Enhanced heat flow in the hydrodynamic-collisionless regime

We study the heat conduction of a cold, thermal cloud in a highly asymmetric trap. The cloud is axially hydrodynamic, but due to the asymmetric trap radially collisionless. By locally heating the cloud we excite a thermal dipole mode and measure its oscillation frequency and damping rate. We find an unexpectedly large heat conduction compared to the homogeneous case. The enhanced heat conduction in this regime is partially caused by atoms with a high angular momentum spiraling in trajectories around the core of the cloud. Since atoms in these trajectories are almost collisionless they strongly contribute to the heat transfer. We observe a second, oscillating hydrodynamic mode, which we identify as a standing wave sound mode.Comment: Sumitted to Phys. Rev. Letters, 4 pages, 4 figure

Designs of magnetic atom-trap lattices for quantum simulation experiments

We have designed and realized magnetic trapping geometries for ultracold atoms based on permanent magnetic films. Magnetic chip based experiments give a high level of control over trap barriers and geometric boundaries in a compact experimental setup. These structures can be used to study quantum spin physics in a wide range of energies and length scales. By introducing defects into a triangular lattice, kagome and hexagonal lattice structures can be created. Rectangular lattices and (quasi-)one-dimensional structures such as ladders and diamond chain trapping potentials have also been created. Quantum spin models can be studied in all these geometries with Rydberg atoms, which allow for controlled interactions over several micrometers. We also present some nonperiodic geometries where the length scales of the traps are varied over a wide range. These tapered structures offer another way to transport large numbers of atoms adiabatically into subwavelength traps and back.Comment: 9 pages, 10 figure

Non-exponential one-body loss in a Bose-Einstein condensate

We have studied the decay of a Bose-Einstein condensate of metastable helium atoms in an optical dipole trap. In the regime where two- and three-body losses can be neglected we show that the Bose-Einstein condensate and the thermal cloud show fundamentally different decay characteristics. The total number of atoms decays exponentially with time constant tau; however, the thermal cloud decays exponentially with time constant (4/3)tau and the condensate decays much faster, and non-exponentially. We show that this behaviour, which should be present for all BECs in thermal equilibrium with a considerable thermal fraction, is due to a transfer of atoms from the condensate to the thermal cloud during its decay.Comment: The intuitive explanation of the atomic transfer effect has been correcte

Lost in the chaos: Flawed literature should not generate new disorders

The paper by Kuss, Griffiths, and Pontes (2016) titled “Chaos and confusion in DSM-5 diagnosis of Internet Gaming Disorder: Issues, concerns, and recommendations for clarity in the field” examines issues relating to the concept of Internet Gaming Disorder. We agree that there are serious issues and extend their arguments by suggesting that the field lacks basic theory, definitions, patient research, and properly validated and standardized assessment tools. As most studies derive data from survey research in functional populations, they exclude people with severe functional impairment and provide only limited information on the hypothesized disorder. Yet findings from such studies are widely used and often exaggerated, leading many to believe that we know more about the problem behavior than we do. We further argue that video game play is associated with several benefits and that formalizing this popular hobby as a psychiatric disorder is not without risks. It might undermine children’s right to play or encourage repressive treatment programs, which ultimately threaten children’s right to protection against violence. While Kuss et al. (2016) express support for the formal implementation of a disorder, we argue that before we have a proper evidence base, a sound theory, and validated assessment tools, it is irresponsible to support a formal category of disorder and doing so would solidify a confirmatory approach to research in this area

Space Saving by Dynamic Algebraization

Dynamic programming is widely used for exact computations based on tree decompositions of graphs. However, the space complexity is usually exponential in the treewidth. We study the problem of designing efficient dynamic programming algorithm based on tree decompositions in polynomial space. We show how to construct a tree decomposition and extend the algebraic techniques of Lokshtanov and Nederlof such that the dynamic programming algorithm runs in time $O^*(2^h)$, where $h$ is the maximum number of vertices in the union of bags on the root to leaf paths on a given tree decomposition, which is a parameter closely related to the tree-depth of a graph. We apply our algorithm to the problem of counting perfect matchings on grids and show that it outperforms other polynomial-space solutions. We also apply the algorithm to other set covering and partitioning problems.Comment: 14 pages, 1 figur

Youth care in time of COVID-19: Experiences of professionals and adolescent clients with telehealth

Measures aimed at preventing the COVID-19 virus from spreading restricted all aspects of public life, including possibilities for meeting in-person. Youth care professionals were forced to turn to telehealth tools, such as video calling and e-health methods, to be able to continue support and treatment of children, adolescents, caregivers, and families. This study consists of two qualitative interview studies on the experiences with and transition to telehealth during COVID-19: (1) interviews with youth care professionals (N = 20), and (2) interviews with adolescents who used mental health care support (N = 14). We specifically asked participants about five themes which were selected based on pre-COVID literature on telehealth: (1) tools (i.e., which programs are being used), (2) privacy, (3) methods (i.e., what was the same and what was different compared to in-person sessions), (4) relationship/therapeutic alliance, and (5) effectiveness (i.e., what was their impression of effectiveness of telehealth). The majority of professionals reported that they had very little to no experience with telehealth prior to the pandemic. Both professionals and adolescent clients mentioned benefits and limitations of telehealth. On several themes professionals and adolescent clients mentioned similar barriers in the transition to telehealth during COVID such as limitations of the available hard- and software (theme 1: tools); forced changes in the content and methods of the sessions (theme 3: methods); and difficulties with non-verbal communication (theme 4: alliance). However, whereas most professionals expressed the intention to keep using several aspects of telehealth after restrictions due to COVID are lifted, most adolescent clients expressed they see telehealth as a temporary solution and prefer meeting professionals in person. Their experiences and the barriers and enabling aspects they mentioned may provide important insights in the acceptability and usability of telehealth for youth care organizations, youth care professionals, researchers and higher educational training programs