bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Sorption of Chelates of Elements with Organic Reagents on Amberlite XAD-2 as a Preconcentration Step for the Emission Spectrometric Determination of the Elements
Authors: Jambor Jaroslav , Javorek Tomáš
Published: April 2003

The macrophorous hydrophobic sorbent Amberlite XAD-2 proved to be well suited to the preconcentration of minority amounts of Al, Au, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sn, Ti and V in the form of their chelates with organic reagents. From among 14 reagents tested, 8-hydroxyquinoline and diethyldithiocarbamate appeared most suitable for the quantitative sorption up to level of 1 μg l-1 of analyte. Emission spectrometry served as the analytical finish; the nitrous oxide-acetylene flame, electric arc and inductively coupled argon plasma were chosen according to the nature of the element. The procedure is convenient for the determination of the minority analytes in waters
A New Dimeric Derivative of Ethoxyquin from Its Reaction with Alkylperoxy Radicals
Authors: Kříž Jaroslav , Taimr Luděk
Published: April 2003

The structure of a new compound formed in the reaction of ethoxyquin with alkylperoxy radicals was resolved by 1H and 13C NMR spectroscopy (including COSY, NOESY, HHC RCT and SSLR INEPT techniques) and confirmed by mass spectrometry. The structure suggest participation of 4-methyl group of ethoxyquin in the deactivation of peroxy radicals. A mechanism of this reaction is proposed.
Synthesis of Some Diaroylhydrazines, 1,3,4-Oxadiazoles and Pyridazin-3-ones Bearing Thiophene Nucleus
Authors: Yassin Salah , Abd El-Aleem Abd El-Aleem H. , El-Sayed Ibraheem E. , Hashem Ahmed I.
Published: April 2003

Diaroylhydrazines I were used for the preparation of 1,3,4-oxadiazoles II and pyridazinones III, respectively.
Behaviour of [4-(3',4'-Dichlorophenyl)-1-(2H)-phthalazinone-2-yl]-3-(4-chlorophenyl)-2-propen-1-one towards Different Nucleophiles
Authors: El-Farargy Ahmed , Yassin Fathi , Hafez Taghrid
Published: April 2003

In our previous paper we reported on the behaviour of α,β-unsaturated carbonyl compounds toward active methylene compounds. In the present paper we report the results of further studies in this area in which carbonyl compounds bear a heterocyclic moiety.
Synthesis of Some New Spirothiazolidinones Incorporated with Quinazoline Moiety
Authors: Hozien Zeinab A. , Ahmed Abd El-Hamid N. , El-Zohry Maher F.
Published: April 2003

In continuation of our previous work, together with the importance of the combination of spirothiazolidinones with quinazoline moieties, this work reports the synthesis of some new spirothiazolidinones incorporated with quinazoline moiety. Our precursors, 2-spiro-1,3-oxathiolan-5-ones IIIa - IIIe were prepared according to our previously reported method, starting with appropriate cyclic ketones.
Synthesis and Some Reactions of 2-Cyano-1,6-dioxo-3-methylpyrido[1,2-a][3,1]benzoxazine
Authors: Hozien Zeinab A.
Published: April 2003

The importance of pyrido compounds as analgesic, antiinflammatory and central nervous system depressing agents together with the diverse biological activities which have been encountered in compounds containing quinqzoline moiety led us to the synthesis of 2-cyano-1,6-dioxo-3-methylpyrido[1,2-a][3,2]benzoxazine to be used as a starting material for pyridoquinazoline derivatives V - IX.
Effect of Impurities on the Width of the Metastable Region of Potassium Sulfate
Authors: Karel Miloslav , Nývlt Jaroslav
Published: April 2003

The width of the metastable region of potassium sulfate was measured in the presence of various concentrations of chromate, copper(II) and aluminium ions. The dependence of the metastable region width on the impurity concentration is generally nonlinear and in some cases even changes its nature; while in low concentrations some impurities make the metastable region narrower, they make it broader if present in higher concentrations. The effect of the impurities increases in order K2Cr2O7 - CuSO4 - Al2(SO4)3.
Corrosion and Passivation of Tin Anode in Na2CO3 Solutions and the Effect of Halide Ions
Authors: Abd El-Rehim Sayed S. , Taha Fouad , Saleh Mohamed B. , Mohamed Said A.
Published: April 2003

The corrosion and passivation of tin anode in Na2CO3 (0.01 to 1.0 M) was investigated using potentiodynamic and cyclic voltammetry techniques and complemented by X-ray and scanning electron microscopy. The polarization curves exhibit two anodic peaks assigned to the electroformation of Sn(II) and Sn(IV) species, respectively, prior to permanent pssive region. The anodic dissolution reactions are controlled by diffusion. X-Ray diffraction showed that the permanent passive layer is duplex and consists of SnO and SnO2. A multiplicity of cathodic peaks is related to the electroconduction of the anodically formed compounds. Addition of Cl-, Br- or I- ions into the carbonate solutions enhances the anodic dissolution of tin to some extent depending upon the sodium carbonate concentration. In the passive region, addition of the halide ions causes pitting of the halide ions causes pitting corrosion at a critical pitting potential. The pitting potential decreases with increasing both the halide ion concentration and the scanning rate but increases with increasing the sodium carbonate concentration. SEM examination confirms the occurance of pitting corrosion.
Modelling of Flow of a Liquid in Apparatus with Mobile Packing: Dispersion Model
Authors: Palatý Zdeněk
Published: April 2003

