Beam emittance preservation using Gaussian density ramps in a beam-driven plasma wakefield accelerator.

A current challenge that is facing the plasma wakefield accelerator (PWFA) community is transverse beam emittance preservation. This can be achieved by balancing the natural divergence of the beam against the strong focusing force provided by the PWFA plasma source in a scheme referred to as beam matching. One method to accomplish beam matching is through the gradual focusing of a beam with a plasma density ramp leading into the bulk plasma. Here, the beam dynamics in a Gaussian plasma density ramp are considered, and an empirical formula is identified that gives the ramp length and beam vacuum waist location needed to achieve near-perfect matching. The method uses only the beam vacuum waist beta function as an input. Numerical studies show that the Gaussian ramp focusing formula is robust for beta function demagnification factors spanning more than an order of magnitude with experimentally favourable tolerances for future PWFA research facilities. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Single-stage plasma-based correlated energy spread compensation for ultrahigh 6D brightness electron beams.

Plasma photocathode wakefield acceleration combines energy gains of tens of GeV m-1 with generation of ultralow emittance electron bunches, and opens a path towards 5D-brightness orders of magnitude larger than state-of-the-art. This holds great promise for compact accelerator building blocks and advanced light sources. However, an intrinsic by-product of the enormous electric field gradients inherent to plasma accelerators is substantial correlated energy spread-an obstacle for key applications such as free-electron-lasers. Here we show that by releasing an additional tailored escort electron beam at a later phase of the acceleration, when the witness bunch is relativistically stable, the plasma wave can be locally overloaded without compromising the witness bunch normalized emittance. This reverses the effective accelerating gradient, and counter-rotates the accumulated negative longitudinal phase space chirp of the witness bunch. Thereby, the energy spread is reduced by an order of magnitude, thus enabling the production of ultrahigh 6D-brightness beams.

Maternal smoking during pregnancy affects neuroendocrine cells in the neonate hamster lung.

Primigravid Syrian golden hamsters were exposed in a Walton smoking machine to the smoke from either weak or strong cigarettes for 10 minute periods, 4 times a day from the 3rd to 14th (2nd last) day of pregnancy. Control hamsters were either similarly restrained in a Walton machine equipped with an unlit cigarette, or were not placed in the machine or restrained. Examination of the progeny in the first 6 days of life showed changes in density indices of grouped pulmonary neuroendocrine (NE) cells (neuroepithelial bodies, NEB) that were related to in utero exposure to maternal smoking. Argyrophil NEB were more numerous, larger, and contained more cells at birth among neonates whose mothers smoked the strong cigarette (2.45 mg nicotine and 36.8 mg tar) during pregnancy. This suggests a dose-related effect as the weak cigarette (0.37 mg nicotine and 33.8 mg tar) group did not show such changes. However, some of the changes described did not last through 3 or 6 days of age. The stress resulting from restraint alone also appeared to increase argyrophil NEB indices. Lung tissue volume fraction was increased in the weak cigarette group over all other groups at birth and 3 days; this suggests that low nicotine has the strongest pharmacological effect on lung tissue growth. The medial thickness of pulmonary arterioles was unchanged by either treatment; this provides morphometric evidence that chronic pulmonary hypertension was not present. We could not determine whether the increased NEB indices were caused by increased stainability, by activation of resident reserve cells, or by actual mitosis.

Interaction of the tick (Haemaphysalis leporispalustris) with a cyclic snowshoe hare (Lepus americanus) population.

Prevalence and intensity of the tick, Haemaphysalis leporispalustris, were monitored during 1963 to 1976 in a cyclic snowshoe hare (Lepus americanus) population near Rochester, Alberta, Canada. Prevalence was near zero from December through March, and near 100% among adult hares from May through September. Prevalence among juvenile hares approached 100% by age 2 mo. Intensity peaked for both adults and juveniles during May-June and again in August. Mean intensities were significantly higher among adult males than adult females in 5 of 13 yr, and almost significant in two others. Tick intensities were lowest during 3 yr, 1969 to 1971, when hare densities were highest. Tick intensities in spring were correlated with intensities the previous fall. Survival of marked adult and juvenile hares was unrelated to intensities of infestation. Mean numbers of corpora lutea and embryos tended to be lower among adult females with heavy tick infestations, and intra-uterine losses rose steadily from about 3 to 13% as tick intensities increased from none to heavy. Comparison of average tick intensities on adults 1-, 2-, and greater than or equal to 3-yr-old yielded no evidence of increased immunity with age.

Parasitism in a declining population of snowshoe hares.

