bluuebunny/crossref_metadata_2025 huggingface dataset:
Prepolymerization of ethylene with a Ziegler–Natta catalyst
Authors: Mirzaei Ahmad , Vakili Mohammad , Tafi Neda
Published: May 2007

The slurry prepolymerization of ethylene using TiCl4/MgCl2 as a catalyst was investigated. A 23‐factorial experimental design method was employed to study the effects of the temperature, hydrogen, and active cocatalyst‐to‐catalyst molar ratio (Al/Ti) on the catalyst activity, prepolymer melt flow index, and powder bulk density. All dependent variables increased when the active Al/Ti ratio increased from 1 to 2. The hydrogen–Al/Ti interaction had a significant effect on the prepolymer melt flow index and catalyst activity. The hydrogen (partial pressure ranging from 0.5 to 1.5 bar) and temperature (ranging from 60 to 80°C) variables as well as the hydrogen–temperature and hydrogen–temperature–Al/Ti interactions increased the prepolymer powder bulk density, which ranged from 0.11 to 0.373 g/cc. To find the reason for the prepolymer powder bulk density variation with the operating conditions, the particle size distribution and crystallinity of the prepolymers were determined. The increasing catalyst activity, ranging from 132 to 660 g of polyethylene/mmol of Ti, enhanced the weight percentage of fines, which ranged from 3 to 60, and decreased the average particle size, which ranged from 562 to 120 μm. This was the reason for the increasing prepolymer powder bulk density and could be due to the breakup of the prepolymer particles during prepolymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Affinity purification of plasmid DNA directly from crude bacterial cell lysates
Authors: Darby Richard A.J. , Forde Gareth M. , Slater Nigel K.H. , Hine Anna V.
Published: May 2007

We have shown previously that a sequence‐specific DNA‐binding protein based on the Lac repressor protein can isolate pre‐purified DNA efficiently from simple buffer solution but our attempts to purify plasmids directly from crude starting materials were disappointing with impractically low DNA yields. We have optimized the procedure and present a simple affinity methodology whereby plasmid DNA is purified directly by mixing two crude cell lysates, one cell lysate containing the plasmid and the other the protein affinity ligand, without the need for treatment by RNaseA. After IMAC chromatography, high purity supercoiled DNA is recovered in good yields of 100–150 µg plasmid per 200 mL shake flask culture. Moreover, the resulting DNA is free from linear or open‐circular plasmid DNA, genomic DNA, RNA, and protein, to the limits of our detection. Furthermore, we show that lyophilized affinity ligand can be stored at room temperature and re‐hydrated for use when required. Biotechnol. Bioeng. 2007;98: 1103–1108. © 2007 Wiley Periodicals, Inc.
Human endothelial cell growth and phenotypic expression on three dimensional poly(lactide‐co‐glycolide) sintered microsphere scaffolds for bone tissue engineering
Authors: Jabbarzadeh Ehsan , Jiang Tao , Deng Meng , Nair Lakshmi S. , Khan Yusuf M. , Laurencin Cato T.
Published: May 2007

Bone tissue engineering offers promising alternatives to repair and restore tissues. Our laboratory has employed poly(lactid‐co‐glycolide) PLAGA microspheres to develop a three dimensional (3‐D) porous bioresorbable scaffold with a biomimetic pore structure. Osseous healing and integration with the surrounding tissue depends in part on new blood vessel formation within the porous structure. Since endothelial cells play a key role in angiogenesis (formation of new blood vessels from pre‐existing vasculature), the purpose of this study was to better understand human endothelial cell attachment, viability, growth, and phenotypic expression on sintered PLAGA microsphere scaffold. Scanning electron microscopy (SEM) examination showed cells attaching to the surface of microspheres and bridging the pores between the microspheres. Cell proliferation studies indicated that cell number increased during early stages and reached a plateau between days 10 and 14. Immunofluorescent staining for actin showed that cells were proliferating three dimensionally through the scaffolds while staining for PECAM‐1 (platelet endothelial cell adhesion molecule) displayed typical localization at cell–cell contacts. Gene expression analysis showed that endothelial cells grown on PLAGA scaffolds maintained their normal characteristic phenotype. The cell proliferation and phenotypic expression were independent of scaffold pore architecture. These results demonstrate that PLAGA sintered microsphere scaffolds can support the growth and biological functions of human endothelial cells. The insights from this study should aid future studies aimed at enhancing angiogenesis in three dimensional tissue engineered scaffolds. Biotechnol. Bioeng. 2007;98: 1094–1102. © 2007 Wiley Periodicals, Inc.
Validated ion pair liquid chromatography/fluorescence detection method for assessing the variability of the loratadine metabolism occurring in bioequivalence studies
Authors: Sora Daniela Iuliana , Udrescu Stefan , David Victor , Medvedovici Andrei
Published: May 2007

