Replacement of failed items in a two commodity retrial queueing-inventory system with multi-component demand and vacation interruption.

This study investigates a crucial aspect of inventory management, which is the process of replacing failed items. In dynamic commercial environments, it is essential to efficiently and strategically replace failed items to maintain operational efficiency and ensure profitability. We consider a two-commodity retrial queueing-inventory system with vacation interruption. Upon purchasing the first commodity, the second commodity is provided as a complimentary item. In contrast, no item is given as a complimentary for the purchase of the second item. Only the first commodity is stored in a dedicated pooled storage for replacement when it fails. The (s,Q) policy governs replenishing the first commodity while the second is replenished through instantaneous ordering. The model considers the multi-component demand rate for customer arrivals. Server vacations are initiated during customer absence in waiting hall or when the first commodity is unavailable. We formulate a level-dependent quasi-birth-and-death process, and its steady-state probability vector is computed using Neuts and Rao's truncation method. The stability condition for the system is derived, and various system performance measures, including expected total cost, number of replaceable items, and customers in the waiting hall and orbit, are established. The comparative analysis between the system with replacement is done with the regular model without replacement, which revealed the efficiency of replacement. The analysis of multi-component demand towards homogeneous arrival highlights the impact of multi-component demand on boosting customer arrival. Also, parametric sensitivity analysis has been conducted numerically over total cost, mean number of failed items for replacement, and mean number of customers in the waiting hall and orbit.

Ultrasensitive self-powered heterojunction ultraviolet photodetector of p-GaN nanowires on Si by halide chemical vapour deposition.

In this study, we report the fabrication of quasi-aligned p-GaN nanowires (NWs) on n-Si (1 1 1) substrate by halide chemical vapour deposition (HCVD) using MgCl2precursor and followed by low-energy electron beam irradiation to activate the Mg acceptor doping in GaN NWs. We aimed to attain a comprehensive understanding of p-doping in GaN NWs growth, extensive characterizations and fabrication of UV photodetector (PDs) based on p-GaN NWs/n-Si heterojunction. To realize the efficient UV photodetectors, we measure the current-voltage (I-V) characteristics of heterojunction PDs under dark and illuminated conditions and theI-Vcurve demonstrates good rectifying behaviours with 0.2 V turn-on voltage. At zero bias, the heterojunction PDs show a reverse photocurrent of 1.27 × 10-6A with a very low dark current of 2.35 × 10-9A under 325 nm UV illumination. Besides, the significance of the self-powered operation of UV PDs and the charge transfer mechanism are discussed with the aid of the energy band diagram. The substantial photocurrent increment with varying applied potential leads to narrowing the photo potential in the interface. The excitonic bound states present in p-GaN NWs/n-Si heterojunction is further elucidated. As a result, the heterojunction PDs demonstrate the high responsivity, detectivity, and external quantum efficiency of 134 mA W-1, 3.73 × 1013Jones, and 51% respectively, at 0.1 V low applied potential under the reverse bias condition. The proposed work provides an archetype for Mg doping in GaN NWs ensembles, which will help to facilitate the heterojunction with n-Si to unleash the potential of self-powered UV PDs.

VS2 wrapped Si nanowires as core-shell heterostructure photocathode for highly efficient photoelectrochemical water reduction performance.

Interfacing an electrocatalyst with photoactive semiconductor surfaces is an emerging strategy to enhance the photocathode performance for the solar water reduction reaction. Herein, a core-shell heterostructure photocathode consisting of vanadium disulfide (VS2) as a 2D layered electrocatalyst directly deposited on silicon nanowire (Si NWs) surface is realized via single-step chemical vapor deposition towards efficient hydrogen evolution under solar irradiation. In an electrochemical study, 2D VS2/Si NWs photocathode exhibits a saturated photocurrent density (17 mA cm-2) with a maximal photoconversion efficiency of 10.8% at -0.53 V vs. RHE in neutral electrolyte condition (pH∼7). Under stimulated irradiation, the heterostructure photocathode produces a hydrogen gas evolution around 23 µmol cm-2 h-1 (at 0 V vs. RHE). Further, electrochemical impedance spectroscopy (EIS) analysis reveals that the high performance of the core-shell photocathode is associated with the generation of the high density of electron-hole pairs and the separation of photocarriers with an extended lifetime. Density functional theory calculations substantiate that core-shell photocathodes are active at very low Gibbs free energy (ΔGH*) with abundant hydrogen evolution reaction (HER) active sulphur sites. The charge density difference plot with Bader analysis of heterostructure reveals the accumulation of electrons on the sulphur sites via modulating the electronic band structure near the interface. Thus, facilitates the barrier-free charge transport owing to the synergistic effect of Si NWs@2D-VS2 core-shell hybrid photocatalyst for enhanced solar water reduction performance.

