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Showing papers by "California Institute of Technology published in 1994"


Journal ArticleDOI
K. Hagiwara, Ken Ichi Hikasa1, Koji Nakamura, Masaharu Tanabashi1, M. Aguilar-Benitez, Claude Amsler2, R. M. Barnett3, Patricia R. Burchat4, C. D. Carone5, C. Caso, G. Conforto6, Olav Dahl3, Michael Doser7, Semen Eidelman8, Jonathan L. Feng9, L. K. Gibbons10, Maury Goodman11, Christoph Grab12, D. E. Groom3, Atul Gurtu7, Atul Gurtu13, K. G. Hayes14, J. J. Herna`ndez-Rey15, K. Honscheid16, Christopher Kolda17, Michelangelo L. Mangano7, David Manley18, Aneesh V. Manohar19, John March-Russell7, Alberto Masoni, Ramon Miquel3, Klaus Mönig, Hitoshi Murayama3, Hitoshi Murayama20, S. Sánchez Navas12, Keith A. Olive21, Luc Pape7, C. Patrignani, A. Piepke22, Matts Roos23, John Terning24, Nils A. Tornqvist23, T. G. Trippe3, Petr Vogel25, C. G. Wohl3, Ron L. Workman26, W-M. Yao3, B. Armstrong3, P. S. Gee3, K. S. Lugovsky, S. B. Lugovsky, V. S. Lugovsky, Marina Artuso27, D. Asner28, K. S. Babu29, E. L. Barberio7, Marco Battaglia7, H. Bichsel30, O. Biebel31, Philippe Bloch7, Robert N. Cahn3, Ariella Cattai7, R. S. Chivukula32, R. Cousins33, G. A. Cowan34, Thibault Damour35, K. Desler, R. J. Donahue3, D. A. Edwards, Victor Daniel Elvira, Jens Erler36, V. V. Ezhela, A Fassò7, W. Fetscher12, Brian D. Fields37, B. Foster38, Daniel Froidevaux7, Masataka Fukugita39, Thomas K. Gaisser40, L. Garren, H.-J. Gerber12, Frederick J. Gilman41, Howard E. Haber42, C. A. Hagmann28, J.L. Hewett4, Ian Hinchliffe3, Craig J. Hogan30, G. Höhler43, P. Igo-Kemenes44, John David Jackson3, Kurtis F Johnson45, D. Karlen, B. Kayser, S. R. Klein3, Konrad Kleinknecht46, I.G. Knowles47, P. Kreitz4, Yu V. Kuyanov, R. Landua7, Paul Langacker36, L. S. Littenberg48, Alan D. Martin49, Tatsuya Nakada7, Tatsuya Nakada50, Meenakshi Narain32, Paolo Nason, John A. Peacock47, Helen R. Quinn4, Stuart Raby16, Georg G. Raffelt31, E. A. Razuvaev, B. Renk46, L. Rolandi7, Michael T Ronan3, L.J. Rosenberg51, Christopher T. Sachrajda52, A. I. Sanda53, Subir Sarkar54, Michael Schmitt55, O. Schneider50, Douglas Scott56, W. G. Seligman57, Michael H. Shaevitz57, Torbjörn Sjöstrand58, George F. Smoot3, Stefan M Spanier4, H. Spieler3, N. J. C. Spooner59, Mark Srednicki60, A. Stahl, Todor Stanev40, M. Suzuki3, N. P. Tkachenko, German Valencia61, K. van Bibber28, Manuella Vincter62, D. R. Ward63, Bryan R. Webber63, M R Whalley49, Lincoln Wolfenstein41, J. Womersley, C. L. Woody48, O. V. Zenin 
Tohoku University1, University of Zurich2, Lawrence Berkeley National Laboratory3, Stanford University4, College of William & Mary5, University of Urbino6, CERN7, Budker Institute of Nuclear Physics8, University of California, Irvine9, Cornell University10, Argonne National Laboratory11, ETH Zurich12, Tata Institute of Fundamental Research13, Hillsdale College14, Spanish National Research Council15, Ohio State University16, University of Notre Dame17, Kent State University18, University of California, San Diego19, University of California, Berkeley20, University of Minnesota21, University of Alabama22, University of Helsinki23, Los Alamos National Laboratory24, California Institute of Technology25, George Washington University26, Syracuse University27, Lawrence Livermore National Laboratory28, Oklahoma State University–Stillwater29, University of Washington30, Max Planck Society31, Boston University32, University of California, Los Angeles33, Royal Holloway, University of London34, Université Paris-Saclay35, University of Pennsylvania36, University of Illinois at Urbana–Champaign37, University of Bristol38, University of Tokyo39, University of Delaware40, Carnegie Mellon University41, University of California, Santa Cruz42, Karlsruhe Institute of Technology43, Heidelberg University44, Florida State University45, University of Mainz46, University of Edinburgh47, Brookhaven National Laboratory48, Durham University49, University of Lausanne50, Massachusetts Institute of Technology51, University of Southampton52, Nagoya University53, University of Oxford54, Northwestern University55, University of British Columbia56, Columbia University57, Lund University58, University of Sheffield59, University of California, Santa Barbara60, Iowa State University61, University of Alberta62, University of Cambridge63
TL;DR: This biennial Review summarizes much of Particle Physics using data from previous editions, plus 2205 new measurements from 667 papers, and features expanded coverage of CP violation in B mesons and of neutrino oscillations.
Abstract: This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 2205 new measurements from 667 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations. For the first time we cover searches for evidence of extra dimensions (both in the particle listings and in a new review). Another new review is on Grand Unified Theories. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.

