967 research outputs found
Is there a Relationship between the Elongational Viscosity and the First Normal Stress Difference in Polymer Solutions?
We investigate a variety of different polymer solutions in shear and
elongational flow. The shear flow is created in the cone-plate-geometry of a
commercial rheometer. We use capillary thinning of a filament that is formed by
a polymer solution in the Capillary Breakup Extensional Rheometer (CaBER) as an
elongational flow. We compare the relaxation time and the elongational
viscosity measured in the CaBER with the first normal stress difference and the
relaxation time that we measured in our rheometer. All of these four quantities
depend on different fluid parameters - the viscosity of the polymer solution,
the polymer concentration within the solution, and the molecular weight of the
polymers - and on the shear rate (in the shear flow measurements).
Nevertheless, we find that the first normal stress coefficient depends
quadratically on the CaBER relaxation time. A simple model is presented that
explains this relation
Topological complexity of the relative closure of a semi-Pfaffian couple
Gabrielov introduced the notion of relative closure of a Pfaffian couple as
an alternative construction of the o-minimal structure generated by
Khovanskii's Pfaffian functions. In this paper, use the notion of format (or
complexity) of a Pfaffian couple to derive explicit upper-bounds for the
homology of its relative closure.
Keywords: Pfaffian functions, fewnomials, o-minimal structures, Betti
numbers.Comment: 12 pages, 1 figure. v3: Proofs and bounds have been slightly improve
Exploring the functional domain and the target of the tetanus toxin light chain in neurohypophysial terminals
The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial nerve terminals. Here we show that histidine residue 233 within the putative zinc binding motif of the tetanus toxin light chain is essential for the inhibition of exocytosis, in the rat. The zinc chelating agent dipicolinic acid as well as captopril, an inhibitor of zinc-dependent peptidases, counteract the effect of the neurotoxin. Synthetic peptides, the sequences of which correspond to motifs present in the cytoplasmic domain of the synaptic vesicle membrane protein synaptobrevin 1 and 2, prevent the effect of the tetanus toxin light chain.
Our results indicate that zinc bound to the zinc binding motif constitutes the active site of the tetanus toxin light chain. Moreover they suggest that cleavage of synaptobrevin by the neurotoxin causes the inhibition of exocytotic release of vasopressin from secretory granules
Die Entwicklung des ländlichen Bauens im ehemals Braunschweigischen Weserdistrikt zwischen 1550 und 1850
Im ehemals Braunschweigischen Weserdistrikt (Landkreis Holzminen) ist ein wertvoller ländlicher Hausbestand überliefert. Die Wohnwirtschaftsgebäude wurden von der Mitte des 16. bis zur Mitte des 18. Jahrhunderts vornehmlich als giebelständige, längsaufgeschlossene Wandständerbauten mit zwei Vollgeschossen und Spitzsäulendachstuhl errichtet. Dabei verfügten die aus Eiche verzimmerten Drei- und Vierständerbauten über eine zumeist außermittige Längsdiele, ein schmales Stallseitenschiff und ein breites Wohnseitenschiff mit straßenseitiger Stube. Im Verlauf des 18. Jahrhunderts setzte der Bau von Nebengebäuden ein und es prägen auch traufständige Querdielenhäuser das Siedlungsbild der Mittelgebirgsregion. Die Fachwerkbauten werden zunehmend in Stockwerksbauweise, mit doppelt stehendem Stuhl und aus Nadelholz errichtet. Neben regionalen Besonderheiten konnten obrigkeitliche Einflussnahme, sozialer Status des Erbauers und die Bauaufgabe als wichtige Einflussfaktoren festgestellt werden
Belastungen mit chlororganischen Schadstoffen und Metallen bei Patienten mit Multipler Sklerose
Bei der Multiplen Sklerose (MS, Encephalomyelitis disseminata) handelt es sich um eine chronische, multilokuläre demyelinisierende Erkrankung des Zentralen Nervensystems, deren Ursachen bisher nicht exakt geklärt werden konnten. Die im ZNS disseminiert auftretenden Entzündungs- und Entmarkungsherde sind Ursache der sehr unterschiedlich verlaufenden klinischen Symptomatik u.a. mit multifokalen sensiblen Ausfällen, Paresen, Hirnnervenbefall, zerebellären Störungen, Blasenstörungen sowie neuropsychologischen Defiziten (z.B. hirnorganisches Psychosyndrom). Bei einer Prävalenz von etwa 50-100/100.000 und einer Inzidenz von 4-6/100.000 in Deutschland beträgt das Verhältnis von Frauen zu Männern etwa 2:1. Ätiologisch werden u.a. T-Zell-vermittelte Autoimmunmechanismen, Virusinfektionen, genetische Dispositionen und der Einfluß verschiedener Umweltfaktoren diskutiert. Es stellt sich auch die Frage nach erhöhten Belastungen mit chlororganischen Schadstoffen und Metallen
TDP-43 regulates global translational yield by splicing of exon junction complex component SKAR
TDP-43 is linked to neurodegenerative diseases including frontotemporal dementia and amyotrophic lateral sclerosis. Mostly localized in the nucleus, TDP-43 acts in conjunction with other ribonucleoproteins as a splicing co-factor. Several RNA targets of TDP-43 have been identified so far, but its role(s) in pathogenesis remains unclear. Using Affymetrix exon arrays, we have screened for the first time for splicing events upon TDP-43 knockdown. We found alternative splicing of the ribosomal S6 kinase 1 (S6K1) Aly/REF-like target (SKAR) upon TDP-43 knockdown in non-neuronal and neuronal cell lines. Alternative SKAR splicing depended on the first RNA recognition motif (RRM1) of TDP-43 and on 5′-GA-3’ and 5′-UG-3′ repeats within the SKAR pre-mRNA. SKAR is a component of the exon junction complex, which recruits S6K1, thereby facilitating the pioneer round of translation and promoting cell growth. Indeed, we found that expression of the alternatively spliced SKAR enhanced S6K1-dependent signaling pathways and the translational yield of a splice-dependent reporter. Consistent with this, TDP-43 knockdown also increased translational yield and significantly increased cell size. This indicates a novel mechanism of deregulated translational control upon TDP-43 deficiency, which might contribute to pathogenesis of the protein aggregation diseases frontotemporal dementia and amyotrophic lateral sclerosis