Inter‐ and intra‐individual variability of the loratadine (LOR) metabolism in Caucasian subjects was assessed during a bioequivalence study for two pharmaceutical formulations (solid oral dosage forms) containing 10 mg of the active substance. The analytical data were obtained by applying a reliable, low‐cost and sensitive ion pair liquid chromatography/fluorescence (IPLC/FLD) method for determination of both loratadine and descarboethoxyloratadine (DCL) in human plasma samples. The sample preparation procedure is based on liquid–liquid extraction of the target analytes from alkalinized plasma using diethyl‐ether. The separation of the analytes and 8‐chloroazatadine as internal standard (IS) was achieved through an isocratic ion pair (IP) elution on a Purospher® STAR RP‐18 column. The mobile phase containing sodium dodecyl sulfate (SDS) as ion pairing agent was pumped at a flow rate of 1 mL/min. Fluorescence detection (FLD) was achieved at 280 nm (excitation) and 440 nm (emission) wavelengths. The increased sensitivity of the method is also based on a large sample injected volume (250 µL). Linear response was found over the 0.5–20 ng/mL concentration interval for both target compounds. Low limits of quantification (LLOQ) around 0.3 ng/mL were found for LOR and DCL. Method validation is presented. Copyright © 2007 John Wiley & Sons, Ltd.
Exploration of Backbone Space in Foldamers Containing α‐ and β‐Amino Acid Residues: Developing Protease‐Resistant Oligomers that Bind Tightly to the BH3‐Recognition Cleft of Bcl‐xL
Authors: Sadowsky Jack D. , Murray Justin K. , Tomita York , Gellman Samuel H.
Published: May 2007

Protein–protein interactions play crucial roles in cell‐signaling events and are often implicated in human disease. Molecules that bind tightly to functional protein‐surface sites and show high stability to degradative enzymes could be valuable pharmacological tools for dissection of cell‐signaling networks and might ultimately lead to therapeutic agents. We recently described oligomers containing both α‐ and β‐amino acid residues that bind tightly to the BH3 recognition site of the anti‐apoptotic protein Bcl‐xL. The oligomers with highest affinity had a nine‐residue N‐terminal segment with a 1:1 α:β residue repeat and a six‐residue C‐terminal segment containing exclusively proteinogenic α‐residues. The N‐terminal portions of such (α/β+α)‐peptides are highly resistant to proteolysis, but the C‐terminal α‐segments are susceptible. This study emerged from efforts to modify the α‐segment in an (α/β+α)‐peptide in a way that would diminish proteolytic degradation but retain high affinity for Bcl‐xL. Some of the oligomers reported here could prove useful in certain biological applications, particularly those for which extended incubation in a biological milieu is required.
HeLa Cell Entry by Guanidinium‐Rich β‐Peptides: Importance of Specific Cation–Cell Surface Interactions
Authors: Potocky Terra B. , Silvius John , Menon Anant K. , Gellman Samuel H.
Published: May 2007

Short cationic oligomers, including arginine‐rich peptides and analogous β‐amino acid oligomers (“β‐peptides”), can enter the cytoplasm and nucleus of a living cell from the extracellular medium. It seems increasingly clear that multiple entry pathways are possible, depending upon the structure of the guanidinium‐rich molecule, the type of cell, and other factors. We have previously shown that conformational stability and spatial clustering of guanidinium groups increase the HeLa cell entry efficiency of short helical β‐peptides bearing six guanidinium groups, results that suggest that these β‐peptides could be useful tools for studying the entry process. Here we describe studies intended to identify the point in the entry process at which helix stability and spatial arrangement of guanidinium groups exert their effect. Our results suggest that key distinctions involve the mode of interaction between different guanidinium‐rich β‐peptides and the HeLa cell surface. A specific guanidinium display appears to be required for proper engagement of cell‐surface heparan sulfate proteoglycans and concomitant induction of endocytic uptake.
Experimental study of group creativity: Task representation, group structure, and performance
Authors: Abric J.‐C.
Published: May 2007

This article attempts to introduce and investigate a new variable in the experimental study of groups: the representation system. This study deals more specifically with the riile played by the representation of the task. This representation of the task constitutes the theory, the system of hypotheses individuals work out with respect to the nature of the task and the means to use in order to carry it out.

The key results of this study are that group performance depends on the representation of the task, with optimum effectiveness achieved when the representation of the task and its objective nature coincide. Another finding is that the structure of communications within the group is determined by the representation of the task rather than by its objective character. It was also established that the representation of the task determines the cognitive process adopted by the group. Thus the entire group activity is tied to the representations in its midst. The group organizes itself, regulates itself interactions, and determines its priorities in terms of these representations.
The effect of judges' attitudes on ratings of attitude statements. A theoretical analysis
Authors: Stroebe Wolfgang
Published: May 2007

Judgments of attitude statements with the method of equal‐appearing intervals have been found to vary as a function of the judges' attitudes. In this paper explanations of the relationship between judges' attitudes and judgments of attitude statements in terms of models of psychophysical judgment are discussed. It is argued that psychophysical models such as adaptation‐level theory, the range‐frequency model, and the ‘rubber‐band’ model and its derivations, cannot account satisfactorily for judges' performance of the attitude rating task in a great number of studies. The reason for this failure, it is argued, is that the stimulus series employed in the psychophysical judgment research on which these models are based typically varied only on the dimension being judged. The sets of statements judged in attitude rating studies, however, vary not only on the dimension of interest (favourability—Unfavourability) but also on a number of other dimensions. It is suggested that this incidental stimulus variation of attitude statements may account for the failure of psychophysical models to predict accurately the performance of judges in the attitude rating task. It is argued that if principles which could account for the effects of this incidental stimulus variation on attitude ratings could be incorporated into psychophysical models, the predictive qualities of these models could be improved considerably. One such model is discussed.
Group risk‐taking and group polarization
Authors: Fraser Colin
Published: May 2007

