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Several series of celestial reference frames have been produced during the past few years as part of VLBI geodynamic programs. They consist in coordinates of 20 to 150 extragalactic radio sources with a precision at the level of 0.001″. The relative orientations of these frames and the evolution of each series of catalogs are studied.
The triennial report of Commission 19 was composed from the contributions of its members. Space does not permit a listing of their names, but their contributions are sincerely appreciated. Unfortunately because of limited space it is also not possible to provide in this report the extensive list of publication of the Commission members. The list of publications is however available on the Commission 19 web site at maia.usno.navy.mil/iauc19.
In this paper we develope an inertia! system of coordinates introducing a new observable: the arc between a pair of radio sources. We shall discuss how the conditional equation involving all the parameters is written in diferent systems when the observations are performed with a two and a three-element interferometers.
The celestial frame of HIPPARCOS astrometric satellite will be materialized by the positions and proper motions of about 120000 stars relative to arbitrary origins. As the HIPPARCOS reference frame is not naturally related to fixed directions in space, it has to be linked to an inertial frame of similar quality. The technique of VLBI determines the coordinates of extragalactic radio sources precise at the milliarcsecond level in an equatorial frame. The precision expected for HIPPARCOS normal mission is 0.002ʺ for the positions, yearly proper motions and parallaxes.
Mesolithic hunter-gatherer settlements generally leave ephemeral archaeological traces and are notoriously difficult to detect. Nowhere is this more so than on the northern coast of Spain, despite a long tradition of Mesolithic research. In this project, evidence of Mesolithic activity together with the geomorphological and topographical suitability of particular locations were used to select areas for large-scale geophysical survey. The results demonstrate the potential of the new methodology: magnetometry survey at El Alloru revealed the very first Asturian open-air settlement site to be discovered.
To prepare cholesteric liquid crystalline nonlinear optical materials with ability to be vitrified on cooling and form long time stability cholesteric glasses at room temperature, a series of platinum acetylide complexes modified with cholesterol has been synthesized. The materials synthesized have the formula trans-Pt(PR3)(cholesterol (3 or 4)-ethynyl benzoate)(1-ethynyl-4-X-benzene), where R = Et, Bu or Oct and X = H, F, OCH3 and CN. A cholesteric liquid crystal phase was observed in the complexes R = Et, and X = F, OCH3 and CN but not in any of the other complexes. When X = CN, a cholesteric glass was observed at room temperature which remained stable up to 130 °C, then converted to a mixed crystalline/cholesteric phase and completely melted to an isotropic phase at 230 °C. When X = F or OCH3 the complexes were crystalline at room temperature with conversion to the cholesteric phase upon heating to 190 and 230 °C, respectively. In the series X = CN, OCH3 and F, the cholesteric pitch was determined to be 1.7, 3.4 and 9.0 µ, respectively.
We review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM). We show that they presently are in the low 10−16 in relative value, based on the performance of primary standards, of the ensemble time scale and of the time transfer techniques. We consider how the 1 × 10−16 value could be reached or superseded and which are the present limitations to attain this goal.
We report large magnetoresistance (in excess of 1000%) in ferromagnet / superconductor / ferromagnet structures made of La0.7Ca0.3MnO3 and YBa2Cu3O7 in the current in plane (CIP) geometry. This magnetoresistance has many of the ingredients of the giant magnetoresistance of metallic superlattices: it is independent on the angle between current and magnetic field, depends on the relative orientation of the magnetization in the ferromagnetic layers, and takes very large values. The origin is enhanced scattering at the F/S interface in the anti parallel configuration of the magnetizations. Furthermore, we examine the dependence of the magnetoresistance effect on the thickness of the superconducting layer, and show that the magnetoresistance dies out for thickness in excess of 30 nm, setting a length scale for the diffusion of spin polarized quasiparticles.
We develop a simple model to derive theoretical continuum energy distributions for B[e] stars, consisting of a B star surrounded by an envelope made of gas and dust. We select a sample of B[e] objects for which we construct the observed energy distributions, from 0.1 to 100 μm, using available photometric and spectroscopic data. We present some preliminary fittings.
Twin and sibling studies have identified specific cognitive phenotypes that may mediate the association between genes and the clinical symptoms of attention deficit hyperactivity disorder (ADHD). ADHD is also associated with lower IQ scores. We aimed to investigate whether the familial association between measures of cognitive performance and the clinical diagnosis of ADHD is mediated through shared familial influences with IQ.
Multivariate familial models were run on data from 1265 individuals aged 6–18 years, comprising 920 participants from ADHD sibling pairs and 345 control participants. Cognitive assessments included a four-choice reaction time (RT) task, a go/no-go task, a choice–delay task and an IQ assessment. The analyses focused on the cognitive variables of mean RT (MRT), RT variability (RTV), commission errors (CE), omission errors (OE) and choice impulsivity (CI).
Significant familial association (rF) was confirmed between cognitive performance and both ADHD (rF=0.41–0.71) and IQ (rF=−0.25 to −0.49). The association between ADHD and cognitive performance was largely independent (80–87%) of any contribution from etiological factors shared with IQ. The exception was for CI, where 49% of the overlap could be accounted for by the familial variance underlying IQ.
The aetiological factors underlying lower IQ in ADHD seem to be distinct from those between ADHD and RT/error measures. This suggests that lower IQ does not account for the key cognitive impairments observed in ADHD. The results have implications for molecular genetic studies designed to identify genes involved in ADHD.
An approach is proposed for the evaluation of surface fatigue
damage of hot forming tools that undergo severe thermo
mechanical loading. Fatigue crack propagation in a hot work
tool steel X38CrMoV5-47HRC is investigated using singleedge
cracked tension specimens with 3 different thicknesses
(2.5, 1, 0.6 mm) and two R-values. The stress intensity factor
is evaluated with ABAQUS®. Paris curves are established for
the crack propagation experiments.
Demonstrating the equivalence of constructs is a key requirement for cross-cultural empirical research. The major purpose of this paper is to demonstrate how to assess measurement and functional equivalence or invariance using the 9-item, 3-factor Love of Money Scale (LOMS, a second-order factor model) and the 4-item, 1-factor Pay Level Satisfaction Scale (PLSS, a first-order factor model) across 29 samples in six continents (N = 5973). In step 1, we tested the configural, metric and scalar invariance of the LOMS and 17 samples achieved measurement invariance. In step 2, we applied the same procedures to the PLSS and nine samples achieved measurement invariance. Five samples (Brazil, China, South Africa, Spain and the USA) passed the measurement invariance criteria for both measures. In step 3, we found that for these two measures, common method variance was non-significant. In step 4, we tested the functional equivalence between the Love of Money Scale and Pay Level Satisfaction Scale. We achieved functional equivalence for these two scales in all five samples. The results of this study suggest the critical importance of evaluating and establishing measurement equivalence in cross-cultural studies. Suggestions for remedying measurement non-equivalence are offered.
The definition of UTC was implemented in 1972, principally to accommodate celestial navigation and follows recommendation 460 of the International Radio Consultative Committee (CCIR) in 1970. Since 1972 the use of electronic means to navigate has overtaken celestial navigation. This fact along with increasing public dissatisfaction with the possible disruption to modern electronic communications and navigation systems caused by the insertion of a leap second has called into question the current definition of UTC. An extensive review of the background and issues relating to the leap second can be found in Nelson, et al (2001).
Scanning probe microscopy (SPM) is unique among the imaging
techniques in which it provides three-dimensional (3-D) real-space
images and among surface analysis techniques in which it allows
spatially localized measurements of structure and properties. Under
optimum conditions, subatomic spatial resolution is achieved. The
development given has not been only because of its ability to obtain
topographic and structural images of the surface at micro and nano
scale, but also for the possibility of performing analysis of
superficial properties such as local adhesion properties, chemical
heterogeneity, and local mechanical properties . The SPM has
different variations depending on the interaction between the tip and
the sample surface, such as AFM, which has the ability of showing
topographic characteristics at atomic scale, LFM, which measures local
friction differences, FMM and PDM that measure differences of local
elasticity. The instrument counts with the spectroscopy mode and with
this it is possible to obtain Force — distance (F-d) curves that give
information about the local elastic properties of the sample surface. In
this work, TiN and ZrN thin films grown by the PAPVD by pulsed arc
technique were studied, using the AFM, LFM, FMM, PDM and spectroscopy F
vs. d techniques.
The distribution of sorbed arsenic(V) among different geochemical fractions for arsenic(V)-loaded red mud, an oxide-rich residue from bauxite refining that has been proposed as an adsorbent for arsenic, was studied as a function of sorbed arsenic(V) concentration using a sequential extraction procedure. The release of previously sorbed arsenic(V) was also studied as a function of pH and arsenic(V) concentration. Most sorbed arsenic(V) (0.39–7.86 mmol kg–1) was associated with amorphous and crystalline Al and Fe oxides (24.1–43.8% and 24.7–59.0% of total sorbed arsenic, respectively). Exchangeable arsenic was the smallest fraction (0.4–5.2% of total sorbed arsenic). The distribution of sorbed arsenic(V) was related to the arsenic surface coverage. For arsenic surface coverages >∼30% the percentage of arsenic(V) associated with the amorphous Al oxide fraction increased and that associated with the crystalline oxide fraction decreased. The arsenic(V) exchangeable fraction increased from 1.4 to 756 μmol kg–1 as surface coverage increased from 388 to 7855 μmol kg–1. The release of sorbed arsenic(V) from red mud was greater at alkaline pH values (maximum release of ∼33% of previously sorbed arsenic at pH = 12), but for high arsenic(V) initial concentration (0.2 mM arsenic) considerable amounts of arsenic (6.5% of previously sorbed arsenic) were released at pH 4, in accordance with the dissolution of amorphous Al oxides in the red mud. The results obtained suggest a greater mobility of sorbed arsenic(V) as its surface concentration approaches saturation.
Merimbla humicoloides sp. nov. was isolated after heat treatment of soil collected in a pine forest of Veracruz state, Mexico. The fungus is characterized by pale buff to cinnamon colonies that become dark brown to black in reverse and conidiophores that vary from irregularly asymmetrical penicilli to symmetrical penicilli with inflated metulae, and Humicola-like chlamydospores on the submerged hyphae. Phylogenetic inferences made from the ITS1-5·8S-ITS2 rDNA sequences indicate that M. humicoloides is a member of the Trichocomaceae and that it is related to M. ingelheimensis, Hamigera avellanea, and Penicillium species.
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