Anomalous flow behavior in closed and open thin walled nanochannels

Molecular dynamics simulations have been carried out to examine water flow in symmetric and asymmetric open and closed ends nanochannels with hydrophilic surfaces. The results are counterintuitive and the opposite of what is observed in macro-systems-closed channels fill faster with fluid than do their open counterparts. In addition, hybrid closed-open asymmetric channels fill up even faster. These results can be explained on the basis of the fluid-structure interaction that arises through the different vibrational behaviors of the surface molecules that are part of the wall forming these channels. Such effects are not expected to be of significance in macro-channels, and point to an important case where macro and nanochannels exhibit contrary behavior. Since these effects results from strong interactions between the fluid molecules and solid surface, one would not expect them with hydrophobic walls, and our simulations confirm such behavior.     

A new semigroup technique in poisson approximation

We present a unified and self-contained approach to Poisson approximation problems for independent Bernoulli summands with respect to several metrics by a general semigroup technique, expanding and completing earlier work on this subject by the first two authors [4], [5], [6].     

Analytical model for the magnetophoretic capture of magnetic microspheres in microfluidic devices

Magnetic microspheres are used as mobile substrates in micro-total-analysis systems (μTAS), since the particles can be selectively functionalized to attach different bioconjugates and can be precisely manipulated using external magnetic field gradients. A large number of MEMS-based bio-analytical devices employ magnetophoretic separation as an important step during their operation. An analytical technique is proposed in this paper that describes the magnetophoretic transport of magnetic microspheres under an imposed magnetic field when there is a pressure-driven or electroosmotic flow through a microchannel. Successful magnetophoretic capture occurs if the strength of the field-inducing magnetic dipole exceeds a critical value, or if the particles are larger than a critical size. The magnetophoretic separator performance is characterized in terms of capture efficiency. The analysis shows that the capture efficiency is a function of two independent non-dimensional parameters, λ and γ that in turn involve all the physical design and operating parameters of the microfluidic separator, e.g., the dipole strength, particle size and susceptibility, fluid viscosity and velocity, channel height, and the separation of the dipole. Parametric plots of capture efficiency as function of λ and γ helps in choosing the right design and operation parameter of a practical microfluidic separator for a target level of performance.     

Response Surface Optimization of Medium Components for Naringinase Production from <Emphasis Type="Italic">Staphylococcus xylosus MAK2</Emphasis>

Response surface methodology was used to optimize the fermentation medium for enhancing naringinase production by Staphylococcus xylosus. The first step of this process involved the individual adjustment and optimization of various medium components at shake flask level. Sources of carbon (sucrose) and nitrogen (sodium nitrate), as well as an inducer (naringin) and pH levels were all found to be the important factors significantly affecting naringinase production. In the second step, a 22 full factorial central composite design was applied to determine the optimal levels of each of the significant variables. A second-order polynomial was derived by multiple regression analysis on the experimental data. Using this methodology, the optimum values for the critical components were obtained as follows: sucrose, 10.0%; sodium nitrate, 10.0%; pH 5.6; biomass concentration, 1.58%; and naringin, 0.50% (w/v), respectively. Under optimal conditions, the experimental naringinase production was 8.45 U/mL. The determination coefficients (R ²) were 0.9908 and 0.9950 for naringinase activity and biomass production, respectively, indicating an adequate degree of reliability in the model.     

Cell Disruption Optimization and Covalent Immobilization of β-D-Galactosidase from <Emphasis Type="Italic">Kluyveromyces marxianus</Emphasis> YW-1 for Lactose Hydrolysis in Milk

β-D-galactosidase (EC 3.2.1.23) from Kluyveromyces marxianus YW-1, an isolate from whey, has been studied in terms of cell disruption to liberate the useful enzyme. The enzyme produced in a bioreactor on a wheat bran medium has been successfully immobilized with a view to developing a commercially usable technology for lactose hydrolysis in the food industry. Three chemical and three physical methods of cell disruption were tested and a method of grinding with river sand was found to give highest enzyme activity (720 U). The enzyme was covalently immobilized on gelatin. Immobilized enzyme had optimum pH and temperature of 7.0 and 40 °C, respectively and was found to give 49% hydrolysis of lactose in milk after 4 h of incubation. The immobilized enzyme was used for eight hydrolysis batches without appreciable loss in activity. The retention of high catalytic activity compared with the losses experienced with several previously reported immobilized versions of the enzyme is significant. The method of immobilization is simple, effective, and can be used for the immobilization of other enzymes.     

Dynamical approach to spectator fragmentation in Au+Au reactions at 35 MeV/A

The characteristics of fragment emission in peripheral ¹⁹⁷Au+¹⁹⁷Au collisions 35 MeV/A are studied using the two clusterization approaches within framework of quantum molecular dynamics model. Our model calculations using minimum spanning tree (MST) algorithm and advanced clusterization method namely simulated annealing clusterization algorithm (SACA) showed that fragment structure can be realized at an earlier time when spectators contribute significantly toward the fragment production even at such a low incident energy. Comparison of model predictions with experimental data reveals that SACA method can nicely reproduce the fragment charge yields and mean charge of the heaviest fragment. This reflects suitability of SACA method over conventional clusterization techniques to investigate spectator matter fragmentation in low energy domain.     

Oxidation temperature dependent properties of MgO thin film on alumina

The magnesium oxide thin films were prepared by thermal oxidation (in air) of vacuum evaporated magnesium thin film on alumina. It was found that oxidation temperature (623 K, 675 K and 723 K) and thickness (103 nm and 546 nm) dependent effects were prominently manifested in the surface morphology. Electrical and microwave properties (8-12 GHz) of the MgO thin films were also carried out. X-ray diffraction showed orientation along (2 0 0) and (2 2 0) directions. Flowerlike morphology was observed from SEM and flake like morphology for films of higher thickness oxidized at higher temperatures. The magnesium oxide thin film showed NTC behavior. Microwave transmittance was found to increase with increase in oxidation temperature but was lower than alumina. Frequency and oxidation temperature dependent microwave permittivity was obtained. The microwave dielectric constant varied in the range 8.3-15.3.     

Development of an HPTLC‐based diagnostic method for invasive aspergillosis

A rapid, sensitive and specific high‐performance thin‐layer chromatographic (HPTLC) method was developed and validated for determination of gliotoxin in Aspergillus infected immunocompromised patients with invasive aspergillosis (IA). Densitometric analysis of gliotoxin was carried out in the absorbance mode at 254 nm after single‐step extraction with chloroform. The method uses TLC aluminum plates pre‐coated with silica gel 60F‐254 as a stationary phase and toluene–isoamyl alcohol–methanol (10:0.5:0.5, v/v/v) as mobile phase, which gives compact spot of gliotoxin (R_f = 0.51). The calibration curve was linear (r² ≥ 0.994) between peak area and concentration in the tested range of 100–1000 ng spot^?1 with minimum detectable range 0.025 ng μ^?1 of serum sample. The mean ± SD value of slope and intercept of the standard chromatogram of gliotoxin were found to be 523.2 ± 1.555635 and 915.8 ± 30.68843, respectively. The developed method is simple, rapid, precise and less costly than earlier diagnostic methods, and different serum samples can be run on a single TLC plate for comparative analysis. The proposed method can be used to analyze gliotoxin in patient serum for easy, rapid and cost‐effective diagnosis of IA. Copyright © 2009 John Wiley & Sons, Ltd.