Spectroscopic studies of catanionic reverse microemulsion: correlation with the superactivity of horseradish peroxidase enzyme in a restricted environment

Catanionic microemulsions formed by dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfate (SDS), n-hexanol, dodecane, and citrate buffer have been characterized by using dynamic light scattering (DLS) and spectroscopic studies. While the DLS measurements provide information about the hydrodynamic diameters of the microemulsion droplets formed upon variation of the constituents, steady-state and time-resolved fluorescence emission experiments probe the polarity and the dynamics of the trapped solvent pool inside of the microemulsion droplets of nanometer dimension. In addition, time-resolved fluorescence anisotropy shows the rigidity of the confined solvent pool as well as the coupling between the motion of a solute and those of the solvent molecules. The results obtained from the DLS and those from the steady-state and time-resolved fluorescence emission studies have been found to correlate well with the superactivity of horseradish peroxidase enzyme in the catanionic microemulsions. Subsequently, the time-zero estimate for the dynamic Stokes shift in these microemulsions reveals that approximately 50% of the total solvent dynamical response is missed due to the limited time resolution employed in our experiments. The amplitude of the missing portion is similar to what has been observed recently for nanoscopic water by Fayer and co-workers (Piletic, I. R.; Tan, H.-S.; Fayer, M. D. J. Phys. Chem. B 2005, 109, 21273).     

Ab initio studies of properties of small potassium clusters

We have studied the properties of various isomers of potassium clusters containing even number of atoms ranging from 2 to 20 at the ab initio level. The geometry optimization calculations of the isomers of each cluster are performed by using all-electron density functional theory with gradient corrected exchange-correlation functional. Using the optimized geometries of different isomers we investigate the evolution of binding energy, ionization potential, and static polarizability with the increasing size of the clusters. The polarizabilities are calculated by employing M?ller-Plesset perturbation theory and time-dependent density functional theory. The polarizabilities of dimer and tetramer are also calculated by employing large basis set coupled cluster theory with single and double excitations and perturbative triple excitations. The time-dependent density functional theory calculations of polarizabilities are carried out with two different exchange-correlation potentials: (i) an asymptotically correct model potential and (ii) within the local density approximation. A systematic comparison with the other available theoretical and experimental data for various properties of small potassium clusters mentioned above has been performed. These comparisons reveal that both the binding energy and the ionization potential obtained with gradient-corrected potential match quite well with the already published data. Similarly, the polarizabilities obtained with M?ller-Plesset perturbation theory and with model potential are quite close to each other and also close to experimental data.     

Interaction of surface water waves with a vertical elastic plate: a hypersingular integral equation approach

In this paper, we present an alternative method to investigate scattering of water waves by a submerged thin vertical elastic plate in the context of linear theory. The plate is submerged either in deep water or in the water of uniform finite depth. Using the condition on the plate, together with the end conditions, the derivative of the velocity potential in the direction of normal to the plate is expressed in terms of a Green’s function. This expression is compared with that obtained by employing Green’s integral theorem to the scattered velocity potential and the Green’s function for the fluid region. This produces a hypersingular integral equation of the first kind in the difference in potential across the plate. The reflection coefficients are computed using the solution of the hypersingular integral equation. We find good agreement when the results for these quantities are compared with those for a vertical elastic plate and submerged and partially immersed rigid plates. New results for the hydrodynamic force on the plate, the shear stress and the shear strain of the vertical elastic plate are also evaluated and represented graphically.     

L_1 regression estimate and its bootstrap

We study the asymptotic distribution of the L1 regression estimator under general condi-tions with matrix norming and possibly non i.i.d.errors.We then introduce an appropriate bootstrap procedure to estimate the distribution of this estimator and study its asymptotic properties.It is shown that this bootstrap is consistent under suitable conditions and in other situations the bootstrap limit is a random distribution.     

Chemomechanics of surface stresses induced by DNA hybridization

When biomolecular reactions occur on one surface of a microcantilever beam, changes in intermolecular forces create surface stresses that bend the cantilever. While this phenomenon has been exploited to create label-free biosensors and biomolecular actuators, the mechanisms through which chemical free energy is transduced to mechanical work in such hybrid systems are not fully understood. To gain insight into these mechanisms, we use DNA hybridization as a model reaction system. We first show that the surface grafting density of single-stranded probe DNA (sspDNA) on a surface is strongly correlated to its radius of gyration in solution, which in turn depends on its persistence length and the DNA chain length. Since the persistence length depends on ionic strength, the grafting density of sspDNA can be controlled by changing a solution's ionic strength. The surface stresses produced by the reaction of complementary single-stranded target DNA (sstDNA) to sspDNA depend on the length of DNA, the grafting density, and the hybridization efficiency. We, however, observe a remarkable trend: regardless of the length and grafting density of sspDNA, the surface stress follows an exponential scaling relation with the density of hybridized sspDNA.     

