Passively Q-switched erbium-doped fiber laser with graphene oxide film as saturable absorber

Passively Q-switched erbium-doped fiber laser (EDFL) have been demonstrated using graphene oxide (GO) film as saturable absorber (SA). The aim of this experiment is to generate and demonstrate passively Q-Switched Erbium-doped fiber laser (EDFL) using GO as a saturable absorber. Stable Q-switched operation can be achieved at 1558.8 nm. By increasing the pump power from 26.32mW to 71.65mW, the repetition rate also increased from 30.58 kHz to 51.81k Hz. The pulse width of the laser were 11.2 - 4.73 µs. The maximum output power and maximum peak power obtained are 128 µW and 521.98 µW respectively at a pump power of 71.65 mW. The pulse energy reaches 2.47nJ. These results show that GO is a new potential SA material for pulsed laser applications

Q-switched ytterbium-doped fiber laser using graphene oxide as passive saturable absorber

A Q-switched ytterbium-doped fiber laser (YDFL) was demonstrated using Graphene Oxide (GO) as a saturable absorber (SA). Without SA, the ring cavity operates in a continuous wave laser at 1038 nm which is shifted to 1030 nm with the implementation of SA. The laser has a threshold pump power of 175 mW, a maximum repetition rate of 141 kHz and the shortest pulse width of 1.94?s. The highest pulse energy of 5.65 nJ is achieved at the pump power of 175mW. A stable Q-switched ytterbium doped fibre laser was successfully achieved in this experiment as the pulses measured SNR of 56.52 dB

From working in the wheat field to managing wheat: women innovators in Nepal

This article presents research conducted in Nepal’s Terai plains in 2014-15 showing that women are innovating in wheat to the extent that wheat farming is experiencing a shift from feminization of agricultural labor towards women taking control over decision making. Processes accounting for this include male out-migration, non-governmental organizations working on promoting women’s equality that has developed women’s confidence, individual support from extension agents, and strong cooperation between women to foster each other’s “innovation journeys.

Off-label use of direct oral anticoagulants in patients receiving surgical mechanical and bioprosthetic heart valves

This cohort study assesses direct oral anticoagulant use in patients with surgical prosthetic heart valves in the United States and evaluates differences in preoperative and postoperative profiles in patients discharged while receiving direct oral anticoagulant vs warfarin

Detecting very-high-frequency relic gravitational waves by electromagnetic wave polarizations in a waveguide

The polarization vector (PV) of an electromagnetic wave (EW) will experience a rotation in a region of spacetime perturbed by gravitational waves (GWs). Based on this idea, Cruise's group has built an annular waveguide to detect GWs. We give detailed calculations of the rotations of the polarization vector of an EW caused by incident GWs from various directions and in various polarization states, and then analyze the accumulative effects on the polarization vector when the EW passes n cycles along the annular waveguide. We reexamine the feasibility and limitation of this method to detect GWs of high frequency around 100 MHz, in particular, the relic gravitational waves (RGWs). By comparing the spectrum of RGWs in the accelerating universe with the detector sensitivity of the current waveguide, it is found that the amplitude of the RGWs is too low to be detected by the waveguide detectors currently running. Possible ways of improvements on detection are discussed also.Comment: 18pages, 10 figures, accepted by ChJA

Quantum fluctuations for drag free geodesic motion

The drag free technique is used to force a proof mass to follow a geodesic motion. The mass is protected from perturbations by a cage, and the motion of the latter is actively controlled to follow the motion of the proof mass. We present a theoretical analysis of the effects of quantum fluctuations for this technique. We show that a perfect drag free operation is in principle possible at the quantum level, in spite of the back action exerted on the mass by the position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change

Upper limits on stray force noise for LISA

We have developed a torsion pendulum facility for LISA gravitational reference sensor ground testing that allows us to put significant upper limits on residual stray forces exerted by LISA-like position sensors on a representative test mass and to characterize specific sources of disturbances for LISA. We present here the details of the facility, the experimental procedures used to maximize its sensitivity, and the techniques used to characterize the pendulum itself that allowed us to reach a torque sensitivity below 20 fNm /sqrt{Hz} from 0.3 to 10 mHz. We also discuss the implications of the obtained results for LISA.Comment: To be published in Classical and Quantum Gravity, special issue on Amaldi5 2003 conference proceedings (10 pages, 6 figures

Collective firm bankruptcies and phase transition in rating dynamics

We present a simple model of firm rating evolution. We consider two sources of defaults: individual dynamics of economic development and Potts-like interactions between firms. We show that such a defined model leads to phase transition, which results in collective defaults. The existence of the collective phase depends on the mean interaction strength. For small interaction strength parameters, there are many independent bankruptcies of individual companies. For large parameters, there are giant collective defaults of firm clusters. In the case when the individual firm dynamics favors dumping of rating changes, there is an optimal strength of the firm's interactions from the systemic risk point of view

Acceleration disturbances and requirements for ASTROD I

ASTRODynamical Space Test of Relativity using Optical Devices I (ASTROD I) mainly aims at testing relativistic gravity and measuring the solar-system parameters with high precision, by carrying out laser ranging between a spacecraft in a solar orbit and ground stations. In order to achieve these goals, the magnitude of the total acceleration disturbance of the proof mass has to be less than 10−13 m s−2 Hz−1/2 at 0.1 m Hz. In this paper, we give a preliminary overview of the sources and magnitude of acceleration disturbances that could arise in the ASTROD I proof mass. Based on the estimates of the acceleration disturbances and by assuming a simple controlloop model, we infer requirements for ASTROD I. Our estimates show that most of the requirements for ASTROD I can be relaxed in comparison with Laser Interferometer Space Antenna (LISA).Comment: 19 pages, two figures, accepted for publication by Class. Quantum Grav. (at press

DC Cancellation As a Method of Generating a t^2 Response and of Solving the Radial Nonobservability Problem in a Concentric Free-Falling Two-Sphere Equivalence-Principle Experiment in a Drag-Free Satellite

This paper solves two major problems which have blocked a free-fall Equivalence-Principle (EP) in a satellite for 25 years: a semimajor-axis error between the two proof masses cannot be distinguished from an EP violation and the response to an EP violation only grows as t not t^2. Using the cancellation method described in this paper, the nonobservability problem can be suppressed and a t^2 response can be generated which lasts between 10^4 and 10^6 seconds depending on the cancellation accuracy. t^2 response times between 10^5 and 10^6 seconds are equivalent to a very tall (0.1 to 10 AU) drop tower with a constant gravitational field of 3/7 ge.Comment: 40 pages, 7 figures, Revision 3.0: Reviewer's suggested corrections for journal submissio