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Search Results: 1 - 10 of 304466 matches for " E. V. van der Plas "
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A quantitative evaluation of the high resolution HARMONIE model for critical weather phenomena
E. V. van der Plas, B. Wichers Schreur,K. Kok
Advances in Science and Research (ASR) , 2012, DOI: 10.5194/asr-8-149-2012
Abstract: The high resolution non-hydrostatic Harmonie model (Seity et al., 2012) seems capable of delivering high quality precipitation forecasts. The quality with respect to the European radar composite is assessed using the Model Evaluation Tool, as distributed by the NCAR DTC (Developmental Testbed Center, 2012), and compared to that of the reference run of Hirlam (Unden et al., 2002), the current operational NWP model at KNMI. Both neighbourhood and object-based verification methods are compared for a week with several high intensity precipitation events in July 2010. It is found that Hirlam scores very well in most metrics, and that in spite of the higher resolution the added value of the Harmonie model is sometimes hard to quantify. However, higher precipitation intensities are better represented in the Harmonie model with its higher resolution. Object-based methods do not yet yield a sharp distinction between the different models, as it proves difficult to construct a meaningful and distinguishing metric with a solid physical basis for the many settings that can be varied.
Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development
J. Zhang, D. Gilbert, A. J. Gooday, L. Levin, S. W. A. Naqvi, J. J. Middelburg, M. Scranton, W. Ekau, A. Pe a, B. Dewitte, T. Oguz, P. M. S. Monteiro, E. Urban, N. N. Rabalais, V. Ittekkot, W. M. Kemp, O. Ulloa, R. Elmgren, E. Escobar-Briones,A. K. Van der Plas
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including estuaries, coastal waters, upwelling areas, fjords and semi-enclosed basins, with various external forcings, ecosystem responses, feedbacks and potential impact on the sustainability of the fishery and economics. The obvious external forcings include freshwater runoff and other factors contributing to stratification, organic matter and nutrient loadings, as well as exchange between coastal and open ocean water masses. Their different interactions set up mechanisms that drive the system towards hypoxia. Coastal systems also vary in their relative susceptibility to hypoxia depending on their physical and geographic settings. It is understood that coastal hypoxia has a profound impact on the sustainability of ecosystems, which can be seen, for example, by the change in the food-web structure and system function; other influences include compression and loss of habitat, as well as changes in organism life cycles and reproduction. In most cases, the ecosystem responds to the low dissolved oxygen in non-linear ways with pronounced feedbacks to other compartments of the Earth System, including those that affect human society. Our knowledge and previous experiences illustrate that there is a need to develop new observational tools and models to support integrated research of biogeochemical dynamics and ecosystem behavior that will improve confidence in remediation management strategies for coastal hypoxia.
The structure of disks around Herbig Ae/Be stars as traced by CO ro-vibrational emission
G. van der Plas,M. E. van den Ancker,L. B. F. M. Waters,C. Dominik
Physics , 2014, DOI: 10.1051/0004-6361/201425052
Abstract: We study the emission and absorption of CO ro-vibrational lines in the spectra of intermediate mass pre-main-sequence stars with the aim to determine both the spatial distribution of the CO gas and its physical properties. We also aim to correlate CO emission properties with disk geometry. Using high-resolution spectra containing fundamental and first overtone CO ro-vibrational emission, observed with CRIRES on the VLT, we probe the physical properties of the circumstellar gas by studying its kinematics and excitation conditions. We detect and spectrally resolve CO fundamental ro-vibrational emission in 12 of the 13 stars observed, and in two cases in absorption. Keeping in mind that we studied a limited sample, we find that the physical properties and spatial distribution of the CO gas correlate with disk geometry. Flaring disks show highly excited CO fundamental emission up to v$_u$ = 5, while self-shadowed disks show CO emission that is not as highly excited. Rotational temperatures range between ~250-2000 K. The $^{13}$CO rotational temperatures are lower than those of $^{12}$CO. The vibrational temperatures in self-shadowed disks are similar to or slightly below the rotational temperatures, suggesting that thermal excitation or IR pumping is important in these lines. In flaring disks the vibrational temperatures reach as high as 6000 K, suggesting fluorescent pumping. Using a simple kinematic model we show that the CO inner radius of the emitting region is $\approx$10 au for flaring disks and $\leq$ 1 au for self-shadowed disks. (abstract truncated due to 1920 character limit for arXiv)
Spatially resolved HCN J=4--3 and CS J=7--6 emission from the disk around HD 142527
G. van der Plas,S. Casassus,F. Menard,S. Perez,W. F. Thi,C. Pinte,V. Christiaens
Physics , 2014, DOI: 10.1088/2041-8205/792/2/L25
Abstract: The disk around HD 142527 attracts a lot of attention, amongst others because of its resolved (sub) mm dust continuum that is concentrated into a horseshoe-shape towards the north of the star. In this manuscript we present spatially resolved ALMA detections of the HCN J=4-3 and CS J=7-6 emission lines. These lines give us a view deeper into the disk compared to the (optically thicker) CO isotopes. This is the first detection of CS J=7-6 coming from a protoplanetary disk. Both emission lines are azimuthally asymmetric and are suppressed under the horseshoe-shaped continuum emission peak. A possible mechanism to explain the decrease under the horseshoe-shaped continuum is the increased opacity coming from the higher dust concentration at the continuum peak. Lower {\gr dust and/or gas} temperatures and an optically thick radio-continuum reduce line emission by freeze-out and shielding of emission from the far side of the disk.
