Recent research provides evidence for a functional role of brain oscillations for perception. For example, auditory temporal resolution seems to be linked to individual gamma frequency of auditory ...cortex. Individual gamma frequency not only correlates with performance in between‐channel gap detection tasks but can be modulated via auditory transcranial alternating current stimulation. Modulation of individual gamma frequency is accompanied by an improvement in gap detection performance. Aging changes electrophysiological frequency components and sensory processing mechanisms. Therefore, we conducted a study to investigate the link between individual gamma frequency and gap detection performance in elderly people using auditory transcranial alternating current stimulation. In a within‐subject design, twelve participants were electrically stimulated with two individualized transcranial alternating current stimulation frequencies: 3 Hz above their individual gamma frequency (experimental condition) and 4 Hz below their individual gamma frequency (control condition), while they were performing a between‐channel gap detection task. As expected, individual gamma frequencies correlated significantly with gap detection performance at baseline and in the experimental condition, transcranial alternating current stimulation modulated gap detection performance. In the control condition, stimulation did not modulate gap detection performance. In addition, in elderly, the effect of transcranial alternating current stimulation on auditory temporal resolution seems to be dependent on endogenous frequencies in auditory cortex: Elderlies with slower individual gamma frequencies and lower auditory temporal resolution profit from auditory transcranial alternating current stimulation and show increased gap detection performance during stimulation. Our results strongly suggest individualized transcranial alternating current stimulation protocols for successful modulation of performance.
Gap detection (GD) performance is assumed to be linked to the individual gamma‐band frequency (IGF). Thus, IGF can be interpreted as a measure of auditory temporal resolution. Elderly people were stimulated with transcranial alternating current stimulation (tACS, left part of Figure) at frequencies above IGF (+3 Hz, experimental condition) and below IGF (−4 Hz) over auditory cortices. Results reveal a correlation of IGF and performance in the experimental but not in the control condition.
Abstract Oscillatory EEG activity in the human brain with frequencies in the gamma range (approx. 30–80 Hz) is known to be relevant for a large number of cognitive processes. Interestingly, each ...subject reveals an individual frequency of the auditory gamma-band response (GBR) that coincides with the peak in the auditory steady state response (ASSR). A common resonance frequency of auditory cortex seems to underlie both the individual frequency of the GBR and the peak of the ASSR. This review sheds light on the functional role of oscillatory gamma activity for auditory processing. For successful processing, the auditory system has to track changes in auditory input over time and store information about past events in memory which allows the construction of auditory objects. Recent findings support the idea of gamma oscillations being involved in the partitioning of auditory input into discrete samples to facilitate higher order processing. We review experiments that seem to suggest that inter-individual differences in the resonance frequency are behaviorally relevant for gap detection and speech processing. A possible application of these resonance frequencies for brain computer interfaces is illustrated with regard to optimized individual presentation rates for auditory input to correspond with endogenous oscillatory activity. This article is part of a Special Issue entitled SI: Auditory working memory. This article is part of a Special Issue entitled SI: Auditory working memory.
Humans are social beings and often have to perceive and perform within groups. In conflict situations, this puts them under pressure to either adhere to the group opinion or to risk controversy with ...the group. Psychological experiments have demonstrated that study participants adapt to erroneous group opinions in visual perception tasks, which they can easily solve correctly when performing on their own. Until this point, however, it is unclear whether this phenomenon of social conformity influences early stages of perception that might not even reach awareness or later stages of conscious decision-making. Using electroencephalography, this study has revealed that social conformity to the wrong group opinion resulted in a decrease of the posterior-lateral P1 in line with a decrease of the later centro-parietal P3. These results suggest that group pressure situations impact early unconscious visual perceptual processing, which results in a later diminished stimulus discrimination and an adaptation even to the wrong group opinion. These findings might have important implications for understanding social behavior in group settings and are discussed within the framework of social influence on eyewitness testimony.
This work deals with the ultra violet laser based fabrication of Bragg gratings in perfluorinated polymer optical fibers and their characterization. This kind of polymer fibers shows a higher ...transparency than typical polymer fibers based on polymers with carbon hydrogen bonds like polymethylmethacrylate, the most used material for polymer optical fibers to date. Up to now only gratings inscribed by the phase mask technique in thin slabs of the amorphous fluoropolymer CYTOP (cyclic transparent optical polymer) made from polymer fibers were successfully detected. Infrared spectra of Bragg gratings in a perfluorinated polymer fiber are presented for the first time here.
