At concentrations near the maximum allowed by steric repulsion, swimming bacteria form a dynamical state exhibiting extended spatiotemporal coherence. The viscous fluid into which locomotive energy of individual micro...
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At concentrations near the maximum allowed by steric repulsion, swimming bacteria form a dynamical state exhibiting extended spatiotemporal coherence. The viscous fluid into which locomotive energy of individual microorganisms is transferred also carries interactions that drive the coherence. The concentration dependence of correlations in the collective state is probed here with a novel technique that herds bacteria into condensed populations of adjustable concentration. For the particular thin-film geometry employed, the correlation lengths vary smoothly and monotonically through the transition from individual to collective behavior.
Using a three-dimensional semiclassical method, we perform a systematic analysis of the effects of an additional static electric field on nonsequential double ionization (NSDI) of a helium atom in an intense, linearly...
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Using a three-dimensional semiclassical method, we perform a systematic analysis of the effects of an additional static electric field on nonsequential double ionization (NSDI) of a helium atom in an intense, linearly polarized laser field. It is found that the static electric field influences not only the ionization rate, but also the kinetic energy of the ionized electron returning to the parent ion, in such a way that, if the rate is increased, then the kinetic energy of the first returning electron is decreased, and vice versa. These two effects compete in NSDI. Since the effect of the static electric field on the ionization of the first electron plays a more crucial role in the competition, the symmetric double-peak structure of the He2+ momentum distribution parallel to the polarization of the laser field is destroyed. Furthermore, the contribution of the trajectories with multiple recollisions to the NSDI is also changed dramatically by the static electric field. As the static electric field increases, the trajectories with two recollisions, which start at the time when the laser and the static electric field are in the same direction, become increasingly important for the NSDI.
Concentrated bacterial suspensions spontaneously develop transient spatiotemporal patterns of coherent locomotion whose correlation lengths greatly exceed the size of individual organisms. Continuum models have indica...
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Concentrated bacterial suspensions spontaneously develop transient spatiotemporal patterns of coherent locomotion whose correlation lengths greatly exceed the size of individual organisms. Continuum models have indicated that a state of uniform swimming order is linearly unstable at finite wavelengths, but have not addressed the nonlinear dynamics of the coherent state, with its biological implications for mixing, transport, and intercellular communication. We investigate a specific model incorporating hydrodynamic interactions in thin-film geometries and show by numerical studies that it displays large scale persistently recurring vortices, as actually observed.
Recent activities at the Tokyo electron beam ion trap related to observations of resonant processes in the collisions of electrons with open-shell highly charged ions are reported. Extracted ion observations and high ...
Interference between radiative and dielectronic recombination in electron and highly charged Bi ion collisions has been studied by observing emitted x-rays with the Tokyo electron beam ion trap. The so-called Fano lin...
A semiclassical molecular nonsequential double ionization theory is developed based on the rescattering model. We show that, in the nonsequential double ionization of D2, the kinetic energy of the returning electron c...
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A semiclassical molecular nonsequential double ionization theory is developed based on the rescattering model. We show that, in the nonsequential double ionization of D2, the kinetic energy of the returning electron changes from below to above the ionization threshold of the parent ion as the laser varies from short to long wavelength, resulting in the dominance of collisional ionization at shorter laser wavelength and field ionization at longer laser wavelength. We also calculate the double ionization time distribution of D2 and the kinetic energy distribution of D+. The theoretical results are qualitatively consistent with experimental measurements. The nonsequential double to single ionization ratio of N22+∕N2+ is also calculated and compared with available experimental results.
High-energy photon detectors are often made thick in order to improve their photon-detection efficiency. To avoid issues of parallax and increased signal variance that result from random interaction depth, we must det...
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High-energy photon detectors are often made thick in order to improve their photon-detection efficiency. To avoid issues of parallax and increased signal variance that result from random interaction depth, we must determine the 3D interaction position in the imaging detector. With this goal in mind, we examine a method of calibrating response statistics of a thick-detector gamma camera to produce a maximum- likelihood estimate of 3D interaction position. We parameterize the mean detector response as a function of 3D position and estimate the parameters by maximizing their likelihood given prior knowledge of the path-length distribution and a complete list of camera signals for an ensemble of gamma-ray interactions. Demonstrating this calibration method with simulated gamma-camera data, we show that the resulting calibration is accurate and can be used to produce unbiased estimates of 3D interaction position.
KLL dielectronic recombination resonances, where a free electron is captured into the L shell and at the same time a K shell electron is excited into the L shell, have been measured for open shell iodine ions by measu...
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KLL dielectronic recombination resonances, where a free electron is captured into the L shell and at the same time a K shell electron is excited into the L shell, have been measured for open shell iodine ions by measuring the detected yield of escaping ions of various charge states and modeling the charge balance in an electron beam ion trap. In the modeling, the escape from the trap and multiple charge exchange were considered. Extracted ions were used to measure the charge balance in the trap. The different charge states were clearly separated, which along with the correction for artifacts connected with ion escape and multiple charge exchange made the open shell highly charged ion measurements of this type possible for the first time. From the measured spectra resonant strengths were obtained. The results were 4.27(39)×10−19cm2eV, 2.91(26)×10−19cm2eV, 2.39(22)×10−19cm2eV, 1.49(14)×10−19cm2eV and 7.64(76)×10−20cm2eV for the iodine ions from He-like to C-like, respectively.
We study transformation pathways leading from 4- to 6-coordinated silica using an improved version of the metadynamics method for the study of structural phase transitions in crystals [Martoňák, Laio, and Parrin...
We study transformation pathways leading from 4- to 6-coordinated silica using an improved version of the metadynamics method for the study of structural phase transitions in crystals [Martoňák, Laio, and Parrinello, Phys. Rev. Lett. 90, 075503 (2003)]. The technique is able to simulate complex reconstructive structural transformations proceeding via number of intermediate states. In particular, we reproduce the experimentally observed crystal structures that are found upon pressurization of α-quartz. We also predict a low-energy transformation pathway from coesite to the metastable α−PbO2 phase.
A one-dimensional quantum hydrodynamic model （or quantum Euler-Poisson system） for semiconductors with initial boundary conditions is considered for general pressure-density function. The existence and uniqueness of...
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A one-dimensional quantum hydrodynamic model （or quantum Euler-Poisson system） for semiconductors with initial boundary conditions is considered for general pressure-density function. The existence and uniqueness of the classical solution of the corresponding steady-state quantum hydrodynamic equations is proved. Furthermore, the global existence of classical solution, when the initial datum is a perturbation of t he steadystate solution, is obtained. This solution tends to the corresponding steady-state solution exponentially fast as the time tends to infinity.
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