Bakker M.,Technical University of Delft |
Calje R.,Artesia |
Schaars F.,Artesia |
Van Der Made K.-J.,Wiertsema and Partners |
De Haas S.,PWN
Water Resources Research | Year: 2015
A new approach is developed to insert fiber optic cables vertically into the ground with direct push equipment. Groundwater temperatures may be measured along the cables with high spatial and temporal resolution using a Distributed Temperature Sensing system. The cables may be inserted up to depths of tens of meters in unconsolidated sedimentary aquifers. The main advantages of the method are that the cables are in direct contact with the aquifer material, the disturbance of the aquifer is minor, and no borehole is needed. This cost-effective approach may be applied to both passive and active heat tracer experiments. An active heat tracer experiment was conducted to estimate horizontal groundwater velocities in a managed aquifer recharge system in the Netherlands. Six fiber optic cables and a separate heating cable were inserted with a 1 m spacing at the surface. The heating cable was turned on for 4 days and temperatures were measured during both heating and cooling of the aquifer. Temperature measurements at the heating cable alone were used to estimate the magnitude of the groundwater velocity and the thermal conductivity of the solids. The direction of the velocity and heat capacity of the solids were estimated by including temperature measurements at the other fiber optic cables in the analysis. The latter analysis suffered from the fact that the cables were not inserted exactly vertical. The three-dimensional position of the fiber optic cables must be measured for future active heat tracer experiments. Key Points Fiber optic cables are inserted into the ground with direct push equipment Temperature is measured along vertical fiber optic cables with DTS unit Active heat tracer experiment is carried out to estimate groundwater velocities © 2015. American Geophysical Union. All Rights Reserved.
News Article | February 15, 2017
Like cosmic lighthouses sweeping the universe with bursts of energy, pulsars have fascinated and baffled astronomers since they were first discovered 50 years ago. In two studies, international teams of astronomers suggest that recent images from NASA's Chandra X-ray Observatory of two pulsars -- Geminga and B0355+54 -- may help shine a light on the distinctive emission signatures of pulsars, as well as their often perplexing geometry. Pulsars are a type of neutron star that are born in supernova explosions when massive stars collapse. Discovered initially by lighthouse-like beams of radio emission, more recent research has found that energetic pulsars also produce beams of high energy gamma rays. Interestingly, the beams rarely match up, said Bettina Posselt, senior research associate in astronomy and astrophysics, Penn State. The shapes of observed radio and gamma-ray pulses are often quite different and some of the objects show only one type of pulse or the other. These differences have generated debate about the pulsar model. "It's not fully understood why there are variations between different pulsars," said Posselt. "One of the main ideas here is that pulse differences have a lot to do with geometry -- and it also depends on how the pulsar's spin and magnetic axes are oriented with respect to line of sight whether you see certain pulsars or not, as well as how you see them." Chandra's images are giving the astronomers a closer than ever look at the distinctive geometry of the charged particle winds radiating in X-ray and other wavelengths from the objects, according to Posselt. Pulsars rhythmically rotate as they rocket through space at speeds reaching hundreds of kilometers a second. Pulsar wind nebulae (PWN) are produced when the energetic particles streaming from pulsars shoot along the stars' magnetic fields, form tori -- donut-shaped rings -- around the pulsar's equatorial plane, and jet along the spin axis, often sweeping back into long tails as the pulsars' quickly cut through the interstellar medium. "This is one of the nicest results of our larger study of pulsar wind nebulae," said Roger W. Romani, professor of physics at Stanford University and principal investigator of the Chandra PWN project. "By making the 3-D structure of these winds visible, we have shown how one can trace back to the plasma injected by the pulsar at the center. Chandra's fantastic X-ray acuity was essential for this study, so we are happy that it was possible to get the deep exposures that made these faint structures visible." A spectacular PWN is seen around the Geminga pulsar. Geminga -- one of the closest pulsars at only 800 light-years away from Earth -- has three unusual tails, said Posselt. The streams of particles spewing out of the alleged poles of Geminga -- or lateral tails -- stretch out for more than half a light-year, longer than 1,000 times the distance between the Sun and Pluto. Another shorter tail also emanates from the pulsar. The astronomers said that a much different PWN picture