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Irradiating a ferromagnet with a femtosecond laser pulse is known to induce an ultrafast demagnetization within a few hundred femtoseconds. Here we demonstrate that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently. We optically excite a Au/Ni layered structure in which the 30 nm Au capping layer absorbs the incident laser pump pulse and subsequently use the X-ray magnetic circular dichroism technique to probe the femtosecond demagnetization of the adjacent 15 nm Ni layer. A demagnetization effect corresponding to the scenario in which the laser directly excites the Ni film is observed, but with a slight temporal delay. We explain this unexpected observation by means of the demagnetizing effect of a superdiffusive current of non-equilibrium, non-spin-polarized electrons generated in the Au layer.
Value creation in scene-based music production - the case of electronic club music in Germany
(2013)
The focus of this article is on the variability of value creation in the popular music industry. Recent trends in electronic music have been based on both the valorization of global tastes and of local specialities in performance and production. Depending on musical styles and market niches, local scenes have become important forces behind heterogeneous globalocal markets. At the same time, technological change and the virtualization of music production and distribution contribute to increasingly differentiated configurations of value creation. It is therefore necessary to reconstruct theoretically and empirically the new interplay among the local music production, digital media markets, and virtual communities that are involved. On the basis of empirical explorations in a German hot spot of electronic club-music production (the city of Berlin), the article indentifies local interaction practice and constellations of stakeholders. The findings show that value creation in these rapidly changing production scenes has moved away from the large-scale distribution of producer-induced media to audience-induced live performance and interactive soundtrack production. This change involves the rising importance of cultural embeddings such as taste building, reputation building among artists and producers, and local community building. Starting from an open theoretical problematization of value creation with regard to fluid scenes and shifting modes of production, the results of first empirical reconstructions are taken as inputs to an evolving discussion on the configurations of value creation in consumer-based strands of music production.
We assessed the automaticity of spatial-numerical and spatial-musical associations by testing their intentionality and load sensitivity in a dual-task paradigm. In separate sessions, 16 healthy adults performed magnitude and pitch comparisons on sung numbers with variable pitch. Stimuli and response alternatives were identical, but the relevant stimulus attribute (pitch or number) differed between tasks. Concomitant tasks required retention of either color or location information. Results show that spatial associations of both magnitude and pitch are load sensitive and that the spatial association for pitch is more powerful than that for magnitude. These findings argue against the automaticity of spatial mappings in either stimulus dimension.
Parafoveal semantic processing has recently been well documented in reading Chinese sentences, presumably because of language-specific features. However, because of a large variation of fixation landing positions on pretarget words, some preview words actually were located in foveal vision when readers' eyes landed close to the end of the pretarget words. None of the previous studies has completely ruled out a possibility that the semantic preview effects might mainly arise from these foveally processed preview words. This case, whether previously observed positive evidence for parafoveal semantic processing can still hold, has been called into question. Using linear mixed models, we demonstrate in this study that semantic preview benefit from word N+1 decreased if fixation on pretarget word N was close to the preview. We argue that parafoveal semantic processing is not a consequence of foveally processed preview words.
Objective: To compare lateralized cerebral activations elicited during self-initiated movement mirroring and observation of movements.
Subjects: A total of 15 right-handed healthy subjects, age range 22-56 years.
Methods: Functional imaging study comparing movement mirroring with movement observation, in both hands, in an otherwise identical setting. Imaging data were analysed using statistical parametric mapping software, with significance threshold set at p<0.01 (false discovery rate) and a minimum cluster size of 20 voxels.
Results: Movement mirroring induced additional activation in primary and higher-order visual areas strictly contralateral to the limb seen by the subject. There was no significant difference of brain activity when comparing movement observation of somebody else's right hand with left hand.
Conclusion: Lateralized cerebral activations are elicited by inversion of visual feedback (movement mirroring), but not by movement observation.
