943 research outputs found
Rapidly reconfigurable optical phase encoder-decoders based on fiber Bragg gratings
We demonstrate the capacity for fast dynamic reconfiguration of optical code-division multiple access (OCDMA) phase en/decoders based on fiber Bragg gratings and a thermal phase-tuning technique. The tuning time between two different phase codes is measured to be less than 2 s. An OCDMA system using tunable-phase decoders is compared with a system using fixed-phase decoders and, although the system using fixed-phase decoders exhibits a shorter output autocorrelation pulsewidth and lower sidelobes, the system using tunable-phase decoders has advantages of flexibility and a more relaxed requirement on the input pulsewidth
One-Up On L1: Can X-rays Provide Longer Advanced Warning of Solar Wind Flux Enhancements Than Upstream Monitors?
Observations of strong solar wind proton flux correlations with ROSAT X-ray
rates along with high spectral resolution Chandra observations of X-rays from
the dark Moon show that soft X-ray emission mirrors the behavior of the solar
wind. In this paper, based on an analysis of an X-ray event observed by
XMM-Newton resulting from charge exchange of high charge state solar wind ions
and contemporaneous neutral solar wind data, we argue that X-ray observations
may be able to provide reliable advance warning, perhaps by as much as half a
day, of dramatic increases in solar wind flux at Earth. Like neutral atom
imaging, this provides the capability to monitor the solar wind remotely rather
than in-situ.Comment: in press in Adv. Space Research, 7 pages, 6 eps figures, resolution
reduced for Astro-ph submission, see http://lena.gsfc.nasa.gov for full
versio
DFT calculation of the intermolecular exchange interaction in the magnetic Mn dimer
The dimeric form of the single-molecule magnet
[MnOCl(OCEt)(py)] recently revealed interesting
phenomena: no quantum tunneling at zero field and tunneling before magnetic
field reversal. This is attributed to substantial antiferromagnetic exchange
interaction between different monomers. The intermolecular exchange
interaction, electronic structure and magnetic properties of this molecular
magnet are calculated using density-functional theory within
generalized-gradient approximation. Calculations are in good agreement with
experiment.Comment: 4 page
Investigating causality between liability to ADHD and substance use, and liability to substance use and ADHD risk, using Mendelian randomization
Influence of a low magnetic field on the thermal diffusivity of Bi-2212
The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured
under a 1T magnetic field applied perpendicularly to the heat flux. The
magnetic contribution to the heat carrier mean free path has been extracted and
is found to behave as a simple power law. This behavior can be attributed to a
percolation process of electrons in the vortex lattice created by the magnetic
field.Comment: 10 pages, 3 figures; to be published in Phys. Rev.
Winter distribution of Calanus finmarchicus in the Northeast Atlantic
Data from plankton sampling and Optical Plankton Counter deployments during six cruises between December of 1994 and 1999 have been used to derive a composite three-dimensional distribution of the abundance of Calanus finmarchicus during winter (December-January) in the Norwegian Sea and Northeast Atlantic. There are two centres of abundance, one in the eastern Norwegian Sea and Faroe-Shetland Channel, associated with the interface between Norwegian Sea Deep Water and Intermediate Water layers, and another in the Irminger Sea southwest of Iceland in association with Labrador Sea Water. In the open Northeast Atlantic, the concentration of wintering animals is around 30% of that in the Norwegian Sea and the vertical distribution ismore diffuse and on average deeper. Modelling studies have shown that the overwinter distribution and transport are key factors determining the spatial persistence of C. finmarchicus but, apart from the data presented here, there is little knowledge of these large-scale properties
Climate fluctuations and the spring invasion of the North Sea by Calanus finmarchicus
