11,475 research outputs found

    Unusually Luminous Giant Molecular Clouds in the Outer Disk of M33

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    We use high spatial resolution (~7pc) CARMA observations to derive detailed properties for 8 giant molecular clouds (GMCs) at a galactocentric radius corresponding to approximately two CO scale lengths, or ~0.5 optical radii (r25), in the Local Group spiral galaxy M33. At this radius, molecular gas fraction, dust-to-gas ratio and metallicity are much lower than in the inner part of M33 or in a typical spiral galaxy. This allows us to probe the impact of environment on GMC properties by comparing our measurements to previous data from the inner disk of M33, the Milky Way and other nearby galaxies. The outer disk clouds roughly fall on the size-linewidth relation defined by extragalactic GMCs, but are slightly displaced from the luminosity-virial mass relation in the sense of having high CO luminosity compared to the inferred virial mass. This implies a different CO-to-H2 conversion factor, which is on average a factor of two lower than the inner disk and the extragalactic average. We attribute this to significantly higher measured brightness temperatures of the outer disk clouds compared to the ancillary sample of GMCs, which is likely an effect of enhanced radiation levels due to massive star formation in the vicinity of our target field. Apart from brightness temperature, the properties we determine for the outer disk GMCs in M33 do not differ significantly from those of our comparison sample. In particular, the combined sample of inner and outer disk M33 clouds covers roughly the same range in size, linewidth, virial mass and CO luminosity than the sample of Milky Way GMCs. When compared to the inner disk clouds in M33, however, we find even the brightest outer disk clouds to be smaller than most of their inner disk counterparts. This may be due to incomplete sampling or a potentially steeper cloud mass function at larger radii.Comment: Accepted for Publication in ApJ; 7 pages, 4 figure

    Activity Dependent Branching Ratios in Stocks, Solar X-ray Flux, and the Bak-Tang-Wiesenfeld Sandpile Model

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    We define an activity dependent branching ratio that allows comparison of different time series XtX_{t}. The branching ratio bxb_x is defined as bx=E[ξx/x]b_x= E[\xi_x/x]. The random variable ξx\xi_x is the value of the next signal given that the previous one is equal to xx, so ξx={Xt+1Xt=x}\xi_x=\{X_{t+1}|X_t=x\}. If bx>1b_x>1, the process is on average supercritical when the signal is equal to xx, while if bx<1b_x<1, it is subcritical. For stock prices we find bx=1b_x=1 within statistical uncertainty, for all xx, consistent with an ``efficient market hypothesis''. For stock volumes, solar X-ray flux intensities, and the Bak-Tang-Wiesenfeld (BTW) sandpile model, bxb_x is supercritical for small values of activity and subcritical for the largest ones, indicating a tendency to return to a typical value. For stock volumes this tendency has an approximate power law behavior. For solar X-ray flux and the BTW model, there is a broad regime of activity where bx1b_x \simeq 1, which we interpret as an indicator of critical behavior. This is true despite different underlying probability distributions for XtX_t, and for ξx\xi_x. For the BTW model the distribution of ξx\xi_x is Gaussian, for xx sufficiently larger than one, and its variance grows linearly with xx. Hence, the activity in the BTW model obeys a central limit theorem when sampling over past histories. The broad region of activity where bxb_x is close to one disappears once bulk dissipation is introduced in the BTW model -- supporting our hypothesis that it is an indicator of criticality.Comment: 7 pages, 11 figure

    Supporting play exploration and early developmental intervention versus usual care to enhance development outcomes during the transition from the neonatal intensive care unit to home: a pilot randomized controlled trial

