Actuators for the generation of highly nonlinear solitary waves

In this paper we present the design of two actuators for the generation of highly nonlinear solitary waves (HNSWs), which are mechanical waves that can form and travel in highly nonlinear systems. These waves are characterized by a constant spatial wavelength and by a tunable propagation speed, dependent on the wave amplitude. To date, the simplest and widely adopted method to generate HNSWs is by impacting a striker onto a chain of beads of equal size and mass. This operation is conducted manually and it might be impracticable if repetition rates higher than 0.1 Hz are necessary. It is known that the HNSWs’ properties, such as amplitude, duration, and speed can be modified by changing the size or the material of the particles, the velocity of the striker, and/or the precompression on the chain. To address the limitations associated with the manual generation of HNSWs we designed, built, and tested two actuators. The first actuator consists of a chain of particles wrapped by an electromagnet that induces static precompression on the chain. This design allows for the generation of solitary waves with controlled properties. The second actuator consists of a chain surmounted by an electromagnet that lifts and releases a striker. This actuator permits the remote and noncontact generation of solitary waves. The performance of both actuators is evaluated by comparing the experimental HNSWs to theoretical predictions, based on the long wavelength approximation

Kinetically Trapped Liquid-State Conformers of a Sodiated Model Peptide Observed in the Gas Phase

We investigate the peptide AcPheAla5LysH+, a model system for studying helix formation in the gas phase, in order to fully understand the forces that stabilize the helical structure. In particular, we address the question of whether the local fixation of the positive charge at the peptide's C-terminus is a prerequisite for forming helices by replacing the protonated C-terminal Lys residue by Ala and a sodium cation. The combination of gas-phase vibrational spectroscopy of cryogenically cooled ions with molecular simulations based on density-functional theory (DFT) allows for detailed structure elucidation. For sodiated AcPheAla6, we find globular rather than helical structures, as the mobile positive charge strongly interacts with the peptide backbone and disrupts secondary structure formation. Interestingly, the global minimum structure from simulation is not present in the experiment. We interpret that this is due to high barriers involved in re-arranging the peptide-cation interaction that ultimately result in kinetically trapped structures being observed in the experiment.Comment: 28 pages, 10 figure

Performance of cable-supported glass façades under time-depending wind action

Cable supported glass façades are sensitive to wind action because of their flexibility. Conventional laboratory testing to check a façade reliability under the wind action is generally carried out by uniformly air pressure tests. However, the typical wind action on a surface is known to be not uniform because it varies due to building aerodynamics and wind flow turbulence, and this aspect should be properly considered for testing protocols. This paper discusses the structural response of cable-supported glass façades, through time history finite element (FE) analyses, under different wind action combinations that varies based on the building aerodynamics (plan shapes and roof curvatures), the wind direction (0° and 90°), and the glass panel position (up and down). Such a finding is further enforced by the presence of flexible supports for the constituent glass modules. The presented results show a strong dependence of the structural response on the wind action configuration, and thus suggest the need of new testing protocols for similar systems

Coupling of Highly Nonlinear Waves with Linear Elastic Media

This paper reports a fundamental study of the coupling between highly nonlinear waves, generated in a one dimensional granular chain of particles, with linear elastic media, for the development of a new Non Destructive Evaluation and Structural Health Monitoring (NDE/SHM) paradigm. We design and use novel acoustic actuators to excite compact highly nonlinear solitary waves in a one-dimensional linear elastic rod and investigate the pulse propagation across the interface. To model the actuator and rod system we use Finite Element Analysis (Abaqus) and obtain excellent agreement between the experimental observations and the numerical results. We also study the response of the system to the presence of defects (cracks) in the steel rod, by comparing the wave propagation properties in pristine and cracked test objects. The obtained results encourage the use of highly nonlinear waves as an effective tool for developing a new, viable NDE/SHM method

Novel sensor technology for NDE of concrete

This paper describes the application of a novel actuator/sensor technology for the generation and detection of stress waves in structural materials like concrete. The technology is aimed at developing an innovative NDE scheme based on the generation of highly nonlinear solitary waves (HNSWs). HNSWs are stress waves that can form and travel in highly nonlinear systems (i.e. granular, layered, fibrous or porous materials) with a finite spatial dimension independent on the wave amplitude. Compared to conventional linear waves, the generation of HNSWs does not rely on the use of electronic equipment (such as an arbitrary function generator) and on the response of piezoelectric crystals or other transduction mechanism. The results of using these new actuator/sensors to test concrete slabs are presented and discussed

Highly nonlinear waves' sensor technology for highway infrastructures

This paper describes preliminary results towards the development of an innovative NDE/SHM scheme for material characterization and defect detection based on the generation of highly nonlinear solitary waves (HNSWs). HNSWs are stress waves that can form and travel in highly nonlinear systems (i.e. granular, layered, fibrous or porous materials) with a finite spatial dimension independent on the wave amplitude. Compared to conventional linear waves, the generation of HNSWs does not rely on the use of electronic equipment (such as an arbitrary function generator) and on the response of piezoelectric crystals or other transduction mechanism. HNSWs possess unique tunable properties that provide a complete control over tailoring: 1) the choice of the wave's width (spatial size) for defects investigation, 2) the composition of the excited train of waves (i.e. number and separation of the waves used for testing), and 3) their amplitude and velocity. HNSWs are excited onto concrete samples and steel rebar. The first pilot study of this ongoing effort between Caltech and the University of Pittsburgh is presented

