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Generalized causal set d'Alembertians
No full textOpen AccessWe introduce a family of generalized d’Alembertian operators in D-dimensional Minkowski spacetimes M D which are manifestly Lorentz-invariant, retarded, and non-local, the extent of the nonlocality being governed by a single parameter ρ. The prototypes of these operators arose in earlier work as averages of matrix operators meant to describe the propagation of a scalar field in a causal set. We generalize the original definitions to produce an infinite family of “Generalized Causet Box (GCB) operators” parametrized by certain coefficients {a, b n }, and we derive the conditions on the latter needed for the usual d’Alembertian to be recovered in the infrared limit. The continuum average of a GCB operator is an integral operator in M D , and it is these continuum operators that we mainly study. To that end, we compute their action on plane waves, or equivalently their Fourier transforms g(p) [p being the momentum-vector]. For timelike p, g(p) has an imaginary part whose sign depends on whether p is past or future-directed. For small p, g(p) is necessarily proportional to p · p, but for large p it becomes constant, raising the possibility of a genuinely Lorentzian perturbative regulator for quantum field theory in M D . We also address the question of whether or not the evolution defined by the GCB operators is stable, finding evidence that the original 4D causal set d’Alembertian is unstable, while its 2D counterpart is stable
Cyclodextrin inclusion Complexes with thiocholesterol and their self-assembly on gold: A combined electrochemical and lateral force microscopy analysis
No full textRestricted Access.The present study is an attempt to understand the properties of an interesting self-assembled monolayer system composed of inclusion complexes of thiocholesterol and cyclodextrins. Cyclodextrins were used as host compound while thiocholesterol was used as the entrant molecule into the cavity of cyclodextrins. The improved electron transfer barrier property towards a redox couple indicates a sturdy inclusion complex monolayer. A very large Rct value, 64.6 kΩ·cm2 for a redox system was obtained in the case of methyl-β-cyclodextrin and thiocholesterol inclusion complex self-assembled monolayer. A rather low value of capacitance 1.2 μF cm− 2 measured in supporting electrolyte further signifies the fact that inclusion complex monolayer is quite impermeable for ionic species. In addition lateral force microscopy combined with force–distance analysis revealed the presence of an interesting mixed hydrophilic/hydrophobic surface
Search for gravitational wave ringdowns from perturbed intermediate mass black holes in LIGO-Virgo data from 2005–2010
No full textOpen AccessWe report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency 50≤f0/Hz≤2000 and decay timescale 0.0001≲τ/s≲0.1 characteristic of those produced in mergers of IMBH pairs. No significant gravitational wave candidate was detected. We report upper limits on the astrophysical coalescence rates of IMBHs with total binary mass 50≤M/M⊙≤450 and component mass ratios of either 1:1 or 4:1. For systems with total mass 100≤M/M⊙≤150, we report a 90% confidence upper limit on the rate of binary IMBH mergers with nonspinning and equal mass components of 6.9×10−8 Mpc−3 yr−1. We also report a rate upper limit for ringdown waveforms from perturbed IMBHs, radiating 1% of their mass as gravitational waves in the fundamental, ℓ=m=2, oscillation mode, that is nearly three orders of magnitude more stringent than previous results
Comment on “Origin of tilted-phase generation in systems of ellipsoidal molecules with dipolar interactions’’
No full textOpen AccessIn this Comment, I point out that the physical origin of molecular tilt in the smectic phase, found in the Monte Carlo simulations of systems of rodlike molecules with two terminal antiparallel transverse dipole moments by Bose and Saha [Phys. Rev. E 86, 050701(R) (2012)], is similar to the one proposed by McMillan. In particular, unlike in smectic-C liquid crystals, in which the molecules are known to have practically free rotations about their long axes, the molecular rotations are found to be partially frozen in the simulations. Further, I suggest that the attractive interaction between correlated splay fluctuations of the antiparallel polarized sublayers which lie close to each other in adjacent molecular layers give rise to the tilting, rather than a reduced attractive interaction between dipoles belonging to the two dipolar sublayers within one molecular layer, as proposed by the authors
Transition metal (Fe, Co and Ni) oxide nanoparticles grafted graphitic carbon nitrides as efficient optical limiters and recyclable photocatalysts
