bluuebunny/crossref_metadata_2025_split huggingface dataset:
A queueing system with multiple service time distributions
Authors: Harris Carl M. 
Published: May 2007

AbstractThis paper explores a modification of the output discipline for the Poisson input, exponential output, single channel, first‐come, first‐served queueing system. Instead, the service time distribution of customers beginning service when alone in the system is considered different from that governing service times of all other customers. More specifically, the service times of lone customers are governed by a one parameter gamma distribution, while the service times of all other customers are exponentially ajstributed. The generating function for the steady‐state probsbilities, nj = Pr { j customers in system at an arbitrary point of departure}, of the imbedded chain, {Xn/Xn = number in system after nth customer is serviced}, is obtained, and the steady‐state probabilities, themselves, are found in closed form.
Bounds on parallel‐processing of queues with multiple‐phase jobs
Authors: Coffman E. G. 
Published: May 2007

AbstractCurrently, both the hardware and software designs of many large computing systems aim at improved system performance through exploitation of parallelism in multiprocessor systems. In studying these systems, mathematical modelling and analysis constitute an important step towards providing design tools that can be used in building such systems. With this view the present paper describes a queueing model of a multiprocessor system operating in a job‐shop environment in which arriving jobs consist of a random number of segments (sub‐jobs). Two service disciplines are considered: one assumes that the sub‐jobs of a given job are capable of parallel operation on different processors while the other assumes that the same sub‐jobs must be operated in a strictly serial sequ'snce. The results (in particular, the mean number in the system and waiting time in queue) obtained for these two disciplines are shown to be bounds for more general job structures.
Congestion analysis of a computer core storage system
Authors: Chang W. 
Published: May 2007

AbstractThis paper studies the congestion problems of the computer core storage units. The principle of storage request interleaving is briefly discussed as means of increasing thruput. An analytic model is proposed to analyze the core storage system with a two‐way interleaving feature. The model, an approximation to the physical system, is an extension of a queueing model with bulk service considered by Bailey in Ref. [1].
The many‐product cargo loading problem
Authors: Pruzan Peter Mark , Jackson J. T. Ross 
Published: May 2007

AbstractAn algorithm, based upon dynamic programming, is developed for a class of fixed‐cost cargo loading problems. The problems can be formulated as integer programming problems, but cannot be efficiently solved as such because of computational difficulties. The algorithm developed has proved to be very efficient in an actual operations research study involving over 500 different cargo items, more than 40 possible stops and several types of transportation vehicles. A numerical illustration is provided.
Optimal scheduling of objects in circulating systems
Authors: Wridman Donald R. 
Published: May 2007

AbstractA “circulating system” is a finite collection of objects, each of which is oscillaling between two states. The prototype system is that of ships on patrcl,each subject to a quasi‐regular “duty‐service” cycle. There are various restrictions on the time spent in either state by an object and on the number of objects in a state at any one time. Schedules are sought in which the total number in one state is as large and as constant as possible. The maximal average number in one state is calculated, and a necessary and sufficient condition is given for a schedule to achieve it. Procedures are developed for constructing a schedule which achieves the maximal average in the most constant manner.
More ado about economic order quantities (EOQ)
Authors: Presutti Victor J. , Trepp Richard C. 
Published: May 2007

AbstractThis paper is concerned with the determination of explicit expressions for economic order quantities and reorder levels, such that the cost of ordering and holding inventory is minimized for specific backorder constraints. Holding costs are applied either to inventory position or on‐hand inventory, and the backorder constraint is considered in terms of the total number of backorders per year or the average number of backorders at any point in time. Through the substitution of a new probability density function in place of the normal p.d.f., explicit expressions are determined for the economic order quantities and the reorder points. The resulting economic order quantities are independent of all backorder constraints. It is also concluded that under certain conditions, the minimization of ordering costs and inventory holding costs (applied to inventory position), subject to a backorder constraint, is equivalent in terms of reorder levels to minimization of the safety level dollar investment subject to the same backorder constraint.
The relationship between decision variables and penalty cost parameter in (Q, R) inventory models
Authors: Kaplan Alan J. 
Published: May 2007

AbstractThis paper is concerned with the optimum decision variables found using order quantity, reorder point (Q, R) inventory models. It examines whether the optimum variables (Q* and R*) are necessarily monotonic functions of the backorder cost parameter (or equivalently of the performance objective). For a general class of models it is proved that R* must increase as the performance objective is raised, and an inequality condition is derived which governs how Q* will change. Probability distributions of lead time demand are cited or found for which Q* increases, Q* decreases, and Q* is independent of increases in performance objectives or backorder cost parameter.
Simple finite element‐based computation of distance functions in unstructured grids
Authors: Elias Renato N. , Martins Marcos A. D. , Coutinho Alvaro L. G. A. 
Published: May 2007

