Effect of thermal annealing on optical and photoelectric properties of microcrystalline hydrogenated silicon films

The effect of thermal annealing in the temperature range T _a=300–600°C of films of microcrystal-line hydrogenated silicon (μc-Si:H) lightly doped with boron on the spectral dependences of the absorption coefficient (α) at photon energies hν=0.8–2.0 eV, dark conductivity (σ_d), and photoconductivity (Δσ_ph) was studied at room temperature. With increasing annealing temperature, a nonmonotonic variation of α (at hν<1.2 eV), σ_d, and Δσ_ph was observed. The data obtained are attributed to a change in the concentration of electrically active impurities and formation of defects, caused by hydrogen effusion and bond restructuring at high annealing temperatures.     

Photoinduced conductivity change in erbium-doped amorphous hydrogenated silicon films

Changes in the dark conductivity of erbium-doped amorphous hydrogenated silicon (a-Si:H(Er)) films after their preliminary illumination at room temperature have been studied. The effect of a compensating boron impurity on the photoinduced change in the conductivity of a-Si:H(Er) films is analyzed. It is established that the magnitude and the sign of the change in conductivity depend on the duration of illumination and position of the Fermi level in the mobility gap. Possible mechanisms leading to a photoinduced change in the conductivity of a-Si:H(Er) films are discussed.     

Erbium electroluminescence in p-i-n amorphous hydrogenated silicon structures

A comparative analysis of λ=1.54 μm electroluminescent structures based on amorphous hydrogenated silicon is made. The possibility of obtaining room-temperature electroluminescence from forward-biased conventional p-i-n structures based on this material is demonstrated for the first time, which is of interest for the development of effective emitting structures with current pumping.     

On the development and characterization of a firebrand generator

A unique experimental apparatus has been constructed in order to generate a controlled and repeatable size and mass distribution of glowing firebrands. The present study reports on a series of experiments conducted in order to characterize the performance of this firebrand generator. Firebrand generator characterization experiments were performed at the Fire Research Wind Tunnel Facility (FRWTF) at the Building Research Institute (BRI) in Tsukuba, Japan. The firebrand generator was fed with three different initial firebrand geometries, two different sized cylinders and one size of disks. Cylinders were used to simulate firebrand fluxes from vegetation, such as trees, while disks were used to simulate a firebrand flux from burning structures. Samples of these geometries were constructed from wood dowels, fed into the firebrand generator, ignited, and the glowing firebrands generated were collected using an array of water filled pans. The pans were filled with water in order to quench combustion. The collected firebrands were subsequently dried and the size and mass distribution was measured. These experiments were performed over a range of wind tunnel speeds, with no wind speed present to 9 m/s, to determine the lofting distance of the firebrands generated. Finally, the size and mass distribution produced from the firebrand generator are compared to those produced from burning trees. Results of the study are presented and discussed.     

Photoelectric phenomena in (μc xa1−x )-Si:H/c-Si heterostructures

Heterostructures (μc _xa_1−x )-Si:H/c-Si with a various volume fraction x of microcrystalline and amorphous Si phases were obtained by plasmochemical deposition. The fraction variation was achieved by changing the silane content in H₂. The steady-state current-voltage characteristics and spectral dependences of photosensitivity of the structures obtained were investigated. The latter dependences were recorded by exposing the samples to the natural and linearly polarized light in relation to the phase composition of thin (d ₁ ≅ 0.6–0.8 μm) films of microcrystalline and amorphous Si. The photovoltaic effect and induced photopleochroism of the structures obtained were detected. The prospects of using a new type of heterojunction in photoconverters of natural and linearly polarized light were assessed. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 11, 2001, pp. 1316–1319. Original Russian Text Copyright ? 2001 by Mell, Nikolaev, V. Rud’, Yu. Rud’, Terukov.     

