Theory of quadratic optical frequency combs

We present theoretical studies of optical frequency comb generation in dispersive quadratically nonlinear resonators. We introduce a mean field equation approach to model cavity enhanced second harmonic generation and find excellent agreement with recent experimental frequency comb observations. We also develop a more general approach based on a single envelope equation for both quadratic and Kerr nonlinear cavities

Singly resonant second-harmonic-generation frequency combs

We consider frequency comb generation in dispersive singly resonant second-harmonic-generation cavity systems. Using a single temporal mean-field equation for the fundamental field that features a noninstantaneous nonlinear response function, we model the temporal and spectral dynamics and analyze comb generation, continuous wave bistability, and modulational instability. It is found that, owing to the significant temporal walk-off between the fundamental and second-harmonic fields, modulational instability can occur even in the complete absence of group-velocity dispersion. We further consider the relation of our model to a previously proposed modal expansion approach, and present a derivation of a general system of coupled mode equations. We show that the two models provide very similar predictions and become exactly equivalent in the limit that absorption losses and group-velocity dispersion at the fundamental frequency are neglected. Finally, we perform numerical simulations that show examples of the variety of comb states that are possible in phase-matched quadratic resonators, and discuss the dynamics of the comb formation process

Nonlinear dynamics of optical frequency combs

We discuss recent advances in the modelling of optical frequency comb generation in quadratic and cubic microresonators. Dierent time domain models are presented and compared, and their solutions are analysed by numerical methods

Performance Benefits of Pre- and Per-cooling on Self-paced Versus Constant Workload Exercise:A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVE: Exercise in hot environments impairs endurance performance. Cooling interventions can attenuate the impact of heat stress on performance, but the influence of an exercise protocol on the magnitude of performance benefit remains unknown. This meta-analytical review compared the effects of pre- and per-cooling interventions on performance during self-paced and constant workload exercise in the heat.METHODS: The study protocol was preregistered at the Open Science Framework ( https://osf.io/wqjb3 ). A systematic literature search was performed in PubMed, Web of Science, and MEDLINE from inception to 9 June, 2023. We included studies that examined the effects of pre- or per-cooling on exercise performance in male individuals under heat stress (&gt; 30 °C) during self-paced or constant workload exercise in cross-over design studies. Risk of bias was assessed using the Cochrane Risk of Bias Tool for randomized trials.RESULTS: Fifty-nine studies (n = 563 athletes) were identified from 3300 records, of which 40 (n = 370 athletes) used a self-paced protocol and 19 (n = 193 athletes) used a constant workload protocol. Eighteen studies compared multiple cooling interventions and were included more than once (total n = 86 experiments and n = 832 paired measurements). Sixty-seven experiments used a pre-cooling intervention and 19 used a per-cooling intervention. Average ambient conditions were 34.0 °C [32.3-35.0 °C] and 50.0% [40.0-55.3%] relative humidity. Cooling interventions attenuated the performance decline in hot conditions and were more effective during a constant workload (effect size [ES] = 0.62, 95% confidence interval [CI] 0.44-0.81) compared with self-paced exercise (ES = 0.30, 95% CI 0.18-0.42, p = 0.004). A difference in performance outcomes between protocols was only observed with pre-cooling (ES = 0.74, 95% CI 0.50-0.98 vs ES = 0.29, 95% CI 0.17-0.42, p = 0.001), but not per-cooling (ES = 0.45, 95% CI 0.16-0.74 vs ES = 0.35, 95% CI 0.01-0.70, p = 0.68).CONCLUSIONS: Cooling interventions attenuated the decline in performance during exercise in the heat, but the magnitude of the effect is dependent on exercise protocol (self-paced vs constant workload) and cooling type (pre- vs per-cooling). Pre-cooling appears to be more effective in attenuating the decline in exercise performance during a constant workload compared with self-paced exercise protocols, whereas no differences were found in the effectiveness of per-cooling.</p

Density functional theory study of single-molecule ferroelectricity in Preyssler-type polyoxometalates

A detailed study on the single-molecule ferroelectric property of Preyssler-type polyoxometalates (POMs), [M3+P5W30O110]12− (M = La, Gd, and Lu), is performed by density functional theory calculations. Linked to one H2O molecule, the cation (M3+) encapsulated in the cavity of the Preyssler framework is off-centered, and it generates a permanent dipole, which is essential for a ferroelectric ground state. Accompanied with a 180° rotation of H2O, the switching of M3+ between two isoenergetic sites on both sides of the cavity results in a calculated barrier of 1.15 eV for Gd3+, leading to the inversion of electric polarization. The height of the barrier is in good agreement with the experimentally measured barrier for the Tb3+ ion, whose ionic radius is similar to Gd3+. The total polarization value of the crystal is estimated to be 4.7 µC/cm2 as calculated by the modern theory of polarization, which is quite close to the experimental value. Considering that the order of contributions to the polarization is M3+–H2O &gt; counter-cations (K+) &gt; [P5W30O110]15−, the interconversion of M3+–H2O between the two isoenergetic sites is predicted to be the main origin of ferroelectricity with a polarization contribution of 3.4 µC/cm2; the K+ counter-cations contribute by 1.2 µC/cm2 and it cannot be disregarded, while the framework appears to contribute negligibly to the total polarization. Our study suggests that a suitable choice of M3+–H2O could be used to tune the single-molecule ferroelectricity in Preyssler-type polyoxometalates

