9,513 research outputs found
Properties of the jet in M87 revealed by its helical structure imaged with the VLBA at 8 and 15 GHz
We present full-track high-resolution radio observations of the jet of the
galaxy M87 at 8 and 15 GHz. These observations were taken over three
consecutive days in May 2009 using the Very Long Baseline Array (VLBA), one
antenna of the Very Large Array (VLA), and the Effelsberg 100 m telescope. Our
produced images have dynamic ranges exceeding 20,000:1 and resolve linear
scales down to approximately 100 Schwarzschild radii, revealing a
limb-brightened jet and a faint, steep spectrum counter-jet. We performed
jet-to-counter-jet analysis, which helped estimate the physical parameters of
the flow. The rich internal structure of the jet is dominated by three helical
threads, likely produced by the Kelvin-Helmholtz (KH) instability developing in
a supersonic flow with a Mach number of approximately 20 and an enthalpy ratio
of around 0.3. We produce a CLEAN imaging bias-corrected 8-15GHz spectral index
image, which shows spectrum flattening in regions of helical thread
intersections. This further supports the KH origin of the observed internal
structure of the jet. We detect polarised emission in the jet at distances of
approximately 20 milliarcseconds from the core and find Faraday rotation which
follows a transverse gradient across the jet. We apply Faraday rotation
correction to the polarisation position angle and find that the position angle
changes as a function of distance from the jet axis, which suggests the
presence of a helical magnetic field.Comment: 15 pages, 10 figures, 1 table, Submitted to MNRAS on 25th March 202
Límites de corta distancia de la contribución HLbL al momento magnético anómalo del muon
Hadronic Light by Light (HLbL) scattering is not the biggest hadronic contribution to the muon’s anomalous magnetic moment, but it has the biggest relative uncertainty of all the contributions to that observable. With the tension between the Standard Model value prediction and the measurement at 4.2 σ, theoretical physicists have set their sights on reducing the HLbL contribution’s uncertainty to reduce the tension or push it beyond the discovery threshold. In such scenario, the high energy contribution of HLbL scattering to anomalous magnetic moment of the muon plays an important role. The aim of the research developed in this thesis is to study
the HLbL leading order contribution in the maximally symmetric high energy region well above the hadronic threshold limit. This is achieved by performing an operator product expansion of the HLbL tensor, which we do systematically in the background field method. We consider our approach very efficient, also because it allows a straightforward renormalization of the field theoretical results. Our approach is also original and at the best of our knowledge not available in literature. The massless quark loop is the leading term and we compute it without neglecting its tensor structure. To this end, we use a tensor–loop–integral decomposition that does not in-
troduce kinematic singularities. The resulting scalar loop integrals with shifted dimensions are computed with their full mass dependence using a Mellin–Barnes representation. Our original method of computation for the quark loop provides an independent check of recent literature results. Furthermore, by conserving the full tensor structure of the amplitude, we are able to
perform an explicit check of a proposed kinematic–singularity–free tensor decomposition for the HLbL scattering amplitude that plays a central role in the dispersive computation in the low–energy regime. (Texto tomado de la fuente)La dispersión HLbL no es la contribución hadrónica más grande para el momento magnético anómalo del muon, pero esta tiene la incertidumbre relativa más grande de todas las contribuciones a ese observable. Con la tensión entre la valor predicho por el Modelo Estándar y las mediciones actualmente en 4.2 σ, los físico teóricos se han centrado en reducir la incertidumbre de la contribución HLbL para reducir la tensión o llevarla más allá del umbral de descubrimiento. En tal escenario, la contribución de alta energía de la dispersión HLbL al momento magnético anómalo del muon juega un papel importante. El objetivo de la investigación desarrollada en esta tesis es estudiar la contribución HLbL de primer orden en la región de alta energía máximamente simétrica muy por encima del límite del umbral hadrónico. Esto se logra al realizar una expansión de productos de operadores del tensor HLbL, la cual realizamos sistemáticamente con el método de campos de fondo. Consideramos nuestra aproximación al problema muy eficiente, entre otras razones, porque esta permite