145 research outputs found
SARAS 2: A Spectral Radiometer for probing Cosmic Dawn and the Epoch of Reionization through detection of the global 21 cm signal
The global 21 cm signal from Cosmic Dawn (CD) and the Epoch of Reionization
(EoR), at redshifts , probes the nature of first sources of
radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the
signal is predicted to be extremely weak, of wide fractional bandwidth, and
lies in a frequency range that is dominated by Galactic and Extragalactic
foregrounds as well as Radio Frequency Interference, detection of the signal is
a daunting task. Critical to the experiment is the manner in which the sky
signal is represented through the instrument. It is of utmost importance to
design a system whose spectral bandpass and additive spurious can be well
calibrated and any calibration residual does not mimic the signal. SARAS is an
ongoing experiment that aims to detect the global 21 cm signal. Here we present
the design philosophy of the SARAS 2 system and discuss its performance and
limitations based on laboratory and field measurements. Laboratory tests with
the antenna replaced with a variety of terminations, including a network model
for the antenna impedance, show that the gain calibration and modeling of
internal additives leave no residuals with Fourier amplitudes exceeding 2~mK,
or residual Gaussians of 25 MHz width with amplitudes exceeding 2~mK. Thus,
even accounting for reflection and radiation efficiency losses in the antenna,
the SARAS~2 system is capable of detection of complex 21-cm profiles at the
level predicted by currently favoured models for thermal baryon evolution.Comment: 44 pages, 17 figures; comments and suggestions are welcom
INTEND AND PROPOSE THE HIGH SPEED LFSR CIRCUIT USING SST METHOD
Linear feedback shift register (LFSR) is an important component of the cyclic redundancy check (CRC) operations and BCH encoders. This thesis presents a mathematical proof of existence of a linear transformation to transform LFSR circuits into equivalent state space formulations. This transformation achieves a full speed-up compared to the serial architecture at the cost of an increase in hardware overhead. This method applies to all irreducible polynomials used in CRC operations and BCH encoders. A new formulation is proposed to modify the LFSR into the form of an CRC filter. We propose a novel high speed parallel LFSR architecture based on parallel Infinite Impulse Response (CRC) filter design, pipelining and retiming algorithms. The advantage of proposed approach over the previous architectures is that it has both feedforward and feedback paths. We further propose to apply combined parallel and pipelining techniques to eliminate the fanout effect in long generator polynomials. The proposed scheme can be applied to any generator polynomial, i.e., any LFSR in general. A comparison between the proposed and previous architectures shows that the proposed parallel architecture achieves the same critical path as that of previous designs with a reduced hardware cost
Anti-Herpes Simplex Virus (HSV-1 and HSV-2) activity of biogenic gold and silver nanoparticles using seaweed Sargassum wightii
1252-1257Biogenic gold (Au) and silver (Ag) nanoparticles were synthesized using seaweed Sargassum wightii (Sw) and their antiviral activity against Herpes Simplex Virus (HSV-1 and HSV-2) was evaluated. Efficacy of Sw-Au and Sw-Ag nanoparticles against HSV was estimated by the reduction of cytopathic effect (CPE) caused by HSV, which was observed in a dose-dependent manner. Sw-Au nanoparticles reduced 70% CPE of HSV-1 and HSV-2 at 10 μL and 25 μL, respectively, whereas 2.5 μL Sw-Ag nanoparticles effectively reduced 70% CPE of HSV-1 and HSV-2. Cytotoxicity was estimated in Vero cells by MTT assay. Sw-Au nanoparticles were significantly non-toxic in all the concentrations tested, whereas Sw-Ag nanoparticles were found to be toxic in higher concentrations. Sw-Au nanoparticles showed cell viability of 93.12-85.18 % in the range of 2.5-25 µL, and Sw-Ag nanoparticles showed cell viability of 97.21-21.91% in the range of 1-10 μL. Sw-Au and Sw-Ag nanoparticles effectively reduce the CPE caused by both HSV-1 and HSV-2 in Vero cells and can be used to treat HSV infections
The giant lobes of Centaurus A observed at 118 MHz with the Murchison Widefield Array
We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118MHz with the Murchison Widefield Array (MWA) 32-tile prototype, with which we investigate the spectral-index distribution of Cen A's giant radio lobes.We compa
The prognostic value of the hypoxia markers CA IX and GLUT 1 and the cytokines VEGF and IL 6 in head and neck squamous cell carcinoma treated by radiotherapy ± chemotherapy
BACKGROUND: Several parameters of the tumor microenvironment, such as hypoxia, inflammation and angiogenesis, play a critical role in tumor aggressiveness and treatment response. A major question remains if these markers can be used to stratify patients to certain treatment protocols. The purpose of this study was to investigate the inter-relationship and the prognostic significance of several biological and clinicopathological parameters in patients with head and neck squamous cell carcinoma (HNSCC) treated by radiotherapy ± chemotherapy. METHODS: We used two subgroups of a retrospective series for which CT-determined tumoral perfusion correlated with local control. In the first subgroup (n = 67), immunohistochemistry for carbonic anhydrase IX (CA IX) and glucose transporter-1 (GLUT-1) was performed on the pretreatment tumor biopsy. In the second subgroup (n = 34), enzyme linked immunosorbent assay (ELISA) was used to determine pretreatment levels of the cytokines vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) in serum. Correlation was investigated between tumoral perfusion and each of these biological markers, as well as between the markers mutually. The prognostic value of these microenvironmental parameters was also evaluated. RESULTS: For CA IX and GLUT-1, the combined assessment of patients with both markers expressed above the median showed an independent correlation with local control (p = 0.02) and disease-free survival (p = 0.04) with a trend for regional control (p = 0.06). In the second subgroup, IL-6 pretreatment serum level above the median was the only independent predictor of local control (p = 0.009), disease-free survival (p = 0.02) and overall survival (p = 0.005). CONCLUSION: To our knowledge, we are the first to report a link in HNSCC between IL-6 pretreatment serum levels and radioresistance in vivo. This link is supported by the strong prognostic association of pretreatment IL-6 with local control, known to be the most important parameter to judge radiotherapy responses. Furthermore, the combined assessment of CA IX and GLUT-1 correlated independently with prognosis. This is a valuable indication that a combined approach is important in the investigation of prognostic markers
The Murchison Widefield Array Transients Survey (MWATS). A search for low frequency variability in a bright Southern hemisphere sample
We report on a search for low-frequency radio variability in 944 bright (>
4Jy at 154 MHz) unresolved, extragalactic radio sources monitored monthly for
several years with the Murchison Widefield Array. In the majority of sources we
find very low levels of variability with typical modulation indices < 5%. We
detect 15 candidate low frequency variables that show significant long term
variability (>2.8 years) with time-averaged modulation indices M = 3.1 - 7.1%.
With 7/15 of these variable sources having peaked spectral energy
distributions, and only 5.7% of the overall sample having peaked spectra, we
find an increase in the prevalence of variability in this spectral class. We
conclude that the variability seen in this survey is most probably a
consequence of refractive interstellar scintillation and that these objects
must have the majority of their flux density contained within angular diameters
less than 50 milli-arcsec (which we support with multi-wavelength data). At 154
MHz we demonstrate that interstellar scintillation time-scales become long
(~decades) and have low modulation indices, whilst synchrotron driven
variability can only produce dynamic changes on time-scales of hundreds of
years, with flux density changes less than one milli-jansky (without
relativistic boosting). From this work we infer that the low frequency
extra-galactic southern sky, as seen by SKA-Low, will be non-variable on
time-scales shorter than one year.Comment: 19 pages, 11 figure
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