Search

High-altitude pseudo-satellites (HAPS) may be kept aloft indefinitely with station-keeping provided by plasma air thrusters (PAT) using wireless power transfer (WPT) from a terrestrial phased array antenna (PAA). One example is the patented “Sitallite” superpressure balloon with a rectifying antenna (rectenna) covering its underside, with thrusters around the periphery. Such a stationary platform can provide continuous observation and communications capabilities covering vast areas for a fraction of the cost required for an orbiting satellite. This work builds upon the design and safety study published elsewhere to provide performance estimates for a long-duration, persistent HAPS powered by electronically-steerable microwave beams. Newly-derived efficiency equations are used to provide accurate estimates of free-space WPT transfer efficiency based on the dimensions of the ground-based PAA and the rectenna. Calculations of air drag for a spheroidal bouyant shape are used to derive PAT power requirements, and these, together with power conversion circuitry, are used to size the overall system. Accurate estimates of cost are derived. These performance estimates can be used to help make economic and logistic decisions, as a fuel-free HAPS with PAT and powered by WPT can be lofted in less time, and with lower risk, than an orbital satellite of comparable capabilities.

'Smart' windows which reversibly increase their reflectivity upon heating are attracting considerable attention as devices for maintaining comfortable indoor environmental conditions. In this work, twisted nematic semi‐interpenetrating liquid crystal networks which lose their order upon heating are sandwiched between reflective linear polarizers. This 'smart' window reversibly decreases its transmission from about 50–10% over a wavelength range between 400 and 1100 nm upon heating, resulting in the window becoming darker and reflecting more light. This 'smart' window is potentially interesting for energy saving window applications where variation between privacy and visible light transparency states is required.

A new principle is developed to fabricate temperature-responsive, multicolor photonic coatings that are capable of switching color. The coating is composed of a non-cross-linked liquid crystal siloxane-based elastomer that is interpenetrated through an acrylate-based liquid crystal network. Discrete temperature changes induce phase separation and mixing between the siloxane and the acrylate polymers and change the reflective colors correspondingly. The temperature-responsive color change of the coatings can be programmed by the processing conditions and coating formulation, which allows for the fabrication of photopatterned multicolor images. The photonic ink can be coated on flexible poly(ethylene terephthalate) films using roll-to-roll flexographic printing, making these temperature-responsive, multicolor-changing polymers appealing for applications such as responsive color decors, optical sensors, and anticounterfeit labels.

Context. The inner few au region of planet-forming disks is a complex environment. High angular resolution observations have a key role in understanding the disk structure and the dynamical processes at work. Aims. In this study we aim to characterize the mid-infrared brightness distribution of the inner disk of the young intermediate-mass star HD 163296, from VLTI/MATISSE observations. Methods. We use geometric models to fit the data. Our models include a smoothed ring, a flat disk with inner cavity, and a 2D Gaussian. The models can account for disk inclination and for azimuthal asymmetries as well. We also perform numerical hydro-dynamical simulations of the inner edge of the disk. Results. Our modeling reveals a significant brightness asymmetry in the L-band disk emission. The brightness maximum of the asymmetry is located at the NW part of the disk image, nearly at the position angle of the semimajor axis. The surface brightness ratio in the azimuthal variation is $3.5 \pm 0.2$. Comparing our result on the location of the asymmetry with other interferometric measurements, we confirm that the morphology of the $r, accepted for publication in A&A

