5,272 research outputs found
Linear Theory of Electron-Plasma Waves at Arbitrary Collisionality
The dynamics of electron-plasma waves are described at arbitrary
collisionality by considering the full Coulomb collision operator. The
description is based on a Hermite-Laguerre decomposition of the velocity
dependence of the electron distribution function. The damping rate, frequency,
and eigenmode spectrum of electron-plasma waves are found as functions of the
collision frequency and wavelength. A comparison is made between the
collisionless Landau damping limit, the Lenard-Bernstein and Dougherty
collision operators, and the electron-ion collision operator, finding large
deviations in the damping rates and eigenmode spectra. A purely damped entropy
mode, characteristic of a plasma where pitch-angle scattering effects are
dominant with respect to collisionless effects, is shown to emerge numerically,
and its dispersion relation is analytically derived. It is shown that such a
mode is absent when simplified collision operators are used, and that
like-particle collisions strongly influence the damping rate of the entropy
mode.Comment: 23 pages, 10 figures, accepted for publication on Journal of Plasma
Physic
Four-dimensional drift-kinetic model for scrape-off layer plasmas
A four-dimensional plasma model able to describe the scrape-off layer region
of tokamak devices at arbitrary collisionality is derived in the drift-reduced
limit. The basis of the model is provided by a drift-kinetic equation that
retains the full non-linear Coulomb collision operator and describes
arbitrarily far from equilibrium distribution functions. By expanding the
dependence of distribution function over the perpendicular velocity in a
Laguerre polynomial basis and integrating over the perpendicular velocity, a
set of four-dimensional moment equations for the expansion coefficients of the
distribution function is obtained. The Coulomb collision operator, as well as
Poisson's equation, are evaluated explicitly in terms of perpendicular velocity
moments of the distribution function.Comment: 12 page
Three-dimensional curvature homogeneous hypersurfaces
summary:This paper is motivated by the open problem whether a three-dimensional curvature homogeneous hypersurface of a real space form is locally homogeneous or not. We give some partial positive answers
Direct radiative effects by anthropogenic particles at a polluted site: Rome (Italy)
The direct radiative effect (DRE) by all (anthropogenic plus natural) and anthropogenic aerosols is calculated at the solar (0.3–4 μm) and infrared (4–200 μm) spectral range to better address the annual cycle of the anthropogenic
aerosol impact at a site (Rome, Italy) significantly affected by pollution. Aerosol optical and microphysical properties from 2003 AERONET Sun/sky-photometer
measurements and solar surface albedos based on MODIS satellite sensor data constitute the necessary input to radiative transfer simulations. Clear- and all-sky
conditions are investigated by adopting ISCCP monthly products for high-, mid-, and low-cloud cover. It is shown that monthly mean values of aerosol optical depths by anthropogenic particles (AODa) are on average more than 50% of the corresponding all-aerosol-optical-depth (AOD) monthly means. In particular, the AODa/AOD ratio that varies within the (0.51–0.83) on autumn-winter (AW,
October-March), varies within the (0.50–0.71) range on spring-summer (SS, April-September) as a consequence of the larger contribution of natural particles on SS. The surface (sfc), all-sky DRE by anthropogenic particles that is negative all year round at solar wavelengths, represents on average 60% and 51% of the all-sky sfc-DRE by all aerosols
on AW and SS, respectively. The all-sky atmospheric forcing by anthropogenic particles (AFa) that is positive all year round, is little dependent on seasons: it varies within the (1.0–4.1)W/m2 and (2.0–4.2)W/m2 range on AW and SS, respectively. Conversely, the all-sky AF by all aerosols is characterized by a marked seasonality. As a consequence, the atmospheric forcing by anthropogenic particles that on average is 50% of the AF value on AW, decreases down to 36% of the AF value on SS. Infrared aerosol DREs that are positive all year round are significantly smaller than the corresponding absolute values of solar DREs. Clouds decrease on average ToA- and sfc-DRE absolute values by anthropogenic particles of 36% and 23%, respectively and are quite responsible of the seasonal dependence of aerosol forcing efficiencies by all and anthropogenic aerosols
Do horizontal relationships matter to production and operations managers?
