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Water Diffusion Coefficient (water + diffusion_coefficient)
Selected AbstractsWATER DIFFUSION COEFFICIENT AND MODELING OF WATER UPTAKE IN PACKAGED YERBA MATEJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 4 2007LAURA A. RAMALLO ABSTRACT Effective water diffusion coefficient (Deff) was determined from the kinetics of moisture gain in a yerba mate bed. A value of 1.5 × 10,9 ± 0.4 × 10,9 m2/s was obtained at 40C and 90% relative humidity, by fitting experimental data to the series solution of Fick's second law. A model was developed to predict moisture profile and water uptake in packaged yerba mate. In order to simulate moisture gain in the packaged food, the model considers that the global process of humidity gain is controlled by combined mechanisms of package permeability, product sorption balances and water diffusion within the food bed. The explicit finite difference method was used to numerically solve the resulting equations. The validity of the model was tested by comparing predicted and experimental moisture profiles for high (WVTR , 20 g/m2/day) and low (WVTR , 400 g/m2/day) barrier packages. The model was found to adequately predict the profile of moisture content. [source] Brain Apparent Water Diffusion Coefficient Magnetic Resonance Image During a Prolonged Visual AuraHEADACHE, Issue 6 2010Robert Belvís MD (Headache 2010;50:1045-1049) Background., Reversible changes in brain magnetic resonance imaging (MRI) weighted in diffusion-weighted images (DWI) and apparent water diffusion coefficient (ADC) maps have been reported in acute stroke, epilepsy, eclampsia, and hypoglycemia, but they are contradictory regarding to migraine aura. Objective., A 41-year-old woman with known basilar migraine for 5 years consulted about a persistent visual aura (visual snow phenomenon) plus bilateral paresthesias in the extremities for 4 days. The headache was treated with success with 10 mg of wafer rizatriptan and 600 mg of ibuprophen. Methods., The neurologic and ophthalmologic examination were normal. An urgent brain MRI detected no lesions in T1, T2, fluid-attenuated inversion recovery, and DWI, but an abnormal signal appeared in the left occipital lobe in ADC and (r)ADC maps. The brain MRI angiography, carotid ultrasound study, transesophageal echocardiography, 24-hour cardiac Holter monitoring, and thrombophilia study were normal. Results., A new brain MRI 8 days after did not show any previous lesion in the same sequences. Conclusions., We present a patient with migraine and transitory abnormal signals in the ADC map of an occipital region during persistent visual aura. The clinical-radiological relationship is congruent. Some similar cases have showed these MRI signals during the aura, suggesting cytotoxic edema, without ischemic lesions in the MRI controls. Theses ADC images probably appear in complex auras. [source] WATER DIFFUSION COEFFICIENT AND MODELING OF WATER UPTAKE IN PACKAGED YERBA MATEJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 4 2007LAURA A. RAMALLO ABSTRACT Effective water diffusion coefficient (Deff) was determined from the kinetics of moisture gain in a yerba mate bed. A value of 1.5 × 10,9 ± 0.4 × 10,9 m2/s was obtained at 40C and 90% relative humidity, by fitting experimental data to the series solution of Fick's second law. A model was developed to predict moisture profile and water uptake in packaged yerba mate. In order to simulate moisture gain in the packaged food, the model considers that the global process of humidity gain is controlled by combined mechanisms of package permeability, product sorption balances and water diffusion within the food bed. The explicit finite difference method was used to numerically solve the resulting equations. The validity of the model was tested by comparing predicted and experimental moisture profiles for high (WVTR , 20 g/m2/day) and low (WVTR , 400 g/m2/day) barrier packages. The model was found to adequately predict the profile of moisture content. [source] Water diffusion in a rat glioma during ganciclovir-thymidine kinase gene therapy-induced programmed cell death in vivo: Correlation with cell densityJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2004Piia K. Valonen MSc Abstract Purpose To study the characteristics of diffusion magnetic resonance imaging (MRI) contrast in a rat brain BT4C glioma during progression of ganciclovir (GCV)-thymidine kinase gene therapy-induced programmed cell death (PCD) in vivo. Materials and Methods The trace of the diffusion tensor (Dav = 1/3Trace ), T2, and spin density were determined by MRI and the apparent diffusion coefficient (ADC) of water by diffusion nuclear MR (NMR) spectroscopy using largely varying b values and diffusion times (tD) at 4.7 T. Cell count and apoptotic cells were quantified by histological means. Results Decline in cell count was strongly associated with increase in both Dav and T2. Spin density ratio between tumor and contralateral parietal cortex increased with a very similar time course as Dav and T2, indicating net water gain into the eradicating tumor. Diffusion spectroscopy showed a nonmonoexponential signal decay at all tD values ranging from 14,192 msec. During PCD, the ADC of the component yielding fast diffusion coefficient (D1), as acquired with tD , 47 msec, increased with kinetics similar to those of Dav (tD = 4.8 msec). The fractional size of D1 increased by 10% to 15% throughout the entire tD range. Apparent water residence time of the slow diffusion component, D2, shortened from a value of 38.3 ± 1.7 msec on day 0 to 33.4 ± 0.5 msec by day 8. Conclusion The present results show that reduced cell density and increased water content, leading to altered water microenvironment, are associated with increased water diffusion coefficient in eradicating gliomas as a result of PCD. J. Magn. Reson. Imaging 2004;19:389,396. © 2004 Wiley-Liss, Inc. [source] Estimation of an effective water diffusion coefficient during infrared-convective drying of a polymer solutionAICHE JOURNAL, Issue 9 2009N. Allanic Abstract This article deals with the drying of an aqueous solution of polyvinyl alcohol mixed with a plasticizer. A heating combining forced convection and short-infrared radiation was investigated. A one-dimensional model taking into account the shrinkage of the product was developed to get the temperature and moisture content evolutions during the drying. The water diffusion coefficient was estimated by an inverse method. A sensitivity analysis and numerical tests showed the relevance of using an objective function taking both mass and temperature measurements into account for the estimation procedure. This estimation was performed on several convective and infrared-convective experimental drying kinetics. The model predictions fit well mass and temperature experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Synthesis and characterization of postsulfonated poly(arylene ether sulfone) diblock copolymers for proton exchange membranesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2009Shogo Takamuku Abstract Sulfonated poly(arylene ether sulfone) diblock copolymers were studied through the postsulfonation process. Two kinds of hydrophobic oligomers with a molecular weight of 20 kDa were prepared in advance as block sequences and then coupled together to obtain diblock copolymers. One oligomer was synthesized from bis(4-hydroxyphenyl) sulfone (BHPS) and 4,4,-difluorodiphenyl sulfone (DFDPS), which was thought to be incapable of postsulfonation. The other oligomer was synthesized from hydroquinone (HQ) and 4,4,-dichlorodiphenyl sulfone (DCDPS), which successfully proceeded to a hydrophilic sequence as a result of sulfonation onto the HQ moiety after the coupling reaction. Consequently, a diblock copolymer with high molecular weight was obtained; although its intrinsic viscosity was too low to form a tough membrane because of its high rigidity and high crystallinity. Therefore, the use of decafluorobiphenyl (10F) as a termination reagent was investigated with the aim of achieving higher coupling reactivity and a kinky property. As a result, a sulfonated diblock copolymer was successfully obtained with sufficient molecular weight and intrinsic viscosity to form the membrane, as well as with adequate thermal properties. It was observed that proton conductivity, water uptake, and the water diffusion coefficient increased with higher ion exchange capacity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 700,712, 2009 [source] | |||||||||||||