Beyond the Horizon

Cosmic horizons arise in general relativity in the context of black holes and in certain cosmologies. Classically, regions beyond a horizon are inaccessible to causal observers. However, quantum mechanical correlations may exist across horizons that may influence local observations. For the case of de Sitter space, we show how a single particle excitation behind the horizon changes the density matrix governing local observables. As compared to the vacuum state, we calculate the change in the average energy and entropy per unit volume. This illustrates what may be a generic property allowing some features of spacetime beyond a horizon to be inferred.Comment: 9 pages, 1 figur

Dispersionless motion in a driven periodic potential

Recently, dispersionless (coherent) motion of (noninteracting) massive Brownian particles, at intermediate time scales, was reported in a sinusoidal potential with a constant tilt. The coherent motion persists for a finite length of time before the motion becomes diffusive. We show that such coherent motion can be obtained repeatedly by applying an external zero-mean square-wave drive of appropriate period and amplitude, instead of a constant tilt. Thus, the cumulative duration of coherent motion of particles is prolonged. Moreover, by taking an appropriate combination of periods of the external field, one can postpone the beginning of the coherent motion and can even have coherent motion at a lower value of position dispersion than in the constant tilt case.Comment: 4 pages, 4 figure

Aperiodic tumbling of microrods advected in a microchannel flow

We report on an experimental investigation of the tumbling of microrods in the shear flow of a microchannel (40 x 2.5 x 0.4 mm). The rods are 20 to 30 microns long and their diameters are of the order of 1 micron. Images of the centre-of-mass motion and the orientational dynamics of the rods are recorded using a microscope equipped with a CCD camera. A motorised microscope stage is used to track individual rods as they move along the channel. Automated image analysis determines the position and orientation of a tracked rods in each video frame. We find different behaviours, depending on the particle shape, its initial position, and orientation. First, we observe periodic as well as aperiodic tumbling. Second, the data show that different tumbling trajectories exhibit different sensitivities to external perturbations. These observations can be explained by slight asymmetries of the rods. Third we observe that after some time, initially periodic trajectories lose their phase. We attribute this to drift of the centre of mass of the rod from one to another stream line of the channel flow.Comment: 14 pages, 8 figures, as accepted for publicatio

The layer disorders defect in coir fiber under thermal and chemical treatment

Natural coir fibers, subjectd to thermal treatments in the range of 0oC to 200oC and alkali treatment with 5% to 30% concentration w/w, have been used in the present investigation to determine the interlayer variability of the cellulose planes (020), (110) and (110). Among the equatorial reflections (110), (110) and (020), the extent of variability is found to be more with the proportion of such affected planes less for (020) reflection in the native cellulose at lower temperature while at higher temperature (110) and (110) become more affected by variability defect. (110) and (1 10) planes are more affected also with alkali treatment.The layer disorders defect in coir fiber under thermal and chemical treatment D N Mahato*, B K Mathur and S Bhattacharjee Department of Physics, Indian Institute of Technology, Kharagpur-721 302, West Bengal, India E-mail : [email protected] of Physics, Indian Institute of Technology, Kharagpur-721 302, West Bengal, Indi

Gravitational Constant and Torsion

Riemann-Cartan space time $U_{4}$ is considered here. It has been shown that when we link topological Nieh-Yan density with the gravitational constant then we get Einstein-Hilbert Lagrangian as a consequence.Comment: 8 page

Effects of Row Spacings and Varieties on Grain Yield and Economics of Maize

Maize is the second most important crop of Nepal. The yield of the crop is low due to lack of appropriate plant density for the varieties. The field experiment was carried out to study the effect of different row spacings on different maize varieties at Deupur, Lamahi municipality of the dang district in province No. 5, Nepal during the rainy season from June to September, 2018. Four levels of spacings (boardcasting and three row spacings of 45, 60 and 75 cm) and two maize varieties (Rampur Composite and Arun-2) were evaluated using randomized complete block design with three replications. The highest grain yield was found in Rampur Composite and Arun-2 while they were planted with row spacing of 60 cm with plant to plant spacing of 25 cm. The highest grain yield, cob length, cob circumference, number of rows per cob, thousand grain weight  were reported when maize was planted in the  row spacing 60×25cm. Among the maize varieties, Rampur Composite produced the highest grain yield, cob length, cob circumference, number of rows per cob as compared to Arun-2. This study suggested that maize production can be maximized by cultivating maize varieties with row spacing of 60 cm with plant to plant spacing of 25 cm