Homogeneous Distance Research Articles

A homogeneous distance catalogue for Galactic RV Tauri objects

AbstractA subset of Post-AGB (PAGB) objects are the highly luminous RV Tauri variables that show similarities to Type-II Cepheids. By using a sample of known RV Tauri stars from the Magellanic Clouds we are able to determine period luminosity relationships (PLRs) in various bands that have been used to determine the luminosities of their Galactic counterparts. We have gathered all available photometry in order to generate an SED for each object and determine the total integrated flux. This total flux combined with a calculated or inferred intrinsic luminosity leads to a distance (Vickers et al. 2015). This distance catalogue has allowed us to begin to constrain the physical parameters of this poorly understood evolutionary phase and to determine links between these physical characteristics as a function of their stellar population.

Hetero-/homogeneous combustion of fuel-lean methane/oxygen/nitrogen mixtures over rhodium at pressures up to 12 bar

The hetero-/homogeneous combustion of CH4/O2/N2 mixtures over rhodium was investigated experimentally and numerically at fuel-lean equivalence ratios φ=0.30–0.40, pressures 2–12bar, and catalyst temperatures 700–1250K. Experiments were performed in an optically accessible channel-flow reactor coated with rhodium and included in situ Raman measurements of major gas-phase species concentrations across the channel boundary layer for evaluating the catalytic processes, and planar laser induced fluorescence (LIF) of the OH radical for assessing homogeneous combustion. Computations were carried out with a 2-D elliptic code, using detailed heterogeneous and homogeneous chemical reaction mechanisms. Comparisons between Raman-measured and numerically-predicted transverse profiles of the limiting reactant (methane) mole fractions have led to the evaluation of the performance of detailed surface reaction mechanisms and to the construction of a one-step catalytic reaction suitable for pressures up to 12bar. For the investigated range 2–12bar, the catalytic reactivity of methane over rhodium exhibited an overall positive pressure dependence ∼p0.30, which was weaker compared to an earlier-reported pressure dependence of methane over platinum (∼p0.47). Comparisons of the planar OH-LIF measurements with numerical simulations employing different gas-phase reaction mechanisms demonstrated that the correct prediction of homogeneous ignition was particularly demanding at the present low equivalence ratios and moderate reactor temperatures. An elementary gaseous reaction mechanism was shown to reproduce the measured homogeneous ignition distances at all pressures, particularly when used in conjunction with the herein proposed one-step catalytic reaction.

Besicovitch covering property for homogeneous distances on the Heisenberg groups

We prove that the Besicovitch Covering Property (BCP) holds for homogeneous distances on the Heisenberg groups whose unit ball centered at the origin coincides with a Euclidean ball. We thus provide the first examples of homogeneous distances that satisfy BCP on these groups. Indeed, commonly used homogeneous distances, such as (Cygan–)Korányi and Carnot–Carathéodory distances, are known not to satisfy BCP. We also generalize those previous results by giving two geometric criteria that imply the non-validity of BCP and showing that in some sense our examples are sharp. To put our result in another perspective, inspired by an observation of D. Preiss, we prove that in a general metric space with an accumulation point, one can always construct bi-Lipschitz equivalent distances that do not satisfy BCP.

Repeated-root constacyclic codes of prime power length over [formula omitted] and their duals

The units of the chain ring Ra=Fpm[u]〈ua〉=Fpm+uFpm+⋯+ua−1Fpm are partitioned into a distinct types. It is shown that for any unit Λ of Type k, a unit λ of Type k∗ can be constructed, such that the class of λ-constacyclic of length ps of Type k∗ codes is one-to-one correspondent to the class of Λ-constacyclic codes of the same length of Type k via a ring isomorphism. The units of Ra of the form Λ=Λ0+uΛ1+⋯+ua−1Λa−1, where Λ0,Λ1,…,Λa−1∈Fpm, Λ0≠0,Λ1≠0, are considered in detail. The structure, duals, Hamming and homogeneous distances of Λ-constacyclic codes of length ps over Ra are established. It is shown that self-dual Λ-constacyclic codes of length ps over Ra exist if and only if a is even, and in such case, it is unique. Among other results, we discuss some conditions when a code is both α- and β-constacyclic over Ra for different units α, β.

