Showing papers by "Brown University published in 2000"

Path dependence in historical sociology

Abstract: Cet article cherche a determiner a quels types d'evenements historiques s'applique l'analyse de path dependence. Selon l'A., il s'agit de sequences historiques au sein desquelles des evenements contingents mettent en mouvement des modeles institutionnels ou des chaines d'evenements ayant des proprietes deterministes. L'identification de la path dependence implique a la fois de relier un resultat a une serie d'evenements et de montrer en quoi ces evenements sont eux-memes des occurences contingentes ne pouvant etre expliquees par des conditions historiques prealables. Ces sequences historiques sont generalement de deux types : les sequences a auto-renforcement et les sequences reactives

Numerical Methods for Stochastic Control Problems in Continuous Time

Abstract: A powerful and usable class of methods for numerically approximating the solutions to optimal stochastic control problems for diffusion, reflected diffusion, or jump-diffusion models is discussed. The basic idea involves uconsistent approximation of the model by a Markov chain, and then solving an appropriate optimization problem for the Murkoy chain model. A general method for obtaining a useful approximation is given. All the standard classes of cost functions can be handled here, for illustrative purposes, discounted and average cost per unit time problems with both reflecting and nonreflecting diffusions are concentrated on. Both the drift and the variance can be controlled. Owing to its increasing importance and to lack of material on numerical methods, an application to the control of queueing and production systems in heavy traffic is developed in detail. The methods of proof of convergence are relatively simple, using only some basic ideas in the theory of weak convergence of a sequence of probabi...

A maximum-entropy-inspired parser

Abstract: We present a new parser for parsing down to Penn tree-bank style parse trees that achieves 90.1% average precision/recall for sentences of length 40 and less, and 89.5% for sentences of length 100 and less when trained and tested on the previously established [5, 9, 10, 15, 17] "standard" sections of the Wall Street Journal treebank. This represents a 13% decrease in error rate over the best single-parser results on this corpus [9]. The major technical innovation is the use of a "maximum-entropy-inspired" model for conditioning and smoothing that let us successfully to test and combine many different conditioning events. We also present some partial results showing the effects of different conditioning information, including a surprising 2% improvement due to guessing the lexical head's pre-terminal before guessing the lexical head.

Population, Technology, and Growth: From Malthusian Stagnation to the Demographic Transition and Beyond

Abstract: This paper develops a unied growth model that captures the historical evolution of population,technology,and output. It encompasses theendogenous transitionbetween three regimes that have characterized economic development. The economy evolves from aMalthusianregime,wheretechnologicalprogressis slow andpopulationgrowthprevents anysustainedriseinincomepercapita,intoaPost-Malthusianregime,wheretechnological progress rises and population growth absorbs only part of output growth. Ultimately, a demographic transition reverses the positive relationship between income and population growth,andtheeconomyentersaModernGrowthregimewithreducedpopulationgrowth

Critique of the Power of Judgment

Abstract: Editor's introduction Part I. The First Draft of the Introduction: 1. The first draft of the introduction Part II. Critique of the Power of Judgment: 2. Preface 3. Introduction Part III. First Part: Critique of the Aesthetic Power of Judgment: 4. First section, first book: analytic of the beautiful 5. First section, second book: analytic of the sublime 6. Deduction of pure aesthetic judgments 7. Second section: the dialectic of the aesthetic power of judgment 8. Appendix: on the methodology of taste Part IV. Second Part: Critique of the Teleological Power of Judgment: 9. First division: analytic of the teleological power of judgment 10. Second division: dialectic of the teleological power of judgment 11. Appendix: methodology of the teleological power of judgment.

Estrogen-induced activation of Erk-1 and Erk-2 requires the G protein-coupled receptor homolog, GPR30, and occurs via trans-activation of the epidermal growth factor receptor through release of HB-EGF.

