Recovery of surface orientation from diffuse polarization.

When unpolarized light is reflected from a smooth dielectric surface, it becomes partially polarized. This is due to the orientation of dipoles induced in the reflecting medium and applies to both specular and diffuse reflection. This paper is concerned with exploiting polarization by surface reflection, using images of smooth dielectric objects, to recover surface normals and, hence, height. This paper presents the underlying physics of polarization by reflection, starting with the Fresnel equations. These equations are used to interpret images taken with a linear polarizer and digital camera, revealing the shape of the objects. Experimental results are presented that illustrate that the technique is accurate near object limbs, as the theory predicts, with less precise, but still useful, results elsewhere. A detailed analysis of the accuracy of the technique for a variety of materials is presented. A method for estimating refractive indices using a laser and linear polarizer is also given.     

Functional imaging in small animals using X-ray computed tomography--study of physiologic measurement reproducibility

X-ray computed tomography (CT) has been traditionally used for morphologic analysis and in the recent past has been used for physiology imaging. This paper seeks to demonstrate functional CT as an effective tool for monitoring changes in tissue physiology associated with disease processes and cellular and molecular level therapeutic processes. We investigated the effect of noise and sampling time on the uncertainty of tissue physiologic parameters. A whole body compartmental model of mouse was formulated to simulate tissue time density curves and study the deviation of tissue physiologic parameters from their true values. These results were then used to determine the appropriate scanning protocols for the experimental studies. Dynamic contrast enhanced CT (DCE-CT) was performed in mice following the injection of hydrophilic iodinated contrast agent (CA) at three different injection rates, namely 0.5 ml/min, 1 ml/min, and 2.0 ml/min. These experiments probed the Nyquist sampling limit for reproducibility of tissue physiologic parameters. Separate experiments were performed with three mice at four different X-ray tube currents corresponding to different image noise values. A two-compartment model (2CM) model was formulated to describe the contrast kinematics in the kidney cortex. Three different 2CMs were implemented namely the 4-parameter (4P), 5-parameter (5P), and the 6-parameter (6P) model. The tissue kinematics is fitted to the models by using the Levenberg-Marquardt algorithm implemented in IDL (RSI Inc.) programming language to minimize the weighted sum of squares. The relevant tissue physiologic parameters extracted from the models are the renal blood flow (RBF), glomerular filtration rate (GFR), fractional plasma volume, fractional tubular volumes and urine formation rates. The experimental results indicate that the deviation of the tissue physiologic parameters is within the limits required for tracking disease physiology in vivo and thus small animal functional X-ray CT would be able to determine changes in tissue physiology in vivo.     

MOCVD Growth of Erbium Monoantimonide Thin Filmand Nanocomposites for Thermoelectrics

We report the growth of erbium monoantimonide (ErSb) thin films on indium antimonide (100) substrates by low-pressure metalorganic chemical vapor deposition. The growth rate of ErSb thin films shows strong dependency on the growth temperature and the Sb/Er precursor molar flow rate ratio. Scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffractometry (XRD) were employed to study the ErSb thin films grown under the growth conditions that gave the maximum growth rate in the range we investigated. We also report the growth of two types of nanocomposites in which ErSb nanocolumns or nanoslabs with lengths ~500 nm and diameters 20 nm to 30 nm are embedded in Zn-doped InGaSb (ErSb/InGaSb:Zn) and ErSb nanoparticles with diameters of ~30 nm are embedded in Zn-doped InSbAs (ErSb/InSbAs:Zn). These nanocomposites were intended to increase phonon scattering in a mid-to-long phonon wavelength range to reduce lattice thermal conductivity. We used time-domain thermoreflectance to measure total thermal conductivity for the two types of nanocomposites, obtaining 4.0 ± 0.6 W/mK and 6.7 ± 0.8 W/mK for the ErSb/InAsSb:Zn and ErSb/InGaSb:Zn nanocomposites, respectively, which suggests that the thermal conductivity was close to or slightly smaller than the alloy limit of the two ternary alloy hosts. The two nanocomposites were further studied by transmission electron microscopy (TEM) to reveal their microscopic features and by XRD to assess their crystalline structures.     

Redundancy resolution of the human arm and an upper limb exoskeleton

The human arm has 7 degrees of freedom (DOF) while only 6 DOF are required to position the wrist and orient the palm. Thus, the inverse kinematics of an human arm has a nonunique solution. Resolving this redundancy becomes critical as the human interacts with a wearable robot and the inverse kinematics solution of these two coupled systems must be identical to guarantee an seamless integration. The redundancy of the arm can be formulated by defining the swivel angle, the rotation angle of the plane defined by the upper and lower arm around a virtual axis that connects the shoulder and wrist joints. Analyzing reaching tasks recorded with a motion capture system indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points to the head. Based on these experimental results, a new criterion is formed to resolve the human arm redundancy. This criterion was implemented into the control algorithm of an upper limb 7-DOF wearable robot. Experimental results indicate that by using the proposed redundancy resolution criterion, the error between the predicted and the actual swivel angle adopted by the motor control system is less then 5°.     