A survey for near-infrared H2 emission in Herbig Ae/Be stars: emission from the outer disks of HD 97048 and HD 100546
A. Carmona,G. van der Plas,M. E. van den Ancker,M. Audard,L. B. F. M Waters,D. Fedele,B. Acke,E. Pantin
Physics , 2011, DOI: 10.1051/0004-6361/201116561
Abstract: We report on a sensitive search for H2 1-0 S(1), 1-0 S(0) and 2-1 S(1) ro-vibrational emission at 2.12, 2.22 and 2.25 micron in a sample of 15 Herbig Ae/Be stars employing CRIRES, the ESO-VLT near-infrared high-resolution spectrograph, at R~90,000. We detect the H2 1-0 S(1) line toward HD 100546 and HD 97048. In the other 13 targets, the line is not detected. The H2 1-0 S(0) and 2-1 S(1) lines are undetected in all sources. This is the first detection of near-IR H2 emission in HD 100546. The H2 1-0 S(1) lines observed in HD 100546 and HD 97048 are observed at a velocity consistent with the rest velocity of both stars, suggesting that they are produced in the circumstellar disk. In HD 97048, the emission is spatially resolved and it is observed to extend at least up to 200 AU. We report an increase of one order of magnitude in the H2 1-0 S(1) line flux with respect to previous measurements taken in 2003 for this star, which suggests line variability. In HD 100546 the emission is tentatively spatially resolved and may extend at least up to 50 AU. Modeling of the H2 1-0 S(1) line profiles and their spatial extent with flat keplerian disks shows that most of the emission is produced at a radius >5 AU. Upper limits to the H2 1-0 S(0)/ 1-0 S(1) and H2 2-1 S(1)/1-0 S(1) line ratios in HD 97048 are consistent with H2 gas at T>2000 K and suggest that the emission observed may be produced by X-ray excitation. The upper limits for the line ratios for HD 100546 are inconclusive. Because the H2 emission is located at large radii, for both sources a thermal emission scenario (i.e., gas heated by collisions with dust) is implausible. We argue that the observation of H2 emission at large radii may be indicative of an extended disk atmosphere at radii >5 AU. This may be explained by a hydrostatic disk in which gas and dust are thermally decoupled or by a disk wind caused by photoevaporation.
CO ro-vibrational lines in HD100546: A search for disc asymmetries and the role of fluorescence
R. P. Hein Bertelsen,I. Kamp,M. Goto,G. van der Plas,W. -F. Thi,L. B. F. M. Waters,M. E. van den Ancker,P. Woitke
Physics , 2013, DOI: 10.1051/0004-6361/201322574
Abstract: We have studied the emission of CO ro-vibrational lines in the disc around the Herbig Be star HD100546 with the final goal of using these lines as a diagnostic to understand inner disc structure in the context of planet formation. High-resolution IR spectra of CO ro-vibrational emission at eight different position angles were taken with CRIRES at the VLT. From these spectra flux tables, CO ro-vibrational line profiles, and population diagrams were produced. We have investigated variations in the line profile shapes and line strengths as a function of slit position angle. We used the thermochemical disc modelling code ProDiMo based on the chemistry, radiation field, and temperature structure of a previously published model for HD100546. Comparing observations and the model, we investigated the possibility of disc asymmetries, the excitation mechanism (UV fluorescence), the geometry, and physical conditions of the inner disc. The observed CO ro-vibrational lines are largely emitted from the inner rim of the outer disc at 10-13 AU. The line shapes are similar for all v levels and line fluxes from all vibrational levels vary only within one order of magnitude. All line profile asymmetries and variations can be explained with a symmetric disc model to which a slit correction and pointing offset is applied. Because the angular size of the CO emitting region (10-13 AU) and the slit width are comparable the line profiles are very sensitive to the placing of the slit. The model reproduces the line shapes and the fluxes of the v=1-0 lines as well as the spatial extent of the CO ro-vibrational emission. It does not reproduce the observed band ratios of 0.5-0.2 with higher vibrational bands. We find that lower gas volume densities at the surface of the inner rim of the outer disc can make the fluorescence pumping more effcient and reproduce the observed band ratios.
