Presentation‐Oriented Key‐Frames Coding Based on Fractals

This paper focuses on the problem of key‐frames coding and proposes a new promising approach based on the use of fractals. The summary, made of a set of key‐frames selected from a full‐length video sequence, is coded by using a 3D fractal scheme. This allows the video presentation tool to expand the video sequence in a “natural” way by using the property of the fractals to reproduce the signal at several resolutions. This feature represents an important novelty of this work with respect to the alternative approaches, which mainly focus on the compression ratio without taking into account the presentation aspect of the video summary. In devising the coding scheme, we have taken care of the computational complexity inherent in fractal coding. Accordingly, the key‐frames are first wavelet transformed, and the fractal coding is then applied to each subband to reduce the search range. Experimental results show the effectiveness of the proposed approach.     

Generation of random variables for modelling VBR multimedia sources

The design and performance evaluation of multimedia systems require the availability of adequate models to mimic the statistical properties of the traffic generated by a multimedia source. In this paper the authors propose a very simple method for the generation of discretetime and discretestate autocorrelated random variables which can be used to model a traffic source by simulation. The probability distribution and autocorrelation sequence of the variables generated exactly match the corresponding experimental histograms of the source to be modelled when the experimental autocorrelation sequence is decreasing with downward convexity. In this paper an analytical demonstration of the method proposed is given and its use is illustrated by three telecommunications examples.     

Clock Faults Induced Min and Max Delay Violations

In this paper, we show that clock faults producing duty-cycle variations, which have been proven very likely, can give rise to min or max delay violations. This mandates new, specific testing approaches for clock faults, to avoid them to compromise the system correct operation in the field, with dramatic effects on product quality and defect level. We then introduce a new scheme that can be employed to detect the clock faults causing duty-cycle variations.     

Pressure‐Tunable Ambipolar Conduction and Hysteresis in Thin Palladium Diselenide Field Effect Transistors

Few‐layer palladium diselenide (PdSe₂) field effect transistors are studied under external stimuli such as electrical and optical fields, electron irradiation, and gas pressure. The ambipolar conduction and hysteresis are observed in the transfer curves of the as‐exfoliated and unprotected PdSe₂ material. The ambipolar conduction and its hysteretic behavior in the air and pure nitrogen environments are tuned. The prevailing p‐type transport observed at atmospheric pressure is reversibly turned into a dominant n‐type conduction by reducing the pressure, which can simultaneously suppress the hysteresis. The pressure control can be exploited to symmetrize and stabilize the transfer characteristics of the device as required in high‐performance logic circuits. The transistors are affected by trap states with characteristic times in the order of minutes. The channel conductance, dramatically reduced by the electron irradiation during scanning electron microscope imaging, is restored after an annealing of several minutes at room temperature. The work paves the way toward the exploitation of PdSe₂ in electronic devices by providing an experiment‐based and deep understanding of charge transport in PdSe₂ transistors subjected to electrical stress and other external agents.     

Low-noise tape preamplifier with new self-biasing architecture

A low-noise ground-compatible preamplifier for audio signal processing is presented. It amplifies the audio signal coming from a magnetic head producing a total input-referred voltage noise less than 300-nV r.m.s. CCIR/ARM weighted in operative conditions thanks to a low-noise bipolar amplifier, while auto-reverse, metal/normal, and mute facilities are available on chip using low-noise offset-free analog CMOS switches. Total harmonic distortion was less than 0.004% in full dynamic range. This performance was obtained using a nonconventional self-biasing ground-compatible preamplifier architecture, particularly intended for single supply applications, that does not require any external components and auxiliary voltage reference. The preamplifier occupies 1.5 mm/sup 2/ and dissipates 38 mW with a 10-V power supply. A measured power supply rejection of about 120 dB at 1 kHz was obtained using internal regulated voltage supply.<>     

Integration of InGaP/GaAs/Ge triple‐junction solar cells on deeply patterned silicon substrates

