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Showing papers by "Rutgers University published in 1999"


Journal ArticleDOI
09 Apr 1999-Science
TL;DR: New insights about the management of large-scale resources that depend on international cooperation and the conditions most likely to favor sustainable uses of common-pool resources are discussed.
Abstract: In a seminal paper, Garrett Hardin argued in 1968 that users of a commons are caught in an inevitable process that leads to the destruction of the resources on which they depend. This article discusses new insights about such problems and the conditions most likely to favor sustainable uses of common-pool resources. Some of the most difficult challenges concern the management of large-scale resources that depend on international cooperation, such as fresh water in international basins or large marine ecosystems. Institutional diversity may be as important as biological diversity for our long-term survival.

2,463 citations


Journal ArticleDOI
11 Jun 1999-Science
TL;DR: Purified IPCs are here shown to be the CD4(+)CD11c- type 2 dendritic cell precursors (pDC2s), which produce 200 to 1000 times more IFN than other blood cells after microbial challenge and are thus an effector cell type of the immune system, critical for antiviral and antitumor immune responses.
Abstract: Interferons (IFNs) are the most important cytokines in antiviral immune responses. “Natural IFN-producing cells” (IPCs) in human blood express CD4 and major histocompatibility complex class II proteins, but have not been isolated and further characterized because of their rarity, rapid apoptosis, and lack of lineage markers. Purified IPCs are here shown to be the CD4+CD11c− type 2 dendritic cell precursors (pDC2s), which produce 200 to 1000 times more IFN than other blood cells after microbial challenge. pDC2s are thus an effector cell type of the immune system, critical for antiviral and antitumor immune responses.

2,328 citations


Journal ArticleDOI
TL;DR: It is reported that the number of adult-generated neurons doubles in the rat dentate gyrus in response to training on associative learning tasks that require the hippocampus, which indicates that adult- generated hippocampal neurons are specifically affected by, and potentially involved in, associative memory formation.
Abstract: Thousands of hippocampal neurons are born in adulthood, suggesting that new cells could be important for hippocampal function. To determine whether hippocampus-dependent learning affects adult-generated neurons, we examined the fate of new cells labeled with the thymidine analog bromodeoxyuridine following specific behavioral tasks. Here we report that the number of adult-generated neurons doubles in the rat dentate gyrus in response to training on associative learning tasks that require the hippocampus. In contrast, training on associative learning tasks that do not require the hippocampus did not alter the number of new cells. These findings indicate that adult-generated hippocampal neurons are specifically affected by, and potentially involved in, associative memory formation.

2,139 citations


Journal ArticleDOI
TL;DR: It is suggested that risk of cardiovascular disease and all-cause mortality is elevated among those who were overweight during childhood and without aggressive approaches to prevention and treatment, the attendant health and social consequences will be both substantial and long-lasting.
Abstract: This report reviews the risks and consequences associated with childhood and adolescent obesity. Although no consensus definition of childhood obesity exists, the various measures encountered in the literature are moderately well correlated. The paper is organized in three parts. The first section reviews childhood obesity sequelae that occur during childhood. These short-term risks, for orthopedic, neurological, pulmonary, gasteroenterological, and endocrine conditions, although largely limited to severely overweight children, are becoming more common as the prevalence of severe overweight rises. The social burden of pediatric obesity, especially during middle childhood and adolescence, may have lasting effects on self-esteem, body image and economic mobility. The second section examines the intermediate consequences, such as the development of cardiovascular risk factors and persistence of obesity into adulthood. These mid-range effects of early obesity presage later adult disease and premature mortality. In the final section, the small body of research on the long-term morbidity and mortality associated with childhood obesity is reviewed. These studies suggest that risk of cardiovascular disease and all-cause mortality is elevated among those who were overweight during childhood. The high prevalence and dramatic secular trend toward increasing childhood obesity suggest that without aggressive approaches to prevention and treatment, the attendant health and social consequences will be both substantial and long-lasting.

