2,415 research outputs found
Preliminary Photomicrographic Studies of Fuel Sprays
Photomicrographs were taken of fuel sprays injected into air at various densities for the purpose of studying the spray structure and the stages in the atomization of the fuel. The photomicrographs were taken at magnifying powers of 2.5, 3.25, and 10, using a spark discharge of very short duration for illumination. The results indicate that the theory advanced by Dr. R. A. Castleman, Jr., on the atomization of fuel in carburetors may also be applied to the atomization of fuel sprays of the solid-injection type. The fuel leaves the nozzle as a solid column, is ruffled and then torn into small, irregular ligaments by the action of the air. These ligaments are then quickly broken up into drops by the surface tension of the fuel. The photomicrographs also show that the dispersion of a fuel spray at a given distance from the nozzle increases with an increase in the jet velocity or an increase in the air density. The first portions of fuel sprays injected from an automatic injection valve into air at atmospheric density have a much greater dispersion than the later portions, but this difference decreases rapidly as the air density is increased
Crystallographic Analyses of Ion Channels: Lessons and Challenges
Membrane proteins fascinate at many levels, from their central functional roles in transport, energy transduction, and signal transduction processes to structural questions concerning how they fold and operate in the exotic environments of the membrane bilayer and the water-bilayer interface and to methodological issues associated with studying membrane proteins either in situ or extracted from the membrane. This interplay is beautifully exemplified by ion channels, a collection of integral membrane proteins that mediate the transmembrane passage of ions down their electrochemical potential gradient (for general reviews, see Refs. 1 and 2). Ion channels are key elements of signaling and sensing pathways, including nerve cell conduction, hormone response, and mechanosensation. The characteristic properties of ion channels reflect their conductance, ion selectivity, and gating. Ion channels are often specific for a particular type of ion (such as potassium or chloride) or a class of ions (such as anions) and are typically regulated by conformational switching of the protein structure between "open" and "closed" states. This conformational switching may be gated in response to changes in membrane potential, ligand binding, or application of mechanical forces. Detailed functional characterizations of channels and their gating mechanisms have been achieved, reflecting exquisite methodological advances such as patch clamp methods that can monitor the activities of individual channels (3). Until recently, corresponding information about the three-dimensional structures of channels was not available, reflecting difficulties in obtaining sufficient quantities of membrane proteins for crystallization trials. Happily, this situation has started to change with the structure determinations of the Streptomyces lividans K+ channel (KcsA (4)) and the Mycobacterium tuberculosis mechanosensitive channel (MscL (5)).
A variety of reviews (6-12) have appeared recently that discuss functional implications of these channel structures. This review discusses these developments from a complementary perspective, by considering the implications of these structures from within the larger framework of membrane protein structure and function. Because of space restrictions, this review necessarily emphasizes membrane proteins that are composed primarily of alpha-helical bundles, such as KcsA and MscL, rather than beta-barrel proteins, such as porins, typically found in bacterial outer membranes
Contractual Versus Generic Outsourcing: The Role of Proximity
We explore the relationship between proximity of buyers and sellers and the organizational form of outsourcing. Outsourcing can be "contractual" in which suppliers undertake specific investments or involve "generic" market transactions. Proximity expands the variety of products sourced through contracts abroad rather than at home, but the range of generic imports is unchanged. A higher-quality foreign workforce raises the variety of contractual trade, but at the expense of generics. We confirm these predictions using data for ordinary versus processing exports from Chinese provinces to destination markets and also the predictions of an extended model that allows for multinational production.
Contractual Versus Non-Contractual Trade: The Role of Institutions in China
Recent research has demonstrated the importance of institutional quality at the country level for both the volume of trade and the ability to trade in differentiated goods that rely on contract enforcement. This paper takes advantage of cross-provincial variation in institutional quality in China, and export data that distinguishes between foreign and domestic exporters and processing versus ordinary trade, to show that institutional quality is a significant factor in determining Chinese provincial export patterns. Institutions matter more for processing trade, and more for foreign firms, just as we would expect from a greater reliance on contracts in these cases.
