1,848 research outputs found
Technical note: Design flood under hydrological uncertainty
Planning and verification of hydraulic infrastructures require a
design estimate of hydrologic variables, usually provided by frequency
analysis, and neglecting hydrologic uncertainty. However, when hydrologic
uncertainty is accounted for, the design flood value for a specific return
period is no longer a unique value, but is represented by a distribution of
values. As a consequence, the design flood is no longer univocally defined,
making the design process undetermined.
The Uncertainty Compliant Design Flood Estimation (UNCODE) procedure is a
novel approach that, starting from a range of possible design flood estimates
obtained in uncertain conditions, converges to a single design value. This is
obtained through a cost–benefit criterion with additional constraints that
is numerically solved in a simulation framework. This paper contributes to
promoting a practical use of the UNCODE procedure without resorting to
numerical computation. A modified procedure is proposed by using a correction
coefficient that modifies the standard (i.e., uncertainty-free) design value
on the basis of sample length and return period only. The procedure is robust
and parsimonious, as it does not require additional parameters with respect
to the traditional uncertainty-free analysis.
Simple equations to compute the correction term are provided for a number of
probability distributions commonly used to represent the flood frequency
curve. The UNCODE procedure, when coupled with this simple correction factor,
provides a robust way to manage the hydrologic uncertainty and to go beyond
the use of traditional safety factors. With all the other parameters being
equal, an increase in the sample length reduces the correction factor, and
thus the construction costs, while still keeping the same safety level
Drops on soft solids: Free energy and double transition of contact angles
The equilibrium shape of liquid drops on elastic substrates is determined by
minimising elastic and capillary free energies, focusing on thick
incompressible substrates. The problem is governed by three length scales: the
size of the drop , the molecular size , and the ratio of surface tension
to elastic modulus . We show that the contact angles undergo two
transitions upon changing the substrates from rigid to soft. The microscopic
wetting angles deviate from Young's law when , while the
apparent macroscopic angle only changes in the very soft limit . The elastic deformations are worked out in the simplifying case where the
solid surface energy is assumed constant. The total free energy turns out lower
on softer substrates, consistent with recent experiments
Unbalanced Langmuir kinetics affects TASEP dynamical transitions: mean-field theory
In a previous study we developed a mean-field theory of dynamical transitions
for the totally-asymmetric simple-exclusion process (TASEP) with open
boundaries and Langmuir kinetics, in the so-called balanced regime,
characterized by equal binding and unbinding rates. Here we show that simply
including the possibility of unbalanced rates gives rise to an unexpectedly
richer dynamical phase diagram. In particular, the current work predicts an
unusual type of dynamical transition, which exhibits certain similarities with
first-order phase transitions of equilibrium systems. We also point out that
different types of dynamical transition are accompanied by different structural
changes in the (mean-field) relaxation spectrum.Comment: 32 pages, 8 figure
A multi-purpose control and power electronic architecture for active magnetic actuators
This paper shows the results related with the
design and implementation of a multi-purpose electronic
architecture used to drive magnetic actuators by means of a
three-phase independent-legs module in place of the
commonly used H-bridge modules. The typical application
is the magnetic actuators drive used in active magnetic
bearings. The architecture is composed of a control unit
with a floating point Digital Signal Processor (DSP), a
power board with six independent phase legs and a carrier
board to interconnect them. When more than one module is
required by the application, the communication between
them is guaranteed by means of CAN bus interconnection.
