Showing papers by "Tel Aviv University published in 2000"

Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei

Abstract: Correlated variations in the line and continuum emission from active galactic nuclei (AGNs) can be used to determine the size and geometry of the broad emission-line regions (BLRs). We have spectro- photometrically monitored a well-de—ned sample of 28 Palomar-Green quasars in order to obtain mea- surements of their BLRs and to investigate the relationships between quasar luminosity, central black hole mass, and BLR size in AGNs. Spectrophotometry was obtained every 1¨4 months for 7.5 yr, yield- ing 20¨70 observing epochs per object. Both the continuum and emission-line —uxes of all of the quasars were observed to change during the duration of the observing program. Seventeen of the 28 objects were observed with adequate sampling independent observing epochs) to search for correlated variations (Z20 between the Balmer emission lines and the continuum —ux. For each of these 17 objects, a signi—cant correlation was observed, with the Balmer-line variations lagging those of the continuum by D100 days (rest frame). Our work increases the available luminosity range for studying the size-mass-luminosity relations in AGNs by 2 orders of magnitude and doubles the number of objects suitable for such studies. Combining our results with comparable published data available for Seyfert 1 galaxies, we —nd the BLR size scales with the rest-frame 5100 luminosity as L0.70B0.03. This determination of the scaling of the Ae size of the BLR as a function of luminosity is signi—cantly diUerent from those previously published and suggests that the eUective ionization parameter in AGNs may be a decreasing function of luminosity. We are also able to constrain, subject to our assumption that gravity dominates the motions of the BLR gas, the scaling relationship between the mass of the central black holes and the luminosity in AGNs. We —nd that the central mass scales with 5100 luminosity as M P L0.5B0.1. This is inconsistent with all Ae AGNs having optical luminosity that is a constant fraction of the Eddington luminosity. Subject headings: galaxies: activequasars: emission linesquasars: general

Y chromosome sequence variation and the history of human populations

Abstract: Binary polymorphisms associated with the non-recombining region of the human Y chromosome (NRY) preserve the paternal genetic legacy of our species that has persisted to the present, permitting inference of human evolution, population affinity and demographic history 1 . We used denaturing highperformance liquid chromatography (DHPLC; ref. 2) to identify 160 of the 166 bi-allelic and 1 tri-allelic site that formed a parsimonious genealogy of 116 haplotypes, several of which display distinct population affinities based on the analysis of 1062 globally representative individuals. A minority of contemporary East Africans and Khoisan represent the descendants of the most ancestral patrilineages of anatomically modern humans that left Africa between 35,000 and 89,000 years ago.

The neurology of syntax: language use without Broca's area.

Abstract: A new view of the functional role of the left anterior cortex in language use is proposed. The experimental record indicates that most human linguistic abilities are not localized in this region. In particular, most of syntax (long thought to be there) is not located in Broca's area and its vicinity (operculum, insula, and subjacent white matter). This cerebral region, implicated in Broca's aphasia, does have a role in syntactic processing, but a highly specific one: It is the neural home to receptive mechanisms involved in the computation of the relation between transformationally moved phrasal constituents and their extraction sites (in line with the Trace-Deletion Hy- pothesis). It is also involved in the construction of higher parts of the syntactic tree in speech production. By contrast, basic combinato- rial capacities necessary for language processing - for example, structure-building operations, lexical insertion - are not supported by the neural tissue of this cerebral region, nor is lexical or combinatorial semantics. The dense body of empirical evidence supporting this restrictive view comes mainly from several angles on lesion studies of syntax in agrammatic Broca's aphasia. Five empirical arguments are presented: experiments in sentence comprehension, cross-linguistic consid- erations (where aphasia findings from several language types are pooled and scrutinized comparatively), grammaticality and plausibility judgments, real-time processing of complex sentences, and rehabilitation. Also discussed are recent results from functional neuroimag- ing and from structured observations on speech production of Broca's aphasics. Syntactic abilities are nonetheless distinct from other cognitive skills and are represented entirely and exclusively in the left cerebral hemisphere. Although more widespread in the left hemisphere than previously thought, they are clearly distinct from other human com- binatorial and intellectual abilities. The neurological record (based on functional imaging, split-brain and right-hemisphere-damaged patients, as well as patients suffering from a breakdown of mathematical skills) indicates that language is a distinct, modularly organized neurological entity. Combinatorial aspects of the language faculty reside in the human left cerebral hemisphere, but only the transfor- mational component (or algorithms that implement it in use) is located in and around Broca's area.

