Polarized Bow Shock Nebulae Reveal Features of the Winds and Environments of Massive Stars

Massive stars strongly affect their surroundings through their energetic stellar winds during their lifetime and through their energetic deaths as supernovae. When a stellar wind interacts with the local interstellar medium (ISM), if the relative velocity between wind and ISM is supersonic, then a stellar wind bow shock is formed. Bow shocks and related density enhancements produced by the winds of massive stars moving through the interstellar medium provide important information regarding the motions of the stars, the properties of their stellar winds, and the characteristics of the local medium. Since bow shock nebulae are aspherical structures, light scattering within them produces a net polarization signal even if the region is spatially unresolved. Scattering opacity arising from free electrons and dust leads to a predictable distribution of polarized intensity across the bow shock structure. That polarization encodes information about the shape, composition, opacity, density, and ionization state of the material within the structure. In my dissertation research, I use a Monte Carlo radiative transfer code that I optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (SWBS) illuminated by a central star and by emission from the bow shock. I derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (SPH) models. In the case of the analytical SWBS and electron scattering, I find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. This is due to the geometrical properties of the bow shock combined with multiple scattering effects. I also find that the source of illumination plays an important role in determining the distribution of polarization for resolved bow shocks. In the case of dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, dust temperature, and viewing angle. The behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models. In the case of SPH density structures, I investigate how the polarization changes as a function of the dust grain size and composition present in the SWBS. I present preliminary results of this implementation. In each case, I discuss the observational implications of these models for the stellar winds and interstellar environments of these influential objects, and predict observable signatures that can help constrain quantities of particular interest

Phytochemical screening, antimicrobial activity and cytotoxicity of Nepalese medicinal plants Swertia chirayita and Dendrobium amoenum

Research on medicinal plants are important to Nepal because most of its rural population relies on it as mode of medicine. Medicinal plants namely Swertia chirayita and Dendrobium amoenum were collected from mid hills of Nepal. The present study was undertaken to find the antimicrobial activity, phytochemical presence and their cytotoxicity in different extraction medium. The percentage yield from the plants were highest in warm methanol extraction with 12.6%, followed by ethyl acetate and lowest was for cold methanol. Plant extract showed the presence of antioxidants like alkaloid, terpenoids, flavonoids, tannin, glycosides. The Brine Shrimp Bioassay of methanol and ethyl acetate extract showed cytotoxicity. Chiraito extract showed LC50 of 199 ppm for Dhunche sample, 128.82 ppm for Daman sample and 131.82 ppm of Illam sample. The antibacterial activity of methanol extract of Chiraito and Dendrobium amoenum showed significant bioactivity by inhibiting growth of microbial species selected for the test. The zone of inhibition shown by the extracts was comparable to the standard antibiotics. Similarly, methanol extract of Chiraito also showed significant antifungal activity with the zone of inhibition comparable to amphotericin.Nepal Journal of Biotechnology. Dec. 2015 Vol. 3, No. 1: 48-5

GIANT CELLS AND GIANT CELL LESIONS OF ORAL CAVITY- A REVIEW

Giant cells are large mononucleated or multinucleated cells that are seen in a variety of physiological as well as pathological conditions. Multinucleated giant cells (MGCs) are important mediators of tissue remodeling and repair and also for removal of foreign materials and various pathogens.  The commonly encountered giant cells arise from monocyte precursors, formed due to different mechanisms. Depending upon the mechanism of their formation these cells assume distinctly variable phenotypes.  The giant cell lesions of oral cavity have been classified on the basis of etio-pathogenesis, the presence of which at times being pathognomic. We attempt to review the basic information regarding the mechanism of formation and morphology of giant cells and its significance in the associated giant cell lesions. Also we have tried to describe the clinical, histopathological and immunohistochemical aspects of various giant cell lesions of the oral cavity