Heat Transfer to Fuel Sprays Injected into Heated Gases
This report presents the results of a study made of the influence of several variables on the pressure decrease accompanying injection of a relatively cool liquid into a heated compressed gas. Indirectly, this pressure decrease and the time rate of change of it are indicative of the total heat transferred as well as the rate of heat transfer between the gas and the injected liquid. Air, nitrogen, and carbon dioxide were used as ambient gases; diesel fuel and benzene were the injected liquids. The gas densities and gas-fuel ratios covered approximately the range used in compression-ignition engines. The gas temperatures ranged from 150 degrees c. to 350 degrees c
Topological generation of exceptional algebraic groups
Let be a simple algebraic group over an algebraically closed field
and let be non-central conjugacy classes in . In this
paper, we consider the problem of determining whether there exist
such that is Zariski dense in . First we
establish a general result, which shows that if is an irreducible
subvariety of , then the set of tuples in generating a dense
subgroup of is either empty or dense in . In the special case
, by considering the dimensions of fixed
point spaces, we prove that this set is dense when is an exceptional
algebraic group and , assuming is not algebraic over a
finite field. In fact, for we only need and both of
these bounds are best possible. As an application, we show that many faithful
representations of exceptional algebraic groups are generically free. We also
establish new results on the topological generation of exceptional groups in
the special case , which have applications to random generation of finite
exceptional groups of Lie type. In particular, we prove a conjecture of Liebeck
and Shalev on the random -generation of exceptional groups.Comment: 40 pages; to appear in Advances in Mathematic
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Effect of Time-of-Flight and Regularized Reconstructions on Quantitative Measurements and Qualitative Assessments in Newly Diagnosed Prostate Cancer With 18F-Fluorocholine Dual Time Point PET/MRI.
Recent technical advances in positron emission tomography/magnetic resonance imaging (PET/MRI) technology allow much improved time-of-flight (TOF) and regularized iterative PET reconstruction regularized iterative reconstruction (RIR) algorithms. We evaluated the effect of TOF and RIR on standardized uptake values (maximum and peak SUV [SUVmax and SUVpeak]) and their metabolic tumor volume dependencies and visual image quality for 18F-fluorocholine PET/MRI in patients with newly diagnosed prostate cancer. Fourteen patients were administered with 3 MBq/kg of 18F-fluorocholine and scanned dynamically for 30 minutes. Positron emission tomography images were divided to early and late time points (1-6 minutes summed and 7-30 minutes summed). The values of the different SUVs were documented for dominant PET-avid lesions, and metabolic tumor volume was estimated using a 50% isocontour and SUV threshold of 2.5. Image quality was assessed via visual acuity scoring (VAS). We found that incorporation of TOF or RIR increased lesion SUVs. The lesion to background ratio was not improved by TOF reconstruction, while RIR improved the lesion to background ratio significantly ( P < .05). The values of the different VAS were all significantly higher ( P < .05) for RIR images over TOF, RIR over non-TOF, and TOF over non-TOF. In conclusion, our data indicate that TOF or RIR should be incorporated into current protocols when available
Topological generation of simple algebraic groups
Let be a simple algebraic group over an algebraically closed field and
let be an irreducible subvariety of with . In this
paper, we consider the general problem of determining if there exists a tuple
such that is
Zariski dense in . We are primarily interested in the case where and each is a conjugacy class of comprising
elements of prime order modulo the center of . In this setting, our main
theorem gives a complete solution to the problem when is a symplectic or
orthogonal group. By combining our results with earlier work on linear and
exceptional groups, this gives a complete solution for all simple algebraic
groups. We also present several applications. For example, we use our main
theorem to show that many faithful representations of symplectic and orthogonal
groups are generically free. We also establish new asymptotic results on the
probabilistic generation of finite simple groups by pairs of prime order
elements, completing a line of research initiated by Liebeck and Shalev over 25
years ago.Comment: 69 pages; to appear in J. Eur. Math. Soc. (JEMS
Unofficial answers to the Uniform certified public accountants examination, May 1948 to November 1950
https://egrove.olemiss.edu/aicpa_exam/1111/thumbnail.jp
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