Simplified Production of Large Prototypes using Visible Slicing

Rapid Prototyping (RP) is a totally automatic generative manufacturing technique based on a “divide-and-conquer” strategy called ‘slicing’. Simple slicing used on 2.5-axis kinematics of the existing RP machines is responsible for the staircase error. Although thinner slices will have less error, the slice thickness has practical limits. Visible Slicing overcomes these limitations. A few visible slices exactly represent the object. Each visible slice can be realized using a 3- axis kinematics machine from two opposite directions. Visible slicing is implemented on Segmented Object Manufacturing (SOM) machine under development. SOM can produce soft large prototypes faster and cheaper with accuracy comparable to that of CNC machining.Mechanical Engineerin

Enhanced Li Capacity in Functionalized Graphene: A First Principle Study with van der Waals Correction

We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material in Li-batteries. We find a high specific capacity of ~860 mAhg-1 by functionalizing the graphene sheet. This capacity is higher than the previously reported capacities that were achieved on graphene with high concentration of Stone-Wales (75%) and divacancy (16%) defects. Creating such high density of defects can make the entire system energetically unstable, whereas graphene oxide is a naturally occurring substance

Octonion Quantum Chromodynamics

Starting with the usual definitions of octonions, an attempt has been made to establish the relations between octonion basis elements and Gell-Mann \lambda matrices of SU(3)symmetry on comparing the multiplication tables for Gell-Mann \lambda matrices of SU(3)symmetry and octonion basis elements. Consequently, the quantum chromo dynamics (QCD) has been reformulated and it is shown that the theory of strong interactions could be explained better in terms of non-associative octonion algebra. Further, the octonion automorphism group SU(3) has been suitably handled with split basis of octonion algebra showing that the SU(3)_{C}gauge theory of colored quarks carries two real gauge fields which are responsible for the existence of two gauge potentials respectively associated with electric charge and magnetic monopole and supports well the idea that the colored quarks are dyons

Quaternion-Octonion Unitary Symmetries and Analogous Casimir Operators

An attempt has been made to investigate the global SU(2) and SU(3) unitary flavor symmetries systematically in terms of quaternion and octonion respectively. It is shown that these symmetries are suitably handled with quaternions and octonions in order to obtain their generators, commutation rules and symmetry properties. Accordingly, Casimir operators for SU(2)and SU(3) flavor symmetries are also constructed for the proper testing of these symmetries in terms of quaternions and octonions

Quaternion Octonion Reformulation of Quantum Chromodynamics

We have made an attempt to develop the quaternionic formulation of Yang - Mill's field equations and octonion reformulation of quantum chromo dynamics (QCD). Starting with the Lagrangian density, we have discussed the field equations of SU(2) and SU(3) gauge fields for both cases of global and local gauge symmetries. It has been shown that the three quaternion units explain the structure of Yang- Mill's field while the seven octonion units provide the consistent structure of SU(3)_{C} gauge symmetry of quantum chromo dynamics

Intergalactic UV Background Radiation Field

We have performed proximity effect analysis of low and high resolution data, considering detailed frequency and redshift dependence of the AGN spectra processed through galactic and intergalactic material. We show that such a background flux, calculated using the observed distribution of AGNs, falls short of the value required by the proximity effect analysis by a factor of $\ge$ 2.7. We have studied the uncertainty in the value of the required flux due to its dependence on the resolution, description of column density distribution, systemic redshifts of QSOs etc. We conclude that in view of these uncertainties the proximity effect is consistent with the background contributed by the observed AGNs and that the hypothesized presence of an additional, dust extinct, population of AGNs may not be necessary.Comment: To be published in the Journal of Astronomy and Astrophysics aasms, 2 figures, 2 tables. Paper replaced to include the figure

Hubble Space Telescope Observations of Element Abundances in Low-redshift Damped Lyman-alpha Galaxies and Implications for the Global Metallicity-Redshift Relation

Most models of cosmic chemical evolution predict that the mass-weighted mean interstellar metallicity of galaxies should rise with time from a low value $\sim 1/30$ solar at $z \sim 3$ to a nearly solar value at $z = 0$. In the absence of any selection effects, the damped Lyman-alpha absorbers (DLAs) in quasar spectra are expected to show such a rise in global metallicity. However, it has been difficult to determine whether or not DLAs show this effect, primarily because of the very small number of DLA metallicity measurements at low redshifts. In an attempt to put tighter constraints on the low-redshift end of the DLA metallicity-redshift relation, we have observed Zn II and Cr II lines in four DLAs at $0.09 < z < 0.52$, using the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST). These observations have provided the first constraints on Zn abundances in DLAs with $z < 0.4$. In all the three DLAs for which our observations offer meaningful constraints on the metallicity, the data suggest that the metallicities are much lower than the solar value. These results are consistent with recent imaging studies indicating that these DLAs may be associated with dwarf or low surface brightness galaxies. We combine our results with higher redshift data from the literature to estimate the global mean metallicity-redshift relation for DLAs. We find that the global mean metallicity shows at most a slow increase with decreasing redshift. ...(Please see the paper for the complete abstract).Comment: 56 pages, including 13 figures. Accepted for publication in the Astrophysical Journa

Exploring the dust content of SDSS DR7 damped Lyman alpha systems at 2.15≤zab<\le z_{ab}< 5.2

We have studied a sample of 1084 intervening absorption systems with 2.15$\le z_{ab}\le$5.2, having log(N$_{\rm HI}$) $>$ 20.0 in the spectra of QSOs in Sloan Digital Sky Survey (SDSS) data release 7 (DR7), with the aim of understanding the nature and abundance of the dust and the chemical abundances in the DLA absorbers. Composite spectra were constructed for the full sample and several subsamples, chosen on the basis of absorber and QSO properties. Average extinction curves were obtained for the samples by comparing their geometric mean composite spectra with those of two samples of QSOs, matching in z$_{em}$ and i magnitude with the DLA sample, one sample without any absorbers along their lines of sight and the other without any DLAs along their lines of sight irrespective of the presence of other absorption systems. While the average reddening in the DLA sample is small, we find definite evidence for the presence of dust in subsamples based on absorber properties, in particular the strength of metal absorption lines. DLAs along lines of sight to QSOs which are not colour selected are found to be more dusty compared to those along the lines of sight to the more numerous colour selected QSOs. From these studies and from the strengths of absorption lines in the composite spectra, we conclude that $\le$ 10% of the DLAs in SDSS DR7 cause significant reddening, have stronger absorption lines and have higher abundances as compared to the rest of the sample. The rest of the sample shows little reddening. Due to the dominant color selection method used to target QSOs in the SDSS DR7, this fraction of 10% likely represents a lower limit for the global fraction of dusty DLAs at high-z.Comment: 12 pages, 9 figures. To appear in MNRA

Computationally Efficient Algorithm for Detecting Moving Objects with Moving Background

Abstract— The area of moving object detection has been a constant topic of research in more than a decade, where a research community have witnessed various significant contribution in the past that mitigates the problem of real-time and moving object detection. In our prior studies, we have addressed such issues using various sophisticated technique yielding superior results. But, it is felt that some light weight algorithm is required for the purpose of performing moving object detection with complete retention of object detection accuracy. This paper have presented a very simple algorithm that uses visual descriptor for extracting the dynamic features during fast transition of frames. The proposed algorithm is tested with one of the most significant work done recently on same purpose with respect to precision and recall rate along with analysis of processing time of proposed algorithm