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Fretting corrosion is considered to be one of the most common failure mechanisms in electrical contacts for many applications. Micro-scale motion at the contact surface is the major driver of fretting degradation and produces material displacement and transfer. As a result, the buildup of an insulating oxide layer at the contact interface leads to a rapid substantial increase in contact resistance, which is the most common measure for contact performance. However, with regard to the high frequency applications, impedance rather than simply resistance is a more comprehensive and descriptive measure of contact performance. Prior work by the authors has investigated the capacitive characteristics of impedance in degraded contacts, with the observed behavior modeled as resistor capacitor network in parallel. Correlation of the experimental results with simulation studies demonstrated a decreasing level of the contact capacitance as fretting degradation proceeds. In the present work, an experimental study was performed using a simplified connector configuration in order to investigate the impact of contact degradation on high frequency signal integrity. A network model incorporating transmission line and capacitive coupling parameters was developed which relates the contact impedance to the signal loss and distortion. The results are presented and discussed. A high level of consistency between this model and the experimental data was demonstrated.

In recent years, the Virtual Block Control (VBC) concept was investigated within the European SESAR Programme as an operational concept for improving weather resilience at airports. The VBC concept uses Virtual Stop Bar (VSB) positions on both controller and flight crew displays with the aim to reduce the size of control blocks used under low visibility conditions and, at the same time, ensure sufficient spacing between taxiing aircraft. In the past, the concept was evaluated for Rotterdam Airport (EHRD) as part of a EUROCONTROL research initiative [1]. Since then it has evolved based on the results of validation activities within the framework of the SESAR Programme. Concept feasibility and operational performance were validated in 2012 on the NLR ATC Research Simulator simulation platform for Tower operations (NARSIM-Tower) at the Netherlands Aerospace Centre (NLR) in Amsterdam (Figure 1). This platform realistically simulated the Milan-Malpensa Airport (LIMC) working environment. The validation experiments presented a positive picture of the proposed operations. The system was seen as an efficient safety net allowing controllers to control traffic flows on an airport in a very structured way during low visibility conditions [2].

There are two current methods for estimating the Raman gain properties of materials - measuring the spontaneous Raman spectrum and comparing it to that of fused silica, and fabricating a fiber and measuring the gain directly. We have developed a new apparatus for measuring directly the absolute value of the Raman gain spectrum in bulk materials whose thicknesses is only a few millimeters. This apparatus will be described and has proven valuable for rapid evaluation of materials. A table of Raman gain will be given for different glass families including tellurites, post-transitional heavy metals, and mixed cation glasses.

In many applications of data mining one knows beforehand that the response variable should be monotone (either increasing or decreasing) in the attributes. In ordinal classification, changing the class labels of a data set (relabeling) so that the data becomes monotone, is useful for at least two reasons. Firstly, models trained on relabeled data tend to have better predictive performance than models trained on the original data. Secondly, relabeling is an important building block for the construction of monotone classifiers. However, optimal monotone relabelings are rarely unique, and so far an efficient algorithm to generate them all has been lacking. The main result of this paper is an efficient algorithm to produce the structure of all optimal monotone relabelings. We also show that counting the solutions is #P-complete and give algorithms for efficiently enumerating all solutions, as well as sampling uniformly from the set of solutions. Experiments show that relabeling non-monotone data can improve the predictive performance of models trained on that data.

In a tDCS model study, the accuracy of isotropic and anisotropic single-layer approximations to the actual three-layered skull is evaluated. For both approximation models, the average difference in brain current density with respect to the layered skull model are shown to be small. We conclude that both approximations can be used to accurately compute the current density in the brain, provided that the radial conductivity in the model matches the effective radial conductivity of the three-layered skull.

Technology is fundamentally important as the NASA Space Communications and Navigation (SCaN) Program builds the communication infrastructure of the future123. SCaN is investing in advanced technologies for Radio Frequency (RF), optical communications, networking and navigation to enable future NASA missions to go far beyond today's current capability. A technology management plan was developed to define a management structure as well as the planning, execution, and evaluation processes to ensure that the needed technology will be developed and matured in time to meet NASA's mission goals in the most cost effective manner. This paper will provide an overview of NASA's Space Communications and Navigation (SCaN) Technology Management Plan (TMP) for technology investment and infusion. The paper will also address leveraging the Small Business Innovative Research (SBIR) Program as a feeder for technology investments as part of the TMP. The TMP also ensures that SCaN has an accurate snap shot of key technology being developed across the nation by industry, NASA centers, other government agencies, small business, national laboratories and academia for consideration by NASA for leveraging.

