Nonstationary westward translation of nonlinear frontal warm-core eddies

For the first time, an analytical theory and a very high-resolution, frontal numerical model, both based on the unsteady, nonlinear, reduced-gravity shallow water equations on a beta plane, have been used to investigate aspects of the migration of homogeneous surface, frontal warm-core eddies on a beta plane. Under the assumption that, initially, such vortices are surface circular anticyclones of paraboloidal shape and having both radial and azimuthal velocities that are linearly dependent on the radial coordinate (i.e., circular pulsons of the first order), approximate analytical expressions are found that describe the nonstationary trajectories of their centers of mass for an initial stage as well as for a mature stage of their westward migration. In particular, near-inertial oscillations are evident in the initial migration stage, whose amplitude linearly increases with time, as a result of the unbalanced vortex initial state on a beta plane. Such an initial amplification of the vortex oscillations is actually found in the first stage of the evolution of warm-core frontal eddies simulated numerically by means of a frontal numerical model initialized using the shape and velocity fields of circular pulsons of the first order. In the numerical simulations, this stage is followed by an adjusted, complex nonstationary state characterized by a noticeable asymmetry in the meridional component of the vortex's horizontal pressure gradient, which develops to compensate for the variations of the Coriolis parameter with latitude. Accordingly, the location of the simulated vortex's maximum depth is always found poleward of the location of the simulated vortex's center of mass. Moreover, during the adjusted stage, near-inertial oscillations emerge that largely deviate from the exactly inertial ones characterizing analytical circular pulsons: a superinertial and a subinertial oscillation in fact appear, and their frequency difference is found to be an increasing function of latitude. A comparison between vortex westward drifts simulated numerically at different latitudes for different vortex radii and pulsation strengths and the corresponding drifts obtained using existing formulas shows that, initially, the simulated vortex drifts correspond to the fastest predicted ones in many realistic cases. As time elapses, however, the development of a beta-adjusted vortex structure, together with the effects of numerical dissipation, tend to slow down the simulated vortex drift

Nonlinear transverse oscillations of a geostrophic front

A planar problem of nonlinear transverse oscillations of the surface (warm) front of a finite width is considered within the framework of a reduced-gravity model of the ocean. The source of oscillations is the departure of the front from its geostrophic equilibrium. When the current velocity is linear in the horizontal coordinate and the front's depth is quadratic in this coordinate, the problem is reduced to a system of four ordinary differential equations in time. As a result, the solution is obtained in a weakly nonlinear approximation and strongly nonlinear oscillations of the front are studied by numerically solving this system of equations by the Runge-Kutta method. The front's oscillations are always superinertial. Nonlinearity can lead to a decrease or increase in the oscillation frequency in comparison with the linear case. The oscillations are most intense when the current velocity is disturbed in the direction of the front's axis. A weakly nonlinear solution of the second order describes the oscillations very accurately even for initial velocity disturbances reaching 50% of its geostrophic value. An increase in the background-current shear leads to the damping of oscillations of the front's boundary. The amplitude of oscillations of the current velocity increases as the intensity of disturbances increases, and it is relatively small if background-current shears are small or large

Frictionally decaying frontal warm-core eddies

Purpose. The dynamics of nonstationary, nonlinear, axisymmetric, warm-core geophysical surface frontal vortices affected by Rayleigh friction is investigated semi-analytically using the nonlinear, nonstationary reduced-gravity shallow-water equations. The scope is to enlarge the number of known (semi)analytical solutions of nonstationary, nonlinear problems referring to geophysical problems and even to pave the way to their extension to broader geometries and/or velocity fields. Methods and Results. The used method to obtain the solutions is based on the decomposition of the original equations in a part expressing their prescribed spatial structure, so that they can be trans-formed into ordinary differential equations depending on time only. Based on that analytical proce-dure, the solutions are then found numerically. In this frame, it is found that vortices characterized by linear distributions of their radial velocity and arbitrary structures of their section and azimuthal velocity can be described exactly by a set of nonstationary, nonlinear coupled ordinary differential equa-tions. The first-order problem (i. e., that describing vortices characterized by a linear azimuthal velocity field and a quadratic section) consists of a system of 4 differential equations, and each further order introduces in the system three additional ordinary differential equations and two algebraic equa-tions. In order to illustrate the behavior of the nonstationary decaying vortices and to put them in the context of observed dynamics in the World Ocean, the system's solution for the first-order and for the second-order problem is then obtained numerically using a Runge-Kutta method. The solutions demonstrate that inertial oscillations and an exponential attenuation dominate the vortex dynamics: expansions and shallowings, contractions and deepenings alternate during an exact inertial period while the vortex decays. The dependence of the vortex dissipation rate on its initial radius is found to be non-monotonic: it is higher for small and large radii. The possibility of solving (semi)analytically complex systems of differential equations representing observed physical phenomena is rare and very valuable. Conclusions. Our analysis adds realism to previous theoretical investigations on mesoscale vortices, represents an ideal tool for testing the accuracy of numerical models in simulating nonlinear, nonsta-tionary frictional frontal phenomena in a rotating ocean, and paves the way to further extensions of (semi-) analytical solutions of hydrodynamical geophysical problems to more arbitrary forms and more complex density stratifications