Neutron-capture elements across the Galactic thin disk using Cepheids

We present new accurate abundances for five neutron-capture (Y, La, Ce, Nd, Eu) elements in 73 classical Cepheids located across the Galactic thin disk. Individual abundances are based on high spectral resolution (R ~ 38,000) and high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO VLT for the DIONYSOS project. Taking account for similar Cepheid abundances provided either by our group (111 stars) or available in the literature, we end up with a sample of 435 Cepheids covering a broad range in iron abundances (-1.6 < [Fe/H] < 0.6). We found, using homogeneous individual distances and abundance scales, well defined gradients for the above elements. However, the slope of the light s-process element (Y) is at least a factor of two steeper than the slopes of heavy s- (La, Ce, Nd) and r- (Eu) process elements. The s to r abundance ratio ([La/Eu]) of Cepheids shows a well defined anticorrelation with of both Eu and Fe. On the other hand, Galactic field stars attain an almost constant value and only when they approach solar iron abundance display a mild enhancement in La. The [Y/Eu] ratio shows a mild evidence of a correlation with Eu and, in particular, with iron abundance for field Galactic stars. We also investigated the s-process index - [hs/ls] - and we found a well defined anticorrelation, as expected, between [La/Y] and iron abundance. Moreover, we found a strong correlation between [La/Y] and [La/Fe] and, in particular, a clear separation between Galactic and Sagittarius red giants. Finally, the comparison between predictions for low-mass asymptotic giant branch stars and the observed [La/Y] ratio indicate a very good agreement over the entire metallicity range covered by Cepheids. However, the observed spread, at fixed iron content, is larger than predicted by current models.

Optimal combination of gridded and ground-observed solar radiation data for regional solar resource assessment

Proper quantification of the available solar resource is essential for the diverse development phases of any solar power plant. At local scale, the solar resource is best assessed from ground radiometric stations. At regional-to-continental scales, however, satellite-based techniques are currently the most suitable approach. Solar radiation evaluation using numerical weather prediction (NWP) models presents some advantages over satellite-based techniques. Nonetheless, gridded solar radiation estimates using either satellite-based or NWP-based techniques still produce biased estimates which are often much higher for the latter. Therefore, a correction needs to be applied before these gridded values are usable for solar applications, especially for NWP-based estimates. This contribution introduces an original method based on the optimal interpolation technique to adjust gridded solar radiation estimates consistently with concomitant radiometric ground observations. The method’s performance is demonstrated using NWP-based gridded estimates with 10-km spacing of global and direct monthly irradiation data during the 10-year period from 2003 to 2012 over continental Spain and the Balearic Islands. It is shown that the proposed methodology produces adjusted gridded values that are (or nearly always are, in the case of direct irradiation) within the expected measurement uncertainty of the ground observations, provided a sufficiently large number of observations is available for correction. For the studied region and these NWP-based gridded datasets, our findings suggest that a homogeneous mean distance between ground observations of 100–150km can result in unbiased gridded estimates.

Isometries of Carnot Groups and Sub-Finsler Homogeneous Manifolds

We show that isometries between open sets of Carnot groups are affine. This result generalizes a result of Hamenstädt. Our proof does not rely on her proof. We show that each isometry of a sub-Riemannian manifold is determined by the horizontal differential at one point. We then extend the result to sub-Finsler homogeneous manifolds. We discuss the regularity of isometries of homogeneous manifolds equipped with homogeneous distances that induce the manifold topology.

HyperLEDA. III. The catalogue of extragalactic distances

We present the compilation catalogue of redshift-independent distances included in the HyperLEDA database. It is actively maintained to be up-to-date, and the current version counts 6640 distance measurements for 2335 galaxies compiled from 430 published articles. Each individual series is recalibrated onto a common distance scale based on a carefully selected set of high-quality measurements. This information together with data on HI line-width, central velocity dispersion, magnitudes, diameters, and redshift is used to derive a homogeneous distance estimate and physical properties of galaxies, such as their absolute magnitudes and intrinsic size.

On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk

We present homogeneous and accurate iron abundances for 42 Galactic Cepheids based on high-spectral resolution (R~38,000) high signal-to-noise ratio (SNR>100) optical spectra collected with UVES at VLT (128 spectra). The above abundances were complemented with high-quality iron abundances provided either by our group (86) or available in the literature. We paid attention in deriving a common metallicity scale and ended up with a sample of 450 Cepheids. We also estimated for the entire sample accurate individual distances by using homogeneous near-infrared photometry and the reddening free Period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (Rg~5-19 kpc) and agrees quite well with similar estimates available in the literature (-0.060+/-0.002 dex/kpc). We also uncover evidence which suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid Groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the residual fluctuations, and in turn for the large intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers: OB stars and open clusters. We found very similar metallicity gradients for ages younger than 3 Gyrs, while for older ages we found a shallower slope and an increase in the intrinsic spread. The above findings rely on homogeneous age, metallicity and distance scales. Finally we found, by using a large sample of Galactic and Magellanic Cepheids for which are available accurate iron abundances, that the dependence of the luminosity amplitude on metallicity is vanishing.

The Effect of Psychological Distance on Intertemporal Choice and Risky Choice

Temporal distance, social distance and probabilistic distance are three basic dimensions of psychological distance. It has been proved that different kinds of psychological distance have similar effects on cognitive representations of events. In general, distant events are represented as high-level construals, whereas near events are represented as low-level construals. As events become more distant, the high-level construals become more influential in shaping preference whereas the low-level construals become less influential(Liberman, Trope, Stephan, 2007; Liberman, Trope, 2008; Trope, Liberman, 2010).This study investigates the effects of temporal, social and probabilistic distance on intertemporal choice and risky choice. We hypothesize that different kinds of distance have similar effects on intertemporal and risky choice, based on the assumptions that these three kinds of distance share the same nature as psychological distance, and that intertemporal choice and risky choice have common processes of option representation and weighting. When psychological distance increases, money magnitude as high-level construal becomes more influential while time and probability as low-level construals become less influential(Sagristano, Trope, Liberman, 2002; Trope Liberman, 2003). Therefore, participants in distant conditions would choose delayed and risky alternatives with larger monetary value.Experiment 1 investigated the effect of temporal distance on intertemporal and risky choices. Participants were told that they would participate in a visual experiment, but before that they needed to make an intertemporal choice as their rewards between "$50 immediately" and "$90 in 3 months"(experiment 1a), or between " $ 50 for sure" and " $ 200 with the probability of 20%"(experiment 1b). In near condition, the experiment would be conducted soon, and in distant condition the experiment would be conducted in 6 months.Experiment 2 investigated the effect of social distance. In near condition, participants would make choice for themselves, and in distant condition, for other people. Experiment 3 investigated the effect of probabilistic distance. In near condition, participants were told that they would participate in the experiment with 90%probability, and in distant condition, with 10% probability. The options of intertemporal choice and risky choice are similar to experiment 1. The results show that no matter what kind of distance was involved, there were more participants in distant condition who chose delayed or risky alternatives than those who did in near condition,which confirms the hypotheses.The similar effects of temporal, social and probabilistic distance on intertemporal and risky choices suggest that intermporal and risky choices share common psychological process, and these three kinds of distance are homogeneous psychological distance.

The Distribution of Homogeneous Distance of constacyclic Codes over

该文研究了环Rk=Fpm ＋ uFpm ＋…＋uk^-1Fpm上任意长的（1＋u）-常循环码的齐次距离分布。首先，介绍了环Rk上给定长度的（1＋u）-常循环码的挠码。然后利用挠码得到环Rk上任意长度的（1＋u）-常循环码的齐次距离的界，并给出了Rk上某些（1＋u）-常循环码的齐次距离的准确值。

Modeling Spatial Patchiness and Hot Spots in Stated Preference Willingness to Pay

Stated preference analyses often impose strong assumptions regarding spatial welfare distributions that can influence the validity of welfare analysis and aggregation. These include spatial homogeneity and continuous distance decay. Global assumptions such as these are increasingly questioned by non-economics disciplines in favor of approaches that allow for local patchiness. Drawing from this literature, this article proposes methods to identify and evaluate hot spots in stated preference welfare estimates using local indicators of spatial association. Methods are illustrated using geocoded choice experiment data addressing river restoration. Results suggest the presence of statistically significant, non-continuous patterns overlooked by current approaches.

