Second-harmonic generation of light at 245 nm in a lithium tetraborate whispering gallery resonator

A millimeter-sized, monolithic whispering gallery resonator made of a lithium tetraborate, Li2B4O7, crystal was employed for doubly resonant second-harmonic generation with a continuous-wave laser source at 490 nm. An intrinsic quality factor of 2×10(8) was observed at the pump wavelength. A conversion efficiency of 2.2% was attained with 5.9 mW of mode-matched pump power. In the lithium tetraborate resonator, it is feasible to achieve phase-matching of second-harmonic generation for pump wavelengths between 486 and 506 nm.

Integration of an opto-chemical detector based on group III-nitride nanowire heterostructures

The photoluminescence intensity of group III nitrides, nanowires, and heterostructures (NWHs) strongly depends on the environmental H(2) and O(2) concentration. We used this opto-chemical transducer principle for the realization of a gas detector. To make this technology prospectively available to commercial gas-monitoring applications, a large-scale laboratory setup was miniaturized. To this end the gas-sensitive NWHs were integrated with electro-optical components for optical addressing and read out within a compact and robust sensor system. This paper covers the entire realization process of the device from its conceptual draft and optical design to its fabrication and assembly. The applied approaches are verified with intermediate results of profilometric characterizations and optical performance measurements of subsystems. Finally the gas-sensing capabilities of the integrated detector are experimentally proven and optimized.

Critical slowing down near the multiferroic phase transition in MnWO4

By using broadband dielectric spectroscopy in the radio frequency and microwave range, we studied the magnetoelectric dynamics in the multiferroic chiral antiferromagnet MnWO_{4}. Above the multiferroic phase transition at T_{N2}≈12.6  K we observe a critical slowing of the corresponding magnetoelectric fluctuations resembling the soft-mode behavior in canonical ferroelectrics. This electric-field-driven excitation carries much less spectral weight than ordinary phonon modes. Also, the critical slowing down of this mode scales with an exponent larger than 1, which is expected for magnetic second-order phase transition scenarios. Therefore, the investigated dynamics have to be interpreted as the softening of an electrically active magnetic excitation, an electromagnon.

Inductive measurement of optically hyperpolarized phosphorous donor nuclei in an isotopically enriched silicon-28 crystal

We experimentally demonstrate the first inductive readout of optically hyperpolarized phosphorus-31 donor nuclear spins in an isotopically enriched silicon-28 crystal. The concentration of phosphorus donors in the crystal was 1.5×10(15)  cm(-3), 3 orders of magnitude lower than has previously been detected via direct inductive detection. The signal-to-noise ratio measured in a single free induction decay from a 1  cm(3) sample (≈10(15) spins) was 113. By transferring the sample to an X-band ESR spectrometer, we were able to obtain a lower bound for the nuclear spin polarization at 1.7 K of ∼64%. The (31)P-T2 measured with a Hahn echo sequence was 420 ms at 1.7 K, which was extended to 1.2 s with a Carr Purcell cycle. The T1 of the (31)P nuclear spins at 1.7 K is extremely long and could not be determined, as no decay was observed even on a time scale of 4.5 h. Optical excitation was performed with a 1047 nm laser, which provided above-band-gap excitation of the silicon. The buildup of the hyperpolarization at 4.2 K followed a single exponential with a characteristic time of 577 s, while the buildup at 1.7 K showed biexponential behavior with characteristic time constants of 578 and 5670 s.

Magnetoelectric properties of A2[FeCl5(H2O)] with A = K, Rb, Cs

The compounds A(2)[FeCl(5)(H(2)O)] with A = K, Rb, Cs are identified as new linear magnetoelectric (non-multiferroic) materials. We present a detailed investigation of their linear magnetoelectric properties through measurements of pyroelectric currents, dielectric constants and magnetization. The anisotropy of the linear magnetoelectric effect of the K-based and Rb-based compound is consistent with the magnetic point group m'm'm', already reported in literature. A symmetry analysis of the magnetoelectric effect of the Cs-based compound allows us to determine the magnetic point group mmm' and to develop a model for its magnetic structure. In addition, magnetic-field versus temperature phase diagrams are derived and compared to the closely related multiferroic (NH(4))(2)[FeCl(5)(H(2)O)].

