Ground State of a trapped Bose-Einstein Condensate in Two Dimensions; Beyond the Mean-field Approximation

We consider the ground state of a trapped Bose-Einstein condensate in two dimensions. In the mean-field approximation, the ground state density profile satisfies the Gross-Pitaevskii equation. We compute the leading quantum corrections to the density profile to second order in an expansion around the Thomas-Fermi limit. By summing the ladder diagrams, we are generalizing Schick's result for the ground state energy of a homogeneouns Bose gas to the case of a trapped Bose gas.Comment: 19 pages, 2 figures, revte

Bose-Einstein Condensation in Anisotropic Harmonic Traps

We study the thermodynamic behaviour of an ideal gas of bosons trapped in a three-dimensional anisotropic harmonic oscillator potential. The condensate fraction as well as the specific heat is calculated using the Euler-Maclaurin approximation. For a finite number of particles there is no phase transition, but there is a well defined temperature at which the condensation starts. We also consider condensation in lower dimensions, and for one-dimensional systems we discuss the dependence of the condensate fraction and heat capacity on the ensemble used.Comment: LaTex, 17 pages, 7 ps-figure

Maximizing hypervisor scalability using minimal virtual machines

The smallest instance offered by Amazon EC2 comes with 615MB memory and a 7.9GB disk image. While small by today's standards, embedded web servers with memory footprints well under 100kB, indicate that there is much to be saved. In this work we investigate how large VM-populations the open Stack hyper visor can be made to sustain, by tuning it for scalability and minimizing virtual machine images. Request-driven Qemu images of 512 byte are written in assembly, and more than 110 000 such instances are successfully booted on a 48 core host, before memory is exhausted. Other factors are shown to dramatically improve scalability, to the point where 10 000 virtual machines consume no more than 2.06% of the hyper visor CPU

Protozoer - de minste "dyra" i jorda

Protozoer, eller dyreliknende protister, er organismer som består av bare en cell. De har en annen type kjerne enn bakterier, og mange a dem kan bevege seg ved hjelp av flageller eller cilier- Protozoer er mikroskopiske og lever av bakterier, sopp, andre encella protister og ulike typer organisk materiale

Kompostering

Kompostering er metoder der organisk materiale, for eksempel matrester, hagerester, halm og/eller husdyrgjødsel, omdannes til næringsrik jord og humus.Organismer som trenger god tilgang på luft sørger for omdanningen, og komposten bør derfor stelles som et levende dyr. Den må ha en riktig blanding av mat (organisk materiale), vann og luft. I tillegg må den vendes og blandes. Sluttproduktet, kompostjorda, har ulike kvaliteter og bør brukes deretter

Density of states for Bose-Einstein condensation in harmonic oscillator potentials

We discuss how it is possible to obtain a reliable approximation for the density of states for a system of particles in an anisotropic harmonic oscillator potential. A direct application of the result to study Bose-Einstein condensation of atomic gases in a potential trap can be given. In contrast to a previous study, our method involves only analytic calculations.Comment: 7 pages, LaTeX2e, no figure

Scaling property of variational perturbation expansion for general anharmonic oscillator

We prove a powerful scaling property for the extremality condition in the recently developed variational perturbation theory which converts divergent perturbation expansions into exponentially fast convergent ones. The proof is given for the energy eigenvalues of an anharmonic oscillator with an arbitrary $x^p$-potential. The scaling property greatly increases the accuracy of the results

Arctic anthropogenic sound contributions from seismic surveys during summer 2013

Statoil deployed three acoustic recorders from fall 2013 to 2014 in the Arctic region as part of a broad scientific campaign. One recorder was installed in the Barentsz Sea south-east of Spitsbergen. Two other recorders were installed in the Greenland Sea north-east of Greenland. All recorders were operating at a duty cycle of 2 min on and 30 min off, sampling at 39,062 Hz and recording in 24 bits. The Greenland recorders both captured air gun surveys performed during the summer months of 2013, allowing to estimate the transmission loss in the Arctic over long ranges. This paper presents “log(R)” transmission loss curves for these scenarios that can help assessing the acoustic shipping impact for future expeditions.Postprint (published version

Bose-Einstein condensation under external conditions

We discuss the phenomenon of Bose-Einstein condensation under general external conditions using connections between partition sums and the heat-equation. Thermodynamical quantities like the critical temperature are given in terms of the heat-kernel coefficients of the associated Schr\"odinger equation. The general approach is applied to situations where the gas is confined by arbitrary potentials or by boxes of arbitrary shape.Comment: 11 pages, LaTeX, to appear in Phys. Lett.