Ms In Water Research Articles

An Ultra-Long-Lived Triplet Excited State in Water at Room Temperature: Insights on the Molecular Design of Tridecafullerenes.

Suitably engineered molecular systems exhibiting triplet excited states with very long lifetimes are important for high‐end applications in nonlinear optics, photocatalysis, or biomedicine. We report the finding of an ultra‐long‐lived triplet state with a mean lifetime of 93 ms in an aqueous phase at room temperature, measured for a globular tridecafullerene with a highly compact glycodendrimeric structure. A series of three tridecafullerenes bearing different glycodendrons and spacers to the C60 units have been synthesized and characterized. UV/Vis spectra and DLS experiments confirm their aggregation in water. Steady‐state and time‐resolved fluorescence experiments suggest a different degree of inner solvation of the multifullerenes depending on their molecular design. Efficient quenching of the triplet states by O2 but not by waterborne azide anions has been observed. Molecular modelling reveals dissimilar access of the aqueous phase to the internal structure of the tridecafullerenes, differently shielded by the glycodendrimeric shell.

Short and long time MR signal behavior of randomly distributed water and fat-numerical simulations.

The MR time-signal behavior of water has been reported to be different on short and long time scales for systems of randomly distributed perturbers in water in the static dephasing regime. Up to now, the signal of the perturbers in such systems has not been taken into consideration. Water-fat emulsions are macroscopically homogeneous systems and can be considered as microscopically randomly distributed perturbing fat spheres embedded in water. In such water-fat systems, the signal of the perturber, fat, cannot be ignored. Since water and fat are within the same system, the fat signal behavior may show similarities with water, with differences in short and long time scales. This could complicate fat-referenced MR thermometry (MRT) methods such as multi-gradient echo-based (MGE) MRT. Simulations were performed using a numerical phantom comprising spherical fat objects embedded in a spherical water medium. To characterize the fat signal, the theoretical signal description of water was fitted to the simulated fat signal. The simulated signals were sampled as an MGE signal and MGE MRT was used to calculate temperatures. The sampling was done with and without delay, to investigate the effect on the temperature error of the time ranges in which the signal was sampled. It was confirmed that the fat signal behavior was similar to that of water and consisted of two regimes. The separation between the short and long time scales was approximately at 55ms for fat, as compared with 8.9ms for water. Without delayed signal sampling, the MGE MRT temperature error was about 2.5°C. With delayed sampling such that both the water and the fat signals were either in the short or in the long time scale the error was reduced to 0.2°C.

1H MRS assessment of hepatic steatosis in overweight children and adolescents: comparison between 3T and open 1T MR-systems

In recent years, proton magnetic resonance spectroscopy (MRS) has emerged as a non-invasive technique for measurement of fat content in the liver. The technique is often applied for overweight and obese patients. However, excessively obese patients cannot be examined in most conventional magnetic resonance systems due to limited space. The purpose of this study was to examine the ability of open 1T system to monitor liver fat with proton MRS and to compare hepatic fat fractions (HFFs) obtained using an open 1T system with assessment with 3T proton MRS. The study included 23 children and adolescents up to 20 years of age with a body mass index above the 97th percentile according to age and gender. Proton MRS for each patient was performed in both 1T and 3T using point resolved spectroscopy sequence in a single volume positioned in the right liver lobe. Average T2 relaxation times obtained for an open 1T system (55 ± 7 ms for water and 85 ± 11 ms for fat) were higher than average T2 relaxation times obtained for a 3T system (31 ± 4 ms for water and 66 ± 10 ms for fat). HFFs measured using an open 1T system showed strong correlation with HFFs measured using a 3T system (r = 0.99, P < 0.0001). Proton MRS measurements of HFF with an open 1T system are feasible. Open 1T system may reliably replace 3T magnetic resonance system for the assessment of liver fat.

Componentes do sinal acústico da deglutição: estudo preliminar

To analyze the components of the acoustic signal of swallowing using a specific software. Fourteen healthy subjects ranging in age from 20 to 50 years (mean age 31 ± 10 years), were evaluated. Data collection consisted on the simultaneous capture of the swallowing audio with a microphone and of the swallowing videofluoroscopic image. The bursts of the swallowing acoustic signal were identified and their duration and the interval between them were later analyzed using a specific software, which allowed the simultaneous analyses between the acoustic wave and the videofluoroscopic image. Three burst components were identified in most of the swallows evaluated. The first burst presented mean time of 87.3 milliseconds (ms) for water and 78.2 for the substance. The second burst presented mean time of 112.9 ms for water and 85.5 for the pasty substance. The mean interval between first and second burst was 82.1 ms for water and 95.3 ms for the pasty consistency, and between second and third burst was 339.8 ms for water and 322.0 ms for the pasty consistency. The software allowed the visualization of three bursts during the swallowing of healthy individuals, and showed that the swallowing signal in normal subjects is highly variable.

