Phase separated thermotropic layers based on UV cured acrylate resins - Effect of material formulation on overheating protection properties and application in a solar collector

This paper focuses on the effect of material composition on the overheating protection properties of thermotropic systems with fixed domains for solar thermal collectors. Numerous functional layers were prepared by a variation of base resin (polyester-, epoxy- or urethane-acrylate) and of thermotropic additives (non-polar and polar waxes) as well as by additive concentration (5 and 7 wt%). A detailed investigation of optical properties, switching temperature and switching process was performed applying UV/Vis/NIR spectroscopy. Thermal transitions of both the thermotropic layers and the additives used were determined by Differential Scanning Calorimetry (DSC). The capability of the produced thermotropic layers to reduce stagnation temperatures in an all-polymeric flat plate collector was evaluated by theoretical modeling. The thermotropic layers showed a hemispheric solar transmittance between 76% and 87% in clear state. Above the switching threshold this transmittance changed by 1-16% to values between 62% and 85%. The layers exhibited switching temperatures between 33 and 80 °C. The transition is fully completed within a temperature frame of 10-25 °C. Resin types with higher glass transition temperatures were detected to benefit the reduction of the hemispheric solar transmittance above the switching threshold. This reduction was also found to increase with increasing molecular weight of the non-polar additive types. The comparison of the switching performance with the thermal transitions of the additives revealed a good correlation. Theoretical modeling showed that by the use of selected thermotropic layers in the glazing the maximum absorber temperatures can be limited to temperatures below 130 °C.     

Aging of polymeric films for transparent insulation wall applications

A research project to develop and optimize a transparent insulation (TI) structure based on commercially available films showed, that in addition to poly(carbonate) (PC) and poly(methylmethacrylate) (PMMA) other amorphous and semicrystalline polymers such as cellulose triacetate (CTA) and poly(ethyleneterephthalate) (PET) exhibit favorable property profiles for application in low temperature systems (e.g. TI wall systems). Investigations were carried out in order to study the influence of time, temperature, humidity and solar radiation on the solar and infrared performance properties of various polymer films. Whereas the infrared properties are only slightly influenced after exposure to elevated temperatures, humidity and solar radiation, in the solar range especially extinction due to scattering increases. Detailed results are presented in the paper for four polymer film types and for TI structures made thereof. Furthermore, the results are interpreted in terms of both the molecular and supermolecular structure of the polymer films. Besides PC and PMMA films, PET and CTA films show an interesting long-term performance, being an interesting alternative to the more expensive PC and PMMA polymers.     

Alignment tolerances for plane-wave to single-mode fiber coupling and their mitigation by use of pigtailed collimators

We discuss the efficiency with which coherent plane waves can be coupled to single-mode fibers in the presence of deterministic or stochastic misalignments of the fiber relative to the focal point of a lens. We point out how the alignment demands can be relaxed by means of graded-index-lens fiber-pigtailed collimators.     

An extended GPU radiosity solver

In this paper we present an extended GPU progressive radiosity solver which integrates ideal diffuse as well as specular transmittance and reflection. The solver is capable to handle multiple specular reflections with correct mirror–object–mirror occlusions. The use of graphics hardware allows to consider attenuation of radiation due to reflections and/or transmissions on a per-pixel basis, enabling us to handle multiple specular triangles with different reflection coefficients at once. Alpha masks are used to replace complex geometry in certain cases to reduce computation times. Furthermore, the inclusion of ambient overshooting into the radiosity solver is discussed.     

Robust feature classification and editing

Sharp edges, ridges, valleys, and prongs are critical for the appearance and an accurate representation of a 3D model. In this paper, we propose a novel approach that deals with the global shape of features in a robust way. Based on a remeshing algorithm which delivers an isotropic mesh in a feature-sensitive metric, features are recognized on multiple scales via integral invariants of local neighborhoods. Morphological and smoothing operations are then used for feature region extraction and classification into basic types such as ridges, valleys, and prongs. The resulting representation of feature regions is further used for feature-specific editing operations     

Risk-based systems security engineering: stopping attacks with intention

In most modern information systems (IS), functionality and security are competing design goals. Therefore, system designers are constantly forced to make security-related trade-off decisions. Systems security engineers must build systems that are secure against real-world attacks without overengineering against any particular one. By understanding which attacks are most likely and which risks are most serious, system designers can make informed security-related trade-off decisions. We describe a systems security engineering methodology designers can use to make these decisions.     

Effect of inter-plies on the short beam shear delamination of steel/composite hybrid laminates

Interlaminar shear test methods (ILS) were implemented to characterize the delamination behavior of asymmetric steel/carbon fiber reinforced plastic (CFRP) hybrids. To improve the delamination behavior thermoplastic inter-plies were inserted between CFRP and steel. Supported by optical strain measurement the maximum shear stress (τ_MAX), the shear stress at interfacial delamination (τ_IF) and the shear stress at large-scale CFRP ply delamination τ_D were evaluated. The significant effect of inter-plies on the adhesion was best reflected by the shear stress value at interfacial delamination. Finite element analysis of the actual shear stress distribution in an asymmetric hybrid sample without inter-ply revealed that the calculated shear strength is just slightly overestimated compared to the standardized evaluation procedure.     

Unusual CC Bond Isomerization of an α,β‐Unsaturated γ‐Butyrolactone Catalysed by Flavoproteins from the Old Yellow Enzyme Family

An unexpected, redox‐neutral C?C bond isomerization of a γ‐butyrolactone bearing an exo‐methylene unit to the thermodynamically more favoured endo isomer (k_cat=0.076 s^?1) catalysed by flavoproteins from the Old Yellow Enzyme family was discovered. Theoretical calculations and kinetic data support a mechanism through which the isomerization proceeds through FMN‐mediated hydride addition onto exo‐Cβ, followed by hydride abstraction from endo‐Cβ′, which is in line with the well‐established C?C bond bioreduction of OYEs. This new isomerase activity enriches the catalytic versatility of ene‐reductases.     

Magnetic resonance imaging study of solid rocket propellants and liners

Magnetic resonance imaging (MRI) has been used to study solid rocket propellants and liner material. The samples studied were simulants, used mainly for safety reasons, of real systems using ammonium sulfate in place of the energetic materials. The polymeric binder was hydroxy-terminated poly(butadiene) (HTPB) reacted with isopherone diisocyanate. MRI was used to observe variations in intensity in the simulant samples due to differing percentages of solids loading. It also showed the homogeneous intensity obtained for an unfilled sample used for comparison with the 82% filled material. The liner material, HTPB and dimeryl diisocyanate, was imaged despite its relative rigidity observed from its short T₂ value. Samples of poly(alkylene) oxide simulants were imaged, and various bubbles and regions of filler inhomogeneity were observed. These defects were correlated with photo-micrographs of the sample. MRI can be used to image real systems of solid rocket components. © 1996 John Wiley & Sons, Inc.     

Smith-Purcell Radiation in the Sub-mm Wavelength Region

Spontaneous Smith-Purcell radiation at wavelengths of 100 and 220μm has been observed. The angles of observation were 17° and 28° and the electron beam energies 1.9 and 1.56MeV, respectively. The radiated power was about 320nW at 17° and 92nW at 28°. These values are in reasonable agreement with what is theoretically expected if the emission process is due to the acceleration of image charges induced on the grating surface by the electrons of the beam.