Abstract: Estrogen rapidly activates the mitogen-activated protein kinases, Erk-1 and Erk-2, via an as yet unknown mechanism. Here, evidence is provided that estrogen-induced Erk-1/-2 activation occurs independently of known estrogen receptors, but requires the expression of the G protein-coupled receptor homolog, GPR30. We show that 17beta-estradiol activates Erk-1/-2 not only in MCF-7 cells, which express both estrogen receptor alpha (ER alpha) and ER beta, but also in SKBR3 breast cancer cells, which fail to express either receptor. Immunoblot analysis using GPR30 peptide antibodies showed that this estrogen response was associated with the presence of GPR30 protein in these cells. MDA-MB-231 breast cancer cells (ER alpha-, ER beta+) are GPR30 deficient and insensitive to Erk-1/-2 activation by 17beta-estradiol. Transfection of MDA-MB-231 cells with a GPR30 complementary DNA resulted in overexpression of GPR30 protein and conversion to an estrogen-responsive phenotype. In addition, GPR30-dependent Erk-1/-2 activation was triggered by ER antagonists, including ICI 182,780, yet not by 17alpha-estradiol or progesterone. Consistent with acting through a G protein-coupled receptor, estradiol signaling to Erk-1/-2 occurred via a Gbetagamma-dependent, pertussis toxin-sensitive pathway that required Src-related tyrosine kinase activity and tyrosine phosphorylation of tyrosine 317 of the Shc adapter protein. Reinforcing this idea, estradiol signaling to Erk-1/-2 was dependent upon trans-activation of the epidermal growth factor (EGF) receptor via release of heparan-bound EGF (HB-EGF). Estradiol signaling to Erk-1/-2 could be blocked by: 1) inhibiting EGF-receptor tyrosine kinase activity, 2) neutralizing HB-EGF with antibodies, or 3) down-modulating HB-EGF from the cell surface with the diphtheria toxin mutant, CRM-197. Our data imply that ER-negative breast tumors that continue to express GPR30 may use estrogen to drive growth factor-dependent cellular responses.

A comparison of nefazodone, the cognitive behavioral-analysis system of psychotherapy, and their combination for the treatment of chronic depression.

Abstract: Background Patients with chronic forms of major depression are difficult to treat, and the relative efficacy of medications and psychotherapy is uncertain. Methods We randomly assigned 681 adults with a chronic nonpsychotic major depressive disorder to 12 weeks of outpatient treatment with nefazodone (maximal dose, 600 mg per day), the cognitive behavioral-analysis system of psychotherapy (16 to 20 sessions), or both. At base line, all patients had scores of at least 20 on the 24-item Hamilton Rating Scale for Depression (indicating clinically significant depression). Remission was defined as a score of 8 or less at weeks 10 and 12. For patients who did not have remission, a satisfactory response was defined as a reduction in the score by at least 50 percent from base line and a score of 15 or less. Raters were unaware of the patients' treatment assignments. Results Of the 681 patients, 662 attended at least one treatment session and were included in the analysis of response. The overall rate of response ...

Runge-Kutta discontinuous Galerkin methods for convection-dominated problems

Abstract: In this paper, we review the development of the Runge–Kutta discontinuous Galerkin (RKDG) methods for non-linear convection-dominated problems. These robust and accurate methods have made their way into the main stream of computational fluid dynamics and are quickly finding use in a wide variety of applications. They combine a special class of Runge–Kutta time discretizations, that allows the method to be non-linearly stable regardless of its accuracy, with a finite element space discretization by discontinuous approximations, that incorporates the ideas of numerical fluxes and slope limiters coined during the remarkable development of the high-resolution finite difference and finite volume schemes. The resulting RKDG methods are stable, high-order accurate, and highly parallelizable schemes that can easily handle complicated geometries and boundary conditions. We review the theoretical and algorithmic aspects of these methods and show several applications including nonlinear conservation laws, the compressible and incompressible Navier–Stokes equations, and Hamilton–Jacobi-like equations.

Plasticity and primary motor cortex.

Abstract: One fundamental function of primary motor cortex (MI) is to control voluntary movements. Recent evidence suggests that this role emerges from distributed networks rather than discrete representations and that in adult mammals these networks are capable of modification. Neuronal recordings and activation patterns revealed with neuroimaging methods have shown considerable plasticity of MI representations and cell properties following pathological or traumatic changes and in relation to everyday experience, including motor-skill learning and cognitive motor actions. The intrinsic horizontal neuronal connections in MI are a strong candidate substrate for map reorganization: They interconnect large regions of MI, they show activity-dependent plasticity, and they modify in association with skill learning. These findings suggest that MI cortex is not simply a static motor control structure. It also contains a dynamic substrate that participates in motor learning and possibly in cognitive events as well.

