Dynamic stability of hydraulic poppet valves

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1963.MICROFICHE COPY AVAILABLE IN ENGINEERING.Includes bibliographical references (leaf 65).by Jens E. Jörgensen.M.S

A transient network of telechelic polymers and microspheres : structure and rheology

We study the structure and dynamics of a transient network composed of droplets of microemulsion connected by telechelic polymers. The polymer induces a bridging attraction between droplets without changing their shape. A viscoelastic behaviour is induced in the initially liquid solution, characterised in the linear regime by a stretched exponential stress relaxation. We analyse this relaxation in the light of classical theories of transient networks. The role of the elastic reorganisations in the deformed network is emphasized. In the non linear regime, a fast relaxation dynamics is followed by a second one having the same rate as in the linear regime. This behaviour, under step strain experiments, should induce a non monotonic behaviour in the elastic component of the stress under constant shear rate. However, we obtain in this case a singularity in the flow curve very different from the one observed in other systems, that we interpret in terms of fracture behaviour.Comment: 9 pages, 4 figure

The stellar content of low redshift BL Lac host galaxies from multicolour imaging

We present B-band imaging of 18 low redshift (z<0.3) BL Lac objects for which their host galaxies were previously resolved in the R-band and the near-infrared H-band. For a subset of the objects, also U- and V-band imaging is presented. These data are used to investigate the blue-red-near-infrared colours and the colour gradients of the host galaxies of BL Lacs in comparison with other elliptical galaxies with and without nuclear activity. In all cases galaxies are well represented by an elliptical model, with average absolute magnitude M_B=-21.6+-0.7 and average scale length R_e=7.6+-3.2 kpc. The best-fit B-band Kormendy relation is in reasonable agreement with that obtained for normal ellipticals and radio galaxies. This structural and dynamical similarity indicates that all massive elliptical galaxies can experience nuclear activity without significant perturbation of their global structure. The distributions of the integrated blue/near-infrared colour (with average B-H=3.5+-0.5) and colour gradient (with average Delta(B-R)/Delta(log r)=-0.14+-0.75) of the BL Lac hosts are much wider than those for normal ellipticals, and most BL Lac objects have bluer hosts and/or steeper colour gradients than those in normal ellipticals. The blue colours are likely caused by a young stellar population component, and indicates a link between star formation caused by an interaction/merging event and the onset of the nuclear activity. This result is corroborated by stellar population modelling, indicating a presence of young/intermediate age populations in the majority of the sample, in agreement with low redshift quasar hosts. The lack of strong signs of interaction may require a significant time delay between the event with associated star formation episodes and the start of the nuclear activity.Comment: 16 pages, 10 figure

OGLE-2005-BLG-018: Characterization of Full Physical and Orbital Parameters of a Gravitational Binary Lens

We present the analysis result of a gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by 2 adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling of the light curve considering the parallax effect and Keplerian orbital motion, we are able to measure not only the physical parameters but also a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance $6.7\pm 0.3$ kpc from the Earth. The individual lens components with masses $0.9\pm 0.3\ M_\odot$ and $0.5\pm 0.1\ M_\odot$ are separated with a semi-major axis of $a=2.5 \pm 1.0$ AU and orbiting each other with a period $P=3.1 \pm 1.3$ yr. The event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves.Comment: 19 pages, 6 figure

Unstable Flow and Non-Monotonic Constitutive Equation of Transient Networks

We have measured the nonlinear rheological response of a model transient network over a large range of steady shear rates. The system is built up from an oil in water droplet microemulsion into which a telechelic polymer is incorporated. The phase behaviour is characterized which comprises a liquid-gas phase separation and a percolation threshold. The rheological measurements are performed in the one phase region above the percolation line. Shear thinning is observed for all samples, leading in most cases to an unstable stress response at intermediate shear rates. We built up a very simple mean field model which involves the reduction of the residence time of the stickers in the droplets due to the chain tensions at high shear. The computed constitutive equation is non-monotonic with a range where the stress is a decreasing function of the rate, a feature that indeed makes homogeneous flows unstable. The computed the flow curves compare well to the experiments.Comment: mai 200

Impact Factor: outdated artefact or stepping-stone to journal certification?

