Assessing network cognition in the Dutch railway system: insights into network situation awareness and workload using social network analysis

Cognition, Technology & Work - This study takes upon a group cognition perspective and investigates the cognition of railway traffic operations, in particular railway traffic and passenger...     

Magneto-optical Kerr effect susceptometer for the analysis of magnetic domain wall dynamics

Domain wall dynamics in thin magnetic films with perpendicular and in-plane anisotropy is studied using a novel magneto-optical Kerr effect susceptometery method. The method allows for measurements of domain wall motion under ac field excitation and the analysis of dynamic modes as a function of driving frequency and magnetic field amplitude. Domain wall dynamics in the perpendicular anisotropy system, a Co/Pt multilayer, is characterized by thermally activated creep motion. For this dynamic mode, a polydispersivity exponent of β = 0.50 ± 0.03 is derived at small excitation energy, which is in excellent agreement with theoretical models. The dynamics of the other system, a Co wire with transverse uniaxial anisotropy, is dominated by viscous slide motion in a regular magnetic stripe pattern. Analytical expressions are derived for this magnetic configuration and by using these expressions, accurate values for the depinning field and the domain wall mobility are extracted from the susceptibility measurements.     

Modelling microbial adaptation to changing availability of substrates

In their natural environment microorganisms encounter changes in substrate availability, involving either nutrient concentrations or nutrient types. They have to adapt to the new conditions in order to survive. We present a model for slow microbial adaptation, involving the synthesis of new enzymes, in response to changes in the availability of substitutable substrates. The model is based on reciprocal (or mutual) inhibition of expression of both the substrate-specific carriers and the associated assimilatory machinery. The inhibition kinetics is derived from the kinetics of synthesizing units. An interesting property of the adaptation model is that the presence of a single limiting resource results in a constant maximum specific substrate consumption rate for fully adapted microorganisms. Because the maximum specific consumption rate is not a function of substrate concentration, for growth on one substrate, the Monod and Pirt models for instance are still valid. Other adaptation models known to us do not fulfil this property. The simplest version of our model describes adaptation during diauxic growth, using only one preference parameter and one initial condition. The applicability of the model is exemplified by fitting it to published data from diauxic growth experiments.     

Exploring the possibilities of cryogenic cooling in liquid chromatography for biological applications: a proof of principle

The possibilities to use cryogenic cooling to trap components in liquid chromatography was investigated. In a first step, van 't Hoff plots were measured with a reversed-phase column using the temperature control unit of a conventional high performance liquid chromatography (HPLC) system to gain insight in the retention behavior of proteins at low temperatures. It was estimated that retention factors in the range of k = 10(4) could be achieved at T = -20 °C for lysozyme, indicating that temperature is a usable parameter to trap components in LC. In a next step, trapping experiments were carried out on a nano-LC system, equipped with a UV-detector, using a commercial reversed-phase column. An in-house built setup, allowing cooling of a segment of the column down to temperatures below T = -20 °C, was used to trap components. Experiments were conducted under isocratic and gradient conditions with methanol as organic solvent. It is demonstrated that, by thermally trapping and elution of components, an enhanced S/N ratio and decreased peak widths can be obtained. At the same time, a significant increase in pressure drop occurs during the cooling process. Limitations and benefits of the technique are further discussed.     

Long-term cognitive deficits following posterior fossa tumor resection: A neuropsychological and functional neuroimaging follow-up study.

The posterior fossa syndrome (PFS) consists of transient cerebellar mutism, cognitive symptoms, and neurobehavioral abnormalities that typically develop in children following posterior fossa (PF) tumor resection. The pathophysiological substrate of the syndrome remains unclear. We investigated eight children of whom five presented with a variety of clinically relevant non-motor language symptoms associated with cognitive and behavioral disturbances after PF tumor resection. Four children developed transient cerebellar mutism followed by dysarthric speech. Non-motor language symptoms consisted of agrammatism, anomia, impaired verbal fluency, comprehension deficits, and aspontaneous speech. Neurocognitive deficits included executive dysfunctions, concentration deficits, and visuo-spatial disorders. In addition, all children presented with behavioral and affective disturbances. Functional neuroimaging studies during the phase of mutism by means of SPECT showed perfusional deficits in the anatomo-clinically suspected supratentorial areas subserving language dynamics, syntax, naming, executive functioning, affective regulation, and behavior. A significant improvement of frontal perfusional deficits paralleled the clinical remission of mutism. These results add to the view that the PFS might represent a cerebello-cerebral diaschisis phenomenon, reflecting the metabolic impact of the cerebellar lesion on supratentorial cognitive and affective functions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Notes on Sum-Tests and Independence Tests

We study statistical sum-tests and independence tests, in particular for computably enumerable semimeasures on a discrete domain. Among other things, we prove that for universal semimeasures every S⁰₁\Sigma ^{0}_{1} -sum-test is bounded, but unbounded P⁰₁\Pi ^{0}_{1} -sum-tests exist, and we study to what extent the latter can be universal. For universal semimeasures, in the unary case of sum-test we leave open whether universal P⁰₁\Pi ^{0}_{1} -sum-tests exist, whereas in the binary case of independence tests we prove that they do not exist.