Shri Singh

Phase transitions in liquid crystals

Abstract Mesogenic materials exhibit a multitude of transitions involving new phases. Studies of these phases are of importance in a wide range of scientific fields and as such have stimulated considerable theoretical and experimental efforts over the decades. This review article presents a comprehensive overview until this date of the developments in this subject. An attempt is made to identify the essential key concepts and points of difficulty associated with the study of phase transitions. The article begins with a brief introduction about the symmetry, structure and types of liquid crystalline phases. This is followed by a discussion of the distribution functions and order parameters which are considered as the basic knowledge essential for the study of ordered phases. A brief discussion of the thermodynamic properties at and in the vicinity of phase transitions, which are required to understand the molecular structure phase stability relationship, is given. The most widely used experimental techniques for measuring these transition properties are critically examined. The remaining parts of the article are concerned with the current status of the theoretical developments and experimental studies in this field. The application of the various theories to the description of isotropic liquid-uniaxial nematic, uniaxial nematic-smectic A, uniaxial nematic-biaxial nematic, smectic A–smectic C phase transitions are reviewed comprehensively. The basic ideas of Landau–de Gennes theory and its applications to study these transitions are discussed. Since the formation of liquid crystals depends on the anisotropy in the intermolecular interactions, questions concerning its role in the mesophase transitions are addressed. The hard particle, Maier-Saupe and van der Waals types of theories are reviewed. The application of density functional theory in studying mesophase transitions is described. A critical assessment of the experimental investigations concerning reentrant phase transitions in liquid crystals is made and the factors which impede its proper understanding are identified. A survey is given of existing computer simulation studies of the isotropic to nematic transition, the nematic to smectic A transition, the smectic A to hexatic S B transition, the smectic A to reentrant nematic transition, and transitions to the discotic phase. The current status of the study of phase transitions involving hexatic smectic, cholesteric, polymeric and ferroelectric liquid crystals is outlined. Finally, a range of unexplored problems and some of the areas which are in greatest need of future attention are identified.

Amphotericin B Treatment for Indian Visceral Leishmaniasis: Conventional versus Lipid Formulations

In Bihar, India, where visceral leishmaniasis is hyperendemic, amphotericin B deoxycholate is now first-line parenteral treatment. To test the efficacy of amphotericin B deoxycholate versus that of its lipid formulations, Indian patients were randomized to receive treatment with amphotericin B deoxycholate (1 mg/kg on alternate days for 30 days; n=51), liposomal amphotericin B (2 mg/kg per day for 5 days; n=51), or amphotericin B lipid complex (2 mg/kg per day for 5 days; n=51). Infusion-associated reactions were frequent and persistent in subjects treated with amphotericin B deoxycholate. The illness of 3 patients failed to respond to treatment, and 5 patients experienced relapse. Final cure rates were similar. Estimated total treatment costs for a 25-kg patient-417 dollars for amphotericin B deoxycholate, 872 dollars for liposomal amphotericin B, and 947 dollars for amphotericin B lipid complex-differed as a result of drug cost. Substantial reductions (approximately 60%) in the price of liposomal amphotericin B and amphotericin B lipid complex would make treatment costs comparable to that of amphotericin B deoxycholate, permitting administration of short-course regimens in India.

Visceral Leishmaniasis Elimination Programme in India, Bangladesh, and Nepal: Reshaping the Case Finding/Case Management Strategy

Objective We sought to estimate visceral leishmaniasis (VL) burden in Bangladesh, India, and Nepal and document care-seeking behaviour for VL to provide baseline information for monitoring the VL elimination program and identify options for improved case finding and management. Design A cross-sectional study using cluster sampling (clusters being villages) of 4 VL endemic districts was used in order to document all current and existing VL cases over the preceding 12 mo. Extended (in-depth) interviews were conducted in a subsample of households to explore (a) VL-related knowledge, attitudes, and practices of the population; (b) use of VL care by patients; and (c) delay between onset of symptoms, diagnosis, and start of treatment, as well as treatment interruption. Findings were discussed with national program managers and policy makers to develop improved strategies. Results Screening for VL was done in 18,933 households (106,425 inhabitants). The estimated annual incidence of VL in the endemic districts was on average 22 times higher than the elimination target of less than one case per 10,000 inhabitants in 2015. This incidence varied widely between study sites, from 9.0 to 29.8 per 10,000 inhabitants. The percentage of newly detected cases through the household screening was high in the districts least covered by health-care services (particularly Rajshahi, Bangladesh, 49%; and to a lesser extent Vaishali in Bihar, India, 32.5%), and much lower in districts with greater availability of VL care (Muzaffarpur, India, 3.8%). On average 267 houses had to be visited, i.e., at least three to four working days per health worker, to identify a new VL (ranging from 1,432 houses in Muzaffarpur, India to only 166 houses in Rajshahi, Bangladesh). Knowledge of the disease and its vectors was good in India and Nepal but poor in Bangladesh (Rajshahi) where very little attention has been given to VL over the last decades. Although all socio-demographic indicators showed high levels of poverty, people in India preferred private medical practitioners for the treatment of VL, whereas in Nepal, and even more in Bangladesh, the public health-care sector was preferred. Delays between onset of symptoms and diagnosis as well as start of treatment was high. Reported non-adherence to treatment was particularly high in the more under-served districts and was mainly due to lack of resources. Discussion The findings suggest that (a) house-to-house screening may be useful in highly endemic districts with a poor passive case detection system, but further evidence on case finding adapted to local conditions has to be collected; (b) strengthening the quality of the public health sector is imperative in the three countries, especially in India, with its largely unregulated private-sector provision of VL care.

