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Showing papers by "Tel Aviv University published in 1998"


Journal ArticleDOI
TL;DR: It is shown that approximating Clique and Independent Set, even in a very weak sense, is NP-hard, and the class NP contains exactly those languages for which membership proofs can be verified probabilistically in polynomial time.
Abstract: We give a new characterization of NP: the class NP contains exactly those languages L for which membership proofs (a proof that an input x is in L) can be verified probabilistically in polynomial time using logarithmic number of random bits and by reading sublogarithmic number of bits from the proof.We discuss implications of this characterization; specifically, we show that approximating Clique and Independent Set, even in a very weak sense, is NP-hard.

1,261 citations


Journal ArticleDOI
01 Aug 1998-Immunity
TL;DR: Findings indicate that Caspase 8 plays a necessary and nonredundant role in death induction by several receptors of the TNF/NGF family and serves a vital role in embryonal development.

1,228 citations


Journal ArticleDOI
TL;DR: In this paper, the authors consider field theories with sixteen supersymmetries, which include U(N) Yang-Mills theories in various dimensions, and argue that their large N limit is related to certain supergravity solutions.
Abstract: We consider field theories with sixteen supersymmetries, which include U(N) Yang-Mills theories in various dimensions, and argue that their large N limit is related to certain supergravity solutions. We study this by considering a system of D-branes in string theory and then taking a limit where the brane world volume theory decouples from gravity. At the same time we study the corresponding D-brane supergravity solution and argue that we can trust it in certain regions where the curvature (and the effective string coupling, where appropriate) are small. The supergravity solutions typically have several weakly coupled regions and interpolate between different limits of string M theory. {copyright} {ital 1998} {ital The American Physical Society}

1,228 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an ISO SWS and ISOPHOT-S, mid-infrared spectroscopic survey of 15 ultraluminous IRAS galaxies (LIR ≥ 1012 L ).
Abstract: We present an ISO SWS and ISOPHOT-S, mid-infrared spectroscopic survey of 15 ultraluminous IRAS galaxies (LIR ≥ 1012 L☉). We combine the survey results with a detailed case study, based on arcsecond resolution, near-IR, and millimeter imaging spectroscopy, of one of the sample galaxies (UGC 5101). We compare the near- and mid-IR characteristics of these ultraluminous galaxies to ISO and literature data of 30 starburst and active galactic nuclei (AGN) template galaxies. We find the following: 1. Of the ultraluminous IRAS galaxies in our sample, 70%-80% are predominantly powered by recently formed massive stars, and 20%-30% are powered by a central AGN. These conclusions are based on a new infrared diagnostic diagram involving the ratio of high- to low-excitation mid-IR emission lines on the one hand, and the strength of the 7.7 μm PAH feature on the other hand. 2. At least half of the sources probably have simultaneously an active nucleus and starburst activity in a 1-2 kpc diameter circumnuclear disk/ring. 3. The mid-IR emitting regions are highly obscured [Av(screen) ~ 5-50 or Av(mixed) ~ 50-1000]. In a model where star-forming regions and dense molecular clouds are fully mixed, the ISO-derived, V-band dust extinctions approach the dust column densities inferred from CO millimeter measurements. After correction for these extinctions, we estimate that the star-forming regions in ultraluminous infrared galaxies have ages between 107 and 108 yr, similar to but somewhat larger than those found in lower luminosity starburst galaxies. 4. In the sample we have studied there is no obvious trend for the AGN component to dominate in the most compact, and thus most advanced mergers. Instead, at any given time during the merger evolution, the time-dependent compression of the circumnuclear interstellar gas, the accretion rate onto the central black hole, and the associated radiation efficiency may determine whether star formation or AGN activity dominates the luminosity of the system.

1,227 citations


Journal ArticleDOI
TL;DR: In this article, the authors explore the recent explosion in university patenting as a source of insight into the changing relationship between the university and the private sector and find that between 1965 and 1988, the rate of increase of important patents from universities was much less than their overall rate of increasing patenting.
Abstract: This paper explores the recent explosion in university patenting as a source of insight into the changing relationship between the university and the private sector. Before the mid-1980s, university patents were more highly cited, and were cited by more diverse patents, than a random sample of all patents. More recently several significant shifts in university patenting behavior have led to the disappearance of this difference. Thus our results suggest that between 1965 and 1988 the rate of increase of important patents from universities was much less than their overall rate of increase of patenting.

