A VSWR-protected silicon bipolar RF power amplifier with soft-slope power control

This paper presents the design and measured performance of a 1.8-GHz power amplifier featuring load mismatch protection and soft-slope power control. Load-mismatch-induced breakdown can be avoided by attenuating the RF power to the final stage during overvoltage conditions. This was accomplished by means of a feedback control system, which detects the peak voltage at the output collector node and clamps its value to a given threshold by varying the circuit gain. The issue of output power control has been addressed as well. To this end, a temperature-compensated bias network is proposed, which allows a moderate power control slope (dB/V) to be achieved by varying the circuit quiescent current according to an exponential law. The nonlinear power amplifier was fabricated using a low-cost silicon bipolar process with a 6.4-V breakdown voltage. It delivers a 33.5-dBm saturated output power with 46% maximum power-added efficiency and 36-dB gain at a nominal 3.5-V supply voltage. The device is able to tolerate a 10:1 load standing-wave ratio up to a 5.1-V supply voltage. Power control slope is lower than 80 dB/V between -15 dBm and the saturated output power level.     

A new bioreactor for the controlled application of complex mechanical stimuli for cartilage tissue engineering

Mechanical stimuli have been shown to enhance chondrogenesis on both animal and human chondrocytes cultured in vitro. Different mechanical stimuli act simultaneously in vivo in cartilage tissue and their effects have been extensively studied in vitro, although often in a separated manner. A new bioreactor is described where different mechanical stimuli, i.e. shear stress and hydrostatic pressure, can be combined in different ways to study the mechanobiology of tissue engineered cartilage. Shear stress is imposed on cells by forcing the culture medium through the scaffolds, whereas a high hydrostatic pressure up to 15 MPa is generated by pressurizing the culture medium. Fluid-dynamic experimental tests have been performed and successful validation of the bioreactor has been carried out by dynamic culture of tissue-engineered cartilage constructs. The bioreactor system allows the investigation of the combined effects of different mechanical stimuli on the development of engineered cartilage, as well as other possible three-dimensional tissue-engineered constructs.     

Crude oil aggregation by microscopy and dynamic light scattering

This research is focused on establishing a methodology to evaluate the aggregation state of Mexican crude oil solutions from two different sources and SARA compositions, by using Dynamic Light Scattering (DLS). Different crude oil concentrations were established and monitored through time in order to determine their effects on the aggregation state. DLS results indicate that the aggregation state of the studied solutions is influenced by crude oil composition, specifically by the amount of resins. Particle size and elemental analysis of the aggregates were performed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX), respectively. Results from these techniques reveal particulated low-porosity smooth surfaces due to the presence of resin, as well as the determination of the characteristic elements found in asphaltenes. High-Resolution Transmission Electron Microscopy (HTEM) indicated the presence of asphaltene aggregates constituted by nanometric particles and asphaltene stacking as well as ultrafine nanocrystalline-oriented structures.     

Non-destructive Estimation of Mandarin Maturity Status Through Portable VIS-NIR Spectrophotometer

Sugar content is one of the most important quality attributes of citrus fruit, either for fresh or for processing market. Since sugars in citrus juice are highly correlated with total soluble solids (TSS) content, which can be determined easily even by the means of a hand refractometer, TSS is one of the most frequently used quality index. Since TSS can be measured only destructively, the results are representative only if carried out on large samples and do not allow classifying marketable fruit one by one according to their specific sugar content. Objective of this experiment was to assess possibility and limits of a non-destructive estimation of citrus fruits internal quality parameters (TSS and titratable acidity) presenting thick peel by the use of a spectrophotometric portable VIS-NIR system. Four hundred fruit of “Miho” satsuma and 150 fruit of “Page” tangelo were used. Each fruit was first subjected to spectrophotometric acquisition and soon after was juiced and TSS and titratable acidity (TA) determined. Partial least squares (PLS) regression analysis was applied for constructing a predictive model based on the spectral normalized response, constructing the model on a sub-sample and verifying the model (prediction test) on independent ones. The TA relative to Page mandarin was predicted in the test with an r = 0.88 and a standard error of prevision (SEP) coefficient of variability of 3.8% while the TSS scored an r = 0.85 and a SEP coefficient of variability equal to 4%. The TA of Miho mandarin was predicted in the test with an r = 0.81 and a SEP coefficient of Variability of 8.3% while the TSS scored an r = 0.84 and a SEP coefficient of variability equal to 5.6%.     