5,143 citations


Journal ArticleDOI
TL;DR: In this article, a detailed derivation of the inertial range spectrum for the weak turbulence of shear Alfven waves is presented, where the authors restrict attention to the symmetric case where the oppositely directed waves carry equal energy fluxes and show that as energy cascades to high perpendicular wavenumbers, interactions become so strong that the assumption of weakness is no longer valid.
Abstract: We continue to investigate the possibility that interstellar turbulence is caused by nonlinear interactions among shear Alfven waves. Here, as in Paper I, we restrict attention to the symmetric case where the oppositely directed waves carry equal energy fluxes. This precludes application to the solar wind in which the outward flux significantly exceeds the ingoing one. All our detailed calculations are carried out for an incompressible magnetized fluid. In incompressible magnetohydrodynamics (MHD), nonlinear interactions only occur between oppositely direct waves. Paper I contains a detailed derivation of the inertial range spectrum for the weak turbulence of shear Alfven waves. As energy cascades to high perpendicular wavenumbers, interactions become so strong that the assumption of weakness is no longer valid. Here, we present a theory for the strong turbulence of shear Alfven waves. It has the following main characteristics. (1) The inertial-range energy spectrum exhibits a critical balance beween linear wave periods and nonlinear turnover timescales. (2) The "eddies" are elongated in the direction of the field on small spatial scales; the parallel and perpendicular components of the wave vector, k_z and k_⊥, are related by k_z ≈ k^(2/3) _⊥L^(-1/3), where L is the outer scale of the turbulence. (3) The "one-dimensional" energy spectrum is proportional to k^(-5/3) _⊥-an anisotropic Kolmogorov energy spectrum. Shear Alfvenic turbulence mixes specific entropy as a passive contaminant. This gives rise to an electron density power spectrum whose form mimics the energy spectrum of the turbulence. Radio, wave scattering by these electron density fluctuations produces anisotropic scatter-broadened images. Damping by ion-neutral collisions restricts Alfvenic turbulence to highly ionized regions of the interstellar medium. We expect negligible generation of compressive MHD waves by shear Alfven waves belonging to the critically balanced cascade. Viscous and collisionless damping are also unimportant in the interstellar medium (ISM). Our calculations support the general picture of interstellar turbulence advanced by Higdon.

2,248 citations


Journal ArticleDOI
TL;DR: This article corrects the article on p. 496 in vol.

1,986 citations


Journal ArticleDOI
TL;DR: In this article, structural features resulting from the interaction of a turbulent jet issuing transversely into a uniform stream are described with the help of flow visualization and hot-wire anemometry.
Abstract: Structural features resulting from the interaction of a turbulent jet issuing transversely into a uniform stream are described with the help of flow visualization and hot-wire anemometry. Jet-to-crossflow velocity ratios from 2 to 10 were investigated at crossflow Reynolds numbers from 3800 to 11400. In particular, the origin and formation of the vortices in the wake are described and shown to be fundamentally different from the well-known phenomenon of vortex shedding from solid bluff bodies. The flow around a transverse jet does not separate from the jet and does not shed vorticity into the wake. Instead, the wake vortices have their origins in the laminar boundary layer of the wall from which the jet issues. It is argued that the closed flow around the jet imposes an adverse pressure gradient on the wall, on the downstream lateral sides of the jet, provoking 'separation events’ in the wall boundary layer on each side. These result in eruptions of boundary-layer fluid and formation of wake vortices that are convected downstream. The measured wake Strouhal frequencies, which depend on the jet-crossflow velocity ratio, match the measured frequencies of the separation events. The wake structure is most orderly and the corresponding wake Strouhal number (0.13) is most sharply defined for velocity ratios near the value 4. Measured wake profiles show deficits of both momentum and total pressure.

