414 research outputs found
Derivation of surface properties from Magellan altimetry data
The fit of the Hagfors model to the Magellan altimetry data provides a means to characterize the surface properties of Venus. However, the derived surface properties are only meaningful if the model provides a good representation of the data. The Hagfors model provides a good representation of the data. The Hagfors model is generally a realistic fit to surface scattering properties of a nadir-directed antenna such as the Magellan altimeter; however, some regions of the surface of Venus are poorly described by the existing model, according to the goodness of fit parameter provided on the ARCDR CD-ROMs. Poorly characterized regions need to be identified and fit to new models in order to derive more accurate surface properties for use in inferring the geological processes that affect the surface in those regions. We have compared the goodness of fit of the Hagfors model to the distribution of features across the planet, and preliminary results show a correlation between steep topographic slopes and poor fits to the standard model, as has been noticed by others. In this paper, we investigate possible relations between many classes of features and the ability of the Hagfors model to fit the observed echo profiles. In the regions that are not well characterized by existing models, we calculate new models that compensate for topographic relief in order to derive improved estimates of surface properties. Areas investigated to date span from longitude 315 through 45, at all latitudes covered by Magellan. A survey of those areas yields preliminary results that suggest that topographically high regions are well suited to the current implementation of the Hagfors model. Striking examples of such large-scale good fits are Alpha Regio, the northern edges of Lada Terra, and the southern edge of Ishtar Terra. Other features that are typically well fit are the rims of coronae such as Heng-O and the peaks of volcanos such as Gula Mons. Surprisingly, topographically low regions, such as the ubiquitous plains areas, are modeled poorly in comparison. However, this generalization has has exceptions: Lakshmi Planum is an elevated region that is not well fit compared to the rest of neighboring Ishtar, while the southern parts of topographically low Guinevere Planitia are characterized quite well by the Hagfors model. Features that are candidates for improved models are impact craters, coronae, ridges of significant scale, complex ridged terrains, moderate-sized mountains, and sharp terrain boundaries. These features are chosen because the goodness of fit is likely to be most affected either by departures from normal incidence angles or by sharp changes in terrain type within a single footprint. Most large features that are elevated with respect to their surroundings will suffer from steep slope effects, and smaller coronae and impact craters will probably suffer due to rapid changes in their appearance within a single footprint (10-20 km)
New perspectives on spectroscopic factor quenching from reactions
The evolution of single-particle strengths as the neutron-to-proton asymmetry
changes informs us of the importance of short- and long-range correlations in
nuclei and has therefore been extensively studied for the last two decades.
Surprisingly, the strong asymmetry dependence of these strengths and their
extreme values for highly-asymmetric nuclei inferred from knockout reaction
measurements on a target nucleus are not consistent with what is extracted from
electron-induced, transfer, and quasi-free reaction data, constituting a
two-decade old puzzle. This work presents the first consistent analysis of
one-nucleon transfer and one-nucleon knockout data, in which theoretical
uncertainties associated with the nucleon-nucleus effective interactions
considered in the reaction models are quantified using a Bayesian analysis. Our
results demonstrate that, taking into account these uncertainties, the
spectroscopic strengths of loosely-bound nucleons extracted from both probes
agree with each other and, although there are still discrepancies for
deeply-bound nucleons, the slope of the asymmetry dependence of the
single-particle strengths inferred from transfer and knockout reactions are
consistent within . Both probes are consistent with a small asymmetry
dependence of these strengths. The uncertainties obtained in this work
represent a lower bound and are already significantly larger than the original
estimates.Comment: 14 pages: 7 pages of the main text (including one and a half of
reference) and 7 pages of supplemental material. Accepted for publication in
Phys. Rev. Let
The complete quantification of parametric uncertainties in (d,p) transfer reactions
Previous work quantified the uncertainty associated with the optical
potentials between the nucleons and the target. In this study, we extend that
work by also including the parameters of the mean field associated with the
overlap function of the final bound state, thus obtaining the full parametric
uncertainty on transfer observables. We use Bayesian Markov Chain Monte Carlo
simulations to obtain parameter posterior distributions. We use
elastic-scattering cross sections to constrain the optical potential parameters
and use the asymptotic normalization coefficient of the final state to
constrain the bound state interaction. We then propagate these posteriors to
the transfer angular distributions and obtain confidence intervals for this
observable. We study (d,p) reactions on 14C, 16O, and 48Ca at energies in the
range E=10-24 MeV. Our results show a strong reduction in uncertainty by using
the asymptotic normalization coefficient as a constraint, particularly for
those reactions most sensitive to ambiguities in the mean-field. For those
reactions, the importance of constraining the bound state interaction is equal
to that of constrain the optical potentials. The case of 14C is an outlier
because it populates a halo state, and the observable is less sensitive to the
nuclear interior. We conclude that when minimal constraints are used on the
parameters of the nucleon-target interaction, the 68% confidence interval
uncertainties on the differential cross sections are very large (~ 140-185%).
