Production inventory with service time and interruptions

This paper considers an (s,S) production inventory system with positive service time, with time for producing each item following Erlang distribution. Customers arrive according to a Poisson process. A customer who arrives when there is no inventory in the system is considered lost. On the other hand, a customer who finds a busy server with at least one inventory in the system joins a queue of infinite capacity. When the inventory level falls to s, production process is switched on, and it is switched off when the inventory level reaches back to S. Service time to each customer also follows an Erlang distribution. The service of a customer may be interrupted, where the time for such a phenomenon follows an exponential distribution, whenever it occurs. An interrupted service, after repair, resumes from where it was stopped. The correction/repair time follows an exponential distribution. We assume that the service of a single customer may encounter any number of interruptions and that the customer being served waits there until his service is completed. Moreover, at a time the server is subject to at most one interruption. We also assume that no inventory is lost due to a service interruption. Like the service process, the production process also is subject to interruptions, where the duration to an interruption follows an exponential distribution. However, in contrast to the service interruption, in the case of interruption to production process, we assume that the item being processed is lost because of interruption. That is, the production process, on being interrupted, restarts from the beginning, after repair. The repair time of an interrupted production process follows exponential distribution. Few of the last service phases are assumed to be protected in the sense that the service will not be interrupted while being in these phases. The same is assumed for the production process also.

The model is analysed as a level-independent quasi-birth–death process. We apply a novel method to obtain an explicit expression for the necessary and sufficient condition for the stability of the system under study. This method works even if we assume general phase-type distributions for the production as well as the service processes, and hence can be used to characterise the stability of inventory systems where the assumption of disallowing the customers to join the system, when there is a shortage of inventory has been made. Under stability, we apply matrix analytic methods to compute the system state distribution. In consequence to that, several system performance measures have been derived, and their dependence on the system parameters has been studied numerically.     

Hydrothermal Modifications of Tropical Tuber Starches. 1. Effect of Heat‐Moisture Treatment on the Physicochemical,Rheological and Gelatinization Characteristics

Cassava, sweet potato and arrowroot starches have been subjected to heat‐moisture treatment (HMT) under different conditions using a response surface design of the variables. A comparative study was performed on the pasting properties, swelling behaviour and the gelatinization properties of the modified starches and also on the rheological and textural properties of their pastes. X‐ray diffraction studies have shown that cassava starch exhibited a slight decrease in crystallinity, whereas sweet potato and arrowroot starches showed an increase in crystallinity after HMT at 120ºC for 14 h with 20% moisture. The swelling volume was reduced and the solubility was enhanced for all three starches after HMT, but both effects were more pronounced in the case of arrowroot starch. The decrease in paste clarity of the starch after HMT was higher in the case of cassava and sweet potato starches. Viscosity studies showed that the peak viscosity of all three starches decreased after HMT, but the paste stability increased as seen from the reduced breakdown ratio and setback viscosity. Studies on rheological properties have shown that storage and loss moduli were higher for the starches heat‐moisture treated at higher moisture and lower temperature levels than the corresponding native starches. Storage of the gel at ‐20ºC resulted in a significant increase in storage modulus for all the three starches. All the textural parameters of the gels were altered after the treatment which depended on the nature of the starch and also the treatment condition.     

“String and bead” model of copper modified polycarbosilane: synthesis and applications

Journal of Materials Science - The synthesis of metal modified polycarbosilanes is currently an area of significant activity. These polymers can be processed to advanced materials such as ceramic...     

Evidence for intergranular tunnelling in polyaniline passivated α-Fe nanoparticles

Nanoparticles are of immense importance both from the fundamental and application points of view. They exhibit quantum size effects which are manifested in their improved magnetic and electric properties. Mechanical attrition by high energy ball milling (HEBM) is a top down process for producing fine particles. However, fineness is associated with high surface area and hence is prone to oxidation which has a detrimental effect on the useful properties of these materials. Passivation of nanoparticles is known to inhibit surface oxidation. At the same time, coating polymer film on inorganic materials modifies the surface properties drastically. In this work a modified set-up consisting of an RF plasma polymerization technique is employed to coat a thin layer of a polymer film on Fe nanoparticles produced by HEBM. Ball-milled particles having different particle size ranges are coated with polyaniline. Their electrical properties are investigated by measuring the dc conductivity in the temperature range 10-300?K. The low temperature dc conductivity (I-V) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the critical path model. There is clear-cut evidence for the occurrence of intergranular tunnelling. The results are presented here in this paper.     