There are two aims to this paper; to report in brief preliminary form a number of studies on group risk‐taking that have been carried out in Bristol in the past two years, and to relate these studies to an explanation of group risk‐taking phenomena primarily in terms of group polarization. The paper has five sections. The first section supplies some background material regarding basic phenomena and previous attempts at explanations. The second section relates to initial individual decisions and the third section to decisions following group discussion and consensus. In the fourth section a tentative explanation of group risk‐taking effects is proposed in terms of group polarization processes, together with something like an overall value for risk. Group polarization itself is discussed in terms of normative and informational aspects of social influence. The final section deals with two implications of the proposed explanation, one relating to the role of individual familiarization and the other to the generality of group polarization processes.
The relationship between riskiness and confidence in choice dilemma decisions
Authors: Stroebe Wolfgang , Fraser Colin
Published: May 2007

The relationship between riskiness of decisions and confidence in decisions was examined using Choice Dilemma items. Graphs show a clear curvilinear relationship between riskiness and confidence; on both risky items and cautious items greater confidence is associate with extremely risky and extremely cautious decisions than with moderate ones. it was also demonstrated that individual subjects have more confidence in their extreme decisions than in their moderate ones.
Single linear ordering versus multiple discrepant orderings in the cognitive representation of social structures
Authors: Kahan James P. , Poitou Jean‐Pierre
Published: May 2007

Previous studies have assumed that people have a predilection for single linear orderings, of which status congruence is a special case. Eighty‐two subjects were run in a two‐stage experiment to examine preference for linear orderings and whether single or multiple discrepant orderings are preferred when 1 instead of having to learn, subjects freely construct social structures, and 2 the material they are presented is more specified and less simplified than is usually the case in cognitive bias studies. In the first stage Ss were presented with sets of five individual characteristic dimensions, of which three were inherently orderable. Their task was to attribute one characteristic from each dimension to each of five fictitious persons. In the second stage, Ss were asked, for three types of influence (professional, political and cultural), to build an influence structure among the five persons constructed in the first stage.

In Stage 1, linear ordering was used for three of the five dimensions. Two of these dimensions used a single ordering, while the third was only weakly related to the first two. In Stage 2, largely transitive but incomplete relations of influence were established, based on a salary‐occupational hierarchy. The completeness of the relation depended on the nature of the influence.
The durations of attention to alternatives and re‐evaluation in choices with two and three alternatives
Authors: East Robert
Published: May 2007

In two experiments on choice the durations of attention to the alternatives were measured. In experiment 1 each subject chose one from two pictures; in experiment 2 the choice was one from three pictures. In both experiments the subjects understood that they would acquire the picture that they selected. In each experiment higher and lower conflict conditions were induced by offering subjects a choice between alternatives that had been evaluated either equally or disparately.

In both experiments a significant relationship appeared between duration of attention and preference order with most subjects looking longest at the alternative that was preferred.

In the comparison between conditions this effect was found to be stronger under lower conflict than under higher conflict; this difference reached a significant level in experiment 2. These results are contrary to findings by Gerard (1967), and this matter is discussed. The relevance of the results to other theories is examined.

Inferences were drawn from dissonance theory about re‐evaluation effects after decision, and evaluation changes were measured in the experiments. After adjustment for measurement regression, the data failed to reveal a significant chronic re‐evaluation effect. Contrary to dissonance theory, the re‐evaluation effect was weaker in the three‐alternative choice experiment than in the two‐alternative choice experiment.
An experimental method for inquiring into communication
Authors: Blakar Rolv Mikkel
Published: May 2007

An experimental method for inquiring into the organization of an act of communication is presented, the basic idea being to create an interactional setting where one of the basic prerequisites for successful communication is not satisfied. In this particular design, the subjects interact under the false belief that they are sharing the same ‚here'. (In mean the subjects interacted more than a quarter of an hour before any doubt or suspicion about the situation was expressed, indicating that our manipulation had been successful.) During the subjects trying (1) to ‚diagnose' their communicative difficulties, and (2) to apply different ‚therapeutic tools' in order to improve their communication, one is in a very good position to study the impact from a variety of basic phenomena upon communication. It is argued that this situation may well be applied as a ‚standard experimental method'. And an experiment where this method revealed interesting differences in the communication between couples having and couples not having a schizophrenic offspring is discussed.
Patterning of the minority's responses and their influence on the majority
Authors: Nemeth Charlan , Swedlund Mark , Kanki Barbara
Published: May 2007

