Next-state comfort in learning a vertical stick transportation sequence

Over the last decade, the end-state comfort effect (e.g., Rosenbaum et al., 2006) has received a considerable amount of attention. However, some of the underlying mechanisms are still to be investigated, amongst others, how sequential planning affects end-state comfort and how this effect develops over learning. In a two-step sequencing task, e.g., postural comfort can be planned on the intermediate position (next state) or on the actual end position (final state). It might be hypothesized that, in initial acquisition, next state’s comfort is crucial for action planning but that, in the course of learning, final state’s comfort is taken more and more into account. To test this hypothesis, a variant of Rosenbaum’s vertical stick transportation task was used. Participants (N = 16, right-handed) received extensive practice on a two-step transportation task (10,000 trials over 12 sessions). From the initial position on the middle stair of a staircase in front of the participant, the stick had to be transported either 20 cm upwards and then 40 cm downwards or 20 cm downwards and then 40 cm upwards (N = 8 per subgroup). Participants were supposed to produce fluid movements without changing grasp. In the pre- and posttest, participants were tested on both two-step sequencing tasks as well as on 20 cm single-step upwards and downwards movements (10 trials per condition). For the test trials, grasp height was calculated kinematographically. In the pretest, large end/next/final-state comfort effects for single-step transportation tasks and large next-state comfort effects for sequenced tasks were found. However, no change in grasp height from pre- to posttest could be revealed. Results show that, in vertical stick transportation sequences, the final state is not taken into account when planning grasp height. Instead, action planning seems to be solely based on aspects of the next action goal that is to be reached.

K-feldspar hygrochronology

The significance of the multi-isotopic record preserved in K-feldspars is assessed on samples from the Aar metagranite, Central Alps, Switzerland having very tight independent geological constraints. Stepwise leaching reveals that two diachronically grown K-feldspar generations coexist: Kfs-1 (≥ 35 Ma old, Ca-poor, Rb-Cl-rich, with low 87Sr/86Sr and high 206Pb/204Pb) and Kfs-2 (≤ 10 Ma old, antithetic isotopic signatures deriving from external fluids). Microtextures imaged by cathodoluminescence, backscattered electrons, and electron probe microanalysis are patchy and chemically heterogeneous, with pronounced enrichments in Ba in the retrogressed regions. This confirms the simultaneous presence of fluid-dominated retrogression and recrystallization and isotopic inheritance. The staircase-shaped 40Ar/39Ar age spectrum correlates with the Ca/K and Cl/K signatures. This reflects a mixture of heterochemical K-feldspar generations, and not an intracrystalline Ar gradient caused by diffusion. The shape of the age spectrum and the in vacuo release kinetics proceed from entirely different physical and geological phenomena. What K-feldspars can be effectively used for is to constrain the timing of the fluids that interacted with them by multi-isotopic analyses, rather than to model a “cooling history” from 39Ar release alone. The identification of multiple mineral generations by imaging combined with multi-isotopic analysis enables the accurate dating of the events of a multistage evolution after the initial crystallization of the rock in which the minerals occur.

A re-examination of petrogenesis and 40Ar/39Ar systematics in the the Chain of Ponds K-feldspar: "diffusion domain" archetype versus polyphase hygrochronology

K-feldspar (Kfs) from the Chain of Ponds Pluton (CPP) is the archetypal reference material, on which thermochronological modeling of Ar diffusion in discrete “domains” was founded. We re-examine the CPP Kfs using cathodoluminescence and back-scattered electron imaging, transmission electron microscopy, and electron probe microanalysis. 40Ar/39Ar stepwise heating experiments on different sieve fractions, and on handpicked and unpicked aliquots, are compared. Our results reproduce the staircase-shaped age spectrum and the Arrhenius trajectory of the literature sample, confirming that samples collected from the same locality have an identical Ar isotope record. Even the most pristine-looking Kfs from the CPP contains successive generations of secondary, metasomatic/retrograde mineral replacements that post-date magmatic crystallization. These chemically and chronologically distinct phases are responsible for its staircase-shaped age spectra, which are modified by handpicking. While genuine within-grain diffusion gradients are not ruled out by these data, this study demonstrates that the most important control on staircase-shaped age spectra is the simultaneous presence of heterochemical, diachronous post-magmatic mineral growth. At least five distinct mineral species were identified in the Kfs separate, three of which can be traced to external fluids interacting with the CPP in a chemically open system. Sieve fractions have size-shifted Arrhenius trajectories, negating the existence of the smallest “diffusion domains”. Heterochemical phases also play an important role in producing non-linear trajectories. In vacuo degassing rates recovered from Arrhenius plots are neither related to true Fick’s Law diffusion nor to the staircase shape of the age spectra. The CPP Kfs used to define the "diffusion domain" model demonstrates the predominance of metasomatic alteration by hydrothermal fluids and recrystallization in establishing the natural Ar distribution amongst different coexisting phases that gives rise to the staircase-shaped age spectrum. Microbeam imaging of textures is as essential for 40Ar-39Ar hygrochronology as it is for U-Pb geochronology.

