Exploring the use of Granger causality for the identification of chemical exposure based on physiological data.

Wearable sensors offer new opportunities for the early detection and identification of toxic chemicals in situations where medical evaluation is not immediately possible. We previously found that continuously recorded physiology in guinea pigs can be used for early detection of exposure to an opioid (fentanyl) or a nerve agent (VX), as well as for differentiating between the two. Here, we investigated how exposure to these different chemicals affects the interactions between ECG and respiration parameters as determined by Granger causality (GC). Features reflecting such interactions may provide additional information and improve models differentiating between chemical agents. Traditional respiration and ECG features, as well as GC features, were extracted from data of 120 guinea pigs exposed to VX (n = 61) or fentanyl (n = 59). Data were divided in a training set (n = 99) and a test set (n = 21). Minimum Redundancy Maximum Relevance (mRMR) and Support Vector Machine (SVM) algorithms were used to, respectively, perform feature selection and train a model to discriminate between the two chemicals. We found that ECG and respiration parameters are Granger-related under healthy conditions, and that exposure to fentanyl and VX affected these relationships in different ways. SVM models discriminated between chemicals with accuracy of 95% or higher on the test set. GC features did not improve the classification compared to traditional features. Respiration features (i.e., peak inspiratory and expiratory flow) were the most important to discriminate between different chemical's exposure. Our results indicate that it may be feasible to discriminate between chemical exposure when using traditional physiological respiration features from wearable sensors. Future research will examine whether GC features can contribute to robust detection and differentiation between chemicals when considering other factors, such as generalizing results across species.

Using supramolecular machinery to engineer directional charge propagation in photoelectrochemical devices.

Molecular photoelectrochemical devices are hampered by electron-hole recombination after photoinduced electron transfer, causing losses in power conversion efficiency. Inspired by natural photosynthesis, we demonstrate the use of supramolecular machinery as a strategy to inhibit recombination through an organization of molecular components that enables unbinding of the final electron acceptor upon reduction. We show that preorganization of a macrocyclic electron acceptor to a dye yields a pseudorotaxane that undergoes a fast (completed within ~50 ps) 'ring-launching' event upon electron transfer from the dye to the macrocycle, releasing the anionic macrocycle and thus reducing charge recombination. Implementing this system into p-type dye-sensitized solar cells yielded a 16-fold and 5-fold increase in power conversion efficiency compared to devices based on the two control dyes that are unable to facilitate pseudorotaxane formation. The active repulsion of the anionic macrocycle with concomitant reformation of a neutral pseudorotaxane complex circumvents recombination at both the semiconductor-electrolyte and semiconductor-dye interfaces, enabling a threefold enhancement in hole lifetime.

Extreme ultraviolet-excited time-resolved luminescence spectroscopy using an ultrafast table-top high-harmonic generation source.

We present a table-top extreme ultraviolet (XUV) beamline for measuring time- and frequency-resolved XUV-excited optical luminescence (XEOL) with additional femtosecond-resolution XUV transient absorption spectroscopy functionality. XUV pulses are generated via high-harmonic generation using a near-infrared pulse in a noble gas medium and focused to excite luminescence from a solid sample. The luminescence is collimated and guided into a streak camera where its spectral components are temporally resolved with picosecond temporal resolution. We time-resolve XUV-excited luminescence and compare the results to luminescence decays excited at longer wavelengths for three different materials: (i) sodium salicylate, an often used XUV scintillator; (ii) fluorescent labeling molecule 4-carbazole benzoic (CB) acid; and (iii) a zirconium metal oxo-cluster labeled with CB, which is a photoresist candidate for extreme-ultraviolet lithography. Our results establish time-resolved XEOL as a new technique to measure transient XUV-driven phenomena in solid-state samples and identify decay mechanisms of molecules following XUV and soft-x-ray excitation.

Ageing of Polymer Frictional Interfaces: The Role of Quantity and Quality of Contact.

When two objects are in contact, the force necessary for one to start sliding over the other is larger than the force necessary to keep the sliding motion going. This difference between static and dynamic friction is thought to result from a reduction in the area of real contact upon the onset of slip. Here, we resolve the structure in the area of contact on the molecular scale by means of environment-sensitive molecular rotors using (super-resolution) fluorescence microscopy and fluorescence lifetime imaging. We demonstrate that the macroscopic friction force is not only controlled by the area of real contact but also controlled by the "quality" of that area of real contact, which determines the friction per unit contact area. We show that the latter is affected by the local density of the contacting surfaces, a parameter that can be expected to change in time at any interface that involves glassy, amorphous materials.

Frictional weakening of slip interfaces.

When two objects are in contact, the force necessary to overcome friction is larger than the force necessary to keep sliding motion going. This difference between static and dynamic friction is usually attributed to the growth of the area of real contact between rough surfaces in time when the system is at rest. We directly measure the area of real contact and show that it actually increases during macroscopic slip, despite the fact that dynamic friction is smaller than static friction. This signals a decrease in the interfacial shear strength, the friction per unit contact area, which is due to a mechanical weakening of the asperities. This provides a novel explanation for stick-slip phenomena in, e.g., earthquakes.

