Mechanisms of Fatigue in Everyday Life

The aim of this thesis was to find out which factors predict and increase fatigue in everyday life with the aim of shedding light on mechanisms relevant for the chronification of fatigue. We expected stress to (prospectively) predict fatigue. Also, we expected fatigue to (prospectively) predict stress because it diminishes subjective coping abilities. Further, we expected hypoactivity of the Hypothalamic Pituitary Adrenal (HPA) axis and hyperactivity of the Autonomic Nervous System (ANS) to be associated with fatigue, and the relationship between stress and fatigue to be mediated by these biological mechanisms. Moreover, sleep quality was expected to mediate the stress-fatigue relationship from one day to the next. Being in a close relationship and physical activity are investigated as important factors directly influencing fatigue, or influencing fatigue mediated by HPA axis and ANS activity. First, in light of the multitude of existing labels and definitions, we decided to review different attempts to define and classify chronic fatigue conditions and their differentiation from depression (Doerr & Nater, 2013). This review helps to grasp the concept of chronic medically unexplained fatigue and shed light on why difficulties with and conflicts regarding this symptom are present in society. In the first empirical study, we then investigated the influence of stress on fatigue and the mediating capability of HPA axis activity, ANS activity, as well as sleep quality in a student sample. As part of these analyses, we were also interested in whether the stress-fatigue relationship is reciprocal in nature (Doerr et al., 2015). In a second study, relationship-specific influences on fatigue were analyzed using a dyadic ambulatory assessment approach (Doerr, Nater, Spoerri, Ehlert, & Ditzen, ready to be submitted). In a third study, we investigated the association of HPA axis, ANS, and physical activity, with fatigue in a sample of female patients with fibromyalgia syndrome (FMS) (Doerr, Fischer, Nater, & Strahler, under review). The narrative review revealed that current definitions of syndromes that present with medically unexplained fatigue as the major symptom overlap and cannot be clearly differentiated. Nevertheless, each of their labels has a different underlying functionality, and one should be aware of this before applying them. As concluded in this review, research on the symptom of fatigue is warranted, and not necessarily comparisons between healthy subjects and persons suffering from fatigue syndromes (as they lack valid definitions). Summary of results from empirical studies: Stress and fatigue. Stress and fatigue co-varied within persons in the student sample and the FMS sample, but not in the sample of couples. Moreover, we found a prospective reciprocal association between stress and fatigue within days as well as between days in the student sample. Fatigue levels were also heightened in the student sample in the exam condition. HPA axis activity. Neither in the student sample nor in the sample of couples was there a momentary association between cortisol and fatigue. The CAR emerged as a negative predictor of mean daily fatigue in the FMS sample, but was not associated with fatigue levels in the student sample. Furthermore, momentary cortisol levels were positively associated with physical fatigue in the FMS sample. In the student sample, morning cortisol levels were heightened in the exam condition. ANS activity. ANS activity, as measured by sAA, only explained variance in momentary fatigue in the women of the couple sample (negative association). It was not associated with fatigue levels in any of the other studies. It was, however, altered (steeper slope) during exam preparation in the student sample. Sleep quality. Sleep quality was found to be a mediator between mean daily stress levels and mean daily fatigue levels in the student sample. Relationship-specific influences. Fatigue, stress, and HPA axis activity were co-regulated within couples. Furthermore, ANS activity co-varied with that of the partner in women. Positive interaction with the partner was associated with reduced fatigue levels. Physical activity. Objectively measured mean daily physical activity was positively associated with mean same-day stress level and negatively associated with mean next-day fatigue in the FMS sample. However, it was not associated with HPA axis or ANS activity. Studies are now needed that investigate the influence of stress and changes in HPA axis and ANS activity using longer time periods of investigation. The clinical implication that emerges most clearly from our studies is that stress management training can be seen as the most important approach for prevention and treatment of chronic fatigue

Rheology of human blood plasma: Viscoelastic versus Newtonian behavior

We investigate the rheological characteristics of human blood plasma in shear and elongational flows. While we can confirm a Newtonian behavior in shear flow within experimental resolution, we find a viscoelastic behavior of blood plasma in the pure extensional flow of a capillary break-up rheometer. The influence of the viscoelasticity of blood plasma on capillary blood flow is tested in a microfluidic device with a contraction-expansion geometry. Differential pressure measurements revealed that the plasma has a pronounced flow resistance compared to that of pure water. Supplementary measurements indicate that the viscoelasticity of the plasma might even lead to viscoelastic instabilities under certain conditions. Our findings show that the viscoelastic properties of plasma should not be ignored in future studies on blood flow.Comment: 4 figures, 1 supplementary material Highlighted in http://physics.aps.org/articles/v6/1

