Fraction Of Decay Research Articles

Fluorometric Measurements of Intermolecular Distances between the α- and β-Subunits of the Na+/K+-ATPase

The Na+/K+-ATPase maintains the physiological Na+ and K+ gradients across the plasma membrane in most animal cells. The functional unit of the ion pump is comprised of two mandatory subunits including the alpha-subunit, which mediates ATP hydrolysis and ion translocation, as well as the beta-subunit, which acts as a chaperone to promote proper membrane insertion and trafficking in the plasma membrane. To examine the conformational dynamics between the alpha- and beta-subunits of the Na+/K+-ATPase during ion transport, we have used fluorescence resonance energy transfer, under voltage clamp conditions on Xenopus laevis oocytes, to differentiate between two models that have been proposed for the relative orientation of the alpha- and beta-subunits. These experiments were performed by measuring the time constant of irreversible donor fluorophore destruction with fluorescein-5-maleimide as the donor fluorophore and in the presence or absence of tetramethylrhodamine-6-maleimide as the acceptor fluorophore following labeling on the M3-M4 or M5-M6 loop of the alpha-subunit and the beta-subunit. We have also used fluorescence resonance energy transfer to investigate the relative movement between the two subunits as the ion pump shuttles between the two main conformational states (E1 and E2) as described by the Albers-Post scheme. The results from this study have identified a model for the orientation of the beta-subunit in relation to the alpha-subunit and suggest that the alpha- and beta-subunits move toward each other during the E2 to E1 conformational transition.

Enhancement of HadronicbQuark Decays

A class of previously unknown strong-interaction corrections is found to enhance the rate of nonleptonic decays of the quark by 5%-8%. This effect decreases the predicted fraction of semileptonic decays and brings it into fair agreement with experimental results. As well as solving a long-standing puzzle of measurements disagreeing with the standard model prediction, our work suggests a way for future precise studies of nonleptonic quark decays and their application to searching for "new physics."

Three-dimensional positron emission tomography imaging with 124I and 86Y

Impure positron emitters have physical characteristics that degrade image quality compared to conventional positron emitters like 18F. Two impure positron emitters with potentially interesting applications are 124I and 86Y. The degradation in image quality due to the imperfection of these isotopes is quantified for a human three-dimensional (3-D) positron emission tomography (PET) system. An acquisition protocol to obtain similar image quality as for 18F imaging is determined by Monte Carlo simulations. The effects of larger positron range, associated singles and the other decay modes on image quality are determined by extensive Monte Carlo simulations of the Allegro scanner. Spatial resolution was evaluated for both isotopes and compared to spatial resolution of 18F. The loss in sensitivity due to triple coincidences was determined as a function of the axial acceptance angle of the PET scanner. The performance of the scanner at low count rates was studied by determining the noise equivalent count (NEC) values for different upper energy thresholds. The image degrading effect of spurious coincidences is taken into account by adding another factor to the NEC calculation. This allowed the contribution of spurious coincidences to be minimized by using a setting for the appropriate energy window. For this optimal energy window the amount of spurious and scattered coincidences was quantified. Simulations of count rate performance were also done to determine the peak NEC and the activity at which the maximum occurred. Spatial resolution degradation, compared to 18F, is about 0.5 mm for 86Y and 1 mm for 124I. Associated singles have a similar effect as scattered coincidences, as they also add a background to the image. The effect, however, is less important than the effect of scatter. The fraction of triple coincidences is quite small for a 3-D PET scanner used for humans as the axial acceptance angle is still moderate. For the Allegro with an energy resolution of 18% the optimal upper energy threshold was determined at 600 keV. For 124I this leads to 2.5% extra contamination that needs to be added to the scatter fraction. For 86Y this fraction is about 5.5%. 3-D PET images of 124I and 86Y have lower spatial resolution. For PET scanners used for humans the difference is not as important as for scanners used for animals. The limited positron decay fraction of both isotopes can be compensated by increasing the imaging time by a factor of 3-5 (same activity). A short coincidence window limits the contamination from other decay modes. Good energy resolution allows setting a selective upper energy threshold to limit the effect of spurious coincidences. With an appropriate setting of the energy window it should be possible to obtain good image quality in a relatively short time because of the high sensitivity of 3-D PET scanners.