Molecular probes reveal deviations from Amontons' law in multi-asperity frictional contacts.

Amontons' law defines the friction coefficient as the ratio between friction force and normal force, and assumes that both these forces depend linearly on the real contact area between the two sliding surfaces. However, experimental testing of frictional contact models has proven difficult, because few in situ experiments are able to resolve this real contact area. Here, we present a contact detection method with molecular-level sensitivity. We find that while the friction force is proportional to the real contact area, the real contact area does not increase linearly with normal force. Contact simulations show that this is due to both elastic interactions between asperities on the surface and contact plasticity of the asperities. We reproduce the contact area and fine details of the measured contact geometry by including plastic hardening into the simulations. These new insights will pave the way for a quantitative microscopic understanding of contact mechanics and tribology.

The Effect of Liposomes on the Kinetics and Mechanism of the Photocatalytic Reduction of 5,5'-Dithiobis(2-Nitrobenzoic Acid) by Triethanolamine.

Recently, the addition of negatively charged liposomes was shown to increase the quantum yield of the photocatalytic reduction of 5,5'-dithio(2-nitrobenzoic acid) (H2DTNB) to 2-nitro-5-thiobenzoic acid (H2NTB) by triethanolamine using meso-tetra(4-(N-methylpyridinium)porphyrinato zinc chloride as photosensitizer. In this work, we investigate in detail the kinetics of this photocatalytic reaction both in homogeneous solution and at the surface of negatively charged liposomes, to unravel the effects of liposomes on the mechanism of the photoreaction. In homogeneous solution, the reaction is initiated by oxidative quenching. Both static (singlet) and dynamic (triplet) quenching of the photosensitizer contribute to the formation of the photoproduct. In these conditions, the reaction is limited by the low efficiency of reductive regeneration of the photosensitizer, compared to charge recombination. Upon adsorption of the positively charged photosensitizer to the negative surface of the liposomes, however, both static and dynamic oxidative quenching become ineffective due to electrostatic repulsion of the dianionic DTNB2- from the negatively charged membrane. In such conditions, photoreduction occurs via reductive quenching, showing that the addition of liposomes can truly modify the mechanism of photocatalyzed redox reactions.

Effect of beta and gamma neurofeedback on memory and intelligence in the elderly.

Recent research showed a correlation between cognitive decline and a decrease of EEG gamma activity. In the present double-blind randomized control study, we investigated whether gamma and beta neurofeedback protocols, that have been shown to modulate performance on cognitive control and memory in young adults, also leads to increased brain activity and cognitive performance in elderly. Twenty older adults either performed eight 30-min gamma neurofeedback session or beta neurofeedback session within a period of 21 days. Cognitive performance was determined before and after the training through an IQ and memory task and we added a subjective well-being questionnaire. Both neurofeedback training protocols resulted in a significant increase of the brain activity within each training session, suggesting that the aging brain is still trainable. However, we found no effects on cognitive performance or transfer of the feedback beyond the trainings. We discuss several possible reasons for the lack of training on rest measurements and cognition and ways to improve the feedback protocols for future studies.

Molecular recognition and self-assembly special feature: Self-assembled biomimetic [2Fe2S]-hydrogenase-based photocatalyst for molecular hydrogen evolution.

The large-scale production of clean energy is one of the major challenges society is currently facing. Molecular hydrogen is envisaged as a key green fuel for the future, but it becomes a sustainable alternative for classical fuels only if it is also produced in a clean fashion. Here, we report a supramolecular biomimetic approach to form a catalyst that produces molecular hydrogen using light as the energy source. It is composed of an assembly of chromophores to a bis(thiolate)-bridged diiron ([2Fe2S]) based hydrogenase catalyst. The supramolecular building block approach introduced in this article enabled the easy formation of a series of complexes, which are all thoroughly characterized, revealing that the photoactivity of the catalyst assembly strongly depends on its nature. The active species, formed from different complexes, appears to be the [Fe(2)(micro-pdt)(CO)(4){PPh(2)(4-py)}(2)] (3) with 2 different types of porphyrins (5a and 5b) coordinated to it. The modular supramolecular approach was important in this study as with a limited number of building blocks several different complexes were generated.

Computational study of radical cations of saturated compounds with sigma-type and pi-type N-N bonds.

Geometrical and electronic properties have been calculated and are compared with experimental data for three saturated diaza compounds and their radical cations and dications. The molecular geometries in the different oxidation states are consistently reproduced very well using the B3PW91 and B3LYP three-parameter density functional methods, with a modest 6-31G* basis set. The performance of the pure density functionals BLYP and BPW91 is less satisfactory. The Hartree-Fock method yields excellent results in some cases but poor results in others. Ionization potentials and electron-nuclear hyperfine interactions are reproduced moderately well with B3LYP and B3PW91. Electronic excitation energies calculated with time-dependent density functional theory agree very well with experiment in most cases. For 2,7-diazatetracyclo[6.2.2.2(3,6).0(2,7)]tetradecane 2 and its radical cation and dication, the reorganization parameters for self-electron exchange were calculated and compared with experimental and earlier computed data. The calculations allow a good estimate of the different contributions to the energy barrier, i.e., the internal and solvent reorganization energies and the work term in the case of 2+/2++.

