Dynamical diseases of brain systems: different routes to epileptic seizures

In this overview, we consider epilepsies as dynamical diseases of brain systems since they are manifestations of the property of neuronal networks to display multistable dynamics. To illustrate this concept we may assume that at least two states of the epileptic brain are possible: the interictal state characterized by a normal, apparently random, steady-state electroencephalography (EEG) ongoing activity, and the ictal state, that is characterized by paroxysmal occurrence of synchronous oscillations and is generally called, in neurology, a seizure. The transition between these two states can either occur: 1) as a continuous sequence of phases, like in some cases of mesial temporal lobe epilepsy (MTLE); or 2) as a sudden leap, like in most cases of absence seizures. In the mathematical terminology of nonlinear systems, we can say that in the first case the system's attractor gradually deforms from an interictal to an ictal attractor. The causes for such a deformation can be either endogenous or external. In this type of ictal transition, the seizure possibly may be anticipated in its early, preclinical phases. In the second case, where a sharp critical transition takes place, we can assume that the system has at least two simultaneous interictal and ictal attractors all the time. To which attractor the trajectories converge, depends on the initial conditions and the system's parameters. An essential question in this scenario is how the transition between the normal ongoing and the seizure activity takes place. Such a transition can occur either due to the influence of external or endogenous factors or due to a random perturbation and, thus, it will be unpredictable. These dynamical changes may not be detectable from the analysis of the ongoing EEG, but they may be observable only by measuring the system's response to externally administered stimuli. In the special cases of reflex epilepsy, the leap between the normal ongoing attractor and the ictal attractor is caused by a well-defined external perturbation. Examples from these different scenarios are presented and discussed.     

Ultra-Low-Power Interface Chip for Autonomous Capacitive Sensor Systems

Traditionally, most of the sensor interfaces must be tailored towards a specific application. This approach results in a high recurrent design cost and time to market. On the other hand, generic sensor interface design reduces the costs and offers a handy solution for multisensor applications. This paper presents a generic sensor interface chip (GSIC), which can read out a broad range of capacitive sensors. It contains capacitance-to-voltage converters, a switched-capacitor amplifier, an analog-to-digital converter, oscillators, clock generation circuits and a reference circuit. The system combines a very low-power design with a smart energy management, which adapts the current consumption according to the accuracy and speed requirements of the application. The GSIC is used in a pressure and an acceleration monitoring system. The pressure monitoring system achieves a current drain of 2.3 muA for a 10-Hz sample frequency and an 8-bit accuracy. In the acceleration monitoring system, we measured a current of 3.3 muA for a sample frequency of 10 Hz and an accuracy of 9 bits     

CrimeSPOT: A language and runtime for developing active wireless sensor network applications

Advances in wireless sensing and actuation technology allow embedding significant amounts of application logic inside wireless sensor networks. Such active WSN applications are more autonomous, but are significantly more complex to implement. Event-based middleware lends itself to implementing these applications. It offers developers fine-grained control over how an individual node interacts with the other nodes of the network. However, this control comes at the cost of event handlers which lack composability and violate software engineering principles such as separation of concerns. In this paper, we present CrimeSPOT as a domain-specific language for programming WSN applications on top of event-driven middleware. Its node-centric features enable programming a node’s interactions through declarative rules rather than event handlers. Its network-centric features support reusing code within and among WSN applications. Unique to CrimeSPOT is its support for associating application-specific semantics with events that carry sensor readings. These preclude transposing existing approaches that address the shortcomings of event-based middleware to the domain of wireless sensor networks. We provide a comprehensive overview of the language and the implementation of its accompanying runtime. The latter comprises several extensions to the Rete forward chaining algorithm. We evaluate the expressiveness of the language and the overhead of its runtime using small, but representative active WSN applications.     

