Non-disturbing quantum measurements

We consider pairs of quantum observables (POVMs) and analyze the relation between the notions of non-disturbance, joint measurability and commutativity. We specify conditions under which these properties coincide or differ---depending for instance on the interplay between the number of outcomes and the Hilbert space dimension or on algebraic properties of the effect operators. We also show that (non-)disturbance is in general not a symmetric relation and that it can be decided and quantified by means of a semidefinite program.Comment: Minor corrections in v

Chloride channels in stellate cells are essential for uniquely high secretion rates in neuropeptide-stimulated Drosophila diuresis

Epithelia frequently segregate transport processes to specific cell types, presumably for improved efficiency and control. The molecular players underlying this functional specialization are of particular interest. In Drosophila, the renal (Malpighian) tubule displays the highest per-cell transport rates known and has two main secretory cell types, principal and stellate. Electrogenic cation transport is known to reside in the principal cells, whereas stellate cells control the anion conductance, but by an as-yet-undefined route. Here, we resolve this issue by showing that a plasma membrane chloride channel, encoded by ClC-a, is exclusively expressed in the stellate cell and is required for Drosophila kinin-mediated induction of diuresis and chloride shunt conductance, evidenced by chloride ion movement through the stellate cells, leading to depolarization of the transepithelial potential. By contrast, ClC-a knockdown had no impact on resting secretion levels. Knockdown of a second CLC gene showing highly abundant expression in adult Malpighian tubules, ClC-c, did not impact depolarization of transepithelial potential after kinin stimulation. Therefore, the diuretic action of kinin in Drosophila can be explained by an increase in ClC-a–mediated chloride conductance, over and above a resting fluid transport level that relies on other (ClC-a–independent) mechanisms or routes. This key segregation of cation and anion transport could explain the extraordinary fluid transport rates displayed by some epithelia

A European Design Code for Pallet Racking

The work leading to a European design code for pallet racking started almost 25 years ago. Many difficulties were encountered in the early days of this work. Notable were the absence of a consistent safety philosophy between the various countries of Europe and the existence of procedures with which the manufacturers were comfortable but which were potentially unsafe. There were also difficulties in defining acceptable standard. test procedures. The emergence of Eurocode 3, especially Part 1.3 dealing with cold formed sections, provided a new impetus to the work because here was a European code which provided the required basis for the design code. Accordingly, Section X of the Federation Europeenne de la Manutention (FEM) commissioned technical experts to draft the new code under the direction of its technical committee. It was a requirement that the code should be, as far as possible, compatible with Eurocode 3. In the early stages of the work, there were a group of these experts but, for most of the drafting period, only the authors of this paper were active. The code was essentially complete in mid 1997 and, since then, it has been subject to trial use by the member companies of FEM and open to consequential comments. However, in May 1997, a significant meeting took place. FEM and the Rack Manufacturers Institute (RMI) of the USA sponsored a meeting between the first author and RMI\u27s own expert , Professor T Pekoz of Cornell University. The intention was to compare the two codes and to report on the potential for possible future harmonisation. It emerged that the two codes were about as different as two codes covering the design of the same structural elements could be! However, the experts took a positive view of the situation and concluding that, from the technical point of view, there was no reason why the two codes could not be brought into convergence and that, in the meantime, we could each learn from the others experience. Consequently, at this late stage in the evolution of the European code, a number of significant changes were made where it was considered that the European code could advantageously be made more compatible with the RMI code without in any way impairing its technical rigour. This paper introduces the new European design code for pallet racking and compares and contrasts it with its American counterpart. As a pallet rack is a particularly demanding application of cold-formed steel sections, it is hoped that the designers of other cold-formed products may also learn from some of the approaches described in this paper

