Showing papers by "Federal University of Rio de Janeiro published in 2011"

Quantifying defects in graphene via Raman spectroscopy at different excitation energies

Abstract: We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities for a given defect density strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an inter-defect distance ~3nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.

Sdss-iii: massive spectroscopic surveys of the distant universe, the milky way, and extra-solar planetary systems

Abstract: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5 million massive galaxies and Lya forest spectra of 150,000 quasars, using the BAO feature of large scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z 100 per resolution element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. (Abridged)

Quantifying defects in graphene via Raman spectroscopy at different excitation energies.

Abstract: We present a Raman study of Ar+-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.

The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III

Abstract: The Sloan Digital Sky Survey (SDSS) started a new phase in 2008 August, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Lyα forest, and a radial velocity search for planets around ~8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg2 in the southern Galactic cap, bringing the total footprint of the SDSS imaging to 14,555 deg2, or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Exploration (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameter pipeline, which has better determination of metallicity for high-metallicity stars.

A Molecular Phylogeny of Living Primates

Abstract: Comparative genomic analyses of primates offer considerable potential to define and understand the processes that mold, shape, and transform the human genome. However, primate taxonomy is both complex and controversial, with marginal unifying consensus of the evolutionary hierarchy of extant primate species. Here we provide new genomic sequence (,8 Mb) from 186 primates representing 61 (,90%) of the described genera, and we include outgroup species from Dermoptera, Scandentia, and Lagomorpha. The resultant phylogeny is exceptionally robust and illuminates events in primate evolution from ancient to recent, clarifying numerous taxonomic controversies and providing new data on human evolution. Ongoing speciation, reticulate evolution, ancient relic lineages, unequal rates of evolution, and disparate distributions of insertions/deletions among the reconstructed primate lineages are uncovered. Our resolution of the primate phylogeny provides an essential evolutionary framework with far-reaching applications including: human selection and adaptation, global emergence of zoonotic diseases, mammalian comparative genomics, primate taxonomy, and conservation of endangered species.

Design concepts for the Cherenkov Telescope Array CTA: An advanced facility for ground-based high-energy gamma-ray astronomy

Abstract: Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

Uniformity of rotavirus strain nomenclature proposed by the Rotavirus Classification Working Group (RCWG).

Abstract: In April 2008, a nucleotide-sequence-based, complete genome classification system was developed for group A rotaviruses (RVs). This system assigns a specific genotype to each of the 11 genome segments of a particular RV strain according to established nucleotide percent cutoff values. Using this approach, the genome of individual RV strains are given the complete descriptor of Gx-P[x]-Ix-Rx-Cx-Mx-Ax-Nx-Tx-Ex-Hx. The Rotavirus Classification Working Group (RCWG) was formed by scientists in the field to maintain, evaluate and develop the RV genotype classification system, in particular to aid in the designation of new genotypes. Since its conception, the group has ratified 51 new genotypes: as of April 2011, new genotypes for VP7 (G20-G27), VP4 (P[28]-P[35]), VP6 (I12-I16), VP1 (R5-R9), VP2 (C6-C9), VP3 (M7-M8), NSP1 (A15-A16), NSP2 (N6-N9), NSP3 (T8-T12), NSP4 (E12-E14) and NSP5/6 (H7-H11) have been defined for RV strains recovered from humans, cows, pigs, horses, mice, South American camelids (guanaco), chickens, turkeys, pheasants, bats and a sugar glider. With increasing numbers of complete RV genome sequences becoming available, a standardized RV strain nomenclature system is needed, and the RCWG proposes that individual RV strains are named as follows: RV group/species of origin/country of identification/common name/year of identification/G- and P-type. In collaboration with the National Center for Biotechnology Information (NCBI), the RCWG is also working on developing a RV-specific resource for the deposition of nucleotide sequences. This resource will provide useful information regarding RV strains, including, but not limited to, the individual gene genotypes and epidemiological and clinical information. Together, the proposed nomenclature system and the NCBI RV resource will offer highly useful tools for investigators to search for, retrieve, and analyze the ever-growing volume of RV genomic data.

General framework for estimating the ultimate precision limit in noisy quantum-enhanced metrology

Abstract: Quantum strategies can help to make parameter-estimation schemes more precise, but for noisy processes it is typically not known how large that improvement may be. Here, a universal quantum bound is derived for the error in the estimation of parameters that characterize dynamical processes.

