3-D Modified Proportional Navigation Guidance Law based on a Total Demand Vector Concept

Different proportional navigation (PN)-based guidance laws-pure proportional navigation (PPN), true proportional navigation (TPN), and proportional navigation with boost accelerationcompensation generally used cannot maintain fundamental parameter of proportional navigation, viz., Navigation constant to the desired value in the presence of significantly high lead angles and missile longitudinal accelerations/decelerations. In a real-life situation with sensor noises and hardware constraints, this navigation constant should be maintained tightly at the selected value, which is generally between 3 and 4, for optimum performance. In this paper; a new 3-D modified PN guidance law based on a total demand vector concept is presented, which can maintain the navigation constant to the designer-selected value for any 3-D engagement scenario with associated lead angles and any velocity profile with missile longitudinal accelerations1 decelerations. Generality of this guidance law is brought out and superiority of this guidance law over the commonly used proportional navigation-based laws like PPN, TPN and PN with boost acceleration compensation has been demonstrated by applying it to the real-life 3-D engagement scenarios of different hypothetical missiles

Radio Frequency Seeker Modelling and Seeker Filter Design

Radio frequency seeker model, including receiver angle error noise modelling and filtering of noise from seeker measurement, is presented in this paper. The effects of eclipsing, radar cross section fluctuation, etc on seeker sight-line rate measurement are highlighted. The formulation for colour noise modelling of sight-line rate noise is derived based on the knowledge of seeker receiver angle error noise model. Two Kalman filter configurations for filtering of noise from seeker output have been considered in this paper, based on sight-line rate kinematics and noise characteristic. It has been  observed from the simulation studies that sight-line rate signal varies slowly at higher interceptor-target ranges; with severe colour noise in sight line rate measurement, and therefore higher weightage for noise attenuation is beneficial in Kalman filter configuration. So, kinematic plus state augmentation for colour noise are considered for adequate filtering for higher interceptor-target ranges. Whereas for lower interceptor-target ranges, sight-line rate changes appreciably, which have been tracked by a simplified/modified spherical coordinate model, which uses knowledge of interceptor-target  engagement dynamics. For both the filters, benefits of colour noise modelling and process model augmentation through coloured noise states, for filtering severe colour noise of seeker, has been demonstrated

Role of microenvironment in the mixed Langmuir-Blodgett films

This paper reports the pi-A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir-Blodgett (LB) films of non-amphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). pi-A isotherm studies of mixed monolayer and as well as also the collapse pressure study of isotherms definitely conclude that CA is incorporated into PMMA and SA matrices. However CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates as is evidenced from the scanning electron micrograph picture. Nature of these aggregated species in the mixed LB films has been revealed by UV-Vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low dimensional aggregates in the mixed LB films. Intensity distribution of different band system is highly sensitive to the microenvironment of two different matrices as well as also on the film thicknessComment: 11 pages, 5 figure

Immobilization of single strand DNA on solid substrate

Thin films based on Layer-by-Layer (LbL) self assembled technique are useful for immobilization of DNA onto solid support. This communication reports the immobilization of DNA onto a solid support by electrostatic interaction with a polycation Poly (allylamine hydrochloride) (PAH). UV-Vis absorption and steady state fluorescence spectroscopic studies exhibit the characteristics of DNA organized in LbL films. The most significant observation is that single strand DNA are immobilized on the PAH backbone of LbL films when the films are fabricated above the melting temperature of DNA. DNA immobilized in this way on LbL films remains as such when the temperature is restored at room temperature and the organization remains unaffected even after several days. UV-Vis absorption spectroscopic studies confirm this finding.Comment: Eight pages, five figure

Photophysical characterizations of 2-(4-Biphenylyl)-5 phenyl-1,3,4- oxadiazole in restricted geometry

Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic 2-(4-Biphenylyl)-5 phenyl-1,3,4- oxadiazole (abbreviated as PBD) mixed with stearic acid (SA) as well as also with the inert polymer matrix poly(methyl methacrylate) (PMMA) have been studied. Surface pressure versus area per molecule (-A) isotherms studies suggest that PBD molecules very likely stand vertically on the air-water interface and this arrangement allows the PBD molecules to form stacks and remain sandwiched between SA/PMMA molecules. At lower surface pressure phase separation between PBD and matrix molecules occur resulting due to repulsive interaction. However at higher surface pressure PBD molecules form aggregates. The UV-Vis absorption and Steady state fluorescence spectroscopic studies of the mixed LB films of PBD reveal the nature of the aggregates. H-type aggregates predominates in the mixed LB films whereas I-type aggregates predominates in the PBD-PMMA spin coated films. The degree of deformation produced in the electronic levels are largely affected by the film thickness and the surface pressure of lifting.Comment: 15 pages, 6 figure

A lower bound on the local extragalactic magnetic field

Assuming that the hard gamma-ray emission of Cen A is a result of synchrotron radiation of ultra-relativistic electrons, we derive a lower bound on the local extragalactic magnetic field, $B> 10^{-8}$ G. This result is consistent with (and close to) upper bounds on magnetic fields derived from consideration of cosmic microwave background distortions and Faraday rotation measurements.Comment: Includes extensive discussion of particle acceleration above 10^20 eV in the hot spot-like region of Cen

