► We study recrystallization kinetics – and activation energies of individual grains. ► The kinetics is found to deviate significantly from mean kinetics. ► An explanation for the observed kinetics ...is proposed. ► Activation energies of individual grains are found to form a broad distribution.
Three-dimensional X-ray diffraction has been used to study the growth kinetics of 1406 individual grains recrystallizing in 50% cold-rolled aluminium. It is found that each grain follows its own kinetics. The radial growth of individual grains is found to often be piecewise linear, and an explanation based on the cell block microstructure of cold-rolled aluminium is proposed. Grain-averaged activation energies of 793 individual grains are determined, and found to constitute a broad distribution. Reasons and implications of these findings are discussed.
A key issue regarding the use of stem cells in cardiovascular regenerative medicine is their retention in target tissues. Here, we have generated and assessed a bispecific antibody heterodimer ...designed to improve the retention of bone-marrow-derived multipotent stromal cells (BMMSC) in cardiac tissue damaged by myocardial infarction. The heterodimer comprises an anti-human CD90 monoclonal antibody (mAb) (clone 5E10) and an anti-myosin light chain 1 (MLC1) mAb (clone MLM508) covalently cross-linked by a bis-arylhydrazone. We modified the anti-CD90 antibody with a pegylated-4-formylbenzamide moiety to a molar substitution ratio (MSR) of 2.6 and the anti-MLC1 antibody with a 6-hydrazinonicotinamide moiety to a MSR of 0.9. The covalent modifications had no significant deleterious effect on mAb epitope binding. Furthermore, the binding of anti-CD90 antibody to BMMSCs did not prevent their differentiation into adipo-, chondro-, or osteogenic lineages. Modified antibodies were combined under mild conditions (room temperature, pH 6, 1 h) in the presence of a catalyst (aniline) to allow for rapid generation of the covalent bis-arylhydrazone, which was monitored at A 354. We evaluated epitope immunoreactivity for each mAb in the construct. Flow cytometry demonstrated binding of the bispecific construct to BMMSCs that was competed by free anti-CD90 mAb, verifying that modification and cross-linking were not detrimental to the anti-CD90 complementarity-determining region. Similarly, ELISA-based assays demonstrated bispecific antibody binding to plastic-immobilized recombinant MLC1. Excess anti-MLC1 mAb competed for bispecific antibody binding. Finally, the anti-CD90 × anti-MLC1 bispecific antibody construct induced BMMSC adhesion to plastic-immobilized MLC1 that was resistant to shear stress, as measured in parallel-plate flow chamber assays. We used mAbs that bind both human antigens and the respective pig homologues. Thus, the anti-CD90 × anti-MLC1 bispecific antibody may be used in large animal studies of acute myocardial infarction and may provide a starting point for clinical studies.
We investigate the run-up of a shock wave from inside to the surface of a perfect fluid star in equilibrium and bounded by vacuum. Near the surface we approximate the fluid motion as plane-symmetric ...and the gravitational field as constant. We consider the ‘hot’ equation of state P = (Γ − 1)ρe and its ‘cold’ (fixed entropy, barotropic) form P = K0ρΓ (the latter does not allow for shock heating). We numerically find that the evolution of generic initial data approaches universal similarity solutions sufficiently near the surface, and we explicitly construct these similarity solutions. The two equations of state show very different behaviour because shock heating becomes the dominant effect when it is allowed. In the barotropic case, the fluid velocity behind the shock approaches a constant value, while the density behind the shock approaches a power law in space, as the shock approaches the surface. In the hot case with shock heating, the density jumps by a constant factor through the shock, while the sound speed and fluid velocity behind the shock diverge in a whiplash effect. We tabulate the similarity exponents as a function of the equation of state parameter Γ and the stratification index n∗.
