Comment on Transverse Mass Dependence of Partonic Dilepton Production in Ultra-Relativistic Heavy Ion Collisions

Comment on scale breaking effects in dilepton emission from partons during the early stage of ultra-relativistic heavy ion collisionsComment: 6 pages, RevTe

Comment on: "Transverse-Mass M⊥M_\perp Dependence of Dilepton Emission from Preequilibrium and Quark-Gluon Plasma in High Energy Nucleus-Nucleus Collisions"

In a recent Letter, Geiger presents calculations of the dilepton emission from the early stage of ultrarelativistic heavy ion collisions using the parton cascade model (PCM). He shows that the $M_\perp$ scaling is not observed. In this Comment, we point out that this is largely due to a defect in the PCM.Comment: 3 pages, LaTex, LBL-3526

Two new Miocene limpets (Fissurellidae) from southern California, with notes on other fossil occurrences of the family in northwestern North America

Two new fissurellid limpets (Mollusca: Gastropoda: Fissurellidae), Fissurella? stantoni n. sp. and Scelidotoma aldersoni n. sp., are described from Miocene deposits in southern California. Fissurella? stantoni is described from a single specimen from the middle Miocene Topanga Canyon Formation in the Santa Monica Mountains, Los Angeles County, California. Scelidotoma aldersoni is described from two specimens, one from the middle Miocene Topanga Canyon Formation, and another provisionally (cf.) identified specimen of an internal mold from the middle Miocene “Vaqueros” Formation on Santa Cruz Island, Santa Barbara County, southern California. Other unreported fossil occurrences of Scelidotoma are a juvenile specimen attributed only to genus collected in the middle Eocene Crescent Formation in Washington state and S. bella from the Pliocene part of the San Diego Formation, San Diego County, California. The Scelidotoma occurrences extend the chronostratigraphic range of S. bella from the Holocene (living) to the middle Pliocene, and the range of the genus back to the middle Eocene

Parton cascade description of relativistic heavy-ion collisions at CERN SPS energies ?

We examine Pb+Pb collisions at CERN SPS energy 158 A GeV, by employing the earlier developed and recently refined parton-cascade/cluster-hadronization model and its Monte Carlo implementation. This space-time model involves the dynamical interplay of perturbative QCD parton production and evolution, with non-perturbative parton-cluster formation and hadron production through cluster decays. Using computer simulations, we are able to follow the entwined time-evolution of parton and hadron degrees of freedom in both position and momentum space, from the instant of nuclear overlap to the final yield of particles. We present and discuss results for the multiplicity distributions, which agree well with the measured data from the CERN SPS, including those for K mesons. The transverse momentum distributions of the produced hadrons are also found to be in good agreement with the preliminary data measured by the NA49 and the WA98 collaboration for the collision of lead nuclei at the CERN SPS. The analysis of the time evolution of transverse energy deposited in the collision zone and the energy density suggests an existence of partonic matter for a time of more than 5 fm.Comment: 16 pages including 7 postscript figure

Flash of photons from the early stage of heavy-ion collisions

The dynamics of partonic cascades may be an important aspect for particle production in relativistic collisions of nuclei at CERN SPS and BNL RHIC energies. Within the Parton-Cascade Model, we estimate the production of single photons from such cascades due to scattering of quarks and gluons q g -> q gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter QED branching process plays the dominant role for photon production, similarly as the QCD branchings q -> q g and g -> g g play a crucial role for parton multiplication. We conclude therefore that photons accompanying the parton cascade evolution during the early stage of heavy-ion collisions shed light on the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure

Reflection and interference of electromagnetic waves in inhomogeneous media

Solutions were obtained of the wave equation for a plane horizontally polarized electro-magnetic wave incident on a semi infinite two dimensional inhomogeneous medium. Two problems were considered: An inhomogeneous half space, and an inhomogeneous layer of arbitrary thickness. Solutions of the wave equation were obtained in terms of Hankel functions with complex arguments. Numerical calculations were made of the reflection coefficient R at the interface of the homogeneous medium. The startling results show that the reflection coefficient for a complex dielectric constant with gradient, can be less than that of the same medium with zero gradient

