2,133 research outputs found
Energy dependent wavelength of the ion induced nanoscale ripple
Wavelength variation of ion beam induced nanoscale ripple structure has
received much attention recently due to its possible application in
nanotechnology. We present here results of Ar bombarded Si in the energy
range 50 to 140 keV to demonstrate that with beam scanning the ripple
wavelength increases with ion energy and decreases with energy for irradiation
without ion beam scanning. An expression for the energy dependence of ripple
wavelength is proposed taking into simultaneous effect of thermally activated
surface diffusion and ion induced effective surface diffusion.Comment: REVTeX (4 pages), 3 EPS figure
On Labour Migration in India: Trends, Causes and Impacts
The paper considers the issue of labour migration which is very significant for economic development of any nation. It presents in a nutshell the trends and patterns of migration in India, its causes and impacts as discussed in the literature so far. After doing a rigorous survey of the literature we observe that the issue is, in some sense, neglected and its importance is underestimated. Hence, the paper would serve as a useful guide to the future research on this area
What does it mean for urban life to see livestock grazing in post-industrial American cities?
Until the nineteenth century, American urban dwellers cohabited with livestock and cities formed ecologically diverse spaces. In the late nineteenth century, a series of urban livestock policies coupled with industrial agricultural transformations displaced livestock to urban fringes and rural areas. These developments radically altered human–animal relationships in the urban context, limited economic opportunity and over time have shaped contemporary issues of food access and food justice within cities. Post-industrial cities in the United States, such as Detroit, are characterised by patterns of urban shrinkage and high levels of vacancy. Within this context, urban farming has emerged as a framework and movement to stabilise communities, address local food access and leverage vacancy towards new models of occupation. In 2013, the City of Detroit Urban Agricultural Ordinance was passed to formalise decades of community-driven urban agricultural practices. The ordinance provides guidelines for urban farms and gardens and for managing allied resources. Deliberation on urban agriculture and livestock ordinances continues today. While existing policies provide a framework for food-based development of neighbourhoods, they remain focused on the incremental scale of existing single-family housing and adjacent vacant plots versus larger assemblages that may participate in the production of new urban collectives and assemblages. Detroit’s current context presents opportunities to scale operations via new urban design typologies and socially integrated models that leverage vacancy to construct alternate, collective models of urban life. A speculative urban design proposition for Riverbend Farming Cooperative is presented and proposes a courtyard-based cooperative farming development incorporating permaculture and animal husbandry within a formerly residential superblock as an alternative model of urban development. Through this design speculation, the article reflects upon the social, economic and ecological potentials for cohabiting with livestock and illustrates opportunities and challenges for new models of community development balancing social, environmental and economic interests through new models of agri-urbanism
Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18
Massive rotating single stars with an initial metal composition appropriate
for the dwarf galaxy I Zw 18 ([Fe/H]=1.7) are modelled during hydrogen
burning for initial masses of 9-300 M and rotational velocities of
0-900 km s. Internal mixing processes in these models were calibrated
based on an observed sample of OB-type stars in the Magellanic Clouds. Even
moderately fast rotators, which may be abundant at this metallicity, are found
to undergo efficient mixing induced by rotation resulting in quasi
chemically-homogeneous evolution. These homogeneously-evolving models reach
effective temperatures of up to 90 kK during core hydrogen burning. This,
together with their moderate mass-loss rates, make them Transparent Wind
Ultraviolet INtense stars (TWUIN star), and their expected numbers might
explain the observed HeII ionizing photon flux in I Zw 18 and other
low-metallicity HeII galaxies. Our slowly rotating stars above 80
M evolve into late B- to M-type supergiants during core hydrogen
burning, with visual magnitudes up to 19 at the distance of I Zw
18. Both types of stars, TWUIN stars and luminous late-type supergiants, are
only predicted at low metallicity. Massive star evolution at low metallicity is
shown to differ qualitatively from that in metal-rich environments. Our grid
can be used to interpret observations of local star-forming dwarf galaxies and
high-redshift galaxies, as well as the metal-poor components of our Milky Way
and its globular clusters.Comment: accepted for publication in A\&
Viability of Noether symmetry of F(R) theory of gravity
Canonization of F(R) theory of gravity to explore Noether symmetry is
performed treating R - 6(\frac{\ddot a}{a} + \frac{\dot a^2}{a^2} +
\frac{k}{a^2}) = 0 as a constraint of the theory in Robertson-Walker
space-time, which implies that R is taken as an auxiliary variable. Although it
yields correct field equations, Noether symmetry does not allow linear term in
the action, and as such does not produce a viable cosmological model. Here, we
show that this technique of exploring Noether symmetry does not allow even a
non-linear form of F(R), if the configuration space is enlarged by including a
scalar field in addition, or taking anisotropic models into account.