CosmogenicC11production and sensitivity of organic scintillator detectors topepand CNO neutrinos

Several possible background sources determine the detectability of pep and CNO solar neutrinos in organic liquid scintillator detectors. Among such sources, the cosmogenic 11C nuclide plays a central role. 11C is produced underground in reactions induced by the residual cosmic muon flux. Experimental data available for the effective cross section for 11C by muons indicate that 11C will be the dominant source of background for the observation of pep and CNO neutrinos. 11C decays are expected to total a rate 2.5 (20) times higher than the combined rate of pep and CNO neutrinos in Borexino (KamLAND) in the energy window preferred for the pep measurement, between 0.8 and 1.3 MeV. This study examines the production mechanism of 11C by muon-induced showers in organic liquid scintillators with a novel approach: for the first time, we perform a detailed ab initio calculation of the production of a cosmogenic nuclide, 11C, taking into consideration all relevant production channels. Results of the calculation are compared with the effective cross sections measured by target experiments in muon beams. This paper also discusses a technique for reduction of background from 11C in organic liquid scintillator detectors, which allows to identify on a one-by-one basis and remove from the data set a large fraction of 11C decays. The background reduction technique hinges on an idea proposed by Martin Deutsch, who suggested that a neutron must be ejected in every interaction producing a 11C nuclide from 12C. 11C events are tagged by a three-fold coincidence with the parent muon track and the subsequent neutron capture on protons.

Study of the ρ and ω meson decays into a pseudoscalar meson and [formula omitted] pair with the CMD-2 detector

Using 3.3 pb−1 of data collected with the CMD-2 detector in the 720–840 MeV c.m. energy range, the branching fraction of the conversion decay ω→π0e+e− has been measured: B(ω→π0e+e−)=(8.19±0.71±0.62)×10−4. The upper limits for the branching fractions of the following conversion decays have been obtained at the 90% confidence level: B(ρ→π0e+e−)<1.6×10−5, B(ρ→ηe+e−)<0.7×10−5 and B(ω→ηe+e−)<1.1×10−5.

A study of kinetic modelling and reaction pathway of 2,4-dichlorophenol transformation by photo-fenton-like oxidation

The degradation of 2,4-dichlorophenol (2,4-DCP) by the photo-Fenton-like (Fe 3+/H 2O 2/UVC) process under various reaction conditions was investigated. It was interesting to find that the reaction kinetics of 2,4-DCP in Fe 3+/H 2O 2/UVC systems varied depending on the initial [Fe 3+] concentration. A pseudo first-order kinetic and a non-conventional kinetic were discovered at low and higher [Fe 3+] concentrations, respectively. A model was used to simulate the non-conventional kinetic process, where two character parameters (the initial decay rate and the final decay fraction) were found to be critical in determining the process. The two parameters successfully quantify the photo-Fenton-like oxidation under different concentrations of [Fe 3+] and [H 2O 2] and the corresponding ratios of Fe(III)/H 2O 2. The reaction intermediates were identified by an LC/MS analysis and a reaction mechanism was proposed.

Spectral characterization of local magnetic field inhomogeneities

The purpose of this study was the characterization of local magnetic susceptibility deviations by spectral analysis of their induced magnetic field inhomogeneities. Magnetic resonance spectra and related signal decay curves of local susceptibility deviations were simulated for different volume fractions and compositions of the object within the VOI. The size or composition of the object was varied at constant volume fraction, constant object size, or at constant ‘magnetic strength’ (defined as the product of the volume and the volume susceptibility of the object). Experimental spectra were acquired for individual metal spherical particles and a spherical air cavity. Where possible, spectra were used to characterize objects in terms of volume and composition. By simulations, a numerical relation was determined between the spectral broadening and the object's volume and composition. Comparison of spectra for various spherical objects showed the possibility of characterization with respect to size and composition. Experimental results confirmed the numerical results to a large extent, although the characterization was compromised by background signal decay, low volume fractions and limitations in signal-to-noise. In conclusion, spectral description of the field inhomogeneities related to small objects allows characterization of such objects with respect to size and composition. Practical applicability of the simulation results depends on background signal decay and volume fraction of the object.