1,633 citations


Journal ArticleDOI
TL;DR: Prophylactic cranial irradiation improves both overall survival and disease-free survival among patients with small-cell lung cancer in complete remission and identifies a trend toward a decrease in the risk of brain metastasis with earlier administration of cranials irradiation after the initiation of induction chemotherapy.
Abstract: Background Prophylactic cranial irradiation reduces the incidence of brain metastasis in patients with small-cell lung cancer. Whether this treatment, when given to patients in complete remission, improves survival is not known. We performed a meta-analysis to determine whether prophylactic cranial irradiation prolongs survival. Methods We analyzed individual data on 987 patients with small-cell lung cancer in complete remission who took part in seven trials that compared prophylactic cranial irradiation with no prophylactic cranial irradiation. The main end point was survival. Results The relative risk of death in the treatment group as compared with the control group was 0.84 (95 percent confidence interval, 0.73 to 0.97; P= 0.01), which corresponds to a 5.4 percent increase in the rate of survival at three years (15.3 percent in the control group vs. 20.7 percent in the treatment group). Prophylactic cranial irradiation also increased the rate of disease-free survival (relative risk of recurrence or death, 0.75; 95 percent confidence interval, 0.65 to 0.86; P<0.001) and decreased the cumulative incidence of brain metastasis (relative risk, 0.46; 95 percent confidence interval, 0.38 to 0.57; P<0.001). Larger doses of radiation led to greater decreases in the risk of brain metastasis, according to an analysis of four total doses (8 Gy, 24 to 25 Gy, 30 Gy, and 36 to 40 Gy) (P for trend=0.02), but the effect on survival did not differ significantly according to the dose. We also identified a trend (P=0.01) toward a decrease in the risk of brain metastasis with earlier administration of cranial irradiation after the initiation of induction chemotherapy. Conclusions Prophylactic cranial irradiation improves both overall survival and disease-free survival among patients with small-cell lung cancer in complete remission.

1,463 citations


Journal ArticleDOI
10 Jun 1999-Nature
TL;DR: In this article, it was shown that the magnetoresistive response increases dramatically when the Curie temperature (T C) is reduced, and that the massive magnetoresistance in low-T C systems can be explained by percolative transport through the ferromagnetic domains; this depends sensitively on the relative spin orientation of adjacent magnetoric domains which can be controlled by applied magnetic fields.
Abstract: Colossal magnetoresistance1—an unusually large change of resistivity observed in certain materials following application of magnetic field—has been extensively researched in ferromagnetic perovskite manganites. But it remains unclear why the magnetoresistive response increases dramatically when the Curie temperature (T C) is reduced. In these materials, T C varies sensitively with changing chemical pressure; this can be achieved by introducing trivalent rare-earth ions of differing size into the perovskite structure2,3,4, without affecting the valency of the Mn ions. The chemical pressure modifies local structural parameters such as the Mn–O bond distance and Mn–O–Mn bond angle, which directly influence the case of electron hopping between Mn ions (that is, the electronic bandwidth). But these effects cannot satisfactorily explain the dependence of magnetoresistance on T C. Here we demonstrate, using electron microscopy data, that the prototypical (La,Pr,Ca)MnO3 system is electronically phase-separated into a sub-micrometre-scale mixture of insulating regions (with a particular type of charge-ordering) and metallic, ferromagnetic domains. We find that the colossal magnetoresistive effect in low-T C systems can be explained by percolative transport through the ferromagnetic domains; this depends sensitively on the relative spin orientation of adjacent ferromagnetic domains which can be controlled by applied magnetic fields.

1,417 citations


Journal ArticleDOI
TL;DR: In this article, the authors extend the work of Kurchan on the Gallavotti-Cohen fluctuation theorem, which yields a symmetry property of the large deviation function, to general Markov processes.
Abstract: We extend the work of Kurchan on the Gallavotti–Cohen fluctuation theorem, which yields a symmetry property of the large deviation function, to general Markov processes. These include jump processes describing the evolution of stochastic lattice gases driven in the bulk or through particle reservoirs, general diffusive processes in physical and/or velocity space, as well as Hamiltonian systems with stochastic boundary conditions. For dynamics satisfying local detailed balance we establish a link between the average of the action functional in the fluctuation theorem and the macroscopic entropy production. This gives, in the linear regime, an alternative derivation of the Green–Kubo formula and the Onsager reciprocity relations. In the nonlinear regime consequences of the new symmetry are harder to come by and the large deviation functional difficult to compute. For the asymmetric simple exclusion process the latter is determined explicitly using the Bethe ansatz in the limit of large N.