Optical Polarimetry of the May 2022 Lunar Eclipse

The sunlight reflected from the Moon during a total lunar eclipse has been transmitted through the Earth's atmosphere on the way to the Moon. The combination of multiple scattering and inhomogeneous atmospheric characteristics during that transmission can potentially polarize that light. A similar (although much smaller) effect should also be observable from the atmosphere of a transiting exoplanet. We present the results of polarization observations during the first 15 minutes of totality of the lunar eclipse of 2022 May 16. We find degrees of polarization of 2.1 +/- 0.4 per cent in B, 1.2 +/- 0.3 per cent in V, 0.5 +/- 0.2 per cent in R and 0.2 +/- 0.2 per cent in I. Our polarization values lie in the middle of the range of those reported for previous eclipses, providing further evidence that the induced polarization can change from event to event. We found no significant polarization difference (<0.02 per cent) between a region of dark Mare and nearby bright uplands or between the lunar limb and regions closer to the disk centre due to the different angle of incidence. This further strengthens the interpretation of the polarization's origin being due to scattering in the Earth's atmosphere rather than by the lunar regolith.Comment: Accepted for publication in MNRA

Family Caregivers’ Satisfaction towards the Communication of Health Service Providers in Tertiary Care Hospital of Nepal

Introduction: Patient and family caregivers’ satisfaction is an essential measure of the quality of care and a determinant of health service utilization. Measuring family caregivers’ satisfaction with health service providers is important for understanding and improving the quality of care at health facilities. Therefore, the present study aimed to assess the satisfaction of family caregivers towards the communication of health service providers. Methods: A descriptive cross-sectional study was conducted by the development of a questionnaire at one of the tertiary care hospitals. Self-administered questionnaires related to demography and different dimensions on the satisfaction of caregivers towards the communication of health service provider was designed. Sixty caregivers were provided questionnaire and data was collected. In descriptive analysis, frequency and percentage were calculated using SPSS 23 (SPSS Inc., Chicago, IL, USA). Results: The study showed that the majority of the caregivers (40%) were of the young age group (31-40 years). More than half (53%) of the caregivers were satisfied with different ways of communication about the patient’s condition and treatment. In terms of communication mode, the majority of the caregivers were satisfied with related different ways of communication about the patient’s condition and treatment (53.3%) followed by verbal (63.6 %) and non-verbal (50.6 %) respectively during their stay at the hospital. Conclusion: The current study found that caregivers were satisfied with the communication provided by health service providers. This suggests that the treatment provided to patients might have better outcome measures. Additionally, it may help to reduce the anxiety among caregivers regarding the patients’ condition

Effect of foliar spray of ethephon doses and pruning intensities on growth, sex expression, and yield of cucumber (var- Bhaktapur local) in Kaski, Nepal

A field experiment was conducted to study the effect of foliar spray of ethephon doses and pruning intensities on the performance of Bhaktapur local cultivar of cucumber in Kaski, Nepal from Feb- May 2021. The study was laid out in Randomized Complete Block design (RCBD) with 2G and 3G cutting, and four different doses of ethephon (@125ppm, @250ppm, @375ppm @500ppm) as six treatments against control and were replicated four times with 28 plots each of 20.8 m2 size having 4 rows with 4 plants per row. The data regarding plant height, leaf number, largest leaf area, days to 1st male and female flowering and fruit harvest, the total number of male and female flowers per plant, M: F flower ratio, fruit length, circumference, weight/fruit, fruit number per plant, fruit set % and yield were recorded and analyzed using MS-Excel and R-studio. The result revealed that growth and yield were significantly influenced by the levels of ethephon and pruning. Highest yield was recorded with ethephon @125ppm (83.54 t ha-1) which is as par with 3G (72.57 t ha-1) which was accompanied by a significantly higher number of fruits per plant {(125ppm=18.33), (3G=15.67)}, average fruit weight {(3G=674gm)}, (125ppm=608gm)}, and fruit set % {(3G=30.66 %)}, (125ppm=24.93 %)}. Significantly higher plant height (149.78 cm), and the highest number of leaves per plant (40) were recorded in control and Ethephon @125ppm at 50 DAT, respectively. The largest leaf area (626.84 cm2) was recorded in 2G which is at par with 3G (613.31 cm2) at 50 DAT. Higher dose of ethephon @500ppm (47.87 days) and 375 ppm (47.17 days) delayed days to 1st male flowering while all ethephon doses (T4=31.83 days, T5=32.5 days, T6=34.81 days, and T7=34.83 days) hastened female flowering than control and pruning. A significantly higher number of male flowers were obtained in the control (89.75), while the number of female flowers and M: F flower ratio increased with increasing ethephon level than in pruning (2G and 3G) and control. Hence, appropriate ethephon (125ppm) dose and pruning (3G) were highly conducive for better growth, sex expression, and yield of cucumber using Bhaktapur Local variety of cucumber in the hilly region of Nepal has a climatic condition similar to Kaski