Photoinduction of fast, reversible translational motion in a hydrogen-bonded molecular shuttle.

A rotaxane is described in which a macrocycle moves reversibly between two hydrogen-bonding stations after a nanosecond laser pulse. Observation of transient changes in the optical absorption spectrum after photoexcitation allows direct quantitative monitoring of the submolecular translational process. The rate of shuttling was determined and the influence of the surrounding medium was studied: At room temperature in acetonitrile, the photoinduced movement of the macrocycle to the second station takes about 1 microsecond and, after charge recombination (about 100 microseconds), the macrocycle shuttles back to its original position. The process is reversible and cyclable and has properties characteristic of an energy-driven piston.

Long-lived short-distance intramolecular charge separation via intermolecular triplet sensitisation.

Sensitised excitation of the DMN[3]DCME donor[bridge]acceptor system allows population of a triplet CT state with a microsecond lifetime in polar solvents. This is more than five orders of magnitude longer than the lifetime of the corresponding singlet CT state which is populated exclusively upon direct excitation. The picture indicates the spin-forbidden nature of the charge recombination between the acceptor (red) to donor (green) moieties.

Hitting moving objects. The dependency of hand velocity on the speed of the target.

In previous studies, subjects did not hit slowly moving objects as quickly as fast ones, despite being instructed to hit them all as quickly as possible. In those studies the targets moved at constant but unpredictable velocities, and it has been suggested that subjects were unable to adjust the hand's path to suit the velocity of the target. To compensate for this, they adjusted the speed of their hand to that of the target (speed coupling). According to this hypothesis, speed coupling is necessary only when subjects are unable to correctly predict the next target velocity and only if they have to be accurate. We show here that decreasing the uncertainty about the upcoming target's velocity or enlarging the tip of the hitting weapon does not make speed coupling disappear. Moreover, there is a negative correlation between hand velocity and strength of speed coupling, whereas the hypothesis predicts a positive correlation. The hypothesis is therefore rejected. We propose that speed coupling is a result of different speed-accuracy tradeoffs applying to different target velocities.

Measurement and global analysis of the absorbance changes in the photocycle of the photoactive yellow protein from Ectothiorhodospira halophila.

The photocycle of the photoactive yellow protein (PYP) from Ectothiorhodospira halophila was examined by time-resolved difference absorption spectroscopy in the wavelength range of 300-600 nm. Both time-gated spectra and single wavelength traces were measured. Global analysis of the data established that in the time domain between 5 ns and 2 s only two intermediates are involved in the room temperature photocycle of PYP, as has been proposed before (Meyer T.E., E. Yakali, M. A. Cusanovich, and G. Tollin. 1987. Biochemistry. 26:418-423; Meyer, T. E., G. Tollin, T. P. Causgrove, P. Cheng, and R. E. Blankenship. 1991. Biophys. J. 59:988-991). The first, red-shifted intermediate decays biexponentially (60% with tau = 0.25 ms and 40% with tau = 1.2 ms) to a blue-shifted intermediate. The last step of the photocycle is the biexponential (93% with tau = 0.15 s and 7% with tau = 2.0 s) recovery to the ground state of the protein. Reconstruction of the absolute spectra of these photointermediates yielded absorbance maxima of about 465 and 355 nm for the red- and blue-shifted intermediate with an epsilon max at about 50% and 40% relative to the epsilon max of the ground state. The quantitative analysis of the photocycle in PYP described here paves the way to a detailed biophysical analysis of the processes occurring in this photoreceptor molecule.

Characterization of Salmonella enteritidis strains.

A study was conducted to characterize 318 Salmonella enteritidis strains that were mainly isolated from poultry and their environment in Canada. Biotype, phagetype (PT), plasmid profile (PP), hybridization with a plasmid-derived virulence sequence probe, antibiotic resistance, outer membrane proteins (OMPs), and lipopolysaccharide (LPS) profiles were determined. Relationships of these properties to one another, and their diagnostic and pathogenic significance were assessed. Biotyping indicated that failure to ferment rhamnose was sometimes useful as a marker for epidemiologically related strains. Phagetyping was the most effective method for subdividing S. enteritidis; it distinguished 12 PTs. Phagetype 13 was occasionally associated with septicemia and mortality in chickens. The strains belonged to 15 PPs. A 36 megadalton (MDa) plasmid was found in 97% of the strains. Only the 36 MDa plasmid hybridized with the probe. Seventeen percent of the strains were drug resistant; all strains were sensitive to ciprofloxacin. Thirty-five of 36 strains possessed the same OMP profile, and 36 of 41 strains contained smooth LPS.