Fernando de Souza Campos

Probing neutrino mass with multilepton production at the Tevatron in the simplest R-parity violation model

We analyse the production of multileptons in the simplest supergravity model with bilinear violation of R parity at the Fermilab Tevatron. Despite the small R-parity violating couplings needed to generate the neutrino masses indicated by current atmospheric neutrino data, the lightest supersymmetric particle is unstable and can decay inside the detector. This leads to a phenomenology quite distinct from that of the R-parity conserving scenario. We quantify by how much the supersymmetric multilepton signals differ from the R-parity conserving expectations, displaying our results in the m0?m1/2 plane. We show that the presence of bilinear R-parity violating interactions enhances the supersymmetric multilepton signals over most of the parameter space, specially at moderate and large m0.

Partial Discharge Monitoring in Power Transformers Using Low-Cost Piezoelectric Sensors.

Power transformers are crucial in an electric power system. Failures in transformers can affect the quality and cause interruptions in the power supply. Partial discharges are a phenomenon that can cause failures in the transformers if not properly monitored. Typically, the monitoring requires high-cost corrective maintenance or even interruptions of the power system. Therefore, the development of online non-invasive monitoring systems to detect partial discharges in power transformers has great relevance since it can reduce significant maintenance costs. Although commercial acoustic emission sensors have been used to monitor partial discharges in power transformers, they still represent a significant cost. In order to overcome this drawback, this paper presents a study of the feasibility of low-cost piezoelectric sensors to identify partial discharges in mineral insulating oil of power transformers. The analysis of the feasibility of the proposed low-cost sensor is performed by its comparison with a commercial acoustic emission sensor commonly used to detect partial discharges. The comparison between the responses in the time and frequency domain of both sensors was carried out and the experimental results indicate that the proposed piezoelectric sensors have great potential in the detection of acoustic waves generated by partial discharges in insulation oil, contributing for the popularization of this noninvasive technique.

MLP and ANFIS Applied to the Prediction of Hole Diameters in the Drilling Process

The control of industrial machining manufacturing processes is of great economic impor‐ tance due to the ongoing search to reduce raw materials and labor wastage. Indirect manufacturing operations such as dimensional quality control generate indirect costs that can be avoided or reduced through the use of control systems [1]. The use of intelligent manufacturing systems (IMS), which is the next step in the monitoring of manufacturing processes, has been researched through the application of artificial neural networks (ANN) since the 1980s [2].

A low cost system for acoustic monitoring of partial discharge in power transformer by piezeletic sensor

Partial discharge damages in power transformers require high cost monitoring procedures based on corrective maintenance or even interruptions of the power system. The development of online non-invasive monitoring systems to detect partial discharges in power transformers has great relevance since it can reduce significant maintenance costs. Some critical factors in the operation of transformers such as overload, nonlinear loads, transient voltage surges by atmospheric origin and switching, can make the insulation system of transformers to lose their physical and chemical properties. Therefore, these operating conditions can cause early deterioration of the insulation, causing internal partial discharges that may develop into major defects and thus shorten the useful life of electrical equipment. This research aimed to apply a low cost piezoelectric sensors (PZTs) for partial discharge identification in power transformers and a study was conducted on the obtained a good results for identification with PZTs.

A logarithmic CMOS image sensor with wide output voltage swing range

This paper presents logarithmic CMOS image sensor with wide output voltage swing range. Wide output voltage swing range is achieved by increasing the number of transistors connected as diodes of logarithmic CMOS image sensor. A prototype has been fabricated in 0.35μm AMS opto process. Four different pixels were fabricated using 20μmx20μm Nwel/Psub photodiodes with one, two, three and four transistors in series. The sensitivity measured were 136mV/Dec, 191mV/Dec, 281mV/Dec and 425mV/Dec for the pixels using one, two, three and four transistors in series respectively. This results shows that the sensitivity is increased by N approximately, were N is the number of transistors in series at pixels. Considering that the supply voltage the four-transistor pixel presents total output voltage swing range of 2.65V over a range of 120dB being the supply voltage 3.3V.