In reaction to the decades of research that tended to assume that social influence is synonymous with conformity, recent work has concentrated on the ability of a minority, by having a system of answers of its own, to influence the majority in the direction of their judgments. A study by Moscovici, Lage and Naffrechoux (1969) demonstrated this phenomenon but found that consistency of response, in the sense of repetition, was necessary for minority influence to be effected. They assumed that repetition was necessary to give the minority judgment the same value as that of the majority and to intensify the conflict that was engendered by the differences in opinion. Our position is that the lack of repetition in that study was construed to mean that the minority did not really have a position in which they were confident. As such, they were discounted. Thus, it is the attribution of consistency and confidence that leads to minority influence, not intensification of the conflict. The present study found that non‐repetitious behavior by a minority could be seen as reflecting consistency and confidence and could lead to minority influence provided the inconsistency was patterned with some property of the stimulus. Such ‘inconsistency’ was perceived as favorable and as effective as any other condition and even more effective than one of the repetitious conditions.
Proteins involved in neuronal differentiation of neuroblastoma cell line N1E‐115
Authors: Oh Ji‐eun , Freilinger Angelika , Gelpi Ellen , Pollak Arnold , Hengstschläger Markus , Lubec Gert
Published: May 2007

Neuronal differentiation (ND) represents a well‐defined phenomenon in biological terms but proteins involved have not been studied systematically. We therefore aimed to study ND by retinoic acid (RA) in a widely used neuroblastoma cell line by comparative proteomics. The ND was induced in the N1E‐115 cell line by serum deprivation and RA treatment. Undifferentiated cells and cells undergoing serum deprivation served as controls. Protein extracts were run on 2‐DE followed by MALDI‐TOF or MALDI‐TOF‐TOF analysis. Quantification was carried out using specific software and stringent statistical analysis was performed. Tubulin beta 5, cat eye syndrome critical region protein 5 homolog, putative GTP‐binding protein PTD004 homolog, and the metabolic proteins glyceraldehyde‐3‐phosphate dehydrogenase and transketolase were differentially regulated. Differential protein levels of cytoskeleton proteins including tubulins and metabolic proteins have been reported to be regulated by ND. Herein, specific signaling differences as reflected by putative GTP‐binding protein PTD004 changes in differentiated cells are shown and a possible role for the Cat eye syndrome critical region protein 5 homolog is proposed. The protein disulfide isomerase associated 3 protein fits the already proposed findings of chaperon regulation by ND. The study forms the molecular basis for further evaluation of the functional roles of the differentially expressed proteins in ND.
Assessment of natural and synthetic wollastonite as source for bioceramics preparation
Authors: Carrodeguas R. G. , De Aza A. H. , De Aza P. N. , Baudín C. , Jiménez J. , López‐Bravo A. , Pena P. , De Aza S.
Published: May 2007

Pseudowollastonite ceramics (β‐CaSiO3) from synthetic and natural sources were assessed with regard to their properties relevant to biomedical applications. Synthetic and natural CaSiO3 powders, with average particle size of 1.6 and 13.2 μm, respectively, were first employed. Powders were pressed and sintered at 1400°C for 2 h. Pseudowollastonite was the only crystalline phase in sintered materials. Glassy phase, eight times more abundant in sintered natural wollastonite (SNW) than in the synthetic one (SSW), was observed in grain boundaries and in triple points. Larger grains and bigger and more abundant pores were present in SNW, resulting in lower diametral tensile strength (26 MPa), than in SSW (42 MPa). However, by milling the natural wollastonite starting powder to a particle size of 2.0 μm and sintering (SNW‐M), the microstructure became finer and less porous, and diametral tensile strength increased (48 MPa). Weibull modulus of SNW and SNW‐M samples was twice that of the SSW. All the samples released Si and Ca ions, and removed phosphate ions from simulated body fluid in similar amounts and were completely coated by apatite‐like spherules after soaking in simulated body fluid for 3 wk. The aqueous extracts from all samples studied were not cytotoxic in a culture of human fibroblastic cells. No differences in fibroblast‐like human cells adhesion and proliferation were observed between samples. According to the obtained results, properly processed pseudowollastonite bioceramics, obtained from the natural source, exhibit the same in vitro behavior and better performance in terms of strength and reliability than do the more expensive synthetic materials. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2007
Monocyte activation in response to polyethylene glycol hydrogels grafted with RGD and PHSRN separated by interpositional spacers of various lengths
Authors: Schmidt David Richard , Kao Weiyuan John
Published: May 2007

Polyethylene glycol (PEG) is often cited as a “stealth” polymer, capable of resisting both protein adsorption and cell adhesion. By extension, PEG would then be expected to limit the host response. Monocyte‐derived macrophages play an integral role in inflammation, and thus their response to a material can potentially dictate the overall host response to a biomaterial. In the present study, monocyte responses following interaction with a photopolymerized PEG hydrogel were compared with those from standard tissue culture polystyrene (TCPS). Additionally, the effect of the spacing between RGD and PHSRN, the corresponding synergy sequence on fibronectin (FN), was evaluated using peptides with differing spacer lengths grafted to the PEG hydrogel. Monocyte adherent density on the PEG‐only hydrogel was comparable with that of TCPS; however, the secretion of the proinflammatory molecules interleukin‐1β (IL‐1β), tumor necrosis factor‐α (TNF‐α), and granulocyte‐macrophage colony stimulating factor (GM‐CSF) increased dramatically following monocyte interaction with PEG‐only hydrogels as compared with TCPS. The matrix metalloproteinase‐2 (MMP‐2) concentration was similar for all surfaces, while both the matrix metalloproteinase‐9 (MMP‐9) and FN concentrations were above the range of the assay for all substrates. Cell density was higher on the PHSRNG13RGD grafted substrate as compared with PHSRNG6RGD, but neither sequence increased cell density versus RGD alone. Although protein concentration did sometimes vary with different peptides, this variation was minimal in comparison with the surface effects between TCPS and the PEG‐only hydrogel. This study explores the roles of PEG and FN‐derived peptides on monocyte activation. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2007
SER(R)S of porphyrins on Ag nanoparticles immobilized by silane: a unique way to obtain free‐base porphyrin spectra
Authors: Molnár Peter , Procházka Marek
Published: May 2007

