Thermal hysteresis in scattering by VO2 spheres.

Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal when heated from 58°C to 72°C, and the transformation is reversible but hysteretic. Electromagnetically, VO2 transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength is λ0<1100nm; it transforms from a dissipative dielectric to a plasmonic metal (or vice versa) if λ0>1100nm. Calculating the extinction, total scattering, absorption, radiation pressure, backscattering and forward-scattering efficiencies of a VO2 sphere, we found clear signatures of thermal hysteresis in (i) the forward-scattering, backscattering, and absorption efficiencies for λ0<1100nm, and (ii) the forward-scattering, backscattering, total scattering, and absorption efficiencies for λ0>1100nm. Vacuum and null-permittivity quasistates occur between 58°C and 72°C, when tetragonal VO2 is a plasmonic metal, once each on the heating branch and once each on the cooling branch of thermal hysteresis. But none of the six efficiencies show significant differences between the two quasistates.

Haematocrit level in obesity hypoventilation syndrome: a predictor of mortality?

BACKGROUND: The connection between obstructive sleep apnea and secondary erythrocytosis is controversial. We hypothesised that there may be a higher prevalence of erythrocytosis in patients with obesity hypoventilation syndrome (OHS) due to persistent hypoxemia. METHODS: The study was a retrospective, cross-sectional review of patients with OHS derived from an established cohort of "non-invasive ventilation" patients at the Department of Sleep Medicine at the Royal Infirmary Medical Centre, Edinburgh (2004-2017). Relevant clinical data were obtained from patient records. RESULTS: The cohort comprised 74 patients with OHS, 44 men (60%), mean age at diagnosis 54 ± 10 years. The mean haematocrit level for the group overall was 0.44, in men 0.45, and in women 0.41. Of 11 patients with erythrocytosis (15%), 7 were men. Thirteen patients (18%) died during follow-up (2004-2017). There was a statistically significant increase in risk of death in patients with higher and lower haematocrit levels compared to that in patients with OHS who had normal haematocrits. CONCLUSIONS: This is the first study showing increased prevalence of erythrocytosis in OHS patients. There was a "U"-shaped correlation with mortality according to haematocrit levels.

Toward a cylindrical cloak via inverse homogenization.

An effective cylindrical cloak may be conceptualized as an assembly of adjacent local neighborhoods, each of which is made from a homogenized composite material (HCM). The HCM is required to be a certain uniaxial dielectric-magnetic material, characterized by positive-definite constitutive dyadics. It can arise from the homogenization of component materials that are remarkably simple in terms of their structure and constitutive relations. For example, the components can be two isotropic dielectric-magnetic materials, randomly distributed as oriented spheroidal particles. By carefully controlling the spheroidal shape of the component particles, a high degree of HCM anisotropy may be achieved which is necessary for the cloaking effect to be realized. The inverse Bruggeman formalism can provide estimates of the shape and constitutive parameters for the component materials, as well as their volume fractions.

On the sensitivity of generic porous optical sensors.

A porous material was considered as a platform for optical sensing. It was envisaged that the porous material was infiltrated by a fluid that contains an agent to be sensed. Changes in the optical properties of the infiltrated porous material provide the basis for detection of the agent to be sensed. Using a homogenization approach based on the Bruggeman formalism, wherein the infiltrated porous material was regarded as a homogenized composite material, the sensitivity of such a sensor was investigated. For the case of an isotropic dielectric porous material of relative permittivity ε(a) and an isotropic dielectric fluid of relative permittivity ε(b), it was found that the sensitivity was maximized when there was a large contrast between ε(a) and ε(b); the maximum sensitivity was achieved at midrange values of porosity. Especially high sensitivities may be achieved for ε(b) close to unity when ε(a)>>1, for example. Furthermore, higher sensitivities may be achieved by incorporating pores that have elongated spheroidal shapes.

Randomized controlled trial of variable-pressure versus fixed-pressure continuous positive airway pressure (CPAP) treatment for patients with obstructive sleep apnea/hypopnea syndrome (OSAHS).

STUDY OBJECTIVE: To determine whether fixed-pressure or variable-pressure CPAP was preferred by patients and gave better outcomes in patients with the obstructive sleep apnea/hypopnea syndrome (OSAHS). DESIGN: Randomized blinded cross-over trial with 6 weeks of fixed and 6 weeks of variable-pressure CPAP. SETTING: Sleep center. PATIENTS: 200 consecutive consenting CPAP naïve patients with daytime sleepiness and > 15 apneas + hypopneas/h after an attended auto-CPAP titration night. INTERVENTIONS: CPAP therapy using the same device (Autoset Spirit) set for 6 weeks in fixed pressure mode and for 6 weeks in variable pressure mode, the order of therapies being randomized. MEASUREMENTS AND RESULTS: All measurements were recorded at the end of each limb by a researcher blind to treatment. These included symptoms, Epworth Score, CPAP usage, objective sleepiness by modified Osler test, vigilance and health related quality of life. A total of 181 of 200 patients completed the study. At the end of the study, patients expressed no significant difference in the primary outcome, patient preference, 72 patients preferring fixed and 69 preferring variable-pressure CPAP. Epworth score was lower on variable (9.5, SEM 0.4) than fixed-pressure CPAP (10.0, SEM 0.3; P = 0.031). Mean CPAP use was higher on variable (4.2, SEM 0.2 h/night) than fixed-pressure CPAP (4.0, SEM 0.2 h/night; P = 0.047). There were no other significant differences between treatments. CONCLUSIONS This study shows no difference in patient preference and only a marginal benefit of variable over fixed-pressure CPAP in OSAHS in terms of subjective sleepiness and CPAP use. The clinical value of this difference remains to be determined. CLINICAL TRIAL INFORMATION: Variable-pressure versus fixed-pressure continuous positive airway pressure (CPAP) treatment for patients with obstructive sleep apnoea/hypopnoea syndrome (OSAHS); Registration # ISRCTN43085025.http://www.controlled-trials.com//SRCTN43085025.