The paper deals with determination of parameters of a dispersion model used for describing the flow of liquid on a plate with mobile packing in the region of gas velocities up to 1.5 m s-1. The parameters of the model - the diffusion Peclet number and mean residence time of liquid - were determined from the nonideal input impulse of tracer concentration and its response by the method of numerical integration of differential equation with subsequent optimization of parameters. The results of measurements are presented graphically and in the form of criterion equations.
The Crystal and Molecular Structure of Charge-Transfer Complex of Azo Dyestuff 5-(4-Chloro-2-nitrophenyl)-azo-6-hydroxy-1-ethyl-3-cyano-4-methyl-2-pyridone with Naphthalene
Authors: Přikryl Josef , Kratochvíl Bohumil , Ondráček Jan , Maixner Jaroslav , Klicnar Jiří , Huml Karel
Published: April 2003

The title charge-transfer complex crystallizes in the ratio of two molecules of azo dyestuff to one molecule of naphthalene. The crystals are triclinic, space group P1, lattice parameters a = 7.953(1), b = 11.608(2), c = 11.717(2) Å, α = 101.89(2), β = 94.27(2), γ = 109.91(2)°, Z = 2. The structure was solved by direct methods and refined anisotropically to R = 0.054 for 1 768 unique observed reflections. Crystal packing is stabilized by van der Waals forces and partly by π-π stacking interaction among naphthalene, phenyl and pyridine ring of pyridon azo dyestuff.
Synthesis of Thioxanthenyl Substituted Heterocycles with Potential Molluscicidal and Nematocidal Activity
Authors: El-Sakka Ibrahim , Zeid Ibrahim Fathy , Abdel-Mageed Ahmed El-Sayed
Published: April 2003

The reaction of thioxanthen-9-ol with nucleophiles such as pyrazoles, succinamide, phthalimide and aminotriazoles was investigated. In the reactions, thioxanthen-9-yl is introduced in the 4-position of pyrazoles, on nitrogen in the carboximides and on amino group of aminotriazoles. The synthesized compounds were tested for molluscidal and nematocidal activity.
Synthesis of Some Triazolyl Acetanilides
Authors: Stankovský Štefan , Jedlovská Eva , Špirková Katarína
Published: April 2003

A series of substituted derivatives of triazolyl acetanilides (IIa - IIn) by reaction of 1-chloroacetanilides with 1,2,4-triazole was prepared. The basic IR and 1H NMR spectral data of final products are presented. Investigation of herbicidal, fungicidal and growth-regulation activity showed, that none of the studied compounds was more efficient that currently used compounds.
Special Features of Network Formation by Chain Crosslinking Copolymerization
Authors: Dušek Karel
Published: April 2003

Special features of free-radical crosslinking copolymerization and the structure of the resulting products have been reviewed. Characteristic is the effect of spatial correlations on the apparent reactivity of pendant double bonds. These correlation make the apparent reactivity in the course of copolymerization to increase (cyclization) and decrease (steric hindrances). At intermediate and higher concentrations of the crosslinker, compact structures are formed which are internally crosslinked. Only pendant double bonds in the peripheral layer are able to take part in polymerization reactions whereas the internal ones cannot react. The state of theoretical simulations of this structure growth is discussed with a special emphasis on the development of the kinetic (coagulation) network formation theories so that the above mentioned features may be taken into account. Also, the important role of the presence of a diluent during polymerization id discussed. It can result in a change of network chain conformations necessary for networks exhibiting volume phase transitions. Alternatively, it can induce liquid-gel phase separations resulting in inhomogeneous networks having a variety of morphologies.
Synthesis and Photoproperties of a Substituted Zinc(II) Phthalocyanine-N-(2-hydroxypropyl)methacrylamide Copolymer Conjugate
Authors: Gu Zhong-wei , Spikes John D. , Kopečková Pavla , Kopeček Jindřich
Published: April 2003

In cancer photodynamic therapy (PDT), improved efficiency of photosensitizer delivery to tumors may be obtained by binding them to targetable water soluble polymeric carriers. However, attachment of photosensitizers to Macromolecular carriers may alter their spectral and photosensitizing properties. In this study, a new monosubstituted phthalocyanine derivative, N-glycyl zinc(II) 4,9,16,23-tetraaminophthalocyanine (G-TAPC-Zn) was synthesized by the reaction of zinc(II) 4,9,16,23-tetraaminophthalocyanine (TAPC-Zn) with N-tert-butoxycarbonyl-glycine N'-hydroxybenzotriazole ester followed by deprotection of the tert-butoxycarbonyl (BOC) group. G-TAPC-Zn contains an aliphatic amino group suitable for attachment to water soluble polymeric carriers. By aminolysis of a polymeric precursor, an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing oligopeptide (GFLG) side-chains terminated in p-nitrophenyl ester groups, with G-TAPC-Zn a polymeric derivative of the latter (P-GFLGG-TAPC-Zn) was synthesized. Spectral data indicated that in aqueous solutions P-GFLGG-TAPC-Zn formed aggregates. The degree of aggregation decreased with increasing concentration of detergents or organic solvents in buffer solutions. Consequently, the release of the drug from carrier catalyzed by thiol proteinases, papain or cathepsin B, took place only in the presence of detergents or organic solvents, i.e., under conditions with a lower probability of aggregate formation. Binding of G-TAPC-Zn to HPMA copolymers decreased the quantum yield of singlet oxygen generation from 0.24 to 0.063 and significantly increased its resistance to photobleaching.
Kinetic Modelling of Anionic Polymerization Involving a Dynamic Equilibrium between Two Growth Centres with Different Growth Rates
Authors: Jakeš Jaromír
Published: April 2003

