1,484 research outputs found

    Quark Confinement in Restricted SU(2) Gauge Theory

    Full text link
    We apply Zwanziger formalism to Cho restricted SU(2) SU(2) theory to obtain the potential in a static quark-antiquark pair. Cho restricted theory is a self-consistent subset of a non-Abelian SU(2) SU(2) gauge theory which tries to describe the infrared regime of Yang-Mills gauge theories. In Zwanziger formalism, a local Lagrangian depending on two electric and magnetic gauge fields is constructed for the theories where both electric and magnetic charges exist. Based on this local Lagrangian the propagator and then the potential between quarks is calculated in two limits: mCr≪1 m_{C} r \ll 1 and mCr≫1 m_{C} r \gg 1, where mC m_{C} is the mass of the dual gauge boson and r r is the distance between the quark and the antiquark.Comment: 2 Figures, 15 pages, Version accepted for publication in PR

    Molecular Tracers of the Central 12 pc of the Galactic Center

    Full text link
    We have used the BIMA array to image the Galactic Center with a 19-pointing mosaic in HCN(1-0), HCO+(1-0), and H 42-alpha emission with 5 km/s velocity resolution and 13'' x 4'' angular resolution. The 5' field includes the circumnuclear ring (CND) and parts of the 20 and 50 km/s clouds. HCN(1-0) and HCO+ trace the CND and nearby giant molecular clouds while the H 42-alpha emission traces the ionized gas in Sgr A West. We find that the CND has a definite outer edge in HCN and HCO+ emission at ~45'' radius and appears to be composed of two or three distinct streams of molecular gas rotating around the nucleus. Outside the CND, HCN and HCO+ trace dense clumps of high-velocity gas in addition to optically thick emission from the 20 and 50 km/s clouds. A molecular ridge of compressed gas and dust, traced in NH3 emission and self-absorbed HCN and HCO+, wraps around the eastern edge of Sgr A East. Just inside this ridge are several arcs of gas which have been accelerated by the impact of Sgr A East with the 50 km/s cloud. HCN and HCO+ emission trace the extension of the northern arm of Sgr A West which appears to be an independent stream of neutral and ionized gas and dust originating outside the CND. Broad line widths and OH maser emission mark the intersection of the northern arm and the CND. Comparison to previous NH3 and 1.2mm dust observations shows that HCN and HCO+ preferentially trace the CND and are weaker tracers of the GMCs than NH3 and dust. We discuss possible scenarios for the emission mechanisms and environment at the Galactic center which could explain the differences in these images.Comment: 24 pages, including 17 figures; to appear in The Astrophysical Journa

    Mode Coupling Analysis of Hollow Ring-Core Fibers for OAM Transmission

    Get PDF
    We present an analytical and numerical description of coupling between OAM modes in hollow ring-core fibers affected by stress birefringence and ellipticity The analysis paves the way to a better modeling of propagation in these fibers

    The ortho-to-para ratio of ammonia in the L1157 outflow

    Get PDF
    We have measured the ortho-to-para ratio of ammonia in the blueshifted gas of the L1157 outflow by observing the six metastable inversion lines from (J, K) = (1, 1) to (6, 6). The highly excited (5, 5) and (6, 6) lines were first detected in the low-mass star forming regions. The rotational temperature derived from the ratio of four transition lines from (3, 3) to (6, 6) is 130-140 K, suggesting that the blueshifted gas is heated by a factor of ~10 as compared to the quiescent gas. The ortho-to-para ratio of the NH3 molecules in the blueshifted gas is estimated to be 1.3--1.7, which is higher than the statistical equilibrium value. This ratio provides us with evidence that the NH3 molecules have been evaporated from dust grains with the formation temperature between 18 and 25 K. It is most likely that the NH3 molecules on dust grains have been released into the gas phase through the passage of strong shock waves produced by the outflow. Such a scenario is supported by the fact that the ammonia abundance in the blueshifted gas is enhanced by a factor of ~5 with respect to the dense quiescent gas.Comment: 16 pages, including 3 PS figures. To appear in the ApJ (Letters). aastex macro

    Review of existing numerical methods and validation procedure available for bird strike modelling

    Get PDF
    Summary This paper reviews numerical methods that are currently available to simulate bird strike as well as the theory of the event. It also summarizes important parameters and provides guidelines as to how to set up the analysis and how to evaluate a model. The information provided is based on physical properties and available results regarding a bird and its behaviour upon impact. The simulations have been performed with LS-DYNA 970 but can be done in similar dynamic finite elements analysis codes

