High speed digital holographic interferometry for hypersonic flow visualization

Optical imaging techniques have played a major role in understanding the flow dynamics of varieties of fluid flows, particularly in the study of hypersonic flows. Schlieren and shadowgraph techniques have been the flow diagnostic tools for the investigation of compressible flows since more than a century. However these techniques provide only the qualitative information about the flow field. Other optical techniques such as holographic interferometry and laser induced fluorescence (LIF) have been used extensively for extracting quantitative information about the high speed flows. In this paper we present the application of digital holographic interferometry (DHI) technique integrated with short duration hypersonic shock tunnel facility having 1 ms test time, for quantitative flow visualization. Dynamics of the flow fields in hypersonic/supersonic speeds around different test models is visualized with DHI using a high-speed digital camera (0.2 million fps). These visualization results are compared with schlieren visualization and CFD simulation results. Fringe analysis is carried out to estimate the density of the flow field.

Projection-based atom selection in orthogonal matching pursuit for compressive sensing

For compressive sensing, we endeavor to improve the atom selection strategy of the existing orthogonal matching pursuit (OMP) algorithm. To achieve a better estimate of the underlying support set progressively through iterations, we use a least squares solution based atom selection method. From a set of promising atoms, the choice of an atom is performed through a new method that uses orthogonal projection along-with a standard matched filter. Through experimental evaluations, the effect of projection based atom selection strategy is shown to provide a significant improvement for the support set recovery performance, in turn, the compressive sensing recovery.

Dynamics of H-atom exchange in stable cis-dihydrogen/hydride complexes of ruthenium( II) bearing phosphine and N-N bidentate ligands

Synthesis and characterization of cis, trans-RuH(eta(2)-H-2)(PPh3)(2)(N-N)]OTf] (N-N = 2,2'-bipyridyl (bpy) 1a, 2,2'-bipyrimidine (bpm) 2a; OTf = trifluoromethane sulfonate (CF3SO3)) complexes are reported. The cis-H-2/hydride ligands are involved in H-atom site exchange between the two moieties. This dynamics was investigated by variable temperature NMR spectral studies based on which the mechanism of the exchange process was deduced. The Delta G(#) for the exchange of H-atoms between the eta(2)-H-2 and hydride ligands was determined to be around 8 and 13 kJ mol(-1), respectively, for 1a and 2a. The H-H distances (d(HH), A) in complexes 1a and 2a have been calculated from the T-1(minimum) and (1)J(H, D) and are found to be 1.07 A (slow) and 0.95 A for 1a and 1.04 A (slow) and 0.94 A for 2a, respectively. The molecular structure of 1a was determined by X-ray crystallography.

Two new atom centered fragment descriptors and scoring function enhance classification of antibacterial activity

Classification of pharmacologic activity of a chemical compound is an essential step in any drug discovery process. We develop two new atom-centered fragment descriptors (vertex indices) - one based solely on topological considerations without discriminating atomor bond types, and another based on topological and electronic features. We also assess their usefulness by devising a method to rank and classify molecules with regard to their antibacterial activity. Classification performances of our method are found to be superior compared to two previous studies on large heterogeneous data sets for hit finding and hit-to-lead studies even though we use much fewer parameters. It is found that for hit finding studies topological features (simple graph) alone provide significant discriminating power, and for hit-to-lead process small but consistent improvement can be made by additionally including electronic features (colored graph). Our approach is simple, interpretable, and suitable for design of molecules as we do not use any physicochemical properties. The singular use of vertex index as descriptor, novel range based feature extraction, and rigorous statistical validation are the key elements of this study.