1,382 citations


Journal ArticleDOI
TL;DR: Four cycles of cisplatin plus etoposide and a course of radiotherapy beginning with cycle 1 of the chemotherapy resulted in overall two- and five-year survival rates of 44 percent and 23 percent, a considerable improvement in survival rates over previous results.
Abstract: Background For small-cell lung cancer confined to one hemithorax (limited small-cell lung cancer), thoracic radiotherapy improves survival, but the best ways of integrating chemotherapy and thoracic radiotherapy remain unsettled. Twice-daily accelerated thoracic radiotherapy has potential advantages over once-daily radiotherapy. Methods We studied 417 patients with limited small-cell lung cancer. All the patients received four 21-day cycles of cisplatin plus etoposide. We randomly assigned these patients to receive a total of 45 Gy of concurrent thoracic radiotherapy, given either twice daily over a three-week period or once daily over a period of five weeks. Results Twice-daily treatment beginning with the first cycle of chemotherapy significantly improved survival as compared with concurrent once-daily radiotherapy (P=0.04 by the log-rank test). After a median follow-up of almost 8 years, the median survival was 19 months for the once-daily group and 23 months for the twice-daily group. The survival rat...

1,291 citations


Journal ArticleDOI
01 May 1999-Heredity
TL;DR: A very general multivariate method, based on genetic distance methods, is developed that is applicable to multiallelic codominant, multilocus arrays and illustrated with an example data set from the orchid Caladenia tentaculata.
Abstract: Population genetic theory predicts that plant populations will exhibit internal spatial autocorrelation when propagule flow is restricted, but as an empirical reality, spatial structure is rarely consistent across loci or sites, and is generally weak. A lack of sensitivity in the statistical procedures may explain the discrepancy. Most work to date, based on allozymes, has involved pattern analysis for individual alleles, but new PCR-based genetic markers are coming into vogue, with vastly increased numbers of alleles. The field is badly in need of an explicitly multivariate approach to autocorrelation analysis, and our purpose here is to introduce a new approach that is applicable to multiallelic codominant, multilocus arrays. The procedure treats the genetic data set as a whole, strengthening the spatial signal and reducing the stochastic (allele-to-allele, and locus-to-locus) noise. We (i) develop a very general multivariate method, based on genetic distance methods, (ii) illustrate it for multiallelic codominant loci, and (iii) provide nonparametric permutational testing procedures for the full correlogram. We illustrate the new method with an example data set from the orchid Caladenia tentaculata, for which we show (iv) how the multivariate treatment compares with the single-allele treatment, (v) that intermediate frequency alleles from highly polymorphic loci perform well and rare alleles poorly, (vi) that a multilocus treatment provides clearer answers than separate single-locus treatments, and (vii) that weighting alleles differentially improves our resolution minimally. The results, though specific to Caladenia, offer encouragement for wider application.

1,078 citations


Proceedings ArticleDOI
20 Sep 1999
TL;DR: A nonparametric estimator of density gradient, the mean shift, is employed in the joint, spatial-range (value) domain of gray level and color images for discontinuity preserving filtering and image segmentation and its convergence on lattices is proven.
Abstract: A nonparametric estimator of density gradient, the mean shift, is employed in the joint, spatial-range (value) domain of gray level and color images for discontinuity preserving filtering and image segmentation. Properties of the mean shift are reviewed and its convergence on lattices is proven. The proposed filtering method associates with each pixel in the image the closest local mode in the density distribution of the joint domain. Segmentation into a piecewise constant structure requires only one more step, fusion of the regions associated with nearby modes. The proposed technique has two parameters controlling the resolution in the spatial and range domains. Since convergence is guaranteed, the technique does not require the intervention of the user to stop the filtering at the desired image quality. Several examples, for gray and color images, show the versatility of the method and compare favorably with results described in the literature for the same images.

1,067 citations


Journal ArticleDOI
TL;DR: It is shown that after administration of MPTP to mice, there was a robust gliosis in the substantia nigra pars compacta associated with significant upregulation of inducible nitric oxide synthase (iNOS), which indicates that inhibitors of iNOS may provide protective benefit in the treatment of Parkinson disease.
Abstract: MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) damages dopaminergic neurons as seen in Parkinson disease. Here we show that after administration of MPTP to mice, there was a robust gliosis in the substantia nigra pars compacta associated with significant upregulation of inducible nitric oxide synthase (iNOS). These changes preceded or paralleled MPTP-induced dopaminergic neurodegeneration. We also show that mutant mice lacking the iNOS gene were significantly more resistant to MPTP than their wild-type littermates. This study demonstrates that iNOS is important in the MPTP neurotoxic process and indicates that inhibitors of iNOS may provide protective benefit in the treatment of Parkinson disease.