A review of Garfield's journal impact factor and its specific implementation as the Thomson Reuters Impact Factor reveals several weaknesses in this commonly-used indicator of journal standing. Key limitations include the mismatch between citing and cited documents, the deceptive display of three decimals that belies the real precision, and the absence of confidence intervals. These are minor issues that are easily amended and should be corrected, but more substantive improvements are needed. There are indications that the scientific community seeks and needs better certification of journal procedures to improve the quality of published science. Comprehensive certification of editorial and review procedures could help ensure adequate procedures to detect duplicate and fraudulent submissions.Comment: 25 pages, 12 figures, 6 table

Subordinated masculinities : A critical inquiry into reproduction of gender norms in handovers and rounds in a forensic psychiatric care

Aims and objectives To examine how gendered discursive norms and notions of masculinity are (re)produced in professional conversations about men cared for as patients in forensic psychiatric care, with a particular focus on the centrality of language and gender. Background During verbal handovers and ward rounds, care staff converse to share information about patients and make decisions about their mental status. Spoken language is thus a pivotal tool in verbal handovers and ward rounds, one able to reproduce discourses and gender norms. Design Qualitative. Data collected from audio recordings of verbal handovers and ward rounds in a forensic psychiatric clinic were subjected to discourse analysis. The COREQ checklist was used. Results While discussing patients, staff subordinated them by reproducing a discourse typical of heteronormative, family-oriented care. The overarching discourse, which we labelledsubordinated masculinities, was supported by three other discourses:being unable to take responsibility,being drug-addictedandperforming masculinity. Such discourse was identified as a disciplining practice that subordinate's patients as a means to maintain order, rules and gender norms. Conclusion The study reveals a caring practice that position male patients as children or disabled individuals and, in that way, as subordinated other men within a context were staff reproduces a heteronormative family structured care. The process also reveals a practice were downplaying aggressive and deviant behaviour could disempower and reduce patients ' responsibility for personal actions and their possibilities to participate in their care. That finding especially seems to contradict previous findings that patients want to be able to act responsibly and, to that end, want care staff to help them. Relevance to clinical practice Nurses need to deepen their understanding of how language (re)produces discursive norms of gender and masculinity in forensic care and that process's consequences for such care.Peer reviewe

Robust Phase Behavior of Model Transient networks

In order to study the viscoelastic properties of certain complex fluids which are described in terms of a multiconnected transient network we have developed a convenient model system composed of microemulsion droplets linked by telechelic polymers. The phase behavior of such systems has two characteristic features: a large monophasic region which consists of two sub-regions (a fluid sol phase and a viscoelastic gel phase) separated by a percolation line and a two phase region at low volume fraction with separation into a dilute sol phase and a concentrated gel phase. From the plausible origin of these features we expect them to be very similar in different systems. We describe here the phase behavior of four different systems we prepared in order to vary the time scale of the dynamical response of the transient network; they consist of the combination of two oil(decane) in water microemulsions differing by the stabilizing surfactant monolayer (Cetyl pyridinium chloride/octanol or TX100/TX35) and of two telechelic polymers which are end-grafted poly (ethylene oxide) chains, differing by the end-grafted hydrophobic aliphatic chains (C12H25 or C18H37).Comment: April 9 200

The Cyst-Theca Relationship Of The Dinoflagellate Cyst Trinovantedinium Pallidifulvum, With Erection Of Protoperidinium Lousianensis Sp Nov And Their Phylogenetic Position Within The Conica Group

We establish the cyst-theca relationship of the dinoflagellate cyst species Trinovantedinium pallidifulvum Matsuoka 1987 based on germination experiments of specimens isolated from the Gulf of Mexico. We show that the motile stage is a new species, designated as Protoperidinium louisianensis. We also determine its phylogenetic position based on single-cell polymerase chain reaction (PCR) of a single cell germinated from the Gulf of Mexico cysts. To further refine the phylogeny, we determined the large subunit (LSU) sequence through single-cell PCR of the cyst Selenopemphix undulata isolated from Brentwood Bay (Saanich Inlet, BC, Canada). The phylogeny shows that P. louisianensis is closest to P. shanghaiense, the motile stage of T. applanatum, and is consistent with the monophyly of the genus Trinovantedinium. Selenopemphix undulata belongs to a different clade than Selenopemphix quanta (alleged cyst of P. conicum), suggesting that the genus Selenopemphix is polyphyletic. Trinovantedinium pallidifulvum is widely distributed with occurrences in the Gulf of Mexico, the North Atlantic, the northeast Pacific and southeast Asia. In addition, we illustrate the two other extant species, Trinovantedinium applanatum and Trinovantedinium variabile, and two morphotypes of Trinovantedinium. Geochemical analyses of the cyst wall of T. pallidifulvum indicate the presence of amide groups in agreement with other heterotrophic dinoflagellate species, although the cyst wall of T. pallidifulvum also includes some unique features