GaN nanowires grown by halide chemical vapour deposition as photoanodes for photo-electrochemical water oxidation reactions.

Manifold morphologies of GaN nanowires (NWs) were fabricated using halide chemical vapour deposition (HCVD) on an n-Si (111) substrate and demonstrated to be a promising photoelectrode for photo-electrochemical (PEC) water splitting applications. We report a substantial enhancement in the photocurrent for vertically-grown GaN NWs on a buffer layer as compared to other counterparts such as GaN whiskers, tapered nanostructures and thin films. GaN NWs grown on Si have advantages due to the absorption of photons in a wide spectral range from ultraviolet to infrared and thus are directly involved in PEC reactions. A GaN NW photoanode was demonstrated with a saturation photocurrent density of 0.55 mA cm-2 under 1 sun of illumination, which is much greater than its counterparts. The role of the buffer layer and the carrier density on the PEC performance of vertically-grown GaN NW photoanodes is further elucidated. Photo-electrochemical impedance spectroscopy and Mott-Schottky characterizations were employed to further explain the PEC performance of GaN NW embedded photoanodes. Here, photoanodes based on diverse GaN nanostructures were examined for a better PEC evaluation in order to support the conclusion. The results may pave the way for the fabrication of efficient photoelectrodes and GaN as a protective layer against corrosion for improved photo-stability in an NaOH electrolyte for enhancing the efficiency of water splitting.

Synthesis and characterization of BiVO4 nanoparticles for environmental applications.

In the present study, a chemical precipitation method is adopted to synthesize bismuth vanadate nanoparticles. The calcination temperature dependent photocatalytic and antibacterial activities of BiVO4 nanoparticles are examined. The structural analysis evidences the monoclinic phase of BiVO4 nanoparticles, where the grain size increases with calcination temperature. Interestingly, BiVO4 nanoparticles calcined at 400 °C exhibit superior photocatalytic behaviour against methylene blue dye (K = 0.02169 min-1) under natural solar irradiation, which exhibits good stability for up to three cycles. The evolution of antibacterial activity studies using a well diffusion assay suggest that the BiVO4 nanoparticles calcined at 400 °C can act as an effective growth inhibitor of pathogenic Gram-negative (P. aeruginosa & A. baumannii) and Gram-positive bacteria (S. aureus).

Surface engineered Amphora subtropica frustules using chitosan as a drug delivery platform for anticancer therapy.

Drug delivery using synthetic mesoporous nanomaterials, including porous silicon, has been extensively used to ameliorate the constraints currently experienced with conventional chemotherapy. Owing to the amazing potential, the silica based nanomaterials have been used widely. Nevertheless, synthetic nanomaterial involves high cost, lack of scalability, and the use of toxic substances limits its utilization. These issues can be overcome by the use of nature generated nanoscale materials, such as diatoms would serve as a boon for pharmaceutical industries. In this study we investigate the use of a mesoporous, biodegradable nanomaterial obtained from the natural silica found in the diatom species Amphora subtropica (AMPS) for drug delivery applications. AMPS cultures cleaned and chemically treated to obtain Amphora frustules (exoskeleton) (AF), followed by surface functionalization with chitosan (Chi). Results of our experiments demonstrate high drug loading, strong luminescence, biodegradable and biocompatible nature of the doxorubicin tethered diatom. Further, toxicity studies employing immortalized lung cancer cell line (A549) indicates sustained drug delivery and less toxic compared to the free doxorubicin (DOX), suggesting AF could be an excellent substitute for synthetic nanomaterials used in drug delivery applications.

High-dose immunosuppression to prevent death after paraquat self-poisoning - a randomised controlled trial.