Practice parameter: Screening and diagnosis of autism Report of the Quality Standards Subcommittee of the American Academy of Neurology and the Child Neurology Society

Abstract: Autism is a common disorder of childhood, affecting 1 in 500 children. Yet, it often remains unrecognized and undiagnosed until or after late preschool age because appropriate tools for routine developmental screening and screening specifically for autism have not been available. Early identification of children with autism and intensive, early intervention during the toddler and preschool years improves outcome for most young children with autism. This practice parameter reviews the available empirical evidence and gives specific recommendations for the identification of children with autism. This approach requires a dual process: 1) routine developmental surveillance and screening specifically for autism to be performed on all children to first identify those at risk for any type of atypical development, and to identify those specifically at risk for autism; and 2) to diagnose and evaluate autism, to differentiate autism from other developmental disorders.

Antiretroviral Therapy in Adults: Updated Recommendations of the International AIDS Society–USA Panel

Abstract: Objective To update recommendations for antiretroviral therapy for adult human immunodeficiency virus type 1 (HIV-1) infection, based on new information and drugs that are available. Participants A 17-member international physician panel with antiretroviral research and HIV patient care experience initially convened by the International AIDS Society–USA in December 1995. Evidence Available clinical and basic science data including phase 3 controlled trials; data on clinical, virologic, and immunologic end points; research conference reports; HIV pathogenesis data; and panel expert opinion. Recommendations were limited to therapies available (US Food and Drug Administration approved) in 1999. Consensus Process The panel assesses new research reports and interim results and regularly meets to consider how the new data affect therapy recommendations. Recommendations are updated via full-panel consensus. Guidelines are presented as recommendations if the supporting evidence warrants routine use in the particular situation and as considerations if data are preliminary or incomplete but suggestive. Conclusions The availability of new antiretroviral drugs has expanded treatment choices. The importance of adherence, emerging long-term complications of therapy, recognition and management of antiretroviral failure, and new monitoring tools are addressed. Optimal care requires individualized management and ongoing attention to relevant scientific and clinical information in the field.

A discussion of cybersickness in virtual environments

Abstract: An important and troublesome problem with current virtual environment (VE) technology is the tendency for some users to exhibit symptoms that parallel symptoms of classical motion sickness both during and after the VE experience. This type of sickness, cybersickness, is distinct from motion sickness in that the user is often stationary but has a compelling sense of self motion through moving visual imagery. Unfortunately, there are many factors that can cause cybersickness and there is no foolproof method for eliminating the problem. In this paper, I discuss a number of the primary factors that contribute to the cause of cybersickness, describe three conflicting cybersickness theories that have been postulated, and discuss some possible methods for reducing cybersickness in VEs.

Learning-induced LTP in neocortex.

Abstract: The hypothesis that learning occurs through long-term potentiation (LTP)- and long-term depression (LTD)-like mechanisms is widely held but unproven. This hypothesis makes three assumptions: Synapses are modifiable, they modify with learning, and they strengthen through an LTP-like mechanism. We previously established the ability for synaptic modification and a synaptic strengthening with motor skill learning in horizontal connections of the rat motor cortex (MI). Here we investigated whether learning strengthened these connections through LTP. We demonstrated that synapses in the trained MI were near the ceiling of their modification range, compared with the untrained MI, but the range of synaptic modification was not affected by learning. In the trained MI, LTP was markedly reduced and LTD was enhanced. These results are consistent with the use of LTP to strengthen synapses during learning.

Role for rapid dendritic protein synthesis in hippocampal mGluR-dependent long-term depression.

Abstract: A hippocampal pyramidal neuron receives more than 10(4) excitatory glutamatergic synapses. Many of these synapses contain the molecular machinery for messenger RNA translation, suggesting that the protein complement (and thus function) of each synapse can be regulated on the basis of activity. Here, local postsynaptic protein synthesis, triggered by synaptic activation of metabotropic glutamate receptors, was found to modify synaptic transmission within minutes.

Stability of peakons

Abstract: The peakons are peaked solitary wave solutions of a certain nonlinear dispersive equation that is a model in shallow water theory and the theory of hyperelastic rods We give a very simple proof of the orbital stability of the peakons in the H1 norm © 2000 John Wiley & Sons, Inc

The Development of Discontinuous Galerkin Methods

Abstract: In this paper, we present an overview of the evolution of the discontinuous Galerkin methods since their introduction in 1973 by Reed and Hill, in the framework of neutron transport, until their most recent developments. We show how these methods made their way into the main stream of computational fluid dynamics and how they are quickly finding use in a wide variety of applications. We review the theoretical and algorithmic aspects of these methods as well as their applications to equations including nonlinear conservation laws, the compressible Navier-Stokes equations, and Hamilton-Jacobi-like equations.