Three-Stage Thin-Film Superlattice Thermoelectric Multistage Microcoolers with a Δ<Emphasis Type="Italic">T</Emphasis><Subscript>max</Subscript> of 102 K

Thin-film Bi₂Te₃- and Sb₂Te₃-based superlattice (SL) thermoelectric (TE) devices are an enabling technology for high-power and low-temperature applications, which include low-noise amplifier cooling, electronics hot-spot cooling, radio frequency (RF) amplifier thermal management, and direct sensor cooling. Bulk TE devices, which can pump heat loads on the order of 10 W/cm², are not suitable in these applications due to their large size and low heat pumping capacity. Recently, we have demonstrated an external maximum temperature difference, ΔT _max, as high as 58 K in an SL thin-film p–n couple. This state-of-the-art couple exhibited a cold-side minimum temperature, T _cmin, of −30.9°C. We regularly attain ΔT _max values in excess of 53 K, in spite of the many significant electrical and thermal parasitics that are unique to thin-film devices. These measurements do not use any complex thermal management at the heat sink to remove the heat flux from the TE device’s hot side. We describe here multistage SL cooling technologies currently being developed at RTI that can provide useful microcooling cold-side temperatures of 200 K. This effort includes a three-stage module employing independently powered stages which produced a ΔT _max of 101.6 K with a T _cmin of −75°C, as well as a novel two-wire three-stage SL cascade which demonstrated a T _cmin of −46°C and a ΔT _max of nearly 74 K. These RTI modules are only 2.5 mm thick, significantly thinner than a similar commercial three-stage module (5.3 mm thick) that produces a ΔT _max of 96 K. In addition, TE coolers fabricated from these thin-film SL materials perform significantly better than the extrapolated performance of similar thickness bulk alloy materials.     

From volatility to value: analysing and managing financial and performance risk in energy savings projects

Many energy-related investments are made without a clear financial understanding of their values, risks, and volatilities. In the face of this uncertainty, the investor—such as a building owner or an energy service company—will often choose to implement only the most certain and thus limited energy-efficiency measures. Conversely, commodities traders and other sophisticated investors accustomed to evaluating investments on a value, risk, and volatility basis often overlook energy-efficiency investments because risk and volatility information are not provided. Fortunately, energy-efficiency investments easily lend themselves to such analysis using tools similar to those applied to supply side risk management. Accurate and robust analysis demands a high level of understanding of the physical aspects of energy-efficiency, which enables the translation of physical performance data into the language of investment. With a risk management analysis framework in place, the two groups—energy-efficiency experts and investment decision-makers—can exchange the information they need to expand investment in demand-side energy projects. In this article, we first present the case for financial risk analysis in energy efficiency in the buildings sector. We then describe techniques and examples of how to identify, quantify, and manage risk. Finally, we describe emerging market-based opportunities in risk management for energy efficiency.     

Power Evaluation of the Los Angeles Oxygen–Fed Ozone System

The Los Angeles Department of Water and Power (LADWP) operates a 600 mgd (2,270 ML/day) direct filtration water treatment plant which includes a 7,900 lb/day (149 kg/hr) ozonation system. Ozone is applied as a preoxidant for the purposes of disinfection and microflocculation. The ozonation system is unique in that high purity oxygen is generated on–site and is used as the feed–gas in a once–through system. The process was selected through competitive bids and evaluated for total present worth from 20–year life cycle costs which included capital plus energy expenses. Power consumption (and penalty) was valued at $6,500/kW. System power demand was measured at nine ozone production rates. A minimum specific energy of 6.5 kWh/lb (14.3 kWh/kg) of ozone was observed when generating ozone at a concentration between 5 and 6 % (wt) [65 and 80 g/m³; where the standard temperature and pressure are 70F (21.11 C) and 1 atm, respectively]. The test methodology and data assessment considerations were developed jointly by the owner and manufacturer, and produced results with practical significance beyond the performance testing objective.     

Kinetic Analysis of Solution-Precipitation During Liquid-Phase Sintering of Alumina

Densification controlled by solution-precipitation during liquid-phase sintering was analyzed for the aluminamagnesium aluminosilicate glass system. As a model system for liquid-phase sintering, narrowly sized alumina powders and up to 20 vol% magnesium aluminosilicate glass samples were isothermally sintered at 1550° to 1650°C. Densification rate increases with increasing liquid content and sintering temperature but decreases with increasing density. For samples with >15% grain growth, the densification rate during the solution-precipitation stage of sintering was proportional to (particle size)⁻² and thus interface reaction-controlled. Activation energies ranged from 270 to 500 kJ/mol over the relative density range of 66% to 96%, respectively. The low activation energy is attributed to densification by particle rearrangement, whereas the higher activation energy is due to densification controlled by interface-reaction-controlled solution-precipitation. Intermediate activation energies are attributed to simultaneous densification by the two mechanisms.     

Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors

Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me₃Si)_0.80((CH₂=CH)MeSi)_1.0(MeHSi)_0.35] _n (VPS) or [MeHSiCH₂] _n (MPCS) with [R₂AlNH₂]₃, where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et₂AlNH₂]₃. In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu₂AlNH₂]₃ yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed.     

Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Partially crystalline Si₃N₄, with nanosized crystals and a specific surface area greater than 200 m²/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH₃ to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si₃N₄ proceeds with additional heating above 1400°C under N₂. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N₂, are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes.