Consequences of t-channel unitarity for the interaction of real and virtual photons at high energies

We analyze the consequences of t-channel unitarity for photon cross sections and show what assumptions are necessary to allow for the existence of new singularities at $Q^{2}=0$ for the $\gamma p$ and $\gamma \gamma$ total cross sections. For virtual photons, such singularities can in general be present, but we show that, apart from the perturbative singularity associated with $\gamma ^{*}\gamma ^{*}\to q\bar q$, no new ingredient is needed to reproduce the data from LEP and HERA, in the Regge region.Comment: 10 pages, LaTeX2e with kluwer.sty, 7 figures. Talk presented at the Second International "Cetraro" Workshop & NATO Advanced Research Workshop "Diffraction 2002", Alushta, Crimea, Ukraine, August 31 - September 6, 200

Luther-Emery Phase and Atomic-Density Waves in a Trapped Fermion Gas

The Luther-Emery liquid is a state of matter that is predicted to occur in one-dimensional systems of interacting fermions and is characterized by a gapless charge spectrum and a gapped spin spectrum. In this Letter we discuss a realization of the Luther-Emery phase in a trapped cold-atom gas. We study by means of the density-matrix renormalization-group technique a two-component atomic Fermi gas with attractive interactions subject to parabolic trapping inside an optical lattice. We demonstrate how this system exhibits compound phases characterized by the coexistence of spin pairing and atomic-density waves. A smooth crossover occurs with increasing magnitude of the atom-atom attraction to a state in which tightly bound spin-singlet dimers occupy the center of the trap. The existence of atomic-density waves could be detected in the elastic contribution to the light-scattering diffraction pattern.Comment: 10 pages, 3 figures, 1 Table, submitted to Phys. Rev. on July 25th 200

Acute pseudo-obstruction of the large bowel with caecal perforation following normal vaginal delivery: a case report

<p>Abstract</p> <p>Introduction</p> <p>Acute pseudo-obstruction of the large bowel following normal vaginal delivery is an extremely rare complication of normal vaginal delivery. It can be fatal if not recognized early. Only one previous report has been found in the English literature.</p> <p>Case presentation</p> <p>A 36-year old Caucasian, normally fit woman presented with abdominal distension and vomiting five days post-normal vaginal delivery at term. Localised peritonitis in the right iliac fossa developed in the next few days, and caecal perforation was found at laparotomy, without evidence of appendicitis or colitis.</p> <p>Conclusion</p> <p>Although very rare, Ogilvie's syndrome should be considered by obstetricians, general surgeons and general practitioners as a potential cause of vomiting and abdominal pain following normal vaginal delivery. Early recognition and management are essential to minimize the possibility of developing serious complications.</p

Zinc binding to lambda phage DNA studied by voltammetric techniques

A interação do zinco com o DNA do fago lambda foi investigada utilizando a voltametria de pulso diferencial e a voltametria cíclica. Os métodos baseiam-se no monitoramento direto da corrente de redução e oxidação do zinco na ausência e na presença do DNA viral. Curvas de titulação do Zn2+ com o DNA do fago lambda foram obtidas nos intervalos de concentração 3,57 x 10-12 a 3,92 x 10-11 mol L-1 e 6,97 x 10-12 a 5,56 x 10-11 mol L-1. Estes dados foram utilizados para o cálculo da constante de dissociação do complexo e da estequiometria. O mecanismo da reação foi estudado utilizando a voltametria cíclica. Curvas do tipo I (corrente de oxidação do zinco) versus v½ (raiz quadrada da velocidade de varredura) mostraram que o processo oxidação-redução do zinco deixa de ser difusional na presença do DNA do fago lambda.Binding of zinc to lambda phage DNA was investigated by differential pulse voltammetry and cyclic voltammetry. These methods rely on the direct monitoring of reduction and oxidation current of zinc in the absence and presence of this virion DNA. Titration graphs of Zn2+ with DNA were obtained in the concentration ranges from 3.57 x 10-12 to 3.92 x 10-11 mol L-1 and 6.97 x 10-12 to 5.56 x 10-11 mol L-1. These data were used to calculate the dissociation constant of the complex and the stoichiometry. The mechanism of this reaction was studied by cyclic voltammetry through curves I (oxidation current of Zn2+) versus v½ (square root of scan rate). These curves showed that the oxidation-reduction process of Zn2+ was not controlled by diffusion in the presence of lambda phage DNA

The KLN Theorem and Soft Radiation in Gauge Theories: Abelian Case

We present a covariant formulation of the Kinoshita, Lee, Nauenberg (KLN) theorem for processes involving the radiation of soft particles. The role of the disconnected diagrams is explored and a rearrangement of the perturbation theory is performed such that the purely disconnected diagrams are factored out. The remaining effect of the disconnected diagrams results in a simple modification of the usual Feynman rules for the S-matrix elements. As an application, we show that when combined with the Low theorem, this leads to a proof of the absense of the $1/Q$ corrections to inclusive processes (like the Drell-Yan process). In this paper the abelian case is discussed to all orders in the coupling.Comment: 27 pages, LaTeX, 14 figure

Quantum-fluid dynamics of microcavity polaritons

Semiconductor microcavities offer a unique system to investigate the physics of weakly interacting bosons. Their elementary excitations, polaritons--a mixture of excitons and photons--behave, in the low density limit, as bosons that can undergo a phase transition to a regime characterised by long range coherence. Condensates of polaritons have been advocated as candidates for superfluidity; and the formation of vortices as well as elementary excitations with a linear dispersion are actively sought after. In this work, we have created and set in motion a macroscopically degenerate state of polaritons and let it collide with a variety of defects present in the sample. Our experiments show striking manifestations of a coherent light-matter packet that displays features of a superfluid, although one of a highly unusual character as it involves an out-of-equilibrium dissipative system where it travels at ultra-fast velocity of the order of 1% the speed of light. Our main results are the observation of i) a linear polariton dispersion accompanied with diffusion-less motion, ii) flow without resistance when crossing an obstacle, iii) suppression of Rayleigh scattering and iv) splitting into two fluids when the size of the obstacle is comparable with the size of the wavepacket. This work opens the way to the investigation of new phenomenology of out-of-equilibrium condensates.Comment: 22 pages, 5 figure

An annotated bibliography of C.J. van der Klaauw with notes on the impact of his work

Van der Klaauw was a professor of Descriptive Zoology in the period 1934–1958. This paper presents a concise annotated overview of his publications. In his work three main topics can be recognized: comparative anatomy of the mammalian auditory region, theoretical studies about ecology and ecological morphology, and vertebrate functional morphology. In particular van der Klaauw developed new concepts on functional morphology, based upon a holistic approach. A series of studies in functional morphology of Vertebrates by his students is added. An overview of recent morphological and theoretical studies show that this new approach had a long lasting impact in studies of functional morphology