Charmonium at high temperature in two-flavor QCD

We compute charmonium spectral functions in 2-flavor QCD on anisotropic lattices using the maximum entropy method. Our results suggest that the S-waves (J/psi and eta_c) survive up to temperatures close to 2Tc, while the P-waves (chi_c0 and chi_c1) melt away below 1.2Tc.Comment: 11 pages, 19 figures. v2: expanded discussion and modified conclusions. One figure changed. To appear in PR

Colossal proximity effect in a superconducting triplet spin valve based on halfmetallic ferromagnetic CrO2

Ferromagnets can sustain supercurrents through the formation of equal spin triplet Cooper pairs and the mechanism of odd-frequency pairing. Since such pairs are not broken by the exchange energy of the ferromagnet, superconducting triplet correlations are long-ranged and spin-polarized, with promises for superconducting spintronics devices. The main challenge is to understand how triplets are generated at the superconductor (S)/ ferromagnet (F) interface. Here we use the concept of a so-called triplet spin valve (TSV) to investigate the conversion of singlets in a conventional superconductor to triplets in the halfmetallic ferromagnet CrO_2. TSV's are composed of two ferromagnetic layers (separated by a thin normal metal (N) layer) and a superconductor (F_1/N/F_2/S). The package F_1/N/F_2 generates triplets in F_1 when the magnetization directions of the F_{1,2}-layers are not collinear. This drains singlet pairs from the S-layer, and triplet generation is therefore signalled by a decrease of the critical temperature $T_c$. Recently, experiments with TSV's were reported with Co draining layers, using in-plane fields, and finding T_c-shifts up to 100~mK. Using CrO_2 instead of Co and rotating a magnetic field from in-plane to out-of-plane, we find strong T_c variations of almost a Kelvin up to fields of the order of a Tesla. Such strong drainage is consistent with the large lengths over which supercurrents can flow in CrO_2, which are significantly larger than in conventional ferromagnets. Our results point to the special interest of halfmetals for superconducting spintronics.Comment: 6 pages, 5 figures; supplementary information separat

Mindfulness reduces reactivity to food cues: underlying mechanisms and applications in daily life

Purpose of Review: Mindfulness-based interventions are becoming increasingly popular as a means to facilitate healthy eating. We suggest that the decentering component of mindfulness, which is the metacognitive insight that all experiences are impermanent, plays an especially important role in such interventions. To facilitate the application of decentering, we address its psychological mechanism to reduce reactivity to food cues, proposing that it makes thoughts and simulations in response to food cues less compelling. We discuss supporting evidence, applications, and challenges for future research. Recent Findings: Experimental and correlational studies consistently find that the adoption of a decentering perspective reduces subjective cravings, physiological reactivity such as salivation, and unhealthy eating. Summary: We suggest that the decentering perspective can be adopted in any situation to reduce reactivity to food cues. Considering people’s high exposure to food temptations in daily life, this makes it a powerful tool to empower people to eat healthily

Nonequilibrium time evolution of the spectral function in quantum field theory

Transport or kinetic equations are often derived assuming a quasi-particle (on-shell) representation of the spectral function. We investigate this assumption using a three-loop approximation of the 2PI effective action in real time, without a gradient expansion or on-shell approximation. For a scalar field in 1+1 dimensions the nonlinear evolution, including the integration over memory kernels, can be solved numerically. We find that a spectral function approximately described by a nonzero width emerges dynamically. During the nonequilibrium time evolution the Wigner transformed spectral function is slowly varying, even in presence of strong qualitative changes in the effective particle distribution. These results may be used to make further analytical progress towards a quantum Boltzmann equation including off-shell effects and a nonzero width.Comment: 20 pages with 6 eps figures, explanation and references added; to appear in Phys.Rev.

Flux-flow induced giant magnetoresistance in all-amorphous superconductor-ferromagnet hybrids

We present magnetoresistance measurements on all-amorphous ferromagnet (F) / superconductor (S) heterostructures. The F/S/F trilayers show large magnetoresistance peaks in a small field range around the coercive field of the F layers, at temperatures within and below the superconducting transition. This is interpreted as flux flow of weakly pinned vortices induced by the stray field of Bloch magnetic domains in the F layers. Bilayers show much smaller effects, implying that the Bloch walls of the F-layers in the trilayer line up and focus the stray fields. The data are used to discuss the expected minimum F-layer thickness needed to nucleate vortices.Comment: 6 pages, 6 figure

On the Complexity of Local Search for Weighted Standard Set Problems

In this paper, we study the complexity of computing locally optimal solutions for weighted versions of standard set problems such as SetCover, SetPacking, and many more. For our investigation, we use the framework of PLS, as defined in Johnson et al., [JPY88]. We show that for most of these problems, computing a locally optimal solution is already PLS-complete for a simple neighborhood of size one. For the local search versions of weighted SetPacking and SetCover, we derive tight bounds for a simple neighborhood of size two. To the best of our knowledge, these are one of the very few PLS results about local search for weighted standard set problems

Performance optimization of large stroke flexure hinges for high stiffness and eigenfrequency

Two flexure hinge types are optimized for high support stiffness and high first unwanted eigenfrequency for two different working ranges, ±5.7° and ±20°. We show how multiple performance specifications lead to different designs with different performance. The optimization uses efficient parameterized non-linear beam-based models. The constraints and load case are taken from an electron microscopy use case. Optimization results show that the Three Flexure Cross Hinge has the highest first unwanted eigenfrequencies, while the new Infinity Flexure Hinge shows highest support stiffnesses. The design of the optimal geometry is detailed such that a prototype mechanism is manufactured and tested. Experiments show that the first unwanted eigenfrequency is 35 times higher than the first eigenfrequency throughout the working range

Planning is for doing: implementation intentions go beyond the mere creation of goal-directed associations

Studies on implementation intentions so far have mainly pointed towards strengthened cue-behavior associations as the mechanism underlying the effectiveness of this self-regulatory tool. However, we propose that because it triggers people to look into the future and to mentally simulate their future behavior, planning by means of implementation intentions might go beyond the creation of goal-directed associations and thus lead to more enduring effects on behavior. We tested this hypothesis in an experiment using a longitudinal design, where participants formed an intention for a behavior that deviates from their routine, and furnished it either with associative learning of cue and behavior, forming implementation intentions, or nothing at all. Results showed that initially, learning cue-behavior associations led to the same rate of goal completion as forming implementation intentions. However, only the effect of implementation intentions was maintained at the second measurement one week later. These findings suggest that planning does more than merely create goal-directed associations, which might offer a new perspective on the workings and use of this important tool for behavior change