1,155 research outputs found
Porphyridium purpureum: Strukturierte Modellbildung und experimentelle Validierung der Stoffwechselreaktion auf Hell-Dunkel-Zyklen
Weit ĂŒber 25.000 Arten von Mikroalgen stellen ein bislang kaum erschlossenes Potential fĂŒr die Biotechnologie dar. Sie bilden vielfĂ€ltige Produkte wie Farbstoffe, ungesĂ€ttigte FettsĂ€uren, Polysaccharide und Antioxidanten mit interessanten Einsatzgebieten u.a. in der Lebensmittel- und Kosmetikindustrie. Pharmazeutisch wirksame Produkte aus Mikroalgen sind bekannt, aber noch unzulĂ€nglich untersucht. Um ihre Bildung nĂ€her verstehen und in gröĂerem MaĂstab (scale up) durch geeignete Auswahl von Kultivierungsparametern beeinflussen zu können, wird ein mathematisches Modell entwickelt, welches das Wachstum und die Produktbildung einer einzelligen Mikroalge Porphyridium purpureum abbildet.
Die Validierung des entwickelten mathematischen Modells erfolgt durch den Einsatz von geeigneten experimentell gewonnenen Kultivierungsdaten der Mikroalge Porphyridium purpureum in AbhĂ€ngigkeit von Kultivierungsparametern wie der LichtquantitĂ€t oder -qualitĂ€t in einem am Institut fĂŒr Mechanische Verfahrenstechnik und Mechanik entwickelten Photobioreaktor. Die experimentellen Untersuchungen zu Wachstum und Produktbildung der Mikroalge sowie die Modellierung ihrer StoffwechselaktivitĂ€t zur besseren Vorhersagbarkeit und zur Auslegung von Pilotanlagen stellen die beiden Hauptschwerpunkte dieser Arbeit dar
Inner ear tissue preservation by rapid freezing: improving fixation by high-pressure freezing and hybrid methods
In the preservation of tissues in as âclose to lifeâ state as possible, rapid freeze fixation has many benefits over conventional chemical fixation. One technique by which rapid freeze-fixation can be achieved, high pressure freezing (HPF), has been shown to enable ice crystal artefact-free freezing and tissue preservation to greater depths (more than 40ÎŒm) than other quick-freezing methods. Despite increasingly becoming routine in electron microscopy, the use of HPF for the fixation of inner ear tissue has been limited. Assessment of the quality of preservation showed routine HPF techniques were suitable for preparation of inner ear tissues in a variety of species. Good preservation throughout the depth of sensory epithelia was achievable. Comparison to chemically fixed tissue indicated that fresh frozen preparations exhibited overall superior structural preservation of cells. However, HPF fixation caused characteristic artefacts in stereocilia that suggested poor quality freezing of the actin bundles. The hybrid technique of pre-fixation and high pressure freezing was shown to produce cellular preservation throughout the tissue, similar to that seen in HPF alone. Pre-fixation HPF produced consistent high quality preservation of stereociliary actin bundles. Optimising the preparation of samples with minimal artefact formation allows analysis of the links between ultrastructure and function in inner ear tissues
Clumpy outer Galaxy molecular clouds and the steepening of the IMF
We report the results of high-resolution (~0.2 pc) CO(1-0) and CS(2-1)
observations of the central regions of three star-forming molecular clouds in
the far-outer Galaxy (~16 kpc from the Galactic Center): WB89 85 (Sh 2-127),
WB89 380, and WB89 437. We used the BIMA array in combination with IRAM 30-m
and NRAO 12-m observations. The GMC's in which the regions are embedded were
studied by means of KOSMA 3-m CO(2-1) observations. The properties the CO and
CS clumps are analyzed and compared with newly derived results of previously
published single-dish measurements of local clouds (OrionB South and Rosette).
We find that the slopes of the clump mass distributions (-1.28 and -1.49, for
WB89 85 and WB89 380, respectively) are somewhat less steep than found for most
local clouds, but similar to those of clouds which have been analyzed with the
same clumpfind program. We investigate the clump stability by using the virial
theorem, including all possible contributions (gravity, turbulence, magnetic
fields, and pressure due to the interclump gas). It appears that under
reasonable assumptions a combination of these forces would render most clumps
stable. Comparing only gravity and turbulence, we find that in the far-outer
Galaxy clouds, these forces are in equilibium (virial parameter alpha~1) for
clumps down to the lowest masses found (a few Msol). For clumps in the local
clouds alpha~1 only for clumps with masses larger than a few tens of Msol. Thus
it appears that in these outer Galaxy clumps gravity is the dominant force down
to a much lower mass than in local clouds, implying that gravitational collapse
and star formation may occur more readily even in the smallest clumps. Although
there are some caveats, due to the inhomogeneity of the data used, this might
explain the apparently steeper IMF found in the outer Galaxy.Comment: 29 pages, including 9 tables, 21 figures. Accepted for Astron.