Three Months of Rifapentine and Isoniazid for Latent Tuberculosis Infection

Abstract: In the modified intention-to-treat analysis, tuberculosis developed in 7 of 3986 subjects in the combination-therapy group (cumulative rate, 0.19%) and in 15 of 3745 subjects in the isoniazid-only group (cumulative rate, 0.43%), for a difference of 0.24 percentage points. Rates of treatment completion were 82.1% in the combination-therapy group and 69.0% in the isoniazid-only group (P<0.001). Rates of permanent drug discontinuation owing to an adverse event were 4.9% in the combination-therapy group and 3.7% in the isoniazid-only group (P = 0.009). Rates of investigator-assessed drug-related hepatotoxicity were 0.4% and 2.7%, respectively (P<0.001). Conclusions The use of rifapentine plus isoniazid for 3 months was as effective as 9 months of isoniazid alone in preventing tuberculosis and had a higher treatment-completion rate. Long-term safety monitoring will be important. (Funded by the Centers for Disease Control and Prevention; PREVENT TB ClinicalTrials.gov number, NCT00023452.)

Spatially resolving edge states of chiral graphene nanoribbons

Abstract: Edge effects matter in graphene, particularly in nanoribbons. A study using scanning tunnelling microscopy and spectroscopy reveals how chirality at the atomically well-defined edges of a graphene nanoribbon affects its electronic structure.

Carbon emission from hydroelectric reservoirs linked to reservoir age and latitude

Abstract: Hydroelectric reservoirs cover an area of 3.4 x 10(5) km(2) and comprise about 20% of all reservoirs. In addition, they contain large stores of formerly terrestrial organic carbon. Significant amou ...

The methylation effect in medicinal chemistry.

Abstract: The Methylation Effect in Medicinal Chemistry Eliezer J. Barreiro,* Arthur E. K€ummerle, and Carlos A. M. Fraga Laborat orio de Avaliac-~ao e Síntese de Subst̂ancias Bioativas (LASSBio), Faculdade de Farm acia, Universidade Federal do Rio de Janeiro, CCS, Cidade Universit aria, CP 68.006, 21941-902 Rio de Janeiro, RJ, Brazil Programa de P os-Graduac-~ao em Farmacologia e Química Medicinal, Instituto de Cîencias Biom edicas, Universidade Federal do Rio de Janeiro, Cidade Universit aria, Ilha do Fund~ao, Rio de Janeiro, RJ, Brazil Programa de P os-Graduac-~ao em Química, Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universit aria, Ilha do Fund~ao, Rio de Janeiro, RJ, Brazil

Pseudoprogression and pseudoresponse: imaging challenges in the assessment of posttreatment glioma.

Abstract: The current standard of care for newly diagnosed cases of high-grade glioma is surgical resection followed by RT with concurrent chemotherapy. The most widely used criteria for assessing treatment response are based on a 2D measurement of the enhancing area on MR imaging known as the Macdonald Criteria. Recently, nontumoral increases (pseudoprogression) and decreases (pseudoresponse) in enhancement have been found, and these can confuse outcome evaluation. Here we review pseudoprogression and pseudoresponse and describe how better understanding of these phenomena can aid interpretation.

Nodular diagnosis for ecological engineering of the symbiotic nitrogen fixation with legumes

Abstract: As a major contributor to the reduced nitrogen pool in the biosphere, symbiotic nitrogen fixation by legumes plays a critical role in a sustainable production system. However this legume contribution varies with the physico-chemical and biological conditions of the nodulated-root rhizosphere. In order to assess the abiotic and biotic constrains that might limit this symbiosis at the agroecosystem level, a nodular diagnosis is proposed with common bean as a model grain-legume, and a major source of plant proteins for world human nutrition. The engineering of the legume symbiosis is addressed by participatory assessment of bean recombinant inbred lines contrasting for their efficiency in use of phosphorous for symbiotic nitrogen fixation. With this methodology, in field-sites chosen with farmers of an area of cereal-cropping in the Mediterranean basin, a large spatial and temporal variation in the legume nodulation was found. Soil P availability was a major limiting factor of the rhizobial symbiosis. In order to relate the field measurements with progress in functional genomics of the symbiosis, in situ RT-PCR on nodule sections has been implemented showing that the phytase gene is expressed in the cortex with significantly higher number of transcripts in P-efficient RILs. It is concluded that various tools and indicators are available for developing the ecological engineering of the rhizobial symbiosis, in particular for its beneficial contribution to the bio-geochemical cycle of N, and also P and C.

Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC

Abstract: Measurements are presented from proton-proton collisions at centre-of-mass energies of root s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with p(T) > 100 MeV, is measured to be 3.483 +/- 0.009 (stat) +/- 0.106 (syst) at root s = 0.9 TeV and 5.630 +/- 0.003 (stat) +/- 0.169 (syst) at root s = 7 TeV.

Performance of the LHCb Vertex Locator

Abstract: The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the proton-proton interaction region in the LHCb experiment The performance of the detector during the first years of its physics operation is reviewed The system is operated in vacuum, uses a bi-phase CO2 cooling system, and the sensors are moved to 7mm from the LHC beam for physics data taking The performance and stability of these characteristic features of the detector are described, and details of the material budget are given The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described The system performance is fully characterised The sensors have a signal to noise ratio of approximately 20 and a best hit resolution of 4 mu m is achieved at the optimal track angle The typical detector occupancy for minimum bias events in standard operating conditions in 2011 is around 05%, and the detector has less than 1% of faulty strips The proximity of the detector to the beam means that the inner regions of the n(+)-on-n sensors have undergone space-charge sign inversion due to radiation damage The VELO performance parameters that drive the experiment's physics sensitivity are also given The track finding efficiency of the VELO is typically above 98% and the modules have been aligned to a precision of 1 mu m for translations in the plane transverse to the beam A primary vertex resolution of 13 mu m in the transverse plane and 71 mu m along the beam axis is achieved for vertices with 25 tracks An impact parameter resolution of less than 35 mu m is achieved for particles with transverse momentum greater than 1GeV/c

Epidemiology of endemic systemic fungal infections in Latin America

Abstract: Although endemic mycoses are a frequent health problem in Latin American countries, clinical and epidemiological data remain scarce and fragmentary. These mycoses have a significant impact on publi...

Measurement of J/psi production in pp collisions at root s=7 TeV

Abstract: The production of J/psi mesons in proton-proton collisions at root s = 7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/psi production is measured as a function of the J/psi transverse momentum p(T) and rapidity y in the fiducial region p(T) is an element of [0; 14] GeV/c and y is an element of [2.0; 4.5]. The differential cross-section and fraction of J/psi from b-hadron decays are also measured in the same p(T) and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2 pb(-1). The measured cross-sections integrated over the fiducial region are 10.52 +/- 0.04 +/- 1.40(-2.20)(+1.64) mu b for prompt J/psi production and 1.14 +/- 0.01 +/- 0.16 mu b for J/psi from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/psi production cross-section is obtained assuming no J/psi polarisation and the third error indicates the acceptance uncertainty due to this assumption.

Scaling of Brain Metabolism with a Fixed Energy Budget per Neuron: Implications for Neuronal Activity, Plasticity and Evolution

Abstract: It is usually considered that larger brains have larger neurons, which consume more energy individually, and are therefore accompanied by a larger number of glial cells per neuron. These notions, however, have never been tested. Based on glucose and oxygen metabolic rates in awake animals and their recently determined numbers of neurons, here I show that, contrary to the expected, the estimated glucose use per neuron is remarkably constant, varying only by 40% across the six species of rodents and primates (including humans). The estimated average glucose use per neuron does not correlate with neuronal density in any structure. This suggests that the energy budget of the whole brain per neuron is fixed across species and brain sizes, such that total glucose use by the brain as a whole, by the cerebral cortex and also by the cerebellum alone are linear functions of the number of neurons in the structures across the species (although the average glucose consumption per neuron is at least 10× higher in the cerebral cortex than in the cerebellum). These results indicate that the apparently remarkable use in humans of 20% of the whole body energy budget by a brain that represents only 2% of body mass is explained simply by its large number of neurons. Because synaptic activity is considered the major determinant of metabolic cost, a conserved energy budget per neuron has several profound implications for synaptic homeostasis and the regulation of firing rates, synaptic plasticity, brain imaging, pathologies, and for brain scaling in evolution.

Raman signature of graphene superlattices.