Kinetic modelling of the molecular weight distribution (MWD) of polymer obtained by an anionic polymerization with two types of growth centres in a dynamic equilibrium, having different growth rates and lifetimes comparable to the polymerization time, was made for low monomer conversions. On the basis of distribution of the growth centres according to the total time spent in the fast growth state, it was shown that MWD of the resulting polymer are mostly bimodal at the beginning of the polymerization and change to unimodal MWD at sufficiently high polymerization degrees depending on the equilibrization rate. When all centres are in the fast state in the beginning, MWD are essentially unimodal throughout. A hint of trimodality is observed in some cases, in an extent hardly detectable in real chromatograms. Hence, a polymodal MWD can be explained only when more than two growth centres with different growth rates are assumed.
The Second Virial Coefficients of n-Alkanes and Their Mixtures from the Kihara Convex Core Intermolecular Pair Potential
Authors: Pavlíček Jan , Aim Karel , Boublík Tomáš
Published: April 2003

The second virial coefficients for a series of C2 to C8 n-alkanes and the second virial cross coefficients for their binary mixtures were calculated as a function of temperature from the exact expressions derived for the Kihara rod-like molecules. The three parameters of Kihara pair potential, ε/k, σ and l for the individual compounds were either used as determined from vapour-liquid equilibrium and saturated liquid density data in a previous study or with ε/k adjusted to the second virial coefficient data. The results are accurate almost within experimental uncertainty estimates of the data. In the case of mixtures the second virial cross coefficients were calculated from a similar expression in which only the ε12/k parameter was adjusted whereas σ12 = (σ1 + σ2)/2 and l1 and l2 of pure compounds were employed. It appears that the correction factor to the geometric mean combining rule for ε12/k is always less than and close to unity. Comparison with the values obtained from the Tsonopoulos generalized correlation reveals fair agreement between the characteristic binary k12 parameters from the two methods.
Gas Transport Properties and Structure of Poly(2,6-dimethyl-1,4-phenylene oxide)/Poly(N-arylmaleimide) Membranes
Authors: Lokaj Jan , Bleha Miroslav , Pientka Zbyněk , Lednický František
Published: April 2003

Blend membranes containing poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and homopolymers of substituted N-phenmylmaleimides were prepared by casting from chloroform solutions of mixtures of the polymers. The polyimides were synthesized by the radical polymerization of dimethylamino, chloro, and bromo derivatives of N-phenylmaleimide. The membranes were characterized by permeabilities to oxygen and nitrogen; the permeability ratio O2/N2 equaled to 5.3 - 6.8. Unlike transparent PPO membranes, PPO/polyimide membranes were cloudy. The phase structure of the membranes was examined by optical and scanning electron microscopy. The relation between gas transport properties and the structure of the membranes is discussed.
Cholecystokinin Heptapeptide Analogues with Multiple Modification in Peptide Chain
Authors: Hlaváček Jan , Pírková Jana , Žertová Miroslava , Pospíšek Jan , Maletínská Lenka , Slaninová Jiřina
Published: April 2003

Using solid phase synthesis we prepared the cholecystokinin fragment Boc-CCK-7 (Boc-Tyr(SO3-Na+)-Met-Gly-Trp-Met-Asp-Phe-NH2) Ia and its seven analogues Ib - Ih. In the analogues Ib and Ic the Met residue in the carboxyterminal part of the molecule was substituted for L- or D-Phe Me3. In the analogues Id and Ie with Phe residue substituted by L- or D-Phe Me3 the Neo was inserted in the place of this Met residue and in the analogues If and Ig, an addition to PheMe3 substitution in the carboxyterminus, both Met residues were replaced for Neo. This dual substitution for Met residues was also applied in the analogue Ih with coded Phe residue in the C-terminus.
Vibrational Dynamics of the H2O . HF Complex. Potential Energy and Electric Dipole Moment Surfaces
Authors: Sadlej Andrzej J. , Bludský Ota , Špirko Vladimír
Published: April 2003

A total of 330 points on the potential energy and electric dipole moment surfaces of the ground electronic state of the H2O . HF complex have been calculated ab initio using the SCF method and many-body perturbation theory (MBPT). To keep the calculations manageable, the geometry parameters of H2O were fixed at their experimental values and only certain two dimensional sections of the total surfaces have been evaluated. for each of the two-dimensional surface section, analytic potential energy and electric dipole moment functions have been fitted through the points and corresponding vibrational energy levels and effective electric dipole moments have been calculated using approximate vibrational Hamiltonians. The calculated values of resulting vibrational energies and effective electric dipoles from differently wide intervals for different vibrational modes. The intervals corresponding to the most interesting low frequency modes (out-of-plane and H2O vs HF stretching) are very narrow and coincide satisfactory with the corresponding experimental values. A very reasonable agreement has also been obtained for the equilibrium geometry, electric dipole moment and dissociation energy De of the complex. These findings lead us to believe that the calculated potential energy and electric dipole moment surfaces are sufficiently accurate for predicting purposes and rationalization of the so far unassigned spectral data of H2O . HF.
Homogeneous Nucleation of Supersaturated Vapors. A Comparison of Experimental Results with Theory
Authors: Smolík Jiří , Ždímal Vladimír
Published: April 2003

