Microstructure and fatigue characteristics of direct chill cast and electromagnetic cast 2024 Al alloy ingots

The distinct advantages of the electromagnetic casting (EMC) process consist in the presence of stirring motions in the melt, which lead to significant grain size reduction in solidified ingot. Furthermore, surface and subsurface qualities are improved due to the absence of ingot mold. However, it is impossible to achieve the aforementioned advantages in conventional direct chill casting (DCC). In order to contrast the before and after heat treatments of the microstructural and mechanical characteristics of EMC and DCC 2024 aluminium alloys, optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffractions (XRD), differential scanning calorimetry (DSC), etc. were carried out. Compared with the DCC ingot, the EMC ingot has better mechanical properties not only in the ascast condition but also in the as-aged condition. The DSC curves show that the EMC specimens have high enthalpy, i.e., the thermal kinetic energy to form precipitates during the aging treatment process. Despite heat treatments applied to the DCC ingot, it fails to attain the same mechanical properties as the EMC ingot. Moreover, considering the expernsive scalping operation for DCC ingots, the EMC technique, which offers a lower manufacturing cost, is one of the best manufacturing methods used in obtaining the ingots of wrought aluminum alloys.     

Exact controllability for semilinear parabolic equations with Neumann boundary conditions

This paper studies the problem of exact boundary controllability of second-order semilinear parabolic equations when the control is under Neumann's boundary conditions. For a nonlinear term with a sublinear growth we prove the global null-controllability and for the superlinear growth case we prove the local exact controllability of the equations.     

Perceptions of elder abuse and help-seeking patterns among African-American, Caucasian American, and Korean-American elderly women

Thirteen scenarios were used to measure and compare the perceptions of elder abuse and help-seeking behaviors of African-American, Caucasian American, and Korean-American elderly women. Significant group differences existed in their perceptions of elder abuse with regard to six scenarios, and the Korean-American women were substantially less likely to perceive a given situation as abusive than the other groups. The three groups also showed significant differences in their intended use of formal and informal sources of help in the case of elder abuse.     

New queueing strategies employing service interval-based priority for real-time communications in atm networks

In this paper, we propose queueing strategies employing the service interval-based priority (sip) which can provide delay-bounded, and loss-free services, while maximizing bandwidth utilization in the atm network. We also describe a variation of the sip, the residual service interval-based priority (rsip) which can achieve almost full utilization by assigning priorities dynamically on the basis of the residual service interval. We store the realtime cells belonging to different connections in logically separated queues, and for each queue, we set a parameter called service interval, during which only one cell is allowed to be transmitted. The sip server takes and transmits the head-of-line (hol) cell of the queue which has the smallest service interval, while the rsip server selects the queue with the smallest residual service interval. When there is no eligible real-time cell, it transmits non-real-time cell, thus enabling a maximized bandwidth utilization. Employing the above queueing strategies, we analyze the delay characteristics deterministically with the leaky bucket bounded input traffic and then dimension the optimal service interval. In dimensioning the service interval and buffer space of each real-time service queue, we consider burstiness of traffic in conjunction with delay constraints, so that bandwidth utilization can get maximized. In addition, we consider the issues of protection from malicious users, average bandwidth utilization, and coupling between the delay bound and the bandwidth allocation granularity.     

Analysis of culture fluorescence by a fiber-optic sensor inNicotiana tabacum plant cell culture

The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight estimated by the structured kinetic model as well as by empirical correlation.     

Vertex-based inter-frame boundary encoding scheme

The boundary is approximated by a polygon which can be encoded with the smallest number of bits for maximum distortion. The temporal redundancy between two successive frames is efficiently removed with the proposed scheme, resulting in a lower bit rate than the conventional algorithms     

Classification and prediction of the critical heat flux using fuzzy theory and artificial neural networks

A new method to predict the critical heat flux (CHF) is proposed, based on the fuzzy clustering and artificial neural network. The fuzzy clustering classifies the experimental CHF data into a few data clusters (data groups) according to the data characteristics. After classification of the experimental data, the characteristics of the resulting clusters are discussed with emphasis on the distribution of the experimental conditions and physical mechanism. The CHF data in each group are trained in an artificial neural network to predict the CHF. The artificial neural network adjusts the weight so as to minimize the prediction error within the corresponding cluster. Application of the proposed method to the KAIST CHF data bank shows good prediction capability of the CHF, better than other existing methods.     

Radiation-laminar free convection in a square duct with specular reflection by absorbing-emitting medium

The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of 10^-3 for the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased. As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter the fluid motion.