Kevin Grizzard | Yale University School of Medicine (original) (raw)

Papers by Kevin Grizzard

Journal of Applied Clinical Medical Physics, 2022

This study presents a methodology to develop an X-ray technique chart for portable chest and abdo... more This study presents a methodology to develop an X-ray technique chart for portable chest and abdomen imaging which utilizes patient data available in the modality worklist (MWL) to reliably achieve a predetermined exposure index (EI) at the detector for any patient size. The method assumes a correlation between the patients' tissue equivalent thickness and the square root of the ratio of the patient's weight to height. To assess variability in detector exposures, the EI statistics for 75 chest examinations and 99 abdominal portable X-ray images acquired with the new technique chart were compared to those from a single portable unit (chest: 3877 images; abdomen: 200 images) using a conventional technique chart with three patient sizes, and to a stationary radiography room utilizing automatic exposure control (AEC) (chest: 360 images; abdomen: 112 images). The results showed that when using the new technique chart on a group of portable units, the variability in EI was significantly reduced (p < 0.01) for both AP chest and AP abdomen images compared to the single portable using a standard technique chart with three patient sizes. The variability in EI for the images acquired with the new chart was comparable to the stationary X-ray room with an AEC system (p > 0.05). This method could be used to streamline the entire imaging chain by automatically selecting an X-ray technique based on patient demographic information contained in the MWL to provide higher quality examinations to clinicians by eliminating outliers. In addition, patient height and weight can be used to estimate the patients' tissue equivalent thickness.

X-ray line pro¯le analysis has proved to be the most direct diagnostic of the kine-matics and spa... more X-ray line pro¯le analysis has proved to be the most direct diagnostic of the kine-matics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line pro¯les provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line pro¯le provides in-formation about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper we apply several analysis techniques to the emission lines in the Chandra HETGS spectrum of the late-O supergiant Ori (O9.7 Ib), including the ¯tting of a simple line-pro¯le model. We show that there is distinct evidence for blue shifts and pro¯le asymmetry, as well as broadening in the X-ray emission lines of Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for Ori are very similar to those for the earlier O star, Pup, which we have previously shown to be well-¯t by the same wind-shock line...

X-ray line pro¯le analysis has proved to be the most direct diagnostic of the kinematics and spat... more X-ray line pro¯le analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line pro¯les provide information about the velocity distribu-tion of the hot plasma, while the wavelength-dependent attenuation across a line pro¯le provides information about the absorption to the hot plasma, thus pro-viding a strong constraint on its physical location. In this paper we apply several analysis techniques to the emission lines in the Chandra HETGS spectrum of the late-O supergiant Ori (O9.7 Ib), including the ¯tting of a simple line-pro¯le model. We show that there is distinct evidence for blue shifts and pro¯le asym-metry, as well as broadening in the X-ray emission lines of Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for Ori are very similar to those for the earlier O star, Pup, which we have previously shown to be well-¯t by the same wind-shock lin...

In this article we propose a new strategy to address the Little Hierarchy problem. We show that t... more In this article we propose a new strategy to address the Little Hierarchy problem. We show that the addition of a fourth generation with vector-like quarks to the minimal supersymmetric standard model (MSSM) can raise the predicted value of the physical Higgs mass by mixing with the top sector. The mixing requires a larger top quark Yukawa coupling (by up to ∼ 6 %) to produce the same top mass. Since loop corrections to mh go as ytop4, this will in turn increase the predicted value of the physical Higgs mass, a point not previously emphasized in the literature. In the presence of mixing, for A-terms and soft masses around 900 GeV, a Higgs mass of 125 GeV can be generated while retaining perturbativity of the gauge couplings, evading constraints from electroweak precision measurements (EWPM) and recent LHC searches, and pushing the Landau pole for the top Yukawa above the GUT scale. Soft masses can be as low as 800 GeV in parts of parameter space with a Landau pole at ∼ 1010 GeV. However, the Landau pole can still be pushed above the GUT scale if one sacrifices perturbative unification by adding fields in a 5+5 representation. With a ratio of weak-scale vector masses ≠ 1, soft masses may be slightly below 800 GeV. The model predicts new quarks and squarks with masses \gtrapprox 750 GeV. We briefly discuss potential paths for discovery or exclusion at the LHC.

