Modelamento netrosférico aumentado para a determinação de campos de vapor d’água atmosféricos com base em sinais de alta resolução gnss

Signals of global navigation satellite systems (GNSS) are delayed by propagatingthrough the Earth’s electrically neutral atmosphere. This delay term plays animportant role in GNSS positioning and has been taken into account in highprecisiongeodetic applications. The neutrospheric delay can be subdivided into adry and a complementary wet component. The wet component amounts to typicallyless than 10% of the total neutrospheric delay and can be used to determine highresolutionatmospheric water vapour fields based on extended neutrosphericmodelling. The approach outlined in the present paper combines empiricalneutrospheric a priori model, site-specific neutrosphere parameters and residuals ofGNSS phase observations. Using so-called single-layer models, the derivedatmospheric water vapour fields are two-dimensionally reconstructed andvisualised. Applying this extended neutrospheric model to generate water vapourfields within a regional GNSS network, the results indicate that both the temporaland the spatial resolution of the determined water vapour fields are improved incomparison to the conventional neutrospheric modelling.Os sinais oriundos dos sistemas de navegação globais por satélite (GNSS) sofremum atraso durante sua propagação através da camada eletricamente neutra daatmosfera terrestre. Este atraso tem um papel fundamental no posicionamentoGNSS e tem sido levado em conta nas aplicações geodésicas de alta precisão. Oatraso neutrosférico pode ser subdividido em uma componente seca e umacomponente complementar úmida. A quantidade correspondente a componenteúmida é tipicamente inferior a 10% do atraso total, e pode ser utilizada nadeterminação de campos de vapor d’água atmosférico de alta resolução baseados nomodelo aumentado da neutrosfera. A abordagem apresentada neste trabalhocombina um modelo a priori empirico, parâmetros neutrosféricos específicos daestação e resíduos das observações de fase GNSS. Utilizando os chamados modelosde camada única, os campos de vapor d’água atmosférico derivados sãoreconstruídos e visualizados, ambos em duas dimensões. Utilizando este modeloneutrosférico aumentado na geração de campos de vapor d’água dentro de uma rederegional GNSS, os resultados indicam uma melhora tanto na resolução temporalquanto na espacial dos campos de vapor d’água determinados, quando comparadoscom a modelagem neutrosférica convencional

IMPACT OF VARIOUS FACTORS ON THE QUALITY OF SITE-SPECIFIC NEUTROSPHERIC PARAMETERS WITHIN GNSS DATA PROCESSING: A CASE STUDY

Os atrasos na propagação dos sinais dos sistemas de navegação globais por satélite (GNSS), causados pela atmosfera neutra, são importantes fatores que limitam a acurácia de aplicações geodésicas precisas. Uma abordagem comum para tratar o atraso neutrosférico é estimar os chamados parâmetros neutrosféricos específicos da estação (SSNP – site-specific neutrospheric parameters) no processamento de dados GNSS, os quais são, então, combinados com valores de um modelo predito calculados principalmente utilizando dados meteorológicos. Portanto, a qualidade do atraso neutrosférico determinado depende não somente dos efeitos que atuam nos sinais GNSS, mas também da estratégia utilizada no processamento dos dados. Neste trabalho, as influências dos fatores que afetam a modelagem neutrosférica como: o comprimento da linha de base, multicaminho, ponderação do peso das observações, resolução das ambigüidades e o modelo de predição neutrosférica, são analisados e quantificados baseando-se nos desvios-padrão dos SSNP estimados. Além disso, um modelo melhorado para a ponderação dos pesos das observações, baseado nas medidas de potência da razão sinal-ruído, é brevemente descrito. Os resultados apresentados nos testes indicam que a aplicação deste avançado modelo de ponderação dos pesos no processamento de dados GNSS, incluindo observações com baixa elevação, pode melhorar os desvios-padrão dos SSNP estimados em torno de 25% comparado com o modelo padrão de ponderação dos pesos dependente de elevação.Propagation delays of the signals of global navigation satellite systems (GNSS) caused by the neutral atmosphere are an important accuracy-limiting factor for precise geodetic applications. A common approach to handle the neutrospheric delay is to estimate so-called site-specific neutrospheric parameters (SSNP) within GNSS data processing which are then combined with the predicted model values calculated primarily based on meteorological data. Therefore, the quality of the determined neutrospheric delay depends not only on the factors impacting the GNSS signals but also on data processing strategies. In this paper, the influence of the factors impacting neutrospheric modelling such as baseline length, multipath, observation weighting, ambiguity resolution, and neutrospheric prediction models are analysed and quantified based on the standard deviations of the estimated SSNP. Additionally, an improved observation weighting scheme based on signal-to-noise power ratio measurements is briefly described. Test results indicate that applying this advanced weight model within GNSS data processing, including observations at low elevation, the standard deviation of the estimated SSNP can be improved by nearly 25% compared with the standard elevation-dependent weighting model

