Slow Absorber Research Articles

Plasmonic induced reflection based on Al2O3 nanoslit side coupled with silicon nanodisk resonator

plasmonic induced reflection (PIR) effect has potential applications in many nanophotonics devices, Such as slow light, absorber and filter. To realize plasmonic induced interference, in this paper, we present PIR effect in a periodic subwavelength array of nanoslit side-coupled to nanodisk resonator. Both finite-difference time-domain (FDTD) and coupled-mode theory (CMT) method indicate that the destructive interference between the bright mode resonator (nanosilt) and dark mode resonator (nanodisk) leads to PIR effect. Double-band absorption with maximum absorbance up to 96% and 90% is achieved 1440 nm and 1661 nm, respectively. The effect of structural parameters on reflection and the field distribution are also studied in detail. Moreover, multiple PIR effect can be realized by introducing more dark mode resonators. The results will pave the way towards the design of double band PIR, which may have potential application in slow light technology, plasmonic modulator, plasmonic filter and multiband plasmonic absorbers.

No Impact of Pharmacokinetics Profiles on the Clinical and Biological Response to Hydroxyurea in Children with Sickle Cell Disease

▪Hydroxyurea (HU) is an important drug for sickle cell disease (SCD) that improves clinical outcome and survival. However, its pharmacokinetics (PK) and pharmacodynamics (PD) are highly variable. HU has an excellent oral bioavailability, with half-life of 2-4 hours and renal elimination. Two oral absorption phenotypes have been identified: slow phenotype with a peak concentration reached after 60 to 120 minutes and rapid phenotype with a peak at 15 to 30 minutes. These phenotypes seem to be linked to the maximal tolerated dose of hydroxyurea and could affect the response to HU.The aim of this study was to explore the possible correlation between clinical and biological response to HU and PK and PD parameters.This study was conducted at Hôpital Universitaire des Enfants Reine Fabiola (Brussels, Belgium) and included SCD children older than 7 years, regularly followed for more than 3 years. PK samples (salivary and plasmatic) were collected at 0, 30, 60 and 180 minutes after oral HU intake. Patients have been classified as good (GR) or poor responders (PR) to HU according to the absence of recurrence of acute chest syndrome on HU and the number of vaso-occlusive crisis (VOC) and hospitalization days on HU. Changes in biological parameters were assessed after 1 year on HU. Chi square test was used for the comparison between good and poor responders on HU. Paired T test was used to compare biological effect of HU for each oral absorption phenotype and ANOVA to compare PK profile among them.Thirty-one patients have been included in this study. The characteristics of the patients are detailed in the Table 1. On HU, a significant decrease of the number of VOC and hospitalization days was observed with an improvement of biological parameters (Table 2). The numbers of VOC and hospitalization days were significantly lower in girls compared to boys on HU (0.33 vs. 0, P=0.02 and 3.17 vs. 1.33, P = 0.02 respectively). However except for reticulocyte count, biological data, age, dose of HU or PK parameters were similar in both sexes.Eighteen patients have been classified as GR (14 girls) and 13 as PR (5 girls). Their demographic characteristics and biological values (pre and on HU) were not significantly different, except a higher change of HbF level in GR compared to PR (+13% vs. +3.7% ; P=0.034). Girls had a non-significant trend to belong to the GR group (P = 0.059).The median plasmatic peak concentration (Cpmax) was 42.25mg/l (Range: 14.8-62), the median salivary peak concentration (Csmax) was 19.54 mg/l (Range: 5.03-124.43) and the median AUC was 4650mg.min/l (Range: 1197-8742). AUC was similar in both sexes (4650mg.min/l vs. 4666mg.min/l; P=0.79). Except for salivary concentration at 60 minutes, all PK parameters were not significantly different between the GR and PR (Table 3). No significant correlation was found between peak concentration (Cmax) and demographic parameters.We identified 3 absorption phenotypes with a Cpmax reached at 30, 60 and 180 minutes for rapid, intermediate and slow absorbers (Table 4). Biological changes on HU were similar among the 3 phenotypes, but did not reached statistical signification in slow absorbers (only 5 patients). 16/18 GR patients reach Cpmax at 30 and 60 minutes compared to 10/13 for PR (P=0.63). The AUC in the 3 absorption phenotypes was not significantly different (P=0.069). No correlation was found between salivary and plasmatic concentration at time-points studied.In conclusion, no correlation between the absorption phenotype and the clinical response to HU could be found. No correlation was found between AUC, Cpmax and clinical response. Nevertheless our study has limitation due to the limited sample size. Salivary measurement did not provide reliable information and cannot be used instead of plasmatic samples. The gender is the only factor identified that can predict the biological response to HU (with a trend to a better clinical response in girls) despite similar AUC and PK parameters. This finding may reflect the better adherence to treatment in girls compared to boys.The variability of the clinical response to HU remains to be elucidated. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Tri-control large angle electromagnetically induced reflection in metamaterials with graphene and vanadium dioxide