CO gas inside the protoplanetary disk cavity in HD 142527: disk structure from ALMA
Sebastian Perez,S. Casassus,F. Ménard,P. Roman,G. van der Plas,L. Cieza,C. Pinte,V. Christiaens,A. S. Hales
Physics , 2014, DOI: 10.1088/0004-637X/798/2/85
Abstract: Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 au from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue observations of the gas-rich disk HD 142527, in the J=2-1 line of 12CO, 13CO and C18O, obtained with the Atacama Large Millimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the 12CO emission is optically thick, while 13CO and C18O emission are both optically thin. The total mass of residual gas inside the cavity is about 1.5-2 Jupiter masses. We model the gas with an axisymmetric disk model. Our best fit model shows that the cavity radius is much smaller in CO than it is in millimeter continuum and scattered light observations, with a gas cavity that does not extend beyond 105 au (at 3-sigma). The gap wall at its outer edge is diffuse and smooth in the gas distribution, while in dust continuum it is manifestly sharper. The inclination angle, as estimated from the high velocity channel maps, is 28+/-0.5 degrees, higher than in previous estimates, assuming a fix central star mass of 2.2 Solar masses.
Generic and disease-specific health related quality of life in non-cirrhotic, cirrhotic and transplanted liver patients: a cross-sectional study
Simone M van der Plas, Bettina E Hansen, Josien B de Boer, Theo Stijnen, Jan Passchier, Robert A de Man, Solko W Schalm
BMC Gastroenterology , 2003, DOI: 10.1186/1471-230x-3-33
Abstract: Members of the Dutch liver patient association received the Short Form-36, the Liver Disease Symptom Index and the Multidimensional Fatigue Index-20. Based on reported clinical characteristics we classified respondents (n = 1175) as non-cirrhotic, compensated cirrhotic, decompensated cirrhotic or transplants. We used linear, ordinal and logistic regression to compare the HRQoL between groups.All liver patients showed a significantly worse generic HRQoL and fatigue than healthy controls. Decompensated cirrhotic patients showed a significantly worse disease-specific and generic HRQoL and fatigue than non-cirrhotic patients, while HRQoL differences between non-cirrhotic and compensated cirrhotic patients were predominantly insignificant. Transplanted patients showed a better generic HRQoL, less fatigue and lower probabilities of severe symptoms than non-cirrhotic patients, but almost equal probabilities of symptom hindrance.HRQoL in chronic liver patients depends on disease stage and transplant history. Non-cirrhotic and compensated cirrhotic patients have a similar HRQoL. Decompensated patients show the worst HRQoL, while transplanted patients show a significantly better HRQoL than cirrhotic and non-cirrhotic patients.In the year 2000, 40.9% of the Dutch population suffered from a chronic disease. In that same year, more than 800 Dutch men and women died of a chronic liver disease (0.6% of year specific total mortality) [1]. Until today, the Dutch liver patient association (Nederlandse Leverpati?nten Vereniging (NLV)) and many other patient associations fight for recognition of disease related physical, mental and social problems of chronic patients. Quality of life research could contribute to a better understanding of these problems and may fulfil this quest for recognition.One of the first studies done on Health Related Quality of Life (HRQoL) of chronic liver patients was conducted in 1979 and studied the effect of liver transplantation on HRQoL of chronic liver p
High prevalence of comorbidity and need for up-referral among inpatients at a district-level hospital with specialist tuberculosis services in South Africa – the need for specialist support
H van der Plas, M Mendelson
South African Medical Journal , 2011,
