Maximum power density for an endoreversible carnot heat engine

An analysis using maximum power-density criteria has been carried out for an endoreversible Carnot heat engine. The results have been compared with known results on maximum power analysis. The design parameters at maximum power density lead to smaller and more efficient endoreversible Carnot heat engines than those working at maximum power output.     

Validity of dynamic electrochemical impedance spectra of some amine corrosion inhibitors in petroleum/water corrosive mixtures by Kramers-Kronig transformation

In our previous works, the corrosion inhibition properties of propylamine (PA), iso-propylamine (i-PA), butylamine (BA), tert-butylamine (t-BA), hexylamine (HA), ethylenediamine (EDA), diethanolamine (DEA), 3-amino-1-propanol (3-AP), 2-dimethylethanolamine (2-DEA), cyclohexylamine (CHA), N-methylcyclohexylamine (N-MCA) and dicyclohexylamine (DCHA) have been investigated by means of electrochemical impedance spectroscopy (EIS) with a carbon steel rotating disc electrode in some petroleum/water corrosive mixtures containing acetic acid and NaCl at 25 °C. In this work, the Kramers-Kronig transformations (KKTs) were applied to evaluate the validity of the impedance data of these amine compounds in hydrodynamic condition. The results obtained showed that experimental impedance data did not satisfy in K-K relations completely viz. indicated some errors. These errors were related to stray capacitances, external transmission line effects, pits formation and change in interface during data acquisition at high and low frequencies regions. In addition, the selection of a suitable equivalent circuit strongly emphasized to better interpret of EIS data which in turn cause better resulted KKTs spectra. With considering obtained transformations, more effective inhibitor was selected with regard to its charge transfer resistance, the corrosion capacitance and well satisfying in K-K relations.     

Low-loss high power RF switching using multifinger AlGaN/GaN MOSHFETs

We demonstrate a novel RF switch based on a multifinger AlGaN/GaN MOSHFET. Record high saturation current and breakdown voltage, extremely low gate leakage current and low gate capacitance of the III-N MOSHFETs make them excellent active elements for RF switching. Using a single element test circuit with 1-mm wide multifinger MOSHFET we achieved 0.27 dB insertion loss and more than 40 dB isolation. These parameters can be further improved by impedance matching and by using submicron gate devices. The maximum switching power extrapolated from the results for 1A/mm 100 /spl mu/m wide device exceeds 40 W for a 1-mm wide 2-A/mm MOSHFET.     

Effect of variable friction coefficient on sheet metal drawing

A variable friction model that relates the parameters of sheet metal drawing to the local lubrication conditions taking place during the deformation, has been integrated to a finite element program. Variable friction coefficients for the contacting surfaces are determined from the friction model, which uses the related parameters obtained at each time step of the finite element program as inputs. A number of numerical runs have been performed and the strains are compared with the experimental results for circular blanks. A good agreement is obtained between the numerical and experimental results for the variable friction model used.     

Rapid determination of the fracture toughness of metallic materials using circumferentially notched bars

Three types of material whose fracture toughness tests were previously performed by using circumferentially notched bars, namely (1) a dual-phase steel with three different morphologies; (2) an Al-Zn-Mg-Cu-wrought alloy; and (3) Al-Si-cast alloys with three different Si contents, were investigated in terms of accuracy and reliability of the testing method. Also, the advantages of using circumferentially notched bars for fracture toughness determination of metallic materials were discussed. With the help of stress concentration factors, which are associated with the bluntness of the notch, correction factors for the fracture toughness calculations are derived. The corrected fracture toughness values are found to be close to the uncorrected ones, implying that the testing procedure is reliable.     

Compact WLAN disc antennas

A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes.     

BATCH SEQUENCING

Consider the single machine scheduling problem where there are a number of part types to be processed. A part type is defined as follows: Two parts are of the same part type if the machine does not require a setup in between the processing of these parts. The problem investigated in this paper is to find a sequence of batches of parts (if there are any) where all the requirements for parts are met. A heuristic and an exact algorithm are developed, and computational analysis is performed to measure the performance of the heuristic. The time complexity function of the heuristic is O(n²), and the exact algorithm runs in polynomial time given a fixed upper bound on the number of setups.