Higher Reflectance Values Research Articles

DISPLAYED REFLECTIVITY OF CHOROIDAL NEOVASCULAR MEMBRANES BY OPTICAL COHERENCE TOMOGRAPHY CORRELATES WITH PRESENCE of LEAKAGE BY FLUORESCEIN ANGIOGRAPHY

To evaluate and correlate the displayed optical reflectivity of choroidal neovascularization (CNV) subretinal material on spectral-domain optical coherence tomography with the presence of dye leakage on fluorescein angiography (FA). Thirty-nine eyes of 39 patients with a diagnosis of predominantly classic CNV from age-related macular degeneration underwent simultaneous spectral-domain optical coherence tomography and FA imaging. Eight patients had a newly diagnosed untreated CNV. Thirty-one patients had already been treated with anti-vascular endothelial growth factor agents. In 18 of these eyes, CNV lesions showed persistent leakage on FA. In 13 eyes, CNV lesions did not show leakage by FA. Subretinal CNV material boundaries visualized on spectral-domain optical coherence tomography B-scans were manually traced, and optical reflectivity was calculated using the mean grayscale value. To account for variable image brightness, the retinal pigment epithelial reflectivity was measured. The absolute difference between CNV material and retinal pigment epithelial reflectivity (ΔREF) from the three groups (newly diagnosed CNV, previously treated CNV showing FA leakage, and previously treated CNV not showing FA leakage) was compared. In untreated lesions, ΔREF was significantly higher compared with previously treated, but still leaky CNV (P < 0.0001). Lesions showing FA leakage had significantly higher ΔREF compared with those that did not display leakage (P < 0.0001). The displayed reflectivity of subretinal CNV material in spectral-domain optical coherence tomography appears to be an important parameter that can provide information regarding the FA leakage status.

Bioclimatic design of open public spaces in the historic centre of Tirana, Albania

Abstract The aim of this paper is to study the urban micro-climatic conditions in the historic centre of Tirana in order to integrate the information in the rehabilitation of specific open spaces. The process included field measurements of the thermal characteristics in the examined area, bioclimatic design and use of passive cooling techniques (cool materials, green spaces, water, solar control & earth to air heat exchangers). Advanced simulation tools were used to evaluate and optimize the planed microclimatic modifications. CFD calculations with model PHOENICS have been applied for the simulation of the air flow and the temperature field at the concept design stage. The proposed design solutions included the increase of vegetation (planting of trees), the use of shading, as well as the use of cool materials with appropriate thermal and optical properties. In parallel, earth to air heat exchangers, are proposed to supply cool air during the summer period and preheat the ambient air during the winter. Simulations have shown that the use of the proposed bioclimatic measures can decrease the peak summer ambient temperatures up to 3 °C, while surface temperatures are decreased seriously. In parallel, the calculation of appropriate bioclimatic indices showed that the thermal comfort conditions were significantly improved with the application of interventions mainly because of the increase of shading as well as because of the use of construction materials with high emissivity and reflectivity values.

Locating Convection in Landfalling Tropical Cyclones: A Gis-Based Analysis of Radar Reflectivities and Comparison to Lightning-Based Observations

Researchers have utilized radar reflectivity returns and lightning flashes separately and together to locate convection with tropical cyclones (TCs). Most studies utilizing both datasets have examined TCs over the ocean, while landfall observations have been limited to a few TCs. This study employs a GIS to delineate regions of high radar reflectivity values within 45 landfalling TCs. The percentage of convective regions contained within each quadrant placed relative to storm motion and deep-layer vertical wind shear is calculated. These percentages are then compared to those from previous studies of quadrant-based lightning flash locations. Results indicate that the GIS-based radar analysis may be identifying TC regions that are electrically active. Both the radar- and lightning-based analyses show that convection shifts from the right to the front of the storm as forward velocity increases. Convection is located left of the shear vector when storm motion is 45-135° counterclockwise from the shear vector, and downshear when shear-minus-motion angles are 315-45°. Additionally, storms that became extratropical within 72 hours of landfall had more convection forward of the circulation center and left of the shear vector, and may produce less lightning than the remaining TCs.