1,186 citations


Journal ArticleDOI
TL;DR: This work investigates how accurately the distance to the source and the masses and spins of the two bodies will be measured from the inspiral gravitational wave signals by the three-detector LIGO-VIRGO network using ``advanced detectors'' (those present a few years after initial operation).
Abstract: The most promising source of gravitational waves for the planned kilometer-size laser-interferometer detectors LIGO and VIRGO are merging compact binaries, i.e., neutron-star--neutron-star (NS-NS), neutron-star--black-hole (NS-BH), and black-hole--black-hole (BH-BH) binaries. We investigate how accurately the distance to the source and the masses and spins of the two bodies will be measured from the inspiral gravitational wave signals by the three-detector LIGO-VIRGO network using ``advanced detectors'' (those present a few years after initial operation). The large number of cycles in the observable waveform increases our sensitivity to those parameters that affect the inspiral rate, and thereby the evolution of the waveform's phase. These parameters are thus measured much more accurately than parameters which affect the waveform's polarization or amplitude. To lowest order in a post-Newtonian expansion, the evolution of the waveform's phase depends only on the combination scrM\ensuremath{\equiv}(${\mathit{M}}_{1}$${\mathit{M}}_{2}$${)}^{3/5}$(${\mathit{M}}_{1}$+${\mathit{M}}_{2}$${)}^{\mathrm{\ensuremath{-}}1/5}$ of the masses ${\mathit{M}}_{1}$ and ${\mathit{M}}_{2}$ of the two bodies, which is known as the ``chirp mass.'' To post-1-Newtonian order, the waveform's phase also depends sensitively on the binary's reduced mass \ensuremath{\mu}\ensuremath{\equiv}${\mathit{M}}_{1}$${\mathit{M}}_{2}$/(${\mathit{M}}_{1}$+${\mathit{M}}_{2}$) allowing, in principle, a measurement of both ${\mathit{M}}_{1}$ and ${\mathit{M}}_{2}$ with high accuracy.We show that the principal obstruction to measuring ${\mathit{M}}_{1}$ and ${\mathit{M}}_{2}$ is the post-1.5-Newtonian effect of the bodies' spins on the waveform's phase, which can mimic the effects that allow \ensuremath{\mu} to be determined. The chirp mass is measurable with an accuracy \ensuremath{\Delta}scrM/scrM\ensuremath{\approxeq}0.1%--1%. Although this is a remarkably small error bar, it is \ensuremath{\sim}10 times larger than previous estimates of \ensuremath{\Delta}scrM/scrM which neglected post-Newtonian effects. The reduced mass is measurable to \ensuremath{\sim}10%--15% for NS-NS and NS-BH binaries, and \ensuremath{\sim}50% for BH-BH binaries (assuming 10${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ BH's). Measurements of the masses and spins are strongly correlated; there is a combination of \ensuremath{\mu} and the spin angular momenta that is measured to within \ensuremath{\sim}1%. Moreover, if both spins were somehow known to be small (\ensuremath{\lesssim}0.01${\mathit{M}}_{1}^{2}$ and \ensuremath{\lesssim}0.01${\mathit{M}}_{2}^{2}$, respectively), then \ensuremath{\mu} could be determined to within \ensuremath{\sim}1%. Finally, building on earlier work of Markovi\ifmmode \acute{c}\else \'{c}\fi{}, we derive an approximate, analytic expression for the accuracy \ensuremath{\Delta}D of mesurements of the distance D to the binary, for an arbitrary network of detectors. This expression is accurate to linear order in 1/\ensuremath{\rho}, where \ensuremath{\rho} is the signal-to-noise ratio. We also show that, contrary to previous expectations, contributions to \ensuremath{\Delta}D/D that are nonlinear in 1/\ensuremath{\rho} are significant, and we develop an approximation scheme for including the dominant of these nonlinear effects. Using a Monte Carlo simulation we estimate that distance measurement accuracies will be \ensuremath{\le}15% for \ensuremath{\sim}8% of the detected signals, and \ensuremath{\le}30% for \ensuremath{\sim}60% of the signals, for the LIGO-VIRGO three-detector network.