Market Value and Patent Citations: A First Look

Abstract: As patent data become more available in machine-readable form, an increasing number of researchers have begun to use measures based on patents and their citations as indicators of technological output and information flow. This paper explores the economic meaning of these citation-based patent measures using the financial market valuation of the firms that own the patents. Using a new and comprehensive dataset containing over 4800 U. S. Manufacturing firms and their patenting activity for the past 30 years, we explore the contributions of R&D spending, patents, and citation-weighted patents to measures of Tobin's Q for the firms. We find that citation-weighted patent stocks are more highly correlated with market value than patent stocks themselves and that this fact is due mainly to the high valuation placed on firms that hold very highly cited patents.

Pancreatic and duodenal homeobox gene 1 induces expression of insulin genes in liver and ameliorates streptozotocin-induced hyperglycemia.

Abstract: Insulin gene expression is restricted to islet β cells of the mammalian pancreas through specific control mechanisms mediated in part by specific transcription factors1,2. The protein encoded by the pancreatic and duodenal homeobox gene 1 (PDX-1) is central in regulating pancreatic development and islet cell function3. PDX-1 regulates insulin gene expression and is involved in islet cell-specific expression of various genes4,5,6,7. Involvement of PDX-1 in islet-cell differentiation and function has been demonstrated mainly by ‘loss-of-function’ studies8,9,10,11. We used a ‘gain-of-function’ approach to test whether PDX-1 could endow a non-islet tissue with pancreatic β-cell characteristics in vivo. Recombinant-adenovirus-mediated gene transfer of PDX-1 to the livers of BALB/C and C57BL/6 mice activated expression of the endogenous, otherwise silent, genes for mouse insulin 1 and 2 and prohormone convertase 1/3 (PC 1/3). Expression of PDX-1 resulted in a substantial increase in hepatic immunoreactive insulin content and an increase of 300% in plasma immunoreactive insulin levels, compared with that in mice treated with control adenovirus. Hepatic immunoreactive insulin induced by PDX-1 was processed to mature mouse insulin 1 and 2 and was biologically active; it ameliorated hyperglycemia in diabetic mice treated with streptozotocin. These data indicate the capacity of PDX-1 to reprogram extrapancreatic tissue towards a β-cell phenotype, may provide a valuable approach for generating ‘self’ surrogate β cells, suitable for replacing impaired islet-cell function in diabetics.

Efficient presentation of exogenous antigen by liver endothelial cells to CD8+ T cells results in antigen-specific T-cell tolerance.

Abstract: Myeloid antigen-presenting cells (APC) are known to cross-present exogenous antigen on major histocompatibility class I molecules to CD8+ T cells and thereby induce protective immunity against infecting microorganisms. Here we report that liver sinusoidal endothelial cells (LSEC) are organ-resident, non-myeloid APC capable of cross-presenting soluble exogenous antigen to CD8+ T cells. Though LSEC employ similar molecular mechanisms for cross-presentation as dendritic cells, the outcome of cross-presentation by LSEC is CD8+ T cell tolerance rather than immunity. As uptake of circulating antigens into LSEC occurs efficiently in vivo, it is likely that cross-presentation by LSEC contributes to CD8+ T cell tolerance observed in situations where soluble antigen is present in the circulation.

From continuous time random walks to the fractional fokker-planck equation

Abstract: We generalize the continuous time random walk (CTRW) to include the effect of space dependent jump probabilities. When the mean waiting time diverges we derive a fractional Fokker-Planck equation (FFPE). This equation describes anomalous diffusion in an external force field and close to thermal equilibrium. We discuss the domain of validity of the fractional kinetic equation. For the force free case we compare between the CTRW solution and that of the FFPE.

Genome-wide, large-scale production of mutant mice by ENU mutagenesis

Abstract: In the post-genome era, the mouse will have a major role as a model system for functional genome analysis. This requires a large number of mutants similar to the collections available from other model organisms such as Drosophila melanogaster and Caenorhabditis elegans. Here we report on a systematic, genome-wide, mutagenesis screen in mice. As part of the German Human Genome Project, we have undertaken a large-scale ENU-mutagenesis screen for dominant mutations and a limited screen for recessive mutations1. In screening over 14,000 mice for a large number of clinically relevant parameters, we recovered 182 mouse mutants for a variety of phenotypes. In addition, 247 variant mouse mutants are currently in genetic confirmation testing and will result in additional new mutant lines. This mutagenesis screen, along with the screen described in the accompanying paper2, leads to a significant increase in the number of mouse models3 available to the scientific community. Our mutant lines are freely accessible to non-commercial users (for information, see http://www.gsf.de/ieg/groups/enu-mouse.html ).

When the Underwriter Is the Market Maker: An Examination of Trading in the IPO Aftermarket

Abstract: This paper examines aftermarket trading of underwriters and unaffiliated market makers in the three-month period after an IPO. We find that the lead underwriter is always the dominant market maker; he takes substantial inventory positions in the aftermarket trading, and co-managers play a negligible role in aftermarket trading. The lead underwriter engages in stabilization activity for less successful IPOs, and uses the overallotment option to reduce his inventory risk. Compensation to the underwriter arises primarily from fees, but aftermarket trading does generate positive profits, which are positively related to the degree of underpricing.

As-rigid-as-possible shape interpolation

Abstract: We present an object-space morphing technique that blends the interiors of given two- or three-dimensional shapes rather than their boundaries. The morph is rigid in the sense that local volumes are least-distorting as they vary from their source to target configurations. Given a boundary vertex correspondence, the source and target shapes are decomposed into isomorphic simplicial complexes. For the simplicial complexes, we find a closed-form expression allocating the paths of both boundary and interior vertices from source to target locations as a function of time. Key points are the identification of the optimal simplex morphing and the appropriate definition of an error functional whose minimization defines the paths of the vertices. Each pair of corresponding simplices defines an affine transformation, which is factored into a rotation and a stretching transformation. These local transformations are naturally interpolated over time and serve as the basis for composing a global coherent least-distorting transformation.

From Intractable Conflict Through Conflict Resolution To Reconciliation: Psychological Analysis

Abstract: Intractable intergroup conflicts require the formation of a conflictive ethos that enables a society to adapt to the conflict situation, survive the stressful period, and struggle successfully with the adversary. The formal termination of such a conflict begins with the elimination of the perceived incompatibility between the opposing parties through negotiation by their representatives—that is, a conflict resolution process. But this is only part of the long-term reconciliation process, which requires the formation of peaceful relations based on mutual trust and acceptance, cooperation, and consideration of mutual needs. The psychological aspect of reconciliation requires a change in the conflictive ethos, especially with respect to societal beliefs about group goals, about the adversary group, about the ingroup, about intergroup relations, and about the nature of peace. In essence, psychological reconciliation requires the formation of an ethos of peace, but this is extremely difficult in cases of intractable conflict. Political psychologists can and should work to improve the state of knowledge about reconciliation, which until now has received much less attention than conflict resolution. Conflicts are a natural part of human interaction. People in conflicts, whether at the individual or group level, perceive that their goals or interests are contradicted by the goals or interests of the other party (Kriesberg, 1998a; Mitchell, 1981; Rubin, Pruitt, & Kim, 1994). When we focus on intergroup conflicts, they concern contradictory, concrete goals in the domains of territories, resources, trade, selfdetermination, religious rights, cultural values, and so on. But a conflict becomes a reality for society members 1 only when a particular situation is identified as

On an optimal control problem of train operation

Abstract: This paper examines the operation of a train on a variable grade profile subject to arbitrary speed restrictions. The purpose of the study is to determine a detailed program for traction and brake applications, which minimizes energy consumption in moving the train along a given route for a given time. Stated in the form of optimal control, this problem is solved by constructing a numerical algorithm which essentially exploits analytical properties of the optimal solution obtained from the maximum principle analysis. Due to its analytical origin, the algorithm has inherent accuracy and adequate quick-operation that are demonstrated in numerical examples.

