Low-latitude Scintillation weakening during sudden stratospheric warming events

Global Positioning System (GPS) L1-frequency (1.575 GHz) amplitude scintillations at São José dos Campos (23.1°S, 45.8°W, dip latitude 17.3°S), located under the southern crest of the equatorial ionization anomaly, are analyzed during the Northern Hemisphere winter sudden stratospheric warming (SSW) events of 2001/2002, 2002/2003, and 2012/2013. The events occurred during a period when moderate to strong scintillations are normally observed in the Brazilian longitude sector. The selected SSW events were of moderate and major categories and under low Kp conditions. The most important result of the current study is the long-lasting (many weeks) weakening of scintillation amplitudes at this low-latitude station, compared to their pre-SSW periods. Ionosonde-derived evening vertical plasma drifts and meridional neutral wind effects inferred from total electron content measurements are consistent with the observed weakening of GPS scintillations during these SSW events. This work provides strong evidence of SSW effects on ionospheric scintillations and the potential consequences of such SSW events on Global Navigation Satellite System-based applications

Modulational instability in periodic quadratic nonlinear materials

We investigate the modulational instability of plane waves in quadratic nonlinear materials with linear and nonlinear quasi-phase-matching gratings. Exact Floquet calculations, confirmed by numerical simulations, show that the periodicity can drastically alter the gain spectrum but never completely removes the instability. The low-frequency part of the gain spectrum is accurately predicted by an averaged theory and disappears for certain gratings. The high-frequency part is related to the inherent gain of the homogeneous non-phase-matched material and is a consistent spectral feature.Comment: 4 pages, 7 figures corrected minor misprint

Measurements of a low temperature mechanical dissipation peak in a single layer of Ta2O5 doped with TiO2

Thermal noise arising from mechanical dissipation in oxide coatings is a major limitation to many precision measurement systems, including optical frequency standards, high resolution optical spectroscopy and interferometric gravity wave detectors. Presented here are measurements of dissipation as a function of temperature between 7 K and 290 K in ion-beam sputtered Ta2O5 doped with TiO2, showing a loss peak at 20 K. Analysis of the peak provides the first evidence of the source of dissipation in doped Ta2O5 coatings, leading to possibilities for the reduction of thermal noise effects

Dispersive properties of quasi-phase-matched optical parametric amplifiers

The dispersive properties of non-degenerate optical parametric amplification in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary grating profile are theoretically investigated in the no-pump-depletion limit. The spectral group delay curve of the amplifier is shown to be univocally determined by its spectral power gain curve through a Hilbert transform. Such a constraint has important implications on the propagation of spectrally-narrow optical pulses through the amplifier. In particular, it is shown that anomalous transit times, corresponding to superluminal or even negative group velocities, are possible near local minima of the spectral gain curve. A possible experimental observation of such effects using a QPM Lithium-Niobate crystal is suggested.Comment: submitted for publicatio

Consequences of spinal pain: Do age and gender matter? A Danish cross-sectional population-based study of 34,902 individuals 20-71 years of age

<p>Abstract</p> <p>Background</p> <p>While low back pain (LBP) and neck pain (NP) have been extensively studied, knowledge on mid back pain (MBP) is still lacking. Furthermore, pain from these three spinal areas is typically studied or reported separately and in depth understanding of pain from the entire spine and its consequences is still needed.</p> <p>Objectives</p> <p>To describe self-reported consequences of pain in the three spinal regions in relation to age and gender.</p> <p>Methods</p> <p>This was a cross-sectional postal survey, comprising 34,902 twin individuals, representative of the general Danish adult population. The variables of interest in relation to consequences of spinal pain were: Care-seeking, reduced physical activity, sick-leave, change in work situation, and disability pension.</p> <p>Results</p> <p>Almost two-thirds of individuals with spinal pain did not report any consequence. Generally, consequences due to LBP were more frequently reported than those due to NP or MBP. Regardless of area of complaint, care seeking and reduced physical activities were the most commonly reported consequences, followed by sick-leave, change of work, and disability pension. There was a small mid-life peak for care-seeking and a slow general increase in reduced activities with increasing age. Increasing age was not associated with a higher reporting of sick-leave but the duration of the sick-leave increased somewhat with age. Disability pension due to spinal pain was reported exceedingly rare before the age of 50. Typically, women slightly more often than men reported some kind of consequences due to spinal pain.</p> <p>Conclusions</p> <p>Most people reporting spinal pain manage without any serious consequences. Low back pain more commonly results in some kind of consequence when compared to NP and MBP. Few age-related trends in consequences were seen with a slight predominance of women reporting consequences.</p