Abstract: When two identical two-dimensional periodic structures are superposed, a mismatch rotation angle between the structures generates a superlattice. This effect is commonly observed in graphite, where the rotation between graphene layers generates Moire patterns in scanning tunneling microscopy images. Here, a study of intravalley and intervalley double-resonance Raman processes mediated by static potentials in rotationally stacked bilayer graphene is presented. The peak properties depend on the mismatch rotation angle and can be used as an optical signature for superlattices in bilayer graphene. An atomic force microscopy system is used to produce and identify specific rotationally stacked bilayer graphenes that demonstrate the validity of our model.

Marine biodiversity in the Atlantic and Pacific coasts of South America: knowledge and gaps.

Abstract: The South American region The marine areas of the South American continent extend for almost 30,000 km of coastline and encompass three different oceanic domains—the Caribbean, the Pacific, and the Atlantic. The latitudinal and longitudinal ranges within this region are similarly wide, from 12°N to 55°S, and from 34° to 81°W. Ten countries border on these coasts, each with different research capabilities and taxonomic traditions; therefore, taxonomic knowledge differs among countries. Coastal biodiversity is strongly influenced by the physical and geological history of these coasts. The eastern tropical Pacific region, which encompasses the continental coasts of southern Central America (Costa Rica and Panama) and of northwestern South America (Colombia and Ecuador) is characterized by cliffs alternating with pocket beaches, alluvial and deltaic plains with extensive sandy beaches, well-developed mangrove forests, estuaries, lagoons, and, reefs. It also includes important offshore island systems such as the Pearl and Galapagos islands [1], [2]. The Peruvian coast also is diverse with bays, cliffs, kelp and macroalgal beds, rocky shores and sandy beaches, islands, and peninsulas, as well as wetlands, which include the southernmost limit to the tropical Pacific mangrove ecosystem [3], [4]. The Chilean coast is 4,500 km of mainly rocky shores, but does include some sandy-beach bays with channels and archipelagos toward the south (Patagonian region) [5], [6]. Some of the most diverse ecosystems in Chile are the beds of kelp (Lessonia and Macrosystis) and macroalgae (Gracillaria and Ulva). The combination of the unique oceanographic conditions and coastal heterogeneity in the Chilean coast has resulted in high levels of endemism (near 40%) in many invertebrate groups [5], and several marine invertebrate taxa show latitudinal biodiversity patterns, some of them explained by the presence of Antarctic fauna [7]–[9]. Ecuador, Peru, and Chile are under the influence of the Humboldt upwelling system and subject to high environmental variability caused by the ENSO (El Nino Southern Oscillation) and LNSO (La Nina Southern Oscillation), which cause important changes in community composition and abundance, particularly of the plankton [1], [10]. The Atlantic coast of the South American continent is distinctly different from the Pacific coast. It includes three major rivers (Orinoco, Amazon, and La Plata), which discharge enormous amounts of freshwater and sediment to the ocean, and the coast has an extensive continental platform. Argentina's coast has mostly sandy beaches [6], [11] and some rocky formations located mainly at Mar del Plata and at Peninsula Valdes. At Mar del Plata, these rocky shores are dominated by two mussel species and by a diverse macroalgal community with a clear tidal zonation [12], [13]. The Uruguayan coast is dominated by sandy beaches with a narrow portion of rocky habitats known to sustain a rich biological diversity [14]. Observed variations in community composition and distribution may be related to the salinity gradient caused by La Plata River discharge [15]. The coast of Brazil, extending almost 7,500 km, is under the influence of the warm Brazil Current, the cold Malvinas/Falklands Current, and many rivers and upwelling regions [16]. The warm northern coast, where the Amazon discharges into the ocean, is characterized by a combination of freshwater, estuarine, and marine ecosystems, with diverse but poorly known habitats [17]. The colder southern coast is characterized by a variety of ecosystems, including mangrove forests, seagrass beds, coral reefs, sandy beaches, rocky shores, lagoons, and estuaries. Because of its vastness, extensive areas of Brazil's coast remain unexplored. North of Brazil are Suriname, French Guiana, Guyana, and the Venezuelan Atlantic Front. This area, including about 1,900 km of coastline, is under the strong influence of the Amazon River. Therefore, the typical ecosystems are estuaries, mudflats, sandy beaches, and mangrove forests, which extend along most of the coastline [18]. The Venezuelan Atlantic coast is also under the influence of the Orinoco River, with coastal mudflats and extensive mangrove forests [19]. In this paper, we analyze the status of knowledge of marine biodiversity in five subregions along the Atlantic and Pacific coasts of South America. As most of the information is based in national reports, these subregions were based in the Large Marine Ecosystem boundaries as defined for South America, with a few practical adaptations, based in country political borders. The paper also provides an updated review of ecosystem threats, such as invasive species, and the marine conservation strategies employed by South American countries with access to the coast, excluding the Caribbean coasts of Venezuela and Colombia, as these are included in another paper of this collection [20].