1,076 citations


Journal ArticleDOI
TL;DR: The objective of this work is to survey and put in perspective the existing IMM methods for target tracking problems, with special attention to the assumptions underlying each algorithm and its applicability to various situations.
Abstract: The Interacting Multiple Model (IMM) estimator is a suboptimal hybrid filter that has been shown to be one of the most cost-effective hybrid state estimation schemes. The main feature of this algorithm is its ability to estimate the state of a dynamic system with several behavior modes which can "switch" from one to another. In particular, the IMM estimator can be a self-adjusting variable-bandwidth filter, which makes it natural for tracking maneuvering targets. The importance of this approach is that it is the best compromise available currently-between complexity and performance: its computational requirements are nearly linear in the size of the problem (number of models) while its performance is almost the same as that of an algorithm with quadratic complexity. The objective of this work is to survey and put in perspective the existing IMM methods for target tracking problems. Special attention is given to the assumptions underlying each algorithm and its applicability to various situations.

1,024 citations


Journal ArticleDOI
David Levin1
TL;DR: The interpolation approximation in R d is shown to be a C∞ function, and an approximation order result is proven for quasi-uniform sets of data points.
Abstract: A general method for near-best approximations to functionals on R d , using scattered-data information is discussed. The method is actually the moving least-squares method, presented by the Backus-Gilbert approach. It is shown that the method works very well for interpolation, smoothing and derivatives' approximations. For the interpolation problem this approach gives Mclain's method. The method is near-best in the sense that the local error is bounded in terms of the error of a local best polynomial approximation. The interpolation approximation in R d is shown to be a C∞ function, and an approximation order result is proven for quasi-uniform sets of data points.

778 citations


Journal ArticleDOI
TL;DR: In this article, the main applications of current interest including some discussions of the underlying phenomena are dealt with, including some experiments for synthesizing nanoparticles in the gas phase aiming at any of the above mentioned functional applications.

713 citations


Journal ArticleDOI
TL;DR: The energetic-dynamic relations, in conjunction with the energetic data for d*/d- and for B/B+, determine the realization of the two distinct mechanisms in different hole donor systems, establishing the conditions for "chemistry at a distance" after charge transport in DNA.
Abstract: We explore charge migration in DNA, advancing two distinct mechanisms of charge separation in a donor (d)–bridge ({Bj})–acceptor (a) system, where {Bj} = B1,B2, … , BN are the N-specific adjacent bases of B-DNA: (i) two-center unistep superexchange induced charge transfer, d*{Bj}a → d∓{Bj}a±, and (ii) multistep charge transport involves charge injection from d* (or d+) to {Bj}, charge hopping within {Bj}, and charge trapping by a. For off-resonance coupling, mechanism i prevails with the charge separation rate and yield exhibiting an exponential dependence ∝ exp(−βR) on the d-a distance (R). Resonance coupling results in mechanism ii with the charge separation lifetime τ ∝ Nη and yield Y ≃ (1 + δ Nη)−1 exhibiting a weak (algebraic) N and distance dependence. The power parameter η is determined by charge hopping random walk. Energetic control of the charge migration mechanism is exerted by the energetics of the ion pair state d∓B1±B2 … BNa relative to the electronically excited donor doorway state d*B1B2 … BNa. The realization of charge separation via superexchange or hopping is determined by the base sequence within the bridge. Our energetic–dynamic relations, in conjunction with the energetic data for d*/d− and for B/B+, determine the realization of the two distinct mechanisms in different hole donor systems, establishing the conditions for “chemistry at a distance” after charge transport in DNA. The energetic control of the charge migration mechanisms attained by the sequence specificity of the bridge is universal for large molecular-scale systems, for proteins, and for DNA.

657 citations


Journal ArticleDOI
TL;DR: An extensive survey and comparative assessment of different existing methods for constructing the ABCs are presented and a new ABCs technique proposed in recent work is described, which allows one to obtain highly accurate ABCs in the form of certain (nonlocal) boundary operator equations.

