Distribution system simulator

In a series of tests performed under the Department of Energy auspices, power line carrier propagation was observed to be anomalous under certain circumstances. To investigate the cause, a distribution system simulator was constructed. The simulator was a physical simulator that accurately represented the distribution system from below power frequency to above 50 kHz. Effects such as phase-to-phase coupling and skin effect were modeled. Construction details of the simulator, and experimental results from its use are presented

Confidence intervals for exposure risk assessment

The problem of estimating exposure to a pollutant involves estimation of chemical intake Q. Typically, Q has the form Q = q11q12&cdots;q 1r1/q211q22 &cdots;q2r2t where all thetaij\u27s are unknown means of certain random variables. In assessing the risk to human health from exposure to the pollutant of concern, a confidence interval estimate of Q is needed. In the case of independent normal random variables, point estimates and certain types of interval estimates of a product of several parameters exist in the literature, but not for a ratio of products. In many situations, lot of prior knowledge is available regarding the random variables corresponding to these parameters. In the case of independent normal random variables, we look at this problem from a Bayesian approach, and show how to incorporate prior knowledge to calculate confidence interval for Q. In situations with no prior knowledge, generalized Bayes approach with noninformative priors can be used. Several real and simulated examples are provided to demonstrate the proposed procedures

Predicting Performance on the Tennessee Comprehensive Assessment for Reading for Third Graders using Reading Curriculum Based Measures

Despite flexibility waivers granted to states by the United States Department of Education from some provisions of the No Child Left Behind Act, our nation’s public schools continue to struggle to improve reading proficiency as measured by high stakes assessments. To reach state targets for reading proficiency schools must use data at the earliest point possible to inform instructional strategies and identify students at risk of failure. The response to intervention model holds promise for improving reading outcomes particularly for early elementary students. The effective use of reading curriculum based measures (R-CBM) to determine if instruction is adequate to produce students who score proficient or advanced on state mandated reading assessments is critical to achieving the goals for student learning. The population selected for this study included all third grade students from an East Tennessee school district. The third graders attended 13 schools and included 911 third grade students of which 770 students participated in the study. This included 372 male and 398 female students. Approximately 47% of the students were economically disadvantaged as determined by qualifying for free and reduced priced meals. The purpose of this study was to investigate the relationship between 4 predictor variables (fall R-CBM, winter R-CBM, spring R-CBM, and median R-CBM) and the Tennessee Comprehensive Assessment Program (TCAP) third grade reading and language arts assessment. Each data set included 4 R-CBM scores expressed in words read correctly and TCAP reading language arts scale scores. Gender and free and reduced price meals eligibility information for all third graders from the 2010-2011 school year were also collected. Results reflected a strong predictive relationship between the AIMSweb R-CBM and TCAP reading and language arts measure for third grade students. Zero order correlations in the multiple regression analysis ranged from .70 to .74 for the 4 predictor variables. A linear equation was developed to predict TCAP scores from a single R-CBM score (fall, winter, spring, and median). Based on this study practitioners may be able to establish goals for student reading that are strongly correlated with achieving proficiency on the TCAP reading and language arts assessment

Structural concepts and experimental considerations for a versatile high-speed research airplane

Future aircraft may be hydrogen fueled and fly at hypersonic speeds. The resulting environments will require new structural concepts to satisfy performance goals. Large representative structures will have to be flight tested prior to commitment to a costly vehicle fleet. To perform flight tests, a versatile, economical, high-speed research airplane is defined. Results of this study including experimental considerations for a hypersonic research airplane are reported

Investigating soil-water retention characteristics at high suctions using Relative Humidity control

A technique for controlling relative humidity (RH) is presented, which involves supplying a sealed chamber with a continuous flow of air at a computer-regulated RH. The desired value of RH is achieved by mixing dry and wet air at appropriate volumes and is measured for servo-control at three locations in the chamber with capacitive RH sensors and checked with a sensitive VAISALA sensor. The setup is capable of controlling RH steadily and continuously with a deviation of less than 0.2% RH. The technique was adopted to determine wetting soil-water retention curves (SWRC) of statically compacted London Clay, under both free-swelling and constant volume conditions. The RH within the chamber was increased in a step-wise fashion, with each step maintained until vapour equilibrium between the chamber atmosphere and the soil samples was established. Independent filter paper measurements further validate the method, while the obtained retention curves complement those available in the literature for lower ranges of suction