Functional link between ataxia-telangiectasia and Nijmegen breakage syndrome gene products

Abstract: Ataxia-telangiectasia (A-T) and Nijmegen breakage syndrome (NBS) are recessive genetic disorders with susceptibility to cancer and similar cellular phenotypes1. The protein product of the gene responsible for A-T, designated ATM, is a member of a family of kinases characterized by a carboxy-terminal phosphatidylinositol 3-kinase-like domain2,3. The NBS1 protein is specifically mutated in patients with Nijmegen breakage syndrome and forms a complex with the DNA repair proteins Rad50 and Mre114,5,6,7. Here we show that phosphorylation of NBS1, induced by ionizing radiation, requires catalytically active ATM. Complexes containing ATM and NBS1 exist in vivo in both untreated cells and cells treated with ionizing radiation. We have identified two residues of NBS1, Ser 278 and Ser 343 that are phosphorylated in vitro by ATM and whose modification in vivo is essential for the cellular response to DNA damage. This response includes S-phase checkpoint activation, formation of the NBS1/Mre11/Rad50 nuclear foci and rescue of hypersensitivity to ionizing radiation. Together, these results demonstrate a biochemical link between cell-cycle checkpoints activated by DNA damage and DNA repair in two genetic diseases with overlapping phenotypes.

Representation and simulation of biochemical processes using the pi-calculus process algebra.

Abstract: Despite the rapidly accumulating body of knowledge about protein networks, there is currently no convenient way of sharing and manipulation of such information. We suggest that a formal computer language for describing the biomolecular processes underlying protein networks is essential for rapid advancement in this field. We propose to model biomolecular processes by using the pi-Calculus, a process algebra, originally developed for describing computer processes. Our model for biochemical processes is mathematically well-defined, while remaining biologically faithful and transparent. It is amenable to computer simulation, analysis and formal verification. We have developed a computer simulation system, the PiFCP, for execution and analysis of pi-calculus programs. The system allows us to trace, debug and monitor the behavior of biochemical networks under various manipulations. We present a pi-calculus model for the RTK-MAPK signal transduction pathway, formally represent detailed molecular and biochemical information, and study it by various PiFCP simulations.

Financial Packaging of IPO Firms in China

Abstract: This paper examines the earnings patterns of initial public offering (IPO) firms in China to shed light on the role of earnings management in the "financial packaging" of Chinese state-owned enterprises (SOEs) for public listing. We base our analysis on the case of B-Shares and H-Shares in China, two types of securities that now allow foreign investors to buy shares in SOEs previously wholly owned by the state. These IPOs mark the beginning of the stock market in China and signify an important step of Chinese economic reform. We examine the pre- and post-IPO earnings patterns for the entire sample, and separately for firms in protected vs. unprotected industries and for B-Shares vs. H-Shares. We find a statistically significant post-issue earnings decline for unprotected industry firms. This earnings decline is most significant for unprotected B-Share firms, and marginally significant for protected B-Share and unprotected H-Share firms, but not significant for protected H-Share firms. In addition, we find some evidence that the accounting accruals of sample firms in unprotected industries decline whereas their cash flows from operations increase after the IPO. Taken together, earnings management in the process of financial packaging seems to depend on the firm's relationship with the central government and on where the securities are listed. The evidence also suggests that the SOEs in unprotected industries may manage accounting accruals to boost earnings and/or list those business units with temporarily high profits resulting from high accounting accruals during the process of financial packaging.

The Information Value of Bond Ratings

Abstract: We test whether bond ratings contain pricing-relevant information by examining security price reactions to Moody’s refinement of its rating system, which was not accompanied by any fundamental change in issuers’ risks, was not preceded by any announcement, and was carried simultaneously for all bonds. We find that rating information does not affect firm value, but that debt value increases ~decreases! and equity value falls ~rises! when Moody’s announces better- ~worse-! thanexpected ratings. We also find that when Moody’s announces better- ~worse-! thanexpected ratings, the volatilities implied by prices of options on the fine-rated issuers’ shares decline ~rise!. VIRTUALLY ALL LARGE CORPORATE BOND ISSUES are rated by at least one rating agency. These ratings are costly: $25,000 for issues of up to $500 million and half a basis point of the issued amount for issues exceeding $500 million. Interestingly, although bonds are rated whether the issuer pays for the rating or not, about 98 percent of the issuers choose to pay to have their bonds rated. Why do corporations pay for ratings? Perhaps to gain better ratings. However, this is inconsistent with raters’ income being so crucially dependent on their reputation. Alternatively, paying for ratings may allow firms to incorporate inside information into the assigned ratings without disclosing specific details to the public at large. Publicly revealing inside information might benefit competitors or subject insiders to lawsuits should the projections not materialize, whereas rating agencies can incorporate privately disclosed information into the ratings that they assign without fully revealing it. Indeed, during the rating process, corporations provide raters with detailed inside information ~e.g., five-year forecasts and pro-forma statements, internal reports!. 1

Boundary value problems for fractional diffusion equations

Abstract: The fractional diffusion equation is solved for different boundary value problems, these being absorbing and reflecting boundaries in half-space and in a box. Thereby, the method of images and the Fourier–Laplace transformation technique are employed. The separation of variables is studied for a fractional diffusion equation with a potential term, describing a generalisation of an escape problem through a fluctuating bottleneck. The results lead to a further understanding of the fractional framework in the description of complex systems which exhibit anomalous diffusion.

