A dynamical system approach to higher order gravity

The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review the main results and I give brief comments on the perspectives for further developments.Comment: 6 pages, 1 figure, 2 tables, talk given at IRGAC 2006, July 200

Are Compact High-Velocity Clouds Extragalactic Objects?

Compact high-velocity clouds (CHVCs) are the most distant of the HVCs in the Local Group model and would have HI volume densities of order 0.0003/cm^3. Clouds with these volume densities and the observed neutral hydrogen column densities will be largely ionized, even if exposed only to the extragalactic ionizing radiation field. Here we examine the implications of this process for models of CHVCs. We have modeled the ionization structure of spherical clouds (with and without dark matter halos) for a large range of densities and sizes, appropriate to CHVCs over the range of suggested distances, exposed to the extragalactic ionizing photon flux. Constant-density cloud models in which the CHVCs are at Local Group distances have total (ionized plus neutral) gas masses roughly 20-30 times larger than the neutral gas masses, implying that the gas mass alone of the observed population of CHVCs is about 40 billion solar masses. With a realistic (10:1) dark matter to gas mass ratio, the total mass in such CHVCs is a significant fraction of the dynamical mass of the Local Group, and their line widths would exceed the observed FWHM. Models with dark matter halos fare even more poorly; they must lie within approximately 200 kpc of the Galaxy. We show that exponential neutral hydrogen column density profiles are a natural consequence of an external source of ionizing photons, and argue that these profiles cannot be used to derive model-independent distances to the CHVCs. These results argue strongly that the CHVCs are not cosmological objects, and are instead associated with the Galactic halo.Comment: 30 pages, 14 figures; to appear in The Astrophysical Journa

Local Surface Density of the Galactic Disk from a 3-D Stellar Velocity Sample

We have re-estimated the surface density of the Galactic disk in the solar neighborhood within $\pm$ 0.4 kpc of the Sun using parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon (2000). We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample, (14.4 $\pm$ 0.26 km/sec), and combine these to derive the surface density of gravitating matter in the Galactic disk as a function of the galactic coordinate $z$. The surface density of the disk increases from 10.5 $\pm$ 0.5 $M_{\odot}$ / pc$^2$ within $\pm$ 50 pc to 42 $\pm$ 6 $M_{\odot}$ / pc$^2$ within $\pm$ 350 pc. The estimated volume density of the galactic disk within $\pm$ 50 pc is about 0.1 $M_{\odot}$ / pc$^3$ which is close to the volume density estimates of the observed baryonic matter in the solar neighborhood.Comment: 24 pages, 15 figures, AJ in pres

Toekomstspijt, dat is wat ik voel

Met dit kwalitatief fenomenologisch onderzoek is getracht inzicht te verkrijgen in de beleving van mensen die zich in de laatste levensfase bevinden. Systematisch is gezocht naar de essentie van de ervaring, het fenomeen, waar ieder mens in de laatste levensfase mee te maken krijgt. Hierop zijn 40 interviews bestudeerd, die in 2012 en 2013 gepubliceerd stonden in de wekelijkse rubriek “Het laatste Woord” van het NRC dagblad. De vraag die leidend was in het onderzoek, was de vraag naar de (geleefde) ervaring van mensen die mensen die zich bewust zijn van het naderende levenseinde. Wat is voor hen in essentie van belang, hoe reageren zij hierop, hoe gaan zij om met dit besef dat de dood in zicht is? Ingaan op die vragen vraagt, naast het doen van het onderzoek zelf, om een verkenning van diverse theorieën die handelen over het proces van dood gaan. In het theoretisch kader komt dit aan bod. Hier gaat het om de emotionele ervaringen die tijdens het proces van afscheid nemen van het leven ondervonden worden, ervaringen van het verwerkingsproces tijdens deze levensfase, rouw- en verlieservaringen. Maar ook theorieën over wat mensen geestelijk op de been houdt, waar ze geluk in ervaren, wat troost biedt. Vervolgens komen in de resultaten, de bevindingen van het onderzoek naar voren. Hier blijkt dat mensen in de laatste levensfase tegen het licht van de dood een diepe verbondenheid voelen met het leven zelf, met hun naasten, met de natuur. De reacties op deze intens gevoelde verbondenheid en de wijze van omgaan zijn heel verscheiden van aard en variëren van verzet tot overgave. In de conclusie worden de bevindingen van de resultaten, die de basis vormen van het onderzoek, geconfronteerd met de bestudeerde literatuur. De vraag welke praktische implicaties dit heeft op de zorg is hieruit herleidbaar en komt hier eveneens aan de orde

Can yield gap analysis be used to inform R & D prioritisation?

