Flexural gravity wave generation by initial disturbances in the presence of current

The effect of uniform current on the generation of flexural gravity waves resulting from initial disturbances at a point was analyzed in two dimensions. The problem was formulated as an initial boundary value problem under the assumptions of the linearized theory of water waves. By direct application of the Laplace transform and then the Fourier transform, explicit expressions for the velocity potential and free surface elevation were obtained in integral forms; these were evaluated asymptotically for large distances and times by the application of the method of the stationary phase to obtain the far field behavior of the surface elevations in specific cases. Simple numerical computations were performed to illustrate the effect of uniform current on the surface elevation, wavelength, phase velocity, and group velocity of the flexural gravity waves and on the far field behavior of the progressive waves in two different cases, namely, when there is an initial depression concentrated at the origin and an initial impulse concentrated at the origin.     

Management of coastal eutrophication: Integration of field data, ecosystem-scale simulations and screening models

A hybrid approach for eutrophication assessment in estuarine and coastal ecosystems is presented. The ASSETS screening model (http://www.eutro.org) classifies eutrophication status into five classes: High (better), Good, Moderate, Poor and Bad (worse). This model was applied to a dataset from a shallow coastal barrier island system in southwest Europe (Ria Formosa), with a resulting score of Good. A detailed dynamic model was developed for this ecosystem, and the outputs were used to drive the screening model. Four scenarios were run on the research model: pristine, standard (simulates present loading), half and double the current nutrient loading. The Ria Formosa has a short water residence time and eutrophication symptoms are not apparent in the water column. However, benthic symptoms are expressed as excessive macroalgal growth and strong dissolved oxygen fluctuations in the tide pools. The standard simulation results showed an ASSETS grade identical to the field data application. The application of the screening model to the other scenario outputs showed the responsiveness of ASSETS to changes in pressure, state and response, scoring a grade of High under pristine conditions, Good for half the standard scenario and Moderate for double the present loadings. The use of this hybrid approach allows managers to test the outcome of measures against a set of well-defined metrics for the evaluation of state. It additionally provides a way of testing and improving the pressure component of ASSETS. Sensitivity analysis revealed that sub-sampling the output of the research model at a monthly scale, typical for the acquisition of field data, may significantly affect the outcome of the screening model, by overlooking extreme events such as occasional night-time anoxia in tide pools.     

Improving the predictiveness of the quasi-d combustion model for spark ignition engines with flexible intake systems

Fast and predictive simulation tools are prerequisites for pursuing simulation based engine control development. A particularly attractive tradeoff between speed and fidelity is achieved with a co-simulation approach that marries a commercial gas dynamic code WAVE™ with an in-house quasi-dimensional combustion model. Gas dynamics are critical for predicting the effect of wave action in intake and exhaust systems, while the quasi-D turbulent flame entrainment model provides sensitivity to variations of composition and turbulence in the cylinder. This paper proposes a calibration procedure for such a tool that maximizes its range of validity and therefore achieves a fully predictive combustion model for the analysis of a high degree of freedom (HDOF) engines. Inclusion of a charge motion control device in the intake runner presented a particular challenge, since anything altering the flow upstream of the intake valve remains “invisible” to the zero-D turbulence model applied to the cylinder control volume. The solution is based on the use of turbulence multiplier and scheduling of its value. Consequently, proposed calibration procedure considers two scalar variables (dissipation constant C _β and turbulence multiplier C _M ), and the refinements of flame front area maps to capture details of the spark-plug design, i.e. the actual distance between the spark and the surface of the cylinder head. The procedure is demonstrated using an SI engine system with dual-independent cam phasing and charge motion control valves (CMCV) in the intake runner. A limited number of iterations led to convergence, thanks to a small number of adjustable constants. After calibrating constants at the reference operating point, the predictions are validated for a range of engine speeds, loads and residual fractions.     

Sensitivity analysis of the probabilistic damage stability regulations for RoPax vessels

In the light of the newly developed harmonised probabilistic damage stability regulations, set to come into force in 2009, this article presents a systematic and thorough analysis of the sensitivity of the Attained Subdivision Index with reference to a wide range of related design parameters. The sensitivity of the probabilistic regulations was investigated for a typical large RoPax vessel, with variation of parameters, such as the number, positioning and local optimisation of transverse bulkheads; the presence and position of longitudinal bulkheads below the main vehicle deck; the presence of side casings; and the height of the main deck and double bottom. The effects of water on deck and of operational parameters (draught, centre of gravity and trim) were also investigated. The results of the study, presented in graphical form, can provide valuable assistance to the designer when determining subdivision characteristics at the very early stage of the design process, resulting in optimal, efficient and safe ships.     