High reflectivity airgap distributed Bragg reflectors realized by wet etching of AlInN sacrificial layers

The authors report on the achievement of a vertically oriented three pair airgap/GaN distributed Bragg reflector realized by controlled oxidation and wet-chemical etching of AlInN sacrificial layers. Microreflectivity measurements exhibit high peak reflectivity values of 87% around 500 nm after the oxidation process and 90% around 600 nm after the etching process in overall good agreement with simulations. The broad stopband of airgap/GaN mirrors, about 250 nm wide, results from the strong refractive index contrast between air and GaN layers.

Comparison of the reflectances of black plant fragments in melanic Andisols with those of fresh charcoal from modern fires

We investigated the reflectances of black plant fragments in melanic Andisols and of fresh charcoal produced during modern grassland and forest fires with the aim of clarifying the origin of fragments in melanic Andisols. The reflectance values of most Andisol plant fragments were less than 2%; all values were below 3%. These values are considered to have formed at temperatures of at least 200°C, indicating that these fragments are charcoal fragments. The reflectances of the fragments in melanic Andisols were similar to those of grass charcoal from grassland fires rather than wood charcoal produced during forest fires. This finding indicates that most charcoal fragments in melanic Andisols are the product of grassland fires. The small difference between the reflectance values of the charcoal fragments in the Andisols and the grass charcoal is possibly derived from the fact that charcoal fragments with lower reflectance are more likely to be retained in the soil than fragments with higher reflectance values.

A study of lightning flashes attending periods of banded snowfall

Lightning flashes (N = 1088) associated with 24 thundersnow events in the central United States were analyzed to document flash polarity, signal strength, and multiplicity. Negative lightning flashes (N = 872; 80%) dominated positive flashes (N = 216; 20%) with wintry precipitation in this study, which stands in contrast to the majority of the research done on winter thunderstorms (primarily in Japan). Otherwise, limited work has been done, although thundersnow has been documented in the mid‐latitudes of North America, Europe and Asia. Statistics on peak amplitude were determined for negative (positive) flashes, yielding mean and standard deviation values of −24 kA ± 22 kA (+38 kA ± 34 kA). A subset of winter lightning events (N = 16) were then sought that occurred with banded (single or multiple) snowfall, as banding often denotes greater organization in the atmosphere (e.g., a jet streak aloft to aid in ascent, or a low level jet streak to aid with moisture and thermal transport) and thus the potential for deeper snow totals. Radar reflectivity values were recorded at the location of each lightning flash, as well as the maximum radar reflectivity within the associated snow band. The location of the lightning activity within the snow band was also noted as being either leading edge (LE), trailing edge (TE), core (C), or not correlated (NC), with respect to the motion of the parent band. The majority of lightning flashes were found downstream of areas of highest radar reflectivity with respect to the motion of the snow bands, and not with the highest reflectivity values. If one uses the highest reflectivity values in a snowband as a proxy for the greatest surface snowfall intensity, then the ground terminus of a cloud‐to‐ground lightning (CG) flash is often not co‐located with the heaviest snowfall rates. However, the work completed here does place the location of the typical CG flash ∼15 km downstream of the snowband location, so one could use the occurrence of lightning as a nowcasting tool for impending snow intensification at the site of the CG flash.