Brownian motion of a charged particle in electromagnetic fluctuations at finite temperature

The fluctuation-dissipation theorem is a central theorem in nonequilibrium statistical mechanics by which the evolution of velocity fluctuations of the Brownian particle under a fluctuating environment is intimately related to its dissipative behavior. This can be illuminated in particular by an example of Brownian motion in an ohmic environment where the dissipative effect can be accounted for by the first-order time derivative of the position. Here we explore the dynamics of the Brownian particle coupled to a supraohmic environment by considering the motion of a charged particle interacting with the electromagnetic fluctuations at finite temperature. We also derive particle's equation of motion, the Langevin equation, by minimizing the corresponding stochastic effective action, which is obtained with the method of Feynman-Vernon influence functional. The fluctuation-dissipation theorem is established from first principles. The backreaction on the charge is known in terms of electromagnetic self-force given by a third-order time derivative of the position, leading to the supraohmic dynamics. This self-force can be argued to be insignificant throughout the evolution when the charge barely moves. The stochastic force arising from the supraohmic environment is found to have both positive and negative correlations, and it drives the charge into a fluctuating motion. Although positive force correlations give rise to the growth of the velocity dispersion initially, its growth slows down when correlation turns negative, and finally halts, thus leading to the saturation of the velocity dispersion. The saturation mechanism in a suparohmic environment is found to be distinctly different from that in an ohmic environment. The comparison is discussed.Comment: accepter by Foundation of Physics, for IARD 6, 200

Validating polyp and instrument segmentation methods in colonoscopy through Medico 2020 and MedAI 2021 Challenges

Automatic analysis of colonoscopy images has been an active field of research motivated by the importance of early detection of precancerous polyps. However, detecting polyps during the live examination can be challenging due to various factors such as variation of skills and experience among the endoscopists, lack of attentiveness, and fatigue leading to a high polyp miss-rate. Therefore, there is a need for an automated system that can flag missed polyps during the examination and improve patient care. Deep learning has emerged as a promising solution to this challenge as it can assist endoscopists in detecting and classifying overlooked polyps and abnormalities in real time, improving the accuracy of diagnosis and enhancing treatment. In addition to the algorithm’s accuracy, transparency and interpretability are crucial to explaining the whys and hows of the algorithm’s prediction. Further, conclusions based on incorrect decisions may be fatal, especially in medicine. Despite these pitfalls, most algorithms are developed in private data, closed source, or proprietary software, and methods lack reproducibility. Therefore, to promote the development of efficient and transparent methods, we have organized the “Medico automatic polyp segmentation (Medico 2020)” and “MedAI: Transparency in Medical Image Segmentation (MedAI 2021)” competitions. The Medico 2020 challenge received submissions from 17 teams, while the MedAI 2021 challenge also gathered submissions from another 17 distinct teams in the following year. We present a comprehensive summary and analyze each contribution, highlight the strength of the best-performing methods, and discuss the possibility of clinical translations of such methods into the clinic. Our analysis revealed that the participants improved dice coefficient metrics from 0.8607 in 2020 to 0.8993 in 2021 despite adding diverse and challenging frames (containing irregular, smaller, sessile, or flat polyps), which are frequently missed during a routine clinical examination. For the instrument segmentation task, the best team obtained a mean Intersection over union metric of 0.9364. For the transparency task, a multi-disciplinary team, including expert gastroenterologists, accessed each submission and evaluated the team based on open-source practices, failure case analysis, ablation studies, usability and understandability of evaluations to gain a deeper understanding of the models’ credibility for clinical deployment. The best team obtained a final transparency score of 21 out of 25. Through the comprehensive analysis of the challenge, we not only highlight the advancements in polyp and surgical instrument segmentation but also encourage subjective evaluation for building more transparent and understandable AI-based colonoscopy systems. Moreover, we discuss the need for multi-center and out-of-distribution testing to address the current limitations of the methods to reduce the cancer burden and improve patient care

Anemia prevalence in women of reproductive age in low- and middle-income countries between 2000 and 2018

Anemia is a globally widespread condition in women and is associated with reduced economic productivity and increased mortality worldwide. Here we map annual 2000–2018 geospatial estimates of anemia prevalence in women of reproductive age (15–49 years) across 82 low- and middle-income countries (LMICs), stratify anemia by severity and aggregate results to policy-relevant administrative and national levels. Additionally, we provide subnational disparity analyses to provide a comprehensive overview of anemia prevalence inequalities within these countries and predict progress toward the World Health Organization’s Global Nutrition Target (WHO GNT) to reduce anemia by half by 2030. Our results demonstrate widespread moderate improvements in overall anemia prevalence but identify only three LMICs with a high probability of achieving the WHO GNT by 2030 at a national scale, and no LMIC is expected to achieve the target in all their subnational administrative units. Our maps show where large within-country disparities occur, as well as areas likely to fall short of the WHO GNT, offering precision public health tools so that adequate resource allocation and subsequent interventions can be targeted to the most vulnerable populations.Peer reviewe