Prevalence and intensity of six endoparasites were determined in 346 snowshoe hares (Lepus americanus) obtained at Rochester, Alberta, during December-April 1981-1982, the second winter of a cyclic population decline. The data were analyzed for (1) differences among host sex and age classes, and among months and sample sources, and (2) evidence that parasitism was of demographic significance to the hare population. Prevalence and intensity of Obeliscoides cuniculi were consistently highest among adult hares, but rose most sharply from February to March among juveniles. In contrast, prevalence and intensity of Nematodirus triangularis were highest among juveniles; prevalence reached 90-100% by January, whereas intensity continued to rise through April. Prevalence and intensity of both Trichuris leporis and Protostrongylus boughtoni were highest also among juvenile hares; neither parameter exhibited a definite trend over time. Prevalences of Taenia pisiformis (cysticerci) and Eimeria spp. were unrelated to sex, age or month; but Taenia intensity was highest among juveniles, and Eimeria intensity tended to decrease from December to April. Intensities of Nematodirus, Protostrongylus and Eimeria were higher in male hares than in females. Prevalence and intensity were correlated directly in Obeliscoides, Nematodirus, Trichuris and Eimeria. Hares that died during trapping and handling, or from natural predation, had greater intensities of Obeliscoides than did animals killed on purpose. There was no indication, however, that risk of death was increased by the other parasitic infections. Age-related immune responses to parasitism (except Obeliscoides) were evidenced by reduced or stabilized prevalence and/or intensity among older hares. A multiple-regression model predicted depressed body weight with increasing intensities of Nematodirus, Trichuris or Protostrongylus. Other body-condition and reproductive indices were unassociated with parasite intensities. Within the hare population, Obeliscoides, Trichuris, Protostrongylus and Taenia had overdispersed distributions (typical of many endoparasites) that did not differ from a negative binomial. The frequency with which each possible combination of helminth species occurred within individual hares was consistent with the assumption that such infections occurred independently. There was no compelling reason to believe parasitism was a significant factor in the overwinter decline of this population of snowshoe hares.

Prevalence of helminths in a cyclic snowshoe hare population.

Five species of helminths were monitored in a population of snowshoe hares (Lepus americanus) near Rochester, Alberta, during 1961-1977. Prevalence of both Obeliscoides cuniculi and Protostrongylus boughtoni among young hares averaged about 50% by age 2 mo, then tended to level off. Prevalence of Taenia pisiformis (cysticerci) and Dirofilaria scapiceps rose more slowly, but continued to increase steadily beyond their mean levels of 8% and 1% at age 2 mo. There were well defined seasonal (within-year) cycles in prevalence of O. cuniculi and P. boughtoni that were generated evidently to a major degree by arrested development of larvae in fall and renewed development in late winter. It was hypothesized that renewed larval development was triggered (in February) in O. cuniculi by the seasonal rise of circulating pituitary gonadotrophins, and (in April) in P. boughtoni by the seasonal rise of gonadal androgens and estrogens. Indices to gonadal hormone levels in hares indicated that these increased most rapidly among males, and may have accounted for the higher prevalences of P. boughtoni in males during April-May. Neither T. pisiformis nor D. scapiceps exhibited conspicuous seasonal changes in prevalence. Maximum prevalence of T. pisiformis was attained at about 1 yr of age, whereas D. scapiceps increased among adult snowshoes through age 2 yr before stabilizing. Long-term (between-year) changes in prevalence of O. cuniculi, T. pisiformis, and D. scapiceps were correlated significantly with the cyclic hare population which declined from a peak in fall 1961 to a low in 1965-1966, rose to another peak by fall 1970, and declined again to a low in 1975. There was no detectable time lage between this "10-yr" cycle in hare density and the cycles of parasite prevalence among juveniles (less than 1 yr of age). Among adult hares, the cycle of O. cuniculi prevalence was likewise synchronous with that of the hare population, but the cycles of D. scapiceps and T. pisiformis lagged by approximately 1 and 2 yr, respectively. This lag in T. pisiformis prevalence was largely inexplicable to us. Our data on P. boughtoni were not suitable for analyses of between-year trends; nor were those for the fifth helminth, Taenia serialis (coenuri), because mean prevalence was less than 1% among both juveniles and adults. An apparent decline in T. serialis after the early 1950's, and its continued scarcity thereafter, paralleled a major change in numbers of one important definitive host--the red fox (Vulpes vulpes).(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma-density-gradient injection of low absolute-momentum-spread electron bunches.

Plasma density gradients in a gas jet were used to control the wake phase velocity and trapping threshold in a laser wakefield accelerator, producing stable electron bunches with longitudinal and transverse momentum spreads more than 10 times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76+/-0.02 MeV/c. Transition radiation measurements combined with simulations indicated that the bunches can be used as a wakefield accelerator injector to produce stable beams with 0.2 MeV/c-class momentum spread at high energies.

Verapamil for unstable angina at rest: a short-term randomized, double-blind study.

