Resampling-based confidence regions and multiple tests for a correlated random vector

We derive non-asymptotic confidence regions for the mean of a random vector whose coordinates have an unknown dependence structure. The random vector is supposed to be either Gaussian or to have a symmetric bounded distribution, and we observe $n$ i.i.d copies of it. The confidence regions are built using a data-dependent threshold based on a weighted bootstrap procedure. We consider two approaches, the first based on a concentration approach and the second on a direct boostrapped quantile approach. The first one allows to deal with a very large class of resampling weights while our results for the second are restricted to Rademacher weights. However, the second method seems more accurate in practice. Our results are motivated by multiple testing problems, and we show on simulations that our procedures are better than the Bonferroni procedure (union bound) as soon as the observed vector has sufficiently correlated coordinates.Comment: submitted to COL

The feathertop problem in Mitchell grass pastures

Seeds of Aristida latifolia (feathertop grass) in Mitchell grass (Astrebla spp.) pastures are the main cause of vegetable fault in wool from sheep grazing these areas. High stocking rates, particularly when the plants were young, reduced the build up of A. latifolia to only 4 000 plants compared with 35 000 in an adjacent field at low stocking rate. Control of A. latifolia by management strategies, (heavy grazing followed by pasture recovery in the wet season) is recommended

Keeping fit

Cover title

The algebra of adjacency patterns: Rees matrix semigroups with reversion

We establish a surprisingly close relationship between universal Horn classes of directed graphs and varieties generated by so-called adjacency semigroups which are Rees matrix semigroups over the trivial group with the unary operation of reversion. In particular, the lattice of subvarieties of the variety generated by adjacency semigroups that are regular unary semigroups is essentially the same as the lattice of universal Horn classes of reflexive directed graphs. A number of examples follow, including a limit variety of regular unary semigroups and finite unary semigroups with NP-hard variety membership problems.Comment: 30 pages, 9 figure

Effects of CO2 and H2S on corrosion of martensitic steels in brines at low temperature

Corrosion studies were conducted for martensitic carbon steels in 5 wt% NaCl brine solutions at 4°C and 10 MPa (1,450 psi). These studies simulated different subsurface environments relevant to Arctic drilling. Here, two high-strength martensitic carbon steels, S-135 and UD-165, were studied in three different environments: (1) a CO2-NaCl-H2O solution with a CO2:H2O molar ratio of 0.312 in the whole system, (2) an H2SNaCl- H2O solution with an H2S:H2O molar ratio of 3.12 × 10−4, and (3) a CO2-H2S-NaCl-H2O solution with the same acid gas to water ratios as environments 1 and 2. Results from the CO2+H2S mixed environment indicated that sour corrosion mechanism was dominant when the CO2:H2S molar ratio was 1,000. This impact of a small amount of H2S on the corrosion mechanism could be attributed to the specific adsorption of H2S on the steel surface. Electrochemical and mass loss measurements showed a distinct drop in the corrosion rate (CR) by more than one order of magnitude when transitioning from sweet to sour corrosion. This inhibiting effect on CR was attributed to the formation of a protective sulfide thin film

Topology of the ground state of two interacting Bose-Einstein condensates

We investigate the spatial patterns of the ground state of two interacting Bose-Einstein condensates. We consider the general case of two different atomic species (with different mass and in different hyperfine states) trapped in a magnetic potential whose eigenaxes can be tilted with respect to the vertical direction, giving rise to a non trivial gravitational sag. Despite the complicated geometry, we show that within the Thomas-Fermi approximations and upon appropriate coordinate transformations, the equations for the density distributions can be put in a very simple form. Starting from this expressions we give explicit rules to classify the different spatial topologies which can be produced, and we discuss how the behavior of the system is influenced by the inter-atomic scattering length. We also compare explicit examples with the full numeric Gross-Pitaevskii calculation.Comment: RevTex4, 8 pages, 7 figure

Corrosion behavior of 13Cr casing steel in cement-synthetic pore solution exposed to high pressure CO2 and H2S

The electrochemical corrosion behavior of grade L-80, type 13Cr casing steel was investigated in cement-synthetic pore solution (CSPS) exposed to CO2 and H2S using in-situ electrochemical methods and ex-situ surface analyses at 85 and 200 °C, respectively. Total system pressure was 10 MPa. Corrosion rates increased significantly when the temperature increased from 85 to 200 °C. Limiting current behavior was observed for the anode reaction, while charge-transfer control was observed for the cathode reaction. Surface analyses revealed the presence of CaCO3 on the surface at both temperatures and FeCO3-like deposits at 200 °C

Decoherence in Bose-Einstein Condensates: towards Bigger and Better Schroedinger Cats

We consider a quantum superposition of Bose-Einstein condensates in two immiscible internal states. A decoherence rate for the resulting Schroedinger cat is calculated and shown to be a significant threat to this macroscopic quantum superposition of BEC's. An experimental scenario is outlined where the decoherence rate due to the thermal cloud is dramatically reduced thanks to trap engineering and "symmetrization" of the environment which allow for the Schroedinger cat to be an approximate pointer states.Comment: 12 pages in RevTex; improved presentation; a new comment on decoherence-free pointer subspaces in BEC; accepted in Phys.Rev.

Symmetric-Asymmetric transition in mixtures of Bose-Einstein condensates

We propose a new kind of quantum phase transition in phase separated mixtures of Bose-Einstein condensates. In this transition, the distribution of the two components changes from a symmetric to an asymmetric shape. We discuss the nature of the phase transition, the role of interface tension and the phase diagram. The symmetric to asymmetric transition is the simplest quantum phase transition that one can imagine. Careful study of this problem should provide us new insight into this burgeoning field of discovery.Comment: 6 pages, 3 eps figure