Polarization fields in nitride nanostructures: ten points to think about

Macroscopic polarization, both of intrinsic and piezoelectric nature, is unusually strong in III-V nitrides, and the built in electric fields in the layers of nitride-based nanostructures, stemming from polarization changes at heterointerfaces, have a major impact on the properties of single and multiple quantum wells, high mobility transistors, and thin films. The concepts involved in the theory and applications of polarization in nitrides have encountered some resistance in the field. Here we discuss critically ten ``propositions'' aimed at clarifying the main controversial issues.Comment: RevTeX 5 pages, 2 embedded figure

Vibration damping performances of buildings with moving façades under harmonic excitation

Façade technologies are in continuous evolution and the idea to realize buildings equipped with cladding systems capable to undergo significant displacements relatively to the main structure has been considered by many authors as an opportunity to improve their vibration performances. From a structural dynamics viewpoint, a building with a monolithic Moving Façade is essentially the same thing as a building with a Tuned Mass Damper. However, in the presence of excitations directly acting on the external surface of the building, there may be significant diferences of behavior. In this work, a first step towards a systematic comparison between the performances of buildings with Moving Façades and Tuned Mass Dampers is carried out in the simplest setting of 2 degrees of freedom modeling and harmonic excitation. Results Despite the deceptive simplicity of the setting, some of the aspects related to the potential applicability of moving façades to vibration damping and the correlated limitations are discussed and critically analyzed. The analyses show that, depending on the tuning of the system, monolithic Moving Façades could effectively act as vibration absorbers with a potentially high efficiency. However, it turns out that good performances could be realized at the price of extremely large displacements of the façade. The possibility to pursue potential applications of this type of systems seems therefore to be subordinated to the search of solutions to limit such displacements within functionally acceptable ranges

Active learning approach to enhance rotor dynamics understanding: A classroom demonstration

In the last decades, novel teaching strategies have been increasingly adopted to improve and enhance the students learning process by promoting their involvement and engagement during classes. In this context, this work presents a laboratory experience proposed to the third-year bachelor students of the course of ‘Mechanics of Vibrations’, held at the faculty of mechanical engineering of Politecnico di Milano. The experience consisted in the presentation of a rotor test bench specifically designed for educational purposes. Main concepts of rotor dynamics were analysed and showed, together with a critical discussion on the discrepancies between the Jeffcott–Laval model and experimental results. This project, that is one of the outcomes of an educational project for post-covid teaching promoted by Politecnico di Milano, involved almost 200 students in total. An anonymous evaluation survey proposed to students revealed a general appreciation of the experience, especially for the possibility of visualising important theoretical concepts. Given the positive feedback, the demonstration will be repeated in the next academic year, with some changes according to students’ suggestions

A P. menziesii var. menziesii (=viridis) (Schwerin) Franco stand description dataset: a case study of Pavari's experimental Plot 412 ninety years after plantation

This paper describes a dataset containing the historical series of dendrometric data from a P. menziesii var. menziesii (=viridis) (Schwerin) Franco plantation. Implemented in 1932, the plantation is located in “Rio di Mercurella” place, in the Tyrrhenian coastal mountain range of Calabria region (Southern Italy). The experimental plot has been identified as Plot 412 and is characterized by trees with a relevant role for forest community biodiversity. The monitoring started in 1940.  The dataset reported five of all the inventories Until 2013, inventories have been carried out by Istituto Sperimentale di Selvicoltura and Unità di Ricerca per la Selvicoltura in Ambiente Mediterraneo, now CREA Forestry and Wood research centre which has taken over the last two. The following data have been collected: position, number, diameter at breast heigh (DBH) of all the trees and total height (Ht) of a trees sample. Collected data are an important historical source and testimony the first experimental test of P. menziesii introduction which will have to be monitored in the future and will constitute a fundamental contribution to enrich the knowledge on appropriate management in Calabria and evaluate the health state and stability of the forest stand in the future

COVID-19 impact on end-user's maintenance requests. A text mining approach

COVID-19 pandemic changed our way of working, limiting the usual physical attendance of working spaces. Despite the drastic reduction in the number of daily users due to the pandemic restrictions, working buildings were often kept open to provide services to internal and external users. Pandemic obliged to change operation and maintenance (O&M) plans, due to the increase of ventilation requirements and the reduction of other types of services, with a strong impact on cost and management. Now the pandemic is reducing its effects and is time to question the future asset of buildings’ O&M plans, based on the pandemic lesson. Data collected by Computerized Maintenance Management Systems (CMMS) during COVID-19 then become an important source of understanding the future management of working places. End-users’ maintenance requests are usually expressed by natural language, then a text mining approach can be a useful tool to discover hidden knowledge from unstructured data stored in CMMS. This study applies text mining methods, including sentiment analysis, to the field of building maintenance, with the scope to evaluate how COVID-19 changed some aspects of the facility management process, including users’ perception

