1,650 research outputs found
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Simulation of the Process Step Polymer Removal in Indirect Metal Laser Sintering
With the Indirect Metal Laser Sintering and by means of a heat treatment in an oven process
metal components can be produced. In the first step the polymer is transformed from the solid
state into the gas phase. This takes place all over the component at different velocities depending
on the local temperatures and temperature gradients. The creation of the gas phase develops a
pressure inside of the component because the diffusion of the polymer within the part has a finite
velocity. The pressure may contribute to a damage of the component. This essay deals with the
procedure to simulate the gas pressure on the basis of the implementation of kinetic models in the
Finite-Element-Analysis.Mechanical Engineerin
TGF-beta signaling in onset and progression of hepatocellular carcinoma
Transforming growth factor (TGF)-beta is a central regulator in chronic liver disease, contributing to all stages of disease progression from initial liver injury through inflammation and fibrosis to cirrhosis and hepatocellular carcinoma. Liver damage-induced levels of active TGF-beta enhance hepatocyte destruction and mediate hepatic stellate cell and fibroblast activation resulting in a wound-healing response, including myofibroblast generation and extracellular matrix deposition. Further evidence points to a decisive role of cytostatic and apoptotic functions mediated on hepatocytes, which is critical for the control of liver mass, with loss of TGF-beta activities resulting in hyperproliferative disorders and cancer. This concept is based on studies that describe a bipartite role of TGF-beta with tumor suppressor functions at early stages of liver damage and regeneration, whereas during cancer progression TGF-beta may turn from a tumor suppressor into a tumor promoter that exacerbates invasive and metastatic behavior. We have delineated this molecular switch of the pathway from cytostatic to tumor promoting in further detail and identify activation of survival signaling pathways in hepatocytes as a most critical requirement. Targeting the TGF-beta signaling pathway has been explored to inhibit liver disease progression. While interfering with TGF-beta signaling in various short-term animal models has demonstrated promising results, liver disease progression in humans is a process of decades with different phases in which TGF-beta or its targeting may have both beneficial and adverse outcomes.
We emphasize that, in order to achieve therapeutic
effects, targeting TGF-beta signaling in the right cell type at the right time is required. Copyright © 2012 S. Karger AG, Base
Double ring-closing approach for the synthesis of 2,3,6,7-substituted anthracene derivatives.
A method for the synthesis of 2,3,6,7-substituted anthracene derivatives, one of the most challenging anthracene substitution patterns to obtain, is presented. The method is exemplified by the preparation of 2,3,6,7-anthracenetetracarbonitrile and employs a newly developed, stable, protected 1,2,4,5-benzenetetracarbaldehyde as the precursor. The precursor can be obtained in two scalable synthetic steps from 2,5-dibromoterephthalaldehyde and is converted into the anthracene derivative by a double intermolecular Wittig reaction under very mild conditions, followed by a deprotection and intramolecular double ring-closing condensation reaction
Finite-temperature magnetism of FePd and CoPt alloys
The finite-temperature magnetic properties of FePd and
CoPt alloys have been investigated. It is shown that the
temperature-dependent magnetic behaviour of alloys, composed of originally
magnetic and non-magnetic elements, cannot be described properly unless the
coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through
the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is
included. A scheme for the calculation of the Curie temperature () for
this type of systems is presented which is based on the extended Heisenberg
Hamiltonian with the appropriate exchange parameters obtained from
{\em ab-initio} electronic structure calculations. Within the present study the
KKR Green's function method has been used to calculate the parameters.
