Analytic Treatment of Positronium Spin Splittings in Light-Front QED

We study the QED bound-state problem in a light-front hamiltonian approach. Starting with a bare cutoff QED Hamiltonian, $H_{_{B}}$, with matrix elements between free states of drastically different energies removed, we perform a similarity transformation that removes the matrix elements between free states with energy differences between the bare cutoff, $\Lambda$, and effective cutoff, \lam (\lam < \Lam). This generates effective interactions in the renormalized Hamiltonian, $H_{_{R}}$. These effective interactions are derived to order $\alpha$ in this work, with $\alpha \ll 1$. $H_{_{R}}$ is renormalized by requiring it to satisfy coupling coherence. A nonrelativistic limit of the theory is taken, and the resulting Hamiltonian is studied using bound-state perturbation theory (BSPT). The effective cutoff, \lam^2, is fixed, and the limit, 0 \longleftarrow m^2 \alpha^2\ll \lam^2 \ll m^2 \alpha \longrightarrow \infty, is taken. This upper bound on \lam^2 places the effects of low-energy (energy transfer below \lam) emission in the effective interactions in the $| e {\overline e} >$ sector. This lower bound on \lam^2 insures that the nonperturbative scale of interest is not removed by the similarity transformation. As an explicit example of the general formalism introduced, we show that the Hamiltonian renormalized to $O(\alpha)$ reproduces the exact spectrum of spin splittings, with degeneracies dictated by rotational symmetry, for the ground state through $O(\alpha^4)$. The entire calculation is performed analytically, and gives the well known singlet-triplet ground state spin splitting of positronium, $7/6 \alpha^2 Ryd$. We discuss remaining corrections other than the spin splittings and how they can be treated in calculating the spectrum with higher precision.Comment: 46 pages, latex, 3 Postscript figures included, section on remaining corrections added, title changed, error in older version corrected, cutoff placed in a windo

N-Terminal Pro–B-Type Natriuretic Peptide in the Emergency Department: The ICON-RELOADED Study

Background Contemporary reconsideration of diagnostic N-terminal pro–B-type natriuretic peptide (NT-proBNP) cutoffs for diagnosis of heart failure (HF) is needed. Objectives This study sought to evaluate the diagnostic performance of NT-proBNP for acute HF in patients with dyspnea in the emergency department (ED) setting. Methods Dyspneic patients presenting to 19 EDs in North America were enrolled and had blood drawn for subsequent NT-proBNP measurement. Primary endpoints were positive predictive values of age-stratified cutoffs (450, 900, and 1,800 pg/ml) for diagnosis of acute HF and negative predictive value of the rule-out cutoff to exclude acute HF. Secondary endpoints included sensitivity, specificity, and positive (+) and negative (−) likelihood ratios (LRs) for acute HF. Results Of 1,461 subjects, 277 (19%) were adjudicated as having acute HF. The area under the receiver-operating characteristic curve for diagnosis of acute HF was 0.91 (95% confidence interval [CI]: 0.90 to 0.93; p < 0.001). Sensitivity for age stratified cutoffs of 450, 900, and 1,800 pg/ml was 85.7%, 79.3%, and 75.9%, respectively; specificity was 93.9%, 84.0%, and 75.0%, respectively. Positive predictive values were 53.6%, 58.4%, and 62.0%, respectively. Overall LR+ across age-dependent cutoffs was 5.99 (95% CI: 5.05 to 6.93); individual LR+ for age-dependent cutoffs was 14.08, 4.95, and 3.03, respectively. The sensitivity and negative predictive value for the rule-out cutoff of 300 pg/ml were 93.9% and 98.0%, respectively; LR− was 0.09 (95% CI: 0.05 to 0.13). Conclusions In acutely dyspneic patients seen in the ED setting, age-stratified NT-proBNP cutpoints may aid in the diagnosis of acute HF. An NT-proBNP <300 pg/ml strongly excludes the presence of acute HF

Vegetative Change on South Padre Island, Texas, over Twenty Years and Evaluation of Multispectral Videography in Determining Vegetative Cover and Species Identity

