Emission dynamics of hybrid plasmonic gold/organic GaN nanorods.

We studied the emission of bare and aluminum quinoline (Alq3)/gold coated wurtzite GaN nanorods by temperature- and intensity-dependent time-integrated and time-resolved photoluminescence (PL). The GaN nanorods of ∼1.5 µm length and ∼250 nm diameter were grown by plasma-assisted molecular beam epitaxy. Gold/Alq3 coated GaN nanorods were synthesized by organic molecular beam deposition. The near band-edge and donor-acceptor pair luminescence was investigated in bare GaN nanorods and compared with multilevel model calculations providing the dynamical parameters for electron-hole pairs, excitons, impurity bound excitons, donors and acceptors. Subsequently, the influence of a 10 nm gold coating without and with an Alq3 spacer layer was studied and the experimental results were analyzed with the multilevel model. Without a spacer layer, a significant PL quenching and lifetime reduction of the near band-edge emission is found. The behavior is attributed to surface band-bending and Förster energy transfer from excitons to surface plasmons in the gold layer. Inserting a 5 nm Alq3 spacer layer reduces the PL quenching and lifetime reduction which is consistent with a reduced band-bending and Förster energy transfer. Increasing the spacer layer to 30 nm results in lifetimes which are similar to uncoated structures, showing a significantly decreased influence of the gold coating on the excitonic dynamics.

From Dark to Bright: First-Order Perturbation Theory with Analytical Mode Normalization for Plasmonic Nanoantenna Arrays Applied to Refractive Index Sensing.

We present a first-order perturbation theory to calculate the frequency shift and linewidth change of photonic resonances in one- and two-dimensional periodic structures under modifications of the surrounding refractive index. Our method is based on the resonant state expansion, for which we extend the analytical mode normalization to periodic structures. We apply this theory to calculate the sensitivity of bright dipolar and much darker quadrupolar plasmonic modes by determining the maximum shift and optimal sensing volume.

Linear wave dynamics explains observations attributed to dark solitons in a polariton quantum fluid.

We investigate the propagation and scattering of polaritons in a planar GaAs microcavity in the linear regime under resonant excitation. The propagation of the coherent polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons. We demonstrate that these features are observed for negligible nonlinearity (i.e., polariton-polariton interaction) and are, therefore, not sufficient to identify dark and half-dark solitons. A linear model based on the Maxwell equations is shown to reproduce the experimental observations.

Measuring the lamellarity of giant lipid vesicles with differential interference contrast microscopy.

Giant unilamellar vesicles are a widely utilized model membrane system, providing free-standing bilayers unaffected by support-induced artifacts. To measure the lamellarity of such vesicles, fluorescence microscopy is one commonly utilized technique, but it has the inherent disadvantages of requiring lipid staining, thereby affecting the intrinsic physical and chemical properties of the vesicles, and it requires a calibration by statistical analysis of a vesicle ensemble. Herein we present what we believe to be a novel label-free optical method to determine the lamellarity of giant vesicles based on quantitative differential interference contrast (qDIC) microscopy. The method is validated by comparison with fluorescence microscopy on a statistically significant number of vesicles, showing correlated quantization of the lamellarity. Importantly, qDIC requires neither sample-dependent calibration nor sample staining, and thus can measure the lamellarity of any giant vesicle without additional preparation or interference with subsequent investigations. Furthermore, qDIC requires only a microscope equipped with differential interference contrast and a digital camera.

Brillouin-Raman microspectroscopy for the morpho-mechanical imaging of human lamellar bone.

Bone has a sophisticated architecture characterized by a hierarchical organization, starting at the sub-micrometre level. Thus, the analysis of the mechanical and structural properties of bone at this scale is essential to understand the relationship between its physiology, physical properties and chemical composition. Here, we unveil the potential of Brillouin-Raman microspectroscopy (BRaMS), an emerging correlative optical approach that can simultaneously assess bone mechanics and chemistry with micrometric resolution. Correlative hyperspectral imaging, performed on a human diaphyseal ring, reveals a complex microarchitecture that is reflected in extremely rich and informative spectra. An innovative method for mechanical properties analysis is proposed, mapping the intermixing of soft and hard tissue areas and revealing the coexistence of regions involved in remodelling processes, nutrient transportation and structural support. The mineralized regions appear elastically inhomogeneous, resembling the pattern of the osteons' lamellae, while Raman and energy-dispersive X-ray images through scanning electron microscopy show an overall uniform distribution of the mineral content, suggesting that other structural factors are responsible for lamellar micromechanical heterogeneity. These results, besides giving an important insight into cortical bone tissue properties, highlight the potential of BRaMS to access the origin of anisotropic mechanical properties, which are almost ubiquitous in other biological tissues.