NEW PROBES FOR SURFACTANT SOLUTIONS: PHOSPHORESCENT LABELLED DETERGENTS

— A series of alkyltrimethylammonium bromides containing terminal phosphorescent chromo-phores have been prepared and characterized. 10-(4-bromo, l-naphthoyl)decyltrimethylammonium bromide(BND–10) has a critical micelle concentration (CMC) of 14 mM and a micellar mean aggregation number () of 105. Analogous detergents,BND–11, -8, and -5 have also been prepared; in each case, the naphthoyl group is located at the terminal carbon of an alkyl chain of the indicated length. The normal behavior of increasing and decreasing CMC with increasing aliphatic chain length is observed. When compared with unsubstituted alkyltrimethylammonium bromides, the 4-bromo, 1-naphthoyl chromo-phore is roughly equivalent to 6 methylenes with respect to hydrophobic contribution. A broad phosphorescence maximizing at about 590 nm is readily detected upon photoexcitation of the BND molecules in various solvents. The weak fluorescence of the probes is consistent with efficient intersystem crossing of the BND molecules. BND–10 has a phosphorescence yield of 0.023 and a lifetime of 1 ms in water at 250C. The probes are useful for the study of micelle-detergent exchange dynamics.

Prediction of Coalescence Properties of Gas Bubbles in a Gas–Liquid Reactor Using Persistence Time Measurements

The continuous coalescence and redispersion process of gas bubbles is an important phenomenon that has great significance on bubble size, gas holdup and gas–liquid mass transfer in gas–liquid reactors. The physical laws that determine the bubble coalescence rate are not yet well understood. Therefore, there is a great need for more detailed information about the coalescence process. The coalescence models can be utilized, for example, in multiphase CFD simulations. A combination of CFD and population balances with coalescence and break-up models is a promising topic, which enables a more detailed calculation of local hydrodynamics, gas holdup and gas–liquid mass transfer. The measurement of persistence time, defined as a time that a bubble remains attached at free gas–liquid surface, was used in this work to predict the coalescence properties in a bubble column. The persistence time was evaluated for different liquids and different bubble sizes using highspeed video camera. The applied method for measuring the persistence time is very simple and fast. The measured persistence times range from 10 ms for de-ionized water up to 15 s for water isopropanol solution. In addition, bubble size distributions were photometrically determined in a bubble column at several height positions using different liquids and operational conditions. The measured persistence times were applied in a simplified bubble column simulation model together with population balances and the measured and predicted bubble sizes were compared. A good agreement with calculated and measured size distributions was observed.

Separating changes in the intra- and extracellular water apparent diffusion coefficient following focal cerebral ischemia in the rat brain.

Selective intracellular (IC) and extracellular (EC) brain water apparent diffusion coefficient (ADC) values were measured in normal and ischemic rat brain. Selective T(1)-relaxation enhancement of the EC water, using intracerebroventricular (ICV) infusion of an NMR contrast reagent (CR), was used to separate the IC and EC signal contributions. In the CR-infused, normal brain (n = 4), T(1) = 235 +/- 10 ms and T(2) = 46 +/- 2 ms for IC water (85%) and T(1) = 48 +/- 8 ms and T(2) = 6 +/- 2 ms for EC water (15%). Volume-localized ADC(z) (z-gradient axis) values were 0.90 +/- 0.02 (EC+IC), 0.81 +/- 0.05 (IC), 0.51 +/- 0.02 (EC+IC), and 0.53 +/- 0.07 (IC), for normal, CR-infused, ischemic, and ischemic/CR-infused groups, respectively (ADC values are x10(-3) mm(2)/s; n = 5 for each group). Imaging ADC(z) values were 0.81 +/- 0.03 (EC+IC), 0.75 +/- 0.05 (IC), 0.51 +/- 0.04 (EC+IC), and 0.52 +/- 0.05 (IC), respectively, for the same groups. Imaging ADC(av) (average diffusivity) values for the same groups were 0.70 +/- 0.05 (EC+IC), 0.69 +/- 0.06 (IC), 0.45 +/- 0.06 (EC+IC), and 0.44 +/- 0.06 (IC), respectively. These results suggest that the IC water ADC determines the overall water ADC value in normal and ischemic rat brain.