Detection of Anomalous Microwave Emission in the Pleiades Reflection Nebula with WMAP and the COSMOSOMAS Experiment

We present evidence for anomalous microwave emission (AME) in the Pleiades reflection nebula, using data from the seven-year release of the Wilkinson Microwave Anisotropy Probe (WMAP) and from the COSMOSOMAS experiment. The flux integrated in a 1-degree radius around R.A.=56.24^{\circ}, Dec.=23.78^{\circ} (J2000) is 2.15 +/- 0.12 Jy at 22.8 GHz, where AME is dominant. COSMOSOMAS data show no significant emission, but allow to set upper limits of 0.94 and 1.58 Jy (99.7% C.L.) respectively at 10.9 and 14.7 GHz, which are crucial to pin down the AME spectrum at these frequencies, and to discard any other emission mechanisms which could have an important contribution to the signal detected at 22.8 GHz. We estimate the expected level of free-free emission from an extinction-corrected H-alpha template, while the thermal dust emission is characterized from infrared DIRBE data and extrapolated to microwave frequencies. When we deduct the contribution from these two components at 22.8 GHz the residual flux, associated with AME, is 2.12 +/- 0.12 Jy (17.7-sigma). The spectral energy distribution from 10 to 60 GHz can be accurately fitted with a model of electric dipole emission from small spinning dust grains distributed in two separated phases of molecular and atomic gas, respectively. The dust emissivity, calculated by correlating the 22.8 GHz data with 100-micron data, is found to be 4.36+/-0.17 muK/MJy/sr, a value that is rather low compared with typical values in dust clouds. The physical properties of the Pleiades nebula indicate that this is indeed a much less opaque object than others were AME has usually been detected. This fact, together with the broad knowledge of the stellar content of this region, provides an excellent testbed for AME characterization in physical conditions different from those generally explored up to now.Comment: Accepted for publication in ApJ. 12 pages, 8 figure

Is the Atlantic a Source for Decadal Predictability of Sea-Level Rise in Venice?

Sea-level rise is one of the most critical consequences of global warming, with potentially vast impacts on coastal environments and societies. Sea-level changes are spatially and temporally heterogeneous on multiannual-to-multidecadal timescales. Here, we demonstrate that the observed rate of winter sea-level rise in the Italian city of Venice contains significant multidecadal fluctuations, including interdecadal periods of near-zero trend. Previous literature established a connection between the local sea-level trend in Venice and over the broad subpolar and eastern North Atlantic. We demonstrate that for multidecadal variations in sea-level trend such connection holds only since the mid-20th Century. Such multidecadal sea-level fluctuations relate to North Atlantic sea-surface temperature changes described by the Atlantic multidecadal variability, or AMV. The link is explained by combined effect of AMV-linked steric variations in the North Atlantic propagating in the Mediterranean Sea, and large-scale atmospheric circulation anomalies over the North Atlantic with a local effect on sea level in Venice. We discuss the implications of such variability for near-term predictability of winter sea-level changes in Venice. Combining available sea-level projections for Venice with a scenario of imminent AMV cooling yields a slowdown in the rate of sea-level rise in Venice, with the possibility of mean values remaining even roughly constant in the next two decades as AMV effects contrast the expected long-term sea-level rise. Acknowledging, understanding, and communicating this multidecadal variability in local sea-level rise is crucial for management and protection of this world-class historical site.Plain Language Summary Environmental and socioeconomic impacts of sea-level rise are one of the major concerns of global warming. Here, we consider the case of the Italian city of Venice, one of the iconic locations for the potentially dramatic effects of sea-level rise. We show that the sea-level evolution in Venice during the past similar to 150 years contains strong multidecadal fluctuations, so that periods of more than two decades when there is little or no trend occurred even in the recent past. We link these fluctuations with sea-level and climatic variations in the North Atlantic. In particular, we focus on the phenomenon known as Atlantic multidecadal variability, or AMV, which describes the alternation over multidecadal periods of warm and cold phases of the North Atlantic surface. Our results indicate that warm AMV phases are linked to faster sea-level rise in Venice and vice versa. Accordingly, we build sea-level rise scenarios for Venice until 2035 by considering an imminent AMV cooling as suggested by recent studies. The scenarios yield a temporary slowdown of sea-level rise as the AMV contrasts the effects of global warming. This sea-level variability can strongly impact on the management of protective measures against flooding currently operative in Venice

