2,705 research outputs found
Dichroic atomic vapor laser lock with multi-gigahertz stabilization range
A dichroic atomic vapor laser lock (DAVLL) system exploiting
buffer-gas-filled millimeter-scale vapor cells is presented. This system offers
similar stability as achievable with conventional DAVLL system using bulk vapor
cells, but has several important advantages. In addition to its compactness, it
may provide continuous stabilization in a multi-gigahertz range around the
optical transition. This range may be controlled either by changing the
temperature of the vapor or by application of a buffer gas under an appropriate
pressure. In particular, we experimentally demonstrate the ability of the
system to lock the laser frequency between two hyperfine components of the
Rb ground state or as far as 16 GHz away from the closest optical
transition.Comment: 11 pages, 7 figures. Published in Review of Scientific Instruments
201
Adsorptionsuntersuchungen an Organokieselsäurepolymeren
BET-Oberflächen und Isothermen von n-Hexan, Benzen, Wasser und Stickstoff wurden an vier Organokieselsäurepolymeren vermessen, die sich im Vernetzungsgrad der Doppelvierring-Kieselsäureeinheiten Si8O20 und in der Struktur der Brücken unterscheiden. Ein Polymer ist mikroporös, die anderen sind makroporös. Alle Polymere verhalten sich hydrophob. Neben der Adsorption tritt Quellung bei der Einwirkung organischer Adsorptive auf. Die Zusammenhänge zwischen der Länge der Brücken und der Porosität werden diskutiert
Preparation and execution of voluntary action both contribute to awareness of intention
How and when motor intentions form has long been controversial. In particular, the extent to which motor preparation and action-related processes produce a conscious experience of intention remains unknown. Here, we used a brain–computer interface (BCI) while participants performed a self-paced movement task to trigger cues upon the detection of a readiness potential (a well-characterized brain signal that precedes movement) or in its absence. The BCI-triggered cues instructed participants either to move or not to move. Following this instruction, participants reported whether they felt they were about to move at the time the cue was presented. Participants were more likely to report an intention (i) when the cue was triggered by the presence of a readiness potential than when the same cue was triggered by its absence, and (ii) when they had just made an action than when they had not. We further describe a time-dependent integration of these two factors: the probability of reporting an intention was maximal when cues were triggered in the presence of a readiness potential, and when participants also executed an action shortly afterwards. Our results provide a first systematic investigation of how prospective and retrospective components are integrated in forming a conscious intention to move
Four-Hundred-and-Ninety-Million-Year Record of Bacteriogenic Iron Oxide Precipitation at Sea-Floor Hydrothermal Vents
Fe oxide deposits are commonly found at hydrothermal vent sites at mid-ocean ridge and back-arc sea floor spreading centers, seamounts associated with these spreading centers, and intra-plate seamounts, and can cover extensive areas of the seafloor. These deposits can be attributed to several abiogenic processes and commonly contain micron-scale filamentous textures. Some filaments are cylindrical casts of Fe oxyhydroxides formed around bacterial cells and are thus unquestionably biogenic. The filaments have distinctive morphologies very like structures formed by neutrophilic Fe oxidizing bacteria. It is becoming increasingly apparent that Fe oxidizing bacteria have a significant role in the formation of Fe oxide deposits at marine hydrothermal vents. The presence of Fe oxide filaments in Fe oxides is thus of great potential as a biomarker for Fe oxidizing bacteria in modern and ancient marine hydrothermal vent deposits. The ancient analogues of modern deep-sea hydrothermal Fe oxide deposits are jaspers. A number of jaspers, ranging in age from the early Ordovician to late Eocene, contain abundant Fe oxide filamentous textures with a wide variety of morphologies. Some of these filaments are like structures formed by modern Fe oxidizing bacteria. Together with new data from the modern TAG site, we show that there is direct evidence for bacteriogenic Fe oxide precipitation at marine hydrothermal vent sites for at least the last 490 Ma of the Phanerozoic
Coherent control for the spherical symmetric box potential in short and intensive XUV laser fields
Coherent control calculations are presented for a spherically symmetric box
potential for non-resonant two photon transition probabilities. With the help
of a genetic algorithm (GA) the population of the excited states are maximized
and minimized. The external driving field is a superposition of three intensive
extreme ultraviolet (XUV) linearly polarized laser pulses with different
frequencies in the femtosecond duration range. We solved the quantum mechanical
problem within the dipole approximation. Our investigation clearly shows that
the dynamics of the electron current has a strong correlation with the
optimized and neutralizing pulse shape.Comment: 11 Pages 3 Figure
Selective loss of noradrenaline exacerbates early cognitive dysfunction and synaptic deficits in APP/PS1 mice.
