to be induced by the interaction of these components. A Bayesian inference scheme is used to perform failure rate estimation on the basis of N failure free test runs. The approach splits the problem of constructing a system prior up into the smaller, conceivably simpler problems of constructing subtask priors. Thereby a wider range of prior information is used in the process of assessing system safety. The work in this paper constitutes a first step towards a formal statistical understanding of the relationship between system complexity and system testing for reliability. Long-term implications are the achievement of more informative reliability estimates and guidelines on cost-effective testing.
SURGICAL MANAGEMENT PROTOCOL FOR MIDDLE LEVEL TRAUMATIC TETRAPLEGIA: A case for “Surgical Internalisation” of External Splints
Authors: Mennen Ulrich
Published: July 2002

In most places the surgical and rehabilitative management of tetraplegic patients is done on an ad hoc basis. We believe that the best interests of these unfortunate patients can only be served by a comprehensive surgical and rehabilitative management protocol through a dedicated team of professionals.

The surgical protocol should be a basic standard programme known to the whole team. Depending on the patient's basic needs, variations to this basic surgical programme could be worked out.

We propose a basic surgical programme for the mid-cervical tetraplegic patient in order to get rid of cumbersome external splints during the rehabilitative period. Substituting surgical procedures for external splints has become known as “internalisation of splints”. These include:

1. Motorising elbow extension using an improved bone-to-bone posterior deltoid to triceps tendon transfer.

2. Motorising forearm pronation by rerouting biceps tendon around radius.

3. Motorising thumb and finger extension, using M. brachioradialis.

4. Metacarpophalangcal finger flexion, using flexor digitorum superficialis tendon Zancolli lasso procedure (tenodesis effect).

5. Motorising distal interphalangeal finger joint flexion, using extensor carpi radialis longus transfer.

6. Thumb pinch/adduction against the fingers, rerouting flexor pollicis longus tendon to extensor carpi radialis brevis tendon, end-to-side.

7. Thumb stabilisation procedures on any one or two thumb joints.

The above procedures contribute greatly to the independent function of the patient. Careful preoperative assessment and prerequisites include the patient’s needs, patient’s motivation, muscle power and endurance and important “trick movements”.
END-TO-SIDE NERVE SUTURE IN THE PRIMATE (CHACMA BABOON)
Authors: Mennen Ulrich
Published: July 2002

It has been shown that the tropic factors at the end of a distal nerve segment attracts growing axons. Subsequently, it was shown that this attraction enables intact axons to sprout into a recipient end-to-side anastomosed nerve in rats. We have demonstrated that this ability of a donor nerve also occurs in the non-human primate as well as in the human.

Three Chacma baboons (6 end-to-side anastomoses at the wrist level) consistently confirmed collateral sprouting on histology and recovery of function (motor and sensory) on electro-conduction tests.

Preliminary results in 21 human patients (21 end-to-side anastomoses in a variety of procedures) demonstrated clinically and by electro-conduction tests that sensory and motor recovery occurs satisfactorily.
DATA CURRENCY QUALITY SATISFACTION IN THE DESIGN OF A DATA WAREHOUSE
Authors: THEODORATOS DIMITRI , BOUZEGHOUB MOKRANE
Published: July 2002

A Data Warehouse (DW) is a large collection of data integrated from multiple distributed autonomous databases and other information sources. A DW can be seen as a set of materialized views defined over the remote source data. Until now research work on DW design is restricted to quantitatively selecting view sets for materialization. However, quality issues in the DW design are neglected. In this paper we suggest a novel statement of the DW design problem that takes into account quality factors. We design a DW system architecture that supports performance and data consistency quality goals. In this framework we present a high level approach that allows to check whether a view selection guaranteeing a data completeness quality goal also satisfies a data currency quality goal. This approach is based on an AND/OR dag representation for multiple queries and views. It also allows determining the minimal change propagation frequencies that satisfy the data currency quality goal along with the optimal query evaluation and change propagation plans. Our results can be directly used for a quality driven design of a DW.
AN EVALUATION OF THE JAVA-BASED APPROACHES TO WEB DATABASE ACCESS
Authors: PAPASTAVROU STAVROS , CHRYSANTHIS PANOS K. , SAMARAS GEORGE , PITOURA EVAGGELIA
Published: July 2002