Immune and virologic responses to Truvada or Combivir as a first-line therapy of HIV-infected, treatment-naïve patients

Methods 107 HIV-infected, ARV-naive patients were prospectively enrolled and treated with TVD (300 mg TDF + 200 mg FTC QD) or CBV (300 mg AZT + 150 mg 3TC BID) in combination with EFV (600 mg QD) or a PI (LPV/r, ATV/ r, fAPV/r and SQV/r). Twenty-seven patients received TVD-EFV, 33 received TVD-PI, 24 received CBV-EFV, and 23 received CBV-PI. Fifty-one of these patients have, so far, reached 12 months of therapy. Clinical, immunological and virologic parameters at baseline and after 12 months of therapy are presented

Evidence for genetic factors explaining the association between birth weight and low-density lipoprotein cholesterol and possible intrauterine factors influencing the association between birth weight and high-density lipoprotein cholesterol: Analysis in twins

Recent studies have demonstrated an association between low weight at birth and an atherogenic lipid profile in later life. To examine the influences of intrauterine and genetic factors, we investigated 53 dizygotic and 61 monozygotic adolescent twin pairs. Regression analysis demonstrated that low birth weight was associated with high levels of total cholesterol, low-density lipoprotein (LDL) cholesterol and apolipoprotein B (-0.17 mmol/liter per kg, P = 0.07; -0.18 mmol/liter per kg, P = 0.04; and -0.07 g/liter per kg, P = 0.02, respectively) and with low levels of high-density lipoprotein (HDL) cholesterol (+0.04 mmol/liter per kg, P = 0.1), after adjustment for age, sex, and body mass index. Intrapair differences in birth weight were significantly associated with differences in total cholesterol, LDL cholesterol, and apolipoprotein B in dizygotic twins after adjustment for differences in current body mass index (-0.49 mmol/liter per kg, P = 0.02; -0.51 mmol/liter per kg, P = 0.01; and -0.10 g/liter per kg, P = 0.04, respectively), demonstrating that the larger the difference in birth weight, the higher these risk factors in the twin with the lower birth weight, compared with the cotwin with the higher birth weight. In monozygotic twins, however, the associations between intrapair differences in birth weight and differences in total cholesterol, LDL cholesterol, and apolipoprotein B were in the opposite direction (+0.32 mmol/liter per kg, P = 0.03; +0.23 mmol/liter per kg, P = 0.08; and +0.06 g/liter per kg, P = 0.04, respectively). The association between intrapair differences in birth weight and differences in HDL cholesterol was not significant in dizygotic twins (+0.04 mmol/liter per kg, P = 0.6) and of borderline significance in monozygotic twins (+0.11 mmol/liter per kg, P = 0.05). These data suggest that genetic factors account for the association of low birth weight with high levels of total cholesterol, LDL cholesterol, and apolipoprotein B, whereas intrauterine factors possibly play a role in the association between birth weight and HDL cholesterol

Training for the HandbikeBattle:an explorative analysis of training load and handcycling physical capacity in recreationally active wheelchair users

Purpose: (1) to analyze training characteristics of recreationally active wheelchair users during handcycle training, and (2) to examine the associations between training load and change in physical capacity. Methods: Former rehabilitation patients (N = 60) with health conditions such as spinal cord injury or amputation were included. Participants trained for five months. A handcycling/arm crank graded exercise test was performed before and after the training period. Outcomes: peak power output per kg (POpeak/kg) and peak oxygen uptake per kg (VO 2peak/kg). Training load was defined as Training Impulse (TRIMP), which is rating of perceived exertion (sRPE) multiplied by duration of the session, in arbitrary units (AU). Training intensity distribution (TID) was also determined (time in zone 1, RPE ≤4; zone 2, RPE 5–6; zone 3, RPE ≥7). Results: Multilevel regression analyses showed that TRIMP sRPE was not significantly associated with change in physical capacity. Time in zone 2 (RPE 5–6) was significantly associated with ΔVO 2peak, %ΔVO 2peak, ΔVO 2peak/kg and %ΔVO 2peak/kg. Conclusion: Training at RPE 5–6 was the only determinant that was significantly associated with improvement in physical capacity. Additional controlled studies are necessary to demonstrate causality and gather more information about its usefulness, and optimal handcycle training regimes for recreationally active wheelchair users.IMPLICATIONS FOR REHABILITATION Monitoring of handcycle training load is important to structure the training effort and intensity over time and to eventually optimize performance capacity. This is especially important for relatively untrained wheelchair users, who have a low physical capacity and a high risk of overuse injuries and shoulder pain. Training load can be easily calculated by multiplying the intensity of the training (RPE 0–10) with the duration of the training in minutes. Results on handcycle training at RPE 5–6 intensity in recreationally active wheelchair users suggests to be promising and should be further investigated with controlled studies