Página 1 dos resultados de 138 itens digitais encontrados em 0.022 segundos

‣ Simulação CFD de jatos em espaços confinados

Almeida, Celso Oliveira
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Trabalho de Conclusão de Curso
Publicado em //2013 Português
Relevância na Pesquisa
27.596118%
Dissertação de mestrado integrado em Engenharia Mecânica; A presente tese tem por objetivo o estudo da interação de um jato num escoamento livre. Com este objetivo efetuou-se a modelação do escoamento usando o software de Computação em Dinâmica dos Fluidos – CFD – ANSYS FLUENT. Este baseia-se na utilização da técnica de volumes finitos para a solução das equações de conservação de um fluido: massa, momentum e energia. Neste estudo foram consideradas três situações: interação de um jato com um fluido em repouso; interação de um jato com um fluxo perpendicular e a interação de 13 jatos com um fluxo perpendicular. Neste estudo foram avaliados vários modelos de turbulência e a influência de gradientes térmicos entre os dois fluxos. Os dados obtidos foram comparados com resultados experimentais obtidos por Nunes (2003) num túnel de vento subsónico. De entre os vários modelos de turbulência o k-e mostrou ser o mais adequado. A convergência da solução exigiu um elevado refinamento da malha na região de interação dos fluxos. Os resultados mostram que a injeção cruzada de caudais relativamente pequenos pode provocar o estabelecimento de extensas regiões de interação com a corrente principal...

‣ Study of water entry of circular cylinder by using analytical and numerical solutions

Ghadimi,Parviz; Dashtimanesh,Abbas; Djeddi,Seyed Reza
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2012 Português
Relevância na Pesquisa
37.322668%
Water impact phenomenon in the case of a circular cylinder is an important issue in offshore industry where cross members may be in the splash zone of the incident wave. An analytical method as well as a numerical solution are employed to study the water entry problem of a circular section. The procedure for derivation of the analytical formulas is demonstrated step by step. The volume of fluid (VOF) simulation of the water entry problem is also performed to offer comparison of the results of the linearized analytical solution with a fully nonlinear and viscous fluid flow solution. To achieve this, the FLOW-3D code is utilized. Some consideration has also been given to the points of intersection of the free surface and the body, where the singularities exist in the free surface deformation and velocities, as predicted by the linear theory. These singularities appear to be avoided in the real fluid by the formation of jets which quickly break up into sprays under the action of surface tension. Slamming force, free surface profile, impact force, pressure distribution and evolution of intersection points are also presented and comparisons of the obtained results against the results of previous studies illustrate favorable agreements.

‣ Simulação de grandes escalas de jatos periódicos temporais utilizando a metodologia psedo-espectral de Fourier; Large eddy simulation of periodic temporal jets using the Fourier pseudo-spectral method

Moreira, Leonardo de Queiroz
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
Português
Relevância na Pesquisa
47.401357%
A turbulência nos fluídos é um dos problemas mais desafiadores da atualidade, em especial no que se refere às aplicações industriais que envolvem processos de mistura de componentes, transferência de calor, lubrificação e degelo, injeção de combustível em câmaras de combustão, sistemas de propulsão de aviões e aeronaves. Diante de considerável interesse, no presente trabalho objetivou-se a análise da transição a turbulência de jatos em desenvolvimento temporal a números de Reynolds moderados utilizando a metodologia LES. Primeiramente desenvolveu-se um código computacional ESPC3D, com alta ordem de resolução para simulação de escoamentos do tipo jatos em desenvolvimento temporal em transição e/ou turbulentos. O código foi desenvolvido no Laboratório de Transferência de Calor e Massa e Dinâmica dos Fluidos (LTCM). Resultados consistentes foram obtidos do ponto de vista da análise física utilizando o código ESPC3D, com o qual realizou-se simulações de grandes escalas empregando o método pseudo-espectral de Fourier. Os resultados das simulações permitem verificar a transição a turbulência bem como suas estruturas típicas. Foi possível também verificar a influência da modelagem da turbulência utilizando a metodologia LES...