We measured the surface‐enhanced resonance Raman scattering (SER(R)S) spectra of 5,10,15,20‐tetrakis (1‐methyl‐4‐pyridyl)porphyrin (TMPyP) by using solid SERS‐active substrates: Ag nanoparticles immobilized by aminosilane on glass plates. We report the surprising result that by using such substrates it is possible to obtain SER(R)S spectra of porphyrins in the unperturbed free‐base form, although by using silver nanoparticles directly in solution, the porphyrin molecules are completely metalated. We suggest that silane used for nanoparticle immobilization modifies the surface properties and, therefore, makes porphyrin metalation impossible. Copyright © 2007 John Wiley & Sons, Ltd.
Effects of a CRF2R agonist and exercise on mdx and wildtype skeletal muscle
Authors: Hall Julie E. , Kaczor Jan J. , Hettinga Bart P. , Isfort Robert J. , Tarnopolsky Mark A.
Published: May 2007

Corticotrophin‐releasing factor 2 receptor (CRF2R) agonists prevent muscle atrophy due to immobilization, denervation, and corticosteroid‐induced muscle atrophy in wildtype mice. We hypothesized that a CRF2R agonist will increase skeletal muscle mass in mdx mice. Mdx (C57BL/10ScSn‐Dmdmdx) and wildtype (C57BL/6) mice were divided into four groups: sedentary placebo, sedentary CRF2R agonist, exercised placebo, and exercised CRF2R agonist. Mice exercised on a treadmill twice weekly for 30 min (8–12 m/min, 8 weeks). Muscle and heart weights, serum creatine kinase, and γ‐glutamyltransferase activities were measured. The CRF2R agonist increased extensor digitorum longus and soleus muscle weights (P < 0.05) in wildtype and mdx mice. Sedentary mdx CRF2R and exercised mdx placebo mice had lower serum creatine kinase activity than sedentary mdx placebo mice. CRF2R‐treated mice had decreased heart weights compared to placebo‐treated mice. We conclude that CRF2R agonists should be further evaluated as a potential therapy for dystrophinopathies. Muscle Nerve, 2007
A new approach
Authors: Smallwood Frank
Published: May 2007

Three alternatives outlined to make our traditional home rule doctrines compatible with modern needs.
Federalism at work
Authors: Gober James L.
Published: May 2007

Total governmental cooperation and citizen interest combine to give Tennessee town a new lease on life.
A more perfect union
Authors: Humphrey Hubert H.
Published: May 2007

Vice President calls for innovation, collaboration at all levels to make federal system fully capable.
Not without aid
Authors: Naftalin Arthur
Published: May 2007

Mayor Naftalin scores critics of federal programs, cites foremost examples of Minneapolis' progress.
A clear dichotomy
Authors: Conley Patrick T. , Goodman Jay S.
Published: May 2007

R. I. con‐con passes new local government article that both broadens and restricts home rule powers.
Perils of not sharing
Authors: Freeman Roger A.
Published: May 2007

Block grants to states are called necessary to “restore federalism” and prevent centralization.
‘Better men’ running?
Authors: Masotti Louis H. , Barber Kathleen D.
Published: May 2007

Effects of the change to single‐member from multimember legislative districts in Ohio are obscure.
Down with ugly wires
Authors: Hamilton Andrew
Published: May 2007

Fewer poles going up now as newer methods and materials reduce cost of undergrounding.
Electoral reform needed to end political alienation
Authors: Zimmerman Joseph F.
Published: May 2007

An analysis of various voting systems' capacity to guarantee minority‐group representation.
Connecticut probate courts are slow to change
Authors: Davis I. Ridgway
Published: May 2007

Survey of efforts to reform historic probate function in Connecticut, court challenges and legislative action.
‘One man, one vote’—What happens next?
Authors: Dixon Robert G.
Published: May 2007

A bipartisan commission with tie breaker is the best method for achieving fair representation under the one man, one vote principle enunciated by the Supreme Court.
Representation in Congress: A projection for 1972
Authors: Lehne Richard
Published: May 2007

Projection of location of congressional districts, voting patterns and impact of redistricting on central city, rural and suburban areas.
Cities in West Germany face emerging crisis
Authors: Wollmann Hellmut
Published: May 2007

Urbanization and metropolitanization are causing problems in renewal, transit, finance and relationships among federal, state and local governments.
Preservation for profit: Restorations come alive
Authors: Miller James Nathan
Published: May 2007

