476 research outputs found
A study of 60 Gigahertz intersatellite link applications
Applications of intersatellite links operating at 60 GHz are reviewed. Likely scenarios, ranging from transmission of moderate and high data rates over long distances to low data rates over short distances are examined. A limited parametric tradeoff is performed with system variables such as radiofrequency power, receiver noise temperature, link distance, data rate, and antenna size. Present status is discussed and projections are given for both electron tube and solid state transmitter technologies. Monolithic transmit and receive module technology, already under development at 20 to 30 GHz, is reviewed and its extension to 60 GHz, and possible applicability is discussed
Electroweak Radiative Corrections to Muon Capture
Electroweak radiative corrections to muon capture on nuclei are computed and
found to be sizable. They enhance the capture rates for hydrogen and helium by
2.8% and 3.0% respectively. As a result, the value of the induced pseudoscalar
coupling, g_P^exp, extracted from a recent hydrogen 1S singlet capture
experiment is increased by about 21% to g_P^exp = 7.3 +/- 1.2 and brought into
good agreement with the prediction of chiral perturbation theory,
g_P^theory=8.2 +/- 0.2. Implications for helium capture rate predictions are
also discussed.Comment: 6 page
Pattern formation in leaves via small RNA mobility
Small RNAs, including microRNAs (miRNAs) and trans-acting short interfering RNAs (ta-siRNAs), have important regulatory roles in development. In plants, members of these classes of small RNAs act to pattern the adaxial–abaxial (dorsal–ventral) axis of leaves. The AUXIN-RESPONSE FACTOR (ARF) family members ARF3 and ARF4 are together necessary to establish abaxial (ventral) fate in leaves. ARF3 and ARF4 are targets of ta-siRNAs that are termed “tasiR-ARFs.” To begin to understand the possible role of tasiR-ARFs in leaf polarity, we have localized the biogenesis components of the tasiR-ARF pathway, including the microRNA miR390, the activity of the ARGONAUTE gene required for miR390 activity (AGO7), and the activity of tasiR-ARFs themselves. We provide evidence that the tasiR-ARF pathway in Arabidopsis acts non-cell autonomously to maintain the polarized accumulation of ARF3 in leaf primordia. Small RNAs (both miR390 and tasiR-ARFs) in this specialized RNAi pathway may contribute to its non-cell autonomous activity, as they accumulate outside their discrete regions of biogenesis. We propose that small RNAs can possibly function as mobile inductive signals to direct patterning events during developmen
Effect of Flow on Caloric Curve for Finite Nuclei
In a finite temperature Thomas-Fermi theory, we construct caloric curves for
finite nuclei enclosed in a freeze-out volume few times the normal nuclear
volume, with and without inclusion of flow. Without flow, the caloric curve
indicates a smooth liquid-gas phase transition whereas with flow, the
transition may be very sharp. We discuss these results in the context of two
recent experiments, one for heavy symmetric system (Au + Au at 600A MeV) and
the other for highly asymmetric system (Au + C at 1A GeV) where different
behaviours in the caloric curves are seen.Comment: 11 pages revtex; 4 figs; version to appear in Phys. Rev. Let
Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling
The rate of nuclear muon capture by the proton has been measured using a new
experimental technique based on a time projection chamber operating in
ultra-clean, deuterium-depleted hydrogen gas at 1 MPa pressure. The capture
rate was obtained from the difference between the measured
disappearance rate in hydrogen and the world average for the decay
rate. The target's low gas density of 1% compared to liquid hydrogen is key to
avoiding uncertainties that arise from the formation of muonic molecules. The
capture rate from the hyperfine singlet ground state of the atom is
measured to be , from which the induced
pseudoscalar coupling of the nucleon, , is
extracted. This result is consistent with theoretical predictions for
that are based on the approximate chiral symmetry of QCD.Comment: submitted to Phys.Rev.Let
Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant to Part-per-Million Precision
We report a measurement of the positive muon lifetime to a precision of 1.0
parts per million (ppm); it is the most precise particle lifetime ever
measured. The experiment used a time-structured, low-energy muon beam and a
segmented plastic scintillator array to record more than 2 x 10^{12} decays.
Two different stopping target configurations were employed in independent
data-taking periods. The combined results give tau_{mu^+}(MuLan) =
2196980.3(2.2) ps, more than 15 times as precise as any previous experiment.
The muon lifetime gives the most precise value for the Fermi constant:
G_F(MuLan) = 1.1663788 (7) x 10^-5 GeV^-2 (0.6 ppm). It is also used to extract
the mu^-p singlet capture rate, which determines the proton's weak induced
pseudoscalar coupling g_P.Comment: Accepted for publication in Phys. Rev. Let
Are the 2005 Dietary Guidelines for Americans Associated With Reduced Risk of Type 2 Diabetes and Cardiometabolic Risk Factors?: Twenty-year findings from the CARDIA study
OBJECTIVE To examine the prospective association between accordance with the 2005 Dietary Guidelines for Americans (DGA) and subsequent diabetes incidence and changes in cardiometabolic risk factors
Caloric curve in Au + Au collisions
Realistic caloric curves are obtained for reaction with
incident energy ranging from 35 to 130 MeV/nucleon in the dynamic statistical
multifragmentation model. It is shown that for excitation energy 3 to 8
MeV/nucleon, the temperature remains constant in the range 5 to 6 MeV, which is
close to experiment. The mechanism of energy deposition through the
tripartition of colliding system envisaged in this model together with
inter-fragment nuclear interaction are found to play important role. A possible
signature of liquid-gas phase transition is seen in the specific heat
distribution calculated from these caloric curves, and the critical temperature
is found to be 6 to 6.5 MeV.Comment: Revtex, 10 pages, 4 postscipt figures, To appear in Phys. Rev. C
(Rapid Communications
Improved Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant
The mean life of the positive muon has been measured to a precision of 11 ppm
using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which
was surrounded by a scintillator detector array. The result, tau_mu =
2.197013(24) us, is in excellent agreement with the previous world average. The
new world average tau_mu = 2.197019(21) us determines the Fermi constant G_F =
1.166371(6) x 10^-5 GeV^-2 (5 ppm). Additionally, the precision measurement of
the positive muon lifetime is needed to determine the nucleon pseudoscalar
coupling g_P.Comment: As published version (PRL, July 2007
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