1,736 research outputs found
Solar off-limb line widths: Alfven waves, ion-cyclotron waves, and preferential heating
Alfven waves and ion-cyclotron absorption of high-frequency waves are
frequently brought into models devoted to coronal heating and fast solar-wind
acceleration. Signatures of ion-cyclotron resonance have already been observed
in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper
corona (UVCS/SOHO remote-sensing results). We propose a method to constrain
both the Alfven wave amplitude and the preferential heating induced by
ion-cyclotron resonance, above a partially developed polar coronal hole
observed with the SUMER/SOHO spectrometer. The instrumental stray light
contribution is first substracted from the spectra. By supposing that the
non-thermal velocity is related to the Alfven wave amplitude, it is constrained
through a density diagnostic and the gradient of the width of the Mg X 625 A
line. The temperatures of several coronal ions, as functions of the distance
above the limb, are then determined by substracting the non-thermal component
to the observed line widths. The effect of stray light explains the apparent
decrease with height in the width of several spectral lines, this decrease
usually starting about 0.1-0.2 Rs above the limb. This result rules out any
direct evidence of damping of the Alfven waves, often suggested by other
authors. We also find that the ions with the smallest charge-to-mass ratios are
the hottest ones at a fixed altitude and that they are subject to a stronger
heating, as compared to the others, between 57" and 102" above the limb. This
constitutes a serious clue to ion-cyclotron preferential heating.Comment: 15 pages, 12 figures, 3 table
Microfabricated Gaps Reveal the Effect of Geometrical Control in Wound Healing
The geometry (size and shape) of gaps is a key determinant in controlling gap closure during wound healing. However, conventional methods for creating gaps result in un‐defined geometries and poorly characterized conditions (cell death factors and cell debris), which can influence the gap closure process. To overcome these limitations, a novel method to create well‐defined geometrical gaps is developed. First, smooth muscle cells (SMCs) are seeded in variously shaped micro‐containers made out of hyaluronic acid hydrogels. Cell proliferation and cell tension induce fibrous collagen production by SMCs predominantly around the edges of the micro‐containers. Upon removal of SMCs, the selectively deposited collagen results in micro‐containers with cell‐adhesive regions along the edges and walls. Fibroblasts are seeded in these micro‐containers, and upon attaching and spreading, they naturally form gaps with different geometries. The rapid proliferation of fibroblasts from the edge results in filling and closure of the gaps. It is demonstrated that gap closure rate as well as closure mechanism is strongly influenced by geometrical features, which points to an important role for cellular tension and cell proliferation in gap closure
Microfabricated Gaps Reveal the Effect of Geometrical Control in Wound Healing
The geometry (size and shape) of gaps is a key determinant in controlling gap closure during wound healing. However, conventional methods for creating gaps result in un‐defined geometries and poorly characterized conditions (cell death factors and cell debris), which can influence the gap closure process. To overcome these limitations, a novel method to create well‐defined geometrical gaps is developed. First, smooth muscle cells (SMCs) are seeded in variously shaped micro‐containers made out of hyaluronic acid hydrogels. Cell proliferation and cell tension induce fibrous collagen production by SMCs predominantly around the edges of the micro‐containers. Upon removal of SMCs, the selectively deposited collagen results in micro‐containers with cell‐adhesive regions along the edges and walls. Fibroblasts are seeded in these micro‐containers, and upon attaching and spreading, they naturally form gaps with different geometries. The rapid proliferation of fibroblasts from the edge results in filling and closure of the gaps. It is demonstrated that gap closure rate as well as closure mechanism is strongly influenced by geometrical features, which points to an important role for cellular tension and cell proliferation in gap closure
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Electron dynamics in laser-driven atoms near the continuum threshold
