Showing papers by "Ben-Gurion University of the Negev published in 1995"

Patterns in Hydrogen Bonding: Functionality and Graph Set Analysis in Crystals

Abstract: Whereas much of organic chemistry has classically dealt with the preparation and study of the properties of individual molecules, an increasingly significant portion of the activity in chemical research involves understanding and utilizing the nature of the interactions between molecules. Two representative areas of this evolution are supramolecular chemistry and molecular recognition. The interactions between molecules are governed by intermolecular forces whose energetic and geometric properties are much less well understood than those of classical chemical bonds between atoms. Among the strongest of these interactions, however, are hydrogen bonds, whose directional properties are better understood on the local level (that is, for a single hydrogen bond) than many other types of non-bonded interactions. Nevertheless, the means by which to characterize, understand, and predict the consequences of many hydrogen bonds among molecules, and the resulting formation of molecular aggregates (on the microscopic scale) or crystals (on the macroscopic scale) has remained largely enigmatic. One of the most promising systematic approaches to resolving this enigma was initially developed by the late M. C. Etter, who applied graph theory to recognize, and then utilize, patterns of hydrogen bonding for the understanding and design of molecular crystals. In working with Etter's original ideas the power and potential utility of this approach on one hand, and on the other, the need to develop and extend the initial Etter formalism was generally recognized. It with that latter purpose that we originally undertook the present review.

Five-hundred life-saving interventions and their cost-effectiveness.

Abstract: We gathered information on the cost-effectiveness of life-saving interventions in the United States from publicly available economic analyses. "Life-saving interventions" were defined as any behavioral and/or technological strategy that reduces the probability of premature death among a specified target population. We defined cost-effectiveness as the net resource costs of an intervention per year of life saved. To improve the comparability of cost-effectiveness ratios arrived at with diverse methods, we established fixed definitional goals and revised published estimates, when necessary and feasible, to meet these goals. The 587 interventions identified ranged from those that save more resources than they cost, to those costing more than 10 billion dollars per year of life saved. Overall, the median intervention costs $42,000 per life-year saved. The median medical intervention cost $19,000/life-year; injury reduction $48,000/life-year; and toxin control $2,800,000/life-year. Cost/life-year ratios and bibliographic references for more than 500 life-saving interventions are provided.

Lycopene is a more potent inhibitor of human cancer cell proliferation than either alpha-carotene or beta-carotene.

Abstract: The antiproliferative properties of lycopene, the major tomato carotenoid, were compared with those of alpha- and beta-carotene. Lycopene, delivered in cell culture medium from stock solutions in tetrahydrofuran, strongly inhibited proliferation of endometrial (Ishikawa), mammary (MCF-7), and lung (NCI-H226) human cancer cells with half-maximal inhibitory concentration of 1-2 microM; alpha- and beta-carotene were far less effective inhibitors. For example, in Ishikawa cells, a 4-fold higher concentration of alpha-carotene or a 10-fold higher concentration of beta-carotene was needed for the same order of growth suppression. The inhibitory effect of lycopene was detected after 24 hours of incubation, and it was maintained for at least three days. In contrast to cancer cells, human fibroblasts were less sensitive to lycopene, and the cells gradually escaped growth inhibition over time. In addition to its inhibitory effect on basal endometrial cancer cell proliferation, lycopene also suppressed insulin-like growth factor-I-stimulated growth. Insulin-like growth factors are major autocrine/paracrine regulators of mammary and endometrial cancer cell growth. Therefore, lycopene interference in this major autocrine/paracrine system may open new avenues for research on the role of lycopene in the regulation of endometrial cancer and other tumors.

