231 research outputs found
The replacement histone H2A.Z in a hyperacetylated form is a feature of active genes in the chicken
The replacement histone H2A.Z is variously reported
as being linked to gene expression and preventing the
spread of heterochromatin in yeast, or concentrated
at heterochromatin in mammals. To resolve this
apparent dichotomy, affinity-purified antibodies
against the N-terminal region of H2A.Z, in both a triacetylatedandnon-
acetylatedstate, areusedin native
chromatin immmuno-precipitation experiments with
mononucleosomes from three chicken cell types. The
hyperacetylated species concentrates at the 50 end of
active genes, both tissue specific and housekeeping
but is absent from inactive genes, while the
unacetylated form is absent from both active and
inactive genes. A concentration of H2A.Z is also
found at insulators under circumstances implying a
link to barrier activity but not to enhancer blocking.
Although acetylated H2A.Z is widespread throughout
the interphase genome, at mitosis its acetylation is
erased, the unmodified form remaining. Thus,
although H2A.Z may operate as an epigenetic marker
for active genes, its N-terminal acetylation does not
The replacement histone H2A.Z in a hyperacetylated form is a feature of active genes in the chicken
The replacement histone H2A.Z is variously reported
as being linked to gene expression and preventing the
spread of heterochromatin in yeast, or concentrated
at heterochromatin in mammals. To resolve this
apparent dichotomy, affinity-purified antibodies
against the N-terminal region of H2A.Z, in both a triacetylatedandnon-
acetylatedstate, areusedin native
chromatin immmuno-precipitation experiments with
mononucleosomes from three chicken cell types. The
hyperacetylated species concentrates at the 50 end of
active genes, both tissue specific and housekeeping
but is absent from inactive genes, while the
unacetylated form is absent from both active and
inactive genes. A concentration of H2A.Z is also
found at insulators under circumstances implying a
link to barrier activity but not to enhancer blocking.
Although acetylated H2A.Z is widespread throughout
the interphase genome, at mitosis its acetylation is
erased, the unmodified form remaining. Thus,
although H2A.Z may operate as an epigenetic marker
for active genes, its N-terminal acetylation does not
Understanding person acquisition using an interactive activation and competition network
Face perception is one of the most developed visual skills that humans display, and recent work has attempted to examine the mechanisms involved in face perception through noting how neural networks achieve the same performance. The purpose of the present paper is to extend this approach to look not just at human face recognition, but also at human face acquisition. Experiment 1 presents empirical data to describe the acquisition over time of appropriate representations for newly encountered faces. These results are compared with those of Simulation 1, in which a modified IAC network capable of modelling the acquisition process is generated. Experiment 2 and Simulation 2 explore the mechanisms of learning further, and it is demonstrated that the acquisition of a set of associated new facts is easier than the acquisition of individual facts in isolation of one another. This is explained in terms of the advantage gained from additional inputs and mutual reinforcement of developing links within an interactive neural network system. <br/
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Dimensional errors in LIGA-produced metal structures due to thermal expansion and swelling of PMMA.