Businessmen are turning old, rundown areas into immensely profitable centers of office buildings, shops and restaurants in cities throughout the country; major examples are San Francisco and Denver.
The monopoly of choice: Independents on the ballot
Authors: Lindsay David
Published: May 2007

Harsh access laws in most states deter minority political parties and independent candidates from getting on the ballot, much less winning an election.
Land use management: The vermont experience
Authors: Ristau Arthur
Published: May 2007

New environmental legislation, passed with state administration support, may create a process for bargaining and economic value choosing that will allow Vermonters to make careful decisions about the future of the state.
Personal registration systems discourage voter participation
Authors: Carlson Richard J.
Published: May 2007

Once people are registered to vote, they apparently do so in respectable numbers. But getting them to register, via reliance on personal appearance before election officials and fulfilling obscure regulations, is another matter.
The Los Angeles charter: Lessons of defeat
Authors: Herbert Adam W.
Published: May 2007

Despite wide civic‐group support, two efforts at reforming the 1925 charter were defeated at the polls. This presents some reflections on why it happened, with perhaps some “insights” for other cities.
Efficient storage of nonadaptive routing tables
Authors: Manber Udi , McVoy Lawrence
Published: May 2007

An algorithm for improving storage utilization for nonadaptive routing tables in point‐to‐point networks is presented. It allows storage vs. access time tradeoffs. The algorithm is quite general, and it can be used for other applications to improve storage in tree‐like structures. The algorithm was applied to the UUCP routing tables resulting in a threefold storage improvement.
Polymatroidal flow network models with multiple sinks
Authors: Federgruen A. , Groenevelt H.
Published: May 2007

We consider the polymatroidal flow network model which incorporates two important extensions of the standard maximal flow problem: general concave objective functions of the vector of supplies to a collection of sinks, as well as polymatroidal capacity restrictions on sets of arcs emanating from or pointing to a common node. A number of important applications are reviewed. We show that in this general model the set of feasible supply vectors is itself a polymatroid, and that an optimal solution may be determined by at most 2|V*| — 1 maximum flow computations and optimizations of the objective over a single budget constraint, where |V*| is the number of sinks. Also, it is shown that for the most common types of polymatroidal structures an equivalent flow network can be constructed on an expanded graph but with capacity restrictions on individual arcs only. This transformation allows for the use of classical maximum flow procedures resulting in an often dramatic reduction in complexity.
A survey of gossiping and broadcasting in communication networks
Authors: Hedetniemi Sandra M. , Hedetniemi Stephen T. , Liestman Arthur L.
Published: May 2007

Gossiping and broadcasting are two problems of information dissemination described for a group of individuals connected by a communication network. In gossiping every person in the network knows a unique item of information and needs to communicate it to everyone else. In broadcasting one individual has an item of information which needs to be communicated to everyone else. We review the results that have been obtained on these and related problems.
An SST‐based algorithm for the steiner problem in graphs
Authors: Beasley J. E.
Published: May 2007

In this paper we consider the Steiner problem in graphs which is the problem of connecting together, at minimum cost, a number of vertices in an undirected graphs. We present a formulation of the problem as a shortest spanning tree (SST) problem with additional constraints. By relaxing thses additional constraints in a lagrangean fashion we obtain a lower bound for the problem based upon the solution of an unconstrained SST problem. Problem reduction tests derived from both the original problem and the lagrangean relaxation are given. Incorporating the bound and the reduction tests into a tree search procedure enables us to solve problems involving the connection of up to 1250 vertices in a graph with 62500 edges and 2500 vertices.
Some properties of 2‐threshold graphs
Authors: Hammer P. L. , Mahadev N. V. R. , Peled U. N.
Published: May 2007

A 2‐threshold graph is defined to be the edge‐union of two threshold graphs. We prove that all chordless cycles of size at least 5 and their complements are forbidden for 2‐threshold graphs. We also obtain a sufficient condition for a 2‐threshold graph to be a comparability graph. Finally, we show that 2‐threshold graphs can have at most three cutpoints and obtain efficient algorithms to recognize, decompose and obtain a maximum stable set of 2‐threshold graphs with exactly three cutpoints.
Minimum order graphs with specified diameter, connectivity, and regularity
Authors: Krishnamoorthy V. , Thulasiraman K. , Swamy M. N. S.
Published: May 2007

Relationships among graph invariants such as the number of vertices, diameter, connectivity, maximum and minimum degrees, and regularity are being studied recently, motivated by their usefulness in the design of fault‐tolerant and low‐cost communication and interconnection networks. A graph is called a (d,c,r) graph if it has diameter d, connectivity c, and regularity r. The minimum number of vertices in (d, 1,3), (d,2,3), (d,3,3), and (d,c,c) graphs have been reported in the literature. In this paper, the minimum number of vertices in a (d,c,r) graph with r > c is determined, thereby exhausting all the possible choices of values for d, c, and r. Our proof is constructive and hence we get a collection of optimal (d,c,r) graphs.
Transitively reduced and transitively closed event networks
Authors: Mrozek Marian
Published: May 2007

