LED pumped polymer laser sensor for explosives

The authors would like to acknowledge financial support for this research from the EPSRC HYPIX project (grant number EP/ F059922/1 and EP/F05999X/1), and the TIRAMISU project, funded by the European Commission's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 284747.A very compact explosive vapor sensor is demonstrated based on a distributed feedback polymer laser pumped by a commercial InGaN light-emitting diode. The laser shows a two-stage turn on of the laser emission, for pulsed drive currents above 15.7 A. The 'double-threshold' phenomenon is attributed to the slow rise of the ∼30 ns duration LED pump pulses. The laser emits a 533 nm pulsed output beam of ∼10 ns duration perpendicular to the polymer film. When exposed to nitroaromatic model explosive vapors at ∼8 ppb concentration, the laser shows a 46% change in the surface-emitted output under optimized LED excitation. A very compact explosive vapor sensor is demonstrated based on a distributed feedback polymer laser pumped by a commercial InGaN light-emitting diode. The laser shows a two-stage turn on of the laser emission, for pulsed drive currents above 15.7 A. The 'double-threshold' phenomenon is attributed to the slow rise of the ∼30 ns duration LED pump pulses. The laser emits a 533 nm pulsed output beam of ∼10 ns duration perpendicular to the polymer film. When exposed to nitroaromatic model explosive vapors at ∼8 ppb concentration, the laser shows a 46% change in the surface-emitted output under optimized LED excitation.Publisher PDFPeer reviewe

Low-threshold organic laser based on an oligofluorene truxene with low optical losses

A blue-emitting distributed feedback laser based on a star-shaped oligofluorene truxene molecule is presented. The gain, loss, refractive index, and (lack of) anisotropy are measured by amplified spontaneous emission and variable-angle ellipsometry. The waveguide losses are very low for an organic semiconductor gain medium, particularly for a neat film. The results suggest that truxenes are promising for reducing loss, a key parameter in the operation of organic semiconductor lasers. Distributed feedback lasers fabricated from solution by spin-coating show a low lasing threshold of 270 W/cm(2) and broad tunability across 25 nm in the blue part of the spectrum

Identifying the internalizing disorder clusters among recently hospitalized cardiovascular disease patients: a receiver operating characteristics study

Depression and anxiety disorders are common among cardiovascular disease (CVD) populations, leading several cardiology societies to recommend routine screening to streamline psychological interventions. However, it remains poorly understood whether routine screening in CVD populations identifies the broader groups of disorders that cluster together within individuals, known as anxious-misery and fear. This study examines the screening utility of four anxiety and depression questionnaires to identify the two internalizing disorder clusters; anxious-misery and fear. Patients with a recent hospital admission for CVD (n = 85, 69.4% males) underwent a structured clinical interview with the MINI International Neuropsychiatric Interview. The participants also completed the Patient Health Questionnaire (PHQ-9), Generalized Anxiety Disorder (GAD-7) scale, Overall Anxiety Severity Impairment Scale (OASIS), and the stress subscale of the Depression Anxiety Stress Scale (DASS). The PHQ-9 and the GAD-7 yielded appropriate screening properties to detect three different iterations of the anxious-misery cluster (sensitivity >80.95% and specificity >82.81%). The GAD-7 was the only instrument to display favorable screening properties to detect a fear cluster omitting post-traumatic stress disorder (PTSD) but including obsessive-compulsive disorder (OCD; sensitivity 81.25%, specificity 76.81%). These findings indicate that the PHQ-9 and GAD-7 could be implemented to reliably screen for anxious-misery disorders among CVD in-patients, however, the receiver operating characteristics (ROC) to detect fear disorders were contingent on the placement of PTSD and OCD within clusters. The findings are discussed in relation to routine screening guidelines in CVD populations and contemporary understandings of the internalizing disorders.Megan Grech, Deborah A. Turnbull, Gary A. Wittert, Phillip J. Tully and the CHAMPS Investigator

Novel fast color-converter for visible light communication using a blend of conjugated polymers

The authors thank EPSRC for financial support from UP-VLC Project Grant (EP/K00042X/1).Visible Light Communications (VLC) is a promising new technology which could offer higher data transmission rates than existing broadband RF/microwave wireless technologies. In this paper, we show that a blend of semiconducting polymers can be used to make a broadband, balanced color converter with a very high modulation bandwidth to replace commercial phosphors in hybrid LEDs for visible light communications. The resulting color converter exploits partial Förster energy transfer in a blend of the highly fluorescent green emitter BBEHP-PPV and orange-red emitting MEH-PPV. We quantify the efficiency of the photoinduced energy transfer from BBEHP-PPV to MEH-PPV, and demonstrate modulation bandwidths (electrical-electrical) of ∼200 MHz, which are 40 times higher than commercially available phosphor LEDs. Furthermore, the VLC data rate achieved with this blend using On-Off Keying (OOK) is many times (∼35) higher than that measured with a commercially available phosphor color converter.PostprintPeer reviewe

Side-chain influence on the mass density and refractive index of polyfluorenes and star-shaped oligofluorene truxenes