DEFINING alpha-HELIX GEOMETRY BY C-alpha ATOM TRACE vs (phi-psi) TORSION ANGLES: A COMPARATIVE ANALYSIS

A regular secondary structure is described by a well defined set of values for the backbone dihedral angles (phi,psi and omega) in a polypeptide chain. However in real protein structures small local variations give rise to distortions from the ideal structures, which can lead to considerable variation in higher order organization. Protein structure analysis and accurate assignment of various structural elements, especially their terminii, are important first step in protein structure prediction and design. Various algorithms are available for assigning secondary structure elements in proteins but some lacunae still exist. In this study, results of a recently developed in-house program ASSP have been compared with those from STRIDE, in identification of alpha-helical regions in both globular and membrane proteins. It is found that, while a combination of hydrogen bond patterns and backbone torsional angles (phi-psi) are generally used to define secondary structure elements, the geometry of the C-alpha atom trace by itself is sufficient to define the parameters of helical structures in proteins. It is also possible to differentiate the various helical structures by their C-alpha trace and identify the deviations occurring both at mid-positions as well as at the terminii of alpha-helices, which often lead to occurrence of 3(10) and pi-helical fragments in both globular and membrane proteins.

Signal tracking approach for phase estimation in digital holographic interferometry

In this research work, we introduce a novel approach for phase estimation from noisy reconstructed interference fields in digital holographic interferometry using an unscented Kalman filter. Unlike conventionally used unwrapping algorithms and piecewise polynomial approximation approaches, this paper proposes, for the first time to the best of our knowledge, a signal tracking approach for phase estimation. The state space model derived in this approach is inspired from the Taylor series expansion of the phase function as the process model, and polar to Cartesian conversion as the measurement model. We have characterized our approach by simulations and validated the performance on experimental data (holograms) recorded under various practical conditions. Our study reveals that the proposed approach, when compared with various phase estimation methods available in the literature, outperforms at lower SNR values (i.e., especially in the range 0-20 dB). It is demonstrated with experimental data as well that the proposed approach is a better choice for estimating rapidly varying phase with high dynamic range and noise. (C) 2014 Optical Society of America

Atom Lithography

We review the two kinds of forces that near-resonant light exerts on atoms the spontaneous force that is used for laser cooling, and the stimulated force that is used for coherent manipulation of atoms. We will discuss an experiment where laser cooling is used to collimate an atomic beam of sodium atoms, and the stimulated force within one period of a one-dimensional standing wave is used as a lens to focus the atoms to a narrow line about 20 nm wide. This kind of atom lithography is an example of the general field of atom optics in which light is used to manipulate atoms.

Size Modulation of Colloidal Au Nanoparticles via Digestive Ripening in Conjunction with a Solvated Metal Atom Dispersion Method: An Insight Into Mechanism

Digestive ripening, a postsynthetic treatment of colloidal nanoparticles, is a versatile method to produce monodisperse nanoparticles and to prepare various bimetallic nanostructures. The mechanism of this process is largely unknown. Herein, we present a systematic study conducted using Au nanoparticles prepared by a solvated metal atom dispersion method to probe the mechanistic aspects of digestive ripening. In our study, experimental conditions such as concentration of capping agent, reaction time, and temperature, were found to influence the course of the digestive ripening process. Here it is shown that, during digestive ripening under reflux, nanoparticles within an optimum size window are conserved, and surface etching facilitated mass transfer resulted in monodisperse nanoparticles. Overall, digestive ripening can be considered as a kinetically controlled thermodynamic process.

First hyperpolarizability of Ru-half-sandwich complexes: The effect of halogen atom substitution on the ancillary ligand

The first hyperpolarizability (beta) of a series of half-sandwich Ru complexes with a mercaptobenzothiazole ligand bearing a halogen atom substitution in the para-position has been investigated by hyper-Rayleigh scattering and quantum chemical calculations. The heterocyclic ligand with a bromine atom in the para position makes it a very good donor and charge flows to the Ru center enhancing the beta value of the complex by a factor of 2 compared to the complex with the ligand without the halogen substitution. The resonance (+R) and the inductive (-I) effects exerted by the halogen atom in the para position push electrons in opposing directions in the complex. For the Br and Cl atoms the resonance effect dominates which enables the ligand to donate electrons to the metal center thereby increasing the hyperpolarizability whereas for the fluorine atom, the inductive effect is dominant which reduces the charge flow to the metal and the hyperpolarizability drops even below that of the unsubstituted ligand. This unprecedented halogen atom effect on beta of metal complexes is reported. (C) 2015 Elsevier By. All rights reserved.

