A thermo-mechanically coupled theory for fluid permeation in elastomeric materials: Application to thermally responsive gels

An elastomeric gel is a cross-linked polymer network swollen with a solvent, and certain gels can undergo large reversible volume changes as they are cycled about a critical temperature. We have developed a continuum-level theory to describe the coupled mechanical deformation, fluid permeation, and heat transfer of such thermally responsive gels. In discussing special constitutive equations we limit our attention to isotropic materials, and consider a model based on a Flory–Huggins model for the free energy change due to mixing of the fluid with the polymer network, coupled with a non-Gaussian statistical–mechanical model for the change in configurational entropy—a model which accounts for the limited extensibility of polymer chains. We have numerically implemented our theory in a finite element program. We show that our theory is capable of simulating swelling, squeezing of fluid by applied mechanical forces, and thermally responsive swelling/de-swelling of such materials.     

Protein unfolding and subsequent refolding: a spectroscopic investigation

The mechanism by which the protein Bovine Serum Albumin (BSA) undergoes unfolding induced by Guanidine Hydrochloride (GdHCl) and then the subsequent refolding brought in by many-fold dilution was studied by steady-state fluorescence, anisotropy, time resolved measurements and Circular Dichroism (CD) spectroscopy. CD data reveal that the protein attains a degree of extra rigidity at low concentrations of the denaturant, GdHCl, and this observation was correlated with other techniques used in this present work. The unfolding and refolding of BSA appear to proceed through intermediates and both the processes are sequential in nature. The intrinsic fluorescence from the tryptophan amino acid residue of BSA and another external fluorophore Nile Red was made use of in order to investigate the mechanisms of unfolding and refolding and we have conclusively proved that both these processes follow a reversible mechanism.     

Lithium-doped PEO—a prospective solid electrolyte with high ionic conductivity,developed using <Emphasis Type="Italic">n</Emphasis>-Butyllithium in hexane as dopant

The present work is an effort to study the effects of Li doping on the structural and transport properties of the solid polymer electrolyte, poly-ethelene oxide (PEO) (molecular weight, 200,000). Li-doped PEO was synthesized by treating PEO with n-Butyllithium in hexane for different doping concentrations. It is seen that the crystallinity of the doped PEO decreases on increasing the Li doping concentration and XRD and FTIR studies support this observation. FESEM images give better details of surface morphology of doped PEO samples. The TGA curves of PEO and Li-doped PEO samples reveal the weight loss region, and it is observed that the weight loss process of the solid polymer electrolyte is gradual rather than abrupt, contrary to the case of liquid electrolytes. The purity and the electrochemical stability of the samples were established by cyclic voltammetry studies. Impedance measurements were carried out to estimate the ionic conductivity of Li-doped PEO samples. The present value of ionic conductivity observed at room temperature in Li-doped PEO is about five orders higher than that of pure PEO and is quite close to that of liquid electrolytes. It is inferred that, ionic conductivity of the sample is increasing on increasing the Li doping concentration due to enhanced charge carrier density and flexibility of the doped sample structure. The ionic mobility and ionic transport are significantly improved by the less crystallinity and higher flexibility of the Li-doped PEO samples which in turn are responsible for the enhanced ionic conductivity observed.     

<Emphasis Type="Italic">K</Emphasis><Subscript>β</Subscript> to <Emphasis Type="Italic">K</Emphasis><Subscript>α</Subscript> X-ray intensity ratios and K to L shell vacancy transfer probabilities of Co,Ni, Cu,and Zn

The K to L shell total vacancy transfer probabilities of low Z elements Co, Ni, Cu, and Zn are estimated by measuring the K _β to K _α intensity ratio adopting the 2π-geometry. The target elements were excited by 32.86 keV barium K-shell X-rays from a weak ¹³⁷Cs γ-ray source. The emitted K-shell X-rays were detected using a low energy HPGe X-ray detector coupled to a 16 k MCA. The measured intensity ratios and the total vacancy transfer probabilities are compared with theoretical results and others’ work, establishing a good agreement.     

Graphene Oxide as Recyclable Catalyst for One-Pot Synthesis of α-Aminophosphonates

We report the synthesis of α-aminophosphonates from aromatic aldehydes, aromatic and aliphatic amines, and trimethylphosphite (Kabachnik–Fields reaction) using a “carbocatalyst,” graphene oxide, at room temperature with excellent yield and recyclability. Enhanced catalytic activity of graphene oxide as compared to other catalysts studied is possibly due to the presence of carboxylic acid and hydroxyl groups.     

