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Diffusion Chambers (diffusion + chamber)
Selected AbstractsLaboratory investigation of positive streamer discharges from simulated ice hydrometeorsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 615 2006Danyal Petersen Abstract Positive streamer discharges have been observed from ice crystals grown from the vapour under controlled temperature and air pressure corresponding to the standard atmosphere and also constant air pressure of 850 hPa. Crystals of size comparable to larger precipitation crystals were grown in a vapour diffusion chamber at various temperatures and pressures, and were subject to electric fields using an in situ electrode assembly. Results show that individual positive streamer discharges can occur at temperatures from near freezing down to at least ,38°C when subject to electric fields on the order of 500kV m,1, in contrast to previous reports of continuous positive streamer discharges occurring only at temperatures warmer than ,18°C for pure ice crystals. These results suggest that positive streamer discharges can occur on frozen precipitation particles at high altitudes in thunderclouds, given a sufficiently strong electric field. Such discharges may be a necessary element of the lightning-initiation process. Copyright © 2006 Royal Meteorological Society [source] Notochordal intervertebral disc cells: Sensitivity to nutrient deprivationARTHRITIS & RHEUMATISM, Issue 4 2009Thorsten Guehring Objective The nucleus pulposus (NP) of the intervertebral disc develops from the notochord. Humans and other species in which notochordal cells (NCs) disappear to be replaced by chondrocyte-like mature NP cells (MNPCs) frequently develop disc degeneration, unlike other species that retain NCs. The reasons for NC disappearance are unknown. In humans, the change in cell phenotype (to MNPCs) coincides with changes that decrease nutrient supply to the avascular disc. We undertook this study to test the hypothesis that the consequent nutrient stress could be associated with NC disappearance. Methods We measured cell densities and metabolic rates in 3-dimensional cultures of porcine NCs and bovine MNPCs, and we determined survival rates under conditions of nutrient deprivation. We used scanning electron microscopy to examine end plate porosity of discs with NCs and those with MNPCs. Nutrient,metabolite profiles and cell viability were calculated as a function of cell density and disc size in a consumption/diffusion mathematical model. Results NCs were more active metabolically and more susceptible to nutrient deprivation than were MNPCs. Hypoxia increased rates of glycolysis in NCs but not in MNPCs. Higher end plate porosity in discs with NCs suggested greater nutrient supply in keeping with higher nutritional demands. Mathematical simulations and experiments using an analog disc diffusion chamber indicated that a fall in nutrient concentrations resulting from increased diffusion distance during growth and/or a fall in blood supply through end plate changes could instigate NC disappearance. Conclusion NCs demand more energy and are less resistant to nutritional stress than MNPCs, which may shed light on the fate of NCs in humans. This provides important information about prospective NC tissue engineering approaches. [source] Automated diffusion chambers to monitor diurnal and seasonal dynamics of the soil CO2 concentration profileEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009F. Albanito Summary To better understand the factors controlling carbon dioxide (CO2) production and transport in soil, we developed a new method to continuously monitor soil CO2 concentration at multiple depths, by using diffusion chambers. The soil diffusion chambers are constructed from a high-density polyethylene cylindrical frame enclosed by a micro-polyvinylidene difluoride flat membrane (PVDF). All chambers are linked to an infrared gas analyser positioned above-ground through a multi-port valve system. We set up two experimental sites for long-term measurements of soil CO2 concentration, soil temperature and soil water content at depths of 0, 10, 20, 40 and 80 cm. The system provides the following advantages : (i) the use of the PVDF combined with the small dimensions of the diffusion chambers allows rapid diffusion of soil gas into the chambers and therefore a short equilibration time of the gas phase with the surrounding soil atmosphere, (ii) the equilibrating closed loop system allows the semi-continuous measurement of soil profile CO2 concentrations without creating a pressure differential within the chambers, thus