The proposed system allows to drive two pairs of opposite
electromagnets, such as those typically used to control active
magnetic bearings. The study is motivated by the
opportunity of reducing the amount of power and control
electronic components resulting in a more straightforward,
efficient and cost reduction design
Comparison of contact parameters measured with two different friction rigs for nonlinear dynamic analysis
The accurate measurement of contact interface parameters is of great importance for nonlinear dynamic response computations since there is a lack of predictive capabilities for such input parameters. Several test rigs have been developed at different institutions, and a series of measurements published, but their reliability remains unknown due to a lack of direct comparisons. To somehow address this issue, a Round-Robin test campaign was performed including the high frequency friction rigs of Imperial College London and Politecnico di Torino. Comparable hysteresis loops were recorded on specimen pairs manufactured from the same batch of raw stainless steel, for a wide range of test conditions, including varying normal loads, sliding distances and nominal areas of contact. Measurements from the two rigs were compared to quantify the level of agreement between the two very different experimental setup, showing a reasonably good matching in the results, but also highlighting some differences. Results also demonstrated that loading conditions can strongly affect the contact parameters, and consequently their effect must be included in future nonlinear dynamic simulations for more reliable predictions
A Neutral and Stable Macrocyclic Mn(II) Complex for MRI Tumor Visualization
A stable and inert amphiphilic Mn(II) complex based on a bisamide derivative of 1,4-DO2A (DO2A=tetraazacyclododecane-1,4-diacetic acid) was synthesized and its H-1 NMR relaxometric behavior was investigated as a function of the magnetic field strength, pH and temperature. The interaction with human serum albumin (HSA) was also studied via relaxometry showing a good relaxivity enhancement at low field (at 1T and 298 K the relaxivity increases from 4.5 mM(-1) s(-1) of the Mn(II)-complex to 14.0 mM(-1) s(-1) of the complex-HSA supramolecular adduct). In vivo biodistribution and MRI studies highlighted a rapid and mixed renal/liver elimination without spleen accumulation from healthy mice and good contrast enhancing properties in a breast tumor murine model. A comparison with a clinically approved Gd(III) agent (GdBOPTA, Multihance (R)) underlined that the proposed Mn(II) contrast agent gave comparable tumor contrast enhancement up to 3 hours post-injection
Evaluation of the effects of hydroxyethyl starch (130/0.4) administration as a constant rate infusion on plasma colloid osmotic pressure in hypoabluminemic dogs
Vibrational Spectroscopy of Selected Natural Uranyl Vanadates
Raman spectroscopy has been used to study a selection of uranyl vanadate minerals including carnotite, curienite, francevillite, tyuyamunite and metatyuyamunite. The minerals are characterised by an intense band in the 800 to 824 cm-1 region, assigned to the ν1 symmetric stretching vibrations of the (UO2)2+ units. A second intense band is observed in the 965 to 985 cm-1 range and is attributed to the ν1 (VO3) symmetric stretching vibrations in the (V2O8) units. This band is split with a second component observed at around 963 cm-1. A band of very low intensity is observed around 948 cm-1 and is assigned to the ν3 antisymmetric stretching vibrations of the (VO3) units. Bands in the range 608-655 cm-1 may be attributed to molecular water librational modes or the stretching modes ○(V2O2) units. Bands in the range 573-583 cm-1 may be connected with the ○ (U-Oequatorial) vibrations or ○ (V2O2) units. Bands located in the range 467-539 cm-1 may be also attributed to the ○ (U-Oequatorial) units vibrations. The bending modes of the (VO3) units are observed in the 463 to 480 cm-1 range – there may be some coincidence with ○ (U-Oequatorial). The bending modes of the (V2O2) in the (V2O8) units are located in a series of bands around 407, 365 and 347 cm-1 (ν2). Two intense bands are observed in the 304 to 312 cm-1 range and 241 to 264 cm-1 range and are assigned to the doubly degenerate ν2 modes of the (UO2)2+ units. The study of the vibrational spectroscopy of uranyl vanadates is complicated by the overlap of bands from the (VO3) and (UO2)2+ units. Raman spectroscopy has proven most useful in assigning bands to these two units since Raman bands are sharp and well separated as compared with infrared bands. The uranyl vanadate minerals are often found as crystals on a host matrix and Raman spectroscopy enables their in-situ characterisation without sample preparation
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