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    Background While therapy services may start in the Neonatal Intensive Care Unit (NICU) there is often a gap in therapy after discharge. Supporting Play Exploration and Early Development Intervention (SPEEDI) supports parents, helping them build capacity to provide developmentally supportive opportunities starting in the NICU and continuing at home. The purpose of this single blinded randomized pilot clinical trial was to evaluate the initial efficacy of SPEEDI to improve early reaching and exploratory problem solving behaviors. Methods Fourteen infants born very preterm or with neonatal brain injury were randomly assigned to SPEEDI or Usual Care. The SPEEDI group participated in 5 collaborative parent, therapist, and infant interventions sessions in the NICU (Phase 1) and 5 at home (Phase 2). Parents provided daily opportunities designed to support the infants emerging motor control and exploratory behaviors. Primary outcome measures were assessed at the end of the intervention, 1 and 3 months after the intervention ended. Reaching was assessed with the infant supported in an infant chair using four 30 s trials. The Early Problem Solving Indicator was used to evaluate the frequency of behaviors during standardized play based assessment. Effect sizes are including for secondary outcomes including the Test of Infant Motor Performance and Bayley Scales of Infant and Toddler Development. Results No group differences were found in the duration of toy contact. There was a significant group effect on (F1,8 = 4.04, p = 0.08) early exploratory problem-solving behaviors with infants in the SPEEDI group demonstrating greater exploration with effect sizes of 1.3, 0.6, and 0.9 at the end of the intervention, 1 and 3 months post-intervention. Conclusions While further research is needed, this initial efficacy study showed promising results for the ability of SPEEDI to impact early problem solving behaviors at the end of intervention and at least 3 months after the intervention is over. While reaching did not show group differences, a ceiling effect may have contributed to this finding. This single blinded pilot RCT was registered prior to subject enrollment on 5/27/14 at ClinicalTrials.Gov with number NCT02153736

    Habitat Management for Northern Bobwhites in Wisconsin: A Long-Term Assessment

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    An experimental habitat management program was initiated to improve the carrying capacity for northern bobwhites ( Colinus virginianus) on private lands by the Wisconsin Department of Natural Resources (WDNR) in 1974. During 1975-80, extensive habitat restoration was undertaken on a 60-mi2 (l55-km 2) study area in Richland County to restore hedge row cover, improve riparian corridors and woodlot edges, and construct plots of food and shelter to function as wintering sites for bobwhites. Previous investigations in Wisconsin have documented that the long-term decline of bobwhites was the result of habitat deterioration, principally hedgerow cover. Elsewhere, continuous declines in bobwhite abundance suggest a re-evaluation of the validity of time-honored habitat management practices is in order. Therefore, it seemed appropriate to test the impact of extensive attempts at habitat restoration, especially the development of hedgerows, on one small treatment area in the northern fringe of the geographic range of the northern bobwhite. After 10-15 years of growth, only 25% of the planted hedges were found to be effective for wintering bobwhites (i.e., closed canopies and producing fruits). Planted hedgerow cover suffered from poor survival due to deer browsing, competition from other surrounding vegetation, and changes in property owners and attitudes as farms were sold. Linear brushy cover was measured in 1990 and compared to similar estimates from 1978. During the 12-year span, brushy linear cover, including project hedges, decreased by 41% (5,995 to 3,545 yards/square mile; 2,531 to 1,497 meters/square kilometer). In addition, managed winter food resources after 1980 were reduced by half compared to earlier efforts. Through 1991, bobwhite population trends on the treatment area did not differ from statewide trends, indicating that extensive habitat restoration work had no discernible impact with respect to reversing population declines. Over 60% of the annual variability in bobwhite abundance in Richland County is related to the severity of winters. Despite these results, we still cannot discount the value of managing for hedgerows in Wisconsin. Achievements of this project include: (I) developing a bobwhite management strategy on a landscape scale, (2) gaining a high level of landowner cooperation, and (3) implementing an extensive amount of habitat restoration on private agricultural lands at minimal costs. The major problem with our overall approach is that such habitat restoration work requires continuous attention and maintenance over time to maintain effectiveness. Landowners, while highly cooperative, are not interested in protecting or maintaining habitat improvements for wildlife unless they have a vested stake in the project (i.e., a sense of ownership ). Habitat restoration on private agricultural lands necessitates first working to change landowner attitudes towards wildlife, with the development of private lands habitat programs as a secondary concern. The outlook for northern bobwhites in the northern fringe of their range is not bright. Northern bobwhite populations will not recover unless they become a by-product of the contemporary agricultural landscape. Unfortunately, this is not the case in Wisconsin and it is unlikely to change in the foreseeable future

    A Unified Picture of the FIP and Inverse FIP Effects

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    We discuss models for coronal abundance anomalies observed in the coronae of the sun and other late-type stars following a scenario first introduced by Schwadron, Fisk & Zurbuchen of the interaction of waves at loop footpoints with the partially neutral gas. Instead of considering wave heating of ions in this location, we explore the effects on the upper chromospheric plasma of the wave ponderomotive forces. These can arise as upward propagating waves from the chromosphere transmit or reflect upon reaching the chromosphere-corona boundary, and are in large part determined by the properties of the coronal loop above. Our scenario has the advantage that for realistic wave energy densities, both positive and negative changes in the abundance of ionized species compared to neutrals can result, allowing both FIP and Inverse FIP effects to come out of the model. We discuss how variations in model parameters can account for essentially all of the abundance anomalies observed in solar spectra. Expected variations with stellar spectral type are also qualitatively consistent with observations of the FIP effect in stellar coronae.Comment: 25 pages, 4 figures, submitted to Ap

