Evidence for a bubble-competition regime in indirectly driven ablative Rayleigh-Taylor instability experiments on the NIF.

We investigate on the National Ignition Facility the ablative Rayleigh-Taylor instability in the transition from weakly nonlinear to highly nonlinear regimes. A planar plastic package with preimposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130 µm thick foil. Measurements of the modulation optical density performed by x-ray radiography show that a bubble-merger regime for the Rayleigh-Taylor instability at an ablation front is achieved for the first time in indirect drive. The mutimode modulation amplitudes are in the nonlinear regime, grow beyond the Haan multimode saturation level, evolve toward the longer wavelengths, and show insensitivity to the initial conditions.

Observation of the stabilizing effect of a laminated ablator on the ablative Rayleigh-Taylor instability.

A laminated ablator is explored as an alternative concept for stabilizing the ablative Rayleigh-Taylor instability which develops in inertial fusion targets. Experiments measuring the growth of the Rayleigh-Taylor instability of laminated planar foils are reported. Consistent with both theory and simulations, a significant reduction of the perturbation growth is experimentally observed for laminated ablators in comparison to what is observed for classical uniform ablators. Such an enhanced hydrodynamic stability opens opportunities for the design of high-gain inertial fusion targets.

Experimental demonstration of X-ray drive enhancement with rugby-shaped hohlraums.

Rugby-shaped hohlraums have been suggested as a way to enhance x-ray drive in the indirect drive approach to inertial confinement fusion. This Letter presents an experimental comparison of rugby-shaped and cylinder hohlraums used for D2 and D3He-filled capsules implosions on the Omega laser facility, demonstrating an increase of x-ray flux by 18% in rugby-shaped hohlraums. The highest yields to date for deuterium gas implosions in indirect drive on Omega (1.5x10{10} neutrons) were obtained, allowing for the first time the measurement of a DD burn history. Proton spectra measurements provide additional validation of the higher drive in rugby-shaped hohlraums.

Prolate-spheroid ("rugby-shaped") hohlraum for inertial confinement fusion.

A novel rugby-ball shaped hohlraum is designed in the context of the indirect-drive scheme of inertial-confinement fusion (ICF). Experiments were performed on the OMEGA laser and are the first use of rugby hohlraums for ICF studies. Analysis of experimental data shows that the hohlraum energetics is well understood. We show that the rugby-ball shape exhibits advantages over cylinder, in terms of temperature and of symmetry control of the capsule implosion. Simulations indicate that rugby hohlraum driven targets may be candidates for ignition in a context of early Laser MegaJoule experiments with reduced laser energy.

Prevalence of diphtheria toxin antibodies in human sera from a cross-section of the Italian population.

A polycentric study was carried out between 1993 and 1995 in order to evaluate diphtheria immunity on a representative sample of population from different areas of Italy. To determine diphtheria antitoxin, sera from 5187 apparently healthy subjects, divided according to sex and age groups, were titrated using an ELISA indirect method. A basic protective titre of diphtheria antitoxin (> 0.01 IU ml-1) was found in 4080 (78.6%) subjects. No statistically significant differences between males and females were observed. Our findings show that the proportion of susceptibles increases with age and a high proportion of adults no longer has diphtheria antitoxin at protective levels since toxigenic C. diphtheriae circulation is presently lacking in Italy.

[Abnormal autonomic cardiovascular responses in patients with sickle cell anemia]. / Respuestas cardiovasculares autónomas anormales en pacientes con anemia drepanocítica.

PURPOSE: To evaluate the presence of anomalies of the autonomic reflex cardiovascular response in patients with chronic sickle-cell anaemia. PATIENTS AND METHODS: The study was extended to 30 patients with sickle-cell anaemia, 10 patients with iron-lack anaemia and 30 healthy subjects. Age and sex distribution was similar in each group. To be included in the study, patients should have had no painful crisis or blood transfusion in the 6 months previous to the assay. Clinico-laboratory survey, chest x-ray and EKG were performed in every case. Blood cell count and abnormal haemoglobin study on cellulose acetate were carried out as well. The evaluation of reflex autonomic responses was performed by means of active orthostatism, cold pressor test, Valsalva maneuver and urine catecholamine output. The statistical analysis was performed with the variance analysis (ANOVA) for multiple groups. RESULTS: The following abnormalities were found: 12 patients had haemoglobin SS, 8 had haemoglobin SS and F, 3 had haemoglobin SC, 2 had haemoglobin S and beta-thalassaemia, and 5 had combined haemoglobin SS,F and A2. Systolic pressure and heart frequency in the supine position were similar in all groups. Diastolic pressure was lower in the sickle-cell anaemia group with respect to the normals. Patients with sickle-cell disease had lower heart frequency in the active orthostatism test with regard to the other groups, along with paradoxal changes in systolic pressure and lesser increase of the diastolic pressure. Significantly lower response to the cold pressor test was seen in the sickle-cell patients as compared with the iron-lack cases and the normal controls. Reduced sympathetic tachycardia was seen with the Valsalva maneuver, whereas the bradycardia was similar to the other groups. The urine noradrenaline in output was significantly lower in the sickle-cell patients, it was normal in the other groups (p < 0.01). CONCLUSION: These results suggest a defective sympathetic activity of heart and arteries in patients with sickle-cell anaemia.

Addition of captopril versus increasing diuretics in moderate but deteriorating heart failure: a double-blind comparative trial.

In 15 patients with moderate congestive heart failure not completely controlled on digoxin (0.25 mg o.d.) and frusemide (25 mg o.d.), we compared the addition of captopril (12.5 to 50 mg b.i.d.) with increasing doses of frusemide (25 to 100 mg o.d.), in a randomized double-blind, double-dummy, comparative trial. Thirteen patients completed the 3 months study: two dropped-out in the frusemide group. Statistically significant clinical improvement occurred in both treatment groups. Exercise tolerance also significantly improved in both groups in a parallel fashion. Echocardiographic cardiac function data showed a significantly better pattern of changes in the captopril group. The addition of low doses of captopril to basal therapy seems to be as effective as the addition of high doses of frusemide in uncontrolled moderate congestive heart failure. This approach with captopril also appears to be more physiological and safe.

Detection of ventilation unevenness by nitrogen washout and forced vital capacity manoeuvres: its limits and reliability.

We investigated the behaviour of several indices of ventilation unevenness in a sample of 234 normal subjects aged between 20 and 80 years, divided into 12 classes of 5 years each. The aim of the present study was to find out whether it is possible to predict a reliable value for each of these indices as a function of age, height and TLC. For each index a large dispersion of experimental points and a high unexplained variance was found, so that it does not seem worthwhile predicting its value as a function of age, height and TLC. We concluded that there is no reason to employ these indices to detect the beginning of a lung function impairment.

Respiratory function during pregnancy.

We studied the respiratory mechanics, acid-base status, alveolar ventilation and ventilatory response to hypercapnia in pregnant women at the first and third trimesters and postpartum. We found alveolar hyperventilation and hypersensitivity of the respiratory centers to carbon dioxide with no significant differences between the first and third trimesters. After delivery we found a sudden decrease in these parameters. The changes seem to be due to a direct primary (probably hormonal) stimulation on the medulla oblongata and cannot be correlated to the metabolic needs of the fetus and are aimed at favoring placental gas exchanges, especially at the beginning of the pregnancy, when the fetal cardiovascular system is not yet developed.