Some theories of homogeneous nucleation based on liquid droplet model were tested by comparing with experimental supersaturations of naphthalene, phthalic anhydride, stearic acid, bis(2-ethylhexyl) phthalate, and bis(2-ethylhexyl) sebacate required to bring about the rate of homogeneous nucleation of about 5 drops/cm3 s-1. It was found that except for highly polar substance phthalic anhydride, the classical (Becker-Doring) theory of homogeneous nucleation, if suitably scaled, yielded fairly good predictions of the nucleation behaviour.
Synthesis of [1]Benzothieno[3,2-b]furan - A New Fused Benzoheterocyclic System
Authors: Svoboda Jiří , Nič Miloslav , Paleček Jaroslav
Published: April 2003

A new heterocyclic compound has been prepared by four step synthesis. The reaction of methyl thiosalicylate I with excess methyl chloroacetate in the presence of potassium carbonate gives methyl 3-[(methoxycarbonyl)methoxy]benzo[b]thiofen-2-carboxylate (II) which on cyclization by action of potassium tert-butoxide gives methyl 3-hydroxy[1]benzothieno[3,2-b]furan-2-carboxylate (III). Its base catalyzed hydrolysis and decarboxylation forms [1]benzothieno[3,2-b]furan-3(2H)-one (IV) whose reduction with NaBH4 gives the title compound.
Synthesis and Antiproliferative Activity of Spirocyclic Cyclodipeptides, Derivatives of 1-Amino-1-cyclobutanecarboxylic Acid
Authors: Vinšová Jarmila , Kosař Karel , Kasafírek Evžen
Published: April 2003

A series of chiral spirocyclic cyclodipeptides of the general formula I was synthesized; the aim was to determine how the substitution of cyclobutane for cyclopentane in cyclo(-alanyl-1-amino-1-cyclopentanecarbonyl-) would influence the inhibition of the proliferative activity of the caudal morphogenic system (CMS) of Chick embryos. Spirocyclic cyclodipeptides Ia - Il were obtained by cyclization of linear dipeptides IIa - IIf, prepared by condensation of protected amino acids by DCCI method. The inhibition was investigated by the Chick Embryotoxicity Screening Test. The results show generally lower activity in the tested series, as compared with derivatives containing 1-amino-1-cyclopentanecarboxylic acid.
Synthesis and Some Pharmacological Properties of Six New Analogs of Arginine-Vasopressin Substituted in Position 2 with β-Thienylalanine or Prolonged on the N-Terminus with 1-Adamantaneacetic Acid
Authors: Konieczna Ewa , Czaja Malgorzata , Lammek Bernard , Slaninová Jiřina , Barth Tomislav
Published: April 2003

Six new analogs of arginine-vasopressin, four of them substituted in position 2 with β-thienylalanine and two prolonged on the n-terminus by acylation with 1-adamantaneacetic acid, were synthesized on chloromethylated resin using Boc strategy and DCC or DCC-HOBt to form peptide bond. The activity of the analogs was fairly low, however, one of the peptides, namely [Cpp1, Thi2, Val4]AVP, showed selectivity in antiuterotonic, antipressor and anti-antidiuretic effects.
Preparation of 3-(6-Deoxy-β-D-glucopyranosyloxy) and 3-(6-Deoxy-α-L-mannopyranosyloxy)androstane Derivatives with Unsaturated Side Chain in Position 17β
Authors: Chodounská Hana , Pouzar Vladimír
Published: April 2003

In our previous papers we described the preparation of 3-β-D-glucopyranosyloxy) and 3-β-D-galactopyranosyloxy) derivatives of steroids with an α,β-unsaturated ester chain in position 17β of androstane skeleton. In conection with this project we have studied silver silicate promoted glycosylation of some of above mentioned steroidal derivatives with 2,3,4-tri-O-acetyl-6-deoxy-α-D-glucopyranosyl bromide and 2,3,4-tri-O-acetyl-6-deoxy-α-L-mannopyranosyl bromide.
Reaction of 5-Arylidenerhodamine Derivatives with 1-Piperidinocyclohexene and Diethylaminoheptene Enamines
Authors: Abdel-Rahman Mahmoud A.
Published: April 2003

The present paper deals with the reaction of arylidenerhodamine derivatives Ia - Id with enamines 1-piperidinocyclohexane IIa and diethylaminoheptene IIb, stronger nucleophiles than 1-morpholinocyclohexane described earlier.
Synthesis and Reactions of Triazine Azide towards Nucleophilic Reagents
Authors: Abbas Temerik H. H. , Younes M. I. , Metwally S. A.
Published: April 2003

The hydrazinotriazine compound I was used for preparation of various fused heterocycles.
On the existence of submultiplicative moments for the stationary distributions of some Markovian random walks
Authors: Sgibnev M. S.
Published: April 2003

This paper is concerned with submultiplicative moments for the stationary distributions π of some Markov chains taking values in ℝ+ or ℝ which are closely related to the random walks generated by sequences of independent identically distributed random variables. Necessary and sufficient conditions are given for ∫φ(x)π(dx) < ∞, where φ(x) is a submultiplicative function, i.e. φ(0) = 1 and φ(x+y) ≤ φ(x)φ(y) for all x, y.
Mass transportation problems with capacity constraints
Authors: Rachev S. T. , Olkin I.
Published: April 2003