Light-induced antibacterial activity of symmetrical and asymmetrical oligophenylene ethynylenes

The light-induced antibacterial activity of symmetric and asymmetric oligophenylene ethynylenes (OPEs) was investigated against Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Escherichia coli) bacteria. To understand the light-induced biocidal effect better, the transient absorption and triplet lifetime of OPEs were studied in methanol and water. A higher triplet lifetime was observed for OPE samples in water than in methanol. The magnitudes of the changes in optical density (ΔOD) of the S-OPE-n(H) series of symmetric oligomers are much higher than that of the asymmetric OPE-n series in water and are generally correlated with the singlet oxygen yield. It was found that the antibacterial activity against both Gram-positive and Gram-negative bacteria is size-, concentration-, and time-dependent. The light-induced antibacterial activity may result from the coordinated interactions of membrane disruption and interfacial or intracellular singlet oxygen generation, and the dominant factor is most likely the latter. The results obtained in this study will aid in the design of more efficient biocides in the future.     

Exact solution of the CPMG pulse sequence with phase variation down the echo train: application to R₂ measurements

An implicit exact algebraic solution of CPMG experiments is presented and applied to fit experiments. Approximate solutions are also employed to explore oscillations and effective decay rates of CPMG experiments. The simplest algebraic approximate solution has illustrated that measured intensities will oscillate in the conventional CPMG experiments and that using even echoes can suppress errors of measurements of R? due to the imperfection of high-power pulses. To deal with low-power pulses with finite width, we adapt the effective field to calculate oscillations. An optimization model with the effective field approximation and dimensionless variables is proposed to quantify oscillations of measured intensities of CPMG experiments of different phases of the π pulses. We show, as was known using other methods, that repeating one group of four pulses with different phases in CPMG experiments, which we call phase variation, but others call phase alternation or phase cycling, can significantly smooth the dependence of measured intensities on frequency offset in the range of ±?γB?. In this paper, a second-order expression with respect to the ratio of frequency offset to π-pulse amplitude is developed to describe the effective R? of CPMG experiments when using a group phase variation scheme. Experiments demonstrate that (1) the exact calculation of CPMG experiments can remarkably eliminate systematic errors in measured R?s due to the effects of frequency offset, even in the absence of phase variation; (2) CPMG experiments with group phase variation can substantially remove oscillations and effects of the field inhomogeneity; (3) the second-order expression of the effective decay rate with phase variation is able to provide reliable estimates of R? when offsets are roughly within ±?γB?; and, most significantly, (4) the more sophisticated optimization model using an exact solution of the discretized CPMG experiment extends, to ±γB?, the range of offsets for which reliable estimates of R? can be obtained when using the preferred phase variation scheme.     

Use of continuous optimization methods to find carbon links in 2D INADEQUATE spectra

The 2-D INADEQUATE experiment is a useful experiment for determining carbon structures of organic molecules, which is known for having low signal-to-noise ratios. A non-linear optimization method for solving low-signal spectra resulting from this experiment is introduced to compensate. The method relies on the peak locations defined by the INADEQUATE experiment to create boxes around these areas and measure the signal in each. By measuring pairs of these boxes and applying penalty functions that represent a priori information, we are able to quickly and reliably solve spectra with an acquisition time approximately a quarter of that required by traditional methods. Examples are shown using the spectrum of sucrose.     

Crystal growth,optical, mechanical and electrical properties of organic NLO material γ‐glycine

Single crystals of organic non‐linear optical material, γ‐glycine have been grown by gel method for the first time. The γ‐phase is confirmed by single crystal XRD. The presence of various functional groups of γ‐glycine are confirmed by FTIR. The UV‐Vis‐NIR spectrum reveals the high percentage of transmission of the sample in the entire visible region. The SHG of γ‐glycine is confirmed by Kurtz powder technique. TGA‐DTA studies indicate that the crystal is structurally stable upto 170 °C. Microhardness investigations are conducted on the grown crystals. The dielectric constant measurements are carried out and the nature of variation of dielectric constant ε′ and dielectric loss D in the frequency range of 50 Hz to 5 MHz is studied and reported. Photoconductivity studies of γ‐glycine crystals revealed the negative photoconducting nature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Logic design for a self-contained diver navigation system

A major criterion in the design of a diver-held acoustic navigation system we are developing is that it must be very compact so that a diver can operate it easily and safely. With space at a premium, a logic circuit has been designed as a convenient way of measuring and storing the relative distances of the diver from up to four fixed transponders. A battery-powered microprocessor allows the diver's location to be computed. With one of the logic circuits the location can be found in two-dimensional space in the plane of three transponders; with two or three logic circuits the location can be found in three-dimensional space using four transponders. The circuit could be used in any other application which involves measuring the relative arrival times of acoustic pulses at a receiver.