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Search Results: 1 - 10 of 174915 matches for " Carl E. Johnson "
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Can CT Perfusion Guide Patient Selection for Treatment of Delayed Cerebral Ischemia?  [PDF]
Rachel Gold, Pina C. Sanelli, Nikesh Anumula, Austin Ferrone, Carl E. Johnson, Joseph P. Comunale, Apostolos J. Tsiouris, Howard Riina, Halinder Mangat, Axel Rosengart, Alan Z. Segal
Advances in Computed Tomography (ACT) , 2013, DOI: 10.4236/act.2013.21002

Purpose: To evaluate qualitative and quantitative CT perfusion (CTP) for different treatment options of delayed cerebral ischemia (DCI) in aneurysmal SAH. Methods: Retrospective study of consecutive SAH patients enrolled in a prospective IRB-approved clinical trial. Qualitative analysis of CTP deficits were determined by two blinded neuroradiologists. Quantitative CTP was performed using standardized protocol with region-of-interest placement sampling the cortex. DCI was assessed by clinical and imaging criteria. Patients were classified into treatment groups: 1) hypertension-hemodilution-hypervolemia (HHH); 2) intra-arterial (IA) vasodilators and/or angioplasty; 3) no treatment. Mean quantitative CTP values were compared using ANOVA pairwise comparisons. Receiver operating characteristic (ROC) curves, standard error (SE) and optimal threshold values were calculated. Results: Ninety-six patients were classified into three treatment groups; 21% (19/96) HHH, 34% (33/96) IA-therapy and 46% (44/96) no treatment. DCI was diagnosed in 42% (40/96); of which 18% (7/40) received HHH, 80% (32/40) IA-therapy, and 2% (1/40) no treatment. CTP deficits were seen in 50% (48/96); occurring in 63% (12/19) HHH, 94% (31/33) IA-therapy, and 11% (5/44) no treatment. Presence of CTP deficits had 83% sensitivity, 89% specificity, 90% positive predictive and 81% negative predic

Brachial Artery Constriction during Brachial Artery Reactivity Testing Predicts Major Adverse Clinical Outcomes in Women with Suspected Myocardial Ischemia: Results from the NHLBI-Sponsored Women’s Ischemia Syndrome Evaluation (WISE) Study
Tara L. Sedlak, B. Delia Johnson, Carl J. Pepine, Steven E. Reis, C. Noel Bairey Merz
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0074585
Abstract: Background Limited brachial artery (BA) flow-mediated dilation during brachial artery reactivity testing (BART) has been linked to increased cardiovascular risk. We report on the phenomenon of BA constriction (BAC) following hyperemia. Objectives To determine whether BAC predicts adverse CV outcomes and/or mortality in the women’s ischemic Syndrome Evaluation Study (WISE). Further, as a secondary objective we sought to determine the risk factors associated with BAC. Methods We performed BART on 377 women with chest pain referred for coronary angiography and followed for a median of 9.5 years. Forearm ischemia was induced with 4 minutes occlusion by a cuff placed distal to the BA and inflated to 40mm Hg > systolic pressure. BAC was defined as >4.8% artery constriction following release of the cuff. The main outcome was major adverse events (MACE) including all-cause mortality, non-fatal MI, non-fatal stroke, or hospitalization for heart failure. Results BA diameter change ranged from -20.6% to +44.9%, and 41 (11%) women experienced BAC. Obstructive CAD and traditional CAD risk factors were not predictive of BAC. Overall, 39% of women with BAC experienced MACE vs. 22% without BAC (p=0.004). In multivariate Cox proportional hazards regression, BAC was a significant independent predictor of MACE (p=0.018) when adjusting for obstructive CAD and traditional risk factors. Conclusions BAC predicts almost double the risk for major adverse events compared to patients without BAC. This risk was not accounted for by CAD or traditional risk factors. The novel risk marker of BAC requires further investigation in women.
On the Metric of Space-Time  [PDF]
Carl E. Wulfman
Journal of Modern Physics (JMP) , 2013, DOI: 10.4236/jmp.2013.411184

Maxwell’s equations are obeyed in a one-parameter group of isotropic gravity-free flat space-times whose metric depends upon the value of the group parameter. An experimental determination of this value has been proposed. If it is zero, the metric is Minkowski’s. If it is non-zero, the metric is not Poincare invariant and local frequencies of electromagnetic waves change as they propagate. If the group parameter is positive, velocity-independent red-shifts develop and the group parameter play a role similar to that of Hubble’s constant in determining the relation of these red-shifts to propagation distance. In the resulting space-times, the velocity-dependence of red shifts is a function of propagation distance. If 2c times the group parameter and Hubble’s constant have approximately the same value, observed frequency shifts in radiation received from stellar sources can imply source velocities quite different from those implied in Minkowski space. Electromagnetic waves received from bodies in galactic Kepler orbits undergo frequency shifts which are indistinguishable from shifts currently attributed to dark matter and dark energy in Minkowski space, or to a non-Newtonian physics.