Loop expansion around the Bethe approximation through the MM-layer construction

For every physical model defined on a generic graph or factor graph, the Bethe $M$-layer construction allows building a different model for which the Bethe approximation is exact in the large $M$ limit and it coincides with the original model for $M=1$. The $1/M$ perturbative series is then expressed by a diagrammatic loop expansion in terms of so-called fat-diagrams. Our motivation is to study some important second-order phase transitions that do exist on the Bethe lattice but are either qualitatively different or absent in the corresponding fully connected case. In this case the standard approach based on a perturbative expansion around the naive mean field theory (essentially a fully connected model) fails. On physical grounds, we expect that when the construction is applied to a lattice in finite dimension there is a small region of the external parameters close to the Bethe critical point where strong deviations from mean-field behavior will be observed. In this region, the $1/M$ expansion for the corrections diverges and it can be the starting point for determining the correct non-mean-field critical exponents using renormalization group arguments. In the end, we will show that the critical series for the generic observable can be expressed as a sum of Feynman diagrams with the same numerical prefactors of field theories. However, the contribution of a given diagram is not evaluated associating Gaussian propagators to its lines as in field theories: one has to consider the graph as a portion of the original lattice, replacing the internal lines with appropriate one-dimensional chains, and attaching to the internal points the appropriate number of infinite-size Bethe trees to restore the correct local connectivity of the original model

Più ombre che luci nei decreti svuota-carceri del 2013

Sommario1. Premessa. – 2. Gli svuota-carceri del 2013: ricognizione normativa e paralogismi. – 3. Conclusioni

Morphological and chemical analysis of Tremolite related to natural asbestos in the road paving

Tremolite group minerals could be present in the aggregate used as filler in the mix asphalt floor in the road sur- faces and are subject to wear for vehicular traffic and materials ageing. Dust produced by the degradation of asphalt surfaces can disperse tremolite group minerals present in road paving causing exposure by asbestos fiber to an increasing number of people and animals. In recent years, attention has been focused on naturally occurring asbestos (NOA) as the greatest frequency of lung cancer has been observed in environments characterized by rocks and soils rich in Tremolite that characterize asbestos minerals. Asphalt samples object of this study were collected in a motorway segment of the Lombardia Region (north of Italy) for an exposure assessment research on road paving workers. The evaluation was performed using a metrological approach based on petrographic and mineralogical analyses in order to reduce the epidemiologic risks and to define the best treatment strategies on waste management with sustainable costs in fulfilment of Council Directive 67/548/EEC (1967) and EC Regulation 1272/2008 (2008) (Paglietti et al., 2016). The fibers are generally not broken down to other compounds in the environment, but asbestos hazard could be related to the occurrence of tremolite fiber in road paving arises when natural weathering processes (e.g., erosion) or human activities (e.g., continuous passage of motorized vehicles) separate and breakdown the fibers, which could be lost into the environment as airborne and easily penetrate into the human respiratory tract (Punturo et al., 2019). Despite this, this work is not an epidemiological risk analysis but obtained data could be useful to other specialists to define the exposure risks

Interacting dark energy from the joint analysis of the power spectrum and bispectrum multipoles with the EFTofLSS

Interacting dark energy models have been suggested as alternatives to the standard cosmological model, $\Lambda$CDM. We focus on a phenomenologically interesting class of dark scattering models that is characterised by pure momentum exchange between dark energy and dark matter. This model extends the parameter space with respect to $\Lambda$CDM by two parameters, $w$ and $A$, which define the dark energy equation of state and the strength of the coupling between dark energy and dark matter, respectively. In order to test non-standard cosmologies with Stage-IV galaxy clustering surveys, it is crucial to model mildly nonlinear scales and perform precision vs accuracy tests. We use the Effective Field Theory of Large-Scale Structure, and we perform validation tests by means of an MCMC analysis using a large set of N-body simulations. We find that adding the bispectrum monopole to the power spectrum multipoles improves the constraints on the dark energy parameters by $\sim 30 \%$ for $k_{\mathrm{max}, B}^{l=0} = 0.11$ $h$ Mpc$^{-1}$ without introducing biases in the parameter estimation. We also find that the same improvement can be achieved with more moderate scale cuts and the use of bias relations, or with the addition of the bispectrum quadrupole. Finally, we study degeneracies between the dark energy parameters and the scalar amplitude $A_\mathrm{s}$ and discuss the corresponding projection effects, as well as degeneracies with other cosmological parameters.Comment: 22 pages, 13 figures; V2: Matches version accepted for publication in MNRAS, includes a new analysis of degeneracies with cosmological parameter