Graphene and vanadium dioxide (VO2) have been widely studied because of their flexibly tunable conductivity. In this study, a multilayer structure of a graphene disk and a VO2 square ring is investigated. The proposed structure exhibits an electromagnetically induced reflection (EIR) that is caused by a bright mode coupled with a dark mode. Since the permittivity of graphene can be modulated by chemical potential and electron–phonon relaxation time, while that of VO2 can be modulated by temperature, the EIR effect of the proposed structure can be tuned by the chemical potential and relaxation time of graphene as well as the surrounding temperature. Therefore, a triple-tunable EIR effect is obtained. Simulation results confirm that the tunable EIR phenomenon is polarization-independent owing to the symmetry of the structure. Moreover, a large angle EIR effect is obtained up to an angle of 80°. Our results can contribute significantly in applications of terahertz devices, such as slow light devices, absorbers, switching devices, and sensors.

Regulation of accretion by its outflow in a symbiotic star: the 2016 outflow fast state of MWC 560

ABSTRACT How are accretion discs affected by their outflows? To address this question for white dwarfs accreting from cool giants, we performed optical, radio, X-ray, and ultraviolet observations of the outflow-driving symbiotic star MWC 560 (≡V694 Mon) during its 2016 optical high state. We tracked multi-wavelength changes that signalled an abrupt increase in outflow power at the initiation of a months-long outflow fast state, just as the optical flux peaked: (1) an abrupt doubling of Balmer absorption velocities; (2) the onset of a 20 μJy per month increase in radio flux; and (3) an order-of-magnitude increase in soft X-ray flux. Juxtaposing to prior X-ray observations and their coeval optical spectra, we infer that both high-velocity and low-velocity optical outflow components must be simultaneously present to yield a large soft X-ray flux, which may originate in shocks where these fast and slow absorbers collide. Our optical and ultraviolet spectra indicate that the broad absorption-line gas was fast, stable, and dense (≳106.5 cm−3) throughout the 2016 outflow fast state, steadily feeding a lower density (≲105.5 cm−3) region of radio-emitting gas. Persistent optical and ultraviolet flickering indicate that the accretion disc remained intact. The stability of these properties in 2016 contrasts to their instability during MWC 560’s 1990 outburst, even though the disc reached a similar accretion rate. We propose that the self-regulatory effect of a steady fast outflow from the disc in 2016 prevented a catastrophic ejection of the inner disc. This behaviour in a symbiotic binary resembles disc/outflow relationships governing accretion state changes in X-ray binaries.

Picosecond Relaxation of Photoexcitations in a LiLuF4:Ce3+ Crystal

The characteristic durations of energy exchange for Ce3+ impurity centers with lattices in a LiLuF4 crystal and the characteristic lifetime of free photoexcited charge carriers are determined in time-resolved experiments using a pump–probe scheme. The absorption saturation parameters of femtosecond laser pulses with a wavelength of 263 nm are characteristic of a slow absorber that participates in absorption from the excited state.

Age-related differences in plasma and intracellular tenofovir concentrations in HIV-1-infected children, adolescents and adults

There is limited pediatric information on the complex relationships among the dose of tenofovir disoproxil fumarate (TDF), plasma concentrations of tenofovir (TFV), and intracellular TFV diphosphate (TFV-DP) concentrations. Our objectives were to describe TFV-DP pharmacokinetics in children and adolescents and investigate the effect of age on TFV and TFV-DP concentrations. TFV-DP pharmacokinetics were determined in 47 children and adolescents. TFV and TFV-DP were quantified with validated liquid chromatography/tandem mass spectrometry methods. Data were pooled with other studies in HIV-infected adults (N = 55). Nonlinear mixed effects modeling was used to develop the population model and explore the influence of covariates on TFV. A two-compartment model, partitioned for slow and fast absorbers by age, with weight allometrically scaled for children and adolescents, best described TFV pharmacokinetics. An indirect stimulation of response model best described TFV-DP formation. Apparent oral TFV clearance was significantly faster in patients less than 25 versus 25 years or more. The most significant covariate on apparent TFV oral clearance and central distribution volume was creatinine clearance. The TFV plasma concentration producing 50% of maximal TFV-DP concentrations was almost two-fold lower in patients less than 25 versus 25 years or more. The estimated intracellular TFV-DP half-life for these groups was 70 and 87 h, respectively. These data demonstrate that children and adolescents receiving standard TDF dosing of 300 mg once daily achieve higher intracellular TFV-DP concentrations than adults, despite lower plasma TFV concentrations. This age-related difference appears to arise from an increased sensitivity to formation of TFV-DP.

Pharmacokinetics of Rifampin in Peruvian Tuberculosis Patients with and without Comorbid Diabetes or HIV

For drug-compliant patients, poor responses to tuberculosis (TB) treatment might be attributable to subtherapeutic drug concentrations. An impaired absorption of rifampin was previously reported for patients with diabetes mellitus (DM) or HIV. The objectives of this study were to determine whether TB drug pharmacokinetics differed in Peruvian TB patients with DM or HIV. In this cross-sectional study, TB patients, recruited from health centers in Lima, Peru, had blood samples taken at 2 and 6 h after directly observed TB drug ingestion, to determine plasma concentrations of rifampin. Of 105 patients, 50 had TB without a comorbidity, 26 had coexistent DM, and 29 had coexistent HIV. Unexpectedly, the overall median 2- and 6-h levels of rifampin were 1.6 and 3.2 mg/liter, respectively, and the time to the peak concentration was 6 h (slow absorber) instead of 2 h (fast absorber) for 61 patients (62.2%). The geometric mean peak concentration of drug in serum (C(max)) was significantly higher in fast absorbers than in slow absorbers (5.0 versus 3.8 mg/liter; P = 0.05). The rifampin C(max) was significantly lower in male patients than in female patients (3.3 versus 6.3 mg/liter; P < 0.001). Neither slow nor fast absorbers with comorbidities (DM or HIV) had significantly different C(max) results compared to those of TB patients without comorbidities. An analysis of variance regression analysis showed that female gender (P < 0.001) and the time to maximum concentration of drug in serum (T(max)) at 2 h (P = 0.012) were independently correlated with increased exposure to rifampin. Most of this Peruvian study population exhibited rifampin pharmacokinetics different from those conventionally reported, with delayed absorption and low plasma concentrations, independent of the presence of an HIV or DM comorbidity.

Temporal control of vector soliton bunching by slow/fast saturable absorption

Saturable absorbers exhibiting complex dynamics are shown to provide efficient means for control of soliton interactions. This study, focused specifically on dynamics of vector soliton interactions, demonstrates that a soliton bunch can be efficiently compressed by attractive force generated in a saturable absorber. Effect of absorption recovery time on soliton bunching is explored by using fast and slow semiconductor and carbon nanotube absorbers.

Theory of the ultrafast mode-locked GaN lasers in a large-signal regime

Analytical theory of the high-power passively mode-locked laser with a slow absorber is developed. In distinguishing from previous treatment, our model is valid at pulse energies well exceeding the saturation energy of absorber. This is achieved by solving the mode-locking master equation in the pulse energy-domain representation. The performances of monolithic sub-picosecond blue-violet GaN mode-locked diode laser in the high-power operation regime are analyzed using the developed approach.

Theory of high-power mode-locked lasers with a slow absorber

We develop an analytical theory of high-power passively mode-locked lasers with a slow absorber; the theory is valid at pulse energies well exceeding the saturation energy. We analyze the Haus modelocking master equation in the pulse-energy-domain representation, approximating the intensity profile function by a series in the vicinity of its peak value. We consider the high-power operation regime of subpicosecond blue–violet GaN mode-locked diode lasers, using the approach developed.

Dysprosium as a resonance absorber and its effect on the coolant void reactivity in Advanced Heavy Water Reactor (AHWR)

Abstract Dysprosium has been used as a slow neutron absorber in the fuel assembly of Advanced Heavy Water Reactor (AHWR) to achieve a negative coolant void reactivity. Dysprosium as occurring in nature has as many as seven isotopes namely, 156 Dy, 158 Dy, 160 Dy, 161 Dy, 162 Dy, 163 Dy, and 164 Dy. Of these, the isotope 164 Dy has the largest absorption cross section for thermal neutrons. In the past, nuclear data libraries used in our studies have considered only 164 Dy isotope and this was sufficient for performing foil activation studies of Dy. The other isotopes of Dy have significant resonances and could affect the design. The treatment of the dysprosium isotopes with resonance tabulations is required for a more accurate estimation of the lattice characteristics like the coolant void reactivity. The use of resonance tabulations for the dysprosium isotopes and its effect on the coolant void reactivity of AHWR fuel cluster has been studied in this paper. Also, the treatment of the stand-alone structural rod with dysprosium as burnable absorber having resonance tabulations has been done for the first time.

Gain balance of pulses and noise in passive mode locking with slow saturable absorber

We employ a recently developed gain balance principle to study the problem of passive mode locking with a slow saturable absorber in the presence of noise and solitonic pulse compression. We calculate the compression of the chirped pulse under general conditions and show that there is a minimal achievable pulse width owing to stability requirements. We derive the slow-absorber mode locking parameter, which must exceed a pulse-width-dependent minimal value to sustain mode locking, and calculate the fraction of the total intracavity power that resides in the pulse. We show that choosing the system parameters in an attempt to achieve shorter pulses reduces the pulse power, which, in contrast to fast-absorber passive mode locking, can attain arbitrary small values. Finally, we discuss the modification of the continuum stability condition needed to account for the effect of noise.

Dissipative solitons in quantum dot lasers

The spatiotemporal dynamics of radiation in wide-aperture semiconductor quantum-dot lasers is studied analytically and numerically. It was found that the choice of relatively rapid amplifying layers with quantum dots of a small size and slow absorbing layers with a maximal rate of exciton capture from wetting layers is optimal for the stability of spatial dissipative solitons in a single-longitudinal-mode laser. A large relaxation time of the slow absorber was found to result in a substantial decrease in the sensitivity of solitons to the tilt of the mirrors, which increases their stability and gives real chances of the experimental revealing of laser solitons.

Population Pharmacokinetics and Pharmacodynamics of Rivaroxaban – an Oral, Direct Factor Xa Inhibitor – in Patients Undergoing Major Orthopaedic Surgery

There is a clinical need for novel oral anticoagulants with predictable pharmacokinetics and pharmacodynamics. Rivaroxaban is an oral direct Factor Xa (FXa) inhibitor in clinical development for the prevention and treatment of thromboembolic disorders. This analysis was performed to characterize the population pharmacokinetics and pharmacodynamics of rivaroxaban in patients participating in two phase II, double-blind, randomized, active-comparator-controlled studies of twice-daily rivaroxaban for the prevention of venous thromboembolism after total hip- or knee-replacement surgery. Sparse blood samples were taken from all patients participating in the studies (n = 1009). In addition, a subset of patients in the hip study (n = 36) underwent full profiling. Rivaroxaban plasma concentrations, FXa activity and the prothrombin time were determined. Nonlinear mixed-effects modelling was used to model the population pharmacokinetics and pharmacodynamics of rivaroxaban. An oral one-compartment model described the population pharmacokinetics of rivaroxaban well. On the first postoperative day only, categorization of patients as slow or fast absorbers as a tool to address variability in absorption improved the fit of the model. Clearance of rivaroxaban was lower and more variable on the first postoperative day, and so time was factored into the model. Overall, the only major difference between the models for the hip study and the knee study was that clearance was 26% lower in the knee study, resulting in approximately 30% higher exposure. Residual variability in the models was moderate (37% and 34% in the hip and knee studies, respectively). Plasma concentrations of rivaroxaban increased dose dependently. Pharmacokinetic parameters that were estimated using the models agreed closely with results from full-profile patients in the hip study, demonstrating that rivaroxaban pharmacokinetics are predictable. The pharmacokinetics of rivaroxaban were affected by expected covariates: age affected clearance in the hip study only, haematocrit (on the first postoperative day only) and gender affected clearance in the knee study only, and renal function affected clearance in both studies. Bodyweight affected the volume of distribution in both studies. However, the effects of covariates on the pharmacokinetics of rivaroxaban were generally small, and predictions of 'extreme' case scenarios suggested that fixed dosing of rivaroxaban was likely to be possible. FXa activity and the prothrombin time were both affected by surgery, probably because of perioperative bleeding and intravenous administration of fluids; therefore, time was included in the pharmacodynamic models. In both studies, FXa activity correlated with rivaroxaban plasma concentrations following a maximum effect model, whereas prothrombin time prolongation correlated following a linear model with intercept. The slope of the prothrombin time prolongation correlation was 3.2 seconds/(100 microg/L) in the hip study and 4.2 seconds/(100 microg/L) in the knee study. Both pharmacodynamic models in both studies demonstrated low residual variability of approximately 10%. This population analysis in patients undergoing major orthopaedic surgery demonstrated that rivaroxaban has predictable, dose-dependent pharmacokinetics that were well described by an oral one-compartment model and affected by expected covariates. Rivaroxaban exposure could be assessed using the prothrombin time, if necessary, but not the international normalized ratio. The findings suggested that fixed dosing of rivaroxaban may be possible in patients undergoing major orthopaedic surgery.

Heterodyne Z-scan measurements of slow absorbers

We report a single-beam heterodyne Z-scan method capable of measuring slow response nonlinear refraction of absorbers with excellent sensitivity. By imposing a small sinusoidal modulation on the incoming continuous wave laser beam and recording both the magnitude and phase of the intensity transmitted through a small aperture, we are able to eliminate parasitic linear effects and achieve a sensitivity good enough to determine the absorption coefficient of a 2 mm-thick water sample at 532 nm with moderate power.

Variability in the population pharmacokinetics of pyrazinamide in South African tuberculosis patients

This study was designed to characterize the population pharmacokinetics of pyrazinamide in South African pulmonary tuberculosis patients, with special reference to interindividual and interoccasional variability (IIV and IOV, respectively). Concentration-time measurements obtained from 227 patients receiving oral doses of pyrazinamide were pooled to create a dataset containing 3,092 data points spanning multiple dosing occasions. The software program NONMEM was used to analyze the data. A one-compartment model with first-order absorption, including a zero-order component describing release from formulation, and first-order elimination best described the data. The absorption rate constant was estimated to be bimodally distributed between two distinct subgroups, fast and slow, in approximately even proportion. Absorption rate was threefold greater in fast absorbers (3.56 h(-1)) in comparison to slow absorbers (1.25 h(-1)). Typical values of oral clearance and apparent volume of distribution were estimated as 3.42 L h(-1) and 29.2 l, respectively. IOV was supported in oral clearance (0.0238, variance) and absorption rate (0.623, variance). The duration of zero-order absorption was estimated as 0.290 h, and was quite variable between patients (0.957, variance). The absorption of pyrazinamide in the studied population was highly variable and two separate subpopulations were identified. IOV accounted for a proportion of the variability in clearance and the absorption rate constant.