Reciprocal Ontological Models Show Indeterminism Comparable to Quantum Theory

We show that within the class of ontological models due to Harrigan and Spekkens, those satisfying preparation-measurement reciprocity must allow indeterminism comparable to that in quantum theory. Our result implies that one can design quantum random number generator, for which it is impossible, even in principle, to construct a reciprocal deterministic model.     

Anomalous temperature dependence of speed of sound of bulk poly(N-isopropylacrylamide) hydrogels near the phase transition

Bulk Poly(N-isopropylacrylamide) (PNIPAm) hydrogels are thermally responsive polymers that undergo a sharp volumetric phase transition around its lower critical solution temperature of 33 °C. The physical characteristics of bulk, micro-, and nano-form PNIPAm hydrogel have been well-studied, and have applications ranging from biomedical devices to mechanical actuators. An important physical characteristics which reveals lack of available information is speed of sound. Prior studies have utilized Brillouin scattering, multi-echo reflection ultrasound spectroscopy, the sing-around method, and others in measuring the speed of sound. We use a planar resonant cavity with bulk PNIPAm hydrogel in aqueous solution to determine the temperature dependent speed of sound around the lower critical solution temperature. The results show sharp nonmonotonic behavior of the sound velocity in vicinity of the phase transition.     

Limiting Spectral Distribution of Random k-Circulants

Consider random k-circulants A _k,n with n????,k=k(n) and whose input sequence {a _l } _l??0 is independent with mean zero and variance one and $\sup_{n}n^{-1}\sum_{l=1}^{n}\mathbb{E}|a_{l}|^{2+\delta}<\infty$ for some ??>0. Under suitable restrictions on the sequence {k(n)} _n??1, we show that the limiting spectral distribution (LSD) of the empirical distribution of suitably scaled eigenvalues exists, and we identify the limits. In particular, we prove the following: Suppose g??1 is fixed and p ₁ is the smallest prime divisor of g. Suppose $P_{g}=\prod_{j=1}^{g}E_{j}$ where {E _j }_1??j??g are i.i.d. exponential random variables with mean one. (i) If k ^g =?1+sn where s=1 if g=1 and $s=o(n^{p_{1}-1})$ if g>1, then the empirical spectral distribution of n ^?1/2 A _k,n converges weakly in probability to $U_{1}P_{g}^{1/(2g)}$ where U ₁ is uniformly distributed over the (2g)th roots of unity, independent of P _g . (ii) If g??2 and k ^g =1+sn with $s=o(n^{p_{1}-1})$ , then the empirical spectral distribution of n ^?1/2 A _k,n converges weakly in probability to $U_{2}P_{g}^{1/(2g)}$ where U ₂ is uniformly distributed over the unit circle in ?², independent of P _g . On the other hand, if k??2, k=n ^o(1) with gcd?(n,k)=1, and the input is i.i.d. standard normal variables, then $F_{n^{-1/2}A_{k,n}}$ converges weakly in probability to the uniform distribution over the circle with center at (0,0) and radius $r=\exp(\mathbb{E}[\log\sqrt{E}_{1}])$ .     

Interesting periodic variations in physical and chemical properties of homonuclear diatomic molecules

We carry out a systematic study of various ground state and response properties of homonuclear diatomic molecules (from hydrogen to rubidium, including transition metals) as a function of atomic number of constituent atoms. We perform the ground state and response property calculations by using state of the art density functional theory/time dependent density functional theory. We observe that several properties of homonuclear diatomic molecules show periodic variations along rows and columns of the periodic table. The periodic variations in the ground state properties of diatomic molecules may be explained by the nature and type of the bond that exists between the constituent atoms. Similarly, the periodic variations in the response properties such as static dipole polarizability and strength of the van der Waals interaction between diatomic molecules have been correlated with the variations in metallic/nonmetallic character of the elements along the periodic table. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012