Ion-beam-assisted fabrication and manipulation of metallic nanowires

Metallic nanowires (NWs) are the key performers for future micro/nanodevices. The controlled manoeuvring and integration of such nanoscale entities are essential requirements. Presented is a discussion of a fabrication approach that combines chemical etching and ion beam milling to fabricate metallic NWs. The shape modification of the metallic NWs using ion beam irradiation (bending towards the ion beam side) is investigated. The bending effect of the NWs is observed to be instantaneous and permanent. The ion beam-assisted shape manoeuvre of the metallic structures is studied in the light of ion-induced vacancy formation and reconfiguration of the damaged layers. The manipulation method can be used for fabricating structures of desired shapes and aligning structures at a large scale. The controlled bending method of the metallic NWs also provides an understanding of the strain formation process in nanoscale metals

A polarized beam splitter using an anisotropic medium slab

The propagation of electromagnetic waves in the anisotropic medium with a single-sheeted hyperboloid dispersion relation is investigated. It is found that in such an anisotropic medium E- and H-polarized waves have the same dispersion relation, while E- and H-polarized waves exhibit opposite amphoteric refraction characteristics. E- (or H-) polarized waves are positively refracted whereas H- (or E-) polarized waves are negatively refracted at the interface associated with the anisotropic medium. By suitably using the properties of anomalous refraction in the anisotropic medium it is possible to realize a very simple and very efficient beam splitter to route the light. It is shown that the splitting angle and the splitting distance between E- and H- polarized beam is the function of anisotropic parameters, incident angle and slab thickness.Comment: 14 pages, 6 figure

Dynamical and Stationary Properties of On-line Learning from Finite Training Sets

The dynamical and stationary properties of on-line learning from finite training sets are analysed using the cavity method. For large input dimensions, we derive equations for the macroscopic parameters, namely, the student-teacher correlation, the student-student autocorrelation and the learning force uctuation. This enables us to provide analytical solutions to Adaline learning as a benchmark. Theoretical predictions of training errors in transient and stationary states are obtained by a Monte Carlo sampling procedure. Generalization and training errors are found to agree with simulations. The physical origin of the critical learning rate is presented. Comparison with batch learning is discussed throughout the paper.Comment: 30 pages, 4 figure

Ultrastrong conductive in situ composite composed of nanodiamond incoherently embedded in disordered multilayer graphene

Traditional ceramics or metals cannot simultaneously achieve ultrahigh strength and high electrical conductivity. The elemental carbon can form a variety of allotropes with entirely different physical properties, providing versatility for tuning mechanical and electrical properties in a wide range. Here, by precisely controlling the extent of transformation of amorphous carbon into diamond within a narrow temperature–pressure range, we synthesize an in situ composite consisting of ultrafine nanodiamond homogeneously dispersed in disordered multilayer graphene with incoherent interfaces, which demonstrates a Knoop hardness of up to ~53 GPa, a compressive strength of up to ~54 GPa and an electrical conductivity of 670–1,240 S m(–1) at room temperature. With atomically resolving interface structures and molecular dynamics simulations, we reveal that amorphous carbon transforms into diamond through a nucleation process via a local rearrangement of carbon atoms and diffusion-driven growth, different from the transformation of graphite into diamond. The complex bonding between the diamond-like and graphite-like components greatly improves the mechanical properties of the composite. This superhard, ultrastrong, conductive elemental carbon composite has comprehensive properties that are superior to those of the known conductive ceramics and C/C composites. The intermediate hybridization state at the interfaces also provides insights into the amorphous-to-crystalline phase transition of carbon

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe

Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV

A search for a Higgs boson decaying into two photons is described. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross section of the standard model Higgs boson decaying to two photons. The expected exclusion limit at 95% confidence level is between 1.4 and 2.4 times the standard model cross section in the mass range between 110 and 150 GeV. The analysis of the data excludes, at 95% confidence level, the standard model Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The largest excess of events above the expected standard model background is observed for a Higgs boson mass hypothesis of 124 GeV with a local significance of 3.1 sigma. The global significance of observing an excess with a local significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is estimated to be 1.8 sigma. More data are required to ascertain the origin of this excess.Comment: Submitted to Physics Letters

Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV

The Lambda(b) differential production cross section and the cross section ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Lambda(b) decays reconstructed in the exclusive final state J/Psi Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and Lambda to proton pion, using a data sample corresponding to an integrated luminosity of 1.9 inverse femtobarns. The product of the cross section times the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls faster than that of b mesons. The measured value of the cross section times the branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06 +/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are statistical and systematic, respectively.Comment: Submitted to Physics Letters