441 research outputs found
Two-parametric deformation and its induced representations
The two-parametric quantum superalgebra is consistently
defined. A construction procedure for induced representations of
is described and allows us to construct explicitly all
(typical and nontypical) finite-dimensional representations of this quantum
superalgebra. In spite of some specific features, the present approach is
similar to a previously developed method [1] which, as shown here, is
applicable not only to the one-parametric quantum deformations but also to the
multi-parametric ones.Comment: Latex, 13 pages, no figur
Paradoxien des Digital Turn in der Architektur 1990â2015. Von den Verlockungen des Organischen: digitales Entwerfen zwischen informellem Denken und biomorphem Resultat
Vor dem Hintergrund der EinfĂŒhrung des Computers und der damit verbundenen Digitalisierung in der Architektur mit ihrer breiten Anwendung in den 1990er Jahren geht die Arbeit von der Frage aus, warum es im Formbildungsprozess eine Diskrepanz zwischen informellem Denken und biomorphem Resultat gibt. Es werden Paradoxien aufgedeckt, deren FehlschlĂŒsse zu einer Vielfalt von digitalen Strömungen bei gleichzeitiger Vereinheitlichung der Ausdrucksmittel fĂŒhrten. Im Mittelpunkt steht eine vergleichende und disziplinĂŒbergreifende GegenĂŒberstellung informeller und biomorpher AnsĂ€tze. Der informelle Ansatz findet seinen Ursprung im Konzept des Formlosen bei Georges Bataille in den 1920er Jahren und in der informellen Kunst in den 1950er/1960er Jahren. Der biomorphe Ansatz prĂ€sentiert sich in dieser Arbeit durch den Nachweis der Verlockungen, aufgrund derer die Architektur die Natur immer wieder als Vorbild nimmt. Es wird aufgezeigt, wo der aktuelle Architekturdiskurs in der Vermischung beider AnsĂ€tze feststeckt. Die Konklusion und der Ausblick bilden den Abschluss, in dem die "Unfreiheit" des Programmierens mit dem Wesen der Unbestimmtheit in einer postdigitalen Ăra zusammengedacht wird. Dabei wird eine Antwort auf die Frage gegeben, warum sich das digitale Entwerfen vielfach einer biomorphen Formensprache bedient und wie ein Weg aussehen kann, der aus dieser Sackgasse herausfĂŒhrt
Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak"
We consider a system of coupled classical harmonic oscillators with spatially
fluctuating nearest-neighbor force constants on a simple cubic lattice. The
model is solved both by numerically diagonalizing the Hamiltonian and by
applying the single-bond coherent potential approximation. The results for the
density of states are in excellent agreement with each other. As
the degree of disorder is increased the system becomes unstable due to the
presence of negative force constants. If the system is near the borderline of
stability a low-frequency peak appears in the reduced density of states
as a precursor of the instability. We argue that this peak
is the analogon of the "boson peak", observed in structural glasses. By means
of the level distance statistics we show that the peak is not associated with
localized states
The evolution of vibrational excitations in glassy systems
The equations of the mode-coupling theory (MCT) for ideal liquid-glass
transitions are used for a discussion of the evolution of the
density-fluctuation spectra of glass-forming systems for frequencies within the
dynamical window between the band of high-frequency motion and the band of
low-frequency-structural-relaxation processes. It is shown that the strong
interaction between density fluctuations with microscopic wave length and the
arrested glass structure causes an anomalous-oscillation peak, which exhibits
the properties of the so-called boson peak. It produces an elastic modulus
which governs the hybridization of density fluctuations of mesoscopic wave
length with the boson-peak oscillations. This leads to the existence of
high-frequency sound with properties as found by X-ray-scattering spectroscopy
of glasses and glassy liquids. The results of the theory are demonstrated for a
model of the hard-sphere system. It is also derived that certain schematic MCT
models, whose spectra for the stiff-glass states can be expressed by elementary
formulas, provide reasonable approximations for the solutions of the general
MCT equations.Comment: 50 pages, 17 postscript files including 18 figures, to be published
in Phys. Rev.