Impact of jets on kilonova photometric and polarimetric emission from binary neutron star mergers

A merger of binary neutron stars creates heavy unstable elements whose radioactive decay produces a thermal emission known as a kilonova. In this paper, we predict the photometric and polarimetric behaviour of this emission by performing 3-D Monte Carlo radiative transfer simulations. In particular, we choose three hydrodynamical models for merger ejecta, two including jets with different luminosities and one without a jet structure, to help decipher the impact of jets on the light curve and polarimetric behaviour. In terms of photometry, we find distinct color evolutions across the three models. Models without a jet show the highest variation in light curves for different viewing angles. In contrast, to previous studies, we find models with a jet to produce fainter kilonovae when viewed from orientations close to the jet axis, compared to a model without a jet. In terms of polarimetry, we predict relatively low levels (<~0.3-0.4%) at all orientations that, however, remain non-negligible until a few days after the merger and longer than previously found. Despite the low levels, we find that the presence of a jet enhances the degree of polarization at wavelengths ranging from 0.25 to 2.5\micron, an effect that is found to increase with the jet luminosity. Thus, future photometric and polarimetric campaigns should observe kilonovae in blue and red filters for a few days after the merger to help constrain the properties of the ejecta (e.g. composition) and jet.Comment: 11 pages, 7 figures, accepted for publication and in pres

Backbone Interactions Between Transcriptional Activator ExsA and Anti-Activator ExsD Facilitate Regulation of the Type III Secretion System in \u3cem\u3ePseudomonas aeruginosa\u3c/em\u3e

The type III secretion system (T3SS) is a pivotal virulence mechanism of many Gram-negative bacteria. During infection, the syringe-like T3SS injects cytotoxic proteins directly into the eukaryotic host cell cytoplasm. In Pseudomonas aeruginosa, expression of the T3SS is regulated by a signaling cascade involving the proteins ExsA, ExsC, ExsD, and ExsE. The AraC-type transcription factor ExsA activates transcription of all T3SS-associated genes. Prior to host cell contact, ExsA is inhibited through direct binding of the anti-activator protein ExsD. Host cell contact triggers secretion of ExsE and sequestration of ExsD by ExsC to cause the release of ExsA. ExsA does not bind ExsD through the canonical ligand binding pocket of AraC-type proteins. Using site-directed mutagenesis and a specific in vitro transcription assay, we have now discovered that backbone interactions between the amino terminus of ExsD and the ExsA beta barrel constitute a pivotal part of the ExsD-ExsA interface. Follow-up bacterial two-hybrid experiments suggest additional contacts create an even larger protein–protein interface. The discovered role of the amino terminus of ExsD in ExsA binding explains how ExsC might relieve the ExsD-mediated inhibition of T3SS gene expression, because the same region of ExsD interacts with ExsC following host cell contact

Polarization simulations of stellar wind bow shock nebulae. II. The case of dust scattering

We study the polarization produced by scattering from dust in a bow shock-shaped region of enhanced density surrounding a stellar source, using the Monte Carlo radiative transfer code SLIP. Bow shocks are structures formed by the interaction of the winds of fast-moving stars with the interstellar medium. Our previous study focused on the polarization produced in these structures by electron scattering; we showed that polarization is highly dependent on inclination angle and that multiple scattering changes the shape and degree of polarization. In contrast to electron scattering, dust scattering is wavelength-dependent, which changes the polarization behaviour. Here we explore different dust particle sizes and compositions and generate polarized spectral energy distributions for each case. We find that the polarization SED behaviour depends on the dust composition and grain size. Including dust emission leads to polarization changes with temperature at higher optical depth in ways that are sensitive to the orientation of the bow shock. In various scenarios and under certain assumptions, our simulations can constrain the optical depth and dust properties of resolved and unresolved bow shock-shaped scattering regions.Constraints on optical depth can provide estimates of local ISM density for observed bow shocks. We also study the impact of dust grains filling the region between the star and bow shock. We see that as the density of dust between the star and bow shock increases, the resulting polarization is suppressed for all the optical depth regimes.Comment: 21 pages, accepted for publication in MNRA

Virtual Inertia: Current Trends and Future Directions

The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems