ABSTRACT
A new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h of data obtained with the Low-Frequency Array (LOFAR). The analysis includes ...significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted power spectrum inference. Previously seen ‘excess power’ due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25–0.45 MHz and is partially correlated between nights, especially in the foreground wedge region. The correlation is stronger between nights covering similar local sidereal times. A best 2-σ upper limit of $\Delta ^2_{21} \lt (73)^2\, \mathrm{mK^2}$ at $k = 0.075\, \mathrm{h\, cMpc^{-1}}$ is found, an improvement by a factor ≈8 in power compared to the previously reported upper limit. The remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radiofrequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.
ABSTRACT
We derive constraints on the thermal and ionization states of the intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits on the 21-cm power spectrum measured by the LOFAR radio ...telescope and a prior on the ionized fraction at that redshift estimated from recent cosmic microwave background (CMB) observations. We have used results from the reionization simulation code grizzly and a Bayesian inference framework to constrain the parameters which describe the physical state of the IGM. We find that, if the gas heating remains negligible, an IGM with ionized fraction ≳0.13 and a distribution of the ionized regions with a characteristic size ≳ 8 h−1 comoving megaparsec (Mpc) and a full width at half-maximum (FWHM) ≳16 h−1 Mpc is ruled out. For an IGM with a uniform spin temperature TS ≳ 3 K, no constraints on the ionized component can be computed. If the large-scale fluctuations of the signal are driven by spin temperature fluctuations, an IGM with a volume fraction ≲0.34 of heated regions with a temperature larger than CMB, average gas temperature 7–160 K, and a distribution of the heated regions with characteristic size 3.5–70 h−1 Mpc and FWHM of ≲110 h−1 Mpc is ruled out. These constraints are within the 95 per cent credible intervals. With more stringent future upper limits from LOFAR at multiple redshifts, the constraints will become tighter and will exclude an increasingly large region of the parameter space.
ABSTRACT
The ARCADE2 and LWA1 experiments have claimed an excess over the cosmic microwave background (CMB) at low radio frequencies. If the cosmological high-redshift contribution to this radio ...background is between 0.1 per cent and 22 per cent of the CMB at 1.42 GHz, it could explain the tentative EDGES low-band detection of the anomalously deep absorption in the 21-cm signal of neutral hydrogen. We use the upper limit on the 21-cm signal from the Epoch of Reionization (z = 9.1) based on 141 h of observations with LOFAR to evaluate the contribution of the high-redshift Universe to the detected radio background. Marginalizing over astrophysical properties of star-forming haloes, we find (at 95 per cent CL) that the cosmological radio background can be at most 9.6 per cent of the CMB at 1.42 GHz. This limit rules out strong contribution of the high-redshift Universe to the ARCADE2 and LWA1 measurements. Even though LOFAR places limit on the extra radio background, excess of 0.1–9.6 per cent over the CMB (at 1.42 GHz) is still allowed and could explain the EDGES low-band detection. We also constrain the thermal and ionization state of the gas at z = 9.1, and put limits on the properties of the first star-forming objects. We find that, in agreement with the limits from EDGES high-band data, LOFAR data constrain scenarios with inefficient X-ray sources, and cases where the Universe was ionized by stars in massive haloes only.
Microwave-vacuum dehydration characteristics of button mushroom (
Agaricus bisporus) were evaluated in a commercially available microwave oven (0–600
W) modified to a drying system by incorporating a ...vacuum chamber in the cavity. The effect of drying parameters, namely microwave power, system pressure and product thickness on the drying kinetics and rehydration characteristics were investigated. The drying system was operated in the microwave power range of 115–285
W, pressure range of 6.5–23.5
kPa having mushroom slices of 6–14
mm thickness. Convective air drying at different air temperatures (50, 60 and 70
°C) was performed to compare the drying rate and rehydration properties of microwave-vacuum drying with conventional method. Microwave-vacuum drying resulted in 70–90% decrease in the drying time and the dried products had better rehydration characteristics as compared to convective air drying. The rate constants of the exponential and Page’s model for thin layer drying were established by regression analysis of the experimental data which were found to be affected mainly by the microwave power level followed by sample thickness while system pressure had a little effect on the drying rate. Rehydration ratio was significantly affected by the system pressure. Empirical models are also developed for estimating the drying rate constant and rehydration ratio as a function of the microwave-vacuum drying process parameters.
Ionic liquids (ILs) are important for their antimicrobial activity and are found to be toxic to some microorganisms. To shed light on the mechanism of their activities, the interaction of an ...imidazolium-based IL 1-butyl-3-methylimidazolium tetrfluoroborate (BMIMBF4) with E. coli bacteria and cell-membrane-mimicking lipid mono- and bilayers has been studied. The survival of the bacteria and corresponding growth inhibition are observed to be functions of the concentration of the IL. The IL alters the pressure–area isotherm of the monolayer formed at an air–water interface by the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid. The in-plane elasticity of the lipid layer is reduced as a consequence of the insertion of this IL. The X-ray reflectivity study from a polymer-supported lipid bilayer shows strong perturbation in the self-assembled structure of the bilayer due to the interaction. As a consequence, there is a considerable decrease in bilayer thickness and a corresponding increase in electron density. These results, however, depend on the chain configurations of the lipid molecules.
This paper presents a review of the advances of deteriorating inventory literature since the early 1990s. The models available in the relevant literature have been suitably classified by the ...shelf-life characteristic of the inventoried goods. They have further been sub-classified on the basis of demand variations and various other conditions or constraints. The motivations, extensions and generalizations of various models in each sub-class have been discussed in brief to bring out pertinent information regarding model developments in the last decade.