Given the undeniable popularity of the Web, providing efficient and secure access to remote databases using a Web browser is crucial for the emerging cooperative information systems and applications. In this paper, we evaluate all currently available Java-based approaches that support persistent connections between Web clients and database servers. These approaches include Java applets, Java Sockets, Servlets, Remote Method Invocation, CORBA, and mobile agents technology. Our comparison is along the dimensions of performance and programmability. Our findings point out that best performance is not always achievable with high programmability and low resource requirements. Moreover, the mobile agent technology needs to improve its programmability while giving particular emphasis on its infrastructure.
FINANCIAL FRICTION AND MULTIPLICATIVE MARKOV MARKET GAMES
Authors: AURELL ERIK , MURATORE-GINANNESCHI PAOLO
Published: July 2002

We study long-term growth-optimal strategies on a simple market with transaction costs. We show that several problems of this sort can be solved in closed form, and explicit the non-analytic dependance of optimal strategies and expected frictional losses of the friction parameter.
On the Chinese Lunar New Year Effect in Six Asian Stock Markets: An Empirical Analysis (1991–2000)
Authors: Yen Gili , Lee Cheng F. , Chen Cheng-Lung , Lin Wei-Chi
Published: July 2002

This paper examines the existence/nonexistence of the Chinese Lunar New Year effect in Hong Kong, Japan, South Korea, Malaysia, Singapore, and Taiwan in recent years. Using longitudinal stock price index data from 1991 to 2000, the authors find that cumulative returns based on stock indices in the above mentioned Asian markets exhibit a consistently up-moving trend before or after the Chinese Lunar New Year, providing evidence for continued existence of the Chinese Lunar New Year effect in these six Asian stock markets in recent years. However, when the sample period is divided into before- vs. after-Asian financial crisis period, different patterns emerge. In the wake of the Asian financial crisis, the crisis effect has some role to play, especially, for Malaysia and Singapore. In viewing the timing and patterns of the Chinese Lunar New Year effect in these six Asian markets differ from each other, the authors also recommend to investors the best investment strategy to capture the largest returns.
PERFORMANCE EVALUATION OF A REQUEST-TDMA/CDMA PROTOCOL FOR WIRELESS NETWORKS
Authors: CHATTERJEE MAINAK , DAS SAJAL K.
Published: July 2002

This paper proposes a new medium access control (MAC) protocol, called Request-TDMA/CDMA, for supporting multimedia traffic in wireless networks. In this hybrid protocol, CDMA (code division multiple access) is laid over TDMA (time division multiple access), where a time frame has two kinds of slots, namely data slots and control slots. The data slots are used to the user to transmit their data while the control slot holds the information for the next frame's slot allocation. Each data slot in a frame can be simultaneously used by multiple users with the help of uniquely assigned codes. Whenever a user needs to transmit a message, he first sends a request message to the central controller and enters the contention process. The controller takes into consideration the time of generation of a call, the bit rate requirement and the message length while reserving slots for the entire length of the message generated. The user then goes into the transmission phase if he is successful in the contention process, and continues to transmit his data till the entire message is sent. Three scheduling algorithms for the allocation of data slots are proposed and their performance are studied for four classes of traffic. We also analyze our protocol using a two-dimensional Markov chain model, and compute the state transition probabilities and derive the average waiting time for a given system load. By simulation experiments we show that our request-TDMA/CDMA protocol is able to effectively combine the orthogonality of both time and code division multiplexing. Further enhancements are also proposed to decrease the waiting time and increase the average channel utilization.
ON ESTIMATION OF THE LINEARIZED DRIFT FOR NONLINEAR STOCHASTIC DIFFERENTIAL EQUATIONS
Authors: KHASMINSKII R. , MILSTEIN G. N.
Published: July 2002

The estimation of the linearized drift for stochastic differential equations with equilibrium points is considered. It is proved that the linearized drift matrix can be estimated efficiently if the initial condition for the system is chosen close enough to the equilibrium point. Some bounds for initial conditions ensuring the asymptotical efficiency of the estimator are found.
ON THE NOTION OF DERIVED TAMENESS
Authors: GEISS CHRISTOF , KRAUSE HENNING
Published: July 2002

The notion of tameness for the derived category of a finite dimensional algebra is introduced and standard properties are established. This is based on classical tameness definitions of Drozd and Crawley-Boevey for the category of finite dimensional representations.
AN INTERNATIONAL OVERVIEW OF STRATEGIC ENVIRONMENTAL ASSESSMENT, WITH REFERENCE TO WORLD HERITAGE AREAS GLOBALLY AND IN AUSTRALIAN COASTAL ZONES
Authors: MARSDEN SIMON
Published: July 2002

