The physiological effects of pallidal deep brain stimulation in dystonia.

Dystonia is an involuntary movement disorder characterized by muscle contractions causing abnormal postures and spasms, affecting part or all of the body. Dystonia may be primary where an abnormal gene, most commonly DYT1, may be identified, or secondary to structural brain lesions or heredodegenerative disorders. The underlying defect is believed to be abnormal basal ganglia modulation of cortical motor pathways, and various motor and sensory physiological abnormalities have been demonstrated. The failure of medical treatment in many patients with the more severe and generalized forms of dystonia has led to renewed interest in neurosurgical treatment approaches. In recent years, deep brain stimulation (DBS) of globus pallidus internus (GPi) has emerged as an effective treatment for dystonia, particularly patients with primary generalized dystonia, where remarkable improvement may occur. In contrast to Parkinson's disease, the beneficial effects of DBS in dystonia are not immediate but progressive over weeks to months. Physiological and imaging studies in dystonia patients with GPi DBS have demonstrated both short and long-term effects of GPi DBS on motor cortex and subcortical circuits including progressive normalization of spinal and brainstem excitability after GPi DBS which correlate with clinical improvement. These effects, in light of existing physiological data in dystonia, suggest that GPi DBS acts primarily by major modification of basal ganglia output to brainstem, thalamus, and cortex resulting in neural reorganization, which may explain the characteristic progressive improvement in dystonia after GPi DBS.     

Adaptive frequency‐hopping schemes for CR‐based multi‐link satellite networks

In this paper, we study two dynamic frequency hopping (DFH)–based interference mitigation approaches for satellite communications. These techniques exploit the sensing capabilities of a cognitive radio to predict future interference on the upcoming frequency hops. We consider a topology where multiple low Earth orbit satellites transmit packets to a common geostationary equatorial orbit satellite. The FH sequence of each low Earth orbit–geostationary equatorial orbit link is adjusted according to the outcome of out‐of‐band proactive sensing scheme, performed by a cognitive radio module in the geostationary equatorial orbit satellite. On the basis of sensing results, new frequency assignments are made for the upcoming slots, taking into account the transmit powers, achievable rates, and overhead of modifying the FH sequences. In addition, we ensure that all satellite links are assigned channels such that their minimum signal‐to‐interference‐plus‐noise ratio requirements are met, if such an assignment is possible. We formulate two multi‐objective optimization problems: DFH‐Power and DFH‐Rate. Discrete‐time Markov chain analysis is used to predict future channel conditions, where the number of states are inferred using k‐means clustering, and the state transition probabilities are computed using maximum likelihood estimation. Finally, simulation results are presented to evaluate the effects of different system parameters on the performance of the proposed designs.     

Applications of aeromagnetic data to detect the Basement Tectonics of Eastern Yemen region

The present study aims to throw light on the tectonic implications concerned with the distribution of the sedimentary sequence belts and the related basement complex zones, as well as to differentiate between the causative sources (contacts, dykes and faults) of Eastern Yemen region. The total intensity aeromagnetic map of the study area was first corrected by the application of the Reduction To the magnetic pole (for low latitude areas). The visual inspection of the RTP magnetic map defines a rapid change in the subsurface geologic conditions in the form of lithologic characters and tectonic inferences. On the other hand, this map showed different anomalies of varying frequencies and amplitudes that revealed various causative sources, as well as varying compositions and depths. At the interpretation stage, various techniques and software tools are available for extracting the geologic information from the data concerned. The magnetic fields of shallow sources can be separated from those of deeper causatives, using two processes known as power spectrum transformation and matched band pass filtering. Three methods for locating magnetic sources (Magnitude of Horizontal Gradients (HGM), the analytical signals (AS) and the local wavenumbers (LW)) in three dimensions and identifying the properties of their sources indicated that, the area was affected by some intrusions at various depths in sill or dyke forms, almost oriented in the NW–SE, NE–SW, E–W and N–S trends. Tectonically, the area is highly affected by the tectonics related to the Arabian Sea, Gulf of Aden and Red Sea. It is affecting both the basement and sedimentary rocks, dividing the study area into several faulted blocks.     

Compact low-power time-based conversion with noise immunity similar to digital conversion

An analog signal representation based on the inter-pulse-interval (IPI) time is presented. Voltage-to-IPI and IPI-to-voltage conversion circuits based on the representation are described. The circuits have been fabricated using a 0.35 μm mixed-signal CMOS process. Simulation and test results agree with the theory. Voltage-to-IPI conversion needs significantly less area and power than ADC and is significantly more immune to noise and other problems than using analog voltage/current signals.     

New approach to gas pressure profile prediction for high temperature AA5083 sheet forming

A new theoretical approach to the prediction of gas pressure profiles that vary smoothly with time in high temperature forming of fine-grained AA5083 sheet is presented. The required pressure-flow stress relationship, which couples the gas pressure profile and the material constitutive model, was implemented in ABAQUS implicit. Forming of a rectangular pan in a die with variable entry radii was simulated with a single creep mechanism model that accounts for hardening/softening in AA5083. Predicted sheet thickness and thinning in a die entry radius region at the end of forming are examined in detail. Results are compared with those from two additional gas pressure schemes. One of these is taken directly from experiments and the other is based upon an algorithm that is internal to ABAQUS. The effect of friction on forming time is explored in the absence of a stability criterion for necking.     

On the gas pressure forming of aluminium foam sandwich panels: Experiments and numerical simulations

Forming of light-weight highly stiff aluminium foam sandwich (AFS) panels into complex 3D components would mark a development in the manufacturing of these materials. In this work, gas pressure forming of AFS panels is investigated experimentally and using numerical simulations. Deformation behaviour of AFS panels is studied during high-temperature uniaxial tension and compression, and constitutive models are developed and incorporated into FE simulations of the gas pressure forming process. Simulation results and experimental observations show reasonable agreement and demonstrate the possibility of forming AFS panels to significant deformations while maintaining considerable core porosity.     

A model for improved solar irradiation measurement at low flux

Accurate measurement of solar radiation heat flux is important in characterizing the performance of CSP plants. Thermopile type Heat Flux Sensors (HFSs) are usually used for this purpose. These sensors are typically reasonably accurate at high heat fluxes. However measurement accuracy drops significantly as the measured radiation is below 1 kW/m², this often leads to underestimation of the actual flux. At the Masdar Institute Beam Down Solar Thermal Concentrator (BDSTC), measurement of fluxes ranging from 0 kW/m² to more than 100 kW/m² is required. To improve the accuracy of the sensors in the lower range around 1 kW/m², we have performed a test under ambient (not-concentrated) sunlight. Such low irradiation levels are experienced in characterizing the concentration quality of individual heliostats. It was found during the test that the measurement at this low range is significantly affected by ambient conditions and transients in the HFS cooling water temperature. A Root Mean Square Error (RMSE) of more than 100 W/m² was observed even though we kept the transients in water temperature to a minimum. Hence we devised a model to account for this measurement error at this flux range. Using the proposed model decreased the RMSE to less than 10 W/m². The application of the model on existing heat flux measurement installations is facilitated by the fact that it only employs easily measurable variables. This model was checked by using a test data set and the results were in good agreement with the training data set.     

MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).