3,453 research outputs found
Novel Fiber Design for Wideband Conversion and Amplification in Multimode Fibers
We propose an operating principle to achieve broadband and highly tunable
mode conversion and amplification exploiting inter-modal four wave mixing in a
multimode fiber. A bandwidth of 30 nanometers is demonstrated by properly
designing a simple step-index silica fiber.Comment: Ecoc conference 201
Bistatic LIDAR experiment proposed for the shuttle/tethered satellite system missions
A new experiment concept has been proposed for the shuttle/tethered satellite system missions, which can provide high resolution, global density mappings of certain ionospheric species. The technique utilizes bistatic LIDAR to take advantage of the unique dual platform configuration offered by these missions. A tuned, shuttle-based laser is used to excite a column of the atmosphere adjacent to the tethered satellite, while triangulating photometic detectors on the satellite are employed to measure the fluorescence from sections of the column. The fluorescent intensity at the detectors is increased about six decades over both ground-based and monostatic shuttle-based LIDAR sounding of the same region. In addition, the orbital motion of the Shuttle provides for quasi-global mapping unattainable with ground-based observations. Since this technique provides such vastly improved resolution on a synoptic scale, many important middle atmospheric studies, heretofore untenable, may soon be addressed
Spatio-temporal self-focusing in femtosecond pulse transmission through multimode optical fibers
We numerically investigate ultra-short pulse propagation in multimode optical fibers with launch peak powers approaching the critical power for self-focusing using a generalized multimode nonlinear Schrödinger equation approach. Nonlinear spatial and temporal effects combined with fiber dispersion govern pulse compression in space and time which can result in damage inducing intensity levels. Here we identify pulse parameters for which damage is avoided and high-power delivery through optical fiber is possible near the fiber zero-dispersion wavelength
The efficacy of a generic doxycycline tablet in the treatment of canine monocytic ehrlichiosis
The objective of the present study was to evaluate the therapeutic efficacy of a generic doxycycline tablet (DoxyVet®) against Ehrlichia canis infection in dogs. Canine monocytic ehrlichiosis is caused by the bacterium E. canis and transmitted by the brown kennel tick (Rhipicephalus sanguineus). Six disease-free and tick-free dogs were infested with E. canisinfected ticks. Once diagnosed (with polymerase chain reaction [PCR] analysis and platelet counts) as positive for infection, doxycycline tablets were administered orally once a day for 20 consecutive days, at a target dose level of 10 mg/kg. The actual dose administered was calculated as ranging between 10 mg/kg and 11.7 mg/kg. The PCR analysis, 28 days after the first administration of the tablets, failed to detect E. canis in any of the dogs. On Day 56 of the study, four of the dogs were diagnosed with E. canis for the second time and a fifth dog was diagnosed on Day 70. The platelet counts of the sixth dog remained within normal levels and it was discharged from the study on Day 84. Doxycycline tablets were then administered to the remaining five infected dogs for 28 consecutive days. Four of these dogs had no positive PCR results during the following 3 months. The fifth dog was diagnosed with E. canis for the third time 58 days after the last tablets of the second treatment had been administered, after which it was rescue treated (doxycycline for a further 28 days). The results indicate that doxycycline administered in tablet form (DoxyVet®) at 10 mg/kg – 11.7 mg/kg body mass once daily for 28 consecutive days clears most dogs of infection. The importance of a concomitant tick-control programme is therefore stressed
Postural Compensation for Unilateral Vestibular Loss
Postural control of upright stance was investigated in well-compensated, unilateral vestibular loss (UVL) subjects compared to age-matched control subjects. The goal was to determine how sensory weighting for postural control in UVL subjects differed from control subjects, and how sensory weighting related to UVL subjects’ functional compensation, as assessed by standardized balance and dizziness questionnaires. Postural control mechanisms were identified using a model-based interpretation of medial–lateral center-of-mass body-sway evoked by support-surface rotational stimuli during eyes-closed stance. The surface-tilt stimuli consisted of continuous pseudorandom rotations presented at four different amplitudes. Parameters of a feedback control model were obtained that accounted for each subject’s sway response to the surface-tilt stimuli. Sensory weighting factors quantified the relative contributions to stance control of vestibular sensory information, signaling body-sway relative to earth-vertical, and proprioceptive information, signaling body-sway relative to the surface. Results showed that UVL subjects made significantly greater use of proprioceptive, and therefore less use of vestibular, orientation information on all tests. There was relatively little overlap in the distributions of sensory weights measured in UVL and control subjects, although UVL subjects varied widely in the amount they could use their remaining vestibular function. Increased reliance on proprioceptive information by UVL subjects was associated with their balance being more disturbed by the surface-tilt perturbations than control subjects, thus indicating a deficiency of balance control even in well-compensated UVL subjects. Furthermore, there was some tendency for UVL subjects who were less able to utilize remaining vestibular information to also indicate worse functional compensation on questionnaires
The hidden phase of Fock states; quantum non-local effects
We revisit the question of how a definite phase between Bose-Einstein
condensates can spontaneously appear under the effect of measurements. We first
consider a system that is the juxtaposition of two subsystems in Fock states
with high populations, and assume that successive individual position
measurements are performed. Initially, the relative phase is totally undefined,
and no interference effect takes place in the first position measurement. But,
while successive measurements are accumulated, the relative phase becomes
better and better known, and a clear interference pattern emerges. It turns out
that all observed results can be interpreted in terms of a pre-existing, but
totally unknown, relative phase, which remains exactly constant during the
experiment. We then generalize the results to more condensates. We also
consider other initial quantum states than pure Fock states, and distinguish
between intrinsic phase of a quantum state and phase induced by measurements.
Finally, we examine the case of multiple condensates of spin states. We discuss
a curious quantum effect, where the measurement of the spin angular momentum of
a small number of particles can induce a big angular momentum in a much larger
assembly of particles, even at an arbitrary distance. This spin observable can
be macroscopic, assimilable to the pointer of a measurement apparatus, which
illustrates the non-locality of quantum mechanics with particular clarity.Comment: a factor 1/2 added in equation (9); reference (30) completed, DOI
adde
Bosons in Disordered Optical Potentials
In this work we systematically investigate the condensate properties,
superfluid properties and quantum phase transitions in interacting Bose gases
trapped in disordered optical potentials. We numerically solve the Bose-Hubbard
Hamiltonian exactly for different: (a) types of disorder, (b) disorder
strengths, and (c) interatomic interactions. The three types of disorder
studied are: quasiperiodic disorder, uniform random disorder and random
speckle-type disorder. We find that the Bose glass, as identified by Fisher et
al [Phys. Rev. B {\bf 40}, 546 (1989)], contains a normal condensate component
and we show how the three different factors listed above affect it.Comment: 4 pages, 4 figures (low res) v2 Title,Abstract,Introduction: changes;
Figure 3: Add label to axi
- …