Heat transfer and pressure drop in a new type of corrugated channels

An experimental investigation of heat transfer and pressure drop from a new type of corrugated channels is presented. The investigation has been carried out for Reynolds numbers in the range of $\text{800 <}\text{Re}\text{< 5000}$ for one corrugated and one smooth channel. It is found that the heat transfer from the corrugated channel is up to 3.5 times higher than for the smooth one. The pressure drop is however large (5 – 6 times the value of a smooth channel) and it is suggested that the corrugation height and length should be altered in order to balance the increases in heat transfer and pressure drop.     

Tobramycin-EDTA conjugate: a noninnocent affinity-cleaving reagent

The design, synthesis, and ribozyme inhibitory activity of a novel EDTA-aminoglycoside conjugate are reported. This affinity cleaving reagent is a noninnocent RNA binder: its RNA affinity, judged by its ability to inhibit the hammerhead ribozyme HH16, is different than the parent natural product and is markedly dependent on the oxidation state of the chelated metal ion.     

High-Temperature Creep Behavior of Mixed Conducting La0.5Sr0.5Fe1−xCoxO3-δ (0.5≤x≤1) Materials

Steady-state compressive creep rate of La_0.5Sr_0.5Fe_0.5Co_0.5O_3−δ (LSFC) and La_0.5Sr_0.5CoO_3−δ (LSC) is reported in the temperature region 900°–1050°C and stress range 5–28 MPa. The stress exponents for the two materials were 1.71±0.18 and 1.24±0.15, respectively. The activation energy for creep was considerably higher for LSC (619±56 kJ/mol) than for LSFC (392±28 kJ/mol). The grain size exponent for LSC was 1.28±0.14. Considerably higher creep rates were observed for both materials in N₂ compared with air. Relaxation by creep of chemical-induced stresses in oxygen-permeable membranes is addressed, especially at low partial pressure of oxygen.     

Sintering behaviour of La1−xSrxFeO3−δ mixed conductors

The sintering properties of La_1−xSr_xFeO_3−δ (x = 0.1, 0.25) mixed conductors have been investigated with particular emphasis on the effect of secondary phases due to cation non-stoichiometry (±5 mol% La excess and deficiency). Secondary phases, located at grain boundaries in cation non-stoichiometric materials, increased the sintering temperature compared to single-phase materials. Extensive swelling in final stage of sintering was observed in all materials, which resulted in micro-porous materials. The swelling was most pronounced in the phase pure and two-phase materials due to La-deficiency, while refractory secondary phases in La-excess materials inhibited both sintering, grain growth and swelling. In La-deficient materials, formation of molten secondary phases resulted in rapid swelling due to viscous flow. The present findings demonstrated the importance of controlling sintering temperature and time, as well as careful control of the cation stoichiometry of La_1−xSr_xFeO_3−δ in order to achieve fully dense and homogenous La_1−xSr_xFeO_3−δ ceramics.     

The stability of refractory oxides in sodium-rich environments

The infiltration of molten electrolyte and sodium is known to deteriorate the refractory in aluminum electrolysis. The mineralogical changes due to reactions with molten fluorides have previously been described throughly, while the effect of sodium has not been considered in detail. This paper presents an experimental study of the chemical stability of some refractory materials in sodium-rich environments. The materials were exposed to sodium vapor at 800°C for 4 hours. The mineralogical transformations and deterioration of the materials due to reactions with sodium were analyzed by x-ray diffraction and optical and electron microscopy.     

Object-Oriented Systems Development

Object-oriented design is an approach to systems development that proposes the use of system objects to build new systems and rebuild old ones. An important goal of object-oriented development is to change the nature of traditional software development from designing and writing models from scratch to building systems through the assembly of reusable software objects. This article discusses the productivity potential as well as the limitations of object-oriented systems development and makes recommendations for its use.     

Will musculoskeletal and visual stress change when Visual Display Unit (VDU) operators move from small offices to an ergonomically optimized office landscape?

This study investigated the effect of moving from small offices to a landscape environment for 19 Visual Display Unit (VDU) operators at Alcatel Denmark AS. The operators reported significantly improved lighting condition and glare situation. Further, visual discomfort was also significantly reduced on a Visual Analogue Scale (VAS). There was no significant correlation between lighting condition and visual discomfort neither in the small offices nor in the office landscape. However, visual discomfort correlated significantly with glare in small offices i.e. more glare is related to more visual discomfort. This correlation disappeared after the lighting system in the office landscape had been improved. There was also a significant correlation between glare and itching of the eyes as well as blurred vision in the small offices, i.e. more glare more visual symptoms. Experience of pain was found to reduce the subjective assessment of work capacity during VDU tasks. There was a significant correlation between visual discomfort and reduced work capacity in small offices and in the office landscape. When moving from the small offices to the office landscape, there was a significant reduction in headache as well as back pain. No significant changes in pain intensity in the neck, shoulder, forearm, and wrist/hand were observed.The pain levels in different body areas were significantly correlated with subjective assessment of reduced work capacity in small offices and in the office landscape.By careful design and construction of an office landscape with regard to lighting and visual conditions, transfer from small offices may be acceptable from a visual-ergonomic point of view.     

Using hash tables to manage the time-storage complexity in a point location problem: Application to explicit model predictive control

The online computational burden of linear model predictive control (MPC) can be moved offline by using multi-parametric programming, so-called explicit MPC. The solution to the explicit MPC problem is a piecewise affine (PWA) state feedback function defined over a polyhedral subdivision of the set of feasible states. The online evaluation of such a control law needs to determine the polyhedral region in which the current state lies. This procedure is called point location; its computational complexity is challenging, and determines the minimum possible sampling time of the system. A new flexible algorithm is proposed which enables the designer to trade off between time and storage complexities. Utilizing the concept of hash tables and the associated hash functions, the proposed method solves an aggregated point location problem that overcomes prohibitive complexity growth with the number of polyhedral regions, while the storage–processing trade-off can be optimized via scaling parameters. The flexibility and power of this approach is supported by several numerical examples.     

Path Planning for UAVs Under Communication Constraints Using SPLAT! and MILP

We will in this paper address the problem of offline path planning for Unmanned Aerial Vehicles (UAVs). Our goal is to find paths that meet mission objectives, are safe with respect to collision and grounding, fuel efficient and satisfy criteria for communication. Due to the many nonconvex constraints of the problem, Mixed Integer Linear Programming (MILP) will be used in finding the path. Approximate communication constraints and terrain avoidance constraints are used in the MILP formulation. To achieve more accurate prediction of the ability to communicate, the path is then analyzed in the radio propagation toolbox SPLAT!, and if the UAVs are not able to communicate according to design criteria for bandwidth, constraints are modified in the optimization problem in an iterative manner. The approach is exemplified with the following setup: The path of two UAVs are planned so they can serve as relay nodes between a target without line of sight to the base station.