A microfluidic device for performing pressure-driven separations

Microchannels in microfluidic devices are frequently chemically modified to introduce specific functional elements or operational modalities. In this work, we describe a miniaturized hydraulic pump created by coating selective channels in a glass microfluidic manifold with a polyelectrolyte multilayer (PEM) that alters the surface charge of the substrate. Pressure-driven flow is generated due to a mismatch in the electroosmotic flow (EOF) rates induced upon the application of an electric field to a tee channel junction that has one arm coated with a positively charged PEM and the other arm left uncoated in its native state. In this design, the channels that generate the hydraulic pressure are interconnected via the third arm of the tee to a field-free analysis channel for performing pressure-driven separations. We have also shown that modifications in the cross-sectional area of the channels in the pumping unit can enhance the hydrodynamic flow through the separation section of the manifold. The integrated device has been demonstrated by separating Coumarin dyes in the field-free analysis channel using open-channel liquid chromatography under pressure-driven flow conditions.     

Superior performance of Mukherjee’s state-specific multi-reference coupled-cluster theory at the singles and doubles truncation scheme with localized active orbitals

The state-specific multi-reference coupled-cluster (SS-MRCC) theory of Mukherjee et al., in its singles and doubles truncation scheme (SS-MRCCSD), misses important couplings between the virtual functions reached by single and double excitations from different model functions. Since the SS-MRCC theory is not invariant with respect to the transformations among the active orbitals, the results are dependent on the active orbitals chosen. We demonstrate in this paper with results for potential energy curves for several example molecules involving single and multiple bond dissociation that the performance of SS-MRCCSD is significantly improved if localized active orbitals are used. The improvement is remarkable both in terms of the non-parallelity error and the magnitude of correlation energy recovered vis-a-vis the full configuration interaction results with the same basis set. The results bolster our claim that SS-MRCCSD with localized orbitals is an accurate general theory for potential energy surfaces.     

Raman spectroscopic studies of pulsed laser‐induced defect evolution in graphene

Raman spectra were obtained for graphene after irradiating the samples by pulsed laser (λ = 248 nm). Changes in the spectra were observed as the pulse laser energy density (PLED) was varied from 0.1 to 0.25 J/cm². Changes in bilayer graphene were accompanied by the appearance of the D peak and the broadening of the G peak. Changes in multilayer graphene are more profound as the Raman spectra changes from a multilayer to bilayer and subsequently to monolayer graphene in response to a slow increase in the PLED. The threshold PLED was found to be dependent on the number of graphene layers. We also irradiate graphene with very high PLED (much above the threshold), and the Raman spectra were found to be significantly changed. The G‐band became broader, and red shifted, while the intensity of the 2D‐band was drastically reduced and an intense defect‐related D peak appeared at about 1350 cm⁻¹. The laser ablation of graphene, both with low‐ and high‐energy intensity, is consistent with the reported theoretical predictions. Copyright © 2013 John Wiley & Sons, Ltd.     

Silver nitrate-catalyzed oxidation of aldehydes to carboxylic acids by H2O2

A variety of aromatic, aliphatic and conjugated aldehydes were converted to the corresponding carboxylic acid derivatives with 30% H₂O₂ as the oxidant in the presence of catalytic amounts of AgNO₃. The method described has wide range of applicabilities, does not involve cumbersome work-up, exhibits chemoselectivity and proceeds under mild reaction conditions, and the resulting products are obtained in good yields within reasonable time.     

Relativistic coupled-cluster theory of atomic parity nonconservation: application to 137Ba+

We report the result of our ab initio calculation of the 6s2S1/2-->5d2D3/2 parity nonconserving electric dipole transition amplitude in 137Ba+ based on relativistic coupled-cluster theory. Considering single, double, and partial triple excitations, we have achieved an accuracy of less than 1%. If the accuracy of our calculation can be matched by the proposed parity nonconservation experiment in Ba+ for the above transition, then the combination of the two results would provide an independent nonaccelerator test of the standard model of particle physics.     

