656 research outputs found
Improved estimates of rare K decay matrix-elements from Kl3 decays
The estimation of rare K decay matrix-elements from Kl3 experimental data is
extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at
NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative
corrections are now accounted for. The analysis relies mainly on the cleanness
of two specific ratios of form-factors, for which the theoretical control is
excellent. As a result, the uncertainties on the K+ --> pi+ nu nubar and KL -->
pi0 nu nubar matrix-elements are reduced by a factor of about 7 and 4,
respectively, and similarly for the direct CP-violating contribution to KL -->
pi0 l+ l-. They could be reduced even further with better experimental data for
the Kl3 slopes and the K+l3 branching ratios. As a result, the non-parametric
errors for B(K --> pi nu nubar) and for the direct CP-violating contributions
to B(KL --> pi0 l+ l-) are now completely dominated by those on the
short-distance physics.Comment: 16 pages, 1 figure. Numerical analysis updated to include the recent
Kl3 data. To appear in Phys. Rev.
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
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
Eddy-current inspection of shuttle heat exchanger tube welds
The goal of this project was to develop the system necessary to demonstrate in the laboratory that an eddy current system can inspect the tubes and welds described, screening for the existence of flaws equal in size to, or larger than, the target flaw. The laboratory system was to include the probe necessary to traverse the tubing, the electronics to drive (i.e., electrically excite) the probe and receive and process signals from it, a data display, data recording, and playback devices, and microprocessor software or firmware necessary to operate the system
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
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
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
- …