1,122 research outputs found
finite element modelling tuned on experimental testing for the structural health assessment of an ancient masonry arch bridge
This paper presents the structural health assessment of a railway ancient masonry arch bridge located in Bologna, Italy. A three-dimensional finite element model of the entire bridge, tuned on in situ experimental tests, has been used for the assessment. In particular, the finite element model has been employed to evaluate the structural health of the bridge both in its actual state and in the hypothesis of a structural strengthening intervention
Canopy structure, topography, and weather are equally important drivers of small-scale snow cover dynamics in sub-alpine forests
In mountain regions, forests that overlap with seasonal
snow mostly reside in complex terrain. Due to persisting major observational
challenges in these environments, the combined impact of forest structure
and topography on seasonal snow cover dynamics is still poorly understood.
Recent advances in forest snow process representation and increasing
availability of detailed canopy structure datasets, however, now allow for
hyper-resolution (<5 m) snow model simulations capable of resolving
tree-scale processes. These can shed light on the complex process
interactions that govern forest snow dynamics. We present multi-year
simulations at 2 m resolution obtained with FSM2, a mass- and energy-balance-based forest snow model specifically developed and validated for metre-scale
applications. We simulate an ∼3 km2 model domain
encompassing forested slopes of a sub-alpine valley in the eastern Swiss
Alps and six snow seasons. Simulations thus span a wide range of canopy
structures, terrain characteristics, and meteorological conditions. We
analyse spatial and temporal variations in forest snow energy balance
partitioning, aiming to quantify and understand the contribution of
individual energy exchange processes at different locations and times. Our
results suggest that snow cover evolution is equally affected by canopy
structure, terrain characteristics, and meteorological conditions. We show
that the interaction of these three factors can lead to snow accumulation
and ablation patterns that vary between years. We further identify higher
snow distribution variability and complexity in slopes that receive solar
radiation early in winter. Our process-level insights corroborate and
complement existing empirical findings that are largely based on snow
distribution datasets only. Hyper-resolution simulations as presented here
thus help to better understand how snowpacks and ecohydrological regimes in
sub-alpine regions may evolve due to forest disturbances and a warming
climate. They could further support the development of process-based
sub-grid forest snow cover parameterizations or tiling approaches for
coarse-resolution modelling applications.</p
Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit
A comprehensive investigation of the frequency-noise spectral density of a
free-running mid-infrared quantum-cascade laser is presented for the first
time. It provides direct evidence of the leveling of this noise down to a white
noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The
experiment is in agreement with the most recent theory on the fundamental
mechanism of line broadening in quantum-cascade lasers, which provides a new
insight into the Schawlow-Townes formula and predicts a narrowing beyond the
limit set by the radiative lifetime of the upper level.Comment: 4 pages, 4 figure
Layered Video Transmission on Adaptive OFDM Wireless Systems
Future wireless video transmission systems will consider orthogonal frequency division multiplexing (OFDM) as the basic modulation technique due to its robustness and low complexity implementation in the presence of frequency-selective channels. Recently, adaptive bit loading techniques have been applied to OFDM showing good performance gains in cable transmission systems. In this paper a multilayer bit loading technique, based on the so called "ordered subcarrier selection algorithm," is proposed and applied to a Hiperlan2-like wireless system at 5 GHz for efficient layered multimedia transmission. Different schemes realizing unequal error protection both at coding and modulation levels are compared. The strong impact of this technique in terms of video quality is evaluated for MPEG-4 video transmission
Analysis of the effect of temperature, pH, CO2 pressure and salinity on the olivine dissolution kinetics
AbstractThe dissolution kinetics of olivine has been extensively studied under several temperatures, CO2 pressures, and solution compositions. Dissolution is an important mechanism in the aqueous mineral carbonation process. The overall carbonation reaction consists of dissolution of mineral silicate, e.g. olivine, serpentine and wollastonite, followed by carbonate precipitation, thus fixing CO2 into naturally occurring stable solids, such as magnesite and calcite. The slowness of the dissolution kinetics hinders the overall carbonation reaction and in order to make the process technically and economically feasible, such a reaction should be sped up by finding the optimum operating conditions. Experiments were performed in a flow-through reactor at 90–120–150 ∘C. The pH was adjusted by adding either acids (e.g., HCl, citric acid) or LiOH, and by changing PCO2. The salinity was changed by adding NaCl and NaNO3. From the experimental data, the dissolution rate was estimated by using the population balance equation (PBE) model coupled with a mass balance, and the obtained values were regressed with a linear model log(r)=−npH−B, where r is the specific dissolution rate (mol s−1 cm−2)