617 citations


Journal ArticleDOI
TL;DR: In this paper, a prior distribution is imposed on the wavelet coefficients of the unknown response function, designed to capture the sparseness of wavelet expansion that is common to most applications.
Abstract: We discuss a Bayesian formalism which gives rise to a type of wavelet threshold estimation in nonparametric regression. A prior distribution is imposed on the wavelet coefficients of the unknown response function, designed to capture the sparseness of wavelet expansion that is common to most applications. For the prior specified, the posterior median yields a thresholding procedure. Our prior model for the underlying function can be adjusted to give functions falling in any specific Besov space. We establish a relationship between the hyperparameters of the prior model and the parameters of those Besov spaces within which realizations from the prior will fall. Such a relationship gives insight into the meaning of the Besov space parameters. Moreover, the relationship established makes it possible in principle to incorporate prior knowledge about the function's regularity properties into the prior model for its wavelet coefficients. However, prior knowledge about a function's regularity properties might be difficult to elicit; with this in mind, we propose a standard choice of prior hyperparameters that works well in our examples. Several simulated examples are used to illustrate our method, and comparisons are made with other thresholding methods. We also present an application to a data set that was collected in an anaesthesiological study.

Journal ArticleDOI
TL;DR: A combination of molecular genetic, biochemical, chemical, crystallographic and microscopic techniques are paving the way for new insights into both the structure of cellulose and the mechanisms of its hydrolysis.

Journal ArticleDOI
TL;DR: High-dose isosorbide dinitrate, given as repeated intravenous boluses after low-dose intravenous furosemide, is safe and effective in controlling severe pulmonary oedema.

Proceedings ArticleDOI
01 Jun 1998
TL;DR: This paper introduces two new sampling-based summary statistics, concise samples and counting samples, and presents new techniques for their fast incremental maintenance regardless of the data distribution, and considers their application to providing fast approximate answers to hot list queries.
Abstract: In large data recording and warehousing environments, it is often advantageous to provide fast, approximate answers to queries, whenever possible. Before DBMSs providing highly-accurate approximate answers can become a reality, many new techniques for summarizing data and for estimating answers from summarized data must be developed. This paper introduces two new sampling-based summary statistics, concise samples and counting samples, and presents new techniques for their fast incremental maintenance regardless of the data distribution. We quantify their advantages over standard sample views in terms of the number of additional sample points for the same view size, and hence in providing more accurate query answers. Finally, we consider their application to providing fast approximate answers to hot list queries. Our algorithms maintain their accuracy in the presence of ongoing insertions to the data warehouse.

Journal ArticleDOI
TL;DR: Theoretical results show that the measles ‘pulse’ vaccination strategy can be distinguished from the conventional strategies in leading to disease eradication at relatively low values of vaccination.

Journal ArticleDOI
TL;DR: In this article, the authors explore income and consumption smoothing patterns among European Community (EC) countries and among OECD countries during the period 1966-90 and find that, for OECD as well as for EC countries, about 40 percent of shocks to GDP are smoothed at the one year frequency, with about half the smoothing achieved through national government budget deficits and half by corporate saving.

Proceedings ArticleDOI
01 Jun 1998
TL;DR: This paper presents a technique based upon a multiresolution wavelet decomposition for building histograms on the underlying data distributions, with applications to databases, statistics, and simulation.
Abstract: Query optimization is an integral part of relational database management systems. One important task in query optimization is selectivity estimation, that is, given a query P, we need to estimate the fraction of records in the database that satisfy P. Many commercial database systems maintain histograms to approximate the frequency distribution of values in the attributes of relations.In this paper, we present a technique based upon a multiresolution wavelet decomposition for building histograms on the underlying data distributions, with applications to databases, statistics, and simulation. Histograms built on the cumulative data distributions give very good approximations with limited space usage. We give fast algorithms for constructing histograms and using them in an on-line fashion for selectivity estimation. Our histograms also provide quick approximate answers to OLAP queries when the exact answers are not required. Our method captures the joint distribution of multiple attributes effectively, even when the attributes are correlated. Experiments confirm that our histograms offer substantial improvements in accuracy over random sampling and other previous approaches.

