1,451 research outputs found
Implications of solar flare hard X-ray "knee" spectra observed by RHESSI
We analyse the RHESSI photon spectra of four flares that exhibit significant deviations from power laws - i.e. changes in the "local" Hard X-ray spectral index. These spectra are characterised by two regions of constant power law index connected by a region of changing spectral index - the "knee". We develop theoretical and numerical methods of describing such knees in terms of variable photon spectral indices and we study the results of their inversions for source mean thin target and collisional thick target injection electron spectra. We show that a particularly sharp knee can produce unphysical negative values in the electron spectra, and we derive inequalities that can be used to test for this without the need for an inversion to be performed. Such unphysical features would indicate that source model assumptions were being violated, particularly strongly for the collisional thick target model which assumes a specific form for electron energy loss. For all four flares considered here we find that the knees do not correspond to unphysical electron spectra. In the three flares that have downward knees we conclude that the knee can be explained in terms of transport effects through a region of non-uniform ionisation. In the other flare, which has an upward knee, we conclude that it is most likely a feature of the accelerated spectrum
Energy saving in typical architecture: The flow energy in traditional solutions in a sustainable perspective
Quick urbanization increment causes a few difficult problems, such as social assessment, more energy demands, and pollution increase. A positive factor for a city is the concentration of energy requests. On the other hand, urbanization trend is going to fragmentation of settlements, with a consequent expansion of the energy distribution networks but also an increase of the energy wasted. Each building needs some of the total energy distributed in the city. Energy needs can be grouped into four essential parameters: construction, heating, electricity, and water. How were these four parameters satisfied in the XIX century, before the industrial revolution? In those days' energy requirement wasn't so high and could be supplied with basic energy production technology. The knowledge of appropriate building technology (project), the use of (energy saving) materials, with a low and punctual heating system (fireplace, stove) or passive refreshment all intervened in this process. These requirements were achieved in each country using building plans studied to face different weather conditions with different architectural typology and with human effort and time (work-energy). This paper analyses an energy balance in a single typical building in the center of Italy, describing the energy flow that will show the logical and technical solution for "energy-saving". Old buildings (before the introduction of "building-plant") were always designed and built with an energy-saving concern. This article wants to propose the study of a typical building in which are used only low-energy systems to meet all the comfort requirements, to demonstrate that it is not necessary to use high-energy technology. This is how architecture urbanization studies and implementation can be used to reduce high-energy production needs. © 2019 Author(s)
Feature augmentation for the inversion of the Fourier transform with limited data
We investigate an interpolation/extrapolation method that, given scattered observations of the Fourier transform, approximates its inverse. The interpolation algorithm takes advantage of modeling the available data via a shape-driven interpolation based on variably scaled Kernels (VSKs), whose implementation is here tailored for inverse problems. The so-constructed interpolants are used as inputs for a standard iterative inversion scheme. After providing theoretical results concerning the spectrum of the VSK collocation matrix, we test the method on astrophysical imaging benchmarks
Principles at the basis of the denorms round robin test on the low frequency sound absorption measurements in reverberation rooms and impedance tube
In recent years low frequency measurements in building and room acoustics fields gained attention. Moreover the low frequency sound absorption coefficient (below 100 Hz) has always been difficult to determine and the results coming from different laboratories cannot always be compared. This paper describes the principles at the basis of the round robin test carried out in the framework of the DENORMS cost action (Designs for Noise Reducing Materials and Structures). The same samples have been measured in reverberation rooms and in impedance tube by the different laboratories participating to the Round Robin Test.status: accepte
Slip distribution inversion by trans-dimensional Monte Carlo sampling: application to the 2009 L’Aquila Earthquake (Central Italy)
Non-uniform slip distribution on a fault plane from geodetic data is usually
estimated in two steps. First, the geometric fault parameters are inferred by
non -linear inversion assuming a uniform slip on a rectangular fault. A second
analysis, based on linear inversion techniques, infers the slip distribution on
an arbitrary subdivision of the fault plane into patches. Two main concerns
arise. First, the fault geometry determined under the assumption of a uniform
slip i s not guaranteed to properly represent the fault geometry for a spatially
variable slip distribution. Moreover, an arbitrary fault subdivision into patches
u nrelated to the observed data could bias the model resolution, introducing
spurious features.
In recent years, the availability of large coverage data, such as DInSAR
images, improved mapping the coseismic displacements. The large amount of
geodetic da ta from the area surrounding earthquake faults allows for improving
the slip models and refining the knowledge of earthquake dynamics. Less
attention has been given to the development of new inversion algorithms that
can resolve the main concerns above. In particular, the question is whether
the data themselves ca n constrain the slip model complexity, i.e., the unknown
number and distribution of the fault patches needed to fit the observations. The
reversible jump Mar kov chain Monte Carlo (RJMCMC) algorithm has been recently
introduced in the geosciences to solve a variety of non linear inverse
problems. RJMCMC combines a classical Markov chain Monte Carlo method
with the ability to shift between models with a different number of unknowns.