1,121 citations


Journal ArticleDOI
TL;DR: It is shown how this framework can handle standard issues such as the analysis of stability and performance with or without uncertainties in the plant model, and robustness issues are problems in their own right and hence not detailed here.

986 citations


Journal ArticleDOI
29 Jul 1994-Cell
TL;DR: The term homeosis dates from Bateson’s work (1894) on organismal variation, in which he expanded Masters’treatment (1889) of abnormal metamorphosis in plants to animals and introduced the term homoeosis as a replacement for the older term.

950 citations


Journal ArticleDOI
TL;DR: It is concluded that the PAC cloning system will be useful in the mapping and detailed analysis of complex genomes.
Abstract: We have designed a P1 vector (pCYPAC−1) for the introduction of recombinant DNA into E. coli using electroporation procedures. The new cloning system, P1−derived arteficial chromosomes (PACs), was used to establish an initial 15,000 clone library with an average insert size of 130−150 kilobase pairs (kb). No chimaerism has been observed in 34 clones, by fluorescence in situ hybridization. Similarly, no insert instability has been observed after extended culturing, for 20 clones. We conclude that the PAC cloning system will be useful in the mapping and detailed analysis of complex genomes.

873 citations


Book
01 Dec 1994
TL;DR: This publication explains how to use the GENESIS simulation/modeling software system available through the Internet file-server at the California Institute of Technology, Pasadena, California, USA.
Abstract: This publication explains how to use the GENESIS simulation/modeling software system available through the Internet file-server at the California Institute of Technology, Pasadena, California, USA. The first part of the book consists of edited contributions from an international team of neural networks researchers working with GENESIS. They show the user the kind of models/simulations which can be created by using the software. The second part is a step-by-step tutorial for all professionals, researchers and students working in the area of neural networks and the cognitive sciences.

815 citations


Journal ArticleDOI
TL;DR: This method, termed USPS (ubiquitin-based split-protein sensor), makes it possible to monitor a protein-protein interaction as a function of time, at the natural sites of this interaction in a living cell.
Abstract: We describe an assay for in vivo protein interactions. Protein fusions containing ubiquitin, a 76-residue, single-domain protein, are rapidly cleaved in vivo by ubiquitin-specific proteases, which recognize the folded conformation of ubiquitin. When a C-terminal fragment of ubiquitin (C(ub)) is expressed as a fusion to a reporter protein, the fusion is cleaved only if an N-terminal fragment of ubiquitin (Nub) is also expressed in the same cell. This reconstitution of native ubiquitin from its fragments, detectable by the in vivo cleavage assay, is not observed with a mutationally altered Nub. However, if C(ub) and the altered Nub are each linked to polypeptides that interact in vivo, the cleavage of the fusion containing C(ub) is restored, yielding a generally applicable assay for kinetic and equilibrium aspects of in vivo protein interactions. This method, termed USPS (ubiquitin-based split-protein sensor), makes it possible to monitor a protein-protein interaction as a function of time, at the natural sites of this interaction in a living cell.

800 citations


Journal ArticleDOI
TL;DR: In this article, the authors simulated the dehydration-melting of a natural, low-K, calcic amphibolite (67.4% hornblende, 32.5% anorthite) in piston-cylinder experiments at 10 kbar and 750-1000°C, for 1-9 days.
Abstract: We have simulated the dehydration-melting of a natural, low-K, calcic amphibolite (67.4% hornblende, 32.5% anorthite) in piston-cylinder experiments at 10 kbar and 750–1000°C, for 1–9 days. The solidus temperature is lower than 750°C; garnet appears at 850°C. The overall reaction is: Hb+P→L+Cpx+Al-Hb+Ca-Hb+Ga+Opx. Three stages of reaction are: (1) melting dominated by the growth of clinopyroxene and garnet, with little change in composition of liquid or garnet, (2) a reversal of this reaction between 875°C and 900°C, with decreases in the amounts of liquid and garnet, and (3) a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase. Garnet is enriched in pyrope and zoned from Fe-cores to Mg-edges (range ∼3 mol % pyrope); liquid composition is enriched first in An (to ∼950°C) and then in Ab. The liquids are more calcic and aluminous than natural tonalites, which is attributed to the plagioclase composition (An90). The formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite — not H2O-saturated conditions. The results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet-absent field (900–1000°C), but with a solidus backbend at ∼7–9 kbar, coincident with the garnet-in boundary. Hornblende breakdown due to garnet formation in a closed system must make H2O available for H2O-undersaturated melting right down to the H2O-saturated solidus, below 700°C, which defines a large low-temperature PT area where hydrous granitoid melts can be generated with residual garnet and hornblende.