AbstractA distance field is a representation of the closest distance from a point to a given surface. Distance fields are widely used in applications ranging from computer vision, physics and computer graphics and have been the subject of research of many authors in the last decade. Most of the methods for computing distance fields are devoted to Cartesian grids while little attention has been paid to unstructured grids. Finite element methods are well known for their ability to deal with partial differential equations in unstructured grids. Therefore, we propose an extension of the fast marching method for computing a distance field in a finite element context employing the element interpolation to hold the Eikonal property (∥∇φ∥ = 1). A simple algorithm to develop the computations is also presented and its efficiency demonstrated through various unstructured grid examples. We observed that the presented algorithm has processing times proportional to the number of mesh nodes. Copyright © 2007 John Wiley & Sons, Ltd.
Hydrophobic guar gum derivatives prepared by controlled grafting processes
Authors: Bahamdan Ahmad , Daly William H. 
Published: May 2007

AbstractIntroduction of polyalkoxyalkyleneamide grafts to guar gum produces a new water soluble guar derivative. Modification of either guar gum or hydroxyopropyl guar is achieved in a three‐step process: carboxymethylation with sodium chloroacetate, esterification with dimethyl sulfate (DMS) and amidation with a series of polyalkoxyalkyleneamines. The process was followed using infrared spectroscopy; the grafted guar derivatives were characterized using 1H NMR. A series of hydroxypropyl guar (HPR) derivatives with degrees of carboxymethylations ranging from 0.2–0.3 were modified with polyalkoxyalkyleneamines with molecular weights ranging from 300 to 3000. The ratio of oxypropylene to oxoethylene units in the polyalkoxyalkyleneamines was varied from 9/1 to 8/58 to adjust the hydrophobicity of the grafts. Aqueous solutions of the graft copolymers exhibit viscosities one to two orders of magnitude lower than the corresponding solutions of the parent guar gum. Copyright © 2007 John Wiley & Sons, Ltd.
Hydrophobic guar gum derivatives prepared by controlled grafting processes–Part II: rheological and degradation properties toward fracturing fluids applications
Authors: Bahamdan Ahmad , Daly William H. 
Published: May 2007

AbstractIntroduction of polyalkoxyalkyleneamide grafts to guar gum produces new water soluble guar derivatives as described in an earlier publication.10 In this paper, the rhelogical behavior of these products was explored in more detail at 25 and 65°C. In addition, the viscosity was measured at high temperatures (90 and 120°C) and pressure (150 psi) to partially simulate the down hole conditions of oil wells. Upon treatment with zirconium lactate, the cross‐linked hydrophobically‐modified CMG derivatives exhibited better high‐temperature stability and higher gel viscosities than the corresponding CMHPG derivatives. The cross‐linked gel viscosities indicate that gels will be capable of supporting a high proppant carrying capacity. To facilitate removal of the gels from the formation, the hydrophobically modified derivatives were treated with an enzyme breaker system which produced fragments capable of producing stable emulsions when extracted with toluene. Thus, the clean up process will be enhanced by emulsification of the gel fragments produced by the gel hydrolysis. The low viscosities of the linear derivatives, the rapid formation of high viscosity gels upon cross‐linking and generation of emulsifiers during the gel removal suggest that these new derivatives are good candidates for fracturing fluid applications. Copyright © 2007 John Wiley & Sons, Ltd.
On the testing, characterization, and evaluation of PV inverters and dynamic MPPT performance under real varying operating conditions
Authors: Sanchis Pablo , López Jesús , Ursúa Alfredo , Gubía Eugenio , Marroyo Luis 
Published: May 2007

AbstractThe increasing number of photovoltaic inverters that are coming on to the PV market stresses the need to carry out a dynamic characterization of these elements and their maximum power point tracking (MPPT) algorithms under real operating conditions. In order to make these conditions repeatable at the laboratory, PV array simulators are used. However, actual simulators, including the commercial simulators, recreate only a single or small set of PV array characteristic curves in which quite commonly theoretical calculations are included in order to simulate irradiance and temperature artificial variations. This is far from being a recreation of the real and long dynamic behavior of a PV array or generator. The testing and evaluation of the performance of PV inverters and MPPT algorithms has to be carried out when the PV system moves dynamically according to real operating conditions, including processes such as rapidly changing atmospheric conditions, partial shadows, dawn, and nightfall. This paper tries to contribute to the analysis of this problem by means of an electronic system that both measures the real evolution of the characteristic curves of PV arrays at outdoor operation and then recreates them at the laboratory to test PV inverters. This way the equipment can highlight the different performances of PV inverters and MPPT techniques when they operate under real operating conditions. As an example, two commercial inverters are tested and analyzed under the recreated behavior of a PV generator during 2 singular days that include processes of partial shading and fast irradiance variations. Copyright © 2007 John Wiley & Sons, Ltd.
8% Efficient thin‐film polycrystalline‐silicon solar cells based on aluminum‐ induced crystallization and thermal CVD
Authors: Gordon I. , Carnel L. , Van Gestel D. , Beaucarne G. , Poortmans J. 
Published: May 2007