A comparative vegetation analysis of an island-wide transect of South Padre Island, Texas, was conducted in 1997 using aerial multispectral digital videography and line intercept ground truth techniques to assess the usefulness of videography in estimating vegetative cover and species identifications. Ground truth data were used to assess vegetative change occurring in the 20 years since the report of Judd et al. (1977) on the vegetation of South Padre Island. Estimates of total cover by ground truth and remote sensing techniques were similar (2.45% difference) on South Padre Island. Thus, airborne multispectral digital videography is an effective technique for assessing changes in total vegetative cover of Texas barrier islands. This technique will be an effective tool for documenting changes in total cover on barrier islands due to natural perturbations such as hurricanes and human disturbances including vehicular traffic. Imagery obtained at altitudes of 200 m or greater did not permit discrimination of dominant species in each of an island\u27s topographic zones. However, acquisition of imagery at a time of the year when dominant species are in specific phenological stages, such as flowering, and at a lower altitude may facilitate their recognition. Comparison of data from a single trans-island transect in 1997 with data from three trans-island transects and 18 transects across the foreshore, backshore, and primary dunes in 1977 suggests that there has been a marked decrease in species richness of the backshore and primary dune zones of South Padre Island. There also was a change in dominant species in the backshore zone. These changes in species richness and dominance may be largely attributable to vehicular traffic in these zones. - Un análisis comparativo de la vegetación de un transecto transinsular de la isla South Padre en el estado de Texas fue realizado en 1997 usando videografía aérea multiesprectral digital y técnicas de validación de intercepción linear terrestre para evaluar la utilidad de la videografía en la estimación de la cobertura vegetal e identificación de especies. Los datos de estudios de validación terrestre fueron utilizados para evaluar el cambio vegetativo que ocurrió durante 20 años después del informe de Judd et al (1977) sobre la vegetación de la isla South Padre. Las estimaciones de la cobertura total mediante técnicas de validación terrestres y de medición remota fueron similares (2.45% de diferencia) en la isla South Padre. Por lo tanto, la videografía multiesprectral digital aérea se considera una técnica eficaz para evaluar cambios en la cobertura vegetal de las islas barrera de Texas. Esta técnica será una herramienta efectiva para documentar los cambios de cobertura total en las islas barrera debido a las perturbaciones naturales tales como huracanes y disturbios humanos como tráfico vehicular. Las imágenes obtenidas en altitudes de 200 metros o mayores no permitieron la discriminación de las especies dominantes de las varias zonas topográficas de una isla. Sin embargo, la adquisición de imágenes de una época del año en que las especies dominantes están en etapas fenológicas específicas, tales como la floración, y desde una altitud menor, puede facilitar su reconocimiento. Al comparar datos de un transecto transinsular de 1977 con los de tres transectos transinsulares y de 18 transectos correspondientes a la parte frontal, trasera, y de las dunas primarias de la isla en 1977, se sugiere que ha habido una marcada disminución en la riqueza de especies en la parte trasera y en la zona de dunas primarias de la isla South Padre. También hubo un cambio de especies dominantes en la zona trasera. Estos cambios en la riqueza y dominancia de especies pueden ser atribuidos en gran parte al tráfico vehicular en estas zonas

Society for Cardiovascular Magnetic Resonance (SCMR) recommended CMR protocols for scanning patients with active or convalescent phase COVID-19 infection

The aim of this document is to provide specific recommendations on the use of cardiovascular magnetic resonance (CMR) protocols in the era of the COVID-19 pandemic. In patients without COVID-19, standard CMR protocols should be used based on clinical indication as usual. Protocols used in patients who have known / suspected active COVID-19 or post COVID-19 should be performed based on the specific clinical question with an emphasis on cardiac function and myocardial tissue characterization. Short and dedicated protocols are recommended

Activation of Penile Proadipogenic Peroxisome Proliferator-Activated Receptor γ with an Estrogen: Interaction with Estrogen Receptor Alpha during Postnatal Development

Exposure to the estrogen receptor alpha (ERα) ligand diethylstilbesterol (DES) between neonatal days 2 to 12 induces penile adipogenesis and adult infertility in rats. The objective of this study was to investigate the in vivo interaction between DES-activated ERα and the proadipogenic transcription factor peroxisome proliferator-activated receptor gamma (PPARγ). Transcripts for PPARs α, β, and γ and γ1a splice variant were detected in Sprague-Dawley normal rat penis with PPARγ predominating. In addition, PPARγ1b and PPARγ2 were newly induced by DES. The PPARγ transcripts were significantly upregulated with DES and reduced by antiestrogen ICI 182, 780. At the cellular level, PPARγ protein was detected in urethral transitional epithelium and stromal, endothelial, neuronal, and smooth muscular cells. Treatment with DES activated ERα and induced adipocyte differentiation in corpus cavernosum penis. Those adipocytes exhibited strong nuclear PPARγ expression. These results suggest a biological overlap between PPARγ and ERα and highlight a mechanism for endocrine disruption