7,542 research outputs found
The rf control and detection system for PACO the parametric converter detector
In this technical note the rf control and detection system for a detector of
small harmonic displacements based on two coupled microwave cavities (PACO) is
presented. The basic idea underlying this detector is the principle of
parametric power conversion between two resonant modes of the system,
stimulated by the (small) harmonic modulation of one system parameter. In this
experiment we change the cavity length applying an harmonic voltage to a
piezo-electric crystal. The system can achieve a great sensitivity to small
harmonic displacements and can be an interesting candidate for the detection of
small, mechanically coupled, interactions (e.g. high frequency gravitational
waves).Comment: 13 pages, 4 postscript figure
Body Fat is Associated with Decreased Endocrine and Cognitive Resilience to Acute Emotional Stress
*Objective:* Cortisol is elevated both in individuals with increased emotional stress as well as with higher percentages of body fat. Cortisol is also known to affect cognitive performance, particularly spatial processing, selective attention, and working memory. We hypothesized that increased body fat might therefore be associated with decreased performance on a spatial processing task, in response to an acute real-world stressor. 

*Design:* We tested two separate samples of subjects undergoing their first (tandem) skydive. In the first sample (N=78), subjects were tested for salivary cortisol and state-anxiety (Spielberger State Anxiety Scale) during the plane's fifteen-minute ascent to altitude in immediate anticipation of the jump. In a second sample (N=20), subjects were tested for salivary cortisol, as well as cardiac variables (heart rate, autonomic regulation via heart rate variability) and performance on a cognitive task of spatial processing, selective attention, and working memory. 

*Results:* In response to the skydive, individuals with greater body fat percentages showed significantly increased reactivity for both cortisol (on both samples) and cognition, including decreased accuracy of our task of spatial processing, selective attention, and working memory. These cognitive effects were restricted to the stress response and were not found under baseline conditions. There were no body fat interactions with cardiac changes in response to the stressor, suggesting that the cognitive effects were specifically hormone-mediated rather than secondary to general activation of the autonomic nervous system. 

*Conclusions:* Our results indicate that, under real-world stress, increased body fat may be associated with endocrine stress-vulnerability, with consequences for deleterious cognitive performance
Parametric gravity wave detector
Since 1978 superconducting coupled cavities have been proposed as a sensitive
detector of gravitational waves. The interaction of the gravitational wave with
the cavity walls, and the esulting motion, induces the transition of some
energy from an initially excited cavity mode to an empty one. The energy
transfer is maximum when the frequency of the wave is equal to the frequency
difference of the two cavity modes. In 1984 Reece, Reiner and Melissinos built
a detector of the type proposed, and used it as a transducer of harmonic
mechanical motion, achieving a sensitivity to fractional deformations of the
order dx/x ~ 10^(-18). In this paper the working principles of the detector are
discussed and the last experimental results summarized. New ideas for the
development of a realistic gravitational waves detector are considered; the
outline of a possible detector design and its expected sensitivity are also
shown.Comment: 9 pages, 6 figures. Talk given at the Workshop on Electromagnetic
Probes of Fundamentals Physics, Erice (Italy), October 200
A detector of gravitational waves based on coupled microwave cavities
Since 1978 superconducting coupled cavities have been proposed as sensitive
detector of gravitational waves. The interaction of the gravitational wave with
the cavity walls, and the resulting motion, induces the transition of some
electromagnetic energy from an initially excited cavity mode to an empty one.
The energy transfer is maximum when the frequency of the wave is equal to the
frequency difference of the two cavity modes. In this paper the basic
principles of the detector are discussed. The interaction of a gravitational
wave with the cavity walls is studied in the proper reference frame of the
detector, and the coupling between two electromagnetic normal modes induced by
the wall motion is analyzed in detail. Noise sources are also considered; in
particular the noise coming from the brownian motion of the cavity walls is
analyzed. Some ideas for the developement of a realistic detector of
gravitational waves are discussed; the outline of a possible detector design
and its expected sensitivity are also shown.Comment: 29 pages, 12 eps figures. Typeset by REVTe
A detector of small harmonic displacements based on two coupled microwave cavities
The design and test of a detector of small harmonic displacements is
presented. The detector is based on the principle of the parametric conversion
of power between the resonant modes of two superconducting coupled microwave
cavities. The work is based on the original ideas of Bernard, Pegoraro, Picasso
and Radicati, who, in 1978, suggested that superconducting coupled cavities
could be used as sensitive detectors of gravitational waves, and on the work of
Reece, Reiner and Melissinos, who, {in 1984}, built a detector of this kind.
They showed that an harmonic modulation of the cavity length l produced an
energy transfer between two modes of the cavity, provided that the frequency of
the modulation was equal to the frequency difference of the two modes. They
achieved a sensitivity to fractional deformations of dl/l~10^{-17} Hz^{-1/2}.
We repeated the Reece, Reiner and Melissinos experiment, and with an improved
experimental configuration and better cavity quality, increased the sensitivity
to dl/l~10^{-20} Hz^{-1/2}. In this paper the basic principles of the device
are discussed and the experimental technique is explained in detail. Possible
future developments, aiming at gravitational waves detection, are also
outlined.Comment: 28 pages, 12 eps figures, ReVteX. \tightenlines command added to
reduce number of pages. The following article has been accepted by Review of
Scientific Instruments. After it is published, it will be found at
http://link.aip.org/link/?rs
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