The population of Calanus finmarchicus in the North Sea is replenished each spring by invasion from an overwintering stock located beyond the shelf edge. A combincation of field observations, statistical analysis of Continuous Plankton Recorder (CPR) data, and particle tracking model simulations, was used to investigate the processes involved in the cross-shelf invasion. The results showed that the main source of overwintering animals entering the North Sea in the spring is at depths of greater than 600m in the Faroe Shetland Channel, where concentrations of up to 620m -3 are found in association with the overflow of Norwegian Sea Deep Water (NSDW) across the Iceland Scotland Ridge. The input of this water mass to the Faroe Shetland Channel, and hence the supply of overwintering C. finmarchicus, has declined since the late 1960s due to changes in convective processes in the Greenland Sea. Beginning in February, animals start to emerge from the overwintering state and migrate to the surface waters, where their transport into the North Sea is mainly determined by the incidence of north-westerly winds that have declined since the 1960s. Together, these two factors explain a high proportion of the 30-year trends in spring abundance in the North Sea as measured by the CPR survey. Both the regional winds and the NSDW overflow are connected to the North Atlantic Oscillation Index (NAO), which is an atmospheric climate index, but with different time scales of response. Thus, interannual fluctuations in the NAO can cause immediate changes in the incidence of north-westerly winds without leading to corresponding changes in C. finmarchicus abundance in the North Sea, because the NSDW overflow responds over longer (decadal) time scales
Age‐related changes in the biophysical and morphological characteristics of mouse cochlear outer hair cells
Outer hair cells (OHCs) are electromotile sensory receptors that provide sound amplification within the mammalian cochlea. Although OHCs appear susceptible to ageing, the progression of the pathophysiological changes in these cells is still poorly understood. By using mouse strains with a different progression of hearing loss (C57BL/6J, C57BL/6NTac, C57BL/6NTacCdh23+ , C3H/HeJ), we have identified morphological, physiological and molecular changes in ageing OHCs (9–12 kHz cochlear region). We show that by 6 months of age, OHCs from all strains underwent a reduction in surface area, which was not a sign of degeneration. Although the ageing OHCs retained a normal basolateral membrane protein profile, they showed a reduction in the size of the K+ current and non‐linear capacitance, a readout of prestin‐dependent electromotility. Despite these changes, OHCs have a normal V m and retain the ability to amplify sound, as distortion product otoacoustic emission thresholds were not affected in aged, good‐hearing mice (C3H/HeJ, C57BL/6NTacCdh23+ ). The loss of afferent synapses was present in all strains at 15 months. The number of efferent synapses per OHCs, defined as postsynaptic SK2 puncta, was reduced in aged OHCs of all strains apart from C3H mice. Several of the identified changes occurred in aged OHCs from all mouse strains, thus representing a general trait in the pathophysiological progression of age‐related hearing loss, possibly aimed at preserving functionality. We have also shown that the mechanoelectrical transduction (MET) current from OHCs of mice harbouring the Cdh23ahl allele is reduced with age, highlighting the possibility that changes in the MET apparatus could play a role in cochlear ageing
Nonequilibrium Dynamics in Low Dimensional Systems
In these lectures we give an overview of nonequilibrium stochastic systems.
In particular we discuss in detail two models, the asymmetric exclusion process
and a ballistic reaction model, that illustrate many general features of
nonequilibrium dynamics: for example coarsening dynamics and nonequilibrium
phase transitions. As a secondary theme we shall show how a common mathematical
structure, the q-deformed harmonic oscillator algebra, serves to furnish exact
results for both systems. Thus the lectures also serve as a gentle introduction
to things q-deformed.Comment: 48 pages LaTeX2e with 9 figures and using elsart.cls (included);
Lectures at the International Summer School on Fundamental Problems in
Statistical Physics X, August-September 2001, Altenberg, Germany. v2 corrects
some errors and includes further discussion/reference
Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere
A method for the full three-dimensional (3-D) reconstruction of the
trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations
Observatory (STEREO) data is presented. Four CMEs that were simultaneously
observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and
Behind STEREO satellites were analysed. These observations were used to derive
CME trajectories in 3-D out to ~15Rsun. The reconstructions using COR1/2 data
support a radial propagation model. Assuming pseudo-radial propagation at large
distances from the Sun (15-240Rsun), the CME positions were extrapolated into
the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in
the different fields-of-view. It was found that CMEs slower than the solar wind
were accelerated, while CMEs faster than the solar wind were decelerated, with
both tending to the solar wind velocity.Comment: 17 pages, 10 figures, 1 appendi
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