However, if elastic-scattering data and the asymptotic normalization
coefficient are used in the analysis, with an error of 10% (5%), this
uncertainty reduces to ~30% (~15%)
Predictors of engagement wth between-session work in Cognitive Behavioural Therapy (CBT) - based interventions:a mixed-methods systematic review and "best-fit" framework synthesis
Between-session work (BSW) acts as the vehicle to translate skills learnt in therapy sessions into adaptive changes in everyday life, a key goal in Cognitive Behavioural Therapies (CBT). Despite a well-established relationship between engagement with BSW and enhanced treatment outcomes, difficulties completing between-session tasks are common and factors affecting patient engagement with BSW are poorly understood. This mixed-methods systematic review and “best fit” framework synthesis explored predictors of engagement with BSW in CBT-based interventions. Comprehensive searches were conducted across five databases, identifying 59 eligible studies. This combined theory and empirical evidence approach depicted ten predictor themes related to between-session engagement, spanning individual, relational and contextual concepts. While ambiguous findings were generated by existing evidence, several factors emerged as relatively consistent predictors of engagement with BSW: positive patient beliefs regarding BSW and treatment such as perceived helpfulness, and practitioner competency in planning and reviewing BSW, including providing a rationale and addressing difficulties were associated with greater engagement. Conversely, patient in-session resistance, including counter change talk, was an indicator of disengagement between-sessions. The impact of patient symptomology, sociocultural environment, practitioner beliefs and the therapeutic relationship is unclear. The conceptual model presented offers a testable framework for researchers and a guideline for practitioners
Resolving topographic detail on Venus by modeling complex Magellan altimetry echoes
Magellan's altimeter is providing some of the finest resolution topography of Venus achieved to date. Nevertheless, efforts continue to improve the topographic resolution whenever possible. One effort to this end is stereoscopic imaging, which provides topography at scales similar to that of the synthetic aperture radar (SAR). However, this technique requires two SAR images of the same site to be obtained and limits the utility of this method. In this paper, we present another method to resolve topographic features at scales smaller than that of an altimeter footprint, which is more globally applicable than the stereoscopic approach. Each pulse which is transmitted by Magellan's altimeter scatters from the planet and echoes to the receiver, delayed based on the distance between the spacecraft and each surface element. As resolved in time, each element of an altimetry echo represents the sum of all points on the surface which are equidistant from the spacecraft. Thus, individual returns, as a function of time, create an echo profile which may be used to derive properties of the surface, such as the scattering law or, in this case, the topography within the footprint. The Magellan project has derived some of this information by fitting model templates to radar echo profiles. The templates are calculated based on Hagfor's Law, which assumes a smooth, gently undulating surface. In most regions these templates provide a reasonable fit to the observed echo profile; however, in some cases the surface departs from these simple assumptions and more complex profiles are observed. Specifically, we note that sub-footprint topographic relief apparently has a strong effect on the shape of the echo profile. To demonstrate the effects of sub-resolution relief on echo profiles, we have calculated the echo shapes from a wide range of simple topographic models. At this point, our topographic models have emphasized surfaces where only two dominant elevations are contained within a footprint, such as graben, ridges, crater rims, and central features in impact craters
Quantifying uncertainties due to optical potentials in one-neutron knockout reactions
One-neutron knockout reactions have been widely used to extract information
about the single-particle structure of nuclei from the valley of stability to
the driplines. The interpretation of knockout data relies on reaction models,
where the uncertainties are typically not accounted for. In this work we
quantify uncertainties of optical potentials used in these reaction models and
propagate them, for the first time, to knockout observables using a Bayesian
analysis. We study two reactions in the present paper, the first of which
involves a loosely-bound halo projectile, Be, and the second a
tightly-bound projectile, C. We first quantify the parametric
uncertainties associated with phenomenological optical potentials.
