Coast-ocean-atmosphere-ocean mesoscale interaction

In the case of cold air outbreaks, the combination of the coastal shape and the sea surface temperature (SST) pattern have a profound effect in establishing a low level mesoscale atmospheric circulation as a result of differential heating due to both variations in overwater path length and the SST. A convergence (or divergence) line then forms along a line exactly downwind of the major bend in the coastline. All this is consistent with the structure of the cloud patterns seen in a high resolution Landsat picture of the cloud streets and the major features are simulated well with a boundary layer model. The dominant convergence line is marked by notably larger clouds. To its east the convective roll clouds grow downstream in accord with the deepening of the boundary layer. To its west (i.e., coastal side) where the induced pressure field forces a strong westerly component in the boundary layer, the wind shear across the inversion gives rise to Kelvin-Helmholtz waves and billow clouds whose orientation is perpendicular to the shear vector and to the major convergence line. The induced mesoscale circulation will feedback on the ocean by intensifying the wind generated ocean wave growth and altering their orientation. Coastal cyclogenesis is due in large part not only to the fluxes of heat and moisture from the ocean, but particularly to the differential heating and moistening of the boundary layer air when the air trajectories pass over a well defined pattern of SST

Barrier RF Stacking

A novel wideband RF system, nicknamed the barrier RF, has been designed, fabricated and installed in the Fermilab Main Injector. The cavity is made of seven Finemet cores, and the modulator made of two bipolar high-voltage fast solid-state switches. The system can deliver ±7 kV square pulses at 90 kHz. The main application is to stack two proton batches injected from the Booster and squeeze them into the size of one so that the bunch intensity can be doubled. High intensity beams have been successfully stacked and accelerated to 120 GeV with small losses. The problem of large longitudinal emittance growth is the focus of the present study. An upgraded system with two barrier RF cavities for continuous stacking is under construction. This work is part of the US-Japan collaborative agreement

Research study on materials processing in space experiment number M512: Nickel - 12 wt percent tin alloy evaluation

Nickel-tin (12 wt percent tin) samples were processed in the sphere forming experiment on Skylab 2. The results were characterized for sphericity, density, microhardness, porosity, surface morphology, segregation, chemical composition, Curie point, and crystallography. These results are discussed along with conclusions and recommendations

Optimal Correlation Estimators for Quantized Signals

Using a maximum-likelihood criterion, we derive optimal correlation strategies for signals with and without digitization. We assume that the signals are drawn from zero-mean Gaussian distributions, as is expected in radio-astronomical applications, and we present correlation estimators both with and without a priori knowledge of the signal variances. We demonstrate that traditional estimators of correlation, which rely on averaging products, exhibit large and paradoxical noise when the correlation is strong. However, we also show that these estimators are fully optimal in the limit of vanishing correlation. We calculate the bias and noise in each of these estimators and discuss their suitability for implementation in modern digital correlators.Comment: 8 Pages, 3 Figures, Submitted to Ap

Temporal Dynamics of Photon Pairs Generated by an Atomic Ensemble

The time dependence of nonclassical correlations is investigated for two fields (1,2) generated by an ensemble of cold Cesium atoms via the protocol of Duan et al. [Nature Vol. 414, p. 413 (2001)]. The correlation function R(t1,t2) for the ratio of cross to auto-correlations for the (1,2) fields at times (t1,t2) is found to have a maximum value Rmax=292(+-)57, which significantly violates the Cauchy-Schwarz inequality R<=1 for classical fields. Decoherence of quantum correlations is observed over 175 ns, and is described by our model, as is a new scheme to mitigate this effect.Comment: 5 pages, 5 figure

Models of dynamic extraction of lipid tethers from cell membranes

When a ligand that is bound to an integral membrane receptor is pulled, the membrane and the underlying cytoskeleton can deform before either the membrane delaminates from the cytoskeleton or the ligand detaches from the receptor. If the membrane delaminates from the cytoskeleton, it may be further extruded and form a membrane tether. We develop a phenomenological model for this processes by assuming that deformations obey Hooke's law up to a critical force at which the cell membrane locally detaches from the cytoskeleton and a membrane tether forms. We compute the probability of tether formation and show that they can be extruded only within an intermediate range of force loading rates and pulling velocities. The mean tether length that arises at the moment of ligand detachment is computed as are the force loading rates and pulling velocities that yield the longest tethers.Comment: 16 pages, 7 figure

Functional Quantum Nodes for Entanglement Distribution over Scalable Quantum Networks

We demonstrate entanglement distribution between two remote quantum nodes located 3 meters apart. This distribution involves the asynchronous preparation of two pairs of atomic memories and the coherent mapping of stored atomic states into light fields in an effective state of near maximum polarization entanglement. Entanglement is verified by way of the measured violation of a Bell inequality, and can be used for communication protocols such as quantum cryptography. The demonstrated quantum nodes and channels can be used as segments of a quantum repeater, providing an essential tool for robust long-distance quantum communication.Comment: 10 pages, 7 figures. Text revised, additional information included in Appendix. Published online in Science Express, 5 April, 200

Ising metamagnets in thin film geometry: equilibrium properties

Artificial antiferromagnets and synthetic metamagnets have attracted much attention recently due to their potential for many different applications. Under some simplifying assumptions these systems can be modeled by thin Ising metamagnetic films. In this paper we study, using both the Wang/Landau scheme and importance sampling Monte Carlo simulations, the equilibrium properties of these films. On the one hand we discuss the microcanonical density of states and its prominent features. On the other we analyze canonically various global and layer quantities. We obtain the phase diagram of thin Ising metamagnets as a function of temperature and external magnetic field. Whereas the phase diagram of the bulk system only exhibits one phase transition between the antiferromagnetic and paramagnetic phases, the phase diagram of thin Ising metamagnets includes an additional intermediate phase where one of the surface layers has aligned itself with the direction of the applied magnetic field. This additional phase transition is discontinuous and ends in a critical end point. Consequently, it is possible to gradually go from the antiferromagnetic phase to the intermediate phase without passing through a phase transition.Comment: 8 figures, accepted for publication in Physical Review

Surface roughness during depositional growth and sublimation of ice crystals

Full version of an earlier discussion paper (Chou et al. 2018)Ice surface properties can modify the scattering properties of atmospheric ice crystals and therefore affect the radiative properties of mixed-phase and cirrus clouds. The Ice Roughness Investigation System (IRIS) is a new laboratory setup designed to investigate the conditions under which roughness develops on single ice crystals, based on their size, morphology and growth conditions (relative humidity and temperature). Ice roughness is quantified through the analysis of speckle in 2-D light-scattering patterns. Characterization of the setup shows that a supersaturation of 20 % with respect to ice and a temperature at the sample position as low as-40 °C could be achieved within IRIS. Investigations of the influence of humidity show that higher supersaturations with respect to ice lead to enhanced roughness and irregularities of ice crystal surfaces. Moreover, relative humidity oscillations lead to gradual ratcheting-up of roughness and irregularities, as the crystals undergo repeated growth-sublimation cycles. This memory effect also appears to result in reduced growth rates in later cycles. Thus, growth history, as well as supersaturation and temperature, influences ice crystal growth and properties, and future atmospheric models may benefit from its inclusion in the cloud evolution process and allow more accurate representation of not just roughness but crystal size too, and possibly also electrification properties.Peer reviewe