Sound radiation and sound insulation performances of maritime bulkheads

The research of materials matching low weight and high resistance has always been a key factor in the shipbuilding industry to increase performances and loading capacity. Nowadays, other issues add up to economical convenience, and building quiet ships is important not only for passengers and cabin crew, but also to make harbor areas more comfortable and to respect the aquatic environment. In this context, using sandwich or composite materials must be carefully evaluated and the sound insulation performances must be considered throughout all stages of the design process. This work presents some evaluations about the sound insulation performances of a ribbed fiberglass bulkhead and of a balsa-core sandwich bulkhead. In particular, the bending stiffness and the sound transmission loss obtained by sound transmission suites and mobility measurements are provided. From such measurements it has also been possible to determine the radiation efficiency of the structures, whose optimization is particularly important when a reduction of the noise pollution is required

Acoustic quality of auditoria: Relationship between acoustical energy parameters and subjective perception

The acoustic design auditoria is founded on objective acoustic parameters determined on the basis of the computed or measured impulse response. Such objective parameters are related on the average response of the human ear to transient sounds, without considering the subjective perception of the individual, which, in turn, is related also to social and education aspects. The aim of this study is to investigate the relationship between individual sound perceptions and energy parameters. In detail, a questionnaire has been submitted to a sample of people listening to tracks of different musical genres. The questionnaire has been conceived to come up with a classification model for the audience allowing to express the listener's experience according to different indicators, such as overall acoustic quality and overall acoustic experience. Results of this experiment are analyzed by means of Random Forest non-parametric model belonging to the data mining algorithms. The final purpose of the study is to define which physical and acoustical characteristics are the most suitable to represent the subjective perceptions of the listeners

Limb reconstruction with knee mega-prosthesis in patients with distal femur primary tumours: gait analysis and alignment evaluation

Introduction: The aim of this study was the functional evaluation and lower limb alignment assessment of patients with a modular knee prosthesis after distal femur resection for primary bone tumour. Materials and methods: 15 patients affected by distal femur tumor and treated with a megaprosthesis implant (6 females and 9 males, mean age: 41 years, range: 15-74 years) and 15 controls were recruited for the study. For each subject the function evaluation included an instrumented gait analysis, while only patients underwent a teleradiography and a latero-lateral X-ray projection of the knee. Results: The duration of the stance phase of gait was shortened in the prosthetic limb with respect to the contralateral limb (57.5±3.6 % gait cycle vs. 60.9±4.8 % gait cycle, P = 0.01), with a correspondent increase of the swing phase. The prosthetic limb also showed an altered knee joint kinematic curve during gait, with a flexion deficit at load response with respect to the contralateral limb (4.5±3.6° vs. 13.4±5.0°, P = 0.000003). Abnormal timing in the muscle activation intervals were observed for tibialis anterior, gastrocnemius lateralis and rectus femoris of the prosthetic limb. The prosthetic limb was found to be misaligned with respect to the contralateral limb, both for the femorotibial (P<0.05) and the ankle joints (P<0.05). Conclusions: Gait analysis performed widely in reference centres could lead to a change in the design of megaprostheses to improve the function and prevent degenerative changes in not involved joint. A multicentric expertise is mandator

The sub-arcsecond hard X-ray structure of loop footpoints in a solar flare

The newly developed X-ray visibility forward fitting technique is applied to Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data of a limb flare to investigate the energy and height dependence on sizes, shapes, and position of hard X-ray chromospheric footpoint sources. This provides information about the electron transport and chromospheric density structure. The spatial distribution of two footpoint X-ray sources is analyzed using PIXON, Maximum Entropy Method, CLEAN and visibility forward fit algorithms at nonthermal energies from $\sim 20$ to $\sim 200$ keV. We report, for the first time, the vertical extents and widths of hard X-ray chromospheric sources measured as a function of energy for a limb event. Our observations suggest that both the vertical and horizontal sizes of footpoints are decreasing with energy. Higher energy emission originates progressively deeper in the chromosphere consistent with downward flare accelerated streaming electrons. The ellipticity of the footpoints grows with energy from $\sim 0.5$ at $\sim 20$ keV to $\sim 0.9$ at $\sim 150$ keV. The positions of X-ray emission are in agreement with an exponential density profile of scale height $\sim 150$~km. The characteristic size of the hard X-ray footpoint source along the limb is decreasing with energy suggesting a converging magnetic field in the footpoint. The vertical sizes of X-ray sources are inconsistent with simple collisional transport in a single density scale height but can be explained using a multi-threaded density structure in the chromosphere.Comment: 7 pages, 7 figures, submitted to Ap

Estimating the intrinsic dimension of datasets by a minimal neighborhood information

Analyzing large volumes of high-dimensional data is an issue of fundamental importance in data science, molecular simulations and beyond. Several approaches work on the assumption that the important content of a dataset belongs to a manifold whose Intrinsic Dimension (ID) is much lower than the crude large number of coordinates. Such manifold is generally twisted and curved; in addition points on it will be non-uniformly distributed: two factors that make the identification of the ID and its exploitation really hard. Here we propose a new ID estimator using only the distance of the first and the second nearest neighbor of each point in the sample. This extreme minimality enables us to reduce the effects of curvature, of density variation, and the resulting computational cost. The ID estimator is theoretically exact in uniformly distributed datasets, and provides consistent measures in general. When used in combination with block analysis, it allows discriminating the relevant dimensions as a function of the block size. This allows estimating the ID even when the data lie on a manifold perturbed by a high-dimensional noise, a situation often encountered in real world data sets. We demonstrate the usefulness of the approach on molecular simulations and image analysis

Crustal Structure in the Southern Apennines from Teleseismic Receiver Functions

While the upper structure of the Southern Apennines is known, lack of control on the deep structure allows competing thin-skin and tick-skin models of the orogen. In thin-skin models the detachment decouples a stack of rootless nappes from the basement. In the tick-skin models, besement is involved in the most recent phase of thrusting. To examine crustal structure, we use teleseismic data from the CAT/SCAN array in southern Italy. We use receiver functions (RF) processed into a Common Conversion Point (CCP) stack to generate images of the crust. Interpretation and correlation to geological structure is done using inversions of individual station RFs. We focus on a shallow discontinuity where P-to-S conversions occur. In the foreland, it corresponds to velocity jumps between carbonate and clastic strata with basement. A similar interpretation for the Apennines provides the most parsimonious explanation and supports a tick-skin interpretation. In a thick-skin reconstruction, the amount of shortening is much smaller than for a thin-skin model. This implies considerably less Plio-Pleistocene shortening across the Apennines and suggests an E-SE motion of the Calabrian Arc subparallel to the southern Apennines rather than a radial expansion of the Arc