Resolution-effective diameters for asymmetric-knife-edge pinhole collimators

The effects of penetration are included in the formulas for the prediction of the resolution of pinhole collimators through the use of effective diameters. Expressions of the resolution-effective diameter for pinholes with a double-knife-edge (DKE) profile are available in the literature. In this paper the expressions applicable to asymmetric-knife-edge (AKE) profiles, which include the important case of the single-knife-edge (SKE), are presented. Results indicate that the simplest methods that are still accurate in the calculation of DKE effective diameters do not produce in general formulas with similar accuracy for AKE profiles, due to increased susceptibility to penetration. Especially at high energy (365 keV), for the SKE case more advanced formulas are necessary and were, therefore, derived.     

Manganese oxide thin-films for current-signal sensing and thermal insulation

Manganese oxide thin-films for current-signal sensing and thermal insulation were synthesized by high-vacuum evaporation and thermal oxidation processes at low-temperature conditions. Structure-formation of the films with orthorhombic-partial structure of MnO₂/Mn₂O₃ was investigated by X-ray diffraction. Raman studies have demonstrated that thermal properties can be influenced by the symmetry of the Mn–O bonds and it associated with the dynamic Jahn–Teller distortion. Dynamic behavior of samples as a function of the frequency response to verify their performance as signal sensors was evaluated by resistive–inductive circuit (RL circuit). To demonstrate the thermal capability of samples from current–voltage (I–V) characteristics, a Schottky emission model was used.     

A fast and reliable technique for muscle activity detection from surface EMG signals

The estimation of on-off timing of human skeletal muscles during movement is an important issue in surface electromyography (EMG) signal processing with relevant clinical applications. In this paper, a novel approach to address this issue is proposed. The method is based on the identification of single motor unit action potentials from the surface EMG signal with the use of the continuous wavelet transform. A manifestation variable is computed as the maximum of the outputs of a bank of matched filters at different scales. A threshold is applied to the manifestation variable to detect EMG activity. A model, based on the physical structure of the muscle, is used to test the proposed technique on synthetic signals with known features. The resultant bias of the onset estimate is lower than 40 ms and the standard deviation lower than 30 ms in case of additive colored Gaussian noise with signal-to-noise ratio as low as 2 dB. Comparison with previously developed methods was performed, and representative applications to experimental signals are presented. The method is designed for a complete real-time implementation and, thus, may be applied in clinical routine activity.     

Impact of Fiber Non-linearity in High Capacity WDM Systems and in Cross-Connected Backbone Networks

The rapidly increasing data traffic volumes will demand for very high transmission capacity and network nodes throughput. Wavelength division multiplexing (WDM) technology will be asked to support many channels on the same fiber, both in point-to-point links and in WDM optical networks. The transmission of a high number of wavelength channels in all these systems is a key issue. This paper analyzes this topic, in both high capacity links and optical networks, highlighting the impact of fiber non-linearity, and addressing the main source of impairments. This is done through the use of a semi-analytical model recently upgraded to account for all the contributions deriving from Kerr effects, particularly four-wave mixing and cross-phase modulation. The analysis reveals that more than one hundred of channels at 2.5 Gbit/s can be transmitted in point-to-point links whose length can span until the order of 1000 km, and 32 channels per fiber, at the previous bit rate, can be handled in WDM networks, without dispersion compensation. For a higher number of channels (e.g., 64) dispersion compensation is needed.     

Joint scheduling and routing with power control for centralized wireless sensor networks

We consider a TDMA-based multi-hop wireless sensor network, where nodes send data to a sink, which is aware of received powers at all receivers; the sink is responsible for creating the network topology and assigning time slots to links. Under this centralized approach, we propose two algorithms that jointly define the tree topology connecting nodes to the sink, and assign time slots, avoiding any packet loss. In contrast with previous works, the proposed algorithms accurately account for interference effects; when evaluating the signal-to-interference ratio to establish the tree and schedule transmissions, we consider the sum of all actual interfering signals, a fact of relevance for networks with increasing number of nodes. Optimal selection of transmit powers, minimizing energy consumption, is also applied. Our algorithms are compared to a benchmark solution and other proposals from the literature; it is shown that they bring to better radio resource utilization, higher throughput and lower energy consumption, while keeping the average delay limited.