Journal ArticleDOI
TL;DR: In this article, it was shown that most variations in composition among primitive basalts from the Mariana back-arc trough can be explained by melting mixtures of an NMORB-type mantle source and an H 2O-rich component, provided the degree of melting is positively and approximately linearly correlated with the proportion of the H 2 O-rich components in the mixture.

Journal ArticleDOI
TL;DR: The cloned PI gene is cloned and the time and places of its expression in developing flowers are determined, Surprisingly, the initial patterns of PI and AP3 expression are different.
Abstract: Mutations in the PISTILLATA (PI) gene of Arabidopsis thaliana cause homeotic conversion of petals to sepals and of stamens to carpels. It is thus classed as a B function floral homeotic gene and acts together with the product of the other known B function gene, APETALA3 (AP3). We have cloned PI and determined the time and places of its expression in developing flowers. Surprisingly, the initial patterns of PI and AP3 expression are different. By positive regulatory interactions between PI and AP3, later expression patterns are coincident or nearly coincident. The pattern of PI expression also depends on the activity of the floral development genes APETALA2 and SUPERMAN and on the activity of PI itself. The PI and APETALA3 proteins specifically associate in solution and so may act together in regulating PI and other genes.

Journal ArticleDOI
TL;DR: In this paper, a model for suspension flow is proposed in which macroscopic mass, momentum and energy balances are constructed and solved simultaneously, and the concept of the suspension temperature is introduced in order to provide a nonlocal description of suspension behaviour.
Abstract: Dynamic simulations of the pressure-driven flow in a channel of a non-Brownian suspension at zero Reynolds number were conducted using Stokesian Dynamics. The simulations are for a monolayer of identical particles as a function of the dimensionless channel width and the bulk particle concentration. Starting from a homogeneous dispersion, the particles gradually migrate towards the centre of the channel, resulting in an homogeneous concentration profile and a blunting of the particle velocity profile. The time for achieving steady state scales as (H/a)3a/[left angle bracket]u[right angle bracket], where H is the channel width, a the radii of the particles, and [left angle bracket]u[right angle bracket] the average suspension velocity in the channel. The concentration and velocity profiles determined from the simulations are in qualitative agreement with experiment. A model for suspension flow has been proposed in which macroscopic mass, momentum and energy balances are constructed and solved simultaneously. It is shown that the requirement that the suspension pressure be constant in directions perpendicular to the mean motion leads to particle migration and concentration variations in inhomogeneous flow. The concept of the suspension ‘temperature’ – a measure of the particle velocity fluctuations – is introduced in order to provide a nonlocal description of suspension behaviour. The results of this model for channel flow are in good agreement with the simulations.

Journal ArticleDOI
22 Jul 1994-Science
TL;DR: The first retroreflector array was placed on the moon by Apollo 11, enabling highly accurate measurements of the Earthmoon separation by means of laser ranging as discussed by the authors, which has been used for a broad range of investigations, including astronomy, lunar science, gravitational physics, geodesy, and geodynamics.
Abstract: On 21 July 1969, during the first manned lunar mission, Apollo 11, the first retroreflector array was placed on the moon, enabling highly accurate measurements of the Earthmoon separation by means of laser ranging. Lunar laser ranging (LLR) turns the Earthmoon system into a laboratory for a broad range of investigations, including astronomy, lunar science, gravitational physics, geodesy, and geodynamics. Contributions from LLR include the three-orders-of-magnitude improvement in accuracy in the lunar ephemeris, a several-orders-of-magnitude improvement in the measurement of the variations in the moon's rotation, and the verification of the principle of equivalence for massive bodies with unprecedented accuracy. Lunar laser ranging analysis has provided measurements of the Earth's precession, the moon's tidal acceleration, and lunar rotational dissipation. These scientific results, current technological developments, and prospects for the future are discussed here.

