bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shape Optimization of a Labyrinth Seal Applying the Simulated Annealing Method
Authors: Schramm V. , Denecke J. , Kim S. , Wittig S. 
Published: March 2007

In the present work, an environment for the shape optimization of a labyrinth seal is described. A program for a parameterized, automated grid generation is coupled with
a commercial Computational Fluid Dynamics (CFD) flow solver and an optimization algorithm. Standard optimization strategies, like gradient‐based methods, mostly are
trapped to local optima. Therefore, the simulated annealing method is applied. It allows the finding of global minima or maxima of arbitrary functions.The presented optimization method is used to minimize the leakage through a three‐finned, stepped labyrinth seal. For the optimization, the step position and the step height are chosen to be variable. The characteristics of the flow fields of selected seal configurations are compared and discussed against the background of the leakage behavior of the seal.
Improvement of Stability of Rotor System by Introducing a Hydraulic Damper into an Active JournalBearing
Authors: Krodkiewski J. M. , Cen Y. , Sun L. 
Published: March 2007

Modelling and analysis of a rotor‐‐bearing system with a new type of active oil bearing is
presented. The active bearing is supplied with a flexible sleeve whose deformation can be
changed during operation of the rotor. The flexible sleeve is also a part of a hydraulic damper
whose parameters can be controlled during operation as well.Finite Element Method (FEM) and the Guyan condensation technique was utilised to
create mathematical model of both, the rotor and the flexible sleeve. The hydrodynamic
pressure distribution in the oil film, for the instantaneous position of the flexible sleeve and
rotor, was approximated by Reynolds equation.The mathematical model of motion of a rotor system with the described active bearing
developed in this paper allowed the influence of the introduced hydraulic damper on stability
of the rotor‐bearing system to be investigated. Results of the computer simulation shows that
within a large region of configuration parameters of the rotor bearing system, the self exciting
vibration can be eliminated or greatly reduced during operation by properly controlled
deformation of the flexible sleeve and optimal choice of the hydraulic damper parameters.
Investigation of the Flow in Pelton Turbinesand the Influence of the Casing
Authors: Matthias Heinz-Bernd , Prost Josef , Rossegger Christian 
Published: March 2007

At the institute for waterpower and pumps at the University of Technology Vienna we do a
lot of research work observing the flow in the casing and the buckets of Pelton turbines. One
interest of our research is to find criteria to estimate the influence of the splash water
distribution in the casing on the turbine efficiency. Knowing the splash water distribution it
is further possible to develop methods to provide visual documentation of the flow in and
around the buckets from the beginning to the end of interaction.Our measurements have been done on a single jet Pelton turbine with a runner pitch
diameter of 420 mm. Our research shows that the casing has great influence to the operation
of a Pelton turbine and so it is very important to include the casing as an important factor in
all investigations. Aluminum honeycombs have been successful to bring the splashing water
under control and to make good visual documentations of the flow.
Axial Compressor Stall and Surge Prediction by Measurements
Authors: Hönen H. 
Published: March 2007

The paper deals with experimental investigations and analyses of unsteady pressure distributions in different axial compressors. Based on measurements in a single stage research compressor the influence of increasing aerodynamic load onto the pressure and velocity fluctuations is demonstrated. Detailed measurements in a 14‐stage and a 17‐stage gas turbine compressor are reported. For both compressors parameters could be found which are clearly influenced by the aerodynamic load.For the 14‐stage compressor the principles for the monitoring of aerodynamic load and stall are reported. Results derived from a monitoring system for multi stage compressors based on these principles are demonstrated. For the 17‐stage compressor the data enhancement of the measuring signals is shown. The parameters derived from these results provide a good base for the development of another prediction method for the compressor stability limit. In order design an on‐line system the classification of the operating and load conditions is provided by a neural net. The training results of the net show a good agreement with different experiments.
A New Approach to Assess the Quality of Small High‐Speed Centrifugal Fans Using Noise Measurement
Authors: Cui Dingjun , Craighead Ian A. 
Published: March 2007

The requirements for a special approach for the quality assessment of small high‐speed centrifugal fans are outlined and a new parameter designating the noise levels from the product in comprehensive form will be discussed and described as a criterion for such quality assessment.By applying techniques of signal processing and condition monitoring, the sources of the vibration and noise in different sections of the product can be identified, then the noise from each source from different components can be determined. Using this criterion, more aspects of the quality of the products can be assessed and suggestions to improve the quality of the products can be made. Finally, the assessment of a number ofvacuum cleaner motor/fan units available in the commercial market will be presented and compared with conventional specifications. It will be shown that the new parameter provides a more useful indication of appliance quality.
A classical approach to eigenvalue problems associated with a pair of mixed regular Sturm‐Liouville equations I
Authors: Venkatesulu M. , Baruah Pallav Kumar 
Published: March 2007