This paper examines international best practice with strategic environmental assessment (SEA), which is designed to advance sustainability and overcome weaknesses in environmental impact assessment (EIA). It illustrates how government, business and the community have identified the need for SEA. It explains why there has been a substantial debate regarding the importance of establishing key principles, and why consideration must be given to decision and policy contexts in order to guide future successful development. Methods and procedures are outlined, and SEA practice and potential nationally, regionally and globally is considered with particular regard to World Heritage Areas (WHAs). Conclusions and recommendations are drawn with specific reference to the current and future position of SEA and WHAs in Australian coastal zones.
Efficient simulation of finite automata by neural nets
Authors: Alon Noga , Dewdney A. K. , Ott Teunis J.
Published: July 2002

Let
K
(
m
) denote the smallest number with the property that every
m
-state finite automaton can be built as a neural net using
K
(
m
) or fewer neurons. A counting argument shows that
K
(
m
) is at least Ω((
m
log
m
)
1/3
), and a construction shows that
K
(
m
) is at most
O
(
m
3/4
). The counting argument and the construction allow neural nets with arbitrarily complex local structure and thus may require neurons that themselves amount to complicated networks. Mild, and in practical situations almost necessary, constraints on the local structure of the network give, again by a counting argument and a construction, lower and upper bounds for
K
(
m
) that are both linear in
m
.
Legally speaking
Authors: Samuelson Pamela
Published: July 2002

Applying the First Amendment of the U.S. Constitution to computerized communication of information is raising many interesting questions. While the general principle of this amendment can be simply stated—it forbids the government from interfering with freedom of speech—the specifies of its application over two centuries of American history have yielded a complex matrix of principles whose application depends on a variety of factors. Where computerized communication of information fits into this schema has yet to be definitely determined. The last “Legally Speaking” column (Mar. 1991) discussed some First Amendment issues raised by treating computerized information as private property, theft of which might be criminally prosecutable. This column will discuss quite a different First Amendment issue. But these two columns can only begin to introduce a few of the challenging First Amendment issues presented by the “Electronic Frontier.”
Mixed signals about social responsibility
Authors: Rosenberg Ronni
Published: July 2002

What is the appropriate role of computer professionals in determining how their work is used? Should they consider the societal implications of their work?
Database performance evaluation in an indexed file environment
Authors: Fedorowicz Jane
Published: July 2002

The use of database systems for managerial decision making often incorporates information-retrieval capabilities with numeric report generation. Of great concern to the user of such a system is the response time associated with issuing a query to the database. This study presents a procedure for estimating response time for one of the most frequently encountered physical storage mechanisms, the indexed file. The model provides a fairly high degree of accuracy, but is simple enough so that the cost of applying the model is not exorbitant. The model incorporates the knowledge that the distribution of access key occurrences is known to follow Zipf's law. It first estimates the access time required to complete the query, which includes the time needed for all input and output transactions, and CPU time used in performing the search. The effects of multiple users on an individual's response time are then assessed using a simple regression estimation technique. The two-step procedure allows for the separation of access time from multiuser influences.
Technical correspondence
Authors: Crawford Diane
Published: July 2002

I read with interest Peter Pearson's article, “Fast Hashing of Variable-Length Text Strings” (June 1990, pp. 677-680). In it he defines a hash function, given a text C
1
… C
N
, by Exclusive OR'ing the bytes and modifying each intermediate result through a table of 256 randomish bytes.
An analysis of the longest match and the greedy heuristics in text encoding
Authors: Katajainen Jyrki , Raita Timo
Published: July 2002

Text compression is often done using a fixed, previously formed dictionary (code book) that expresses which substrings of the text can be replaced by code words. There always exists an optimal solution for text-encoding problem. Due to the long processing times of the various optimal algorithms, several heuristics have been proposed in the literature. In this paper, the worst-case compression gains obtained by the longest match and the greedy heuristics for various types of dictionaries is studied. For general dictionaries, the performance of the heuristics can be almost the weakest possible. In practice, however, the dictionaries have usually properties that lead to a space-optimal or near-space-optimal coding result with the heuristics.
Implementation and tests of low-discrepancy sequences
Authors: Bratley Paul , Fox Bennett L. , Niederreiter Harald
Published: July 2002

Low-discrepancy sequences are used for numerical integration, in simulation, and in related applications. Techniques for producing such sequences have been proposed by, among others, Halton, Sobol´, Faure, and Niederreiter. Niederreiter's sequences have the best theoretical asymptotic properties. The paper describes two ways to implement the latter sequences on a computer and discusses the results obtained in various practical tests on particular integrals.
Enhancements of ANALYZE
Authors: Greenberg Harvey J.
Published: July 2002