Frontal-midline (fm) theta oscillations as measured via the electroencephalogram (EEG) have been suggested as neural "working language" of executive functioning. Their power has been shown to ...increase when cognitive processing or task performance is enhanced. Thus, the question arises whether learning to increase fm-theta amplitudes would functionally impact the behavioral performance in tasks probing executive functions (EFs). Here, the effects of neurofeedback (NF), a learning method to self-up-regulate fm-theta over fm electrodes, on the four most representative EFs, memory updating, set shifting, conflict monitoring, and motor inhibition are presented. Before beginning and after completing an individualized, eight-session gap-spaced NF intervention, the three-back, letter/number task-switching, Stroop, and stop-signal tasks were tested while measuring the EEG. Self-determined up-regulation of fm-theta and its putative role for executive functioning were compared to an active control group, the so-called pseudo-neurofeedback group. Task-related fm-theta activity after training differed significantly between groups. More importantly, though, after NF significantly enhanced behavioral performance was observed. The training group showed higher accuracy scores in the three-back task and reduced mixing and shifting costs in letter/number task-switching. However, this specific protocol type did not affect performance in tasks probing conflict monitoring and motor inhibition. Thus, our results suggest a modulation of proactive but not reactive mechanisms of cognitive control. Furthermore, task-related EEG changes show a distinct pattern for fm-theta after training between the NF and the pseudo-neurofeedback group, which indicates that NF training indeed tackles EFs-networks. In sum, the modulation of fm-theta via NF may serve as potent treatment approach for executive dysfunctions.
A brief silent gap embedded in an otherwise continuous sound is missed by a human listener when it falls below a certain threshold: the gap detection threshold. This can be interpreted as an ...indicator that auditory perception is a non-continuous process, during which acoustic input is fragmented into a discrete chain of events. Current research provides evidence for a covariation between rhythmic properties of speech and ongoing rhythmic activity in the brain. Therefore, the discretization of acoustic input is thought to facilitate speech processing. Ongoing oscillations in the auditory cortex are suggested to represent a neuronal mechanism which implements the discretization process and leads to a limited auditory temporal resolution. Since gap detection thresholds seem to vary considerably between individuals, the present study addresses the question of whether individual differences in the frequency of underlying ongoing oscillatory mechanisms can be associated with auditory temporal resolution. To address this question we determined an individual gap detection threshold and a preferred oscillatory frequency for each participant. The preferred frequency of the auditory cortex was identified using an auditory steady state response (ASSR) paradigm: amplitude-modulated sounds with modulation frequencies in the gamma range were presented binaurally; the frequency which elicited the largest spectral amplitude was considered the preferred oscillatory frequency. Our results show that individuals with higher preferred auditory frequencies perform significantly better in the gap detection task. Moreover, this correlation between oscillation frequency and gap detection was supported by high test–retest reliabilities for gap detection thresholds as well as preferred frequencies.
•Human auditory perception is assumed to be a discrete process.•Discreteness is believed to be relevant for auditory temporal resolution.•Known auditory temporal resolution matches electrophysiological gamma frequencies.•We examine the relation of gamma frequency and auditory temporal resolution.•We found a negative correlation between gamma frequency and gap detection score.
Black manganese-rich crusts on a Gothic cathedral Macholdt, Dorothea S.; Herrmann, Siegfried; Jochum, Klaus Peter ...
Atmospheric environment (1994),
12/2017, Letnik:
171, Številka:
C
Journal Article
Recenzirano
Odprti dostop
Black manganese-rich crusts are found worldwide on the façades of historical buildings. In this study, they were studied exemplarily on the façade of the Freiburger Münster (Freiburg Minster), ...Germany, and measured in-situ by portable X-ray fluorescence (XRF). The XRF was calibrated to allow the conversion from apparent mass fractions to Mn surface density (Mn mass per area), to compensate for the fact that portable XRF mass fraction measurements from thin layers violate the assumption of a homogeneous measurement volume. Additionally, 200-nm femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS) measurements, scanning transmission X-ray microscopy-near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS), Raman spectroscopy, and imaging by light microscopy were conducted to obtain further insight into the crust material, such as potential biogenic contributions, element distributions, trace element compositions, and organic functional groups.
