Installation of electric generators on turbine engines

The installation of generators on turbine aircraft is discussed. Emphasis is placed on the use of the samarium cobalt generator. Potential advantages of an electric secondary power system at the engine level are listed. The integrated generator and the externally mounted generator are discussed. It is concluded that the integrated generator is best used in turbojet and low bypass ratio engines where there is no easy way of placing generators externally without influencing frontal areas

Manifestation of the magnetic depopulation of one-dimensional subbands in the optical absorption of acoustic magnetoplasmons in side-gated quantum wires

We have investigated experimentally and theoretically the far-infrared (FIR) absorption of gated, deep-mesa-etched GaAs/Al$_x$Ga$_{1-x}$As quantum wires. To overcome Kohn's theorem we have in particular prepared double-layered wires and studied the acoustic magnetoplasmon branch. We find oscillations in the magnetic-field dispersion of the acoustic plasmon which are traced back to the self-consistently screened density profile in its dependence on the magnetic depopulation of the one-dimensional subbands.Comment: LaTeX-file, 4 pages with 3 included ps-figures, to appear in Physica

Deforestation, wood famine and environmental degradation in highland ecosystems of Ethiopia: urgent need for actions

One of the major challenges facing Ethiopia in its strive for development is environmental degradation, which is manifested in the form of land and water resources degradation as well as loss of biodiversity. Land degradation, in turn, is expressed in terms of soil erosion and loss of soil fertility. Deforestation/devegetation has been held as one of the major factors contributing to land degradation through exposing the soil for various agents of erosion. Ethiopia, with high-intensity rainstorms and extensive steep slopes, is highly susceptible to soil erosion, especially in the highlands. The organic content of soils is often low due to the widespread use of dung and crop residues for energy. Land degradation exerts heavy impacts on agricultural productivity and production. For instance, in 1990 alone, reduced soil depth, caused by erosion, resulted in a loss in grain production of 57,000 (at 3.5 mm soil loss) - 128,000 tons (at 8 mm soil depth). It has been estimated that the grain production lost due to land degradation in 1990 would have been sufficient to feed more than four million people. The availability of land suitable for agriculture is shrinking. At the same time, the amount of land required to feed the growing population is steadily increasing. With agricultural productivity increases lagging behind population growth rates, the gap between the availability and the demand for agricultural land continues to grow. This results in severe land-use conflicts between crop farming, animal grazing and forestry. National high forests and plantations are encroached upon and cleared for cultivation or grazing by local people. State and community forest interests collide with local grazing interests on hillside land, and grazing and fuelwood / charcoal interests confront each other in the woodlands and bushlands. Forestry can play a role in reducing land pressure and land degradation. It is important to note, however, that forestry alone will not be able to solve the problem. Even if the management of existing forest resources is improved and new trees and forests are established, this may well prove futile if the need for crop and grazing land continues to grow due to high population growth rates. Using the land for forestry to improve soil fertility or to rehabilitate and conserve the environment will be viewed as secondary to using the land for cropping and grazing to meet immediate needs of survival. Hence, attempts to alleviate land degradation are critically dependent on efforts to deal with the three main underlying causes of land degradation, namely population growth, low agricultural productivity and high dependence on fuelwood, dung and crop residue as sources of household energy. Considering the magnitude of the land 2 degradation problem, the conservation programs implemented so far are inadequate. The policy, institutional, planning and technical constraints that have been considered responsible for the inadequacy of past conservation efforts are presented. Any future initiatives aiming at overcoming the escalating land degradation problem in Ethiopia should first address these constraints realistically. There are no universal formulae or solutions to the constraints that can work across the board. Solutions should be locality specific and closely tied up with the socio-economic setup of the communities. In this regard, forestry can play a significant role in either preventing or arresting land degradation by avoiding or reducing soil erosion through reduced surface runoff and maintenance of organic matter and soil fertility. It can help in not only addressing off-farm and on-farm dimensions of soil erosion but also in maintaining the fertility of the soil thereby contributing to the alleviation of land degradation and the destruction of natural resources. The various means by which forestry can be used to address problems of land degradation are discussed as outlined in the Ethiopian Forestry Action Program

Transient transcriptome sequencing captures enhancer landscapes immediately after T-cell stimulation