‣ On turbulent jets issuing from notched-rectangular and circular orifice plates

Mi, J.; Kalt, P.; Nathan, G.
Fonte: Kluwer Academic Publ Publicador: Kluwer Academic Publ
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
Relevância na Pesquisa
27.757288%
This paper reports an experimental investigation of the near-field flow characteristics of two air/air turbulent jets issuing respectively from notched-rectangular and circular orifice plates with identical opening areas or equivalent diameters (D e ). Planar particle image velocimetry (PIV) was used to measure the velocity field at the same Reynolds number, based on D e , of Re = 72,000. Consistent with previous work on other noncircular jets, the present study finds that the notched jet has a higher rate of mixing than does the circular counterpart. In particular, this jet in the very near field transfers its momentum to the surroundings at a greater rate, evidenced by a notably shorter unmixed core and faster turbulence intensity growth. The higher rates of overall decay and spread of the notched jet are maintained over the entire measurement region and likely beyond. In addition, the phenomenon of axis switching is also found to occur in this jet.; Jianchun Mi, P. Kalt and G.J.Nathan; First published online in 2009

‣ Strouhal number of naturally-oscillating triangular and circular jets

Lee, S.; Lanspeary, P.; Nathan, G.
Fonte: University of Queensland; CDROM Publicador: University of Queensland; CDROM
Tipo: Conference paper
Publicado em //2007 Português
Relevância na Pesquisa
37.389854%
A nozzle consisting of an abrupt expansion into a short open- ended tube can produce a naturally-excited oscillating-jet flow. The characteristics of the oscillating jet depend on jet-orifice to chamber expansion ratio (D/d1), chamber length-to-diameter ratio (L/D), and shape of the jet orifice. In experiments using water as a flow medium, air-bubble visualisation and signals from a pressure transducer show that a triangular-jet orifice produces aperiodic oscillation without a spectral peak. In contrast, oscillation of the circular jet has clearly visible periodicity and the spectrum has a broad peak. The circular and triangular orifices produce completely different dependence of Strouhal number on expansion ratio. For a circular orifice, Strouhal number is inversely proportional to (D/d1−1). For a triangular orifice, Strouhal number is directly proportional to (D/d1−1). The two curves intersect at an expansion ratio of 4.8, which is approximately the minimum possible expansion ratio for a circular oscillating jet.; http://espace.library.uq.edu.au/view.php?pid=UQ:120835; S. K. Lee, P. V. Lanspeary and G. J. Nathan

‣ PIV measurements of turbulent jets issuing from triangular and circular orifice plates

Xu, M.; Zhang, J.; Mi, J.; Nathan, G.; Kalt, P.
Fonte: Zhongguo Kexue Zazhishe Publicador: Zhongguo Kexue Zazhishe
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
Relevância na Pesquisa
27.923652%
The present study experimentally investigated the near-field flow mixing characteristics of two turbulent jets issuing from equilateral triangular and circular orifice plates into effectively unbounded surroundings, respectively. Planar particle image velocimetry (PIV) was applied to measure the velocity field at the same Reynolds number of Re=50,000, where Re = U(e)D(e)/ν with U(e) being the exit bulk velocity and ν the kinematic viscosity of fluid, D(e) the equivalent diameters. The instantaneous velocity, mean velocity, Reynolds stresses were obtained. From the mean velocity field, the centreline velocity decay rate and half-velocity width were derived. Comparing the mixing characteristics of the two jets, it is found that the triangular jet has a faster mixing rate than the circular counterpart. The triangular jet entrainments with the ambient fluid at a higher rate in the near field. This is evidenced by a shorter unmixed core, faster Reynolds stress and centreline turbulence intensity growth. The primary coherent structures in the near field are found to break down more rapidly in the triangular jet as compared to the circular jet. Over the entire measurement region, the triangular jet maintained a higher rate of decay and spread. Moreover...

‣ Absolute instability in the near field of low-density jets

Coenen, Wilfried
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/doctoralThesis Formato: application/octet-stream; application/octet-stream; application/pdf
Português
Relevância na Pesquisa
37.963105%
Variable density jets are known to support self-sustained oscillations when the jet-to-ambient density ratio is sufficiently small. This change in dynamical response to small perturbations is associated with a transition from convective to absolute instability of the underlying unperturbed base flow. The focus of this dissertation lies in the use of linear stability theory to describe the convective to absolute instability transition of buoyancy-free low-density jets emerging from a circular injector tube at moderately high Reynolds numbers and low Mach numbers. Particular interest is given to the in- fluence of the length of the injector tube on the stability characteristics of the resulting jet flow, whose base velocity profile at the jet exit is computed in terms of the nondimen- sional tube length L$_{t}$ by integrating the boundary layer equations along the injector. We begin with the investigation of inviscid axisymmetric and helical modes of in- stability in a heated jet for different values of the jet-to-ambient density ratio. For short tubes L$_{t}$ $ll$ 1 the base velocity profile at the tube exit is uniform except in a thin sur- rounding boundary layer. Correspondingly, the stability analysis reproduces previous results of uniform velocity jets...

‣ Erosion of finite thickness sediment beds by single and multiple circular jets

Niño Campos, Yarko; García, Marcelo; Sequeiros, Octavio E.
Fonte: Universidade do Chile Publicador: Universidade do Chile
Tipo: Artículo de revista
Português
Relevância na Pesquisa
47.70904%
Publicación ISI; Sediment management in reservoirs with the help of water jets has motivated this work. Erosion caused by single and multiple submerged circular turbulent wall jets on a noncohesive sediment bed of finite thickness lying on a fixed boundary was studied with the help of laboratory experiments. Different combinations of jet diameter, jet separation, and sediment thickness to jet diameter ratio were tested. Results show a relation between dimensionless parameters characterizing the steady state bed profile and the densimetric particle Froude number F-0 given by the velocity at the nozzle and the effective diameter and submerged specific density of the sediment. Evolution of scour with time confirms previous studies where the erosion was found to initially grow with the logarithm of time up to a certain reference time t*. This time, made dimensionless with a time scale t(c), involving the volume of sediment scoured and the rate of erosion, was also related to the densimetric Fronde number. A comparison with studies regarding erosion of a semiinfinite layer of sediment is also presented.

‣ Baryons in the relativistic jets of the stellar-mass black hole candidate 4U 1630-47

Trigo, María Díaz; Miller-Jones, James C. A.; Migliari, Simone; Broderick, Jess W.; Tzioumis, Tasso
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/11/2013 Português
Relevância na Pesquisa
27.607554%
Accreting black holes are known to power relativistic jets, both in stellar-mass binary systems and at the centres of galaxies. The power carried away by the jets, and hence the feedback they provide to their surroundings, depends strongly on their composition. Jets containing a baryonic component should carry significantly more energy than electron-positron jets. While energetic considerations and circular polarisation measurements have provided conflicting circumstantial evidence for the presence or absence of baryons, the only system in which baryons have been unequivocally detected in the jets is the X-ray binary SS 433. Here we report the detection of Doppler-shifted X-ray emission lines from a more typical black hole candidate X-ray binary, 4U1630-47, coincident with the reappearance of radio emission from the jets of the source. We argue that these lines arise in a jet with velocity 0.66c, thereby establishing the presence of baryons in the jet. Such baryonic jets are more likely to be powered by the accretion disc rather than the spin of the black hole, and if the baryons can be accelerated to relativistic speeds, should be strong sources of gamma rays and neutrino emission.; Comment: Nature, published online on 13/11/13

‣ Circular polarization in the optical afterglow of GRB 121024A

Wiersema, K.; Covino, S.; Toma, K.; van der Horst, A. J.; Varela, K.; Min, M.; Greiner, J.; Starling, R. L. C.; Tanvir, N. R.; Wijers, R. A. M. J.; Campana, S.; Curran, P. A.; Fan, Y.; Fynbo, J. P. U.; Gorosabel, J.; Gomboc, A.; Gotz, D.; Hjorth, J.; Jin,
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/10/2014 Português
Relevância na Pesquisa
27.573794%
Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet, when measured minutes after the burst, and the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after burst in GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and negligable circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blastwave. Here we report the detection of circularly polarized optical light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch angle distributions...

‣ Detection and Measurement of Parsec-Scale Circular Polarization in Four AGN

Homan, D. C.; Wardle, J. F. C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/07/2000 Português
Relevância na Pesquisa
27.575127%
We present five epochs of 15 GHz VLBA observations of 13 AGN. These observations were specially calibrated to detect parsec scale circular polarization and our calibration techniques are discussed and analyzed in detail. We obtained reliable detections of parsec scale circular polarization in the radio jets of 4 AGN: 3C84, PKS 0528+134, 3C273, and 3C279. For each of these objects our detections are at the level of ~ 0.3-1% local fractional circular polarization. Our observations are consistent across multiple epochs (and different calibration techniques) in the sign and magnitude of the circular polarization observed. 3C273 and 3C279 both undergo core outbursts during our observations and changes in the circular polarization of both sources are correlated with these outbursts. In general, we observe the circular polarization to be nearly coincident with the strong VLBI cores of these objects; however, in 3C84 the circular polarization is located a full milli-arcsecond south of the source peak, and in the 1996.73 epoch of 3C273 the circular polarization is predominately associated with the newly emerging jet component. Circular polarization may be produced as an intrinsic component of synchrotron radiation or by the Faraday conversion of linear to circular polarization. Our single frequency observations do not easily distinguish between these possible mechanisms...

‣ MOJAVE: Monitoring of Jets in AGN with VLBA Experiments - II. First-Epoch 15 GHz Circular Polarization Results

Homan, D. C.; Lister, M. L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/11/2005 Português
Relevância na Pesquisa
27.896128%
We report first-epoch circular polarization results for 133 active galactic nuclei in the MOJAVE program to monitor the structure and polarization of a flux limited sample of extra-galactic radio jets with the VLBA at 15 GHz. We found strong circular polarization ($\geq 0.3$%) in approximately 15% of our sample. The circular polarization was usually associated with jet cores; however, we did find a few strong jet components to be circularly polarized. The levels of circular polarization were typically in the range of $0.3-0.5$% of the local Stokes-$I$. We found no strong correlations between fractional circular polarization of jet cores and source type, redshift, EGRET detections, linear polarization, or other observed parsec-scale jet properties. There were differences between the circular-to-linear polarization ratios of two nearby galaxies versus more distant quasars and BL Lac objects. We suggest this is because the more distant sources either have (1) less depolarization of their linear polarization, and/or (2) poorer effective linear resolution and therefore their VLBA cores apparently contain a larger amount of linearly polarized jet emission. The jet of 3C 84 shows a complex circular polarization structure, similar to observations by Homan & Wardle five years earlier; however...

‣ Small-scale chromospheric jets above a sunspot light bridge

Louis, Rohan E.; Beck, Christian; Ichimoto, Kiyoshi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.633835%
High-resolution broadband filtergrams of active region NOAA 11271 in Ca ii H and G band were obtained with the Solar Optical Telescope on board Hinode to identify the physical driver responsible for the dynamic and small-scale chromospheric jets above a sunspot light bridge. We identified the jets in the Ca images using a semi-automatic routine. The chromospheric jets consist of a bright, triangular-shaped blob that lies on the light bridge, while the apex of this blob extends into a spike-like structure that is bright against the dark umbral background. Most of the jets have apparent lengths of less than 1000 km and about 30% of them have lengths between 1000-1600 km. They are oriented within +/-35 deg. to the normal of the light bridge axis. Many of them are clustered near the central part within a 2 arcsec area. The jets are seen to move rapidly along the light bridge and most of them cannot be identified in successive images taken with a 2 min cadence. The jets are primarily located on one side of the light bridge and are directed into the umbral core. The Stokes profiles at or close to the location of the blobs on the LB exhibit both a significant net circular polarization and multiple components, including opposite-polarity lobes. The magnetic field diverges from the light bridge towards the umbral cores that it separates. In the photosphere there is a predominantly uni-directional flow with speeds of 100-150 m/s along the light bridge which is interrupted by a patch of weak motions that also moves along the light bridge. The dynamic short-lived jets above the LB seem to be guided by the magnetic field lines. Reconnection events are a likely trigger for such phenomenon since they occur at locations where the magnetic field changes orientation sharply. We find no clear relation between the jets and the photospheric flow pattern.; Comment: Accepted for publication in A&A...

‣ Circular Polarization of Radio Emission from Relativistic Jets

Beckert, Thomas; Falcke, Heino
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/12/2001 Português
Relevância na Pesquisa
28.150498%
In inhomogeneous optically thick synchrotron sources a substantial part of the electron population at low energies can be hidden by self-absorption and overpowered by high energy electrons in optically thin emission. These invisible electrons produce Faraday rotation and conversion, leaving their footprints in the linear and circular polarized radiation of the source. An important factor is also the magnetic field structure, which can be characterized in most cases by a global magnetic field and a turbulent component. We present the basic radiative transfer coefficients for polarized synchrotron radiation and apply them to the standard jet model for relativistic radio jets. The model can successfully explain the unusual circular and linear polarization of the Galactic Centre radio source Sgr A* and its sibling M81*. It also can account for the circular polarization found in jets of more luminous quasars and X-ray binaries. The high ratio of circular to linear polarization requires the presence of a significant fraction of hidden matter and low-energy electrons in these jets. The stable handedness of circular polarization requires stable global magnetic field components with non-vanishing magnetic flux along the jet, while the low degree of total polarization implies also a significant turbulent field. The most favoured magnetic field configuration is that of a helix...

