Improvements to Emissive Plume and Shock Wave Diagnostics and Interpretation During Pulsed Laser Ablation of Graphite

This dissertation covers nanosecond pulsed laser ablation of graphite for 4-5.7 J/cm2 fluences with 248 nm and 532 nm lasers in 1-180 Torr helium, argon, nitrogen, air, and mixed gas. Three experiments were performed to improve the interpretation of common diagnostics used to characterize pulsed laser ablation, find simple but universal scaling relationships for comparing dynamics across different materials and ablation conditions, and provide a systematic analysis of graphite emissive plume and shock wave dynamics. A scaling of the Sedov-Taylor energy ratio was developed and validated for a range of studies despite differences in wavelength, pulse duration, fluence, and target material. Normalized shock thickness for Mach 48 plumes were compared to prior ablation and shock tube studies (Mach ≤ 10) using a common analytical model. Shock detachment distances were identified by comparing plume and schlieren shock propagation trajectories. The shock detachment points were used to improve Sedov-Taylor blast analysis, allowing for enhanced estimates of laser-plume energy coupling. Finally, plume and shock wave morphology were compared

An Empirical Analysis of the Cascade Secret Key Reconciliation Protocol for Quantum Key Distribution

The need to share key material with authorized entities in a secure, efficient and timely manner has driven efforts to develop new key distribution methods. The most promising method is Quantum Key Distribution (QKD) and is considered to be “unconditionally secure” because it relies upon the immutable laws of quantum physics rather than computational complexity. Unfortunately, the nonidealities present in actual implementations of QKD systems also result in errors manifested in the quantum data channel. As a consequence, an important component of any QKD system is the error reconciliation protocol which is used to identify and correct inconsistencies in the exchanged key material. This research provides an empirical analysis of the Cascade secret key reconciliation protocol to measure its efficacy under different error rates, sampling rates, error distributions and larger sifted key sizes. The key findings of the research are that 1) an error sampling rate of 25% provides optimal Cascade performance when using variable block sizes, 2) the choice of sifted key length directly impacts the accuracy of Cascade error estimation, 3) the Cascade algorithm performs well in burst error environments with initial permutation, and 4) a tradeoff exists between buffer size and information leaked

Shock Front Detachment during Pulsed Laser Ablation of Graphite

Pulsed laser ablation of pyrolytic graphite with a 5.7 J/cm2 frequency-doubled Nd:YAG laser in backgrounds of argon, nitrogen, and mixed gas at pressures from 3 to 180 Torr was performed to study the dynamics of the ablation shock wave and plume emissive contact front. White light schlieren shock wave imaging and optical emission imaging with a 2.88–40 ns gated ICCD camera was used to determine shock wave and emissive plume trajectories to find the location of shock detachment from the plume and for blast energy characterization by Sedov-Taylor theory. The shock detachment points are used to limit emissive contact front Sedov-Taylor fits to the portion of the plume which exhibits a shock-like trajectory, resulting in improved laser-plume coupling energy estimates compared to standard fits. The emissive plume expands with initial Mach numbers up to M ~ 54 at t = 62 ns, decreasing to M ~ 7 as the emission becomes too weak to detect after several microseconds. The shock wave expands with initial Mach numbers up to M ~ 55 at t = 62 ns, decreasing to M ~ 1 at t = 20 µs. The shock waves exhibit spherical shock fronts, but the dimensionality, n, decreases as pressure and mass of the background gas increase, while the plumes exhibit an opposite trend. The Sedov-Taylor energy released in the sudden ablation is typically 55–75% of the laser pulse energy. The detachment-limited blast energy calculations for the emissive plume agree to within 3–5% of the shock wave energy values. Shock detachment points are nearer the target at higher pressure and scale with the mean free path

Heavy Alcohol Use Among Women and Men Living With HIV in Uganda, Russia, and the United States.