We present the notion of a generalized inverse of a digraph. The notion includes two different kinds of event networks, both discussed in literature. We show how different techniques used separately in both special cases can be applied to the general case. We prove that the problem of minimization of the number of dummy arcs among al event networks having the minimum number of vertices is polynomially transformable to a certain covering problem. We use the transformation method to provide a necessary and sufficient condition for a certain suboptimal solution to the problem to be optimal in general. We show that the verification of this condition can be done in polynomial time.
Extremal connectivity and vulnerability in graphs
Authors: Doty Lynne L.
Published: May 2007

If a practical network is modelled as a graph in which the lines are perfect but the points may fail then a primary measure of vulnerability is the point connectivity of the graph and one possible secondary measure of vulnerability is the number of minimum point disconnecting sets. The graph shold have the maximum possible point connectivity and the minimum number of point disconnecting sets. A lower bound for the number of minimum point disconnecting sets is derived by identifying points with identical adjacencies.
Optimal enclosing regions in planar graphs
Authors: Bienstock Daniel , Monma Clyde L.
Published: May 2007

In this paper we study the problem of finding a minimum‐weight collection of edges in a planar graph which separates a given set of vertices from the outer face. This problem has two variants: either a given embedding is specified, or the best possible embedding is to be found. We present polynomial‐time algorithms for each case. We show how to use these results to recognize a special case of the steiner tree problem in graphs which is polynomially solvable. A closely related problem is shown to be NP‐complete.
Implementing an “exact” Newton method for separable convex transportation problems
Authors: Klincewicz John G.
Published: May 2007

Convex transportation problems represent an important special class of convex network flow problems, with particular applications in telecommunications, economics and engineering. This paper describes an implementation of an “exact” Newton algorithm for separable convex transportation problems. Previously in the literature, only approximate Newton algorithms had been described for the general case of convex network flow problems. The special structure of the transportation problem is used to simplify computation of dual multiplier estimates. In general, this would require factorization of a square matrix of dimension n + m − 1, were n is the number of sources and m is the number of sinks. By exploiting structure, the work of factorization is limited to a square matrix of dimension n − 1 or m − 1, whichever is smaller. Some computational experience is described. We also note an analogy between this Newton algorithm for convex problem and a particular variant of Karmarkar's algorithm for linear problems.
Paths, chains, and antipaths
Authors: de Werra D. , Pasche C.
Published: May 2007

Some variations on Eulerian partitions of edge sets and arc sets are discussed. We consider partitions into (odd) paths, chains and antipaths; these are paths where every second are is reversed. Packing problems are also examined and min‐max results are derived by using network flow techniques.
Triconnected decomposition for computing K‐terminal network reliability
Authors: Wood R. Kevin
Published: May 2007

Let R(Gk) denote the probability that a subset of vertices K in the undirected graph G = (V, E) can communicate when the edge of G fail independently with known probabilities. Suppose that Gk contains as separting pair of vertices {u, v} such that Gk= G̃k̃ ∪ Ǧǩ, Ṽ ∩ V̂ ={u v}, Ẽ ∩ Ê = ø, |Ẽ| ⩾ 2, and |Ê| ⩾2. It is shown that Ĝk may be replaced by a chain χ of at most three edges between u and v such that R(Gk) = ΩR ((G̃ ∪ χ)k̃′) where Ω is a derived constant and K̃′ is defined by the procedure. The failure probabilities of the edges in χ and the value of Ω are shown to be computable by evaluating the reliability of one of four variants of Ĝk̂. Minimal components Ĝk̂ can be efficiently found using triconnected decomposition and the above procedure embedded within a recursive factoring algorithm for computing K‐terminal reliability. Conditions are derived which guarantee the new algorithm is at least as good as a pure factoring algorithm, and an example shows that the new algorithm can be exponentially better.
Connected reorientations of mixed multigraphs
Authors: Shi Weigeng , Juels Ronald J.
Published: May 2007

We study here the problem of reorienting the directed edges of mixed multigraphs so as to establish or preserve reachability, which may be destroyed by edge removal. We develop a linear time/space algorithm which tests whether reorienting designated directed edges can reestablish reachability, and which constructs such a reorientation whenever possible. We also develop a linear time/space algorithm which, when reachability has been destroyed by the removal of a single edge, optimally restores reachability through the reversal of selected edges. Finally, we show the reliability of a graph allowing reversals to be twice that of a graph for which reversals are not permitted.
On graphs with polynomially solvable maximum‐weight clique problem
Authors: Balas Egon , Yu Chang Sung
Published: May 2007

We give a new bound on the number of maximal cliques in a graph, along with a bound on the length of odd antiholes that the graph can contain. Based on these bounds we then identify a family of graphs with polynomially solvable maximum weight clique problem, using the edgebicoloring approach developed in a recent paper by Balas, Chvatal, and Nesetril.
A tree‐network has the fixed point property
Authors: Labbé Martine , Thisse Jacques‐François
Published: May 2007

We prove that any continuous mapping from a network into itself has a fixed point if and only if the network is a tree‐network.
A functional equation for finding the largest expected capacity of a graph
Authors: Sancho N. G. F.
Published: May 2007

