Statistical Properties of Interacting Bose Gases in Quasi-2D Harmonic Traps

The analytical probability distribution of the quasi-2D (and purely 2D) ideal and interacting Bose gas are investigated by using a canonical ensemble approach. Using the analytical probability distribution of the condensate, the statistical properties such as the mean occupation number and particle number fluctuations of the condensate are calculated. Researches show that there is a continuous crossover of the statistical properties from a quasi-2D to a purely 2D ideal or interacting gases. Different from the case of a 3D Bose gas, the interaction between atoms changes in a deep way the nature of the particle number fluctuations.Comment: RevTex, 10pages, 4 figures, E-mail: [email protected]

Loss of TOP3B leads to increased R-loop formation and genome instability

Topoisomerase III beta (TOP3B) is one of the least understood members of the topoisomerase family of proteins and remains enigmatic. Our recent data shed light on the function and relevance of TOP3B to disease. A homozygous deletion for the TOP3B gene was identified in a patient with bilateral renal cancer. Analyses in both patient and modelled human cells show the disruption of TOP3B causes genome instability with a rise in DNA damage and chromosome bridging (mis-segregation). The primary molecular defect underlying this pathology is a significant increase in R-loop formation. Our data show that TOP3B is necessary to prevent the accumulation of excessive R-loops and identify TOP3B as a putative cancer gene, and support recent data showing that R-loops are involved in cancer aetiology

Specific protein-protein binding in many-component mixtures of proteins

Proteins must bind to specific other proteins in vivo in order to function. The proteins must bind only to one or a few other proteins of the of order a thousand proteins typically present in vivo. Using a simple model of a protein, specific binding in many component mixtures is studied. It is found to be a demanding function in the sense that it demands that the binding sites of the proteins be encoded by long sequences of bits, and the requirement for specific binding then strongly constrains these sequences. This is quantified by the capacity of proteins of a given size (sequence length), which is the maximum number of specific-binding interactions possible in a mixture. This calculation of the maximum number possible is in the same spirit as the work of Shannon and others on the maximum rate of communication through noisy channels.Comment: 13 pages, 3 figures (changes for v2 mainly notational - to be more in line with notation in information theory literature

The diversity of bioactive proteins in Australian snake venoms

Australian elapid snakes are among the most venomous in the world. Their venoms contain multiple components that target blood hemostasis, neuromuscular signaling, and the cardiovascular system. We describe here a comprehensive approach to separation and identification of the venom proteins from 18 of these snake species, representing nine genera. The venom protein components were separated by two-dimensional PAGE and identified using mass spectrometry and de novo peptide sequencing. The venoms are complex mixtures showing up to 200 protein spots varying in size from 10. These include many proteins identified previously in Australian snake venoms, homologs identified in other snake species, and some novel proteins. In many cases multiple trains of spots were typically observed in the higher molecular mass range (> 20 kDa) (indicative of post-translational modification). Venom proteins and their post-translational modifications were characterized using specific kantibodies, phosphoprotein- and glycoprotein-specific stains, enzymatic digestion, lectin binding, and antivenom reactivity. In the lower molecular weight range, several proteins were identified, but the predominant species were phospholipase A(2) and alpha-neurotoxins, both represented by different sequence variants. The higher molecular weight range contained proteases, nucleotidases, oxidases, and homologs of mammalian coagulation factors. This information together with the identification of several novel proteins (metalloproteinases, vespryns, phospholipase A(2) inhibitors, protein-disulfide isomerase, 5'-nucleotidases, cysteinerich secreted proteins, C-type lectins, and acetylcholinesterases) aids in understanding the lethal mechanisms of elapid snake venoms and represents a valuable resource for future development of novel human therapeutics

Direct Observation of Site-specific Valence Electronic Structure at Interface: SiO2/Si Interface

Atom specific valence electronic structures at interface are elucidated successfully using soft x-ray absorption and emission spectroscopy. In order to demonstrate the versatility of this method, we investigated SiO2/Si interface as a prototype and directly observed valence electronic states projected at the particular atoms of the SiO2/Si interface; local electronic structure strongly depends on the chemical states of each atom. In addition we compared the experimental results with first-principle calculations, which quantitatively revealed the interfacial properties in atomic-scale.Comment: 4 pages, 3 figure

Doppler cooling and trapping on forbidden transitions

Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 \mu K by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo simulations of the cooling process are in good agreement with the experiments

Mesoscopic Fermi gas in a harmonic trap

We study the thermodynamical properties of a mesoscopic Fermi gas in view of recent possibilities to trap ultracold atoms in a harmonic potential. We focus on the effects of shell closure for finite small atom numbers. The dependence of the chemical potential, the specific heat and the density distribution on particle number and temperature is obtained. Isotropic and anisotropic traps are compared. Possibilities of experimental observations are discussed.Comment: 8 pages, 9 eps-figures included, Revtex, submitted to Phys. Rev. A, minor changes to figures and captions, corrected typo

Interference of Bose-Einstein condensates in momentum space

We suggest an experiment to investigate the linear superposition of two spatially separated Bose-Einstein condensates. Due to the coherent combination of the two wave functions, the dynamic structure factor, measurable through inelastic photon scattering at high momentum transfer $q$, is predicted to exhibit interference fringes with frequency period $\Delta\nu = q/md$ where $d$ is the distance between the condensates. We show that the coherent configuration corresponds to an eigenstate of the physical observable measured in the experiment and that the relative phase of the condensates is hence created through the measurement process.Comment: 4 pages and 2 eps figure