The Unrecognized Value of Bio-Medical Engineers in Healthcare Projects in Developing Countries  [PDF]
Carl E. Bartecchi, Robert Preston
International Journal of Clinical Medicine (IJCM) , 2014, DOI: 10.4236/ijcm.2014.56043

The healthcare needs of developing countries are great and ever increasing as their populations grow. Few assistance programs have recognized the value of the bio-medical engineer as part of the approach to the provision of healthcare in developing countries. An example of a program, the Bach Mai Hospital Project, in Vietnam, utilizing the talents of the bio-medical engineer, attests to the potential value of bio-medical engineers as part of the healthcare team. Their inclusion in such efforts can result in the saving of lives, time and money. Knowledge of their hospital's excess equipment inventory and their ability to restore medical equipment badly needed in a developing country makes them valuable additions to any medical assistance program.

Concurrent and Predictive Relationships Between Compulsive Internet Use and Substance Use: Findings from Vocational High School Students in China and the USA
Ping Sun,Carl Anderson Johnson,Paula Palmer,Thalida E. Arpawong,Jennifer B. Unger,Bin Xie,Louise A. Rohrbach,Donna Spruijt-Metz,Steve Sussman
International Journal of Environmental Research and Public Health , 2012, DOI: 10.3390/ijerph9030660
Abstract: Purpose: Compulsive Internet Use (CIU) has increasingly become an area of research among process addictions. Largely based on data from cross-sectional studies, a positive association between CIU and substance use has previously been reported. This study presents gender and country-specific longitudinal findings on the relationships between CIU and substance use. Methods: Data were drawn from youth attending non-conventional high schools, recruited into two similarly implemented trials conducted in China and the USA. The Chinese sample included 1,761 students (49% male); the US sample included 1,182 students (57% male) with over half (65%) of the US youth being of Hispanic ethnicity. Path analyses were applied to detect the concurrent and predictive relationships between baseline and one-year follow-up measures of CIU level, 30-day cigarette smoking, and 30-day binge drinking. Results: (1) CIU was not positively related with substance use at baseline. (2) There was a positive predictive relationship between baseline CIU and change in substance use among female, but not male students. (3) Relationships between concurrent changes in CIU and substance use were also found among female, but not male students. (4) Baseline substance use did not predict an increase in CIU from baseline to 1-year follow-up. Conclusions: While CIU was found to be related to substance use, the relationship was not consistently positive. More longitudinal studies with better measures for Internet Addiction are needed to ascertain the detailed relationship between Internet addiction and substance use.
Embedding effective depression care: using theory for primary care organisational and systems change
Jane M Gunn, Victoria J Palmer, Christopher F Dowrick, Helen E Herrman, Frances E Griffiths, Renata Kokanovic, Grant A Blashki, Kelsey L Hegarty, Caroline L Johnson, Maria Potiriadis, Carl R May
Implementation Science , 2010, DOI: 10.1186/1748-5908-5-62
Abstract: We used a mixed method, observational approach to gather data about routine depression care in a range of primary care settings via: audit of electronic health records; observation of routine clinical care; and structured, facilitated whole of organisation meetings. Audit data were summarised using simple descriptive statistics. Observational data were collected using field notes. Organisational meetings were audio taped and transcribed. All the data sets were grouped, by organisation, and considered as a whole case. Normalisation Process Theory (NPT) was identified as an analytical theory to guide the conceptual framework development.Five privately owned primary care organisations (general practices) and one community health centre took part over the course of 18 months. We successfully developed a conceptual framework for implementing an effective model of depression care based on the four constructs of NPT: coherence, which proposes that depression work requires the conceptualisation of boundaries of who is depressed and who is not depressed and techniques for dealing with diffuseness; cognitive participation, which proposes that depression work requires engagement with a shared set of techniques that deal with depression as a health problem; collective action, which proposes that agreement is reached about how care is organised; and reflexive monitoring, which proposes that depression work requires agreement about how depression work will be monitored at the patient and practice level. We describe how these constructs can be used to guide the design and implementation of effective depression care in a way that can take account of contextual differences.Ideas about what is required for an effective model and system of depression care in primary care need to be accompanied by theoretically informed frameworks that consider how these can be implemented. The conceptual framework we have presented can be used to guide organisational and system change to develop commo