A posterior probability distribution of the num ber of unknowns is obtained at
the end of the Markov chain, so that the model resolution is determined by the
observed data.
In this study, we apply a RJMCMC method to the Mw 6.3 L’Aquila earthquake
that occurred on April 6th 2009 in Central Italy. Three DInSAR images,
mapping the c oseismic displacement, are inverted to constrain not only the slip
distribution but also the number of unknowns (i.e., the number of fault patches)
and the ge ometry of non-rectangular patches
Impedance tube measurements on the denorms round robin test material samples
The DENORMS Round Robin Test aims to study and improve the techniques used to determine the sound absorption coefficient of materials. Within this framework, samples taken from the same batch have been tested in both reverberation room and impedance tube. The latter technique presents some challenges in that the results may strongly depend on the specimen preparation and set-up. The purpose of this paper is to present the results obtained in custom-made impedance tube for the RRT set of materials. The tests have been carried out using a four-microphone impedance tube, according to the method outlined in the ASTM E2611-09 standard. The results obtained for the different parameters provided by the test, in particular the sound absorption coefficient and the sound transmission loss, are taken into account and discussed
Sound transmission loss of cross-laminated timber walls: Comparison between measurements carried out in transmission suites and point mobility measurements
The transition from concrete-based to wood-based construction is drawing more attention to the use of cross-laminated timber elements, especially in the building sector. In this context, there is a need to assess the transmission loss performances of such elements already during the research and development phase, when making several tests in sound transmission suites would be overly expensive and time-consuming. The flexural behavior of a composite structure can be determined by point mobility tests. From this kind of measurements, it is possible to estimate the loss factor of the partition and its bending stiffness which, in turn, can be used to determine its sound transmission loss once some basic physical properties are known. In this paper, the sound transmission of cross-laminated timber partitions is obtained with this method. Results are validated by means of measurements in sound transmission suites
Effect of local stiffeners and warping constraints on the buckling of symmetric open thin-walled beams with high warping stiffness
Local stiffeners affect the behaviour of thin-walled beams (TWBs). An in-house code based on a one-dimensional model proved effective in several instances of compressive buckling of TWBs but gave counterintuitive results for locally stiffened TWBs. To clarify the matter, we investigated TWBs with multi-symmetric double I cross-section, widely used in practical applications where high bending stiffness is required. Several samples were manufactured and stiffened on purpose, closing them over a small portion of the axis at different places. The samples were tested with end constraints accounting for various warping conditions. The experimental and numerical outputs from a commercial FEM code gave a key to overcome the unexpected results by the in-house code, paving the way for further studies
The DENORMS Round Robin test: Measurement procedure and post-processing of time data
The DENORMS Round Robin Test (RRT) is intended to study and improve the techniques used for the determination of the sound absorption coefficient of materials, with particular focus on the low-frequency range and on measurements in reverberation rooms. It is well known that the main reason why it is difficult to extend the frequency range of interest below 100 Hz is the low modal density. The modal behavior of a room is dependent on its geometry and this is one of the reasons why a discrepancy of the results coming from different laboratories can be found even if the same material is tested. This paper describes the measurement procedure developed to allow uniform acquisition and post-processing of acoustic response data of laboratories participating in the RRT, with and without absorbing materials inside. The tests and the post-processing operations performed on the measured data are also discussed in the paper
Numerical and experimental study on metamaterials featuring acoustical and thermal properties
Metamaterials can be defined as materials which, for their peculiar composition or structure, exhibit characteristics that are not normally found in nature. "Multifunctional" metamaterials could be used to optimise different characteristics at the same time. In this paper the authors try to apply them for thermal and acoustic optimization of external building walls. Thermal optimization consists in obtaining a low transmittance, important in winter, and a low periodic thermal transmittance, important in summer. Acoustic optimization consists in obtaining high sound transmission loss, to respect the law prescriptions, and a good sound absorption coefficient, if possible. In this way should be possible enhance the comfort conditions in buildings and reduce the energy demand for winter heating and summer cooling. The proposed solution consists of several layers with different suitable characteristics: the sequence of the layers has been chosen with particular care. The thermal analysis has been performed by means of a self-developed code based on the ISO 13786 standard. The acoustic behaviour of the single layers has been determined following the procedure given by the ASTM E2611-09 standard using a four-microphone impedance tube and the transfer matrix method has been used for the complete assembly. This preliminary combined study showed encouraging results
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