Inert gas accumulation in sonoluminescing bubbles

In this paper we elaborate on the idea [Lohse et al., Phys. Rev. Lett. 78, 1359-1362 (1997)] that (single) sonoluminescing air bubbles rectify argon. The reason for the rectification is that nitrogen and oxygen dissociate and their reaction products dissolve in water. We give further experimental and theoretical evidence and extend the theory to other gas mixtures. We show that in the absence of chemical reactions (e.g., for inert gas mixtures) gas accumulation in strongly acoustically driven bubbles can also occur.Comment: J. Chem. Phys., in press (to appear in November 1997), 30 pages, 15 eps-figure

Semiconducting-to-metallic photoconductivity crossover and temperature-dependent Drude weight in graphene

We investigated the transient photoconductivity of graphene at various gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We demonstrated that graphene exhibits semiconducting positive photoconductivity near zero carrier density, which crosses over to metallic negative photoconductivity at high carrier density. Our observations are accounted for by considering the interplay between photo-induced changes of both the Drude weight and the carrier scattering rate. Notably, we observed multiple sign changes in the temporal photoconductivity dynamics at low carrier density. This behavior reflects the non-monotonic temperature dependence of the Drude weight, a unique property of massless Dirac fermions

Defect-sensitivity analysis of an SEU immune CMOS logic family

Fault testing of resistive manufacturing defects is done on a recently developed single event upset immune logic family. Resistive ranges and delay times are compared with those of traditional CMOS logic. Reaction of the logic to these defects is observed for a NOR gate, and an evaluation of its ability to cope with them is determined

Developmental waves of mechanosensitivity acquisition in sensory neuron subtypes during embryonic development

Somatic sensation relies on the transduction of physical stimuli into electrical signals by sensory neurons of the dorsal root ganglia. Little is known about how and when during development different types of sensory neurons acquire transduction competence. We directly investigated the emergence of electrical excitability and mechanosensitivity of embryonic and postnatal mouse sensory neurons. We show that sensory neurons acquire mechanotransduction competence coincident with peripheral target innervation. Mechanotransduction competence arises in different sensory lineages in waves, coordinated by distinct developmental mechanisms. Sensory neurons that are mechanoreceptors or proprioceptors acquire mature mechanotransduction indistinguishable from the adult already at E13. This process is independent of neurotrophin-3 and may be driven by a genetic program. In contrast, most nociceptive (pain sensing) sensory neurons acquire mechanosensitive competence as a result of exposure to target-derived nerve growth factor. The highly regulated process of mechanosensory acquisition unveiled here, reveals new strategies to identify molecules required for sensory neuron mechanotransduction

Two-component radiation model of the sonoluminescing bubble

Based on the experimental data from Weninger, Putterman & Barber, Phys. Rev. (E), 54, R2205 (1996), we offer an alternative interpretation of their experimetal results. A model of sonoluminescing bubble which proposes that the electromagnetic radiation originates from two sources: the isotropic black body or bramsstrahlung emitting core and dipole radiation-emitting shell of accelerated electrons driven by the liquid-bubble interface is outlined.Comment: 5 pages Revtex, submitted to Phys. Rev.

Intra-cell dynamics and cyclotron motion without magnetic field

Intra-cell motion endows rich non-trivial phenomena to a wide variety of quantum materials. The most prominent example is a transverse current in the absence of a magnetic field (i.e. the anomalous Hall effect). Here we show that, in addition to a dc Hall effect, anomalous Hall materials possess circulating currents and cyclotron motion without magnetic field. These are generated from the intricate wavefunction dynamics within the unit cell, and correspond to interband transitions (coherences) in much the same way that cyclotron resonances arise from inter-Landau level transitions in magneto-optics. Curiously, anomalous cyclotron motion exhibits an intrinsic decay in time (even in pristine materials) displaying a characteristic power law decay. This reveals an intrinsic dephasing similar to that of inhomogeneous broadening of spinors. Circulating currents can manifest as the emission of circularly polarized light pulses in response to incident linearly polarized (pulsed) electric field, and provide a direct means of interrogating the intra-unit-cell dynamics of quantum materials

Dynamical Casimir effect for a massless scalar field between two concentric spherical shells

In this work we consider the dynamical Casimir effect for a massless scalar field -- under Dirichlet boundary conditions -- between two concentric spherical shells. We obtain a general expression for the average number of particle creation, for an arbitrary law of radial motion of the spherical shells, using two distinct methods: by computing the density operator of the system and by calculating the Bogoliubov coefficients. We apply our general expression to breathing modes: when only one of the shells oscillates and when both shells oscillate in or out of phase. We also analyze the number of particle production and compare it with the results for the case of plane geometry.Comment: Final version. To apear in Physical Review

The impact on atmospheric CO2 of iron fertilization induced changes in the ocean's biological pump

© Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 5 (2008): 385-406, doi:10.5194/bg-5-385-2008Using numerical simulations, we quantify the impact of changes in the ocean's biological pump on the air-sea balance of CO2 by fertilizing a small surface patch in the high-nutrient, low-chlorophyll region of the eastern tropical Pacific with iron. Decade-long fertilization experiments are conducted in a basin-scale, eddy-permitting coupled physical/biogeochemical/ecological model. In contrast to previous studies, we find that most of the dissolved inorganic carbon (DIC) removed from the euphotic zone by the enhanced biological export is replaced by uptake of CO2 from the atmosphere. Atmospheric uptake efficiencies, the ratio of the perturbation in air-sea CO2 flux to the perturbation in export flux across 100 m, integrated over 10 years, are 0.75 to 0.93 in our patch size-scale experiments. The atmospheric uptake efficiency is insensitive to the duration of the experiment. The primary factor controlling the atmospheric uptake efficiency is the vertical distribution of the enhanced biological production and export. Iron fertilization at the surface tends to induce production anomalies primarily near the surface, leading to high efficiencies. In contrast, mechanisms that induce deep production anomalies (e.g. altered light availability) tend to have a low uptake efficiency, since most of the removed DIC is replaced by lateral and vertical transport and mixing. Despite high atmospheric uptake efficiencies, patch-scale iron fertilization of the ocean's biological pump tends to remove little CO2 from the atmosphere over the decadal timescale considered here.The majority of this work was funded by the Office of Science (BER) of the US Department of Energy through Grant No. DE-FG03-00ER63010. Additional funding was provided by the Information and Technology Research section of the US National Science Foundation (NG, HF, and SD) and ETH Zurich (NG)