Homogeneous Distances to Several Stellar Groups in the Second Galactic Quadrant

A photometric study in the uvbyβ system of a 20° × 20° field in direction of the Cas OB6 and Per OB1 associations is presented. All currently available uvbyβ photoelectric data are used to obtain homogeneous color excesses and distances of nearly 230 stars of spectral types O-B9. The double cluster h & χ Per, NGC 663 and NGC 1502 are well represented in our sample. The sample also contains the brightest members of the young open clusters IC 1805, IC 1848, St 2, St 7 and ASCC9. We found that, within the errors, h & χ Per, NGC 663, IC 1805, IC 1848 and ASCC9, together with the Per OB1 association are located at very similar distance moduli between 11.0 to 11.3 mag. Our results indicate that the distance spread among these objects is less than the previously estimated, suggested that they could represent starforming complexes located at the same distance.

Cepheus Star-Forming Field Revisited

We present a photometric investigation in the uvbyβ system of a 20° × 20° field centered at galactic coordinates (l, b) = (105°, 5°). This region contains a relatively isolated structure of numerous HII regions in the direction of some of the OB associations in Cepheus and Cassiopeia. Photoelectric uvbyβ data of more than 220 stars of spectral types O-B9 are available for this field and are used to obtain homogeneous distance estimates for a number of prominent stellar groups, among which are the Cep OB2 and Cep OB3 associations and the open clusters NGC 7243 and NGC 7654.

Global survey of star clusters in the Milky Way: The open cluster distance scale

AbstractWe present the Milky Way Star Clusters (MWSC) survey based on 470 million stars extracted from the all-sky catalogues PPMXL and 2mass. The target list comprises 3784 entries and includes all open and globular clusters, as well as all cluster candidates, known at present. By means of a combined photometric/astrometric pipeline process, we determine individual membership probabilities for cluster stars and provide fundamental cluster parameters such as cluster centre coordinates, mean proper motions, radial velocity, distance, reddening, age and tidal radius. This sample includes ~ 700 clusters with fundamental parameters based on optical data and offers a good opportunity for a comparison of the near-infrared (NIR) and optical cluster distance scales. We find that distances and reddening values obtained from the colour–magnitude diagrams (CMDs) in the NIR agree well with earlier distance estimates based on optical CMDs. These newly obtained homogeneous distances, together with the other cluster parameters, allow us to study the properties of the open cluster population in the Galactic disk.

Negacyclic codes over Galois rings of characteristic 2 a

We investigate negacyclic codes over the Galois ring GR(2 a ,m) of length N = 2 k n, where n is odd and k ⩾ 0. We first determine the structure of u-constacyclic codes of length n over the finite chain ring $GR(2^a ,m)[u]/\langle u^{2^k } + 1\rangle $ . Then using a ring isomorphism we obtain the structure of negacyclic codes over GR(2 a ,m) of length N = 2 k n (n odd) and explore the existence of self-dual negacyclic codes over GR(2 a ,m). A bound for the homogeneous distance of such negacyclic codes is also given.

Reproducibility of phantom-based quality assurance parameters in real-time ultrasound imaging

In a large radiological center, the ultrasound (US) quality assurance (QA) program involves several professionals. Although the operator and the parameters utilized can contribute to the results, the selected QA parameters should still reflect the quality of the US scanner, not the measuring process. To evaluate the reproducibility of recommended phantom-based US QA parameters in a realistic environment. Six sonographers measured six high-end US scanners with 20 transducers using a general purpose phantom. Every transducer was measured altogether seven times, using one frequency per transducer. The QA parameters studied were homogeneity, visualization depth, vertical and horizontal distance measurements, axial and lateral resolution, and the correct visibility of anechoic and high-contrast masses. The evaluation of the homogeneity was based on visual observations. Inter-observer interquartile ranges were computed for the grading of the masses. For the other QA parameters, the mean inter- and intra-observer coefficients of variation (CoV) were calculated. In addition, the symmetry of the reverberations when imaging air with a clean transducer was checked. The mean inter-observer CoVs were: visualization depth 11 ± 4%, vertical distance 1.7 ± 0.4%, horizontal distance 1.4 ± 0.6%, axial resolution 22 ± 7%, and lateral resolution 16 ± 8%. The mean intra-observer values were about half of these values with similar standard deviations. The visual evaluation of the homogeneity and the symmetry of the reverberations produced false-positive findings in 5% of the cases, but were found useful in detecting a defective transducer. The grading of the masses had mean interquartile ranges of 20-30% of the grading scale. The inter-observer variability in measuring phantom-based QA parameters can be relatively high. This should be considered when implementing a phantom-based QA protocol and evaluating the results.

