Emissive Langmuir Probes in the Strong Emission Regime for the Determination of the Plasma Properties

The determination of the plasma potential Vpl of unmagnetized plasmas by using the floating potential of emissive Langmuir probes operated in the strong emission regime is investigated. The experiments evidence that, for most cases, the electron thermionic emission is orders of magnitude larger than the plasma thermal electron current. The temperature-dependent floating potentials of negatively biased Vpmenor queVpl emissive probes are in agreement with the predictions of a simple phenomenological model that considers, in addition to the plasma electrons, an ad-ditional electron group that contributes to the probe current. The latter would be constituted by a fraction of the repelled electron thermionic current, which might return back to the probe with a different energy spectrum. Its origin would be a plasma potential well formed in the plasma sheath around the probe, acting as a virtual cathode or by collisions and electron thermalization pro-cesses. These results suggest that, for probe bias voltages close to the plasma potential Vp?Vpl, two electron populations coexist, i.e., the electrons from the plasma with temperatureTeand a large group of returned thermionic electrons. These results question the theoretical possibility of measuring the electron temperature by using emissive probes biased to potentials Vp about lower equal than ?Vpl.

New device for continuous-wave THz emission: large area emitter

We discuss two different approaches to overcome the power limitations of CW THz generation imposed to conventional photomixers. The increase in power achievable by using arrays of AEs is studied. Then ?large area emitters? are proposed as an alternate approach to overcome the power limitations. In this antenna-free new scheme of photomixing, the THz radiation originates directly from the acceleration of photo-induced charge carriers generated within a large semiconductor area. The quasi-continuous distribution of emitting elements corresponds to a high-density array and results in particularly favorable radiation profiles.

Enhanced radon emission in natural CO2 flows in Campo de Calatrava region (central Spain)

Activity of radon gas in natural soils is commonly low (in the order of few thousands of Bq��m-3) due to the fast decay (half-life= 3.8 days in the case of 222Rn) that prevents accumulation in soil pores. Exceptionally, high Rn soil activity (up to 430 KBq��m-3) is found around point sources of deep CO2 fluxes. These fluxes allow the transport of trace gases (including Rn) to long distances in the geosphere leading to a potential hazard as Rn accumulation in buildings. CO2 degassing is common in active or ancient volcanic fields and occurs as free gas fluxes or dissolved in groundwater. In this work, the occurrence of Rnbearing, CO2 fluxes from the Campo de Calatrava region in Central Spain has been studied in order to determine their (1) magnitude, (2) migration paths and (3) potential impact on the environment, and (4) methodologies to best detection and measurement.

Crop rotation and residues influence N2O emission and N efficiency rather than tillage under a rainfed Mediterranean agroecosystem

Conservation tillage and crop rotation have spread during the last decades because promotes several positive effects (increase of soil organic content, reduction of soil erosion, and enhancement of carbon sequestration) (Six et al., 2004). However, these benefits could be partly counterbalanced by negative effects on the release of nitrous oxide (N2O) (Linn and Doran, 1984). There is a lack of data on long-term tillage system study, particularly in Mediterranean agro-ecosystems. The aim of this study was to evaluate the effects of long-term (>17 year) tillage systems (no tillage (NT), minimum tillage (MT) and conventional tillage (CT)); and crop rotation (wheat (W)-vetch (V)-barley (B)) versus wheat monoculture (M) on N2O emissions. Additionally, Yield-scaled N2O emissions (YSNE) and N uptake efficiency (NUpE) were assessed for each treatment.

Influence of Tillage and Liming on N2O emission from a rainfed crop

Nitrous oxide (N2O) is the main greenhouse gas (GHG) produced by agricultural soils due to microbial processes. The application of N fertilizers is associated with an increase of N2O losses. However, it is possible to mitigate these emissions by the introduction of adequate management practices (Snyder et al., 2009). Soil conservation practices (i.e.no tillage, NT) have recently become widespread because they promote several positive effects (increases in soil organic carbonand soil fertility, reduction of soil erosion, etc). In terms of GHG emissions, there is no consensus in the literature on the effects of tillage on N2O. Several studies found that NT can produce greater (Baggs et al., 2003), lower (Malhi et al., 2006) or similar (Grandey et al., 2006) N2O emissions compared to traditional tillage (TT). This large uncertainty is associated with the duration of tillage practices and climatic variability. Liming is widely use to solve problems of soil acidity (Al toxicity, yield penalties, etc). Several studies show a decrease in N2O emissions with liming (Barton et al., 2013) whereas no significant effects or increases were observed in others (Galbally et al., 2010). The aim of this work was to evaluate the effects of tillage (NT vs TT) and liming application or not of Ca-amendment) on N2O emissions from an acid soil during a rainfed crop.

