Integrals over Products of Distributions and Coordinate Independence of Zero-Temperature Path Integrals

In perturbative calculations of quantum-statistical zero-temperature path integrals in curvilinear coordinates one encounters Feynman diagrams involving multiple temporal integrals over products of distributions, which are mathematically undefined. In addition, there are terms proportional to powers of Dirac delta-functions at the origin coming from the measure of path integration. We give simple rules for integrating products of distributions in such a way that the results ensure coordinate independence of the path integrals. The rules are derived by using equations of motion and partial integration, while keeping track of certain minimal features originating in the unique definition of all singular integrals in $1 - \epsilon$ dimensions. Our rules yield the same results as the much more cumbersome calculations in 1- epsilon dimensions where the limit epsilon --> 0 is taken at the end. They also agree with the rules found in an independent treatment on a finite time interval.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of paper (including all PS fonts) at http://www.physik.fu-berlin.de/~kleinert/33

High-velocity gas towards the LMC resides in the Milky Way halo

To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d=9.2 kpc distance. We study the velocity-component structure of low and intermediate metal ions in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard HST, and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer spectrum of the nearby LMC star Sk-69 59 and with HI 21cm data from the Leiden-Argentina-Bonn (LAB) survey. Metal absorption towards RXJ0439.8-6809 is unambiguously detected in three different velocity components near v_LSR=0,+60, and +150 km/s. The presence of absorption proves that all three gas components are situated in front of the star, thus being located in the disk and inner halo of the Milky Way. For the high-velocity cloud (HVC) at v_LSR=+150 km/s we derive an oxygen abundance of [O/H]=-0.63 (~0.2 solar) from the neighbouring Sk-69 59 sightline, in accordance with previous abundance measurements for this HVC. From the observed kinematics we infer that the HVC hardly participates in the Galactic rotation. Our study shows that the HVC towards the LMC represents a Milky Way halo cloud that traces low-column density gas with relatively low metallicity. It rules out scenarios in which the HVC represents material close to the LMC that stems from a LMC outflow.Comment: 4 pages, 3 figures; submitted to A&A Letter

Response to Invasion by Antigen and Effects of Threshold in an Immune Network Dynamical System Model with a Small Number of Degrees of Freedom

We study a dynamical system model of an idiotypic immune network with a small number of degrees of freedom, mainly focusing on the effect of a threshold above which antibodies can recognise antibodies. The response of the system to invasions by antigens is investigated in the both models with and without the threshold and it turns out that the system changes in a desirable direction for moderate magnitude of perturbation. direction for moderate magnitude of perturbation. Also, the propagation of disturbance by an antigen is investigated in the system of one-dimensionally connected basic units taking the closed 3-clone system as a unit, and it is clarified that the threshold of the system has effects to enhance the stability of the network and to localise the immune response.Comment: 6 pages, 6 figures. Submitted to Prog. Theor. Phy

High-pressure study of the non-Fermi liquid material U_2Pt_2In

The effect of hydrostatic pressure (p<= 1.8 GPa) on the non-Fermi liquid state of U_2Pt_2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried out on single-crystals with the current along (I||c) and perpendicular (I||a) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I||a we observe a rapid recovery of the Fermi-liquid T^2-term with pressure. The low-temperature resistivity can be analysed satisfactorily within the magnetotransport theory of Rosch, which provides strong evidence for the location of U_2Pt_2In at an antiferromagnetic quantum critical point. For I||c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism. In addition, we have measured the pressure dependence of the antiferromagnetic ordering temperature (T_N= 37.6 K) of the related compound U_2Pd_2In. A simple Doniach-type diagram for U_2Pt_2In and U_2Pd_2In under pressure is presented.Comment: 21 pages (including 5 figures); pdf forma

The Wilson-Polchinski Renormalization Group Equation in the Planar Limit

We derive the Wilson-Polchinski RG equation in the planar limit. We explain that the equation necessarily involves also non-planar amplitudes with sphere topology, which represent multi-trace contributions to the effective action. The resulting RG equation turns out to be of the Hamilton-Jacobi type since loop effects manifest themselves through terms which are linear in first order derivatives of the effective action with respect to the sources. We briefly outline applications to renormalization of non-commutative field theories, matrix models with external sources and holography.Comment: 22 pages, Latex, 3 eps figure

Inversion symmetry in the spin-Peierls compound NaV2O5

At room-temperature NaV2O5 was found to have the centrosymmetric space group Pmmn. This space group implies the presence of only one kind of V site in contrast with previous reports of the non-centrosymmetric counterpart P21mn. This indicates a non-integer valence state of vanadium. Furthermore, this symmetry has consequences for the interpretation of the transition at 34 K, which was ascribed to a spin-Peierls transition of one dimensional chains of V4+.Comment: Revtex, 3 pages, 2 postscript pictures embedded in the text. Corrected a mistake in one pictur

Environmental factors influencing the spread of the highly pathogenic avian influenza H5N1 virus in wild birds in Europe

A large number of occurrences of the highly pathogenic avian influenza (HPAI) H5N1 virus in wild birds were reported in Europe. The relationship between the occurrence pattern and environmental factors has, however, not yet been explored. This research uses logistic regression to quantify the relationships between anthropogenic or physical environmental factors and HPAI H5N1 occurrences. Our results indicate that HPAI H5N1 occurrences are highly correlated with the following: the increased normalized difference vegetation index (NDVI) in December; intermediate NDVI in March; lower elevations; increased minimum temperatures in January; and reduced precipitation in January. A predictive risk map of HPAI H5N1 occurrences in wild birds in Europe was generated on the basis of five key environmental factors. Independent validation of the risk map showed the predictive model to be of high accuracy (79%). The analysis suggests that HPAI H5N1 occurrences in wild birds are strongly influenced by the availability of food resources and are facilitated by increased temperatures and reduced precipitation. We therefore deduced that HPAI H5N1 occurrences in wild birds in Europe are probably caused by contact with other wild birds and not by contact with domestic poultry. These findings are important considerations for the global surveillance of HPAI H5N1 occurrences in wild birds