Combining rotation curves and gravitational lensing: how to measure the equation of state of dark matter in the galactic halo     

Tristan Faber  Matt Visser 《Monthly notices of the Royal Astronomical Society》2006,372(1):136-142

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A method to determine regional lunar gravity fields from earth-based satellite tracking data     

S. Goossens  P.N.A.M. Visser  B.A.C. Ambrosius 《Planetary and Space Science》2005,53(13):1331-1340

A method to determine regional gravity fields of the Moon from Earth-based Doppler and range satellite tracking data residuals of a low Moon-orbiting satellite has been developed and thoroughly tested in a controlled simulation environment. A short-arc approach, where one arc consists of the time it takes the satellite to cross the grid of interest on the lunar surface, is used in order to filter out most long-wavelength signal that can still be present in the residuals. Simulation results where the data are contaminated with either typical systematic or stochastic noise show that recovery of the local gravity field down to the level of several mGal is possible. The inclusion of extremely low-altitude data also means that regularisation in the sense of including a priori information in the form of a regularisation matrix is not necessary in order to obtain a good solution at high resolution.  相似文献   

Erratum: The thermal impact of aquifer thermal energy storage (ATES) systems: a case study in The Netherlands,combining monitoring and modeling     

Philip W. Visser  Henk Kooi  Pieter J. Stuyfzand 《Hydrogeology Journal》2015,23(3):613-613

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Uncertainties in hydrocarbon charge prediction     

W. Visser  A. Bell 《International Journal of Earth Sciences》1997,86(2):332-341

Computer simulations allow the prediction of hydrocarbon volumes, composition and charge timing in undrilled petroleum prospects. Whereas different models may give different hydrocarbon charge predictions, it has now become evident that a dominant cause of erroneous predictions is the poor quality of input data. The main culprit for prediction errors is the uncertainty in the initial hydrogen index (H/C) of the source rock. A 10% uncertainty in the H/C may lead to 50% error in the predicted hydrocarbon volumes, and associated gas–oil ratio. Similarly, uncertainties in the maximum burial temperature and the kinetics of hydrocarbon generation may lead to 20–50% error. Despite this, charge modelling can have great value for the ranking of prospects in the same area with comparable geological histories.  相似文献   

Turbulence and zooplankton production: insights from PROVESS   总被引：1，自引：0，他引：1  

Andr W. Visser  Adolf Stips 《Journal of Sea Research》2002,47(3-4)

Zooplankton are directly influenced by turbulence in both a passive and an active manner. Passively, zooplankton are at the mercy of turbulence in how it affects their vertical mixing, encounter rate, detection abilities and feeding current efficiency. Many zooplankton species, however, are actively able to mitigate the effects of turbulence by modifying their behaviour, e.g. vertical migration, prey switching and habituation to hydromechanical stimuli. Both theoretical treatments of these processes and field observations from the northern North Sea are examined. Field observations show that some copepod species actively migrate to avoid high turbulence levels in surface waters. Furthermore, observations show a negative relationship between turbulence and zooplankton ingestion rates. This supports the paradigm of a dome-shaped response for zooplankton production with environmental turbulence. A theoretical treatment shows that the reaction distance, R, for an ambush-feeding copepod feeding on swimming organisms follows R ∝ ^−1/6 where is the turbulent dissipation rate, a result that shows close agreement with previously reported experimental results.  相似文献   

Laboratory measurements of uniform longshore currents   总被引：4，自引：0，他引：4  

Paul J. Visser 《Coastal Engineering》1991,15(5-6)

Experiments on uniform longshore currents in a wave basin are described. The measurements were performed in a basin with a pumped recirculation through openings in the wave guides. Minimal return flows in the offshore region of the basin are found to be accompanied with longshore currents which are virtually uniform alongshore. Three-dimensional longshore current velocity distributions were measured with much attention to quality control. Detailed experimental results are presented for different wave fields, two beach slopes and two beach roughnesses.  相似文献   