Generic superconducting phase behavior in high- T c cuprates: T c variation with hole concentration in YBa 2 Cu 3 O 7 − δ

Abstract: A direct determination of the relationship between ${\mathit{T}}_{\mathit{c}}$ and hole concentration p for ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ is obtained by investigating the properties of the fully oxygen-deficient (\ensuremath{\delta}\ensuremath{\approxeq}1.0) compound for which p=x/2. Measurements of ${\mathit{T}}_{\mathit{c}}$, the thermoelectric power S, and bond-valence sums calculated from neutron-diffraction refinements for various values of x and \ensuremath{\delta} allow the full determination of the relations p=p(\ensuremath{\delta}), ${\mathit{T}}_{\mathit{c}}$=${\mathit{T}}_{\mathit{c}}$(p), and S=S(T,p) confirming that ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ satisfies the same universal relations in these quantities as the other high-${\mathit{T}}_{\mathit{c}}$ superconducting cuprates.

Gas-Phase Non-Identity SN2 Reactions of Halide Anions with Methyl Halides: A High-Level Computational Study

Abstract: High-level ab initio molecular orbital calculations at the G2(+) level of theory have been carried out for the six non-identity nucleophilic substitution reactions, Y- + CH3X → YCH3 + X-, for Y, X = F, Cl, Br, and I. Central barrier heights (ΔH⧧cent) for reaction in the exothermic direction vary from 0.8 kJ mol-1 for Y = F, X = I up to 39.5 kJ mol-1 for Y = Cl, X = Br (at 0 K), and are in most cases significantly lower than those for the set of identity SN2 reactions X- + CH3X → XCH3 + X- (X = F−I). Overall barriers (ΔH⧧ovr) for reaction in the exothermic direction are all negative (varying from −68.9 kJ mol-1 for Y = F, X = I to −2.3 kJ mol-1 for Y = Br, X = I), in contrast to the overall barriers for the identity reactions where only the value for X = F is negative. Complexation enthalpies (ΔHcomp) of the ion−molecule complexes Y-···CH3X vary from 30.4 kJ mol-1 for Y = F, X = I to 69.6 kJ mol-1 for Y = I, X = F (at 298 K), in good agreement with experimental and earlier computational studies. Complexati...

SuperStabilizing protocols for dynamic distributed systems

Abstract: Two aspects of distributed-protocol reliability are the ability to recover from transient faults and the ability to function in a dynamic environment. Approaches for both of these aspects have been separately developed, but have revealed drawbacks when applied to environments with both transient faults and dynamic changes. This paper introduces definitions and methods for addressing both concerns in system design. A protocol is superstabilizing if it is (1) self-stabilizing, meaning that it is guaranteed to respond to an arbitrary transient fault by eventually satisfying and maintaining a legitimacy predicate, and it is (2) guaranteed to satisfy a passage predicate at all times when the system undergoes topology changes starting from a legitimate state. The passage predicate is typically a safety property that should hold while the protocol makes progress toward reestablishing legitimacy following a topology change. Specific contributions of the paper include: the definition of the class of superstabilizing protocols; metrics for evaluating superstabilizing protocols; superstabilizing protocols for coloring and spanning tree construction; a general method for converting self-stabilizing protocols into superstabilizing ones; and a generalized form of a self-stabilizing topology update protocol which may have useful applications for other research.

The source-channel separation theorem revisited

Abstract: The single-user separation theorem of joint source-channel coding has been proved previously for wide classes of sources and channels. We find an information-stable source/channel pair which does not satisfy the separation theorem. New necessary and sufficient conditions for the transmissibility of a source through a channel are found, and we characterize the class of channels for which the separation theorem holds regardless of the source statistics. >

Use of a DNA pooling strategy to identify a human obesity syndrome locus on chromosome 15

Abstract: Bardet-Biedl syndrome is a heterogeneous autosomal recessive disorder characterized by obesity, mental retardation, polydactyly, retinitis pigmentosa and hypogonadism. Patients with this disorder also have a high incidence of hypertension, diabetes mellitus, and renal and cardiovascular anomalies. Three independent loci causing Bardet-Biedl syndrome have previously been reported. In this study, we we utilized a DNA pooling approach using DNA samples from a highly inbred Bedouin kindred to identify a new Bardet-Biedl syndrome locus on chromosome 15. The results further demonstrate the genetic heterogeneity of this disorder. In addition, the results demonstrate the efficiency of the DNA pooling approach for identifying recessive disease loci in highly inbred human populations.

