9,642 research outputs found
Conversion from linear to circular polarization in FPGA
Context: Radio astronomical receivers are now expanding their frequency range
to cover large (octave) fractional bandwidths for sensitivity and spectral
flexibility, which makes the design of good analogue circular polarizers
challenging. Better polarization purity requires a flatter phase response over
increasingly wide bandwidth, which is most easily achieved with digital
techniques. They offer the ability to form circular polarization with perfect
polarization purity over arbitrarily wide fractional bandwidths, due to the
ease of introducing a perfect quadrature phase shift. Further, the rapid
improvements in field programmable gate arrays provide the high processing
power, low cost, portability and reconfigurability needed to make practical the
implementation of the formation of circular polarization digitally. Aims: Here
we explore the performance of a circular polarizer implemented with digital
techniques. Methods: We designed a digital circular polarizer in which the
intermediate frequency signals from a receiver with native linear polarizations
were sampled and converted to circular polarization. The frequency-dependent
instrumental phase difference and gain scaling factors were determined using an
injected noise signal and applied to the two linear polarizations to equalize
the transfer characteristics of the two polarization channels. This
equalization was performed in 512 frequency channels over a 512 MHz bandwidth.
Circular polarization was formed by quadrature phase shifting and summing the
equalized linear polarization signals. Results: We obtained polarization purity
of -25 dB corresponding to a D-term of 0.06 over the whole bandwidth.
Conclusions: This technique enables construction of broad-band radio astronomy
receivers with native linear polarization to form circular polarization for
VLBI.Comment: 11 pages 8 figure
Sinusoidal Excitations in Two Component Bose-Einstein Condensates
The non-linear coupled Gross-Pitaevskii equation governing the dynamics of
the two component Bose-Einstein condensate (TBEC) is shown to admit pure
sinusoidal, propagating wave solutions in quasi one dimensional geometry. These
solutions, which exist for a wide parameter range, are then investigated in the
presence of a harmonic oscillator trap with time dependent scattering length.
This illustrates the procedure for coherent control of these modes through
temporal modulation of the parameters, like scattering length and oscillator
frequency. We subsequently analyzed this system in an optical lattice, where
the occurrence of an irreversible phase transition from superfluid to insulator
phase is seen.Comment: 6 pages, 1 figur
Universality in Fluid Domain Coarsening: The case of vapor-liquid transition
Domain growth during the kinetics of phase separation is studied following
vapor-liquid transition in a single component Lennard-Jones fluid. Results are
analyzed after appropriately mapping the continuum snapshots obtained from
extensive molecular dynamics simulations to a simple cubic lattice. For near
critical quench interconnected domain morphology is observed. A brief period of
slow diffusive growth is followed by a linear viscous hydrodynamic growth that
lasts for an extended period of time. This result is in contradiction with
earlier inclusive reports of late time growth exponent 1/2 that questions the
uniqueness of the non-equilibrium universality for liquid-liquid and
vapor-liquid transitions.Comment: 6 pages, 5 figure
Freshwater Availability for Agriculture in Sundarbans. Variability due to changes in the summer monsoon under current and climate change conditions
The India–UK Water Centre (IUKWC) funded a Pump Priming Project (PPP) titled: “The influence of the monsoon on freshwater availability for agriculture in the Sundarbans region of West Bengal, India, under current and climate change conditions” between June and September 2019. This Knowledge Exchange brief was developed from the outputs of the activities conducted during this study: i) investigating the variability of the Indian Summer Monsoon (ISM) and the ensuing freshwater availability for agriculture in the Sundarbans region through the collection and analysis of climatic data and outputs from Global Climate Models (GCMs); and ii) understanding how changes in water resource availability are affecting livelihoods and discussing issues related to adaptation to those changes through meetings with farmers, NGOs and local government officials engaged in water resource management. The research results were communicated through a workshop with agricultural, water and climate scientists, NGOs and government stakeholders working in the Sundarbans region, where the team gained feedback, and shared knowledge and ideas for future research. This Brief was prepared by Professor Lalu Das, Principal Investigator (PI) and India Project Lead, and Professor Gautam Saha, both from Bidhan Chandra Krishi Viswavidyalaya (BCKV) in India, and Dr Alexandre Gagnon, UK Project Lead, and Dr Indrani Roy from Liverpool John Moores University (LJMU) in the UK
Nanodot to Nanowire: A strain-driven shape transition in self-organized endotaxial CoSi2 on Si (100)
We report a phenomenon of strain-driven shape transition in the growth of
nanoscale self-organized endotaxial CoSi2 islands on Si (100) substrates. Small
square shaped islands as small as 15\times15 nm2 have been observed. Islands
grow in the square shape following the four fold symmetry of the Si (100)
substrate, up to a critical size of 67 \times 67 nm2. A shape transition takes
place at this critical size. Larger islands adopt a rectangular shape with ever
increasing length and the width decreasing to an asymptotic value of ~25 nm.