Abstract: Objectives. To define the patient population at Cape Town’s district-level hospital offering specialist tuberculosis (TB) services, concerning the noted increase in complex, sick HIV-TB co-infected patients requiring increased levels of care. Methods. A cross-sectional study of all hospitalised adult patients in Brooklyn Chest Hospital (a district-level hospital offering specialist TB services) from 27 to 30 October 2008. Outcome measures were: type of TB and drug sensitivity, HIV co-infection, comorbidity, Karnofsky performance score, and frequency and reason for referral to other health care facilities. Results. More than two-thirds of patients in the acute wards were HIV-co-infected, of whom 98% had significant comorbidities and 60% had a Karnofsky performance score ≤30. Twenty-eight per cent of patients did not have a confirmed diagnosis of TB. In contrast, long-stay patients with multidrug-resistant (MDR), pre-extensively (pre-XDR) and extensively drug-resistant (XDR) TB had a lower prevalence of HIV co-infection, but manifested high rates of comorbidity. Overall, one-fifth of patients required up-referral to higher levels of care. Conclusions. District-level hospitals such as Brooklyn Chest Hospital that offer specialist TB services share the increasing burden of complex, sick, largely HIV-co-infected TB patients with their secondary and tertiary level counterparts. To support these hospitals effectively, outreach, skills transfer through training, and improved radiology resources are required to optimise patient care.
An exploration of personal, relational and collective well-being in nursing students during their training at a tertiary education institution
KD Watkins, V Roos, E Van der Walt
Health SA Gesondheid , 2011,
Abstract: The well-being of nursing students has become crucial because of the multidimensional challenges that nursing professionals have to deal with. A community psychology framework was adopted in this study. The aim of the research was to explore the different dimensions of well-being as described by nursing students. A purposive and availability sample was used to gather qualitative data (interviews, focus groups and visual presentations) during 2008 and 2010 from first-year nursing students, which were thematically analysed. The emergent themes were grouped according to personal, relational and collective well-being. The findings indicated that nursing students’ personal well-being was undermined by a lack of autonomy, feelings of uncertainty, and feelings of pressure and disillusionment with the nursing profession and their training. Personal well-being was also described in terms of dispositional optimism and the need for a sense of purpose and deeper meaning. Relational well-being was expressed by the nursing students in relation to their friends, family and lecturers. The different relationships were important sources of comfort and encouragement. Their collective well-being was threatened by a challenging work environment, lack of role models in clinical settings as well as incongruence between theoretical training and practical application. Recommendations for improving the different dimensions of well-being are suggested. Die welsyn van verpleegkundestudente het deurslaggewend geword as gevolg van die uiteenlopende uitdagings wat verpleegkundiges moet hanteer. ‘n Gemeenskapsielkunde raamwerk is in hierdie studie gebruik. Die doel van die navorsing was om die verskillende dimensies van welsyn van verpleegkundestudente te ondersoek. ‘n Doelgerigte en beskikbaarheidsteekproef is gebruik om kwalitatiewe data (onderhoude, fokusgroepe en visuele voorstellings) wat gedurende 2008 en 2010 van eerstejaar-verpleegkundestudente bekom is, deur middel van tematiese inhoudsontleding te analiseer. Die temas wat na vore gekom het, is gegroepeer volgens persoonlike, verhoudings- en gemeenskaplike welsyn. Die bevindinge het aangedui dat die verpleegkundestudente se persoonlike welsyn ondermyn word deur ‘n gebrek aan outonomie, gevoelens van onsekerheid en om onder druk te verkeer, asook ‘n ontnugtering met die verpleegkunde professie en opleiding. Persoonlike welyn is ook beskryf in terme van ‘n optimistiese ingesteldheid en die behoefte aan sinvolheid en ‘n dieper betekenis. Verhoudingswelsyn is deur die verpleegkundestudente uitgedruk in terme van hulle verhouding met hul vriende, familie en dosente. Die verskillende verhoudings word as belangrike bronne van ondersteuning en aanmoediging geag. Gemeenskaplike welsyn word bedreig deur ‘n uitdagende werksomgewing, die afwesigheid van rolmodelle in die kliniese omgewings asook die teenstrydigheid van die teoretiese opleiding met die praktiese toepassing daarvan. Aanbevelings vir die bevordering van welsyn in die
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