Critical analysis on the use of the shove test for investigating the shear-sliding behavior of brick masonry
The shove test (ASTM Standard C1531) is an experimental technique aimed at studying the shear-sliding behavior of brick masonry. It can be executed according to various testing methods that differ in the way the vertical compression load is applied and in the way bricks and/or joints are locally removed for inserting jacks. One of the most critical aspects is the correct evaluation of the compressive stress state on the sliding brick. The objective of the present paper is to investigate the capability of the shove test in determining the shear strength parameters of brick masonries and to highlight the main advantages and disadvantages of the various testing methods. To this aim, nonlinear numerical simulations of the shove test were performed by adopting a brick-to-brick modeling strategy. The 2D numerical model was calibrated and validated through comparisons with experimental results of triplet tests and shove tests. The numerical analyses allowed to understand the influence the different testing methods and the masonry mechanical properties, such as dilatancy, may have on the test results. Based on the numerical outcomes, correction factors were calibrated for the proper evaluation of the compressive stress state on the sliding brick. Improvements with regards to the experimental procedures, i.e. additional test phases and measurements, were also proposed to enhance the results interpretation
A new ligament-compatible patient-specific 3D-printed implant and instrumentation for total ankle arthroplasty: from biomechanical studies to clinical cases
Background: Computer navigation and patient-specific instrumentation for total ankle arthroplasty have still to demonstrate their theoretical ability to improve implant positioning and functional outcomes. The purpose of this paper is to present a new and complete total ankle arthroplasty customization process for severe posttraumatic ankle joint arthritis, consisting of patient-specific 3D-printed implant and instrumentation, starting from a ligament-compatible design. Case presentation: The new customization process was proposed in a 57-year-old male patient and involved image analysis, joint modeling, prosthesis design, patient-specific implant and instrumentation development, relevant prototyping, manufacturing, and implantation. Images obtained from a CT scan were processed for a 3D model of the ankle, and the BOX ankle prosthesis (MatOrtho, UK) geometries were customized to best fit the model. Virtual in silico, i.e., at the computer, implantation was performed to optimize positioning of these components. Corresponding patient-specific cutting guides for bone preparation were designed. The obtained models were printed in ABS by additive manufacturing for a final check. Once the planning procedure was approved, the models were sent to final state-of-the-art additive manufacturing (the metal components using cobalt-chromium-molybdenum powders, and the guides using polyamide). The custom-made prosthesis was then implanted using the cutting guides. The design, manufacturing, and implantation procedures were completed successfully and consistently, and final dimensions and location for the implant corresponded with the preoperative plan. Immediate post-op X-rays showed good implant positioning and alignment. After 4 months, clinical scores and functional abilities were excellent. Gait analysis showed satisfactory joint moment at the ankle complex and muscle activation timing within normality. Conclusions: The complete customization process for total ankle arthroplasty provided accurate and reliable implant positioning, with satisfactory short-term clinical outcomes. However, further studies are needed to confirm the potential benefits of this complete customization process. Level of evidence: 5. Case report
Surface effects on the Mott-Hubbard transition in archetypal VO
We present an experimental and theoretical study exploring surface effects on
the evolution of the metal-insulator transition in the model Mott-Hubbard
compound Cr-doped VO. We find a microscopic domain formation that is
clearly affected by the surface crystallographic orientation. Using scanning
photoelectron microscopy and X-ray diffraction, we find that surface defects
act as nucleation centers for the formation of domains at the
temperature-induced isostructural transition and favor the formation of
microscopic metallic regions. A density functional theory plus dynamical mean
field theory study of different surface terminations shows that the surface
reconstruction with excess vanadyl cations leads to doped, and hence more
metallic surface states, explaining our experimental observations.Comment: 5 pages, 4 figure
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