Direct Numerical Investigation of Turbulence of Capillary Waves

We consider the inertial range spectrum of capillary wave turbulence. Under the assumptions of weak turbulence, the theoretical surface elevation spectrum scales with wave number k as I[subscript η] ∼ k[superscript α], where α = α[subscript 0] = -19/4, energy (density) flux P as P[superscript 1/2]. The proportional factor C, known as the Kolmogorov constant, has a theoretical value of C = C[subscript 0] = 9.85 (we show that this value holds only after a formulation in the original derivation is corrected). The k[superscript -19/4] scaling has been extensively, but not conclusively, tested; the P[superscript 1/2] scaling has been investigated experimentally, but until recently remains controversial, while direct confirmation of the value of C[subscript 0] remains elusive. We conduct a direct numerical investigation implementing the primitive Euler equations. For sufficiently high nonlinearity, the theoretical k[superscript -19/4] and P[superscript 1/2] scalings as well as value of C[subscript 0] are well recovered by our numerical results. For a given number of numerical modes N, as nonlinearity decreases, the long-time spectra deviate from theoretical predictions with respect to scaling with P, with calculated values of α C[subscript 0], all due to finite box effect

Gold-free GaAs/GaAsSb heterostructure nanowires grown on silicon

Growth of GaAs/GaAsSb heterostructurenanowires on silicon without the need for gold seed particles is presented. A high vertical yield of GaAsnanowires is first obtained, and then GaAsₓSb₁ˍₓ segments are successfully grown axially in these nanowires. GaAsSb can also be integrated as a shell around the GaAs core. Finally, two GaAsSb segments are grown inside a GaAsnanowire and passivated using an AlₓGa₁ˍₓAs shell. It is found that no stacking faults or twin planes occur in the GaAsSb segments.Part of this work was funded by the Swedish Foundation for Strategic Research SSF, the Swedish Research Council VR, and the Knut and Alice Wallenberg Foundation

Brans-Dicke DGP Brane Cosmology

We consider a five dimensional DGP-brane scenario endowed with a non-minimally coupled scalar field within the context of Brans-Dicke theory. This theory predicts that the mass appearing in the gravitational potential is modified by the addition of the mass of the effective intrinsic curvature on the brane. We also derive the effective four dimensional field equations on a 3+1 dimensional brane where the fifth dimension is assumed to have an orbifold symmetry. Finally, we discuss the cosmological implications of this setup, predicting an accelerated expanding universe with a value of the Brans-Dicke parameter $\omega$ consistent with values resulting from the solar system observations.Comment: 12 pages, 1 figure, to appear in JCA

Physics-Based Learning Models for Ship Hydrodynamics

We present the concepts of physics-based learning models (PBLM) and their relevance and application to the field of ship hydrodynamics. The utility of physics-based learning is motivated by contrasting generic learning models for regression predictions, which do not presume any knowledge of the system other than the training data provided with methods such as semi-empirical models, which incorporate physical insights along with data-fitting. PBLM provides a framework wherein intermediate models, which capture (some) physical aspects of the problem, are incorporated into modern generic learning tools to substantially improve the predictions of the latter, minimizing the reliance on costly experimental measurements or high-resolution high-fidelity numerical solutions. To illustrate the versatility and efficacy of PBLM, we present three wave-ship interaction problems: 1) at speed waterline profiles; 2) ship motions in head seas; and 3) three-dimensional breaking bow waves. PBLM is shown to be robust and produce error rates at or below the uncertainty in the generated data at a small fraction of the expense of high-resolution numerical predictions.United States. Office of Naval Researc

Phase-Resolved Wave Field Simulation Calibration of Sea Surface Reconstruction Using Noncoherent Marine Radar

