Beam Incidence Angle Research Articles

Adaptive x‐ray techniques for coherent scattering from distributed amyloid targets in the brain

AbstractBackgroundRecently, spectral small‐angle x‐ray scattering (SAXS) techniques have been proposed for interrogating deep targets including amyloid plaques and other protein aggregates in the brain, which could aid in the early diagnosis of neurodegenerative diseases such as Alzheimer's disease.MethodA model was developed to predict the main features of SAXS profiles from targets with varying shape, size and location corresponding to brain regions of interest. An optimization approach was devised adapting the beam orientation for improving deep target characterization. We calculate a figure of merit based on relative scattering intensity, scattering vector smearing , and path length.ResultIncreasing target size introduced additional signal smearing due to location uncertainty. Beam incidence angle and target shape affected the scattering profile by altering the path length or effective target size. For temporal and frontal lobe targets, beam effectiveness varied by up to 2 orders of magnitude.ConclusionBeam orientation optimization for coherent x‐ray scattering could allow a clinical implementation to target regions of interest while minimizing the radiation does to other radiosensitive areas of the head.

Monte Carlo calculation of detector perturbation and quality correction factors in a 1.5 T magnetic resonance guided radiation therapy small photon beams

Objective. With future advances in magnetic resonance imaging-guided radiation therapy, small photon beams are expected to be included regularly in clinical treatments. This study provides physical insights on detector dose-response to multiple megavoltage photon beam sizes coupled to magnetic fields and determines optimal orientations for measurements. Approach. Monte Carlo simulations determine small-cavity detector (solid-state: PTW60012 and PTW60019, ionization chambers: PTW31010, PTW31021, and PTW31022) dose-responses in water to an Elekta Unity 7 MV FFF photon beam. Investigations are performed for field widths between 0.25 and 10 cm in four detector axis orientations with respect to the 1.5 T magnetic field and the photon beam. The magnetic field effect on the overall perturbation factor (P MC) accounting for the extracameral components, atomic composition, and density is quantified in each orientation. The density (P ρ ) and volume averaging (P vol) perturbation factors and quality correction factors () accounting for the magnetic field are also calculated in each orientation. Main results. Results show that P vol remains the most significant perturbation both with and without magnetic fields. In most cases, the magnetic field effect on P vol is 1% or less. The magnetic field effect on P ρ is more significant on ionization chambers than on solid-state detectors. This effect increases up to 1.564 ± 0.001 with decreasing field size for chambers. On the contrary, the magnetic field effect on the extracameral perturbation factor is higher on solid-state detectors than on ionization chambers. For chambers, the magnetic field effect on P MC is only significant for field widths <1 cm, while, for solid-state detectors, this effect exhibits different trends with orientation, indicating that the beam incident angle and geometry play a crucial role. Significance. Solid-state detectors’ dose-response is strongly affected by the magnetic field in all orientations. The magnetic field impact on ionization chamber response increases with decreasing field size. In general, ionization chambers yield closer to unity, especially in orientations where the chamber axis is parallel to the magnetic field.

Infrared reflection spectroscopy of adsorbed intermediates in real time during chemical vapor deposition of oxides

