The Asian red seaweed Grateloupia turuturu (Rhodophyta) invades the Gulf of Maine

We report the invasion of the Gulf of Maine, in the northwest Atlantic Ocean, by the largest red seaweed in the world, the Asian Grateloupia turuturu. First detected in 1994 in Narragansett Bay, Rhode Island, south of Cape Cod, this alga had expanded its range in the following years only over to Long Island and into Long Island Sound. In July 2007 we found Grateloupia in the Cape Cod Canal and as far north (east) as Boston, Massachusetts, establishing its presence in the Gulf of Maine. Grateloupia can be invasive and may be capable of disrupting low intertidal and shallow subtidal seaweeds. The plant\u27s broad physiological tolerances suggest that it will be able to expand possibly as far north as the Bay of Fundy. We predict its continued spread in North America and around the world, noting that its arrival in the major international port of Boston may now launch G. turuturu on to new global shipping corridors

Determination of the hydrodynamic performance of marine propellers using fibre Bragg gratings

Downloading of the abstract is permitted for personal use only. A critical aspect in the design of marine propellers is their hydrodynamic performance which, when evaluated experimentally, requires a number of parameters to be monitored at the same time, i.e.The thrust and torque a propeller generates as well as the propeller shaft and vessel speed. In this investigation, three of those parameters are measured using Fibre Bragg Grating-based sensors, thus allowing for computationally derived performance values to be verified. For that purpose, open water tests were carried out where an instrumented propeller shaft was installed into a research vessel and measurements taken, evaluated and the results compared favorably with advanced computer-based simulations

Underwater free-vibration analysis of full-scale marine propeller using a Fibre Bragg Grating-based sensor system

A detailed experimentally-based study has been carried out on instrumented, full-scale marine propeller blades in order to investigate their vibration behaviour, both in air and underwater. To obtain data with minimum perturbation to the characteristics of the blades, a Fibre Bragg Grating-based sensor network system was designed and implemented, for the first time. The individual vibration frequencies at each measurement point and thus the broader vibration patterns seen for each of the blades were obtained, with excitation both in air and in water and the results are compared favourably with those obtained from Finite Element (FE) analysis. The vibration patterns obtained show that the same modes of vibration occur in air and in water, although in some natural frequencies the mode order is seen to change from one blade to another on the same propeller. The extensive performance survey carried out and experimental data obtained have also shown that while the effect of the added mass of water on the natural frequencies of the blades in the fundamental modes is considerable, this effect diminishes as the natural frequencies of the blades increase. The results obtained from the optical fibre sensor network were compared to those from previous work in this area using different and less satisfactory techniques and it was confirmed that the ratio of the natural frequencies in water to those in air increases in a linear manner as the frequencies were increasing. Additionally, the natural frequencies of a blade were measured under different depths of propeller immersion

Fibre Bragg Grating-based Acoustic Sensor Array for Improved Condition Monitoring of Marine Lifting Surfaces

This paper discusses a novel approach to monitor marine lifting surface conditions through using arrays of Fibre Bragg Grating (FBG)-based acoustic sensors in a marine rudder. Results from these optical sensor arrays are then cross compared with those from conventional piezoelectric (PZT) sensors. A successful proof-of-concept evaluation of the optical sensor approach was, however, first undertaken by using cascaded FBGs integrated into a glass plate, monitoring the response to dropping a standard metal ball at different locations. Data obtained were compared with colocated conventional PZT sensors acoustic sensors for comparison using triangulation to determine the location of the excitation source (a sonotrode). The results obtained verify the excellent performance of the FBG-based sensors due to the excellent agreement between these different sensor types. This gives confidence to the next-stage to scale-up the FBG sensor arrays for other marine structures, with early identification of the initiation of cavitation erosion an important priority for better operational reliability and scheduling of maintenance of marine vessels

Quantum metrology with Bose-Einstein condensates

We show how a generalized quantum metrology protocol can be implemented in a two-mode Bose-Einstein condensate of n atoms, achieving a sensitivity that scales better than 1/n and approaches 1/n^(3/2) for appropriate design of the condensate

