333 research outputs found
Anisotropic Solutions in Symmetric Teleparallel -theory: Kantowski-Sachs and Bianchi III LRS Cosmologies
We investigate the existence of anisotropic self-similar exact solutions in
symmetric teleparallel -theory. For the background geometry
we consider the Kantowski-Sachs and the Locally Rotationally Symmetric Bianchi
type III geometries. These two anisotropic spacetimes are of special interest
because in the limit of isotropy they are related to the closed and open
Friedmann--Lema\^{\i}tre--Robertson--Walker cosmologies respectively. For each
spacetime there exist two distinct families of flat, symmetric connections,
which share the symmetries of the spacetime. We present the field equations,
and from them, we determine the functional form of the
Lagrangian which yields self-similar solutions. We initially consider the
vacuum case and subsequently we introduce a matter source in terms of a perfect
fluid. Last but not least, we report some self-similar solutions corresponding
to static spherically symmetric spacetimes.Comment: 31 pages, no figures, Latex2e source fil
Pearling and SKCS Analysis of Australian Barley for the Asian Food Market
Australian barley sold to the Asian food market (apart from malt) is mainly pearled for use either as a rice extender, in the production of miso paste or for the Japanese spirit, shochu. The shochu market is the most profitable of the Asian staple foods to Australian barley producers. Barley that meets shochu grade will suit the majority of Asian food market requirements. Pearling quality is of greatest importance to buyers of shochu quality barley. Measurements of pearling quality using a small-scale pearler are laborious and qualitative. The Single Kernel Characterisation System from Perten Instruments has been under investigation, to quantitatively measure barley uniformity and determine its usefulness in predicting pearling quality. Previously, we found that SKCS could be used to predict pearling yield, screenings less than 2.0mm and broken kernels (Washington et al., 2001). Since these findings were based on a two-year study only, Pearling and SKCS analysis was performed over four years to validate the use of SKCS as a predictor of pearling quality. The diverse climate and soil types unique to South Australia have enabled a thorough investigation of grain quality for the shochu market. South Australia and Western Australia currently export Schooner (SA) and Stirling (WA) to Japan for shochu. Each variety provides unique properties desirable to shochu manufacturers. However, there is a need to investigate the quality of other varieties and breeding lines in order to select grain that provides consistent uniformity over diverse environmental conditions. A calibration to predict hardness using Near Infrared (NIR) Spectroscopy was investigated as a useful rapid screening tool at the silo. In this paper we discuss the environmental conditions, varieties and breeding lines most suitable for production of premium shochu grade barley
Force-free twisted magnetospheres of neutron stars
The X-ray spectra observed in the persistent emission of magnetars are
evidence for the existence of a magnetosphere. The high-energy part of the
spectra is explained by resonant cyclotron upscattering of soft thermal photons
in a twisted magnetosphere, which has motivated an increasing number of efforts
to improve and generalize existing magnetosphere models. We want to build more
general configurations of twisted, force-free magnetospheres as a first step to
understanding the role played by the magnetic field geometry in the observed
spectra. First we reviewed and extended previous analytical works to assess the
viability and limitations of semi-analytical approaches. Second, we built a
numerical code able to relax an initial configuration of a nonrotating
magnetosphere to a force-free geometry, provided any arbitrary form of the
magnetic field at the star surface. The numerical code is based on a
finite-difference time-domain, divergence-free, and conservative scheme, based
of the magneto-frictional method used in other scenarios. We obtain new
numerical configurations of twisted magnetospheres, with distributions of twist
and currents that differ from previous analytical solutions. The range of
global twist of the new family of solutions is similar to the existing
semi-analytical models (up to some radians), but the achieved geometry may be
quite different. The geometry of twisted, force-free magnetospheres shows a
wider variety of possibilities than previously considered. This has