Analysis and Methodology for Determining the Parasitic Capacitances in VSI-fed IM Drives Based on PWM Technique

Three-phase induction motors present stray capacitances. The aim of this chapter is to present a methodology to experimentally determine these capacitances and also evaluate the effects of electromagnetic interference on motors in common mode. The proposed procedures for this methodology consist of: a) identifying the motor equivalent electrical circuit parameters through characteristic tests performed in the laboratory; b) setting up configurations between the PWM inverter and the motor for voltage and current meas‐ urements: common mode and shaft voltages, leakage and shaft (bearing) currents by us‐ ing a dedicated measuring circuit; c) calculating the parasitic capacitance values between stator and frame, stator and rotor, rotor and frame and bearings of the motor using the capacitance characteristic equation; d) using the dedicated software Pspice to simulate the system composed by the three-phase induction motor fed by PWM inverter with the equivalent electrical circuit parameters; e) determining the characteristic waveforms in‐ volved in the common mode phenomenon.

A New FPN Cancellation Circuit for Time-Domain CMOS Image Sensors

A fixed-pattern noise correction technique for time-domain CMOS imagers with high dynamic range is presented in this chapter. Analytical derivations are presented showing how the circuit variations affect the time measured. The error in the time measured can be reduced by using lower reference voltages achieving values smaller than 4%. The fixed-pattern noise correction technique proposed is based on a new readout method for time-domain imagers employing two reference voltages for the discharge time measurement. This new technique is non-sensitive to circuit parameter variations that contribute to fixed-pattern noise such as hold voltages of transistors. A simple electronic circuit is proposed to implement the technique. Circuit and simulation results are presented to demonstrate the feasibility of the proposed technique.

Temporal noise analysis and measurements of CMOS active pixel sensor operating in time domain

Image sensors in standard CMOS technology are increasing used for consumer, industrial and scientific applications due to their low cost, high level of integration and low power consumption. Further, image sensors in mainstream complementary metal-oxide-semiconductor (CMOS) technology are preferred because they are the lowest cost and easiest/fastest option to implement. For CMOS image sensors, a key issue is their noise behavior. Therefore, we have studied the noise characteristics of CMOS image sensors operating in time domain. Two important noise sources are the reset noise and integration noise. The reset noise is due to the reset in CMOS image sensors operating in voltage domain. The integration noise is that accumulated during light integration and was found to be the constant, independent of light intensity. Our circuit analysis shows that the signal-to-noise ratio (SNR) is also constant and independent of light intensity. At low light levels the constant SNR is higher compared to others CMOS image sensors presented in the literature. We have implemented a time domain CMOS image sensor in AMS CMOS 0.35um technology. Our measurements results show that the SNR level is approximately constant to 43dB.

Noise Performance of Time-Domain CMOS Image Sensors

Temporal noise is the main disadvantage of CMOS image sensors when compared to charg‐ ed couple devices (CCDs) sensor. The typical 3T active pixel sensor (APS) architecture presents as main noise sources the photodiode shot noise, the reset transistor and follower thermal and shot noise, the amplifier thermal and 1/f noise, the column amplifier thermal and reset noise (Zheng, 2011; Brouk, 2010; Jung, 2005; Tian, 2001; Derli, 2000; Yadid-Pecht, 1997). In order to reduce the APS noise several approaches have been proposed in the litera‐ ture. Some of these approaches are the use of high gain preamplifiers, correlated multiple sampling (CMS) and low bandwidth column-parallel single slope A/D converters (Sakaki‐ bara, 2005; Kawai, 2004; Suh, 2010; Lim, 2010; Yoshihara, 2006; Chen, 2012). However, APS in time domain has as advantage to show lower source of noise since it is composed only by a photodiode, a reset transistor and a voltage comparator. It shows as noise source only the reset transistor and the photodiode. Therefore, in principle, APS in time domain may presents lower overall noise.

A multisampling time-domain CMOS imager with synchronous readout circuit

A novel multisampling time-domain architecture for CMOS imagers with synchronous readout and wide dynamic range is proposed. The architecture was implemented in a prototype of imager with 32x32 pixel array fabricated in AMS CMOS 0.35µm and was characterized for sensitivity and color response. The pixel is composed of an n+/psub photodiode, a comparator and a D flip-flop having 16% fill-factor and 30µmx26µm dimensions. The multisampling architecture requires only a 1 bit per pixel memory instead of 8 bits which is typical for time-domain active pixel architectures. The advantage is that the number of transistors in the pixel is low, saving area and providing higher fill-factor. The maximum frame rate is analyzed as a function of number of bits and array size. The analysis shows that it is possible to achieve high frame rates and operation in video mode with 10 bits. Also, we present analysis for the impact of comparator offset voltage in the fixed pattern noise.