517 research outputs found
The Celestial Reference Frame at 24 and 43 GHz. II. Imaging
We have measured the sub-milli-arcsecond structure of 274 extragalactic
sources at 24 and 43 GHz in order to assess their astrometric suitability for
use in a high frequency celestial reference frame (CRF). Ten sessions of
observations with the Very Long Baseline Array have been conducted over the
course of 5 years, with a total of 1339 images produced for the 274
sources. There are several quantities that can be used to characterize the
impact of intrinsic source structure on astrometric observations including the
source flux density, the flux density variability, the source structure index,
the source compactness, and the compactness variability. A detailed analysis of
these imaging quantities shows that (1) our selection of compact sources from
8.4 GHz catalogs yielded sources with flux densities, averaged over the
sessions in which each source was observed, of about 1 Jy at both 24 and 43
GHz, (2) on average the source flux densities at 24 GHz varied by 20%-25%
relative to their mean values, with variations in the session-to-session flux
density scale being less than 10%, (3) sources were found to be more compact
with less intrinsic structure at higher frequencies, and (4) variations of the
core radio emission relative to the total flux density of the source are less
than 8% on average at 24 GHz. We conclude that the reduction in the effects due
to source structure gained by observing at higher frequencies will result in an
improved CRF and a pool of high-quality fiducial reference points for use in
spacecraft navigation over the next decade.Comment: 63 pages, 18 figures, 6 tables, accepted by the Astronomical Journa
Protein Conformational Changes in the Bacteriorhodopsin Photocycle: Comparison of Findings from Electron and X-Ray Crystallographic Analyses
Light-driven conformational changes in the membrane protein bacteriorhodopsin have been studied extensively using X-ray and electron crystallography, resulting in the deposition of >30 sets of coordinates describing structural changes at various stages of proton transport. Using projection difference Fourier maps, we show that coordinates reported by different groups for the same photocycle intermediates vary considerably in the extent and nature of conformational changes. The different structures reported for the same intermediate cannot be reconciled in terms of differing extents of change on a single conformational trajectory. New measurements of image phases obtained by cryo-electron microscopy of the D96G/F171C/F219L triple mutant provide independent validation for the description of the large protein conformational change derived at 3.2 Å resolution by electron crystallography of 2D crystals, but do not support atomic models for light-driven conformational changes derived using X-ray crystallography of 3D crystals. Our findings suggest that independent determination of phase information from 2D crystals can be an important tool for testing the accuracy of atomic models for membrane protein conformational changes
Rotational Alignment Altered by Source Position Correlations
In the construction of modern Celestial Reference Frames (CRFs) the overall rotational alignment is only weakly constrained by the data. Therefore, common practice has been to apply a 3-dimensional No-Net-Rotation (NNR) constraint in order to align an under-construction frame to the ICRF. We present evidence that correlations amongst source position parameters must be accounted for in order to properly align a CRF at the 5-10 (mu)as level of uncertainty found in current work. Failure to do so creates errors at the 10-40 (mu)as level
Co-expression and purification of the RadA recombinase with the RadB paralog from Haloferax volcanii yields heteromeric ring-like structures
The study of archaeal proteins and the processes to which they contribute poses particular challenges due to the often extreme environments in which they function. DNA recombination, replication and repair proteins of the halophilic euryarchaeon, Haloferax volcanii (Hvo) are of particular interest as they tend to resemble eukaryotic counterparts in both structure and activity, and genetic tools are available to facilitate their analysis. In the present study, we show using bioinformatics approaches that the Hvo RecA-like protein RadA is structurally similar to other recombinases although is distinguished by a unique acidic insertion loop. To facilitate expression of Hvo RadA a co-expression approach was used, providing its lone paralog, RadB, as a binding partner. At present, structural and biochemical characterization of Hvo RadA is lacking. Here, we describe for the first time co-expression of Hvo RadA with RadB and purification of these proteins as a complex under in vitro conditions. Purification procedures were performed under high salt concentration (>1 M sodium chloride) to maintain the solubility of the proteins. Quantitative densitometry analysis of the co-expressed and co-purified RadAB complex estimated the ratio of RadA to RadB to be 4 : 1, which suggests that the proteins interact with a specific stoichiometry. Based on a combination of analyses, including size exclusion chromatography, Western blot and electron microscopy observations, we suggest that RadA multimerizes into a ring-like structure in the absence of DNA and nucleoside co-factor
