2,779 research outputs found
The microbial zoo in the C. elegans intestine: Bacteria, fungi and viruses
Press freedom has become one of the major challenges facing Journalism practice in the world. This paper explores the factors hindering press freedom in Nigeria using some relevant examples. The researcher used the qualitative method of research; using secondary data comprising of books and journals. The study is embedded on social responsibility theory. The study reveals that there are a lot of factors in Nigeria that hinders press freedom ranging from secrecy, legal pressure, direct censorship and force among others. Findings also reveal that Nigerian press freedom is a paradox and only exist on paper i.e. in the constitution but not in practice. The study recommends that since press freedom is granted in the constitution of Nigeria, there should be statutory backup and in order not to hinder press freedom, journalist should be allowed to have access to government sources and records so long as it will not bring chaos to the society at large
Orientation-dependent indentation response of helium-implanted tungsten
A literature review of studies investigating the topography of nano-indents
in ion-implanted materials reveals seemingly inconsistent observations, with
report of both pile-up and sink-in. This may be due to the crystallographic
orientation of the measured sample point, which is often not considered when
evaluating implantation-induced changes in the deformation response. Here we
explore the orientation dependence of spherical nano-indentation in pure and
helium-implanted tungsten, considering grains with , and
out-of-plane orientations. Atomic force microscopy (AFM) of indents in
unimplanted tungsten shows little orientation dependence. However, in the
implanted material a much larger, more localised pile-up is observed for
grains than for and orientations. Based on the observations for
grains, we hypothesise that a large initial hardening due to
helium-induced defects is followed by localised defect removal and subsequent
strain softening. A crystal plasticity finite element model of the indentation
process, formulated based on this hypothesis, accurately reproduces the
experimentally-observed orientation-dependence of indent morphology. The
results suggest that the mechanism governing the interaction of helium-induced
defects with glide dislocations is orientation independent. Rather, differences
in pile-up morphology are due to the relative orientations of the crystal slip
systems, sample surface and spherical indenter. This highlights the importance
of accounting for crystallographic orientation when probing the deformation
behaviour of ion-implanted materials using nano-indentation
Hardening and Strain Localisation in Helium-Ion-Implanted Tungsten
Tungsten is the main candidate material for plasma-facing armour components
in future fusion reactors. In-service, fusion neutron irradiation creates
lattice defects through collision cascades. Helium, injected from plasma,
aggravates damage by increasing defect retention. Both can be mimicked using
helium-ion-implantation. In a recent study on 3000 appm helium-implanted
tungsten (W-3000He), we hypothesized helium-induced irradiation hardening,
followed by softening during deformation. The hypothesis was founded on
observations of large increase in hardness, substantial pile-up and slip-step
formation around nano-indents and Laue diffraction measurements of localised
deformation underlying indents. Here we test this hypothesis by implementing it
in a crystal plasticity finite element (CPFE) formulation, simulating
nano-indentation in W-3000He at 300 K. The model considers thermally-activated
dislocation glide through helium-defect obstacles, whose barrier strength is
derived as a function of defect concentration and morphology. Only one fitting
parameter is used for the simulated helium-implanted tungsten; defect removal
rate. The simulation captures the localised large pile-up remarkably well and
predicts confined fields of lattice distortions and geometrically necessary
dislocation underlying indents which agree quantitatively with previous Laue
measurements. Strain localisation is further confirmed through high resolution
electron backscatter diffraction and transmission electron microscopy
measurements on cross-section lift-outs from centre of nano-indents in
W-3000He
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Pressing Challenges in China’s Greenway Planning and Design: Promoting or Diminishing Cultural Identities and Values?
Greenways are networks of land containing linear elements that are planned, designed and managed for multiple purposes including ecological, recreational, cultural, aesthetic, or other purposes compatible with the concept of sustainable land use (Ahern, 1995). The greenway movement is a new concept that integrates many established landscape architectural, planning and design ideas, concepts, and implementation techniques. (Fabos, 1995).
This paper is primarily focused on pressing challenges in the greenway movement taking place in many parts of China that are out of cultural and historic contexts, resulting in diminishing cultural identities and values. It attempts to re-examine the greenway planning strategies and design guidelines to promote a culturally-sensitive, sustainable approach in order to preserve China’s rich history and diverse cultural heritage
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