In this paper, we develop multilayer optical theory to model the real-time (in operando) optical response of a growing dielectric film being deposited by chemical vapor deposition (CVD), with a particular emphasis on understanding the deposition mechanism through direct detection of the adsorbates responsible for film growth by infrared reflection-absorption spectroscopy (IRRAS). The model involves a four-layer stack consisting of a vacuum over a monolayer or submonolayer of molecules adsorbed on the surface of a dielectric thin film, which, in turn, is growing on a metal substrate. It is well known that, in IRRAS, the sensitivity of p-polarized light to absorption by the molecular adsorbates is a function of the incident angle of the IR beam: at high angles, the sensitivity is highest. We show that, for incident beam angles above 70° (which are typically used in IRRAS experiments), the sensitivity also depends on the thickness and refractive index of the insulating thin film; as a result, the sensitivity changes dynamically during the growth of the dielectric layer. Our analysis shows that, at incident beam angles of ∼60°–70°, the sensitivity to molecular adsorbates is somewhat lower, but is almost independent of the oxide thickness from 0 to 100 nm and also independent of the oxide refractive index from 1.0 to 2.5. Despite the loss of sensitivity relative to that achievable at higher incident beam angles, 1000 scans at an incident angle of 60° are sufficient to obtain IR spectra of the adsorbed molecules with reasonable signal-to-noise ratios even at submonolayer coverages. Because the sensitivity at this incident beam angle is not thickness dependent, it is not an issue (as it is at higher beam angles) that additional oxide grows during the time required to acquire 1000 scans. Experiments can be performed using a conventional vacuum deposition system, in which the internal beam path is tens of cm. We demonstrate the use of these smaller incident beam angles to study the mechanism of a CVD process in real time by polarization-modulation IRRAS, obtained by subtracting the s-polarized from the p-polarized infrared spectra in order to eliminate the unpolarized component due to molecules in the beam path and on windows. We explore the surface coverage of various adsorbed intermediates during CVD of HfO2 from tetrakis-(dimethylamido)-hafnium (TDMAH) and water in the presence of the consumable inhibitor magnesium N,N-dimethylamino-diboranate [Mg(DMADB)2]. We find that the addition of the Mg(DMADB)2 inhibitor causes a decrease in the IR absorption from the adsorbed TDMAH precursor that correlates with the observed decrease in the HfO2 growth rate; this result indicates that the mechanism of inhibition involves Mg(DMADB)2 acting as a dynamic site-blocker that lowers the surface coverage of TDMAH.

ANALYTICAL MODELLING BASED ON RESONANCE SCATTERING THEORY EXPLAINING THE NEEDLE VISIBILITY INCONSISTENCY IN B-MODE ULTRASOUND

In an ultrasound-guided needle insertion, physicians should adjust a certain insertion angle and the position of the transducer to ensure that the initial point and final target are in-plane inside the imaging plane. One of the crucial problems in this interventional procedure is poor and inconsistent needle visibility in B-mode ultrasound. In this research, some potential physical parameters, i.e., ultrasound frequency, the incident angle of the ultrasound beam, needle density, and dimension, are investigated through analytical modeling based on the resonance scattering model to understand their behavior in affecting needle visibility. 25G non-echogenic needle is used as a model object and assumed as stainless-steel hollow cylinder insonified by oblique incident plane wave varied within the frequency of 0–10 MHz and incident angle of 0°–45°. The results suggest that those physical parameters simultaneously affect the occurrence possibility of the resonant modes, which eventually affect the total scattering pressure field Ps in a non-linear way. These observed behaviors in the form of the spectrum map of resonance scattering pressure amplitude can be used to adapt a more beneficial combination of those physical parameters to obtain a higher possibility of good needle visibility through practical insertion application and potential echogenic technology or adaptive beamforming.

Angular Goos-Hanchen shift in subwavelength gratings enhanced by surface plasmon resonance

The angular Goos-Hanchen shift dependence on the subwavelength grating parameters and the incident Gaussian beam width is investigated theoretically. High sensitivity of the angular Goos-Hanchen shift to the incident angle of a light beam near the surface plasmon resonance is demonstrated. Splitting of the reflected beam into two angularly separated beams is shown for strongly focused beam incident at the surface plasmon resonance angle.

Evaluation of the role of beam homogeneity on the mechanical coupling of laser-ablation-generated impulse.

The material emitted from a target surface during laser ablation generates a net thrust (propulsion) in the opposite direction. The momentum generation efficiency of this laser-driven propulsion is given by the mechanical coupling coefficient (Cm). In this work, we considered nanosecond UV laser ablation of the aluminum 6061 alloy to study the Cm behavior with different irradiating conditions. This is done by systematically changing fluence, uniform/nonuniform intensity, and incident angle of the laser beam. In particular, we found that when dealing with nonuniform laser intensity, characterizing Cm exclusively in terms of fluence is not fully satisfactory because the energy distribution over the irradiated area plays a key role in the way material is removed-interplay between vaporization and phase explosion-and thrust is generated.

