An Updating Method for Finite Element Models of Flexible-Link Mechanisms Based on an Equivalent Rigid-Link System

This paper proposes a comprehensive methodology to update dynamic models of flexible-link mechanisms (FLMs) modeled through ordinary differential equations. The aim is to correct mass, stiffness, and damping matrices of dynamic models, usually based on nominal and uncertain parameters, to accurately represent the main vibrational modes within the bandwidth of interest. Indeed, the availability of accurate models is a fundamental step for the synthesis of effective controllers, state observers, and optimized motion profiles, as those employed in modern control schemes. The method takes advantage of the system dynamic model formulated through finite elements and through the representation of the total motion as the sum of a large rigid-body motion and the elastic deformation. Model updating is not straightforward since the resulting model is nonlinear and its coordinates cannot be directly measured. Hence, the nonlinear model is linearized about an equilibrium point to compute the eigenstructure and to compare it with the results of experimental modal analysis. Once consistency between the model coordinates and the experimental data is obtained through a suitable transformation, model updating has been performed solving a constrained convex optimization problem. Constraints also include results from static tests. Some tools to improve the problem conditioning are also proposed in the formulation adopted, to handle large dimensional models and achieve reliable results. The method has been experimentally applied to a challenging system: a planar six-bar linkage manipulator. The results prove their capability to improve the model accuracy in terms of eigenfrequencies and mode shapes

Parallel Robot Translational Performance Evaluation through Direction-Selective Index (DSI)

Performance indexes usually provide global evaluations of robot performances mixing their translational and/or rotational capabilities. This paper proposes a definition of performance index, called direction-selective index (DSI), which has been specifically developed for parallel manipulators and can provide uncoupled evaluations of robot translational capabilities along relevant directions. The DSI formulation is first presented within a general framework, highlighting its relationship with traditional manipulability definitions, and then applied to a family of parallel manipulators (4-RUU) of industrial interest. The investigation is both numerical and experimental and allows highlighting the two chief advantages of the proposed DSIs over more conventional manipulability indexes: not only are DSIs more accurate in predicting the workspace regions where manipulators can best perform translational movements along specific directions, but also they allow foreseeing satisfactorily the dynamic performance variations within the workspace, though being purely kinematic indexes. The experiments have been carried out on an instrumented 4-RUU commercial robot

Portraying the life cycle of ideas in social psychology through functional (textual) data analysis: a toolkit for digital history

This paper presents a method for the digital history of a discipline (social psychology in this application) through the analysis of scientific publications. The titles of a comprehensive set of papers published in the Journal of Personality and Social Psychology (1965–2021) were collected, yielding a total of 10,222 items. The corpus thus constructed underwent several stages of preprocessing until the final conversion into a terms x time-points matrix, where terms are stemmed words and multi-words. After normalizing frequencies via a chi square-like transformation, clusters of words portraying similar temporal patterns were identified by functional (textual) data analysis and distance-based curve clustering. Among the best candidates in terms of the number of clusters, the solutions with six, nine and thirteen clusters (from lower to higher resolution) have been chosen and the nesting relationship demonstrated. They reveal—at different levels of granularity—increasing, decreasing, and stable keywords trends, highlighting methods, theories, and application domains that have become more popular in recent years, lost popularity, or have remained in common use. Moreover, this method allows to highlight historical issues (such as crises in the discipline or debates over the use of terms). The results highlight the core topics of social psychology in the past and today, underlying the crucial contribution of this method for the digital history of a discipline

Multi-domain optimization of the eigenstructure of controlled underactuated vibrating systems

The paper proposes a multi-domain approach to the optimization of the dynamic response of an underactuated vibrating linear system through eigenstructure assignment, by exploiting the concurrent design of the mechanical properties, the regulator and state observers. The approach relies on handling simultaneously mechanical design and controller synthesis in order to enlarge the set of the achievable performances. The underlying novel idea is that structural properties of controlled mechanical systems should be designed considering the presence of the controller through a concurrent approach: this can considerably improve the optimization possibilities. The method is, first, developed theoretically. Starting from the definition of the set of feasible system responses, defined through the feasible mode shapes, an original formulation of the optimality criterion is proposed to properly shape the allowable subspace through the optimal modification of the design variables. A proper choice of the modifications of the elastic and inertial parameters, indeed, changes the space of the allowable eigenvectors that can be achieved through active control and allows obtaining the desired performances. The problem is then solved through a rank-minimization with constraints on the design variables: a convex optimization problem is formulated through the \u201csemidefinite embedding lemma\u201d and the \u201ctrace heuristics\u201d. Finally, experimental validation is provided through the assignment of a mode shape and of the related eigenfrequency to a cantilever beam controlled by a piezoelectric actuator, in order to obtain a region of the beam with negligible oscillations and the other one with large oscillations. The results prove the effectiveness of the proposed approach that outperforms active control and mechanical design when used alone