A threatening intellectual environment: why females are susceptible to experiencing problem-solving deficits in the presence of males.

Abstract: Does placing females in environments in which they have contact with males cause deficits in their problem-solving perfor- mance? Is a situational cue, such as gender composition, sufficient for creating a threatening intellectual environment for females—an en- vironment that elicits performance-impinging stereotypes? Two stud- ies explored these questions. Participants completed a difficult math or verbal test in 3-person groups, each of which included 2 additional people of the same sex as the participant (same-sex condition) or of the opposite sex (minority condition). Female participants in the mi- nority condition experienced performance deficits in the math test only, whereas males performed equally well on the math test in the two conditions. Further investigation showed that females' deficits were proportional to the number of males in their group. Even females who were placed in a mixed-sex majority condition (2 females and 1 male) experienced moderate but significant deficits. Findings are dis- cussed in relation to theories of distinctiveness, stereotype threat, and tokenism. Females currently are a small minority of students and researchers in the natural and physical sciences. A recent National Science Foun- dation (1996) report showed that females constitute 35% of under- graduate students enrolled in physics, math, and computer science classes; 16% of undergraduate students enrolled in engineering classes; and less than 10% of graduate students in physics and engi- neering. Moreover, this report showed that females suffer from higher attrition rates in their academic careers than do males, so that by the time women reach the workplace, they occupy only 22% of jobs in mathematical and scientific domains. Does females' problem-solving performance diminish when they are placed in an environment in which males outnumber them? If so, are such performance deficits specifically linked to domains that are associated with negative ste- reotypes about females' intellectual capacity? Examining these ques- tions can inform theories of how social stereotypes affect the intellectual processing of individuals who are the targets of these stereotypes, as well as educational practice.

The Fusiform Face Area is Part of a Network that Processes Faces at the Individual Level

Abstract: According to modular models of cortical organization, many areas of the extrastriate cortex are dedicated to object categories. These models often assume an early processing stage for the detection of category membership. Can functional imaging isolate areas responsible for detection of members of a category, such as faces or letters? We consider whether responses in three different areas (two selective for faces and one selective for letters) support category detection. Activity in these areas habituates to the repeated presentation of one exemplar more than to the presentation of different exemplars of the same category, but only for the category for which the area is selective. Thus, these areas appear to play computational roles more complex than detection, processing stimuli at the individual level. Drawing from prior work, we suggest that face-selective areas may be involved in the perception of faces at the individual level, whereas letter-selective regions may be tuning themselves to font information in order to recognize letters more efficiently.

Practice parameter: Anticonvulsant prophylaxis in patients with newly diagnosed brain tumors Report of the Quality Standards Subcommittee of the American Academy of Neurology

Abstract: The Quality Standards Subcommittee seeks to develop scientifically sound, clinically relevant practice parameters for the practice of neurology. Practice parameters are strategies for patient management that assist physicians in clinical decision making. A practice parameter is one or more specific recommendations based on analysis of evidence on a specific clinical problem. These might include diagnosis, symptoms, treatment, or procedure evaluation. American Academy of Neurology (AAN) members have requested the publication of a practice parameter on the use of prophylactic anticonvulsants in patients with primary and metastatic brain tumors. Physicians often administer anticonvulsant medication prophylactically to patients with brain tumors, despite the lack of definitive evidence that prophylactic anticonvulsant therapy is effective in preventing first seizures.1-4 If anticonvulsant medications were free of side effects, their prophylactic use might be attractive even without such evidence. However, discomfort, expense, and inconvenience result from drug treatment and periodic monitoring of serum drug concentrations. Typical anticonvulsant-induced side effects, including cognitive impairment, myelosuppression, liver dysfunction, and dermatologic reactions (ranging from minor rashes to life-threatening Stevens–Johnson syndrome), appear to occur more frequently in patients with brain tumors than in other patient groups,3,5-16 although direct comparison studies have not been published. A spectrum of side effects unique to patients with brain tumors must also be considered. Phenytoin, carbamazepine, and phenobarbital reduce the efficacy of corticosteroids,17-21 which are administered almost universally to brain tumor patients. In addition, the ability of these anticonvulsants to stimulate the cytochrome P450 enzyme system results in markedly accelerated metabolism of a wide spectrum of chemotherapeutic agents including nitrosoureas, paclitaxel, cyclophosphamide, topotecan, irinotecan, thiotepa, 9-aminocampothecin, adriamycin, and methotrexate.22-34 As a result, inadequate chemotherapeutic dosing of brain tumor patients has been identified recently as a widespread and critically important problem.35 Conversely, …