‣ The Power of Jets: New Clues from Radio Circular Polarization and X-rays

Falcke, Heino; Beckert, Thomas; Markoff, Sera; Koerding, Elmar; Bower, Geoffrey C.; Fender, Rob
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/11/2001 Português
Relevância na Pesquisa
27.785532%
Jets are ubiquitous in accreting black holes. Often ignored, they may be a major contributor to the emitted spectral energy distribution for sub-Eddington black holes. For example, recent observations of radio-to-X-ray correlations and broad band spectra of X-ray binaries in the low/hard state can be explained by a significant synchrotron contribution from jets also to their IR-to-X-ray spectrum as proposed by Markoff, Falcke, Fender 2001. This model can also explain state-transitions from low/hard to high/soft states. Relativistic beaming of the jet X-ray emission could lead to the appearance of seemingly Super-Eddington X-rays sources in other galaxies. We show that a simple population synthesis model of X-ray binaries with relativistic beaming can well explain the currently found distribution of off-nucleus X-ray point sources in nearby galaxies. Specifically we suggest that the so-called ultra-luminous X-ray sources (ULXs, also IXOs) could well be relativistically beamed microblazars. The same model that can be used to explain X-ray binaries also fits Low-Luminosity AGN (LLAGN) and especially Sgr A* in the Galactic Center. The recent detection of significant circular polarization in AGN radio cores, ranging from bright quasars down to low-luminosity AGN like M81*...

‣ One-dimensional reduction of viscous jets

Pitrou, Cyril
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/11/2015 Português
Relevância na Pesquisa
27.533093%
We build a general formalism to describe thin viscous jets as one-dimensional objects with an internal structure. We present in full generality the steps needed to describe the viscous jets around their central line, and we argue that the Taylor expansion of all fields around that line is conveniently expressed in terms of symmetric trace-free tensors living in the two dimensions of the fiber sections. We recover the standard results of axisymmetric jets and we report the first and second corrections to the lowest order description, also allowing for a rotational component around the axis of symmetry. When applied to generally curved fibers, the lowest order description corresponds to a viscous string model whose sections are circular. However, when including the first corrections we find that curved jets generically develop elliptic sections. Several subtle effects imply that the first corrections cannot be described by a rod model, since it amounts to selectively discard some corrections. However, in a fast rotating frame we find that the dominant effects induced by inertial and Coriolis forces should be correctly described by rod models. For completeness, we also recover the constitutive relations for forces and torques in rod models and exhibit a missing term in the lowest order expression of viscous torque. Given that our method is based on tensors...

‣ Circular Ribbon Flares and Homologous Jets

Wang, Haimin; Liu, Chang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.877168%
Solar flare emissions in the chromosphere often appear as elongated ribbons on both sides of the magnetic polarity inversion line (PIL), which has been regarded as evidence of a typical configuration of magnetic reconnection. However, flares having a circular ribbon have rarely been reported, although it is expected in the fan--spine magnetic topology involving reconnection at a three-dimensional (3D) coronal null point. We present five circular ribbon flares with associated surges, using high-resolution and high-cadence halpha blue wing observations obtained from the recently digitized films of Big Bear Solar Observatory. In all the events, a central parasitic magnetic field is encompassed by the opposite polarity, forming a circular PIL traced by filament material. Consequently, a flare kernel at the center is surrounded by a circular flare ribbon. The four homologous jet-related flares on 1991 March 17 and 18 are of particular interest, as (1) the circular ribbons brighten sequentially, with co-spatial surges, rather than simultaneously, (2) the central flare kernels show an intriguing "round-trip" motion and become elongated, and (3) remote brightenings occur at a region with the same magnetic polarity as the central parasitic field and are co-temporal with a separate phase of flare emissions. In another flare on 1991 February 25...

