Optical parametric generator based on orientation-patterned gallium phosphide

We report the first pulsed optical parametric generator based on Orientation-patterned Gallium Phosphide. The output is tunable from 1721-1850 nm (signal) and 2504-2787 nm (idler), providing a total output power of 18 mW.Peer ReviewedPostprint (author's final draft

Singly-Resonant Optical Parametric Oscillator Based on Orientation-Patterned Gallium Phosphide

We report a pulsed singly-resonant optical parametric oscillator based on orientation-patterned gallium phosphide pumped by a Q-switched Nd:YAG laser. The mid-IR idler can be tuned across 2.8-3.1 μm with an average power of 20 mW.Peer ReviewedPostprint (author's final draft

Optical parametric generation in orientation-patterned gallium phosphide

We report an optical parametric generator (OPG) based on the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched nanosecond Nd:YAG laser at 1064 nm with 25 kHz pulse repetition rate, the OPG can be tuned across 1721–1850 nm in the signal and 2504–2787 nm in the idler. Using a 40-mm-long crystal in single-pass configuration, we have generated a total average output power of up to ∼18  mW∼18  mW, with ∼5  mW∼5  mW of idler power at 2670 nm, for 2 W of input pump power. The OPG exhibits a passive stability in total output power better than 0.87% rms over 1 h, at a crystal temperature of 120°C, compared to 0.14% rms for the input pump. The output signal pulses, recorded at 1769 nm, have duration of 5.9 ns for input pump pulses of 9 ns. Temperature-dependent loss measurements for the pump polarization along the [100] axis in the OP-GaP crystal have also been performed, for the first time, indicating a drop in transmission from 28.8% at 50°C to 19.4% at 160°C.Peer ReviewedPostprint (author's final draft

Performance characterization of mid-infrared difference-frequency-generation in orientation-patterned gallium phosphide

We present a detailed characterization of the optical properties of the recently developed nonlinear material, orientation-patterned gallium phosphide (OP-GaP), by performing difference-frequency-generation experiments in the 2548-2782 nm wavelength range in the mid-infrared (mid-IR). Temperature and spectral acceptance bandwidth measurements have been performed to study the phase-matching characteristics of OP-GaP, and the dependence of nonlinear gain on the polarization of input incident fields has been investigated. The transmission of the OP-GaP crystal at the pump and signal wavelengths has been studied and found to be dependent on polarization as well as temperature. Further, we have observed a polarization-dependent spatial shift in the transmitted pump beam through the OP-GaP sample. We have also measured the damage threshold of the OP-GaP crystal to be 0.84 J/cm2 at 1064 nm.Peer ReviewedPostprint (published version

Early clinical and laboratory risk factors of intensive care unit requirement during 2004–2008 dengue epidemics in Singapore: a matched case–control study

Background: Dengue infection can result in severe clinical manifestations requiring intensive care. Effective triage is critical for early clinical management to reduce morbidity and mortality. However, there is limited knowledge on early risk factors of intensive care unit (ICU) requirement. This study aims to identify early clinical and laboratory risk factors of ICU requirement at first presentation in hospital and 24 hours prior to ICU requirement. Method: A retrospective 1:4 matched case–control study was performed with 27 dengue patients who required ICU, and 108 dengue patients who did not require ICU from year 2004–2008, matched by year of dengue presentation. Univariate and multivariate conditional logistic regression were performed. Optimal predictive models were generated with statistically significant risk factors identified using stepwise forward and backward elimination method. Results: ICU dengue patients were significantly older (P=0.003) and had diabetes (P=0.031), compared with non-ICU dengue patients. There were seven deaths among ICU patients at median seven days post fever. At first presentation, the WHO 2009 classification of dengue severity was significantly associated (P<0.001) with ICU, but not the WHO 1997 classification. Early clinical risk factors at presentation associated with ICU requirement were hematocrit change ≥20% concurrent with platelet <50 K [95% confidence-interval (CI)=2.46-30.53], hypoproteinemia (95% CI=1.09-19.74), hypotension (95% CI=1.83-31.79) and severe organ involvement (95% CI=3.30-331). Early laboratory risk factors at presentation were neutrophil proportion (95% CI=1.04-1.17), serum urea (95% CI=1.02-1.56) and alanine aminotransferase level (95% CI=1.001-1.06). This predictive model has sensitivity and specificity up to 88%. Early laboratory risk factors at 24 hours prior to ICU were lymphocyte (95% CI=1.03-1.38) and monocyte proportions (95% CI=1.02-1.78), pulse rate (95% CI=1.002-1.14) and blood pressure (95% CI=0.92-0.996). This predictive model has sensitivity and specificity up to 88.9% and 78%, respectively. Conclusions: This is the first matched case–control study, to our best knowledge, that identified early clinical and laboratory risk factors of ICU requirement during hospitalization. These factors suggested differential pathophysiological background of dengue patients as early as first presentation prior to ICU requirement, which may reflect the pathogenesis of dengue severity. These risk models may facilitate clinicians in triage of patients, after validating in larger independent studies.Published versio