Muster aus H‐Brücken: ihre Funktionalität und ihre graphentheoretische Analyse in Kristallen

Abstract: Wahrend sich die klassische Organische Chemie bisher weitgehend mit der Synthese individueller Molekule und der Untersuchung ihrer Eigenschaften beschaftigte, gewinnen nunmehr zunehmend Forschungsaktivitaten an Bedeutung, die sich mit dem Verstandnis und dem Ausnutzen von Wechselwirkungen zwischen Molekulen befassen. Zwei fur diese Entwicklung reprasentative Gebiete sind die supramolekulare Chemie und die molekulare Erkennung. Die Wechselwirkungen zwischen Molekulen werden durch intermolekulare Krafte bestimmt, deren energetische und geometrische Eigenschaften viel weniger gut verstanden sind als die von klassischen chemischen Bindungen zwischen Atomen. Zu den starksten dieser Wechselwirkungen gehoren die H-Brucken, deren gerichtete Eigenschaften auf lokalem Niveau (d. h. fur nur eine H-Brucke) besser als die vieler anderer Typen nichtbindender Wechselwirkungen verstanden werden. Trotzdem ist noch weithin ungeklart, wie man vorgehen muste, um die Konsequenzen der Bildung vieler H-Brucken zwischen Molekulen und den daraus folgenden Aufbau von molekularen Aggregaten (im mikroskopischen Bereich) oder von Kristallen (im makroskopischen Bereich) zu charakterisieren, zu verstehen und vorherzusagen. Einer der vielversprechendsten systematischen Ansatze, um dieses Problem zu losen, wurde ursprunglich von der inzwischen verstorbenen M. C. Etter entwickelt. In den letzten Jahren wurden ihre Ideen von anderen ubernommen und angewendet. Diese Arbeiten bewiesen einerseits die Bedeutung und die potentielle Nutzlichkeit der ursprunglichen Ideen und Ansatze, zeigten andererseits aber auch die Notwendigkeit auf, Etters Formalismus zu erweitern. Gerade letzteres war der Ausloser fur die hier vorgestellten Arbeiten.

Information systems design decisions in a global versus domestic context

Abstract: This study was motivated by the existence of two opposing schools of thought on managing information technology (IT) in a global context. One study proposes that managing IT in a global context is largely the same as managing IT in a domestic context. The other proposes that there is a difference. The results from interviews with 65 project managers, of whom 27 had international management experience, reflect a reality that lies somewhere between the two extremes. Using Q-methodology techniques, the project managers rated the relative importance of 33 items for decisions about the distribution of IT applications' hardware, software, and data. Although the most important factors influencing an application's IT distribution decision appear to hold across both domestic and global contexts, the global context contributes variability, unfamiliarity, and complexity that cannot be ignored. Compared with their domestic counterparts, project managers with global experience tended to be more cosmopolitan in their viewpoints, emphasized more local units' responsiveness, were more sensitive to power issues at headquarters as well as in local units, stressed the need for continuous, uninterrupted 24-hour services, and took into greater account the legal issues related to governmental regulations.

