1,114 research outputs found

### Analysis of Super-Kamiokande 5-day Measurements of the Solar Neutrino Flux

Data in 5-day bins, recently released by the Super-Kamiodande Consortium, has
been analyzed by a likelihood procedure that has certain advantages over the
Lomb-Scargle procedure used by the consortium. The two most prominent peaks in
the power spectrum of the 10-day data were at 9.42 y-1 and 26.57 y-1, and it
was clear that one was an alias of the other caused by the regularity of the
binning. There were reasons to believe that the 9.42 y-1 peak was an alias of
the 26.57 y-1 peak, but analysis of the 5-day data makes it clear that the
reverse is the case. In addition to a strong peak near 9.42 y-1, we find peaks
at 43.72 y-1and at 39.28 y-1. After comparing this analysis with a
power-spectrum analysis of magnetic-field data, we suggest that these three
peaks may be attributed to a harmonic of the solar rotation rate and to an
r-mode oscillation with spherical harmonic indices l = 2, m = 2.Comment: Accepted for publication in Astrophysical Journa

### Time-Series Analysis of Super-Kamiokande Measurements of the Solar Neutrino Flux

The Super-Kamiokande Consortium has recently released data suitable for
time-series analysis. The binning is highly regular: the power spectrum of the
acquisition times has a huge peak (power S > 120) at the frequency (in cycles
per year) 35.98 (period 10.15 days), where power measurements are such that the
probability of obtaining a peak of strength S or more by chance at a specified
frequency is exp(-S). This inevitably leads to severe aliasing of the power
spectrum. The strongest peak in the range 0 - 100 in a power spectrum formed by
a likelihood procedure is at 26.57 (period 13.75 days) with S = 11.26. For the
range 0 - 40, the second-strongest peak is at 9.42 (period 38.82 days) with S =
7.3. Since 26.57 + 9.42 = 35.99, we conclude that the weaker peak at 9.42 is an
alias of the stronger peak at 26.57. We note that 26.57 falls in the band 26.36
- 27.66, formed from twice the range of synodic rotation frequencies of an
equatorial section of the Sun for normalized radius larger than 0.1.
Oscillations at twice the rotation frequency, attributable to "m = 2"
structures, are not uncommon in solar data. We find from the shuffle test that
the probability of obtaining a peak of S = 11.26 or more by chance in this band
is 0.1 %. This new result therefore supports at the 99.9% confidence level
previous evidence, found in Homestake and GALLEX-GNO data, for rotational
modulation of the solar neutrino flux. The frequency 25.57 points to a source
of modulation at or near the tachocline.Comment: 15 pages, 8 figure

### Uncertainty in estimates of the number of extraterrestrial civilizations

An estimation of the number N of communicative civilizations is made by means of Drake's formula which involves the combination of several quantities, each of which is to some extent uncertain. It is shown that the uncertainty in any quantity may be represented by a probability distribution function, even if that quantity is itself a probability. The uncertainty of current estimates of N is derived principally from uncertainty in estimates of the lifetime of advanced civilizations. It is argued that this is due primarily to uncertainty concerning the existence of a Galactic Federation which is in turn contingent upon uncertainty about whether the limitations of present-day physics are absolute or (in the event that there exists a yet undiscovered hyperphysics) transient. It is further argued that it is advantageous to consider explicitly these underlying assumptions in order to compare the probable numbers of civilizations operating radio beacons, permitting radio leakage, dispatching probes for radio surveillance for dispatching vehicles for manned surveillance

### A theory of theories

Theory comparisons with facts obtained by reduction of observed dat

### Examination of time series through randomly broken windows

The effect of irregular interruption of data collection (the breaking of the window function) on the spectrum determination of a time series is investigated. It is assumed that there is a uniform probability p that each interval of length tau, of the total interval of length T = tau, yields no data. For the linear case (Fourier transform) it is found that the noise to signal ratio has a (one sigma) value less than epsilon if N exceeds p(-1) (1-p) epsilon (-2). For the quadratic case, the same requirement is met by the less restrictive requirement that N exceed p(-1) (1-p) epsilon (-1). It appears that, if four observatories spaced around the Earth were to operate for 25 days, each for six hours a day (N = 100), and if the probability of cloud cover at any site on any day is 20% (p = 0.8), the r.m.s. noise to signal ratio is 0.25% for frequencies displaced from a sharp strong signal by 15 micro Hz. The noise to signal ratio drops off rapidly if the frequency offset exceeds 15 micro Hz

### Plasma phenomena at magnetic neutral points

A model of the plasma focus is considered, in which large axial electric fields are induced by the imploding current sheet during the final few nanoseconds of the collapse phase. This field provides a mechanism for creation of a beam of electrons of highly suprathermal energies. For this beam, the bremsstrahlung radiation is calculated, which is expected either from electron-deuteron collisions in the focused plasma itself or from the beam as it reaches the walls of the device. Comparison with experimental results indicates that the walls are the more likely source of these hard X-rays and also find qualitative agreement of the expected angular distribution of X-rays with experiment

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