66 research outputs found

### Compensated Current Injection circuit, theory and applications

This paper presents a detailed description, analysis and example of practical
application of a wide frequency band voltage-to-current converter. The
converter is characterized by a combination of positive and negative feedback
loops. This feature allows compensation for parasitic impedance connected in
parallel with the useful load, which in turn keeps an excitation current
flowing through the useful load independent of its impedance. The simplicity of
the circuit and its good electrical properties are additional advantages of the
scheme.Comment: 9 pages and 7 figures in one PDF fil

### 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

### 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

### STEP: Satellite Test of the Equivalence Principle. Report on the phase A study

During Phase A, the STEP Study Team identified three types of experiments that can be accommodated on the STEP satellite within the mission constraints and whose performance is orders of magnitude better than any present or planned future experiment of the same kind on the ground. The scientific objectives of the STEP mission are to: test the Equivalence Principle to one part in 10(exp 17), six orders of magnitude better than has been achieved on the ground; search for a new interaction between quantum-mechanical spin and ordinary matter with a sensitivity of the mass-spin coupling constant g(sub p)g(sub s) = 6 x 10(exp -34) at a range of 1 mm, which represents a seven order-of-magnitude improvement over comparable ground-based measurements; and determine the constant of gravity G with a precision of one part in 10(exp 6) and to test the validity of the inverse square law with the same precision, both two orders of magnitude better than has been achieved on the ground

### Using polarized maser to detect high-frequency relic gravitational waves

A GHz maser beam with Gaussian-type distribution passing through a homogenous
static magnetic field can be used to detect gravitational waves (GWs) with the
same frequency. The presence of GWs will perturb the electromagnetic (EM)
fields, giving rise to perturbed photon fluxes (PPFs). After being reflected by
a fractal membrane, the perturbed photons suffer little decay and can be
measured by a microwave receiver. This idea has been explored to certain extent
as a method for very high frequency gravitational waves. In this paper, we
examine and develop this method more extensively, and confront the possible
detection with the predicted signal of relic gravitational waves (RGWs). A
maser beam with high linear polarization is used to reduce the background
photon fluxes (BPFs) in the detecting direction as the main noise. As a key
factor of applicability of this method, we give a preliminary estimation of the
sensitivity of a sample detector limited by thermal noise using currently
common technology.
The minimal detectable amplitude of GWs is found to be
$h_{\rm{min}}\sim10^{-30}$. Comparing with the known spectrum of the RGWs in
the accelerating universe for $\beta=-1.9$, there is still roughly a gap of
$4\sim 5$ orders. However, possible improvements on the detector can further
narrow down the gap and make it a feasible method to detect high frequency
RGWs.Comment: 20 pages, 6 figures, accepted for Phys. Rev.

### 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

### 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

### 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

### 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

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