Power system applications of fiber optic sensors

This document is a progress report of work done in 1985 on the Communications and Control for Electric Power Systems Project at the Jet Propulsion Laboratory. These topics are covered: Electric Field Measurement, Fiber Optic Temperature Sensing, and Optical Power transfer. Work was done on the measurement of ac and dc electric fields. A prototype sensor for measuring alternating fields was made using a very simple electroscope approach. An electronic field mill sensor for dc fields was made using a fiber optic readout, so that the entire probe could be operated isolated from ground. There are several instances in which more precise knowledge of the temperature of electrical power apparatus would be useful. This report describes a number of methods whereby the distributed temperature profile can be obtained using a fiber optic sensor. The ability to energize electronics by means of an optical fiber has the advantage that electrical isolation is maintained at low cost. In order to accomplish this, it is necessary to convert the light energy into electrical form by means of photovoltaic cells. JPL has developed an array of PV cells in gallium arsenide specifically for this purpose. This work is described

Power system applications of fiber optics

Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described

Structure of self-assembled Mn atom chains on Si(001)

Mn has been found to self-assemble into atomic chains running perpendicular to the surface dimer reconstruction on Si(001). They differ from other atomic chains by a striking asymmetric appearance in filled state scanning tunneling microscopy (STM) images. This has prompted complicated structural models involving up to three Mn atoms per chain unit. Combining STM, atomic force microscopy and density functional theory we find that a simple necklace-like chain of single Mn atoms reproduces all their prominent features, including their asymmetry not captured by current models. The upshot is a remarkably simpler structure for modelling the electronic and magnetic properties of Mn atom chains on Si(001).Comment: 5 pages, 4 figure

Electronic coupling between Bi nanolines and the Si(001) substrate: An experimental and theoretical study

Atomic nanolines are one dimensional systems realized by assembling many atoms on a substrate into long arrays. The electronic properties of the nanolines depend on those of the substrate. Here, we demonstrate that to fully understand the electronic properties of Bi nanolines on clean Si(001) several different contributions must be accounted for. Scanning tunneling microscopy reveals a variety of different patterns along the nanolines as the imaging bias is varied. We observe an electronic phase shift of the Bi dimers, associated with imaging atomic p-orbitals, and an electronic coupling between the Bi nanoline and neighbouring Si dimers, which influences the appearance of both. Understanding the interplay between the Bi nanolines and Si substrate could open a novel route to modifying the electronic properties of the nanolines.Comment: 6 pages (main), 2 pages (SI), accepted by Phys. Rev.

White coat hypertension is associated with increased small vessel disease in the brain

Objective: Small vessel disease, as measured by white matter hyperintensity (WMH) in the brain, is known to be associated with increased stroke risk and cognitive impairment. This study explored the relationship between WMH on computerised tomography (CT) and white coat hypertension/effect (WCH/E) in patients with recent transient ischaemic attack (TIA) or lacunar stroke (LS). Design and method: Ninety-six patients recruited for the ASIST trial (Arterial Stiffness in Lacunar Stroke and TIA) underwent measurement of clinic blood pressure (BP) and ambulatory BP monitoring (APBM) within two weeks of TIA or LS. Twenty-three patients had normotension (clinic BP / = 140/90mmHg and day-time ABPM < 135/85mmHg). Arterial stiffness was measured using carotid-femoral pulse wave velocity (PWV) (Complior®, ALAM Medical) and carotid-ankle vascular index (CAVI) (VaSera VS-1500N®, Fukuda Denshi). CT images were scored for WMH using the four-point Fazekas visual rating scale. Patients were grouped into no-mild WMH (scores 0–1) or moderate-severe (scores 2–3) groups. The relationship between BP, vascular stiffness and WMH was explored with t-tests, chi-square and logistic regression accounting for known cardiovascular risk factors. Results: Forty-four percent of patients with WCH/E had moderate-severe WMH compared to 17% of normotensives (p = 0.047). The regression model with WMH as the dependent factor, and WCH/E and cardiovascular risk factors as independent factors showed WCH/E and either CAVI or PWV to be the only independent significant factor contributing to WMH (CAVI:p = 0.038, PWV:p = 0.043)