Gauge invariance in two-particle scattering

It is shown how gauge invariance is obtained for the coupling of a photon to a two-body state described by the solution of the Bethe-Salpeter equation. This is illustrated both for a complex scalar field theory and for interaction kernels derived from chiral effective Lagrangians.Comment: 16 pages, 2 figures, references added and commented o

State of Harmonization of 24 Serum Albumin Measurement Procedures and Implications for Medical Decisions

BACKGROUND: Measurements of serum and plasma albumin are widely used in medicine, including as indicators of quality of patient care in renal dialysis centers. METHODS: Pools were prepared from residual patient serum (n = 50) and heparin plasma (n = 48) from patients without renal disease, and serum from patients with kidney failure before hemodialysis (n = 53). Albumin was measured in all samples and in ERM-DA470k/IFCC reference material (RM) by 3 immunochemical, 9 bromcresol green (BCG), and 12 bromcresol purple (BCP) methods. RESULTS: Two of 3 immunochemical procedures, 5 of 9 BCG, and 10 of 12 BCP methods recovered the RM value within its uncertainty. One immunochemical and 3 BCG methods were biased vs the RM value. Random error components were small for all measurement procedures. The Tina-quant immunochemical method was chosen as the reference measurement procedure based on recovery and results of error analyses. Mean biases for BCG vs Tina-quant were 1.5% to 13.9% and were larger at lower albumin concentrations. BCP methods\u27 mean biases were -5.4% to 1.2% irrespective of albumin concentration. Biases for plasma samples were generally higher than for serum samples for all method types. For most measurement procedures, biases were lower for serum from patients on hemodialysis vs patients without kidney disease. CONCLUSIONS: Significant differences among immunochemical, BCG, and BCP methods compromise interpretation of serum. albumin results. Guidelines and calculations for clinical management of kidney and other diseases must consider the method used for albumin measurement until harmonization can be achieved

Pion photoproduction off the proton in a gauge-invariant chiral unitary framework

We investigate pion photoproduction off the proton in a manifestly gauge-invariant chiral unitary extension of chiral perturbation theory. In a first step, we consider meson-baryon scattering taking into account all next-to-leading order contact interactions. The resulting low-energy constants are determined by a fit to s-wave pion-nucleon scattering and the low-energy data for the reaction pi- p --> eta n. To assess the theoretical uncertainty, we perform two different fit strategies. Having determined the low-energy constants, we then analyse the data on the s-wave multipole amplitudes E0+ of pion and eta photoproduction. These are parameter-free predictions, as the two new low-energy constants are determined by the neutron and proton magnetic moments.Comment: 23 pages, 17 figure

"I don't know": a usage-based approach to familiar collocations in non-fluent aphasia

Background: Familiar collocations (e.g., “it’s alright”) are an important part of everyday conversation. Such word combinations are often retained in speakers with Broca’s aphasia. However, only few investigations have studied the forms and functions of familiar collocations available to speakers with Broca’s aphasia. // Aims: We first apply a frequency-based perspective to word combinations produced by speakers with Broca’s aphasia and their conversation partners (CPs), and compare the frequency characteristics of word combinations in dyadic and non-dyadic speech. Second, we investigate the conversational functions of one prominent familiar collocation, “I don’t know” (IDK). // Methods & Procedures: In the first analysis, speech samples from interactions of nine dyads (each a speaker with Broca’s aphasia and their CP) were examined. Non-dyadic samples were selected from 39 speakers with Broca’s aphasia from AphasiaBank (MacWhinney et al., 2011). The Frequency in Language Analysis Tool (FLAT; Zimmerer & Wibrow, 2015) was used to estimate collocation strength (the degree of association between words in a combination) of well-formed bigrams (two-word combinations) and trigrams (three-word combinations). The second analysis presents a qualitative investigation of uses of IDK in dyadic exchanges. // Outcomes & Results: Analysis 1 revealed that residual trigrams in Broca’s aphasia were more strongly collocated in comparison to language produced by CPs. There was no difference in frequency-based profiles between dyadic and non-dyadic aphasic speech. Analysis 2 indicated that speakers with Broca’s aphasia and CPs used IDK to achieve a variety of communicative functions. However, patterns specific to each participant group were found. // Conclusions: These findings highlight that frequency-based analysis is useful in explaining residual, grammatically well-formed word combinations in Broca’s aphasia. This study provides evidence that IDK can aid turn construction in aphasia

High Velocity Cloud Complex H: A Satellite of the Milky Way in a Retrograde Orbit?

Observations with the Green Bank Telescope of 21cm HI emission from the high-velocity cloud Complex H suggest that it is interacting with the Milky Way. A model in which the cloud is a satellite of the Galaxy in an inclined, retrograde circular orbit reproduces both the cloud's average velocity and its velocity gradient with latitude. The model places Complex H at approximately 33 kpc from the Galactic Center on a retrograde orbit inclined about 45 degrees to the Galactic plane. At this location it has an HI mass > 6 10^6 Msun and dimensions of at least 10 by 5 kpc. Some of the diffuse HI associated with the cloud has apparently been decelerated by interaction with Galactic gas. Complex H has similarities to the dwarf irregular galaxy Leo A and to some compact high-velocity clouds, and has an internal structure nearly identical to parts of the Magellanic Stream, with a pressure P/k about 100 cm^{-3} K.Comment: 12 pages includes 4 figures. To be published in Astrophysical Journal Letters, 1 July 200

Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology

We present Arecibo L-band Feed Array 21-cm observations of a sub-complex of HVCs at the tip of the Anti-Center Complex. These observations show morphological details that point to interaction with the ambient halo medium and differential drag within the cloud sub-complex. We develop a new technique for measuring cloud distances, which relies upon these observed morphological and kinematic characteristics, and show that it is consistent with H-alpha distances. These results are consistent with distances to HVCs and halo densities derived from models in which HVCs are formed from cooling halo gas.Comment: 8 pages, 2 figures, 1 tabe, Accepted to Ap