Longlasting insecticidal nets for prevention of Leishmania donovani infection in India and Nepal: paired cluster randomised trial

Objective To test the effectiveness of large scale distribution of longlasting nets treated with insecticide in reducing the incidence of visceral leishmaniasis in India and Nepal. Design Paired cluster randomised controlled trial designed to detect a 50% reduction in incidence of Leishmania donovani infection. Setting Villages in Muzaffarpur district in India and Saptari, Sunsari, and Morang districts in Nepal. Participants 13 intervention and 13 control clusters. 12 691 people were included in the analysis of the main outcome (infection), and 19 810 were enrolled for the secondary (disease) end point. Intervention Longlasting insecticidal nets (treated with deltamethrin) were distributed in the intervention clusters in December 2006. Main outcome measures Infection was determined by direct agglutination test at 12 and 24 months after the intervention in those who had negative results (titre <1:1600) at baseline. The effect estimate was computed as the geometric mean of the risk ratios for seroconversion for each cluster pair (net/no net), with its 95% confidence interval. Formal tests of effect of no intervention were obtained with a paired t test. Results There was no significant difference in the risk of seroconversion over 24 months in intervention (5.4%; 347/6372) compared with control (5.5%; 345/6319 people) clusters (risk ratio 0.90, 95% confidence interval 0.49 to 1.65) nor in the risk of clinical visceral leishmaniasis (0.99, 0.46 to 1.40). Adjustment for covariates did not alter these conclusions. Conclusions There is no evidence that large scale distribution of longlasting insecticidal nets provides additional protection against visceral leishmaniasis compared with existing control practice in the Indian subcontinent. The observed effect was small and not significant, though the confidence intervals did not exclude a 50% change in either direction. Trial registration Clinical Trials NCT 2005-015374.

Epidemiology of Leishmania donovani infection in high-transmission foci in Nepal

Objective  Visceral Leishmaniasis (VL) is highly prevalent in Bihar, India. India and its neighbours aim at eliminating VL, but several knowledge gaps in the epidemiology of VL may hamper that effort. The prevalence of asymptomatic infections with Leishmania donovani and their role in transmission dynamics are not well understood. We report data from a sero‐survey in Bihar.

Amphotericin B Treatment for Indian Visceral Leishmaniasis: Response to 15 Daily versus Alternate-Day Infusions

BACKGROUND For patients with Indian visceral leishmaniasis, amphotericin B deoxycholate is usually given as 15 alternate-day infusions of 1 mg/kg over 30 days (total dose, 15 mg/kg); daily treatment with 1 mg/kg for 20 days (total dose, 20 mg/kg) is also used. This study was done to address the unsettled therapeutic questions of administration schedule (alternate-day vs. daily administration) and dose (1 vs. 0.75 mg/kg) and to determine whether the duration of amphotericin B treatment in Bihar, India, can be shortened to 15 days. METHODS To compare alternate-day versus daily administration and 1-mg/kg versus 0.75-mg/kg doses and to determine whether the duration of treatment could be abbreviated, Indian subjects randomly received 15 infusions of 1 mg/kg (group A; 245 patients) or 0.75 mg/kg (group B; 244 patients) on alternate days or 1 mg/kg (group C; 500 patients) or 0.75 mg/kg (group D; 496 patients) daily. Noninferiority testing compared 6-month cure rates using a 5% margin. RESULTS Overall, 1439 of the 1485 subjects completed treatment and responded. Treatment interruptions (nephrotoxicity) but not infusion-associated reactions or study removals were more common with daily administration. Final cure rates at 6 months were similar: group A, 234 patients (96%; 95% confidence interval [CI], 92%-98%); group B, 225 patients (92%; 95% CI, 88%-95%); group C, 483 patients (97%; 95% CI, 95%-98%); and group D, 476 patients (96%; 95% CI, 94%-97%; P>.05). CONCLUSIONS Provided that the serum creatinine level is repeated once, daily treatment with amphotericin B, 0.75 mg/kg for 15 days (total dose, 11.25 mg/kg), is efficient and effective for visceral leishmaniasis in India. TRIAL REGISTRATION ClinicalTrials.gov identifier: NCT00310505.

