Can tetraplex recombination models explain observations in induced mitotic gene conversion?

Induced mitotic gene conversion studies on the CYC1 gene of yeast have shown that the actual base pair changes, the types of changes (base substitution, deletion or addition) and the distances between mutations all affect gene conversion yields. In crosses between mutations less than four bases apart, gene conversion rates are as low as back mutation rates. The same mutants crossed to alleles more than five bases away may recombine 50-fold more. In crosses between mutations five or more base pairs apart, recombination rates varying by up to ten-fold are observed when comparing mutations at the same codon sites. The actual mutations in crosses affect recombination rates at these distances. The data rules out models in which mutants are repaired independently. Models with large gaps at the initiation site are ruled out if the mutants are within the gap. Recombination models are favoured in which both mutations can interact at a distance to affect the probability of recombination; such interactions may reflect the geometry of the recombinational junctions. The specific interactions proposed are that the actual mutations, and residual mismatches arising on excision resynthesis, affect both the further migration of the recombinational junction, and the probability that excision-repair will detect and correct residual mismatches. Junction models in which interactions are expected include those composed of base tetraplexes. The data is interpreted in terms of these models. Meiotic recombination data is consistent with these models.     

Gas-phase synthesis of single-walled carbon nanotubes on catalysts producing high yield

Composite catalysts are employed for high yield gas-phase synthesis of single-walled carbon nanotubes (SWCNTs). Specifically, silicon is investigated as an additive to iron catalysts for synthesis of SWCNTs in inverse diffusion flames. While silicon is often used as a substrate in supported-catalyst processes to promote nanotube growth, this study demonstrates that it can also be beneficial for gas-phase nanotube synthesis in diffusion flames. An oxy-fuel ethylene inverse diffusion flame is employed to provide a soot-free, carbon-rich environment for nanotube growth. Iron and silicon precursors are added to the fuel stream for nucleation of iron/silicon/oxygen catalyst particles, with the amount of particle oxidation determined by the amount of oxygen-enrichment and fuel dilution at a given temperature. Under optimum conditions, nearly 90% of the catalyst particles produce single-walled carbon nanotubes as compared to less than 10% when the catalyst consists of only iron and oxygen. The effect of silicon addition is investigated through variation of the iron/silicon ratio and measurement of nanotube growth rates. Silicon is shown to primarily affect SWCNT inception with minimal influence on growth rate.     

Electrically pumped, micro-cavity based single photon source driven at 1 GHz

A resonant cavity light emitting diode combined with a submicron oxide current aperture, to pump individual InGaAs/GaAs quantum dots electrically, has been designed and fabricated. Pulsed correlation measurements demonstrated true single photon emission with g²(0) = 0 at a rate of 1 GHz.     

Auswirkungen der Reifendimension auf den Energieaufwand im Umfeld verschiedener Fahrzyklen und Fahrzeugkonzepte

The efficiency of a vehicle has a direct impact on its consumption as well as on its range and is essential for both the achievement of customer-specific and legal requirements. The reduction of driving resistors is therefore one of the greatest priorities within the automotive development process. Due to the considerable impact on aerodynamics, mass inertia and rolling resistance, the selection of the dimensions of the rims and tyres in the early development phase is an important basis for the subsequent achievement of the efficiency targets of the entire vehicle. In the context of changing mobility and new vehicle concepts, the current design limits are changing, which creates new design spaces in the dimensioning of the vehicle. Within the scope of this study the significance of the efficiency-relevant tyre parameters aerodynamics, mass inertia and rolling resistance within the individual cycle components of the WLTP are analysed in simulations. The variation of the vehicle parameters mass, aerodynamic end face and recuperation efficiency makes it possible to evaluate the individual tyre parameters with regard to different vehicle concepts. Using measured data, physical relationships and literature research, the efficiency-relevant parameters of the tyre are set in relation to the rim and tyre dimension and dimensional recommendations for exemplary scenarios are presented.     