Up on the Jaynes-Cummings ladder of a quantum-dot/microcavity system.

In spite of their different natures, light and matter can be unified under the strong-coupling regime, yielding superpositions of the two, referred to as dressed states or polaritons. After initially being demonstrated in bulk semiconductors and atomic systems, strong-coupling phenomena have been recently realized in solid-state optical microcavities. Strong coupling is an essential ingredient in the physics spanning from many-body quantum coherence phenomena, such as Bose-Einstein condensation and superfluidity, to cavity quantum electrodynamics. Within cavity quantum electrodynamics, the Jaynes-Cummings model describes the interaction of a single fermionic two-level system with a single bosonic photon mode. For a photon number larger than one, known as quantum strong coupling, a significant anharmonicity is predicted for the ladder-like spectrum of dressed states. For optical transitions in semiconductor nanostructures, first signatures of the quantum strong coupling were recently reported. Here we use advanced coherent nonlinear spectroscopy to explore a strongly coupled exciton-cavity system. We measure and simulate its four-wave mixing response, granting direct access to the coherent dynamics of the first and second rungs of the Jaynes-Cummings ladder. The agreement of the rich experimental evidence with the predictions of the Jaynes-Cummings model is proof of the quantum strong-coupling regime in the investigated solid-state system.

Can ventilation-feedback training augment exercise tolerance in patients with chronic obstructive pulmonary disease?

RATIONALE: Exercise-induced dynamic hyperinflation contributes to decreased exercise tolerance in chronic obstructive pulmonary disease (COPD). It is unknown whether respiratory retraining (ventilation-feedback [VF] training) can affect exercise-induced dynamic hyperinflation and increase exercise tolerance. OBJECTIVES: To determine whether patients with COPD would achieve longer exercise duration if randomized to a combination of exercise training plus VF training than either form of training on its own. METHODS: A total of 64 patients randomized to 1 of 3 groups: VF plus exercise (n = 22), exercise alone (n = 20), and VF alone (n = 22). MEASUREMENTS AND MAIN RESULTS: Exercise duration before and after 36 training sessions and exercise-induced dynamic hyperinflation and respiratory pattern before and after training were measured. In the 49 patients who completed training, duration of constant work-rate exercise was 40.0 (+/- 20.4) minutes (mean +/- SD) with VF plus exercise, 31.5 (+/- 17.3) minutes with exercise alone, and 16.1 (+/- 19.3) minutes with VF alone. Exercise duration was longer in VF plus exercise than in VF alone (P < 0.0001), but did not reach predetermined statistical significance when VF plus exercise was compared with exercise alone (P = 0.022) (because of multiple comparisons, P

Physiological improvement with moderate exercise in type II diabetic neuropathy.

OBJECTIVE: The objective of this study was to demonstrate improvement in nerve function with moderate exercise in patients with type II diabetic neuropathies. RESEARCH DESIGN AND METHODS: Fives subjects with type II diabetes mellitus and distal, predominantly sensory polyneuropathies were studied. The subjects completed an 8-week program of a supervised moderate exercise program (40-75% of maximal 02 uptake reserve) with a subsequent 16-week program of monitored similar exercise. The same experienced electrophysiologist performed the electrodiagnostic studies both before and after the 24-week exercise period. These studies monitored physiological changes (conduction velocities, response amplitudes) in motor and sensory fibers as well as F-wave latencies. RESULTS: The exercise program produced a documented increase in aerobic exercise capacity. Despite the small number of subjects studied and the relatively short exercise period, there was a statistically significant improvement in nearly all electrophysiological parameters evaluated post exercise including motor conduction velocities and amplitudes, sensory conduction velocities, and F-wave latencies. This improvement included a statistically significant improvement in absolute median motor evoked response amplitudes as well as the recording of sensory nerve action potentials not present prior to exercise. There were no adverse effects from the exercise. CONCLUSIONS: This study supports the hypothesis that exercise can be performed safely in patients with type II diabetic neuropathies and can produce improvement in their nerve function. This study also supports the hypothesis that ischemia may have a meaningful role in the pathogenesis of neuropathies in patients with type II diabetes mellitus.

