217 research outputs found
Evolutionary synthesis models for the formation of S0 galaxies in clusters
No full textRich galaxy clusters in the local Universe show a large population of S0 galaxies
(~40% of all luminous galaxies). With increasing redshift the fraction of this S0
galaxy population is observed to strongly decrease (e.g. by a factor ~ to
) in favor of the spiral galaxy fraction while the number of bright ellipticals
does not seem to change. The infalling field galaxy population that successively builds
up the cluster also is spiral rich and S0 poor. It has hence been suspected that galaxy
transformation processes, either due to galaxy – galaxy or to galaxy – ICM
interactions, are responsible for this change. Complementing dynamical and morphological
studies, we use evolutionary synthesis models describing various possible effects of
those interactions on the star formation rates of the infalling spirals. We study the
effects of starbursts of various strengths as well as of the truncation of star formation
on the color and luminosity evolution of model galaxies of various spectral types.
Comparison with observed properties of the local S0 galaxy population is used to
constrain possible S0 formation mechanisms. We find that star formation truncation
in spiral galaxies earlier than Sd-type, if occurring not too long ago, as well as
starbursts more than 3 Gyr ago and followed by complete star formation extinction in
spirals – again earlier than Sd– may well account for the observed average S0
luminosities and colors. Late-type galaxies (Sd), even after a strong burst, remain
either too blue or too faint. Our results are in agreement with studies of spectral
features of cluster S0s but allow for stronger constraints
Determination of enantiomerization barriers of hypericin and pseudohypericin by dynamic high-performance liquid chromatography on immobilized polysaccharide-type chiral stationary phases and off-column racemization experiments
No full textDirect enantiomer separation of hypericin, pseudohypericin, and protohypericin
was accomplished by high-performance liquid chromatography (HPLC) using
immobilized polysaccharide-type chiral stationary phases (CSPs). Enantioselectivities
up to 1.30 were obtained in the polar-organic elution mode whereby for hypericin and
pseudohypericin Chiralpak IC [chiral selector being cellulose tris(3,5-dichlorophenylcarbamate)]
and for protohypericin Chiralpak IA (chiral selector being the 3,5-dimethylphenylcarbamate
of amylose) gave favorable results. Enantiomers were distinguished by
on-line electronic circular dichroism detection. Optimized enantioselective chromatographic
conditions were the basis for determining stereodynamic parameters of the
enantiomer interconversion process of hypericin and pseudohypericin. Rate constants
delivered by computational simulation of dynamic HPLC elution profiles (stochastic
model, consideration of peak tailing) were used to calculate averaged enantiomerization
barriers (DG]
enant) of 97.6–99.6 kJ/mol for both compounds (investigated temperature
range 25–458C). Complementary variable temperature off-column (i.e., in solution) racemization
experiments delivered DG]
enant 5 97.1–98.0 kJ/mol (27–458C) for hypericin and
DG]
enant 5 98.9–101.4 kJ/mol (25–558C) for pseudohypericin. An activation enthalpy of
DH# 5 86.0 kJ/mol and an activation entropy of DS# 5 237.7 J/(K mol) were calculated
from hypericin racemization kinetics in solution, whereas for pseudohypericin these
figures amounted to 74.1 kJ/mol and 282.6 J/(K mol), respectively. Although the natural
phenanthroperylene quinone pigments hypericin and pseudohypericin as well as
their biological precursor protohypericin are chiral and can be separated by enantioselective
HPLC low enantiomerization barriers seem to prevent the occurrence of an
excess of one enantiomer under typical physiological conditions—at least as long as
stereoselective intermolecular interactions with other chiral entities are absen
Chemically consistent evolution of galaxies II. Spectrophotometric evolution from zero to high redshift
No full textThe composite stellar populations of galaxies comprise stars of a
wide range of metallicities. Subsolar metallicities become increasingly
important, both in the local universe when going from early towards later galaxy
types as well as for dwarf galaxies and for all types of galaxies towards higher
redshifts.
We present a new generation of chemically consistent evolutionary synthesis models
for galaxies of various spectral types from E through Sd. The models follow the
chemical enrichment of the ISM and take into account the increasing initial
metallicity of successive stellar generations using recently published metallicity
dependent stellar evolutionary isochrones, spectra and yields.
Our first set of closed-box 1-zone models does not include any spatial resolution or
dynamics. For a Salpeter initial mass function (IMF) the star formation rate
(SFR) and its time evolution are shown to successfully parameterise spectral
galaxy types E, ..., Sd. We show how the stellar metallicity distribution in various
galaxy types build up with time to yield after ~12 Gyr agreement with stellar
metallicity distributions observed in our and other local galaxies.
