1,949 research outputs found
Interesting times: a short introduction from the new editorial team of Gender and Education
Editoria
Averaging and sampling for magnetic-observatory hourly data
A time and frequency-domain analysis is made of the effects of averaging and
sampling methods used for constructing magnetic-observatory hourly data
values. Using 1-min data as a proxy for continuous, geomagnetic variation,
we construct synthetic hourly values of two standard types: instantaneous
"spot" measurements and simple 1-h "boxcar" averages. We compare these
average-sample types with others: 2-h average, Gaussian, and "brick-wall"
low-frequency-pass. Hourly spot measurements provide a statistically unbiased
representation of the amplitude range of geomagnetic-field variation, but as
a representation of continuous field variation over time, they are
significantly affected by aliasing, especially at high latitudes. The 1-h,
2-h, and Gaussian average-samples are affected by a combination of amplitude
distortion and aliasing. Brick-wall values are not affected by either
amplitude distortion or aliasing, but constructing them is, in an operational
setting, relatively more difficult than it is for other average-sample types.
It is noteworthy that 1-h average-samples, the present standard for
observatory hourly data, have properties similar to Gaussian average-samples
that have been optimized for a minimum residual sum of amplitude distortion
and aliasing. For 1-h average-samples from medium and low-latitude
observatories, the average of the combination of amplitude distortion and
aliasing is less than the 5.0 nT accuracy standard established by Intermagnet
for modern 1-min data. For medium and low-latitude observatories, average
differences between monthly means constructed from 1-min data and monthly
means constructed from any of the hourly average-sample types considered here
are less than the 1.0 nT resolution of standard databases. We recommend that
observatories and World Data Centers continue the standard practice of
reporting simple 1-h-average hourly values
Lie group weight multiplicities from conformal field theory
Dominant weight multiplicities of simple Lie groups are expressed in terms of
the modular matrices of Wess-Zumino-Witten conformal field theories, and
related objects. Symmetries of the modular matrices give rise to new relations
among multiplicities. At least for some Lie groups, these new relations are
strong enough to completely fix all multiplicities.Comment: 12 pages, Plain TeX, no figure
Can a Lattice String Have a Vanishing Cosmological Constant?
We prove that a class of one-loop partition functions found by Dienes, giving
rise to a vanishing cosmological constant to one-loop, cannot be realized by a
consistent lattice string. The construction of non-supersymmetric string with a
vanishing cosmological constant therefore remains as elusive as ever. We also
discuss a new test that any one-loop partition function for a lattice string
must satisfy.Comment: 14 page
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