While black crusts of various types are present at many places on the minster's facade, crusts rich in Mn (with a Mn surface density >150 μg cm−2) are restricted to a maximum height of about 7 m. The only exceptions are those developed on the Renaissance-Vorhalle (Renaissance Portico) at a height of about 8 m. This part of the façade had been cleaned and treated with a silicon resin as recently as 2003. These crusts thus accumulated over a period of only 12 years. Yet, they are exceptionally Mn-rich with a surface density of 1200 μg cm−2, and therefore require an accumulation rate of about 100 μg cm−2 Mn per year.
Trace element analyses support the theory that vehicle emissions are responsible for most of the Mn supply. Lead, barium, and zinc correlate with manganese, indicating that tire material, brake pads, and resuspended road dust are likely to be the element sources. Microscopic investigations show no organisms on or in the Mn-rich crusts. In contrast, Mn-free black crusts sampled at greater heights (>8 m) exhibited fungal and cyanobacterial encrustation. Carbon-rich spots were found by STXM-NEXAFS underneath one of the Mn-rich crusts. However, these carbon occurrences originate from soot and polycyclic aromatic hydrocarbons (PAHs) deposited on top of the crust, rather than from organisms responsible for the crust's formation, as shown by STXM-NEXAFS and Raman spectroscopic measurements. Our results suggest that the crusts develop abiogenically, with vehicle emissions as dominant element sources.
•Mn-rich crusts are abiogenic, Mn-poor crusts are soot, cyanobacteria, and fungi.•Vehicle emissions are the sources of Mn, Ba, Zn, and Pb in the crusts.•A combination of dry and wet deposition allow the fast accumulation of manganese.•pH and Eh shifts allow the oxidation and precipitation of Mn oxyhydroxides.•Carbon associated with the Mn-rich crusts shows the signature of soot and PAHs.
For many applications, the production of large-scale lightweight parts using composite materials requires a curing stage at elevated temperatures with long cycles resulting from necessary heating and ...cooling steps. Here, an accelerated cooling stage after curing of the matrix can shorten process times and make it possible to demould the components in a hot state. In this paper, the impact of higher cooling rates on residual stresses and strains and the criticality for internal failures are investigated. A literature model using the pultrusion process including thick laminates and the interaction with a production tool was used for the implementation of a thermochemical calculation and an incremental linear-elastic mechanical model to calculate residual stresses induced during manufacturing stage. This way, the capability of flexible simulation environments for handling state of the art calculation schemes is investigated to allow the extension of the physics of those models. The model is implemented in both a representative environment for advanced structural analysis with highly customised element formulation such as Abaqus and a general-purpose FE package. Here, Comsol Multiphysics is used and extended by the calculation of the inter-fibre failure initiation. Using the proposed models applied to a plate geometry, stresses and strains induced in different cooling scenarios are investigated. The assumptions are validated by simulations including the whole curing process, by manufacturing trials on the coupon level and with mechanical tests.
Black manganese-rich crusts on a Gothic cathedral Macholdt, Dorothea S.; Herrmann, Siegfried; Jochum, Klaus Peter ...
Atmospheric environment (1994),
12/2017, Letnik:
171, Številka:
C
Journal Article
– Sample preparation, involving physical and chemical methods, is an unavoidable step in geochemical analysis. From a noble gas perspective, the two important effects are loss of sample gas and/or ...incorporation of air, which are significant sources of analytical artifacts. This article reports on the effects of sample exposure to laboratory air without mechanical influence and during sample grinding. The experiments include pure adsorption on terrestrial analog materials (gibbsite and olivine) and grinding of Martian meteorites. A consistent observation is the presence of an elementally fractionated air component in the samples studied. This is a critical form of terrestrial contamination in meteorites as it often mimics the heavy noble gas signatures of known extra‐terrestrial end‐members that are the basis of important conclusions about the origin and evolution of a meteorite. Although the effects of such contamination can be minimized by avoiding elaborate sample preparation protocols, caution should be exercised in interpreting the elemental ratios (Ar/Xe, Kr/Xe), especially in the low‐temperature step extractions. The experiments can also be transferred to the investigation of Martian meteorites with long terrestrial residence times, and to Mars, where the Mars Science Laboratory mission will be able to measure noble gas signatures in the current atmosphere and in rocks and soils collected on the surface in Gale crater.
PDF
