Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna

We report on the first demonstration of time-delay interferometry (TDI) for LISA, the Laser Interferometer Space Antenna. TDI was implemented in a laboratory experiment designed to mimic the noise couplings that will occur in LISA. TDI suppressed laser frequency noise by approximately 10^9 and clock phase noise by 6x10^4, recovering the intrinsic displacement noise floor of our laboratory test bed. This removal of laser frequency noise and clock phase noise in post-processing marks the first experimental validation of the LISA measurement scheme.Comment: 4 pages, 4 figures, to appear in Physical Review Letters end of May 201

Calculation of the ultracold neutron upscattering loss probability in fluid walled storage bottles using experimental measurements of the thermomechanical properties of Fomblin

We present experimental measurements of the properties of a liquid "Fomblin" surface obtained by the quasielastic scattering of laser light. The properties include the surface tension and viscosity as a function of temperature. The results are compared to the measurements of the bulk fluid properties. We then calculate the upscattering rate of ultracold neutrons (UCN) from thermally excited surface capillary waves on the liquid surface and compare the results to experimental measurements of the UCN lifetime in Fomblin fluid-walled UCN storage bottles, and show that the excess loss rate for UCN energies near the Fomblin potential can be explained. The rapid temperature dependence of the Fomblin storage lifetime is explained by our analysis.Comment: 25 pages, 13 figures; 2nd version corrects several error

Time Domain Simulations of Arm Locking in LISA

Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that comprise LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of arm locking including the expected limiting noise sources (shot noise, clock noise, spacecraft jitter noise, and residual laser frequency noise). The effect of imperfect a priori knowledge of the LISA heterodyne frequencies and the associated 'pulling' of an arm locked laser is included. We find that our implementation meets requirements both on the noise and dynamic range of the laser frequency.Comment: Revised to address reviewer comments. Accepted by Phys. Rev.

Realization of an Interacting Two-Valley AlAs Bilayer System

By using different widths for two AlAs quantum wells comprising a bilayer system, we force the X-point conduction-band electrons in the two layers to occupy valleys with different Fermi contours, electron effective masses, and g-factors. Since the occupied valleys are at different X-points of the Brillouin zone, the interlayer tunneling is negligibly small despite the close electron layer spacing. We demonstrate the realization of this system via magneto-transport measurements and the observation of a phase-coherent, bilayer $\nu$=1 quantum Hall state flanked by a reentrant insulating phase.Comment: 5 page

Modulator noise suppression in the LISA Time-Delay Interferometric combinations

We previously showed how the measurements of some eighteen time series of relative frequency or phase shifts could be combined (1) to cancel the phase noise of the lasers, (2) to cancel the Doppler fluctuations due to non-inertial motions of the six optical benches, and (3) to remove the phase noise of the onboard reference oscillators required to track the photodetector fringes, all the while preserving signals from passinggravitational waves. Here we analyze the effect of the additional noise due to the optical modulators used for removing the phase fluctuations of the onboard reference oscillators. We use a recently measured noise spectrum of an individual modulator to quantify the contribution of modulator noise to the first and second-generation Time-Delay Interferometric (TDI) combinations as a function of the modulation frequency. We show that modulator noise can be made smaller than the expected proof-mass acceleration and optical-path noises if the modulation frequencies are larger than $\approx 682$ MHz in the case of the unequal-arm Michelson TDI combination $X_1$, $\approx 1.08$ GHz for the Sagnac TDI combination $\alpha_1$, and $\approx 706$ MHz for the symmetrical Sagnac TDI combination $\zeta_1$. These modulation frequencies are substantially smaller than previously estimated and may lead to less stringent requirements on the LISA's oscillator noise calibration subsystem.Comment: 17 pages, 5 figures. Submitted to: Phys. Rev. D 1

Оценка влияния горных работ на формирование поля напряжений и деформирование выработок в условиях шахты «Нестор»

Наведено результати аналітичних та експериментальних досліджень з оцінки впливу гірничих робіт на напружено-деформований стан покрівлі в умовах шахти «Нестор».The results of analytical and experimental studies on the impact of mining on the stress-strain state of the roof in the mine "Nestor"

Satellite-Satellite Laser Links for Future Gravity Missions

A strong candidate for use in future missions to map time variations in the Earth\u27s gravity field is laser heterodyne measurements between separate spacecraft. At the shortest wavelengths that can be measured in space, the main accuracy limitation for variations in the potential with latitude is expected to be the frequency stability of the laser. Thus the development of simple and reliable space-qualified lasers with high frequency stability appears to be an important goal for the near future. In the last few years, quite high stability has been achieved by locking the second harmonic of a Nd:YAG laser to a resonant absorption line of iodine molecules in an absorption cell. Such a laser system can be made quite robust, and temperature related frequency shifts can be controlled at a low value. Recent results from laboratory systems are described. The Allan standard deviation for the beat between two such lasers was 2 × 10−14 at 10 s, and reached 7 × 10−15 at 600 s

Nutritional status and HIV in rural South African children.

BACKGROUND: Achieving the Millennium Development Goals that aim to reduce malnutrition and child mortality depends in part on the ability of governments/policymakers to address nutritional status of children in general and those infected or affected by HIV/AIDS in particular. This study describes HIV prevalence in children, patterns of malnutrition by HIV status and determinants of nutritional status. METHODS: The study involved 671 children aged 12-59 months living in the Agincourt sub-district, rural South Africa in 2007. Anthropometric measurements were taken and HIV testing with disclosure was done using two rapid tests. Z-scores were generated using WHO 2006 standards as indicators of nutritional status. Linear and logistic regression analyses were conducted to establish the determinants of child nutritional status. RESULTS: Prevalence of malnutrition, particularly stunting (18%), was high in the overall sample of children. HIV prevalence in this age group was 4.4% (95% CI: 2.79 to 5.97). HIV positive children had significantly poorer nutritional outcomes than their HIV negative counterparts. Besides HIV status, other significant determinants of nutritional outcomes included age of the child, birth weight, maternal age, age of household head, and area of residence. CONCLUSIONS: This study documents poor nutritional status among children aged 12-59 months in rural South Africa. HIV is an independent modifiable risk factor for poor nutritional outcomes and makes a significant contribution to nutritional outcomes at the individual level. Early paediatric HIV testing of exposed or at risk children, followed by appropriate health care for infected children, may improve their nutritional status and survival.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are