Ensayo no destructivo de soldaduras en pernos conectores mediante inspecci��n ac��stica = Non-destructive test of welding headed studs through acoustic emission

Los pernos conectores aportan m��ltiples ventajas de uso, entre las que se encuentra el elevado margen de seguridad que ofrecen sus soldaduras ejecutadas mediante arco el��ctrico. Estas soldaduras, aunque ampliamente fiables, son dif��cilmente comprobadas mediante ensayos no destructivos. Aparte de la inspecci��n visual, que aporta gran informaci��n sobre la calidad de ejecuci��n de la soldadura, el resto de ensayos no destructivos (l��quidos penetrantes, part��culas magn��ticas, ultrasonidos, radiograf��as, etc.) resultan inviables en estos elementos. Por otro lado, los ensayos ac��sticos de piezas met��licas han existido siempre. Su comprobaci��n se basaba en el an��lisis por medio de ��un o��do fino�� del sonido resultante tras ser golpeado el elemento a evaluar. Con estas premisas se plantea el presente estudio de inspecci��n de las soldaduras en pernos conectores mediante su espectro ac��stico. Anal��ticamente, la investigaci��n se ha centrado en el c��lculo inform��tico de los primeros modos propios de vibraci��n mediante elementos finitos. Se han modelizado diferentes grados de penetraci��n de la soldadura mediante la modificaci��n de las condiciones de contorno. Se ha observado que variando el n��mero de movimientos coaccionados en los nodos pertenecientes a la soldadura se produce una reducci��n en su frecuencia de vibraci��n.

A methodology to compute emission projections from road transport (EmiTRANS)

Atmospheric emissions from road transport have increased all around the world during the last decades more rapidly than from other pollution sources. For instance, they contribute to more than 25% of total CO, CO2, NOx, and fine particle emissions in most of the European countries. This situation shows the importance of road transport when complying with emission ceilings and air quality standards applied to these pollutants. This paper presents a modelling system to perform atmospheric emission projections (simultaneously both air quality pollutants and greenhouse gases) from road transport including the development of a tailored software tool (EmiTRANS) as a planning tool. The methodology has been developed with two purposes: 1) to obtain outputs used as inputs to the COPERT4 software to calculate emission projections and 2) to summarize outputs for policy making evaluating the effect of emission abatement measures for a vehicle fleet. This methodology has been applied to the calculation of emission projections in Spain up to 2020 under several scenarios, including a sensitivity analysis useful for a better interpretation and confidence building on the results. This case study demonstrates the EmiTRANS applicability to a country, and points out the need for combining both technical and non-technical measures (such as behavioural changes or demand management) to reduce emissions, indirectly improving air quality and contributing to mitigate climate change.

Road Dust Emission Sources and Assessment of Street Washing Effect

Although previous studies report on the effect of street washing on ambient particulate matter levels, there is a lack of studies investigating the results of street washing on the emission strength of road dust. A sampling campaign was conducted in Madrid urban area during July 2009 where road dust samples were collected in two sites, namely Reference site (where the road surface was not washed) and Pelayo site (where street washing was performed daily during night). Following the chemical characterization of the road dust particles the emission sources were resolved by means of Positive Matrix Factorization, PMF (Multilinear Engine scripting) and the mass contribution of each source was calculated for the two sites. Mineral dust, brake wear, tire wear, carbonaceous emissions and construction dust were the main sources of road dust with mineral and construction dust being the major contributors to inhalable road dust load. To evaluate the effectiveness of street washing on the emission sources, the sources mass contributions between the two sites were compared. Although brake wear and tire wear had lower concentrations at the site where street washing was performed, these mass differences were not statistically significant and the temporal variation did not show the expected build-up after dust removal. It was concluded that the washing activities resulted merely in a road dust moistening, without effective removal and that mobilization of particles took place in a few hours between washing and sampling. The results also indicated that it is worth paying attention to the dust dispersed from the construction sites as they affect the emission strength in nearby streets.

Animal feeding strategies to reduce N2O and NH3 emission from surface-applied pig slurry to a grassland soil.

It is estimated that N losses from fertilized crops range between 50-70%, depending on management practices, climate and soil conditions. Ammonia (NH3) emissions following land application of animal manures give rise to a significant proportion of the total NH3 emissions from agricultural sources.

Ammonia and Greenhouse Gases Emission from Slurry Storage with impermeable Cover and Landspreading of Cattle Slurry

Intensive farm systems handle large volume of livestock wastes, resulting in adverse environmental effects, such as gaseous losses into the atmosphere in form of ammonia (NH3) and greenhouse gases (GHG), i.e. methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O). In this study, the manure management continuum of slurry storage with impermeable cover and following cattle slurry band spreading and incorporation to soil was assessed for NH3 and GHG emissions. The experiment was conducted in an outdoor covered storage (flexible bag system) (study I), which collected the slurry produced in 7 dairy cattle farms (2,000 m3 slurry) during 12 days in the northern Spain.

Comparison of micrometeorological techinques for estimating ammonia emission from covered slurry storage and land spreading of cattle slurry

The micrometeorological mass-balance integrated horizontal flux (IHF) technique has been commonly employed for measuring ammonia (NH3) emissions inon-field experiments. However, the inverse-dispersion modeling technique, such as the backward Lagrangian stochastic (bLS) modeling approach, is currently highlighted as offering flexibility in plot design and requiring a minimum number of samplers (Ro et al., 2013). The objective of this study was to make a comparison between the bLS technique with the IHF technique for estimating NH3 emission from flexible bag storage and following landspreading of dairy cattle slurry. Moreover, considering that NH3 emission in storage could have been non uniform, the effect on bLS estimates of a single point and multiple downwind concentration measurements was tested, as proposed by Sanz et al. (2010).

Development and assessment of traffic-related emission abatement measures for the Madrid city (Spain) through the WRF-SMOKE-CMAQ modelling system

The achievement of the limit values established in the European legislation pose an important handicap for large urban areas with intense road traffic, such as Madrid (Spain). Despite permanent measures included in air quality plans it is important to assess additional measures that may be temporally applied under unfavourable conditions. This paper reports on the simulation of different traffic restriction strategies in Madrid for high-pollution episodes.

Low Work-Function Thermionic Emission and Orbital-Motion-Limited Ion Collection at Bare-Tether Cathodic Contact