This produces long wires of nearly constant width.We have observed nanowire
islands with aspect ratios as large as ~ 20:1. The long nanowire
heterostructures grow partly above (~ 3 nm) the surface, but mostly into (~17
nm) the Si substrate. These self-organized nanostructures behave as nanoscale
Schottky diodes. They may be useful in Si-nanofabrication and find potential
application in constructing nano devices.Comment: 9 pages, 7 figure
One-loop contribution to the neutrino mass matrix in NMSSM with right-handed neutrinos and tri-bimaximal mixing
Neutrino mass patterns and mixing have been studied in the context of
next-to-minimal supersymmetric standard model (NMSSM) with three gauge singlet
neutrino superfields. We consider the case with the assumption of R-parity
conservation. The vacuum expectation value of the singlet scalar field of
NMSSM induces the Majorana masses for the right-handed neutrinos as well as the
usual -term. The contributions to the light neutrino mass matrix at the
tree level as well as one-loop level are considered, consistent with the
tri-bimaximal pattern of neutrino mixing. Light neutrino masses arise at the
tree level through a TeV scale seesaw mechanism involving the right-handed
neutrinos. Although all the three light neutrinos acquire non-zero masses at
the tree-level, we show that the one-loop contributions can be comparable in
size under certain conditions.Comment: 14 pages, 7 figure
Exacerbated metastatic disease in a mouse mammary tumor model following latent gammaherpesvirus infection
BACKGROUND: Controversy exists as to the ability of human gammaherpesviruses to cause or exacerbate breast cancer disease in patients. The difficulty in conducting definitive human studies can be overcome by investigating developing breast cancer in a mouse model. In this study, we utilized mice latently infected with murine gammaherpesvirus 68 (HV-68) to question whether such a viral burden could exacerbate metastatic breast cancer disease using a mouse mammary tumor model. RESULTS: Mice latently infected with HV-68 had a similar primary tumor burden, but much greater metastatic disease, when compared to mock treated mice given the transplantable tumor, 4 T1. This was true for lung lesions, as well as secondary tumor masses. Increased expression of pan-cytokeratin and VEGF-A in tumors from HV-68 infected mice was consistent with increased metastatic disease in these animals. Surprisingly, no viral particles could be cultured from tumor tissues, and the presence of viral DNA or RNA transcripts could not be detected in primary or secondary tumor tissues. CONCLUSIONS: Latent HV-68 infection had no significant effect on the size of primary 4 T1 mammary tumors, but exacerbated the number of metastatic lung lesions and secondary tumors when compared to mock treated mice. Increased expression of the tumor marker, pan-cytokeratin, and VEGF-A in tumors of mice harboring latent virus was consistent with an exacerbated metastatic disease. Mechanisms responsible for this exacerbation are indirect, since no virus could be detected in cancerous tissues
Systemic neutralization of IL-17A significantly reduces breast cancer associated metastasis in arthritic mice by reducing CXCL12/SDF-1 expression in the metastatic niches
BACKGROUND: IL-17A is a pro-inflammatory cytokine that is normally associated with autoimmune arthritis and other pro-inflammatory conditions. Recently, IL-17A has emerged as a critical factor in enhancing breast cancer (BC)-associated metastases. We generated immune competent arthritic mouse models that develop spontaneous BC-associated bone and lung metastasis. Using these models, we have previously shown that neutralization of IL-17A resulted in significant reduction in metastasis. However, the underlying mechanism/s remains unknown. METHODS: We have utilized two previously published mouse models for this study: 1) the pro-arthritic mouse model (designated SKG) injected with metastatic BC cell line (4T1) in the mammary fat pad, and 2) the PyV MT mice that develop spontaneous mammary gland tumors injected with type II collagen to induce autoimmune arthritis. Mice were treated with anti-IL-17A neutralizing antibody and monitored for metastasis and assessed for pro-inflammatory cytokines and chemokines associated with BC-associated metastasis. RESULTS: We first corroborate our previous finding that in vivo neutralization of IL-17A significantly reduced metastasis to the bones and lungs in both models. Next, we report that treatment with anti-IL17A antibody significantly reduced the expression of a key chemokine, CXCL12 (also known as stromal derived factor-1 (SDF - 1)) in the bones and lungs of treated mice. CXCL12 is a ligand for CXCR4 (expressed on BC cells) and their interaction is known to be critical for metastasis. Interestingly, levels of CXCR4 in the tumor remained unchanged with treatment. Consequently, protein lysates derived from the bones and lungs of treated mice were significantly less chemotactic for the BC cells than lysates from untreated mice; and addition of exogenous SDF-1 to the lysates from treated mice completely restored BC cell migration. In addition, cytokines such as IL-6 and M-CSF were significantly reduced in the lung and bone lysates following treatment. The data presented suggests that systemic neutralization of IL-17A can block the CXCR4/SDF-1 signaling pathway by reducing the expression of SDF-1 in the metastatic niches and significantly reducing metastasis in both mouse models. CONCLUSION: In our model, neutralization of IL-17A regulates SDF-1 expression in the metastatic niches either directly or indirectly via reducing levels of IL-6 and M-CSF
Fetomaternal outcome in eclampsia
Background: Eclampsia is the third most common cause of maternal mortality, after haemorrhage and infection in the developing countries. Majority of cases of eclampsia are young primigravidas. The reduction in both maternal and perinatal morbidity and mortality remains the yard stick of success in the management of eclampsia.Methods: A hospital based analytical cross-sectional study was conducted among the pregnant women with eclampsia admitted in the department of Obstetrics and Gynecology in Regional Institute of Medical Sciences, Imphal. The study was conducted for a period of one and half years from September 2018 to March 2020.Results: Fifty-five (55) patients in the age group between 21 and 25 years constitute the maximum percentage of eclampsia (67.3%). Forty-five (81.8%) cases were antepartum eclampsia, 2 (3.6%) were intrapartum eclampsia and 8 (14.5%) cases were postpartum eclampsia. Majority (78.2%) of the cases were primigravidae, which is comparable to other studies. As much as 23 (41.8%) of the cases presented at 32-37 weeks period of gestation. There were two maternal deaths (3.6%) due to eclampsia related complications. There were 13 (21.7%) perinatal deaths in this study, out of which 10 (16.7%) were still births and 3(5%) were early neonatal deaths.Conclusions: Eclampsia is still an important obstetric emergency in the community contributing to significant maternal and perinatal morbidity and mortality. Eclampsia may not develop de novo and as such, it is not always a preventable condition. Early detection and prompt intervention of complications is vital to ensure a healthy outcome for both mother and baby
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