2,820 research outputs found
Non-linear dynamics near exceptional points of synthetic antiferromagnetic spin-torque oscillators
We consider a synthetic antiferromagnetic spin-torque oscillator with
anisotropic interlayer exchange coupling. This system exhibits exceptional
points in its linearized dynamics. We find the non-linear dynamics and the
dynamical phase diagram of the system both analytically and numerically.
Moreover, we show that, near one of the exceptional points, the power of the
oscillator depends extremely sensitively on the injected spin current. Our
findings may be useful for designing sensitive magnetometers and for other
applications of spin-torque oscillators.Comment: 7 pages, 4 figure
Seismic topographic scattering in the context of GW detector site selection
In this paper, we present a calculation of seismic scattering from irregular
surface topography in the Born approximation. Based on US-wide topographic
data, we investigate topographic scattering at specific sites to demonstrate
its impact on Newtonian-noise estimation and subtraction for future
gravitational-wave detectors. We find that topographic scattering at a
comparatively flat site in Oregon would not pose any problems, whereas
scattering at a second site in Montana leads to significant broadening of wave
amplitudes in wavenumber space that would make Newtonian-noise subtraction very
challenging. Therefore, it is shown that topographic scattering should be
included as criterion in the site-selection process of future low-frequency
gravitational-wave detectors.Comment: 16 pages, 7 figure
Automated quantitative analysis of single and double label autoradiographs
A method for the analysis of silver grain content in both single and double label autoradiographs is presented. The total grain area is calculated by counting the number of pixels at which the recorded light intensity in transmission dark field illumination exceeds a selected threshold. The calibration tests included autoradiographs with low (3H- thymidin) and high (3H-desoxyuridin) silver grain density. The results are proportional to the customary visual grain count. For the range of visibly countable grain densities in single labeled specimens, the correlation coefficient between the computed values and the visual grain counts is better than 0.96. In the first emulsion of the two emulsion layer autoradiographs of double labeled specimens (3H-14C- thymidin) the correlation coefficient is 0.919 and 0.906. The method provides a statistical correction for the background grains not due to the isotope. The possibility to record 14C tracks by shifting the focus through the second emulsion of the double labeled specimens is also demonstrated. The reported technique is essentially independent of size, shape and density of the grains
Squeezed Light for the Interferometric Detection of High Frequency Gravitational Waves
The quantum noise of the light field is a fundamental noise source in
interferometric gravitational wave detectors. Injected squeezed light is
capable of reducing the quantum noise contribution to the detector noise floor
to values that surpass the so-called Standard-Quantum-Limit (SQL). In
particular, squeezed light is useful for the detection of gravitational waves
at high frequencies where interferometers are typically shot-noise limited,
although the SQL might not be beaten in this case. We theoretically analyze the
quantum noise of the signal-recycled laser interferometric gravitational-wave
detector GEO600 with additional input and output optics, namely
frequency-dependent squeezing of the vacuum state of light entering the dark
port and frequency-dependent homodyne detection. We focus on the frequency
range between 1 kHz and 10 kHz, where, although signal recycled, the detector
is still shot-noise limited. It is found that the GEO600 detector with present
design parameters will benefit from frequency dependent squeezed light.
Assuming a squeezing strength of -6 dB in quantum noise variance, the
interferometer will become thermal noise limited up to 4 kHz without further
reduction of bandwidth. At higher frequencies the linear noise spectral density
of GEO600 will still be dominated by shot-noise and improved by a factor of
10^{6dB/20dB}~2 according to the squeezing strength assumed. The interferometer
might reach a strain sensitivity of 6x10^{-23} above 1 kHz (tunable) with a
bandwidth of around 350 Hz. We propose a scheme to implement the desired
frequency dependent squeezing by introducing an additional optical component to
GEO600s signal-recycling cavity.Comment: Presentation at AMALDI Conference 2003 in Pis
Density of Superfluid Helium Droplets
The classical integral cross sections of large superfluid 4He_N droplets and
the number of atoms in the droplets (N=10^3-10^4) have been measured in
molecular beam scattering experiments. These measurements are found to be in
good agreement with the cross sections predicted from density functional
calculations of the radial density distributions with a 10-90 % surface
thickness of 5.7\AA. By using a simple model for the density profile of the
droplets a thickness of about 6-8\AA is extracted directly from the data.Comment: 27 pages, REVTeX, 5 postscript figure
Bosonic Description of Spinning Strings in Dimensions
We write down a general action principle for spinning strings in 2+1
dimensional space-time without introducing Grassmann variables. The action is
written solely in terms of coordinates taking values in the 2+1 Poincare group,
and it has the usual string symmetries, i.e. it is invariant under a)
diffeomorphisms of the world sheet and b) Poincare transformations. The system
can be generalized to an arbitrary number of space-time dimensions, and also to
spinning membranes and p-branes.Comment: Latex, 12 page
Microcanonical statistics of black holes and bootstrap condition
The microcanonical statistics of the Schwarzschild black holes as well as the
Reissner-Nordstrm black holes are analyzed. In both cases we set
up the inequalities in the microcanonical density of states.
These are then used to show that the most probable configuration in the gases
of black holes is that one black hole acquires all of the mass and all of the
charge at high energy limit. Thus the black holes obey the statistical
bootstrap condition and, in contrast to the other investigation, we see that
U(1) charge does not break the bootstrap property.Comment: 16 pages. late
Spectrum of Sizes for Perfect Deletion-Correcting Codes
One peculiarity with deletion-correcting codes is that perfect
-deletion-correcting codes of the same length over the same alphabet can
have different numbers of codewords, because the balls of radius with
respect to the Levenshte\u{\i}n distance may be of different sizes. There is
interest, therefore, in determining all possible sizes of a perfect
-deletion-correcting code, given the length and the alphabet size~.
In this paper, we determine completely the spectrum of possible sizes for
perfect -ary 1-deletion-correcting codes of length three for all , and
perfect -ary 2-deletion-correcting codes of length four for almost all ,
leaving only a small finite number of cases in doubt.Comment: 23 page
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