AbstractA considerable cost reduction could be achieved in photovoltaics if efficient solar cells could be made from polycrystalline‐silicon (pc‐Si) thin films on inexpensive substrates. We recently showed promising solar cell results using pc‐Si layers obtained by aluminum‐induced crystallization (AIC) of amorphous silicon in combination with thermal chemical vapor deposition (CVD). To obtain highly efficient pc‐Si solar cells, however, the material quality has to be optimized and cell processes different from those applied for standard bulk‐Si solar cells have to be developed. In this work, we present the different process steps that we recently developed to enhance the efficiency of pc‐Si solar cells on alumina substrates made by AIC in combination with thermal CVD. Our present pc‐Si solar cell process yields cells in substrate configuration with efficiencies so far of up to 8·0%. Spin‐on oxides are used to smoothen the alumina substrate surface to enhance the electronic quality of the absorber layers. The cells have heterojunction emitters consisting of thin a‐Si layers that yield much higherVocvalues than classical diffused emitters. Base and emitter contacts are on top of the cell in interdigitated finger patterns, leading to fill factors above 70%. The front surface of the cells is plasma textured to increase the current density. Our present pc‐Si solar cell efficiency of 8% together with the fast progression that we have made over the last few years indicate the large potential of pc‐Si solar cells based on the AIC seed layer approach. Copyright © 2007 John Wiley & Sons, Ltd.
Voltage dependent photocurrent collection in CdTe/CdS solar cells
Authors: Hegedus Steven , Desai Darshini , Thompson Chris 
Published: May 2007

AbstractThe voltage dependence of the photocurrent JL(V) of CdTe/CdS solar cells has been characterized by separating the forward current from the photocurrent at several illumination intensities. JL(V) reduces the fill factor (FF) of typical cells by 10–15 points, the open circuit voltage (VOC) by 20–50 mV, and the efficiency by 2–4 points. Eliminating the effect of JL(V) establishes superposition between light and dark J(V) curves for some cells. Two models for voltage dependent collection give reasonable fits to the data: (1) a single carrier Hecht model developed for drift collection in p‐i‐n solar cells in which fitting yields a parameter consistent with lifetimes of 10−9 s as measured by others; or (2) the standard depletion region and bulk diffusion length model fits almost as well. The simple Hecht‐like drift collection model for photocurrent gives very good agreement to J(V) curves measured under AM1·5 light on CdTe/CdS solar cells with FF from 53% to 70%, CdTe thickness from 1·8 to 7·0 µm, in initial and stressed states. Accelerated thermal and bias stressing increases JL(V) losses as does insufficient Cu. This method provides a new metric for tracking device performance, characterizes transport in the high field depletion region, and quantifies a significant FF loss in CdTe solar cells. Copyright © 2007 John Wiley & Sons, Ltd.
Theory and experiments on the back side reflectance of silicon wafer solar cells
Authors: Kray Daniel , Hermle Martin , Glunz Stefan W. 
Published: May 2007

AbstractNew passivation layers for the back side of silicon solar cells have to show high performance in terms of electrical passivation as well as high internal reflectivity. This optical performance is often shown as values for the back side reflectance Rb which describes the rear internal reflection. In this paper, we investigate in detail the meaning of this single‐value parameter, its correct determination and the use in one‐dimensional simulations with PC1D. The free‐carrier‐absorption (FCA) as non‐carrier‐generating absorption channel is analyzed for solar cells with varying thickness. We apply the optical analysis to samples with different thickness, silicon oxide layer thickness, rear side topography as well as passivation layers (SiO2, SiNx, SiC and stack systems). Additionally, the optical influence of the laser‐fired contacts (LFC) process is experimentally investigated. Finally, we show that with correct parameters, the one‐dimensional simulation of very thin silicon solar cells can successfully be performed. Copyright © 2007 John Wiley & Sons, Ltd.
Natural products that have been used commercially as crop protection agents
Authors: Copping Leonard G , Duke Stephen O 
Published: May 2007

AbstractMany compounds derived from living organisms have found a use in crop protection. These compounds have formed the basis of chemical synthesis programmes to derive new chemical products; they have been used to identify new biochemical modes of action that can be exploited by industry‐led discovery programmes; some have been used as starting materials for semi‐synthetic derivatives; and many have been used or continue to be used directly as crop protection agents. This review examines only those compounds derived from living organisms that are currently used as pesticides. Plant growth regulators and semiochemicals have been excluded from the review, as have living organisms that exert their effects by the production of biologically active secondary metabolites. Copyright © 2007 Society of Chemical Industry
Development of a potent and selective GPR7 (NPBW1) agonist: a systematic structure–activity study of neuropeptide B
Authors: Kanesaka Maki , Matsuda Masao , Hirano Atsushi , Tanaka Kenichi , Kanatani Akio , Tokita Shigeru 
Published: May 2007