Changes in cloud and aerosol cover (1980–2006) from reflectivity time series using SeaWiFS, N7‐TOMS, EP‐TOMS, SBUV‐2, and OMI radiance data

The amount of solar radiation reflected back to space or reaching the Earth's surface is primarily governed by the amount of cloud cover and, to a much lesser extent, by Rayleigh scattering, aerosols, and various absorbing gases (e.g., O3, NO2, H2O). A useful measure of the effect of cloud plus aerosol cover is given by the amount that the 331 nm Lambert Equivalent Reflectivity (LER) of a scene exceeds the surface reflectivity for snow/ice‐free scenes after Rayleigh scattering has been removed. Twenty‐eight years of reflectivity data are available by overlapping data from several satellites: N7 (Nimbus 7, TOMS; 331 nm) from 1979 to 1992, SBUV‐2 series (Solar Backscatter Ultraviolet, NOAA; 331 nm) 1985 to 2007, EP (Earth‐Probe, TOMS; 331 nm) 1997 to 2006, SW (SeaWiFS; 412 nm) 1998 to 2006, and OMI (Ozone Measuring Instrument; 331 nm) 2004–2007. Only N7 and SW have a sufficiently long data record, Sun‐synchronous orbits, and are adequately calibrated for long‐term reflectivity trend estimation. Reflectivity data derived from these instruments and the SBUV‐2 series are compared during the overlapping years. Key issues in determining long‐term reflectivity changes that have occurred during the N7 and SW operating periods are discussed. The largest reflectivity changes in the 412 nm SW LER and 331 nm EP LER are found to occur near the equator and are associated with a large El Nino‐Southern Oscillation event. Most other changes that have occurred are regional, such as the apparent cloud decrease over northern Europe since 1998. The fractional occurrence (fraction of days) of high reflectivity values over Hudson Bay, Canada (snow/ice and clouds) appears to have decreased when comparing reflectivity data from 1980 to 1992 to 1997–2006, suggesting shorter duration of ice in Hudson Bay since 1980.

Distributed Bragg reflectors in comparison to RUGATE and nested super lattices – growth, reflectivity, and conductivity

AbstractThis paper investigates the feasibility of conductive Al‐GaN reflectors with corRUGATEd (RUGATE) index profiles in comparison to standard distributed bragg reflectors (DBR) and nested super lattice (NSL) DBRs. The samples are analyzed by reflectometry, x‐ray diffraction, and electrical measurements.The RUGATE implementation of the reflectors exhibited two times higher vertical conductivity in comparison to the DBRs and showed slightly lower reflectivity. The nested super lattice approach for DBRs turned out to be an alternative which is easy to manufacture and which shows high reflectivity values. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Evolving Complex Electrical Structures of the STEPS 25 June 2000 Multicell Storm

Abstract Data from a three-dimensional lightning mapping array (LMA) and from two soundings by balloon-borne electric field meters (EFMs) were used to analyze the electrical structures of a multicell storm observed on 25 June 2000 during the Severe Thunderstorm Electrification and Precipitation Study (STEPS). This storm had a complex, multicell structure with four sections, each of whose electrical structure differed from that of the others during all or part of the analyzed period. The number of vertically stacked charge regions in any given section of the storm ranged from two to six. The most complex charge and lightning structures occurred in regions with the highest reflectivity values and the deepest reflectivity cores. Intracloud flashes tended to concentrate in areas with large radar reflectivity values, though some propagated across more than one core of high reflectivity or into the low-reflectivity anvil. Intracloud lightning flash rates decreased as the vertical extent and maximum value of reflectivity cores decreased. Cloud-to-ground flash rates increased as cores of high reflectivity descended to low altitudes. Most cloud-to-ground flashes were positive. All observed positive ground flashes initiated between the lowest-altitude negative charge region and a positive charge region just above it. The storm’s complexity makes it hard to classify the vertical polarity of its overall charge structure, but most of the storm had a different vertical polarity than what is typically observed outside the Great Plains. The electrical structure can vary considerably from storm to storm, or even within the same storm, as in the present case.