Some remarks on the european monsoon     

Prof. Dr. S. W. Visser 《Pure and Applied Geophysics》1953,24(1):135-148

Summary 1. The so called sigularities want all reality and are of no value in monsoon investigations. — 2. In this section a short summary ofChromow's monsoon studies is given (Fig. 1). — 3. The monsoon in Western Europe manifests itself in impulses during some days alternating with the general west circulation. Monthly means of the wind direction give the resultant direction of these two independent wind systems and do by no means elucidate the true behaviour of the wind.Chromow's method, the appliance of monthly means of pressure gradients, is also insufficient. The only reliable method of researching the monsoon in moderate regions is the investigation of the separate wind octants. A month is too long to reveal the rather short impulses and therefore calculating decade means is recommended. The monsoon depends upon the direction and the velocity of the wind. Calculating the product of the frequency of the direction (in %) and the wind velocity is in practice a sufficient approximation. I have called this product the «relative wind vector». — 4. Whereas generally the months of January and July are accepted as the central monsoon months, in the Netherlands and Germany these months appear to be November–December and May–June (Table 1, 2; Fig. 2, 3, 5, 6, 7), respectively with S and NE winds. The summer monsoon seems to back from E to N and perhaps even to NW. This backing may be caused by the form of the european continent. — 5. A research into the maximal development of the monsoon impulses shows that they equal or even surpass the general western ciruclation concerning both their number (Table 1, right-hand side) and their intensity (Table 3).Willett's opinion that the normal geographical distribution of air mass source regions in the spring and the autumn are intermediate between those of the months of Janaury and July cannot be maintained for West Europe. — 6. A research by means ofConrad's monsoon index also shows that the full monsoon months in W-Europe are November–December and May–June (Table 4). The application of his method to the relative wind vector at Den Helder and Maastricht confirms this result (Table 5). — All results arrived at show the activity of the monsoon phenomenon in a good deal of West Europe.

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Zusammenfassung 1. Die Singularitäten entbehren jede Realität und sind wertlos für Monsununtersuchungen. — 2. In diesem Paragraph findet man eine Zusammenfassung vonChromow's Anschauungen (Fig. 1). — 3 Der europäische Monsun äussert sich in Stössen während einiger Tage, abwechselnd mit der allgemeinen Westzirkulation. Montasmittel der Windrichtung geben nur die resultierende Richtung dieser zwei unabhängigen Windsystemen und zeigen in keinem Fall die wahren Windverhältnisse. Die einzige Methode ist die Untersuchung der einzelnen Windoktanten. Eine Monat, ist zu lang um die ziemlich kurzen Stösse zu zeigen. Ein gutes Mass ist das Produkt der Richtungsverteilung in Prozenten mit der Geschwindigkeit, der «relative Windvektor» genannt. — 4. In den Niederlanden und Deutschland sind nicht die allgemein angenommenen Monate Januar und Juli die Zentralmonate des Monsuns, sondern November–Dezember und Mai–Juni (Tab. 1, 2.; Fig. 2, 3, 5, 6, 7), beziehungsweise mit S- und NE-Winden. Der NE-Monsun scheint zurückzudrehen von E nach N, vielleicht selbst, nach NW. Diese Eigenschaft kann verursacht werden von der Form des europäischen Kontinents. — 5. Die Wichtigkeit der Monsunstösse ist gleich, der Westzirkulation oder selbst stärker als diese, sowohl was ihre Zahl (Tab. 1, rechts) als ihre Intensität (Tab. 3) betrifft.Willett's Behauptung, dass die normale geographische Verteilung der Luftmassen im Frühling und im Herbst die mittleren Eigenschaften der Verteilung im Januar und im Juli besitzt kann für Westeuropa nicht aufrecht gehalten werden. — 6.Conrad's Monsunindex zeigt auch dass die vollen Monsunmonate in Westeuropa die oben genannten sind (Tab. 4). Die Anwendung seiner Methode auf dem relativen Windvektor bestätigt dieses Resultat (Tab. 5). Alle gefundenen Resultate zeigen die Aktivität des Monsunphänomens in Westeuropa.