is seen in the X-ray image of another pulsar called B0355+54, which is about 3,300 light-years away from Earth. The tail of this pulsar has a cap of emission, followed by a narrow double tail that extends almost five light-years away from the star. While Geminga shows pulses in the gamma ray spectrum, but is radio quiet, B0355+54 is one of the brightest radio pulsars, but fails to show gamma rays. "The tails seem to tell us why that is," said Posselt, adding that the pulsars' spin axis and magnetic axis orientations influence what emissions are seen on Earth. According to Posselt, Geminga may have magnetic poles quite close to the top and bottom of the object, and nearly aligned spin poles, much like Earth. One of the magnetic poles of B0355+54 could directly face the Earth. Because the radio emission occurs near the site of the magnetic poles, the radio waves may point along the direction of the jets, she said. Gamma-ray emission, on the other hand, is produced at higher altitudes in a larger region, allowing the respective pulses to sweep larger areas of the sky. "For Geminga, we view the bright gamma ray pulses and the edge of the pulsar wind nebula torus, but the radio beams near the jets point off to the sides and remain unseen," Posselt said. The strongly bent lateral tails offer the astronomers clues to the geometry of the pulsar, which could be compared to either jet contrails soaring into space, or to a bow shock similar to the shockwave created by a bullet as it is shot through the air. Oleg Kargaltsev, assistant professor of physics, George Washington University, who worked on the study on B0355+54, said that the orientation of B0355+54 plays a role in how astronomers see the pulsar, as well. The study is available online in arXiv. "For B0355+54, a jet points nearly at us so we detect the bright radio pulses while most of the gamma-ray emission is directed in the plane of the sky and misses the Earth," said Kargaltsev. "This implies that the pulsar's spin axis direction is close to our line-of-sight direction and that the pulsar is moving nearly perpendicularly to its spin axis." Noel Klingler, a graduate research assistant in physics, George Washington University, and lead author of the B0355+54 paper, added that the angles between the three vectors -- the spin axis, the line-of-sight, and the velocity -- are different for different pulsars, thus affecting the appearances of their nebulae. "In particular, it may be tricky to detect a PWN from a pulsar moving close to the line-of-sight and having a small angle between the spin axis and our line-of-sight," said Klingler. In the bow-shock interpretation of the Geminga X-ray data, Geminga's two long tails and their unusual spectrum may suggest that the particles are accelerated to nearly the speed of light through a process called Fermi acceleration. The Fermi acceleration takes place at the intersection of a pulsar wind and the interstellar material, according to the researchers, who report their findings on Geminga online and in the current issue of Astrophysical Journal. Although different interpretations remain on the table for Geminga's geometry, Posselt said that Chandra's images of the pulsar are helping astrophysicists use pulsars as particle physics laboratories. Studying the objects gives astrophysicists a chance to investigate particle physics in conditions that would be impossible to replicate in a particle accelerator on earth. "In both scenarios, Geminga provides exciting new constraints on the acceleration physics in pulsar wind nebulae and their interaction with the surrounding interstellar matter," she said. * "Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54," Noel Klingler et al., 2016 Dec. 20, Astrophysical Journal [http://iopscience.iop.org/article/10.3847/1538-4357/833/2/253, preprint: https://arxiv.org/abs/1610.06167]. * "Geminga's Puzzling Pulsar Wind Nebula," B. Posselt et al., 2017, to appear in Astrophysical Journal [http://apj.aas.org, preprint: https://arxiv.org/abs/1611.03496]. Other team members include George C. Pavlov, senior scientist in astronomy and astrophysics, Penn State; Pat O. Slane, lecturer and senior astrophysicist, Harvard Smithsonian Center for Astrophysics; Roger Romani, professor of physics, Stanford University; Niccolo Bucciantini, permanent researcher, INAF Osservatorio Astorfisico di Arcetri; Andrei M. Bykov, head of the Laboratory for High Energy Astrophysics, Ioffe Physical-Technical Institute; Martin C. Weisskopf, project scientist, NASA/Marshall Space Flight Center; Stephen Chi-Yung Ng, assistant professor of physics, University of Hong Kong. Additional team members for the study on B0355+54 include Blagoy Rangelov, postdoctoral researcher, George Washington University; Tea Temim, JWST Support Scientist, Space Telescope Science Institute; Douglas A. Swartz, research scientist, Marshall Space Flight Center and Rolf Buehler, staff scientist, DESY Zeuthen. NASA and the Russian Science Foundation supported this work. Please follow SpaceRef on Twitter and Like us on Facebook.
