Quadrupole ionization gage measures ultrahigh vacuum

Quadrupole system, energized with a 200 MHz electric field, restrains ionizing electrons within the center of the ionization gage. Oscillatory trajectory of the electrons increases the probability of ionizing the gas molecules, lowers background X-ray level, and increases the signal-to-noise ratio

The first second of the Universe

The history of the Universe after its first second is now tested by high quality observations of light element abundances and temperature anisotropies of the cosmic microwave background. The epoch of the first second itself has not been tested directly yet; however, it is constrained by experiments at particle and heavy ion accelerators. Here I attempt to describe the epoch between the electroweak transition and the primordial nucleosynthesis. The most dramatic event in that era is the quark--hadron transition at 10 $\mu$s. Quarks and gluons condense to form a gas of nucleons and light mesons, the latter decay subsequently. At the end of the first second, neutrinos and neutrons decouple from the radiation fluid. The quark--hadron transition and dissipative processes during the first second prepare the initial conditions for the synthesis of the first nuclei. As for the cold dark matter (CDM), WIMPs (weakly interacting massive particles) -- the most popular candidates for the CDM -- decouple from the presently known forms of matter, chemically (freeze-out) at 10 ns and kinetically at 1 ms. The chemical decoupling fixes their present abundances and dissipative processes during and after thermal decoupling set the scale for the very first WIMP clouds.Comment: review to appear in Annalen der Physik (51 pages, 16 figures); references added (v2); typos corrected, resembles published version (v3

Accelerated expansion without dark energy

The fact that the LambdaCDM model fits the observations does not necessarily imply the physical existence of `dark energy'. Dropping the assumption that cold dark matter (CDM) is a perfect fluid opens the possibility to fit the data without dark energy. For imperfect CDM, negative bulk pressure is favoured by thermodynamical arguments and might drive the cosmic acceleration. The coincidence between the onset of accelerated expansion and the epoch of structure formation at large scales might suggest that the two phenomena are linked. A specific example is considered in which effective (anti-frictional) forces, which may be due to dissipative processes during the formation of inhomogeneities, give rise to accelerated expansion of a CDM universe.Comment: 5 pages, Talk at ``On the nature of dark energy: Observational and theoretical results on the accelerating universe'', Institut d'Astrophysique de Paris, France, July 1 -- 5, 2002 (v1); one reference updated (v2

Analytic Solutions for Cosmological Perturbations in Multi-Dimensional Space-Time

We obtain analytic solutions for the density contrast and the anisotropic pressure in a multi-dimensional FRW cosmology with collisionless, massless matter. These are compared with perturbations of a perfect fluid universe. To describe the metric perturbations we use manifest gauge invariant metric potentials. The matter perturbations are calculated by means of (automatically gauge invariant) finite temperature field theory, instead of kinetic theory. (Talk given at the Journ\'ees Relativistes '93, 5 -- 7 April, Brussels, Belgium)Comment: 6 pages (incl. 3 figures), LaTeX (epsf), TUW-93-07, two misprints corrected (one formula, one reference

Evolution of gravitational waves through the cosmological QCD transition

The spectrum of gravitational waves that have been produced in inflation is modified during cosmological transitions. Large drops in the number of relativistic particles, like during the QCD transition or at $e^+e^-$ annihilation, lead to steps in the spectrum of gravitational waves. We calculate the transfer function for the differential energy density of gravitational waves for a first-order and for a crossover QCD transition.Comment: 10 pages, LaTeX2e, 1 figure; analytic estimate for the modification of the spectral slope near f_* added, minor changes to improve the presentation; accepted for publication in Mod. Phys. Lett.

Cosmological and astrophysical aspects of finite-density QCD

The different phases of QCD at finite temperature and density lead to interesting effects in cosmology and astrophysics. In this work I review some aspects of the cosmological QCD transition and of astrophysics at high baryon density.Comment: 13 pages, 4 figures. Invited talk at 'QCD at Finite Baryon Density', Bielefeld (Germany), April 199

A Sense Of Their Own Power : Self-Determination in Recent Writings on Black Virginians

Discusses historical visibility of African American Virginians from 1619 to the present in relation to the concept of self-determination and power

The QCD phase transition in the inhomogeneous Universe

We investigate a new mechanism for the cosmological QCD phase transition: inhomogeneous nucleation. The primordial temperature fluctuations, measured to be $\delta T/T \sim 10^{-5}$, are larger than the tiny temperature interval, in which bubbles would form in the standard picture of homogeneous nucleation. Thus the bubbles nucleate at cold spots. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis.Comment: Version to appear in Phys. Rev. Lett., 4 pages, 1 figure. Difference to heterogeneous nucleation emphasized, amplitude of temperature fluctuations analyzed in more detail, new length scale l_heat introduced, more complicated geometry of baryon number discussed shortly (relevant for low values of l_heat