Nanostructure fabrication by glancing angle ion beam assisted deposition of silicon

Glancing angle deposition by utilizing an ion beam sputter process and a controlled substrate rotation is used to deposit silicon nanostructures with different structure varieties. The structures are grown on seeded and plain [100] silicon substrates at room temperature. The ratio of deposition rate to substrate angular frequency and the substrate surface properties determine the nanostructure geometry, size and assembly. PACS 61.46.+w; 81.05.Gc; 81.15.Cd     

Influence of place synchrony on detection of a sinusoid

A series of experiments was performed to study the ability of the ear to code the temporal envelope of a waveform as demonstrated by comodulation masking release (CMR). The stimulus for all experiments was composed of a tone-burst signal, a 100-Hz-wide masker band centered at the signal frequency, and a second 100-Hz-wide noise band of variable frequency, the cue band. The cue band had a temporal envelope which was either correlated with or independent of that of the masker. The signal was a 100-Hz tone burst for most experiments. For the monotic stimulus, the correlated cue band results in lowered signal detection thresholds over a range extending from around 2/3 oct below the signal frequency to 1/3 oct above that frequency. When measured dichotically, with the signal and masker band in one ear and the cue band in the opposite ear, that effective range is expanded but the detection threshold shifts are a bit smaller. The greatest CMR is observed when the stimulus is presented diotically. With regard to effects of level and frequency, our data show CMR increasing with increasing stimulus level for a cue band lower in frequency than the signal, but show little effect of level for a cue band higher in frequency. Similarly, CMR increases with increasing stimulus frequency when the cue band is lower in frequency, but shows little effect of frequency for a cue band higher in frequency.     

Pressure-induced phase transition(s) in KMnF3 and the importance of the excess volume for phase transitions in perovskite structures

We report a pressure-dependent investigation of KMnF(3) by x-ray diffraction up to 30 GPa. The results are discussed in the framework of Landau theory and in relation to the isostructural phase transition in SrTiO(3). The phase transition temperature near 186 K in KMnF(3) shifts to room temperature at a critical pressure of P(c) = 3.4 GPa; the pressure dependence of the transition point follows ΔP(c)/ΔT(c) = 0.0315 GPa K(-1). The transition becomes second order under high pressure, close to the tricritical point. The phase transition is determined by the rotation of MnF(6) octahedra with their simultaneous expansion along the rotation axis. The rotation angle was found to increase to 10.5° at 24 GPa. An additional anomaly was observed at higher pressure around 25 GPa, suggesting a further phase transition.     

Light charged particle release in252Cf spontaneous fission: Tripartition versus fragment de-excitation

Double-differential emission probabilities P (E, θ) in angle θ and energy E of protons, tritons, and α-particles were measured in the case of spontaneous fission of²⁵²Cf. A detector system consisting of position-sensitive parallel-plate avalanche counters (PPAC) and ΔE?E-telescopes allowed a coincidence measurement of fission fragments (FF) and light charged particles (LCP) in the whole region from 0 deg. to 180 deg. with respect to the light-fragment direction. Previous results for α-particle emission were confirmed. The background contributions for protons are discussed in detail. For proton emission the background arising from (n, p)-reactions was measured and compared with a corresponding Monte-Carlo simulation of elastic (n, p)-clusions. Unlike for tritons and a-particles the P (E, θ) distribution for protons does not show equatorial peaking in 0 between 80 deg. and 90 deg. and contradicts classical scission point emission. The proton distribution, however, agrees with fragment de-excitation calculations in the framework of the cascade evaporation model (CEM) whereas an analogous calculation forα-particles completely fails. Upper limits for an additional scission component of proton emission are given.     

Assignment of h.f.s. constants of 1,4-benzosemiquinones by additivity rules. The free rotation of t-butyl groups

A set of equations for assigning hyperfine coupling constants of substituted 1,4-benzosemiquinones are presented. The equations, based on additivity rules, yield assignments for a range of substituents with a correlation between predicted and experimental constants to better than five per cent. The investigation shows that t-butyl groups in semiquinones rotate freely against prior assertions.     

Exploring structure–selectivity relationships of biogenic amine GPCR antagonists using similarity searching and dynamic compound mapping

We design and analyze compound selectivity sets of antagonists with differential selectivity against seven biogenic amine G-protein coupled receptors. The selectivity sets consist of a total of 267 antagonists and contain a spectrum of in part closely related molecular scaffolds. Each set represents a different selectivity profile. Using these com- pound sets, a systematic computational analysis of structure-selectivity relationships is carried out with different 2D similarity methods including fingerprints, recursive partitioning, clustering, and dynamic compound mapping. Screening calculations are performed in a background database containing nearly four million molecules. Fingerprint searching and compound mapping are found to enrich target-selective antagonists over family-selective ones. Dynamic compound mapping effectively discriminates database compounds from GPCR antagonists and consistently retains target-selective antagonists during the final dimension extension levels. Furthermore, the widely used MACCS key fingerprint displays a strong tendency to distinguish between target- and family-selective GPCR antagonists. Taken together, the results indicate that different types of 2D similarity methods are capable of distinguishing closely related molecules having different selectivity. The reported compound benchmark system is made freely available in order to enable selectivity-oriented analyses using other computational approaches.     

DNA based molecular motors

Most of the essential cellular processes such as polymerisation reactions, gene expression and regulation are governed by mechanical processes. Controlled mechanical investigations of these processes are therefore required in order to take our understanding of molecular biology to the next level. Single-molecule manipulation and force spectroscopy have over the last 15 years been developed into extremely powerful techniques. Applying these techniques to the investigation of proteins and DNA molecules has led to a mechanistic understanding of protein function on the level of single molecules. As examples for DNA based molecular machines we will describe single-molecule experiments on RNA polymerases as well as on the packaging of DNA into a viral capsid—a process that is driven by one of the most powerful molecular motors.     

Crystal and molecular structure of 3-methoxy-estra-1,3,5(10)-triene-14β,17β-diol,C19H26O3

The crystal and molecular structure of 3-methoxy-estra-1,3,5(10)-triene-14β,17β-diol has been determined by single crystal X-ray analysis. It crystallizes in the orthorhombic space group P2₁2₁2₁ with cell parameters a = 8.965(2), b = 30.520(7), and c = 6.031(2) A. The structure was solved by the POSIT system and refined by least-squares calculations to the conventional R factor of 0.075. The steroid rings A, B, and C have planar, 7α, 8β-half chair, and chair conformations, respectively. The ring D is intermediate between 13α, 14β-half chair and 13α-envelope. Rings B and C are trans-fused, and rings C and D are cis-fused. There are intra- as well as intermolecular hydrogen bonds between both hydroxyl groups of the steroid molecule.