CONTEXT: Intentional self-poisoning with the herbicide paraquat has a very high case-fatality and is a major problem in rural Asia and Pacific. OBJECTIVES: We aimed to determine whether the addition of immunosuppression to supportive care offers benefit in resource poor Asian district hospitals. MATERIALS AND METHODS: We performed a randomised placebo-controlled trial comparing immunosuppression (intravenous cyclophosphamide up to 1 g/day for two days and methylprednisolone 1 g/day for three days, and then oral dexamethasone 8 mg three-times-a-day for 14 days) with saline and placebo tablets, in addition to standard care, in patients with acute paraquat self-poisoning admitted to six Sri Lankan hospitals between 1st March 2007 and 15th November 2010. The primary outcome was in-hospital mortality. RESULTS: 299 patients were randomised to receive immunosuppression (147) or saline/placebo (152). There was no significant difference in in-hospital mortality rates between the groups (immunosuppression 78 [53%] vs. placebo 94 [62%] (Chi squared test 2.4, p = .12). There was no difference in mortality at three months between the immunosuppression (101/147 [69%]) and placebo groups (108/152 [71%]); (mortality reduction 2%, 95% CI: -8 to +12%). A Cox model did not support benefit from high-dose immunosuppression but suggested potential benefit from the subsequent two weeks of dexamethasone. CONCLUSIONS: We found no evidence that high dose immunosuppression improves survival in paraquat-poisoned patients. The continuing high mortality means further research on the use of dexamethasone and other potential treatments is urgently needed.

Plant extract mediated synthesis of silver and gold nanoparticles and its antibacterial activity against clinically isolated pathogens.

Biosynthesis of nanoparticles is under exploration is due to wide biomedical applications and research interest in nanotechnology. Bioreduction of silver nitrate (AgNO(3)) and chloroauric acid (HAuCl(4)) for the synthesis of silver and gold nanoparticles respectively with the plant extract, Mentha piperita (Lamiaceae). The plant extract is mixed with AgNO(3) and HAuCl(2), incubated and studied synthesis of nanoparticles using UV-Vis spectroscopy. The nanoparticles were characterized by FTIR, SEM equipped with EDS. The silver nanoparticles synthesized were generally found to be spherical in shape with 90 nm, whereas the synthesized gold nanoparticles were found to be 150 nm. The results showed that the leaf extract of menthol is very good bioreductant for the synthesis of silver and gold nanoparticles and synthesized nanoparticles active against clinically isolated human pathogens, Staphylococcus aureus and Escherichia coli.

Properties of uniform diameter InN nanowires obtained under Si doping.

High quality, well-separated, homogeneous sizes and high aspect ratio Si-doped InN nanowires (NWs) were grown by catalyst-free molecular beam epitaxy (MBE) after optimization of the growth conditions. To this end, statistical analysis of NW density and size distribution was performed. The high crystal quality and smooth NW surfaces were observed by high resolution transmission electron microscopy. Spectral photoluminescence has shown the increase of the band filling effect with Si flux, indicating successful n-type doping. A Raman LO scattering mode appears with a pronounced low energy tail, also reported for highly doped InN films.

Poisoning with the S-Alkyl organophosphorus insecticides profenofos and prothiofos.

BACKGROUND: Many organophosphorus (OP) insecticides have either two O-methyl or two O-ethyl groups attached to the phosphorus atom. This chemical structure affects their responsiveness to oxime-induced acetylcholinesterase (AChE) reactivation after poisoning. However, several OP insecticides are atypical and do not have these structures. AIM: We aimed to describe the clinical course and responsiveness to therapy of people poisoned with two S-alkyl OP insecticides-profenofos and prothiofos. DESIGN: We set up a prospective cohort of patients with acute profenofos or prothiofos self-poisoning admitted to acute medical wards in two Sri Lankan district hospitals. Clinical observation was carried out throughout their inpatient stay; blood samples were taken in a subgroup for assay of cholinesterases and insecticide. RESULTS: Ninety-five patients poisoned with profenofos and 12 with prothiofos were recruited over 5 years. Median time to admission was 4 (IQR 3-7) h. Eleven patients poisoned with profenofos died (11/95; 11.6%, 95% CI 5.9-20); one prothiofos patient died (1/12; 8.3%, 95% CI 0.2-38). Thirteen patients poisoned with profenofos required intubation for respiratory failure (13/95; 13.7%, 95% CI 7.5-22); two prothiofos-poisoned patients required intubation. Both intubations and death occurred late compared with other OP insecticides. Prolonged ventilation was needed in those who survived-a median of 310 (IQR 154-349) h. Unexpectedly, red cell AChE activity on admission did not correlate with clinical severity-all patients had severe AChE inhibition (about 1% of normal) but most had only mild cholinergic features, were conscious, and did not require ventilatory support. CONCLUSION: Compared with other commonly used OP insecticides, profenofos and prothiofos are of moderately severe toxicity, causing relatively delayed respiratory failure and death. There was no apparent response to oxime therapy. The lack of correlation between red cell AChE activity and clinical features suggests that this parameter may not always be a useful marker of synaptic AChE activity and severity after OP pesticide poisoning.