reducing gas concentration distortions in the soil, (iii) the small size of the closed diffusion chambers reduces the initial soil disturbance during installation, (iv) it allows sampling in wet, humid soils, including ones that are waterlogged or temporarily saturated, and (v) the chambers do not require removal for maintenance purposes and are inexpensive. [source] Evaluation of creatine transport using Caco-2 monolayers as an in vitro model for intestinal absorptionJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2001Alekha K. Dash Abstract Creatine is a nutraceutical that has gained popularity in both well-trained and casual athletes for its performance-enhancing or ergogenic properties. The major disadvantages of creatine monohydrate formulations are poor solubility and oral bioavailability. In the present study, creatine transport was examined using Caco-2 monolayers as an in vitro model for intestinal absorption. Confluent monolayers of Caco-2 cells (passage 25,35) were used for the permeability studies. Monolayers were placed in side-by-side diffusion chambers. 14C-Creatine (0.1,0.5 ,Ci/mL) was added to either the apical or basolateral side, and the transport of the creatine across the Caco-2 monolayer was measured over a 90-min period. The apical to basolateral transport of 14C-creatine was small, ranging from 0.2,3% of the original amount appearing on the receiver side in a 90-min period. Interestingly, the basolateral to apical permeability of radiolabeled creatine was substantially greater than that observed in the apical to basolateral direction. Studies with drug efflux transport inhibitors indicate that neither the P-glycoprotein nor multidrug resistance-associated protein is involved in the enhanced basolateral to apical transport of creatine. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1593,1598, 2001 [source] Permeability of a novel ,-lactamase inhibitor LK-157 and its ester prodrugs across rat jejunum in vitroJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 9 2009Petra Igli Abstract Objectives LK-157 is a novel 10-ethylidene tricyclic carbapenem that resembles the structure of the broad-spectrum antibiotic sanfetrinem and acts as a potent inactivator of ,-lactamases of classes A, C and D. LK-157 is a highly soluble but poorly permeable drug. Since most of the ,-lactams are poorly absorbed, ester prodrugs LK-159, LK-157E1 and LK-157E2 were designed to enhance membrane permeability. This study investigated the permeability of LK-157 and the three ester prodrugs across rat intestine in vitro. The morpholinoethyl ester of sanfetrinem was also investigated. Method Permeability across rat jejunum was determined using EasyMount side-by-side diffusion chambers. Key findings The solubility and permeability of morpholinoethyl ester LK-157E2 were superior to those of LK-159 and LK-157E1. The morpholinoethyl ester of sanfetrinem LK-176E1 had the highest observed permeability coefficient and consequently the highest predicted absorption in humans. Conclusions These results suggest that the morpholinoethyl esters of LK-157 and sanfetrinem could be further investigated to assess bioavailability in vivo. [source] Permeability of intestinal mucosa from urinary reservoirs in man and ratBJU INTERNATIONAL, Issue 9 2000P. Nejdfors Objective To evaluate the barrier properties of intestinal mucosa chronically exposed to urine and to evaluate possible differences between ileal and colonic segments used in the reconstruction of the urinary tract. Materials and methods Mucosal specimens from patients with continent reservoirs with an abdominal stoma, or orthotopic neobladders constructed from colonic segments, were obtained at revisional surgery. Control segments were obtained during right-sided hemicolectomy. In addition, ileal and colonic segments from enterocystoplasties in rats were assessed. The mucosa-to-serosa passage of marker molecules, i.e. 14C-mannitol, 3H-glucose, fluorescein isothiocyanate-dextran 4400 and ovalbumin, was measured using modified Ussing diffusion chambers. Results In man, there were no permeability differences between segments exposed to urine and control segments for any of the marker molecules. In rats, there was less passage of markers in ileal and colonic transplanted segments than in intestinal segments from sham-operated animals. Conclusions Intestinal mucosa that has been in chronic contact with urine maintains its barrier function; in the rat model the permeability was even decreased. In addition, there were no detectable differences between ileal and colonic segments in this model. [source] | |||||||||||||