Characteristics of acoustic streaming created and measured by pulsed Doppler ultrasound

Self measurement of acoustic streaming by Doppler ultrasound could be used to evaluate properties of fluids such as viscosity or the coagulation of blood. To characterize acoustic streaming caused by pulsed ultrasonic beams, Doppler signal processing was used to measure streaming velocity under a variety of conditions in vitro using blood and water. Velocities as high as 5 mm/s were measured in blood at the diagnostic power levels (3.5 mW) used in 20 MHz catheter velocimetry. It was found that streaming decreases with distance due to absorption and beam spreading, increases with applied acoustic power, and decreases with increased viscosity during blood coagulation. However, the increase in velocity with acoustic power is nonlinear with an exponent of 0.67 for water and 1.42 for blood even though the radiation force as measured by deflection of a suspended transducer is linear with power. The time constant of streaming to a step change in acoustic power is 80 ms in blood and 200 ms in water. It is concluded that streaming is measurable in pulsed Doppler beams, that it could produce artifacts or unintended effects, and that it could be used to characterize fluid properties and to detect coagulation of whole blood.

Folding of the disulfide-bonded β-sheet protein tendamistat: rapid two-state folding without hydrophobic collapse

We investigated the reversible folding and unfolding reactions of the small 74 amino acid residue protein tendamistat. The secondary structure of tendamistat contains only β-sheets and loop regions and the protein contains two disulfide bonds. Fluorescence-detected refolding kinetics of tendamistat (disulfide bonds intact) comprise of a major rapid fast reaction (τ=10 ms in water) and two minor slow reactions. In the fast reaction 80% of the unfolded molecules are converted to native protein. The two slow reactions are part of a parallel slow folding pathway. On this pathway the rate-limiting step in the formation of native molecules is cis to trans isomerization of at least one of the three trans Xaa-Pro peptide bonds. This reaction is catalyzed efficiently by the enzyme peptidyl-prolyl cis-trans isomerase. Comparison of kinetic data with equilibrium unfolding transitions shows that the fast folding pathway follows a two-state process without populated intermediate states. Additionally, various sensitive tests did not detect any rapid chain collapse during tendamistat folding prior to the acquisition of the native three-dimensional structure. These results show that pre-formed disulfide bonds do not prevent efficient and rapid protein folding.

Code Development for Ship Structures—A Demonstration

A demonstration summary of a reliability-based structural design code for ships is presented for two ship types: a cruiser and a tanker. One reason for the development of such a code is to provide specifications which produce ship structure having a weight savings and/or improvement in reliability relative to structure designed by traditional methods. Another reason is to provide uniform safety margin for ships within each type. For both ship types, code requirements cover four failure modes: hull girder bulkling, unstiffened plate yielding and buckling, stiffened plate buckling, and fatigue of critical detail. Both serviceability and ultimate limit states are considered. Because of limitation on the length, only hull girder modes are presented in this paper. Code requirements for other modes will be presented in future publication. A specific provision of the code will be safety check expression, which, for example, for three bending moments (still water Ms, wave Mw, and dynamic Md), and strength Mu, might have the form, following the partial safety factor format: γsMs+γwMw+γdMd≤φMu γs, γw, γd, and φ are the partial safety factors. The design variables (M’s) are to be taken at their nominal values, typically values in the safe side of the respective distributions. Other safety check expressions for hull girder failure that include load combination factors, as well as consequence of failure factors, are considered. This paper provides a summary of safety check expressions for the hull girder modes.

High-pressure stopped-flow spectrometry at low temperatures

A stopped-flow instrument operating over temperature and pressure ranges of +30 to −20°C and 10 −3 to 2 kbar, respectively, is described. The system has been designed so that it can be easily interfaced with many commercially available spectrophotometers of fast response time, with the aid of quartz fiber optics. The materials used for the construction are inert, metal free and the apparatus has proven to be leak free at temperatures as low as −20°C under a pressure of 2 kbar. The performance of the instrument was tested by measuring the rate of reduction of cytochrome c with sodium dithionite and the 2,6-dichloroindophenol/ascorbate reaction. The dead time of the system has been evaluated to be 20, 50, and ⋍100 ms in water at 20°C, in 40% ethylene glycol/water, and at 20°C and −15°C, respectively. These values are rather pressure independent up to 2 kbar. Application of the bomb was demonstrated using the cytochrome c peroxidase/ethyl peroxide reaction. This process occurred in two phases and an increase in pressure decreased the rates of reactions indicating two positive volumes of activation (Δ V app ≠(fast) = 9.2 ± 1.5 ml·mol −1; Δ V app ≠(slow) = 14 ± 1.5 ml·mol −1, temperature 2°C). The data suggest that the fast reaction could involve a hydrophobic bond, whereas the slow process could be associated with a stereochemical change of the protein. The problem of temperature equilibrium for high-pressure experiments is also discussed.

Factors Involved in Plasticity of Kaolin‐Water Systems

The factors involved in the development of plasticity are discussed. The importance of the rigidity of the adsorbed water ms and the effect of various ions on this rigidity is shown by entropy calculations. All the monovalent ions with the exception of the smallest (Li+ and F−) indicate an increase in the disorder of the water structure that agrees with observations on plasticity.