Risk Sharing and Industrial Specialization: Regional and International Evidence

Abstract: We provide empirical evidence that risk sharing enhances specialization in production. First, we calculate an index of specialization for each of the European Community (EC) and non-EC OECD countries, U.S. states, Canadian provinces, Japanese prefectures, Latin American countries, and regions of Italy, Spain, and the United Kingdom. Then, we estimate the degree of capital market integration (risk sharing) within each of these groups of regions. Finally, we perform a regression of the specialization index on the degree of risk sharing, controlling for relevant economic variables and find a positive relation between the degree of specialization and the amount of risk sharing within a group. Instrumental variables regressions confirm that risk sharing is a causal determinant of specialization.

Self-organization in systems of self-propelled particles.

Abstract: We investigate a discrete model consisting of self-propelled particles that obey simple interaction rules. We show that this model can self-organize and exhibit coherent localized solutions in one- and in two-dimensions. In one-dimension, the self-organized solution is a localized flock of finite extent in which the density abruptly drops to zero at the edges. In two-dimensions, we focus on the vortex solution in which the particles rotate around a common center and show that this solution can be obtained from random initial conditions, even in the absence of a confining boundary. Furthermore, we develop a continuum version of our discrete model and demonstrate that the agreement between the discrete and the continuum model is excellent.

The Cradle of Agriculture

Abstract: It has long been debated exactly where and when crops were first domesticated and farming began--events that directly contributed to the emergence of Western civilization. In their Perspective, Lev-Yadun and colleagues discuss botanical, genetic and archeological evidence suggesting that the cradle of agriculture lay within a small region of the Fertile Crescent (in what is now southeastern Turkey/ northern Syria) and began in the 7th millennium B.C.

Isospecific Living Polymerization of 1-Hexene by a Readily Available Nonmetallocene C2-Symmetrical Zirconium Catalyst

Abstract: The search for newR-olefin polymerization catalysts based on transition metal complexes is a field of major interest involving many academic and industrial research groups. The ligands surrounding the metal play a crucial role in determining the activity as well as the stereospecifity of the catalyst, by affecting the steric and electronic properties at the metal. Over the last two decades, this field has been dominated by the metallocene complexes of group IV metals. Especially, ansa-metallocenes of C2 symmetry were found to induce isospecificity in the resulting polymers. 1 Recently, there has been a growing interest in the development ofnon-cyclopentadienyl ligands for the polymerization of R-olefins.2 Most attention was drawn to chelating di(amido) ligands, 3 some of whose group IV transition metal complexes induce polymerization in a liVing manner, 3a-c whereas chelating di(alkoxo) ligands 4 drew a more limited attention. The number of nonmetallocene systems, which were found to induce tacticity in the resulting polymer, is, however, quite small. 5 In this communication we introduce a novel family of di(alkoxo) complexes, one member of which is the first nonmetallocene C2symmetrical complex, which, upon activation, leads to a highly isospecific living polymerization of 1-hexene. Recently, we introduced the amine bis(phenolate) family of ligands to group IV transition metals. 6 We found that the presence of an extra donor group on a sidearm leads to octahedral LigMX 2type complexes, in which the two labile X groups are forced into a cis geometry. 6a Catalysts derived from these complexes (e.g. 1a) lead to highly reactive 1-hexene polymerization catalysts. 6b The Cs-symmetry of1a allows olefin approach from the two possible directions in each active position without preference, thus the polymer obtained is atactic. Therefore, we aimed at complexes of a different symmetry which may induce tactic polymerization, that incorporate ligands having similar functional groups yet having a different connectivity. Our approach is based on replacing the “branched” mode of connectivity of donor atoms with a sequential connectivity mode, namely diamine bis(phenolate) ligands. This new family of dianionic tetradentate chelating ligands is easily synthesized by a one-pot Mannich condensation between readily available di(secondary) amines, formaldehyde, and substituted phenols as demonstrated in eq 2. 2, a structural isomer