Proceedings ArticleDOI
01 Aug 1999
TL;DR: Kea as mentioned in this paper identifies candidate keyphrases using lexical methods, calculates feature values for each candidate, and uses a machine learning algorithm to predict which candidates are good keyphrase candidates.
Abstract: Keyphrases provide semantic metadata that summarize and characterize documents. This paper describes Kea, an algorithm for automatically extracting keyphrases from text. Kea identifies candidate keyphrases using lexical methods, calculates feature values for each candidate, and uses a machinelearning algorithm to predict which candidates are good keyphrases. The machine learning scheme first builds a prediction model using training documents with known keyphrases, and then uses the model to find keyphrases in new documents. We use a large test corpus to evaluate Kea’s effectiveness in terms of how many author-assigned keyphrases are correctly identified. The system is simple, robust, and publicly available.

Journal ArticleDOI
TL;DR: The paper discusses arguments from computer vision and psychology showing that vision is "intelligent" and involves elements of "problem solving" and examines a number of examples where instructions and "hints" are alleged to affect what is seen.
Abstract: Although the study of visual perception has made more progress in the past 40 years than any other area of cognitive science, there remain major disagreements as to how closely vision is tied to cognition. This target article sets out some of the arguments for both sides (arguments from computer vision, neuroscience, psychophysics, perceptual learning, and other areas of vision science) and defends the position that an important part of visual perception, corresponding to what some people have called early vision, is prohibited from accessing relevant expectations, knowledge, and utilities in determining the function it computes - in other words, it is cognitively im- penetrable. That part of vision is complex and involves top-down interactions that are internal to the early vision system. Its function is to provide a structured representation of the 3-D surfaces of objects sufficient to serve as an index into memory, with somewhat differ- ent outputs being made available to other systems such as those dealing with motor control. The paper also addresses certain concep- tual and methodological issues raised by this claim, such as whether signal detection theory and event-related potentials can be used to assess cognitive penetration of vision. A distinction is made among several stages in visual processing, including, in addition to the inflexible early-vision stage, a pre-per- ceptual attention-allocation stage and a post-perceptual evaluation, selection, and inference stage, which accesses long-term memory. These two stages provide the primary ways in which cognition can affect the outcome of visual perception. The paper discusses argu- ments from computer vision and psychology showing that vision is "intelligent" and involves elements of "problem solving." The cases of apparently intelligent interpretation sometimes cited in support of this claim do not show cognitive penetration; rather, they show that certain natural constraints on interpretation, concerned primarily with optical and geometrical properties of the world, have been com- piled into the visual system. The paper also examines a number of examples where instructions and "hints" are alleged to affect what is seen. In each case it is concluded that the evidence is more readily assimilated to the view that when cognitive effects are found, they have a locus outside early vision, in such processes as the allocation of focal attention and the identification of the stimulus.

Journal ArticleDOI
TL;DR: In this article, the second-layer atoms in the direction perpendicular to the surface support this anomalous contraction, and provide a novel mechanism for the formation of adatom-vacancy pairs, preliminary to the disordering and premelting transition.
Abstract: Al(110) has been studied for temperatures up to 900 K via ensemble density-functional molecular dynamics. The strong anharmonicity displayed by this surface results in a negative coefficient of thermal expansion, where the first interlayer distance decreases with increasing temperature. Very shallow channels of oscillation for the second-layer atoms in the direction perpendicular to the surface support this anomalous contraction, and provide a novel mechanism for the formation of adatom-vacancy pairs, preliminary to the disordering and premelting transition. Such characteristic behaviour originates in the free-electron-gas bonding at a loosely packed surface. [S0031-9007(99)08925-5].

