We discuss the effect of the kinetics of pH change on the mechanical properties of dipeptide hydrogels. Data from other peptide-based low molecular weight gelator (LMWG) systems suggest that the rheological properties are often highly dependent on the assembly rate. To examine kinetics here, we have used the hydrolysis of glucono-8-lactone (GdL). The hydrolysis of GdL to gluconic acid results in a decrease in pH, the rate of which is temperature sensitive. Hence, we can adjust the rate of pH decrease, whilst achieving the same absolute final pH. Our data shows that at all temperatures the rheological profile is very similar, with an increase to a plateau, followed by a second increase in moduli, despite very different kinetics of assembly. Surprisingly, the final mechanical properties are very similar in all cases. We also show that the structures formed at the plateau can be accessed by adjusting the pH using CO2. By carefully balancing the pKa. of the gelator with the pH achievable using CO2, flexible hydrogel membranes can be formed as opposed to a bulk gel. The rheological characteristics of the membranes are typical of a highly entangled polymer network. These membranes can be rigidified by post-addition of GdL to further lower the pH.
The performance of a new rapid lateral-flow chromatographic membrane immunoassay test kit for detection of influenza virus was evaluated and compared to that of viral culture in respiratory secretions collected from 400 adults and children seen at three large university hospitals during the recent 2003 influenza season. The rapid test provided results in 15 min, with excellent overall performance statistics (sensitivity, 94.4%; specificity, 100%; positive predictive value, 100%; negative predictive value, 97.5%). Both influenza A and B type viruses were reliably detected, with no significant difference in performance statistics noted by influenza virus type or by the center performing the test.Influenza virus is a major cause of respiratory infection in both adults and children and is a common cause of hospitalization, especially in young children, elderly adults, and persons with chronic diseases (17,20). Influenza epidemics also account for over 47,000 deaths annually in the United States. Furthermore, three global pandemics during the 20th century caused over 50 million deaths (22). Readily available, rapid, and accurate detection methods for influenza virus allow for prompt administration of appropriate antiviral therapy and judicious use of antibiotics, assist in isolation of patients in hospitals and emergency centers to reduce health care-associated spread of infection, and identify local epidemics of influenza in a timely manner (10, 13-15, 19, 21, 22). Rapid detection of influenza virus also is currently important because of increased concern for pandemic influenza caused by either naturally occurring strains, such as avian H5N1, or altered strains that may be used in an act of bioterrorism (7,8,18). Also, the diagnosis of influenza based on clinical grounds alone may be inaccurate, because the presenting symptoms of influenza are similar to those caused by other infectious agents (13). Furthermore, the rapid and accurate determination that a severe respiratory or flu-like illness is caused by influenza virus rather than severe acute respiratory syndrome-associated coronavirus or a bioterrorism agent, such as smallpox or tularemia, is helpful not only to the individual patient but also from the public health perspective (6).Currently, there are at least seven different test kits approved by the Food and Drug Administration for detection of influenza virus in respiratory samples (2-4, 9, 12, 16, 21, 23). However, not all available methods distinguish the type of influenza virus present in the sample, and those that do distinguish type A and B influenza viruses have not shown consistently reliable performance for both types of virus (3,4,9,12). This recent multicenter study documented promising performance of a new rapid lateral-flow chromatographic immunoassay for both detection and differentiation of influenza A and B type viruses in respiratory samples. . Most (239 of 400, or 59.75%) specimens were nasal washes, 122 of 400 (30.5%) were nasopharyngeal swabs, 30 of 400 (7.5%) were throat swabs, 4 of 400 ...
Improving oil recovery in mature carbonate reservoirs is challenging due to inherent harsh conditions, i.e. high temperature, salinity and divalent ion concentration. This paper reports the development of a surfactant formulation that injected in sea water resulted in an incremental oil recovery higher than 20% at 120°C in carbonate field rocks. A systematic study comprising blend and salinity scans of a lineal alkyl benzene sulfonate (ABS) and a co-surfactant was done in order to select a suitable formulation optimized to be injected in sea water. The formulation performance was evaluated by measuring the solubility, interfacial tension (IFT) and phase behavior. The robustness of the formulation was assessed by changing the surfactant concentration and the brine salinity. Sandpack experiments with the addition of tracers were performed to determine the dynamic adsorption and coreflood experiments in low permeability reservoir cores were conducted to determine the injectivity, incremental oil recovery and surfactant adsorption/retention. The formulation was designed by blending at different ratios lipophilic surfactants that reduce the oil/water IFT with more hydrophilic co-surfactants that improve the solubility. The obtained formulation, comprising an ABS and a co-surfactant, was stable at ambient temperature and 120°C. It was optimized to be injected at sea water salinity providing ultra-low IFT (<0.005 mN/m) and creating a microemulsion. The designed formulation was tested by injection in a previously water flooded low permeability core. Promising results were obtained in terms of incremental oil recovery (+20%) and injectivity, but too high adsorption/retention produced a delay on oil production. In order to reduce surfactant losses, an optimization step consisting on the addition of a mineral oil and/or a low MW polymer was faced. A substantial reduction on adsorption/retention, maintaining incremental oil recovery values, was achieved by adding a specific amount of a specific mineral oil and/or a low MW polymer. The results presented show a robust formulation able to produce high incremental oil recovery under harsh carbonate reservoir conditions.
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