Exact Results for Wetting and Filling on a Triangular Lattice

New exact analytical results are described for surface tension on the triangular Ising lattice. The triangular Ising lattice forms naturally 60° and 120° corners, and a thermodynamic argument is used, which incorporates the exact results, to obtain conditions for the filling transition for both angles. Monte Carlo simulations with Wang–Landau sampling are performed to independently verify the applicability of this argument. Results are in agreement with previous conjectures for the phase boundary in these systems.     

Energy-efficient neighbor discovery protocol for mobile wireless sensor networks

Low energy consumption is a critical design requirement for most wireless sensor network (WSN) applications. Due to minimal transmission power levels, time-varying environmental factors and mobility of nodes, network neighborhood changes frequently. In these conditions, the most critical issue for energy is to minimize the transactions and time consumed for neighbor discovery operations. In this paper, we present an energy-efficient neighbor discovery protocol targeted at synchronized low duty-cycle medium access control (MAC) schemes such as IEEE 802.15.4 and S-MAC. The protocol effectively reduces the need for costly network scans by proactively distributing node schedule information in MAC protocol beacons and by using this information for establishing new communication links. Energy consumption is further reduced by optimizing the beacon transmission rate. The protocol is validated by performance analysis and experimental measurements with physical WSN prototypes. Experimental results show that the protocol can reduce node energy consumption up to 80% at 1–3 m/s node mobility.     

Activelets: Wavelets for sparse representation of hemodynamic responses

We propose a new framework to extract the activity-related component in the BOLD functional magnetic resonance imaging (fMRI) signal. As opposed to traditional fMRI signal analysis techniques, we do not impose any prior knowledge of the event timing. Instead, our basic assumption is that the activation pattern is a sequence of short and sparsely distributed stimuli, as is the case in slow event-related fMRI.We introduce new wavelet bases, termed “activelets”, which sparsify the activity-related BOLD signal. These wavelets mimic the behavior of the differential operator underlying the hemodynamic system. To recover the sparse representation, we deploy a sparse-solution search algorithm.The feasibility of the method is evaluated using both synthetic and experimental fMRI data. The importance of the activelet basis and the non-linear sparse recovery algorithm is demonstrated by comparison against classical B-spline wavelets and linear regularization, respectively.     

Analog baseband chain of synthetic aperture radar (SAR) receiver

An analog baseband chain for a synthetic aperture radar receiver implemented in a 130 nm CMOS technology is presented in this paper. Occupying 0.23 mm² of silicon area, the baseband chain consists of a three-stage variable gain amplifier (VGA), a 5th-order gm-C low-pass filter (LPF) and an output buffer. The gain of the chain can be controlled by tuning the control voltages of the VGA and has a range from 25 to 34 dB. 8 dB of the gain is embedded into the LPF. The bandwidth of the LPF is programmable from 100 to 190 MHz by means of capacitor matrices. The chain, which uses a 1.2 V supply voltage, achieves an input-referred noise density of 4 nV/ $ \sqrt {\text{Hz}} $ and an in-band IIP3 of ?46 dBV rms.     

Lithium niobate electro-optic tunable filter with high sidelobe suppression

The first demonstration of a high sidelobe suppression, tunable, electro-optic filter fabricated in lithium niobate for 1.55 mu m is reported. Weighting of the mode convertor structure using a Taylor distribution resulted in a -3 dB passband width of 1.6 nm and nearest sidelobes of -25 dB. A continuous, linear electro-optic tuning rate of +or-30 V/nm is also reported.<>     

Antibacterial effect of bioactive glasses on clinically important anaerobic bacteria in vitro

Bioactive glasses (BAGs) of different compositions have been studied for decades for clinical use and they have found many dental and orthopaedic applications. Particulate BAGs have also been shown to have antibacterial properties. This large-scale study shows that two bioactive glass powders (S53P4 and 13–93) and a sol–gel derived material (CaPSiO II) have an antibacterial effect on 17 clinically important anaerobic bacterial species. All the materials tested demonstrated growth inhibition, although the concentration and time needed for the effect varied depending on the BAG. Glass S53P4 had a strong growth-inhibitory effect on all pathogens tested. Glass 13–93 and sol–gel derived material CaPSiO II showed moderate antibacterial properties.     

The influence of annealing processes on the structural, compositional and electro-optical properties of CuIn0.75Ga0.25Se2 thin films

Crystalline defects, such as the density of voids, grain boundaries and dislocations, in Cu(In,Ga) Se₂ absorber layers depend on the fabrication conditions and determine to a large extent the efficiency of photovoltaic devices. The material properties, however, can be improved significantly by using post-deposition processes. In this paper, the effects of post-deposition heat treatments on properties of CuIn_0.75Ga_0.25Se₂ (CIGS) thin films are investigated. Selected flash evaporated samples were subsequently processed under several sets of conditions, including vacuum, selenium, inert (argon) and forming gas (a 9:1 mixture of N₂:H₂) ambients, at different temperature and times. Structural, compositional and electro-optical properties of both as-deposited and annealed films were studied using a variety of analytical techniques. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies of the films showed a columnar grain structure with strong < 112 > preferred orientation, which after heat treatments relaxed to give a chalcopyrite structure. Raman analysis showed that the annealing process reduced the full-wave half-maximum (FWHM) value from 20 to 10 cm^–1 indicating a change in both film composition and microstructure. In addition, X-ray fluorescence (XRF) and Rutherford backscattering spectroscopy (RBS) revealed that the composition was approaching that of the polycrystalline starting material. Both n- and p-type conductivities were observed with resistivity values in the range 10^–1 to 10⁶ cm. Annealing in selenium atmosphere altered the n-type conductivity to p-type. To confirm improvements in optical properties of annealed films, photoacoustic spectroscopy (PAS) was employed.     

Ships as a sensor network to observe ice field properties

This paper introduces a concept and a prototype system of using ships and coastal stations as a sensor network to obtain additional information about the ice field. The system collects marine radar images and ship performance observations, forms mosaics of images from multiples radars, calculates ice drift from subsequent radar images, analyzes trafficability in different sea areas using performance observations, and delivers processed images, trafficability estimation, and ice drift information to end-users. The prototype was developed and tested during the winters of 2008 and 2009 in the Baltic Sea. In this paper, we describe the prototype and discuss the usability of a ship sensor network. The concept appears to be feasible, and such a system would provide additional information about prevailing ice conditions.     

An orthogonal family of quincunx wavelets with continuously adjustable order.

We present a new family of two-dimensional and three-dimensional orthogonal wavelets which uses quincunx sampling. The orthogonal refinement filters have a simple analytical expression in the Fourier domain as a function of the order lamda, which may be noninteger. We can also prove that they yield wavelet bases of L2(R2) for any lambda > 0. The wavelets are fractional in the sense that the approximation error at a given scale a decays like O(a(lamda)); they also essentially behave like fractional derivative operators. To make our construction practical, we propose a fast Fourier transform-based implementation that turns out to be surprisingly fast. In fact, our method is almost as efficient as the standard Mallat algorithm for separable wavelets.