Determinants of cough effectiveness in patients with respiratory muscle weakness.

Experiments were undertaken to mechanistically define expiratory-muscle contribution to effectiveness of cough while controlling glottic movement. We hypothesized that electrical abdominal-muscle stimulation in patients with respiratory-muscle weakness produces effective coughs only when glottic closure accompanies coughs. In ten spinal-cord-injury patients, esophago-gastric pressure and airflow were recorded during solicited-coughs, coughs augmented by abdominal-muscle stimulation, and passive open-glottis exhalations. During solicited-coughs, patients closed the glottis initially; five were flow-limited, five non-flow-limited. Stimulations during solicited-coughs or open-glottis exhalations elicited similar driving pressures (changes in gastric pressure; p<0.001). Despite high driving pressures, stimulations induced flow-limitation only when patients transiently closed the glottis - not during open-glottis exhalations. That is, transient glottic closure enabled transmission of abdominal (driving) pressure to the thorax during cough, while impeding dissipation of intrathoracic pressure. In conclusion, transient glottic closure is necessary to render cough effective in patients with respiratory-muscle weakness, indicating that failure to close the glottis contributes to ineffective cough in weak tracheostomized patients and patients with bulbar disorders.

Separation of coherent and incoherent nonlinearities in a heterodyne pump-probe experiment.

We demonstrate that the transient coherent nonlinearity (coherent artifact) affecting the pump-probe response of semiconductor optical amplifiers can be experimentally separated from the incoherent transient. The technique is based on measuring the mirror component of the coherent artifact which is a background-free four--wave mixing signal at a different frequency with respect to the transmitted probe in a heterodyne detection scheme. Measurements on amplifiers of different length reveal strong deviations from the commonly expected symmetric shape of the coherent artifact in case of long waveguides.

PoleStriding exercise and vitamin E for management of peripheral vascular disease.

PURPOSE: The purpose of this investigation was to evaluate the efficacy of PoleStriding exercise (a form of walking that uses muscles of the upper and lower body in a continuous movement similar to cross-country skiing) and vitamin E (alpha-tocopherol) to improve walking ability and perceived quality of life (QOL) of patients with claudication pain secondary to peripheral arterial disease (PAD). METHODS: Fifty-two subjects were randomized into four groups: PoleStriding with vitamin E (N = 13), PoleStriding with placebo (N= 14), vitamin E without exercise (N= 13), and placebo without exercise (N = 12). The dose of vitamin E was 400 IU daily. Only the PoleStriding with vitamin E and PoleStriding with placebo groups received PoleStriding instruction and training. Assignment to vitamin E or placebo was double blind. Subjects trained three times weekly for 30-45 min (rest time excluded). Individuals in vitamin E and placebo groups came to the laboratory biweekly for ankle blood-pressure measurements. RESULTS: Results of this randomized clinical trial provide strong evidence that PoleStriding significantly (P< 0.001) improved exercise tolerance on the constant work-rate and incremental treadmill tests. Ratings of perceived claudication pain were significantly less after the PoleStriding training program (P= 0.02). In contrast, vitamin E did not have a statistically significant effect on the subjects' ratings of perceived leg pain (P= 0.35) or treadmill walking duration ( P= 0.36). Perceived distance and walking speed (Walking Impairment Questionnaire) and perceived physical function (Rand Short Form-36) improved in the PoleStriding trained group only (P< 0.001, 0.022 and 0.003, respectively). CONCLUSION: PoleStriding effectively improved the exercise tolerance and perceived QOL of patients with PAD. Little additional benefit to exercise capacity was realized from vitamin E supplementation.

Effects of exercise training on aerobic capacity and quality of life in individuals with heart failure.

