Operational Modal Analysis for Rotating Machines: Challenges and Solutions

Operational Modal Analysis (OMA) is widely employed and became an industrial standard technique for identifying the modal parameters (i.e. resonance frequencies, damping ratios and mode shapes) of mechanical structures. Its main applications are in the automotive, aerospace, civil engineering domains and many others. The advantage, if compared with Experimental Modal Analysis (EMA), is that it is not necessary to stop the machine, but its modal characteristics can be estimated during its operating cycles. In other words, OMA does not rely on known and deterministic excitation, but it uses exclusively the natural vibrations of the structure. It is very useful in cases in which the forces cannot be measured or when it is very difficult to excite a structure and it is more convenient to exploit the natural ambient excitation. The input forces are unknown and the main concept behind OMA is that the structure can be identified from a dynamic perspective by analyzing only the measured output signals. Several hypothesis need to be verified in order to apply OMA. First of all the structure must be Linear Time Invariant (LTI), but this is not the case if several parts are moving with respect to each other. Secondly, the forces acting on the structure must be represented by white noise in the frequency range of interest. This means that all the frequencies must be uniformly excited. This is often the case for wind excitation, but it is not valid anymore if periodical loads due to rotating elements are introduced in the system. The main scope of this dissertation is to fully understand and propose solutions to the challenges and the limitations occurring when applying classical OMA techniques in case of rotating machines. Several simulation and test cases will be discussed in order to validate the proposed solutions

Black Hole entropy for two higher derivative theories of gravity

The dark energy issue is focusing the attention of an incresing number of physicists all over the world. Among the possible alternatives in order to explain what as been named the "Mystery of the Millennium" are the so-called Modified Theories of Gravity. A crucial test for such models is represented by the existence and (if this is the case) the properties of their black hole solutions. Nowadays, to our knowledge, only two non-trivial, spherically symmetric, solutions with vanishing cosmological constant are known by Barrow & Clifton (2005) and Deser, Sarioglu & Tekin (2008). Aim of the paper is to discuss some features of such solutions, with emphasis on their thermodynamic properties such as entropy and temperature, little progress being possible along the way which leads to a consistent definition of mass.Comment: 10 pages, 1 figur

Dynamic edge computing empowered by reconfigurable intelligent surfaces

In this paper, we propose a novel algorithm for energy-efficient low-latency dynamic mobile edge computing (MEC), in the context of beyond 5G networks endowed with reconfigurable intelligent surfaces (RISs). We consider a scenario where new computing requests are continuously generated by a set of devices and are handled through a dynamic queueing system. Building on stochastic optimization tools, we devise a dynamic learning algorithm that jointly optimizes the allocation of radio resources (i.e., power, transmission rates, sleep mode and duty cycle), computation resources (i.e., CPU cycles), and RIS reflectivity parameters (i.e., phase shifts), while guaranteeing a target performance in terms of average end-to-end delay. The proposed strategy enables dynamic control of the system, performing a low-complexity optimization on a per-slot basis while dealing with time-varying radio channels and task arrivals, whose statistics are unknown. The presence and optimization of RISs helps boosting the performance of dynamic MEC, thanks to the capability to shape and adapt the wireless propagation environment. Numerical results assess the performance in terms of service delay, learning, and adaptation capabilities of the proposed strategy for RIS-empowered MEC

structural health monitoring strategies based on the estimation of modal parameters

Abstract Rotating machines have always been used in a wide variety of industrial applications. Nowadays it is very difficult to find machines or mechanical systems which do not have any rotating component such as gears, bearings, shafts, wheels and so on. Wind turbines, gearboxes, combustion and electrical engines, generators and gas turbines are just few examples of objects with several rotating substructures. These machines face very complex and non-linear conditions during their operating cycles. they are often subjected to the fatigue problem and it is fundamental to detect faults or damages well in advance in order to reschedule the maintenance cycles. This is especially true for big machines (i.e. wind turbines) where the maintenance costs are a huge part of the total costs. Structural Health Monitoring (SHM) is a technology which is able to provide a continuous indication of the health and the reliability of the structure along its lifecycle. A damage detection technique is an essential part of any SHM system. Its scope consists in the identification of some structural and environmental parameters which have to be monitored regularly during the operation of the machine. This technique should be able to distinguish if the damage is present or not in the structure, but it should also locate and quantify the same damage. A damage can be seen as a change in material and/or geometric properties of a structure, including variation of boundary conditions and structural connections. Several studies have been performed and two different SHM strategies have been defined. The first one is based upon the whirling phenomenon. The whirling modes are the most identifiable modes in operating conditions and they appear to be very sensitive to changes of stiffness. Their amplitude and phase can be used as damage indicators because they allow to identify the loss of isotropy in the rotor. A second parameter which is quite sensitive even to small changes of stiffness is the curvature of the mode shapes. For beam-like structure it has been demonstrated being a very good damage indicator. Several simulations have been run together with some experimental validation on a wind turbine blade

Study of the Electronic Structure in Oxides Using Absorption and Resonant X-Ray Scattering

Resonant X-ray scattering (RXS) is a spectroscopy where both the power of site selective diffraction and the power of local absorption spectroscopy regarding atomic species are combined. By virtue of the dependence on the core level state energy and the three dimensional electronic structure of the intermediate state, this technique is specially suited to study charge, orbital or spin orderings and associated crystal distortions. In the case of charge ordering, we exploit the fact that atoms with closely related site symmetries but with small charge differences exhibit resonances at slightly different energies. The sensitivity of this effect allows for quantitative estimations of the charge disproportion. Opposite to fluorescence or absorption measurements, the power of diffraction relies on the capability of detecting differences that are smaller than the inverse lifetime of the core hole level. To account for the uncertainty of the crystallographic structure and the fact that the charge ordering must be disentangled from the associated atomic displacements, a complete methodology is proposed and applied to the low temperature phase of magnetite. Relative sensitivity on spin, toroidal and orbital ordering is also shown and compared in different transition metal oxide compounds, like V2O3 and GaFeO3

Goal-oriented Communications for the IoT: System Design and Adaptive Resource Optimization

Internet of Things (IoT) applications combine sensing, wireless communication, intelligence, and actuation, enabling the interaction among heterogeneous devices that collect and process considerable amounts of data. However, the effectiveness of IoT applications needs to face the limitation of available resources, including spectrum, energy, computing, learning and inference capabilities. This paper challenges the prevailing approach to IoT communication, which prioritizes the usage of resources in order to guarantee perfect recovery, at the bit level, of the data transmitted by the sensors to the central unit. We propose a novel approach, called goal-oriented (GO) IoT system design, that transcends traditional bit-related metrics and focuses directly on the fulfillment of the goal motivating the exchange of data. The improvement is then achieved through a comprehensive system optimization, integrating sensing, communication, computation, learning, and control. We provide numerical results demonstrating the practical applications of our methodology in compelling use cases such as edge inference, cooperative sensing, and federated learning. These examples highlight the effectiveness and real-world implications of our proposed approach, with the potential to revolutionize IoT systems.Comment: Accepted for publication on IEEE Internet of Things Magazine, special issue on "Task-Oriented Communications and Networking for the Internet of Things

765 Is acute response to calcium sensitizers drugs predictive of response to cardiac contractility modulation in NYHA IV patients?

Abstract A 53-years old man presented to our institution with a diagnosis of decompensated heart failure NYHA Class IV. He had a history of ischaemic heart disease with severe biventricular dysfunction, diabetes, hypertension, dyslipidaemia, advanced chronic kidney disease, previous explanation of dual-chamber implantable electronic device (ICD) due to endocarditis and subsequent implantation of subcutaneous ICD in primary prevention. Home therapy included uptitrated angiotensin-converting enzyme inhibitor, β-blocker, loop-diuretic, spironolactone, acetylsalicylic acid, and oral hypoglycemics. Clinical examination showed signs and symptoms of systemic and pulmonary congestion with pleural effusion and ascites. Echocardiography revealed diffuse left ventricular (LV) hypokinesis with an ejection fraction (EF) of 25%, severe right ventricular dysfunction and increased filling pressures. He was treated with high dose of i.v. diuretics with mild improvement of dyspnoea. However, haemodynamic stability was labile with worsening of symptoms as soon as mild down-titration of iv diuretics was attempted. Levosimendan, a calcium-sensitizer inodilator, indicated for short-term treatment of acutely decompensated severe chronic heart failure (HF), was administered with good clinical response. Thus, we thought that the patient could have benefited from contractility modulation therapy (CCM) which acts on intramyocardial calcium handling. CCM is a novel therapeutic option for patients with classes III–IV HF with EF ≥ 25% to ≤ 45% and narrow QRS complex that acts on intramyocardial calcium-handling. CCM proved effective in alleviating symptoms, improving exercise tolerance and quality of life, and reducing hospitalization rates in HF. It improves myocardial contractility, reverses the foetal myocyte gene program associated with HF and facilitates cardiac reverse remodelling. Therefore, an Optimizer Smart System (Impulse Dynamics) was implanted. Two pacing electrodes were placed on the interventricular septum in apical and mid-septal position, respectively. The leads were connected to a pulse-generator in a right pectoral pocket. In the following days, we observed a progressive improvement in clinical status, with gradual resolution of peripheral oedema, dyspnoea and fatigue and significant weight loss. Six-month echocardiography showed a stable value of EF and significant improvement in stroke volume (35.2 ml from 24.8 ml at baseline). The patient did not undergo further hospitalization for decompensated HF and was in stable ambulatory NYHA Class IV. We believe CCM is an option in patients with advanced HF in which avoiding recurrent hospitalizations, with their overt increase mortality, is often a challenging therapeutic goal. 765 Figur