Geochemical test for branching decay of 176Lu

Two different groups of values for the 176Lu decay constant have been determined by recent high-precision experiments. The λ 176Lu values of 1.86–1.87 × 10 −11 a −1 were determined by age comparisons using terrestrial minerals of Proterozoic and late Archean age, whereas values of ∼1.94 × 10 −11 a −1 were determined in age comparison studies of meteorites. A possible branched decay of 176Lu could be the cause of this discrepancy. The β + decay of 176Lu to 176Yb was detected in the early studies of radioactivity of 176Lu, with reported values of λβ +/(λβ + + λβ −) in the total 176Lu ranging from less than 0.03 to 0.67. If the β + decay fraction is close to the upper limit of the reported values, it can explain the 4%–6% difference between the apparent λ 176Lu values. To get a reliable estimate for the β + decay of 176Lu, we have measured Yb isotopic composition in 2.7 Ga zircons with Lu/Yb N (chondrite-normalized) ratios of 1.40 and 1.45, in 1.0 Ga xenotime with Lu/Yb N = 1.23, using Yb from the 28.4 Ma Fish Canyon Tuff (FCT) zircon and titanite as the modern reference value. Multiple analyses yielded the following weighted mean values (± 2σ) for the 176Yb/ 174Yb ratio: 0.4022134 ± 0.0000017 for the FCT zircon and titanite, 0.4022134 ± 0.0000019 for the 1.0 Ga xenotime, and 0.4022124 ± 0.0000033 for the 2.7 Ga zircons. These data yield λβ +/(λβ + + λβ −) = −0.005 ± 0.015 (2σ) and establish an upper limit of 0.9% of total decays for the β + decay branch. Branching decay can therefore be eliminated as the cause of the discrepancy in 176Lu decay constant estimates. We discuss other possible causes of the λ 176Lu terrestrial vs. meteorite discrepancy.

Charmless two-body decays

We report the latest results of a study of charmless two-body B meson decays using data recorded by the Belle experiment at KEKB. Branching fractions or upper limits are provided for the complete set of Kμ, μμ and K K final states; the B → ϱπ decays with final states ϱ 0 π +, ϱ ± π ± and ϱ 0 π 0; we also provide a first measurement of the branching fraction of the vector-vector decay B + → ϱ + ϱ 0.

Heat flux pattern on the toroidal pump limiter of Tore Supra: first observations and preliminary analysis

Tore Supra has re-started operation in 2001 with a partial toroidal pump limiter as the main plasma facing component. Assembled with actively cooled high heat flux elements, it has the shape of a toroidal ring. Thermal equilibrium is achieved within 4 s and the stabilised surface temperature is comparable to the design calculation. The observed heat flux pattern is similar to calculations realised beforehand with the heat deposition code TOKAFLU, and is dominated by the large toroidal field ripple. The power deposition is a combination of parallel convection and cross-field transport of similar magnitudes. The heat flux decay length is evaluated by three independent diagnostics to 10 mm. The excellent agreement between experiment and modelling indicates that the description of the power deposition mechanism is reasonable, although parameters such as the heat flux decay length and fraction of perpendicular power are still difficult to predict.

Optical Conductivity and Pseudo-Momentum Conservation in Anisotropic Fermi Liquids

Umklapp scattering determines the conductivity of clean metals. In typical quasi one-dimensional Fermi liquids with an open Fermi surface, certain pseudo-momenta do not decay by 2-particle collisions even in situations where Umklapp scattering relaxes the momentum of the quasi particles efficiently. Due to this approximate conservation of pseudo-momentum, a certain fraction of the electrical current decays very slowly and a well-pronounced low-frequency peak emerges in the optical conductivity. We develop simple criteria to determine under what conditions approximate pseudomomentum conservation is relevant and calculate within in Fermi liquid theory the weights of the corresponding low-frequency peaks and the temperature dependence of the various relevant decay rates. Based on these considerations, we obtain a qualitative picture of the frequency and temperature dependence of the optical conductivity of an anisotropic Fermi liquid.