Magnetometry using Ramsey interferometry in a Yb atomic beam

We use the Ramsey separated oscillatory fields technique in a 400 degrees C thermal beam of ytterbium (Yb) atoms to measure the Larmor precession frequency (and hence the magnetic field) with high precision. For the experiment, we use the strongly allowed S-1(0) P-1(1) transition at 399 nm, and choose the odd isotope Yb-171 with nuclear spin I = 1/2, so that the ground state has only two magnetic sublevels m(F) = +/- 1/2. With a magnetic field of 22.2 G and a separation of about 400 mm between the oscillatory fields, the central Ramsey fringe is at 16.64 kHz and has a width of 350 Hz. The technique can be readily adapted to a cold atomic beam, which is expected to give more than an order-of-magnitude improvement in precision. The signal-to-noise ratio is comparable to other techniques of magnetometry; therefore it should be useful for all kinds of precision measurements such as searching for a permanent electric dipole moment in atoms.

Hetero-atom Doped Carbon Nanotubes for Dye Degradation and Oxygen Reduction Reaction

We report the synthesis of nitrogen doped vertically aligned multi-walled (MWNCNTs) carbon nanotubes by pyrolysis and its catalytic performance for degradation of methylene blue (MB) dye & oxygen reduction reaction (ORR). The degradation of MB was monitored spectrophotometrically with time. Kinetic studies show the degradation of MB follows a first order kinetic with rate constant k=0.0178 min(-1). The present rate constant is better than that reported for various supported/non-supported semiconducting nanomaterials. Further ORR performance in alkaline media makes MWNCNTs a promising cost-effective, fuel crossover tolerance, metal-free, eco-friendly cathode catalyst for direct alcohol fuel cell.

Differential dynamics of the serotonin(1A) receptor in membrane bilayers of varying cholesterol content revealed by all atom molecular dynamics simulation

The serotonin(1A) receptor belongs to the superfamily of G protein-coupled receptors (GPCRs) and is a potential drug target in neuropsychiatric disorders. The receptor has been shown to require membrane cholesterol for its organization, dynamics and function. Although recent work suggests a close interaction of cholesterol with the receptor, the structural integrity of the serotonin(1A) receptor in the presence of cholesterol has not been explored. In this work, we have carried out all atom molecular dynamics simulations, totaling to 3s, to analyze the effect of cholesterol on the structure and dynamics of the serotonin(1A) receptor. Our results show that the presence of physiologically relevant concentration of membrane cholesterol alters conformational dynamics of the serotonin(1A) receptor and, on an average lowers conformational fluctuations. Our results show that, in general, transmembrane helix VII is most affected by the absence of membrane cholesterol. These results are in overall agreement with experimental data showing enhancement of GPCR stability in the presence of membrane cholesterol. Our results constitute a molecular level understanding of GPCR-cholesterol interaction, and represent an important step in our overall understanding of GPCR function in health and disease.

DPIV and Interferometry Technique for Velocity Field and Concentration Fields Measurement in Crystal Growth

The property of crystal depends seriously on the solution concentration distribution near the growth surface of a crystal. However, the concentration distributions are affected by the diffusion and convection of the solution. In the present experiment, the two methods of optical measurement are used to obtained velocity field and concentration field of NaClO₃ solution. The convection patterns in sodium chlorate (NaClO₃) crystal growth are measured by Digital Particle image Velocimetry (DPIV) technology. The 2-dimentional velocity distributions in the solution of NaClO3 are obtained from experiments. And concentration field are obtained by a Mach-Zehnder interferometer with a phase shift servo system. Interference patterns were recorded directly by a computer via a CCD camera. The evolution of velocity field and concentration field from dissolution to crystallization are visualized clearly. The structures of velocity fields were compared with that of concentration field.