Entanglement and the Power of One Qubit

The "Power of One Qubit" refers to a computational model that has access to only one pure bit of quantum information, along with n qubits in the totally mixed state. This model, though not as powerful as a pure-state quantum computer, is capable of performing some computational tasks exponentially faster than any known classical algorithm. One such task is to estimate with fixed accuracy the normalized trace of a unitary operator that can be implemented efficiently in a quantum circuit. We show that circuits of this type generally lead to entangled states, and we investigate the amount of entanglement possible in such circuits, as measured by the multiplicative negativity. We show that the multiplicative negativity is bounded by a constant, independent of n, for all bipartite divisions of the n+1 qubits, and so becomes, when n is large, a vanishingly small fraction of the maximum possible multiplicative negativity for roughly equal divisions. This suggests that the global nature of entanglement is a more important resource for quantum computation than the magnitude of the entanglement.Comment: 22 pages, 4 figure

KINEMATIC COMPARISON OF TWO RACING WHEELCHAIR PROPULSION TECHNIQUES

The purpose of this study was to quantify selected 3-D kinematic characteristics of the upper body during racing wheelchair stroking over a roller system using the conventional technique (CVT) and para-backhand technique (PBT). Eight CVT and seven PBT users served as the subjects. Each subject performed maximum effort stroking for 30 s at two loads and was recorded by two S-VHS camcorders (60 Hz). The CVT was found to have significant shorter push time, smaller relative push time, and greater relative recovery time than the PBT. Significant difference in arm position at the instant of hand release was found between the two techniques and the difference may have implications for the stress placed on the structures around the shoulder joint. When compared to each other, the CVT is a more compact stroke and the PBT has a faster overall movement speed

Quantum-limited metrology with product states

We study the performance of initial product states of n-body systems in generalized quantum metrology protocols that involve estimating an unknown coupling constant in a nonlinear k-body (k << n) Hamiltonian. We obtain the theoretical lower bound on the uncertainty in the estimate of the parameter. For arbitrary initial states, the lower bound scales as 1/n^k, and for initial product states, it scales as 1/n^(k-1/2). We show that the latter scaling can be achieved using simple, separable measurements. We analyze in detail the case of a quadratic Hamiltonian (k = 2), implementable with Bose-Einstein condensates. We formulate a simple model, based on the evolution of angular-momentum coherent states, which explains the O(n^(-3/2)) scaling for k = 2; the model shows that the entanglement generated by the quadratic Hamiltonian does not play a role in the enhanced sensitivity scaling. We show that phase decoherence does not affect the O(n^(-3/2)) sensitivity scaling for initial product states.Comment: 15 pages, 6 figure

Fiber bragg grating-based system for 2-D analysis of vibrational modes of a steel propeller blade

This paper reports results obtained using fiber Bragg grating (FBG)-based sensors to investigate the displacement mode shapes of a cantilevered steel propeller blade, using FBG arrays for vibration monitoring for the first time. The experimental data obtained are cross compared with those from a finite element analysis of the same blade, undertaken using proprietary software. In the experimental configuration used, a network of gratings, forming a series of sensor arrays, was mounted on the blade under study to monitor its bending modes, while a further set was mounted perpendicular to this array to monitor torsional modes. To obtain the shape of the strain modes generated in the blade at specific frequencies, the dynamic response of the FBG arrays, as a function of time, was captured and then processed using Fourier transform algorithms to show the natural frequencies of the blade. As a result, the displacement modes shapes for the bending, torsional, and coupled modes of the first nine natural frequencies of the plate were obtained. The experimental data show very good agreement with theoretical analysis. This paper demonstrates the potential of using the lightweight, minimally invasive sensing technique described for the analysis of propeller blades and, thus, illustrating an effective method to overcome the deleterious effects of propellers seen in some commercial propeller designs

Fibre Bragg Grating-based Cascaded Acoustic Sensors for Potential Marine Structural Condition Monitoring

This paper explores the potential of using multiple Fibre Bragg grating (FBG)-based sensors for acoustic emission (AE) detection, thus offering an effective alternative to conventional piezoelectric (PZT) sensors, especially where they have shown limitations in use, such as in the marine sector. A cascaded fibre optic acoustic sensor system, using optical filter signal demodulation has been developed and its performance extensively evaluated. To undertake this under standardized conditions, the optical sensor system was evaluated using a glass plate to detect the acoustic signal, followed by an evaluation using a metal plate to identify the location of acoustic sources, when subjected to sonotrode excitation, mimicking acoustic detection in cavitation detection. Under these circumstances, a very good agreement has been reached between the outputs of the optical acoustic sensors and of the co-located PZT acoustic sensors. This work confirms the utility of these sensors – they can detect not only weak AE signals, but also enable multipoint simultaneous measurement, showing their potential for condition monitoring applications, especially in the marine sector