Thruster Allocation for Dynamical Positioning

Positioning a vessel at a fixed position in deep water is of great importance when working offshore. In recent years a Dynamical Positioning (DP) system was developed at Marin [2]. After the measurement of the current position and external forces (like waves, wind etc.), each thruster of the vessel is actively controlled to hold the desired location. In this paper we focus on the allocation process to determine the settings for each thruster that results in the minimal total power and thus fuel consumption. The mathematical formulation of this situation leads to a nonlinear optimization problem with equality and inequality constraints, which can be solved by applying Lagrange multipliers. We give three approaches: first of all, the full problem was solved using the MATLAB fmincon routine with the solution from the linearised problem as a starting point. This implementation, with robust handling of the situations where the thrusters are overloaded, lead to promising results: an average reduction in fuel consumption of approximately two percent. However, further analysis proved useful. A second approach changes the set of variables and so reduces the number of equations. The third and last approach solves the Lagrange equations with an iterative method on the linearized Lagrange problem

Character, distribution, and ecological significance of storm wave-induced scour in Rhode Island Sound, USA

This paper is not subject to U.S. copyright. The definitive version was published in Geo-Marine Letters 35 (2015): 135-144, doi:10.1007/s00367-014-0392-0.Multibeam bathymetry, collected during NOAA hydrographic surveys in 2008 and 2009, is coupled with USGS data from sampling and photographic stations to map the seabed morphology and composition of Rhode Island Sound along the US Atlantic coast, and to provide information on sediment transport and benthic habitats. Patchworks of scour depressions cover large areas on seaward-facing slopes and bathymetric highs in the sound. These depressions average 0.5–0.8 m deep and occur in water depths reaching as much as 42 m. They have relatively steep well-defined sides and coarser-grained floors, and vary strongly in shape, size, and configuration. Some individual scour depressions have apparently expanded to combine with adjacent depressions, forming larger eroded areas that commonly contain outliers of the original seafloor sediments. Where cobbles and scattered boulders are present on the depression floors, the muddy Holocene sands have been completely removed and the winnowed relict Pleistocene deposits exposed. Low tidal-current velocities and the lack of obstacle marks suggest that bidirectional tidal currents alone are not capable of forming these features. These depressions are formed and maintained under high-energy shelf conditions owing to repetitive cyclic loading imposed by high-amplitude, long-period, storm-driven waves that reduce the effective shear strength of the sediment, cause resuspension, and expose the suspended sediments to erosion by wind-driven and tidal currents. Because epifauna dominate on gravel floors of the depressions and infauna are prevalent in the finer-grained Holocene deposits, it is concluded that the resultant close juxtaposition of silty sand-, sand-, and gravel-dependent communities promotes regional faunal complexity. These findings expand on earlier interpretations, documenting how storm wave-induced scour produces sorted bedforms that control much of the benthic geologic and biologic diversity in Rhode Island Sound.This work was supported by the Coastal and Marine Geology Program of the U.S. Geological Survey and the Atlantic Hydrographic Branch of the National Oceanic and Atmospheric Administration

Challenging Depressive Beliefs: Habitual and Recollective Components of Stability or Change

Background and objectives. Depressed people tend to hold stable negative beliefs that resist challenges. Two experiments investigated the cognitive bases of belief change or resistance to change following the provision of supportive or challenging pseudo-evidence. Method. Students scoring high and low on a measure of depressed state read belief statements, each followed by invented experimental evidence to either verify or discount them. Two days later, they read all the belief statements again, together with new statements, this time rating belief. Results. The students agreed that the statements described common beliefs and that the evidence was plausible. Discounted statements were believed less than new statements on the test. Also, dysphoric students believed discounted and new statements less than verified statements, but that difference was larger for the nondysphoric students. Parameter estimates of the habitual basis for belief ratings, obtained with process-dissociation procedures, were higher in the dysphoric group, and estimates of evidence recollection were lower. The latter finding was conceptually supported by deficient recognition of the gist of the discounting evidence in the dysphoric group (Experiment 2). Limitations. Experiment 2 results replicated the rating effects in Experiment 1, but not the parameter differences, due to low power as a consequence of the university response to the pandemic. Conclusions. We interpret these results in the context of other evidence regarding belief change and depressive cognition, such as habitual rumination and deficient cognitive control

