Effect of built-in-polarization field on mean free path of phonons in binary nitrides

In this paper, the built-in-polarization field effect on mean free path of acoustic phonons in bulk wurtzite binary nitrides (GaN, AlN) has been theoretically investigated. Due to the modification of elastic constant of the material by the effect of polarization field, there is a corresponding enhancement in group velocity and Debye frequency of phonons. The scattering rate of phonons also affected by this field, as it is a function of velocity or/and Debye frequency. The result shows that polarization field suppresses various scattering rates as well as combined scattering rate of phonons. This implies an increased combined relaxation time of phonons. Hence, the mean free path of phonons increases. Thus, phonons travel freely for a longer distance between two successive scatterings. It is found that, the mean free path of low frequency phonons is longer than that of the high frequency phonons. It indicates that, the low frequency phonons are significantly affected by the built-in-polarization field. This can enhance thermal transport properties of the material, when built-in-polarization field taken into account. It may be a method to control the thermal transport properties of such materials by the application of electric field in a desired way, which can be considered in addressing thermal management issues in nitride based optoelectronic devices to minimize self-heating effects

Effect of built-in-polarization field on mean free path of phonons in binary nitrides

179-186In this paper, the built-in-polarization field effect on mean free path of acoustic phonons in bulk wurtzite binary nitrides (GaN, AlN) has been theoretically investigated. Due to the modification of elastic constant of the material by the effect of polarization field, there is a corresponding enhancement in group velocity and Debye frequency of phonons. The scattering rate of phonons also affected by this field, as it is a function of velocity or/and Debye frequency. The result shows that polarization field suppresses various scattering rates as well as combined scattering rate of phonons. This implies an increased combined relaxation time of phonons. Hence, the mean free path of phonons increases. Thus, phonons travel freely for a longer distance between two successive scatterings. It is found that, the mean free path of low frequency phonons is longer than that of the high frequency phonons. It indicates that, the low frequency phonons are significantly affected by the built-in-polarization field. This can enhance thermal transport properties of the material, when built-in-polarization field taken into account. It may be a method to control the thermal transport properties of such materials by the application of electric field in a desired way, which can be considered in addressing thermal management issues in nitride based optoelectronic devices to minimize self-heating effects

A study on the tensile force and shear strain of trilayer graphene

The study of mechanical properties of graphene is one of the hottest topics in graphene physics. As the number of graphene layers increases, the mechanical property changes. Y. Liu et al., J. Mech. Phys. Solids, 60, 591 (2012) [

Molecular Imaging Targeting Corticotropin Releasing Hormone Receptor for Corticotropinoma: A Changing Paradigm

Corticotrophin releasing hormone (CRH) is the major regulator of ACTH secretion from the anterior pituitary and acts via CRH-1 receptors (CRH-1R). Corticotropinoma though autonomous still retain their responsiveness to CRH and hence, we hypothesize that in vivo detection of CRH-1 receptors on pituitary adenoma using Gallium-68 ( 68Ga) tagged CRH can indicate the functionality of adenoma and combining it with Positron emission tomography-computed tomography (PET-CT) can provide requisite anatomical information

Experience of establishing and coordinating a nationwide network for bidirectional intussusception surveillance in India: lessons for multisite research studies

Objectives To document and share the process of establishing the nationally representative multisite surveillance network for intussusception in India, coordination, data management and lessons learnt from the implementation.Design This study combined both retrospective and prospective surveillance approaches.Setting 19 tertiary care institutions were selected in India considering the geographic representation and public and private mixParticipants All children under-2 years of age with intussusceptionPrimary and secondary outcome measures The experience of site selection, regulatory approvals, data collection, quality assurance and network coordination were documented.Results The site selection process involved systematic and objective four steps including shortlisting of potential institutions, information seeking and telephonic interaction, site visits and site selection using objective criteria. Out of over 400 hospitals screened across India, 40 potential institutions were shortlisted and information was sought by questionnaire and interaction with investigators. Out of these, 25 institutes were visited and 19 sites were finally selected to participate in the study. The multistep selection process allowed filtering and identification of sites with adequate capacity and motivated investigators. The retrospective surveillance documented 1588 cases (range: 14–652 cases/site) and prospective surveillance recruited 621 cases (range: 5–191 cases/site). The multilayer quality assurance measures monitored and ensured protocol adherence, complete record retrieval and data completeness. The key challenges experienced included time taken for obtaining regulatory and ethical approvals, which delayed completion of the study. Ten sites continued with another multisite vaccine safety surveillance study.Conclusion The experience and results of this systematic and objective site selection method in India are promising. The systematic multistep site selection and data quality assurance methods presented here are feasible and practical. The lessons from the establishment and coordination of this surveillance network can be useful in planning, selecting the sites and conducting multisite and surveillance studies in India and developing countries

Association of meteorological parameters with intussusception in children aged under 2 years: results from a multisite bidirectional surveillance over 7 years in India

Objectives The study aimed to document the association between intussusception in Indian children and meteorological parameters and examine regional variations.Design A bidirectional (retrospective and prospective) surveillance between July 2010 and September 2017.Setting At 20 hospitals in India, retrospective case record review during July 2010 and March 2016 and prospective surveillance during April 2016 and September 2017 were performed.Participants 2161 children aged 2–24 months with first intussusception episode were included.Interventions The monthly mean meteorological parameters (temperature, sunshine, rainfall, humidity and wind speed) for the study sites were collected.Methods The association between monthly intussusception cases and meteorological parameters was examined at pooled, regional and site levels using Pearson (r) and Spearman’s rank-order (ρ) correlation, factorial analysis of variance, and Poisson regression or negative binomial regression analyses.Results The intussusception cases were highest in summer and lowest in autumn seasons. Pearson correlation analysis showed that temperature (r=0.056; p<0.05), wind speed (r=0.134; p<0.01) and humidity (r=0.075; p<0.01) were associated with monthly intussusception cases. Spearman’s rank-order correlation analysis found that temperature (ρ=0.049; p<0.05), wind speed (ρ=0.096; p<0.01) and sunshine (ρ=0.051; p<0.05) were associated with monthly intussusception cases. Poisson regression analysis resulted that monthly intussusception case was associated with rising temperature (North region, p<0.01 and East region, p<0.05), sunshine (North region, p<0.01), humidity (East region, p<0.01) and wind speed (East region, p<0.01). Factorial analysis of variance revealed a significant seasonal difference in intussusception cases for pooled level (p<0.05), 2–6 months age group (p<0.05) and North region (p<0.01). Significant differences in intussusception cases between summer and autumn seasons were observed for pooled (p<0.01), children aged 2–6 months (p<0.05) and 7–12 months (p<0.05).Conclusions Significant correlations between intussusception cases and temperature, humidity, and wind speed were observed at pooled and regional level in India. A peak in summer months was noted, which may be used for prediction, early detection and referral for appropriate management of intussusception