Introduction In electroencephalography (EEG) research, frequency-tagging has become an important measure for investigating sustained attention in the field of vision, audition and both (cf. Keitel et ...al., 2011; Saupe et al., 2009; Müller et al., 2003 ). Frequency-tagged stimuli elicit the steady state evoked potential (SSEP), which is an oscillatory brain response of the same frequency as the driving frequency. Crucially, paying attention to such a stimulus causes an increase in SSEP amplitude compared to when the respective stimulus had to be ignored. In the somatosensory domain however, attentional modulation of the steady state signal seems to be highly variable across and within subjects; i.e. there is either an increased or decreased amplitude when attention is paid to a vibrotactile stimulus. Interestingly, despite this opposing pattern behavioral performance showed that participants seemed to perform the task correctly. The present study wanted to shed light on possible factors causing these inter-and intra-individual differences. Methods and hypotheses We conducted a simultaneous EEG and functional magnetic resonance imaging (fMRI) study because both methods provide us with different markers of attention and brain states at different time scales. We expected to find a direct relationship between the attentional modulation seen in the EEG and fMRI signal. Participants with an increased amplitude of the EEG steady state signal should show an increased BOLD response in primary somatosensory cortex compared to participants with a decreased amplitude. Besides differences in pre-stimulus EEG oscillations (e.g. μ-alpha or μ-beta) and resting state fMRI measures might account for inter and intra-individual alterations in attention effects. Conclusion The present study allows the direct comparisons of EEG, fMRI and behavioral attention markers and thereby paves the road for multi-method approaches in sustained somatosensory attention research.
Introduction Ongoing oscillations are associated with brain functions such as somatosensory perception. For example, the amplitude of the sensorimotor mu rhythm can be linked to the perception of ...near-detection-threshold somatosensory stimuli ( Linkenkaer-Hansen et al., 2004 ). Furthermore the phase of neuronal oscillations affects the perception of near-threshold stimuli ( Busch et al., 2009 ). Transcranial alternating current stimulation (tACS) may offer the possibility to modulate oscillatory activity. Recently it was shown that tACS increased the amplitude of visual alpha oscillations ( Zaehle et al., 2010 ) and had a phase dependent influence on auditory perception ( Neuling et al., 2012 ). Objectives We examined the effect of tACS applied at participants’ individual mu frequency on threshold levels of somatosensory perception. We hypothesized that (a) tACS modulates somatosensory perception thresholds as compared to sham and (b) perception thresholds vary as a function of the phase of tACS. Methods In a randomized, single-blinded, crossover design, 17 participants (mean age: 27; female: 10) underwent a combined EEG/tACS experiment in two separate sessions (real or sham tACS). In the beginning, subject’s individual mu frequency was derived from the event-related desynchronization over the left somatosensory cortex (S1) induced by electric pulses to the right index finger ( Fig. 1 b). Subsequently, somatosensory detection thresholds were determined in a block of 16 min using an adaptive staircase procedure of weak electric stimuli that were presented with electrodes at the right index finger. During the second third of the task 5 min of tACS was applied at the individual mu frequency in a bilateral montage over both primary somatosensory cortices (S1). For sham, 30 s of 1 mA random noise stimulation was applied ( Fig. 1 a). Behavioral performance was assessed with respect to (i) an average effect of tACS as compared to sham and (ii) a modulation dependent on the tACS phase. Results No differences in the average somatosensory perception thresholds were observed between real and sham stimulation. However, during tACS, somatosensory detection thresholds changed as a function of the phase of tACS. Thresholds were differing maximally for stimuli presented at opposite phases in both maxima of the tACS signal curve( Fig. 2 ). Conclusion We conclude that tACS applied at the individual mu frequency over S1 is capable of modulating perception of near-threshold somatosensory stimuli in a phase-dependent manner. Our findings suggest that functionally relevant intrinsic oscillations may be modulated using non-invasive brain stimulation.