AbstractNeuropeptide B (NPB) has been recently identified as an endogenous ligand for GPR7 (NPBW1) and GPR8 (NPBW2) and has been shown to possess a relatively high selectivity for GPR7. In order to identify useful experimental tools to address physiological roles of GPR7, we synthesized a series of NPB analogs based on modification of an unbrominated form of 23 amino acids with amidated C‐terminal, Br(−)NPB‐23‐NH2. We confirmed that truncation of the N‐terminal Trp residue resulted in almost complete loss of the binding affinity of NPB for GPR7 and GPR8, supporting the special importance of this residue for binding. Br(−)NPB‐23‐NH2 analogs in which each amino acid in positions 4, 5, 7, 8, 9, 10, 12 and 21 was replaced with alanine or glycine exhibited potent binding affinity comparable to the parent peptide. In contrast, replacement of Tyr11 with alanine reduced the binding affinity for both GPR7 and GPR8 four fold. Of particular interest, several NPB analogs in which the consecutive amino acids from Pro4 to Val13 were replaced with several units of 5‐aminovaleric acid (Ava) linkers retained their potent affinity for GPR7. Furthermore, these Ava‐substituted NPB analogs exhibited potent agonistic activities for GPR7 expressed in HEK293 cells. Among the Ava‐substituted NPB analogs, analog 15 (Ava‐5) and 17 (Ava‐3) exhibited potency comparable to the parent peptide for GPR7 with significantly reduced activity for GPR8, resulting in high selectivity for GPR7. These highly potent and selective NPB analogs may be useful pharmacological tools to investigate the physiological and pharmacological roles of GPR7. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Characterization of the branched antimicrobial peptide M6 by analyzing its mechanism of action and in vivo toxicity
Authors: Pini Alessandro , Giuliani Andrea , Falciani Chiara , Fabbrini Monica , Pileri Silvia , Lelli Barbara , Bracci Luisa 
Published: May 2007

AbstractWe analyzed functional activity of the antimicrobial peptide M6 in vitro and in vivo. The peptide was identified by our group by phage library selection, rational modification and synthesis in a tetrabranched form (Pini et al., Antimicrob. Agents Chemother. 2005; 49: 2665–72). We found that it binds lipopolysaccharide, causes perforation of cell membranes without destroying external cell morphology and strongly binds DNA. The latter feature suggests that it could inhibit metabolic pathways, blocking DNA replication and/or transcription. We also observed that M6 does not stimulate humoral immune response when repeatedly administered to animals. We also analyzed M6 toxicity when administered to animals by intraperitoneal or by intravenous injection, determining a preliminary LD50 (125 and 37.5 mg/kg, respectively), which suggested that M6 could be used in vivo. These features make the antimicrobial branched peptide M6 a promising candidate for the development of a new antibacterial drug. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Conformation–activity relationship of peptide T and new pseudocyclic hexapeptide analogs
Authors: D'ursi Annamaria , Caliendo Giuseppe , Perissutti Elisa , Santagada Vincenzo , Severino Beatrice , Albrizio Stefania , Bifulco Giuseppe , Spisani Susanna , Temussi Piero A. 
Published: May 2007

AbstractPeptide T (ASTTTNYT), a segment corresponding to residues 185–192 of gp120, the coat protein of HIV, has several important biological properties in vitro that have stimulated the search for simpler and possibly more active analogs. We have previously shown that pseudocyclic hexapeptide analogs containing the central residues of peptide T retain considerable chemotactic activity. We have now extended the design of this type of analogs to peptides containing different aromatic residues and/or Ser in lieu of Thr. The complex conformation‐activity relationship of these analogs called for a reexamination of the basic conformational tendencies of peptide T itself. Here, we present an exhaustive NMR conformational study of peptide T in different media. Peptide T assumes a γ‐turn in aqueous mixtures of ethylene glycol, a type‐IV β‐turn conformation in aqueous mixtures of DMF, and a type‐II β‐turn conformation in aqueous mixtures of DMSO. The preferred conformations for the analogs were derived from modeling, starting from the preferred conformations of peptide T. The best models derived from the γ‐turn conformation of peptide T are those of peptides XII (DSNYSR), XIII (ETNYTK) and XVI (ESNYSR). The best models derived from the type‐IV β‐turn conformation of peptide T are those of peptides XIV (KTTNYE) and XV (DSSNYR). No low‐energy models could be derived starting from the type‐II β‐turn conformation of peptide T. The analogs with the most favored conformations are also the most active in the chemotactic test. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.