Analysis on ultrasonic waves generated in anisotropic carbon fiber reinforced plastic laminate by laser incidence from various directions

Laser-ultrasonic waves are used in nondestructive inspections because they can be excited on arbitrarily shaped surfaces by irradiation of a pulsed laser from a distance. During the non-contact scanning of a laser, the waveform of excited ultrasonic wave is changed because the incident angle varies substantially. The change of the waveform will be more obvious for carbon fiber reinforced plastics (CFRP) laminates that have anisotropic properties. In order to guarantee the inspection, in this paper, we investigated the generation of ultrasonic waves in CFRP laminates by a laser irradiation with various incident angles and azimuth angles. Firstly, we constructed a simulation model: the thermal force field caused by the laser absorption is derived from a heat conduction equation, and it is introduced into an FEM software for analyzing the propagation behavior of generated ultrasonic waves. Then, the simulation result is compared with an experiment result. Through the FEM analysis, we found that the amplitude of the excited waves has an obvious directivity because of the strong anisotropy in the thermo-elastic property of the CFRP. In addition, the change in propagation behavior in the case of a small incident angle of 30° was found to be inconspicuous. However, when the incident angle of the laser beam is larger than 60°, the directivity pattern changes depending on the azimuth angle. Thus, it is important to control the incident angle and direction when a laser ultrasonic inspection is applied to CFRP structures.

Expanding of Excimer Laser Photoablation’s Functionality in Ophthalmology

One of the significant weaknesses of excimer laser-based vision correction devices is the difficulty of achieving a required change in the refractive properties of the cornea to sharply focus the image on the retina with distance from the working area (ablation zone) center to the periphery due to a change in the laser beam incidence angle. The study is aimed at improving the quality of laser action on the eye cornea by introducing an optical corrective system into the existing excimer laser vision correction equipment, ensuring the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.It has been shown that the greater the reflection coefficient, the lower the absorbed energy, and the shallower the laser radiation penetration and ablation depths, which reduces the laser action opportunities and quality. When using excimer laser vision correction devices, it has been proposed to change the angle of the laser beam incidence on the cornea with a distance from the working area (ablation zone) center to the periphery during the surgery by introducing an optical corrective system based on a lightweight controllable and movable mirror, which allows achieving the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.The studies have shown that the coincidence of the laser beam incidence on the corneal surface at any point with the normal when using a priori data on the specifics of the patient's eye allows expanding the functional opportunities of excimer laser photoablation, i. e., expand the ablation zone by 30 % and eliminate the possibility of errors caused by the human factor. The technique proposed can be used for excimer laser vision correction according to PRK, LASIK, Femto-LASIK, and other methods. To implement this approach, a patented excimer laser vision correction unit has been proposed with a PCcontrolled optical shaping system comprising galvo motor platforms and galvo mirrors installed on them.

Modelling of beam energy absorbed locally in conduction mode laser metal fusion

Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used to be pre-set by extrapolating absorptance measurements made at different conditions or adjusted to reproduce experimental bead shapes. In this study a new approach is developed. It consists in predicting the absorptance as a function of local surface conditions, including the surface temperature. The proposed absorptance model is applied to the metal alloy Ti-6Al-4V. It is found that the absorptance of this alloy changes with surface temperature over a wide range of beam incidence angles. Thermo-fluid simulations with tracking of the free-surface deformation are performed for conduction mode beam welding test cases with a Yb fibre laser and different travel speeds. It is found that the absorptivity coefficient commonly used for this process clearly underestimates the absorptance and the melt pool geometry predicted for the process conditions of this study. The computational results are also compared against experimental results and good quantitative agreement of the melt pool depth, width, length, free surface contour geometry, and the curvature of the end depression left after re-solidification at the laser switch-off location is obtained. The results show that the absorptance field predicted depends on the melt pool development stage, on the spatial location within the beam spot, and on the process conditions.