Numerical methods are used to examine dimensional errors in metal structures microfabricated by the LIGA process. These errors result from elastic displacements of the PMMA mold during electrodeposition and arise from thermal expansion of the PMMA when electroforming is performed at elevated temperatures and from PMMA swelling due to absorption of water from aqueous electrolytes. Both numerical solutions and simple analytical approximations describing PMMA displacements for idealized linear and axisymmetric geometries are presented and discussed. We find that such displacements result in tapered metal structures having sidewall slopes up to 14 {micro}m per millimeter of height for linear structures bounded by large areas of PMMA. Tapers for curved structures are of similar magnitude, but these structures are additionally skewed from the vertical. Potential remedies for reducing dimensional errors are also discussed. Here we find that auxiliary moat-like features patterned into the PMMA surrounding mold cavities can reduce taper by an order of magnitude or more. Such moats dramatically reduce tapers for all structures, but increase skew for curved structures when the radius of curvature is comparable to the structure height
The microscopic spin-phonon coupling constants in CuGeO_3
Using RPA results, mean field theory, and refined data for the polarization
vectors we determine the coupling constants of the four Peierls-active phonon
modes to the spin chains of CuGeO_3. We then derive the values of the coupling
of the spin system to the linear ionic displacements, the bond lengths and the
angles between bonds. Our values are consistent with microscopic theories and
various experimental results. We discuss the applicability of static approaches
to the spin-phonon coupling. The c-axis anomaly of the thermal expansion is
explained. We give the values of the coupling constants in an effective
one-dimensional Hamiltonian.Comment: 11 pages, two figures, 13 tables, PRB 59 (in press
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Development of a 20 MeV Dielectric-Loaded Test Accelerator
This paper presents a progress report on a joint project by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a dielectric-loaded test accelerator in the magnicon facility at NRL. The accelerator will be powered by an experimental 11.424-GHz magnicon amplifier that presently produces 25 MW of output power in a {approx}250-ns pulse at up to 10 Hz. The accelerator will include a 5-MeV electron injector originally developed at the Tsinghua University in Beijing, China, and can incorporate DLA structures up to 0.5 m in length. The DLA structures are being developed by ANL, and shorter test structures fabricated from a variety of dielectric materials have undergone testing at NRL at gradients up to {approx}8 MV/m. SLAC has developed components to distribute the power from the two magnicon output arms to the injector and to the DLA accelerating structure with separate control of the power ratio and relative phase. RWBruce Associates, Inc., working with NRL, has investigated means to join short ceramic sections into a continuous accelerator tube by a brazing process using an intense 83-GHz beam. The installation and testing of the first dielectric-loaded test accelerator, including injector, DLA test structure, and spectrometer, should take place within the next year
How the freshwater biodiversity information system (FBIS) is supporting national freshwater fish conservation decisions in South Africa
DATA AVAILABILITY STATEMENT : The datasets presented in this study can be found in online
repositories. The names of the repository/repositories and accession
number(s) can be found in the article/Supplementary Material.
Alternatively, the dataset can be accessed via the Freshwater
Biodiversity Information System (freshwaterbiodiversity.org).In South Africa, anthropogenic pressures such as water over-abstraction, invasive
species impacts, land-use change, pollution, and climate change have caused
widespread deterioration of the health of river ecosystems. This comes at great
cost to both people and biodiversity, with freshwater fishes ranked as the country’s
most threatened species group. Effective conservation and management of South
Africa’s freshwater ecosystems requires access to reliable and comprehensive
biodiversity data. Despite the existence of a wealth of freshwater biodiversity data,
access to these data has been limited. The Freshwater Biodiversity Information
System (FBIS) was built to address this knowledge gap by developing an intuitive,
accessible and reliable platform for freshwater biodiversity data in South Africa.
The FBIS hosts high quality, high accuracy biodiversity data that are freely available
to a wide range of stakeholders, including researchers, conservation practitioners
and policymakers. We describe how the system is being used to provide
freshwater fish data to a national conservation decision-support tool—The
Department of Forestry, Fisheries, and the Environment (DFFE) National
Environmental Screening Tool (NEST). The NEST uses empirical and modelled
biodiversity data to guide Environmental Impact Assessment Practitioners in
conducting environmental assessments of proposed developments.
Occurrence records for 34 threatened freshwater fishes occurring in South
Africa were extracted from the FBIS and verified by taxon specialists, resulting
in 6 660 records being used to generate modelled and empirical national distribution (or sensitivity) layers. This represents the first inclusion of freshwater
biodiversity data in the NEST, and future iterations of the tool will incorporate
additional freshwater taxa. This case study demonstrates how the FBIS fills a pivotal
role in the data-to-decision pipeline through supporting data-driven conservation
and management decisions at a national level.Funding for the development of the Freshwater Biodiversity Information System (FBIS) was provided by the JRS Biodiversity Foundation Funding for the development of the Freshwater Biodiversity Information System (FBIS) was provided by the JRS Biodiversity Foundation. This work is based on the research supported in part by the National Research Foundation (NRF) of South Africa and the NRF-SAIAB DSI/ NRF Research Chair in Inland Fisheries and Freshwater Ecology.http://www.frontiersin.org/Environmental_Scienceam2024Zoology and EntomologySDG-14:Life below wate
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