Strain-induced insulator state in La_0.7Sr_0.3CoO_3

We report on the observation of a strain-induced insulator state in ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to enhance the resistivity by several orders of magnitude. Reversible strain of 0.15% applied using a piezoelectric substrate triggers huge resistance modulations, including a change by a factor of 10 in the paramagnetic regime at 300 K. However, below the ferromagnetic ordering temperature, the magnetization data indicate weak dependence on strain for the spin state of the Co ions. We interpret the changes observed in the transport properties in terms of a strain-induced splitting of the Co e_g levels and reduced double exchange, combined with a percolation-type conduction in an electronic cluster state

Reversible strain effect on the magnetization of LaCoO3 films

The magnetization of ferromagnetic LaCoO3 films grown epitaxially on piezoelectric substrates has been found to systematically decrease with the reduction of tensile strain. The magnetization change induced by the reversible strain variation reveals an increase of the Co magnetic moment with tensile strain. The biaxial strain dependence of the Curie temperature is estimated to be below 4K/% in the as-grown tensile strain state of our films. This is in agreement with results from statically strained films on various substrates

Influence of strain on magnetization and magnetoelectric effect in La0.7A0.3MnO3 / PMN-PT(001) (A = Sr; Ca)

We investigate the influence of a well-defined reversible biaxial strain <=0.12 % on the magnetization (M) of epitaxial ferromagnetic manganite films. M has been recorded depending on temperature, strain and magnetic field in 20 - 50 nm thick films. This is accomplished by reversibly compressing the isotropic in-plane lattice parameter of the rhombohedral piezoelectric 0.72PMN-0.28PT (001) substrates by application of an electric field E <= 12 kV cm-1. The magnitude of the total variable in-plane strain has been derived. Strain-induced shifts of the ferromagnetic Curie temperature (Tc) of up to 19 K were found in La0.7Sr0.3MnO3 (LSMO) and La0.7Ca0.3MnO3 films and are quantitatively analysed for LSMO within a cubic model. The observed large magnetoelectric coupling coefficient alpha=mu0 dM/dE <= 6 10-8 s m-1 at ambient temperature results from the strain-induced M change in the magnetic-film-ferroelectric-substrate system. It corresponds to an enhancement of mu0 DeltaM <= 19 mT upon biaxial compression of 0.1 %. The extraordinary large alpha originates from the combination of three crucial properties: (i) the strong strain dependence of M in the ferromagnetic manganites, (ii) large piezo-strain of the PMN-PT substrates and (iii) effective elastic coupling at the film-substrate interface.Comment: 15 pages, 6 figures, 1 tabl

The 14C(n,g) cross section between 10 keV and 1 MeV

The neutron capture cross section of 14C is of relevance for several nucleosynthesis scenarios such as inhomogeneous Big Bang models, neutron induced CNO cycles, and neutrino driven wind models for the r process. The 14C(n,g) reaction is also important for the validation of the Coulomb dissociation method, where the (n,g) cross section can be indirectly obtained via the time-reversed process. So far, the example of 14C is the only case with neutrons where both, direct measurement and indirect Coulomb dissociation, have been applied. Unfortunately, the interpretation is obscured by discrepancies between several experiments and theory. Therefore, we report on new direct measurements of the 14C(n,g) reaction with neutron energies ranging from 20 to 800 keV

Music as a Service as an Alternative to Music Piracy? - An Empirical Investigation of the Intention to Use Music Streaming Services

Despite increasing acceptance of digital channels, total sales in the music business decreased by 31 % from 2004 to 2010. Music piracy is still considered one of the main causes for this. However, several studies found no effects or even positive effects of illegal downloading on record sales. In the past, piracy has been counteracted especially by prosecution and legal offers. Music as a Service (MaaS) represents a new, differing distribution approach in digital music. In contrast to the wellknown music platforms for so-called àla- carte downloads, such as the iTunes Store, MaaS possesses two important characteristics: transmission (streaming instead of downloading) and pricing model (flat rate instead of pay-perdownload). Therefore, the consumption of music by means of purchasing and downloading is replaced by a monthly payment service (paid MaaS) and an ad-supported (free MaaS) service. First user surveys suggest that many music pirates are making use of these offers. To find out if MaaS is an attractive distribution channel for music pirates, we developed a model to explain the intention to use MaaS based on the Theory of Planned Behavior. To empirically test this model, we surveyed 132 music pirates. Among others, the outcome shows that the intention to use free MaaS is mainly affected by the attitude towardsMaaS, while using paid MaaS is predominantly a result of the influence of users’ closest peers. The attitude towards MaaS is positively influenced by the desire to receive music recommendations, the payment type (in the form of a flat rate model), and the relative advantage of MaaS compared to illegal choices