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)A single-step pyrolysis assisted route towards the large scale fabrication of metal oxide nanoparticles (Fe2O3, Co3O4 and NiO) ingrained in graphitic carbon nitride (GCN) is demonstrated. Urea, an abundantly available precursor, plays a dual role during the synthesis: while it acts as a reducing agent, it also gets converted to GCN. The formation of GCN and the in-situ growth and embedment of oxide nanoparticles are discussed on the basis of the experimental results. The wide absorption of the samples in the visible light region makes them suitable for nonlinear transmission and photocatalytic activity studies. Visible light photocatalytic activities of the samples are studied by monitoring the degradation of Rhodamine B dye. Optical limiting properties of the prepared samples are studied through the open aperture z-scan technique using 5 ns laser pulses at a wavelength of 532 nm. The cost-efficient and time saving synthetic approach is complemented by the magnetic behaviour of the samples, which enables their use as recyclable photocatalyst and magnetically controllable optical limiters
Application of a Hough search for continuous gravitational waves on data from the fifth LIGO science run
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report on an all-sky search for periodic gravitational waves in the frequency range 50–1000 Hz with the first derivative of frequency in the range −8.9 × 10−10 Hz s−1 to zero in two years of data collected during LIGO's fifth science run. Our results employ a Hough transform technique, introducing a χ2 test and analysis of coincidences between the signal levels in years 1 and 2 of observations that offers a significant improvement in the product of strain sensitivity with compute cycles per data sample compared to previously published searches. Since our search yields no surviving candidates, we present results taking the form of frequency dependent, 95% confidence upper limits on the strain amplitude h0. The most stringent upper limit from year 1 is 1.0 × 10−24 in the 158.00–158.25 Hz band. In year 2, the most stringent upper limit is 8.9 × 10−25 in the 146.50–146.75 Hz band. This improved detection pipeline, which is computationally efficient by at least two orders of magnitude better than our flagship Einstein@Home search, will be important for 'quick-look' searches in the Advanced LIGO and Virgo detector era
In situ fabrication of electrochemically grown mesoporous metallic thin films by anodic dissolution in deep eutectic solvents.
No full textRestricted Access.We describe here a simple electrodeposition process of forming thin films of noble metallic nanoparticles such as Au, Ag and Pd in deep eutectic solvents (DES). The method consists of anodic dissolution of the corresponding metal in DES followed by the deposition on the cathodic surface. The anodic dissolution process in DES overcomes the problems associated with copious hydrogen and oxygen evolution on the electrode surface when carried out in aqueous medium. The proposed method utilizes the inherent abilities of DES to act as a reducing medium while simultaneously stabilizing the nanoparticles that are formed. The mesoporous metal films were characterized by SEM, XRD and electrochemical techniques. Potential applications of these substrates in surface enhanced Raman spectroscopy and electrocatalysis have been investigated. A large enhancement of Raman signal of analyte was achieved on the mesoporous silver substrate after removing all the stabilizer molecules from the surface by calcination. The highly porous texture of the electrodeposited film provides superior electro catalytic performance for hydrogen evolution reaction (HER). The mechanisms of HER on the fabricated substrates were studied by Tafel analysis and electrochemical impedance spectroscopy (EIS)
Work fluctuations for a Brownian particle driven by a correlated external random force
No full textopen AccessWe have considered the underdamped motion of a Brownian particle in the presence of a correlated external random force. The force is modeled by an Ornstein-Uhlenbeck process. We investigate the fluctuations of the work done by the external force on the Brownian particle in a given time interval in the steady state. We calculate the large deviation functions as well as the complete asymptotic form of the probability density function of the performed work. We also discuss the symmetry properties of the large deviation functions for this system. Finally we perform numerical simulations and they are in a very good agreement with the analytic results
The First Murchison Widefield Array low-frequency radio observations of cluster scale non-thermal emission: the case of Abell 3667
No full textOpen AccessWe present the first Murchison Widefield Array observations of the well-known cluster of galaxies Abell 3667 (A3667) between 105 and 241 MHz. A3667 is one of the best known examples of a galaxy cluster hosting a double radio relic and has been reported to contain a faint radio halo and bridge. The origin of radio haloes, relics and bridges is still unclear, however galaxy cluster merger seems to be an important factor. We clearly detect the north-west (NW) and south-east radio relics in A3667 and find an integrated flux density at 149 MHz of 28.1 ± 1.7 and 2.4 ± 0.1 Jy, respectively, with an average spectral index, between 120 and 1400 MHz, of −0.9 ± 0.1 for both relics. We find evidence of a spatial variation in the spectral index across the NW relic steepening towards the centre of the cluster, which indicates an ageing electron population. These properties are consistent with higher frequency observations. We detect emission that could be associated with a radio halo and bridge. However, due to the presence of poorly sampled large-scale Galactic emission and blended point sources we are unable to verify the exact nature of these features