In this study, the feasibility of BiPlane strain imaging during controlled muscle contraction by means of electrical stimulation was examined. Two superficial muscles, the tibialis anterior and the biceps, were imaged using triggered BiPlane ultrasound. Raw frequency data were acquired at 100 Hz during induced muscle contraction. The responses, in terms of strain, to different electrical stimuli were assessed as well as the ability to track a tetanic response to an electrical pulse train of 10 and 20 Hz. An rf-based 2D strain algorithm was applied to the BiPlane data to measure strain in three orthogonal directions in the two simultaneously measured planes. Preliminary results in four volunteers revealed that BiPlane rf-based strain imaging in muscles during induced contraction is feasible. Vertical strains were measured between 10 and 30% as well as horizontal strains of −20 to −10%. A correlation was found between measured strain and electrical stimulus level, although the response could vary at lower excitation levels, since different (and fewer) motor units could be excited. The tetanic response in the muscle was tracked properly as well and individual contractions could be distinct at 10 Hz. In conclusion, BiPlane strain imaging in muscles can be used for semi-3D strain assessment in muscles. However, considering the out-of-plane motion in the images orthogonal to the fiber direction, full 3D strain imaging might be beneficial.

A method to estimate the potential and current density distribution during transcranial DC stimulation (tDCS) is introduced. The volume conductor model consists of a realistic head model (concerning shape as well as conductivity), obtained from TI-, PD- and DT-MR images. The model includes five compartments with different conductivities. For the skull and the white matter compartments, the conductivities are anisotropic. Using this model, the potentials inside the head that are generated by tDCS electrodes positioned on the scalp were computed by using the Finite Element Method. The results show that this is a promising method for the study of the effects of tDCS.

AlGaAs nanowires are ideal waveguides for the observation of nonlinear effects. The sub-micron geometry and tight field confinement, due to the high index contrast between core and cladding, yield very intense pulsed beams at low power levels. Observations of Kerr nonlinearities are thus possible at power levels of a few watts in just a few millimeters of propagation. By using pulses of 52 W of peak power we obtain a 0.9pi nonlinear phase shift from self-phase modulation. By way of cross-polarised co-propagating pulses we also obtain a cross-phase modulation to self-phase modulation ratio of 0.88 at 1557 nm. Nonlinear transmission arising from three photon absorption is also analysed. We find good agreement between our experimental results and those from our simulations based on a nonlinear Schrodinger model. These results may eventually lead to the development of nonlinear all-optical devices operating in sub-micrometer interaction lengths with but a few watts of power.

We demonstrated the highest electro-optic (EO) coefficient with the highest poling efficiency (~100%) in actual modulator devices. This breakthrough was accomplished with contact poling of a crosslinkable EO polymer with an electrically conductive sol-gel cladding.

We have investigated the power threshold of discrete Kerr surface solitons at the interface between discrete and continuous 1D AlGaAs medium. Distinct thresholds were measured for interface solitons localized at different sites from the interface.

We have studied numerically and experimentally the linear diffraction and trapping of light at the hetero-interface between two different 1D AlGaAs waveguide arrays. A new ?breather? state guided by the interface was observed.

We report the first observation of two-dimensional surface solitons at the first bandgap with a self-defocusing nonlinearity and at the semi-infinite gap with a self- focusing nonlinearity. Experimental results are in agreement with theoretical predictions.

In this paper, we will introduce the concept of discrete solitons and we will discuss some of their spatio-temporal dynamics, which leads to interesting consequences in both the fundamental and the applied domain

We provide an overview of recent theoretical and experimental results in the area of surface lattice solitons. The observation of these waves in Kerr and quadratic nonlinear periodic structures is discussed.

Recent progress achieved with integrated optical devices exploiting quasi-phasematched second order nonlinear interactions in periodically poled Ti: LiNbO3 waveguide structures is reported. Wavelength conversion, parametric amplification, multiplexing, and switching are demonstrated as examples of ultra-fast all-optical signal processing in the 1.5-µ m wavelength range for transparent optical networks.

We demonstrate that optical solitons can exist in dispersion-inverted highly-nonlinear AlGaAs nanowires. These self-localized waves are possible at very low power levels in millimeter long nanowire structures.

We report the first observation of discrete optical surface solitons at the interface between a nonlinear self-focusing waveguide lattice and a continuous medium. The effect of power on localization process of these states is investigated.