Economic Integration and Political Disintegration

Abstract: In a world of trade restrictions, large countries enjoy economic benefits, because political boundaries determine the size of the market. Under free trade and global markets even relatively small cultural, linguistic or ethnic groups can benefit from forming small, homogeneous political jurisdictions. This paper provides a formal model of the relationship between openness and the equilibrium number and size of countries, and successfully tests two implications of the model. Firstly, the economic benefits of country size are mediated by the degree of openness to trade. Secondly, the history of nation-state creations and secessions is influenced by the trade regime.

FFA: a flexible fusiform area for subordinate-level visual processing automatized by expertise

Abstract: Much evidence suggests that the fusiform face area is involved in face processing. In contrast to the accompanying article by Kanwisher, we conclude that the apparent face selectivity of this area reflects a more generalized form of processing not intrinsically specific to faces.

Phenylpropanolamine and the Risk of Hemorrhagic Stroke

Abstract: Background Phenylpropanolamine is commonly found in appetite suppressants and cough or cold remedies. Case reports have linked the use of products containing phenylpropanolamine to hemorrhagic stroke, often after the first use of these products. To study the association, we designed a case–control study. Methods Men and women 18 to 49 years of age were recruited from 43 U.S. hospitals. Eligibility criteria included the occurrence of a subarachnoid or intracerebral hemorrhage within 30 days before enrollment and the absence of a previously diagnosed brain lesion. Random-digit dialing identified two matched control subjects per patient. Results There were 702 patients and 1376 control subjects. For women, the adjusted odds ratio was 16.58 (95 percent confidence interval, 1.51 to 182.21; P=0.02) for the association between the use of appetite suppressants containing phenylpropanolamine and the risk of a hemorrhagic stroke and 3.13 (95 percent confidence interval, 0.86 to 11.46; P=0.08) for the association wi...

Saving and Growth with Habit Formation

Abstract: Saving and growth are strongly positively correlated across countries. Recent empirical evidence suggests that this correlation holds largely because high growth leads to high saving, not the other way around. This evidence is difficult to reconcile with standard growth models, since forward-looking consumers with standard utility should save less in a fast-growing economy because they know they will be richer in the future than they are today. We show that if utility depends partly on how consumption compares to a ‘habit stock’ determined by past consumption, an otherwise-standard growth model can imply that increases in growth can cause increased saving

From Chance to Choice: Genetics and Justice

Abstract: This book, written by four internationally renowned bioethicists and first published in 2000, was the first systematic treatment of the fundamental ethical issues underlying the application of genetic technologies to human beings. Probing the implications of the remarkable advances in genetics, the authors ask how should these affect our understanding of distributive justice, equality of opportunity, the rights and obligations as parents, the meaning of disability, and the role of the concept of human nature in ethical theory and practice. The book offers a historical context to contemporary debate over the use of these technologies by examining the eugenics movement of the late nineteenth and early twentieth centuries. The questions raised in this book will be of interest to any reflective reader concerned about science and society and the rapid development of biotechnology, as well as to professionals in such areas as philosophy, bioethics, medical ethics, health management, law, and political science.

Space weathering on airless bodies: Resolving a mystery with lunar samples

Abstract: — Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S-type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.

Value-function approximations for partially observable Markov decision processes

Abstract: Partially observable Markov decision processes (POMDPs) provide an elegant mathematical framework for modeling complex decision and planning problems in stochastic domains in which states of the system are observable only indirectly, via a set of imperfect or noisy observations. The modeling advantage of POMDPs, however, comes at a price -- exact methods for solving them are computationally very expensive and thus applicable in practice only to very simple problems. We focus on efficient approximation (heuristic) methods that attempt to alleviate the computational problem and trade off accuracy for speed. We have two objectives here. First, we survey various approximation methods, analyze their properties and relations and provide some new insights into their differences. Second, we present a number of new approximation methods and novel refinements of existing techniques. The theoretical results are supported by experiments on a problem from the agent navigation domain.