Free-carrier screening of polarization fields in wurtzite GaN/InGaN laser structures

The free-carrier screening of macroscopic polarization fields in wurtzite GaN/InGaN quantum wells lasers is investigated via a self-consistent tight-binding approach. We show that the high carrier concentrations found experimentally in nitride laser structures effectively screen the built-in spontaneous and piezoelectric polarization fields, thus inducing a ``field-free'' band profile. Our results explain some heretofore puzzling experimental data on nitride lasers, such as the unusually high lasing excitation thresholds and emission blue-shifts for increasing excitation levels.Comment: RevTeX 4 pages, 4 figure

The efficacy of an association of palmitoylethanolamide and alpha-lipoic acid in patients with chronic prostatitis/chronic pelvic pain syndrome: A randomized clinical trial

Background: Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a complex condition, characterized by uncertain etiology and by limited response to therapy. The definition of CP/CPPS includes genitourinary pain with or without voiding symptoms in the absence of uropathogenic bacteria, as detected by standard microbiological methods, or another identifiable cause such as malignancy. The efficacy of various medical therapies, has been evaluated in clinical studies, but evidence is lacking or conflicting. We compared Serenoa Repens in monotherapy versus Palmitoylethanolamide (PEA) in combination with Alpha-lipoic acid (ALA) and evaluated the efficacy of these treatments in patients with CP/CPPS. Methods: We conducted a randomized, single-blind trial. 44 patients diagnosed with CP/CPPS (mean age 41.32 ± 1.686 years) were randomly assigned to treatment with Palmitoylethanolamide 300 mg plus Alpha-lipoic acid 300 mg (Peanase®), or Serenoa Repens at 320 mg. Three questionnaires (NIH-CPSI, IPSS and IIEF5) were administered at baseline and after 12 weeks of treatment in each group. Results: 12 week treatment with Peanase significantly improved the IPSS score compared to the same period of treatment with Serenoa Repens, and significantly reduced NIH-CPSI score. Similar results were observed in the different NIH-CPSI subscores break down. However, the same treatment did not result in significant improvement of the IIEF5 score. Both treatments did not produce undesired effects. Conclusions: The present results document the efficacy of an association of Palmitoylethanolamide (PEA) and Alpha-lipoic acid (ALA) administered for 12 weeks for treating patients with CP/CPPS, compared with Serenoa Repens monotherapy

Effects of macroscopic polarization in III-V nitride multi-quantum-wells

Huge built-in electric fields have been predicted to exist in wurtzite III-V nitrides thin films and multilayers. Such fields originate from heterointerface discontinuities of the macroscopic bulk polarization of the nitrides. Here we discuss the background theory, the role of spontaneous polarization in this context, and the practical implications of built-in polarization fields in nitride nanostructures. To support our arguments, we present detailed self-consistent tight-binding simulations of typical nitride QW structures in which polarization effects are dominant.Comment: 11 pages, 9 figures, uses revtex/epsf. submitted to PR

Calibration of material parameters for the Chang-Mander model for unconfined concrete

The current basic OpenSees distribution includes several uniaxial models for concrete. Among them, the model proposed by Chang and Mander in 1994 offers a comprehensive setting applicable both to confined and unconfined concrete, by a proper selection of material parameters. The model offers the possibility to smoothly combine Tsai equation, for the first part of the curve, with a linear branch for the final part. This option is useful to model spalling of unconfined concrete while keeping the smoothness of the curve. Two basic parameters of the Chang-Mander model for compression, denoted by n and r, govern initial and post-peak stiffness of the Tsai equation, respectively. Besides them, there is a further parameter, denoted by α, which received less attention in the literature and determines the position of the switch between nonlinear and linear parts of the curve. In the first part of this work, the calibration of the parameters n and r is discussed in some detail. In the second part, the problem of the calibration of α is analyzed. Changes in the value of α may produce large variations in the evaluation of the spalling strain for unconfined concrete. After some comparative analyses with existing models, a simple expression to calibrate α parameter is finally proposed