The phrase “biggest bang for a buck” is associated with the policy making question that governments and development agencies face: “Where and which crops should receive highest priority for improving local and global food supply?”. A first step of prioritisation is to identify region x crop combinations for which high impact can be anticipated. We developed a new method for this prioritisation exercise and applied it to data from the Global Yield Gap and Water Productivity Atlas (GYGA). Our prioritisation distinguishes between two policy objectives (humanitarian and economic) and builds upon the relative yield gap and climate risk. Results of the prioritisation are presented and visualised in Google Earth

Polarization-controlled optimal scatter suppression in transient absorption spectroscopy

Ultrafast transient absorption spectroscopy is a powerful technique to study fast photo-induced processes, such as electron, proton and energy transfer, isomerization and molecular dynamics, in a diverse range of samples, including solid state materials and proteins. Many such experiments suffer from signal distortion by scattered excitation light, in particular close to the excitation (pump) frequency. Scattered light can be effectively suppressed by a polarizer oriented perpendicular to the excitation polarization and positioned behind the sample in the optical path of the probe beam. However, this introduces anisotropic polarization contributions into the recorded signal. We present an approach based on setting specific polarizations of the pump and probe pulses, combined with a polarizer behind the sample. Together, this controls the signal-to-scatter ratio (SSR), while maintaining isotropic signal. We present SSR for the full range of polarizations and analytically derive the optimal configuration at angles of 40.5° between probe and pump and of 66.9° between polarizer and pump polarizations. This improves SSR by 33 52 ≈. (or 3 compared to polarizer parallel to probe). The calculations are validated by transient absorption experiments on the common fluorescent dye Rhodamine B. This approach provides a simple method to considerably improve the SSR in transient absorption spectroscopy

Computerized cyclic voltammetric detection after HPLC of the antineoplastic agents etoposide, teniposide, adriamycin and its metabolite adriamycinol in urine samples

A computerized electrochemical detection system for application after HPLC, provided with a cyclic voltammetric oxidative and reductive module, is described for the on-line qualitative determination of electroactive antineoplastic agents and metabolites in urine samples, collected from cancer patients, following intravenous administration

The Reproducibility and Applicability of an EFD(®) Dispenser in the Prosthetic Technology of Maxillofacial Prostheses

A reproducible method of dosing pigments can be beneficial and more efficient in the current colour matching procedure in maxillofacial prosthetics. In this study the reproducibility and applicability for pigment dosing of a commercial available EFD(®) dispenser were tested. The reproducibility of a Performus™ II type EFD(®) dispenser was tested by repeating dosing experiments with a set of eight syringes filled with pigment pastes (Factor 2; Flagstaff, USA). To evaluate conventional colour matching, four conventionally colour matched samples were polymerized and compared to the original ones. To investigate the reproducibility of the dispenser in practice, a fifth recipe was dispensed 10 times and colour differences were evaluated visually and as well calculated from measurements with a colour and translucency meter (CTM, PBSensortechnology bv). All dispensed amounts of pigment pastes showed a coefficient of variation in weight of less than 10 %. Evaluating the reproductions of four skin batches compared to the original batches, a ∆E2000 colour difference of 3–7 was measured. Evaluating ten reproductions of one skin coloured batch made with the dispenser, color difference ∆E2000 values compared to the average L*a*b* values, were less than 2 and no visual colour differences could be estimated. Conform these results, low colour differences could be measured with the CTM, indicating no visually observable consequences. Despite the estimated coefficient of variation, the reproducibility of the EFD(®) dispenser in terms of colour difference ∆E2000 of successive dispensing is applicable for colour reproduction in facial prosthetics. Segregation of the current color pastes in due time needs to be taken into consideration

A prosthodontic concept using implants in the resorbed edentulous maxilla

For the treatment of the atrophic edentulous maxilla implant supported overdentures provide the opportunity to obtain proper lip support, speech and cleanliness. A superstructure with high rigidity is needed for an optimal distribution of occlusal loading, to ensure good prognosis for implant survival. A prosthodontic concept using a hybrid construction meets these criteria. It consists of a cast and precision-milled mesostructure fixed to the implants, over which that a removable cast prosthodontic device is placed to which the teeth are attached. It is essential to follow a strict treatment protocol to obtain a good and predictable result.</p