Transmission through abrupt heterojunction potential barriers

A new expression is derived for the transmission coefficient of incident electrons scattered by a varying potential with discontinuities. The expression is applicable above, below, and near the potential peak. As an example, electron transmission across the energy barrier in the emitter of an InP/InGaAs heterojunction bipolar transistor is calculated. Excellent agreement with a numerical calculation is obtained, even for electron energies close to the potential peak, where other expressions fail. It is shown how this new approach reduces to other expressions in limiting cases, and its validity in comparison to other approximations is discussed     

Untersuchungen zum SwRK-Verhalten des unlegierten Stahles Ck 45 in chloridionenhaltigen wäßrigen Medien

Corrosion fatigue behaviour of steel Ck 45 in aqueous solutions containing chloride ions The fatigue behaviour of carbon steel Ck 45 (comparable to AISI 1045x) is investigated for cyclic tension and rotating bending load with a frequency of 25 Hz. The fatigue limits under cyclic tension load in air are 410 N/mm² for smooth specimens and 290 N/mm² for notched specimens. For rotating bending load a value of 200 N/mm² is found for smooth specimen. The fatigue limits for N = 10⁷ in two different environments (0.3% and 3% NaCl-solution) reach only 37–57% of the according values in air. Cathodic protection of smooth specimens causes an improvement to 95% of the air fatigue limit. The evaluation of the free corrosion potential for all corrosion fatigue tests and the appearence of fracture show typical attributes of corrosion fatigue in the active state.     

Exploring the Groß Schönebeck (Germany) geothermal site using a statistical joint interpretation of magnetotelluric and seismic tomography models

Exploration for geothermal resources is often challenging because there are no geophysical techniques that provide direct images of the parameters of interest, such as porosity, permeability and fluid content. Magnetotelluric (MT) and seismic tomography methods yield information about subsurface distribution of resistivity and seismic velocity on similar scales and resolution. The lack of a fundamental law linking the two parameters, however, has limited joint interpretation to a qualitative analysis. By using a statistical approach in which the resistivity and velocity models are investigated in the joint parameter space, we are able to identify regions of high correlation and map these classes (or structures) back onto the spatial domain. This technique, applied to a seismic tomography-MT profile in the area of the Groß Schönebeck geothermal site, allows us to identify a number of classes in accordance with the local geology. In particular, a high-velocity, low-resistivity class is interpreted as related to areas with thinner layers of evaporites; regions where these sedimentary layers are highly fractured may be of higher permeability.     

Economic impacts from the promotion of renewable energy technologies: The German experience

The allure of an environmentally benign, abundant, and cost-effective energy source has led an increasing number of industrialized countries to back public financing of renewable energies. Germany’s experience with renewable energy promotion is often cited as a model to be replicated elsewhere, being based on a combination of far-reaching energy and environmental laws that stretch back nearly two decades. This paper critically reviews the centerpiece of this effort, the Renewable Energy Sources Act (EEG), focusing on its costs and the associated implications for job creation and climate protection. We argue that German renewable energy policy, and in particular the adopted feed-in tariff scheme, has failed to harness the market incentives needed to ensure a viable and cost-effective introduction of renewable energies into the country’s energy portfolio. To the contrary, the government’s support mechanisms have in many respects subverted these incentives, resulting in massive expenditures that show little long-term promise for stimulating the economy, protecting the environment, or increasing energy security.     

Catalytic conditioning of synthesis gas produced by biomass gasification

The catalytic steam reforming of aromatic hydrocarbons in a background of synthesis gas was investigated for two catalysts. A proprietary non-nickel based catalyst, designated DN-34, and a commercial nickel steam reforming catalyst ICI 46-1 were tested. Statistically designed experiments were used to examine the effects of temperature, space velocity and percent of steam in the feed on catalyst performance. All experiments were performed in a plug-flow micro-reactor interfaced with a molecular beam mass spectrometer. The catalyst DN-34 was also tested in slip-stream fluidized bed reactors attached to a 9 tonne day⁻¹ indirectly heated biomass gasifier at Battelle Columbus Laboratory.

DN-34 was found to be effective for destroying a variety of aromatic hydrocarbons found in biomass gasifier tar in both the micro-reactor and gasifier-scale experiments. DN-34 also exhibited significant water-gas shift activity but was unsatisfactory for methane destruction. ICI 46-1 exhibited excellent methane steam reforming activity. A process is suggested that uses DN-34 to steam reform tar and perform the water-gas shift, followed by a second reactor with ICI 46-1 to reform methane. Differences and similarities with other dual-bed processes described in the literature are discussed.     

Sarcomatoid carcinomas of the lung: a clinicopathologic review

Sarcomatoid carcinomas (SC) of the lung are the most common pulmonary neoplasms that exhibit a composition by spindled or pleomorphic tumor cells. As such, many of them may be confused easily with true sarcomas diagnostically unless special immunohistological or ultrastructural analyses are performed. Reactivity is expected for keratin, epithelial membrane antigen, or collagen type IV in the sarcomalike elements in SC, although it may be focal. Electron microscopy often shows the presence of junctional complexes between tumor cells, with or without pericellular basal lamina and cytoplasmic skeins of intermediate filaments. Current terminological preferences are such that several formerly used terms--including "spindle-cell carcinoma," "pulmonary blastoma," "squamous cell carcinoma with pseudosarcomatous stroma," "pseudosarcoma," and "carcinosarcoma"--are now encompassed by the more generic designation of "sarcomatoid carcinoma." The clinical course of patients with this neoplasm is aggressive, with an overall 5-year survival rate approximating 20%.     

Effet of Billet Difference on the High–Temperature Strength of Hot–Pressed Silicon Nitride

The strength and fatigue resistance of silicon nitride was determined from specimens machined from two hot–pressed billets. The results indicate that although fatigue resistance is not affected up to 1100°C, differences in chemical composition between the two billets result in different high–temperature strengths. Billet acceptance criteria include both high–temperature strength and oxidation resistance specifications.     

Characterization of nanometer-sized, mechanically exfoliated graphene on the H-passivated Si(100) surface using scanning tunneling microscopy

We have developed a method for depositing graphene monolayers and bilayers with minimum lateral dimensions of 2-10?nm by the mechanical exfoliation of graphite onto the Si(100)-2 × 1:H surface. Room temperature, ultrahigh vacuum tunneling spectroscopy measurements of nanometer-sized single layer graphene reveal a size-dependent energy gap ranging from 0.1 to 1?eV. Furthermore, the number of graphene layers can be directly determined from scanning tunneling microscopy topographic contours. This atomistic study provides an experimental basis for probing the electronic structure of nanometer-sized graphene which can assist the development of graphene-based nanoelectronics.     

Influence of the microstructure on the deformation behaviour of metal–matrix composites

In this contribution, investigations of the influence of the microstructure on the macro-, meso- and micro-effects in metal–matrix composites are presented by direct combination of experiment and simulation. The aim of the presented work consists in an improved understanding of the mechanical behaviour of heterogeneous materials by combining information of different length scales.