     

Savoir faire et faire savoir: what I learned about innovation while I thought I was doing a Ph.D.

This short text is a reflection of lessons learned about innovation during my studies at the signal processing laboratory of the Swiss Federal Institute of Technology, while I thought I was studying video segmentation based on multiple features for interactive multimedia applications.     

Joint near-lossless compression and watermarking of still images for authentication and tamper localization

A system is presented to jointly achieve image watermarking and compression. The watermark is a fragile one being intended for authentication purposes. The watermarked and compressed images are fully compliant with the JPEG-LS standard, the only price to pay being a slight reduction of compression efficiency and an additional distortion that can be anyway tuned to grant a maximum preset error. Watermark detection is possible both in the compressed and in the pixel domain, thus increasing the flexibility and usability of the system. The system is expressly designed to be used in remote sensing and telemedicine applications, hence we designed it in such a way that the maximum compression and watermarking error can be strictly controlled (near-lossless compression and watermarking). Experimental results show the ability of the system to detect tampering and to limit the peak error between the original and the processed images.     

Estimating the growth kinetics of experimental tumors from as few as two determinations of tumor size: implications for clinical oncology

Clinical information on tumor growth is often limited to a few determinations of the size of the tumor burden taken at variable time. As a consequence, fitting of growth equations to clinical data is hampered by the small number of available data. On the other hand, characterising the tumor growth kinetics in terms of clinically relevant parameters, such as the doubling time of the tumors, is increasingly required to optimize and personalise treatments. A computational method is presented which can estimate the growth kinetics of tumors from as few as two determinations of its size taken at two successive time points, provided the size at which tumor growth saturates is known. The method is studied by using experimental data obtained in vitro with multicell tumor spheroids and in vivo with tumors grown in mice, and its outputs are compared to those obtained by fitting of experimental data with the Gompertz growth equation. Under certain assumptions and limitations the method provides comparable estimates of the doubling time of tumors with respect to the classical nonlinear fitting approach. The method is then tested against simulated tumor growth trajectories spanning the range of tumor sizes observed in the clinics. The simulations show that a relative classification of tumors on the basis of their growth kinetics can be obtained even if the size at which tumor growth saturates is not known. This result opens the possibility to classify patients bearing fast or slow growing tumors and, hence, to adapt therapeutic regimens under a more rationale basis.     

Performance Evaluation of a Bluetooth-Based WLAN Adopting a Polling Protocol Under Realistic Channel Conditions

Even if Bluetooth has not been specifically designated for WLANs (Wireless Local Area Networks) and the interconnection of computers, the possibility of establishing low-cost wireless connections makes this technology attractive for this kind of context also. In this paper we assess, by means of a simulative approach that takes the complete physical and MAC level aspects into account, the performance of a Bluetooth-based WLAN adopting a roll-call polling protocol under realistic channel conditions, that is, in the presence of the typical impairments of indoor wireless communications (fading, etc); moreover, we propose an analytical formulation to derive the maximum throughput offered by a Bluetooth link and we suggest a call admission control technique based on the previous analytical considerations.     

Melanin films on Au(1 1 1): Adsorption and molecular conductance

We have studied the adsorption and electronic properties of thin melanin films on Au(1 1 1) by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and density functional (DF) calculations. We have found that the minimum melanin unit detected under different adsorption conditions is consistent with the structural model for eumelanin protomolecules based on tetramer macrocycles formed by four monomer units (hydroquinone, indolequinone and its tautomers) with an inner porphyrin ring. DF calculations reveal that the entire π structure of the tetramers is implied in the chemisorption process through its frontier orbitals (HOMO and LUMO), a fact that is reflected in the change of intramolecular bonds. Also van der Waals interactions give an important contribution to the adsorption energy (≈0.02 eV/Ų). Dried thin melanin films (1 monolayer in thickness) exhibit good electronic conductance due to the presence of localized states near the Fermi level while dried thicker films exhibit a semiconductor-like behavior. Illumination of the thicker films with white light results in significant photo-induced tunneling currents when the melanin-covered Au is made negative with respect to the tip.