News Article | November 2, 2016
PWNs are nebulae powered by the wind of a pulsar. Pulsar wind is composed of charged particles and when it collides with the pulsar's surroundings, in particular with the slowly expanding supernova ejecta, it develops a PWN. Therefore, these nebulae could provide interesting information about the interaction of a pulsar with its surroundings. Scientists believe that their properties can be used to infer the geometry, energetics, and composition of the pulsar wind. HESS J1825−137, discovered in 2005 by the High Energy Stereoscopic System (H.E.S.S.), an array of four imaging atmospheric Cherenkov telescopes located in Namibia, is a highly extended PWN powered by the PSR B1823-13 pulsar. Located some 13,000 light years away, PSR B1823-13 is about 21,000 years old and has a spin period of 101.48 miliseconds. HESS J1825-137 is known for its strong energy-dependent morphology, as its observed size decreases with increasing energy, which makes it more compact around the position of the pulsar. Last year, a new dataset from the H.E.S.S. galactic plane survey was released, enabling more detailed studies of this peculiar nebula. These data were recently thoroughly analyzed by a team of researchers led by Alison Mitchell of the Max Planck Institute for Nuclear Physics in Germany, to improve our knowledge of HESS J1825-137 and PWNs in general. "A rich dataset is currently available with H.E.S.S., including H.E.S.S. II data with a low energy threshold, enabling detailed studies of the source properties and environment. We present new views of the changing nature of the PWN with energy, including maps of the region and spectral studies," the scientists wrote in the paper. They noted that the new dataset is much enhanced compared to the previous one, and offers significantly more sensitive studies. Due to better sensitivity to large areas of weak, low-energy emission, the H.E.S.S. II data allowed the team to detect an additional area of extended emission, revealing that HESS J1825-137 extends further than previously thought. However, even more crucial to the understanding of the nature of HESS J1825-137, the researchers found that the nebula's size reduces with increasing energy. According to the authors of the paper, this is a clear evidence of the emission being attributable to the pulsar. It also provides some indication of cooling of the electron population over time as the particles are transported away from PSR B1823-13. "The spectral index of the emission increases with increasing distance from the pulsar, due to the electrons cooling over time, causing the index to become softer. Additionally, the high energy flux decreases with distance from the pulsar, due also to this gradual change in the energy distribution of the electron population, as they cool and are transported through the nebula," the researchers concluded. All the new findings confirm the strong energy-dependent morphology of HESS J1825-137, proving that the second H.E.S.S. dataset could be helpful in more detailed studies of PWNs that could not have been performed based only on the first data release. Explore further: Researchers suggest high energy emissions from Crab Nebula come from wind More information: Detailed VHE Studies of the Pulsar Wind Nebula HESS J1825-137, arXiv:1610.08894 [astro-ph.HE] arxiv.org/abs/1610.08894 Abstract The pulsar wind nebula (PWN) HESS~J1825-137, known to exhibit strong energy dependent morphology, was discovered by HESS in 2005. Powered by the pulsar PSR~B1823-13, the TeV gamma-ray emitting nebula is significantly offset from the pulsar. The asymmetric shape and 21~kyr characteristic age of the pulsar suggest that HESS~J1825-137 is in an evolved state, having possibly already undergone reverse shock interactions from the progenitor supernova. Given its large angular extent, despite its 4~kpc distance, it may have the largest intrinsic size of any TeV PWN so far detected. A rich dataset is currently available with H.E.S.S., including H.E.S.S. II data with a low energy threshold, enabling detailed studies of the source properties and environment. We present new views of the changing nature of the PWN with energy, including maps of the region and spectral studies.
Van Thienen P.,KWR Watercycle Research Institute |
Vries D.,KWR Watercycle Research Institute |
Vries D.,Center of Excellence for Sustainable Water Technology |
De Graaf B.,Vitens |
And 3 more authors.
Procedia Engineering | Year: 2014
In this paper, we investigate the relevance of the stochastic nature of water demand for backtracing of contaminations in drinking water distribution networks. We present an approach to deal with the uncertainty introduced by stochastic demand, which is applied to a full detail part (all pipes) of a hydraulic model of a distribution network in the Netherlands. It is demonstrated that stochastic water demand can introduce significant amounts of uncertainty for backtracing in some parts of tertiary (reticulation) networks in specific, looped configurations. In other parts, the additional uncertainty introduced by stochastic water demand can be limited. © 2013 The Authors. Published by Elsevier Ltd.
News Article | November 10, 2016
BOSTON--(BUSINESS WIRE)--#stt--State Street Corporation (NYSE: STT) announced today that it has received the 2016 ERG & Council Honors Award™ from the Association of ERGs & Councils, in recognition of its Flexible Work Employee Network (FWEN) and Professional Women’s Network (PWN). The award is the only annual national award that recognizes and honors the outstanding contributions and achievements of Employee Resource Groups (ERGs), Business Resource Groups (BRGs) and Diversity Councils. This
Worm G.I.M.,PWN |
Worm G.I.M.,Technical University of Delft |
Kelderman J.P.,PWN |
Kelderman J.P.,Technical University of Delft |
And 4 more authors.