Surprisingly enough, it does not reproduce the symmetry that already exists in
the literature (A. K. Sanyal, B. Modak, C. Rubano and E. Piedipalumbo,
Gen.Relativ.Grav.37, 407 (2005), arXiv:astro-ph/0310610) for scalar tensor
theory of gravity in the presence of R^2 term. Thus, R can not be treated as an
auxiliary variable and hence Noether symmetry of arbitrary form of F(R) theory
of gravity remains obscure. However, there exists in general, a conserved
current for F(R) theory of gravity in the presence of a non-minimally coupled
scalar-tensor theory (A. K. Sanyal, Phys.Lett.B624, 81 (2005),
arXiv:hep-th/0504021 and Mod.Phys.Lett.A25, 2667 (2010), arXiv:0910.2385
[astro-ph.CO]). Here, we briefly expatiate the non-Noether conserved current
and cite an example to reveal its importance in finding cosmological solution
for such an action, taking F(R) \propto R^{3/2}.Comment: 16 pages, 1 figure. appears in Int J Theoretical Phys (2012
Structure, bonding and magnetism in cobalt clusters
The structural, electronic and magnetic properties of Co clusters
(20) have been investigated using density functional theory within the
pseudopotential plane wave method. An unusual hexagonal growth pattern has been
observed in the intermediate size range, 20. The cobalt atoms are
ferromagnetically ordered and the calculated magnetic moments are found to be
higher than that of corresponding hcp bulk value, which are in good agreement
with the recent Stern-Gerlach experiments. The average coordination number is
found to dominate over the average bond length to determine the effective
hybridization and consequently the cluster magnetic moment.Comment: 12 pages and 9 figure
Erosion - Deposition in Hooghly Estuary
An attempt has been made to give an overall idea of erosion-deposition at theBalari-Haldia-Gangra reach of the Hooghly estuary in India. The sediment transport relationships developed by van Rijn and AcKers- White have been tried. Calculation of bed-load transport has beenmade based on'bed material sizes, flow conditions, depth and width of the channels, during 1993-97 Comparison of the results indicates the discrepancies between calculated and observed quantum of deposition/erosion to the extent of 0.6 to 0 :8 times in case ofvan Rijn ' sequation and 0.8 to 1.8 times incase of Ackers-White's model. Results sugges  that the Haldia-Balari channel is deteriorating due toaccumulation of sediment
Emergent moments and random singlet physics in a Majorana spin liquid
We exhibit an exactly solvable example of a SU(2) symmetric Majorana spin
liquid phase, in which quenched disorder leads to random-singlet phenomenology.
More precisely, we argue that a strong-disorder fixed point controls the low
temperature susceptibility of an exactly solvable model on
the decorated honeycomb lattice with quenched bond disorder and/or vacancies,
leading to where
as . The first term is a Curie tail
that represents the emergent response of vacancy-induced spin textures spread
over many unit cells: it is an intrinsic feature of the site-diluted system,
rather than an extraneous effect arising from isolated free spins. The second
term, common to both vacancy and bond disorder (with different in
the two cases) is the response of a random singlet phase, familiar from random
antiferromagnetic spin chains and the analogous regime in phosphorus-doped
silicon (Si:P).Comment: two-column format; 4+pages; 3 figure
Study of correlation between intraoperative crush smears, frozen section diagnosis and biopsy results of intracranial lesions
Crush cytology and frozen sections of intracranial space occupying lesions (ICSOLs) are an effective and time saving tool for intra operative consultation. In a stereotactic biopsy, it enables the pathologist to rightly comment whether (a) brain tissue is there or not in the biopsy, (b) possible nature of the lesion. In a resection for an ICSOL, the techniques help the surgeon with an intra operative working diagnosis
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