Journal ArticleDOI
TL;DR: It is suggested that network-driven excitability changes provide temporal windows of opportunity for single pyramidal cells to suppress, enable, or facilitate selective synaptic inputs.
Abstract: We examined whether excitation and inhibition are balanced in hippocampal cortical networks. Extracellular field and single-unit activity were recorded by multiple tetrodes and multisite silicon probes to reveal the timing of the activity of hippocampal CA1 pyramidal cells and classes of interneurons during theta waves and sharp wave burst (SPW)-associated field ripples. The somatic and dendritic inhibition of pyramidal cells was deduced from the activity of interneurons in the pyramidal layer [int(p)] and in the alveus and st. oriens [int(a/o)], respectively. Int(p) and int(a/o) discharged an average of 60 and 20° before the population discharge of pyramidal cells during the theta cycle, respectively. SPW ripples were associated with a 2.5-fold net increase of excitation. The discharge frequency of int(a/o) increased, decreased (“anti-SPW” cells), or did not change (“SPW-independent” cells) during SPW, suggesting that not all interneurons are innervated by pyramidal cells. Int(p) either fired together with (unimodal cells) or both before and after (bimodal cells) the pyramidal cell burst. During fast-ripple oscillation, the activity of interneurons in both the int(p) and int(a/o) groups lagged the maximum discharge probability of pyramidal neurons by 1–2 msec. Network state changes, as reflected by field activity, covaried with changes in the spike train dynamics of single cells and their interactions. Summed activity of parallel-recorded interneurons, but not of pyramidal cells, reliably predicted theta cycles, whereas the reverse was true for the ripple cycles of SPWs. We suggest that network-driven excitability changes provide temporal windows of opportunity for single pyramidal cells to suppress, enable, or facilitate selective synaptic inputs.

Posted Content
TL;DR: This paper uses a large test corpus to evaluate Kea’s effectiveness in terms of how many author-assigned keyphrases are correctly identified, and describes the system, which is simple, robust, and publicly available.
Abstract: Keyphrases provide semantic metadata that summarize and characterize documents. This paper describes Kea, an algorithm for automatically extracting keyphrases from text. Kea identifies candidate keyphrases using lexical methods, calculates feature values for each candidate, and uses a machine-learning algorithm to predict which candidates are good keyphrases. The machine learning scheme first builds a prediction model using training documents with known keyphrases, and then uses the model to find keyphrases in new documents. We use a large test corpus to evaluate Kea's effectiveness in terms of how many author-assigned keyphrases are correctly identified. The system is simple, robust, and publicly available.

Journal ArticleDOI
John K. Wald1
TL;DR: In this article, the authors examine the factors correlated with capital structure in France, Germany, Japan, United Kingdom, and the United States and suggest links between varying choices in capital structure across countries and legal and institutional differences.
Abstract: In this empirical study I examine the factors correlated with capital structure in France, Germany, Japan, the United Kingdom, and the United States. Although mean leverage and many firm factors appear to be similar across countries, some significant differences remain. Specifically, differences appear in the correlation between long-term debt/asset ratios and the firms' riskiness, profitability, size, and growth. These correlations may be explained by differences in tax policies and agency problems, including differences in bankruptcy costs, information asymmetries, and shareholder/creditor conflicts. The findings of this study suggest links between varying choices in capital structure across countries and legal and institutional differences.

Journal ArticleDOI
TL;DR: It is hypothesized that the endogenously expressed spike sequences during sleep reflect reactivation of the circuitry modified by previous experience and serve to consolidate information in neuronal networks.
Abstract: Information in neuronal networks may be represented by the spatiotemporal patterns of spikes. Here we examined the temporal coordination of pyramidal cell spikes in the rat hippocampus during slow-wave sleep. In addition, rats were trained to run in a defined position in space (running wheel) to activate a selected group of pyramidal cells. A template-matching method and a joint probability map method were used for sequence search. Repeating spike sequences in excess of chance occurrence were examined by comparing the number of repeating sequences in the original spike trains and in surrogate trains after Monte Carlo shuffling of the spikes. Four different shuffling procedures were used to control for the population dynamics of hippocampal neurons. Repeating spike sequences in the recorded cell assemblies were present in both the awake and sleeping animal in excess of what might be predicted by random variations. Spike sequences observed during wheel running were “replayed” at a faster timescale during single sharp-wave bursts of slow-wave sleep. We hypothesize that the endogenously expressed spike sequences during sleep reflect reactivation of the circuitry modified by previous experience. Reactivation of acquired sequences may serve to consolidate information.