Technical Note: Clinical modeling and validation of breast tissue expander metallic ports in a commercial treatment planning system for proton therapy.

To validate breast tissue expander metallic port (MP) models in a commercial treatment planning system (TPS) in proton pencil beam scanning (PBS) treatments for breast cancer patients with breast tissue expanders. Three types of MPs taken out of a Mentor CPX4, a Natrelle 133, and a PMT Integra breast tissue expanders and a 650 cc saline filled Mentor CPX4 expander were placed on top of acrylic slabs, and scanned using a Siemens Somatom Definition AS Open RT CT scanner. Structure templates for each of the MPs were designed within Eclipse TPS. The CT numbers for the metallic parts were overridden to reflect measured or calculated relative proton stopping powers (RPSPs). Mock targets were contoured in acrylic to represent postmastectomy chest-wall radiation therapy (PMRT) targets. Plans with different beam incident angles were optimized using the Eclipse TPS to deliver uniform prescription dose to the target using Hitachi Probeat-V PBS beams. Eclipse calculated doses and an in-house Monte Carlo (MC) code calculated doses were compared to the measured Gafchromic EBT3 film doses in acrylic. TPS/MC and film dose comparison results showed that (1) 3%/2mm/10% threshold Gamma pass rates were better than 90.8% in the acrylic target region for all plans; (2) comparing TPS and film doses for the individual beam plans in the MP dose shadow areas, the area with dose difference above 5% ([ΔA] 5%) ranged from 1.1 to 5.0 cm2 , and the maximum dose difference ([ΔD] 0.01 cm2 ) ranged from 12.5% to 25.0%; (3) comparing MC and film doses for the individual beam plans in the MP dose shadow areas, the (ΔA) 5% varied from 1.1 to 2.9 cm2 and (ΔD) 0.01 cm2 varied from 8.5% to 24.2%; (4) for a plan composed of three individual beams treating through the Mentor CPX4 expander, the TPS (ΔA) 5% was less than 0.13 cm2 , and the (ΔD) 0.01 cm2 was less than 6% in the MP dose shadow areas. It is feasible to treat patients with tissue expanders using multiple PBS beams using a structure template with CT number overridden to represent the measured/calculated RPSP for MPs for PBS treatment planning. MC dose was more accurate than analytical dose in the areas with high dose gradient caused by the density heterogeneity of the breast tissue expander MPs.

Laser precession machining of cross-shaped terahertz bandpass filters

The laser micro-machining technology is an attractive alternative to conventional photoresist-based technologies for manufacturing terahertz (THz) cross-shaped mesh filters. It can address some limitations related to filter's quality, process complexity, unit cost and available materials. However, there are also open issues associated with the laser micro-machining technology that have to be addressed. In particular, some intrinsic characteristics of laser micro-machined structures, i.e. the side-wall tapering, that impact both achievable geometrical and dimensional accuracy and the filters’ performance. This research proposes a novel fabrication process, called laser precession machining, that addresses some of the key laser micro-machining limitations in producing THz mesh filters. It employs an ultrafast laser and a “precess” module to vary the beam incident angle and thus to minimise the taper angle on the sidewalls of the filters’ cross-shaped through holes. A significant reduction of this negative tapering effect was achieved on micro-structures produced with this new method that led to a significant improvement of filters’ performance. The filters’ performance was compared with the simulation results and they were in good agreement. X-ray photoelectron spectroscopy (XPS) analysis was carried out to analyze the effects of laser precession machining on the composition of copper substrates as a potential factor affecting the filters’ performance.