Journal ArticleDOI
23 Sep 1994-Science
TL;DR: Analysis of the Greenland ice core covering the period from 3000 to 500 years ago—the Greek, Roman, Medieval and Renaissance times— shows that lead is present at concentrations four times as great as natural values from about 2500 to 1700 years ago.
Abstract: Analysis of the Greenland ice core covering the period from 3000 to 500 years ago-the Greek, Roman, Medieval and Renaissance times-shows that lead is present at concentrations four times as great as natural values from about 2500 to 1700 years ago (500 B.C. to 300 A.D.). These results show that Greek and Roman lead and silver mining and smelting activities polluted the middle troposphere of the Northern Hemisphere on a hemispheric scale two millennia ago, long before the Industrial Revolution. Cumulative lead fallout to the Greenland Ice Sheet during these eight centuries was as high as 15 percent of that caused by the massive use of lead alkyl additives in gasoline since the 1930s. Pronounced lead pollution is also observed during Medieval and Renaissance times.

Proceedings ArticleDOI
29 Jun 1994
TL;DR: In this article, the authors address the robustness issue in MPC by directly incorporating the description of plant uncertainty in the MPC problem formulation, where the plant uncertainty is expressed in the time domain by allowing the state-space matrices of the discrete-time plant to be arbitrarily time-varying and belonging to a polytope.
Abstract: The primary disadvantage of current design techniques for model predictive control (MPC) is their inability to explicitly deal with model uncertainty. In this paper, the authors address the robustness issue in MPC by directly incorporating the description of plant uncertainty in the MPC problem formulation. The plant uncertainty is expressed in the time-domain by allowing the state-space matrices of the discrete-time plant to be arbitrarily time-varying and belonging to a polytope. The existence of a feedback control law minimizing an upper bound on the infinite horizon objective function and satisfying the input and output constraints is reduced to a convex optimization over linear matrix inequalities (LMIs). It is shown that for the plant uncertainty described by the polytope, the feasible receding horizon state feedback control design is robustly stabilizing.

Journal ArticleDOI
01 Oct 1994
TL;DR: A fast and exact planner for the mobile robot model, based upon recursive subdivision of a collision-free path generated by a lower-level geometric planner that ignores the motion constraints, is presented.
Abstract: This paper considers the problem of motion planning for a car-like robot (i.e., a mobile robot with a nonholonomic constraint whose turning radius is lower-bounded). We present a fast and exact planner for our mobile robot model, based upon recursive subdivision of a collision-free path generated by a lower-level geometric planner that ignores the motion constraints. The resultant trajectory is optimized to give a path that is of near-minimal length in its homotopy class. Our claims of high speed are supported by experimental results for implementations that assume a robot moving amid polygonal obstacles. The completeness and the complexity of the algorithm are proven using an appropriate metric in the configuration space R/sup 2//spl times/S/sup 1/ of the robot. This metric is defined by using the length of the shortest paths in the absence of obstacles as the distance between two configurations. We prove that the new induced topology and the classical one are the same. Although we concentrate upon the car-like robot, the generalization of these techniques leads to new theoretical issues involving sub-Riemannian geometry and to practical results for nonholonomic motion planning. >

Journal ArticleDOI
29 Jul 1994-Science
TL;DR: These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes and allow for predictions of structure-property relations of higher order hyperp polarizabilities.
Abstract: An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability α, the first hyperpolarizability β, and the second hyperpolarizability γ are seen to be derivatives, with respect to F, of their next lower order polarization (for α) or polarizability (for β and γ). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities.

