DTI segmentation by statistical surface evolution

We address the problem of the segmentation of cerebral white matter structures from diffusion tensor images (DTI). A DTI produces, from a set of diffusion-weighted MR images, tensor-valued images where each voxel is assigned with a 3 x 3 symmetric, positive-definite matrix. This second order tensor is simply the covariance matrix of a local Gaussian process, with zero-mean, modeling the average motion of water molecules. As we will show in this paper, the definition of a dissimilarity measure and statistics between such quantities is a nontrivial task which must be tackled carefully. We claim and demonstrate that, by using the theoretically well-founded differential geometrical properties of the manifold of multivariate normal distributions, it is possible to improve the quality of the segmentation results obtained with other dissimilarity measures such as the Euclidean distance or the Kullback-Leibler divergence. The main goal of this paper is to prove that the choice of the probability metric, i.e., the dissimilarity measure, has a deep impact on the tensor statistics and, hence, on the achieved results. We introduce a variational formulation, in the level-set framework, to estimate the optimal segmentation of a DTI according to the following hypothesis: Diffusion tensors exhibit a Gaussian distribution in the different partitions. We must also respect the geometric constraints imposed by the interfaces existing among the cerebral structures and detected by the gradient of the DTI. We show how to express all the statistical quantities for the different probability metrics. We validate and compare the results obtained on various synthetic data-sets, a biological rat spinal cord phantom and human brain DTIs.     

Assembly and Characterizations of Bifunctional Fluorescent and Magnetic Microneedles With One Decade Length Tunability

This report presents the fabrication of bifunctional magnetic and fluorescent microneedles (µNDs) made of a ternary mixture of magnetic nanoparticles (NPs), quantum dots (QDs), and polyelectrolyte. The assembly relies on the electrostatic complexation of negatively charged NPs with positively charged polymer strands and is controlled by the charge ratio between the nanoparticle building blocks and the polymer mortar. The resulting 1D objects can be actuated using an external magnetic field and can be imaged using fluorescence microscopy, thanks to the fluorescent and superparamagnetic properties inherited from their NP constituents. Using a combination of core and surface characterizations and a state‐of‐the‐art image analysis algorithm, the dependence of the brightness and length on the ternary composition is thoroughly investigated. In particular, statistics on hundreds of µNDs with a range of compositions show that the µNDs have a log‐lormal length distribution and that their mean length can be robustly tuned in the 5–50 µm range to match the relevant length scales of various applications in micromixing, bioassays or biomechanics.     

SR3: secure resilient reputation-based routing

In this paper, we propose SR3 (which means secure resilient reputation-based routing), a secure and resilient algorithm for convergecast routing in wireless sensor networks. SR3 uses lightweight cryptographic primitives to achieve data confidentiality and unforgeability. Security of SR3 has been proven formally using two verification tools: CryptoVerif and Scyther. We made simulations to show the resiliency of SR3 against various scenarios, where we mixed selective forwarding, blackhole, wormhole, and Sybil attacks. We compared our solution to several routing algorithms of the literature. Our results show that the resiliency accomplished by SR3 is drastically better than the one achieved by those protocols, especially when the network is sparse. Moreover, unlike previous solutions, SR3 self-adapts after compromised nodes suddenly change their behavior.     

Design of UWB switched gain controlled LNA using 0.18 μm CMOS

A switched gain controlled low noise amplifier (LNA) for the 3.1- 4.8 GHz ultra-wideband system is presented. The LNA is fabricated with the 0.18 mum 1P6M standard CMOS process. Measurement of the LNA was performed using an RF probe station. In gain mode, measured results show a noise figure of 4.68-4.97 dB, gain of 12.5-13.9 dB, and input/output return loss higher than 10/8.2 dB. The input IP3 (IIP3) at 4.1 GHz is 1 dBm, and consumes 14.6 mW of power. In bypass mode, measured results show a gain of-7.0 to -8.7 dB, and input/output return loss higher than 10/6.3 dB. The input IP3 at 4.1 GHz is 9.2 dBm, and consumes 1 muW of power.     

Electrical and photovoltaic properties of an organic-inorganic heterojunction based on a BODIPY dye

An organic-inorganic heterojunction based on a BODIPY dyes has been produced by forming dye thin film on n-Si. The electrical parameters of the structure have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The ideality factor, the barrier height and the series resistance values of the diode have been calculated as 2.43, 0.84 eV, and about 1.3 kΩ, respectively. The diode behaves as a non-ideal diode because of the series resistance and interface layer. The barrier height value obtained from I-V measurement has been compared with one from C-V measurement. Moreover, it has been seen that the diode is highly sensitive to the light and the reverse bias current increases about 1 × 10⁴ times at −1 V under 100 mW/cm² and AM1.5 illumination condition. The short photocurrent density (J_sc) and the open circuit voltage (V_oc), the fill factor (FF) and power conversion efficiency (η) have been determined as 3.78 mA/cm², 327 mV, 0.28 and 0.48 %, respectively.     

Detection of Carbon Dioxide in Air Using Difference-Frequency Generation Based Infrared Spectrometer

Spectroscopic detection of carbon dioxide (CO₂) in ambient air was performed using a continuous-wave mid-infrared spectrometer based on difference-frequency generation in an AgGaS₂ crystal. Significant improvement in nonlinear optical frequency conversion efficiency was achieved by Gaussian beam optical design consideration. CO₂ concentration was determined from direct-absorption spectral measurement.     

A Survey of Handover Techniques for Wireless ATM Networks

This paper provides a review and comprehensivecomparison of existing handover schemes proposed forwireless ATM networks. Existing schemes include thoseproposed by NEC, Olivetti, Bell Labs, Cambridge, Stanford, CMU, Berkeley, Michigan, VTT, andColumbia. We highlight the methodologies employed by thevarious schemes and reveal their differences. We discussissues related to the effect of ATM switch architectures on mobility implementation and on futurehandover paradigms.     

Handover and Uplink Power Control Performance in the 3.84 Mcps TDD mode of UTRA Network

In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out.     

Sequential Decoding of Convolutional Codes for Rayleigh Fading Channels

The performance of sequential decoding of long constraint length convolutional codes is evaluated for Rayleigh fading channels. Sequential decoding is not practical below a certain theoretical signal-to-noise ratio, and these theoretical limits are calculated for a number of modulation methods and code rates. As an example, with BPSK modulation, soft decisions and code rate 1/2, the theoretical signal-to-noise ratio per information bit is 5.7 dB. Above this limit the bit error rate can be made arbitrarily small by increasing the constraint length at no significant complexity cost. Furthermore, it is shown that with carefully chosen quantization steps, 8 level uniform quantization gives a negligible loss also for sequential decoding on a Rayleigh fading channel. Simulation results using 8 level quantization correspond well with the theoretical performance bounds. Also, the performance on a correlated channel with finite interleaving has been obtained. With an interleaver depth of 50×50 and a normalized doppler frequency equal to 0.01 we are only 0.5 dB away from the performance with perfect interleaving. Finally, bit error rate results show this scheme to compete well with Turbo codes.