Evaluation of mosquito larvicidal activity of fruit extracts of Acacia auriculiformis against the Japanese encephalitis vector Culex vishnui

The larvicidal potentiality of crude and ethyl acetate extracts of fruits of Acacia auriculiformis was investigated against all the larval instars of JE vector Culex vishnui. The crude extracts showed good results against all the larval instars with highest mortality at 0.09%. Highest mortality was found at 300 ppm of ethyl acetate extract. Lowest LC₅₀ value was obtained at 72 h for third instar larvae. Non target organisms tested, showed no to very less mortality to ethyl acetate solvent extract. Presence of N–H stretching, a C=O stretching, C=C and C–N stretching vibrations of secondary amide or amine group were confirmed from IR analysis. GC-MS analysis revealed the presence of three compounds namely Ethane 2-chloro-1,1-dimethoxy, Acetic acid, 1-methyl ether ester and [4-[1-[3,5-Dimethyl-4[(trimethylsilyl)oxy)phenyl]-1,3-dimethylbutyl)-2,6dimethylphenoxy)(trimethyl) silane, responsible for mosquito larval death.     

On‐chip pressure generation using a gel membrane fabricated outside of the microfluidic network

On‐chip generation of pressure gradients via electrokinetic means can offer several advantages to microfluidic assay design and operation in a variety of applications. In this article, we describe a simple approach to realizing this capability by employing a polyacrylamide‐based gel structure fabricated within a fluid reservoir located at the terminating end of a microchannel. Application of an electric field across this membrane has been shown to block a majority of the electroosmotic flow generated within the open duct yielding a high pressure at the channel–membrane junction. Experiments show the realization of higher pressure‐driven velocities in an electric field‐free separation channel integrated to the micropump with this design compared to other similar micropumps described in the literature. In addition, the noted velocity was found to be less sensitive to the extent of Debye layer overlap in the channel network, and therefore more impressive when working with background electrolytes having higher ionic strengths. With the current system, pressure‐driven velocities up to 3.6 mm/s were realized in a 300‐nm‐deep separation channel applying a maximum voltage of 3 kV at a channel terminal. To demonstrate the separative performance of our device, a nanofluidic pressure‐driven ion‐chromatographic analysis was subsequently implemented that relied on the slower migration of cationic analytes relative to the neutral and anionic ones in the separation channel likely due to their strong electrostatic interaction with the channel surface charges. A mixture of amino acids was thus separated with resolutions greater than those reported by our group for a similar analysis previously.     

Three-flavoured neutrino oscillations and the Leggett–Garg inequality

Three-flavoured neutrino oscillations are investigated in the light of the Leggett–Garg inequality (LGI). The results obtained are: (a) The maximum violation of the LGI is 2.17036 for neutrino path length \(L_{1}=140.15 \) km and \(\Delta L=1255.7 \) km. (b) The presence of the mixing angle \(\theta _{13}\) enhances the maximum violation of LGI by \(4.6\%\). (c) The currently known mass hierarchy parameter \(\alpha = 0.0305\) increases the maximum violation of LGI by \(3.7\%\). (d) The presence of a CP-violating phase parameter enhances the maximum violation of LGI by \(0.24\%\), thus providing an alternative indicator of CP violation in three-flavoured neutrino oscillations. The outline of an experimental proposal is suggested whereby the findings of this investigation may be verified.     

Drainage and water clusters in Gillette foam

Raman measurements on Gillette foam have been carried out to analyze different phases of water in the system. We have shown that in addition to free water molecules, which drain out with aging of foam, water clusters of only a few water molecules are also present in foam. We have analyzed the rate of drainage with the existing theory available in the literature. The nature of water clusters in Gillette foam has also been obtained from ab initio self‐consistent field calculations for [H₂O]_n clusters. Copyright © 2008 John Wiley & Sons, Ltd.