We exhibit solutions of Monge–Kantorovich mass transportation problems with constraints on the support of the feasible transportation plans and additional capacity restrictions. The Hoeffding–Fréchet inequalities are extended for bivariate distribution functions having fixed marginal distributions and satisfying additional constraints. Sharp bounds for different probabilistic functionals (e.g. Lp-distances, covariances, etc.) are given when the family of joint distribution functions has prescribed marginal distributions, satisfies restrictions on the support, and is bounded from above, or below, by other distributions.
A brokered market with heterogeneous suppliers and consumers
Authors: Righter Rhonda
Published: April 2003

We consider a brokered market with heterogeneous suppliers and consumers of identical items or services. Each supplier determines a minimum acceptable price for the items it supplies, based on its costs and target rate of return. The broker begins with a fixed set of items from the suppliers. Customers arrive periodically to the market and offer a bid for an item. If a customer wants more than one item, a set of bids is made. If the broker accepts a bid it must be assigned an item with minimum accceptable price less than or equal to the bid, and the price paid is the bid price. The broker has the option of rejecting a bid. The broker makes acceptance and assignment decisions to maximize the total expected discounted revenue. We show the optimal policy has a simple threshold structure where thresholds can be easily determined by finding the individually optimal policies subject to priorities.
A laplace transform representation in a class of renewal queueing and risk processes
Authors: Willmot Gordon E.
Published: April 2003

For a class of renewal queueing processes characterized by a rational Laplace–Stieltjes transform of the arrival inter-occurrence time distribution, the Laplace–Stieltjes transform of the equilibrium (actual) waiting time distribution is re-expressed in a manner which facilitates explicit inversion under certain conditions. The results are of interest in other contexts as well, as for example in insurance ruin theory. Various analytic properties of these quantities are then obtained as a result.
On the probabilistic properties of a double threshold ARMA conditional heteroskedastic model
Authors: Ling Shiqing
Published: April 2003

Following Tweedie (1988), this paper constructs a special test function which leads to sufficient conditions for the stationarity and finiteness of the moments of a general non-linear time series model, the double threshold ARMA conditional heteroskedastic (DTARMACH) model. The results are applied to two well-known special cases, the GARCH and threshold ARMA (TARMA) models. The condition for the finiteness of the moments of the GARCH model is simple and easier to check than the condition given by Milhøj (1985) for the ARCH model. The condition for the stationarity of the TARMA model is identical to the condition given by Brockwellet al. (1992) for a special case, and verifies their conjecture that the moving average component does not affect the stationarity of the model. Under an additional irreducibility assumption, the geometric ergodicity of the GARCH and TARMA models is also established.
Outcomes of epidemic models with general infection and removal rate functions at certain stopping times
Authors: Clancy Damian
Published: April 2003

This paper aims to show how certain known martingales for epidemic models may be derived using general techniques from the theory of stochastic integration, and hence to extend the allowable infection and removal rate functions of the model as far as possible. Denoting byx,ythe numbers of susceptible and infective individuals in the population, then we assume that new infections occur at rate βxyxyand infectives are removed at rate γxyy, where the ratio βxy/ γxycan be written in the formq(x+y) /xp(x) for appropriate functionsp,q. Under this condition, we find equations giving the distribution of the number of susceptibles remaining in the population at appropriately defined stopping times. Using results on Abel–Gontcharoff pseudopolynomials we also derive an expression for the expectation of any function of the number of susceptibles at these times, as well as considering certain integrals over the course of the epidemic. Finally, some simple examples are given to illustrate our results.
Asymptotic distributions for downtimes of monotone systems
Authors: Gåsemyr J. , Aven Terje
Published: April 2003

Consider a monotone system with independent alternating renewal processes as component processes, and assume the component uptimes are exponentially distributed. In this paper we study the asymptotic properties of the distribution of the rth downtime of the system, as the failure rates of the components converge to zero. We show that this distribution converges, and the limiting function has a simple form. Thus we have established an easy computable approximation formula for the downtime distribution of the system for highly available systems. We also show that the steady state downtime distribution, i.e. the downtime distribution of a system failure occurring after an infinite run-in period, converges to the same limiting function as the failure rates converge to zero.
On the transient delays of M/G/1 queues
Authors: Wang Chia-Li
Published: April 2003

A recent study on the GI/G/1 queue derives the Maclaurin series for the moments of the waiting time and the delay to respect to some parameters. By the same approach, we obtain an identity on the moments of the transient delay of the M/G/1 queue. This identity allows us to understand the transient behavior of the process better. We apply the identity with other established results to study convergence rate and stochastic concavity of the transient delay process, and to derive bounds and approximations of the moments. Our approximation and bound both have simple closed forms and are asymptotically exact as either the traffic intensity goes to zero or the process approaches stationarity. Performance of the approximation of several M/G/1 queues is illustrated by numerical experiments. It is interesting to note that our results can also help to gain variance reduction in simulation.
A unified approach to the study of tail probabilities of compound distributions
Authors: Cai Jun , Garrido José
Published: April 2003

We consider the tail probabilities of a class of compound distributions. First, the relations between reliability distribution classes and heavy-tailed distributions are discussed. These relations reveal that many previous results on estimating the tail probabilities are not applicable to heavy-tailed distributions.