This describes enhancements to provide more advanced computer-assisted analysis of instances of linear programming models. Three categories of enhancements are described: views, engines for obtaining information, and rule-based advising. Examples of their uses include redundancy and infeasiblity diagnoses.
The evaluation of trigonometric integrals avoiding spurious discontinuities
Authors: Jeffrey D. J. , Rich A. D.
Published: July 2002

The tan(x/2) substitution, also called the Weierstrass substitution, is one method currently used by computer-algebra systems for the evaluation of trigonometric integrals. The method needs to be improved, because the expressions obtained using it sometimes contain discontinuities, which unnecessarily limit the domains over which the expressions are correct. We show that the discontinuities are spurious in the following sense: Given an integrand and an expression for its antiderivative that was obtained by the Weierstrass substition, a better expression can be found that is continuous on wider intervals than the first expression and yet is still an antiderivative of the integrand. The origin of the discontinuities is identified, and an algorithm is presented for automatically finding the improved type of antiderivative. The new algorithm also enlarges the set of functions that can be used in the substitution. The algorithm works by first evaluating the given integral using the Weierstrass substitution in the usual way and then removing any spurious discontinuities present in the antiderivative.
Programs to generate Niederreiter's low-discrepancy sequences
Authors: Bratley Paul , Fox Bennett L. , Niederreiter Harald
Published: July 2002

This note points out programs to implement Niederreiter's low-discrepancy sequences.
Exceptions and exception handling in computerized information processes
Authors: Strong Diane M. , Miller Steven M.
Published: July 2002

Exceptions, situations that cannot be correctly processed by computer systems, occur frequently in computer-based information processes. Five perspectives on exceptions provide insights into why exceptions occur and how they might be eliminated or more efficiently handled. We investigate these perspectives using an in-depth study of an operating information process that has frequent exceptions. Our results support the use of a total quality management (TQM) approach of eliminating exceptions for some exceptions, in particular, those caused by computer systems that are poor matches to organizational processes. However, some exceptions are explained better by a political system perspective of conflicting goals between subunits. For these exceptions and several other types, designing an integrated human-computer process will provide better performance than will eliminating exceptions and moving toward an entirely automated process.
Declarative updates of relational databases
Authors: Chen Weidong
Published: July 2002

This article presents a declarative language, called
update calculus
, of relational database updates. A formula in update calculus involves conditions for the current database, as well as assertions about a new database. Logical connectives and quantifiers become constructors of complex updates, offering flexible specifications of database transformations. Update calculus can express all nondeterministic database transformations that are polynomial time.

For set-at-a-time evaluation of updates, we present a corresponding
update algebra
. Existing techniques of query processing can be incorporated into update evaluation. We show that updates in update calculus can be translated into expressions in update algebra and vice versa.
Algorithm 752: SRFPACK
Authors: Renka R. J.
Published: July 2002

SRFPACK is a Fortran 77 software package that constructs a smooth interpolatory or approximating surface to data values associated with arbitrarily distributed points in the plane. It employs automatically selected tension factors to preserve shape properties of the data and to avoid overshoot and undershoot associated with steep gradients. The domain of the fitting function may be nonconvex or multiply connected, and the surface may be constrained to have discontinuous value or derivative across a user-specified curve representing, for example, a geological fault line. Although triangle based, the method provides a means of avoiding the inaccuracy associated with long thin triangles on the boundary of the convex hull of the data abscissae.
Using design patterns to develop reusable object-oriented communication software
Authors: Schmidt Douglas C.
Published: July 2002

Despite dramatic increases in network and host performance, it remains difficult to design, implement, and reuse communication software for complex distributed systems. Examples of these systems include global personal communication systems, network management platforms, enterprise medical imaging systems, and real-time market data monitoring and analysis systems. In addition, it is often hard to directly reuse existing algorithms, detailed designs, interfaces, or implementations in these systems due to the growing heterogeneity of hardware/software architectures and the increasing diversity of operating system platforms.
On computational efficiency of the iterative methods for the simultaneous approximation of polynomial zeros
Authors: Milovanovic G. V. , Petkovic M. S.
Published: July 2002

A measure of efficiency of simultaneous methods for determination of polynomial zeros, defined by the coefficient of efficiency, is considered. This coefficient takes into consideration (1) the R-order of convergence in the sense of the definition introduced by Ortega and Rheinboldt (Iterative Solution of Nonlinear Equations in Several Variables. Academic Press, New York, 1970) and (2) the number of basic arithmetic operations per iteration, taken with certain weights depending on a processor time. The introduced definition of computational efficiency was used for comparison of the simultaneous methods with various structures.
Exploiting zeros on the diagonal in the direct solution of indefinite sparse symmetric linear systems
Authors: Duff I. S. , Reid J. K.
Published: July 2002