ABSTRACT
We compare various foreground removal techniques that are being utilized to remove bright foregrounds in various experiments aiming to detect the redshifted 21 cm signal of neutral hydrogen ...from the epoch of reionization. In this work, we test the performance of removal techniques (FastICA, GMCA, and GPR) on 10 nights of LOFAR data and investigate the possibility of recovering the latest upper limit on the 21 cm signal. Interestingly, we find that GMCA and FastICA reproduce the most recent 2σ upper limit of $\Delta ^2_{21} \lt $ (73)2 mK2 at k = 0.075 hcMpc−1, which resulted from the application of GPR. We also find that FastICA and GMCA begin to deviate from the noise-limit at k-scales larger than ∼0.1 hcMpc−1. We then replicate the data via simulations to see the source of FastICA and GMCA’s limitations, by testing them against various instrumental effects. We find that no single instrumental effect, such as primary beam effects or mode-mixing, can explain the poorer recovery by FastICA and GMCA at larger k-scales. We then test scale-independence of FastICA and GMCA, and find that lower k-scales can be modelled by a smaller number of independent components. For larger scales (k ≳ 0.1 hcMpc−1), more independent components are needed to fit the foregrounds. We conclude that, the current usage of GPR by the LOFAR collaboration is the appropriate removal technique. It is both robust and less prone to overfitting, with future improvements to GPR’s fitting optimization to yield deeper limits.
Stable molecular Bose-Einstein condensate (MBEC) can be formed through the Bose-stimulated Raman adiabatic passage from atomic Bose-Einstein condensate (ABEC) via an intermediate excited MBEC state. ...Such a three-mode atom-molecule Bose-Einstein condensates (AMBECs) system is consists of three Bose-Einstein condensates (BECs) in which there are one ABEC, one excited MBEC, and one stable MBEC. Nonzero intermodal couplings and intramodal interactions are present in the system. The free-bound coupling is present between the ABEC and the excited MBEC, and the bound-bound coupling is present between the excited MBEC and the stable MBEC. The intraspecies interactions are due to the third order nonlinearity of the system. The quantum mechanical Hamiltonian of the system is constructed considering the intermodal couplings and intramodal interactions. We solve the system Hamiltonian analytically to find out the time evaluation of the field operators associated with all three BEC modes. In our solution process we have considered up to the second order of all coupling and interaction constants. Employing these solutions and starting from an initial composite coherent state of three BEC modes, we study the second order quantum coherence function of three pure BEC modes and three coupled modes (ABEC-exited MBEC, excited MBEC-stable MBEC, and ABEC-stable MBEC). Quantum antibunching is reported in all three pure BEC modes and in ABEC-excited MBEC, excited MBEC-stable MBEC coupled modes whereas the joint mode of ABEC and stable MBEC is always coherent. We also study the quantum statistical properties of the system by introducing an initial phase to the coherent states of pure BEC modes. The quantum statistical properties of different pure and coupled modes also depend on the initial phase angles of the pure BEC modes. A comprehensive study on this is also reported here.
Ultracold atoms in the atomic Bose-Einstein condensate (ABEC) state can form molecular Bose-Einstein condensate (MBEC) through photoassociation. In the atom-molecule Bose-Einstein condensates (BECs), ...two or more atoms in the ABEC can combine to form a molecule in the MBEC and again a molecule from a MBEC can decompose to atoms in the ABEC. The Bose-stimulated Raman adiabatic passage is an efficient mechanism for conversion of an atomic BEC to a molecular BEC. A three-mode atom-molecule Bose-Einstein condensates system can be prepared through the photoassociative Bose-stimulated Raman adiabatic passage. In our system, three modes are one ABEC, one excited MBEC, and one stable MBEC. The intramodal interactions due to the χ(3) nonlinearity is present in all three BEC modes along with ABEC-excited MBEC and excited MBEC-stable MBEC intermodal couplings. The quantum mechanical Hamiltonian of the system is constructed considering all three intraspecies interactions and intermodal couplings among the modes. The Hamiltonian of the system is solved analytically using a special intuitive approach which is more general and gives more accurate result than the well-known short time approximation method. The correctness of the solution is verified through the equal time commutation relation. Staring from a three-mode composite coherent state we compute the time evolution of the field annihilation operators of all three modes in presence of all possible interactions and couplings. Using these solutions, we investigate the quantum entanglement properties of the system for all three two-mode combinations. Entanglement is found for two combinations of modes, where as one combination is always separable. Also, we study the dependence of the entanglement properties of the system with the interaction and coupling constants.
•The present studies effective removal of xylene under transient and high loading conditions.•More than 90% RE was obtained up to inlet loading rate of 350gm−3h−1.•The maximum EC of 405.7gm−3h−1 was ...observed at an inlet loading of 538.8gm−3h−1.•The Ottengraf’s model was found to be applicable in all phases of biofilter operation.•Bacillus sp. was found the dominating group in the biofilm.
The main objective of this study was to evaluate the performance of wood charcoal as biofilter media under transient and high loading condition. Biofiltration of xylene was investigated for 150days in a laboratory scale unit packed with wood charcoal and inoculated with mixed microbial culture at the xylene loading rates ranged from 12 to 553gm−3h−1. The kinetic analysis of the xylene revealed absence of substrate inhibition and possibility of achieving higher elimination under optimum condition. The pH, temperature, pressure drop and CO2 production rate were regularly monitored during the experiments. Throughout experimental period, the removal efficiency (RE) was found to be in the range of 65–98.7% and the maximum elimination capacity (EC) was 405.7gm−3h−1. Molecular characterization results show Bacillus sp. as dominating microbial group in the biofilm.
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