Application of the boundary integral method to the interaction of rising two-dimensional deformable gas bubbles

The boundary integral method is applied to model the initial motion of two-dimensional or cylindrical deformable gas bubbles in an inviscid, incompressible fluid. Following the success of recent boundary integral studies to predict the qualitative behaviour of a single gas bubble, this numerical study is extended to consider the interaction of several bubbles. Surface tension, relative initial position and volume are all found to be important factors affecting the bubble interaction, jet formation, trapping of fluid between bubbles and bubble shedding. As well as computing the evolution of the bubble surfaces, consideration of the pressure fields and resulting instantaneous streamlines is given.     

Long-range correlation properties of coding and noncoding DNA sequences: GenBank analysis

An open question in computational molecular biology is whether long-range correlations are present in both coding and noncoding DNA or only in the latter. To answer this question, we consider all 33301 coding and all 29453 noncoding eukaryotic sequences--each of length larger than 512 base pairs (bp)--in the present release of the GenBank to dtermine whether there is any statistically significant distinction in their long-range correlation properties. Standard fast Fourier transform (FFT) analysis indicates that coding sequences have practically no correlations in the range from 10 bp to 100 bp (spectral exponent beta=0.00 +/- 0.04, where the uncertainty is two standard deviations). In contrast, for noncoding sequences, the average value of the spectral exponent beta is positive (0.16 +/- 0.05) which unambiguously shows the presence of long-range correlations. We also separately analyze the 874 coding and the 1157 noncoding sequences that have more than 4096 bp and find a larger region of power-law behavior. We calculate the probability that these two data sets (coding and noncoding) were drawn from the same distribution and we find that it is less than 10(-10). We obtain independent confirmation of these findings using the method of detrended fluctuation analysis (DFA), which is designed to treat sequences with statistical heterogeneity, such as DNA's known mosaic structure ("patchiness") arising from the nonstationarity of nucleotide concentration. The near-perfect agreement between the two independent analysis methods, FFT and DFA, increases the confidence in the reliability of our conclusion.     

FBDR-Fuzzy Based DDoS Attack Detection and Recovery Mechanism for Wireless Sensor Networks

Wireless sensor networks (WSN) is considered as one of the exploring technology for its deployment of the massive number of dedicated sensor nodes which sense the environment and collect the data. The collected data are sent to the sink node through the intermediate nodes. Since the sensors node data are exposed to the internet, there is a possibility of vulnerability in the WSN. The common attack that affects most of the sensor nodes is the Distributed Denial of Services (DDoS) attack. This paper aims to identify the DDoS (Flooding) attack quickly and to recover the data of sensor nodes using the fuzzy logic mechanism. Fuzzy based DDoS attack Detection and Recovery mechanism (FBDR) uses type 1 fuzzy logic to detect the occurrence of DDoS attack in a node. Similarly fuzzy- type 2 is used for the recovery of data from the DDoS attack. Both the type 1 fuzzy-based rule and type 2 fuzzy-based rule perform well in terms of identifying the DDoS attack and recover the data under attack. It also helps to reduce the energy consumption of each node and improves the lifetime of the network. The proposed FBDR scheme is also compared with other related existing schemes. The proposed method saves energy usage by up to 20% compared with the related schemes. The experimental results represent that the FBDR method works better than other similar schemes.

     

Exploration of channel width scaling and edge states in transition metal dichalcogenides

We explore the impact of edge states in three types of transition metal dichalcogenides (TMDs), namely metallic Td-phase WTe₂ and semiconducting 2H-phase MoTe₂ and MoS₂, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, in contrast to observations made for graphene nanoribbon devices. The semiconducting ribbons are characterized in a three-terminal field-effect transistor (FET) geometry. In addition, two ribbon array designs have been carefully investigated and found to exhibit current levels higher than those observed for conventional one-channel devices. Our results suggest that device structures incorporating a high number of edges can improve the performance of TMD FETs. This improvement is attributed to a higher local electric field, resulting from the edges, increasing the effective number of charge carriers, and the absence of any detrimental edge-related scattering.