Supervised Multivariate Analysis of Hyper-spectral NIR Images to Evaluate the Starch Index of Apples

Fruit maturity indexes are crucial in harvest time determination and commercial context. The harvest time of apples, matching the desired commercial characteristics, is assessed through starch–iodine test in practice. Fruit halves are dipped into iodine solution and patterns are visually evaluated by experts comparing them to reference charts. Aim of the work was to study the relationships of near infrared (NIR) spectral images (1,000–1,700 nm), starch/starch-free patterns visually assessed and RGB color images. Spectral images of 88 Golden Delicious Klon B apples were sampled at seven different maturity stages. Partial least-squares discriminant analysis (PLSDA) technique was used on hyper-spectral NIR images to classify single pixels using its NIR reflectance spectrum. The response variable (i.e. the classification for each pixel) was identified through the matching of single pixel obtained with the color images, segmented in two classes (starch and starch-free), and the NIR hyper-spectral matrix. Mean hyper-spectral classification obtained through PLSDA modeling on individual apple correctly classified 80.81% of the total pixels, while the unique model, i.e. a single model including all the fruits, resulted in 66.33%. In the latter case, the relationship with the RGB classification showed high values (Pearson correlation coefficient r = 0.95). The present work shows the feasibility of NIR imaging spectroscopy as a tool for apple fruit maturity determination, avoiding expert’s subjective interpretation by traditional starch index assignments.     

Influence of counterface roughness on friction properties of engineering plastics for bearing applications

The study investigates the effects of the roughness of the metal counterface (mirror finished or polished) on the coefficient of dry friction for some of the most common engineering plastics used in current bearing technology. The results show that an optimal roughness for minimum friction is likely to exist for any polymer, and it depends on the bulk properties of the polymer itself. “Soft” plastics characterized by a low modulus of elasticity exhibit better sliding behaviour on very smooth, mirror finished surfaces, whereas for high-modulus plastics lower friction is measured in combination with rougher, polished counterfaces. The influence of the contact pressure and sliding velocity are also investigated and found to depend on the layout of the tribological system.     

Multi-agent location system in wireless networks

In this paper we propose a flexible Multi-Agent Architecture together with a methodology for indoor location which allows us to locate any mobile station (MS) such as a Laptop, Smartphone, Tablet or a robotic system in an indoor environment using wireless technology. Our technology is complementary to the GPS location finder as it allows us to locate a mobile system in a specific room on a specific floor using the Wi-Fi networks.The idea is that any MS will have an agent known at a Fuzzy Location Software Agent (FLSA) with a minimum capacity processing at its disposal which collects the power received at different Access Points distributed around the floor and establish its location on a plan of the floor of the building. In order to do so it will have to communicate with the Fuzzy Location Manager Software Agent (FLMSA). The FLMSAs are local agents that form part of the management infrastructure of the Wi-Fi network of the Organization.The FLMSA implements a location estimation methodology divided into three phases (measurement, calibration and estimation) for locating mobile stations (MS). Our solution is a fingerprint-based positioning system that overcomes the problem of the relative effect of doors and walls on signal strength and is independent of the network device manufacturer.In the measurement phase, our system collects received signal strength indicator (RSSI) measurements from multiple access points. In the calibration phase, our system uses these measurements in a normalization process to create a radio map, a database of RSS patterns. Unlike traditional radio map-based methods, our methodology normalizes RSS measurements collected at different locations on a floor. In the third phase, we use Fuzzy Controllers to locate an MS on the plan of the floor of a building.Experimental results demonstrate the accuracy of the proposed method. From these results it is clear that the system is highly likely to be able to locate an MS in a room or adjacent room.     

A comparison of atmospheric phase delay estimated by ASAR and MERIS over the Campania area

Propagation delay through the atmosphere is a key problem in coherent processing of synthetic aperture radar (SAR) data. Modern multitemporal interferometric techniques compensate the atmospheric phase delay contribution by analysing a stack of data. However, assessment of the achieved accuracy of the retrieved atmospheric component is still an open issue. In this work we report the results of an experiment carried out over a wide area aimed at comparing the zenith delay (ZD) estimated by radar and multispectral sensors. In particular, we refer to the instruments onboard the Envisat satellite and specifically to the Advanced Synthetic Aperture Radar (ASAR) and Multispectral Medium Resolution Imaging Spectrometer (MERIS) sensors that simultaneously acquire data along the same orbit. The study is preliminary to the possible exploitation of the MERIS water vapour product for compensating the atmospheric phase delay signals in a long series of acquisitions used in the multipass differential interferometric synthetic aperture radar (DInSAR) techniques to achieve higher accuracy and/or to extend the applicability of the technique to emergency situations, as well as to the possible use of SAR interferometry in meteorological applications.     

Stability evaluation of high-precision multifunction instrumentsfor traceability transfer

In the traceability transfer process from the national standards of the Istituto Elettrotecnico Nazionale “Galileo Ferraris” to standards of calibration laboratories accredited by Servizio di Taratura in Italia, the use of high-precision multifunction instruments, in particular digital multimeters, as reference standards turned out to be a good transfer method. In fact, their use provides swift and less expensive transfer at an uncertainty level comparable to that one obtained using high-precision individual standards, such as 10 V DC voltage standards, standard resistors, or AC/DC transfer standards. In this paper, how this transfer process is performed and what results are obtained, are described