Optimal pilot waveform assisted modulation for ultrawideband communications

Ultrawideband (UWB) transmissions induce pronounced frequency-selective fading effects in their multipath propagation. Multipath diversity gains can be collected to enhance performance, provided that the underlying channel can be estimated at the receiver. To this end, we develop a novel pilot waveform assisted modulation (PWAM) scheme that is tailored for UWB communications. We select our PWAM parameters by jointly optimizing channel estimation performance and information rate. The resulting transmitter design maximizes the average capacity, which is shown to be equivalent to minimizing the mean-square channel estimation error, and thereby achieves the Crame/spl acute/r-Rao lower bound. Application of PWAM to practical UWB systems is promising because it entails simple integrate-and-dump operations at the frame rate. Equally important, it offers a flexible UWB channel estimator, capable of striking desirable rate-performance tradeoffs depending on the channel coherence time.     

Securing Mobile Ad hoc Networks — A Motivational Approach

Mobile ad hoc networks rely on the co-operation of devices that route for each other. This immediately presents security problems. Each device's data passes through the not so friendly hands of other devices. Forwarding devices must use their processing power and battery power to route packets for others. When bandwidth is limited they must also use bandwidth that they might want to use for themselves. These are not great issues with the first incarnations of ad hoc networks — military systems or others where all the devices are owned by a single organisation. However, if ad hoc networks are to be generally deployed and become an alternative or adjunct to future cellular systems, then ways to encourage co-operation are required. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-performance MIM capacitor using ALD high-k HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectrics

For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications.     

Elastic and Strength Properties of Thermoplasts Randomly Reinforced with Short Carbon Fibres

The linearity of the modulus of elasticity of a randomly reinforced composite as a function of the volume content of fibre filler is experimentally established. The basic factors that determine the modulus of elasticity of the thermoplastic composite are determined: the modulus of elasticity, shape, and volume content of filler. The modulus of elasticity of the composite is not a function of the adhesion of the fibre filler to the matrix. Realization of the strength of fibre fillers in randomly reinforced composites should obey the mechanisms that hold for unidirectional, continuously reinforced composites with consideration of the effect of the filler and process parameters on the rheology and morphology of the binder.     

The effects of nonlocal impact ionization on the speed of avalanche photodiodes

The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions.     

Evaluation of Atmospheric and Vacuum Residues Using Molecular Distillation and Optimization

The term atmospheric residue describes the material at the bottom of the atmospheric distillation tower having a lower boiling point limit of about 340°C; the term vacuum residue (heavy petroleum fractions) refers to the bottom of the vacuum distillation, which has an atmospheric equivalent boiling point (AEBP) above 540°C. In this work, the objective is to evaluate the behavior of different kinds of Brazilian atmospheric and vacuum residues using molecular distillation. The Falling Film Molecular Distillator was used. For the results obtained through this process, a significant range of temperature can be explored avoiding the thermal decomposition of the material. So these results are very important to the refinery decisions and improvements. The Experimental Factorial Design results showed that the temperature has more influence on the process than the feed flow rate, when a higher percentage of distillate is required.     

Mobile Device Security Using Transient Authentication

Mobile devices are vulnerable to theft and loss due to their small size and the characteristics of their common usage environment. Since they allow users to work while away from their desk, they are most useful in public locations and while traveling. Unfortunately, this is also where they are most at risk. Existing schemes for securing data either do not protect the device after it is stolen or require bothersome reauthentication. Transient Authentication lifts the burden of authentication from the user by use of a wearable token that constantly attests to the user's presence. When the user departs, the token and device lose contact and the device secures itself. We show how to leverage this authentication framework to secure all the memory and storage locations on a device into which secrets may creep. Our evaluation shows this is done without inconveniencing the user, while imposing a minimal performance overhead     

Mechanism of the inhibiting effect of diphenylamine in the oxidation of hydraulic oils

The mechanism of the inhibiting effect of diphenylamine during the oxidation of two base stocks of hydraulic oils were studied at 120, 130, and 140°C. The key reactions in the mechanism of the action of the inhibitor were identified, and the values of the kinetic parameters and their activation energies were determined. The kinetic parameters were calculated, and the salient kinetic features of the inhibited oxidation of the two specimens were compared at 70°C, the temperature of accelerated testing of hydraulic oils. The results of this prediction were analyzed, and the reasons for differences in the oxidation stability of the samples examined were established.