Geospatial Remote Sensing Using Advanced Sensor Systems

ABSTRACTRecently, various nanoscale materials, devices, and systems with remarkable properties have been developed, with numerous unique applications in chem.-bio sensors, nanophotonics, and nanobiotechnology. This presentation covers satellite and aerial remote sensing science and methodologies employing nanotechnology based advanced sensor systems to improve performance, resolutions, and security. Increased demand on monitoring, surveillance due to global war on terrorism, weather prediction, and environmental pollution detection and monitoring have necessitated geospatial sensing with high accuracy, speed, and authenticity. Plasmonic interactions on the nanoscale and nanophotonics have produced new phenomena and technologies surpassing the realms of possibilities with conventional photonics and electronics. These new technologies could include high spatial resolution near-field imaging, high efficiency information processing and transferring, high capacity optical data storage, flexible- and high contrast displays, and precise detection, control and manipulation of nanoscale devices and integrated systems. Elements utilizing refractive or diffractive surfaces have found applications in novel sub-wavelength nanostructures satellites. The nanophotonics structures coupled with lightweight structures and advanced nanotechnology based sensors have resulted in launching of nano-satellites by several countries. The use of nanophotonics in space through the combination of micro, nano, integrated and fibre-optic technologies is to reduce susceptibility of the system to EMI, reduction in the weight of the signal cables (&lt; 1/20 of electrical), higher information transmission capacity (GHz), reduced weight and volume, opto-isolation of critical spacecraft subsystems, high speed optical processing of RF and microwave signals, low propagation loss, and enhanced security encryption capabilities. Carbon Nanotubes (CNTs) based field emission electron gun (FEG) employ low voltage for emission and are actively researched as cold cathode microwave generation devices. CNTs based composites provide light-weight and compact platform with mechanical and thermal robustness. Such satellite system can be placed in low Earth orbit (LEO) to medium Earth orbit (MEO) as multi-sensor satellite imagers with panchromatic, multi-spectral, area and hyper spectral sensors on a single focal plane array (FPA), to achieve medium to high resolution (2.5m to 15m) spatial sampling, wide swaths (up to 45km) and noise equivalent reflectance (NER) values of less than 0.5%. An evaluation of security risks, vulnerability, and strategies is presented for communications technologies used in gathering, processing, storing, and disseminating global environmental micro and nano sensors and satellite data.

Emission studies on photonic crystals fabricated using dyed polystyrene colloids

Three dimensionally ordered photonic crystals are fabricated with rhodamine B dyed polystyrene colloidal spheres using the inward growing self-assembling method in less than 3 h. This avoids the difficulties due to infiltration of active materials into passive photonic crystals. The superior optical quality of the photonic crystals fabricated using this method results in high reflectance values even at large angles of incidence. The study of emission characteristics on these functionalized photonic crystals shows a clear trend dependent on the angle of emission, wavelength, and the angle-resolved transmittance. The dip observed in the emission spectrum clearly matches the photonic stop band position at different angles of observation. The emission spectrum measured at different angles was found to follow a simple functional form related to the intrinsic emission of the dye and the stop band effect due to the photonic crystal environment.

Structural and optical characterization of photonic crystals synthesized using the inward growing self-assembling method

We present a systematic analysis of three-dimensionally (3D) ordered photonic crystals fabricated using the recently reported inward growing self-assembling method. The structural and optical characterizations reveal extremely high quality features in these crystals. These include the high reflectance values in the first order stop band and the high energy optical response observed in all the samples, irrespective of the diameter of the spheres, even though the time for fabrication is less than three hours. The photonic stop band is tuned by varying the angle of incidence of light. The peak reflectance and the width of the photonic stop band are unaffected up to an angle of incidence of 45°. At higher angles of incidence, the involvement of other planes in the Bragg reflection is qualitatively demonstrated, emphasizing the extent of ordering and the quality of photonic crystals.