Isodiametric inequality in Carnot groups

The classical isodiametric inequality in the Euclidean space says that balls maxi- mize the volume among all sets with a given diameter. We consider in this paper the case of Carnot groups. We prove that for any non abelian Carnot group equipped with a Haar measure one can find a homogeneous distance for which this fails to hold. We also consider Carnot-Caratheodory distances and prove that this also fails for these distances as soon as there are length minimiz- ing curves that stop to be minimizing in finite time. Next we study some connections with the comparison between Hausdor and spherical Hausdor measures, rectifiability and the generalized 1/2-Besicovitch conjecture, giving in particular some cases where this conjecture fails.

Experimental and numerical investigation of hetero-/homogeneous combustion of CO/H 2/O 2/N 2 mixtures over platinum at pressures up to 5 bar

The hetero-/homogeneous combustion of fuel-lean CO/H 2/O 2/N 2 mixtures over platinum is investigated at pressures up to 5 bar, inlet temperatures ( T IN) up to 874 K, and a constant CO:H 2 molar ratio of 2:1. Experiments are performed in an optically accessible channel-flow catalytic reactor and involve planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition and 1-D Raman measurements of major gas-phase species concentrations over the catalyst boundary layer for the evaluation of the heterogeneous (catalytic) processes. Simulations are carried out with an elliptic 2-D model that includes detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduce the Raman-measured catalytic CO and H 2 consumption, and it is further shown that for wall temperatures in the range 975 ⩽ T w ⩽ 1165 K the heterogeneous pathways of CO and H 2 are largely decoupled. However, for wall temperatures below a limiting value of 710–720 K and for the range of pressures and mixture preheats investigated, CO(s) blockage of the surface inhibits the catalytic conversion of both fuel components. The homogeneous ignition distance is well-reproduced by the model for T IN > 426 K, but it is modestly overpredicted at lower T IN. Possible reasons for these modest differences can be the values of third body efficiencies in the gas-phase reaction mechanism. The sensitivity of homogeneous ignition distance on the catalytic reactions is weak, while the H 2/O 2 subset of the CO/H 2/O 2 gaseous reaction mechanism controls the onset of homogeneous ignition. Pure hydrogen hetero-/homogeneous combustion results in flames established very close to the catalytic walls. However, in the presence of CO the gaseous combustion of hydrogen extends well-inside the channel core, thus allowing homogeneous consumption of H 2 at considerably shorter reactor lengths. Finally, implications of the above findings for the design of syngas-based catalytic reactors for power generation systems are discussed.

The Carina spiral feature: Strömgren-β photometry approach

Aims. In recent years a significant development has become evident in the study of the stellar structure of the Galactic disk. This is especially true for the 3rd Galactic quadrant, where the stellar population was extensively investigated beyond 10 kpc, revealing details about the warped geometry of the thin and thick disks and outer arm. The 4th Galactic quadrant offers even better opportunity to follow the distribution of the young stellar populace to a large distance, since the line of sight is parallel to the largest single segment of a spiral arm seen from our position in the Galaxy: the Carina spiral feature. This paper further contributes to the study of the structure of the Galactic disk in the direction of Carina field utilizing homogeneous photometric distances of a sample of about 600 bright early-type stars seen in this direction up to 6 kpc. Methods. The derived stellar distances are based on uvbyβ photometry. All O and B type stars with uvbyβ data presently available are included in the study. Results. The photometry-derived parameters allow us to study the structure and characteristics of this segment of the Carina arm. We find that the stellar distribution is consistent with a location of the apparent edge of the arm at l = 287 ◦ . Toward the edge of the arm the warp of the Galactic plane can be traced up to 6 kpc where it reaches negative 200 pc. The field toward the edge seems to be much more complex than harboring just one OB association, and it is likely that some of the apparent concentrations in this field represent parts of long segments of the edge. In the 284 ◦ ‐289 ◦ longitude range an interarm space about 1 kpc wide is found beyond 850 pc from the Sun. The giant molecular clouds and open clusters do not follow the edge of the arm as defined by the OB stars and indicate a possible presence of an age gradient in a direction perpendicular to the formal Galactic plane.