A covariance matrix method to compute bit error rates in a highly nonlinear dispersion-managed soliton system

We completely describe the covariance matrix method for the first time, and we use it to compute the noise evolution in a 10-Gb/s single-channel dispersion-managed soliton system propagating over 24000 km. The linearization assumption upon which the covariance matrix method is based breaks down, unless we explicitly separate the phase and timing jitter of each pulse from the noise. We describe a procedure for carrying out this separation.     

Polarization-mode-dispersion emulator using variable differential-Group-delay (DGD) elements and its use for experimental importance sampling

We demonstrate a practical polarization-mode-dispersion (PMD) emulator using programmable differential-group-delay (DGD) elements. The output PMD statistics of the emulator can be chosen by varying the average of the Maxwellian DGD distribution applied to each element. The emulator exhibits good stability and repeatability in a laboratory environment. In addition, we demonstrate how this emulator may be used to experimentally employ the powerful technique of importance sampling to quickly generate extremely low probability events. This technique is used to measure the Q-factor degradation due to both average and rare PMD values in a 10-Gb/s transmission system.     

A comparison of SPECT and planar ventilation perfusion lung scanning

In order to define the role of Single Photon Emission Computed Tomography (SPECT) in the diagnosis of pulmonary embolus; SPECT and Planar ventilation and perfusion lung studies were performed consecutively on eleven patients referred with suspected embolus. Three patients were shown to have 'high probability' ventilation perfusion mismatches. SPECT imaging allowed segmental localisation of the perfusion defect and revealed additional defects not seen on planar scans. SPECT lung study was performed with minimal technical difficulty and was well tolerated by all patients studied. SPECT is likely to become the method of choice for investigating patients referred with suspected pulmonary embolus.     

PCBN tool wear modes and mechanisms in finish hard turning

The use of polycrystalline cubic boron nitride (PCBN) cutting tools in hard turning applications is continuously growing with the number of commercially available grades increasing, allowing new application areas to be explored. In order to take full advantage of the benefits offered by PCBN it is necessary to understand the behaviour of the material in application. Tool behaviour is influenced by many factors which include the composition of the PCBN material, the steel workpiece, the nature of the cutting operation, the cutting conditions and the tool geometry.

The focus of this paper is the continuous turning of hardened steels. A significant amount of research has been carried out in this area and a literature review of the relevant work is presented. This identifies the primary wear modes and discusses the many theories proposed to explain the mechanisms contributing to PCBN tool wear and failure. The final section of the paper considers the critical factors that influence the behaviour of PCBN tools in continuous hard turning and how this knowledge can be applied to optimise tool performance.     

Kinetics of the peritectic phase transformation: In-situ measurements and phase field modeling

An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation in a Fe−C alloy. The interfacial growth velocities of the peritectic phase transformation were measuredin situ for cooling rates of 100, 50, and 10 K/min.In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite (γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as the cooling rate increased there was a transition point where the L/γ interface propagated at a higher velocity than the γ/δ interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent, multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation.     

Allocation of transmission losses to bilateral contracts in acompetitive environment

Under open access, market driven transactions have become the new independent decision variables defining the behavior of the power system. Understanding the impact of bilateral transactions on system losses is important to be able to allocate a loss component to each individual transaction and improve economic efficiency. The theory presented here is based on the argument that it is always possible to compute the exact loss allocation corresponding to an infinitesimal bilateral transaction. This leads to a set of governing differential equations whose solution yields the loss allocation for contracts of any size. Several examples illustrate the properties of both the proposed allocation equations and other methods, the dependence of the proposed solution on the path of integration, and a number of implementation issues     

A Compact UHV Tandem Quadrupole Mass Spectrometer for Surface-Induced Dissociation Studies Using Well-Characterized Surfaces

Collision of low-energy polyatomic ions with surfaces can be an effective method for ion activation and fragmentation for ion structural analysis. In order for this method to be more widely used, a better understanding of low-energy ion-surface reactions must be obtained. The design and construction of a compact tandem quadrupole mass spectrometer which can be used to investigate low-energy ion-surface reactions on well-characterized surfaces is described. This UHV-compatible instrument is designed to fit entirely on a standard eight-inch UHV flange, and so can be easily mounted on a typical UHV electron spectroscopy system for preparing and characterizing the scattering surface. The operation of this instrument is illustrated by the discussion of two examples: the first, the associative reaction between benzene ions and a hydrocarbon surface to form C₇H₇⁺ via a sputtered-ion mechanism; the second, an examination of the effect of organic monolayer structure on the reactivity of the monolayer for protonation of incident benzene ions.     