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Résumé 1. Les singularités manquent toute réalité et n'ont pas de valeur pour l'étude des moussons dans les régions modérées. — 2. Un résumé court des études deChromow est donné (Fig. 1). — 3. Le mousson européen se manifeste par des impulsions pendant quelques jours alternant avec la circulation atmosphérique générale. Les moyennes mensuelles de la direction du vent ne donnent que la direction résultante mais ne démontrent rien concernant les particularités réelles du vent. La méthode deChromow, l'application des gradients mensuels de la pression, est aussi insuffisante. En outre la durée d'une mois est trop longue pour révéler ces impulsions courtes. Il faut préférer les décades. Pour conclure il faut tenir compte de la vitesse du vent aussi. J'ai calculé le produit de la fréquence (en pourcentage) et la vitesse, le «vecteur relatif du vent» 4. Tandis que généralement les mois de Janvier et de Juin sont acceptées comme les mois centrales du mousson, dans les Pays Bas et en Allemagne ces mois sont Novembre–Décembre et Mai–Juin (Tabl. 1, 2; Fig. 2, 3, 5, 6, 7) avec resp. le mousson de S et le mousson de NE. Le mousson de NE semble changer de l'E à N et peutêtre même à NW. Ce recul du vent peut être causé par la configuration du continent européen. — 5. Une recherche des impulsions du mousson démontre qu'elles égalent, même surpassent la circulation générale aussi bien concernant leur nombre (Tabl. 1, à droite) que leur intensité (Tabl. 3). L'opinion deWillett que les masses d'air du printemps et de l'automne sont intermédiaires entre celles de Janvier et de Juin n'est pas acceptable pour l'Europe occidentale. — 6. Une recherche au moyen de l'index deConrad montre aussi que les mois essentielles du mousson européen sont les mois mentionnées (Tabl. 4). L'application de la méthode deConrad sur le vecteur du vent relatif confirme ce résultat (Tabl. 5). — Tous les résultats gagnés montrent l'activité du mousson dans une grande partie de l'Europe occidentale.

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Submillimetre continuum images of the NGC 2024 star-forming ridge     

Anja E. Visser  John S. Richer  Claire J. Chandler  & Rachael Padman 《Monthly notices of the Royal Astronomical Society》1998,301(2):585-592

We present 450- and 800-μm images, made with the James Clerk Maxwell Telescope, of the NGC 2024 molecular ridge. The seven previously known compact cores, FIR1–7, have been detected, and FIR5 has been resolved into a compact object and an associated extended source to the east. The estimated masses of the dense cores vary between 1.6 and 5.1 M⊙ per 14-arcsec beam, assuming a dust temperature of 30 K and a dust opacity of κ_800 μm = 0.002 m² kg⁻¹. A spectral index map made from the 450- and 800-μm images shows spatial variations, with the spectral index, α ( F _ν ∝ ν^α), being systematically lower towards the dense cores. We interpret this as evidence for a lower value of the frequency dependence of the dust opacity, β, towards the denser cores relative to the surrounding molecular material. This may indicate that grain growth is occurring in the cores, prior to planetesimal formation. By comparing the high-resolution 450-μm image with interferometer maps of the integrated CS(2–1) emission, the previously reported discrepancy between dust continuum emission and molecular line emission is found to be very localized. Depletion and temperature variations are discussed as possible explanations.  相似文献   

Tracking and orbit determination performance of the GRAS instrument on MetOp-A   总被引：8，自引：3，他引：5  

Oliver Montenbruck  Yago Andres  Heike Bock  Tom van Helleputte  Jose van den Ijssel  Marc Loiselet  Christian Marquardt  Pierluigi Silvestrin  Pieter Visser  Yoke Yoon 《GPS Solutions》2008,12(4):289-299

The global navigation satellite system receiver for atmospheric sounding (GRAS) on MetOp-A is the first European GPS receiver providing dual-frequency navigation and occultation measurements from a spaceborne platform on a routine basis. The receiver is based on ESA’s AGGA-2 correlator chip, which implements a high-quality tracking scheme for semi-codeless P(Y) code tracking on the L1 and L2 frequency. Data collected with the zenith antenna on MetOp-A have been used to perform an in-flight characterization of the GRAS instrument with focus on the tracking and navigation performance. Besides an assessment of the receiver noise and systematic measurement errors, the study addresses the precise orbit determination accuracy achievable with the GRAS receiver. A consistency on the 5 cm level is demonstrated for reduced dynamics orbit solutions computed independently by four different agencies and software packages. With purely kinematic solutions, 10 cm accuracy is obtained. As a part of the analysis, an empirical antenna offset correction and preliminary phase center correction map are derived, which notably reduce the carrier phase residuals and improve the consistency of kinematic orbit determination results.

Oliver MontenbruckEmail:

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Anomalously Low Temperature Orthopyroxene, Spinel, and Sapphirine Occurrences in Metasediments from the Bamble Amphibolite-to-Granulite Facies Transition Zone (South Norway): Possible Evidence for Localized Action of Saline Fluids: A Reply     

Nijland TG  Touret JL  Visser D 《The Journal of geology》2000,108(2):247-249

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