779 research outputs found
Utilization of waste heat in trucks for increased fuel economy
Improvements in fuel economy for a broad spectrum of truck engines and waste heat utilization concepts are evaluated and compared. The engines considered are the diesel, spark ignition, gas turbine, and Stirling. The waste heat utilization concepts include preheating, regeneration, turbocharging, turbocompounding, and Rankine engine compounding. Predictions were based on fuel-air cycle analyses, computer simulation, and engine test data. The results reveal that diesel driving cycle performance can be increased by 20% through increased turbocharging, turbocompounding, and Rankine engine compounding. The Rankine engine compounding provides about three times as much improvement as turbocompounding but also costs about three times as much. Performance for either is approximately doubled if applied to an adiabatic diesel
Utilization of waste heat in trucks for increased fuel economy
The waste heat utilization concepts include preheating, regeneration, turbocharging, turbocompounding, and Rankine engine compounding. Predictions are based on fuel-air cycle analyses, computer simulation, and engine test data. All options are evaluated in terms of maximum theoretical improvements, but the Diesel and adiabatic Diesel are also compared on the basis of maximum expected improvement and expected improvement over a driving cycle. The study indicates that Diesels should be turbocharged and aftercooled to the maximum possible level. The results reveal that Diesel driving cycle performance can be increased by 20% through increased turbocharging, turbocompounding, and Rankine engine compounding. The Rankine engine compounding provides about three times as much improvement as turbocompounding but also costs about three times as much. Performance for either can be approximately doubled if applied to an adiabatic Diesel
Sterols sense swelling in lipid bilayers
In the mimetic membrane system of phosphatidylcholine bilayers, thickening
(pre-critical behavior, anomalous swelling) of the bilayers is observed, in the
vicinity of the main transition, which is non-linear with temperature. The
sterols cholesterol and androsten are used as sensors in a time-resolved
simultaneous small- and wide angle x-ray diffraction study to investigate the
cause of the thickening. We observe precritical behavior in the pure lipid
system, as well as with sterol concentrations less than 15%. To describe the
precritical behavior we introduce a theory of precritical phenomena.The good
temperature resolution of the data shows that a theory of the influence of
fluctuations needs modification. The main cause of the critical behavior
appears to be a changing hydration of the bilayer.Comment: 11 pages, 7 ps figures included, to appear in Phys.Rev.
Theoretical and numerical studies of chemisorption on a line with precursor layer diffusion
We consider a model for random deposition of monomers on a line with
extrinsic precursor states. As the adsorbate coverage increases, the system
develops non-trivial correlations due to the diffusion mediated deposition
mechanism. In a numeric simulation, we study various quantities describing the
evolution of the island structure. We propose a simple, self-consistent theory
which incorporates pair correlations. The results for the correlations, island
density number, average island size and probabilities of island nucleation,
growth and coagulation show good agreement with the simulation data.Comment: 17 pages(LaTeX), 11 figures(1 PS file, uuencoded), submmited to Phys.
Rev.
Robust high-dimensional precision matrix estimation
The dependency structure of multivariate data can be analyzed using the
covariance matrix . In many fields the precision matrix
is even more informative. As the sample covariance estimator is singular in
high-dimensions, it cannot be used to obtain a precision matrix estimator. A
popular high-dimensional estimator is the graphical lasso, but it lacks
robustness. We consider the high-dimensional independent contamination model.
Here, even a small percentage of contaminated cells in the data matrix may lead
to a high percentage of contaminated rows. Downweighting entire observations,
which is done by traditional robust procedures, would then results in a loss of
information. In this paper, we formally prove that replacing the sample
covariance matrix in the graphical lasso with an elementwise robust covariance
matrix leads to an elementwise robust, sparse precision matrix estimator
computable in high-dimensions. Examples of such elementwise robust covariance
estimators are given. The final precision matrix estimator is positive
definite, has a high breakdown point under elementwise contamination and can be
computed fast
Kinetics and Jamming Coverage in a Random Sequential Adsorption of Polymer Chains
Using a highly efficient Monte Carlo algorithm, we are able to study the
growth of coverage in a random sequential adsorption (RSA) of self-avoiding
walk (SAW) chains for up to 10^{12} time steps on a square lattice. For the
first time, the true jamming coverage (theta_J) is found to decay with the
chain length (N) with a power-law theta_J propto N^{-0.1}. The growth of the
coverage to its jamming limit can be described by a power-law, theta(t) approx
theta_J -c/t^y with an effective exponent y which depends on the chain length,
i.e., y = 0.50 for N=4 to y = 0.07 for N=30 with y -> 0 in the asymptotic limit
N -> infinity.Comment: RevTeX, 5 pages inclduing figure
Bacteroides fragilis requires the ferrous-iron transporter FeoAB and the CobN-like proteins BtuS1 and BtuS2 for assimilation of iron released from heme
The intestinal commensal and opportunistic anaerobic pathogen Bacteroides fragilis has an essential requirement for both heme and free iron to support growth in extraintestinal infections. In the absence of free iron, B. fragilis can utilize heme as the sole source of iron. However, the mechanisms to remove iron from heme are not completely understood. In this study, we show that the inner membrane ferrous iron
transporter ∆feoAB mutant strain is no longer able to grow with heme as the sole source of iron. Genetic complementation with the feoAB gene operon completely restored growth. Our data indicate that iron is removed from heme in the periplasmic space, and the released iron is transported by the FeoAB system. Interestingly, when B. fragilis utilizes iron from heme, it releases heme-derived porphyrins by a dechelatase activity which is upregulated under low iron conditions. This is supported by the findings showing that formation of heme-derived porphyrins in the ∆feoAB mutant and the parent strain increased 30-fold and fivefold (respectively) under low iron conditions compared to iron replete conditions. Moreover, the btuS1 btuS2 doublemutant strain (lacking the predicted periplasmic, membrane anchored CobN-like proteins) also showed growth defect with heme as the sole source of iron, suggesting that BtuS1 and BtuS2 are involved in heme-iron assimilation. Though the dechelatase mechanism remains uncharacterized, assays performed in bacterial crude extracts show that BtuS1 and BtuS2 affect the regulation of the dechelatase-specific activities in an iron-dependent manner. These findings suggest that the mechanism to extract iron from heme in Bacteroides requires a group of proteins, which spans the
periplasmic space to make iron available for cellular functions
An orbital fistula complicating anaerobic frontal sinusitis and osteomyelitis
A patient is described with an orbital fistula complicating frontal sinusitis and osteomyelitis of the frontal bone. The fistula was excised, but a fortnight later an acute exacerbation occurred. From the discharging pus a Staphylococcus aureus was cultured and from mucosa obtained during surgery a microaerophilic Streptococcus. These findings led to the diagnosis: synergistic bacterial inflammation of the frontal sinus, with osteomyelitis and orbital cellulitis
Rationalising "for" and "against" a policy of school-led careers guidance in STEM in the U.K. : a teacher perspective
This paper reports on teacher attitudes to changes in the provision of careers guidance in the U.K., particularly as it relates to Science, Technology, Engineering and Mathematics (STEM). It draws on survey data of n = 94 secondary-school teachers operating in STEM domains and their attitudes towards a U.K. and devolved policy of internalising careers guidance within schools. The survey presents a mixed message of teachers recognising the significance of their unique position in providing learners with careers guidance yet concern that their ‘relational proximity’ to students and ‘informational distance’ from higher education and STEM industry may produce bias and misinformation that is harmful to their educational and occupational futures
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