Structural Analysis in Virtual Reality for Education with BMLY
Virtual reality (VR) is an engaging and immersive medium for interacting with a digital environment. The educational benefits of implementing virtual reality into learning modules has recently been explored. This work presents a process for creating a virtual reality learning module on beam bending and a preliminary study on its effectiveness. In this work, virtual reality and structural analysis are combined to create an interactive virtual experiment on a steel beam. A VR user can select the location of a gravity load along the member and increase its magnitude while following the deformation and stresses in real time. The VR environment is implemented using the open source three.js library. The results of a survey to assess student interaction and evaluation of the developed learning module is presented.The authors would like to acknowledge the support of The University of Sydney for the time in the Immersive Learning Laboratory which facilitated this work
What works to support carers of older people and older carers? an international evidence map of interventions and outcomes
\ua9 The Author(s) 2024.Background: Unpaid carers of older people, and older unpaid carers, experience a range of adverse outcomes. Supporting carers should therefore be a public health priority. Our understanding of what works to support carers could be enhanced if future evaluations prioritise under-researched interventions and outcomes. To support this, we aimed to: map evidence about interventions to support carers, and the outcomes evaluated; and identify key gaps in current evidence. Methods: Evidence gap map review methods were used. Searches were carried out in three bibliographic databases for quantitative evaluations of carer interventions published in OECD high-income countries between 2013 and 2023. Interventions were eligible if they supported older carers (50 + years) of any aged recipient, or any aged carers of older people (50 + years). Findings: 205 studies reported across 208 publications were included in the evidence map. The majority evaluated the impact of therapeutic and educational interventions on carer burden and carers’ mental health. Some studies reported evidence about physical exercise interventions and befriending and peer support for carers, but these considered a limited range of outcomes. Few studies evaluated interventions that focused on delivering financial information and advice, pain management, and physical skills training for carers. Evaluations rarely considered the impact of interventions on carers’ physical health, quality of life, and social and financial wellbeing. Very few studies considered whether interventions delivered equitable outcomes. Conclusion: Evidence on what works best to support carers is extensive but limited in scope. A disproportionate focus on mental health and burden outcomes neglects other important areas where carers may need support. Given the impact of caring on carers’ physical health, financial and social wellbeing, future research could evaluate interventions that aim to support these outcomes. Appraisal of whether interventions deliver equitable outcomes across diverse carer populations is critical
Single-epoch VLBI imaging study of bright active galactic nuclei at 2 and 8 GHz
We investigate statistical and individual astrophysical properties of active
galactic nuclei (AGNs), such as parsec-scale flux density, core dominance,
angular and linear sizes, maximum observed brightness temperatures of VLBI core
components, spectral index distributions for core and jet components, and
evolution of brightness temperature along the jets. Furthermore, we
statistically compare core flux densities and brightness temperature as well as
jet spectral indices of gamma-ray bright and weak sources. We used 19 very long
baseline interferometry (VLBI) observing sessions carried out simultaneously at
2.3 and 8.6 GHz with the participation of 10 Very Long Baseline Array (VLBA)
stations and up to 10 additional geodetic telescopes. The observations span the
period 1998-2003. We present here single-epoch results from high-resolution
radio observations of 370 AGNs. Our VLBI images at 2.3 and 8.6 GHz as well as
Gaussian models are presented and analyzed. At least one-fourth of the cores
are completely unresolved on the longest baselines of the global VLBI
observations. The VLBI core components are partially opaque with the median
value of spectral index of alpha_core=0.3, while the jet features are usually
optically thin alpha_jet=-0.7. The spectral index typically decreases along the
jet ridge line owing to the spectral aging, with a median value of -0.05