Multiple Rayleigh waves guided by the planar surface of a continuously twisted structurally chiral material.

The Stroh formalism was adapted for Rayleigh-wave propagation guided by the planar traction-free surface of a continuously twisted structurally chiral material (CTSCM), which is an anisotropic solid that is periodically non-homogeneous in the direction normal to the planar surface. Numerical studies reveal that this surface can support either one or two Rayleigh waves at a fixed frequency, depending on the structural period and orientation of the CTSCM. In the case of two Rayleigh waves, each wave possesses a different wavenumber. The Rayleigh wave with the larger wavenumber is more localized to the surface and has a phase speed that changes less as the angular frequency varies in comparison with the Rayleigh wave with the smaller wavenumber.

Two Dyakonov-Voigt surface waves guided by a biaxial-isotropic dielectric interface.

Electromagnetic surface waves guided by the planar interface of an orthorhombic dielectric material and an isotropic dielectric material were analyzed theoretically and numerically. Both naturally occurring minerals (crocoite, tellurite, and cerussite) and engineered materials were considered as the orthorhombic partnering material. In addition to conventional Dyakonov surface waves, the analysis revealed that as many as two Dyakonov-Voigt surface waves can propagate in each quadrant of the interface plane, depending upon the birefringence of the orthorhombic partnering material. The coexistence of two Dyakonov-Voigt surface waves marks a fundamental departure from the corresponding case involving the planar interface of a uniaxial dielectric material and an isotropic dielectric material for which only one Dyakonov-Voigt surface wave is possible. The two Dyakonov-Voigt surface waves propagate in different directions in each quadrant of the interface plane, with different relative phase speeds and different penetration depths. Furthermore, the localization characteristics of the two Dyakonov-Voigt surface waves at the planar interface are quite different: the Dyakonov-Voigt surface wave with the higher relative phase speed is much less tightly localized at the interface in the isotropic dielectric partnering material.

Dyakonov-Voigt surface waves.

Electromagnetic surface waves guided by the planar interface of an isotropic dielectric medium and a uniaxial dielectric medium, both non-dissipative, were considered, the optic axis of the uniaxial medium lying in the interface plane. Whereas this interface is known to support the propagation of Dyakonov surface waves when certain constraints are satisfied by the constitutive parameters of the two partnering mediums, we identified a different set of constraints that allow the propagation of surface waves of a new type. The fields of the new surface waves, named Dyakonov-Voigt (DV) surface waves, decay as the product of a linear and an exponential function of the distance from the interface in the anisotropic medium, whereas the fields of the Dyakonov surface waves decay only exponentially in the anisotropic medium. In contrast to Dyakonov surface waves, the wavenumber of a DV surface wave can be found analytically. Also, unlike Dyakonov surface waves, DV surface waves propagate only in one direction in each quadrant of the interface plane.

Theory of light emission from a dipole source embedded in a chiral sculptured thin film.

Developing a theory based on a spectral Green function for light emission from a point-dipole source embedded in a chiral sculptured thin film (CSTF), we found that the intensity and polarization of the emitted light are strongly influenced by the structural handedness of the CSTF as well as the placement and orientation of the source dipole. The emission patterns across both pupils of the dipole-containing CSTF can be explained in terms of the circular Bragg phenomenon exhibited by CSTFs when illuminated by normally as well as obliquely incident plane waves. The emission characteristics augur well for the future of CSTFs as optical biosensors as well as light emitters with controlled circular polarization and bandwidth.

When does the choice of the refractive index of a linear, homogeneous, isotropic, active, dielectric medium matter?

Two choices are possible for the refractive index of a linear, homogeneous, isotropic, active, dielectric material. Either of the choices is adequate for obtaining frequency-domain solutions for (i) scattering by slabs, spheres, and other objects of bounded extent; (ii) guided--wave propagation in homogeneously filled, cross-sectionally uniform, straight waveguide sections with perfectly conducting walls; and (iii) image formation due to flat lenses. The correct choice does matter for the half-space problem, but that problem is not realistic.

Case report: Endobronchial valve placement for treatment of a persistent air leak.

Demonstration of the therapeutic utility of endobronchial valves in elderly high-risk patients unsuitable for surgery http://ow.ly/Y7eEx.

Plane waves with negative phase velocity in Faraday chiral mediums.

The propagation of plane waves in a Faraday chiral medium is investigated. Conditions for the phase velocity to be directed opposite to the direction of power flow are derived for propagation in an arbitrary direction; simplified conditions which apply to propagation parallel to the distinguished axis are also established. These negative phase-velocity conditions are explored numerically using a representative Faraday chiral medium, arising from the homogenization of an isotropic chiral medium and a magnetically biased ferrite. It is demonstrated that the phase velocity may be directed opposite to power flow, provided that the gyrotropic parameter of the ferrite component medium is sufficiently large compared with the corresponding nongyrotropic permeability parameters.