Transition from Cassie to impaled state during drop impact on groove-textured solid surfaces

Liquid drops impacted on textured surfaces undergo a transition from the Cassie state characterized by the presence of air pockets inside the roughness valleys below the drop to an impaled state with at least one of the roughness valleys filled with drop liquid. This occurs when the drop impact velocity exceeds a particular value referred to as the critical impact velocity. The present study investigates such a transition process during water drop impact on surfaces textured with unidirectional parallel grooves referred to as groove-textured surfaces. The process of liquid impalement into a groove in the vicinity of drop impact through de-pinning of the three-phase contact line (TPCL) beneath the drop as well as the critical impact velocity were identified experimentally from high speed video recordings of water drop impact on six different groove-textured surfaces made from intrinsically hydrophilic (stainless steel) as well as intrinsically hydrophobic (PDMS and rough aluminum) materials. The surface energy of various 2-D configurations of liquid-vapor interface beneath the drop near the drop impact point was theoretically investigated to identify the locally stable configurations and establish a pathway for the liquid impalement process. A force balance analysis performed on the liquid-vapor interface configuration just prior to TPCL de-pinning provided an expression for the critical drop impact velocity, U-o,U-cr, beyond which the drop state transitions from the Cassie to an impaled state. The theoretical model predicts that Uo, cr increases with the increase in pillar side angle, a, and intrinsic hydrophobicity whereas it decreases with the increase in groove top width, w, of the groove-textured surface. The quantitative predictions of the theoretical model were found to show good agreement with the experimental measurements of U-o,U-cr plotted against the surface texture geometry factor in our model, {tan(alpha/2)/w}(0.5).

CONVERGENCE ANALYSIS OF THE LOWEST ORDER WEAKLY PENALIZED ADAPTIVE DISCONTINUOUS GALERKIN METHODS

In this article, we prove convergence of the weakly penalized adaptive discontinuous Galerkin methods. Unlike other works, we derive the contraction property for various discontinuous Galerkin methods only assuming the stabilizing parameters are large enough to stabilize the method. A central idea in the analysis is to construct an auxiliary solution from the discontinuous Galerkin solution by a simple post processing. Based on the auxiliary solution, we define the adaptive algorithm which guides to the convergence of adaptive discontinuous Galerkin methods.

Symbiosis in Solid State Interconversion and Synthon Modularity in Hydroxybenzoic Acid-Hexamine Adducts

Systematic cocrystallization of hydroxybenzoic acids with hexamine using liquid-assisted grinding shows facile solid state interconversion among different stoichiometric variants. The reversible interconversion caused by varying both the acid and base components in tandem is shown to be a consequence of hydrogen-bonded synthon modularity present in all representative crystal structures. Among a total of 11 complexes, three are salts and eight are cocrystals. The insulated synthons appear as conserved tetrameric motifs in the structures, and the mechanism of interconversion is closely monitored by the synthon modularity. The interconversion is consistent with the theoretically computed stabilization energies of all the tetramers found in this series of cocrystals based on atoms in molecule calculations.

Study of ground state phases for spin-1/2 Falicov-Kimball model on a triangular lattice

The spin dependent Falicov-Kimball model (FKM) is studied on a triangular lattice using numerical diagonalization technique and Monte-Carlo simulation algorithm. Magnetic properties have been explored for different values of parameters: on-site Coulomb correlation U, exchange interaction J and filling of electrons. We have found that the ground state configurations exhibit long range Neel order, ferromagnetism or a mixture of both as J is varied. The magnetic moments of itinerant (d) and localized U) electrons are also studied. For the one-fourth filling case we found no magnetic moment from d- and f-electrons for U less than a critical value. `.2014 Elsevier Ltd. All rights reserved.

Assessing GCM Convergence for India Using the Variable Convergence Score

General circulation models (GCMs) use transient climate simulations to predict climate conditions in the future. Coarse-grid resolutions and process uncertainties necessitate the use of downscaling models to simulate precipitation. However, in the downscaling models, with multiple GCMs now available, selecting an atmospheric variable from a particular model which is representative of the ensemble mean becomes an important consideration. The variable convergence score (VCS) provides a simple yet meaningful approach to address this issue, providing a mechanism to evaluate variables against each other with respect to the stability they exhibit in future climate simulations. In this study, VCS methodology is applied to 10 atmospheric variables of particular interest in downscaling precipitation over India and also on a regional basis. The nested bias-correction methodology is used to remove the systematic biases in the GCMs simulations, and a single VCS curve is developed for the entire country. The generated VCS curve is expected to assist in quantifying the variable performance across different GCMs, thus reducing the uncertainty in climate impact-assessment studies. The results indicate higher consistency across GCMs for pressure and temperature, and lower consistency for precipitation and related variables. Regional assessments, while broadly consistent with the overall results, indicate low convergence in atmospheric attributes for the Northeastern parts of India.