Enhancement of two-wave mixing gain coefficient by resonant mechanism in photorefractive semiconductor

In this paper, two-wave mixing in photorefractive semiconductors at large modulation depth is theoretically analyzed and discussed. An analytic expression of space-charge field normalized to the weak externally applied dc electric field value is presented and a one center-two band model which includes both temperature and electron-hole is considered. The variations of space-charge field with dc field and Fe2+ concentration are investigated. Furthermore, the variations of the gain coefficient with temperature, intensity beam ratio, incident angle, and incident light intensity are analyzed. The results show that both the space-charge field and gain coefficient can increase with a stronger dc field. When the dc field is less than 10 kV/cm, applying a strong dc field can significantly improve the space charge filed and gain coefficient. As the incident intensity rises, under the influence of the intensity-dependent resonant effect, a maximum gain coefficient is achieved for an optimum incident intensity which increases with the temperature. Besides, an optimal angle of incidence is obtained at which the gain coefficient is maximum. It is demonstrated that the optimal incident intensity of 21 mW/cm2 and the optimal angle of 5° can be obtained under the temperature of 300 K and the dc field of 10 kV/cm conditions. The present work can provide theoretical guidance for the practical application of two-wave mixing in photorefractive crystals.

Defect visualization of cylindrical and conical CFRP lattice structures using rotational ultrasonic propagation imager

A composite lattice structure has been used in an aircraft and a space launcher to reduce the structural weight. Defects can occur during fabrication because of structural complexity and they are mostly invisible as occurring inside a structure. Also, they lead to the deterioration of structural performance and expensive failures. Therefore, non-destructive evaluation (NDE) to detect defects should be conducted not to damage an initially intact part. So far, various NDEs methods have been attempted, however, a standard inspection method has not been proposed for the large and curved lattice structures. In this study, two modified rotational through-transmission (TT) ultrasonic propagation imagers (UPIs) are proposed to inspect a skinless cylindrical lattice structure and a conical lattice structure with skin. In the first case of the skinless cylindrical specimen, there is a problem with the breakdown of the laser Doppler vibrometer (LDV) when an ultrasonic generation beam directly entered the LDV through an empty space of the specimen. For this issue, a wavelength domain beam splitting mechanism was included in the system. A proof-of-concept for the proposed inspection setup was performed using unit cells of the lattice structure, and defects could be visualized. The results were reliable compared with the radiation tomographic results. We also inspected the full-scale skinless lattice structure and visualized its internal defects. Conventional radiographic and visual inspection verified the location to be the same as that obtained using the TT UPI. In the second case of the conic specimen with skin, there is a problem with a change in a stand-off distance due to its shape. The change of the stand-off distance causes a steady decrease in signal-to-noise ratio (SNR), a change in the incident angle of the LDV beam and a change in a time-of-flight (ToF) at a received signal. These make defect visibility worse. For this issue, an additional manual rotational stage was incorporated into the rotational TT UPI to ensure that the sensing beam from the LDV would be perpendicularly incident on the skin surface. First, an appropriate scanning width was determined by measuring the variation in the SNR based on the stand-off distance. Furthermore, a ToF compensation algorithm was used to match the arrival times of signals for conic geometry. Then, the full-scale conical lattice structure with skin was inspected, and de-bonding defect was visualized via ultrasonic wave propagation imaging. As a result, it was possible to quickly inspect a large area of composite lattice structures regardless of the shape condition.

Time of flight diffraction for rough planar defects

Ultrasonic non-destructive evaluation techniques, such as time-of-flight diffraction (ToFD) for which the arrival times of waves diffracted from crack tips are analysed to locate and size defects, are well understood for smooth defects. In environments where extreme changes in temperature and pressure occur, the damage that may arise is often non-uniform and more difficult to characterise when designing and qualifying an inspection. This article investigates the implementation of ToFD methods for sizing rough defects using a purely theoretical approach. High-fidelity finite element modelling and stochastic Monte Carlo methods are used to provide physical and statistical insights for the dependence on both incident beam angle and degree of roughness for the case of planar defects. Optimal incident angles for ultrasonic ToFD techniques were determined in the 1980s but largely based on theoretical and experimental investigations for smooth defects. However, rough defects produce tip-diffracted signatures that are more complicated than for their smooth counterparts, largely due to multiple scattering effects related to mode conversion and propagation of surface waves along the rough surface. It is shown that roughness may cause larger diffraction amplitude values at different angles, which leads to increased uncertainty when sizing, with illustrative examples and physical interpretations provided. Comparisons of amplitudes for smooth and rough defects of the same size are also demonstrated. The ToFD method, using envelope peak detection and autocorrelation approaches, is implemented to estimate the size of rough cracks, and the effects of roughness on the accuracy of this sizing are investigated with statistical analysis.