We report preliminary results on InGaP/InGaAs/Ge photovoltaic cells for concentrated terrestrial applications, monolithically integrated on engineered Si(001) substrates. Cells deposited on planar Ge/Si(001) epilayers, grown by plasma‐enhanced chemical vapor deposition, provide good efficiency and spectral response, despite the small thickness of the Ge epilayers and a threading dislocation density as large as 10⁷/cm². The presence of microcracks generated by the thermal misfit is compensated by a dense collection grid that avoids insulated areas. In order to avoid the excessive shadowing introduced by the use of a dense grid, the crack density needs to be lowered. Here, we show that deep patterning of the Si substrate in blocks can be an option, provided that a continuous Ge layer is formed at the top, and it is suitably planarized before the metalorganic chemical vapor deposition. The crack density is effectively decreased, despite that the efficiency is also lowered with respect to unpatterned devices. The reasons of this efficiency reduction are discussed, and a strategy for improvement is proposed and explored. Full morphological analysis of the coalesced Ge blocks is reported, and the final devices are tested under concentrated AM1.5D spectrum. Copyright © 2016 John Wiley & Sons, Ltd.     

Automatic generation of noise-free time-activity curve with gated blood-pool emission tomography using deformation of a reference curve

This paper describes a new method for assessing clinical parameters from a noisy regional time-activity curve (TAC) in tomographic gated blood-pool ventriculography. This method is based on a priori knowledge on the shape of a TAC, and shape approximation. The rejection method was used to generate different random Poisson deviates, covering standard count levels, of six representative TACs in order to test and compare the proposed method with harmonic and multiharmonic reconstruction methods. These methods were compared by evaluating four clinical parameters: time of end systole, amplitude, peak ejection and filling rates. Overall, the accuracy of assessment of these parameters was found to be better with the method described in this paper than with standard multiharmonic fits.     

n+-SnO2/a-SiC:H/metal thin-film photodiodeswith voltage-controlled spectral sensitivity

n⁺-SnO₂/a-SiC/metal photodiodes with voltage-controlled photosensitivity have been realized by using both carbon-rich and silicon-rich a-SiC alloys. Carbon-rich devices show a response peak located at 530 nm independent of the applied voltage, which in turn only affects the peak height. At variance, in silicon-rich structures the response peak is located at 480, 510, and 570 nm when the applied voltage is -4, 0, and +4 V, respectively, with corresponding quantum yield values of 17, 3, and 25%. For explaining the observed behavior we present a simple model of n⁺-SnO₂/a-SiC/metal diodes, which takes into account light-induced modulation of n⁺-SnO₂/a-SiC barrier height, primary photocurrent generation and photoconductivity effects     

Understanding and Predicting Data Hotspots in Cellular Networks

The unprecedented growth in mobile data usage is posing significant challenges to cellular operators. One key challenge is how to provide quality of service to subscribers when their residing cell is experiencing a significant amount of traffic, i.e. becoming a traffic hotspot. In this paper, we perform an empirical study on data hotspots in today’s cellular networks using a 9-week cellular dataset with 734K+ users and 5327 cell sites. Our analysis examines in details static and dynamic characteristics, predictability, and causes of data hotspots, and their correlation with call hotspots. We show that using standard machine learning methods, future hotspots can be accurately predicted from past observations. We believe the understanding of these key issues will lead to more efficient and responsive resource management and thus better QoS provision in cellular networks. To the best of our knowledge, our work is the first to empirically characterize traffic hotspots in today’s cellular networks.     

Noninvasive ECG as a tool for predicting termination of paroxysmal atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia and entails an increased risk of thromboembolic events. Prediction of the termination of an AF episode, based on noninvasive techniques, can benefit patients, doctors and health systems. The method described in this paper is based on two-lead surface electrocardiograms (ECGs): 1-min ECG recordings of AF episodes including N-type (not terminating within an hour after the end of the record), S-type (terminating 1 min after the end of the record) and T-type (terminating immediately after the end of the record). These records are organised into three learning sets (N, S and T) and two test sets (A and B). Starting from these ECGs, the atrial and ventricular activities were separated using beat classification and class averaged beat subtraction, followed by the evaluation of seven parameters representing atrial or ventricular activity. Stepwise discriminant analysis selected the set including dominant atrial frequency (DAF, index of atrial activity) and average HR (HRmean, index of ventricular activity) as optimal for discrimination between N/T-type episodes. The linear classifier, estimated on the 20 cases of the N and T learning sets, provided a performance of 90% on the 30 cases of a test set for the N/T-type discrimination. The same classifier led to correct classification in 89% of the 46 cases for N/S-type discrimination. The method has shown good results and seems to be suitable for clinical application, although a larger dataset would be very useful for improvement and validation of the algorithms and the development of an earlier predictor of paroxysmal AF spontaneous termination time.