Astrop
The stellar mass spectrum from non-isothermal gravoturbulent fragmentation
Identifying the processes that determine the initial mass function of stars
(IMF) is a fundamental problem in star formation theory. One of the major
uncertainties is the exact chemical state of the star forming gas and its
influence on the dynamical evolution. Most simulations of star forming clusters
use an isothermal equation of state (EOS). However, theoretical predictions and
observations suggest that the effective polytropic exponent gamma in the EOS
varies with density.
We address these issues and study the effect of a piecewise polytropic EOS on
the formation of stellar clusters in turbulent, self-gravitating molecular
clouds using three-dimensional, smoothed particle hydrodynamics simulations. To
approximate the results of published predictions of the thermal behavior of
collapsing clouds, we increase the polytropic exponent gamma from 0.7 to 1.1 at
some chosen density n_c, which we vary. The change of thermodynamic state at
n_c selects a characteristic mass scale for fragmentation M_ch, which we relate
to the peak of the observed IMF. Our investigation generally supports the idea
that the distribution of stellar masses depends mainly on the thermodynamic
state of the star-forming gas. The thermodynamic state of interstellar gas is a
result of the balance between heating and cooling processes, which in turn are
determined by fundamental atomic and molecular physics and by chemical
abundances. Given the abundances, the derivation of a characteristic stellar
mass can thus be based on universal quantities and constants.Comment: 13 pages, 7 figures, accepted by A&
Cervical spine biomechanics: A review of the literature
This article reviews the many clinical and laboratory investigative research reports on the frequency, causes, and biomechanics of human cervical spine impact injuries and tolerances. Neck injury mechanisms have been hypothesized from clinically observed cervical spine injuries without laboratory verification. However, many of the laboratory experiments used static loading techniques of cervical spine segments. Only recently have dynamic impact studies been conducted. Results indicate that crown-of-head impacts can routinely produce compression of the neck with extension or flexion motion. However, the two-dimensional (midsagittal) movement of the head bowing into the chest does not routinely produce flexion/compression type damage to the cervical spine. Flexion/compression damage to the cervical spine can be produced by prepositioning the subject so that upon impact, a three-dimensional motion of the head and neck occurs. Future laboratory research is needed to determine the forces and impact directions required to produce the various known fracture types and dislocations for a clear, accurate description of the cervical spine impact dynamics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50376/1/1100040212_ftp.pd
The Hubbard model within the equations of motion approach
The Hubbard model has a special role in Condensed Matter Theory as it is
considered as the simplest Hamiltonian model one can write in order to describe
anomalous physical properties of some class of real materials. Unfortunately,
this model is not exactly solved except for some limits and therefore one
should resort to analytical methods, like the Equations of Motion Approach, or
to numerical techniques in order to attain a description of its relevant
features in the whole range of physical parameters (interaction, filling and
temperature). In this manuscript, the Composite Operator Method, which exploits
the above mentioned analytical technique, is presented and systematically
applied in order to get information about the behavior of all relevant
properties of the model (local, thermodynamic, single- and two- particle ones)
in comparison with many other analytical techniques, the above cited known
limits and numerical simulations. Within this approach, the Hubbard model is
shown to be also capable to describe some anomalous behaviors of the cuprate
superconductors.Comment: 232 pages, more than 300 figures, more than 500 reference
Quantification and characterisation of porosity in selectively laser melted AlâSi10âMg using x-ray computed tomography
We used X-ray computed tomography (CT), microscopy and hardness measurements to study AlâSi10âMg produced by selective laser melting (SLM). Specimens were subject to a series of heat treatments including annealing and precipitation hardening. The specimen interiors were imaged with X-ray CT, allowing the non-destructive quantification and characterisation of pores, including their spatial distribution. The specimens had porosities less than 0.1%, but included some pores with effective cross-sectional diameters up to 260 ÎŒm. The largest pores were highly anisotropic, being flat and lying in the plane normal to the build direction. Annealing cycles caused significant coarsening of the microstructure and a reduction of the hardness from (114 ± 3) HV, in the as-built state, to (45 ± 1) HV, while precipitation hardening increased this to a final hardness of (59 ± 1) HV. The pore size and shape distributions were unaffected by the heat treatments. We demonstrate the applicability of CT measurements and quantitative defect analysis for the purposes of SLM process monitoring and refinement
Measurement of the cross-section of high transverse momentum vector bosons reconstructed as single jets and studies of jet substructure in pp collisions at âs = 7 TeV with the ATLAS detector
This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of âs = 7 TeV;{\rm Te}{\rm V}4.6\;{\rm f}{{{\rm b}}^{-1}}{{p}_{{\rm T}}}\gt 320\;{\rm Ge}{\rm V}|\eta |\lt 1.9{{\sigma }_{W+Z}}=8.5\pm 1.7$ pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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