Improvement of the electron beam (e-beam) lunar dust mitigation technology with varying the beam incident angle

Dust hazards are considered to be one of the technical challenges for future lunar exploration. In our past work a new dust mitigation technology was introduced utilizing an electron beam to remove dust particles from various surfaces. This technology was developed based on a patched charge model, which shows that the emission and re-absorption of electron beam induced secondary electrons inside microcavities between dust particles can lead to sufficiently large charges on the dust particles, causing their release from the surface due to strong repulsive forces. In this paper an improvement in the effectiveness of this technology is demonstrated with varying the beam incident angle on dust-covered sample surfaces by rotating the samples relative to the beam. Due to random arrangements of the microcavities, more of them will be exposed to the beam with various incident angles, thereby causing more dust release from the surface. The cleaning performance is tested against three samples: glass, spacesuit, and a photovoltaic (PV) panel. Lunar simulant (<25 μm in diameter) is deposited onto the sample surfaces such that the initial cleanliness of the samples is 0 % (full dust coverage) and 40 %. Varying the beam incident angle shows an overall surface cleanliness increase of 10–20 % in addition to the cleanliness achieved with a fixed beam angle. The ultimate cleanliness reaches 83–92 % for the glass and spacesuit samples. The PV panel coated with MgF2 is shown to be more adhesive to the dust with the maximum cleanliness of 50–63 %.

Thermal characterization of a heating cylinder under ultrasonic effects

Ultrasonic effects were investigated on the heat transfer characteristics of a vertical cylinder releasing a constant heat flux of 14,150 W/m2 in distilled water. A triple-frequency ultrasonic transducer was installed at the center of the lateral wall of the cubic test section to emit 40, 80, and 120 kHz ultrasonic waves. The thermal characterization was investigated by varying the distance (5, 10, and 15 cm) between the ultrasonic transducer and the heating surface. The surface temperature of the heater, detected using 12 thin-leaf thermocouples, decreased rapidly because of the ultrasonic effect, leading to an increase in the Nusselt number. An infrared camera and a video camera were used for the visualization and investigation of acoustic streaming and acoustic cavitation. The results showed that ultrasound enhanced heat transfer to the maximum level of 82.4% using 40 kHz waves at a distance of 5 cm. At distances of 10 and 15 cm, 120 kHz ultrasonic waves produced the highest heat transfer enhancement levels of 74.2% and 59.7%, respectively. The heat transfer enhancement ratio decreased with increasing incident angle of the wave beam as well as with the distance between the ultrasonic transducer and the heating surface. The key mechanisms leading to the enhancement of heat transfer in the near and far fields were identified and discussed. Finally, an accurate prediction formula was proposed for the overall heat transfer enhancement ratio, depending on the ultrasonic frequency and distance.

Focal Loss Analysis of Nerve Fiber Layer Reflectance for Glaucoma Diagnosis.