Epithelial-to-Mesenchymal Transition in Pancreatic Ductal Adenocarcinoma and Pancreatic Tumor Cell Lines: The Role of Neutrophils and Neutrophil-Derived Elastase
Pancreatic ductal adenocarcinoma (PDAC) is frequently associated with fibrosis and a prominent inflammatory infiltrate in the desmoplastic stroma. Moreover, in PDAC, an epithelial-to-mesenchymal transition (EMT) is observed. To explore a possible connection between the infiltrating cells, particularly the polymorphonuclear neutrophils (PMN) and the tumor cell transition, biopsies of patients with PDAC (n=115) were analysed with regard to PMN infiltration and nuclear expression of ÎČ-catenin and of ZEB1, well-established indicators of EMT. In biopsies with a dense PMN infiltrate, a nuclear accumulation of ÎČ-catenin and of ZEB1 was observed. To address the question whether PMN could induce EMT, they were isolated from healthy donors and were cocultivated with pancreatic tumor cells grown as monolayers. Rapid dyshesion of the tumor cells was seen, most likely due to an elastase-mediated degradation of E-cadherin. In parallel, the transcription factor TWIST was upregulated, ÎČ-catenin translocated into the nucleus, ZEB1 appeared in the nucleus, and keratins were downregulated. EMT was also induced when the tumor cells were grown under conditions preventing attachment to the culture plates. Here, also in the absence of elastase, E-cadherin was downmodulated. PMN as well as prevention of adhesion induced EMT also in liver cancer cell line. In conclusion, PMN via elastase induce EMT in vitro, most likely due to the loss of cell-to-cell contact. Because in pancreatic cancers the transition to a mesenchymal phenotype coincides with the PMN infiltrate, a contribution of the inflammatory response to the induction of EMT andâby implicationâto tumor progression is possible
Frustration and sound attenuation in structural glasses
Three classes of harmonic disorder systems (Lennard-Jones like glasses,
percolators above threshold, and spring disordered lattices) have been
numerically investigated in order to clarify the effect of different types of
disorder on the mechanism of high frequency sound attenuation. We introduce the
concept of frustration in structural glasses as a measure of the internal
stress, and find a strong correlation between the degree of frustration and the
exponent alpha that characterizes the momentum dependence of the sound
attenuation . In particular, alpha decreases from
about d+1 in low-frustration systems (where d is the spectral dimension), to
about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure
Nature of vibrational eigenmodes in topologically disordered solids
We use a local projectional analysis method to investigate the effect of
topological disorder on the vibrational dynamics in a model glass simulated by
molecular dynamics. Evidence is presented that the vibrational eigenmodes in
the glass are generically related to the corresponding eigenmodes of its
crystalline counterpart via disorder-induced level-repelling and hybridization
effects. It is argued that the effect of topological disorder in the glass on
the dynamical matrix can be simulated by introducing positional disorder in a
crystalline counterpart.Comment: 7 pages, 6 figures, PRB, to be publishe
Scaling of phononic transport with connectivity in amorphous solids
The effect of coordination on transport is investigated theoretically using
random networks of springs as model systems. An effective medium approximation
is made to compute the density of states of the vibrational modes, their energy
diffusivity (a spectral measure of transport) and their spatial correlations as
the network coordination is varied. Critical behaviors are obtained as
where these networks lose rigidity. A sharp cross-over from a regime
where modes are plane-wave-like toward a regime of extended but
strongly-scattered modes occurs at some frequency , which
does not correspond to the Ioffe-Regel criterion. Above both the
density of states and the diffusivity are nearly constant. These results agree
remarkably with recent numerical observations of repulsive particles near the
jamming threshold \cite{ning}. The analysis further predicts that the length
scale characterizing the correlation of displacements of the scattered modes
decays as with frequency, whereas for
Rayleigh scattering is found with a scattering length . It is argued that this description applies to silica glass
where it compares well with thermal conductivity data, and to transverse
ultrasound propagation in granular matter
Density of states in random lattices with translational invariance
We propose a random matrix approach to describe vibrational excitations in
disordered systems. The dynamical matrix M is taken in the form M=AA^T where A
is some real (not generally symmetric) random matrix. It guaranties that M is a
positive definite matrix which is necessary for mechanical stability of the
system. We built matrix A on a simple cubic lattice with translational
invariance and interaction between nearest neighbors. We found that for certain
type of disorder phonons cannot propagate through the lattice and the density
of states g(w) is a constant at small w. The reason is a breakdown of affine
assumptions and inapplicability of the elasticity theory. Young modulus goes to
zero in the thermodynamic limit. It strongly reminds of the properties of a
granular matter at the jamming transition point. Most of the vibrations are
delocalized and similar to diffusons introduced by Allen, Feldman et al., Phil.
Mag. B v.79, 1715 (1999).Comment: 4 pages, 5 figure
On the high-density expansion for Euclidean Random Matrices
Diagrammatic techniques to compute perturbatively the spectral properties of
Euclidean Random Matrices in the high-density regime are introduced and
discussed in detail. Such techniques are developed in two alternative and very
different formulations of the mathematical problem and are shown to give
identical results up to second order in the perturbative expansion. One method,
based on writing the so-called resolvent function as a Taylor series, allows to
group the diagrams in a small number of topological classes, providing a simple
way to determine the infrared (small momenta) behavior of the theory up to
third order, which is of interest for the comparison with experiments. The
other method, which reformulates the problem as a field theory, can instead be
used to study the infrared behaviour at any perturbative order.Comment: 29 page
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