The Fornax Spectroscopic Survey: The Number of Unresolved Compact Galaxies

We describe a sample of thirteen bright (18.5<Bj<20.1) compact galaxies at low redshift (0.05<z<0.21) behind the Fornax Cluster. These galaxies are unresolved on UK Schmidt sky survey plates, so would be missing from most galaxy catalogs compiled from this material. The objects were found during initial observations of The Fornax Spectroscopic Survey. This project is using the Two-degree Field spectrograph on the Anglo-Australian Telescope to obtain spectra for a complete sample of all 14000 objects, stellar and non-stellar, with 16.5<Bj<19.7, in a 12 square degree area centered on the Fornax cluster of galaxies. The surface density of compact galaxies with magnitudes 16.5<Bj<19.7 is 7+/-3 /sq.deg., representing 2.8+/-1.6% of all local (z<0.2) galaxies to this limit. There are 12+/-3 /sq.deg. with 16.5<Bj<20.2. They are luminous (-21.5<Mb<-18.0, for H0=50 km/s/mpc) and most have strong emission lines (H alpha equivalent widths of 40-200 A) and small sizes typical of luminous HII galaxies and compact narrow emission line galaxies. Four out of thirteen have red colors and early-type spectra, so are unlikely to have been detected in any previous surveys.Comment: LaTeX source; 5 pages including 3 figures; uses emulateapj.st

Archaean and Proterozoic diamond growth from contrasting styles of large-scale magmatism

Precise dating of diamond growth is required to understand the interior workings of the early Earth and the deep carbon cycle. Here we report Sm-Nd isotope data from 26 individual garnet inclusions from 26 harzburgitic diamonds from Venetia, South Africa. Garnet inclusions and host diamonds comprise two compositional suites formed under markedly different conditions and define two isochrons, one Archaean (2.95 Ga) and one Proterozoic (1.15 Ga). The Archaean diamond suite formed from relatively cool fluid-dominated metasomatism during rifting of the southern shelf of the Zimbabwe Craton. The 1.8 billion years younger Proterozoic diamond suite formed by melt-dominated metasomatism related to the 1.1 Ga Umkondo Large Igneous Province. The results demonstrate that resolving the time of diamond growth events requires dating of individual inclusions, and that there was a major change in the magmatic processes responsible for harzburgitic diamond formation beneath Venetia from the Archaean to the Proterozoic

Behaviour of Cold-formed Thin-walled Steel Short Columns with Service Holes At Elevated Temperatures

This paper presents the results of an experimental and numerical investigation into the axial strength of cold-formed thin-walled lipped channel sections with service holes under ambient and uniform high temperature conditions. Short columns of two different thickness with service holes under different temperatures have been tested, and analysed by using a variety of design methods and a commercial finite element program ABAQUS (1998). Three design methods (the British Standard BS5950 Part 5 (1987), Eurocode 3 Part 1.3 (CEN 1996) and the American Specification AISI (1996)) have been used in this paper. In the finite element analysis, both geometrical and material non-linearities are taken into account. The high temperature stress-strain relationships of steel are determined according to Eurocode 3, Part 1.2 (CEN 1995) and Outinen (1999, 2000, 2001). To enable BS5950 Part 5 (1987) and Eurocode 3 Part 1.3 (CEN 1996) to predict the ultimate strength of thin-walled columns with service holes, the AISI (1996) design method is introduced. To extend the capacity of the three design methods to deal with distortional buckling, the method of Young and Hancock (1992) for calculating distortional buckling capacity is introduced in these codes. The ambient temperature design methods for thin-walled columns in BS5950 Part 5 (1987), Eurocode 3 Part 1.3 (CEN 1996) and the AISI specification (1996) are modified to take into account changes in the strength and stiffness of steel at elevated temperatures. It is found that service holes can have a significant effect on the load capacity of a column regardless of the column temperature when thicker members are used. From extensive comparisons between the test results, modified codes\u27 predictions and numerical analyses, it may be concluded that by adopting the aforementioned modifications, the current code design methods are suitable for evaluating the buckling behaviour of perforated short columns at elevated temperatures

Geometric Suppression of Single-Particle Energy Spacings in Quantum Antidots

Quantum Antidot (AD) structures have remarkable properties in the integer quantum Hall regime, exhibiting Coulomb-blockade charging and the Kondo effect despite their open geometry. In some regimes a simple single-particle (SP) model suffices to describe experimental observations while in others interaction effects are clearly important, although exactly how and why interactions emerge is unclear. We present a combination of experimental data and the results of new calculations concerning SP orbital states which show how the observed suppression of the energy spacing between states can be explained through a full consideration of the AD potential, without requiring any effects due to electron interactions such as the formation of compressible regions composed of multiple states, which may occur at higher magnetic fields. A full understanding of the regimes in which these effects occur is important for the design of devices to coherently manipulate electrons in edge states using AD resonances.Comment: 4 pages, 2 figure