Attenuation of Lightning-Induced Effects on Overhead Distribution Systems in Urban Areas

Overhead distribution systems can be strongly affected and damaged by indirect lightning. The induced voltages are usually computed neglecting the surrounding geometry and the presence of buildings in urban areas. Buildings can strongly change the behavior of the measured lighting-induced electromagnetic (EM) fields in the proximity of the point of impact. As a consequence, induced voltages can deviate from what would be measured in the absence of buildings. This work proposes an analysis of the main variables, which affect the deviation of the EM fields and of the consequent induced voltages along an overhead distribution line due to the presence of a building. Different distances between the line and the building and different building heights are considered

Conceptual design upgrade on hybrid powertrains resulting from electric improvements

Hybrid vehicles have experienced a great boom in recent years thanks to the increasing spread of \u2018parallel\u2019 architectures, often realized by a planetary gear train (hybrid Synergy Drive). At the same time, an enhancement of electrical and electronic components has been experienced; these improvements especially concern reliability and efficiency. Particularly, the possibility of using supercapacitors with increasing storage performances makes possible to manage higher power flows together with a superior efficiency. These innovations may challenge the architecture used nowadays on medium size cars. The hybrid series architecture, which allows the optimal management of the combustion engine, has been disadvantaged until now by the electric powertrain efficiency. In the current scenario, this architecture could benefit from the above-mentioned technology, becoming a competitive alternative to the actual powertrain configurations. The aim of this article is the efficiency analysis, in order to evaluate the operational energy efficiency achievable thanks to this configuration. This analysis will be carried out considering all the possible working conditions of the different powertrains

Interaction of molecular motors can enhance their efficiency

Particles moving in oscillating potential with broken mirror symmetry are considered. We calculate their energetic efficiency, when acting as molecular motors carrying a load against external force. It is shown that interaction between particles enhances the efficiency in wide range of parameters. Possible consequences for artificial molecular motors are discussed.Comment: 6 pages, 8 figure

Evaluation of fetal cerebral blood flow perfusion using power Doppler Ultrasound Angiography (3D-PDA) in growth-restricted fetuses

Objective: to explore the potential of 3D Power Doppler Angiography (3D PDA) to evaluate the cerebral circulation in normal and growth restricted fetuses (IUGR). Study design: in a pilot study, we enrolled 51 appropriate for gestational age (AGA) pregnancies and 17 singleton pregnancies presenting IUGR, all between 22 and 38 weeks of gestation. Using 3D power Doppler ultrasound, a volume acquisition of the fetal brain was performed. Two regions of interest (ROI) were defined within the fetal brain. Zone 1 is anterior to the cavum septi pellucidi (CSP). Zone 2 is defined by a rectangle obtained tracing a contour between the temporal bones as wide as the CSP, corresponding to the area of the middle cerebral artery. The Flow Index (FI), the Vascularization Index (VI), the Vascularization and Flow Index (VFI) were determined in both areas in both IUGR and AGA fetuses by a single operator. IUGR fetuses were divided into three groups: Group 1, with normal pulsatility index (PI) of umbilical artery (UA), middle cerebral artery (MCA) and ductus venosus (DV); Group 2, IUGR fetuses with abnormal UA PI, normal MCA PI, normal DV PI; in Group 3, IUGR fetuses with abnormal UA PI, MCA PI and DV PI. Results: FI and VFI values of zone 1 were increased in Group 1.Values of VFI in zone 2 were increased in Group 2. Conclusions: Our findings are in line with recent studies in growth-restricted fetuses suggesting that the anterior cerebral artery shows Doppler signs of vasodilatation before these are observed in the MCA, demonstrating the “frontal brain sparing effect”

Dimer diffusion in a washboard potential

The transport of a dimer, consisting of two Brownian particles bounded by a harmonic potential, moving on a periodic substrate is investigated both numerically and analytically. The mobility and diffusion of the dimer center of mass present distinct properties when compared with those of a monomer under the same transport conditions. Both the average current and the diffusion coefficient are found to be complicated non-monotonic functions of the driving force. The influence of dimer equilibrium length, coupling strength and damping constant on the dimer transport properties are also examined in detail.Comment: Final revised version. 7 pages, 6 figure

Collective shuttling of attracting particles in asymmetric narrow channels

The rectification of a single file of attracting particles subjected to a low frequency ac drive is proposed as a working mechanism for particle shuttling in an asymmetric narrow channel. Increasing the particle attraction results in the file condensing, as signalled by the dramatic enhancement of the net particle current. Magnitude and direction of the current become extremely sensitive to the actual size of the condensate, which can then be made to shuttle between two docking stations, transporting particles in one direction, with an efficiency much larger than conventional diffusive models predict

Superconducting Fluxon Pumps and Lenses

We study stochastic transport of fluxons in superconductors by alternating current (AC) rectification. Our simulated system provides a fluxon pump, "lens", or fluxon "rectifier" because the applied electrical AC is transformed into a net DC motion of fluxons. Thermal fluctuations and the asymmetry of the ratchet channel walls induce this "diode" effect, which can have important applications in devices, like SQUID magnetometers, and for fluxon optics, including convex and concave fluxon lenses. Certain features are unique to this novel two-dimensional (2D) geometric pump, and different from the previously studied 1D ratchets.Comment: Phys. Rev. Lett. 83, in press (1999); 4 pages, 5 .gif figures; figures also available at http://www-personal.engin.umich.edu/~nori/ratche

Building a Prediction Model for Vacuum-Assisted Operative Vaginal Delivery Risk

Aim: The objective of this study was to evaluate the risk factors for operative vaginal delivery and to propose a new nomogram for predicting the risk. Methods: We retrospectively analyzed the data of 1,955 pregnancies that occurred in our clinic between the years 2007 and 2008. Included were singleton pregnancies with labor diagnosis after the 36th gestational week in which spontaneous or operative vaginal deliveries occurred. In this study, the operative delivery was carried out exclusively by vacuum extraction. Results: After univariate analysis and multivariate logistic regression stepwise model selection, maternal age, nulliparity, medically assisted procreation, gestational age at birth, male fetus, epidural analgesia and medical induction of labor were found to be the most predictive variables for operative vaginal delivery. Considering these factors we propose a new nomogram for an objectified determination of the risk of operative vaginal delivery. Conclusions: The new nomogram we propose could be an important tool for an objectified determination of the risk of operative vaginal delivery by vacuum extraction in individualized patient counseling

Statistical Mechanics of Kinks in (1+1)-Dimensions

We investigate the thermal equilibrium properties of kinks in a classical $\phi^4$ field theory in $1+1$ dimensions. The distribution function, kink density, and correlation function are determined from large scale simulations. A dilute gas description of kinks is shown to be valid below a characteristic temperature. A double Gaussian approximation to evaluate the eigenvalues of the transfer operator enables us to extend the theoretical analysis to higher temperatures where the dilute gas approximation fails. This approach accurately predicts the temperature at which the kink description breaks down.Comment: 8 pages, Latex (4 figures available on request), LA-UR-92-399