Then, a generalized Wald's identity and identities for compound geometric distributions are presented in terms of renewal processes. Using these identities, lower and upper bounds for the tail probabilities are derived in a unified way for the class of compound distributions, both under the conditions of NBU and NWU tails, which include exponential tails, as well as under the condition of heavy-tailed distributions.

Finally, simplified bounds are derived by the technique of stochastic ordering. This method removes some unnecessary technical assumptions and corrects errors in the proof of some previous results.
Understanding brachiation: insight from a collisional perspective
Authors: Usherwood James R. , Bertram John E. A.
Published: April 2003

Gibbons are able to brachiate effectively through the forest canopy with a suspended swinging motion via contact with handholds. The swing phase is unlikely to be a cause of significant energy loss as pendulums are able to oscillate with only gradual mechanical energy dissipation. We consider the energetics associated with the transition of either a swing (during continuous-contact brachiation) or a ballistic flight (ricochetal brachiation)to a subsequent swing. In both styles of brachiation, kinematic data suggest that a gibbon overshoots the path that would allow a smooth transition into the swing phase. The sudden change in velocity due to such an overshoot is associated with a collision. Assuming neither the handhold nor the gibbon stores elastic strain energy, the energetic consequences of such overshoots can be calculated.

We suggest two reasons for overshooting smooth transition trajectories: in the case of continuous contact brachiation, excess mechanical energy can be maintained with a high amplitude swing, and an overshoot during ricochetal brachiation produces a safety margin.

The degree of energy loss with the transition to the swing phase is dependent both on the alignment of the pre- and post-transition paths, and on the kinetic energy at that instant. Active mechanisms reduce the effects of overshoots in both brachiation gaits. During continuous-contact brachiation,the path of the centre of mass can be controlled actively by flexion both of the trailing arm and the legs. During ricochetal brachiation, the length between the hand and the centre of mass (determining the subsequent swing path) can be controlled throughout the flight phase with leg flexion/extension. In addition, the elongated arms characteristic of gibbons improves the geometry of a collision for a given overshoot, and so may be viewed as a morphological adaptation reducing the energetic losses caused by overshooting for safety.
Plasma membrane rafts of rainbow trout are subject to thermal acclimation
Authors: Zehmer John K. , Hazel Jeffrey R.
Published: April 2003

Rafts are cholesterol- and sphingolipid-enriched microdomains of the plasma membrane (PM) that organize many signal transduction pathways. Interactions between cholesterol and saturated lipids lead to patches of liquid-ordered membrane (rafts) phase-separating from the remaining PM. Phase behavior is temperature sensitive, and acute changes in temperature experienced by poikilotherms would be expected to perturb raft structure, necessitating an acclimatory response. Therefore, with thermal acclimation, we would expect compositional changes in the raft directed to offset this perturbation. Using differential and density gradient centrifugation, we separated PM from the livers of rainbow trout acclimated to 5°C and 20°C into raft-enriched(raft) and raft-depleted PM (RDPM). Compared with RDPM, the raft fractions were enriched in cholesterol, the β2-adrenergic receptor and adenylyl cyclase, which are commonly used markers for this microdomain. Furthermore, cholesterol was enriched in all fractions from warm-compared with cold-acclimated animals, but this increase was 3.4 times greater in raft than in PM. We developed a novel approach for measuring membrane molecular interaction strength (and thus the tendency to stabilize raft structure) based on the susceptibility of membranes to detergent. Specifically, studies with model vesicles demonstrated that the capacity of a membrane to accommodate detergent prior to solubilization (saturation point) was a good index of this property. The saturation point of the isolated membrane preparations was temperature sensitive and was significantly different in 5°C- and 20°C-acclimated RDPM when assayed at 5°C and 20°C, respectively. By contrast, this comparison in rafts was not significantly different,suggesting compensation of this property. These data suggest that compositional changes made in the PM during thermal acclimation act to offset thermal perturbation of the raft but not the RDPM structural integrity.
Tolerance of chronic hypercapnia by the European eelAnguilla anguilla
Authors: McKenzie D. J. , Piccolella M. , Valle A. Z. Dalla , Taylor E. W. , Bolis C. L. , Steffensen J. F.
Published: April 2003

European eels were exposed for 6 weeks to water CO2 partial pressures (PCO2) from ambient (approx. 0.8 mmHg), through 15±1 mmHg and 30±1 mmHg to 45±1 mmHg in water with a total hardness of 240 mg l–1 as CaCO3, pH 8.2, at 23±1°C. Arterial plasma PCO2 equilibrated at approximately 2 mmHg above water PCO2 in all groups, and plasma bicarbonate accumulated up to 72 mmol l–1 in the group at a water PCO2 of 45 mmHg. This was associated with an equimolar loss of plasma Cl–, which declined to 71 mmol l–1 at the highest water PCO2. Despite this, extracellular acid–base compensation was incomplete; all hypercapnic groups tolerated chronic extracellular acidoses and reductions in arterial blood O2 content (CaO2), of progressive severity with increasing PCO2. All hypercapnic eels, however, regulated the intracellular pH of heart and white muscle to the same levels as normocapnic animals. Hypercapnia had no effect on such indicators of stress as plasma catecholamine or cortisol levels, plasma osmolality or standard metabolic rate. Furthermore, although CaO2 was reduced by approximately 50% at the highest PCO2, there was no effect of hypercapnia on the eels' tolerance of hypoxia, aerobic metabolic scope or sustained swimming performance. The results indicate that, at the levels tested, chronic hypercapnia was not a physiological stress for the eel, which can tolerate extracellular acidosis and extremely low Cl–levels while compensating tissue intracellular pH, and which can meet the O2 requirements of routine and active metabolism despite profound hypoxaemia.
Optimizing Restoration Capacity in the AT&T Network
Authors: Ambs Ken , Cwilich Sebastian , Deng Mei , Houck David J. , Lynch David F. , Yan Dicky
Published: April 2003