The models give integrated galaxy spectra over a wide wavelength
range (90.9 Å–160 μm), which for ages of ~12 Gyr are in good
agreement not only with observed broad band colours but also with template
spectra for the respective galaxy types.
Using filter functions for Johnson-Cousins , IC, as well as
for HST broad band filters in the optical and Bessel & Brett's NIR J, H, K filter
system, we calculate the luminosity and colour evolution of model galaxies over a
Hubble time.
Including a standard cosmological model () and the
attenuation by intergalactic hydrogen we present evolutionary and cosmological
corrections as well as apparent luminosities in various filters over the redshift
range from to the present for our galaxy types and compare to earlier
models using single (=solar) metallicity input physics only. We also resent a first
comparison of our cc models to HDF data. A more detailed comparison with Hubble
Deep Field (HDF) and other deep field data and an analysis and interpretation of high
redshift galaxies in terms of ages, metallicities, star formation histories and,
galaxy types will be the subject of a forthcoming paper
Neurotransmitter Vesicle Release from Human Model Neurons (NT2) is Sensitive to Botulinum Toxin A
No full textBotulinum neurotoxins (BoNTs) internalize into nerve terminals and block the release of neurotransmitters into the synapse. BoNTs are widely used as a therapeutic agent for treatment of movement disorders and recently gained more attention as a biological weapon. Consequently, there is strong interest to develop a cell-based assay platform to screen the toxicity and bioactivity of the BoNTs. In this study, we present an in vitro screening assay for BoNT/A based on differentiated human embryonal carcinoma stem (NT2) cells. The human NT2 cells fully differentiated into mature neurons that display immunoreactivity to cytoskeletal markers (beta III-tubulin and MAP2) and presynaptic proteins (synapsin and synaptotagmin I). We showed that the human NT2 cells undergo a process of exo-endocytotic synaptic vesicle recycling upon depolarization with high K+ buffer. By employing an antibody directed against light chain of BoNT/A, we detected internalized toxin as a punctate staining along the neurites of the NT2 neurons. Using well-established methods of synaptic vesicle exocytosis assay (luminal synaptotagmin I and FM1-43 imaging) we show that pre-incubation with BoNT/A resulted in a blockade of vesicle release from human NT2 neurons in a dose-dependent manner. Moreover, this blocking effect of BoNT/A was abolished by pre-adsorbing the toxin with neutralizing antibody. In a proof of principle, we demonstrate that our cell culture assay for vesicle release is sensitive to BoNT/A and the activity of BoNT/A can be blocked by specific neutralizing antibodies. Overall our data suggest that human NT2 neurons are suitable for large scale screening of botulinum bioactivity.Federal Ministry for Education and Research (BMBF) [0313732
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Knowledge Interfaces and Practices of Negotiation: Cases from a Women's Group in Bolivia and an Oil Refinery in Wales
No full textThis chapter examines encounters between international institutions that frame their objectives through a global policy language, and people whose lives are the focus for change heralded by these institutions. It explores how a global policy language, which seeks consensus and equality, can be at odds with local understandings, conflict and intentions
The use of indigenous knowledge in development: problems and challenges
No full textThe use of indigenous knowledge has been seen by many as an alternative way of promoting development in poor rural communities in many parts of the world. By reviewing much of the recent work on indigenous knowledge, the paper suggests that a number of problems and tensions has resulted in indigenous knowledge not being as useful as hoped for or supposed. These include problems emanating from a focus on the (arte)factual; binary tensions between western science and indigenous knowledge systems; the problem of differentiation and power relations; the romanticization of indigenous knowledge; and the all too frequent decontextualization of indigenous knowledge
Strukturelle Änderungen in dünnen amorphen Zr-Al-Ni-Cu- und Ta-Si-N-Schichten
No full textMit verschiedenen experimentellen Methoden
werden die strukturabhängigen Eigenschaften amorpher Zr-Al-Ni-Cu-
und Ta-Si-N- Multikomponentenschichten untersucht. Aus Messungen
der mechanischen Spannungen in amorphen Zr-Al-Ni-Cu-Schichten
werden mit hoher Empfindlichkeit relative Volumenänderungen
bestimmt, die bei Schichtwachstum, Relaxation und Kristallisation
auftreten. Das Meßverfahren ermöglicht Untersuchungen der
Spannungsrelaxation und Viskosität in der Nähe des Glasübergangs.
Irreversible Spannungsrelaxationen unterhalb von Tg
können mit der "Freie Volumen-Theorie" gedeutet werden. Als Ursache
für eine schnelle Abnahme von Druckspannungen im Bereich des
Glasübergangs wird dagegen ein Fließprozeß vorgeschlagen.