Preparation of thin Co3O4 films on Ni and their electrocatalytic surface properties towards oxygen evolution

Abstract Thin films of Co3O4 of varying thicknesses have been prepared on an Ni substrate by spray pyrolysis and sequential solution coatings and investigated for their physicochemical and electrochemical properties towards O2 evolution. The study indicated that the oxide roughness factor tended to level off with increasing thickness. Further, with an increase in oxide loading, the apparent electrochemical activity enhanced considerably at low range of loadings and then became relatively constant over a range of loadings. The higher loadings were found to be harmful. The layered oxide films (2.4–4.2 mg cm−2) prepared in sequential solution coatings exhibited greatest electrocatalytic activity in 1M KOH. However, the oxide electrode (loading: 3–5.7 mg cm−2) prepared by rotating spray pyrolysis produced the lowest oxygen overpotential—360 ± 3 mV against a current density of 1 A cm−2 in 30 w/o KOH at 70 °C. The oxygen evolution reaction at these film electrodes exhibited two Tafel slopes: 51–68 mV decade−1 at low overpotentials and 120–140 mV decade−1 at high overpotentials. The reaction orders with respect to OH− concentration were found to be ~ 1 for the layered and ~ 2 for the sprayed films. Based on the results, a suitable mechanism is also suggested for oxygen evolution.

Insecticide susceptibility of Phlebotomus argentipes in visceral leishmaniasis endemic districts in India and Nepal.

Objectives To investigate the DDT and deltamethrin susceptibility of Phlebotomus argentipes, the vector of Leishmania donovani, responsible for visceral leishmaniasis (VL), in two countries (India and Nepal) with different histories of insecticide exposure. Methods Standard WHO testing procedures were applied using 4% DDT and 0.05% deltamethrin impregnated papers. The effect of the physiological status (fed and unfed) of females on the outcome of the bioassays was assessed and the optimal time of exposure for deltamethrin was evaluated on a colony population. Field populations from both countries were tested. Results Fed and unfed females responded in a similar way. For exposure time on field samples 60 min was adopted for both DDT and deltamethrin. In Bihar, knockdown and mortality with DDT was respectively 20 and 43%. In Nepal almost all sand flies were killed, except at the border with Bihar (mortality 62%). With 0.05% deltamethrin, between 96 and 100% of the sand flies were killed in both regions. Conclusions Based on literature and present data 4% DDT and 0.05% deltamethrin seem to be acceptable discriminating concentrations to separate resistant from susceptible populations. Resistance to DDT was confirmed in Bihar and in a border village of Nepal, but the sand flies were still susceptible in villages more inside Nepal where only synthetic pyrethroids are used for indoor spraying. The low effectiveness of indoor spraying with DDT in Bihar to control VL can be partially explained by this resistance hence other classes of insecticides should be tested. In both countries P. argentipes sand flies were susceptible to deltamethrin.

Persistence of Leishmania donovani Antibodies in Past Visceral Leishmaniasis Cases in India

ABSTRACT The persistence of anti-Leishmania donovani antibodies in past visceral leishmaniasis (VL) cases was retrospectively assessed by means of the direct agglutination test (DAT) and the rK39 enzyme-linked immunosorbent assay (ELISA). Antibody titers remained high for an extended period of time in past cases of VL. These results highlight the need to carefully elicit the history of patients with VL symptoms.

Effect of TiO2 nanoparticles dispersion on ionic behaviour in nematic liquid crystal

The present study focuses on the ionic behaviour in nanoparticles (NPs) dispersed nematic liquid crystal. Dielectric spectroscopy has been used to investigate the behaviour of ions in suspension of NPs and liquid crystal (LC). Ionic concentration, diffusion coefficient, activation energy and mobility have been calculated from dielectric data. It is found that ion concentration increases initially and then it decreases with increasing concentration of NPs in suspension. The initial increase in ion concentration is attributed to the insertion of more ions due to impurities of TiO2 NPs and various other reasons. Temperature dependence of diffusion constant for different loading of TiO2 NPs is also investigated. The activation energy of NPs dispersed LC is found to be lower than the pristine one and it decreases with increasing concentration of NPs. The decreasing DC conductivity with increasing NPs concentration is attributed to the hindered or restricted motion of ions in the suspension. It is proposed that TiO2 NPs may be a potential candidate to be used to suppress the undesired ionic effect in LCs.