Effect of Surface Waviness on Transition in Three-Dimensional Boundary-Layer Flow

The effect of a surface wave on transition in three-dimensional boundary-layer flow over an infinite swept wing was studied. The mean flow computed using interacting boundary-layer theory, and transition was predicted using linear stability theory coupled with the empirical eN method. It was found that decreasing the wave height, sweep angle, or freestream unit Reynolds number, and increasing the freestream Mach number or suction level all stabilized the flow and moved transition onset to downstream locations

Relationship between transition and modes of instability in supersonic boundary layers

The relationship between the predicted transition location and the first and second modes of instability in two-dimensional supersonic boundary-layer flow on a flat plate is examined. Linear stability theory and the N-factor criterion are used to predict transition location. The effect of heat transfer is also studied; the results demonstrate that the transition reversal phenomenon can be explained by the opposite effect of cooling on the first and second modes of instability. Compressibility of destabilizing at free-stream Mach numbers of 2 to 3.5. The predicted transition location is due to the oblique first modes of instability, up to free-stream Mach numbers between 6 and 6.5. At higher Mach numbers, the predicted transition location is due to a combination of two-dimensional first and second modes of instability

Transition prediction and control in subsonic flow over a hump

The influence of a surface roughness element in the form of a two-dimensional hump on the transition location in a two-dimensional subsonic flow with a free-stream Mach number up to 0.8 is evaluated. Linear stability theory, coupled with the N-factor transition criterion, is used in the evaluation. The mean flow over the hump is calculated by solving the interacting boundary-layer equations; the viscous-inviscid coupling is taken into consideration, and the flow is solved within the separation bubble. The effects of hump height, length, location, and shape; unit Reynolds number; free-stream Mach number, continuous suction level; location of a suction strip; continuous cooling level; and location of a heating strip on the transition location are evaluated. The N-factor criterion predictions agree well with the experimental correlation of Fage; in addition, the N-factor criterion is more general and powerful than experimental correlations. The theoretically predicted effects of the hump's parameters and flow conditions on transition location are consistent and in agreement with both wind-tunnel and flight observations

Stability of separating subsonic boundary layers

The primary and subharmonic instabilities of separating compressible subsonic two-dimensional boundary layers in the presence of a two-dimensional roughness element on a flat plate are investigated. The roughness elements considered are humps and forward- and backward-facing steps. The use of cooling and suction to control these instabilities is studied. The similarities and differences between the instability characteristics of separating boundary layers and those of the boundary layer over a flat plate with a zero pressure gradient are pointed out and discussed. The theoretical results agree qualitatively and quantitatively with the experimental data of Dovgal and Kozlov. Cooling and suction decrease the growth rates of primary and subharmonic waves in the attached-flow regions but increase them in the separated-flow regions

Network disruption and recovery: Co-evolution of defender and attacker in a dynamic game

The evolution of interactions between individuals or organizations are a central theme of complexity research. We aim at modeling a dynamic game on a network where an attacker and a defender compete in disrupting and reconnecting a network. The choices of how to attack and defend the network are governed by a Genetic Algorithm (GA) which is used to dynamically choose among a set of available strategies. Our analysis shows that the choice of strategy is particularly important if the resources available to the defender are slightly higher than the attackers'. The best strategies found through GAs by the attackers and defenders are based on betweenness centrality. Our results agree with previous literature assessing strategies for network attack and defense in a static context. However, our paper is one of the first ones to show how a GA approach can be applied in a dynamic game on a network. This research provides a starting-point to further explore strategies as we currently apply a limited set of strategies only

Comparison Between the Effects of Different Sources of Dietary Fiber on Blood Lipid Profile in Rats

