19 research outputs found
Quasiperiodic ∼5–60 s fluctuations of VLF signals propagating in the Earth-ionosphere waveguide: a result of pulsating auroral particle precipitation?
Subionospheric very low frequency and low-frequency (VLF/LF) transmitter signals received at middle-latitude ground stations at nighttime were found to exhibit pulsating behavior with periods that were typically in the ∼5–60 s range but sometimes reached ∼100 s. The amplitude versus time shape of the pulsations was often triangular or zigzag-like, hence the term “zigzag effect.” Variations in the envelope shape were usually in the direction of faster development than recovery. Episodes of zigzag activity at Siple, Antarctica (L ∼4.3), and Saskatoon, Canada (L ∼4.2), were found to occur widely during the predawn hours and were not observed during geomagnetically quiet periods. The fluctuations appeared to be caused by ionospheric perturbations at the ∼ 85 km nighttime VLF reflection height in regions poleward of the plasmapause. We infer that in the case of the Saskatoon and Siple data, the perturbations were centered within ∼500 km of the stations and within ∼ 100–200 km of the affected signal paths. Their horizontal extent is inferred to have been in the range ∼50–200 km. The assembled evidence, supported by Corcuffs [1996] recent research at Kerguelen (L ∼3.7), suggests that the underlying cause of the effect was pulsating auroral precipitation. The means by which that precipitation produces ionospheric perturbations at 85 km is not yet clear. Candidate mechanisms include (1) acoustic waves that propagate downward from precipitation regions above the ∼ 85 km VLF reflection level; (2) quasi-static perturbation electric fields that give rise to E×B drifts of the bottomside ionosphere; (3) secondary ionization production and subsequent decay at or below 85 km. Those zigzag fluctuations exhibiting notably faster development than recovery probably originated in secondary ionization produced near 85 km by the more energetic (E >40 keV) electrons in the incident electron spectrum
The QCD heavy-quark potential to order v^2: one loop matching conditions
The one-loop QCD heavy quark potential is computed to order v^2 in the color
singlet and octet channels. Several errors in the previous literature are
corrected. To be consistent with the velocity power counting, the full
dependence on |p' + p|/|p' - p| is kept. The matching conditions for the NRQCD
one-loop potential are computed by comparing the QCD calculation with that in
the effective theory. The graphs in the effective theory are also compared to
terms from the hard, soft, potential, and ultrasoft regimes in the threshold
expansion. The issue of off-shell versus on-shell matching and gauge dependence
is discussed in detail for the 1/(m k) term in the potential. Matching on-shell
gives a 1/(m k) potential that is gauge independent and does not vanish for
QED.Comment: 28 pages, References added and minor changes to section III, results
unchange
Effect of Postharvest Storage and Ripening of Apples on the Sensory Quality of Processed Applesauce
The Residential School Feature at Swedish Folk High Schools: A Matter of Education and Leisure
Identification of Oxidative Stress-Induced Tyrosine Phosphorylated Proteins by Immunoprecipitation and Mass Spectrometry
High Temporal and Spectral Resolution Interferometric Observations of Unusual Solar Radio Bursts
We report very high temporal and spectral resolution interferometric observations
of some unusual solar radio bursts near 1420 MHz. These bursts were observed on 13
September 2005, 22 minutes after the peak of a GOES class X flare from the NOAA
region 10808. Our observations show 11 episodes of narrow-band intermittent emission
within a span of ≈8 s. Each episode shows a heavily frequency-modulated band of emission
with a spectral slope of about −245.5 MHz s−1 [s superscript -1], comprising up to 8 individual blobs of
emission and lasts for 10–15 ms. The blobs themselves have a spectral slope of ≈ 0 MHz
s−1 [s superscript -1], are ≈200–250 kHz wide, appear every ≈400 kHz and last for ≈ 4–5 ms. These
bursts show a brightness temperatures in the range 1012 [10 superscript 12] K, which suggests a coherent
emission mechanism. We believe these are the first high temporal and spectral resolution
interferometric observations of such rapid and narrow bandwidth solar bursts close to 1420
MHz and present an analysis of their temporal and spectral characteristics.National Science Foundation (U.S.). Research Experience for Undergraduates (Program) (Grant AST-0138506