Revealing hidden Einstein-Podolsky-Rosen nonlocality.

Abstract: Steering is a form of quantum nonlocality that is intimately related to the famous Einstein-Podolsky-Rosen (EPR) paradox that ignited the ongoing discussion of quantum correlations. Within the hierarchy of nonlocal correlations appearing in nature, EPR steering occupies an intermediate position between Bell nonlocality and entanglement. In continuous variable systems, EPR steering correlations have been observed by violation of Reid's EPR inequality, which is based on inferred variances of complementary observables. Here we propose and experimentally test a new criterion based on entropy functions, and show that it is more powerful than the variance inequality for identifying EPR steering. Using the entropic criterion our experimental results show EPR steering, while the variance criterion does not. Our results open up the possibility of observing this type of nonlocality in a wider variety of quantum states.

Luminosity Determination in pp Collisions at sqrt(s)=7 TeV Using the ATLAS Detector at the LHC

Abstract: Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at root s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of mu, the average number of inelastic interactions per bunch crossing. Residual time- and mu-dependence between the methods is less than 2% for 0 < mu < 2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of +/- 11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most +/- 2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.

FORMATION AND EVOLUTION OF THE DISK SYSTEM OF THE MILKY WAY: [α/Fe] RATIOS AND KINEMATICS OF THE SEGUE G-DWARF SAMPLE

Abstract: We employ measurements of the [{alpha}/Fe] ratio fromlow-resolution (R {approx} 2000) spectra of 17,500 G-type dwarfs included in SDSS Data Release 8, selected using simple and well-understood selection criteria, to separate them into likely thin- and thick-disk subsamples. This classification, based on chemistry, is strongly motivated by the bi-modal distribution of stars in the [{alpha}/Fe] vs. [Fe/H] diagram. The resulting subsamples allow, for the first time, investigations of the kinematic behavior of thin- and thick-disk stars as a function of metallicity and position up to distances of 3 kpc from the Galactic plane. Both subsamples exhibit strong gradients of orbital rotational velocity with metallicity, but with opposite signs (-20 to -30 km s{sup -1} dex{sup -1} for the thin-disk population, and +40 to +50 km s{sup -1} dex{sup -1} for the thick-disk population). We find that the rotational velocity decreases with the distance from the plane for both disk components, with similar slopes (10 km s{sup -1} kpc{sup -1}), and a nearly constant difference in the mean rotational velocity of about 30 km s{sup -1}. The mean rotational velocity is uncorrelated with Galactocentric distance for the thin-disk subsample, and exhibits only a marginally significant correlation for the thick-disk subsample. Thick-diskmore » stars exhibit a very strong trend of orbital eccentricity with metallicity (-0.2 dex{sup -1}), while the eccentricity does not change with metallicity for the thin-disk subsample. The eccentricity is almost independent of Galactocentric radius for the thin-disk stars, while a marginal gradient of the eccentricity with distance exists for the thick-disk population. Both subsamples possess similar trends of increasing eccentricity with distance from the Galactic plane, with a constant difference of about 0.1. The shapes of the overall distributions of orbital eccentricity for the thin- and thick-disk populations are quite different from one another, independent of distance from the plane; neither subsample has significant numbers of stars with eccentricity above 0.6. These observational results provide strong new constraints on models for the formation and evolution of the Milky Way's disk system. For example, the observed dependence of the mean rotational velocity on metallicity for thin-disk stars is inconsistent with predictions from classical local chemical evolution models. We also consider the predictions of several contemporary models of disk evolution, such as radial migration, gas-rich mergers, disk heating, and pure accretion models. We find that radial migration appears to have played an important role in the evolution of the thin-disk population, but possibly less so, relative to the gas-rich merger or disk heating scenarios, for the thick disk. Pure accretion models appear to be ruled out by the observed distribution of eccentricities for thick-disk stars. We emphasize that more physically realistic models, and simulations that probe a greater range of disk formation scenarios, need to be constructed in order to carry out the detailed quantitative comparisons that our new data enable.« less

Confinement of antihydrogen for 1,000 seconds

Abstract: Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.