1,740 research outputs found
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
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”
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
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
field theory in 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
- …