Feasibility study of edge-lit backlight of dual-panel display by a simple configuration model

This study proposes a feasibility study of edge-lit backlight of dual-panel display by a simple configuration model based on a luminous flux flow perspective. The model is applied to investigate the interaction between the backlight configuration parameters, including the dot density of the light guide and the reflectances of the upper and lower films and the lower reflector sheet, respectively. The results show that the luminance difference between the main panel and the sub-panel is determined primarily by the dot reflectance in the region of the light guide common to the two panels and by the reflectances of the upper and lower films, respectively. To maximize the main panel luminance, higher reflectance values should be assigned to the dots in the non-common region of the light guide and to the lower reflector sheet. The dot reflectance in the non-common region is highly sensitive to changes in the value of the dot density in the common region. Finally, the dot density in the common region and the dot density in the non-common region are related by a quadratic function in which the rate of increase of the dot density in the common region is greater than that in the non-common region.

A study of the total lightning activity in two hailstorms

Two thunderstorms which developed in the northeastern region of Spain on 17 August 2004 are analyzed. According to radar and ground observations, one of these storms produced large hail (larger than 19 mm) and therefore could be severe. Both thunderstorms exhibited strong vertical developments with cloud tops reaching 17.5 and 14 km for the severe and the nonsevere ones, respectively. The total lightning activity was monitored, thanks to the Spanish magnetic‐direction‐finding and time‐of‐arrival (MDF/TOA) network and thanks to a regional very‐high‐frequency (VHF) interferometer network. Both storms presented low cloud‐to‐ground (CG) flash rates (lower than 2 min−1) during their mature phase, while the intracloud (IC) flash rate reached 92 min−1 for the severe one. The IC/CG flash ratio was very high for both storms: 35 and 60 in average value for the severe and the nonsevere ones, respectively. The lightning characteristics exhibited low values in terms of peak current and multiplicity for negative CG (−CG) flashes and in terms of VHF source number per flash for IC flashes. The average multiplicity of the −CG flashes was 1.74 and 1.17 for the severe and the nonsevere storms, respectively, and their average peak current was −11.7 and −10.65 kA, respectively. When the presence of hail is suspected from high radar reflectivity values in both cells, the flash rates tended to substantially decrease. The severe storm produced positive CG (+CG) flashes during 1 hour, and at that moment, the multiplicity and peak currents of −CG flashes were very low. Lightning activity for both storms ended with a substantial increase of the −CG flash rate. The elevated charge hypothesis is consistent with the observations, especially if we consider two aspects of this hypothesis, the one about charge separation, which could be limited by the strong updrafts, and the one about the lightning initiation, which could be favored by low pressures at high altitude.

Thermal alteration of coal in the Khasyn coalfield, Magadan region, Russia

Abstract The Early Cretaceous coal deposits of the Khasyn coalfield are intruded by Palaeogene diabase dikes. The coal has vitrinite reflectance values of 2.0–2.5% R o , and characteristics of normal anthracite at some distance from the dikes, but at direct contact with the dike two morphological coal varieties occur: coal inclusions in the diabase dike and dispersed carbonaceous matter within the dike rock. Both types of coaly matter have properties typical of anthracites: strong anisotropy, altered internal structure and high vitrinite reflectance values ranging from 3.8 to 5.5% R o . The X-ray diffraction measurements of the interplanar spacing d (002) and the crystallite sizes Lc and La show rather similar values for coal inclusions in the dike and dispersed carbonaceous matter. The additional reflection at 3.37 A, corresponding to semi-graphite admixture, occurs in the coal and carbonaceous matter inside the dike and is absent in the natural coal outside the dike.