The possibility of reconstructing sea surface wave fields from a noncoherent X-band marine radar return has much potential for maritime operations and ocean engineering. The existing reconstruction method extracts the signal associated with gravity waves that satisfy the dispersion relationship. The process involves parameters related to how the radar signal is modulated by waves of different lengths, propagation directions, amplitudes, and phases. In the absence of independent wave measurements, these reconstruction parameters cannot be rationally adjusted according to wave field conditions, and the predictions are generally of uneven accuracy and reliability. A new reconstruction method based on concurrent phase-resolved wave field simulations is proposed. By maximizing the correlation between the reconstructed and simulated wave fields over time, optimal values of the reconstruction parameters are obtained that are found to vary appreciably with the wave field properties and with the location and size of the subdomain being sensed and reconstructed. With this phase-resolved simulation calibrated (PRSC) approach, the correlation between the evolving reconstructed wave field and that based on phase-resolved simulation, which measures the consistency and fidelity of the reconstruction, is improved significantly (by up to a factor of 2) and is obtained in a substantially broader range of sea states compared to existing methods.United States. Office of Naval Researc

The isolation from Saccharomyces cerevisiae of two antibacterial cationic proteins that inhibit malolactic bacteria

Substances with antibacterial activity were recovered from the extracellular medium and from the acidified cell extract of Saccharomyces cerevisiae R107 by binding onto a cation exchanger. The fraction eluted with NaOH contained two different antibacterial factors, one with the characteristics of lysozyme, the other apparently a small protein with a similar high pI.Die Isolierung von zwei bakteriziden, kationischen Proteinen aus Saccharomyces cerevisiae, die Bakterien des Säureabbaus hemmenSubstanzen mit bakterizider Wirkung wurden sowohl aus dem Kultursubstrat als auch aus angesäuertem Zellextrakt von Saccharomyces cerevisiae Rl07 mit Hilfe von Kationenaustauscher isoliert. Die mit NaOH eluierte Fraktion enthielt zwei unterschiedliche bakterizide Substanzen, eine mit Lysozymeigenschaften, die andere, ein kleines Protein, mit ähnlich hohem isoelektrischen Punkt

Interplay between motility and cell-substratum adhesion in amoeboid cells

The effective migration of amoeboid cells requires a fine regulation of cell-substratum adhesion. These entwined processes have been shown to be regulated by a host of biophysical and biochemical cues. Here, we reveal the pivotal role played by calcium-based mechanosensation in the active regulation of adhesion resulting in a high migratory adaptability. Using mechanotactically driven Dictyostelium discoideum amoebae, we uncover the existence of optimal mechanosensitive conditions—corresponding to specific levels of extracellular calcium—for persistent directional migration over physicochemically different substrates. When these optimal mechanosensitive conditions are met, noticeable enhancement in cell migration directionality and speed is achieved, yet with significant differences among the different substrates. In the same narrow range of calcium concentrations that yields optimal cellular mechanosensory activity, we uncovered an absolute minimum in cell-substratum adhesion activity, for all considered substrates, with differences in adhesion strength among them amplified. The blocking of the mechanosensitive ion channels with gadolinium—i.e., the inhibition of the primary mechanosensory apparatus—hampers the active reduction in substrate adhesion, thereby leading to the same undifferentiated and drastically reduced directed migratory response. The adaptive behavioral responses of Dictyostelium cells sensitive to substrates with varying physicochemical properties suggest the possibility of novel surface analyses based on the mechanobiological ability of mechanosensitive and guidable cells to probe substrates at the nanometer-to-micrometer level.SUTD-MIT International Design Centre (IDC) (IDG31400104

Superheavy dark matter and ultrahigh energy cosmic rays

The phase of inflationary expansion in the early universe produces superheavy relics in a mass window between 10^{12} GeV and 10^{14} GeV. Decay or annihilation of these superheavy relics can explain the observed ultrahigh energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff. We emphasize that the pattern of cosmic ray arrival directions with energies beyond 20 EeV will decide between the different proposals for the origin of ultrahigh energy cosmic rays.Comment: Based on an invited talk given by RD at Theory Canada 1, Vancouver, June 2-5, 200