Evaluation of nutritional and physico-mechanical characteristics of dietary fiber-enriched sweet potato pasta

The objective of the present study was to enhance the utilization of sweet potato (Ipomoea batatas Lam.) as a slowly digestible food by developing dietary fiber-fortified pasta from it. Swelling index as well as cooking loss (%) was more for the pasta made from the pale cream-fleshed variety, Sree Arun (V1) than that from the orange-fleshed variety, Sree Kanaka (V2), and least values were obtained in the pasta fortified with rice bran. Fortification with oat bran, wheat bran, and rice bran elevated the crude protein content to 5–10% in the pasta. Total and insoluble dietary fiber fractions were more in the pasta from Sree Arun (6–17 and 5–14%, respectively) than those from Sree Kanaka (5.25–15 and 3.7–11%, respectively) with the highest values in the wheat bran-fortified pastas. All the fiber-fortified pastas (10 and 20% level of fortification) had slow and progressive starch digestibility over 2 h compared to the control pastas. While approximately 70% of the total starch was rapidly digestible for the control pastas from both the varieties, this was drastically reduced to 45–54% in the test pasta from V1 and 37–50% in V2. Accordingly, the retention of resistant starch (RS; undigested starch after 2 h) in the control pastas was only 14–17%, while it was 38–49% in the test pastas from V1 and 39–55% from V2, with higher RS in the 20% fortified pastas. Texture profile analysis showed that the firmness (N) and toughness (Ns) increased with increase in the fortification level of fiber sources. The progressive starch digestibility coupled with high-resistant starch after 2 h indicated the potential of fiber-fortified sweet potato pasta as an ideal food for the diabetic and obese people.     

Gelatinisation Properties of Cassava Starch in the Presence of Salts,Acids and Oxidising Agents

The effect of various cations, anions, acids and oxidising agents on the gelatinisation properties of cassava starch was studied and wide variation was observed in the pasting and swelling properties. Sodium chloride and sodium thiosulphate slightly lowered the peak viscosity of cassava starch with increase in concentration, whereas with sodium sulphite, calcium chloride and sodium hypochlorite, a more significant decrease in the viscosity and breakdown was observed. Ferrous sulphate, alum, aluminium chloride and acids enhanced the peak viscosity at lower concentrations followed by a decrease at 1% and above. Sodium metabisulphite elevated the viscosity at 0.05 and 0.1%, while sodium hypochlorite lowered the viscosity and breakdown. DSC studies showed that aluminium chloride, sodium sulphite, and sodium thiosulphate brought about an increase in T_onset, T_end and ΔH values at higher concentrations. A decrease in swelling volume was observed from 0.05 to 1% concentration of sodium chloride and above that there was a gradual increase. With sodium sulphite, a significant increase in swelling volume was observed at 2.5 and 5% levels. With 0.05 and 0.1% aluminium chloride and sodium metabisulphite an increase in swelling volume was noticed, but at higher concentrations there was a drastic fall. Sodium chloride, sodium sulphite, sodium thiosulphate and calcium chloride brought about decrease in starch paste clarity with increase in salt concentration, whereas ferrous sulphate, aluminium chloride, sodium hypochlorite, hydrochloric acid and acetic acid improved the starch paste clarity.     

