Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Late permissive hypercapnia and respiratory stability among very preterm infants: a pilot randomised trial

OBJECTIVE

Determine if targeting higher transcutaneous carbon dioxide improves respiratory stability among very preterm infants on ventilatory support.

DESIGN

Single-centre pilot randomised clinical trial.

SETTING

The University of Alabama at Birmingham.

PATIENTS

Very preterm infants on ventilatory support after postnatal day 7.

INTERVENTIONS

Infants were randomised to two different transcutaneous carbon dioxide levels targeting 5 mm Hg (0.67 kPa) changes with four sessions each lasting 24 hours for 96 hours: baseline-increase-baseline-increase or baseline-decrease-baseline-decrease.

MAIN OUTCOME MEASURES

We collected cardiorespiratory data evaluating episodes of intermittent hypoxaemia (oxygen saturations (SpO2)<85% for ≥10 s), bradycardia (<100 bpm for ≥10 s), and cerebral and abdominal hypoxaemia on near-infrared spectroscopy.

RESULTS

We enrolled 25 infants with a gestational age of 24 w 6 d±11 d (mean±SD) and birth weight 645±142 g on postnatal day 14±3. Continuous transcutaneous carbon dioxide values (56.8±6.9 in the higher group vs 54.5±7.8 in the lower group; p=0.36) did not differ significantly between groups during the intervention days. There were no differences in intermittent hypoxaemia (126±64 vs 105±61 per 24 hours; p=0.30) or bradycardia (11±16 vs 15±23 per hour; p=0.89) episodes between groups. The proportion of time with SpO2<85%, SpO2<80%, cerebral hypoxaemia or abdominal hypoxaemia did not differ (all p>0.05). There was moderate negative correlation between mean transcutaneous carbon dioxide and bradycardia episodes (r=-0.56; p<0.001).

CONCLUSION

Targeting 5 mm Hg (0.67 kPa) changes in transcutaneous carbon dioxide did not improve respiratory stability among very preterm infants on ventilatory support but the intended carbon dioxide separation was difficult to achieve and maintain.

TRIAL REGISTRATION NUMBER

NCT03333161.

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

Higher- or Usual-Volume Feedings in Infants Born Very Preterm: A Randomized Clinical Trial

OBJECTIVE

To determine whether higher-volume feedings improve postnatal growth among infants born very preterm.

STUDY DESIGN

Randomized clinical trial with 1:1 parallel allocation conducted from January 2015 to June 2018 in a single academic medical center in the US. In total, 224 infants with a birth weight 1001-2500 g born at <32 weeks of gestation were randomized to higher-volume (180-200 mL/kg/d) or usual-volume (140-160 mL/kg/d) feedings after establishing full enteral feedings (≥120 mL/kg/d). The primary outcome was growth velocity (g/kg/d) from randomization to study completion at 36 weeks of postmenstrual age or hospital discharge if earlier.

RESULTS

Growth velocity increased among infants in the higher-volume group compared with the usual-volume group (mean [SD], 20.5 [4.5] vs 17.9 [4.5] g/kg/d; P < .001). At study completion, all measurements were higher among infants in the higher-volume group compared with the usual-volume group: weight (2365 [324] g, z score -0.60 [0.73] vs 2200 [308] g, z score -0.94 [0.71]; P < .001); head circumference (31.9 [1.3] cm, z score -0.30 [0.91] vs 31.4 [1.3] cm, z score -0.53 [0.84]; P = .01); length (44.9 [2.1] cm, z score -0.68 [0.88] vs 44.4 [2.0], z score -0.83 [0.84]; P = .04); and mid-arm circumference (8.8 [0.8] cm vs 8.4 [0.8] cm; P = .002). Bronchopulmonary dysplasia, patent ductus arteriosus, necrotizing enterocolitis, or other adverse outcomes did not differ between groups.

CONCLUSIONS

In infants born very preterm weighing 1001-2500 g at birth, higher-volume feedings increased growth velocity, weight, head circumference, length, and mid-arm circumference compared with usual-volume feedings without adverse effects.

TRIAL REGISTRATION

ClinicalTrials.gov; NCT02377050.

Survival time of ECMO circuits on and off bleeding protocol: is there a higher risk of circuit clotting?

PURPOSE

Bleeding is a dreaded complication of extracorporeal membrane oxygenation (ECMO). At our institution, we use a bleeding protocol (BP) with or without ε-amino caproic acid (ACA) for certain prophylactic or therapeutic indications. Subjectively, we have felt that placing a child on bleeding protocol shortens the circuit life because of clot formation. In this study, we evaluated the impact of BP with and without ACA on the survival time of the ECMO circuit.

METHODS

A retrospective analysis of all ECMO patients treated in our institution from 2000 to 2008 was performed. An event was defined as a change of the ECMO circuit for thrombosis. The times until occurrence of an event were noted for children off (standard) or on bleeding protocol (BP) and ACA (BP+ACA). Survival curves were generated for each of these study groups and compared using the log rank test.

RESULTS

A total of 164 patients were treated with ECMO during the study period. 32 events were noted in the standard, 20 in the BP, and 25 in the BP+ACA group. Mean survival time of the circuit was 10.5 ± 3.8 days for the standard, 8.6 ± 3.4 days for the BP, and 9.9 ± 4.6 days for BP+ACA protocols. The corresponding Kaplan-Meier survival curves are shown. The log rank test showed no significant differences between groups (standard vs. BP p=0.12; standard vs. BP+ACA p=0.92).

CONCLUSIONS

We found no evidence that instituting a bleeding protocol with or without aminocaproic acid shortens circuit times. Clotting of the ECMO unit should not be a major concern when placing a patient on a bleeding protocol.

Understanding the structure of the turbulent mixing layer in hydrodynamic instabilities

When a heavy fluid is placed above a light fluid, tiny vertical perturbations in the interface create a characteristic structure of rising bubbles and falling spikes known as Rayleigh-Taylor instability. Rayleigh-Taylor instabilities have received much attention over the past half-century because of their importance in understanding many natural and man-made phenomena, ranging from the rate of formation of heavy elements in supernovae to the design of capsules for Inertial Confinement Fusion. We present a new approach to analyze Rayleigh-Taylor instabilities in which we extract a hierarchical segmentation of the mixing envelope surface to identify bubbles and analyze analogous segmentations of fields on the original interface plane. We compute meaningful statistical information that reveals the evolution of topological features and corroborates the observations made by scientists. We also use geometric tracking to follow the evolution of single bubbles and highlight merge/split events leading to the formation of the large and complex structures characteristic of the later stages. In particular we (i) Provide a formal definition of a bubble; (ii) Segment the envelope surface to identify bubbles; (iii) Provide a multi-scale analysis technique to produce statistical measures of bubble growth; (iv) Correlate bubble measurements with analysis of fields on the interface plane; (v) Track the evolution of individual bubbles over time. Our approach is based on the rigorous mathematical foundations of Morse theory and can be applied to a more general class of applications.