    Multi-line Stokes inversion for prominence magnetic-field diagnostics

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    We present test results on the simultaneous inversion of the Stokes profiles of the He I lines at 587.6 nm (D_3) and 1083.0 nm in prominences (90-deg scattering). We created datasets of synthetic Stokes profiles for the case of quiescent prominences (B<200 G), assuming a conservative value of 10^-3 of the peak intensity for the polarimetric sensitivity of the simulated observations. In this work, we focus on the error analysis for the inference of the magnetic field vector, under the usual assumption that the prominence can be assimilated to a slab of finite optical thickness with uniform magnetic and thermodynamic properties. We find that the simultaneous inversion of the two lines significantly reduces the errors on the inference of the magnetic field vector, with respect to the case of single-line inversion. These results provide a solid justification for current and future instrumental efforts with multi-line capabilities for the observations of solar prominences and filaments.Comment: 14 pages, 5 figures, 1 tabl

    Solar rotation rate and its gradients during cycle 23

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    Available helioseismic data now span almost the entire solar activity cycle 23 making it possible to study solar-cycle related changes of the solar rotation rate in detail. In this paper we study how the solar rotation rate, in particular, the zonal flows change with time. In addition to the zonal flows that show a well known pattern in the solar convection zone, we also study changes in the radial and latitudinal gradients of the rotation rate, particularly in the shear layer that is present in the immediate sub-surface layers of the Sun. In the case of the zonal-flow pattern, we find that the band indicating fast rotating region close to the equator seems to have bifurcated around 2005. Our investigation of the rotation-rate gradients show that the relative variation in the rotation-rate gradients is about 20% or more of their average values, which is much larger than the relative variation in the rotation rate itself. These results can be used to test predictions of various solar dynamo models.Comment: To appear in ApJ. Fig 5 has been corrected in this versio

    The continuum limit of the quark mass step scaling function in quenched lattice QCD

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    The renormalisation group running of the quark mass is determined non-perturbatively for a large range of scales, by computing the step scaling function in the Schroedinger Functional formalism of quenched lattice QCD both with and without O(a) improvement. A one-loop perturbative calculation of the discretisation effects has been carried out for both the Wilson and the Clover-improved actions and for a large number of lattice resolutions. The non-perturbative computation yields continuum results which are regularisation independent, thus providing convincing evidence for the uniqueness of the continuum limit. As a byproduct, the ratio of the renormalisation group invariant quark mass to the quark mass, renormalised at a hadronic scale, is obtained with very high accuracy.Comment: 23 pages, 3 figures; minor changes, references adde

    In situ GISAXS study of the growth of Pd on MgO(001)

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    The morphology of growing Pd nano-particles on MgO(001) surfaces have been investigated in situ, during growth, by grazing incidence small angle x-ray scattering, for different substrate temperatures. The 2D patterns obtained are quantitatively analyzed, and the average morphological parameters (shape, size) deduced. Above 650 K, the aggregates adopt their equilibrium shape of truncated octahedron, and the interfacial energy is deduced.Comment: 10 pages, 1 Table, 2 Figure

    Predicting scattering properties of ultracold atoms: adiabatic accumulated phase method and mass scaling

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    Ultracold atoms are increasingly used for high precision experiments that can be utilized to extract accurate scattering properties. This calls for a stronger need to improve on the accuracy of interatomic potentials, and in particular the usually rather inaccurate inner-range potentials. A boundary condition for this inner range can be conveniently given via the accumulated phase method. However, in this approach one should satisfy two conditions, which are in principle conflicting, and the validity of these approximations comes under stress when higher precision is required. We show that a better compromise between the two is possible by allowing for an adiabatic change of the hyperfine mixing of singlet and triplet states for interatomic distances smaller than the separation radius. A mass scaling approach to relate accumulated phase parameters in a combined analysis of isotopically related atom pairs is described in detail and its accuracy is estimated, taking into account both Born-Oppenheimer and WKB breakdown. We demonstrate how numbers of singlet and triplet bound states follow from the mass scaling.Comment: 14 pages, 9 figure
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