A Heat Transfer Model for Firefighters' Protective Clothing

An accurate and flexible model of heat transfer through firefighter protective clothing has many uses, including investigating the degree of protection, in terms of burn injury and heat stress, of a particular fabric assembly and analyzing cheaply and quickly the expected performance of new or candidate fabric designs or fabric combinations.This paper presents the first stage in developing a heat transfer model for firefighters' protective clothing. The protective fabrics are assumed to be dry, which means no moisture from perspiration, and the fabric temperatures considered are below the point of thermal degradation, such as melting or charring. Many firefighter burns occur even when there is no thermal degradation of their protective gear. A planar geometry of the fabric layers is assumed with one-dimensional heat transfer. The forward-reverse model is used for radiative heat transfer. The accuracy of the model is tested by comparing time-dependent temperatures from both within and on the surface of a typical fabric assembly to those obtained experimentally. Overall, the model performed well, especially inside the garment where the temperature difference between the experiment and the stimulation was within 5°C. The predicted temperature on the outer shell of the garment differed most from experimental values, by much as 24°C. This was probably due to the absence of fabric-specific optical properties, such as transmissivity and reflectivity, used for model input.     

Common Vulnerability Scoring System

Vendors have historically used proprietary methods for scoring software vulnerabilities, usually without detailing their criteria or processes. The Common Vulnerability Scoring System (CVSS) is a public initiative designed to address this issue by presenting a framework for consistently and accurately assessing and quantifying software vulnerabilities' impact on organizations.     

Initial Reconnaissance of the 2011 Wildland-Urban Interface Fires in Amarillo, Texas

On February 27, 2011, a fire began in the outskirts of Amarillo, Texas, that destroyed or damaged buildings in three housing developments. The National Institute of Standards and Technology (NIST), as part of its Disaster and Failure Studies Program, deployed a team within 44 h of ignition to conduct an initial reconnaissance to document the fire event losses and fire behavior. The deployment was conducted jointly with the Texas Forest Service. Of interest to the NIST deployment was the fire behavior and effects on fire losses of topographical features, structure construction and defensive actions. The two communities initially evaluated were the Willow Creek South Complex and the Tanglewood Complex. Within 72 h after data collection initiation, the Tanglewood fire became the focus of the deployment. Additionally, destroyed and damaged structure data were collected to support the local and state damage assessment efforts. The Tanglewood Complex wildland-urban interface fire was responsible for the destruction of approximately 101 structures including 35 residences. The overall objectives of this study are to establish the likely technical factor or factors responsible for the damage, failure, and/or successful performance of buildings and/or infrastructure in the aftermath of the fire, and to recommend, as necessary, specific improvements to standards, codes, and practices based on study findings. This study also may be used to define areas of future research. This summary paper addresses the particulars of the deployment and the data collection methodology used. A second more detailed technical paper will provide the event timeline reconstruction and general fire behavior observations as well as investigate the impacts of structure attributes, landscaping characteristics, topographical features and wildland fire exposure on structure survivability.     

A Case Study of a Community Affected by the Witch and Guejito Wildland Fires

Wildland-urban interface (WUI) fires occur when fire spreads through both wildland and community (structures and vegetation) fuels. These fires are capable of causing significant destruction to both the built and the natural environments. When these fires occur under extreme fire danger conditions (e.g., high winds, low humidity) and in areas of significant population (e.g., San Diego, California) firefighters, and other emergency responders, are significantly challenged by the combination of firefighting and aiding the public. This paper presents the results of an in-depth case study of a community of 274 residences which was subjected to two wildland fires (within 2.5 h of each other) during the October 2007 firestorm in southern California. A significant amount of effort was spent obtaining information from residents and emergency responders to determine the fire spread timeline, structure ignition mechanisms, and defensive actions. Of the 274 residences, 245 were within the fire perimeter, 74 were destroyed, and 16 were damaged. When the first fire front arrived, the rate of structure ignitions peaked at 21 per hour. Direct and indirect ember, or firebrand, attack was responsible for the ignition of 2/3 of the destroyed homes. Defensive actions were taken on one of every three homes. Of the 16 damaged homes, 15 were successfully defended. Further study of this community is ongoing to investigate what currently recommended pre-fire hazard reduction actions could be, and were, implemented and their effectiveness at reducing the likelihood of structure ignition.