Transient response of optoelectronic integrated bistable device

In this paper, the transient response of an optical bistable device with optically controlled set and reset functions is analyzed. The device is made from a vertical integration of two heterojunction phototransistors (HPTs) and a laser diode (LD). One of the HPTs (HPT-A) is integrated just above the active layer of the LD and is utilized in the set operation, while the other HPT (HPT-B) is used to achieve the reset operation. The effect of the various device parameters on the set and reset operations is outlined. Finally, expressions for the rise time during the setting, and fall time during the resetting conditions are derived     

Electrochemical Studies on the passive behaviour of tin in different buffer solutions

The effect of pH on the passivity of Sn has been investigated in buffered (phthalate-borate, and citrate phosphate buffer series), and in unbuffered phosphate solutions, using the cyclic voltammetric technique. Two anodic peaks; the first being more pronounced than the second, and on cathodic peak have been observed in the two buffer series at different scan rates and pH values. The anodic and cathodic peak current densities (I_p) and potentials (E_p) are functions of the scan rate (v) and the pH value. Plots of I_p against v^1/2 yield straight lines at each pH value. The effect of pH on I_p for the first anodic peak shows a shallow minimum in the near neutral and slightly alkaline range at all scan rates. Straight lines are also observed between E_p and v^1/2, the extrapolation of which to v = 0 gives the spontaneous (no polarization) oxidation or reduction potentials (E′ and E″). The absence of polarization effects in E′ and E″ make them the most suitable values for comparison with thermodynamic data. Therefore, the two straight lines obtained between E′ and E″ on one hand and the pH on the other hand to give an estimate of (i) the slope (dE°/dpH), and (ii) the value of E° at pH - 0 (from intercept). Comparison of the two experimental values with all available thermodynamic data for Sn(II) and Sn(IV) oxides and hydroxides shows that: (i) the first anodic peak represents the formation of Sn(OH)₂ from Sn and OH^?, (ii) the second anodic peak represents the formation of Sn(OH)₄ directly from Sn and OH^?, and (iii) the cathodic reduction peak correponds to the reduction of Sn(IV) oxidized species to Sn. The results in citratephosphate buffer have been treated in the same manner. However, the result of (dE°/dpH) and E° at pH = 0 deviate from thermodynamic data, because of the possible participation of other anodic reactions such as the formation of soluble Sn compounds, Sn complexes, and incorporation of anions in the anodic film.     

The complete dissolution of goethite

The dissolution of all except one sample of goethite obeyed the cube root kinetic law which implies a uniform rate of disappearance of the crystals. However, the electron microscope showed that this was only true in some cases and that there could be some compensation between size distribution in the sample and the increase in surface area through hole formation in the crystal.     

Galvanostatic formation of barrier-type Anodic oxides

Experimental Factors Affecting Oxide Growth Results of galvanostatic anodization of various metals with varying valve-metal behaviour including Nb, Ta, Zr, Ti, Al, W, Te, Sb, and Bi are compiled and compared with respect to the effect of various experimental factors such as surface pretreatment, stirring, solution composition, temperature of the bath, on the efficiency of oxide growth relative to that for other anodic processes. It is concluded that all of the above factors play an important role in the anodization of the non-typical valve metals, particularly Sb, Bi and W. Typical anodic charging curves associated with the process of oxide growth are given for several valve metals. Experimental data relevant to the phenomena of oxide breakdown are recorded and compared. The results indicate that the mechanism of breakdown varies for the same metal with variations in the experimental conditions.     

Going below the wet-bulb temperature by indirect evaporative cooling: Analysis using a modified ε-NTU method

The objective of this paper is to study a method to achieve sub-wet bulb temperature by indirect evaporative cooling of air (without using a vapor compression machine). For this purpose, an analytical model is developed based on the effectiveness-NTU method (ε-NTU). The main idea for achieving a sub-wet bulb temperature by indirect evaporative cooling of air is by indirectly pre-cooling the working air before it enters the wet passage. It is shown that a modified analytical model for indirect evaporative coolers could be based on the ε-NTU method for sensible heat exchangers when proper adjustments are made by redefining the potential gradients, transfer coefficient, heat capacity rate parameters and assuming a linear saturation temperature-enthalpy relation of air. This modified model is used to find the performance of a regenerative indirect evaporative cooler. The model results show very good agreement with results from experimental measurements and a numerical model.     