Book ChapterDOI
01 Jan 1999
TL;DR: In this article, it was shown that the BPS states (those in reduced multiplets of supersymmetry) are equally fundamental to strong-weak coupling duality and to resolving singularities.
Abstract: Superstring theory has a rich spectrum of solitonic states, and over the last years much has been learned about their important roles in the theory, in strong-weak coupling duality and in resolving singularities [1]. The most important are the BPS states (those in reduced multiplets of supersymmetry) as one can make exact statements about them even at strong coupling, and thus dualities can predict their existence. Many dualities exchange elementary string states with states having Ramond-Ramond gauge charge, which strongly suggests that the two should be considered equally fundamental.

Journal ArticleDOI
TL;DR: Paired whole-cell recordings are used to show that inhibitory synaptic potentials generated from single interneurons are sufficiently powerful to delay or entirely block the generation of action potentials in a large number of projection neurons simultaneously.
Abstract: The basal ganglia are a highly interconnected network of nuclei essential for the modulation and execution of voluntary behavior The neostriatum is the principal input and one of the principal controllers of the output of the basal ganglia Neostriatal projection neurons seem to be dynamically and powerfully controlled by GABAergic inputs, but the source(s) and physiological properties of these inputs remain unclear Here we use paired whole-cell recordings to show that this inhibition derives from small populations of GABAergic interneurons that are themselves interconnected through functional electrotonic synapses Inhibitory synaptic potentials generated from single interneurons are sufficiently powerful to delay or entirely block the generation of action potentials in a large number of projection neurons simultaneously

Journal ArticleDOI
TL;DR: In this article, the full development and analysis of four models for the transversely vibrating uniform beam are presented, including the Euler-Bernoulli, Rayleigh, shear and Timoshenko models.

Journal ArticleDOI
17 Sep 1999-Cell
TL;DR: The X-ray crystal structure of Thermus aquaticus core RNA polymerase reveals a "crab claw"-shaped molecule with a 27 A wide internal channel that places key functional sites, defined by mutational and cross-linking analysis, on the inner walls of the channel in close proximity to the active center Mg2+.

Journal ArticleDOI
TL;DR: Straightforward combination of the mechanisms for transcription activation at class I and class II CAP-dependent promoters permits synergistic transcription activation by multiple molecules of CAP, or by CAP and other activators.

Journal ArticleDOI
TL;DR: In this article, multivariate statistical techniques were used to investigate source apportionment and source/sink relationships for polycyclic aromatic hydrocarbons (PAHs) in the urban and adjacent coastal atmosphere of Chicago/ Lake Michigan in 1994-1995.

Journal ArticleDOI
TL;DR: Women must present themselves as agentic to be hireable, but may therefore be seen as interpersonally deficient, and Ironically, the feminization of management may legitimize discrimination against competent, agentic women.
Abstract: Women who display masculine, agentic traits are viewed as violating prescriptions of feminine niceness (L. A. Rudman, 1998). By legitimizing niceness as an employment criterion, "feminization" of management (requiring both agentic and communal traits for managers) may unintentionally promote discrimination against competent women. Participants made hiring recommendations for a feminized or masculine managerial job. Agentic female job applicants were viewed as less socially skilled than agentic males, but this perception only resulted in hiring discrimination for the feminized, not the masculine, job. Communal applicants (regardless of sex) invariably received low hiring ratings. Thus, women must present themselves as agentic to be hireable, but may therefore be seen as interpersonally deficient. Ironically, the feminization of management may legitimize discrimination against competent, agentic women. Language: en

Journal ArticleDOI
04 Nov 1999-Nature
TL;DR: It is shown using microcosm experiments that extinction risk in warming environments depends on trophic position but remains unaffected by biodiversity, which suggests that high biodiversity buffers against the effects of environmental variation because tolerant species are more likely to be found.
Abstract: We know little about how ecosystems of different complexity will respond to global warming1,2,3,4,5. Microcosms permit experimental control over species composition and rates of environmental change. Here we show using microcosm experiments that extinction risk in warming environments depends on trophic position but remains unaffected by biodiversity. Warmed communities disproportionately lose top predators and herbivores, and become increasingly dominated by autotrophs and bacterivores. Changes in the relative distribution of organisms among trophically defined functional groups lead to differences in ecosystem function beyond those expected from temperature-dependent physiological rates. Diverse communities retain more species than depauperate ones, as predicted by the insurance hypothesis, which suggests that high biodiversity buffers against the effects of environmental variation because tolerant species are more likely to be found6,7. Studies of single trophic levels clearly show that warming can affect the distribution and abundance of species2,4,5, but complex responses generated in entire food webs greatly complicate inferences based on single functional groups.

