An alternative simple solution algorithm of an inventory model with fixed and variable lead time crash costs under unknown demand distribution

Inventory models with controllable lead time both for known and unknown demand distributions have been proposed in the literature. A model is useless unless it is formulated correctly and feasible. A simple solution procedure of a model also plays an important role in its application. This article highlights an erroneous formulation of an inventory model developed with fixed and variable lead time crash costs under unknown demand distribution, and also demonstrates its infeasibility. To attain feasibility we extend the model to include a constraint. Then, we present an alternative simple solution technique of the modified model and carry out a comparative study on a numerical example to show its potential significance.     

A technoeconomic simulation model for A hybrid solar water heating system

A simple mathematical model has been developed to evaluate the technoeconomic performance of a hybrid solar water heating system for commercial and industrial applications. Numerical calculations, corresponding to Delhi climatic data and for the prevalent cost of a solar energy system in the Indian market, show that the optimum collector area (meeting nearly 45 percent of the daily hot water demand M litres) is 0–0075 Mm²; either a reduction of about 35 per cent in the present solar collector costs or a more than 20 per cent rise in the cost of presently subsidized diesel oil makes the solar option economic. With the present parameters the cost of useful solar energy is higher than that obtained from the conventional system.     

Simulation of polymer systems

The present paper describes an algorithm which can generate, even on a small computer, arbitrarily long polymer chains, making sure that the configurations generated do not suffer from boundary effects. This has been achieved by employing the concept of a window, which is an analogue of virtual memory scheme. The algorithm has been tested for the case of dilute polymer solution.     

The location of pyridine in sodium–silver–Y zeolite by powder synchrotron X-ray diffraction

The powder synchrotron X-ray diffraction pattern of a mixed sodium–silver–Y zeolite, Ag_56−xNa_xSi₁₃₆Al₅₆O₃₈₄ x≈19, saturated with pyridine, has been analysed by the Rietveld method to reveal positions for the adsorbed molecules. Cations are distributed over three sites, SII, constrained to 100% occupancy, with 17.2(1) and 14.8(1) Ag(1) and Na(1) ions per unit cell, respectively, SI′ with 18.3(1) Ag(2) ions per cell, and SI with 1.8(1) Ag(3) ions per cell. The refinement suggests that approximately 7.5 pyridine molecules are adsorbed per supercage, located in two sites within the cavities of the zeolite. Pyridine(1) is in the 12-ring window connecting supercages. Three molecules project through each window and approach the SII cations in a supercage, with an average Ag(1)–N distance of 3.17(2) Å. An SII cation can be linked to three pyridine(1) molecules from three separate windows. These sites are full with 5.98(2) molecules per supercage. Pyridine(2) is found in the supercage, oriented with its π electron density towards the SII cations, with its centre at 2.87(2) Å from Ag(1). The average occupancy was fixed at 1.5 molecules per supercage, corresponding to 20% of the pyridine content. A local ordering scheme can be postulated, whereby alternate supercages are filled by pyridine(1) and pyridine(2) molecules, efficiently filling the channels of the zeolite.     

A high-performance, miniaturized X-band active mixer forDBS receiver application with on-chip IF noise filter

A GaAs monolithic microwave integrated circuit (MMIC) dual-gate FET active mixer at X-band is described that is designed for direct broadcast satellite (DBS) applications. All of the components of the mixer, including biasing circuitry, RF, LO, and IF matching networks, as well as the IF noise filter, are implemented monolithically into a 25-mil×30-mil area. The design was process tolerant, and layout was compact for manufacturability and low cost. The mixer was integrated monolithically into a complete single-chip DBS low-noise block (LNB) converter. The active mixer has a conversion gain of 5.5 dB and a single-sideband noise figure of 8.5 dB. The circuit is manufactured using a 0.5-μm gate length, buried p^- depletion mode MESFET process without substrate-through via holes     

HEAT AND MASS TRANSFER RELATIONS FOR CROP DRYING

In present communication, an attempt has been made to study the heat and mass transfer for crops namely wheat and gram. The removal of moisture from the crop was determined under simulated conditions and it was used to develop heat and mass transfer relation using linear as well as multiple regression analysis. The observations were recorded for relative humidity, temperature of crop and air and for moisture evaporated. Experimental error in terms of per cent uncertainty was calculated for recorded data which is in the range of 20 - 30 per cent for forced convection and natural cooling, respectively.     

Studies on corrosion control of naphtha fractions in overhead condensing system using laboratory distillation device

Corrosion in the overhead condensing system of atmospheric distillation units is a common occurrence in petroleum refineries worldwide. These corrosion problems are influenced by the presence of three phases: vapours, liquid hydrocarbons and aqueous phase containing hydrochloric acid formed during distillation by decomposition of chloride salts of calcium and magnesium.Present studies highlight the corrosion control of naphtha fractions of Bombay High and Dubai crude oils in laboratory distillation device by chemical treatment using various corrosion inhibitors having different functional groups. These studies were carried out using two phase systems (aqueous-hydrocarbon) in the distillation device having facilities for monitoring the corrosion and temperatures in vapour condensing region and liquid condensate. Corrosion monitoring was carried out by potentiodynamic polarization technique and dissolved iron analysis using inductively coupled plasma atomic emission spectroscopy (ICPAES). Experimental findings indicate that Dubai naphtha fraction is more corrosive in nature when compared to Bombay High naphtha. This observation can also be explained on the basis of characterization of both crude oils and their naphtha fractions. At normally recommended dosage level as in refinery overhead systems, water soluble corrosion inhibitors are more effective than hydrocarbon soluble ones in the vapour condensing region as well as in the liquid condensate of both naphtha fractions.