The suitability of the infinite NTU model for long-term rock bed thermal storage performance simulation

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Packed beds incorporating rock as the storage medium and air as the heat transfer fluid have been proposed as a cost-effective approach for thermal storage in solar power plants. In order to assess the viability of rock bed thermal energy storage (TES), it is essentially necessary to predict the air and rock temperature profiles through the bed during charging and discharging. A number of models are available for this purpose, including, at the more basic level, the popular Hughes “E-NTU” model and the simplified “Infinite NTU” model. Unlike the E-NTU method, the Infinite NTU method assumes an infinite heat transfer coefficient between the air and the rock, which implies equivalent air and rock temperature profiles. Typically, the more detailed a model, the greater the computational effort required to solve it. For long-term analysis, a time-efficient model is necessary to prevent excessively long computation times. This paper evaluates the comparative accuracy and computational efficiency of the E-NTU and Infinite NTU models when simulating the short- and long-term performance of CSP rock bed TES systems. On the basis of these comparisons, the appropriateness of employing the less realistic but less costly Infinite NTU model in the long-term simulation of CSP rock bed TES systems is evaluated.cf201

Communicating thematic data quality with web map services

Geospatial information of many kinds, from topographic maps to scientific data, is increasingly being made available through web mapping services. These allow georeferenced map images to be served from data stores and displayed in websites and geographic information systems, where they can be integrated with other geographic information. The Open Geospatial Consortium’s Web Map Service (WMS) standard has been widely adopted in diverse communities for sharing data in this way. However, current services typically provide little or no information about the quality or accuracy of the data they serve. In this paper we will describe the design and implementation of a new “quality-enabled” profile of WMS, which we call “WMS-Q”. This describes how information about data quality can be transmitted to the user through WMS. Such information can exist at many levels, from entire datasets to individual measurements, and includes the many different ways in which data uncertainty can be expressed. We also describe proposed extensions to the Symbology Encoding specification, which include provision for visualizing uncertainty in raster data in a number of different ways, including contours, shading and bivariate colour maps. We shall also describe new open-source implementations of the new specifications, which include both clients and servers

Blockchain Application Within a Multi-Sensor Satellite Architecture

With the thrust towards multi-sensor satellite architectures for earth and space exploration, such as constellations and swarms, new technologies are required to enable the transition to this future capability. One of the areas of interest is establishing secure, efficient and prioritized data and command communication pathways among ground and space-based sources for such systems. This paper presents early research results on the potential role, capabilities and value of blockchain usage within constellation and swarm satellite architectures. It demonstrates the use of blockchain's smart contract and distributed ledger capabilities for secure and prioritized multi-sensor satellite collaborative data exchanges, as well as the logging and tracking of command and control events. Adapting and utilizing this emerging technology will aid in addressing technology gaps expected from future constellation flight architectures, such as managing collective computational operations (correlation), dynamic and autonomous observation planning, time-critical events, and provenance tied to ground and space-based autonomous operations and control recordkeeping. In this scenario blockchain is applied in encrypted command transmittal to multiple, yet specific, entities enabling acknowledgement transmittals, performance scalability, and automatic event-based triggering

An Overview of Scientific and Space Weather Results from the Communication/Navigation Outage Forecasting System (C/NOFS) Mission

The Communication/Navigation Outage Forecasting System (C/NOFS) Mission of the Air Force Research Laboratory is described. C/NOFS science objectives may be organized into three categories: (1) to understand physical processes active in the background ionosphere and thermosphere in which plasma instabilities grow; (2) to identify mechanisms that trigger or quench the plasma irregularities responsible for signal degradation; and (3) to determine how the plasma irregularities affect the propagation of electromagnetic waves. The satellite was launched in April, 2008 into a low inclination (13 deg), elliptical (400 x 850 km) orbit. The satellite sensors measure the following parameters in situ: ambient and fluctuating electron densities, AC and DC electric and magnetic fields, ion drifts and large scale ion composition, ion and electron temperatures, and neutral winds. C/NOFS is also equipped with a GPS occultation receiver and a radio beacon. In addition to the satellite sensors, complementary ground-based measurements, theory, and advanced modeling techniques are also important parts of the mission. We report scientific and space weather highlights of the mission after nearly four years in orbi

Estabilidad de la estructura topológica de una región activa en presencia de fuentes de campo externas