implications for the observed spectra and opens the possibility of implementing
alternative models in simulations of radiative transfer aiming at providing
spectra to be compared with observations.Comment: 16 pages, 17 figures, A&A accepte
Nonlinear force-free reconstruction of the global solar magnetic field: methodology
We present a novel numerical method that allows the calculation of nonlinear
force-free magnetostatic solutions above a boundary surface on which only the
distribution of the normal magnetic field component is given. The method relies
on the theory of force-free electrodynamics and applies directly to the
reconstruction of the solar coronal magnetic field for a given distribution of
the photospheric radial field component. The method works as follows: we start
with any initial magnetostatic global field configuration (e.g. zero, dipole),
and along the boundary surface we create an evolving distribution of tangential
(horizontal) electric fields that, via Faraday's equation, give rise to a
respective normal field distribution approaching asymptotically the target
distribution. At the same time, these electric fields are used as boundary
condition to numerically evolve the resulting electromagnetic field above the
boundary surface, modelled as a thin ideal plasma with non-reflecting,
perfectly absorbing outer boundaries. The simulation relaxes to a nonlinear
force-free configuration that satisfies the given normal field distribution on
the boundary. This is different from existing methods relying on a fixed
boundary condition - the boundary evolves toward the a priori given one, at the
same time evolving the three-dimensional field solution above it. Moreover,
this is the first time a nonlinear force-free solution is reached by using only
the normal field component on the boundary. This solution is not unique, but
depends on the initial magnetic field configuration and on the evolutionary
course along the boundary surface. To our knowledge, this is the first time
that the formalism of force-free electrodynamics, used very successfully in
other astrophysical contexts, is applied to the global solar magnetic field.Comment: 18 pages, 5 figures, Solar Physic
Rancang Bangun Alat Pereduksi Particulate Matter (PM) Gas Buang Mesin Diesel Dengan Metode Cyclone
Gas buang dari hasil proses pembakaran berpengaruh terhadap pencemaran udara dan lingkungan khususnya motor diesel. Proses pembakaran bahan bakar pada motor bakar menghasilkan gas buang yang mengandung unsur Nitrogen Oksida (NOx), Sulfur Oksida (SOx), Particulate Matter (PM), Karbon Monoksida (CO), dan Hidrokarbon (HC) yang bersifat mencemari udara. Agar motor diesel yang digunakan tidak mengakibatkan pencemaran udara berlebih, perlu dilakukan suatu penelitian menurunkan emisi gas buang motor diesel dengan pemilihan teknologi dan metode yang tepat. Penelitian cylone separator ini berdasarkan prinsip kerja separator yang memanfaatkan gaya sentrifugal dan perbedaan massa jenis. Karena massa jenis PM lebih besar dari pada massa jenis gas buang, PM akan terpisah dari gas buang karena gaya sentrifugal dan adanya perbedaan massa jenis. Pada tahap awal penelitian ini yaitu dibuat desain dan kemudian dilakukan CFD analisis untuk dicari yang paling efisien dari segi kecepatan dan jenis aliran. Pada hasil analisa CFD disimpulkan bahwa metode Perry lebih efisien dibanding 3 metode yang lain. Setelah didapat desain yang efisien maka dilanjutkan dengan pembuatan prototipe, untuk selanjutnya dilakukan uji ekperimen. Berdasar uji eksperimen, cyclone separator dapar mereduksi PM gas Buang motor diesel pada beban 2000 watt sebesar 8,71%. Sedangkan pada beban 2500 watt, cylone separator dapat mereduksi PM sebesar 34,49%
Magnetic Connectivity between Active Regions 10987, 10988, and 10989 by Means of Nonlinear Force-Free Field Extrapolation
Extrapolation codes for modelling the magnetic field in the corona in
cartesian geometry do not take the curvature of the Sun's surface into account
and can only be applied to relatively small areas, \textit{e.g.}, a single
active region. We apply a method for nonlinear force-free coronal magnetic
field modelling of photospheric vector magnetograms in spherical geometry which
allows us to study the connectivity between multi-active regions. We use vector
magnetograph data from the Synoptic Optical Long-term Investigations of the Sun
survey (SOLIS)/Vector Spectromagnetograph(VSM) to model the coronal magnetic
field, where we study three neighbouring magnetically connected active regions
(ARs: 10987, 10988, 10989) observed on 28, 29, and 30 March 2008, respectively.