To ensure high network reliability, AT&T employs two basic approaches: preventing failures and responding quickly when failures occur. For AT&T to quickly reroute traffic in the event of a network failure, the network must contain sufficient restoration capacity to carry the displaced demand. A team of AT&T OR experts, network planners, and managers developed a method for determining the appropriate quantity and location of restoration capacity required to restore the demand during any single link failure. The approach centers on a linear programming model to minimize the cost of the restoration network and uses column generation to generate new restoration paths as needed. In about 10 months, the team converted the methodology into a tool to optimize the allocation of restoration capacity. This tool was then extended to plan for the recovery of a switching-center disaster and to reoptimize the entire restoration network. It has contributed to AT&T's achieving high-quality service, while saving valuable resources. It resulted in hundreds of millions of dollars in cost savings and increased revenues.
Using Mixed-Integer Programming to Reduce Label Changes in the Coors Aluminum Can Plant
Authors: Katok Elena , Ott Dennis
Published: April 2003

Valley Metal Container (VMC), a joint venture between the Coors Brewing Company and American National Can, operates the world's largest single-site facility for aluminum can production. Located in Golden, Colorado, the plant manufactures over 4 billion cans per year on six production lines. Coors Brewery produces seven products, each requiring a distinct label. We developed an optimization-based decision support system with a spreadsheet user interface that helps VMC planners to determine the weekly can production schedule, aiming to meet brewery demand while minimizing the number of label changes and related costs. VMC has been using the new system since October 1998 and estimates the reduction in direct costs (scrap, labor, and inventory) at over $150,000 per year.
Learning, Information, and Performance Support (LIPS): A Multimedia-Aided Approach
Authors: Callahan Elias R. , Shim J. P. , Oakley Gerald W.
Published: April 2003

We developed a framework that allows individuals to use personal computers to learn the concepts, knowledge, and information required for satisfactory job performance and get the feedback and performance support they need to accomplish specific tasks. This concept, called learning, information, and performance support (LIPS), has been implemented by over 400 government agencies and over 100 private sector companies in 12 countries. LIPS incorporates learning, information, and performance support into an integrated end-user interface. It accommodates all levels of users from novice to expert. LIPS provides end-users with desktop access to the tools they need to perform their jobs. The integration of modules and their technical relationships appears seamless. Many of these modules are multimedia based, incorporating new educational philosophies and technologies. LIPS combines learning, information, and performance support into an integrated source of knowledge that employees and managers can use to perform their jobs with improved quality, higher productivity, and lowered cost. The actual system demonstrated cost savings of 45 to 65 percent and marked improvement in retention times.
Sequence-Dependent Scheduling at Baxter International
Authors: Moss Steven , Dale Cheryl , Brame Glenn
Published: April 2003

We solved Baxter International's IV (intravenous) systems production scheduling as a sequence-dependent scheduling problem. Unlike problems previously studied, Baxter's production line has a large number of components and parts (IV systems) with a nonrepetitive schedule. We compared cluster analysis and mathematical programming as alternative methodologies to solve the scheduling problem. Mathematical programming produces solutions that do better in optimizing setup times. Cluster analysis produces results that managers prefer over mathematical programming because cluster analysis reduces resource requirements relative to mathematical programming. Baxter's implementation of the scheduling model based on cluster analysis on four production lines reduces setup times and saves $165,000 annually.
Stepping Towards Sustainable Business: An Evaluation of Waste Minimization Practices in US Manufacturing
Authors: Clelland Iain J. , Dean Thomas J. , Douglas Thomas J.
Published: April 2003

Central to the movement of organizations toward environmental sustainability is the financial viability and environmental effectiveness of the techniques for improving environmental performance. While waste-minimization practices (WMPs) have been touted as a key element in moving manufacturing organizations toward sustainability, we know little about their utilization and effectiveness across a range of industrial and organizational contexts. Using waste-minimization data collected as part of the Toxics Release Inventory, we studied 250 manufacturing firms to provide empirical evidence to enable plant managers to prioritize waste-minimization options. We found clear evidence of a corporate double bonus WMPs can provide through pollution reduction and enhanced operational efficiency relative to traditional end-of-pipe solutions. In the array of ecologically sustainable business practices, it appears that WMPs provide immediate environmental and operational benefits and build momentum for further steps toward environmentally sustainable economic development.
Simplicity Without Reduction: Thinking Upstream Towards the Sustainable Society
Authors: Broman Göran , Holmberg John , Robört Karl-Henrik
Published: April 2003

The natural-step framework is used by over 100 organizations, including many global corporations in Europe and the United States, to provide strategic direction for their sustainability initiatives. The framework is built on the concept of simplicity without reduction. Out of respect for complexity, we designed it to provide a compass, a guide for strategic direction. The framework consists of a backcasting planning process for sustainable development based on four principles (system conditions) for sustainability. The framework does not prescribe detailed actions. Once an organization understands the framework, it identifies and specifies the detailed means by which to achieve the strategy, because it knows its business best. The steps in the planning process are understanding and discussing the system conditions for sustainability, describing and discussing how the company relates to the system conditions in today's situation, creating a vision of how the company will fulfill its customers' needs in the future while complying with the system conditions, and specifying a program of actions that will take the company from today's situation to the future vision.
Developing a Theory of Reverse Logistics
Authors: Dowlatshahi Shad
Published: April 2003