Fast direction of arrival algorithm based on vector-sensor arrays using wideband sources

An acoustic vector sensor （AVS） can capture more information than a conventional acoustic pressure sensor （APS）. As a result, more output channels are required when multiple AVS are formed into arrays, making processing the data stream computationally intense. This paper proposes a new algorithm based on the propagator method for wideband coherent sources that eliminates eigen-decomposition in order to reduce the computational burden. Data from simulations and lake trials showed that the new algorithm is valid： it resolves coherent sources, breaks left/right ambiguity, and allows inter element spacing to exceed a half-wavelength.     

严峻问题

今年关于太平洋航线有两个不确定因素,即美国进口量增长将会大大放缓,同时美国出口量会继续增加.因此,几乎所有其他的问题都是不确定的:进口量是否会增长还是会减少?     

Transforaminal lumbar interbody fusion for traumatic lumbar spondylolisthesis

To evaluate the clinical outcome, effectiveness and safety of the surgical management of traumatic lumbar spondylolisthesis with transforaminal lumbar interbody fusion (TLIF) with short segmental instrumentation fixation. A retrospective review of a consecutive series of 24 patients with traumatic lumbar spondylolisthesis treated with TLIF procedure was carried out. Intraoperative spinal cord monitoring was used to confirm the peripheral neural function intact during the reduction of the spondylolisthesis. Preoperative clinical and radiographic evaluation of all cases were originally collected prospectively. Data regarding blood loss, operative time, duration of hospital stay, radiographic fusion, instrumentation failure and clinical result were collected and observed at regular follow-up periods. All patients were engaged in high-energy accidents in the lower back and 16 patients had concomitant injuries. The mean operative time was 124 min, mean blood loss was 350 mL, and mean hospital stay was 6.5 days. There were no complications such as incision infection, cerebrospinal fluide (CSF) leakage and nerve root injury and so on. All patients demonstrated a solid lumbar interbody fusion within 4 months, and no evidence of spondylolisthesis correction loss, instrumentation failure and loosing. They all were completely asymptomatic, with normal neurologic findings, and had resumed their previous level of physical activities on the final follow-up. Meticulous clinical examination and careful imaging assessment could assist an early diagonosis in cases of traumatic lumbar spondylolisthesis. Performing open reduction and the TLIF procedure as soon as possible could restore segmental stability and painless function. The TLIF procedure was a safe, effective technique to treat traumatic lumbar spondylolisthesis.     

Face recognition via adaptive image combination

Dimension reduction and manifold learning are the two most popular feature extraction methods. The two methods focus on spatial locality as a guiding principle to find a low-dimensional basis for describing high-dimensional data, but no bases or features are more spatially localized than the original image pixels. So, adaptive image combination is presented to represent a class by a combined sample. The combined sample is a linear combination of original samples in the same class. Adaptive image combination (AIC) find the best combination coefficients by minimizing the intrapersonal distance and maximizing the interpersonal distance. Experimental results show that AIC is effective.     

Parameter transfer of common-metric attributes in choice analysis: implications for willingness to pay

There is a growing literature that promotes the presence of a mix of compensatory and semi-compensatory processing strategies in the way that individuals evaluate packages of attributes in real or hypothetical markets, and make choices. This paper proposes a specification for the utility form in a choice model to test if, given a pair of attributes with a common-metric (e.g., components of travel time or cost), the attribute with the dominating level defines the marginal (dis)utility that is assigned to both attributes. We refer to this processing strategy as a parameter transfer rule. We use a stated choice data set, in the context of car driving individuals choosing between tolled and non-tolled routes, to estimate a mixed logit model which incorporates the presence of the parameter transfer rule and the conventional fully compensatory rule, both existing up to a probability. We find that if this parameter transfer heuristic is part of the mix, the WTP is more than 30% higher, on average, than when only a fully compensatory rule is imposed. We also contrast the parameter transfer rule with other semi-compensatory heuristics which have been investigated in other papers, and show that the finding adds further support to the accumulating evidence that a semi-compensatory attribute processing rules tend to result in higher mean WTP estimates compared to the fully compensatory attribute processing rule.