Complementing to this approach, we also quantify the model uncertainties
associated with the chiral forces that can be used to construct microscopic
optical potentials. For the phenomenological study, we investigate the impact
of the imaginary terms of the optical potential on the breakup and stripping
components of the knockout cross sections as well as the impact of the angular
range. For the Be case, the theoretical uncertainty from the
phenomenological method is on the order of the experiment uncertainty on the
knockout observables; however, for the C case, the theoretical
uncertainty is significantly larger. The widths of the confidence intervals for
the knockout observables obtained for the microscopic study and the
phenomenological approach are of similar order of magnitude. Based on this work
we conclude that structure information inferred from the ratio of the knockout
cross sections, will carry a theoretical uncertainty of at least for
halo nuclei and at least for tightly-bound nuclei.Comment: 12 pages (including 2 of supplemental material and 1 of reference), 5
figures, 2 table
Chlamydia trachomatis CT771 (nudH) is an asymmetric Ap4A hydrolase
Asymmetric diadenosine 5′,5′″-P1,P4-tetraphosphate (Ap4A) hydrolases are members of the Nudix superfamily that asymmetrically cleave the metabolite Ap4A into ATP and AMP while facilitating homeostasis. The obligate intracellular mammalian pathogen Chlamydia trachomatis possesses a single Nudix family protein, CT771. As pathogens that rely on a host for replication and dissemination typically have one or zero Nudix family proteins, this suggests that CT771 could be critical for chlamydial biology and pathogenesis. We identified orthologs to CT771 within environmental Chlamydiales that share active site residues suggesting a common function. Crystal structures of both apo- and ligand-bound CT771 were determined to 2.6 Å and 1.9 Å resolution, respectively. The structure of CT771 shows a αβα-sandwich motif with many conserved elements lining the putative Nudix active site. Numerous aspects of the ligand-bound CT771 structure mirror those observed in the ligand-bound structure of the Ap4A hydrolase from Caenorhabditis elegans. These structures represent only the second Ap4A hydrolase enzyme member determined from eubacteria and suggest that mammalian and bacterial Ap4A hydrolases might be more similar than previously thought. The aforementioned structural similarities, in tandem with molecular docking, guided the enzymatic characterization of CT771. Together, these studies provide the molecular details for substrate binding and specificity, supporting the analysis that CT771 is an Ap4A hydrolase (nudH)
LBADR: The LBA Data Recorder
The LBA (Long-Baseline Array) is an ad-hoc network of radio telescopes within Australia and is the only VLBI array in the Southern Hemisphere. Since 2004 all experiments have been recorded using standard computer hard-disks, replacing the aging tape based S2 system. The recorder developed for this, the LBADR, comprises largely of commercial off-the-shelf components and is closeley related to the PC-EVN syste
Four Weeks of IV Iron Supplementation Reduces Perceived Fatigue and Mood Disturbance in Distance Runners
To determine the effect of intravenous iron supplementation on performance, fatigue and overall mood in runners without clinical iron deficiency.Fourteen distance runners with serum ferritin 30-100 µg · L(-1) were randomly assigned to receive three blinded injections of intravenous ferric-carboxymaltose (2 ml, 100 mg, IRON) or normal saline (PLACEBO) over four weeks (weeks 0, 2, 4). Athletes performed a 3,000 m time trial and 10 × 400 m monitored training session on consecutive days at week 0 and again following each injection. Hemoglobin mass (Hbmass) was assessed via carbon monoxide rebreathing at weeks 0 and 6. Fatigue and mood were determined bi-weekly until week 6 via Total Fatigue Score (TFS) and Total Mood Disturbance (TMD) using the Brief Fatigue Inventory and Brunel Mood Scale. Data were analyzed using magnitude-based inferences, based on the unequal variances t-statistic and Cohen's Effect sizes (ES).Serum ferritin increased in IRON only (Week 0: 62.8 ± 21.9, Week 4: 128.1 ± 46.6 µg · L(-1); p = 0.002) and remained elevated two weeks after the final injection (127.0 ± 66.3 µg · L(-1), p = 0.01), without significant changes in Hbmass. Supplementation had a moderate effect on TMD of IRON (ES -0.77) with scores at week 6 lower than PLACEBO (ES -1.58, p = 0.02). Similarly, at week 6, TFS was significantly improved in IRON vs. PLACEBO (ES -1.54, p = 0.05). There were no significant improvements in 3,000 m time in either group (Week 0 vs. Week 4; Iron: 625.6 ± 55.5 s vs. 625.4 ± 52.7 s; PLACEBO: 624.8 ± 47.2 s vs. 639.1 ± 59.7 s); but IRON reduced their average time for the 10 × 400 m training session at week 2 (Week 0: 78.0 ± 6.6 s, Week 2: 77.2 ± 6.3; ES-0.20, p = 0.004).During 6 weeks of training, intravenous iron supplementation improved perceived fatigue and mood of trained athletes with no clinical iron deficiency, without concurrent improvements in oxygen transport capacity or performance
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