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Digital boundary tracking

In many three-dimensional imaging applications, the three-dimensional space is represented by an array of cubical volume elements (voxels) and a subset of the voxels is specified by some property. Objects in the scene are then recognised by being components of the specified set and individual boundaries are recognised as sets of voxel faces separating objects from components in the complement of the specified set. This paper deals with the problem of algorithmic tracking of such a boundary specified by one of the voxel faces lying in it. The paper is expository in that all ideas are carefully motivated and introduced. Its original contribution is the investigation of the question of whether the use of a queue (of loose ends in the tracking process which are to be picked up again to complete the tracking) is necessary for an algorithmic tracker of boundaries in three-dimensional space. Such a queue is not needed for two-dimensional boundary tracking, but published three-dimensional boundary trackers all make use of such a thing. We prove that this is not accidental: under some mild assumptions, a boundary tracker without a queue will fail its task on some three-dimensional boundaries.     

Operative management of Haglund's deformity in the nonathlete: a retrospective study

Haglund's deformity, or "pump bump," is a common cause of posterior heel pain. Management of the condition usually consists of nonoperative therapy. This study presents a retrospective study of 65 cases (53 patients), with symptomatic Haglund's deformity in nonathletes (13 male and 40 female), who presented during a 4-year period (1989-1994). Sixty-five percent (39 heels) of these patients failed to respond to nonoperative therapy for an average of 62 weeks, (range, 4-260 weeks). This group of patients went on to operative treatment. Surgical management consisted of excision of the posterior calcaneal tuberosity through a medial longitudinal incision with debridement, reattachment of the Achilles tendon using bone anchors, and 4 weeks of postoperative immobilization. Thirty-nine patients (74%) were contacted for follow-up. The average follow-up period for these patients was 155 weeks, (range, 92-335 weeks). There were 50% excellent results, 47% good results, 3% fair results (1 patient), and no poor results. The Maryland Foot Score for operated heels was an average of 67/100 preoperative and an average of 92/100 postoperative. On unoperated heels the score was an average of 81/100 at first evaluation and an average of 86/100 at final evaluation. Complications included one recurrence of painful prominence, one wound infection, and one incisional neuroma. The outcome of these cases demonstrated that in those patients who fail nonoperative treatment, surgical treatment of Haglund's deformity produces a predictably good surgical result when performed using the technique described.     

Acute vasoconstriction after subarachnoid hemorrhage

OBJECTIVE: Decreased cerebral blood flow (CBF) and cerebral ischemia occurring immediately after subarachnoid hemorrhage (SAH) may be caused by acute microvascular constriction. However, CBF can also be influenced by changes in intracranial pressure (ICP) and cerebral perfusion pressure (CPP). The goal of these experiments was to assess the significance of acute vasoconstriction after SAH and its relationship to changes in CBF, ICP, CPP, and extracellular glutamate concentrations. METHODS: Three experiments were performed using the endovascular filament technique to produce SAH. In the first experiment, CBF, ICP, and CPP were measured for 60 minutes after SAH (n = 21) and were correlated with the 24-hour mortality rate. In the second experiment, rats undergoing SAH (n = 23) or a sham procedure (n = 7) were perfused 60 minutes after SAH for measurement of the circumference and wall thickness of the internal carotid and anterior cerebral arteries and correlation with CBF, ICP, and CPP. In the third experiment (n = 11), extracellular glutamate concentrations determined by hippocampal and cortical microdialysis and high performance liquid chromatography were correlated with physiological changes. RESULTS: CBF reductions to less than 40% of baseline for 60 minutes after SAH predicted 24-hour mortality with 100% accuracy and were used to define "lethal" SAH. In contrast, ICP and CPP 60 minutes after SAH were not correlated with the mortality rate. The vascular circumference was significantly smaller in lethal than in sublethal SAH or sham-operated rats (P < 0.001). Vessel measurements were correlated with both CBF and hemorrhage size (P < 0.01). Extracellular glutamate concentration increased to 600% of baseline after lethal SAH in both hippocampus and cortex and was inversely correlated with CBF (r = 0.9, P < 0.001) but did not increase after sublethal SAH. CONCLUSION: Acute vasoconstriction after SAH occurs independently of changes in ICP and CPP and is associated with decreased CBF, larger hemorrhage size, persistent elevations of extracellular glutamate, and poor outcome. Acute vasoconstriction seems to contribute directly to ischemic brain injury after SAH. Further evaluations of pharmacological agents with the potential to reverse acute vasoconstriction may increase CBF and improve outcome.     

