1,151 research outputs found
Depth-Sensing Indentation on REBa2Cu3O(7-\delta) Single Crystals obtained from Xenotime Mineral
A natural mixture of heavy rare earths oxides extracted from xenotime mineral
have been used to prepare large single crystals of high-temperature
REBa2Cu3O(7-\delta) superconductor grown using the CuO-BaO self-flux method.
Its mechanical properties along the ab-plane were characterized using
instrumented indentation. Hardness and elastic modulus were obtained by the
Oliver and Pharr method and corresponds to 7.4 \pm 0.2 GPa and in range 135-175
GPa at small depths, respectively. Increasing the load promotes the nucleation
of lateral cracks that causes a decrease in hardness and the measured elastic
modulus by instrumented indentation at higher loads. The indentation fracture
toughness was estimated by measuring the radial crack length from cube-corner
indentations at various loads and was 0.8 \pm 0.2 MPa.m1/2. The observed slip
systems of REBa2Cu3O(7-\delta) single crystals were [100](001) and [010](001),
the same as for YBa2Cu3O(7-\delta) single crystals. The initial stages of
deformation and fracture in the indentation process were investigated. The
hardness and elastic modulus were not strongly modified by the crystallographic
orientation in the ab-plane. This was interpreted in terms of the resolved
shear stresses in the active slip systems. Evidence of cracking along the {100}
and {110} planes on the ab-plane was observed. As a conclusion, the mechanical
properties of REBa2Cu3O(7-\delta) single crystals prepared from xenotime are
equivalent to those of YBa2Cu3O(7-\delta) single crystals produced by
conventional rare earths oxides.Comment: The paper will appear in Volume 42 (2012) of the Brazilian Journal of
Physic
Socio-Economic Instability and the Scaling of Energy Use with Population Size
The size of the human population is relevant to the development of a sustainable world, yet the forces setting growth or declines in the human population are poorly understood. Generally, population growth rates depend on whether new individuals compete for the same energy (leading to Malthusian or density-dependent growth) or help to generate new energy (leading to exponential and super-exponential growth). It has been hypothesized that exponential and super-exponential growth in humans has resulted from carrying capacity, which is in part determined by energy availability, keeping pace with or exceeding the rate of population growth. We evaluated the relationship between energy use and population size for countries with long records of both and the world as a whole to assess whether energy yields are consistent with the idea of an increasing carrying capacity. We find that on average energy use has indeed kept pace with population size over long time periods. We also show, however, that the energy-population scaling exponent plummets during, and its temporal variability increases preceding, periods of social, political, technological, and environmental change. We suggest that efforts to increase the reliability of future energy yields may be essential for stabilizing both population growth and the global socio-economic system
A systematic review of the evidence for single stage and two stage revision of infected knee replacement
BACKGROUND:
Periprosthetic infection about the knee is a devastating complication that may affect between 1% and 5% of knee replacement. With over 79 000 knee replacements being implanted each year in the UK, periprosthetic infection (PJI) is set to become an important burden of disease and cost to the healthcare economy. One of the important controversies in treatment of PJI is whether a single stage revision operation is superior to a two-stage procedure. This study sought to systematically evaluate the published evidence to determine which technique had lowest reinfection rates.
METHODS:
A systematic review of the literature was undertaken using the MEDLINE and EMBASE databases with the aim to identify existing studies that present the outcomes of each surgical technique. Reinfection rate was the primary outcome measure. Studies of specific subsets of patients such as resistant organisms were excluded.
RESULTS:
63 studies were identified that met the inclusion criteria. The majority of which (58) were reports of two-stage revision. Reinfection rated varied between 0% and 41% in two-stage studies, and 0% and 11% in single stage studies. No clinical trials were identified and the majority of studies were observational studies.