PURPOSE: The purpose of this study was to determine whether subjects with chronic heart failure, who completed a 12-week rehabilitation program, would have significantly greater quality of life, better aerobic fitness, less difficulty with symptoms of heart failure, greater self-efficacy for exercise, and higher daily activity levels when compared with subjects in a control group. METHODS: Thirty-one males, aged 64 +/- 10 years with left ventricular ejection fraction of 29 +/- 7%, were randomized to a moderate intensity supervised aerobic exercise program (n = 15) or a control group (n = 16). Twenty-seven subjects completed at least 1 follow-up assessment. RESULTS: After 12 weeks there were significant differences in the change scores for perceived physical function (using RAND Corporation's 36-item short form) (P =.025) and peak oxygen uptake (P =.019) between the exercise and control groups with the exercise group experiencing improved physical function and fitness. CONCLUSIONS: Exercise training in adults with heart failure increases exercise tolerance and perceived physical function. Improved heart failure symptoms, self-efficacy for exercise, or increased physical activity may not be associated with enhancement of exercise tolerance.

Research device to preproduction prototype: a chronology.

This paper describes the evolution of the Wheelchair Aerobic Fitness Trainer (WAFT), a wheelchair ergometer developed for determination of aerobic capacity and the diagnosis of coronary artery disease in lower limb disabled persons whose mobility depends primarily on the manual wheelchair. The device was originally developed for use in research studies to determine peak exercise capacity in persons with spinal cord injuries and other lower limb disabilities and to formulate associated graded exercise stress test protocols. In subsequent research, the device was incorporated into a specially designed testing station for the detection of coronary artery disease in persons who cannot adequately undergo treadmill or cycle ergometry testing because of lower limb disabilities. Based on the usefulness of the device for both rehabilitation and diagnostic purposes, the WAFT has been brought into the technology transfer process of the Department of Veterans Affairs Rehabilitation Research and Development Service. Under a contract with Packer Engineering, Inc., Naperville, IL, development of a preproduction version of the device and six units for field evaluation has commenced. The preproduction prototype of the WAFT has incorporated numerous improvements over the original device and promises to expand the potential for future research, rehabilitation, and diagnostic applications.

Adequacy of power wheelchair control interfaces for persons with severe disabilities: a clinical survey.

The extreme difficulty with which persons with severe disabilities have been taught to maneuver a power wheelchair has been described in case studies, and anecdotal evidence suggests the existence of a patient population for whom mobility is severely limited if not impossible given currently available power wheelchair control interfaces. Since our review of the literature provided little evidence either in support or refutation of the adequacy of existing power wheelchair control interfaces, we surveyed 200 practicing clinicians, asking them to provide information about their patients and to give their impressions of the potential usefulness of a new power wheelchair navigation technology. Significant survey results were: Clinicians indicated that 9 to 10 percent of patients who receive power wheelchair training find it extremely difficult or impossible to use the wheelchair for activities of daily living. When asked specifically about steering and maneuvering tasks, the percentage of patients reported to find these difficult or impossible jumped to 40. Eighty-five percent of responding clinicians reported seeing some number of patients each year who cannot use a power wheelchair because they lack the requisite motor skills, strength, or visual acuity. Of these clinicians, 32 percent (27 percent of all respondents) reported seeing at least as many patients who cannot use a power wheelchair as who can. Nearly half of patients unable to control a power wheelchair by conventional methods would benefit from an automated navigation system, according to the clinicians who treat them. We believe these results indicate a need, not for more innovation in steering interfaces, but for entirely new technologies for supervised autonomous navigation.

Energy cost and locomotive economy of handbike and rowcycle propulsion by persons with spinal cord injury.

Seven subjects with chronic paralysis due to spinal cord injury completed a series of experiments to 1) determine and compare the metabolic cost of propelling the Handbike and Rowcycle, and 2) evaluate the potential of these upper body-powered devices for improving the cardiorespiratory fitness of persons with lower limb disabilities. Mean intrasubject differences between the Handbike and Rowcycle rides for heart rate, minute ventilation, oxygen uptake, and net locomotive energy cost were small and did not reach statistical significance for any of the ride conditions. Lower net locomotive energy cost (greater economy) during a 5.5 mi.hr-1 ride condition predicted vehicle preference in all cases (P = 0.008). The range of values for percent peak oxygen uptake suggests that all but one of the subjects were able to utilize either vehicle at an intensity sufficient for improving and maintaining cardiorespiratory fitness without undue fatigue.

Effect of exercise on perceived quality of life of individuals with Parkinson's disease.