A new type of ozone generator using Taylor cones on water surfaces

Ozone has been found to be effective in many forms of water treatment. As concerns about the safety of alternate methods of water treatment increase (in particular, chlorination), ozone, which is already extensively used in Europe, offers an effective option. This paper describes a new method of ozone generation particularly suited for use in water purification. Most current industrial ozone production is based on “silent” electrical discharges in a gap between concentric electrodes separated by a glass or ceramic dielectric barrier. The authors present experimental results obtained using a parallel-plate discharge geometry. The lower electrode consists of a grounded “pool” of still water separated by a discharge gap from an upper insulated planar electrode. When the electrode is energized by an AC high voltage, a multitude of “Taylor cones” forms on the water surface. The Taylor cones form and collapse randomly and continuously, depending on the electric field. The tips of the cones provide points for electrical discharge pulses which initiate ozone generation. This method generates ozone in close proximity to the water surface. Laboratory experiments show efficiencies for gaseous ozone production as high as 110 g/kWh     

Coherent lidar airborne wind sensor II: flight-test results at 2 and 10 νm

The use of airborne laser radar (lidar) to measure wind velocities and to detect turbulence in front of an aircraft in real time can significantly increase fuel efficiency, flight safety, and terminal area capacity. We describe the flight-test results for two coherent lidar airborne shear sensor (CLASS) systems and discuss their agreement with our theoretical simulations. The 10.6-μm CO(2) system (CLASS-10) is a flying brassboard; the 2.02-μm Tm:YAG solid-state system (CLASS-2) is configured in a rugged, light-weight, high-performance package. Both lidars have shown a wind measurement accuracy of better than 1 m/s.     

Adrenal chromaffin cells on microcarriers exhibit enhanced long-term functional effects when implanted into the mammalian brain

Rat adrenal chromaffin cells attached to either collagen-coated dextran (Cytodex 3) or glass bead microcarriers, both of 90-200 microns diameter, were used as dopamine-secreting implants in the caudate-putamen of rats with 6-hydroxydopamine-induced unilateral lesions of the substantia nigra. As controls, beads without cells and cells in suspension alone were implanted. Chromaffin cells adhered to microcarriers reduced apomorphine-induced rotation by 75% in lesioned animals. Animals that were lesioned but not receiving cell implants or receiving beads alone showed no reduction. Animals implanted with cells not attached to beads also showed a reduction in rotation but this effect lasted less than three months. Microcarrier-attached cells, however, maintained their effect in reducing rotation for at least eight months (rotations were reduced from a control mean of 10.9 +/- 1.4 to 3.6 +/- 1.1 turns/min) without any "drop-off" of the effect. Histological examination showed that eight months post-implant the cells pre-adhered to beads were still present and could be stained by anti-tyrosine hydroxylase antibody. Sections stained with hematoxylin-eosin showed no signs of an inflammatory response. In contrast to beads implanted into the striatum, Cytodex bead implants injected into the lateral ventricle induced a histopathological response appearing to involve the ependyma and choroid plexus. Results suggest that the striatal parenchyma but not the ventricle is amenable to studies using the microcarrier approach to transplantation.