1,600 research outputs found
Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels
Mitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion
InGaAs/InP hot electron transistors grown by chemical beam epitaxy
In this letter, we report on the dc performance of chemical beam epitaxy grown InGaAs/InP hot electron transistors (HETs). The highest observed differential β (dIC/dIB) is over 100. The HETs have Pd/Ge/Ti/Al shallow ohmic base contacts with diffusion lengths less than 300 Å. Furthermore, we also demonstrated ballistic transport of electrons in an InGaAs/InP HET by obtaining an energy distribution of electrons with ∼60 meV full width at half maximum. The measured conduction band discontinuity of InGaAs/InP is 250.3 meV, which is 39.8% of the band gap difference.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70748/2/APPLAB-61-2-189-1.pd
Making the user more efficient: Design for sustainable behaviour
User behaviour is a significant determinant of a product’s environmental impact; while engineering advances permit increased efficiency of product operation, the user’s decisions and habits ultimately have a major effect on the energy or other resources used by the product. There is thus a need to change users’ behaviour. A range of design techniques developed in diverse contexts suggest opportunities for engineers, designers and other stakeholders working in the field of sustainable innovation to affect users’ behaviour at the point of interaction with the product or system, in effect ‘making the user more efficient’. Approaches to changing users’ behaviour from a number of fields are reviewed and discussed, including: strategic design of affordances and behaviour-shaping constraints to control or affect energyor other resource-using interactions; the use of different kinds of feedback and persuasive technology techniques to encourage or guide users to reduce their environmental impact; and context-based systems which use feedback to adjust their behaviour to run at optimum efficiency and reduce the opportunity for user-affected inefficiency. Example implementations in the sustainable engineering and ecodesign field are suggested and discussed
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Using a runway paradigm to assess the relative strength of rats' motivations for enrichment objects
Laboratory animals should be provided with enrichment objects in their cages; however, it is first necessary to
test whether the proposed enrichment objects provide benefits that increase the animals’ welfare. The two main
paradigms currently used to assess proposed enrichment objects are the choice test, which is limited to determining
relative frequency of choice, and consumer demand studies, which can indicate the strength of a preference but are complex to design. Here, we propose a third methodology: a runway paradigm, which can be used to assess the strength of an animal’s motivation for enrichment objects, is simpler to use than consumer demand studies, and is faster to complete than typical choice tests. Time spent with objects in a standard choice test was used to rank several enrichment objects in order to compare with the ranking found in our runway paradigm. The rats ran significantly more times, ran faster, and interacted longer with objects with which they had previously spent the most time. It was concluded that this simple methodology is suitable for measuring rats’ motivation to reach enrichment objects. This can be used to assess the preference for different types of enrichment objects or to measure reward system processes
Thin-Film Metamaterials called Sculptured Thin Films
Morphology and performance are conjointed attributes of metamaterials, of
which sculptured thin films (STFs) are examples. STFs are assemblies of
nanowires that can be fabricated from many different materials, typically via
physical vapor deposition onto rotating substrates. The curvilinear--nanowire
morphology of STFs is determined by the substrate motions during fabrication.
The optical properties, especially, can be tailored by varying the morphology
of STFs. In many cases prototype devices have been fabricated for various
optical, thermal, chemical, and biological applications.Comment: to be published in Proc. ICTP School on Metamaterials (Augsut 2009,
Sibiu, Romania
Theory of Fast Quantum Control of Exciton Dynamics in Semiconductor Quantum Dots
Optical techniques for the quantum control of the dynamics of multiexciton
states in a semiconductor quantum dot are explored in theory. Composite
bichromatic phase-locked pulses are shown to reduce the time of elementary
quantum operations on excitons and biexcitons by an order of magnitude or more.
Analytic and numerical methods of designing the pulse sequences are
investigated. Fidelity of the operation is used to gauge its quality. A
modified Quantum Fourier Transform algorithm is constructed with only Rabi
rotations and is shown to reduce the number of operations. Application of the
designed pulses to the algorithm is tested by a numerical simulation.Comment: 11 pages,5 figure
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Destabilisation and modification of Tollmien-Schlichting disturbances by a three-dimensional surface indentation
We consider the influence of a smooth three-dimensional (3-D) indentation on the instability of an incompressible boundary layer by linear and nonlinear analyses. The numerical work was complemented by an experimental study to investigate indentations of approximately δ99 and δ99 width at depths of 45%, 52% and 60% of δ99 where δ99 indicates 99% boundary layer thickness. For these indentations a separation bubble confined within the indentation arises. Upstream of the indentation, spanwise-uniform Tollmien-Schlichting (TS) waves are assumed to exist, with the objective to investigate how the 3-D surface indentation modifies the 2-D TS disturbance. Numerical corroboration against experimental data reveals good quantitative agreement. Comparing the structure of the 3-D separation bubble to that created by a purely 2-D indentation, there are a number of topological changes particularly in the case of the widest indentation; more rapid amplification and modification of the upstream TS waves along the symmetry plane of the indentation is observed. For the shortest indentations, beyond a certain depth there are then no distinct topological changes of the separation bubbles and hence on flow instability. The destabilising mechanism is found to be due to the confined separation bubble and is attributed to the inflectional instability of the separated shear layer. Finally for the widest width indentation investigated , results of the linear analysis are compared with direct numerical simulations. A comparison with the traditional criteria of using -factors to assess instability of properly 3-D disturbances reveals that a general indication of flow destabilisation and development of strongly nonlinear behaviour is indicated as values are attained. However -factors, based on linear models, can only be used to provide indications and severity of the destabilisation, since the process of disturbance breakdown to turbulence is inherently nonlinear and dependent on the magnitude and scope of the initial forcing
Detecting and quantifying methane emissions from oil and gas production: algorithm development with ground-truth calibration based on Sentinel-2 satellite imagery
Sentinel-2 satellite imagery has been shown by studies to be
capable of detecting and quantifying methane emissions from oil and gas
production. However, current methods lack performance calibration with
ground-truth testing. This study developed a multi-band–multi-pass–multi-comparison-date methane retrieval algorithm that enhances Sentinel-2 sensitivity to methane plumes. The method was calibrated
using data from a large-scale controlled-release test in Ehrenberg, Arizona,
in fall 2021, with three algorithm parameters tuned based on the true
emission rates. Tuned parameters are the pixel-level concentration upper-bound threshold during extreme value removal, the number of comparison
dates, and the pixel-level methane concentration percentage threshold when
determining the spatial extent of a plume. We found that a low value of the
upper-bound threshold during extreme value removal can result in false
negatives. A high number of comparison dates helps enhance the algorithm
sensitivity to the plumes in the target date, but values in excess of
12 d are neither necessary nor computationally efficient. A high percentage
threshold when determining the spatial extent of a plume helps enhance the
quantification accuracy, but it may harm the yes/no detection accuracy. We
found that there is a trade-off between quantification accuracy and
detection accuracy. In a scenario with the highest quantification accuracy,
we achieved the lowest quantification error and had zero false-positive
detections; however, the algorithm missed three true plumes, which reduced the
yes/no detection accuracy. In contrast, all of the true plumes were
detected in the highest detection accuracy scenario, but the emission rate
quantification had higher errors. We illustrated a two-step method that
updates the emission rate estimates in an interim step, which improves
quantification accuracy while keeping high yes/no detection accuracy. We
also validated the algorithm's ability to detect true positives and true
negatives in two application studies.</p
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