This study was conducted to investigate the effect of different sources of dietary fiber on serum lipids and lipoproteins in Sprague-Dawley rats, namely total cholesterol (TC), Low-density lipoprotein cholesterol (LDL-C), high–density lipoprotein cholesterol (HDL-C) triglyceride (TG), and (HDL-C/LDL-C) ratio. The experimental diets included casein diet, untreated wheat bran diet, soaked wheat bran diet, Arabic white bread diet, lupine diet, chickpea and pectin diet. Each group of rats (6/group) was fed one of the seven prepared diets for 6 weeks. Untreated wheat bran has hypercholesterolemic effect since it significantly (p<0.05) increased TC, LDL-C and decreased HDL-C values as compared with treated bran diets. The soaking process lowered significantly (p<0.05) TC and LDL-C levels in comparison with casein diet. Chickpea diet had higher significant value of HDL-C than soaked wheat bran and lupine diets. However, it was not significantly different from casein and untreated wheat bran diet.  In addition, Chickpea diet had a significantly higher HDL-C value than pectin diet. The values of HDL-C of the Lupine diet are not significantly different (p>0.05) from casein and pectin diets, but it has also decreased LDL-C. White bread was found to have no hypocholesterolemic effect in comparison with treated brans groups and control group; it raised TG, TC and LDL-C levels. Pectin had a similar behavior in a remarkable decrease blood TC and LDL-C cholesterol. White bread was found to have  no hypocholesterolemic effect in comparison with treated brans groups and control group; it raised TG, TC and LDL-C  levels. It is concluded that the behavior of cereals and legumes varies in its effect on cholesterol–lowering ability. Preparation of wheat bran foods by soaking improve some physiological characteristics of insoluble fibers, particularly lowering total cholesterol TC and low-density lipoprotein cholesterol LDL-C). Keywords: Dietary fiber, Arabic bread, Wheat bran, Soaking, Chickpea, Lupine, Pectin, Lipoproteins, Rat

A state-of-the-art review of polymers used in soil stabilization

This paper provides a review of the research on use of polymers for soil stabilization in pavement and geotechnical engineering. First, the properties impacting the effectiveness of widely used polymer classes, including geopolymers, biopolymers, and synthetic organic polymers are discussed. These include types and ratios of the precursor and activator of geopolymers, molecular weight, particle size, charge, conformation, solubility, viscosity, pH, and moisture behavior of organic polymers. Next, the paper reviews the mechanisms governing stabilization of soils with the various polymer classes. The key mechanisms for organic polymer–clay interactions are electrostatic forces and entropy increase, which contribute differently depending on whether the polymer is cationic, neutral, or anionic. On the other hand, the interactions between polymers and coarse-grained soils composed predominantly of sands are mainly attributed to three types of structural changes: a thin film covering sand particles, the formation of polymer ties connecting noncontacted neighboring particles, and the development of adhesion between particles. The mechanism of geopolymer stabilization is through the formation of a sodium and/or calcium aluminosilicate gel, which bind the surrounding soil particles and harden into a denser, stronger matrix. The engineering properties of the soil types after stabilization using polymers, including strength improvement, permeability reduction, swell and shrinkage inhibition, and durability and stability enhancement are discussed. Finally, the paper highlights the challenges for wider use of polymer stabilization of soils including limited evaluation standards, life-cycle cost considerations, and moisture susceptibility. To this end, some future research direction to promote the widespread use of polymers in soil stabilization are recommended including the need for establishment of standard testing protocols, evaluation of in-situ properties of polymer stabilized soils, resolution of durability issues and further in-depth examination of stabilizing mechanisms

Synthesis and properties of 2′-deoxy-2′,4′-difluoroarabinose-modified nucleic acids