In the studies of acoustic waveguides in ocean, buckling of columns with
variable cross sections in applied elasticity, transverse vibrations in non‐homogeneous strings, etc., we encounter a new class of problems of the
type defined on an interval [d1, d2] and
on the adjacent interval [d2, d3] satisfying
certain matching conditions at the interface point x = d2.Here in Part I, we constructed a fundamental system for (L1, L2) and
derive certain estimates for the same. Later, in Part II, we shall consider
four types of boundary value problems associated with (L1, L2) and study
the corresponding spectra.
Parallelization algorithms for modeling ARM processes
Authors: Melamed Benjamin , Singh Santokh 
Published: March 2007

AutoRegressive Modular (ARM) processes are a new class of nonlinear
stochastic processes, which can accurately model a large class of stochastic
processes, by capturing the empirical distribution and autocorrelation function simultaneously. Given an empirical sample path, the ARM modeling
procedure consists of two steps: a global search for locating the minima of
a nonlinear objective function over a large parametric space, and a local
optimization of optimal or near optimal models found in the first step. In
particular, since the first task calls for the evaluation of the objective function at each vector of the search space, the global search is a time consuming procedure. To speed up the computations, parallelization of the global
search can be effectively used by partitioning the search space among
multiple processors, since the requisite communication overhead is negligible.This paper describes two space‐partitioning methods, called Interleaving and Segmentation, respectively. The speedups resulting from these
methods are compared for their performance in modeling real‐life data.
On some queue length controlled stochastic processes
Authors: Abolnikov Lev , Dshalalow Jewgeni E. , Dukhovny Alexander M. 
Published: March 2007

The authors study the input, output and queueing processes in a general controlled single‐server bulk queueing system. It is supposed that inter‐arrival time, service time, batch size of arriving units and the capacity of the server depend on the queue length.The authors establish an ergodicity criterion for both the queueing process with continuous time parameter and the embedded process, study their
transient and steady state behavior and prove ergodic theorems for some functionals of the input, output and queueing processes. The following results are
obtained: Invariant probability measure of the embedded process, stationary
distribution of the process with continuous time parameter, expected value of
a busy period, rates of input and output processes and the relative speed of convergence of the expected queue length. Various examples (including an optimization problem) illustrate methods developed in the paper.
Markov chains with transition delta‐matrix: ergodicityconditions, invariant probability measures and applications
Authors: Abolnikov Lev , Dukhovny Alexander 
Published: March 2007

A large class of Markov chains with so‐called Δm,n‐and
‐transition matrices (“delta‐matrices”) which frequently occur in
applications (queues, inventories, dams) is analyzed.The authors find some structural properties of both types of
Markov chains and develop a simple test for their irreducibility and aperiodicity. Necessary and sufficient conditions for the ergodicity of both
chains are found in the article in two equivalent versions. According to
one of them, these conditions are expressed in terms of certain
restrictions imposed on the generating functions Ai(z) of the elements of
the ith row of the transition matrix, i = 0, 1, 2, …; in the other version
they are connected with the characterization of the roots of a certain associated function in the unit disc of the complex plane. The invariant
probability measures of Markov chains of both kinds are found in terms
of generating functions. It is shown that the general method in some important special cases can be simplified and yields convenient and, sometimes, explicit results.As examples, several queueing and inventory (dam) models, each
of independent interest, are analyzed with the help of the general
methods developed in the article.
A first passage problem and its applications to the analysis of a class of stochastic models
Authors: Abolnikov Lev , Dshalalow Jewgeni H. 
Published: March 2007

A problem of the first passage of a cumulative random process with
generally distributed discrete or continuous increments over a fixed level is considered in the article as an essential part of the analysis of a class of stochastic
models (bulk queueing systems, inventory control and dam models).Using direct probability methods the authors find various characteristics of this problem: the magnitude of the first excess of the process over a
fixed level, the shortage before the first excess, the levels of the first and pre‐first excesses, the index of the first excess and others. The results obtained are
illustrated by a number of numerical examples and then are applied to a bulk
queueing system with a service delay discipline.
A non‐regenerative model of a redundant repairable system: bounds for the unavailability and asymptotical insensitivity to the lifetime distribution
Authors: Kovalenko Igor N. 
Published: March 2007

