Demonstration of a beam loaded nanocoulomb-class laser wakefield accelerator

Laser-plasma wakefield accelerators have seen tremendous progress, now capable of producing quasi-monoenergetic electron beams in the GeV energy range with few-femtoseconds bunch duration. Scaling these accelerators to the nanocoulomb range would yield hundreds of kiloamperes peak current and stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and γ-ray sources, compact free-electron lasers and laboratory-size beam-driven plasma accelerators. However, accelerators generating such currents operate in the beam loading regime where the accelerating field is strongly modified by the self-fields of the injected bunch, potentially deteriorating key beam parameters. Here we demonstrate that, if appropriately controlled, the beam loading effect can be employed to improve the accelerator's performance. Self-truncated ionization injection enables loading of unprecedented charges of ∼0.5 nC within a mono-energetic peak. As the energy balance is reached, we show that the accelerator operates at the theoretically predicted optimal loading condition and the final energy spread is minimized.Higher beam quality and stability are desired in laser-plasma accelerators for their applications in compact light sources. Here the authors demonstrate in laser plasma wakefield electron acceleration that the beam loading effect can be employed to improve beam quality by controlling the beam charge.

Significance of Histoplasma antigen in the cerebrospinal fluid of patients with meningitis

A radioimmunoassay was previously developed for detection of Histoplasma capsulatum antigen in the blood and urine of patients with disseminated histoplasmosis. In this investigation, cerebrospinal fluid (CSF) specimens from 14 episodes of Histoplasma meningitis occurring in 12 patients were tested by radioimmunoassay. Histoplasma capsulatum antigen was detected in the CSF of five patients. Cerebrospinal fluid cultures were positive for H capsulatum in three of these five patients. Antibodies to H capsulatum were found in nine of the 13 CSF specimens tested. The radioimmunoassay for Histoplasma antigen was also positive in the CSF in one of 11 patients with coccidioidal meningitis but not in 17 patients with cryptococcal meningitis. It was concluded that Histoplasma antigen is present in the CSF of some patients with histoplasmosis and chronic meningitis, but cross-reactions may occur in patients with coccidioidal meningitis.

Commercially available (ENDO-STAPH) assay for teichoic acid antibodies. Evaluation in patients with serious Staphylococcus aureus infections and in controls

We have evaluated the clinical usefulness of a commercially available teichoic acid antibody assay (ENDO-STAPH). Teichoic acid antibody titers up to a 1:2 serum dilution were observed in 20% of normal subjects, thus, titers of 1:4 or more were considered positive. Of patients with Staphylococcus aureus infections, 16 of 23 with endocarditis, 12 of 20 with complicated bacteremia, three of 17 with uncomplicated bacteremia, and ten of 20 with nonbacteremic infections had positive titers. Only four of 70 controls had positive titers. Results agreed with those using our standard assay in 130 of 151 specimens. Results were reproducibly positive or negative in 17 of 18 specimens that were retested. Results were also reproducible in ten specimens retested using a different lot of standardized antigen. The ENDO-STAPH assay should broaden the clinical applications of assays for TAA.

Immunoglobulin M and G histoplasmal antibody response in histoplasmosis

Radioimmunoassays for IgM and IgG histoplasmal antibodies were developed and proved to be specific for their respective immunoglobulin classes, sensitive, and reproducible. Elevated IgM antibodies were detected in 59.8% of patients with histoplasmosis and 7.9% of control subjects. Elevated IgG antibodies occurred in 80.4% of patients with histoplasmosis but in only 12.9% of control subjects. Radioimmunoassay was nearly twice as sensitive as complement fixation for identifying patients with mild, presumably asymptomatic, infection. Of 13 patients with serologic follow-up at least 1 yr later, elevated IgM antibodies cleared, whereas IgG antibodies persisted in 7. In an epidemiologic investigation of a recurrent histoplasmosis outbreak, only the radioimmunoassay was able to prove the hypothesis that construction for a swimming complex was the source of exposure. These assays promise to be useful for clinical and epidemiologic investigations.