Quantum Transduction of Telecommunications-band Single Photons from a Quantum Dot by Frequency Upconversion

The ability to transduce non-classical states of light from one wavelength to another is a requirement for integrating disparate quantum systems that take advantage of telecommunications-band photons for optical fiber transmission of quantum information and near-visible, stationary systems for manipulation and storage. In addition, transducing a single-photon source at 1.3 {\mu}m to visible wavelengths for detection would be integral to linear optical quantum computation due to the challenges of detection in the near-infrared. Recently, transduction at single-photon power levels has been accomplished through frequency upconversion, but it has yet to be demonstrated for a true single-photon source. Here, we transduce the triggered single-photon emission of a semiconductor quantum dot at 1.3 {\mu}m to 710 nm with a total detection (internal conversion) efficiency of 21% (75%). We demonstrate that the 710 nm signal maintains the quantum character of the 1.3 {\mu}m signal, yielding a photon anti-bunched second-order intensity correlation, g^(2)(t), that shows the optical field is composed of single photons with g^(2)(0) = 0.165 < 0.5.Comment: 7 pages, 4 figure

Narrowband Biphotons: Generation, Manipulation, and Applications

In this chapter, we review recent advances in generating narrowband biphotons with long coherence time using spontaneous parametric interaction in monolithic cavity with cluster effect as well as in cold atoms with electromagnetically induced transparency. Engineering and manipulating the temporal waveforms of these long biphotons provide efficient means for controlling light-matter quantum interaction at the single-photon level. We also review recent experiments using temporally long biphotons and single photons.Comment: to appear as a book chapter in a compilation "Engineering the Atom-Photon Interaction" published by Springer in 2015, edited by A. Predojevic and M. W. Mitchel

Is there a relationship between pain intensity and postural sway in patients with non-specific low back pain?

Background Increased center of pressure excursions are well documented in patients suffering from non-specific low back pain, whereby the altered postural sway includes both higher mean sway velocities and larger sway area. No investigation has been conducted to evaluate a relationship between pain intensity and postural sway in adults (aged 50 or less) with non-specific low back pain. Methods Seventy-seven patients with non-specific low back pain and a matching number of healthy controls were enrolled. Center of pressure parameters were measured by three static bipedal standing tasks of 90sec duration with eyes closed in narrow stance on a firm surface. The perceived pain intensity was assessed by a numeric rating scale (NRS-11), an equal number of patients (n=11) was enrolled per pain score. Results Generally, our results confirmed increased postural instability in pain sufferers compared to healthy controls. In addition, regression analysis revealed a significant and linear increase in postural sway with higher pain ratings for all included COP parameters. Statistically significant changes in mean sway velocity in antero-posterior and medio lateral direction and sway area were reached with an incremental change in NRS scores of two to three points. Conclusions COP mean velocity and sway area are closely related to self-reported pain scores. This relationship may be of clinical use as an objective monitoring tool for patients under treatment or rehabilitation

The Search for Gravitational Waves

Experiments aimed at searching for gravitational waves from astrophysical sources have been under development for the last 40 years, but only now are sensitivities reaching the level where there is a real possibility of detections being made within the next five years. In this article a history of detector development will be followed by a description of current detectors such as LIGO, VIRGO, GEO 600, TAMA 300, Nautilus and Auriga. Preliminary results from these detectors will be discussed and related to predicted detection rates for some types of sources. Experimental challenges for detector design are introduced and discussed in the context of detector developments for the future.Comment: 21 pages, 7 figures, accepted J. Phys. B: At. Mol. Opt. Phy

A Cryogenic Silicon Interferometer for Gravitational-wave Detection

The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of the existing LIGO observatory facilities, we have designed a new instrument that will have 5 times the range of Advanced LIGO, or greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby universe, as well as observing the universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor