400 research outputs found
Double-lambda microscopic model for entangled light generation by four-wave-mixing
Motivated by recent experiments, we study four-wave-mixing in an atomic
double-{\Lambda} system driven by a far-detuned pump. Using the
Heisenberg-Langevin formalism, and based on the microscopic properties of the
medium, we calculate the classical and quantum properties of seed and conju-
gate beams beyond the linear amplifier approximation. A continuous variable
approach gives us access to relative-intensity noise spectra that can be
directly compared to experiments. Restricting ourselves to the cold-atom
regime, we predict the generation of quantum-correlated beams with a
relative-intensity noise spectrum well below the standard quantum limit (down
to -6 dB). Moreover entanglement between seed and conjugate beams measured by
an inseparability down to 0.25 is expected. This work opens the way to the
generation of entangled beams by four-wave mixing in a cold atomic sample.Comment: 11 pages, 6 figures, submitted to PR
Effect of charging on CdSe/CdS dot-in-rods single-photon emission
The photon statistics of CdSe/CdS dot-in-rods nanocrystals is studied with a
method involving post-selection of the photon detection events based on the
photoluminescence count rate. We show that flickering between two states needs
to be taken into account to interpret the single-photon emission properties.
With post-selection we are able to identify two emitting states: the exciton
and the charged exciton (trion), characterized by different lifetimes and
different second order correlation functions. Measurements of the second order
autocorrelation function at zero delay with post- selection shows a degradation
of the single photon emission for CdSe/CdS dot-in-rods in a charged state that
we explain by deriving the neutral and charged biexciton quantum yields.Comment: 10 pages, 5 figure
Relative intensity squeezing by four-wave mixing with loss: an analytic model and experimental diagnostic
Four-wave mixing near resonance in an atomic vapor can produce relative
intensity squeezed light suitable for precision measurements beyond the
shot-noise limit. We develop an analytic distributed gain/loss model to
describe the competition of mixing and absorption through the non-linear
medium. Using a novel matrix calculus, we present closed-form expressions for
the degree of relative intensity squeezing produced by this system. We use
these theoretical results to analyze experimentally measured squeezing from a
Rb vapor and demonstrate the analytic model's utility as an experimental
diagnostic.Comment: 10 pages, 5 figure
The timing of family commitments in the early work career:Work-family trajectories of young adults in Flanders
OBJECTIVE This article examines the diverse ways in which young adults develop both their professional career and family life in the years immediately after they complete their education. Building a career and starting a family often occur simultaneously in this stage of life. By studying the simultaneous developments in these life domains, we can gain a better understanding of this complex interplay. METHODS The data consist of a sample of 1,657 young adults born in 1976 who were interviewed as part of the SONAR survey of Flanders at ages 23, 26, and 29 about their education, their entry into and early years on the labour market, and their family life. Sequence analysis is used to study the timing of union formation and having children among these young adults, as well as how these events are related to their work career. Multinomial regression analysis is applied to help us gain a better understanding of the extent to which these life course patterns are determined by education and economic status at the start of the career. RESULTS The results reveal a set of work-family trajectories which vary in terms of the extent of labour market participation and the type and timing of family formation. Various aspects of the trajectory are found to be determined by different dimensions of an individualâs educational career (duration, level, field of study). Education is more relevant for women than for men, as a manâs trajectory is more likely than a womanâs to be determined by the first job. CONCLUSIONS By using a simultaneous approach which takes into account both family and work, this life course analysis confirms that men have a head start on the labour market, and examines the factors which influence the distinct trajectories of young women and men
Serum levels and removal by haemodialysis and haemodiafiltration of tryptophan-derived uremic toxins in ESKD patients
Tryptophan is an essential dietary amino acid that originates uremic toxins that contribute to end-stage kidney disease (ESKD) patient outcomes. We evaluated serum levels and removal during haemodialysis and haemodiafiltration of tryptophan and tryptophan-derived uremic toxins, indoxyl sulfate (IS) and indole acetic acid (IAA), in ESKD patients in different dialysis treatment settings. This prospective multicentre study in four European dialysis centres enrolled 78 patients with ESKD. Blood and spent dialysate samples obtained during dialysis were analysed with high-performance liquid chromatography to assess uremic solutes, their reduction ratio (RR) and total removed solute (TRS). Mean free serum tryptophan and IS concentrations increased, and concentration of IAA decreased over pre-dialysis levels (67%, 49%, -0.8%, respectively) during the first hour of dialysis. While mean serum total urea, IS and IAA concentrations decreased during dialysis (-72%, -39%, -43%, respectively), serum tryptophan levels increased, resulting in negative RR (-8%) towards the end of the dialysis session (p < 0.001), despite remarkable Trp losses in dialysate. RR and TRS values based on serum (total, free) and dialysate solute concentrations were lower for conventional low-flux dialysis (p < 0.001). High-efficiency haemodiafiltration resulted in 80% higher Trp losses than conventional low-flux dialysis, despite similar neutral Trp RR values. In conclusion, serum Trp concentrations and RR behave differently from uremic solutes IS, IAA and urea and Trp RR did not reflect dialysis Trp losses. Conventional low-flux dialysis may not adequately clear Trp-related uremic toxins while high efficiency haemodiafiltration increased Trp losses
Photoionisation loading of large Sr+ ion clouds with ultrafast pulses
This paper reports on photoionisation loading based on ultrafast pulses of
singly-ionised strontium ions in a linear Paul trap. We take advantage of an
autoionising resonance of Sr neutral atoms to form Sr+ by two-photon absorption
of femtosecond pulses at a wavelength of 431nm. We compare this technique to
electron-bombardment ionisation and observe several advantages of
photoionisation. It actually allows the loading of a pure Sr+ ion cloud in a
low radio-frequency voltage amplitude regime. In these conditions up to 4x10^4
laser-cooled Sr+ ions were trapped
Soluble tumor necrosis factor receptor 1 and 2 predict outcomes in advanced chronic kidney disease : a prospective cohort study
Background : Soluble tumor necrosis factor receptors 1 (sTNFR1) and 2 (sTNFR2) have been associated to progression of renal failure, end stage renal disease and mortality in early stages of chronic kidney disease (CKD), mostly in the context of diabetic nephropathy. The predictive value of these markers in advanced stages of CKD irrespective of the specific causes of kidney disease has not yet been defined. In this study, the relationship between sTNFR1 and sTNFR2 and the risk for adverse cardiovascular events (CVE) and all-cause mortality was investigated in a population with CKD stage 4-5, not yet on dialysis, to minimize the confounding by renal function.