mas^-1. Brightness temperatures are found to be affected by Doppler boosting
and reaching up to \sim10^13 K with a median of \sim2.5x10^11 K at both
frequencies. The brightness temperature gradients along the jets typically
follow a power law T_b\simr^-2.2 at both frequencies. 147 sources (40%)
positionally associated with gamma-ray detections from the Fermi LAT Second
Source Catalog have higher core flux densities and brightness temperatures, and
are characterized by the less steep radio spectrum of the optically thin jet
emission.Comment: 15 pages, 21 figures, accepted by A&A on May 22, 2012, machine
readable tables are available from the source of the pape
Attractant and Repellent Signaling Conformers of Sensory Rhodopsin−Transducer Complexes†
ABSTRACT: Attractant and repellent signaling conformers of the dual-signaling phototaxis receptor sensory rhodopsin I and its transducer subunit (SRI-HtrI) have recently been distinguished experimentally by the opposite connection of their retinylidene protonated Schiff bases to the outwardly located periplasmic side and inwardly located cytoplasmic side. Here we show that the pKa of the outwardly located Asp76 counterion in the outwardly connected conformer is lowered by ∼1.5 units from that of the inwardly connected conformer. The pK a difference enables quantitative determination of the relative amounts of the two conformers in wild-type cells and behavioral mutants prior to photoexcitation, comparison of their absorption spectra, and determination of their relative signaling efficiency. We have shown that the onephoton excitation of the SRI-HtrI attractant conformer causes a Schiff base connectivity switch from inwardly connected to outwardly connected states in the attractant signaling photoreaction. Conversely, a second near-UV photon drives the complex back to the inwardly connected conformer in the repellent signaling photoreaction. The results suggest a model of the color-discriminating dual-signaling mechanism in which phototaxis responses (his-kinase modulation) result from the photointerconversion of the two oppositely connected SRI-HtrI conformers by one-photon and two-photon activation. Furthermore, we find that the related repellent phototaxis SRII-HtrII receptor complex has an outwardly connecte
Active Membrane Fluctuations Studied by Micropipet Aspiration
We present a detailed analysis of the micropipet experiments recently
reported in J-B. Manneville et al., Phys. Rev. Lett. 82, 4356--4359 (1999),
including a derivation of the expected behaviour of the membrane tension as a
function of the areal strain in the case of an active membrane, i.e.,
containing a nonequilibrium noise source. We give a general expression, which
takes into account the effect of active centers both directly on the membrane,
and on the embedding fluid dynamics, keeping track of the coupling between the
density of active centers and the membrane curvature. The data of the
micropipet experiments are well reproduced by the new expressions. In
particular, we show that a natural choice of the parameters quantifying the
strength of the active noise explains both the large amplitude of the observed
effects and its remarkable insensitivity to the active-center density in the
investigated range. [Submitted to Phys Rev E, 22 March 2001]Comment: 14 pages, 5 encapsulated Postscript figure
The VLBA Galactic Plane Survey -- VGaPS
This paper presents accurate absolute positions from a 24 GHz Very Long
Baseline Array (VLBA) search for compact extragalactic sources in an area where
the density of known calibrators with precise coordinates is low. The goals
were to identify additional sources suitable for use as phase calibrators for
galactic sources, determine their precise positions, and produce radio images.
In order to achieve these goals, we developed a new software package, PIMA, for
determining group delays from wide-band data with much lower detection limit.
With the use of PIMA we have detected 327 sources out of 487 targets observed
in three 24 hour VLBA experiments. Among the 327 detected objects, 176 are
within 10 degrees of the Galactic plane. This VGaPS catalogue of source
positions, plots of correlated flux density versus projected baseline length,
contour plots, as well as weighted CLEAN images and calibrated visibility data
in FITS format, are available on the Web at http://astrogeo.org/vgaps.
Approximately one half of objects from the 24 GHz catalogue were observed at
dual band 8.6 GHz and 2.3 GHz experiments. Position differences at 24 GHz
versus 8.6/2.3 GHz for all but two objects on average are strictly within
reported uncertainties. We found that for two objects with complex structure
positions at different frequencies correspond to different components of a
source.Comment: 23 pages, 20 figures, 11 tables; accepted for publication in the
Astronomical Journal; minor corrections to the text are made; two machine
readable tables in electronic form are availanle from the preprint sourc
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