PurposeTo evaluate nerve fiber layer (NFL) reflectance for glaucoma diagnosis.MethodsParticipants were imaged with 4.5 × 4.5 mm volumetric disc scans using spectral-domain optical coherence tomography. The normalized NFL reflectance map was processed by an azimuthal filter to reduce directional reflectance bias caused by variation of beam incidence angle. The peripapillary area of the map was divided into 160 superpixels. Average reflectance was the mean of superpixel reflectance. Low-reflectance superpixels were identified as those with NFL reflectance below the fifth percentile normative cutoff. Focal reflectance loss was measured by summing loss in low-reflectance superpixels.ResultsThirty-five normal, 30 preperimetric, and 35 perimetric glaucoma participants were enrolled. Azimuthal filtering improved the repeatability of the normalized NFL reflectance, as measured by the pooled superpixel standard deviation (SD), from 0.73 to 0.57 dB (P < 0.001, paired t-test) and reduced the population SD from 2.14 to 1.78 dB (P < 0.001, t-test). Most glaucomatous reflectance maps showed characteristic patterns of contiguous wedge or diffuse defects. Focal NFL reflectance loss had significantly higher diagnostic sensitivity than the best NFL thickness parameter (from map or profile): 77% versus 55% (P < 0.001) in glaucoma eyes with the specificity fixed at 99%.ConclusionsAzimuthal filtering reduces the variability of NFL reflectance measurements. Focal NFL reflectance loss has excellent glaucoma diagnostic accuracy compared to the standard NFL thickness parameters. The reflectance map may be useful for localizing NFL defects.Translational RelevanceThe high diagnostic accuracy of NFL reflectance may make population-based screening feasible.

Experimental investigation about the adoption of high reflectance materials on the envelope cladding on a scaled street canyon

In the last years innovative building envelope materials were studied in order to mitigate the urban heat island phenomenon in cities. Among them, cool materials represent a valid solution to achieve this goal. These materials are characterized by high solar reflectance and high thermal emittance. Another way to reduce the urban heat island effect is the adoption of retroreflective materials on the building façades, in order to reduce the amount of solar radiation entrapped within the urban fabric. The retroreflective materials have a particular surface conformation that allows to reflect the solar radiation back in the same direction of the incident radiation. In this case, the temperature of the surfaces inside an urban canyon should have lower values compared with the case with common construction materials. Consequently, also the air temperature inside the urban canyon has low values with significant advantages on outdoor thermal comfort and on building thermal energy demands. In this work the solar reflectance directional dependence was investigated with a Goniophotometer. Furthermore, experimental measurements of retroreflective materials effects on a scaled urban canyon were performed. It was found that the albedo of the RR material increases with the incident angle of the light beam from 38.2% to 42.3% with an angle of 8° and 60° respectively. An increase of the reflected radiation to the sky in the case of the use RR materials despite of a commercial Lambertian paint with same albedo at 8° of incident light beam was evaluated. In particular, the measurement brings to assess a maximum average percentage canyon albedo difference of 2.03%.

Single-Mode Lasing in Polymer Circular Gratings.

In recent years, conjugated polymers have become the materials of choice to fabricate optoelectronic devices, owing to their properties of high absorbance, high quantum efficiency, and wide luminescence tuning ranges. The efficient feedback mechanism in the concentric ring resonator and its circularly symmetric periodic geometry combined with the broadband photoluminescence spectrum of the conjugated polymer can generate a highly coherent output beam. Here, the detailed design of the ultralow-threshold single-mode circular distributed feedback polymer laser is presented with combined fabrication processes such as electron beam lithography and the spin-coating technique. We observe from the extinction spectra of the circular gratings that the transverse electric mode shows no change with the increase of incident beam angle. The strong enhancement of the conjugated polymer photoluminescence spectra with the circular periodic resonator can reduce the lasing threshold about 19 µJ/cm2. A very thin polymer film of about 110 nm is achieved with the spin-coating technique. The thickness of the gain medium can support only the zero-order transverse electric lasing mode. We expect that such a low threshold lasing device can find application in optoelectronic devices.

Initial Studies of Electron Beams as a Means of Modifying Collagen

We present the initial design studies and specifications for an accelerator and conveyor system to irradiate collagen samples, modifying properties such as the putrescibility and mechanical behaviours in a paradigm shift from existing, widely used technology. We show the integrated design requirements for a magnetic rastering scheme to move the beam position in order to ensure a uniform dose distribution over the full surface of the hide and discuss its dependence on factors such as the size of the hide, the beam current and conveyor speed. We also present initial energy deposition studies using beam particle interaction simulation program G4beamline, in order to determine the numerical beam parameters and angle of incidence needed to ensure a uniform depth-dose distribution throughout the hide thickness.