Characterization of diffusion flames for synthesis of single-walled carbon nanotubes

Recent studies have shown that Fe/Si/O catalysts on the fuel side of an oxygen-enriched inverse diffusion flame produce micron-length single-walled carbon nanotubes at rapid rates (>100 μm/s). Despite the favorable catalyst/flame interaction for nanotube nucleation and growth, the catalyst lifetimes are only a few milliseconds. To increase catalyst lifetime and hence, carbon nanotube length, it is necessary to know how the local environment changes as the catalyst moves through the flame. A 2-D computational fluid dynamics model with detailed chemistry is employed to investigate the nature of the flame environment along various catalyst trajectories. The results indicate that temperature and species concentrations do not change significantly along individual catalyst trajectories, although not all trajectories experience the same environment due to the steep gradients in the radial direction. On the other hand, analysis of catalyst particle composition before and after nanotube growth shows that catalyst oxygen content decreases significantly during nanotube growth. This change in catalyst composition could affect the relative rates of carbon supply versus removal from the catalyst surface, such that carbon encapsulation and thus poisoning of the catalyst is favored after sufficient time. The results of this work indicate that catalyst deactivation, not a changing catalyst environment, is responsible for rapid encapsulation of the catalyst by amorphous carbon and thus, the short catalyst lifetimes observed in oxygen-enriched diffusion flames.     

Assessment of modal effects in local area networks

Differential mode attenuation in LANs with ring and tree topologies consisting of biconical couplers and connectors or splices is assessed by the mode transition matrix method. Comparing the results to simple addition of manufacturers' data for restricted launch demonstrates that deviations in a concatenation of up to four 6 dB couplers are tolerable, if component tolerances are small.     

An Adaptive Data-Shipping Architecture for Client Caching Data Management Systems

Data-shipping is an important form of data distribution architecture where data objects are retrieved from the server, and are cached and operated upon at the client nodes. This architecture reduces network latency and increases resource utilization at the client. Object database management systems (ODBMS), file-systems, mobile data management systems, multi-tiered Web-server systems and hybrid query-shipping/data-shipping architectures all use some variant of the data-shipping. Despite a decade of research, there is still a lack of consensus amongst the proponents of ODBMSs as to the type of data shipping architectures and algorithms that should be used. The absence of both robust (with respect to performance) algorithms, and a comprehensive performance study comparing the competing algorithms are the key reasons for this lack of agreement. In this paper we address both of these problems. We first present an adaptive data-shipping architecture which utilizes adaptive data transfer, cache consistency and recovery algorithms to improve the robustness (with respect to performance) of a data-shipping ODBMS. We then present a comprehensive performance study which evaluates the competing client-server architectures and algorithms. The study verifies the robustness of the new adaptive data-shipping architecture, provides new insights into the performance of the different competing algorithms, and helps to overturn some existing notions about some of the algorithms.     

Novel component to approximate steady-state mode power distribution in graded-index fibres

A new method for approximating steady-state mode power distribution (SMPD) in graded-index fibres is described. It has been shown that a biconical taper is a very simple and effective means to launch SMPD in short lengths of fibres. Prefabricated tapers can be directly used as component between the source and the test fibre. Experimental results are presented.     

Identification of ergosta-8,24(28)-dien-3β,6α-diol in A Δ8 → Δ7 sterol isomerase-blocked yeast mutantsterol isomerase-blocked yeast mutant

In addition to the monohydroxysterols found in the Δ⁸ → Δ⁷ isomerase-blockedSaccharomyces cerevisiae mutanterg 2, a novel dihydroxysterol, ergosta-8,24(28)-dien-3β,6α-diol, was isolated. This sterol accumulated to the extent of 2.1% of the total sterol fraction when this mutant was treated with 23-azacholesterol, a known inhibitor of the 24-methylene-sterol-24(28)-reductase.     

Characterization of a Ho(3+)-doped fluoride fiber laser with a 3.9-mum emission wavelength

The fluoride fiber laser with the longest emission wavelength, the Ho(3+)-transition at 3.9 mum in the attenuation minimum of the 3-5-mum atmospheric window, is characterized. After reviewing the importance of fluoride fibers due to their low phonon energies, we describe room-temperature fluorescence and laser action with liquid-nitrogen cooling. Continuous-wave laser action at 3.9 mum is presented for the 640- and the 890-nm pump ranges. A shift of the emission wavelength is achieved by varying the resonator mirrors. Laser characteristics and temperature dependence are discussed.