The purpose of this study was to determine if individuals with Parkinson's disease (PD) who completed an 8-week, supervised PoleStriding exercise program would undergo significant improvements in cognitive skills, activities of daily living, motor function, and quality of life. The Unified Parkinson's Disease Rating Scale (UPDRS) and the Parkinson's Disease Questionnaire (PDQ-39) were used to measure functional independence. Six male volunteers (72.7+/-3.7 years of age) performed PoleStriding exercise three times per week for 37+/-3 minutes. Differences in the participants' pre- and post-training scores on the UPDRS and PDQ-39 were analyzed using the Wilcoxin Signed Ranks Test. A statistically significant improvement occurred in the UPDRS (P<0.026) and PDQ-39 (P<0.028) scores following the moderate-intensity exercise intervention. The results of this nonrandomized clinical trial indicate that an 8-week individualized PoleStriding exercise program increases perceived functional independence and quality of life in individuals with PD.

Initial clinical evaluation of a wheelchair ergometer for diagnostic exercise testing: a technical note.

The purpose of this initial study was to evaluate a new wheelchair ergometer (WCE) and exercise test protocol for the detection of coronary artery disease in men with lower limb disabilities. Forty-nine patients (63 +/- 9 yr) completed WCE tests without complications. Peak heart rate was 84 +/- 15% (mean +/- SD) of age-predicted maximum and peak double product was 223 +/- 62 x 10(2). The specified target heart rate (> or = 80% age-predicted maximal) or a positive result was achieved in 76% of tests. Fourteen tests were rated positive, 21 as negative and 14 as nondiagnostic for exercise-induced ischemia. In 18 patients who underwent coronary angiography, the predictive value was 100% (10/10) for a positive, and 50% (2/4) for a negative WCE test result. These results suggest that WCE is a viable initial diagnostic option for some persons who cannot adequately perform treadmill or cycle ergometry exercise.

Pulmonary function testing in spinal cord injury: effects of abdominal muscle stimulation.

The purpose of this study was to assess the effects of applying transcutaneous electrical stimulation to paralyzed abdominal muscles during pulmonary function testing (PFT) of individuals with spinal cord injury (SCI). Ten male subjects with anatomical level of SCI between C5-T7 were studied. Subjects performed PFTs with and without electrical stimulation delivered to the abdominal muscles. Subjects with the lowest percentage of predicted expiratory volumes and flows demonstrated the greatest improvement when electrical stimulation was delivered during forced expiration. The overall increases seen in percent of predicted for the study sample were 23 percent for forced vital capacity (FVC), 16 percent for forced expiratory flow in 1 s (FEV1), and 22 percent for peak expiratory flow rate (PEF). Contractions of paralyzed expiratory muscles in response to electrical stimulation during the performance of PFT maneuvers can significantly improve FVC, FEV1, and PEF in some individuals with SCI.

Effect of ventilation-feedback training on endurance and perceived breathlessness during constant work-rate leg-cycle exercise in patients with COPD.

The purpose of this study was to evaluate the efficacy of a unique program of ventilation-feedback training combined with leg-cycle exercise to improve exertional endurance and decrease perceived dyspnea in patients with chronic obstructive pulmonary disease (COPD). Thirty-nine patients (67.5 +/- 8.1 yr of age) with moderate to severe COPD (42.6% of predicted forced expiratory volume in 1 s) were randomized to one of three 6-week experimental interventions: ventilation-feedback with exercise (V(+EX)), exercise only (EX(ONLY)), or ventilation-feedback only (VF(ONLY)). At baseline and at 6 weeks, patients completed a constant work-rate leg-cycle ergometer test at 85 percent of maximal power output. There were increases within the groups in exercise duration: 11.5 min (103%), 8.0 min (66%), and 0.4 min (4%) for the VF(+EX), EX(ONLY) and VF(ONLY) groups, respectively. The VF(ONLY) group experienced no significant within-group changes in selected gas exchange parameters. However, there were significant (p < 0.05) posttraining changes in minute ventilation, tidal volume, breathing frequency (f), and expiratory time (Te) in the VF(+EX) group, and in f and Te in the EX(ONLY) group. After completing the training, VF(+EX) and EX(ONLY) patients reported less breathlessness and perceived exertion (p < 0.05). The VF(ONLY) patients' ratings changed in the hypothesized direction but were not significant. Based on these preliminary data, VF(+EX) and EX(ONLY) were equally effective in improving leg-cycle exercise tolerance in patients with moderate to severe COPD.