Diabetes with Hypertension as Risk Factors for Adult Dengue Hemorrhagic Fever in a Predominantly Dengue Serotype 2 Epidemic: A Case Control Study

Dengue is a major vector borne disease in the tropical and subtropical regions. An estimated 50 million infections occur per annum in over 100 countries. A severe form of dengue, characterized by bleeding and plasma leakage, known as dengue hemorrhagic fever (DHF) is estimated to occur in 1–5% of hospitalized cases. It can be fatal if unrecognized and not treated in a timely manner. Previous studies had found a number of risk factors for DHF. However, screening and clinical management strategies based on these risk factors may not be applicable to all populations and epidemics of different serotypes. In this study, we found significant association between DHF and diabetes mellitus and diabetes mellitus with hypertension during the epidemic of predominantly serotype 2 (year 2007 and 2008), but not during the epidemic of predominantly serotype 1 (year 2006). Diabetes mellitus and hypertension are prevalent in Singapore and most parts of South-East Asia, where dengue is endemic. Therefore, it is important to address the risk effect of these co-morbidities on the development of DHF so as to reduce morbidity and mortality. Our findings may have impact on screening and clinical management of dengue patients, when confirmed in more studies

Clustering, climate and dengue transmission

10.1586/14787210.2015.1028364Expert Review of Anti-Infective Therapy136731-74

Constitutive bone marrow adipocytes suppress local bone formation

Bone marrow adipocytes (BMAd) are a unique cell population derived from bone marrow mesenchymal progenitors and marrow adipogenic lineage precursors. Although they have long been considered to be a space-filler within bone cavities, recent studies have revealed important physiological roles in hematopoiesis and bone metabolism. To date, the approaches used to study BMAd function have been confounded by contributions by non-marrow adipocytes or by bone marrow stromal cells. To address this gap in the field, we have developed a BMAd-specific Cre mouse model to deplete BMAds by expression of diphtheria toxin A (DTA), or by deletion of peroxisome proliferator-activated receptor gamma (Pparg). We found that DTA-induced loss of BMAds results in decreased hematopoietic stem and progenitor cell numbers and increased bone mass in BMAd-enriched locations, including the distal tibiae and caudal vertebrae. Elevated bone mass appears to be secondary to enhanced endosteal bone formation, suggesting a local effect caused by depletion of BMAd. Augmented bone formation with BMAd-depletion protects mice from bone loss induced by caloric restriction or ovariectomy, and facilitates the bone healing process after fracture. Finally, ablation of Pparg also reduces BMAd numbers and largely recapitulates high bone mass phenotypes observed with DTA-induced BMAd depletion

Singly-Resonant Optical Parametric Oscillator Based on Orientation-Patterned Gallium Phosphide

We report a pulsed singly-resonant optical parametric oscillator based on orientation-patterned gallium phosphide pumped by a Q-switched Nd:YAG laser. The mid-IR idler can be tuned across 2.8-3.1 μm with an average power of 20 mW.Peer Reviewe