Optical phase noise and carrier-envelope offset noise of mode-locked lasers

The timing jitter, optical phase noise, and carrier-envelope offset (CEO) noise of passively mode-locked lasers are closely related. New key results concern analytical calculations of the quantum noise limits for optical phase noise and CEO noise. Earlier results for the optical phase noise of actively mode-locked lasers are generalized, particularly for application to passively mode-locked lasers. It is found, for example, that mode locking with slow absorbers can lead to optical linewidths far above the Schawlow–Townes limit. Furthermore, mode-locked lasers can at the same time have nearly quantum-limited timing jitter and a strong optical excess phase noise. A feedback timing stabilization via cavity length control can, depending on the situation, reduce or greatly increase the optical phase noise, while not affecting the CEO noise. Besides presenting such findings, the paper also tries to clarify some basic aspects of phase noise in mode-locked lasers.

Limitations of C2 monitoring in renal transplant recipients

Recent developments have proposed the cyclosporin (CsA) concentration at 2 h post-dose (C(2)) as the best single time-point predictor of the extent of CsA exposure and as the optimal basis for monitoring immunosuppressive therapy in renal transplant patients. The present study sought to validate the cornerstones of the current concept of C(2) monitoring. We assessed the predictive value, dose proportionality and intrapatient variability of C(2) levels in 41 de novo renal transplant recipients treated with CsA microemulsion, steroids, mycophenolate sodium and basiliximab. Patients with rejection and patients with CsA nephrotoxicity had lower C(2) (P = NS) and absorption (P<0.05 for toxicity), while C(0) did not show any significant difference. Receiver operating characteristic analysis did not detect discriminative C(2) values as a predictor of rejection or toxicity. In a substantial number of patients (29%) we observed poor and/or slow absorption, with C(0) >300 ng/ml and C(2) levels <800 ng/ml during the first month and a high rate of complications in these patients (18% rejection, 64% toxicity). Absorption increased over the first month post-transplant. Analysis of dose changes indicated that C(2) levels are not dose-proportional. Intrapatient variability of C(2) was as high as that of C(0). C(2) levels do not predict rejection or toxicity. C(2) monitoring alone does not detect toxicity in poor and/or slow absorbers, who constitute a significant proportion of patients. Changes in absorption over time, high intrapatient variability and lack of dose proportionality constitute further limitations of the C(2) monitoring concept in the early post-transplant phase.

Effect of amplified spontaneous emission and absorber mirror recovery time on the dynamics of mode-locked fiber lasers

The effect of the amplified spontaneous emission (ASE) on the performance of the semiconductor saturable absorber mirrors (SESAMs) in mode-locked fiber lasers has been investigated. We show that high level of ASE intensity typical for fiber lasers can saturate the absorption and degrade significantly the nonlinear response of the SESAM. We studied the effect of the absorber recovery time and demonstrated that the ion-irradiated SESAMs with fast nonlinear response are less affected by the ASE radiation and, consequently, in the presence of the high-power ASE they exhibit better self-starting capability compared with slow absorbers.

Analysis on femtosecond pulses generated by passively mode-locked lasers with higher-order effects

A theoretical model for passively mode-locked lasers is presented, in which the higher-order effects, such as third-order dispersion, nonlinear dispersion, and self-frequency shift arising from stimulated Raman scattering, and a fast as well as a slow saburable absorber responses are taken into account. An exact soliton-like solution is obtained under a definite parameter conditions and its stability is also analyzed numerically under small perturbations in amplitude, chirp and white noise. The results indicate that the pulses can be stable under a finite perturbation and become identical to the exact solution after a distance of evolution. In addition, we have also found that a quite arbitrary initial Gaussian pulse can converge to the exact solution after a distance of evolution.