Estimation of amplitude and phase parameters of multicomponent signals

Abstract: This paper considers the problem of estimating signals consisting of one or more components of the form a(t)e/sup j/spl phi/(t/), where the amplitude and phase functions are represented by a linear parametric model. The Cramer-Rao bound (CRB) on the accuracy of estimating the phase and amplitude parameters is derived. By analyzing the CRB for the single-component case, if is shown that the estimation of the amplitude and the phase are decoupled. Numerical evaluation of the CRB provides further insight into the dependence of estimation accuracy on signal-to-noise ratio (SNR) and the frequency separation of the signal components. A maximum likelihood algorithm for estimating the phase and amplitude parameters is also presented. Its performance is illustrated by Monte-Carlo simulations, and its statistical efficiency is verified. >

Remote sensing of chlorophyll in Lake Kinneret using highspectral-resolution radiometer and Landsat TM: spectral features of reflectance and algorithm development

Abstract: High-resolution reflectance spectra in the range of 400-850 nm were obtained from Lake Kinneret during a period when dense populations of the dinoflagellate Peridinium gatunense dominated the phytoplankton. Chlorophyll (ChI) concentrations ranged from 5.1 to 185 mg mand from 2.4 to 187.5 mg m-3 in the samples of two independent experiments. The most prominent features of the reflectance spectra were: (i) a wide minimum from 400 to 500 nm; (ii) a maximum at 550-570 nm, which did not surpass 3% in samples with high ChI concentration (>20 mg m-3), indicating a strong absorption by pigments in the green range of the spectrum; (iii) a minimum at 676 nm; this was ~ 1 % and was almost insensitive to variation in ChI concentration >10 mg m-3; (iv) a maximum reflectance showed near 700 nm; its magnitude and position were highly dependent on chlorophyll concentration. Highspectral-resolution data were used as a guideline for selection of the most suitable spectral bands for chlorophyll remote sensing. Models were devised, based on the calculation of the integrated area above the baseline from 670 to 850 nm and the reflectance maximal height within this range. Some algorithms already used in previous studies were tested and showed a plausible degree of accuracy when applied to the current data base. However, novel models devised in this study improved substantially the accuracy of ChI estimation by remotely sensed data, by reducing the estimation error from >11 to 6.5 mg m-• Those models were validated by an independent data set where ChI concentration ranged over two orders of magnitude. The use of three relatively narrow spectral bands was sufficient for ChI mapping in Lake Kinneret. Therefore, a relatively simple sensor, measuring only a few bands will be employed in future applications for ChI monitoring in inland waters. Radiometric data were also used to simulate radiances in the channels of TM Landsat and to find the algorithm for ChI assessment. The ratio of channel 4 to channel 3 was used and enabled ChI estimation with an error of <15 mg m-• This algorithm was employed to map ChI in the entire area of Lake Kinneret with 10 gradations.

Intensity of competition, entry and entry deterrence in rent seeking contests

Abstract: In rent seeking contests agents compete over a given amount of resource a prize. To increase the likelihood of winning the prize, the agents expend efforts. This paper addresses the issue of entry to and entry deterrence from rent seeking contest. The main purpose of the analysis is to provide an explanation for the empirical fact that the number of participants in contests is usually small. I also obtain results on the relationship between the intensity of competition in a contest and the amount of the contenders’expenditures.

Reconsideration of oblique shock wave reflections in steady flows. Part 1. Experimental investigation

Abstract: The reflection of shock waves over straight reflecting surfaces in steady flows was investigated experimentally using the supersonic wind tunnel of Laboratoire d'Aerothermique du CNRS, Meudon, France. The results for a flow Mach number M0 = 4.96 contradict the state of the art regarding the regular [harr ] Mach reflection transition in steady flows. Not only was a hysteresis found to exist in this transition, but, unlike previous reports, regular reflection configurations were found to be stable in the dual-solution domain in which theoretically both regular and Mach reflection are possible.

Infection of the amniotic cavity with Ureaplasma urealyticum in the midtrimester of pregnancy.