Biomimetic molecular organization of naphthalene diimide in the solid state: tunable (chiro-) optical, viscoelastic and nanoscale properties

The interfacing of aromatic molecules with biomolecules to design functional molecular materials is a promising area of research. Intermolecular interactions determine the performance of these materials and therefore, precise control over the molecular organization is necessary to improve functional properties. Herein we describe the tunable biomimetic molecular engineering of a promising n-type organic semiconductor, naphthalene diimide (NDI), in the solid state by introducing minute structural mutations in the form of amino acids with variable Ca-functionality. For the first time we could achieve all four possible crystal packing modes, namely cofacial, brickwork, herringbone and slipped stacks of the NDI system. Furthermore, amino acid conjugated NDIs exhibit ultrasonication induced organogels with tunable visco-elastic and temperature responsive emission properties. The amino acid-NDI conjugates self-assemble into 0D nanospheres and 1D nanofibers in their gel state while the ethylamine-NDI conjugate forms 2D sheets from its solution. Photophysical studies indicated the remarkable influence of molecular ordering on the absorption and fluorescence properties of NDIs. Interestingly, the circular dichroism (CD) and X-ray diffraction (XRD) studies revealed the existence of helical ordering of NDIs in both solution and solid state. The chiral amino acids and their conformations with respect to the central NDI core are found to influence the nature of the helical organization of NDIs. Consequently, the origin of the preferential handedness in the helical organization is attributed to transcription of chiral information from the amino acid to the NDI core. On account of these unique properties, the materials derived from NDI-conjugates might find a wide range of future interdisciplinary applications from materials to biomedicine.

Time-Optimal Convergence to a Rectilinear Path in the Presence of Wind

This paper considers the problem of determining the time-optimal path of a fixed-wing Miniature Air Vehicle (MAV), in the presence of wind. The MAV, which is subject to a bounded turn rate, is required to eventually converge to a straight line starting from a known initial position and orientation. Earlier work in the literature uses Pontryagin's Minimum Principle (PMP) to solve this problem only for the no-wind case. In contrast, the present work uses a geometric approach to solve the problem completely in the presence of wind. In addition, it also shows how PMP can be used to partially solve the problem. Using a 6-DOF model of a MAV the generated optimal path is tracked by an autopilot consisting of proportional-integral-derivative (PID) controllers. The simulation results show the path generation and tracking for cases with steady and time-varying wind. Some issues on real-time path planning are also addressed.

C. N. R. Rao and the Growth of Solid State and Materials Chemistry as a Central Domain of Research

In celebrating Professor C. N. R. Rao's 80th birthday, this article recalls his singular contributions to solid state and materials chemistry for about sixty years. In so doing, the article also traces the growth of the field as a central domain of research in chemical sciences from its early origins in Europe. Although Rao's major work lies in solid state and materials chemistry - a field which he started and nurtured in India while its importance was being recognized internationally - his contributions to other areas of chemistry (and physics), viz., molecular spectroscopy, phase transitions, fullerenes, graphene, nanomaterials and multiferroics are equally significant. Illustrative examples of his work devoted to rare earth and transition metal oxides, defects and nonstoichiometry, metal-insulator transitions, investigation of crystal and electronic structures of a variety of solids by means of electron microscopies and photoelectron spectroscopy, superconducting cuprates, magnetoresistive manganites, multiferroic metal oxides of various structures and, last but not the least, development of new strategies for chemical synthesis of a wide variety of solids including nanomaterials and framework solids in different dimensionalities, are highlighted. The article also captures his exemplary role as a science teacher, science educationist and institution builder in post-Independence India.

Progress in tuberculosis vaccine development and host-directed therapies-a state of the art review

Tuberculosis continues to kill 1.4 million people annually. During the past 5 years, an alarming increase in the number of patients with multidrug-resistant tuberculosis and extensively drug-resistant tuberculosis has been noted, particularly in eastern Europe, Asia, and southern Africa. Treatment outcomes with available treatment regimens for drug-resistant tuberculosis are poor. Although substantial progress in drug development for tuberculosis has been made, scientific progress towards development of interventions for prevention and improvement of drug treatment outcomes have lagged behind. Innovative interventions are therefore needed to combat the growing pandemic of multidrug-resistant and extensively drug-resistant tuberculosis. Novel adjunct treatments are needed to accomplish improved cure rates for multidrug-resistant and extensively drug-resistant tuberculosis. A novel, safe, widely applicable, and more effective vaccine against tuberculosis is also desperately sought to achieve disease control. The quest to develop a universally protective vaccine for tuberculosis continues. So far, research and development of tuberculosis vaccines has resulted in almost 20 candidates at different stages of the clinical trial pipeline. Host-directed therapies are now being developed to refocus the anti-Mycobacterium tuberculosis-directed immune responses towards the host; a strategy that could be especially beneficial for patients with multidrug-resistant tuberculosis or extensively drug-resistant tuberculosis. As we are running short of canonical tuberculosis drugs, more attention should be given to host-directed preventive and therapeutic intervention measures.

