The General Primordial Cosmic Perturbation

We consider the most general primordial cosmological perturbation in a universe filled with photons, baryons, neutrinos, and a hypothetical cold dark matter (CDM) component within the framework of linearized perturbation theory. We give a careful discussion of the different allowed modes, distinguishing modes which are regular at early times, singular at early times, or pure gauge. As well as the familiar growing and decaying adiabatic modes and the baryonic and CDM isocurvature modes we identify two {\it neutrino isocurvature} modes which do not seem to have been discussed before. In the first, the ratio of neutrinos to photons varies spatially but the net density perturbation vanishes. In the second the photon-baryon plasma and the neutrino fluid have a spatially varying relative bulk velocity, balanced so that the net momentum density vanishes. Possible mechanisms which could generate the two neutrino isocurvature modes are discussed. If one allows the most general regular primordial perturbation, all quadratic correlators of observables such as the microwave background anisotropy and matter perturbations are completely determined by a $5\times 5,$ real, symmetric matrix-valued function of co-moving wavenumber. In a companion paper we examine prospects for detecting or constraining the amplitudes of the most general allowed regular perturbations using present and future CMB data.Comment: 18 pages, 2 Postscript figures, uses revtex. Revised 2-2000 Minor errors corrected and some references adde

Constraining Isocurvature Perturbations with CMB Polarization

The role of cosmic microwave background (CMB) polarisation data in constraining the presence of primordial isocurvature modes is examined. While the MAP satellite mission will be unable to simultaneously constrain isocurvature modes and cosmological parameters, the PLANCK mission will be able to set strong limits on the presence of isocurvature modes if it makes a precise measurement of the CMB polarisation sky. We find that if we allow for the possible presence of isocurvature modes, the recently obtained BOOMERANG measurement of the curvature of the universe fails. However, a comparably sensitive polarisation measurement on the same angular scales will permit a determination of the curvature of the universe without the prior assumption of adiabaticity.Comment: 4pages, Latex with four eps figures. (Revised 18 Dec 2000. Minor typos corrected

Thermal phase transitions for Dicke-type models in the ultra-strong coupling limit

We consider the Dicke model in the ultra-strong coupling limit to investigate thermal phase transitions and their precursors at finite particle numbers $N$ for bosonic and fermionic systems. We derive partition functions with degeneracy factors that account for the number of configurations and derive explicit expressions for the Landau free energy. This allows us to discuss the difference between the original Dicke (fermionic) and the bosonic case. We find a crossover between these two cases that shows up, e.g., in the specific heat.Comment: 4 pages Brief Report styl

Internal Migration and Regional Population Dynamics in Europe: German Case Study

Report prepared for the Council of Europe (Directorate of Social and Economic Affairs, Population and Migration Division) and for European Commission (Directorate General V, Employment, Industrial Relations and Social Affairs, Unit E1, Analysis and Research on the Social Situation) This paper reports on internal migration and regional population dynamics and to a lesser extend on international migration in Germany. It examines internal migration patterns and trends in two years, 1984, 1989 and 1993, and compares them. Germany has a particularly sophisticated population system with a large number of population categories behaving in a very different way. The indigenous population shows a pattern of urban deconcentration typical for affluent West-European countries, both in the forms of suburbanisation and counterurbanisation. All other groups of migrants, those coming from former East Germany, those of German origin coming from outside Germany (Aussiedler) and other international migrants, show a pattern of strong concentration in urban centres. As far as migrations from East to West Germany is concerned the pattern is changing, as the number of migrants declines rapidly. Also in East Germany itself there is a marked shift. The pattern of rapid concentration of population due mainly to rural to urban migration is moving, for the time being, to weak and fragmented deconcentration. This process will speed up with the economic development of Eastern Länder. Medium density areas gain people, high and low density areas lose people. The relationship between net migration on the one hand and population density on the other was strongly negative for low density areas and for the less populated areas. The gainers were areas with a medium density of population. The age of migrants has a profound impact on their behaviour. There are important variations in redistribution of population by life course stage. The dominant urban deconcentration was most characteristic of middle working and family ages and the pre-retirement and retirement ages. People in the young adult ages migrated in different directions, showing a unique shift to some dense neighbourhoods in big cities, those close to higher education institutions. Unemployment influences migration profoundly. People move between areas of differing unemployment in ways predicted by classical economic equilibrium theory, leaving areas of high unemployment and going to areas of lower unemployment. German population dynamics depends on three factors: natural increase (persistently negative), internal migration and international migration. International migration is the only factor which maintains the size of population and even allows for a moderate growth. There is no direct threat that the population inhabiting German territory, will decline in the near future, but this may happen to the German population