A comparison of the obtained Curie temperatures for FePd and
CoPt alloys with experimental data shows rather good agreement.Comment: 10 pages, 12 figure
Optical Scattering Lengths in Large Liquid-Scintillator Neutrino Detectors
For liquid-scintillator neutrino detectors of kiloton scale, the transparency
of the organic solvent is of central importance. The present paper reports on
laboratory measurements of the optical scattering lengths of the organic
solvents PXE, LAB, and Dodecane which are under discussion for next-generation
experiments like SNO+, Hanohano, or LENA. Results comprise the wavelength range
from 415 to 440nm. The contributions from Rayleigh and Mie scattering as well
as from absorption/re-emission processes are discussed. Based on the present
results, LAB seems to be the preferred solvent for a large-volume detector.Comment: 9 pages, 3 figures, accepted for publication by Rev. Scient. Instr
An assessment of sub-snow GPS for quantification of snow water equivalent
Global Navigation Satellite Systems (GNSS) contribute to various
Earth observation applications. The present study investigates the potential
and limitations of the Global Positioning System (GPS) to estimate in situ
water equivalents of the snow cover (snow water equivalent, SWE) by using
buried GPS antennas. GPS-derived SWE is estimated over three seasons
(2015/16–2017/18) at a high Alpine test site in Switzerland. Results are
validated against state-of-the-art reference sensors: snow scale, snow
pillow, and manual observations. SWE is estimated with a high correspondence
to the reference sensors for all three seasons. Results agree with a median
relative bias below 10 % and are highly correlated to the mean of the three
reference sensors. The sensitivity of the SWE quantification is assessed for
different GPS ambiguity resolution techniques, as the results strongly depend
on the GPS processing.</p
Analyses and localization of pectin-like carbohydrates in cell wall and mucilage of the green alga Netrium digitus
The unicellular, simply shaped desmid Netrium digitus inhabiting acid bog ponds grows in two phases. Prior to division, the cell elongates at its central zone, whereas in a second phase, polar tip growth occurs. Electron microscopy demonstrates that Netrium is surrounded by a morphologically homogeneous cell wall, which lacks pores. Immunocytochemical and biochemical analyses give insight into physical wall properties and, thus, into adaptation to the extreme environment. The monoclonal antibodies JIM5 and JIM7 directed against pectic epitopes with different degrees of esterification label preferentially growing wall zones in Netrium. In contrast, 2F4 marks the cell wall only after experimental de-esterification. Electron energy loss spectroscopy reveals Ca-binding capacities of pectins and gives indirect evidence for the degree of their esterification. An antibody raised against Netrium mucilage is not only specific to mucilage but also recognizes wall components in transmission electron microscopy and dot blots. These results indicate a smooth transition between mucilage and the cell wall in Netrium
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The Influence of Fire on a Rare Serpentine Plant Assemblage: A Five Year Study of Darlingtonia Fens
Premise of the study: Serpentine soils have attracted the attention of evolutionary biologists for decades due to their high number of rare and endemic taxa, though less is known about the ecological factors that govern the diversity and composition of serpentine communities. Theory suggests that vegetation on these low-productivity soils will be relatively resilient to fire, the most common natural disturbance in serpentine systems. Methods: We studied the recovery of vegetation in Darlingtonia fens, a unique habitat dominated by herbaceous perennials, from a major fire that burned ~202,000 hectares in California and Oregon’s Klamath Mountains in 2002. We established permanent plots in 8 unburned and 8 burned fens in 2003 and recorded percent cover of vascular plant species. We re-sampled plots each year through 2007. Key results: Burned fens had less plant cover than unburned fens for two years after the fire. Average species density was ~10% lower in burned fens one year after the fire but ~4-8% higher for the next four years. Burned fens exhibited greater evenness, but not until four years after the fire. Differences in community composition were detected between the two fen types, but species ranks were similar, and species neither were added to, nor removed from, the burned assemblages. Conclusions: Burning of Darlingtonia fens has detectable, albeit modest effects on serpentine communities. Because fens have little or no canopy cover, fire has little influence on light availability in this system. This relatively small resource change, combined with high soil moisture and well-developed underground organs of fen plants, produces a highly resilient assemblage.Organismic and Evolutionary BiologyOther Research Uni
CANVAS: case report on a novel repeat expansion disorder with late-onset ataxia
This article presents the case of a 74-year-old female patient who first developed a progressive disease with sensory neuropathy, cerebellar ataxia and bilateral vestibulopathy at the age of 60 years. The family history was unremarkable. Magnetic resonance imaging (MRI) showed atrophy of the cerebellum predominantly in the vermis and atrophy of the spinal cord. The patient was given the syndromic diagnosis of cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). In 2019 the underlying genetic cause of CANVAS was discovered to be an intronic repeat expansion in the RFC1 gene with autosomal recessive inheritance. The patient exhibited the full clinical picture of CANVAS and was tested positive for this repeat expansion on both alleles. The CANVAS is a relatively frequent cause of late-onset hereditary ataxia (estimated prevalence 5‑13/100,000). In contrast to the present patient, the full clinical picture is not always present. Therefore, testing for the RFC1 gene expansion is recommended in the work-up of patients with otherwise unexplained late-onset sporadic ataxia. As intronic repeat expansions cannot be identified by next generation sequencing methods, specific testing is necessary
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