© 2015 American Chemical Society. We report the synthesis, thermal stability, and RNase H substrate activity of 2′-deoxy-2′,4′-difluoroarabino-modified nucleic acids. 2′-Deoxy-2′,4′-difluoroarabinouridine (2,′4′-diF-araU) was prepared in a stereoselective way in six steps from 2′-deoxy-2′-fluoroarabinouridine (2′-F-araU). NMR analysis and quantum mechanical calculations at the nucleoside level reveal that introduction of 4′-fluorine introduces a strong bias toward the North conformation, despite the presence of the 2′-βF, which generally steers the sugar pucker toward the South/East conformation. Incorporation of the novel monomer into DNA results on a neutral to slightly stabilizing thermal effect on DNA-RNA hybrids. Insertion of 2′,4′-diF-araU nucleotides in the DNA strand of a DNA-RNA hybrid decreases the rate of both human and HIV reverse transcriptase-associated RNase H-mediated cleavage of the complement RNA strand compared to that for an all-DNA strand or a DNA strand containing the corresponding 2′-F-araU nucleotide units, consistent with the notion that a 4′-fluorine in 2′-F-araU switches the preferred sugar conformation from DNA-like (South/East) to RNA-like (North).Peer Reviewe

Synthesis and Properties of 2′-Deoxy-2′,4′-difluoroarabinose-Modified Nucleic Acids

We report the synthesis, thermal stability, and RNase H substrate activity of 2′-deoxy-2′,4′-difluoroarabino-modified nucleic acids. 2′-Deoxy-2′,4′-difluoroarabinouridine (2,′4′-diF-araU) was prepared in a stereoselective way in six steps from 2′-deoxy-2′-fluoroarabinouridine (2′-F-araU). NMR analysis and quantum mechanical calculations at the nucleoside level reveal that introduction of 4′-fluorine introduces a strong bias toward the North conformation, despite the presence of the 2′-βF, which generally steers the sugar pucker toward the South/East conformation. Incorporation of the novel monomer into DNA results on a neutral to slightly stabilizing thermal effect on DNA-RNA hybrids. Insertion of 2′,4′-diF-araU nucleotides in the DNA strand of a DNA-RNA hybrid decreases the rate of both human and HIV reverse transcriptase-associated RNase H-mediated cleavage of the complement RNA strand compared to that for an all-DNA strand or a DNA strand containing the corresponding 2′-F-araU nucleotide units, consistent with the notion that a 4′-fluorine in 2′-F-araU switches the preferred sugar conformation from DNA-like (South/East) to RNA-like (North)

Chronic methamphetamine effects on brain structure and function in rats

Methamphetamine (MA) addiction is a growing epidemic worldwide. Chronic MA use has been shown to lead to neurotoxicity in rodents and humans. Magnetic resonance imaging (MRI) studies in MA users have shown enlarged striatal volumes and positron emission tomography (PET) studies have shown decreased brain glucose metabolism (BGluM) in the striatum of detoxified MA users. The present study examines structural changes of the brain, observes microglial activation, and assesses changes in brain function, in response to chronic MA treatment. Rats were randomly split into three distinct treatment groups and treated daily for four months, via i.p. injection, with saline (controls), or low dose (LD) MA (4 mg/kg), or high dose (HD) MA (8 mg/kg). Sixteen weeks into the treatment period, rats were injected with a glucose analog, [18F] fluorodeoxyglucose (FDG), and their brains were scanned with micro-PET to assess regional BGluM. At the end of MA treatment, magnetic resonance imaging at 21T was performed on perfused rats to determine regional brain volume and in vitro [3H]PK 11195 autoradiography was performed on fresh-frozen brain tissue to measure microglia activation. When compared with controls, chronic HD MA-treated rats had enlarged striatal volumes and increases in [3H]PK 11195 binding in striatum, the nucleus accumbens, frontal cortical areas, the rhinal cortices, and the cerebellar nuclei. FDG microPET imaging showed that LD MA-treated rats had higher BGluM in insular and somatosensory cortices, face sensory nucleus of the thalamus, and brainstem reticular formation, while HD MA-treated rats had higher BGluM in primary and higher order somatosensory and the retrosplenial cortices, compared with controls. HD and LD MA-treated rats had lower BGluM in the tail of the striatum, rhinal cortex, and subiculum and HD MA also had lower BGluM in hippocampus than controls. These results corroborate clinical findings and help further examine the mechanisms behind MA-induced neurotoxicity