Phylogenetic Analysis of Cell Types using Histone Modifications

In cell differentiation, a cell of a less specialized type becomes one of a more specialized type, even though all cells have the same genome. Transcription factors and epigenetic marks like histone modifications can play a significant role in the differentiation process. In this paper, we present a simple analysis of cell types and differentiation paths using phylogenetic inference based on ChIP-Seq histone modification data. We propose new data representation techniques and new distance measures for ChIP-Seq data and use these together with standard phylogenetic inference methods to build biologically meaningful trees that indicate how diverse types of cells are related. We demonstrate our approach on H3K4me3 and H3K27me3 data for 37 and 13 types of cells respectively, using the dataset to explore various issues surrounding replicate data, variability between cells of the same type, and robustness. The promising results we obtain point the way to a new approach to the study of cell differentiation.Comment: Peer-reviewed and presented as part of the 13th Workshop on Algorithms in Bioinformatics (WABI2013

Implications of a Quantum Mechanical Treatment of the Universe

We attempt to treat the very early Universe according to quantum mechanics. Identifying the scale factor of the Universe with the width of the wave packet associated with it, we show that there cannot be an initial singularity and that the Universe expands. Invoking the correspondence principle, we obtain the scale factor of the Universe and demonstrate that the causality problem of the standard model is solved.Comment: LaTex, 5 pages, 1 figure, to be published in Mod. Phys. Lett.

Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions

We have developed a method for the reproducible fabrication of superconducting scanning tunneling microscope (STM) tips. We use these tips to form superconductor/insulator/superconductor tunnel junctions with the STM tip as one of the electrodes. We show that such junctions exhibit fluctuation dominated Josephson effects, and describe how the Josephson product IcRn can be inferred from the junctions' tunneling characteristics in this regime. This is first demonstrated for tunneling into Pb films, and then applied in studies of single crystals of NbSe2. We find that in NbSe2, IcRn is lower than expected, which could be attributed to the interplay between superconductivity and the coexisting charge density wave in this material.Comment: 3 pages, 2 figures. Presented at the New3SC-4 meeting, San Diego, Jan. 16-21 200

Mathematical modeling of the Drosophila neuromuscular junction

Poster presentation: An important challenge in neuroscience is understanding how networks of neurons go about processing information. Synapses are thought to play an essential role in cellular information processing however quantitative and mathematical models of the underlying physiologic processes that occur at synaptic active zones are lacking. We are generating mathematical models of synaptic vesicle dynamics at a well-characterized model synapse, the Drosophila larval neuromuscular junction. This synapse's simplicity, accessibility to various electrophysiological recording and imaging techniques, and the genetic malleability intrinsic to Drosophila system make it ideal for computational and mathematical studies. We have employed a reductionist approach and started by modeling single presynaptic boutons. Synaptic vesicles can be divided into different pools; however, a quantitative understanding of their dynamics at the Drosophila neuromuscular junction is lacking [4]. We performed biologically realistic simulations of high and low release probability boutons [3] using partial differential equations (PDE) taking into account not only the evolution in time but also the spatial structure in two dimensions (the extension to three dimensions will be implemented soon). PDEs are solved using UG, a program library for the calculation of multi-dimensional PDEs solved using a finite volume approach and implicit time stepping methods leading to extended linear equation systems be solvedwith multi-grid methods [3,4]. Numerical calculations are done on multi-processor computers for fast calculations using different parameters in order to asses the biological feasibility of different models. In preliminary simulations, we modeled vesicle dynamics as a diffusion process describing exocytosis as Neumann streams at synaptic active zones. The initial results obtained with these models are consistent with experimental data. However, this should be regarded as a work in progress. Further refinements will be implemented, including simulations using morphologically realistic geometries which were generated from confocal scans of the neuromuscular junction using NeuRA (a Neuron Reconstruction Algorithm). Other parameters such as glutamate diffusion and reuptake dynamics, as well as postsynaptic receptor kinetics will be incorporated as well

SO(10) Cosmic Strings and SU(3) Color Cheshire Charge

Certain cosmic strings that occur in GUT models such as $SO(10)$ can carry a magnetic flux which acts nontrivially on objects carrying $SU(3)_{color}$ quantum numbers. We show that such strings are non-Abelian Alice strings carrying nonlocalizable colored ``Cheshire" charge. We examine claims made in the literature that $SO(10)$ strings can have a long-range, topological Aharonov-Bohm interaction that turns quarks into leptons, and observe that such a process is impossible. We also discuss flux-flux scattering using a multi-sheeted formalism.Comment: 37 Pages, 8 Figures (available upon request) phyzzx, iassns-hep-93-6, itp-sb-93-6

Inflation and the cosmic microwave background

I give a status report and outlook concerning the use of the cosmic microwave background anisotropies to constrain the inflationary cosmology, and stress its crucial role as an underlying paradigm for the estimation of cosmological parameters.Comment: 8 pages LaTeX file, with two figures incorporated using epsf. To appear, proceedings of `The non-sleeping universe', Porto (Astrophysics and Space Science