[en] We present a search for a narrow resonance in the t(bar b) mass spectrum using 1.9 fb^-1 of p(bar p) collisions at √s = 1.96 TeV recorded with the CDF II detector at the Fermilab Tevatron. We select events with a lepton, neutrino candidate, and two or three jets from which to construct the t(bar b) mass. We quantify the result using the model of a massive Standard Model-like charged-boson (W(prime)) decaying to t(bar b), but we are generally sensitive to the presence of any narrow state decaying to the third generation. For a purely right-handed W(prime) with Standard Model couplings, we set a new limit at 95% confidence of σ(p(bar p) → W(prime)_R) x BR(W(prime)_R → t(bar b)) < 0.28 pb and M_W#prime#_#sub R# > 800 GeV/c². The limit increases to M_W#prime#_#sub R# > 825 GeV/c² if decay to right-handed neutrinos is forbidden. These results are shown in Table 7 and plotted in Figure 7.1. The best prior search found M_W#prime# (ge) 768 GeV/c² if leptonic decays are forbidden (16). For a simple W(prime) model with effective coupling g_W#prime#, the cross-section is proportional to g_W#prime#⁴. Relaxing the assumption of the universal weak coupling (g_W#prime# = g_W), our cross-section limits can be rewritten as upper limits on g_W#prime#, as a function of M_W#prime#. This is relevant to both the right-handed W(prime) model as well as a left-handed W(prime) model in which the W(prime)_L-W interference is negligible. The excluded region of the g_W#prime#-M_W#prime# plane is shown in Figure 7.2, with g_W#prime# in units of g_W. At M_W#prime# = 300 GeV/c², we limit (95% C.L.) the effective coupling to be less than 0.40 of the standard weak coupling

[en] DC high voltage GaAs photoguns are key components at accelerator facilities worldwide. New experiments and new accelerator facilities demand improved performance from these guns, in particular higher current operation and longer photocathode operating lifetime. This conference submission explores bulk GaAs photocathode lifetime as a function of beam current, active photocathode area, laser spot size and the vacuum of the gun and beam line. Lifetime measurements were made at 100 microamps, a beam current relevant for accelerators like CEBAF, and at beam currents of 1 milliamps and 5 milliamps, a regime that is interesting for high current Free Electron Laser (FEL) and Energy Recovery Linac (ERL) operation

[en] A new GaAs DC high voltage load lock photogun has been constructed at Jefferson Laboratory (JLab), with improved vacuum and photocathode preparation capabilities. As reported previously, this gun was used to study photocathode lifetime with bulk GaAs at DC beam currents between 1 and 10 mA. In this submission, lifetime measurements were performed using high polarization strained-superlattice GaAs photocathode material at beam currents up to 1 mA, with near bandgap light from a fiber based drive laser having picosecond optical pulses and RF time structure

[en] A nondestructive test method for detecting chlorides in concrete has been developed based on prompt gamma neutron activation (PGNA). Its performance has been modeled using a hybrid MCNP/optical ray tracing approach. Since the chlorides often come from de-icing salts applied to the concrete surface, the Cl concentration has a non-linear depth profile which is typically modeled by the erfc function. The signals from this distribution have been simulated for several significant Cl capture peaks to estimate the erfc function parameters.

[en] In this work, the MCNP code was used to perform Monte Carlo simulations of the operation of a portable prompt gamma neutron activation (PGNA) system for chloride detection in reinforced concrete. The system consists of a moderated ²⁵²Cf neutron source, a high purity germanium (HPGe) gamma ray detector and a portable multichannel analyzer. The system maximum weight is 23 kg with a largest dimension of 31 cm. The simulations utilized a hybrid approach, which consisted of using MCNP simulations to model neutron transport and ray tracing for gamma ray transport, which considerably reduces computation time in comparison to a fully coupled neutron/photon Monte Carlo simulations. The simulations have shown that the current moderator design effectively thermalizes the neutron energy spectrum. At low to moderate chloride concentrations, the hybrid simulation model of the PGNA chloride detector shows very good agreement with experimental data. The MCNP computations predicted that for a standard error of 10% in counting statistics, the detection of a 2000 ppm chloride concentration (the corrosion threshold) in reinforced concrete can be achieved in a seven minute counting period. This represents a significant improvement over the current standard destructive method of measuring chlorides in concrete. Over the range of water to cement (w/c) ratios normally found in concrete mixes (0.38-0.55), the chloride signal strength shows very little variation especially at the lower chloride concentrations. Thus for all practical purposes the chloride signal remains insensitive to the w/c ratio. Similarly, the chloride signal strength does not vary significantly if limestone coarse or fine aggregate is used in place of quartz