Glueball Production in Peripheral Heavy-Ion Collisions

The method of equivalent quanta is applied both to photon-photon and, by analogy, to double pomeron exchange in heavy-ion collisions. This Weizs\"acker-Williams approach is used to calculate production cross sections for the glueball candidate $f_J(1710)$ meson via photon-photon and pomeron-pomeron fusion in peripheral heavy-ion collisions at both RHIC and LHC energies. The impact-parameter dependence for total and elastic cross sections are presented, and are compared to results for proton-proton collisions.Comment: 15 pages, 6 figure

Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation

The manipulation of the antiferromagnetic interlayer coupling in the epitaxial Fe/Cr/Fe(001) trilayer system by moderate 5 keV He ion beam irradiation has been investigated experimentally. It is shown that even for irradiation with very low fluences (10^14 ions/cm^2) a drastic change in strength of the coupling appears. For thin Cr-spacers (below 0.6 - 0.7 nm) the coupling strength decreases with fluence, becoming ferromagnetic for fluences above (2x10^14 ions/cm^2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers (0.8 - 1.2 nm) an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given.Comment: Submitted to PR

Expression and mutational analysis of Nm23-H1 in liver metastases of colorectal cancer.

It has been proposed that nm23-H1, a candidate suppressor gene for metastasis, plays an important role in metastasis formation of human tumours. In order to investigate its role in the progression of colorectal cancer, we analysed 22 liver metastases of this malignancy with respect to mutational changes, loss of heterozygosity and expression levels of nm23-H1. Although genetic alterations in nm23-H1 have recently been described in those colorectal adenocarcinomas which give rise to distant metastases, we were unable to detect any mutation in the coding sequence of nm23-H1 in the metastatic tissue itself. We further analysed the metastases with respect to allelic deletions at the chromosomal locus of nm23. However, no loss of heterozygosity could be detected in ten informative cases. Moreover, the mRNA expression levels of nm23-H1 in the metastatic tissues were not significantly different from those in normal colon mucosa. Thus, although nm23-H1 might be involved in metastasis suppression of certain tumour types, in colorectal tumour progression its role remains to be determined

The Texture of Surficial Sediments in Western Long Island Sound off the Norwalk Islands, Connecticut

Grain-size analyses were performed on 69 samples from western Long Island Sound. The relative grain-size frequency distributions and related statistics are reported herein. Descriptions of the benthic character from video tapes and still camera photographs of the bottom at these stations, and 33 others, are also presented. The southern and eastern parts of the study area are dominated by poorly sorted clayey silts that have nearly symmetrical distributions. Gravelly sediments are prevalent in the shallow northwestern part of the study area, but are also present in central part of the study area. Bands of sand, silty sand, and sand-silt-clay occur on the flanks of the gravelly areas

Solar-Energetic-Particle Track-Production Rates at 1 au: Comparing In-situ Particle Fluxes with Lunar Sample-Derived Track Densities

Heavy (Z>26) solar energetic particles (SEPs) with energies ~1 MeV/nucleon are known to leave visible damage tracks in meteoritic materials. The density of such solar flare tracks in lunar and asteroidal samples has been used as a measure of a sample's exposure time to space, yielding critical information on planetary space weathering rates, the dynamics and lifetimes of interplanetary dust grains, and the long-term history of solar particle fluxes. Knowledge of the SEP track accumulation rate in planetary materials at 1 au is critical for properly interpreting observed track densities. Here, we use in-situ particle observations of the 0.50-3.0 MeV/nuc Fe-group SEP flux taken by NASA's Advanced Composition Explorer (ACE) to calculate a flux of track-inducing particles at 1 au of 6.0x10^5 /cm2/yr/str. Using the observed energy spectrum of Fe-group SEPs, we find that the depth distribution of SEP-induced damage tracks inferred from ACE measurements matches closely to that recently measured in lunar sample 64455; however, the magnitude of the ACE-inferred rate is approximately 25x higher than that observed in the lunar sample. We discuss several hypotheses for the nature of this discrepancy, including inefficiencies in track formation, thermal annealing of lunar samples, erosion via space weathering processing, and variations in the SEP flux at the Moon, yet find no satisfactory explanation. We encourage further research on both the nature of SEP track formation in meteoritic materials and the flux of Fe-group SEPs at the lunar surface in recent and geologic times to resolve this discrepancy.Comment: 18 pages, 4 figures; Accepted for publication in Astrophys. J. Let