From density-matrix renormalization group to matrix product states

In this paper we give an introduction to the numerical density matrix renormalization group (DMRG) algorithm, from the perspective of the more general matrix product state (MPS) formulation. We cover in detail the differences between the original DMRG formulation and the MPS approach, demonstrating the additional flexibility that arises from constructing both the wavefunction and the Hamiltonian in MPS form. We also show how to make use of global symmetries, for both the Abelian and non-Abelian cases.Comment: Numerous small changes and clarifications, added a figur

Effects of appetitive and aversive motivational states on wanting and liking of interpersonal touch

Social rewards represent a strong driving force behind decisions and behaviors. Previous research suggests that the processing of a reward depends on the initial state of the individual. However, empirical research in humans on the influence of motivational states on reward processing is scant, especially for rewards of social nature. In the present study, we aimed at investigating how aversive and appetitive motivation affects the processing of social rewards, such as interpersonal touch. Participants (n = 102) were assigned to an appetitive (positive) or aversive (negative) motivational state condition (via modified versions of the Trier Social Stress Test) or to a control condition. After the state induction, their a) self-reports of wanting and liking, b) effort, and c) hedonic facial reactions during anticipation and consumption of interpersonal touch, were measured. Participants in the aversive group showed higher subjective wanting of interpersonal touch, but no changes in subjective liking, compared to the control group. The aversive group also showed stronger positive hedonic facial reactions during reward anticipation, reflecting stronger anticipatory pleasure. No significant effects were found for the appetitive group. The results indicate that, after having been exposed to an aversive experience, the motivation to obtain interpersonal touch, as well as the associated anticipatory pleasure, increase, without a corresponding change in liking during or after its consumption. The findings point to differential state-dependent effects on the processing of social rewards, possibly due to the action of different neurobiological systems regulating reward anticipation and consumption

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

We present recent highlights from the most recent operation phases of Wendelstein 7-X, the most advanced stellarator in the world. Stable detachment with good particle exhaust, low impurity content, and energy confinement times exceeding 100 ms, have been maintained for tens of seconds. Pellet fueling allows for plasma phases with reduced ion-temperature-gradient turbulence, and during such phases, the overall confinement is so good (energy confinement times often exceeding 200 ms) that the attained density and temperature profiles would not have been possible in less optimized devices, since they would have had neoclassical transport losses exceeding the heating applied in W7-X. This provides proof that the reduction of neoclassical transport through magnetic field optimization is successful. W7-X plasmas generally show good impurity screening and high plasma purity, but there is evidence of longer impurity confinement times during turbulence-suppressed phases.EC/H2020/633053/EU/Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium/ EUROfusio

Reflection Labs: A Space for Researcher Reflexivity in Participatory Collaborations

This paper introduces reflection labs as a tool for researcher reflexivity in participatory collaborations. Participatory methodologies intend to achieve equal partnerships, co-production of knowledge and empowerment processes. In this agenda, reflexivity is key, not only for analytical reasons but also to address power inequalities, challenges in the partnerships and other ethical questions. In this paper, we describe the methodological underpinnings and empirical use of a tool we call a ‘reflection lab’. In a 3-year participatory study with refugees (EMPOW), funded by the German Research Foundation, various online and offline spaces were created for reflexivity among community and academic partners. Reflection labs were developed for the academic partners. The term ‘lab’ points to the somewhat experimental nature of this space. Combining different approaches to reflexivity in creative ways, reflection labs offer a space to explore researcher subjectivities. Using field notes, minutes and analytical notes (‘memos’) as a starting point, in-depth discussions foster critical self-reflexivity and provide peer feedback and support about academic researchers’ roles in participatory collaborations. The paper includes an example of a reflection lab that was organized virtually for more than 2 years due to Corona restrictions. By combining aspects of ‘strong reflexivity’ (analyzing researcher subjectivities for epistemic purposes) and ‘ethical reflexivity’ (addressing power inequalities and socio-political implications) reflection labs provide an innovative tool for an engaged, analytical research practice that pursues participatory goals and strives for ethical conduct and accountability