Noise and age-related hearing loss: a study of 40 123 gold miners in South Africa

OBJECTIVE AND DESIGN

This retrospective cohort study aimed to describe the differential effect of noise exposure and age-related hearing loss in a large sample of gold miners in South Africa.

STUDY SAMPLE

Audiological data of 40 123 South African mine workers were investigated. Data of a non-noise-exposed control group (n = 6162) and group exposed to underground noise (≥ 85 dB A (TWA) (n = 33 961) were included. Within these two larger noise-exposed groups two homogenous exposure groups (HEG) were also selected for analyses, namely the driller group (n = 4399) and the administration group (administrative workers) (n = 2211). Participants were categorized in terms of noise exposure, age, and race.

RESULTS

Significantly different thresholds (worse for underground noise group) with respect to the median for all frequencies after adjusting for age was evident between the noise-exposed and control groups (ANCOVA). The largest differences in hearing thresholds between the noise-exposed and control groups were observed at 3 and 4 kHz in the age group 36 to 45 years. Administration and driller group differed significantly (driller group worse results) with respect to the mean LFA512 and HFA346 after adjusting for age (ANCOVA). Black males had significantly better high-frequency hearing compared with white male counterparts but significantly worse low-frequency hearing.

CONCLUSION

Age was the most important influence on hearing thresholds for the noise and control groups. Race was shown to be a very significant factor determining susceptibility to NIHL and ARHL.

Influence of male hyperinsulinaemia on IVF outcome

The IVF outcome of a group of hyperinsulinaemic men (group B) was compared with a group of IVF males with normal insulin levels (group A). The participating females in the study groups were younger than 38 years old, had blocked Fallopian tubes and/or endometriosis, had normal insulin levels and produced five or more ova on stimulation. The male participants in both groups were normozoospermic with motility above 50% and sperm morphology between 5 and 13% normal forms (G-pattern according to Tygerberg strict criteria). The two groups did not differ statistically in terms of age or semen parameters (P = 0.39; P < 0.05).The group of men that presented with normal insulin levels had a higher fertilisation rate (79.15% versus 74.57%) and superior embryo quality on day 3 (55.77% versus 50.39%) than the group that presented with hyperinsulinaemia, but these differences were not statistically significant (P = 0.28, P = 0.40; P < 0.05). The clinical pregnancy rate of the group with normal insulin was significantly higher than that of the hyperinsulinaemic group, 57.9% versus 31.8% respectively (P = 0.03). The results suggest that hyperinsulinaemia had a negative impact on IVF outcome and patients should be advised accordingly.

Spin-1/2 XXZ chain system Cs2CoCl4 in a transverse magnetic field

Comparing high-resolution specific heat and thermal expansion measurements to exact finite-size diagonalization, we demonstrate that Cs(2)CoCl(4) for a magnetic field along the crystallographic b axis realizes the spin-1/2 XXZ chain in a transverse field. Exploiting both thermal as well as virtual excitations of higher crystal-field states, we find that the spin chain is in the XY limit with an anisotropy J(z)/J[perpindicular] ≈ 0.12, substantially smaller than previously believed. A spin-flop Ising quantum phase transition occurs at a critical field of μ(0)H(b)(cr) ≈ 2 T before around 3.5 T the description in terms of an effective spin-1/2 chain becomes inapplicable.