‣ Linear and Circular Polarization Properties of Jets

Ruszkowski, Mateusz
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/10/2002 Português
Relevância na Pesquisa
27.788684%
I discuss the transfer of polarized synchrotron radiation in relativistic jets. I argue that the main mechanism responsible for the circular polarization properties of compact synchrotron sources is likely to be Faraday conversion and that, contrary to common expectation, a significant rate of Faraday rotation does not necessarily imply strong depolarization. The long-term persistence of the sign of circular polarization, observed in some sources, is most likely due to a small net magnetic flux generated in the central engine, carried along the jet axis and superimposed on a highly turbulent magnetic field. I show that the mean levels of circular and linear polarizations depend on the number of field reversals along the line of sight and that the gradient in Faraday rotation across turbulent regions can lead to "correlation depolarization''. The model is potentially applicable to a wide range of synchrotron sources. In particular, I demonstrate how the model can naturally explain the excess of circular over linear polarization in the Galactic Center (Sgr A*) and the low-luminosity AGN M81*.; Comment: Invited Talk, to appear in "Circular Polarisation in Relativistic Jet Sources", Astrophysics and Space Science, Fender R.P. and Macquart J.-P. (Eds)

‣ Simulation of the measurement of the inclusive jet cross sections in Z(→e⁺e⁻ / →μ⁺μ⁻)+jets events in pp collisions at 14 TeV with the ATLAS experiment

Segura i Solé, Ester
Fonte: Bellaterra: Universitat Autònoma de Barcelona , Publicador: Bellaterra: Universitat Autònoma de Barcelona ,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2009 Português
Relevância na Pesquisa
28.201084%
Descripció del recurs: el 24 de febrer de 2010; Després de 20 anys de preparació, el LHC s'encendrà a finals del 2009, col.lisionant protons a energies de 14TeV, per recrear els primers moments del Big Bang. Les partícules s'acceleraran al llarg del túnel circular de 27 km de circumferència fins a velocitats properes a la de la llum. El túnel, situat prop de Ginebra, i els seus experiments formen un dels més grans esforços de la història per estudiar l'estructura fonamental de la matèria. S'espera que a aquestes altes energies de col.lisió nous fenòmens físics puguin esdevenir i siguin descoberts. Entre les restes resultants de les col.lisions entre protons, evidències de dimensions extres, de la misteriosa matèria fosca que inunda el nostre univers o de la partícula de Higgs que dona massa a les partícules elementals, podran ser observades. ATLAS és un dels experiments del LHC. A més a més del descobriment de nova Física en el seu programa, també està inclosa la investigació de la Física ja coneguda. Un millor coneixement de la teoria pertorbativa de Quantum Chromodynamics és un dels objectius d'ATLAS. QCD és la teoria que descriu les interaccions fortes entre quarks i gluons. Aquesta teoria encara roman sense resoldre...

‣ Face-on dust disks in galaxies with optical jets

Sparks, William; Baum, Stefi; Biretta, John; Macchetto, Ferdinando; Martel, Andre
Fonte: Astrophysical Journal Publicador: Astrophysical Journal
Tipo: Artigo de Revista Científica Formato: 243293 bytes; application/pdf
Português
Relevância na Pesquisa
37.47785%
The presence of optical synchrotron jets in radio galaxies is relatively rare. Here we show that of the nearest Ðve FR I 3CR radio galaxies showing optical jets, four show evidence for almost circular, presumably face-on, dust disks. This is strong support for the twofold idea that (1) jets emerge close to perpendicular to inner gas disks and (2) optical nonthermal synchrotron emission is seen only when the jet points toward the observer. The implied critical angle to the line of sight is approximately 30¡È40¡; i.e., if the angle of the jet to the line of sight is less than about 40¡ we see an optical jet. The corresponding relativistic c factor is B1.5, which is consistent with current observations of jet proper motion that show a range up to cD6 for M87. The relatively low speeds implied by cB1.5 may be due to a global deceleration of the jet as in uniÐed theories or else to stratiÐcation within the jet. Unresolved nuclei are common in the optical. Their luminosities are also consistent with the beaming concept when compared to inclination inferred from the dust lanes. The disk sizes are typically several hundred parsecs to kiloparsec size. The galaxy with an optical jet that does not show a face-on disk, M87, instead has more complex radial dust and ionized gas Ðlaments (Refer to PDF file for exact formulas).; Also archived in: arXiv: astro-ph/0007358 v1 24 Jul 2000; Support for this work was provided by NASA through proposal GO-5476.01-93A from the Space Telescope Science Institute...