Low-mass Star Formation: Observations

I briefly review recent observations of regions forming low mass stars. The discussion is cast in the form of seven questions that have been partially answered, or at least illuminated, by new data. These are the following: where do stars form in molecular clouds; what determines the IMF; how long do the steps of the process take; how efficient is star formation; do any theories explain the data; how are the star and disk built over time; and what chemical changes accompany star and planet formation. I close with a summary and list of open questions.Comment: Proceedings of Computational Star Formation Conference, Barcelon

Differences in physical-fitness test scores between actively and passively recruited older adults: consequences for norm-based classification

This study investigated differences in physical-fitness test scores between actively and passively recruited older adults and the consequences thereof for norm-based classification of individuals. Walking endurance, grip strength, hip flexibility, balance, manual dexterity, and reaction time were measured in participants age 57 years or older: 1 sample recruited through media announcements (passively recruited) and 1 sample recruited through personal contact (actively recruited). Classifications on a 5-point scale based on norms were cross-tabulated. Compared with the actively recruited sample, performance of the passively recruited sample was significantly better on all tests except, for women, hip flexibility and manual dexterity. Cross-tabulation of the 2 classifications showed that percentages of agreement varied from 27.4% to 87.4%. Cohen's Kappa varied from. 11 to .84. Caution should be used when giving feedback on test performance and subsequently making physical activity recommendations if norms are based on the performance of passively recruited older adults

A generation-oriented workbench for performance grammar: Capturing linear order variability in German and Dutch

We describe a generation-oriented workbench for the Performance Grammar (PG) formalism, highlighting the treatment of certain word order and movement constraints in Dutch and German. PG enables a simple and uniform treatment of a heterogeneous collection of linear order phenomena in the domain of verb constructions (variably known as Cross-serial Dependencies, Verb Raising, Clause Union, Extraposition, Third Construction, Particle Hopping, etc.). The central data structures enabling this feature are clausal “topologies”: one-dimensional arrays associated with clauses, whose cells (“slots”) provide landing sites for the constituents of the clause. Movement operations are enabled by unification of lateral slots of topologies at adjacent levels of the clause hierarchy. The PGW generator assists the grammar developer in testing whether the implemented syntactic knowledge allows all and only the well-formed permutations of constituents

A generation-oriented workbench for performance grammar: Capturing linear order variability in German and Dutch

We describe a generation-oriented workbench for the Performance Grammar (PG) formalism, highlighting the treatment of certain word order and movement constraints in Dutch and German. PG enables a simple and uniform treatment of a heterogeneous collection of linear order phenomena in the domain of verb constructions (variably known as Cross-serial Dependencies, Verb Raising, Clause Union, Extraposition, Third Construction, Particle Hopping, etc.). The central data structures enabling this feature are clausal “topologies”: one-dimensional arrays associated with clauses, whose cells (“slots”) provide landing sites for the constituents of the clause. Movement operations are enabled by unification of lateral slots of topologies at adjacent levels of the clause hierarchy. The PGW generator assists the grammar developer in testing whether the implemented syntactic knowledge allows all and only the well-formed permutations of constituents

Identiteit in een neoliberale samenleving

Een bespreking van het boek van Paul Verhaeghe; "Identiteit" met duiding van relevantie voor wetenschap en begeleidingspraktijk. Er is geen wezenlijke identiteit, zegt Verhaeghe. Hij beschouwt genen min of meer als hardware , maar “wie wij worden hangt grotendeels af van onze omgeving”. Identiteit loopt via het proces van enerzijds identificatie (gelijkheid, identificatie met een groep) en anderzijds seperatie (verschil, streven naar eigenheid). In de neoliberale samenleving is de pendel te ver doorgeslagen naar seperatie, omdat de algemene opvatting is dat de mens een economisch en calculerend wezen is. de mens is echter ook sociaal en altruïstisch. De samenleving is sterk geïndividualiseerd en onderlinge verbondenheid is geërodeerd. Verhaeghe pleit voor afschaffing van bonussen en adviseert arbeidsorganisaties af te zien van fatalistische uitspraken als "de mens is van nature gericht op winstmaximalisatie, zo zit de mens nu eenmaal in elkaar". Vragen die leiders en begeleiders zichzelf kunnen stellen zijn: 1. Welke rol speel ik als begeleider in een maatschappij- en organisatiewereld die gedomineerd wordt door neoliberale ideeën? 2. Vanuit welk mens- en wereldbeeld handel ik zelf als begeleider? 3. Hoe verhoud ik mij als begeleider tot het door Verhaeghe geschetste spanningsveld

Performance evaluation of the Mojette erasure code for fault-tolerant distributed hot data storage

Packet erasure codes are today a real alternative to replication in fault tolerant distributed storage systems. In this paper, we propose the Mojette erasure code based on the Mojette transform, a formerly tomographic tool. The performance of coding and decoding are compared to the Reed-Solomon code implementations of the two open-source reference libraries namely ISA-L and Jerasure 2.0. Results clearly show better performances for our discrete geometric code compared to the classical algebraic approaches. A gain factor up to $2$ is measured in comparison with the ISA-L Intel . Those very good performances allow to deploy Mojette erasure code for hot data distributed storage and I/O intensive applications.Comment: 5 page

