73,222 research outputs found
Diel and seasonal timing of sound production by black drum (Pogonias cromis)
Acoustic recorders were used to document black drum (Pogonias cromis) sound production during their spawning season in southwest Florida. Diel patterns of sound production were similar to those of other sciaenid fishes and demonstrated increased sound levels from the late afternoon to early evening—a period that lasted up to 12 hours during peak season. Peak sound production occurred from January through March when water temperatures were between 18° and 22°C. Seasonal trends in sound production
matched patterns of black drum reproductive readiness and spawning reported previously for populations in the Gulf of Mexico. Total acoustic energy of nightly chorus events was
estimated by integration of the sound pressure amplitude with duration above a threshold based on daytime background levels. Maximum chorus sound level was highly correlated with total acoustic energy and was used to quantitatively represent nightly black drum sound production. This study
gives evidence that long-term passive acoustic recordings can provide information on the timing and location of black drum reproductive behavior that is similar to that provided by traditional, more costly methods. The methods and results have broad application for the study of many other
fish species, including commercially and recreationally valuable reef fishes that produce sound in association with
reproductive beha
Inflationary spectra and violations of Bell inequalities
In spite of the macroscopic character of the primordial fluctuations, the
standard inflationary distribution (that obtained using linear mode equations)
exhibits inherently quantum properties, that is, properties which cannot be
mimicked by any stochastic distribution. This is demonstrated by a Gedanken
experiment for which certain Bell inequalities are violated. These violations
are {\it in principle} measurable because, unlike for Hawking radiation from
black holes, in inflationary cosmology we can have access to both members of
correlated pairs of modes delivered in the same state. We then compute the
effect of decoherence and show that the violations persist provided the
decoherence level (and thus the entropy) lies below a certain non-vanishing
threshold. Moreover, there exists a higher threshold above which no violation
of any Bell inequality can occur. In this regime, the distributions are
``separable'' and can be interpreted as stochastic ensembles of fluctuations.
Unfortunately, the precision which is required to have access to the quantum
properties is so high that, {\it in practice}, an observational verification
seems excluded.Comment: 5 pages, 1 figure; new presentation and extended discussio
Isotropic magnetometry with simultaneous excitation of orientation and alignment CPT resonances
Atomic magnetometers have very high absolute precision and sensitivity to
magnetic fields but suffer from a fundamental problem: the vectorial or
tensorial interaction of light with atoms leads to "dead zones", certain
orientations of magnetic field where the magnetometer loses its sensitivity. We
demonstrate a simple polarization modulation scheme that simultaneously creates
coherent population trapping (CPT) in orientation and alignment, thereby
eliminating dead zones. Using Rb in a 10 Torr buffer gas cell we measure
narrow, high-contrast CPT transparency peaks in all orientations and also show
absence of systematic effects associated with non-linear Zeeman splitting.Comment: 4 pages, 4 figure
Observable effects caused by vacuum pair creation in the field of high-power optical lasers
We consider the possibility of an experimental proof of vacuum e+e- pair
creation in the focus of two counter-propagating optical laser beams with an
intensity of the order of 10^20 - 10^22 W/cm^2. Our approach is based on the
collisionless kinetic equation for the distribution function of the e+e- pairs
with the source term for particle production. As a possible experimental signal
of vacuum pair production we consider the refraction of a high-frequency probe
laser beam by the produced e+e- plasma to be observed by an interference
filter. The generation of higher harmonics of the laser frequency in the
self-consistent electric field is also investigated.Comment: 7 pages, 7 figures; typos corrected, Eq.(16) corrected, reference
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