Proceedings Article
24 Aug 1998
TL;DR: This paper presents a new translation system, based on schema-matching, aimed at simplifying the intricate task of data conversion, and shows that it allows a convenient specification and customization of data conversions, and can be easily combined with the traditional data-based translation languages.
Abstract: A broad spectrum of data is available on the Web in distinct heterogeneous sources, and stored under different formats. As the number of systems that utilize this heterogeneous data grows, the importance of data translation and conversion mechanisms increases greatly. In this paper we present a new translation system, based on schema-matching, aimed at simplifying the intricate task of data conversion. We observe that in many cases the schema of the data in the source system is very similar to that of the target system. In such cases, much of the translation work can be done automatically, based on the schemas similarity. This saves a lot of effort for the user, limiting the amount of programming needed. We define common schema and data models, in which schemas and data (resp.) from many common models can be represented. Using a rule-based method, the source schema is compared with the target one, and each component in the source schema is matched with a corresponding component in the target schema. Then, based on the matching achieved, data instances of the source schema can be translated to instances of the target schema. We show that our schema-based translation system allows a convenient specification and customization of data conversions, and can be easily combined with the traditional data-based translation languages.

Journal ArticleDOI
TL;DR: The combination of blood pressure values in the high-normal range with moderately elevated levels of total cholesterol and hemoglobin A1c defines a high-risk group for the progression to diabetic nephropathy and for clinical events related to arteriosclerotic cardiovascular disease.
Abstract: Background: The control of hyperglycemia is of major importance in the treatment of patients with type 1 diabetes mellitus. However, there is no consensus about the required degree of metabolic control in patients with type 2 diabetes mellitus and about the role of hyperglycemia in diabetic nephropathy and in the development of atherosclerosis in relation to other risk factors. Patients and Methods: A prospective, long-term follow-up study was conducted on 574 patients, aged 40 to 60 years, with recent onset of type 2 diabetes mellitus. Patients were initially normotensive and had normal renal function and a normal urinary albumin excretion rate (,30 mg/24 h). The patients were followed up for 2 to 9 years (mean ± SD, 7.8 ± 0.9 years). Levels of hemoglobin A1c and plasma lipids, mean blood pressure, and body mass index (calculated as the weight in kilograms divided by the square of the height in meters) were determined periodically. Cigarette smoking and socioeconomic status were recorded. Renal status was evaluated by the logarithm of the final urinary albumin excretion rate and by the decline in reciprocal creatinine values. Definite clinical events including death, nonfatal myocardial infarction, angina pectoris, congestive heart failure, and peripheral vascular disease were recorded. Results: At the end of the study the urinary albumin excretion rate remained normal (,30 mg/24 h) in 373 patients (65%), 111 (19%) had microalbuminuria (30-300 mg/24 h), and 90 (16%) had overt albuminuria (.300 mg/24 h). Logistic regression models demonstrated that the correlation between hemoglobin A1c levels and the risk of albuminuria is exponential. Multiple logistic regression analysis indicated that levels of total cholesterol, mean blood pressure, and hemoglobin A1c were the main factors associated with the decrease in renal function and with the increase in albuminuria. The combination of values higher than the 50th percentile of all 3 factors defined a high-risk patient population. These high-risk patients had an odds ratio of 43 (95% confidence interval, 25-106) for microalbuminuria and 15 (95% confidence interval, 9-25) for clinical events related to arteriosclerosis compared with the rest of the group. Low levels of high-density lipoprotein, body mass index, cigarette smoking, low socioeconomic status, and male sex were all significantly associated with diabetic nephropathy, as well as with the manifestations of arteriosclerosis. Conclusions: The combination of blood pressure values in the high-normal range with moderately elevated levels of total cholesterol and hemoglobin A1c defines a high-risk group for the progression to diabetic nephropathy and for clinical events related to arteriosclerotic cardiovascular disease. Arch Intern Med. 1998;158:998-1004