Hierarchical self-assembly of nucleotide-appended oligopyrenotides into defined supramolecular objects

Supramolecular DNA assembly blends DNA building blocks with synthetic organic and inorganic molecules giving structural and functional advantages both to the initial self-assembly process and to the final construct. Synthetic molecules can bring a number of additional interactions into DNA nanotechnology. Incorporating extended aromatic molecules as connectors of DNA strands allows folding of these strands through π-π stacking (DNA “foldamers”). In previous work it was shown that short oligopyrenotides (phosphodiester-linked pyrene oligomers) behave as staircase-like foldamers, which cooperatively self-assemble into two-dimensional supramolecular polymers in aqueous medium. Herein, we demonstrate that a 10-mer DNA-sequence modified with 7 pyrene units (see illustration) forms dimensionally-defined supramolecular polymers under thermodynamic conditions in water. We present the self-assembly behavior, morphological studies, and the spectroscopic properties of the investigated DNA-sequences (illustrative AFM picture shown below).

Hierarchical self-assembly of nucleotide-appended oligopyrenotides into defined supramolecular objects

Supramolecular DNA assembly blends DNA building blocks with synthetic organic molecules giving structural and functional advantages. Incorporating extended aromatic molecules as connectors of DNA strands allows folding of these strands through π-π stacking (DNA 'foldamers'). In previous work it was shown that short oligopyrenotides behave as staircase-like foldamers, which cooperatively self-assemble into 2D supramolecular polymers in aqueous medium. Herein, we demonstrate that 10-mer DNA-sequence conjugated with seven pyrene unites forms dimensionally-defined supramolecular polymers under thermodynamic conditions in water. We present the self-assembly behavior, morphologycal studies (AFM and TEM), and the spectroscopic properties (UV/vis, CD) of the investigated pyrene - conjugated DNA-sequence.

Whole-body motion discrimination in the visually impaired

Visually impaired people show superior abilities in various perception tasks such as auditory attention, auditory temporal resolution, auditory spatial tuning, and odor discrimination. However, with the use of psychophysical methods, auditory and olfactory detection thresholds typically do not differ between visually impaired and sighted participants. Using a motion platform we investigated thresholds of passive whole-body motion discrimination in nine visually impaired participants and nine age-matched sighted controls. Participants were rotated in yaw, tilted in roll, and translated along the y-axis at two different frequencies (0.3 Hz and 2 Hz). An adaptive 3-down 1-up staircase procedure was used along with a two-alternative direction (leftward vs. rightward) discrimination task. Superior performance of visually impaired participants was found in the 0.3 Hz roll tilt condition. No differences between the visually impaired and controls were observed in all other types of motion. The superior performance in the 0.3 Hz roll tilt condition could reflect differences in the integration of extra-vestibular cues and increased sensitivity towards changes in the direction of the gravito-inertial force. In the absence of visual information, roll tilts entail a more pronounced risk of falling, and this could eventually account for the group difference. It is argued that differences in experimental procedures (i.e. detection vs. discrimination of stimuli) explain the discrepant findings across perceptual tasks comparing blind and sighted participants.

Stair climbing - An insight and comparison between women with and without joint hypermobility: A descriptive study.

Generalized joint hypermobility (GJH) is a frequent entity in rheumatology with higher prevalence among women. It is associated with chronic widespread pain, joint dislocations, arthralgia, fibromyalgia and early osteoarthritis. Stair climbing is an important functional task and can induce symptoms in hypermobile persons. The aim of this study was to compare ground reaction forces (GRF) and muscle activity during stair climbing in women with and without GJH. A cross-sectional study of 67 women with normal mobility and 128 hypermobile women was performed. The hypermobile women were further divided into 56 symptomatic and 47 asymptomatic. GRFs were measured by force plates embedded in a six step staircase, as well as surface electromyography (EMG) of six leg muscles. Parameters derived from GRF and EMG were compared between groups using t-test and ANOVA. For GRF no significant differences were found. EMG showed lower activity for the quadriceps during ascent and lower activity for hamstrings and quadriceps during descent in hypermobile women. For symptomatic hypermobile women these differences were even more accentuated. The differences in EMG may point towards an altered movement pattern during stair climbing, aimed at avoiding high muscle activation. However, differences were small, since stair climbing seems to be not demanding.