Theory of Alkali Induced Reconstruction of the Cu(100) Surface

LEED experiments show that Li adsorbed at Cu(100) surfaces at room temperature induces a (2x1) missing row substrate reconstruction while adsorption at lower temperatures, T=180 K, results in an unreconstructed Cu(100)+c(2x2)--Li overlayer structure. Substrate reconstruction has not been observed for Na nor for K adsorption. In order to study the specific reconstruction behavior of the Li adsorbate ab initio DFT calculations have been performed on Cu(100)+Ad, Ad = Li, Na, K systems at coverages Theta_Ad=0.25-0.5 with and without reconstruction. The calculations show that the (2x1) MR reconstructed surface lies energetically above the ideal (1x1) surface by 0.2 eV per unit cell. However, alkali binding is stronger in the MR geometry as compared to that of the ideal surface where the increase in bond strength becomes smaller in going from Li to Na to K. As a result, the MR reconstructed and the overlayer adsorbate systems are energetically very close for Cu(100)+Li while for Na and K the overlayer geometry is always favored.Comment: 8 pages, 5 figures, submitted to Surf. Rev. Let

Unsolvability Cores in Classification Problems

Classification problems have been introduced by M. Ziegler as a generalization of promise problems. In this paper we are concerned with solvability and unsolvability questions with respect to a given set or language family, especially with cores of unsolvability. We generalize the results about unsolvability cores in promise problems to classification problems. Our main results are a characterization of unsolvability cores via cohesiveness and existence theorems for such cores in unsolvable classification problems. In contrast to promise problems we have to strengthen the conditions to assert the existence of such cores. In general unsolvable classification problems with more than two components exist, which possess no cores, even if the set family under consideration satisfies the assumptions which are necessary to prove the existence of cores in unsolvable promise problems. But, if one of the components is fixed we can use the results on unsolvability cores in promise problems, to assert the existence of such cores in general. In this case we speak of conditional classification problems and conditional cores. The existence of conditional cores can be related to complexity cores. Using this connection we can prove for language families, that conditional cores with recursive components exist, provided that this family admits an uniform solution for the word problem

Reducing the expense of ear wax

Ear wax is one of the commonest presenting complaints both in Ear Nose and Throat surgery and in General Practice. The commonest treatment by far given for this condition is Arachis oil (Cerumol®). Results from various studies however show that this appears not to be the most effective treatment and that cheaper options exist which may drastically reduce the costs incurred by the Health Department in this respect. We hereby outline the advantages of the use of 0.9% saline drops in the treatment of ear wax.peer-reviewe

Interpreting two-photon imaging data of lymphocyte motility

Recently, using two-photon imaging it has been found that the movement of B and T cells in lymph nodes can be described by a random walk with persistence of orientation in the range of 2 minutes. We interpret this new class of lymphocyte motility data within a theoretical model. The model considers cell movement to be composed of the movement of subunits of the cell membrane. In this way movement and deformation of the cell are correlated to each other. We find that, indeed, the lymphocyte movement in lymph nodes can best be described as a random walk with persistence of orientation. The assumption of motility induced cell elongation is consistent with the data. Within the framework of our model the two-photon data suggest that T and B cells are in a single velocity state with large stochastic width. The alternative of three different velocity states with frequent changes of their state and small stochastic width is less likely. Two velocity states can be excluded

Review of the financial and medicolegal implications of nasal fractures seen at St Luke’s Hospital

Simple nasal bone fractures are the third most common type of all fractures leading to numerous patient visits at the Accident & Emergency department. Nasal fractures are commonly over-investigated in St Luke’s hospital leading to a substantial financial burden on our health system. In this article we review the frequency of simple nasal fractures as well as the necessity or otherwise of nasal x-ray imaging in addition to the financial and health consequences that result from nasal x-ray imaging. These issues are also discussed from a legal perspective.peer-reviewe

Canonical structure of the E10 model and supersymmetry

A coset model based on the hyperbolic Kac-Moody algebra E10 has been conjectured to underly eleven-dimensional supergravity and M theory. In this note we study the canonical structure of the bosonic model for finite- and infinite-dimensional groups. In the case of finite-dimensional groups like GL(n) we exhibit a convenient set of variables with Borel-type canonical brackets. The generalisation to the Kac-Moody case requires a proper treatment of the imaginary roots that remains elusive. As a second result, we show that the supersymmetry constraint of D=11 supergravity can be rewritten in a suggestive way using E10 algebra data. Combined with the canonical structure, this rewriting explains the previously observed association of the canonical constraints with null roots of E10. We also exhibit a basic incompatibility between local supersymmetry and the K(E10) `R symmetry', that can be traced back to the presence of imaginary roots and to the unfaithfulness of the spinor representations occurring in the present formulation of the E10 worldline model, and that may require a novel type of bosonisation/fermionisation for its resolution. This appears to be a key challenge for future progress with E10.Comment: 1+39 pages. v2: small corrections. Version to appear in PR

HOT SCALAR ELECTRODYNAMICS AS A TOY MODEL FOR HOT QCD

Hot scalar electrodynamics is adopted as a toy model for a hot gluon plasma to display some aspects of the compulsory resummation of hard thermal loops when next-to-leading order quantities at soft momentum scales are to be calculated. [Talk given by A.K.R. at a one-day meeting dedicated to the memory of Tanguy ALTHERR, held on November 4, 1994 at CERN, Geneva. To appear in a Gedenkschrift published by World Scientific.]Comment: 11 pages, LaTeX, uses epsf.sty, 1 uuencoded postscript figur

Cutting edge: back to "one-way" germinal centers

The present status of germinal center (GC) research is revisited using in silico simulations based on recent lymphocyte motility data in mice. The generally adopted view of several rounds of somatic hypermutations and positive selection is analyzed with special emphasis on the spatial organization of the GC reaction. We claim that the development of dark zones is not necessary for successful GC reactions to develop. We find that a recirculation of positively selected centrocytes to the dark zone is rather unlikely. Instead we propose a scenario that combines a multiple-step mutation and selection concept with a "one-way" GC in the sense of cell migration

Structure of Polyhedral Nanoparticles with Cubic Lattice: Theoretical Analysis

We examine the structure of compact metal nanoparticles (NPs) forming polyhedral sections of the ideal cubic lattice, face centered (fcc), body centered (bcc), and simple (sc), cubic, which are confined by facets characterized by densest, second, and third densest {hkl} monolayers of the lattice. Together with the constraint that the NPs exhibit the same point symmetry as the ideal cubic lattice, i.e. Oh, different types of generic NPs serve for the definition of general compact polyhedral cubic NPs. Their structural properties, such as shape, size, and surface facets, are discussed in analytical detail with visualization of characteristic examples. This illustrates the complexity of seemingly simple nanoparticles in a quantitative account. The geometric relationships of the model particles can also be used to estimate shapes and sizes of real compact metal nanoparticles observed by experiment

Crystallography and Surface Structure: An Introduction for Surface Scientists and Nanoscientists

A valuable learning tool as well as a reference, this book provides students and researchers in surface science and nanoscience with the theoretical crystallographic foundations, which are necessary to understand local structure and symmetry of bulk crystals, including ideal and real single crystal surfaces. The author deals with the subject at an introductory level, providing numerous graphic examples to illustrate the mathematical formalism. The book brings together and logically connects many seemingly disparate structural issues and notations used frequently by surface scientists and nanoscientists. Numerous exercises of varying difficulty, ranging from simple questions to small research projects, are included to stimulate discussions about the different subjects