Strong-field ionization and Rydberg-state excitation (RSE) near the continuum threshold exhibit two phenomena that have attracted a lot of recent attention: the low-energy structure (LES) just above and frustrated tunneling ionization just below the threshold. The former becomes apparent for longer laser wavelengths, while the latter has been especially investigated in the near infrared; both have been treated as separate phenomena so far. Here we present a unified perspective based on electron trajectories, which emphasizes the very important role of the electron-ion Coulomb interaction as expected in this energy region. Namely, those trajectories that generate the LES can also be recaptured into a Rydberg state. The coherent superposition of the contributions of such trajectories with different travel times (each generating one of the various LES peaks) causes an oscillation in the intensity dependence of the RSE yield, which is especially noticeable for longer wavelengths. The theory is illustrated by RSE experiments at 1800 nm, which agree very well with the theory with respect to position and period of the oscillation. The wavelength scaling of the RSE oscillation is also discussed. Our work establishes a solid relationship between processes below and above the threshold and sheds new light on atomic dynamics driven by intense laser fields in this critical energy region
Controlling Josephson transport by manipulation of Andreev levels in ballistic mesoscopic junctions
We discuss how to control dc Josephson current by influencing the structure
and nonequilibrium population of Andreev levels via external electrostatic
gates, external current injection and electromagnetic radiation. In particular
we will consider the "giant" Josephson current in "long" SIS tunnel junctions
and the regular and anomalous nonequilibrium Josephson currents in three
terminal SNS junctions. We will briefly discuss applications to the Josephson
field effect transistor (JOFET) and to the newly invented Josephson
interference transistor (JOINT).Comment: 10 pages, 3 figures; contribution to a special volume of
Superlattices and Microstructures journal (ed. P.F. Bagwell
Biodiversity and activity of the gut microbiota across the life history of the insect herbivore Spodoptera littoralis
Microbes that live inside insects play critical roles in host nutrition, physiology, and behavior. Although Lepidoptera (butterflies and moths) are one of the most diverse insect taxa, their microbial symbionts are little-studied, particularly during metamorphosis. Here, using ribosomal tag pyrosequencing of DNA and RNA, we investigated biodiversity and activity of gut microbiotas across the holometabolous life cycle of Spodoptera littoralis, a notorious agricultural pest worldwide. Proteobacteria and Firmicutes dominate but undergo a structural “metamorphosis” in tandem with its host. Enterococcus, Pantoea and Citrobacter were abundant and active in early-instar, while Clostridia increased in late-instar. Interestingly, only enterococci persisted through metamorphosis. Female adults harbored high proportions of Enterococcus, Klebsiella and Pantoea, whereas males largely shifted to Klebsiella. Comparative functional analysis with PICRUSt indicated that early-instar larval microbiome was more enriched for genes involved in cell motility and carbohydrate metabolism, whereas in late-instar amino acid, cofactor and vitamin metabolism increased. Genes involved in energy and nucleotide metabolism were abundant in pupae. Female adult microbiome was enriched for genes relevant to energy metabolism, while an increase in the replication and repair pathway was observed in male. Understanding the metabolic activity of these herbivore-associated microbial symbionts may assist the development of novel pest-management strategies
Статические нагрузки упругих зубьев зубчатых передач
Представим себе изготовленную из упругих материалов, статистически нагружен-ную
зубчатую передачу, состоящую из двух зацепляющихся колес и обладающую не-точностями в
нормальном шаге зацепления, характеризуемыми погрешностью α01 . В этом случае для
соблюдения условий уравнения (1), сохранения постоянства угловых перемещений при
вращении и обеспечения непрерывности зубьев, обладающих раз-личными размерами
нормального шага зацепления, потребуется соответствующая сум-марная упругая
деформация, вызванная передаваемым удельным крутящим моментом Mn1, будет
эквивалентна величине углового перемещени
Entanglement and the Kondo effect in double quantum dots
We investigate entanglement between electrons in serially coupled double
quantum dots attached to non interacting leads. In addition to local repulsion
we consider the influence of capacitive inter-dot interaction. We show how the
competition between extended Kondo and local singlet phases determines the
ground state and thereby the entanglement.Comment: EPJ Special Topics 200
Coulomb Drag in Coherent Mesoscopic Systems
We present a theory for Coulomb drag between two mesoscopic systems. Our
formalism expresses the drag in terms of scattering matrices and wave
functions, and its range of validity covers both ballistic and disordered
systems. The consequences can be worked out either by analytic means, such as
the random matrix theory, or by numerical simulations. We show that Coulomb
drag is sensitive to localized states, which usual transport measurements do
not probe. For chaotic 2D-systems we find a vanishing average drag, with a
nonzero variance. Disordered 1D-wires show a finite drag, with a large
variance, giving rise to a possible sign change of the induced current.Comment: 4 pages including 2 figures. Minor changes. Accepted for publication
in Phys. Rev. Let
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