In many hydrological applications, ground-wave velocity measurements are increasingly used to map and monitor shallow soil water content. In this study, we propose an automated spectral velocity analysis method to determine the direct ground-wave (DGW) velocity from common midpoint (CMP) or multi-offset ground-penetrating radar (GPR) data. The method introduced in this paper is a variation of the well-known spectral velocity analysis for seismic and GPR reflection events where velocity spectra are computed using different coherency measures along hyperbolas following the normal moveout model. Here, the unnormalized cross-correlation is computed between waveforms across data gathers that are corrected with a linear moveout equation using a predefined range of velocities. Peaks in the resulting velocity spectra identify linear events in the GPR data gathers like DGW events and allow for estimating the corresponding velocities. In addition to obtaining a DGW velocity measurement, we propose a robust method to estimate the associated velocity uncertainties based on the width of the peak in the calculated velocity spectrum. Our proposed method is tested on synthetic data examples to evaluate the influence of subsurface velocity, surveying geometry and signal frequency on the accuracy of estimated ground-wave velocities. In addition, we investigate the influence of such velocity uncertainties on subsequent soil water content estimates using an established petrophysical relationship. Furthermore, we apply our approach to analyse field data, which were collected across a test site in Canada to monitor a wide range of seasonal soil moisture variations. A comparison between our spectral velocity estimates and results derived from manually picked ground-wave arrivals shows good agreement, which illustrates that our spectral velocity analysis is a feasible tool to analyse DGW arrivals in multi-offset GPR data gathers in an objective and more automated manner.
Beta diversity is a conceptual link between diversity at local and regional scales. Various additional methodologies of quantifying this and related phenomena have been applied. Among them, measures of pairwise (dis)similarity of sites are particularly popular. Undersampling, i.e. not recording all taxa present at a site, is a common situation in ecological data. Bias in many metrics related to beta diversity must be expected, but only few studies have explicitly investigated the properties of various measures under undersampling conditions. On the basis of an empirical data set, representing near-complete local inventories of the Lepidoptera from an isolated Pacific island, as well as simulated communities with varying properties, we mimicked different levels of undersampling. We used 14 different approaches to quantify beta diversity, among them dataset-wide multiplicative partitioning (i.e. true beta diversity') and pairwise site x site dissimilarities. We compared their values from incomplete samples to true results from the full data. We used these comparisons to quantify undersampling bias and we calculated correlations of the dissimilarity measures of undersampled data with complete data of sites. Almost all tested metrics showed bias and low correlations under moderate to severe undersampling conditions (as well as deteriorating precision, i.e. large chance effects on results). Measures that used only species incidence were very sensitive to undersampling, while abundance-based metrics with high dependency on the distribution of the most common taxa were particularly robust. Simulated data showed sensitivity of results to the abundance distribution, confirming that data sets of high evenness and/or the application of metrics that are strongly affected by rare species are particularly sensitive to undersampling. The class of beta measure to be used should depend on the research question being asked as different metrics can lead to quite different conclusions even without undersampling effects. For each class of metric, there is a trade-off between robustness to undersampling and sensitivity to rare species. In consequence, using incidence-based metrics carries a particular risk of false conclusions when undersampled data are involved. Developing bias corrections for such metrics would be desirable.
Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks.
In dynamic H-reflex measurements, the standardisation of the nerve stimulation to the gait cycle is crucial to avoid misinterpretation due to altered pre-synaptic inhibition. In this pilot study, a plantar pressure sole was used to trigger the stimulation of the tibialis nerve with respect to the gait cycle. Consequently, the intersession reliability of the soleus muscle H-reflex during treadmill walking was investigated.
Seven young participants performed walking trials on a treadmill at 5 km/h. The stimulating electrode was placed on the tibial nerve in the popliteal fossa. An EMG was recorded from the soleus muscle. To synchronize the stimulus to the gait cycle, initial heel strike was detected with a plantar pressure sole. Maximum H-reflex amplitude and M-wave amplitude were obtained and the Hmax/Mmax ratio was calculated.
Data reveals excellent reliability, ICC = 0.89. Test-retest variability was 13.0% (+/- 11.8). The Bland-Altman analysis showed a systematic error of 2.4%.
The plantar pressure sole was capable of triggering the stimulation of the tibialis nerve in a reliable way and offers a simple technique for the evaluation of reflex activity during walking.