Multi-cue hand detection and tracking for a head-mounted augmented reality system

With the recent developments in wearable augmented reality (AR), the role of natural human–computer interaction is becoming more important. Utilization of auxiliary hardware for interaction introduces extra complexity, weight and cost to wearable AR systems and natural means of interaction such as gestures are therefore more desirable. In this paper, we present a novel multi-cue hand detection and tracking method for head-mounted AR systems which combines depth, color, intensity and curvilinearity. The combination of different cues increases the detection rate, eliminates the background regions and therefore increases the tracking performance under challenging conditions. Detected hand positions and the trajectories are used to perform actions such as click, select, etc. Moreover, the 6 DOF poses of the hands are calculated by approximating the segmented regions with planes in order to render a planar menu (interface) around the hand and use the hand as a planar selection tool. The proposed system is tested on different scenarios (including markers for reference) and the results show that our system can detect and track the hands successfully in challenging conditions such as cluttered and dynamic environments and illumination variance. The proposed hand tracker outperforms other well-known hand trackers under these conditions.     

Appropriation of a shared workspace: Organizing principles and their application

The use and effects of a CSCL-tool are not always predictable from the properties of the tool alone, but depend on how that tool is appropriated. This paper presents the findings from a case study about the appropriation of a graphical shared workspace. When students are presented with a new tool they may encounter competing constraints and multiple possibilities for interacting with it. We argue that during critical events the students make choices, and in order to collaborate, coordinate these choices as a group. We study appropriation by looking into the ways in which small groups organize their contributions during a computer-mediated argumentative discussion. The results of our study illustrate how certain principles for organization emerge from an implicit negotiation of conventions, with mutual influence between the students and the tool.     

Secreted production of a custom-designed, highly hydrophilic gelatin in Pichia pastoris

A custom-designed, highly hydrophilic gelatin was produced in Pichia pastoris . Secreted production levels in single-copytransformants were in the range 3–6 g/l of clarified brothand purification to near homogeneity could be accomplished bydifferential ammonium sulfate precipitation. Despite the factthat gelatins are highly susceptible to proteolysis becauseof their unfolded structure, the recombinant protein was shownto be fully intact by SDS–PAGE, N-terminal sequencing,gel filtration chromatography and mass spectrometry. Owing toits highly hydrophilic nature, the migration of the syntheticgelatin in SDS–PAGE was severely delayed. Esterificationof the carboxylic amino acid side chains resulted in normalmigration. The high polarity of the synthetic gelatin also accountsfor its negligible surface activity in water at concentrationsup to 5% (w/v), as determined by tensiometry. Circular dichroismspectrometry showed that the non-hydroxylated gelatin did notform triple helices at 4°C. The spectrum was even more representativeof the random coil conformation than the spectrum of naturalnon-hydroxylated gelatins.     

Permeability of low molecular weight organics through nanofiltration membranes

The removal of natural organic matter (NOM) using nanofiltration (NF) is increasingly becoming an option for drinking water treatment. Low molecular weight (LMW) organic compounds are nevertheless only partially retained by such membranes. Bacterial regrowth and biofilm formation in the drinking water distribution system is favoured by the presence of such compounds, which in this context are considered as the assimilable organic carbon (AOC). In this study, the question of whether NF produces microbiologically stable water was addressed. Two NF membranes (cut-off of about 300 Da) were tested with different natural and synthetic water samples in a cross-flow filtration unit. NOM was characterised by liquid chromatography with organic carbon detection (LC-OCD) using a size-exclusion column in addition to specific organic acid measurements, while AOC was measured in a batch growth bioassay.Similarly to high molecular weight organic compounds like polysaccharides or humic substances that have a permeability lower than 1%, charged LMW organic compounds were efficiently retained by the NF membranes tested and showed a permeability lower than 3%. However, LMW neutrals and hydrophobic organic compounds permeate to a higher extent through the membranes and have a permeability of up to 6% and 12%, respectively. Furthermore, AOC was poorly retained by NF and the apparent AOC concentration measured in the permeated water was above the proposed limit for microbiologically stable water. This indicates that the drinking water produced by NF might be biologically unstable in the distribution system. Nevertheless, in comparison with the raw water, NF significantly reduced the AOC concentration.