Process optimization for bioethanol production from cassava starch using novel eco-friendly enzymes

Although cassava (Manihot esculenta Crantz) is a potential bioethanol crop, high operational costs resulted in a negative energy balance in the earlier processes. The present study aimed at optimizing the bioethanol production from cassava starch using new enzymes like Spezyme^® Xtra and Stargen™ 001. The liquefying enzyme Spezyme was optimally active at 90 °C and pH 5.5 on a 10% (w/v) starch slurry at levels of 20.0 mg (280 Amylase Activity Units) for 30 min. Stargen levels of 100 mg (45.6 Granular Starch Hydrolyzing Units) were sufficient to almost completely hydrolyze 10% (w/v) starch at room temperature (30 ± 1 °C). Ethanol yield and fermentation efficiency were very high (533 g/kg and 94.0% respectively) in the Stargen + yeast process with 10% (w/v) starch for 48 h. Raising Spezyme and Stargen levels to 560 AAU and 91.2 GSHU respectively for a two step loading [initial 20% (w/v) followed by 20% starch after Spezyme thinning]/initial higher loading of starch (40% w/v) resulted in poor fermentation efficiency. Upscaling experiments using 1.0 kg starch showed that Stargen to starch ratio of 1:100 (w/w) could yield around 558 g ethanol/kg starch, with a high fermentation efficiency of 98.4%. The study showed that Spezyme level beyond 20.0 mg for a 10% (w/v) starch slurry was not critical for optimizing bioethanol yield from cassava starch, although an initial thinning of starch for 30 min by Spezyme facilitated rapid saccharification-fermentation by Stargen + yeast system. The specific advantage of the new process was that the reaction could be completed within 48.5 h at 30 ± 1 °C.     

Effect of graft-copolymerization with poly(acrylamide) on rheological and thermal properties of cassava starch

Graft copolymers of different grafting levels were synthesised by the free radical initiated reaction of cassava starch with acrylamide in presence of ceric ammonium nitrate. The viscosity properties of the native granular starch and the grafted starches were determined using a Rapid visco analyzer (RVA) and rheological properties by frequency sweep test under different conditions using a rheometer. Some of the grafted starches exhibited significantly higher and some others exhibited drastically reduced peak viscosity values irrespective of the percentage grafting. All the grafted starches exhibited very good viscosity stability as evidenced from the highly reduced breakdown and higher final viscosity values in comparison to native cassava starch. Thermal analysis of the pure granular cassava starch and grafted starches was carried out using a differential scanning calorimetry (DSC) and thermogravimetry. DSC studies showed that in comparison to native starch, the grafted starches showed lower temperatures of transition. The thermal stability of cassava starch was enhanced by grafting as observed from the thermogravimetric data. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymer induced structures in cetylpyridinium chloride–octanol micellar system

The effect of octanol on the interaction of polyethylene glycol (PEG) and cetylpyridinium chloride (CPC) were investigated by viscosity, conductivity, differential scanning calorimetry (DCS), polarizing microscopy, Fourier transform infrared spectroscopy (FTIR) and rheology analysis. The aggregation of polymer-surfactant micelles takes place at a surfactant concentration higher than the critical micelle concentration. The long chain aliphatic alcohol (n-octanol) induced rapid structural transformation in the mixed micellar system by unusual cooperative micellization. The rheological behavior of the viscoelastic system reveals the presence of giant aggregates in this system. The lyotropic nature of the giant aggregates was monitored by DSC and polarizing microscopic studies, and which was confirmed by cryo-TEM.     

On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films

Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effectedin situ. The structural properties of these films were evaluated by FTIR spectroscopy and the optical band gap was estimated from UV-vis-NIR measurements. Comparative studies on the structural, optical and electrical properties of a.c. and rf polymerization are presented here. It has been found that the optical band gap of the polyaniline thin films prepared by rf and a.c. plasma polymerization techniques differ considerably and the band gap is further reduced byin situ doping of iodine. The electrical conductivity measurements on these films show a higher value of electrical conductivity in the case of rf plasma polymerized thin films when compared to the a.c. plasma polymerized films. Also, it is found that the iodine doping enhanced conductivity of the polymer thin films considerably. The results are compared and correlated and have been explained with respect to the different structures adopted under these two preparation techniques.