Transcription regulation is poorly understood. Transcriptional enhancers produce enhancer RNAs (eRNAs), a class of transient RNAs, whose function remains mainly unclear. To monitor transcriptional regulation in human cells, rapid changes in enhancer and promoter activity must be captured with high sensitivity and temporal reso- lution. Here I show that the recently established protocol TT-seq (‘transient tran- scriptome sequencing’) can monitor rapid changes in transcription from enhancers and promoters during the immediate response of T-cells to ionomycin and phorbol 12-myristate 13-acetate (PMA). Transient transcriptome sequencing (TT-seq) maps eRNAs and mRNAs every 5 minutes after T-cell stimulation with high sensitivity, and identifies many new primary response genes. TT-seq reveals that the synthesis of 1,601 eRNAs and 650 mRNAs changes significantly within only 15 minutes after stimulation, when standard RNA-seq does not detect differentially expressed genes. Transcription of enhancers that are primed for activation by nucleosome depletion can occur immediately and simultaneously with transcription of target gene promot- ers. My results indicate that enhancer transcription is a good proxy for enhancer regulatory activity in target gene activation, and establish TT-seq as a tool for monitoring the dynamics of enhancer landscapes and transcription programs during cellular responses and differentiation. Additionally, I developed a normalization method for TT-seq that scales labeled and total RNA-seq samples relative to each other, allowing to determine absolute half-lives. The method provides a powerful tool to normalize various samples relative to each other on a global scale, and therefore allows to observe global changes in RNA synthesis and degradation. Taken together, metabolical labeling of RNA followed by kinetic modeling enables to quantify RNA metabolism rates and to detect dynamic changes in enhancer landscapes and RNA expression levels

Analysis of locking self-taping bone screws for angularly stable plates

Paper focuses on biomechanics, specifically on locking cortical bone screws in angularly stable plates used for the treatment of bone fractures in the medical fields of traumatology and orthopaedics. During extraction of titanium-alloy implants, problems are encountered in an effort to loosen some locking bone screws from the locking holes of an angularly stable plate and the subsequent stripping of the internal hexagon of the screw head. The self-locking of the screw-plate threaded joint was verified by calculation and the effect of the angle of the thread on the head of the locking cortical bone screw on self-locking was evaluated. The magnitude of the torque, causing the stripping of the internal hexagon (the Inbus type head) of a locking cortical bone screw with a shank diameter of 3.5 mm from Ti6Al4 V titanium alloy to ISO 5832-3, was determined experimentally. Also, it was experimentally found that the rotation of the screwdriver end with a hexagonal tip inside the locking cortical bone screw head during stripping of the internal hexagon causes strain of the screw head perimeter and thereby an increase of thread friction. The effect of tightening torque on the possibility of loosening of the locking cortical bone screw from the locking hole of an angularly stable plate was assessed experimentally. From the evaluation of five alternative shapes of locking cortical bone screw heads in terms of the acting stress and generated strains, it follows that the best screw is the screw with the Torx type head, which demonstrates the lowest values of reduced stress and equivalent plastic strain. Based on experiments and simulations the authors recommend that all global producers of locking cortical bone screws for locking holes of angularly stable plates use the Torx type heads, and not heads of the Inbus type or the Square, PH, PZ types.Web of Science37462561

The gadolinium-lead phase system

http://www.worldcat.org/oclc/8165617

Queering black greek-lettered fraternities, masculinity and manhood : a queer of color critique of institutionality in higher education.

Drawing heavily on Roderick Ferguson’s (2012) theory of institutionality, this dissertation constructs a counter-historical genealogy of racialized gender in higher education and U.S. society through the formation of black Greek-lettered fraternities. Ferguson argues that with the insurgence of minority resistance globally and domestically during the mid-twentieth century, hegemonic power took a new form. Instead of rejecting minority difference, power’s new network attempted to work through and with minority difference in an effort to absorb and restrict these radical formations within state, capital and academy frameworks—producing narrow or one-dimensional minority subjectivities. Established at the turn of the twentieth century, black Greek-lettered fraternities reflect the impetus and crossroads of power’s new archive as constituted through two competing yet complementing social movements—the racial uplift and the American fraternal movements—therefore, working within and against institutional normative logics of race, gender, sexuality, and class. As such, this study employs black fraternalism to reveal power’s post-WWII dynamics and its impact on black subjectivity within the academy and the broader U.S. political landscape, particularly in relation to black queer embodiment and politics. This study constitutes a queer of color critique. A queer of color critique centers the queer of color subject, and in doing so, exposes the often-obscured interconnected systems of race, gender, sexuality and class in cultural formations to map the contours of power propagated by state and capital forces. This study finds that as minority difference was institutionalized within the post-civil rights academy, black fraternalism was employed to facilitate and affirm institutional demands for equity and an idealized cis-heteropatriarchal black subjectivity, foreclosing on alternative gendered critical possibilities. As such, this study explores the development of black queer fraternal (BQF) formations, so-called deviant forms of black fraternalism that subvert its institutional masculine homosocial logics, to suggests a critical alternative black gender politics, freedom, memory, and normality