Indirect evaporative cooling: Past,present and future potentials

This paper reported a review based study into the Indirect Evaporative Cooling (IEC) technology, which was undertaken from a variety of aspects including background, history, current status, concept, standardisation, system configuration, operational mode, research and industrialisation, market prospect and barriers, as well as the future focuses on R&D and commercialisation. This review work indicated that the IEC technology has potential to be an alternative to conventional mechanical vapour compression refrigeration systems to take up the air conditioning duty for buildings. Owing to the continuous progress in technology innovation, particularly the M-cycle development and associated heat and mass transfer and material optimisation, the IEC systems have obtained significantly enhanced cooling performance over those the decade ago, with the wet-bulb effectiveness of greater than 90% and energy efficiency ratio (EER) up to 80. Structure of the IEC heat and mass exchanger varied from flat-plate-stack, tube, heat pipe and potentially wave-form. Materials used for making the exchanger elements (plate/tube) included fibre sheet with the single side water proofing, aluminium plate/tube with single side wicked setting (grooved, meshed, toughed etc), and ceramic plate/tube with single side water proofing. Counter-current water flow relevant to the primary air is considered the favourite choice; good distribution of the water stream across the wet surface of the exchanger plate (tube) and adequate (matching up the evaporation) control of the water flow rate are critical to achieving the expected system performance. It was noticed that the IEC devices were always in combined operation with other cooling measures and the commonly available IEC related operational modes are (1) IEC/DEC system; (2) IEC/DEC/mechanical vapour compression system; (3) IEC/desiccant system; (4) IEC/chilled water system; and (5) IEC/heat pipe system. The future potential operational modes may also cover the IEC-inclusive fan coil units, air handle units, cooling towers, solar driven desiccant cycle, and Rankine cycle based power generation system etc. Future works on the IEC technology may focus on (1) heat exchanger structure and material; (2) water flowing, distribution and treatment; (3) incorporation of the IEC components into conventional air conditioning products to enable combined operation between the IEC and other cooling devices; (4) economic, environment and social impacts; (5) standardisation and legislation; (6) public awareness and other dissemination measures; and (7) manufacturing and commercialisation. All above addressed efforts may help increase the market ratio of the IEC to around 20% in the next 20 years, which will lead to significant saving of fossil fuel consumption and cut of carbon emission related to buildings.     

Electrocatalytic evolution of hydrogen on a novel SrPdO3 perovskite electrode

SrPdO₃ was prepared for the first time by the citrate method. XRD, SEM and TGA characterizations were carried out. The catalytic activity toward hydrogen evolution reaction (HER) was investigated, the activation energy, and reaction order and reaction mechanism have been determined using Tafel polarization and impedance techniques. The modified surface showed up to 100 times more efficiency towards electrocatalytic production of hydrogen. Adsorption of hydrogen on the catalyst was the rate-determining step and the reaction order at the surface of the catalyst is 0.86. The molar magnetic susceptibility was measured using Faraday's method and anti-ferromagnetic character was observed.     

Effects of processing conditions and aging on the fracture toughness of rigid PVC pipe materials

Results for given for the fracture toughness of rigid polyvinylchloride (PVC) pipe materials over a range of test temperatures as a function of extrusion temperature. The fracture toughness is shown to be reduced as the extrusion temperature is reduced below standard conditions. The transition temperature for valid fracture toughness tests is increased by reducing the extrusion temperature. The results of a fractographic analysis are also presented, including quantitative data for the extent of drawn, fibrillated material at the crack tip. Although annealing above T_g reduces the fracture toughness relative to as-received pipes, no significant effect of controlled physical aging could be identified.