Given a graph in which every arc (i, j) has two numbers ρij and Cij associated with it representing the reliability and capacity, respectively, a dynamic programming formulation is derived for finding the path from any node i to terminal node N with the largest expected capacity. It is shown that the functional equation obtained may not necessarily be governed by the principle of optimality.
On optimal cycle bases of graphs for mesh analysis of networks
Authors: Kaveh A.
Published: May 2007

An algorithm is developed for the selection of a cycle basis of a graph which corresponds to a highly sparse cycle adjacency matrix, hence providing an efficient means for the mesh analysis of networks. Unlike the existing methods, this algorithm reduces the overlaps of the cycles instead of their lengths. The results are compared with those of the previous methods through some examples. The cycles are also ordered to obtain banded cycle adjacency matrices.
Exact cuts in networks
Authors: Provan J. Scott , Kulkarni V. G.
Published: May 2007

An exact cut in a source‐sink network is a set of arcs which interesects each source‐sink path in exactly one arc. This paper investigates the problem of finding a maximum weight exact cut in a network. The problem is shown to be polynomially equivalent to that of determining the relevant arcs (arcs on at least one source‐sink path) in the network and is NP‐hard for general directed networks. There are, however, several important classes of network—including undirected networks—for which polynominal time algorithms do exist to solve the maximum weight exact cut problem.
Analysis of a flow problem with fixed charges
Authors: Hochbaum Dorit S. , Segev Arie
Published: May 2007

This article addresses a problem that comes up frequently in network design, and routing. A source is to distribute flows to nodes in the network. Sending flow along an arc involves a fixed cost for using the arc and a variable cost for each ujnit of flow. We show tht the problem of finding a minimum cost collection of arcs along which flows will be directed is an NP‐hard problem. We describe a procedure of solving the problem to optimality and several heuristics. In particular, we conclude that the use of polynomially derived Lagrange multipliers yields good quality solutions and bounds and can be implemented in a distributed processing mode in the network.
Networks synthesis and optimum network design problems: Models, solution methods and applications
Authors: Minoux M.
Published: May 2007

This paper is intended as a survey in the area of network synthesis and optimum network design, which, in view of the importance and variety of the underlying applications, has attraced, since the early 1960s, much interest in the Operations Research community. Indeed, if the first models were studied in connection with telecommunication networks, the range of applications kept on getting broader and broader, including transportation networks, computer and teleprocessing networks, energy transport systems, water distribution networks, etc. However, beyond the apparent diversity of practical situations involved, most of these applications can be accounted for (modulo possibly a few minor adaptations), by a rather limited number of basic models. One of the main purposes of this paper is to provide the reader with a relevant classification of the area which will help him identify the fundamental structure of the problem (if any) he has to cope with, and relate it to already published work. In order to obtain a fairly good coverage of the matter, we have thus been led to identify three basic models aroung which the whole paper is organized: a general model using minimum cost multicommodity flows (Section 2); models in terms of tree‐like networks (Section 3); models using nonsmultaneous single‐commodity or multicommodity flows (Section 4). In each bcase the most important variants of the basic models have been surveyed with the purpose of providing as much information as possible concerning (a) the various contexts of applications from which the problem arose; (b) the main computational methods proposed in the literature for solving it, with emphasis on those techniques which appear at present, to be most efficient or promising.
How to find a battleship
Authors: Fiat Amos , Shamir Adi
Published: May 2007

Consider a “sea” of M squares which contains (at some unknown location) a “battleship” of K squares. Both the sea and the battleship can assume any rectangular shape. Our goal is to find the battleship by probing at least one of its squares. In this paper we describe a deterministic strategy for this problem which is guaranteed to locate the battleship in at most c1 M/K probes, where c1 ≈︁ 3.065.
Designing satellite communication networks by zero—one quadratic programming
Authors: Helme Marcia P. , Magnanti Thomas L.
Published: May 2007

In satellite communications networks, distinctive facilities called homing stations perform special transmission functions. Local demand nodes clustered around each homing station communicate with each other via a local switch at the homing station; demand nodes in different cluster communicate with each other via satellite earth stations at the homing stations. Designing such a communication network requires choices on the locations of the earth stations and on the assignments of demand nodes to the local clusters at the earth stations. We formulate this problem as a zero‐one quadratic facility location problem and transform it into an equivalent zero‐one integer linear program. Computational experience on real data shows that a branch and bound procedure is effective in solving problems with up to 40 demand nodes (major cities) and that the solutions that this algorithm finds improve considerably upon management generated solutions. We also show that a greedy add heuristic, as implemented on an IBM PC, consistently generates optimal or near‐optimal solutions.
On mean distance in certain classes of graphs
Authors: Hendry George R. T.
Published: May 2007

The mean distance, μ(G), of a graph G is the arithmetic mean of the distances in G. Upper and lower bounds for the mean distance of a self‐complementary graph of given order are obtained and the extremal grpahs are determined. It is shown that if t ≥ 2 is rational, then there exist (1) graphs with arbitrarily low or high edge density, (2) bipartite graphs and (3) oriented graphs with mean distance equal to t, and also (4) trees and (5) tournaments with mean distance arbitrarily close to t. A number of open problems are mentioned.