We report the first experimental observation of discrete quadratic interface solitons existing at the edge of a PPLN waveguide array. Both in-phase and staggered discrete surface solitons were observed.

It is theoretically shown that nonlinear surface-waves are possible in optical lattices. Such solitons can exist at the interface between two different semi-infinite 1D waveguide arrays and also at the boundaries of a 2D lattice.

We have observed the incoherent interaction between a highly confined (blocker) soliton and wide, moving signal beams of a different wavelength in a one-dimensional discrete Kerr medium. Digital switching of the blocker solitons to successive adjacent channels was measured with increasing signal power via both one and two cascaded interactions in an AlGaAs waveguide array, operations equivalent to a reconfigurable three-output router.

By exploiting the phase sensitivity of second harmonic generation, we measure photonic band structures in PLLN waveguide arrays. Furthermore, we show that the concept can be applied to other photonic structures, as, e.g., photonic crystals.

We have observed all-optical switching in a 1.9-cm-long, nonlinear X-junction. The device was fabricated in AlGaAs and operated in the half band-gap spectral region.

Semiconductors and in particular AlGaAs, have proved to be optimum nonlinear materials when operated below the half band gap. Large phase shifts have been observed, with a minimal nonlinear absorption. The large nonlinear refractive index found in AlGaAs can also be used to observe spatial solitons, at lower power levels that have previously been employed in CS2 and glass waveguides[1,2]. AlGaAs is thus an ideal candidate for the study and implementation of devices which utilise spatial solitons[3]. Here we report on a device which employs spatial solitons for all-optical switching[4].

Efficient second-harmonie generation (SHG), widely used for the fabrication of compact blue light sources, can also be employed for the demonstration of all-optical switching, spatial solitary waves, etc, through cascading of second-order nonlinear effects1

High quality one-dimensional waveguide arrays were fabricated and characterized. Second-harmonic generation in the array waveguides proved to be an ideal tool for a direct measurement of the discrete diffraction relation.

We have investigated the dissipative spatial solitons in optical amplifiers. These solitons have unique properties (such as autosignal recovery) throughout their formation and interactions. They require 10 s of mWs and

We report our experimental and numerical investigation of nonlinear beam interactions in discrete waveguide arrays. We investigated the case of two parallel, copolarized beams interacting for different power levels and varying initial phase.

An efficient all-optical switching and routing scheme for low power optical signals based on parametric difference frequency generation in combination with the unique discrete dispersion characteristics of waveguide arrays was investigated experimentally.

Quasi-phasematched second order nonlinear optical interactions in periodically poled Ti:LiNbO/sub 3/ channel waveguides, directional couplers and waveguide arrays are exploited to develop efficient all-optical wavelength converters, parametric amplifiers, time division (de-)multiplexers, and space-, phase-, and polarisation-switches.

Semiconductor optical amplifiers (SOAs) have proved to be very useful elements for networks and communications systems. As well as amplifying signals, SOAs have been also used for a number of network optical processing functions, such as switching, demultiplexing, frequency shifting etc. Usually the light is guided in SOAs by fixed channel waveguides fabricated by some form of microlithography. As a result, controllable routing functions etc. need to be implemented by electro-optic devices such as Mach-Zehnder interferometers. There is another option for guiding in SOA chips which is more flexible. Spatial solitons, i.e. self-trapped beams which propagate without spreading, have now been observed with many different nonlinearities. These are all essentially lossless systems in which spatial diffraction is compensated by some self-focusing mechanism. However, in an amplifying medium like an SOA, loss must also be balanced by gain, which leads to an inherently different soliton than the lossless ones. In this case, the small signal gain determines completely the soliton properties, i.e., there is no trade-off between the peak intensity and the soliton width as is well-known for solitons in lossless media. We discuss the first observation of these "dissipative" solitons.