Book ChapterDOI
TL;DR: This chapter attempts an interdisciplinary perspective to consider that that both molecular biologists and immunologists have learned about the V (D) J recombination process, as instructed by cross-species (and cross-locus) comparisons.
Abstract: Publisher Summary This chapter attempts an interdisciplinary perspective to consider that that both molecular biologists and immunologists have learned about the V (D) J recombination process, as instructed by cross-species (and cross-locus) comparisons. Immune recognition in vertebrates is based on the antigen receptors manufactured by B and T cells. The antigen-binding polypeptides within these multiunit conglomerates are encoded at the immunoglobulin (Ig) and T cell receptor (TCR) loci. Through the process called “V (D) J joining,” antigen receptor genes are constructed from multiply reiterated DNA segments in B and T cells. By this means, an enormous number of binding specificities can be generated in lymphoid cells from a relatively minimal amount of germline information. V (D) J rearrangement can culminate in the production of alternative or “nonstandard” junction products. Demonstrated nonstandard products can account for all theoretically possible signal end-to-coding end assortments. A picture emerges of V (D) J joining as an orderly process that is the sum of disorderly parts. Variability comes into play at a number of levels—namely, variable crossover sites, variable joining signals, variable strand exchange, variable degrees of reciprocity, and so forth. It is argued that the main tactic employed by other site-directed recombination systems is not in evidence for V (D) J joining.

Journal ArticleDOI
TL;DR: In this article, a thin layer of ~50 μm diamonds is placed above a layer of peridotite powder, and partial melt is extracted from the pore spaces between the diamonds and equilibrates diffusively with the residual peridotoite mineralogy.

Journal ArticleDOI
TL;DR: Steady-state planar spatial solitons are predicted for photorefractive materials when the diffraction of an optical beam is exactly compensated by nonlinear self-defocusing as mentioned in this paper.
Abstract: Steady-state dark (bright) planar spatial solitons are predicted for photorefractive materials when the diffraction of an optical beam is exactly compensated by nonlinear self-defocusing (focusing), due to the screening field set up around a dark notch (or a bright beam) in a photorefractive material to which an external field is applied. These screening solitons appear in steady state and differ from previously observed spatial solitons in their properties and physical origin.

Journal ArticleDOI
TL;DR: In this article, it was shown that the genus of a smooth 2-manifold can be characterized by the formula g = (d − 1)(d − 2)/2.
Abstract: 1. Statement of the result The genus of a smooth algebraic curve of degree d in CP is given by the formula g = (d − 1)(d − 2)/2. A conjecture sometimes attributed to Thom states that the genus of the algebraic curve is a lower bound for the genus of any smooth 2-manifold representing the same homology class. The conjecture has previously been proved for d ≤ 4 and for d = 6, and less sharp lower bounds for the genus are known for all degrees [5,6,7,10,14]. In this note we confirm the conjecture. Theorem 1. Let Σ be an oriented 2-manifold smoothly embedded in CP so as to represent the same homology class as an algebraic curve of degree d. Then the genus g of Σ satisfies g ≥ (d − 1)(d − 2)/2.

Journal ArticleDOI
01 Jun 1994
TL;DR: This paper presents novel and efficient kinematic modeling techniques for "hyper-redundant" robots based on a "backbone curve" that captures the robot's macroscopic geometric features and introduces a "modal" approach, in which a set of intrinsic backbone curve shape functions are restricted to a modal form.
Abstract: This paper presents novel and efficient kinematic modeling techniques for "hyper-redundant" robots. This approach is based on a "backbone curve" that captures the robot's macroscopic geometric features. The inverse kinematic, or "hyper-redundancy resolution," problem reduces to determining the time varying backbone curve behavior. To efficiently solve the inverse kinematics problem, the authors introduce a "modal" approach, in which a set of intrinsic backbone curve shape functions are restricted to a modal form. The singularities of the modal approach, modal non-degeneracy conditions, and modal switching are considered. For discretely segmented morphologies, the authors introduce "fitting" algorithms that determine the actuator displacements that cause the discrete manipulator to adhere to the backbone curve. These techniques are demonstrated with planar and spatial mechanism examples. They have also been implemented on a 30 degree-of-freedom robot prototype. >

Journal ArticleDOI
TL;DR: In this article, a boundary integral time integration method is presented for computing the motion of fluid interfaces with surface tension in two-dimensional, irrotational, and incompressible fluids.