In this paper we investigate steady state reliability parameters of an F : r‐out‐of‐N redundant repairable system with m(1 ≤ m ≤ r − 1) repair channels in light
traffic conditions. Such a system can also be treated as a closed queueing network of a simple kind. It includes two nodes, with infinite number of channels
and m channels, respectively. Each of the N customers pass cyclically from one
node to the other; the service time distributions are of a general form for both the
nodes.It is an N‐component system with a general distribution A(t) of free‐of‐failure periods of the components is considered. Failed components are repaired by
an m‐channel queueing system with a general distribution B(t) of repair times.
The system is assumed to be failed if and only if the number of failed
components is at least r. (Only the rather difficult case r ≥ m + 1 is considered.)Let μ be the intensity of the stationary point process of the occurrences of
(partial) busy periods within which systems failures happen at least once, and let
Q be the steady‐state unavailability of the system.Two‐sided bounds are established for Q and μ based on the behavior of the renewal rate of an auxiliary renewal process. The bounds are used for deriving
some asymptotical insensitivity properties in light traffic conditions.
A probabilistic approach to the trace at the boundary forsolutions of a semilinear parabolic partial differential equation
Authors: Gall Jean-François Le 
Published: March 2007

We use the path‐valued process called the “Brownian snake” to investigate
the trace at the boundary of nonnegative solutions of a semilinear parabolic partial differential equation. In particular, we characterize possible traces and in
dimension one we prove that nonnegative solutions are in one‐to‐one correspondence with their traces at the origin. We also provide probabilistic representations for various classes of solutions.This article is dedicated to the memory of Roland L. Dobrushin.
Analysis of the asymmetrical shortest two‐server queueing model
Authors: Cohen J. W. 
Published: March 2007

This study presents the analytic solution for an asymmetrical two‐server
queueing model for arriving customers joining the shorter queue for the
case of Poisson arrivals and negative exponentially distributed service
times. The bivariate generating function of the stationary joint distribution of the queue lengths is explicitly determined.The determination of this bivariate generating function requires a construction of four generating functions. It is shown that each of these functions is the sum of a polynomial and a meromorphic function. The poles
and residues at the poles of the meromorphic functions can be simply calculated recursively; the coefficients of the polynomials are easily found, in
particular, if the asymmetry in the model parameters is not excessively
large. The starting point for the asymptotic analysis for the queue lengths
is obtained. The approach developed in the present study is applicable to
a larger class of random walks modeling asymmetrical two‐dimensional
queueing processes.
Two service units with interference in the access to servers
Authors: Lillo Rosa E. , Neuts Marcel F. 
Published: March 2007

We examine the service mechanism of two queueing models with two units
in tandem. In the first model, customers who complete service in Unit 1
must wait in an intermediate buffer until the ongoing service in Unit II
ends. In the second model, jobs can be pre‐positioned in an intermediate
buffer to await service in Unit II. Under the assumption of phase‐type service times, the steady‐state regime of the service system is studied in detail.The models are inspired by the gas pump model of A.B. Clarke and
by phenomena observed in cafeteria lines and certain manufacturing systems. However, their primary interest may lie in the methodology of their
exceptionally tractable analysis. We derive formulas for the throughput
and other quantities by using the familiar PH‐formalism. These formulas
turn out to be unusually transparent and have probabilistic interpretations
that do not depend on the PH assumptions. These interpretations therefore also hold for general service time distributions. The methodology is
general and can be applied to other systems with interactions between
servers. The models also present interesting algorithmic problems of didactic interest.
The structure and characteristics of photochromic dithienylethenes
Authors: Krayushkin M. M. , Vorontsova L. G. , Uzhinov B. M. 
Published: March 2007

The data on X‐ray diffraction analysis for dihetarylethenes with perfluorocyclopentene (F), maleic
anhydride (M) and cyclobutenedione (S) bridges between thienyl fragments were summarized and their photochromic
properties were discussed. It was established that benzoxazole and benzothiazole substituents
in position 5 of thienyl rings are coplanar to the plane of thiophene cycles. Thienyl fragments in A form of
all dithienylethenes are considerably turned relative to the plane of bridging cycle. It means that there is no
conjugation between π‐electrons of aromatic heterocycles and double bond of the bridge.Flattening of molecule frameworkand the envelope conformation of thienyl cycles because of aromaticity
loss are characteristic features of the form B structure with F‐bridge. In all cases (excluding the compounds
with alkylthio substituents in position 2 of thiophene cycle) the photochromic transition A → B is observed
independently of different nature and structure of functional groups.
Kinetics and mechanisms of EDTA photocatalytic degradation with TiO2 under different experimental conditions
Authors: Babay Paola A. , Emilio Carina A. , Ferreyra Rosana E. , Gautier Eduardo A. , Gettar Raquel T. , Litter Marta I. 
Published: March 2007