Perinatal mortality and its relationship to the reporting of low-birthweight infants

OBJECTIVE: To determine whether diabetes defined by isolated postchallenge hyperglycemia (IPH) (2-h postchallenge plasma glucose > or = 11.1 mmol/l with fasting plasma glucose [FPG] < 7.0 mmol/l) increases the risk of fatal cardiovascular disease (CVD) in older women and men. RESEARCH DESIGN AND METHODS: In a prospective study, we followed 769 men and 1,089 women, aged 50-89 years, who had no history of diabetes or myocardial infarction and demonstrated no fasting hyperglycemia (i.e., FPG < 7.0 mmol/l) when they underwent oral glucose tolerance testing at baseline in 1984-1987. RESULTS: At baseline, 70% of 125 women and 48% of 133 men with previously undiagnosed diabetes had IPH. Over the next 7 years, women with IPH had a significantly increased risk of fatal CVD and heart disease compared with nondiabetic women. This increased risk was not observed in men with IPH. This association was independent of age, hypertension, central obesity, cigarette smoking, HDL cholesterol, and triglycerides (multiply adjusted hazard ratio and 95% CI: 2.6 and 1.4-4.7 for CVD; 2.9 and 1.3-6.4 for heart disease). CONCLUSIONS: Diabetes defined by IPH alone is common in older adults and more than doubles the risk of fatal CVD and heart disease in older women. Because the prevalence of IPH increases with age, the use of fasting glucose alone for diabetes screening or diagnosis may fail to identify most older adults at high risk for CVD and should be reevaluated.     

Thermodynamic properties and diffusion thermodynamic factors in B2-NiAl

The vaporization of Ni-Al alloys has been investigated in the temperature range 1178 to 1574 K by Knudsen effusion mass spectrometry (KEMS). Thirteen different compositions have been examined in the composition range 38 to 57 at. pct Al. The partial pressures and thermodynamic activities of both Ni and Al have been evaluated both directly from the measured ion intensities for a component in both the alloy and the pure element, I _M ⁺ /I _M ⁺ °, and also from the ion intensity ratios of the alloy components, I _Al ⁺ /I _Ni ⁺ , by means of a Gibbs-Duhem integration. Reliable partial molar enthalpies and entropies for both components have been obtained by mass spectrometry for this system for the first time. Both properties are found to be nearly temperature independent over the wide temperature range investigated. Two separate component diffusion thermodynamic factors have also been evaluated for the first time by taking into account the large vacancy concentrations in these alloys. The enthalpy and Gibbs energy of mixing of stoichiometric Ni_0.5Al_0.5 at 1400 K, evaluated using the Gibbs-Duhem ion intensity ratio (GD-IIR) method, are −78.4±1.2 and −49.0 kJ/mol, respectively, with Al(liquid) and completely paramagnetic Ni(fcc, cpm) as reference states.     

Impact of Federal Environmental Requirements on Proposed Highway or Bridge Project

Prior to construction of a bridge or highway, the National Environmental Protection Act (NEPA) requires an evaluation of the effect of the project on the human environment. The purpose of NEPA is to require the head of the federal agency that is committing funds to the project to consider its actions before deciding to proceed with the project. This paper will analyze the general provisions of NEPA to remove some of the mystery related to the environmental concerns raised by bridge or highway projects and to emphasize to transportation planners that these concerns must be addressed prior to beginning a major bridge or highway project. The intent of this paper is to provide some guidance to transportation planners in light of these statutes as they begin the planning stages for highway and bridge projects.