Ongerief bij gezelschapsdieren

Discomfort among companion animals (over 20 species, mammals, birds, reptiles, amfibians and fish included) is surveyed and prioritized, based on an expert view of animal scientists. Suggestions for diminishing discomfort are given

Symmetry breaking in the Hubbard model at weak coupling

The phase diagram of the Hubbard model is studied at weak coupling in two and three spatial dimensions. It is shown that the Neel temperature and the order parameter in d=3 are smaller than the Hartree-Fock predictions by a factor of q=0.2599. For d=2 we show that the self-consistent (sc) perturbation series bears no relevance to the behavior of the exact solution of the Hubbard model in the symmetry-broken phase. We also investigate an anisotropic model and show that the coupling between planes is essential for the validity of mean-field-type order parameters

Magnetic properties of the three-dimensional Hubbard model at half filling

We study the magnetic properties of the 3d Hubbard model at half-filling in the TPSC formalism, previously developed for the 2d model. We focus on the N\'eel transition approached from the disordered side and on the paramagnetic phase. We find a very good quantitative agreement with Dynamical Mean-Field results for the isotropic 3d model. Calculations on finite size lattices also provide satisfactory comparisons with Monte Carlo results up to the intermediate coupling regime. We point out a qualitative difference between the isotropic 3d case, and the 2d or anisotropic 3d cases for the double occupation factor. Even for this local correlation function, 2d or anisotropic 3d cases are out of reach of DMF: this comes from the inability of DMF to account for antiferromagnetic fluctuations, which are crucial.Comment: RevTex, 9 pages +10 figure

Magnetic and Dynamic Properties of the Hubbard Model in Infinite Dimensions

An essentially exact solution of the infinite dimensional Hubbard model is made possible by using a self-consistent mapping of the Hubbard model in this limit to an effective single impurity Anderson model. Solving the latter with quantum Monte Carlo procedures enables us to obtain exact results for the one and two-particle properties of the infinite dimensional Hubbard model. In particular we find antiferromagnetism and a pseudogap in the single-particle density of states for sufficiently large values of the intrasite Coulomb interaction at half filling. Both the antiferromagnetic phase and the insulating phase above the N\'eel temperature are found to be quickly suppressed on doping. The latter is replaced by a heavy electron metal with a quasiparticle mass strongly dependent on doping as soon as $n<1$. At half filling the antiferromagnetic phase boundary agrees surprisingly well in shape and order of magnitude with results for the three dimensional Hubbard model.Comment: 32 page

Effects of Boson Dispersion in Fermion-Boson Coupled Systems

We study the nonlinear feedback in a fermion-boson system using an extension of dynamical mean-field theory and the quantum Monte Carlo method. In the perturbative regimes (weak-coupling and atomic limits) the effective interaction among fermions increases as the width of the boson dispersion increases. In the strong coupling regime away from the anti-adiabatic limit, the effective interaction decreases as we increase the width of the boson dispersion. This behavior is closely related with complete softening of the boson field. We elucidate the parameters that control this nonperturbative region where fluctuations of the dispersive bosons enhance the delocalization of fermions.Comment: 14 pages RevTeX including 12 PS figure

One particle spectral weight of the three dimensional single band Hubbard model

Dynamic properties of the three-dimensional single-band Hubbard model are studied using Quantum Monte Carlo combined with the maximum entropy technique. At half-filling, there is a clear gap in the density of states and well-defined quasiparticle peaks at the top (bottom) of the lower (upper) Hubbard band. We find an antiferromagnetically induced weight above the naive Fermi momentum. Upon hole doping, the chemical potential moves to the top of the lower band where a robust peak is observed. Results are compared with spin-density-wave (SDW) mean-field and self consistent Born approximation results, and also with the infinite dimensional Hubbard model, and experimental photoemission (PES) for three dimensional transition-metal oxides.Comment: 11 pages, REVTeX, 16 figures included using psfig.sty. Ref.30 correcte

Effects of sleep deprivation on neural functioning: an integrative review

Sleep deprivation has a broad variety of effects on human performance and neural functioning that manifest themselves at different levels of description. On a macroscopic level, sleep deprivation mainly affects executive functions, especially in novel tasks. Macroscopic and mesoscopic effects of sleep deprivation on brain activity include reduced cortical responsiveness to incoming stimuli, reflecting reduced attention. On a microscopic level, sleep deprivation is associated with increased levels of adenosine, a neuromodulator that has a general inhibitory effect on neural activity. The inhibition of cholinergic nuclei appears particularly relevant, as the associated decrease in cortical acetylcholine seems to cause effects of sleep deprivation on macroscopic brain activity. In general, however, the relationships between the neural effects of sleep deprivation across observation scales are poorly understood and uncovering these relationships should be a primary target in future research

Ongerief bij gezelschapsdieren

Discomfort among companion animals (over 20 species, mammals, birds, reptiles, amfibians and fish included) is surveyed and prioritized, based on an expert view of animal scientists. Suggestions for diminishing discomfort are given

Classifying post-stroke shoulder pain: can the DN4 be helpful?

The etiology of post-stroke shoulder pain (PSSP) is largely unclear and may involve both nociceptive and neuropathic mechanisms. No gold standard is present for PSSP diagnosis. The neuropathic pain diagnostic questionnaire (DN4), was originally developed to identify neuropathic pain in the clinical context. In this study we used the DN4 to categorize PSSP patients and compared symptoms and signs suggestive of either nociceptive or neuropathic pain. Pain complaints and sensory functions were compared between patients with chronic PSSP scoring at least four (DN4+, n=9) or less than four (DN4-, n=10) on the DN4. Pain was assessed using a numeric rating scale and the McGill pain questionnaire. Sensory functions were assessed using clinical examination and quantitative sensory testing combined with a cold pressor test. Patients classified as DN4+ reported constant pain, higher pain intensity, a higher impact of pain on daily living, more frequent loss of cold sensation, reduced QST thresholds at the unaffected side and increased QST thresholds at the affected side. Notably, several symptoms and signs suggestive of either neuropathic or nociceptive pain corresponded to the subgroups DN4+ and DN4- respectively. However, since the pathophysiological mechanisms remain unclear and none of the sensory signs could be exclusively related to either DN4+ or DN4-, PSSP prognosis and treatment should not be solely based on the DN4. Nonetheless, a thorough assessment of neuropathic and nociceptive pain complaints and somatosensory functions should be included in the diagnostic work-up of PSSP