A multivariate likelihood method to measure electroweak couplings with the Drell-Yan process at t... more A multivariate likelihood method to measure electroweak couplings with the Drell-Yan process at the LHC is presented. The process is described by the dilepton rapidity, invariant mass, and decay angle distributions. The decay angle ambiguity due to the unknown assignment of the scattered constituent quark and antiquark to the two protons in a collision is resolved statistically using correlations between the observables. The method is applied to a sample of dimuon events from proton-proton collisions at √ s = 7 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 1.1 fb −1 . From the dominant uu, dd → γ * /Z → µ − µ + process, the effective weak mixing angle parameter is measured to be sin 2 θ eff = 0.2287 ± 0.0020 (stat.) ± 0.0025 (syst.) . This result is consistent with measurements from other processes, as expected within the standard model.

X-ray line profile analysis has proved to be the most direct diagnostic of the kinematics and spa... more X-ray line profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Dopplerbroadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper we apply several analysis techniques to the emission lines in the Chandra HETGS spectrum of the late-O supergiant ζ Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blue shifts and profile asymmetry, as well as broadening in the X-ray emission lines of ζ Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for ζ Ori are very similar to those for the earlier O star, ζ Pup, which we have previously shown to be well-fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in ζ Ori, as compared to ζ Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both ζ Ori and ζ Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from ζ Ori can be understood within the framework of the standard wind-shock scenario for hot stars.

$Research paper thumbnail of Wind signatures in the X-ray emission line profiles of the late O supergiant <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>ζ</mi></mrow><annotation encoding="application/x-tex">\zeta</annotation></semantics></math>ζ Orionis$

Monthly Notices of The Royal Astronomical Society, 2006

X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spa... more X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelengthdependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper, we apply several analysis techniques to the emission lines in the Chandra High Energy Transmission Grating Spectrometer (HETGS) spectrum of the late-O supergiant ζ Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blueshifts and profile asymmetry, as well as broadening in the X-ray emission lines of ζ Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for ζ Ori are very similar to those for the earlier O star, ζ Pup, which we have previously shown to be well fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in ζ Ori, as compared to ζ Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both ζ Ori and ζ Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from ζ Ori can be understood within the framework of the standard wind-shock scenario for hot stars.

Monthly Notices of The Royal Astronomical Society, 2006

X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spa... more X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper, we apply several analysis techniques to the emission lines in the Chandra High Energy Transmission Grating Spectrometer (HETGS) spectrum of the late-O supergiant ζ Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blueshifts and profile asymmetry, as well as broadening in the X-ray emission lines of ζ Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for ζ Ori are very similar to those for the earlier O star, ζ Pup, which we have previously shown to be well fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in ζ Ori, as compared to ζ Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both ζ Ori and ζ Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from ζ Ori can be understood within the framework of the standard wind-shock scenario for hot stars.

The profiles of X-ray emission lines from several hot stars are resolved by the Chandra grating s... more The profiles of X-ray emission lines from several hot stars are resolved by the Chandra grating spectrometers. These profile shapes provide information about the kinematics of the hot plasma around these stars and, via signatures of continuum attenuation, also provide information about the overlying cold stellar wind. We present a quantitative analysis of roughly one dozen emission lines in the Chandra HETGS spectrum of zeta Ori (O 9.7 Ib), and analyze the results in the context of the line-force instability shock model. The distribution in velocity space of the emission, along with the separate helium-like line ratio results, are consistent with the wind-shock scenario. But, although there is statistically significant evidence for some wind attenuation, the degree of wind attenuation is a factor of five to ten less than what would be expected in the context of a smooth, spherically symmetric wind and the UV-derived wind mass-loss rate. These results are consistent with those derived from the X-ray emission line profiles of the hotter O star, zeta Pup, and also with recent, independent evidence from UV spectroscopy, that O star mass-loss rates have been overestimated. We acknowledge support from NASA contract NAS8-03060 and from the National Science Foundation, through their REU program at the Keck Northeast Astronomy Consortium, via contract AST-0353997.

Journal of Applied Clinical Medical Physics, 2022

Monthly Notices of The Royal Astronomical Society, 2006

X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spa... more X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper, we apply several analysis techniques to the emission lines in the Chandra High Energy Transmission Grating Spectrometer (HETGS) spectrum of the late-O supergiant ζ Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blueshifts and profile asymmetry, as well as broadening in the X-ray emission lines of ζ Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for ζ Ori are very similar to those for the earlier O star, ζ Pup, which we have previously shown to be well fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in ζ Ori, as compared to ζ Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both ζ Ori and ζ Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from ζ Ori can be understood within the framework of the standard wind-shock scenario for hot stars.