An investigation of peripheral gap and open lane effects on flow-induced vibrations of tube bundles

Experiments were conducted in a wind tunnel to study open lane and peripheral gap effects in heat exchanger tube bundles subjected to cross flow. A rotated triangular array of tubes was tested to obtain critical velocities for uniform flow instability. By removing different rows of tubes, critical velocities for nonuniform flow caused by open lanes and peripheral gaps were recorded. Also, theoretical correction factors due to open lanes and peripheral gaps were developed to predict the critical velocities for nonuniform flow. The correction factor can be multiplied by the critical velocity predictions from existing models for uniform cross-flow. Correlations of the analytical model with experimental data are good.     

Nonsteroidal antiinflammatory drugs could reverse Helicobacter pylori-induced apoptosis and proliferation in gastric epithelial cells

It remains controversial whether the harmful effects of Helicobacter pylori (Hp) and nonsteroidal antiinflammatory drugs (NSAIDs) are additive. We studied the effects of Hp (virulent and nonvirulent strains) and NSAIDs, alone or in combination, on apoptosis and proliferation of gastric epithelial cells in nonulcer dyspepsia (NUD) patients. Forty-four (25 Hp-positive and 19 Hp-negative) consecutive Chinese NUD patients with rheumatoid arthritis who had taken continuously NSAIDs for more than three months were recruited for this study. Another 41 (20 Hp-positive and 21 Hp-negative) NUD patients not on any NSAIDs were included as controls. All patients underwent a gastroscopy examination and gastric biopsies. Hp infection was confirmed by CLOtest, anti-Hp ELISA, and [13C]urea breath test. The CagA status was determined by the anti-CagA antibody assay. The degree of gastritis, apoptosis, and proliferation indices were determined with H&E staining, terminal uridine deoxynucleotidyl nick end-labeling (TUNEL), and proliferating cell nuclear antigen (PCNA) immunostaining methods, respectively. A significantly higher apoptosis was observed in subjects who had Hp infection or had been consuming NSAIDs when compared with the controls. Unlike NSAID-treated subjects, patients with Hp infection were shown to have significantly enhanced cell proliferation. However, the increased apoptosis and proliferation in Hp-positive subjects were reversed by also taking NSAIDs. No correlation was found between apoptosis and proliferation in all the study groups. There was no association found between CagA expression or degree of gastritis with cell proliferation or apoptosis. It was demonstrated at the cellular level that NSAIDs could abrogate apoptosis or proliferation effects induced by Hp. Furthermore, the latter effects appeared not to be influenced by the virulent nature of the Hp strains.     

Patient and staff radiation dose in fluoroscopy-guided TIPS procedures and dose reduction, using dedicated fluoroscopy exposure settings

Fluoroscopy guided interventions, such as transjugular intrahepatic portosystemic shunt (TIPS) procedures, can results in relatively high radiation doses to patients and staff. The purpose of this study was to evaluate the possible benefit of dedicated fluoroscopy exposure factors in the reduction of doses. Doses to patients and staff were measured during fluoroscopy-guided TIPS procedures in two Dutch university hospitals. Patient doses were calculated from dose-area product (DAP) measurements, entrance beam dimensions and DAP conversion factors. Staff doses were measured outside lead aprons using electronic personal dosemeters. Average patient entrance skin dose (ESD) rate during fluoroscopy was 49 mGy min-1 (13 cases, average fluoroscopy duration 32 min) in one hospital, and 6 mGy min-1 (10 cases, average fluoroscopy duration 50 min) in the other. Estimated staff effective dose per procedure was 28 microSv average in the first hospital compared with 4 microSv average in the other. The use of dedicated fluoroscopy exposure factors, with a relatively high tube voltage and lower tube current resulted in a significant dose reduction for patient and staff in this type of radiological intervention.     

An analogy between the spouted bed phenomena and the bubbling-to-spray transition

An analogy is drawn between the onset of minimum spouting and the bubbling-to-spray transition on a sieve tray to derive an analytical equation which relates the bed depth to the minimum air velocity required for the onset of spouting. The derived equation and the significance of the terms appearing in it are discussed and compared with existing correlations and the available data.     

Low-velocity impact response for laminated stepped beam

A numerical method is presented to evaluate the response of a laminated stepped beam under a transverse low velocity impact. The impactor and the laminated beam are considered as a single system and thus the impact force becomes the internal force of the system. The energies associated with each span of the beam and the impactor mass are derived in the form of a higher order shear deformation theory and Sun's modified contact law. These are substituted in the Lagrangian equation of motion to arrive at the governing equations of the system. The equations are uncoupled by principal coordinate transformations and then solved numerically. The solutions can be obtained for arbitrary boundary conditions. Natural frequency parameters are compared with the available literature results wherever possible and very good agreement is achieved. New case studies are discussed in detail to demonstrate the efficiency of the method.     

Assessment of hemodynamic changes in rat stomachs by laser Doppler velocimetry and reflectance spectrophotometry. Effects of ethanol and prostaglandin E2 under ischemic and congestive conditions

One of the ulcerogenic mechanisms by which ethanol induces mucosal lesions in the stomach is the depression of gastric mucosal blood flow (GMBF). The goal of this study was to determine whether lesion formation is the result of vascular ischemia alone or ischemia combined with congestion. The aims of this study were to answer this question by evaluating the relationship between GMBF, oxygen saturation (ISO2) and hemoglobin volume (IHb) in the gastric mucosa under the influences of ethanol and prostaglandin E2 (PGE2) in the ischemic and congestive states, using a laser Doppler flowmeter and tissue spectrum analyzer. Ligation of the gastric celiac artery or vein markedly decreased the GMBF and the ISO2 level. The former procedure also reduced but the latter increased the IHb level. Ethanol administration produced effects similar to venous ligation, i.e. vascular stasis with ischemia. There was a negative correlation between GMBF and severity of lesion formation after ethanol administration. However, at the lesion site all the hemodynamic parameters were significantly reduced, indicating that a necrotic condition had occurred. PGE2 preincubation (25 micrograms) elevated GMBF, ISO2 and IHb levels. It also alleviated the reduction of blood flow induced by ethanol and increased the recovery rate of GMBF and ISO2 after the release of arterial or venous ligation. It is concluded that the decrease in blood flow due to ethanol is probably caused by constriction of venules rather than arterioles inside the mucosa, and this effect could lead to vascular congestion. PGE2 probably dilates both arterioles and venules in the gastric mucosa and thereby increases the blood flow in the gastric mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)