Una amarra electrodin��mica (electrodynamic tether) opera sobre principios electromagn��ticos intercambiando momento con la magnetosfera planetaria e interactuando con su ionosfera. Es un subsistema pasivo fiable para desorbitar etapas de cohetes agotadas y sat��lites al final de su misi��n, mitigando el crecimiento de la basura espacial. Una amarra sin aislamiento captura electrones del plasma ambiente a lo largo de su segmento polarizado positivamente, el cual puede alcanzar varios kil��metros de longitud, mientras que emite electrones de vuelta al plasma mediante un contactor de plasma activo de baja impedancia en su extremo cat��dico, tal como un c��todo hueco (hollow cathode). En ausencia de un contactor cat��dico activo, la corriente que circula por una amarra desnuda en ��rbita es nula en ambos extremos de la amarra y se dice que ��sta est�� flotando el��ctricamente. Para emisi��n termoi��nica despreciable y captura de corriente en condiciones limitadas por movimiento orbital (orbital-motion-limited, OML), el cociente entre las longitudes de los segmentos an��dico y cat��dico es muy peque��o debido a la disparidad de masas entre iones y electrones. Tal modo de operaci��n resulta en una corriente media y fuerza de Lorentz bajas en la amarra, la cual es poco eficiente como dispositivo para desorbitar. El electride C12A7 : e���, que podr��a presentar una funci��n de trabajo (work function) tan baja como W = 0.6 eV y un comportamiento estable a temperaturas relativamente altas, ha sido propuesto como recubrimiento para amarras desnudas. La emisi��n termoi��nica a lo largo de un segmento as�� recubierto y bajo el calentamiento de la operaci��n espacial, puede ser m��s eficiente que la captura i��nica. En el modo m��s simple de fuerza de frenado, podr��a eliminar la necesidad de un contactor cat��dico activo y su correspondientes requisitos de alimentaci��n de gas y subsistema de potencia, lo que resultar��a en un sistema real de amarra ���sin combustible���. Con este recubrimiento de bajo W, cada segmento elemental del segmento cat��dico de una amarra desnuda de kil��metros de longitud emitir��a corriente como si fuese parte de una sonda cil��ndrica, caliente y uniformemente polarizada al potencial local de la amarra. La operaci��n es similar a la de una sonda de Langmuir 2D tanto en los segmentos cat��dico como an��dico. Sin embargo, en presencia de emisi��n, los electrones emitidos resultan en carga espacial (space charge) negativa, la cual reduce el campo el��ctrico que los acelera hacia fuera, o incluso puede desacelerarlos y hacerlos volver a la sonda. Se forma una doble vainas (double sheath) estable con electrones emitidos desde la sonda e iones provenientes del plasma ambiente. La densidad de corriente termoi��nica, variando a lo largo del segmento cat��dico, podr��a seguir dos leyes distintas bajo diferentes condiciones: (i) la ley de corriente limitada por la carga espacial (space-charge-limited, SCL) o (ii) la ley de Richardson-Dushman (RDS). Se presenta un estudio preliminar sobre la corriente SCL frente a una sonda emisora usando la teor��a de vainas (sheath) formada por la captura i��nica en condiciones OML, y la corriente electr��nica SCL entre los electrodos cil��ndricos seg��n Langmuir. El modelo, que incluye efectos ��hmicos y el efecto de transici��n de emisi��n SCL a emisi��n RDS, proporciona los perfiles de corriente y potencial a lo largo de la longitud completa de la amarra. El an��lisis muestra que en el modo m��s simple de fuerza de frenado, bajo condiciones orbitales y de amarras t��picas, la emisi��n termoi��nica proporciona un contacto cat��dico eficiente y resulta en una secci��n cat��dica peque��a. En el an��lisis anterior, tanto la transici��n de emisi��n SCL a RD como la propia ley de emisi��n SCL consiste en un modelo muy simplificado. Por ello, a continuaci��n se ha estudiado con detalle la soluci��n de vaina estacionaria de una sonda con emisi��n termoi��nica polarizada negativamente respecto a un plasma isotr��pico, no colisional y sin campo magn��tico. La existencia de posibles part��culas atrapadas ha sido ignorada y el estudio incluye tanto un estudio semi-anal��tico mediante t��cnica asint��ticas como soluciones num��ricas completas del problema. Bajo las tres condiciones (i) alto potencial, (ii) R = Rmax para la validez de la captura i��nica OML, y (iii) potencial monot��nico, se desarrolla un an��lisis asint��tico auto-consistente para la estructura de plasma compleja que contiene las tres especies de cargas (electrones e iones del plasma, electrones emitidos), y cuatro regiones espaciales distintas, utilizando teor��as de movimiento orbital y modelos cin��ticos de las especies. Aunque los electrones emitidos presentan carga espacial despreciable muy lejos de la sonda, su efecto no se puede despreciar en el an��lisis global de la estructura de la vaina y de dos capas finas entre la vaina y la regi��n cuasi-neutra. El an��lisis proporciona las condiciones param��tricas para que la corriente sea SCL. Tambi��n muestra que la emisi��n termoi��nica aumenta el radio m��ximo de la sonda para operar dentro del r��gimen OML y que la emisi��n de electrones es mucho m��s eficiente que la captura i��nica para el segmento cat��dico de la amarra. En el c��digo num��rico, los movimientos orbitales de las tres especies son modelados para potenciales tanto monot��nico como no-monot��nico, y sonda de radio R arbitrario (dentro o m��s all�� del r��gimen de OML para la captura i��nica). Aprovechando la existencia de dos invariante, el sistema de ecuaciones Poisson-Vlasov se escribe como una ecuaci��n integro-diferencial, la cual se discretiza mediante un m��todo de diferencias finitas. El sistema de ecuaciones algebraicas no lineal resultante se ha resuelto de con un m��todo Newton-Raphson paralelizado. Los resultados, comparados satisfactoriamente con el an��lisis anal��tico, proporcionan la emisi��n de corriente y la estructura del plasma y del potencial electrost��tico. ABSTRACT An electrodynamic tether operates on electromagnetic principles and exchanges momentum through the planetary magnetosphere, by continuously interacting with the ionosphere. It is a reliable passive subsystem to deorbit spent rocket stages and satellites at its end of mission, mitigating the growth of orbital debris. A tether left bare of insulation collects electrons by its own uninsulated and positively biased segment with kilometer range, while electrons are emitted by a low-impedance active device at the cathodic end, such as a hollow cathode, to emit the full electron current. In the absence of an active cathodic device, the current flowing along an orbiting bare tether vanishes at both ends and the tether is said to be electrically floating. For negligible thermionic emission and orbital-motion-limited (OML) collection throughout the entire tether (electron/ion collection at anodic/cathodic segment, respectively), the anodic-to-cathodic length ratio is very small due to ions being much heavier, which results in low average current and Lorentz drag. The electride C12A7 : e���, which might present a possible work function as low as W = 0.6 eV and moderately high temperature stability, has been proposed as coating for floating bare tethers. Thermionic emission along a thus coated cathodic segment, under heating in space operation, can be more efficient than ion collection and, in the simplest drag mode, may eliminate the need for an active cathodic device and its corresponding gas-feed requirements and power subsystem, which would result in a truly ���propellant-less��� tether system. With this low-W coating, each elemental segment on the cathodic segment of a kilometers-long floating bare-tether would emit current as if it were part of a hot cylindrical probe uniformly polarized at the local tether bias, under 2D probe conditions that are also applied to the anodic-segment analysis. In the presence of emission, emitted electrons result in negative space charge, which decreases the electric field that accelerates them outwards, or even reverses it, decelerating electrons near the emitting probe. A double sheath would be established with electrons being emitted from the probe and ions coming from the ambient plasma. The thermionic current density, varying along the cathodic segment, might follow two distinct laws under different con ditions: i) space-charge-limited (SCL) emission or ii) full Richardson-Dushman (RDS) emission. A preliminary study on the SCL current in front of an emissive probe is presented using the orbital-motion-limited (OML) ion-collection sheath and Langmuir���s SCL electron current between cylindrical electrodes. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects considered and the transition from SCL to full RDS emission is included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission provides efficient cathodic contact and leads to a short cathodic section. In the previous analysis, both the transition between SCL and RDS emission and the current law for SCL condition have used a very simple model. To continue, considering an isotropic, unmagnetized, colissionless plasma and a stationary sheath, the probe-plasma contact is studied in detail for a negatively biased probe with thermionic emission. The possible trapped particles are ignored and this study includes both semianalytical solutions using asymptotic analysis and complete numerical solutions. Under conditions of i) high bias, ii) R = Rmax for ion OML collection validity, and iii) monotonic potential, a self-consistent asymptotic analysis is carried out for the complex plasma structure involving all three charge species (plasma electrons and ions, and emitted electrons) and four distinct spatial regions using orbital motion theories and kinetic modeling of the species. Although emitted electrons present negligible space charge far away from the probe, their effect cannot be neglected in the global analysis for the sheath structure and two thin layers in between the sheath and the quasineutral region. The parametric conditions for the current to be space-chargelimited are obtained. It is found that thermionic emission increases the range of probe radius for OML validity and is greatly more effective than ion collection for cathodic contact of tethers. In the numerical code, the orbital motions of all three species are modeled for both monotonic and non-monotonic potential, and for any probe radius R (within or beyond OML regime for ion collection). Taking advantage of two constants of motion (energy and angular momentum), the Poisson-Vlasov equation is described by an integro differential equation, which is discretized using finite difference method. The non-linear algebraic equations are solved using a parallel implementation of the Newton-Raphson method. The results, which show good agreement with the analytical results, provide the results for thermionic current, the sheath structure, and the electrostatic potential.

Emission regimes in a distributed feedback tapered master-oscillator power-amplifier at 1.5 ��m

Integrated master-oscillator power amplifiers driven under steady-state injection conditions are known to show a complex dynamics resulting in a variety of emission regimes. We present experimental results on the emission characteristics of a 1.5 ��m distributed feedback tapered master-oscillator power-amplifier in a wide range of steady-state injection conditions, showing different dynamic behaviors. The study combines the optical and radio-frequency spectra recorded under different levels of injected current into the master oscillator and the power amplifier sections. Under low injection current of the master oscillator the correlation between the optical and radio-frequency spectral maps allows to identify operation regimes in which the device emission arises from either the master oscillator mode or from the compound cavity modes allowed by the residual reflectance of the amplifier front facet. The quasi-periodic occurrence of these emission regimes as a function of the amplifier current is interpreted in terms of a thermally tuned competition between the modes of the master oscillator and the compound cavity modes. Under high injection current of the masteroscillator, two different regimes alternate quasi-periodically as a function of the injected current in the power amplifier: a stable regime with a single mode emission at the master oscillator frequency, and an unstable and complex self-pulsating regime showing strong peaks in the radio-frequency spectra as well as multiple frequencies in the optical spectra.