This paper shifts the focus of production, operations and supply chain management business relationships from the vertical to the horizontal side and calls for more research on this issue. The main intent is to provide managerially oriented arguments regarding the linkages between the achievement of operations-related goals and decisions related to horizontal business relationships. Specifically, we address the following research question: Does a linkage exist between production and operations objectives and the decisions a company makes about horizontal agreements, particularly horizontal governance mode choice? To answer this research question, we develop literature-based hypotheses and collect data from 4316 agreements of mergers and acquisitions and alliances and joint venture announced and completed between 2000 and 2010 by 88 of the first 100-ranked members of the Fortune 500 in the year 2000. We then test the hypotheses through a binary logistic regression model. This study brings interesting results and findings in terms of how and why production management considerations should play a crucial role in the type of strategic decisions that are usually reserved for finance and strategy managers. Operations managers should be fully involved in such decisions if they are to be well acquainted about how their choices impact on operational objectives
Vertically resolved aerosol properties by multi-wavelength lidar measurements
An approach based on the graphical method of Gobbi and co-authors (2007) is
introduced to estimate the dependence on altitude of the aerosol fine mode
radius (<i>R</i><sub>f</sub>) and of the fine mode contribution (η) to the
aerosol optical thickness (AOT) from three-wavelength lidar measurements. The
graphical method of Gobbi and co-authors (2007) was applied to AERONET
(AErosol RObotic NETwork) spectral extinction observations and relies on the
combined analysis of the Ã…ngstrom exponent (<i>Ã¥</i>) and its
spectral curvature Δ<i>å</i>. Lidar measurements at 355, 532 and
1064 nm were used in this study to retrieve the vertical profiles of
<i>å</i> and Δ<i>å</i> and to estimate the dependence on
altitude of <i>R</i><sub>f</sub> and η(532 nm) from the
<i>å</i>–Δ<i>å</i> combined analysis. Lidar measurements
were performed at the Department of Mathematics and Physics of the
Universita' del Salento, in south-eastern Italy. Aerosol from continental
Europe, the Atlantic, northern Africa, and the Mediterranean Sea are often
advected over south-eastern Italy and as a consequence, mixed advection
patterns leading to aerosol properties varying with altitude are dominant.
The proposed approach was applied to ten measurement days to demonstrate its
feasibility in different aerosol load conditions. The selected days were
characterized by AOTs spanning the 0.26–0.67, 0.15–0.39, and 0.04–0.27
range at 355, 532, and 1064 nm, respectively. Mean lidar ratios varied
within the 31–83, 32–84, and 11–47 sr range at 355, 532, and 1064 nm,
respectively, for the high variability of the aerosol optical and
microphysical properties. <i>Ã¥</i> values calculated from lidar
extinction profiles at 355 and 1064 nm ranged between 0.1 and 2.5 with a
mean value ± 1 standard deviation equal to 1.3 ± 0.7.
Δ<i>å</i> varied within the −0.1–1 range with mean value
equal to 0.25 ± 0.43. <i>R</i><sub>f</sub> and η(532 nm) values
spanning the 0.05–0.3 μm and the 0.3–0.99 range,
respectively, were associated with the <i>Ã¥</i>–Δ<i>Ã¥</i> data points. <i>R</i><sub>f</sub> and η values showed no
dependence on the altitude. 60% of the data points were in the Δ<i>Ã¥</i>–<i>Ã¥</i> space delimited by the η and
<i>R</i><sub>f</sub> curves varying within 0.80–0.99 and 0.05–0.15 μm,
respectively, for the dominance of fine-mode particles in driving the AOT
over south-eastern Italy. Vertical profiles of the linear particle
depolarization ratio retrieved from lidar measurements, aerosol products from
AERONET sun photometer measurements collocated in space and time, analytical
back trajectories, satellite true colour images, and dust concentrations from
the BSC–DREAM (Barcelona Super Computing Center-Dust REgional Atmospheric
Model) model were used to demonstrate the robustness of the proposed method
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Strengthening multi-stakeholder cooperation in the international investment regime: The Brazilian model
The rule of law and dispute avoidance and settlement may not be enough to turn FDI into a means to the realization of the SDGs. Multi-stakeholder dialogue and cooperation should also be a central aspect of any institutional design. In this regard, the Brazilian model, at least in theory, scores better than most existing treaties and reform proposals
Kendall's tau estimator for bivariate zero-inflated count data
This paper extends the work of Pimentel et al. (2015), presenting an estimator of Kendall's Ï„ for bivariate zero-inflated count data. We provide achievable bounds of our proposed estimator and suggest how to estimate them, thereby making the estimator useful in practice.</p
Development of a self-powered piezo-resistive smart insole equipped with low-power BLE connectivity for remote gait monitoring
The evolution of low power electronics and the availability of new smart materials are opening new frontiers to develop wearable systems for medical applications, lifestyle monitoring, and performance detection. This paper presents the development and realization of a novel smart insole for monitoring the plantar pressure distribution and gait parameters; indeed, it includes a piezoresistive sensing matrix based on a Velostat layer for transducing applied pressure into an electric signal. At first, an accurate and complete characterization of Velostat-based pressure sensors is reported as a function of sizes, support material, and pressure trend. The realization and testing of a low-cost and reliable piezoresistive sensing matrix based on a sandwich structure are discussed. This last is interfaced with a low power conditioning and processing section based on an Arduino Lilypad board and an analog multiplexer for acquiring the pressure data. The insole includes a 3- axis capacitive accelerometer for detecting the gait parameters (swing time and stance phase time) featuring the walking. A Bluetooth Low Energy (BLE) 5.0 module is included for transmitting in real-time the acquired data toward a PC, tablet or smartphone, for displaying and processing them using a custom Processing® application. Moreover, the smart insole is equipped with a piezoelectric harvesting section for scavenging energy from walking. The onfield tests indicate that for a walking speed higher than 1 ms−1, the device’s power requirements (i.e., P = 5.84 mW ) was fulfilled. However, more than 9 days of autonomy are guaranteed by the integrated 380-mAh Lipo battery in the total absence of energy contributions from the harvesting section
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