Cool-colored coatings fight the urban heat-island effect

The urban heat island effect is becoming increasingly more intense. Among its causative factors are the lower albedo (reflective power) of urban surfaces and the replacement of vegetation by buildings.1 Absorption of solar energy by concrete and paved structures raises their surface temperature several degrees over that of the ambient air, which also then increases. Apart from causing thermal discomfort, heat islands precipitate greater consumption of cooling energy. They also drive up energy demand and costs,2–4 and accelerate the formation of harmful smog.5 Mitigating the urban heat island phenomenon requires cool materials that are characterized by high solar reflectance (SR) and IR emittance values.6 Increasing either reflectance or emittance lowers the surface temperature of the building envelope, which in turn decreases the heat penetrating the structure. These techniques also work by lowering the temperature of the ambient air, because the cooler the surface, the lower the heat convection intensity. A number of cool materials are currently available commercially for buildings and other surfaces of the urban environment, These including cool surface coatings, reflective tiles, and so on: however, they are all white or light colored.7–10 There is a need for cool, nonwhite products for situations where darker colors are preferred or where white products introduce glare. For this reason, new materials that are dark but still reflect more sunlight and stay cooler are being developed using specialized pigments. A cool non-white coating absorbs in the visible range to give the appearance of a specific color. Considering that about half of all solar power arrives as invisible near-IR (NIR) radiation, such a coating should be highly reflective in the NIR part of the spectrum to maintain high solar reflectance. This is achieved by replacing conventional pigments that absorb in the NIRwith novel ones that have the desired properties.11, 12 Figure 1. Spectral reflectance of cool and conventional black coatings.

Influence of the humidity conditions on the reflectivity spectrum of a porous silicon microcavity

We have designed and fabricated a porous silicon (PS) microcavity that shows a reflectivity resonance around 3 μm in between two spectral regions with high reflectivity values. The microcavity has been simulated following the photonic crystals formalism, which results in good agreement with the measured spectrum. The reflectivity spectrum of the microcavity has been analyzed under different humidity conditions. We demonstrate that the reflectivity resonance shifts to higher wavelengths and that the reflectivity decreases when the humidity increases. In addition, the reflectivity spectrum of the as-prepared device is recovered when the humidity returns to the initial laboratory conditions. Finally, the effect on the reflectivity spectrum of a condensed water layer at the surface of the microcavity is also analyzed.

Far-infrared optical investigation of the heavy-fermion semiconductor [formula omitted

We present far-infrared optical properties of the heavy-fermion semiconductor U 2 Ru 2 Sn . The optical reflectivity in the tetragonal plane shows a pronounced suppression at energies below 60 meV and temperatures below 200 K. These optical properties are similar to those reported for canonical heavy-fermion semiconductors. Narrow phonon-like peaks are observed at unusually high reflectivity values. We interpret the data within a temperature dependent, partial opening of a gap (or “pseudo-gap”) in the quasi-particle excitation spectrum.

Bidirectional reflectance of dry and submerged Labsphere Spectralon plaque

We present the bidirectional reflectance of a Labsphere calibration plaque, both dry and submerged in water, at normal illumination. The measurements indicate that when submerged in water, the Labsphere calibration plaque has a higher reflectance value than when dry at viewing angles below 55 degrees . The results are presented in the form of a reflectance factor and are useful for calibrating underwater reflectance measurements.

Total lightning activity in thunderstorms over Paris

A statistical study of two groups of storms that occurred in the Paris area (France) during summer 2000 has been realized. The first group includes 26 high radar reflectivity (HRR) storms with radar reflectivity values exceeding 60 dBZ while the second one includes 19 moderate radar reflectivity (MRR) storms with a maximum radar reflectivity value between 50 and 55 dBZ. The radar reflectivity was provided by a C-band radar and the total lightning activity (cloud-to-ground (CG) and intra-cloud (IC) flashes) was provided by the French Météorage network and a Safir device. HRR storms seem to be characterized by a longer lifetime, and a more extended convective area. On average, they produce more CG and IC flashes than MRR storms. However, a large variability in the number, the rate, and the type of flashes is observed. The HRR storms producing the highest IC flash rates (above 100 min − 1 ) exhibit the lowest CG flash proportion (1.2 and 4.3%). Most of the HRR storms exhibit a peak lightning activity when the radar reflectivity is strong at low level within the cloud. However, several cases of these storms show a large time lag between the strong lightning production and the presence of high radar reflectivity values at low level. Some possible explanations of these observations, taking into account cloud dynamics, microphysics and lightning initiation, are discussed.