Journal ArticleDOI
TL;DR: In this article, Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and 1996bv.
Abstract: We present 1210 Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and 1996bv. Most of the photometry was obtained at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the database for SNe Ia. The redshifts of the sample range from cz = 1200 to 37,000 km s-1 with a mean of cz = 7000 km s-1.

Journal ArticleDOI
TL;DR: In this paper, high quality epitaxial ZnO films were grown on R-plane sapphire substrates by metalorganic chemical vapor deposition, and the structural, piezoelectric, and optical properties of the films were investigated.
Abstract: High-quality ZnO films are receiving increased interest for use in low-loss high-frequency surface acoustic wave (SAW) devices, acousto-optic and optical modulators, as buffer layers for III-nitride growth, and as the active material in ultraviolet solid state lasers. In this work, high quality epitaxial ZnO films were grown on R-plane sapphire substrates by metalorganic chemical vapor deposition. The structural, piezoelectric, and optical properties of the ZnO films on R sapphire have been investigated. The epitaxial relationship between ZnO and R-Al2O3 was found to be (1120) ZnO∥(0112) Al2O3, and [0001] ZnO∥[0111] Al2O3. The interface between as-grown ZnO and R sapphire was atomically sharp and semicoherent, as evaluated by transmission electron microscopy. On annealing the films at temperatures above 850 °C, a solid state reaction occurred between ZnO and Al2O3, resulting in the formation of ZnAl2O4 (spinel) at the interface. A 15–20 nm spinel layer formed when the ZnO film was annealed at 850 °C fo...

Journal ArticleDOI
TL;DR: The characteristic prominence patterns of "novelty focus" and "contrastive focus" both arise from a combination of the Givenness Constraint and AvoidF, which synthesizes insights from the literature on the semantics of focus with older views on information structure.
Abstract: This paper strives to characterize the relation between accent placement and discourse in terms of independent constraints operating at the interface between syntax and interpretation. The Givenness Constraint requires un-F-marked constituents to be given. Key here is our definition of givenness, which synthesizes insights from the literature on the semantics of focus with older views on information structure. AvoidF requires speakers to economize on F-marking. A third constraint requires a subset of F-markers to dominate accents. The characteristic prominence patterns of "novelty focus" and "contrastive focus" both arise from a combination of the Givenness Constraint and AvoidF. Patterns of prominence in questions as well as in answers to questions are explained in terms of the constraints, thanks in part to the way in which the Givenness relation is defined. Head/argument asymmetries noted in the literature on Focus Projection are placed in the phonology-syntax interface, independent of discourse conditions. Deaccenting follows when AvoidF is ranked higher than constraint(s) governing head/argument asymmetries.

Journal ArticleDOI
18 Mar 1999-Nature
TL;DR: The results help to explain why maize is such a variable crop, and suggest that maize domestication required hundreds of years, and confirm previous evidence that maize was domesticated from Balsas teosinte of southwestern Mexico.
Abstract: The domestication of all major crop plants occurred during a brief period in human history about 10,000 years ago1. During this time, ancient agriculturalists selected seed of preferred forms and culled out seed of undesirable types to produce each subsequent generation. Consequently, favoured alleles at genes controlling traits of interest increased in frequency, ultimately reaching fixation. When selection is strong, domestication has the potential to drastically reduce genetic diversity in a crop. To understand the impact of selection during maize domestication, we examined nucleotide polymorphism in teosinte branched1, a gene involved in maize evolution2. Here we show that the effects of selection were limited to the gene's regulatory region and cannot be detected in the protein-coding region. Although selection was apparently strong, high rates of recombination and a prolonged domestication period probably limited its effects. Our results help to explain why maize is such a variable crop. They also suggest that maize domestication required hundreds of years, and confirm previous evidence that maize was domesticated from Balsas teosinte of southwestern Mexico.