Nanostructure and strain in InGaN/GaN superlattices grown in GaN nanowires

The structural properties and the strain state of InGaN/GaN superlattices embedded in GaN nanowires were analyzed as a function of superlattice growth temperature, using complementary transmission electron microscopy techniques supplemented by optical analysis using photoluminescence and spatially resolved microphotoluminescence spectroscopy. A truncated pyramidal shape was observed for the 4 nm thick InGaN inclusions, where their (0001¯) central facet was delimited by six-fold {101¯l} facets towards the m-plane sidewalls of the nanowires. The defect content of the nanowires comprised multiple basal stacking faults localized at the GaN base/superlattice interface, causing the formation of zinc-blende cubic regions, and often single stacking faults at the GaN/InGaN bilayer interfaces. No misfit dislocations or cracks were detected in the heterostructure, implying a fully strained configuration. Geometrical phase analysis showed a rather uniform radial distribution of elastic strain in the (0001¯) facet of the InGaN inclusions. Depending on the superlattice growth temperature, the elastic strain energy is partitioned among the successive InGaN/GaN layers in the case of low-temperature growth, while at higher superlattice growth temperature the in-plane tensile misfit strain of the GaN barriers is accommodated through restrained diffusion of indium from the preceding InGaN layers. The corresponding In contents of the central facet were estimated at 0.42 and 0.25, respectively. However, in the latter case, successful reproduction of the experimental electron microscopy images by image simulations was only feasible, allowing for a much higher occupancy of indium adatoms at lattice sites of the semipolar facets, compared to the invariable 25% assigned to the polar facet. Thus, a high complexity in indium incorporation and strain allocation between the different crystallographic facets of the InGaN inclusions is anticipated and supported by the results of photoluminescence and spatially resolved microphotoluminescence spectroscopy.

Piezoresponse force microscopy at sub-room temperatures

Piezoresponse force microscopy is demonstrated at temperatures between -80 °C and +120 °C using a commercial room temperature atomic force microscope upgraded with a home-built cooling/heating-stage. We applied temperature-ramp-synchronized piezoresponse force microscope (PFM) for tracing the temperature dependence of the formation of ferroelectric domains. The potential of our sub-room temperature PFM is demonstrated by investigating the formation and evolution of ferroelectric domains in RbHSO4 as a function of temperature and time, respectively.

Contamination and current practice in decontamination pof nebulisers in ventilated patients

To examine the incidence of contamination and current practice of decontamination of nebulisers after use within a ventilator circuit, in public- and private sector intensive care units (ICUs) in Johannesburg; to assess the presence of and adherence to a decontamination protocol in these ICUs and to identify which practices were associated with lower or no bacterial growth. Methods: A cross-sectional study design was used which included a semi-structured interview with the ICU manager and an audit of current nebuliser practice. Nebulisers that were identified in the interview were swabbed and streaked on blood agar plates (BAPs). BAPs were incubated and assessed for bacterial colonisation, number of colony forming units (CFUs) and number of different species of CFUs present. Results: Two hundred and sixty-nine ICU beds were surveyed over a two-month period resulting in 45 nebulisers used within a ventilator circuit that could be tested. The majority (93%) were single-use jet nebulisers, all were being re-used and 52% presented with contamination. None of the ICUs had a nebuliser decontamination protocol in place. Contaminated nebulisers that were stored in a sterile drape had significantly higher concentrations of bacterial growth (p=0.03). Conclusion: The rate of colonisation of re-used jet nebulisers is high. Nebuliser decontamination protocols are urgently needed.

Health related quality of life of survivors of trauma six months after discharge

To investigate the health-related quality of life (HRQOL) of survivors of major trauma at six months following discharge, using two popular HRQOL tools. A cross-sectional study was done on adult trauma survivors in Johannesburg. Subjects completed the EQ-5D and SF-36 HRQOL questionnaires. Additional demographic and clinical data were collected. The majority of subjects reported some problems in usual activities and pain/discomfort as measured with the EQ-5D at six months. The mean EQ-5D VAS was 68 (±26.1). lowest scores were reported in the role physical (44.6 ± 41.6) and role emotional (44.1 ± 45.4) domains of the SF-36. mean SF-36 physical component summary (PCS) score (62.1 ± 27.8) was higher than mental component summary score (58.7 ±20.1). EQ-5D VAS was found to be moderately correlated with age (r=-0.4; p=0.05). A negative correlation was found between SF-36 physical function score and ICU length of stay (LOS), hospital LOS and age (r=-0.4 (p=0.03), -0.4 (p=0.03) and -0.6 (p=0.00) respectively). Statistical significance was observed in the correlation between age and SF-36 general health domain (r=-0.4; p=0.02) as well as age and PCS score (r=-0.5; p=0.01). Trauma survivors in Johannesburg experience limitations in specific emotional and physical domains of HRQOL at six months after discharge. Age was associated with the level of self-rated health as well as limitations in general health and physical function. ICU and hospital LOS were associated with limitations in physical function. There is a need for physical and psychological rehabilitation after discharge from trauma intensive care.