Measurement of the 187Re({\alpha},n)190Ir reaction cross section at sub-Coulomb energies using the Cologne Clover Counting Setup
Uncertainties in adopted models of particle+nucleus optical-model potentials
directly influence the accuracy in the theoretical predictions of reaction
rates as they are needed for reaction-network calculations in, for instance,
{\gamma}-process nucleosynthesis. The improvement of the {\alpha}+nucleus
optical-model potential is hampered by the lack of experimental data at
astrophysically relevant energies especially for heavier nuclei. Measuring the
Re187({\alpha},n)Ir190 reaction cross section at sub-Coulomb energies extends
the scarce experimental data available in this mass region and helps
understanding the energy dependence of the imaginary part of the
{\alpha}+nucleus optical-model potential at low energies. Applying the
activation method, after the irradiation of natural rhenium targets with
{\alpha}-particle energies of 12.4 to 14.1 MeV, the reaction yield and thus the
reaction cross section were determined via {\gamma}-ray spectroscopy by using
the Cologne Clover Counting Setup and the method of {\gamma}{\gamma}
coincidences. Cross-section values at five energies close to the
astrophysically relevant energy region were measured. Statistical model
calculations revealed discrepancies between the experimental values and
predictions based on widely used {\alpha}+nucleus optical-model potentials.
However, an excellent reproduction of the measured cross-section values could
be achieved from calculations based on the so-called Sauerwein-Rauscher
{\alpha}+nucleus optical-model potential. The results obtained indicate that
the energy dependence of the imaginary part of the {\alpha}+nucleus
optical-model potential can be described by an exponential decrease. Successful
reproductions of measured cross sections at low energies for {\alpha}-induced
reactions in the mass range 141{\leq}A{\leq}187 confirm the global character of
the Sauerwein-Rauscher potential
Unconditional entanglement interface for quantum networks
Entanglement drives nearly all proposed quantum information technologies. The suppression of the uncertainty in joint quadrature measurements below the level of vacuum fluctuations is a signature of non-classical correlations. Entangling frequency modes of optical fields has attracted increased attention in recent years, as a quantum network would rely on interfacing light at telecommunication wavelengths with matter-based quantum memories that are addressable at visible wavelengths. By up-converting part of a 1550 nm squeezed vacuum state to 532 nm, we demonstrate the generation and complete characterization of strong continuous-variable entanglement between widely separated frequencies. Non-classical correlations were observed in joint quadrature measurements of the 1550 nm and 532 nm fields, showing a maximum noise suppression 5.5 dB below vacuum. A spectrum was measured to demonstrate over 3 dB noise suppression up to 20 MHzmeasurement frequency. Our versatile technique combines strong non-classical correlations, large bandwidth and, in principle, the ability to entangle the telecommunication wavelength of 1550 nm with any optical wavelength, making this approach highly relevant to emerging proposals for quantum communication and computing
Evolution of E2 transition strength in deformed hafnium isotopes from new measurements on Hf, Hf, and Hf
The available data for E2 transition strengths in the region between
neutron-deficient Hf and Pt isotopes are far from complete. More and precise
data are needed to enhance the picture of structure evolution in this region
and to test state-of-the-art nuclear models. In a simple model, the maximum
collectivity is expected at the middle of the major shell. However, for actual
nuclei, this picture may no longer be the case, and one should use a more
realistic nuclear-structure model. We address this point by studying the
spectroscopy of Hf. We remeasure the 2^+_1 half-lives of 172,174,176Hf, for
which there is some disagreement in the literature. The main goal is to
measure, for the first time, the half-lives of higher-lying states of the
rotational band. The new results are compared to a theoretical calculation for
absolute transition strengths. The half-lives were measured using \gamma-\gamma
and conversion-electron-\gamma delayed coincidences with the fast timing
method. For the determination of half-lives in the picosecond region, the
generalized centroid difference method was applied. For the theoretical
calculation of the spectroscopic properties, the interacting boson model is
employed, whose Hamiltonian is determined based on microscopic energy-density
functional calculations. The measured 2^+_1 half-lives disagree with results
from earlier \gamma-\gamma fast timing measurements, but are in agreement with
data from Coulomb excitation experiments and other methods. Half-lives of the
4^+_1 and 6^+_1 states were measured, as well as a lower limit for the 8^+_1
states. We show the importance of the mass-dependence of effective boson charge
in the description of E2 transition rates in chains of nuclei. It encourages
further studies of the microscopic origin of this mass dependence. New data on
transition rates in nuclei from neighboring isotopic chains could support these
studies.Comment: 16 pages, 16 figures, 7 tables; Abstract shortened due to character
limi
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