No abstract available

[en] Full text: The chloride ion is an important promoter of the corrosion of iron reinforcements in concrete. A nondestructive test method for chloride has been developed based on Prompt Gamma Neutron Activation (PGNA). In previous work (Mohamed et al., 2008) the performance of this system was modeled using a hybrid MCNP/optical ray tracing approach to calculate the 6.111 MeV signal which represents the integral over the sample volume of approximately 100,000. These simulations assumed a spatially uniform Cl distribution, which is typical of the case where set accelerators have been added to the concrete mix water. However, much more often the chlorides come from de-icing salts applied to the concrete surface, which then leads to a non-uniform distribution that changes over time. The Cl concentration has a nonlinear depth profile which is typically modeled as a Fick's Law diffusion gradient using the erfc function. The integrated signal can then become ambiguous since different combinations of surface concentrations and diffusion times can produce the same integral value. However, in addition to the 6.110 MeV peak, there are a number of other significant Cl peaks e.g. 0.788, 1.164, 1.95, 2.863 and 5.715 MeV. They have different attenuation coefficients but higher detection efficiencies. The result is an array of different integral values for the same Cl profile. This can be inverted to yield the Cl profile. This can be used to estimate remaining time to reach hazardous concentrations at the rebar

[en] Purpose: To determine how frequently (1) tumor motion and (2) the spatial relationship between tumor and respiratory surrogate markers change during a treatment fraction in lung and pancreas cancer patients. Methods and Materials: A Cyberknife Synchrony system radiographically localized the tumor and simultaneously tracked three respiratory surrogate markers fixed to a form-fitting vest. Data in 55 lung and 29 pancreas fractions were divided into successive 10-min blocks. Mean tumor positions and tumor position distributions were compared across 10-min blocks of data. Treatment margins were calculated from both 10 and 30 min of data. Partial least squares (PLS) regression models of tumor positions as a function of external surrogate marker positions were created from the first 10 min of data in each fraction; the incidence of significant PLS model degradation was used to assess changes in the spatial relationship between tumors and surrogate markers. Results: The absolute change in mean tumor position from first to third 10-min blocks was >5 mm in 13% and 7% of lung and pancreas cases, respectively. Superior–inferior and medial–lateral differences in mean tumor position were significantly associated with the lobe of lung. In 61% and 54% of lung and pancreas fractions, respectively, margins calculated from 30 min of data were larger than margins calculated from 10 min of data. The change in treatment margin magnitude for superior–inferior motion was >1 mm in 42% of lung and 45% of pancreas fractions. Significantly increasing tumor position prediction model error (mean ± standard deviation rates of change of 1.6 ± 2.5 mm per 10 min) over 30 min indicated tumor–surrogate relationship changes in 63% of fractions. Conclusions: Both tumor motion and the relationship between tumor and respiratory surrogate displacements change in most treatment fractions for patient in-room time of 30 min.

[en] This paper introduces a catalog of gravitational waveforms from the bank of simulations by the numerical relativity effort at Georgia Tech. Currently, the catalog consists of 452 distinct waveforms from more than 600 binary black hole simulations: 128 of the waveforms are from binaries with black hole spins aligned with the orbital angular momentum, and 324 are from precessing binary black hole systems. The waveforms from binaries with non-spinning black holes have mass-ratios q  =  m ₁/ m ₂ ≤ 15, and those with precessing, spinning black holes have q  ≤ 8. The waveforms expand a moderate number of orbits in the late inspiral, the burst during coalescence, and the ring-down of the final black hole. Examples of waveforms in the catalog matched against the widely used approximate models are presented. In addition, predictions of the mass and spin of the final black hole by phenomenological fits are tested against the results from the simulation bank. The role of the catalog in interpreting the GW150914 event and future massive binary black-hole search in LIGO is discussed. The Georgia Tech catalog is publicly available at einstein.gatech.edu/catalog. (paper)

[en] As part of its commitments to the Regional Greenhouse Gas Initiative (RGGI), the State of Maryland, USA, auctions emission permits to electric utilities, creating revenue that can be used to benefit consumers and the environment. This paper explores the CO₂ emissions reductions that may be possible by allocating some of that revenue to foster efficiency improvements in the residential sector's use of natural gas. Since these improvements will require changes to the capital stock of houses and end use equipment, efficiency improvements may be accompanied by economic and ancillary health impacts, both of which are quantified in this paper.