CONCLUSIONS:
Evidence for both one-stage and two-stage revision is largely of low quality. The evidence basis for two-stage revision is significantly larger, and further work into direct comparison between the two techniques should be undertaken as a priority
Individual Actions as Community Informative Resources. A Collective Informative Systems Approach
This paper conceives communities (in this case, partnerships) as being able to become collective informative repositories of individual and collective actions that may better-inform their members. This paper presents one approach for studying if a community has become such an informative repository. The approach used here consists of introducing a formal language (Viable Systems Modelling, VSM) into one of the community nodes (a participant) and tracing if its use is seen in another node (another participant) - indicating the presence of a process of diffusion. This research design has been tested in a crime-reduction partnership in the UK. One of its members was asked to engage in the design and testing of this approach as a co-researcher. As a result, a questionnaire to map communication and control devices inside an organization was jointly developed. In keeping with VSM principles, the questionnaire encouraged participants to reflect on attenuation and amplification processes within their communications channels. To test the quality of the outcomes of this approach, members from another crime-reduction partnership were also invited to answer the survey; this was to confirm that VSM notions were not evident for those outside the development and testing of the questionnaire. The questionnaire indicated also its capability to make visible communication and organizational processes within collectives and its potential to stimulate self-organization, for those individuals who became familiar with VSM. Furthermore, this approach provided the authors with the capability to study information flows inside the two collectives, and contributed to an understanding of these flows as a model for building and maintaining a Community Informative System
Genetic Rearrangements Can Modify Chromatin Features at Epialleles
Analogous to genetically distinct alleles, epialleles represent heritable states of different gene expression from sequence-identical genes. Alleles and epialleles both contribute to phenotypic heterogeneity. While alleles originate from mutation and recombination, the source of epialleles is less well understood. We analyze active and inactive epialleles that were found at a transgenic insert with a selectable marker gene in Arabidopsis. Both converse expression states are stably transmitted to progeny. The silent epiallele was previously shown to change its state upon loss-of-function of trans-acting regulators and drug treatments. We analyzed the composition of the epialleles, their chromatin features, their nuclear localization, transcripts, and homologous small RNA. After mutagenesis by T-DNA transformation of plants carrying the silent epiallele, we found new active alleles. These switches were associated with different, larger or smaller, and non-overlapping deletions or rearrangements in the 3′ regions of the epiallele. These cis-mutations caused different degrees of gene expression stability depending on the nature of the sequence alteration, the consequences for transcription and transcripts, and the resulting chromatin organization upstream. This illustrates a tight dependence of epigenetic regulation on local structures and indicates that sequence alterations can cause epigenetic changes at some distance in regions not directly affected by the mutation. Similar effects may also be involved in gene expression and chromatin changes in the vicinity of transposon insertions or excisions, recombination events, or DNA repair processes and could contribute to the origin of new epialleles
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COVID-19, systemic crisis, and possible implications for the wild meat trade in sub-Saharan Africa
Wild animals play an integral and complex role in the economies and ecologies of many
countries across the globe, including those of West and Central Africa, the focus of this
policy perspective. The trade in wild meat, and its role in diets, have been brought into
focus as a consequence of discussions over the origins of COVID-19. As a result, there
have been calls for the closure of China’s “wet markets”; greater scrutiny of the wildlife
trade in general; and a spotlight has been placed on the potential risks posed by growing human populations and shrinking natural habitats for animal to human transmission of
zoonotic diseases. However, to date there has been little attention given to what the consequences of the COVID-19 economic shock may be for the wildlife trade; the people who
rely on it for their livelihoods; and the wildlife that is exploited. In this policy perspective,
we argue that the links between the COVID-19 pandemic, rural livelihoods and wildlife
are likely to be more complex, more nuanced, and more far-reaching, than is represented in
the literature to date. We develop a causal model that tracks the likely implications for the
wild meat trade of the systemic crisis triggered by COVID-19. We focus on the resulting
economic shockwave, as manifested in the collapse in global demand for commodities such
as oil, and international tourism services, and what this may mean for local African economies and livelihoods. We trace the shockwave through to the consequences for the use
of, and demand for, wild meats as households respond to these changes. We suggest that
understanding and predicting the complex dynamics of wild meat use requires increased
collaboration between environmental and resource economics and the ecological and conservation sciences
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