Journal ArticleDOI
TL;DR: In this article, a detailed analysis of the 0.6-10 keV spectra of 23 ASCA observations of 18 objects was carried out and the importance of the covering fraction of the ionized gas and a direct comparison between models of attenuation by ionized versus neutral material was made.
Abstract: We present the results from a detailed analysis of the 0.6-10 keV spectra of 23 ASCA observations of 18 objects. We find that in most cases the underlying continuum can be well represented by a power law with a photon index Γ ~ 2. However, we find strong evidence for photoionized gas in the line of sight to 13/18 objects. We present detailed modeling of this gas based upon the ION photoionization code. Other studies have been made of the "warm absorber" phenomenon, but this paper contains the first consideration of the importance of the covering fraction of the ionized gas and a direct comparison between models of attenuation by ionized versus neutral material. We find the X-ray ionization parameter for the ionized material is strongly peaked at UX ~ 0.1. The column densities of ionized material are typically in the range NH, z ~ 1021-1023 cm-2, although highly ionized (and hence pseudotransparent) column densities up to 1024 cm-2 cannot be excluded in some cases. We also investigate the importance of the emission spectrum from the ionized gas, finding that it significantly improves the fit to many sources with an intensity consistent with material subtending a large solid angle at the central source. Allowing a fraction of the continuum to be observed without attenuation also improves the fit to many sources and is definitely required in the case of NGC 4151. A deficit of counts is observed at ~1 keV in the sources exhibiting the strongest absorption features. We suggest this is likely to be the signature of a second zone of (more highly) ionized gas, which might have been seen previously in the deep Fe K-shell edges observed in some Ginga observations. We find evidence that the ionized material in NGC 3227 and MCG -6-30-15 contains embedded dust, while there is no such evidence in the other sources We discuss these results in the context of previous studies and briefly explore the implications in other wave bands.

Journal ArticleDOI
TL;DR: The results suggest that project success factors are not universal for all projects, suggesting the need for a more contingent approach in project management theory and practice.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed the following societal beliefs which are conducive to the development of these psychological conditions: beliefs about the justness of one's own goals, beliefs about security, beliefs of delegitimizing the opponent, beliefs positive self-image and beliefs about patriotism.
Abstract: Intractable conflicts are characterized as protracted, irreconcilable, violent, of zero‐sum nature, total, and central. They are demanding, stressful, exhausting, and costly both in human and material terms. Societies involved in this type of conflict develop appropriate psychological conditions which enable them to cope successfully with the conflictual situation. The present paper proposes the following societal beliefs which are conducive to the development of these psychological conditions: beliefs about the justness of one's own goals, beliefs about security, beliefs of delegitimizing the opponent, beliefs of positive self‐image, beliefs about patriotism, beliefs about unity and beliefs about peace. These beliefs constitute a kind of ideology which supports the continuation of the conflict. The paper analyzes as an example one such intractable conflict, namely the one between Israel and Arabs, concentrating on the Israeli society. Specifically, it demonstrates the reflection of the discussed societal beliefs in the Israeli school textbooks. Finally, implications of the presented framework for peaceful conflict resolution are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the effect of prolonged ACE inhibition on renal function and albuminuria in patients with type 2 diabetes and found that enalapril treatment resulted in an absolute risk reduction of 12.5% (95% CI, 2% to 23%; P = 0.042) for development of microalbuminuria.
Abstract: BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitors attenuate the decline in renal function in diabetic patients with microalbuminuria. However, no data are available on the use of ACE inhibitors to prevent the decrease in renal function in normotensive, normoalbuminuric patients with type 2 diabetes. OBJECTIVE: To evaluate the effect of prolonged ACE inhibition on renal function and albuminuria in patients with type 2 diabetes. DESIGN: Randomized, double-blind, placebo-controlled trial with 6-year follow-up. SETTING: Eight outpatient clinics coordinated by a department of medicine in a university hospital. PATIENTS: 156 patients in whom type 2 diabetes was diagnosed after 40 years of age who had a baseline mean blood pressure less than 107 mm Hg and albuminuria (albumin excretion < or = 30 mg/24 h). INTERVENTION: Enalapril, 10 mg/d, or placebo. MEASUREMENTS: Degree of albuminuria at 24 hours, creatinine clearance, blood pressure, and hemoglobin A1c values. RESULTS: Enalapril therapy decreased albumin excretion from a mean +/- SD of 11.6 +/- 7 mg/24 h to 9.7 +/- 6 mg/24 h at 2 years. This was followed by a gradual increase to 15.8 +/- 8 mg/24 h at 6 years. In the placebo group, albumin excretion increased from 10.8 +/- 8 mg/24 h to 26.5 +/- 10 mg/24 h at 6 years (P = 0.001 for enalapril compared with placebo). Transition to microalbuminuria occurred in 15 of 79 (19%) placebo recipients and 5 of 77 (6.5%) enalapril recipients. Enalapril treatment resulted in an absolute risk reduction of 12.5% (95% CI, 2% to 23%; P = 0.042) for development of microalbuminuria. After 6 years, creatinine clearance decreased from 1.78 +/- 0.13 mL/s to 1.63 +/- 0.12 mL/s (mean decrease, 0.025 mL/s per year) in enalapril recipients and from 1.81 +/- 0.15 mL/s to 1.57 +/- 0.17 mL/s (mean decrease, 0.04 mL/s per year) in placebo recipients (P = 0.040). Hemoglobin A1c values decreased modestly in both groups. Mean blood pressure remained normal (< 107 mm Hg) in all patients. CONCLUSIONS: Enalapril attenuated the decline in renal function and reduced the extent of albuminuria in normotensive, normoalbuminuric patients with type 2 diabetes. Further research is needed to determine whether this treatment forestalls the development of overt nephropathy.

