Response time correlations for platinum resistance thermometers in flowing fluids

The thermal response of two types of Platinum Resistance Thermometers (PRT's), which are being considered for use in the National Transonic Wind Tunnel Facility, were studied. Response time correlations for each PRT, in flowing water, oil and air, were established separately. A universal correlation, tau WOA = 2.0 + 1264, 9/h, for a Hy-Cal Sensor (with a reference resistance of 100 ohm) within an error of 20% was established while the universal correlation for the Rosemount Sensor (with a reference resistance of 1000 ohm), tau OA = 0.122 + 1105.6/h, was found with a maximum percentage error of 30%. The correlation for the Rosemount Sensor was based on air and oil data only which is certainly not sufficient to make a correlation applicable to every condition. Therefore, the correlation needs more data to be gathered in different fluids. Also, it is necessary to state that the calculation of the parameter, h, was based on the available heat transfer correlations, whose accuracies are already reported in literature uncertain within 20-30%. Therefore, the universal response constant correlations established here for the Hy-Cal and Rosemount sensors are consistent with the uncertainty in the input data and are recommended for future use in flowing liquids and gases

Measuring Corporate Environmental Justice Performance

Measures of corporate environmental justice performance can be a valuable tool in efforts to promote corporate social responsibility and to document systematic patterns of environmental injustice. This paper develops such a measure based on the extent to which toxic air emissions from industrial facilities disproportionately impact racial and ethnic minorities and low-income people. Applying the measure to 100 major corporate air polluters in the United States, we find wide variation in the extent of disproportional exposures. In a number of cases, minorities bear more than half of the total human health impacts from the firm's industrial air pollution.Corporate social responsibility; corporate environmental performance; environmental justice; air pollution

Convective heat transfer from circular cylinders located within perforated cylindrical shrouds

The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied. The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective heat transfer to bare cylinders up to 50%. The maximum enhancement occurred for a radius ratio of 1.4 and ventilation factors between 0.2 and 0.3. It was found that shroud orientation influenced the heat transfer, with maximum heat transfer generally occurring when the shroud's holes were centered on either side of the stagnation line. However, the hole orientation effect is of second order compared to the influence of ventilation factor and radius ratio

Stability of streamwise vortices

A brief overview of some theoretical and computational studies of the stability of streamwise vortices is given. The local induction model and classical hydrodynamic vortex stability theories are discussed in some detail. The importance of the three-dimensionality of the mean velocity profile to the results of stability calculations is discussed briefly. The mean velocity profile is provided by employing the similarity solution of Donaldson and Sullivan. The global method of Bridges and Morris was chosen for the spatial stability calculations for the nonlinear eigenvalue problem. In order to test the numerical method, a second order accurate central difference scheme was used to obtain the coefficient matrices. It was shown that a second order finite difference method lacks the required accuracy for global eigenvalue calculations. Finally the problem was formulated using spectral methods and a truncated Chebyshev series

Application of modern control and nonlinear estimation techniques

Control and nonlinear estimation techniques applied to optimal guidance of low thrust spacecraft, planetary soft landings, and feedback systems desig

Over-The-Air Deramping For Multistatic Perimeter Surveillance

This paper explores the use of an over-the-air deramping (OTAD) system as a solution for perimeter surveillance. Over-the-air deramping is a technique for wirelessly synchronising distributed passive FMCW radar nodes to a dual-frequency master FMCW transmitter node. Such a system allows simultaneous monostatic and multistatic measurements for improved clutter resilience, and multiple looks at a target for reduced susceptibility to signal fading due to target scintillation. To prove the latter, a simultaneous monostatic and OTAD bistatic node were set up with a 5 m baseline and a walking person was measured. The results show that signal fading occurs in both the monostatic and the bistatic node, but rarely at the same time. Hence, combining the measurements from the two nodes gives a consistent response from the target. This demonstrates OTAD as a compelling system for a robust perimeter surveillance system

A New Multistatic FMCW Radar Architecture by Over-the-Air Deramping

© 2015 IEEE. Frequency modulated continuous wave (FMCW) radar is widely adopted solution for low-cost, short to medium range sensing applications. However, a multistatic FMCW architecture suitable for meeting the low-cost requirement has yet to be developed. This paper introduces a new FMCW radar architecture that implements a novel technique of synchronizing nodes in a multistatic system, known as over-the-air deramping (OTAD). The architecture uses a dual-frequency design to simultaneously broadcast an FMCW waveform on a lower frequency channel directly to a receiver as a reference synchronization signal, and a higher frequency channel to illuminate the measurement scene. The target echo is deramped in hardware with the synchronization signal. OTAD allows for low-cost multistatic systems with fine range-resolution, and low peak power and sampling rate requirements. Furthermore, the approach avoids problems with direct signal interference. OTAD is shown to be a compelling solution for low-cost multistatic radar systems through the experimental measurements using a newly developed OTAD radar system

Minimal size of a barchan dune

Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B {\bf{28,}} 321 (2002); G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E {\bf{64,}} 31305 (2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002) that this flux fetch distance is itself constant. Indeed, this could not explain the proto size of barchan dunes, which often occur in coastal areas of high litoral drift, and the scale of dunes on Mars. In the present work, we show from three dimensional calculations of sand transport that the size and the shape of the minimal barchan dune depend on the wind friction speed and the sand flux on the area between dunes in a field. Our results explain the common appearance of barchans a few tens of centimeter high which are observed along coasts. Furthermore, we find that the rate at which grains enter saltation on Mars is one order of magnitude higher than on Earth, and is relevant to correctly obtain the minimal dune size on Mars.Comment: 11 pages, 10 figure

Fitting Voronoi Diagrams to Planar Tesselations

Given a tesselation of the plane, defined by a planar straight-line graph $G$, we want to find a minimal set $S$ of points in the plane, such that the Voronoi diagram associated with $S$ "fits" \ $G$. This is the Generalized Inverse Voronoi Problem (GIVP), defined in \cite{Trin07} and rediscovered recently in \cite{Baner12}. Here we give an algorithm that solves this problem with a number of points that is linear in the size of $G$, assuming that the smallest angle in $G$ is constant.Comment: 14 pages, 8 figures, 1 table. Presented at IWOCA 2013 (Int. Workshop on Combinatorial Algorithms), Rouen, France, July 201

Many Roads to Synchrony: Natural Time Scales and Their Algorithms

We consider two important time scales---the Markov and cryptic orders---that monitor how an observer synchronizes to a finitary stochastic process. We show how to compute these orders exactly and that they are most efficiently calculated from the epsilon-machine, a process's minimal unifilar model. Surprisingly, though the Markov order is a basic concept from stochastic process theory, it is not a probabilistic property of a process. Rather, it is a topological property and, moreover, it is not computable from any finite-state model other than the epsilon-machine. Via an exhaustive survey, we close by demonstrating that infinite Markov and infinite cryptic orders are a dominant feature in the space of finite-memory processes. We draw out the roles played in statistical mechanical spin systems by these two complementary length scales.Comment: 17 pages, 16 figures: http://cse.ucdavis.edu/~cmg/compmech/pubs/kro.htm. Santa Fe Institute Working Paper 10-11-02