Water Science and Technology: Water Supply | Year: 2013
This research deals with the contribution of process simulation models to the factory acceptance test (FAT) of process automation (PA) software of drinking water treatment plants. Two test teams tested the same piece of modified PA-software. One team used an advanced virtual commissioning (AVC) system consisting of PA-emulation and integrated process simulation models. The other team used the same PA-emulation but basic parameter relations instead of the process simulation models, the virtual commissioning (VC) system. Each test team found one (different) error of the 13 errors put into the software prior to the experiment; most of the errors were found prior to the functional test. The team using the AVC-system found three errors, the team using the VC-system found four, but the AVC-team judged 1% of the test items 'not possible', the VC-team 17%. It was concluded that the hypothesis that with AVC more errors could be found than with VC could not be accepted. So, for the FAT of PA-software of drinking water treatment plants, the addition of basic parameter relations to PA-emulation was sufficient. It was not the exact process behavior that helped to find errors, but the passing of process thresholds. © IWA Publishing 2013.
News Article | January 19, 2017
The fascination on pulsars has been long standing among astronomers. Since their discovery 50 years ago, pulsars have both impressed and baffled astronomers considerably. These highly magnetized, rapidly spinning neutron stars are dense remnants of supernova explosions and are known to complete a single rotation in a couple of seconds. Pulsars also stand out for their lighthouse-like radio emissions with some of them discovered to be emitting high-energy gamma rays as well. Thanks to recent images from NASA's Chandra X-ray Observatory on two pulsars – Geminga and B0355+54 – astronomers had new insights on many of the properties of pulsars. The focus on pulsars' geometry intensified after the international team of astronomers, including researchers from Penn State University, started focusing on the distinctive emission signatures of pulsars. The study is published in The Astrophysical Journal. The emission of gamma rays is not uniform in all pulsars. Stark differences have been observed in the shapes of radio and gamma-ray pulses, with some of the objects showing only one type of pulse or the other. Astronomers assume that these differences are rooted in the pulsar model and geometry. "It's not fully understood why there are variations between different pulsars. One of the main ideas here is that pulse differences have a lot to do with geometry," noted Bettina Posselt, senior research associate in astrophysics and astronomy at Penn State. She explained that the pulse variations are also linked to the spin of the pulsars and how the magnetic axis is aligned with the line of sight is determining whether they are seen or how they are seen. The NASA images assisted in giving a broad idea of how pulsars rotate as they hurtle through space in high speeds at the rate of hundreds of kilometers. The relation of type and volume of pulsar emissions with geometry gained strength from the study of Geminga and B0355+54. The images exposed their distinct emission signatures when their Pulsar wind nebulae (PWN) were studied. The PWNs are donut-shaped rings known by the name tori, generated when the energized particles of the star remnants stream into the magnetic field around the equatorial plane of the pulsar, forming tail-like structures while rushing through the interstellar medium. Thus, Chandra's X-ray facility gave a brilliant exposure of the faint structures with better specifics and a grand PWN view of the Geminga. Regarding B0355+54, Oleg Kargaltsev, assistant professor of physics, at George Washington University, also part of the study, noted that the pulsar's orientation had a lot do with its sight. He said a jet of radio waves was pointing to Earth giving a good view of bright beams while the gamma-ray emission has been moving in the plane of the sky and missing out the Earth. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.
Worm G.I.M.,PWN |
Worm G.I.M.,Technical University of Delft |
Wuister J.J.G.,Royal HaskoningDHV |
Van Schagen K.M.,Royal HaskoningDHV |
Rietveld L.C.,Technical University of Delft
Journal of Water Supply: Research and Technology - AQUA | Year: 2013
This research adds a method to evaluate control strategies to the design methodology for drinking water treatment plants. A process model dealing with parameters related to the calcium carbon dioxide equilibrium was set up. Using the process model, the existing control strategy was compared with a new control strategy and the effects of two different sets of input data were studied. It was demonstrated that the efficiency of the pellet softening process and the plant's capacity were increased, and that chemicals and energy usage were reduced. At the same time, the deviation of the total hardness of the produced water to the desired value was decreased. © IWA Publishing 2013.
Beuken R.,KWR Watercycle Research Institute |
Horst P.,PWN |
Diemel R.,Brabant Water |
Mesman G.,KWR Watercycle Research Institute
Procedia Engineering | Year: 2014
The total length of the drinking water distribution network in the Netherlands is approximately 117,000 kilometers. The total replacement value is estimated at 20,000 to 30,000 million Euro. Several methods are available to obtain information to determine which mains should be replaced and when. Recently the echopulse technique was introduced in the Netherlands. The echopulse results were compared to phenolphthalein staining tests and radar. The validation of results reported here shows that the echopulse method provides reliable results for AC mains. However, a prerequisite for reliable results is the availability of reliable data on the properties of the mains, especially the initial wall thickness and the Young's modulus. © 2014 Published by Elsevier Ltd.