A partir de las observaciones del campo magnético longitudinal de la región activa (AR) 6233, obtenidas en el Observatorio Mees (Universidad de Hawaii), derivamos su estructura topológica y estudiamos la evolución de la misma a lo largo de dos días. En el bipolo principal de esta región se desarrollaron numerosas fulguraciones y microfulguraciones en el período de estudio. Dado que en este caso contamos con magnetogramas que cubren distintas escalas espaciales, analizamos la influencia que las fuentes de campo externas a dicho bipolo tienen sobre la estructura topológica de la zona en donde se produjeron las fulguraciones. Esta se obtiene a partir de un modelo del campo de AR 6233 tanto en la aproximación potencial, como en la libre de fuerzas lineal. Nuestros resultados muestran que la estructura topológica básica de la región de interés permanece invariante en ambos casos. Esto justificaría el uso, debido a limitaciones instrumentales, de magnetogramas que cubren una porción limitada de la región activa al modelar el campo como se ha hecho en estudios anteriores.Asociación Argentina de Astronomí

Sondrestrom Overview

This overview of the Sondrestrom radar provides background material to help understand the early scientific results discussed in the following series of papers. It describes the geophysical region probed by the radar, the data acquisition procedure, and the extensive set of physical parameters derived

Observations and Simulations of Formation of Broad Plasma Depletions Through Merging Process

Broad plasma depletions in the equatorial ionosphere near dawn are region in which the plasma density is reduced by 1-3 orders of magnitude over thousands of kilometers in longitude. This phenomenon is observed repeatedly by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during deep solar minimum. The plasma flow inside the depletion region can be strongly upward. The possible causal mechanism for the formation of broad plasma depletions is that the broad depletions result from merging of multiple equatorial plasma bubbles. The purpose of this study is to demonstrate the feasibility of the merging mechanism with new observations and simulations. We present C/NOFS observations for two cases. A series of plasma bubbles is first detected by C/NOFS over a longitudinal range of 3300-3800 km around midnight. Each of the individual bubbles has a typical width of approx 100 km in longitude, and the upward ion drift velocity inside the bubbles is 200-400 m/s. The plasma bubbles rotate with the Earth to the dawn sector and become broad plasma depletions. The observations clearly show the evolution from multiple plasma bubbles to broad depletions. Large upward plasma flow occurs inside the depletion region over 3800 km in longitude and exists for approx 5 h. We also present the numerical simulations of bubble merging with the physics-based low-latitude ionospheric model. It is found that two separate plasma bubbles join together and form a single, wider bubble. The simulations show that the merging process of plasma bubbles can indeed occur in incompressible ionospheric plasma. The simulation results support the merging mechanism for the formation of broad plasma depletions

Effects of seasonal changes in the ionospheric conductances on magnetospheric field‐aligned currents

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95211/1/grl22574.pd

Universal Time Dependence of Nighttime F Region Densities at High Latitudes

Coordinated EISCAT, Chatanika, and Millstone Hill incoherent scatter radar observations have revealed that in the auroral zone, the nighttime F region densities vary substantially with the longitude of the observing site: EISCAT’s densities are the largest and Millstone Hill’s are the lowest. The nighttime F region densities measured by the individual radars are not uniform: the regions where the densities are maximum are the so-called “blobs” or “patches” that have been reported previously. The observations are consistent with the hypothesis that the nighttime densities are produced in significant amounts not by particle precipitation, but by solar EUV radiation, and that they have been transported across the polar cap. The observed differences can be explained by the offset of the geographic and geomagnetic poles. A larger portion of the magnetospheric convection pattern is sunlit when EISCAT is in the midnight sector than when Chatanika is. In winter, when Millstone Hill is in the midnight sector, almost all the auroral oval is in darkness. This universal time effect, which was observed on all coordinated three-radar experiments (September 1981 to February 1982), is illustrated using two periods of coincident radar and satellite observations: November 18-19, and December 15-16, 1981. These two periods were selected because they corresponded to relatively steady conditions. Dynamics Explorer (DE) measurements are used to aid in interpreting the radar observations. DE 1 auroral images show what portion of the oval was sunlit. DE 2 data are used to measure the ion drift across the polar cap. Because the altitude of the ionization peak was high, the decay time of the F region density was substantially longer than the transit time across the polar cap. The southward meridional wind that was observed coincidentally with the ionization patches at Chatanika and EISCAT contributed to the maintenance of the F region by raising the altitude of the peak. DE 2 Langmuir probe measurements of electron density clearly showed a UT dependence, the same as that in the radar measurements

Limitations of Absolute Current Densities Derived from the Semel & Skumanich Method

Semel and Skumanich proposed a method to obtain the absolute electric current density, |Jz|, without disambiguation of 180 degree in the transverse field directions. The advantage of the method is that the uncertainty in the determination of the ambiguity in the magnetic azimuth is removed. Here, we investigate the limits of the calculation when applied to a numerical MHD model. We found that the combination of changes in the magnetic azimuth with vanishing horizontal field component leads to errors, where electric current densities are often strong. Where errors occur, the calculation gives |Jz| too small by factors typically 1.2 ~ 2.0.Comment: 10 pages, 4 figures. To appear on Science in China Series G: Physics, Mechanics & Astronomy, October 200