Semantic Visual Localization

Robust visual localization under a wide range of viewing conditions is a fundamental problem in computer vision. Handling the difficult cases of this problem is not only very challenging but also of high practical relevance, e.g., in the context of life-long localization for augmented reality or autonomous robots. In this paper, we propose a novel approach based on a joint 3D geometric and semantic understanding of the world, enabling it to succeed under conditions where previous approaches failed. Our method leverages a novel generative model for descriptor learning, trained on semantic scene completion as an auxiliary task. The resulting 3D descriptors are robust to missing observations by encoding high-level 3D geometric and semantic information. Experiments on several challenging large-scale localization datasets demonstrate reliable localization under extreme viewpoint, illumination, and geometry changes

Intelligent redundant actuation system requirements and preliminary system design

Several redundant actuation system configurations were designed and demonstrated to satisfy the stringent operational requirements of advanced flight control systems. However, this has been accomplished largely through brute force hardware redundancy, resulting in significantly increased computational requirements on the flight control computers which perform the failure analysis and reconfiguration management. Modern technology now provides powerful, low-cost microprocessors which are effective in performing failure isolation and configuration management at the local actuator level. One such concept, called an Intelligent Redundant Actuation System (IRAS), significantly reduces the flight control computer requirements and performs the local tasks more comprehensively than previously feasible. The requirements and preliminary design of an experimental laboratory system capable of demonstrating the concept and sufficiently flexible to explore a variety of configurations are discussed

Optimisation of DSF and SOA based phase conjugators by incorporating noise-suppressing fibre gratings

We compare the performance of dispersion-shifted-fibre (DSF) and semiconductor-optical-amplifier (SOA) based phase conjugators for a 10 Gb/s non-return-to-zero system with respect to conversion efficiency, noise figure and distortion. Fibre gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF based conjugator has the advantage of distortion tolerance at higher input power. Introduction: Optical phase conjugation has attracted much recent research attention due to its potential application for group-velocity-dispersion and self-phase-modulation compensation in mid-point spectral inversion (MPSI) systems, and also for coherent wavelength conversion in optical switching and routing. The two most promising optical phase conjugation techniques are four-wave mixing (FWM) in either dispersion-shifted fibre (DSF), or semiconductor optical amplifiers (SOA). A DSF based conjugator requires phase matching close to its zero dispersion wavelength for efficient four-wave mixing. This restricts its wavelength flexibility compared to an SOA based conjugator which offers a much wider conversion bandwidth. Furthermore, the low FWM conversion efficiency in passive DSF seems to make the SOA a preferred phase conjugating medium. However, in a practical communication system, conjugation optical signal-to-noise ratio (SNR) is more important than conversion efficiency. The noise at the conjugate wavelength is usually dominated by the amplified spontaneous emission (ASE) noise from the pump and signal. The reduction of this noise has been demonstrated in an SOA based conjugator (i) by bandpass filtering of the pump and/or signal waves before mixing, and (ii) by the insertion of a notch filter at the conjugate wavelength before the conjugator. In this letter, SOA and DSF based conjugators are compared by investigating the conversion efficiency, noise and eye opening in a 10 Gb/s non-return-to-zero (NRZ) externally-modulated system, using an identical filtering network. We report for the first time the use of fibre gratings for efficient ASE noise filtering and conjugate signal extraction. The performance enhancement using these noise-suppressing gratings is also investigated

L'Avenir de la philosophie

S'il est un point que les réflexions contemporaines sur le temps ont mis en relief et inscrit profondément dans notre conscience, c'est que l'avenir qu'on espère dépend directement du présent qu'on réalise. Telle est notre attitude en face du présent, telle elle sera inéluctablement en face de l'avenir; et donc l'avenir lui-même, puisque ce dernier n'est rien sinon un présent caché encore, au cœur d'un présent déjà actuel, et explicite. Il est en effet de l'essence même de notre condition humaine d'avoir un présent structuré et comme stratifié. Certes on peut imaginer le présent comme un point sans épaisseur, comme la limite évanescente entre un segment de ligne qui marque le passé à jamais révolu, et l'avenir qui se meut vers nous pour basculer inexorablement vers le non-être en franchissant ce présent. Mais cette image, utile pour bien des tâches, ne correspond d'aucune manière à la réalité vivante de la conscience humaine et des activités qui lui sont propres. Nous sommes dans le présent ce que nous sommes et ce que, en un sens, nous croyons pouvoir dire que nous avons été. Une grande partie de ce que nous appelons le passé, notre passé personnel et sans doute notre passé spécifique, est présent, non seulement à titre de souvenir, pouvant être, ou non, évoqué, mais à titre de schéma dynamique modifiant notre être-au-monde, notre présente réaction au réel le plus réel, à la situation où nous avons à déployer notre activit