This work is part of the TIRAMISU project, funded by the European Commission’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n◦284747 and the Engineering and Physical Sciences Research Council (EPSRC) grants EP/J009016/1 and EP/F059922/1. I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders.The density of organic semiconductor films is an important quantity because it is related to intermolecular spacing which in turn determines the electronic and photophysical properties. We report thin film density and refractive index measurements of polyfluorenes and star-shaped oligofluorene truxene molecules. An ellipsometer and a procedure using a spectrophotometer were used to determine film thickness and mass of spin-coated films, respectively. We present a study of the effect of alkyl side-chain length on the volumetric mass density and refractive index of the materials studied. The density measured for poly(9,9-di-n-octylfluorene) (PF8) was 0.88 ± 0.04 g/cm3 and decreased with longer alkyl side chains. For the truxene molecule with butyl side chains (T3 butyl), we measured a density of 0.90 ± 0.04 g/cm3, which also decreased with increasing side-chain length.PostprintPeer reviewe

Magnetic order and disorder in a quasi-two-dimensional quantum Heisenberg antiferromagnet with randomized exchange

We present an investigation of the effect of randomizing exchange coupling strengths in the S = 1/2 square lattice quasi-two-dimensional quantum Heisenberg antiferromagnet (QHAF) (QuinH)2Cu(ClxBr1−x )4 · 2H2O (QuinH = Quinolinium, C9H8N+), with 0 x 1. Pulsed-field magnetization measurements allow us to estimate an effective in-plane exchange strength J in a regime where exchange fosters short-range order, while the temperature TN at which long-range order (LRO) occurs is found using muon-spin relaxation, allowing us to construct a phase diagram for the series. We evaluate the effectiveness of disorder in suppressing TN and the ordered moment size, and we find an extended disordered phase in the region 0.4 x 0.8 where no magnetic order occurs. The observed critical substitution levels are accounted for by an energetics-based competition between different local magnetic orders. Furthermore, we demonstrate experimentally that the ground-state disorder is driven by quantum effects of the exchange randomness, which is a feature that has been predicted theoretically and has implications for other disordered quasi-two-dimensional QHAFs

Predictors of care-giver stress in families of preschool-aged children with developmental disabilities

Background This study examined the predictors, mediators and moderators of parent stress in families of preschool-aged children with developmental disability. Method One hundred and five mothers of preschool-aged children with developmental disability completed assessment measures addressing the key variables. Results Analyses demonstrated that the difficulty parents experienced in completing specific caregiving tasks, behaviour problems during these caregiving tasks, and level of child disability, respectively, were significant predictors of level of parent stress. In addition, parents’ cognitive appraisal of care-giving responsibilities had a mediating effect on the relationship between the child’s level of disability and parent stress. Mothers’ level of social support had a moderating effect on the relationship between key independent variables and level of parent stress. Conclusions Difficulty of care-giving tasks, difficult child behaviour during care-giving tasks, and level of child disability are the primary factors which contribute to parent stress. Implications of these findings for future research and clinical practice are outlined

Therapeutic jurisprudence and procedural justice in Scottish drug courts

Scotland, like other Western jurisdictions, has recently witnessed the development of problem-solving courts aimed at responding more effectively to issues that underlie certain types of offending behaviour. The first to be established were two pilot Drug Courts which drew upon experience of Scottish Drug Treatment and Testing Orders. In common with Drug Courts elsewhere, the Scottish pilots combined treatment, drug testing, supervision and judicial oversight. This article focuses upon the role of judicial involvement in the ongoing review of Drug Court participants’ progress, drawing upon court observation and interviews with offenders and Drug Court professionals. Drug Court dialogues were typically encouraging on the part of sheriffs, aimed at recognising and reinforcing the progress made by participants and motivating then to maintain and build upon their achievements to date, while participants were generally responsive to the positive feedback they received from the sheriffs as their orders progressed. Interactions within the Scottish Drug Courts reflect key features of procedural justice (Tyler, 1990), including ethicality, efforts to be fair and representation. By contributing to enhanced perceptions of procedural justice, Drug Court dialogues may, it is argued, increase the perceived legitimacy of the court and by so doing encourage increased compliance with treatment and desistance from crime

Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events

The $B^0$-$\bar B^0$ oscillation frequency has been measured with a sample of 23 million \B\bar B pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d = 0.493 \pm 0.012{(stat)}\pm 0.009{(syst)}$ ps$^{-1}$.Comment: 7 pages, 1 figure, submitted to Physical Review Letter

An EBSD study of the deformation of service-aged 316 austenitic steel

Electron backscatter diffraction (EBSD) has been used to examine the plastic deformation of an ex-service 316 austenitic stainless steel at 297K and 823K (24 °C and 550 °C)at strain rates 3.5x10-3 to 4 x 10-7 s-1. The distribution of local misorientations was found to depend on the imposed plastic strain following a lognormal distribution at true strains 0.1. At 823 K (550 °C), the distribution of misorientations depended on the applied strain rate. The evolution of lattice misorientations with increasing plastic strain up to 0.23 was quantified using the metrics kernel average misorientation, average intragrain misorientation, and low angle misorientation fraction. For strain rate down to 10-5 s-1 all metrics were insensitive to deformation temperature, mode (tension vs. compression) and orientation of the measurement plane. The strain sensitivity of the different metrics was found to depend on the misorientation ranges considered in their calculation. A simple new metric, proportion of undeformed grains, is proposed for assessing strain in both aged and unaged material. Lattice misorientations build up with strain faster in aged steel than in un-aged material and most of the metrics were sensitive to the effects of thermal aging. Ignoring aging effects leads to significant overestimation of the strains around welds. The EBSD results were compared with nanohardness measurements and good agreement established between the two techniques of assessing plastic strain in aged 316 steel