Background: Degeneration of the locus coeruleus (LC), the major noradrenergic nucleus in the brain, occurs early and is ubiquitous in Alzheimer’s disease (AD). Experimental lesions to the LC exacerbate AD-like neuropathology and cognitive deficits in several transgenic mouse models of AD. Because the LC contains multiple neuromodulators known to affect amyloid toxicity and cognitive function, the specific role of noradrenaline (NA) in AD is not well understood. Methods: To determine the consequences of selective NA deficiency in an AD mouse model, we crossed dopamine -hydroxylase (DBH) knockout mice with amyloid precursor protein (APP)/presenilin-1 (PS1) mice overexpressing mutant APP and PS1. Dopamine -hydroxylase (/) mice are unable to synthesize NA but otherwise have normal LC neurons and co-transmitters. Spatial memory, hippocampal long-term potentiation, and synaptic protein levels were assessed. Results: The modest impairments in spatial memory and hippocampal long-term potentiation displayed by young APP/PS1 or DBH (/) single mutant mice were augmented in DBH (/)/APP/PS1 double mutant mice. Deficits were associated with reduced levels of total calcium/calmodulin-dependent protein kinase II and N-methyl-D-aspartate receptor 2A and increased N-methyl-D-aspartate receptor 2B levels and were independent of amyloid accumulation. Spatial memory performance was partly improved by treatment with the NA precursor drug L-threo-dihydroxyphenylserine. Conclusions: These results indicate that early LC degeneration and subsequentNAdeficiency inADmay contribute to cognitive deficits via altered levels of calcium/calmodulin-dependent protein kinase II and N-methyl-D-aspartate receptors and suggest that NA supplementation could be beneficial in early AD
Economic space: On the analysis and interpretation of pottery production and distribution
Ceramics are particularly well suited for investigating general patterns of the distribution of premodern products. Archaeometric methods, used to determine raw materials and production techniques, permit the identification of places of production. The work of the research group presented here pursues two objectives: (i) to investigate the usefulness of portable X-ray fluorescence equipment for the analysis of ceramics and (ii) to identify, interpret and study distribution areas of ceramic products in comparative prospective. The paper discusses key economic concepts, sets out the archaeometric methodology and presents initial results in the context of two examples
Tema Con Variazioni: Quantum Channel Capacity
Channel capacity describes the size of the nearly ideal channels, which can
be obtained from many uses of a given channel, using an optimal error
correcting code. In this paper we collect and compare minor and major
variations in the mathematically precise statements of this idea which have
been put forward in the literature. We show that all the variations considered
lead to equivalent capacity definitions. In particular, it makes no difference
whether one requires mean or maximal errors to go to zero, and it makes no
difference whether errors are required to vanish for any sequence of block
sizes compatible with the rate, or only for one infinite sequence.Comment: 32 pages, uses iopart.cl
How a spin-glass remembers. Memory and rejuvenation from intermittency data: an analysis of temperature shifts
The memory and rejuvenation aspects of intermittent heat transport are
explored theoretically and by numerical simulation for Ising spin glasses with
short-ranged interactions. The theoretical part develops a picture of
non-equilibrium glassy dynamics recently introduced by the authors. Invoking
the concept of marginal stability, this theory links irreversible
`intermittent' events, or `quakes' to thermal fluctuations of record magnitude.
The pivotal idea is that the largest energy barrier surmounted prior
to by thermal fluctuations at temperature determines the rate of the intermittent events occurring near . The idea leads
to a rate of intermittent events after a negative temperature shift given by
, where the `effective age' has
an algebraic dependence on , whose exponent contains the temperatures
before and after the shift. The analytical expression is verified by numerical
simulations. Marginal stability suggests that a positive temperature shift could erase the memory of the barrier . The simulations show
that the barrier controls the intermittent dynamics,
whose rate is hence .
Additional `rejuvenation' effects are also identified in the intermittency
data for shifts of both signs.Comment: Revised introduction and discussion. Final version to appear in
Journal of Statistical Mechanics: Theory and Experimen
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