Design of Relaxation Digital-to-Analog Converters for Internet of Things Applications in 40nm CMOS

A 10-bit-400kS/s and a 10-bit-2MS/s Relaxation Digital to Analog Converters (ReDAC) in 40nm are presented in this paper. The two ReDACs operate from a 600mV power supply, occupy a silicon area of less than 1,000um^2. The first/second DAC achieve a maximum INL of 0.33/0.72 LSB and a maximum DNL of 0.2/1.27 LSB and 9.9/9.4 ENOB based on post-layout simulations. The average energy per conversion is less than 1.1/0.73pJ, corresponding to a FOM of 1.1/1.08 fJ/(conv. step), which make them well suited to Internet of Things (IoT) applications. (PDF) Design of Relaxation Digital-to-Analog Converters for Internet of Things Applications in 40nm CMOS. Available from: https://www.researchgate.net/publication/336552301_Design_of_Relaxation_Digital-to-Analog_Converters_for_Internet_of_Things_Applications_in_40nm_CMOS [accessed Nov 16 2019]

FPGA-Based Relaxation D/A Converters With Parasitics-Induced Error Suppression and Digital Self-Calibration

In this paper, the implementation on a Field Programmable Gate Array (FPGA) of Relaxation Digital to Analog Converters (ReDACs), which take advantage of the impulse response of a first-order RC network to generate and combine binary weighted voltages, is addressed. For this purpose, the dominant ReDAC nonlinearity limitation related to the parasitics of the RC network is analyzed and a simple and robust technique for its effective suppression is proposed. Moreover, a ReDAC foreground digital calibration strategy suitable to FPGA implementation is introduced to tune the clock frequency of the converter, as requested for ReDAC operation. The novel error suppression technique and calibration strategy are finally implemented on a 13-bit, 514,S/s prototype (ReDAC1) and on a 11-bit, 10.5,kS/s prototype (ReDAC2), which are experimentally characterized under static and dynamic conditions. Measured results on ReDAC1 (ReDAC2) reveal 1.68,LSB (1.53,LSB) maximum INL, 1.54,LSB (1.0,LSB) maximum DNL, 76.4,dB (67.9,dB) THD, 79.7,dB (71.4,dB) SFDR and 71.3,dB (63.3,dB) SNDR, corresponding to 11.6 (10.2) effective bits (ENOB)

Establishing health-based biological exposure limits for pesticides : A proof of principle study using mancozeb

Pesticides represent an economical, labor-saving, and efficient tool for pest management, but their intrinsic toxic properties may endanger workers and the general population. Risk assessment is necessary, and biological monitoring represents a potentially valuable tool. Several international agencies propose biological exposure indices (BEI), especially for substances which are commonly absorbed through the skin. Biological monitoring for pesticide exposure and risk assessment seems a natural choice, but biological exposure limits (BEL) for pesticides are lacking. This study aims at establishing equivalent biological exposure limits (EBEL) for pesticides using real-life field data and the Acceptable Operator Exposure Level (AOEL) of mancozeb as the reference. This study included a group of 16 vineyard pesticide applicators from Northern Italy, a subgroup of a more extensive study of 28 applicators. Their exposure was estimated using \u201cpatch\u201d and \u201chand-wash\u201d methodologies, together with biological monitoring of free ethylene-bis-thiourea (ETU) excretion in 24-h pre- and post-exposure urine samples. Modeling was done using univariate linear regression with ETU excretion as the dependent variable and the estimated absorbed dose as the independent variable. The median skin deposition of mancozeb in our study population was 125 \u3bcg, leading to a median absorbed dose of 0.9 \u3bcg/kg. The median post-exposure ETU excretion was 3.7 \u3bcg. The modeled EBEL for mancozeb was 148 \u3bcg of free ETU or 697 \u3bcg of total ETU, accounting for around 75% of the maximum theoretical excretion based on a mass balance model. Although preliminary and based on a small population of low-exposed workers, our results demonstrate a procedure to develop strongly needed biological exposure limits for pesticides

Model predictive Direct Flux Vector Control of multi three-phase induction motor drives

A model predictive control scheme for multiphase induction machines, configured as multi three-phase structures, is proposed in this paper. The predictive algorithm uses a Direct Flux Vector Control scheme based on a multi three-phase approach, where each three-phase winding set is independently controlled. In this way, the fault tolerant behavior of the drive system is improved. The proposed solution has been tested with a multi-modular power converter feeding a six-phase asymmetrical induction machine (10kW, 6000 rpm). Complete details about the predictive control scheme and adopted flux observer are included. The experimental validation in both generation and motoring mode is reported, including post open-winding fault operations. The experimental results demonstrate the feasibility of the proposed drive solution