The use of relative abundance patterns to discriminate among niche apportionment processes

Several different stochastic models of niche apportionment have been proposed to explain the structure of species' relative abundance patterns within communities. Here I deal with the converse issue, i.e., whether it is possible to infer past niche apportionment processes from current relative abundance patterns. Using Monte Carlo methods, I constructed relative abundance patterns for many .communities. of four to 28 species based on five common niche apportionment models (Dominance Decay, Dominance Preemption, MacArthur Fraction, Random Assortment and Random Fraction). The relative abundance patterns of these individual communities were compared by a best-fit test against those expected to emerge over many replications of the different models. The proportion of instances that the past structuring processes were correctly identified was generally quite low for four-species communities, and was inconsistent across niche apportionment models. For 28-species communities, the probability of correct model iden...

Time Variations of Natural Gamma Radiation

Measurement of terrain-emanated natural uranium gamma radiation is difficult because of the inclusion by the measuring device of radiation from the decay of atmospheric radon. This paper presents the results of a 7-year study of time variations of the components of the natural gamma radiation. Accurate measurement and removal of the atmospheric equivalent uranium (eU) decay fraction provides the terrain-emanated eU radiation. Variations in equivalent thorium (eTh), eU, and potassium-40 (40K) natural radiation have been measured over this 7-year period at one location at 5-min intervals. Atmospheric diurnal changes in the concentrations of radon gamma-emitting daughters are observed to exceed surface-emanated eU radiation by more than 400% in the absence of rainfall and up to 3000% in rainfall. Gamma radiation from rainfall-deposited thoron daughters has been seen to increase the surface-emanated eTh radiation by more than 70%. Two different field vehicles currently contain the measurement systems. Data reduction requires the use of environmentally measured gamma ray standard spectra for eTh, eU, and 40K decay and cosmic radiation, plus measurement and use of vehicular system radiation backgrounds. Using these measurement methods, gamma radiation emitted from the earth's surface can be accurately determined day or night, except during and for up to1.5 days following rainfall. Monthly variations of the components of the natural gamma radiation are presented together with daily variations for six selected months of the measurement period.

W properties and decays at LEP2

Preliminary results from W-pair events measured by the four LEP experiments are presented. These results are based on data taken during years 1996–2000 at e +e − centre-of-mass energies between 161–208 GeV and corresponding to a total integrated luminosity of 560 pb −1. A total number of about 7500 W-pair candidates per experiment is used to determine the W decay branching fractions, which are used to test lepton universality to a 1.6% accuracy level. Hadronic decays of W into charm are identified and the fraction of charm decay is 0.494±0.044, corresponding to the CKM matrix element value | V cs|=0.96±0.08. The W mass is measured to be 80.427±0.046 GeV, in agreement with other determinations of this value. The measured value of the W width is Γ W=2.12±0.11 GeV. All results agree with the Standard Model expectations.

Determination of the metastable dissociation pathways for chromium/oxygen cluster ions sputtered from potassium chromate and dichromate using the ion-neutral correlation method

Event-by-event bombardment and detection, coincidence counting, and the ion-neutral correlation method were used to study the dissociation of chromium/oxygen and chromium/oxygen/potassium cluster ions in the drift region of a reflectron time-of-flight (TOF) mass spectrometer. The cluster ions were sputtered from potassium chromate and dichromate by the impacts of 252Cf fission fragments. The dissociation channel observed for the fragmentation of negative cluster ions was the emission of CrO 3 −. The positive secondary cluster ions decayed by shedding K +. Decay fraction measurements were also performed to gain information about the relative stability to secondary ion dissociation and/or neutralization.