la renormalización directa de los resultados de teoría de campos. Nuestro método es también original y, hasta nuestro mejor conocimiento, no se encuentra en la literatura. El quark loop sin masa es el primer término de la expansión y lo calculamos sin dejar de lado su estructura tensorial. Para lograrlo, usamos un método de descomposición tensorial de integrales de loop que no introduce singularidades cinemáticas. Las integrales escalares de loop resultantes con dimensiones modificadas son calculadas considerando toda su dependencia de la masa y utilizando la representación de Mellin-Barnes. Nuestro método original de cálculo para el quark loop proporciona una verificación independiente de los resultados publicados recientemente en la literatura. Más aún, al conservar la estructura tensorial completa de la amplitud, podemos llevar a cabo una verificación explícita de una descomposición libre de singularidades cinemáticas para la dispersión HLbL que juega un papel central en los cálculos dispersivos del régimen de baja energía.Maestrí
Constraining a Model of the Radio Sky Below 6 MHz Using the Parker Solar Probe/FIELDS Instrument in Preparation for Upcoming Lunar-based Experiments
We present a Bayesian analysis of data from the FIELDS instrument on board
the Parker Solar Probe (PSP) spacecraft with the aim of constraining low
frequency ( 6 MHz) sky in preparation for several upcoming
lunar-based experiments. We utilize data recorded during PSP's ``coning roll''
maneuvers, in which the axis of the spacecraft is pointed 45 off of
the Sun. The spacecraft then rotates about a line between the Sun and the
spacecraft with a period of 24 minutes. We reduce the data into two formats:
roll-averaged, in which the spectra are averaged over the roll, and
phase-binned, in which the spectra are binned according to the phase of the
roll. We construct a forward model of the FIELDS observations that includes
numerical simulations of the antenna beam, an analytic emissivity function of
the galaxy, and estimates of the absorption due to free electrons. Fitting 5
parameters, we find that the roll-averaged data can be fit well by this model
and we obtain posterior parameter constraints that are in general agreement
with previous estimates. The model is not, however, able to fit the
phase-binned data well, likely due to limitations such as the lack of
non-smooth emission structure at both small and large scales, enforced symmetry
between the northern and southern galactic hemispheres, and large uncertainties
in the free electron density. This suggests that significant improvement in the
low frequency sky model is needed in order to fully and accurately represent
the sky at frequencies below 6 MHz.Comment: 18 pages, 10 figures, 5 tables. Under review in the Astrophysical
Journa
Micro-Electro Discharge Machining: Principles, Recent Advancements and Applications
Micro electrical discharge machining (micro-EDM) is a thermo-electric and contactless process most suited for micro-manufacturing and high-precision machining, especially when difficult-to-cut materials, such as super alloys, composites, and electro conductive ceramics, are processed. Many industrial domains exploit this technology to fabricate highly demanding components, such as high-aspect-ratio micro holes for fuel injectors, high-precision molds, and biomedical parts.Moreover, the continuous trend towards miniaturization and high precision functional components boosted the development of control strategies and optimization methodologies specifically suited to address the challenges in micro- and nano-scale fabrication.This Special Issue showcases 12 research papers and a review article focusing on novel methodological developments on several aspects of micro electrical discharge machining: machinability studies of hard materials (TiNi shape memory alloys, Si3N4–TiN ceramic composite, ZrB2-based ceramics reinforced with SiC fibers and whiskers, tungsten-cemented carbide, Ti-6Al-4V alloy, duplex stainless steel, and cubic boron nitride), process optimization adopting different dielectrics or electrodes, characterization of mechanical performance of processed surface, process analysis, and optimization via discharge pulse-type discrimination, hybrid processes, fabrication of molds for inflatable soft microactuators, and implementation of low-cost desktop micro-EDM system
CITIES: Energetic Efficiency, Sustainability; Infrastructures, Energy and the Environment; Mobility and IoT; Governance and Citizenship
This book collects important contributions on smart cities. This book was created in collaboration with the ICSC-CITIES2020, held in San José (Costa Rica) in 2020. This book collects articles on: energetic efficiency and sustainability; infrastructures, energy and the environment; mobility and IoT; governance and citizenship