The nature of circumstellar envelopes (CSE) around Cepheids is still a matter of debate. The physical origin of their infrared (IR) excess could be either a shell of ionized gas, or a dust envelope, or both. This study aims at constraining the geometry and the IR excess of the environment of the long-period Cepheid $\ell$ Car (P=35.5 days) at mid-IR wavelengths to understand its physical nature. We first use photometric observations in various bands and Spitzer Space Telescope spectroscopy to constrain the IR excess of $\ell$ Car. Then, we analyze the VLTI/MATISSE measurements at a specific phase of observation, in order to determine the flux contribution, the size and shape of the environment of the star in the L band. We finally test the hypothesis of a shell of ionized gas in order to model the IR excess. We report the first detection in the L band of a centro-symmetric extended emission around l Car, of about 1.7$R_\star$ in FWHM, producing an excess of about 7.0\% in this band. In the N band, there is no clear evidence for dust emission from VLTI/MATISSE correlated flux and Spitzer data. On the other side, the modeled shell of ionized gas implies a more compact CSE ($1.13\pm0.02\,R_\star$) and fainter (IR excess of 1\% in the L band). We provide new evidences for a compact CSE of $\ell$ Car and we demonstrate the capabilities of VLTI/MATISSE for determining common properties of CSEs. While the compact CSE of $\ell$ Car is probably of gaseous nature, the tested model of a shell of ionized gas is not able to simultaneously reproduce the IR excess and the interferometric observations. Further Galactic Cepheids observations with VLTI/MATISSE are necessary for determining the properties of CSEs, which may also depend on both the pulsation period and the evolutionary state of the stars., Comment: 13 pages, 8 figures, accepted in Astronomy and Astrophysics

Stratospheric superpressure balloons are a class of high-altitude pseudo-satellite (HAPS) with excellent observational and communications capabilities. The challenge to long-duration operation is station keeping against the thin but fast zephyrs at altitudes around 25 km. One solution is captured in the US patent 10,404,353, which describes a “Sitallite” HAPS having plasma air thrusters to maneuver against the wind. To hold station for months at a time requires a steady delivery of power, such as a microwave beam transmitted from a terrestrial phased array antenna (PAA) to a rectifying receiving antenna (rectenna) mounted on the underside of the superpressure balloon. This work explores the design and safety considerations for the wireless power transfer (WPT) aspects of such a Sitallite and the tradeoffs between array sizes and power requirements. Presented here are studies of the directivity of the PAA as a function of the number and spacing of antenna elements, and the expected impact on ground personnel, insects, birds, and overflying aircraft. The support and suspension structure of the high-altitude rectenna are developed, along with a comparison of various commercial Schottky diodes for this application. Finally, system studies are presented to illustrate the cost drivers and size optimization. Such a Sitallite can provide line-of-sight visibility for a 1,100 km radius, remain aloft for many months, and provide services normally expected from an orbiting satellite at a fraction of the cost.

A crosslinkable cholesteric main-chain liquid crystal oligomer was prepared, and coated on glass using blade-coating. The coating showed a reflection band that varied as a function of temperature over a range of several hundreds of nanometers. This allowed patterning of the coating in various colours using multiple crosslinking steps at different temperatures.

A temperature-responsive polarization converter, which reversibly changes from a full-wave to a half-wave plate upon heating, is developed. The polymer wave plate has a controlled thickness and is based on a uniaxial aligned nematic semi-interpenetrating network coating containing a specific concentration of a non-crosslinked liquid crystal elastomer. Upon heating, the effective birefringence of the wave plate halves without changing the thickness. The function of the wave plate is demonstrated by sandwiching the tunable polarization converter between two identical right-handed circular polarized light reflective films with a wavelength around 770 nm. At low temperatures, this optical device reflects 50% of light at 770 nm, whereas at elevated temperature 81% is reflected. Such temperature-responsive optical devices have potential applications for both aesthetic purposes as well as energy saving windows.

Wireless Power Transfer (WPT) from space-to-earth at a large scale will not be possible until the Side Lobe Levels (SLL) are reduced many orders of magnitude from the current technology available today. To accomplish this, careful design of the transmitting antenna (spacetenna) is imperative. Any module failures or errors in connectivity, including askew angles between adjacent sandwich modules, reduce the effectiveness of the antenna design and thereby increase SLL. This work examines two interrelated issues; error detection and repair, and spacetenna flatness correction. Multiple different designs of sandwich module mechanical connections, wiring, and control are examined. The results of the analysis and best options are presented in order to facilitate for ultra-low SLL for use in Space Solar Power for the benefit of humanity and the environment.