Journal ArticleDOI
24 Nov 1994-Nature
TL;DR: A dimer of FcRn heterodimers observed in the co-crystals and in the crystals of F cRn alone2 could be involved in binding Fc, correlating with the 2:1 binding stoichiometry between Fc Rn and IgG and suggesting an unusual orientation of FCRn on the membrane.
Abstract: The neonatal Fc receptor (FcRn) transports maternal immunoglobulin G (IgG) to the bloodstream of the newborn. FcRn is structurally similar to class I major histocompatibility complex (MHC) molecules, despite differences in the ligands they bind (the Fc portion of IgG and antigenic peptides, respectively). A low-resolution crystal structure of the complex between FcRn and Fc localizes the binding site for Fc to the side of FcRn, distinct from the tops of the αl and α2 domains which serve as the peptide and T-cell receptor binding sites in class I molecules. FcRn binds to Fc at the interface between the Fc C_H2 and C_H3 domains, which contains several histidine residues that could account for the sharply pH-dependent FcRn/IgG interaction. A dimer of FcRn heterodimers observed in the co-crystals and in the crystals of FcRn alone could be involved in binding Fc, correlating with the 2:1 binding stoichiometry between FcRn and IgG (ref. 4) and suggesting an unusual orientation of FcRn on the membrane.

Journal ArticleDOI
06 May 1994-Cell
TL;DR: It is shown that glial growth factor (GGF), previously defined as a Schwann cell mitogen, strongly suppresses neuronal differentiation of rat neural crest stem cells while promoting or allowing glial differentiation.

Journal ArticleDOI
28 Jan 1994-Science
TL;DR: In this paper, the design strategies demonstrated in chromophores that when incorporated into poled-polymer electrooptic modulators exhibited significant enhancements in electro-optic coefficients relative to polymers containing the commonly used dye Disperse Red-1.
Abstract: Conjugated organic compounds with 3-phenyl-5-isoxazolone or N,N'-diethylthiobarbituric acid acceptors have large first molecular hyperpolarizabilities (β) in comparison with compounds with 4-nitrophenyl acceptors. For example, julolidinyl-(CH=CH)_3-CH=N,N'- diethylthiobarbituric acid, which has 12 atoms between the donor and acceptor, has a β(0) of 911 x 10^(-30) electrostatic units, whereas (CH_3)_2NC_6H_4,–(CH=CH)_4–C_6H_4NO_2, with 16 atoms between its donor and acceptor, has a β(0) of 133 x 10^(-30) electrostatic units. The design strategies demonstrated here have resulted in chromophores that when incorporated into poled-polymer electrooptic modulators exhibited significant enhancements in electrooptic coefficients relative to polymers containing the commonly used dye Disperse Red-1. Poled polymer devices based on these or related chromophores may ultimately lead to high-speed electrooptic switching elements with low drive-power requirements, suitable for telecommunications applications.

Journal ArticleDOI
TL;DR: The nucleotide sequence of the SSA3 and SSB2 genes are presented, completing the nucleotide sequences data for the yeast HSP70 family and indicate that the major eukaryotic H SP70 groups arose prior to the divergence of the earliest eukARYotes, roughly 2 billion years ago.
Abstract: Eukaryotic genomes encode multiple 70-kDa heat-shock proteins (HSP70s). The Saccharomyces cerevisiae HSP70 family is comprised of eight members. Here we present the nucleotide sequence of the SSA3 and SSB2 genes, completing the nucleotide sequence data for the yeast HSP70 family. We have analyzed these yeast sequences as well as 29 HSP70s from 24 additional eukaryotic and prokaryotic species. Comparison of the sequences demonstrates the extreme conservation of HSP70s; proteins from the most distantly related species share at least 45% identity and more than one-sixth of the amino acids are identical in the aligned region (567 amino acids) among all proteins analyzed. Phylogenetic trees constructed by two independent methods indicate that ancient molecular and cellular events have given rise to at least four monophyletic groups of eukaryotic HSP70 proteins. Each group of evolutionarily similar HSP70s shares a common intracellular localization and is presumed to be comprised of functional homologues; these include heat-shock proteins of the cytoplasm, endoplasmic reticulum, mitochondria, and chloroplasts. HSP70s localized in mitochondria and plastids are most similar to the DnaK HSP70 homologues in purple bacteria and cyanobacteria, respectively, which is consistent with the proposed prokaryotic origin of these organelles. The analyses indicate that the major eukaryotic HSP70 groups arose prior to the divergence of the earliest eukaryotes, roughly 2 billion years ago. In some cases, as exemplified by the SSA genes encoding the cytoplasmic HSP70s of S. cerevisiae, more recent duplication events have given rise to subfamilies within the major groups. The S. cerevisiae SSB proteins comprise a unique subfamily not identified in other species to date. This subfamily appears to have resulted from an ancient gene duplication that occurred at approximately the same time as the origin of the major eukaryotic HSP70 groups.