Patients and methods : In 131 patients, CKD stage 4-5, sTNFR1, sTNFR2 were analysed for their association to a composite endpoint of all-cause mortality or first non-fatal CVE by univariate and multivariate Cox proportional hazards models. In the multivariate models, age, gender, CRP, eGFR and significant comorbidities were included as covariates.
Results : During a median follow-up of 33 months, 40 events (30.5%) occurred of which 29 deaths (22.1%) and 11 (8.4%) first non-fatal CVE. In univariate analysis, the hazard ratios (HR) of sTNFR1 and sTNFR2 for negative outcome were 1.49 (95% confidence interval (CI): 1.28-1.75) and 1.13 (95% CI: 1.06-1.20) respectively. After adjustment for clinical covariables (age, CRP, diabetes and a history of cardiovascular disease) both sTNFRs remained independently associated to outcomes (HR: sTNFR1: 1.51, 95% CI: 1.30-1.77; sTNFR2: 1.13, 95% CI: 1.06-1.20). A subanalysis of the non-diabetic patients in the study population confirmed these findings, especially for sTNFR1.
Conclusion : sTNFR1 and sTNFR2 are independently associated to all-cause mortality or an increased risk for cardiovascular events in advanced CKD irrespective of the cause of kidney disease
Growth characteristics in individuals with osteogenesis imperfecta in North America: results from a multicenter study.
PurposeOsteogenesis imperfecta (OI) predisposes people to recurrent fractures, bone deformities, and short stature. There is a lack of large-scale systematic studies that have investigated growth parameters in OI.MethodsUsing data from the Linked Clinical Research Centers, we compared height, growth velocity, weight, and body mass index (BMI) in 552 individuals with OI. Height, weight, and BMI were plotted on Centers for Disease Control and Prevention normative curves.ResultsIn children, the median z-scores for height in OI types I, III, and IV were -0.66, -6.91, and -2.79, respectively. Growth velocity was diminished in OI types III and IV. The median z-score for weight in children with OI type III was -4.55. The median z-scores for BMI in children with OI types I, III, and IV were 0.10, 0.91, and 0.67, respectively. Generalized linear model analyses demonstrated that the height z-score was positively correlated with the severity of the OI subtype (Pâ<â0.001), age, bisphosphonate use, and rodding (Pâ<â0.05).ConclusionFrom the largest cohort of individuals with OI, we provide median values for height, weight, and BMI z-scores that can aid the evaluation of overall growth in the clinic setting. This study is an important first step in the generation of OI-specific growth curves
HRâpQCT measures of bone microarchitecture predict fracture : systematic review and metaâanalysis
HRâpQCT is a nonâinvasive imaging modality for assessing volumetric bone mineral density (vBMD) and microarchitecture of cancellous and cortical bone. The objective was to (i) assess fractureâassociated differences in HRâpQCT bone parameters and (ii) to determine if HRâpQCT is sufficiently precise to reliably detect these differences in individuals. We systematically identified 40 studies that used HRâpQCT (39/40 used XtremeCT scanners) to assess 1291â3253 and 3389â10,687 individuals with and without fractures, respectively, ranging in age from 10.9 to 84.7âyears with no comorbid conditions. Parameters describing radial and tibial bone density, microarchitecture, and strength were extracted and percentage differences between fracture and control subjects were estimated using a random effects metaâanalysis. An additional metaâanalysis of shortâterm in vivo reproducibility of bone parameters assessed by XtremeCT was conducted to determine whether fractureâassociated differences exceeded the least significant change (LSC) required to discern measured differences from precision error. Radial and tibial HRâpQCT parameters, including failure load, were significantly altered in fracture subjects, with differences ranging from â2.6% (95% CI: â3.4 to â1.9) in radial cortical vBMD to â12.6% (95% CI: â15.0 to â10.3) in radial trabecular vBMD. Fractureâassociated differences reported by prospective studies were consistent with those from retrospective studies, indicating that HRâpQCT can predict incident fracture. Assessment of study quality, heterogeneity and publication biases verified the validity of these findings. Finally, we demonstrated that fractureâassociated deficits in total and trabecular vBMD, and certain tibial cortical parameters, can be reliably discerned from HRâpQCTârelated precision error and can be used to detect fractureâassociated differences in individual patients. Although differences in other HRâpQCT measures, including failure load, were significantly associated with fracture, improved reproducibility is needed to ensure reliable individual crossâsectional screening and longitudinal monitoring. In conclusion, our study supports the use of HRâpQCT in clinical fracture prediction
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