Stimulus-responsive photonic polymer materials that change their reflection colour as function of environmental stimuli such as temperature, humidity and light, are attractive for various applications (e.g. sensors, smart windows and communication). Polymers provide low density, tunable and patternable materials. This feature article focusses on various autonomously responding photonic polymer materials such as hydrogels, block copolymers and liquid crystals and discusses their potential industrial implementation.

Engineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super-reflectivity. Simulations match the experimentally observed photonic properties and reveal a distorted helical structure. 3D engineered polymer films can be made that reflect both left- and right handed circular and linear polarized light dependent and exhibit a changing color contrast upon altering the polarization of incident light. Hence, these 3D engineered photonic materials are of interest for new and emerging applications ranging from anti-counterfeit labels and data encryption to aesthetics and super-reflective films.

The fabrication of stimulus-responsive coatings that change both reflectivity and topography is hampered by the lack of easy processable, patternable, and programmable elastomers. Here, an easily applied reflective coating based on a semi-interpenetrating polymer network composed of a liquid crystal elastomer and a liquid crystal network (>15 wt%) is reported. The reflective wavelength of these polysiloxane elastomer photonic coatings can be readily programed by the concentration of chiral reactive mesogen dopant that forms the network. The coatings show a fast and reversible decrease in reflection band intensity with increasing temperature, which can be tuned by the polymer network density. In addition, hierarchical surface relief structures are prepared, which can be reversibly changed with temperature.

MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal., Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2016, 11 pages, 6 Figures

Une cellule electrochimique annulaire est concue dans laquelle l'electrolyte s'ecoule longitudinalement en respectant une microelectrode cylindrique de platine. Les proprietes de transfert de masse dans une cellule annulaire sont determinees par mesure des courants de Faraday correspondant aux oxydations, limitees par le transfert de masse, de ferrocyanure dans l'eau et de ferrocene dans l'acetonitrile. Les mesures sont realisees a l'aide d'electrodes de diametres: 25, 127 μm et 1 mm dans une cellule de diametre: 4,8 mm et a des vitesses d'ecoulement correspondant a des nombres de Reynolds compris entre 1 et 900

Phase-measurement interferometric microscopy (PMIM) was used to measure the topography of Pt microelectrodes fabricated on silicon wafers. Disk (10 {mu}m radius) and band (10 {mu}m {times} 1,000 {mu}m) electrodes were prepared by deposition and lithographic patterning of a 0.2 {mu}m thick SiO{sub 2} layer on a 0.05 {mu}m thick Pt film. Quantitative topographical images of the resulting electrodes are obtained from PMIM by accounting for the complex refractive index of Pt and for multiple reflections of light which occur within the transparent SiO{sub 2} layer. In situ, quantitative measurement of microelectrode topography in water is also demonstrated.

Three-dimensional topographical imaging of electrode surfaces using phase-measurement interferometric microscopy is described. Topographical measurements are based on a rapid, non-destructive optical method that provides ultrahigh vertical resolution (0.6 nm) and moderate horizontal resolution (0.5 microns). In-situ images of electrodes prepared from highly oriented pyrolytic graphite, platinum thin films, and polycrystalline iron are reported. In-situ measurement of the time-dependent growth of corrosion pits on FE in 0.1 M H2S04 is also demonstrated.

We report an optical microscopy technique for mapping variations in refractive index across an electrode surface that result from non-uniform electrochemical generation of a soluble species

Phase detection interferometric microscopy (PDIM) was used to obtain high resolution surface images of 100 micro m diameter iron disk exposed to 0.1M H2SO4. The initiation and growth of corrosion pits at short time (0-30 sec) were observed on relatively smooth regions of the Fe surface (r.m.s. surface roughness approx. 5.5 nm). The growth of pits at open circuit was measured with 1 nm resolution from the time of initiation to depths of 50 nm. The rate of vertical pit growth from PDIM analysis is characterized by the rate equation, y = 0.15 t2, where y is the pit depth (NM) and t is time (s). The topography of the Fe surface surrounding the pits remained virtually unchanged during pit growth, suggesting the presence of microscopic galvanic cells on the electrode surface. Mirroelectrode; High resolution imaging; Corrosion.