Journal ArticleDOI
TL;DR: A combinatorial algorithm that computes a (1+ɛ) approximation to the fractional optimal feedback vertex set, and a generalization of these problems, in which the feedback set has to intersect only a subset of the directed cycles in the graph.
Abstract: This paper deals with approximating feedback sets in directed graphs. We consider two related problems: the weighted feedback vertex set (FVS) problem, and the weighted feedback edge set (FES) problem. In the {FVS} (resp. FES) problem, one is given a directed graph with weights (each of which is at least one) on the vertices (resp. edges), and is asked to find a subset of vertices (resp. edges) with minimum total weight that intersects every directed cycle in the graph. These problems are among the classical NP-hard problems and have many applications. We also consider a generalization of these problems: subset-fvs and subset-fes, in which the feedback set has to intersect only a subset of the directed cycles in the graph. This subset consists of all the cycles that go through a distinguished input subset of vertices and edges, denoted by X . This generalization is also NP-hard even when |X|=2 . We present approximation algorithms for the subset-fvs and subset-fes problems. The first algorithm we present achieves an approximation factor of O(log 2 |X|) . The second algorithm achieves an approximation factor of O(min{log τ * log log τ * , log n log log n)} , where τ * is the value of the optimum fractional solution of the problem at hand, and n is the number of vertices in the graph. We also define a multicut problem in a special type of directed networks which we call circular networks, and show that the subset-fes and subset-fvs problems are equivalent to this multicut problem. Another contribution of our paper is a combinatorial algorithm that computes a (1+ɛ) approximation to the fractional optimal feedback vertex set. Computing the approximate solution is much simpler and more efficient than general linear programming methods. All of our algorithms use this approximate solution.

Journal ArticleDOI
TL;DR: The cellulosome dictates both the binding of the cell to the substrate and its extracellular decomposition to soluble sugars, which are then taken up and assimilated by normal cellular processes.

Journal ArticleDOI
20 Mar 1998-Science
TL;DR: The molecular basis for autosomal dominant progressive nonsyndromic hearing loss in an Israeli Jewish family, Family H, has been determined and an 8-base pair deletion in the POU homeodomain of human POU4F3 was identified in Family H.
Abstract: The molecular basis for autosomal dominant progressive nonsyndromic hearing loss in an Israeli Jewish family, Family H, has been determined. Linkage analysis placed this deafness locus, DFNA15, on chromosome 5q31. The human homolog of mouse Pou4f3, a member of the POU-domain family of transcription factors whose targeted inactivation causes profound deafness in mice, was physically mapped to the 25-centimorgan DFNA15-linked region. An 8-base pair deletion in the POU homeodomain of human POU4F3 was identified in Family H. A truncated protein presumably impairs high-affinity binding of this transcription factor in a dominant negative fashion, leading to progressive hearing loss.