Abstract: The purpose of this study was to determine the clinical significance of invasion of the amniotic fluid (AF) with Ureaplasma urealyticum in the midtrimester of pregnancy Amniotic fluid and cervical swabs obtained from 214 asymptomatic women in the midtrimester of pregnancy (16-20 weeks) were cultured for U urealyticum and Mycoplasma hominis Inoculum size was determined by quantitative culture Six of the 214 women (28%) had Ureaplasma in high titers in the AF The pregnancy outcomes of 129 women were determined Adverse pregnancy outcome occurred more frequently in women with a positive AF culture than in women with a negative AF culture (3/6 [50%] vs 15/123 [12%], respectively; P = 035) We conclude that infection of the amniotic cavity with U urealyticum can be present in asymptomatic patients in the midtrimester of pregnancy and is a significant risk factor for spontaneous preterm labor and delivery These observations suggest that routine culture of AF at the time of midtrimester amniocentesis can identify the group of patients at risk for a poor pregnancy outcome

Spectral reflectance of biogenic crust developed on desert dune sand along the Israel-Egypt border

Abstract: The effect of biogenic crust on imagery acquired by spaceborne sensors is demonstrated. The crust consists mostly of microphytes such as cyanobacteria. The macrophytes (higher vegetation) on the sand dunes are sparse and have a relatively low spectra! reflectance response. However, since a considerable ponton of the ground is covered by this biogenic crust, (which has a different spectral reflectance from that of the mobile sands), a sharp brightness contrast is created between the two areas. It can be concluded that the well-known contrast between Sinai (Egypt) and the Negev (Israel), that has long drawn the attention of many observers, is not a direct result of vegetation cover but is caused by an almost complete cover of biogenic crust in the Negev, and a lack of this crust in Sinai, due largely to man's activities.

Epidemiology, etiology, and clinical features of septic arthritis in children younger than 24 months.

Abstract: Objective: To examine the incidence, etiology, and clinical features of septic arthritis in patients younger than 24 months. Design: Retrospective, 1988 through 1993 period, chart review–based survey. Patients: All children with bacteriologically proved septic arthritis that was diagnosed at a medical center serving southern Israel (population 320 000). Septic arthritis was defined by clinical evidence of joint inflammation and a positive synovial fluid or blood culture, antigen detection test, or a standard tube agglutination titer of 160 or greater for Brucella species. Interventions: None. Results: During the 6-year period, 40 children had septic arthritis diagnosed. Twenty-six (65%) were male. The annual incidence of septic arthritis was 37.1 per 100 000. The two most common organisms isolated were Kingella kingae in 19 (48%) and Haemophilus influenzae type b in eight (20%). The clinical presentation was frequently mild: a body temperature of less than 38.3°C was recorded in 14 (35%) of 40 children, leukocyte count of less than 15×10 9 /L in 13 (34%) of 38, and erythrocyte sedimentation rate of less than 30 mm per hour in four (11%) of 35. In eight (36%) of 22 patients, less than 50×10 9 /L leukocytes were counted in the synovial fluid. Conclusions: The diagnosis of septic arthritis in young children requires a high index of suspicion, and the disease cannot be excluded on the basis of lack of fever or normal results of laboratory tests. Kingella kingae appears to be the most common cause of septic arthritis in patients younger than 24 months, although confirmatory studies from other geographic areas are still needed. (Arch Pediatr Adolesc Med. 1995;149:537-540)

Memory for context and its use in item memory: comparisons of younger and older persons.

Abstract: This study compared memory for words and the font in which they appeared ( or the voice speaking them) in young and old participants, to explore whether age-related differences in episodic word memory are due to age-related differences in memory for perceptual-contextual information. In each of 3 experiments, young and older participants were presented with words to learn. The words were presented in either 1 of 2 font types, or in 1 of 2 male voices, and participants paid attention either to the fonts or voices or to the meaning of the words. Participants were then tested on both word and font or voice memory. Results showed that younger participants had better explicit memory for font and voice memory and for the words themselves but that older participants benefited at least as much as younger people when perceptual characteristics of the words were reinstated. There was no evidence of an age-related impairment in the encoding of perceptual-contextual information.