Feshbach resonances in cold atomic gases

The research described in this thesis is part of an international effort with the aim of studying ultracold quantum degenerate gas samples like Bose-Einstein condensates and Fermi degenerate systems, consisting of atoms confined in magnetic or optical traps. The behavior of such samples is governed by the inter-atomic interactions and the resulting properties of the atom-atom scattering. At the relevant temperatures of 1nK to 10µK a key property is the atom-atom scattering length a. In chapter 2 a theoretical method is presented which enables one to describe the interaction and scattering of (ultra)cold atoms to unprecedented precision. It is also unparalleled in comprehensiveness: it allows the prediction of a large and varied set of experimental data for all isotopes of the same element. The method relies on the extraction from experiments of a few (phase) parameters which completely summarize the behavior of the atoms in the (ultra)cold regime. In chapter 3 the method is applied to the "workhorses" of cold-atom physics: the atomic species 85Rb and 87Rb. We extract the foregoing parameters to a very high precision from several recent high precision experiments, allowing us to predict e.g. the 87Rb spinor condensate to be ferromagnetic: a prediction for which the scattering length has to be calculated with a precision better than 1%. We also predict Feshbach resonances at experimentally accessible magnetic field strengths; resonances searched for and found by the experimental group of Rempe. In close collaboration with his group we "fine-tune" the interaction parameters found previously, by making use of only one of the observed resonances. We then obtain agreement with 42 out of the observed 43 resonance field strengths and are able to identify bound states inducing the Feshbach resonances at these locations. Chapter 4 describes the results of this research. With a thorough understanding of the rubidium interactions, we then switch to lithium which has a fermionic (6Li) and a bosonic (7Li) isotope. Both are being used in cold-atom experiments. In chapter 5 we evaluate the interaction parameters for lithium allowing us to predict magnetic field strengths for which a sample of fermionic 6Li atoms can be regarded as strongly interacting. Furthermore, a three-level method for measuring mean-field shifts, based on radio-frequency techniques, is introduced. For weak interactions we find proportionality of resonance shifts to interaction strengths. In the strongly interacting regime, however, these shifts become very small reflecting the quantum unitarity limit and many-body effects. Most interesting is the fact that in this regime the shifts are small both for large positive a and for large negative a, likely reflecting the universality of the interaction energy. In chapters 6 and 7 the interactions between lithium atoms are reinvestigated, making use of newly available experimental data and with the updated interaction parameters special attention is paid to locating field strengths at which magnetically tunable Feshbach resonances occur in the scattering of lithium atoms. In chapter 6 scattering events in a gas of (fermionic) 6Li atoms are studied. In chapter 7 we show that a consistent description of the 6Li+6Li system can be given. We discuss theoretical uncertainties for the position of the wide 6Li Feshbach resonance and present an analytic scattering model for this resonance, based on the inclusion of a field-dependent virtual open-channel state. We predict new Feshbach resonances for the 6Li-7Li system, and their importance for different types of crossover superfluidity models is discussed. Molecules created by magnetically sweeping over these resonances will have a fermionic character. One magnetic field strength is predicted at which two different fermionic molecules can be created simultaneously

Dense and warm molecular gas in the envelopes and outflows of southern low-mass protostars

Observations of dense molecular gas lie at the basis of our understanding of the density and temperature structure of protostellar envelopes and molecular outflows. We aim to characterize the properties of the protostellar envelope, molecular outflow and surrounding cloud, through observations of high excitation molecular lines within a sample of 16 southern sources presumed to be embedded YSOs. Observations of submillimeter lines of CO, HCO+ and their isotopologues, both single spectra and small maps were taken with the FLASH and APEX-2a instruments mounted on APEX to trace the gas around the sources. The HARP-B instrument on the JCMT was used to map IRAS 15398-3359 in these lines. HCO+ mapping probes the presence of dense centrally condensed gas, a characteristic of protostellar envelopes. The rare isotopologues C18O and H13CO+ are also included to determine the optical depth, column density, and source velocity. The combination of multiple CO transitions, such as 3-2, 4-3 and 7-6, allows to constrain outflow properties, in particular the temperature. Archival submillimeter continuum data are used to determine envelope masses. Eleven of the sixteen sources have associated warm and/or dense quiescent as characteristic of protostellar envelopes, or an associated outflow. Using the strength and degree of concentration of the HCO+ 4-3 and CO 4-3 lines as a diagnostic, five sources classified as Class I based on their spectral energy distributions are found not to be embedded YSOs. The C18O 3-2 lines show that for none of the sources, foreground cloud layers are present. Strong molecular outflows are found around six sources, .. (continued in paper)Comment: Accepted by A&A, 13 figure