In general relativity black holes can be formed from regular initial data that do not contain a black hole already. The space of regular initial data for general relativity therefore splits naturally ...into two halves: data that form a black hole in the evolution and data that do not. The spacetimes that are evolved from initial data near the black hole threshold have many properties that are mathematically analogous to a critical phase transition in statistical mechanics.
Solutions near the black hole threshold go through an intermediate attractor, called the critical solution. The critical solution is either time-independent (static) or scale-independent (self-similar). In the latter case, the final black hole mass scales as
(p−p
∗)
γ
along any 1-parameter family of data with a regular parameter
p such that
p=p
∗
is the black hole threshold in that family. The critical solution and the critical exponent
γ are universal near the black hole threshold for a given type of matter.
We show how the essence of these phenomena can be understood using dynamical systems theory and dimensional analysis. We then review separately the analogy with critical phase transitions in statistical mechanics, and aspects specific to general relativity, such as spacetime singularities. We examine the evidence that critical phenomena in gravitational collapse are generic, and give an overview of their rich phenomenology.
Introduction Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique used to modulate cortical excitability. In the motor domain, there is consensus that anodal ...tDCS increases cortical excitability, whereas cathodal tDCS decreases it. On the other hand, inconsistent results of tDCS-induced effects in the sensory domain have been reported. Objective The aim of the present study was to investigate (A) changes in cortical excitability within primary somatosensory cortex (S1) by means of single-pulse somatosensory evoked potentials (SEPs) and (B) intracortical inhibition by means of paired-pulse SEPs when tDCS was applied over left SM1. Materials and Methods 10 min of anodal, cathodal or sham tDCS was applied over the left SM1 using saline-soaked sponge electrodes (35 cm2 electrodes, 1 mA, current density 0.028 mA/cm2 ). Before, immediately after as well as 10 min after termination of tDCS, single-and paired-pulse SEP recordings were performed. We hypothesized that tDCS will induce polarity specific changes in cortical excitability within left S1. Furthermore, we reasoned that anodal tDCS will reduce paired-pulse inhibition within left S1 while cathodal tDCS will result in an augmentation of inhibition relative to sham stimulation. Results 10 min of anodal and cathodal tDCS over SM1 did not result in any significant excitability changes within left S1. However, anodal tDCS resulted in a reduction of paired-pulse inhibition within left S1 10 min after termination of stimulation. No change in paired-pulse inhibition could be observed after cathodal tDCS. Conclusion Here we provide novel evidence that anodal tDCS affects inhibitory processing within S1, a finding that might improve our understanding about the underlying neural mechanisms of tDCS on somatosensory processing.
A recently developed scheme for evaluation of orientation data gathered by electron backscatter diffraction is employed on individual grains in a deformed state. The potential of the method is ...illustrated on aluminium cold-rolled to 38%. The orientation distribution in each grain is characterized by its anisotropy and the average orientation spread. The dependence of both parameters on grain size is discussed. The preferred rotation axes in each grain are determined and compared with macroscopic directions. From the disorientation angles with respect to the preferred rotation axis characteristic features of the deformation structure as alternating orientation differences or orientation gradients can be resolved.
A quantitative analysis of the retained austenite (RA) fractions in gas tungsten arc welded silicon and aluminium containing transformation induced plasticity steels was carried out by synchrotron ...X-ray diffraction measurements. The variation in RA transverse to the weld line was measured to study the effect of weld thermal cycles on the stabilisation of austenite in the heat affected zone (HAZ) and the fusion zone (FZ). The results showed that the FZ of silicon based steels contained a higher amount of RA (∼7%) than aluminium based steels, which contained only ∼4%. During the solidification of the weld pool, aluminium was found to partition to solidifying δ-ferrite and to stabilise the soft δ-ferrite grains at the fusion boundaries. Owing to this partitioning, the HAZ was enriched in carbon and the RA content was found to increase with distance from the fusion boundaries. In contrast, this partitioning behaviour was not present in silicon based transformation induced plasticity steels and a lesser amount of RA was found in the coarse grained HAZ than in the FZ.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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