Journal ArticleDOI
TL;DR: It is shown that ATM is a key regulator of multiple signaling cascades which respond to DNA strand breaks induced by damaging agents or by normal processes, such as meiotic or V(D)J recombination, which involve the activation of cell cycle checkpoints, DNA repair and apoptosis.
Abstract: The identification of ATM , the gene responsible for the pleiotropic recessive disease ataxia telangiectasia, has initiated extensive research to determine the functions of its multifaceted protein product. The ATM protein belongs to a family of protein kinases that share similarities at their C-terminal region with the catalytic domain of phosphatidylinositol 3-kinases. Studies with ataxia telangiectasia (A-T) cells and Atm-deficient mice have shown that ATM is a key regulator of multiple signaling cascades which respond to DNA strand breaks induced by damaging agents or by normal processes, such as meiotic or V(D)J recombination. These responses involve the activation of cell cycle checkpoints, DNA repair and apoptosis. Other roles outside the cell nucleus might be carried out by the cytoplasmic fraction of ATM. In addition, ATM appears to function as a 'caretaker', suppressing tumorigenesis in specific T cell lineages.

Journal ArticleDOI
TL;DR: In this paper, the authors consider absorbing layers that are extensions of the PML of Berenger (1994), which are constructed both for time problems and for Helmholtz-like equations.

Journal ArticleDOI
TL;DR: In this article, the authors compared seven different inverse approaches for identifying aquifer transmissivity and found that the linearized methods were more accurate than those of nonlinear methods in predicting travel times and travel paths.
Abstract: This paper describes the first major attempt to compare seven different inverse approaches for identifying aquifer transmissivity. The ultimate objective was to determine which of several geostatistical inverse techniques is better suited for making probabilistic forecasts of the potential transport of solutes in an aquifer where spatial variability and uncertainty in hydrogeologic properties are significant. Seven geostatistical methods (fast Fourier transform (FF), fractal simulation (FS), linearized cokriging (LC), linearized semianalytical )LS), maximum likelihood (ML), pilot point (PP), and sequential self-calibration (SS)) were compared on four synthetic data sets. Each data set had specific features meeting (or not) classical assumptions about stationarity, amenability to a geostatistical description, etc. The comparison of the outcome of the methods is based on the prediction of travel times and travel paths taken by conservative solutes migrating in the aquifer for a distance of 5 km. Four of the methods, LS, ML, PP, and SS, were identified as being approximately equivalent for the specific problems considered. The magnitude of the variance of the transmissivity fields, which went as high as 10 times the generally accepted range for linearized approaches, was not a problem for the linearized methods when applied to stationary fields; that is, their inverse solutions and travel time predictions were as accurate as those of the nonlinear methods. Nonstationarity of the “true” transmissivity field, or the presence of “anomalies” such as high-permeability fracture zones was, however, more of a problem for the linearized methods. The importance of the proper selection of the semivariogram of the log10 (T) field (or the ability of the method to optimize this variogram iteratively) was found to have a significant impact on the accuracy and precision of the travel time predictions. Use of additional transient information from pumping tests did not result in major changes in the outcome. While the methods differ in their underlying theory, and the codes developed to implement the theories were limited to varying degrees, the most important factor for achieving a successful solution was the time and experience devoted by the user of the method.

Journal ArticleDOI
TL;DR: A model is presented that postulates the role of the ER and cytoskeleton in targeting the MP and viral ribonucleoprotein from sites of virus synthesis to the plasmodesmata through which infection is spread.
Abstract: Tobacco mosaic virus (TMV) derivatives that encode movement protein (MP) as a fusion to the green fluorescent protein (MP:GFP) were used in combination with antibody staining to identify host cell components to which MP and replicase accumulate in cells of infected Nicotiana benthamiana leaves and in infected BY-2 protoplasts. MP:GFP and replicase colocalized to the endoplasmic reticulum (ER; especially the cortical ER) and were present in large, irregularly shaped, ER-derived structures that may represent "viral factories." The ER-derived structures required an intact cytoskeleton, and microtubules appeared to redistribute MP:GFP from these sites during late stages of infection. In leaves, MP:GFP accumulated in plasmodesmata, whereas in protoplasts, the MP:GFP was targeted to distinct, punctate sites near the plasma membrane. Treating protoplasts with cytochalasin D and brefeldin A at the time of inoculation prevented the accumulation of MP:GFP at these sites. It is proposed that the punctate sites anchor the cortical ER to plasma membrane and are related to sites at which plasmodesmata form in walled cells. Hairlike structures containing MP:GFP appeared on the surface of some of the infected protoplasts and are reminiscent of similar structures induced by other plant viruses. We present a model that postulates the role of the ER and cytoskeleton in targeting the MP and viral ribonucleoprotein from sites of virus synthesis to the plasmodesmata through which infection is spread.