Gravitational Matter Creation, Multi-fluid Cosmology and Kinetic Theory

A macroscopic and kinetic relativistic description for a decoupled multi-fluid cosmology endowed with gravitationally induced particle production of all components is proposed. The temperature law for each decoupled particle species is also kinetically derived. The present approach points to the possibility of an exact (semi-classical) quantum-gravitational kinetic treatment by incorporating back reaction effects for an arbitrary set of dominant decoupled components. As an illustration we show that a cosmology driven by creation of cold dark matter and baryons (without dark energy) evolves like $\Lambda$CDM. However, the complete physical emulation is broken when photon creation is added to the mixture thereby pointing to a crucial test in the future. The present analysis also open up a new window to investigate the Supernova-CMB tension on the values of $H_0$, as well as the $S_8$ tension since creation of all components changes slightly the CMB results and the expansion history both at early and late times. Finally, it is also argued that cross-correlations between CMB temperature maps and the Sunyaev-Zeldovich effect may provide a crucial and accurate test confronting extended CCDM and $\Lambda$CDM models.Comment: 16 pages, 1 figure, accepted for publication in European Physical Journal

Pole assignment for active vibration control of linear vibrating systems through Linear Matrix Inequalities

This paper proposes a novel method for pole placement in linear vibrating systems through state feedback and rank-one control. Rather than assigning all the poles to the desired locations of the complex plane, the proposed method exactly assigns just the dominant poles, while the remaining ones are free to assume arbitrary positions within a pre-specified region in the complex plane. Therefore, the method can be referred to as "regional pole placement". A two-stage approach is proposed to accomplish both the tasks. In the first stage, the subset of dominant poles is assigned to exact locations by exploiting the receptance method, formulated for either symmetric or asymmetric systems. Then, in the second stage, a first-order model formulated with a reduced state, together with the theory of Linear Matrix Inequalities, are exploited to cluster the subset of the unassigned poles into some stable regions of the complex plane while keeping unchanged the poles assigned in the first stage. The additional degrees of freedom in the choice of the gains, i.e., the non-uniqueness of the solution, is exploited through a semidefinite programming problem to reduce the control gains. The method is validated by means of four meaningful and challenging test-cases, also borrowed from the literature. The results are also compared with those of classic partial pole placement, to show the benefits and the effectiveness of the proposed approach

M1 AFLATOXIN, TOTAL BACTERIAL COUNT AND SOMATIC CELL COUNT IN ORGANIC AND CONVENTIONAL MILK

Comparative quality evaluation of organic and conventional milk produced in similar environmental condition was performed. Bulk-tank milk was sampled once a week during 30 weeks from 10 organic and 10 conventional dairy farms where aflatoxin M1 level was previous tested during 11 months on bulk-tank milk from tanker at the processing plant. Somatic Cells and Total Microbial Counts did not show differences that can be related to the organic production system, suggesting an effect induced by farm size and technical factors. Higher level of Aflatoxin M1 was found in organic than conventional milk

DOMANDE E RISPOSTE SUL SISTEMA INTEGRATO DI VALUTAZIONE PREVENTIVA DELL'INQUINAMENTO ELETTROMAGNETICO AMBIENTALE A BASSISSIMA FREQUENZA PLEIA-CERT

L’ARPAT e l’IFAC-CNR collaborano ormai da oltre cinque anni allo sviluppo del Catasto degli Elettrodotti della Regione Toscana (CERT) e di un sistema integrato di applicazioni, denominato PLEIA (Power Line Electromagnetic Impact Assessment), per il suo utilizzo ai fini del calcolo del campo magnetico nello spazio circostante gli elettrodotti e, in particolare, della determinazione delle fasce di rispetto. Per rendere possibile a queste istituzioni un utilizzo corretto e consapevole degli strumenti realizzati e dei risultati da essi forniti, è stato indispensabile documentare innanzitutto i presupposti tecnici e metodologici che stanno alla base delle applicazioni sviluppate: a questo scopo, è venuto spontaneamente a crearsi un gruppo di lavoro informale tra esperti dell’ARPAT, dell’IFAC e della Regione Toscana. Il gruppo ha lavorato secondo un meccanismo virtuoso in cui, da un lato, si è cercato di formulare quesiti puntuali e ben definiti e, dall'altro, di rispondervi nel modo più chiaro ed esauriente possibile. Ne è scaturito un documento a domande e risposte che, opportunamente modificato, è riproposto in questa sede, perché mette in evidenza in modo semplice ma non banale alcuni rilevanti aspetti tecnici, e costituisce un buon documento introduttivo sulle potenzialità del sistema sviluppato. Le prime domande riguardano il sistema PLEIA-CERT in generale, mentre nella seconda parte si approfondiscono in particolare le modalità di calcolo delle fasce di rispetto che, anche alla luce di recenti sviluppi normativi, hanno assunto un ruolo di primaria importanza

Targeting Low-arsenic Groundwater with Mobile-phone Technology in Araihazar, Bangladesh

The Bangladesh Arsenic Mitigation and Water Supply Program (BAMWSP) has compiled field-kit measurements of the arsenic content of groundwater for nearly five million wells. By comparing the spatial distribution of arsenic inferred from these field-kit measurements with geo-referenced laboratory data in a portion of Araihazar upazila, it is shown here that the BAMWSP data could be used for targeting safe aquifers for the installation of community wells in many villages of Bangladesh. Recent experiences with mobile-phone technology to access and update the BAMWSP data in the field are also described. It is shown that the technology, without guaranteeing success, could optimize interventions by guiding the choice of the drilling method that is likely to reach a safe aquifer and identifying those villages where exploratory drilling is needed