ObjectiveWe examined whether gender is associated with heavy drinking in three cohorts of people living with HIV (PLWH) in Mbarara, Uganda; St. Petersburg, Russia; and Boston, Massachusetts.MethodWe conducted secondary analyses of baseline data collected from three cohorts in the Uganda Russia Boston Alcohol Network for Alcohol Research Collaboration on HIV/AIDS (URBAN ARCH) consortium. We used multiple logistic regression models to evaluate the association between gender and heavy drinking (defined in combination with self-report and phosphatidylethanol [PEth]) within each cohort.ResultsIn unadjusted logistic regression models, we found no significant association between gender and heavy drinking in Russia or Boston. In Uganda, women were less likely than men to engage in heavy drinking (odds ratio = 0.38, 95% CI [0.26, 0.58], p <.01). These findings were invariant to adjustment for covariates.ConclusionsWe did not detect associations between gender and heavy drinking in cohorts of PLWH in Russia or Boston, suggesting that heavy drinking may be as common in women living with HIV as in men living with HIV in these locations. Although these cohorts were enriched with heavy drinking participants, which limits broad extrapolation to PLWH in those settings, nonetheless the findings are concerning given the significant morbidity associated with alcohol use among PLWH and women in particular

Effect of transcatheter aortic valve implantation vs surgical aortic valve replacement on all-cause mortality in patients with aortic stenosis

Importance: Transcatheter aortic valve implantation (TAVI) is a less invasive alternative to surgical aortic valve replacement and is the treatment of choice for patients at high operative risk. The role of TAVI in patients at lower risk is unclear. Objective: To determine whether TAVI is noninferior to surgery in patients at moderately increased operative risk. Design, Setting, and Participants: In this randomized clinical trial conducted at 34 UK centers, 913 patients aged 70 years or older with severe, symptomatic aortic stenosis and moderately increased operative risk due to age or comorbidity were enrolled between April 2014 and April 2018 and followed up through April 2019. Interventions: TAVI using any valve with a CE mark (indicating conformity of the valve with all legal and safety requirements for sale throughout the European Economic Area) and any access route (n = 458) or surgical aortic valve replacement (surgery; n = 455). Main Outcomes and Measures: The primary outcome was all-cause mortality at 1 year. The primary hypothesis was that TAVI was noninferior to surgery, with a noninferiority margin of 5% for the upper limit of the 1-sided 97.5% CI for the absolute between-group difference in mortality. There were 36 secondary outcomes (30 reported herein), including duration of hospital stay, major bleeding events, vascular complications, conduction disturbance requiring pacemaker implantation, and aortic regurgitation. Results: Among 913 patients randomized (median age, 81 years [IQR, 78 to 84 years]; 424 [46%] were female; median Society of Thoracic Surgeons mortality risk score, 2.6% [IQR, 2.0% to 3.4%]), 912 (99.9%) completed follow-up and were included in the noninferiority analysis. At 1 year, there were 21 deaths (4.6%) in the TAVI group and 30 deaths (6.6%) in the surgery group, with an adjusted absolute risk difference of −2.0% (1-sided 97.5% CI, −∞ to 1.2%; P < .001 for noninferiority). Of 30 prespecified secondary outcomes reported herein, 24 showed no significant difference at 1 year. TAVI was associated with significantly shorter postprocedural hospitalization (median of 3 days [IQR, 2 to 5 days] vs 8 days [IQR, 6 to 13 days] in the surgery group). At 1 year, there were significantly fewer major bleeding events after TAVI compared with surgery (7.2% vs 20.2%, respectively; adjusted hazard ratio [HR], 0.33 [95% CI, 0.24 to 0.45]) but significantly more vascular complications (10.3% vs 2.4%; adjusted HR, 4.42 [95% CI, 2.54 to 7.71]), conduction disturbances requiring pacemaker implantation (14.2% vs 7.3%; adjusted HR, 2.05 [95% CI, 1.43 to 2.94]), and mild (38.3% vs 11.7%) or moderate (2.3% vs 0.6%) aortic regurgitation (adjusted odds ratio for mild, moderate, or severe [no instance of severe reported] aortic regurgitation combined vs none, 4.89 [95% CI, 3.08 to 7.75]). Conclusions and Relevance: Among patients aged 70 years or older with severe, symptomatic aortic stenosis and moderately increased operative risk, TAVI was noninferior to surgery with respect to all-cause mortality at 1 year. Trial Registration: isrctn.com Identifier: ISRCTN57819173