Model for triplet state engineering in organic light emitting diodes

Engineering the position of the lowest triplet state (T-1) relative to the first excited singlet state (S-1) is of great importance in improving the efficiencies of organic light emitting diodes and organic photovoltaic cells. We have carried out model exact calculations of substituted polyene chains to understand the factors that affect the energy gap between S-1 and T-1. The factors studied are backbone dimerisation, different donor-acceptor substitutions, and twisted geometry. The largest system studied is an 18 carbon polyene which spans a Hilbert space of about 991 x 10(6). We show that for reverse intersystem crossing process, the best system involves substituting all carbon sites on one half of the polyene with donors and the other half with acceptors. (C) 2014 AIP Publishing LLC.

Globally coupled stochastic two-state oscillators: Fluctuations due to finite numbers

Infinite arrays of coupled two-state stochastic oscillators exhibit well-defined steady states. We study the fluctuations that occur when the number N of oscillators in the array is finite. We choose a particular form of global coupling that in the infinite array leads to a pitchfork bifurcation from a monostable to a bistable steady state, the latter with two equally probable stationary states. The control parameter for this bifurcation is the coupling strength. In finite arrays these states become metastable: The fluctuations lead to distributions around the most probable states, with one maximum in the monostable regime and two maxima in the bistable regime. In the latter regime, the fluctuations lead to transitions between the two peak regions of the distribution. Also, we find that the fluctuations break the symmetry in the bimodal regime, that is, one metastable state becomes more probable than the other, increasingly so with increasing array size. To arrive at these results, we start from microscopic dynamical evolution equations from which we derive a Langevin equation that exhibits an interesting multiplicative noise structure. We also present a master equation description of the dynamics. Both of these equations lead to the same Fokker-Planck equation, the master equation via a 1/N expansion and the Langevin equation via standard methods of Ito calculus for multiplicative noise. From the Fokker-Planck equation we obtain an effective potential that reflects the transition from the monomodal to the bimodal distribution as a function of a control parameter. We present a variety of numerical and analytic results that illustrate the strong effects of the fluctuations. We also show that the limits N -> infinity and t -> infinity(t is the time) do not commute. In fact, the two orders of implementation lead to drastically different results.

Fourier spectrum based extraction of an equivalent trap state density in indium gallium zinc oxide transistors

Segregating the dynamics of gate bias induced threshold voltage shift, and in particular, charge trapping in thin film transistors (TFTs) based on time constants provides insight into the different mechanisms underlying TFTs instability. In this Letter we develop a representation of the time constants and model the magnitude of charge trapped in the form of an equivalent density of created trap states. This representation is extracted from the Fourier spectrum of the dynamics of charge trapping. Using amorphous In-Ga-Zn-O TFTs as an example, the charge trapping was modeled within an energy range of Delta E-t approximate to 0.3 eV and with a density of state distribution as D-t(Et-j) = D-t0 exp(-Delta E-t/kT) with D-t0 = 5.02 x 10(11) cm(-2) eV(-1). Such a model is useful for developing simulation tools for circuit design. (C) 2014 AIP Publishing LLC.

Optimal Trajectory Generation for Convergence to a Rectilinear Path

This paper presents a strategy to determine the shortest path of a fixed-wing Miniature Air Vehicle (MAV), constrained by a bounded turning rate, to eventually fly along a given straight line, starting from an arbitrary but known initial position and orientation. Unlike the work available in the literature that solves the problem using the Pontryagin's Minimum Principle (PMP) the trajectory generation algorithm presented here considers a geometrical approach which is intuitive and easy to understand. This also computes the explicit solution for the length of the optimal path as a function of the initial configuration. Further, using a 6-DOF model of a MAV the generated optimal path is tracked by an autopilot consisting of proportional-integral-derivative (PID) controllers. The simulation results show the path generation and tracking for different cases.

Dense network of O-H ... O and C-H ... O interactions in the solid state structure of n-pentyl-2-chloro-2-deoxy-alpha-D-manno-sept 3-uloside

Single crystal X-ray structural analysis of a septanoside, namely, n-pentyl-2-chloro-2-deoxy sept-3-uloside (1) provides many finer details of the molecular structure, in addition to its preferred twist-chair conformation, namely, (TC3,4)-T-5,6 conformation. Structural analysis reveals a dense network of O-H...O, C-H...O and van der Waals interactions that stabilize interdigitized, planar bi-layer structure of the crystal lattice. (C) 2014 Elsevier Ltd. All rights reserved.