Transport properties of the disordered charged bose condensate in two dimensions

Analytical results for the frequency-dependent conductivity of a disordered two-dimensional interacting Bose condensate are presented. Charged and uncharged impurities are considered. We find that for weak disorder the condensate is a superfluid while for strong disorder it is an insulator (a Bose glass). At the superfluid-insulator transition point (at the critical boson densityN _c) the condensate exhibits metallic tranport properties. An loffe-Regel criterion for the transition point is derived. The conductivity at the transition point is of ordere ²/h (h is Planck's constant) and depends on the kind of disorder. For charged impurities (with impurity densityN _i) the conductivity (for a condensate of particles with charge 2e and forN _i=2N _c) at the transition point is given by _c =0.26x(2e)²/h. We discuss recent experiments on superconducting ultra-thin films and on high-T _c superconductors.     

Subband mobilities and dingle temperatures within a two-subband model in the presence of localized states

The transport time and the single-particle relaxation times in a two subband system of a two-dimensional electron gas have been calculated. Screening and density of states effects have been taken into account under the assumption that disorder leads to localized states in both subbands. It has been found that the single-particle relaxation time of the second subband is always larger than that for the first subband. The transport time of the second subband can be smaller or larger than the transport time of the first subband. The text was submitted by the authors in English.     

Improved Cd determination in glasses by laser ablation inductively coupled plasma mass spectrometry using nitrogen as a matrix modifier

The addition of 5-10 mL min-1 nitrogen to the central channel of plasma in Laser ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) increases the sensitivities of Cd by a factor of 3 and decreases oxide interferences by one order of magnitude, which allows the direct analysis of trace levels of Cd in glass samples. This simple method shows a great potential for the direct determination of Cd in various kinds of samples.     

Z3-invariants of real and imaginary quadratic fields

Let $\text{Q}$((?m)^{$\text{1}\text{2}$}) and $\text{Q}$((3m)^{$\text{1}\text{2}$}) be a pair of quadratic fields, m > 0, and let λ^?, μ^?; λ⁺, μ⁺ be the respective Iwasawa invariants of the basic $\text{Z}$₃-extensions of these fields. A generalization of a result of Scholz shows that λ^? ≥ λ⁺ and if μ^? = 0, then μ⁺ = 0.     

Magnetic resonance imaging of neuroblastoma using current techniques

We evaluated the ability of current magnetic resonance (MR) scanning techniques to detect and stage neuroblastoma in children, using surgical and histopathologic correlation. We prospectively and retrospectively reviewed 16 MR examinations from 14 patients with neuroblastoma (13 patients) or ganglioneuroblastoma (1 patient) and compared these to computed tomography (CT) (5 patients) and pathology (all patients). Sequences included: precontrast T1-weighted and T2-weighted images, and gadolinium-enhanced T1-weighted images. The study time for each MR exam was also calculated. Five primary tumors were intrathoracic paraspinous masses, eight were adrenal, and 1 was presacral. Neural foraminal invasion was demonstrated on MR in four of 14 patients. Three of the four patients had undergone CT and neural foraminal invasion was shown in one. Vascular encasement was demonstrated in five of 14 patients on MR images. Three of the five patients had undergone CT and vascular involvement was shown in two. All cases of neural foramina invasion and vascular encasement were proven at surgery. There were no false positive or false negative MR studies of neural foraminal invasion or vascular encasement. Bone marrow invasion was shown in two of 14 patients on MR images which were confirmed by bone marrow aspirate. No false negative cases of bone marrow invasion was shown. In one patient, CT considered one neuroblastoma to be adrenal in location which was correctly shown to be intrathoracic on MR. The mean study time for MR imaging was 49 min. Current MR techniques are accurate at detecting and staging neuroblastoma, and coverage of chest, abdomen, and pelvis can be performed in less than one hour.     

Electronically and Calorimetrically Measured Energy Balances of a Thermal Induction Plasma

The plasma efficiency is one of the most important factors for industrial applications of thermal induction plasmas. An analysis of all the terms contributing to the energy balance of the rf-generator and the induction plasma is presented. In order to measure the plasma power faster than with usual calorimetric methods, a new approach to the instantaneous measurement of electric power was developed, which allowed power measurements at several Megahertz in the oscillator circuit of a self-excited induction generator. Systematic measurements under 26 different operating conditions were carried out on a 12 kW, 5 MHz argon induction plasma and were checked by parallel calorimetric energy balances. The agreement of both methods is within an accuracy of 5%. The total plasma efficiency is over 50% of the plate power. It varies only slightly with the operating parameters (plate voltage and gas flow rates). The measurements indicate clearly where modifications of the system would improve the overall efficiency.     

Misconceptions on Pollution and the Causes of Cancer

The public has numerous misconceptions about the relationship between environmental pollution and human cancer. Underlying these misconceptions is an erroneous belief that nature is benign. In this article we highlight eight of these misconceptions and describe the scientific information that undermines each one.     

Local-field correction of the charged Bose condensate for two and three dimensions

The local-field correction for the dielectric function of the two-dimensional and of the three-dimensional Bose condensate is calculated within a sum-rule version of the Singwi et al. (Phys. Rev.176, 589 (1968)) approach. We derive analytical expressions for small and large wave numbers and give analytical expressions for the density dependence. We compare the results of the groundstate energy for the three-dimensional system with Monte-Carlo computations. In two dimensions a roton structure in the plasmon dispersion is found at low boson density. The plasmon density of states is calculated. A correlation induced charge-density-wave instability in layered structures of two-dimensional Bose gases is discussed.     

Design of triple helix forming C-glycoside molecules

The modeling, synthesis, and characterization of oligomers containing 2-aminoquinazolin-5-yl 2'-deoxynucleotide residues are reported. The 2-aminoquinazoline residues sequence specifically bind via Hoogsteen base pairing as a third strand in the center of the major groove at T:A base pair Watson-Crick duplex sequences. Evidence for the formation of a sequence specific three-stranded structure is based on thermal denaturation UV-vis and fluorescence studies. The novel 2-aminoquinazoline C-nucleotide is a component of a system designed to overcome the homopurine requirement for triple helix structures.