Two factors that are expected to have a large influence on needle recorded EMG signals are the electrical double layer at the metal-electrolyte interface and the presence of an oedemeous layer around the needle electrode. Solutions for this problem can be obtained in a cylinder symmetrical potential field problem, described by Laplace's equation. Analytical expressions have been derived for simulating single muscle fiber-action potentials (SFAPs) recorded by a typical single-fiber needle electrode. Results indicate that, due to the electrical double layer, the SFAP amplitudes decrease or increase, depending on whether the muscle fiber is located at the opposite side or at the same side, respectively, of the electrode as the lead-off surface. The oedemeous layer causes a general decrease in amplitude, the magnitude of which depends, for example, on the thickness of the layer. No important SFAP waveform changes due to the presence of the electrode shaft are found. >

Theoretical volume conductor studies of the neuromuscular system often start by assuming an infinite length muscle or nerve fiber placed in an unbounded volume conductor. Although this approach may apply well to the potential field close to a long nerve fiber, it is expected to be no more than a rough approximation when studying surface EMG. Four different descriptions of an active muscle fiber in a volume conductor are compared in this study to illustrate the separate effects. It is shown that the extinction of a single muscle fiber action potential (SFAP) at the muscle tendon leads to a dominating positive peak in the SFAP at larger observation distances. Another interesting observation is that the amplitude of this peak is considerably enhanced after replacing an infinite volume conductor with a finite description of the volume conductor properties of the limb. The results were experimentally verified by isolation of motor unit activity from the surface EMG. >

Quadratic soliton formation in an array of coupled PPLN channel waveguides was experimentally demonstrated for the first time. The discrete features of the solitons predicted by theory were observed.

Multi-photon absorption and refraction were measured in polydiacetylene-PTS (p-toluene sulfonate) from 1200 to 2200 nm. The four-photon absorption coefficient peaks at 1900 nm and n/sub 2/ decreases monotonically over this range.

We demonstrate experimentally and numerically that strong two photon absorption affects multiple quadratic soliton generation by high power 2D beams in a type-I biaxial crystal (KNbO/sub 3/). Simulations are in a good agreement with the experiment.

We report the first experimental observation of vector discrete solitons. We find that at appropriate power levels two orthogonally polarized beams collapse into a highly confined vector discrete soliton in spite of the presence of energy exchange due to four-wave-mixing.

We report the first experimental observation of spatial dissipative solitons (autosoliton) in a patterned electrode semiconductor amplifier (SOA). Our results fit with the numerical simulations which support the bifurcating behavior of solitons with current pumping.

We report the experimental observation of the formation of multiple optical quadratic solitons in a process mediated by the amplification of minute asymmetries in the diffraction properties of the input light.

We report experiments on beam interactions in nonlinear discrete waveguide arrays. Phase sensitive spatial scanning for medium powers and energy exchange between spatially separated beams across three guides for high powers was observed.

This paper summarizes recent developments in the measurement and analysis of surface EMG in cases where a large number of skin electrodes allows a spatio-temporal view on the EMG signal characteristics. The technical possibilities and different goals of using these topographical EMG techniques are outlined.

In the analysis of surface EMG signals, one of the most important issues to address is the question which motor units are investigated: where are the contributing units located and to what extent is "looking into the muscle" possible. The answer to these questions strongly depends on the behavior of signal amplitude with source depth. In the present paper, this behavior is investigated with the aid of an analytical volume conductor model. For natural values of volume conductor and source parameters, good agreement is obtained between model and experimental results. Changes in these parameters are shown to have major consequences on the behavior of amplitude with source depth.

Insight in the "building-stones" of EMG is essential for a proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, results from a comprehensive study on the contribution of single motor units (MUs) to surface EMG recordings are presented. This study gives insight in the contribution to the surface EMG of the motor unit potentials (MUPs) of motor units at different depths below the skin. It is shown that a distinct difference between the positive and the negative peak of MUPs exists, the latter with a more steep amplitude decline with MU depth. The signal area of the MUPs is least affected by the depth of the MU.

Here, the stable beams are a result of strongly coupled interacting waves. Indeed, the use of second-order effects has proven sucessful in stabilizing 2D beams in KTP both experimentally and in numerical simulations of beam propagation. We discuss experimental demonstrations of 2D spatial solitary waves, and the application of these beams to the practical problems of spatial beam clean-up and all-optical switching.

Here we describe a systematic interferometric investigation of the influence of the wavevector-mismatch on cascading. Titanium indiffused LiNbO/sub 3/ waveguides are used because their superior optical quality and the detailed knowledge of their fabrication and characterization make them promising candidates for the first application of cascading in all-optical data processing. >

The results presented here give a demonstration of the potential of all-optical switching using X/sup 2/ nonlinearities. The switching irradiance scales as [X/sup 2/]/sup -2/ so that new organic crystals with X/sup 2/ more than ten times that of KTP will significantly reduce switching irradiances. In addition, waveguide geometries will lead to further reductions in the switching energy. >