Secondary cluster ion emission from megaelectron volts ion impacts on NaBF 4. 1. Ion decay fractions and dissociation pathways

Megaelectron volt ion impacts, event-by-event bombardment/detection, coincidence counting and a time-of-flight (TOF) mass spectrometer equipped with an electrostatic ion mirror were used to study the emission and dissociation of secondary cluster ions sputtered from sodium tetrafluoroborate (NaBF 4). The positive and negative plasma desorption spectra produced from NaBF 4 are distinct. The negative ion spectrum contains BF 4 − and cluster ions composed of Na + and BF 4 −, with a small series of peaks corresponding to (NaF) n F −. The positive spectrum, however, is dominated by a cluster ion series with composition (NaF) n Na +, n = 0–15. Magic numbers are observed in the positive cluster ion intensity distribution, highlighting n = 4 and 7 as stable cluster compositions. The presence of magic number enhancements in the linear TOF spectrum indicates that the stable cluster compositions are generated prior to entering the drift region of the TOF analyzer (i.e. during ion formation and acceleration). Decay fraction measurements demonstrate that both positive and negative secondary cluster ions carry residual internal energy and undergo dissociation reactions in the drift region of the TOF spectrometer. Decay pathway measurements show that the preferred neutral loss, in general, for positive and negative cluster ions is (NaF) 0. In the positive ion mode, the most probable dissociation pathway for many cluster ions is the formation of a product ion with a magic number composition.

Glitches in southern pulsars

Timing observations of 40 mostly young pulsars using the ATNF Parkes radio telescope between 1990 January and 1998 December are reported. In total, 20 previously unreported glitches and ten other glitches were detected in 11 pulsars. These included 12 glitches in PSR J1341$- $6220, corresponding to a glitch rate of 1.5 glitches per year. We also detected the largest known glitch, in PSR J1614$-$5047, with $\Delta\nu_g/\nu \approx 6.5 \times 10^{-6}$ where $\nu = 1/P$ is the pulse frequency. Glitch parameters were determined both by extrapolating timing solutions to inter-glitch intervals and by phase-coherent timing fits across the glitch(es). Analysis of glitch parameters, both from this work and from previously published results, shows that most glitches have a fractional amplitude $\Delta\nu_g/\nu$ of between $10^{-8}$ and $10^{-6}$. There is no consistent relationship between glitch amplitude and the time since the previous glitch or the time to the following glitch, either for the ensemble or for individual pulsars. As previously recognised, the largest glitch activity is seen in pulsars with ages of order 10$^4$ years, but for about 30 per cent of such pulsars, no glitches were detected in the 8-year data span. There is some evidence for a new type of timing irregularity in which there is a significant increase in pulse frequency over a few days, accompanied by a decrease in the magnitude of the slowdown rate. Fits of an exponential recovery to post-glitch data show that for most older pulsars, only a small fraction of the glitch decays. In some younger pulsars, a large fraction of the glitch decays, but in others, there is very little decay.

Large acceptance 30 GeV muon storage rings for neutrino production: lattice design

Two competing goals control the lattice design of a muon storage ring for a neutrino factory [1]. One goal is achieving large transverse and longitudinal acceptances in order to minimize the degree of muon-beam cooling required. (This condition presumes large-emittance muon beams can be effectively accelerated.) The second is provision of a long insertion in which a significant fraction of the stored muons decay and produce a relatively colinear beam of neutrinos. In this work, a 30 GeV muon storage ring is presented which is optimized for acceptance and maximal neutrino-beam production.

Experimental evidence for a light and broad scalar resonance in D+-> pi-pi+pi+ decay

From a sample of 1240 ± 51 D+ <FONT FACE=Symbol>®</font> pi- pi+ pi+ we find gamma(D+ -> pi- pi+ pi+)/gamma(D+ -> K- pi+ pi+) = 0:0329 ± 0:0015 <img src="http:/img/fbpe/bjp/v30n2/10eq01.gif" border="0" align="absmiddle">. Using a coherent amplitude analysis to t the Dalitz plot of this decay, we find strong evidence that a scalar resonance of mass 483<img src="http:/img/fbpe/bjp/v30n2/10eq02.gif" border="0" align="absmiddle"> ± 17 MeV/c² and width 338<img src="http:/img/fbpe/bjp/v30n2/10eq03.gif" border="0" align="absmiddle"> ± 21 MeV/c² produces a decay fraction of approximately one half.

Search for second-generation leptoquark pairs in &pmacr;p collisions at radicals = 1.8 TeV

We have searched for second-generation leptoquark (LQ) pairs in the &mgr;&mgr;+jets channel using 94+/-5 pb(-1) of &pmacr;p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the &mgr;nu+jets and nunu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c(2) for beta = 1(1 / 2) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of beta.