To assess the efficacy of verapamil in individuals with unstable angina at rest, 11 patients (five men and six women, average age 55 years) with recurrent chest pain at rest and transient ST segment deviation (elevation or depression greater than or equal to 0.1 mV) on continuous ECG monitoring were enrolled in a 3-day double-blind, randomized study. The day before randomization (day 1), all received single-blind placebo. On day 2 they were randomized to placebo (n = 6) or verapamil, 320 mg per day (n = 5). On placebo, the number of chest pains (day 1, 2.8 +/- 2.1; day 2, 2.2 +/- 2.5; NS), nitroglycerin used (day 1, 2.7 +/- 4.4 tablets; day 2, 2.2 +/- 3.5 tablets; NS), and ST segment deviations (day 1, 8.5 +/- 5.9; day 2, 5.3 +/- 7.1; NS) did not change. On verapamil, the number of chest pains (day 1, 5.4 +/- 2.2; day 2, 1.6 +/- 2.1; p less than 0.01), nitroglycerin used (day 1, 5.0 +/- 4.5 tablets; day 2, 1.6 +/- 2.6 tablets; p = 0.057), and ST segment deviations (day 1, 12.6 +/- 4.7; day 2, 6.2 +/- 6.2; p less than 0.05) fell. Since five of six placebo patients had frequent chest pain and ST segment deviations on day 2, they were changed blindly to verapamil, 320 mg per day. Of the five verapamil patients, three had no chest pain or ST segment deviations on day 2, but two had continued chest pain and ST segment deviations and were increased blindly to 480 mg verapamil per day. Of the eight patients given verapamil (320 mg per day) on day 3, five had chest pain or ST segment deviations and were increased blindly to 480 mg verapamil per day on day 4. Of the seven who received 480 mg verapamil per day on day 4, three had chest pain and ST segment deviations similar in frequency to that occurring on day 1. Thus in patients with unstable angina at rest, verapamil exerts an initial beneficial effect, but in some individuals this salutary influence is not sustained.

Oral verapamil for paroxysmal supraventricular tachycardia: a long-term, double-blind randomized trial.

The effectiveness and safety of orally administered verapamil was tested in 11 patients with frequent paroxysmal supraventricular tachycardia. In a 4-month randomized, double-blind, placebo-controlled trial, the frequency of paroxysmal supraventricular tachycardia fell from 0.3 +/- 0.3 (mean +/- SD) to 0.1 +/- 0.1 episodes per day by patient diary (p less than 0.05) and from 0.7 +/- 0.7 to 0.3 +/- 0.5 episodes per day by Holter monitor (p less than 0.05) for placebo and verapamil treatment periods, respectively. Verapamil caused a decrease in the duration of paroxysmal supraventricular tachycardia (in minutes per day): placebo 27 +/- 51 by dairy, 67 +/- 111 by Holter; verapamil, 3 +/- 3 by diary, 1 +/- 2 by Holter (p less than 0.05). Five patients required a total of 35 pharmacologic cardioversions for sustained tachycardia: two during verapamil and 33 during placebo (p less than 0.001). No verapamil treatment period was shortened due to unacceptable paroxysmal supraventricular tachycardia, but five of 22 placebo treatment periods were shortened (p equal to 0.02). Verapamil was well-tolerated, causing mild constipation in five patients and headache in one. Oral verapamil is both safe and effective in the long-term treatment of patients with paroxysmal supraventricular tachycardia.

Verapamil administration in variant angina pectoris. Efficacy shown by ecg monitoring.

Six patients with Prinzmetal's variant angina were treated with oral verapamil administration. Before and after the initiation of therapy, ambulatory ECG monitoring was performed to assess objectively the response to therapy. With verapamil administration, the frequency of both chest pain and transient ST-segment deviations was sharply diminished.

Continuous electrocardiographic monitoring in patients with unstable angina pectoris: Identification of high-risk subgroup with severe coronary disease, variant angina, and/or impaired early prognosis.

We assessed the value of two-channel Holter monitoring during the initial hours of hospitalization in patients with unstable angina pectoris (UAP) to identify those with severe coronary artery disease (CAD), variant angina, and/or poor prognosis over the next 3 months. Accordingly, 116 UAP patients had Holter monitoring for 27 +/- 7 (mean +/- SD) (range 12 to 50) hours following hospitalization. Of these, 24 evolved myocardial infarction (MI) during monitoring and 92 did not. Transient ST segment alterations occurred in 21 of the 92. Of these 21, 4 had variant angina, were treated with calcium antagonists, and did well. Each of the remaining 17 had severe fixed CAD (left main or three-vessel) (n = 12) and/or poor prognosis over the 3 months after discharge as manifested by death (n = 1), MI (n = 3), and/or severe angina (n = 3). In contrast, 71 patients did not demonstrate transient ST segment alterations: none had variant angina (p less than 0.001), nine had left main or three-vessel CAD (p less than 0.001), and 50 were alive and well 3 months after discharge (p less than 0.001). Ventricular tachycardia (VT) was demonstrated by Holter monitor in 5 of the 92 patients: four had three-vessel CAD and the other had severe persistent angina. Thus in patients hospitalized with unstable angina, transient ST segment alterations and/or VT on Holter monitor are specific predictors of "high-risk" subgroup UAP patients with left main or three-vessel CAD, variant angina, and/or impaired 3-month prognosis.