The Uşaklı Höyük Survey Project (2008-2012)
This book presents the results of the survey conducted by the University of Florence, in the years 2008-2012, at the site and in the surrounding territory of Uşaklı Höyük on the central Anatolian plateau in Turkey. Geological, geomorphological, topographic and geophysical research have provided new information and data relating to the environment and the settlement landscape, as well as producing new maps of the area and indicating the presence of large buried buildings on the site. Analysis of the rich corpus of pottery collected from the surface indicates that the site and its territory were continuously settled from the late Early Bronze Age through the Iron Age and down to the Late Roman and Byzantine periods. A few fragments of cuneiform tablets with Hittite texts, a sealing with two impressions of a stamp seal, and pottery stamps illustrate the importance of Uşaklı Höyük and support the hypothesis of its identification with the town of Zippalanda, known from the Hittite sources as a seat of the cult of the Storm God
A Late Iron Age farmstead in the Outer Hebrides
The settlement at Bornais consists of a complex of mounds which protrude from the relatively flat machair plain in the township of Bornais on the island of South Uist. This sandy plain has proved an attractive settlement from the Beaker period onwards; it appears to have been intensively occupied from the Late Bronze Age to the end of the Norse period. Mound 1 was the original location for settlement in this part of the machair plain; pre-Viking activity of some complexity is present and it is likely that the settlement activity started in the Middle Iron Age, if not earlier. The examination of the mound 1 deposits provides an important contribution to our understanding of the Iron Age sequence in the Atlantic province. The principal contribution comprises the large quantities of mammal, fish and bird bones, carbonised plant remains and pottery, which can be accurately dated to a fairly precise and narrow period in the 1st millennium AD. These are augmented by a substantial collection of small finds which included distinctive bone artefacts. The contextual significance of the site is based on the survival of floor deposits and a burnt-down roof; the floor deposits can be compared with abandonment and adjacent midden deposits providing contrasting contextual environments that help to clarify depositional processes. The burning down of the house and the excellent preservation of the deposits within it provide an unparalleled opportunity to examine the timber superstructure of the building and the layout of the material used by the inhabitants
Thermal-Hydraulics in Nuclear Fusion Technology: R&D and Applications
In nuclear fusion technology, thermal-hydraulics is a key discipline employed in the design phase of the systems and components to demonstrate performance, and to ensure the reliability and their efficient and economical operation. ITER is in charge of investigating the transients of the engineering systems; this included safety analysis. The thermal-hydraulics is required for the design and analysis of the cooling and ancillary systems such as the blanket, the divertor, the cryogenic, and the balance of plant systems, as well as the tritium carrier, extraction and recovery systems. This Special Issue collects and documents the recent scientific advancements which include, but are not limited to: thermal-hydraulic analyses of systems and components, including magneto-hydrodynamics; safety investigations of systems and components; numerical models and code development and application; codes coupling methodology; code assessment and validation, including benchmarks; experimental infrastructures design and operation; experimental campaigns and investigations; scaling issue in experiments
Advanced Modeling, Control, and Optimization Methods in Power Hybrid Systems - 2021
The climate changes that are becoming visible today are a challenge for the global research community. In this context, renewable energy sources, fuel cell systems and other energy generating sources must be optimally combined and connected to the grid system using advanced energy transaction methods. As this reprint presents the latest solutions in the implementation of fuel cell and renewable energy in mobile and stationary applications such as hybrid and microgrid power systems based on the Energy Internet, blockchain technology and smart contracts, we hope that they will be of interest to readers working in the related fields mentioned above
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