The photocatalytic degradationof EDTA over TiO2 has been analyzed to establish the influence
of oxidants on the reaction rate, the nature of the intermediates and the kinetic regime. Degussa P‐25 suspensions
containing EDTA at initial pH 3 in different concentrations were irradiated under near UV light.
A Langmuirian behavior was observed. O2 at saturation concentrations was found to be crucial for EDTA
degradation. The rapid depletion of EDTA was not accompanied by a corresponding TOC decrease, indicating
formation of refractory intermediates. An enhancement in TOC reduction could be achieved by keeping pH
constant or by hydrogen peroxide addition. Addition of Fe(III) caused a remarkable increase on the initial
rate of EDTA consumption and also on TOC decrease. Changes in both parameters clearly increased under
the simultaneous addition of Fe(III) and H2O2, until limiting values.Some of the possible intermediates of EDTA degradation were evaluated in the filtered solution. So far,
glycine, ethylenediamine, ammonium, formaldehyde, and formic, iminodiacetic, oxalic, oxamic, glycolic and
glyoxylic acids have been identified in different proportions, depending on the experimental conditions.
Different degradationpathways are proposed. Inthe presence of Fe(III), photo‐Fenton reactions would contribute
also to the degradation process.
The phthalocyanines applications in photodynamic therapy investigated by time‐resolved and steady‐state photothermal methods
Authors: Frackowiak Danuta , Wiktorowicz Krzysztof , Planner Alfons , Waszkowiak Aneta , Ion Rodica-Mariana 
Published: March 2007

The time‐resolved photothermal methods are used in order to establish the yield of intersystem
(singlet‐triplet) crossing of dyes that are candidates for the application in photodynamic therapy. It is known
that molecules with long living triplet state cause efficient photosensitization by direct interaction with the
cells or by singlet oxygen generation.The steady state photoacoustic spectra enables one to establish the dye incorporation into cells.Both methods were applied to several phthalocyanines and the results gathered by photothermal measurements
were compared with the results obtained by means of other methods.The six investigated dyes were
compared.
On order 5 symplectic explicit Runge-Kutta Nyström methods
Authors: Chou Lin-Yi , Sharp P. W. 
Published: March 2007

Order five symplectic explicit Runge-Kutta Nyström methods of
five stages are known to exist. However, these methods do not have
free parameters with which to minimise the principal error
coefficients. By adding one derivative evaluation per step, to give
either a six-stage non-FSAL family or a seven-stage FSAL family of
methods, two free parameters become available for the minimisation.
This raises the possibility of improving the efficiency of order five
methods despite the extra cost of taking a step.We perform a minimisation of the two families to obtain an optimal
method and then compare its numerical performance with published
methods of orders four to seven. These comparisons along with those
based on the principal error coefficients show the new method is
significantly more efficient than the five-stage, order five methods.
The numerical comparisons also suggest the new methods can be more
efficient than published methods of other orders.
A non-iterative alternative to ordinal Log-Linear models
Authors: Beh Eric J. , Davy Pamela J. 
Published: March 2007

Log-linear modeling is a popular statistical tool for analysing a contingency
table. This presentation focuses on an alternative approach to modeling ordinal categorical
data. The technique, based on orthogonal polynomials, provides a much simpler
method of model fitting than the conventional approach of maximum likelihood estimation,
as it does not require iterative calculations nor the fitting and re-fitting to search
for the best model. Another advantage is that quadratic and higher order effects can
readily be included, in contrast to conventional log-linear models which incorporate linear
terms only.The focus of the discussion is the application of the new parameter estimation technique
to multi-way contingency tables with at least one ordered variable. This will also
be done by considering singly and doubly ordered two-way contingency tables. It will
be shown by example that the resulting parameter estimates are numerically similar to
corresponding maximum likelihood estimates for ordinal log-linear models.
Managing cost uncertainties in transportation and assignment problems
Authors: Adlakha V. , Arsham H. 
Published: March 2007

In a fast changing global market, a manager is concerned with cost uncertainties
of the cost matrix in transportation problems (TP) and assignment problems (AP).A time lag
between the development and application of the model could cause cost parameters to assume
different values when an optimal assignment is implemented.
The manager might wish to determine the responsiveness of the current optimal solution to such uncertainties.
A desirable tool is
to construct a perturbation set (PS) of cost coeffcients which ensures the stability of an optimal
solution under such uncertainties.The widely-used methods of solving the TP and AP are the stepping-stone (SS) method and the
Hungarian method, respectively. Both methods fail to provide direct information to construct the
needed PS. An added difficulty is that these problems might be highly pivotal degenerate.
Therefore, the sensitivity results obtained via the available linear programming (LP) software might be
misleading.We propose a unified pivotal solution algorithm for both TP and AP.
The algorithm is free of pivotal degeneracy, which may cause cycling, and does not require any extra variables such as slack, surplus, or artificial variables used in dual and primal simplex. The algorithm permits higher-order assignment problems and side-constraints. Computational results comparing the proposed
algorithm to the closely-related pivotal solution algorithm, the simplex, via the widely-used pack-age Lindo, are provided. The proposed algorithm has the advantage of being computationally
practical, being easy to understand, and providing useful information for managers. The results
empower the manager to assess and monitor various types of cost uncertainties encountered in
real-life situations. Some illustrative numerical examples are also presented.