6,361 research outputs found
Observations on Chromaffin Tissue
An attempt has been made to give in this article a review of some of our activities since I first met Ernst Fischer in Göttingen many years ago. I have not related the work of our laboratory to that of others. Also, I have only described observations made on chromaffin tissue. The catecholamines have acquired a much wider importance with their discovery in adrenergic neurones, and, more recently, in the central nervous system. However, the study of a more homogenous tissue has the advantage of greater simplicity. Some of the findings made on the adrenal medulla, e.g. the enzyme studies, are of immediate relevance to nervous tissue. To what extent the new findings on amine storage and release have a counterpart in neurones, remains to be elucidated in the future
Harmonic Love wave devices for biosensing applications
Simultaneous operation of a Love wave biosensor at the fundamental frequency and third harmonic, including the optimisation of IDT metallisation thickness, has been investigated. Data is presented showing a sequence of deposition and removal of a model mass layer of palmitoyl-oleoyl-sn-glycerophosphocholine (POPC) vesicles while frequency hopping between 110 and 330 MH
Displacement energy of unit disk cotangent bundles
We give an upper bound of a Hamiltonian displacement energy of a unit disk
cotangent bundle in a cotangent bundle , when the base manifold
is an open Riemannian manifold. Our main result is that the displacement
energy is not greater than , where is the inner radius of ,
and is a dimensional constant. As an immediate application, we study
symplectic embedding problems of unit disk cotangent bundles. Moreover,
combined with results in symplectic geometry, our main result shows the
existence of short periodic billiard trajectories and short geodesic loops.Comment: Title slightly changed. Close to the version published online in Math
Zei
On optimality of constants in the Little Grothendieck Theorem
A. M. Peralta was partially supported by the Spanish Ministry of Science, Innovation and Universities (MICINN) and European Regional Development Fund project no. PGC2018-093332-B-I00, the IMAG -Maria de Maeztu grant CEX2020-001105-M/AEI/10.13039/501100011033, and by Junta de Andalucia grants FQM375 and A-FQM-242-UGR18.We explore the optimality of the constants making valid the recently established little Grothendieck inequality for JB*-triples and JB*-algebras. In our main result we prove that for each bounded linear operator T from a JB*-algebra B into a complex Hilbert space H and epsilon > 0, there is a norm-one functional phi is an element of B* such that
parallel to Tx parallel to <= (root 2 + epsilon)parallel to T parallel to parallel to x parallel to(phi) for x is an element of B.
The constant appearing in this theorem improves the best value known up to date (even for C*-algebras). We also present an easy example witnessing that the constant cannot be strictly smaller than root 2, hence our main theorem is 'asymptotically optimal'. For type I JBW*-algebras we establish a canonical decomposition of normal functionals which may be used to prove the main result in this special case and also seems to be of an independent interest. As a tool we prove a measurable version of the Schmidt representation of compact operators on a Hilbert space.Spanish Ministry of Science, Innovation and Universities (MICINN)European Commission PGC2018-093332-B-I00IMAG -Maria de Maeztu grant CEX2020-001105-M/AEI/10.13039/501100011033Junta de Andalucia FQM375
A-FQM-242-UGR1
A thermodynamical fiber bundle model for the fracture of disordered materials
We investigate a disordered version of a thermodynamic fiber bundle model
proposed by Selinger, Wang, Gelbart, and Ben-Shaul a few years ago. For simple
forms of disorder, the model is analytically tractable and displays some new
features. At either constant stress or constant strain, there is a non
monotonic increase of the fraction of broken fibers as a function of
temperature. Moreover, the same values of some macroscopic quantities as stress
and strain may correspond to different microscopic cofigurations, which can be
essential for determining the thermal activation time of the fracture. We argue
that different microscopic states may be characterized by an experimentally
accessible analog of the Edwards-Anderson parameter. At zero temperature, we
recover the behavior of the irreversible fiber bundle model.Comment: 18 pages, 10 figure
Geometric and electronic structure of vanadium pentoxide: A density functional bulk and surface study
Epitaxial Co2Cr0.6Fe0.4Al thin films and magnetic tunneling junctions
Epitaxial thin films of the theoretically predicted half metal
Co2Cr0.6Fe0.4Al were deposited by dc magnetron sputtering on different
substrates and buffer layers. The samples were characterized by x-ray and
electron beam diffraction (RHEED) demonstrating the B2 order of the Heusler
compound with only a small partition of disorder on the Co sites. Magnetic
tunneling junctions with Co2Cr0.6Fe0.4Al electrode, AlOx barrier and Co counter
electrode were prepared. From the Julliere model a spin polarisation of
Co2Cr0.6Fe0.4Al of 54% at T=4K is deduced. The relation between the annealing
temperature of the Heusler electrodes and the magnitude of the tunneling
magnetoresistance effect was investigated and the results are discussed in the
framework of morphology and surface order based of in situ STM and RHEED
investigations.Comment: accepted by J. Phys. D: Appl. Phy
The self-assembly and evolution of homomeric protein complexes
We introduce a simple "patchy particle" model to study the thermodynamics and
dynamics of self-assembly of homomeric protein complexes. Our calculations
allow us to rationalize recent results for dihedral complexes. Namely, why
evolution of such complexes naturally takes the system into a region of
interaction space where (i) the evolutionarily newer interactions are weaker,
(ii) subcomplexes involving the stronger interactions are observed to be
thermodynamically stable on destabilization of the protein-protein interactions
and (iii) the self-assembly dynamics are hierarchical with these same
subcomplexes acting as kinetic intermediates.Comment: 4 pages, 4 figure
On the robustness of the slotine-Li and the FPT/SVD-based adaptive controllers
A comparative study concerning the robustness of a novel, Fixed Point Transformations/Singular Value Decomposition (FPT/SVD)-based adaptive controller and the Slotine-Li (S&L) approach is given by numerical simulations using a three degree of freedom paradigm of typical Classical Mechanical systems, the cart + double pendulum. The effects of the imprecision of the available dynamical model, presence of dynamic friction at the axles of the drives, and the existence of external disturbance forces unknown and not modeled by the controller are considered. While the Slotine-Li approach tries to identify the parameters of the formally precise, available analytical model of the controlled system with the implicit assumption that the generalized forces are precisely known, the novel one makes do with a very rough, affine form and a formally more precise approximate model of that system, and uses temporal observations of its desired vs. realized responses. Furthermore, it does not assume the lack of unknown perturbations caused either by internal friction and/or external disturbances. Its another advantage is that it needs the execution of the SVD as a relatively time-consuming operation on a grid of a rough system-model only one time, before the commencement of the control cycle within which it works only with simple computations. The simulation examples exemplify the superiority of the FPT/SVD-based control that otherwise has the deficiency that it can get out of the region of its convergence. Therefore its design and use needs preliminary simulation investigations. However, the simulations also exemplify that its convergence can be guaranteed for various practical purposes
2D Potts Model Correlation Lengths: Numerical Evidence for at
We have studied spin-spin correlation functions in the ordered phase of the
two-dimensional -state Potts model with , 15, and 20 at the
first-order transition point . Through extensive Monte Carlo
simulations we obtain strong numerical evidence that the correlation length in
the ordered phase agrees with the exactly known and recently numerically
confirmed correlation length in the disordered phase: . As a byproduct we find the energy moments in the ordered phase
at in very good agreement with a recent large -expansion.Comment: 11 pages, PostScript. To appear in Europhys. Lett. (September 1995).
See also http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm
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