We describe the design of a new code for the solution of sparse indefinite symmetric linear systems of equations. The principal difference between this new code and earlier work lies in the exploitation of the additional sparsity available when the matrix has a significant number of zero diagonal entries. Other new features have been included to enhance the execution speed, particularly on vector and parallel machines.
Implementation and performance of integrated application-controlled file caching, prefetching, and disk scheduling
Authors: Cao Pei , Felten Edward W. , Karlin Anna R. , Li Kai
Published: July 2002

As the performance gap between disks and micropocessors continues to increase, effective utilization of the file cache becomes increasingly immportant. Application-controlled file caching and prefetching can apply application-specific knowledge to improve file cache management. However, supporting application-controlled file caching and prefetching is nontrivial because caching and prefetching need to be integrated carefully, and the kernel needs to allocate cache blocks among processes appropriately. This article presents the design, implementation, and performance of a file system that integrates application-controlled caching, prefetching, and disk scheduling. We use a two-level cache management strategy. The kernel uses the LRU-SP (Least-Recently-Used with Swapping and Placeholders) policy to allocate blocks to processes, and each process integrates application-specific caching and prefetching based on thecontrolled-aggressivepolicy, an algorithm previously shown in a theoretical sense to be nearly optimal. Each process also improves its disk access latency by submittint its prefetches in batches so that the requests can be scheduled to optimize disk access performance. Our measurements show that this combination of techniques greatly improves the performance of the file system. We measured that the running time is reduced by 3% to 49% (average 26%) for single-process workloads and by 5% to 76% (average 32%) for multiprocess workloads.
Three approaches to heuristic search in networks
Authors: Bagchi A. , Mahanti A.
Published: July 2002

Three different approaches to heuristic search in networks are analyzed. In the first approach, as formulated initially by Hart, Nilsson, and Raphael, and later modified by Martelli, the basic idea is to choose for expansion that node for which the evaluation function has a minimum value. A second approach has recently been suggested by Nilsson. In this method, in contrast to the earlier one, a node that is expanded once is not expanded again; instead, a “propagation” of values takes place. The third approach is an adaptation for networks of an AND/OR graph “marking” algorithm, originally due to Martelli and Montanari.

Five algorithms are presented. Algorithms A and C illustrate the first approach; PropA and PropC, the second one; and MarkA, the third one. The performances of these algorithms are compared for both admissible and inadmissible heuristics using the following two criteria: (i) cost of the solution found; (ii) time of execution in the worst case, as measured by the number of node expansions (A, C), or node “selections” (PropA, PropC), or arc “markings” (MarkA).

The relative merits and demerits of the algorithms are summarized and indications are given regarding which algorithm to use in different situations.
Theory of neuromata
Authors: Šíma Jiří , Wiedermann Jiří
Published: July 2002

A finite automaton—the so-called neuromaton, realized by a finite discrete recurrent neural network, working in parallel computation mode, is considered. Both the size of neuromata (i.e., the number of neurons) and their descriptional complexity (i.e., the number of bits in the neuromaton representation) are studied. It is proved that a constraint time delay of the neuromaton output does not play a role within a polynomial descriptional complexity. It is shown that any regular language given by a regular expression of length
n
is recognized by a neuromaton with Θ(
n
) neurons. Further, it is proved that this network size is, in the worst case, optimal. On the other hand, generally there is not an equivalent polynomial length regular expression for a given neuromaton. Then, two specialized constructions of neural acceptors of the optimal descriptional complexity Θ(
n
) for a single
n
-bit string recognition are described. They both require

O(n
1/2
)

neurons and either
O(n)
connections with constant weights or

O(n
1/2
)

edges with weights of the

O(2
√n
)

size. Furthermore, the concept of Hopfield languages is introduced by means of so-called Hopfield neuromata (i.e., of neural networks with symmetric weights). It is proved that the class of Hopfield languages is strictly contained in the class of regular languages. The necessary and sufficient so-called Hopfield condition stating when a regular language is a Hopfield language, is formulated. A construction of a Hopfield neuromaton is presented for a regular language satisfying the Hopfield condition. The class of Hopfield languages is shown to be closed under union, intersection, concatenation and complement, and it is not closed under iteration. Finally, the problem whether a regular language given by a neuromaton (or by a Hopfield acceptor) is nonempty, is proved to be PSPACE-complete. As a consequence, the same result for a neuromaton equivalence problem is achieved.
Designing large real-time systems with Ada
Authors: Nielsen Kjell W. , Shumate Ken
Published: July 2002

The programming language Ada encourages improved methods for the design of real-time systems.