Islamic finance and conventional financial systems. Market trends, supervisory perspectives and implications for central banking activity

The paper analyses Islamic finance from the central bank and supervisory authorityÂ’s perspective, focusing on the European and Italian context. It depicts a rapidly expanding sector, with recent annual growth rates of between 10 and 15 percent and a geographical presence that now reaches several Western countries. Future prospects, however, could be hampered by problems concerning the standardization of products, governance structure, supervisory regulation, monetary policy instruments, and liquidity management. Islamic intermediaries are not necessarily riskier than traditional counterparts but their operational structure tends to be more complex. Key issues in supervision include the treatment of investment accounts and transparency. It has been seen that there are limits to the efficiency of the monetary policy instruments developed so far to remedy the prohibition of interest; moreover, the growth of interbank and money markets is hindered by a shortage of "Shari'ah-compliant" products. Problems arising from the participation of Islamic banks in payment systems are also discussed.Islamic finance, Islamic financial institutions, supervision, monetary policy instrments, payment systems

Defective Neurogenesis in Citron Kinase Knockout Mice by Altered Cytokinesis and Massive Apoptosis

AbstractCitron-kinase (Citron-K) has been proposed by in vitro studies as a crucial effector of Rho in regulation of cytokinesis. To further investigate in vivo its biologic functions, we have inactivated Citron-K gene in mice by homologous recombination. Citron-K−/− mice grow at slower rates, are severely ataxic, and die before adulthood as a consequence of fatal seizures. Their brains display defective neurogenesis, with depletion of specific neuronal populations. These abnormalities arise during development of the central nervous system due to altered cytokinesis and massive apoptosis. Our results indicate that Citron-K is essential for cytokinesis in vivo but only in specific neuronal precursors. Moreover, they suggest a novel molecular mechanism for a subset of human malformative syndromes of the CNS

Pain Modulation in WAG/Rij Epileptic Rats (A Genetic Model of Absence Epilepsy): Effects of Biological and Pharmacological Histone Deacetylase Inhibitors

Epigenetic mechanisms are involved in epilepsy and chronic pain development. About that, we studied the effects of the natural histone deacetylase (HDAC) inhibitor sodium butyrate (BUT) in comparison with valproic acid (VPA) in a validated genetic model of generalized absence epilepsy and epileptogenesis. WAG/Rij rats were treated with BUT (30 mg/kg), VPA (300 mg/kg), and their combination (BUT + VPA) daily per os for 6 months. Rats were subjected at Randall-Selitto, von Frey, hot plate, and tail flick tests after 1, 3, and 6 months of treatment to evaluate hypersensitivity to noxious and non-noxiuous stimuli. Moreover, PPAR-γ (G3335 1 mg/kg), GABA-B (CGP35348 80 mg/kg), and opioid (naloxone 1 mg/kg) receptor antagonists were administrated to investigate the possible mechanisms involved in analgesic activity. The expression of NFkB, glutathione reductase, and protein oxidation (carbonylation) was also evaluated by Western blot analysis. WAG/Rij rats showed an altered pain threshold throughout the study (p < 0.001). BUT and BUT + VPA treatment reduced hypersensitivity (p < 0.01). VPA was significantly effective only after 1 month (p < 0.01). All the three receptors are involved in BUT + VPA effects (p < 0.001). BUT and BUT + VPA decreased the expression of NFkB and enhanced glutathione reductase (p < 0.01); protein oxidation (carbonylation) was reduced (p < 0.01). No effect was reported with VPA. In conclusion BUT, alone or in coadministration with VPA, is a valuable candidate for managing the epilepsy-related persistent pain