We compare the magnetic field topologies and the magnetic energy densities and
study the connectivities between the active regions(ARs). We have studied the
time evolution of magnetic field over the period of three days and found no
major changes in topologies as there was no major eruption event. From this
study we have concluded that active regions are much more connected
magnetically than the electric current.Comment: Solar Physic
Assessing Alternative Fuels for Helicopter Operation
At present, nearly 100% of aviation fuel is derived from petroleum using conventional and well known refining technology. However, the fluctuations of the fuel price and the vulnerability of crude oil sources have increased the interest of the aviation industry in alternate energy sources. The motivation of this interest is actually twofold: firstly, alternative fuels will help to stabilize price fluctuations by relieving the worldwide demand for conventional fuel. Secondly, alternative fuels could provide environmental benefits including a substantial reduction of emitted CO 2 over the fuel life cycle. Thus, the ideal alternative fuel will fulfill both requirements: relieve the demand for fuels derived from crude oil and significantly reduce CO 2 emissions. In the present paper, the effects of various alternative fuels on the operation of a medium transport/utility helicopter are investigated using performance models of the helicopter and its associated turboshaft engine. These models are developed in an object-oriented simulation environment that allows a direct mechanical connection to be established between them in order to create an integrated model. Considering the case of a typical mission for the specific helicopter/engine combination, a comparative evaluation of conventional and alternative fuels is then carried out and performance results are presented at both engine and helicopter levels
Comparing magnetic field extrapolations with measurements of magnetic loops
We compare magnetic field extrapolations from a photospheric magnetogram with
the observationally inferred structure of magnetic loops in a newly developed
active region. This is the first time that the reconstructed 3D-topology of the
magnetic field is available to test the extrapolations. We compare the
observations with potential fields, linear force-free fields and non-linear
force-free fields. This comparison reveals that a potential field extrapolation
is not suitable for a reconstruction of the magnetic field in this young,
developing active region. The inclusion of field-line-parallel electric
currents, the so called force-free approach, gives much better results.
Furthermore, a non-linear force-free computation reproduces the observations
better than the linear force-free approximation, although no free parameters
are available in the former case.Comment: 5 pages, 3 figure
HSP90-CDC37-PP5 forms a structural platform for kinase dephosphorylation
Activation of client protein kinases by the HSP90 molecular chaperone system is affected by phosphorylation at multiple sites on HSP90, the kinase-specific co-chaperone CDC37, and the kinase client itself. Removal of regulatory phosphorylation from client kinases and their release from the HSP90-CDC37 system depends on the Ser/Thr phosphatase PP5, which associates with HSP90 via its N-terminal TPR domain. Here, we present the cryoEM structure of the oncogenic protein kinase client BRAFV600E bound to HSP90-CDC37, showing how the V600E mutation favours BRAF association with HSP90-CDC37. Structures of HSP90-CDC37-BRAFV600E complexes with PP5 in autoinhibited and activated conformations, together with proteomic analysis of its phosphatase activity on BRAFV600E and CRAF, reveal how PP5 is activated by recruitment to HSP90 complexes. PP5 comprehensively dephosphorylates client proteins, removing interaction sites for regulatory partners such as 14-3-3 proteins and thus performing a ‘factory reset’ of the kinase prior to release
A systematic CRISPR screen defines mutational mechanisms underpinning signatures caused by replication errors and endogenous DNA damage
Mutational signatures are imprints of pathophysiological processes arising through tumorigenesis. We generated isogenic CRISPR-Cas9 knockouts (Δ) of 43 genes in human induced pluripotent stem cells, cultured them in the absence of added DNA damage, and performed whole-genome sequencing of 173 subclones. ΔOGG1, ΔUNG, ΔEXO1, ΔRNF168, ΔMLH1, ΔMSH2, ΔMSH6, ΔPMS1, and ΔPMS2 produced marked mutational signatures indicative of being critical mitigators of endogenous DNA modifications. Detailed analyses revealed mutational mechanistic insights, including how 8-oxo-dG elimination is sequence-context-specific while uracil clearance is sequence-context-independent. Mismatch repair (MMR) deficiency signatures are engendered by oxidative damage (C>A transversions), differential misincorporation by replicative polymerases (T>C and C>T transitions), and we propose a 'reverse template slippage' model for T>A transversions. ΔMLH1, ΔMSH6, and ΔMSH2 signatures were similar to each other but distinct from ΔPMS2. Finally, we developed a classifier, MMRDetect, where application to 7,695 WGS cancers showed enhanced detection of MMR-deficient tumors, with implications for responsiveness to immunotherapies
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