    Campo ambiental midiatizado: a vigilância colaborativa da Amazônia

    Get PDF
    RESUMO A manifestação do complexo processo de midiatização potencializou-se nas últimas décadas. Nesse cenário, os campos sociais se apropriaram de mecanismos discursivos do campo midiático, o que possibilitou a emergência de um espaço para a reflexão, vigilância e monitoramento de questões globais como os problemas ambientais. O objetivo desse artigo é mostrar como ocorrem imbricações entre os campos midiático e ambiental a partir da intensificação do processo de midiatização através do qual distintos cidadãos constroem o InfoAmazonia, banco de dados sobre as problemáticas da Amazônia. Para tanto, o trabalho se assenta metodologicamente na perspectiva da análise semiológica para identificar o contrato de leitura (VERÓN, 2004) construído pela plataforma. A investigação aponta que este enunciador se caracteriza pela legitimação de um sujeito protagonista, cogestor na vigilância colaborativa da Amazônia. Palavras-chave: midiatização; campo ambiental; contrato de leitura   RESUMEN La manifestación del complejo proceso de mediatización se intensifica en las últimas décadas. En este escenario, los mecanismos discursivos del campo de los medios son apropiados por los campos sociales, lo que permitió el surgimento de un espacio de reflexión, vigilancia y rastreo de temas globales como los problemas ambientales. Lo objetivo deste artículo és mostrar cómo se producen solapamientos entre los campos mediático e ambiental gracias a intensificación del proceso de mediatizatión, además analizar y describir el contracto de lectura que emerge del proceso de construcción de InfoAmazonia, base de datos sobre los problemas de la Amazonía. Por lo tanto, el trabajo se basa metodológicamente en la perspectiva semiológica para identificar el contrato de lectura (VERÓN, 2004) de la plataforma. La investigación muestra que este enunciador se caracteriza por la legitimación de un actor protagonista, cogestor en la vigilancia de colaboración de la Amazonia.   Palabras clave: mediatización; campo ambiental; contracto de lectura   ABSTRACT The manifestation of the complex process of mediatization is leveraged in recent decades. Under this scenario, the social fields appropriated discursive mechanisms of the media field, which allowed the emergence of a space for reflection, surveillance and monitoring of global issues such as environmental problems. This research aims to show how they occur overlaps between the media and environmental fields with the intensification of mediatization, besides analyze and describe the reading agreement emerging from the construction process of InfoAmazonia, a database about the problems of the Amazon. Therefore, the work is methodologically based on semiological perspective to identify the platform reading contract (VERÓN, 2004). Research shows that this annunciator is characterized by the legitimation of a subject protagonist, who helps oversee the collaborative surveillance of the Amazon.   Keywords: mediatization; environmental field; reading agreement

    Probing the structure of a birthplace of intermediate-mass stars: Ammonia cores in Lynds 1340

    Full text link
    Lynds 1340, a molecular cloud forming intermediate-mass stars, has been mapped in the NH_3(1,1) and (2,2) transitions with the Effelsberg 100m telescope. We observed the whole area of the cloud where C18O emission was detected earlier, at a 40 arcsec grid, with additional positions towards the C18O peaks and optically invisible IRAS point sources. Our observations covered an area of 170 arcmin^2, corresponding to about 5.15 pc^2 at a distance of 600 pc, and revealed 10 ammonia cores. The cores, occupying some 7% of the mapped area, probably represent the highest density regions of L1340. Their total mass is 80 solar mass, about 6% of the mass traced by C18O. Six cores are associated with optically invisible IRAS point sources. Their average nonthermal line width is 0.78 kms^{-1}, while the same quantity for the four starless cores is 0.28 kms^{-1}. We suggest that the narrow-line cores are destined to form low-mass stars, whereas small groups of intermediate-mass stars are being formed in the turbulent cores. The features traced by NH_3, 13CO, C18O and HI obey the line width-size relation log Delta v_{NT} = 0.41(0.06)log R_{1/2}+ 0.12(0.06). Comparison of sizes, densities and nonthermal line widths of ammonia cores with those of C18O and 13CO structures supports the scenario in which core formation has been induced by turbulent fragmentation. The typical physical properties of the ammonia cores of L1340, R_{1/2} =0.08 pc, T_{kin}=13.8 K, Delta v_{total}=0.64 kms^{-1}, and M =9 solar mass are close to those of the high-mass star forming Perseus and Orion B clouds.Comment: 13 pages, 11 figures. Accepted by A&

    Superradiance Transition in Photosynthetic Light-Harvesting Complexes

    Full text link
    We investigate the role of long-lasting quantum coherence in the efficiency of energy transport at room temperature in Fenna-Matthews-Olson photosynthetic complexes. The excitation energy transfer due to the coupling of the light harvesting complex to the reaction center ("sink") is analyzed using an effective non-Hermitian Hamiltonian. We show that, as the coupling to the reaction center is varied, maximal efficiency in energy transport is achieved in the vicinity of the superradiance transition, characterized by a segregation of the imaginary parts of the eigenvalues of the effective non-Hermitian Hamiltonian. Our results demonstrate that the presence of the sink (which provides a quasi--continuum in the energy spectrum) is the dominant effect in the energy transfer which takes place even in absence of a thermal bath. This approach allows one to study the effects of finite temperature and the effects of any coupling scheme to the reaction center. Moreover, taking into account a realistic electric dipole interaction, we show that the optimal distance from the reaction center to the Fenna-Matthews-Olson system occurs at the superradiance transition, and we show that this is consistent with available experimental data.Comment: 9 page
    • …
    corecore