Simulation optimization of buffer allocations in production lines with unreliable machines

We use a recent simulation08.gif" alt="dash" align="MIDDLE" BORDER="0">based optimization method, sample path optimization, to find optimal buffer allocations in tandem production lines where machines are subject to random breakdowns and repairs, and the product is fluid08.gif" alt="dash" align="MIDDLE" BORDER="0">type. We explore some of the functional properties of throughput of such systems and exploit these properties to prove the almost sure convergence of our optimization technique, under a regularity condition on the steady state. Utilizing a generalized semi08.gif" alt="dash" align="MIDDLE" BORDER="0">Markov process (GSMP) representation of the system, we derive recursive expressions to compute one08.gif" alt="dash" align="MIDDLE" BORDER="0">sided directional derivatives of throughput, from a single simulation run. Finally, we give computational results for lines with up to 50 machines. We also compare results for smaller lines with the results from a more conventional method, stochastic approximation, whenever applicable. In these numerical studies, our method performed quite well on problems that are considered difficult by current computational standards.     

Strongly Regular Graphs and Designs with Three Intersection Numbers

We investigate BIBDs with three intersection numbers,x, y, and z, such that the relation on the block set given byA 0j2911x37h56475/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0"> B iff the cardinality of the intersectionof A and B is not equal to x is an equivalence relation. Withsuch a design, we associate a family of strongly regular graphswith the same parameters. Two constructions producing infinitefamilies of such designs are given.     

On the étale Descent Problem for Topological Cyclic Homology and Algebraic K-Theory

We investigate étale descent properties of topological Hochschild and cyclic homology. Using these properties we deduce a general injectivity result for the descent map in algebraic K-theory, and show that algebraic K-theory has étale descent for rings of integers in unramified and tamely ramified p-adic fields.     

Generalizations of Perfect, Semiperfect, and Semiregular Rings

For a ring R and a right R-module M, a submodule N of M is said to be 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-small in M if, whenever N + X = M with M/X singular, we have X = M. If there exists an epimorphism p: P 07271N1810560/xxlarge8594.gif" alt="rarr" align="BASELINE" BORDER="0"> M such that P is projective and Ker(p) is 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-small in P, then we say that P is a projective 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-cover of M. A ring R is called 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-perfect (resp., 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-semiperfect, 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-semiregular) if every R-module (resp., simple R-module, cyclically presented R-module) has a projective 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-cover. The class of all 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-perfect (resp., 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-semiperfect, 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-semiregular) rings contains properly the class of all right perfect (resp., semiperfect, semiregular) rings. This paper is devoted to various properties and characterizations of 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-perfect, 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-semiperfect, and 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-semiregular rings. We define 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">(R) by 07271N1810560/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">(R)/Soc(R_R) = Jac(R/Soc(R_R)) and show, among others, the following results:

Kernel polynomials for the solution of indefinite and ill-posed problems

We introduce a new family of semiiterative schemes for the solution of ill-posed linear equations with selfadjoint and indefinite operators. These schemes avoid the normal equation system and thus benefit directly from the structure of the problem. As input our method requires an enclosing interval of the spectrum of the indefinite operator, based on some a priori knowledge. In particular, for positive operators the schemes are mathematically equivalent to the so-called 057785/xxlarge957.gif" alt="ngr" align="BASELINE" BORDER="0">-methods of Brakhage. In a way, they can therefore be seen as appropriate extensions of the 057785/xxlarge957.gif" alt="ngr" align="BASELINE" BORDER="0">-methods to the indefinite case. This extension is achieved by substituting the orthogonal polynomials employed by Brakhage in the definition of the 057785/xxlarge957.gif" alt="ngr" align="BASELINE" BORDER="0">-methods by appropriate kernel polynomials. We determine the rate of convergence of the new methods and establish their regularizing properties.     

Convergence de mesures spectrales aléatoires et applications à des principes d'invariance

Nous présentons un cadre unificateur pour un certain nombre de résultats connus de convergence en loi pour des processus admettant une représentation linéaire par rapport à un bruit blanc faible pour lequel il existe un principe d021u12v/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">invariance faible. Nous montrons que ce principe d021u12v/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">invariance est équivalent à la convergence d021u12v/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">une suite de mesures aléatoires spectrales. Ceci permet d021u12v/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">affaiblir les hypothèses usuelles et donc d021u12v/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">obtenir des résultats nouveaux de convergence en loi, notamment pour des processus à longue portée.     

Spaces with Dual Order-Isomorphic to ℓ1

We establish that an ordered Banach space is order-isomorphic to c₀ if and only if it is a 01k0qg6340/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">-Dedekind complete vector lattice and its norm dual is order-isomorphic to 01k0qg6340/xxlarge8467.gif" alt="ell" align="BASELINE" BORDER="0">₁.     

A GaAs–InGaAs optoelectronic switch with multiple operation states

An optoelectronic switch with both n- and p-type delta-doped (0182n16137/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-doped) quantum wells was investigated. The 0182n16137/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-doped structures formed potential wells for the carrier accumulation and potential barriers for the carrier injection. Being possessed of 0182n16137/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-doped sheets with different doping levels, the potential barriers were sequentially collapsed to produce a double negative-differential-resistance (NDR) phenomenon in the current013;voltage (I013;V) characteristics of the device, due to the carrier accumulation in the potential wells. The device also showed an optical function related to the barrier heights controllable by incident light.     

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.     

On the efficiency of small-angle Čerenkov second harmonic generation in optical waveguides

It is well known that in the non-depleted pump approximation, the efficiency of a second harmonic generation (SHG) of a guided mode in a non-linear optical waveguide increases quadratically with the interaction length (P ₂ 062/xxlarge8733.gif" alt="prop" align="MIDDLE" BORDER="0"> L ²), and linearly (P ₂ 062/xxlarge8733.gif" alt="prop" align="MIDDLE" BORDER="0"> L) in the 062/xxlarge268.gif" alt="Ccaron" align="BASELINE" BORDER="0">erenkov regime. The efficiency of the 062/xxlarge268.gif" alt="Ccaron" align="BASELINE" BORDER="0">erenkov SHG in the waveguide with a non-linear substrate and linear guiding layer is known to be strongly peaked at a particular pump wavelength and a particular waveguide thickness, with the 062/xxlarge268.gif" alt="Ccaron" align="BASELINE" BORDER="0">erenkov angle approaching zero. The known theory predicts an infinite efficiency value at the peak, however. In this contribution, a simple integral expression for the SHG efficiency in the 062/xxlarge268.gif" alt="Ccaron" align="BASELINE" BORDER="0">erenkov regime is derived. For large 062/xxlarge268.gif" alt="Ccaron" align="BASELINE" BORDER="0">erenkov angles and interaction lengths it yields the expected P ₂ 062/xxlarge8733.gif" alt="prop" align="MIDDLE" BORDER="0"> L dependence, while in the limit of small 062/xxlarge268.gif" alt="Ccaron" align="BASELINE" BORDER="0">erenkov angles the dependence is found to have the form of P 062/xxlarge8733.gif" alt="prop" align="MIDDLE" BORDER="0"> L ^3/2, possessing also a finite value at the efficiency peak. The condition determining the accurate position of the efficiency peak in the waveguide thickness013;pump wavelength plane is given, too.