Imaging an Event Horizon: Mitigation of Scattering Toward Sagittarius A*
Vincent L. Fish,Michael D. Johnson,Ru-Sen Lu,Sheperd S. Doeleman,Katherine L. Bouman,Daniel Zoran,William T. Freeman,Dimitrios Psaltis,Ramesh Narayan,Victor Pankratius,Avery E. Broderick,Carl R. Gwinn,Laura E. Vertatschitsch
Physics , 2014, DOI: 10.1088/0004-637X/795/2/134
Abstract: The image of the emission surrounding the black hole in the center of the Milky Way is predicted to exhibit the imprint of general relativistic (GR) effects, including the existence of a shadow feature and a photon ring of diameter ~50 microarcseconds. Structure on these scales can be resolved by millimeter-wavelength very long baseline interferometry (VLBI). However, strong-field GR features of interest will be blurred at lambda >= 1.3 mm due to scattering by interstellar electrons. The scattering properties are well understood over most of the relevant range of baseline lengths, suggesting that the scattering may be (mostly) invertible. We simulate observations of a model image of Sgr A* and demonstrate that the effects of scattering can indeed be mitigated by correcting the visibilities before reconstructing the image. This technique is also applicable to Sgr A* at longer wavelengths.
Theory and Simulations of Refractive Substructure in Resolved Scatter-Broadened Images
Michael D. Johnson,Carl R. Gwinn
Physics , 2015, DOI: 10.1088/0004-637X/805/2/180
Abstract: At radio wavelengths, scattering in the interstellar medium distorts the appearance of astronomical sources. Averaged over a scattering ensemble, the result is a blurred image of the source. However, Narayan & Goodman (1989) and Goodman & Narayan (1989) showed that for an incomplete average, scattering introduces refractive substructure in the image of a point source that is both persistent and wideband. We show that this substructure is quenched but not smoothed by an extended source. As a result, when the scatter-broadening is comparable to or exceeds the unscattered source size, the scattering can introduce spurious compact features into images. In addition, we derive efficient strategies to numerically compute realistic scattered images, and we present characteristic examples from simulations. Our results show that refractive substructure is an important consideration for ongoing missions at the highest angular resolutions, and we discuss specific implications for RadioAstron and the Event Horizon Telescope.
Noise and Signal for Spectra of Intermittent Noiselike Emission
Carl R. Gwinn,Michael D. Johnson
Physics , 2011, DOI: 10.1088/0004-637X/733/1/51
Abstract: We show that intermittency of noiselike emission, after propagation through a scattering medium, affects the distribution of noise in the observed correlation function. Intermittency also affects correlation of noise among channels of the spectrum, but leaves the average spectrum, average correlation function, and distribution of noise among channels of the spectrum unchanged. Pulsars are examples of such sources: intermittent and affected by interstellar propagation. We assume that the source emits Gaussian white noise, modulated by a time-envelope. Propagation convolves the resulting time series with an impulse-response function that represents effects of dispersion, scattering, and absorption. We assume that this propagation kernel is shorter than the time for an observer to accumulate a single spectrum. We show that rapidly-varying intermittent emission tends to concentrate noise near the central lag of the correlation function. We derive mathematical expressions for this effect, in terms of the time envelope and the propagation kernel. We present examples, discuss effects of background noise, and compare our results with observations.
Ultra-High Resolution Intensity Statistics of a Scintillating Source
Michael D. Johnson,Carl R. Gwinn
Physics , 2012, DOI: 10.1088/0004-637X/755/2/179
Abstract: We derive the distribution of flux density of a compact source exhibiting strong diffractive scintillation. Our treatment accounts for arbitrary spectral averaging, spatially-extended source emission, and the possibility of intrinsic variability within the averaging time, as is typical for pulsars. We also derive the modulation index and present a technique for estimating the self-noise of the distribution, which can be used to identify amplitude variations on timescales shorter than the spectral accumulation time. Our results enable a for direct comparison with ultra-high resolution observations of pulsars, particularly single-pulse studies with Nyquist-limited resolution, and can be used to identify the spatial emission structure of individual pulses at a small fraction of the diffractive scale.
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