Unmittelbar während der Kristallisation werden nur geringe
Spannungsänderungen festgestellt. Aus Messungen der isothermen
Spannungsrelaxation werden Viskositäten der amorphen Schichten
bestimmt. Aus den Spannungsmessungen ergeben sich neue Erkenntnisse
über das Relaxations- und Kristallisationsverhalten von
Multikomponentengläsern. Es werden grundlegende Fragestellungen zu
Entmischungs- und Kristallisationsvorgängen in amorphen
Ta-Si-N-Schichten untersucht, die auch für technologische
Anwendungen der Schichten als Diffusionsbarrieren relevant sind.
ASAXS-, TEM- und XRD- Messungen ergeben, daß in amorphen
Ta40Si14N46-Schichten bei
Temperaturen zwischen 1073 K und 1273 K komplexe Prozesse, wie eine
Phasenseparation und eine nachfolgende Nanokristallisation
ablaufen. Diese Prozesse führen zu einer Bildung von Strukturen mit
charakteristischen Ausdehnungen und wirken sich auf die
mechanischen Spannungen aus. Durch die vorliegenden Ergebnisse wird
gezeigt, daß die Stabilität der Diffusionsbarrieren bereits
unterhalb der Kristallisationstemperatur durch die Entmischung und
Nanokristallisation begrenzt ist
Professional Doctorate in Sport and Exercise Psychology
No full textAbstract The present portfolio gives account of the research and applied experiences of a Professional Doctorate Candidate at Liverpool John Moores University. Contained within are a range of research and applied works that aim to inform and develop the sport and exercise psychology field. In parallel, the portfolio encompasses the professional development of the primary author as a trainee sport psychologist, and their journey to individuation (McEwan et al., 2019). The portfolio contains three applied case studies and one teaching case study. The consultancy case studies demonstrate a wide range of psychological interventions from a variety of psychological schools. The first case study concerns an acceptance and commitment therapy (ACT) intervention that is rooted in the school of cognitive behavioural psychology. The second is an existential approach to the consultancy that centres around the subjective lived experience of the client. These case studies contain unique outcomes that aim to provide informative and thoughtful implications for both the discipline of sport psychology and sport psychology practitioners. Within the present portfolio is a meta-study that aims to both develop and broaden the present body of organisational psychology literature, and provide insights into sport professionals’ work-life balance, a concept that has become increasingly popular over the years. Two empirical studies, one concerning exercise dependency in CrossFit, and the other, a narrative exploration of athletes’ return to sport following the COVID-19 pandemic, also demonstrate a variety of research skill and competencies required of the candidate. Readers of this portfolio will also gain some insight into the philosophical development of the candidate throughout their professional doctorate enrolment. Ontological and epistemological positionings are examined, challenged, and subsequently evolve throughout the portfolio. In particular, the author demonstrates their development from a positivist/post-positivist to a constructivist paradigm concerning their underpinning philosophical paradigm. This development is also paralleled in their consultancy practice, where the practitioner’s consultancy values move from a practitioner-led, performance focused lens to a person centred, client led consultancy style. This process of individuation is examined through commentary and reflections, where the candidate seeks to understand their values and beliefs and face up to challenges associated in their development
SYNTHETIC APPROACHES TO CYCLOPROPYL PEPTIDOMIMETICS AS 20S PROTEASOME INHIBITORS
No full textProteasome inhibitors are a relatively new class of chemotherapeutics with only three drugs currently on the market. Belactosin A, a natural product found in Streptomyces sp., possesses anti-tumor effects due to its proteasome inhibition properties, however it is not used clinically due to its toxicity. This led to several syntheses of belactosin A analogs in hopes of similar efficacy and lower toxicity. Most reported syntheses require a substantial number of steps to synthesize the cyclopropyl backbone and the b-lactone warhead of belactosin A. An efficient stereoselective cyclopropanation of amino acid enones that undergo a Michael-induced ring closure is reported here with the use of cinchona alkaloids as a catalysts, and lactonization of L-threonine to afford the a-substituted b-lactone warhead. The proposed synthetic route of the L-threonine-derived b-lactone analog of belactosin A is significantly more efficient compared to alternative analogs reported in literature.M.S
Calcium imaging reveals nicotinic acetylcholine receptors on cultured mushroom body neurons
No full text1. We used fluorescence imaging with the visible wavelength indicator fluo-3 to investigate the calcium responses to cholinergic ligands of honeybee Kenyon cells in primary culture.2. Application of acetylcholine ( ACh) or nicotine, but not pilocarpine, promoted a calcium influx into the cell body and neurites. The increase in intracellular calcium after ACh stimulation was blocked by tu-bungarotoxin. These results support previous histochemical studies that suggested the expression of nicotinic cholinergic receptors on Kenyon cells.3. After depolarization with high K+ solution fluorescence increasedin the somata and neurites, which indicates the presence ofvoltage-gated Ca *+ channels in Kenyon cell membranes.publishe
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