Nonlinear analysis of rectangular orthotropic plates

The present study deals with the large deflections and nonlinear flexural vibrations of orthotropic rectangular plates. In this paper, generalized double Fourier series in terms of generalized beam eigenfunctions for deflection and force functions are presented. The influences of aspect ratio, material properties, transverse load, rotational edge restraint coefficients, and two types of in-plane conditions are studied. The results of deflection and frequency ratio for special cases are compared with those values given in the literature and good agreement is obtained.     

Gaseous hydrogen embrittlement of a hydrided zirconium alloy

ZIRCALOY-4 plate specimens were gaseously hydrided up to 340 ppm H and then tested in a hydrogen gas environment of various pressures up to 2020 kPa a at 25 °C, 100 °C, and 200 °C. Notched tensile specimens were chosen to better understand the “ductile-brittle transition” associated with hydrogen content and hydrogen pressure. The purpose of the present investigation is to understand the synergistic effect of hydrogen gas and internal hydrides on the mechanical properties of ZIR-CALOY-4. The results showed that for both uncharged and hydrided specimens, the notch tensile strength decreased with increasing hydrogen pressure as well as increasing temperature. Compared with uncharged specimens, the specimens with hydrides had lower values of notch tensile strength. A ductile-brittle transition was found on specimens tested at 25 °C and at hydrogen pressures between 0 and 1010 kPa. For the specimen containing 220 ppm H, the reduction of area (RA) at 25 °C and at hydrogen pressures of 1010 kPa and above was drastically reduced, resulting in almost completely brittle behavior. This hydrogen and hydride-induced cracking was found to be an autocatalytic process. From the fractographic finding, the ductile-brittle transition was closely related to the precipitation and distribution of brittle hydrides. The ductile-brittle transition disappeared as the temperature increased to 100 °C and above. This can be attributed to the improved ductility of the zirconium matrix with increasing temperature.     

A new approach to the d-MC problem

Many real-world systems (such as cellular telephones, transportation, etc.) are multistate-node acyclic network (MNAN) composed of multistate-nodes. Such network has a source node (position) where the signal source is located, a number of sink nodes that only receive the signal, and a number of intermediate nodes that retransmit the received signal to some other nodes. The non-sink node has different states determined by a set of nodes receiving the signal directly from it. The reliability of MNAN can be computed in terms of minimal trees (MTs). Based on the Branch-and-Bound algorithm, we developed an intuitive algorithm that is simpler than the best-known existing method. The computational complexity of the proposed algorithm is also analyzed. One example is illustrated to show how all MTs are generated by the proposed algorithm. The reliability of this example is then computed.     

The trauma response of children and adolescents. Future directions in research

Although trauma research in children lags behind that of adults and is often preliminary or unreplicated, current work promises rich understanding of the neurobiologic and psychologic mechanisms underlying the trauma response of the young. Epidemiologic and longitudinal, prospective, controlled studies sensitive to cultural and developmental differences are needed to illuminate the natural history of posttraumatic stress disorder and to show how trauma and its response interact with family, school, and community factors. Promising profound implications for society, such data would enable mental health professionals, educators, and policy makers to develop standards for prevention, detection, and intervention to optimize children's developmental trajectory.     

Design of random inspection rate for a flexible assembly system: a heuristic genetic algorithm approach

Because of parts failure in a flexible assembly system (FAS), in-process quality control is necessary. To maximize profit, it is important to derive the inspection rate for each cell. This paper proposes an analytical model using an open queuing network theory for an FAS with feedback and reworking. The problem is solved by a modified genetic algorithm which has two major characteristics. First, the probability of mutation is variable rather than fixed in processing the search. Second, a specified mutation operator with calculating decoded values is proposed according to the status of the solution. These modifications enhance the efficiency and accuracy of the algorithm in empirical experiments.     

Internal stress superplasticity in anisotropic

Internal stress superplasticity is assessed in powder metallurgy and wrought polycrystalline Zn and in polycrystalline α-U. These materials are anisotropic in their thermal expansion coefficients, and, as a result, internal stresses are generated during thermal cycling. A creep model is developed based on the contribution of internal stress to the enhancement and inhibition of normal plastic flow. This creep model, which has no disposable parameters, is shown to describe quantitatively the flow behavior of anisotropic materials under thermal cycling conditions, and correctly predicts the attainment of Newtonian flow characteristics at low stresses. It is predicted that certain polycrystalline ceramics can be made superplastic in tension when thermally cycled under small applied stress.     

A thermosyphon water cooler with a parallel, flat-plate radiator

The performance of a thermosyphon water cooler with a parallel, flat-plate radiator has been studied, both theoretically and experimentally. Some theoretical predictions of water temperatures in the storage tank and of the cooling intensity have been obtained from energy and momentum balances. Theoretical values are in agreement with experimental data. This research will be useful in assessing the combination of solar heating and radiative cooling in a single device.     

A family of nonlinear H∞-output feedbackcontrollers

State-space formulas are derived for a family of controllers solving the nonlinear H^∞-output feedback control problem. The formulas given are expressed in terms of the solutions to two Hamilton-Jacobi inequalities in n independent variables. These controllers are obtained by interconnecting the “central controller” with an asymptotically stable, free system having L ²-gain ⩽γ. All proofs given are simple and clear and provide deeper insight in the synthesis of the corresponding linear H^∞ controllers     

Pyogenic liver abscesses in patients with malignant disease: a report of 52 cases treated at a single institution

OBJECTIVE: To generate baseline data about the experiences of researchers applying to five or more local research ethics committees (LRECs) for ethical review. The new multi-centre review system will be compared with these data. DESIGN: Ninety-seven researchers, whose status as multicentre researchers was unclear, were identified from various sources in the South Thames Region. They were each sent a questionnaire asking for their views on the substance of ethical review and their experiences of the process of ethical review. RESULTS: Of the completed questionnaires, 24 fitted the multicentre criteria of applying to five or more LRECs. Responses showed dissatisfaction with LRECs' treatment of the scientific aspects of research, but satisfaction with aspects relating to consent and protection of patients' welfare. Respondents experienced great difficulty in the administration of the process of ethical review. CONCLUSIONS: The need for a new system of ethical review for multi-centre research is beyond doubt. It remains to be seen whether it will be an improvement.