Reverse logistics, a fairly new concept in logistics, has gained increasing importance as a profitable and sustainable business strategy. I describe a holistic view of reverse logistics and distill 11 insights for successful implementation of reverse logistics from the existing literature and published case studies. The strategic factors consist of strategic costs, overall quality, customer service, environmental concerns, and legislative concerns. The operational factors consist of cost-benefit analysis, transportation, warehousing, supply management, remanufacturing and recycling, and packaging. Insights about these factors together form the state-of-the-art knowledge about the keys to successful design and use of reverse-logistics systems.
E Media's Global Zero: Design for Environment in a Small Firm
Authors: Carlson-Skalak Susan , Leschke John , Sondeen Mark , Gelardi Paul
Published: April 2003

Shape, Inc. is the last remaining videocassette manufacturer in the United States. It successfully competes against foreign suppliers with a nearly 50-fold labor-cost advantage using a combination of automation and innovative design. One of its products, the Global Zero (G0) videocassette, exemplifies many of the precepts outlined by sustainable design. Developed over a period of three years by the design firm E Media and coming into production in January 1993, the Global Zero offers an alternative that is cost-effective to manufacture, offers consumer advantages, is 100-percent recyclable, and has the potential for a closed-loop material usage cycle.
Supply-Chain Excellence for Accelerated Improvement
Authors: Lockamy Archie , Beal Reginald M. , Smith Wilbur I.
Published: April 2003

Many firms have begun employing an integrative approach called supply-chain management (SCM) to manage their raw-materials-supply-production-distribution systems. 3M Company uses SCM to achieve its companywide goals of increasing customer satisfaction and loyalty, doubling the speed of key business processes, and reducing inventories and costs. 3M's experience indicates that to derive tangible benefits from SCM a firm must (1) create a clear vision of what it wants to accomplish, (2) establish and communicate companywide supply-chain goals, (3) develop a definition of its supply chain and formulate goals for improving supply-chain operations, (4) develop a process for implementing SCM, and (5) develop measures for assessing progress toward achieving business-unit and companywide goals.
Supply-Chain Synchronization: Lessons from Hyundai Motor Company
Authors: Hahn Chan K. , Duplaga Edward A. , Hartley Janet L.
Published: April 2003

One of the challenges of supply-chain management is developing ways to effectively integrate activities across organizations on the supply chain. Hyundai Motor Company developed mechanisms to coordinate production planning and scheduling activities among supply-chain members. Hyundai Motor's production-and-sales-control (P/SC) department uses regularly scheduled cross-functional meetings and scheduling policies to coordinate supply-chain activities. When implementing this process, the P/SC department overcame structural, environmental, and behavioral problems. Although Hyundai management concedes that the process is not perfect, communication among supply-chain members has improved, and the P/SC group has successfully promoted mutual understanding and respect among functional areas. The primary benefit, ultimately, is improved customer satisfaction through better integration of functional activities.
Oral‐facial‐digital syndrome gabrielli type: Second report
Authors: Obregón Maria Gabriela , Barreiro Cristina Zulema
Published: April 2003

We describe a second sporadic case, a girl, with the features of Oral‐Facial‐Digital, type Gabrielli. We comment on several aspects of this condition and confirm this entity as a unique syndrome, different from the other OFDS. To date, the diagnosis is based only on clinical and radiographic findings. © 2003 Wiley‐Liss, Inc.
Prenatal detection of rare chromosomal autosomal abnormalities in Europe
Authors: Baena N. , De Vigan C. , Cariati E. , Clementi M. , Stoll C. , Caballin M.R. , Guitart M.
Published: April 2003

The aim of the present study was to evaluate the prenatal detection of rare chromosomal autosomal abnormalities by ultrasound (US) examination. Data were obtained from 19 congenital malformation registries from 11 European countries, between 01/07/96 and 31/12/98. A total of 664,340 births were covered and 7,758 cases with congenital malformations were recorded. Rare autosomal abnormalities were diagnosed in 114 cases (6.6%) from a total of 1,738 chromosome abnormalities. There were a wide variety of autosomal abnormalities: the most common were deletions (33 cases), duplications (32 cases), trisomies of chromosomes 8, 9, 10, 14, 15, and 16 (23 cases), and unbalanced rearrangements (19 cases). Out of these cases, 45.6% were detected prenatally by US examination due to the presence of congenital anomaly. As for the types of chromosomal anomaly, unbalanced rearrangements and deletions were the most frequently detected by US. A high percentage of cases with balanced rearrangements were associated with severe congenital anomalies. The most frequent congenital anomalies detected by US were cystic hygroma (20.6%), central nervous system defects (17.6%), cardiac defects (13.2%), and diaphragm defects (10.3%). This large series offers useful information about prenatal diagnosis by US of congenital defects associated with rare autosomal abnormalities and it provides a valuable knowledge about outcome. Fetal anomalies detected by US that were associated with rare autosomal abnormalities were significantly more frequent than those associated with common chromosomal abnormalities (45.6 vs. 34.7%). This study indicates the need to increase the detection of congenital anomalies by US. © 2003 Wiley‐Liss, Inc.