4,991 research outputs found
Nodal-to-nodeless superconducting order parameter in LaFeAsPO synthesized under high pressure
Similar to chemical doping, pressure produces and stabilizes new phases of
known materials, whose properties may differ greatly from those of their
standard counterparts. Here, by considering a series of LaFeAsPO
iron-pnictides synthesized under high-pressure high-temperature conditions, we
investigate the simultaneous effects of pressure and isoelectronic doping in
the 1111 family. Results of numerous macro- and microscopic technique
measurements, unambiguously show a radically different phase diagram for the
pressure-grown materials, characterized by the lack of magnetic order and the
persistence of superconductivity across the whole doping
range. This unexpected scenario is accompanied by a branching in the electronic
properties across , involving both the normal and superconducting
phases. Most notably, the superconducting order parameter evolves from nodal
(for ) to nodeless (for ), in clear contrast to other 1111
and 122 iron-based materials grown under ambient-pressure conditions.Comment: 9 pages, 7 figures, Suppl. materia
Design and Performance of the CMS Pixel Detector Readout Chip
The readout chip for the CMS pixel detector has to deal with an enormous data
rate. On-chip zero suppression is inevitable and hit data must be buffered
locally during the latency of the first level trigger. Dead-time must be kept
at a minimum. It is dominated by contributions coming from the readout. To keep
it low an analog readout scheme has been adopted where pixel addresses are
analog coded. We present the architecture of the final CMS pixel detector
readout chip with special emphasis on the analog readout chain. Measurements of
its performance are discussed.Comment: 8 pages, 11 figures. Contribution to the Proceedings of the Pixel2005
Workshop, Bonn, German
Towards defining the role of glycans as hardware in information storage and transfer: Basic principles, experimental approaches and recent progress
The term `code' in biological information transfer appears to be tightly and hitherto exclusively connected with the genetic code based on nucleotides and translated into functional activities via proteins. However, the recent appreciation of the enormous coding capacity of oligosaccharide chains of natural glycoconjugates has spurred to give heed to a new concept: versatile glycan assembly by the genetically encoded glycosyltransferases endows cells with a probably not yet fully catalogued array of meaningful messages. Enciphered by sugar receptors such as endogenous lectins the information of code words established by a series of covalently linked monosaccharides as fetters for example guides correct intra- and intercellular routing of glycoproteins, modulates cell proliferation or migration and mediates cell adhesion. Evidently, the elucidation of the structural frameworks and the recognition strategies within the operation of the sugar code poses a fascinating conundrum. The far-reaching impact of this recognition mode on the level of cells, tissues and organs has fueled vigorous investigations to probe the subtleties of protein-carbohydrate interactions. This review presents information on the necessarily concerted approach using X-ray crystallography, molecular modeling, nuclear magnetic resonance spectroscopy, thermodynamic analysis and engineered ligands and receptors. This part of the treatise is flanked by exemplarily chosen insights made possible by these techniques. Copyright (C) 2001 S. Karger AG, Basel
Prime numbers, quantum field theory and the Goldbach conjecture
Motivated by the Goldbach conjecture in Number Theory and the abelian
bosonization mechanism on a cylindrical two-dimensional spacetime we study the
reconstruction of a real scalar field as a product of two real fermion
(so-called \textit{prime}) fields whose Fourier expansion exclusively contains
prime modes. We undertake the canonical quantization of such prime fields and
construct the corresponding Fock space by introducing creation operators
--labeled by prime numbers -- acting on the vacuum. The
analysis of our model, based on the standard rules of quantum field theory and
the assumption of the Riemann hypothesis, allow us to prove that the theory is
not renormalizable. We also comment on the potential consequences of this
result concerning the validity or breakdown of the Goldbach conjecture for
large integer numbers.Comment: 20 pages in A4 format, 2 figure
Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)(ClO)
Cu(pz)(ClO) (with pz denoting pyrazine CHN) is a
two-dimensional spin-1/2 square-lattice antiferromagnet with =
4.24 K. Due to a persisting focus on the low-temperature magnetic properties,
its room-temperature structural and physical properties caught no attention up
to now. Here we report a study of the structural features of
Cu(pz)(ClO) in the paramagnetic phase, up to 330 K. By employing
magnetization, specific heat, Cl nuclear magnetic resonance, and neutron
diffraction measurements, we provide evidence of a second-order phase
transition at = 294 K, not reported before. The absence of a
magnetic ordering across in the magnetization data, yet the
presence of a sizable anomaly in the specific heat, suggest a structural
order-to-disorder type transition. NMR and neutron-diffraction data corroborate
our conjecture, by revealing subtle angular distortions of the pyrazine rings
and of ClO counteranion tetrahedra, shown to adopt a configuration of
higher symmetry above the transition temperature.Comment: 10 pages, 12 figure
Minisuperspace Examples of Quantization Using Canonical Variables of the Ashtekar Type: Structure and Solutions
The Ashtekar variables have been use to find a number of exact solutions in
quantum gravity and quantum cosmology. We investigate the origin of these
solutions in the context of a number of canonical transformations (both complex
and real) of the basic Hamiltonian variables of general relativity. We are able
to present several new solutions in the minisuperspace (quantum cosmology)
sector. The meaning of these solutions is then discussed.Comment: 23 pages, latex, 3 figures (uuencoded, separate file
Quantum Cylindrical Waves and Sigma Models
We analyze cylindrical gravitational waves in vacuo with general polarization
and develop a viewpoint complementary to that presented recently by Niedermaier
showing that the auxiliary sigma model associated with this family of waves is
not renormalizable in the standard perturbative sense.Comment: 11 pages (DIN A4), accepted in International Journal of Modern
Physics
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