Describing many-body localized systems in thermal environments

In this work we formulate an efficient method for the description of fully many-body localized systems in weak contact with thermal environments at temperature T. The key idea is to exploit the representation of the system in terms of quasi-local integrals of motion (l-bits) to efficiently derive the generator for the quantum master equation in Born-Markov approximation. We, moreover, show how to compute the steady state of this equation efficiently by using quantum-jump Monte-Carlo techniques as well as by deriving approximate kinetic equations of motion. As an example, we consider a one-dimensional disordered extended Hubbard model for spinless fermions, for which we derive the l-bit representation approximately by employing a recently proposed method valid in the limit of strong disorder and weak interactions. Coupling the system to a global thermal bath, we study the transport between two leads with different chemical potentials at both of its ends. We find that the temperature-dependent current is captured by an interaction-dependent version of Mott's law for variable range hopping, where transport is enhanced/lowered depending on whether the interactions are attractive or repulsive, respectively. We interpret these results in terms of spatio-energetic correlations between the l-bits

Insulation for cryogenic tanks has reduced thickness and weight

Dual seal insulation, consisting of an inner layer of sealed-cell Mylar honeycomb core and an outer helium purge channel of fiber glass reinforced phenolic honeycomb core, is used as a thin, lightweight insulation for external surfaces of cryogenic-propellant tanks

A novel application of queueing theory on the Caulerpenyne secreted by invasive Caulerpa taxifolia (Vahl) C.Agardh (Ulvophyceae, Caulerpales): a preliminary study

Aquarium originated marine green alga Caulerpa taxifolia was introduced into the Mediterranean Sea accidentally in 1984. This invasion has been negatively affecting the sub-littoral ecosystem of the Mediterranean. One of the important reasons for its success in the Mediterranean is its secondary toxic metabolite called caulerpenyne (CPN). Furthermore, CPN has anti-proliferative and apoptotic activities, therefore, CPN can be considered as a potential native source in cancer therapy. For that reason, modeling this metabolite might be of importance. Increase and decrease of the CPN level before reaching the critical level can be expressed by means of a queueing system in which the number of ‘customers' increases and decreases. In fact, production of CPN shows fluctuations for many environmental reasons, which allow us to apply queueing theory. In the present study, the expected time to reach the maximum caulerpenyne level was analyzed and evaluated using queueing theory

Institutional context: What elements shape how community occupational therapists think about their clients’ care?

Abstract : Clinical reasoning (CR) is the cognitive process that therapists use to plan, direct, perform and reflect on client care. Linked to intervention efficiency and quality, CR is a core competency that occurs within an institutional context (legal, regulatory, administrative and organisational elements). Because this context can shape how community therapists think about their clients’ care, its involvement in their CR could have a major impact on the interventions delivered. However, little is known about this involvement. Our study thus aimed to describe the elements of the institutional context involved in community therapists’ CR. From March 2012 to June 2014, we conducted an institutional ethnography (IE) inquiry in three Health and Social Services Centres in Québec (Canada). We observed participants and conducted semi-structured interviews with 10 occupational therapists. We also interviewed 12 secondary key informants (colleagues and managers) and collected administrative documents (n = 50). We analysed data using the IE process. Of the 13 elements of the institutional context identified, we found that four are almost constantly involved in participants’ CR. These four elements, that is, institutional procedures, organisation's basket of services, occupational therapists’ mandate and wait times for their services, restrictively shape CR. Specifically, occupational therapists restrict their representation of the client's situation and exploration of potential solutions to what is possible within the bounds of these four elements. In light of such restrictions on the way they think about their clients’ care, therapists should pay close attention to the elements of their own institutional context and how they are involved in their CR. Because of its potentially important impact on the future of professions (e.g. further restrictions on professionals’ role, reduced contribution to population health and well-being), this involvement of the institutional context in CR concerns all professionals, be they clinicians, educators, researchers or regulatory college officers

Mutational Analysis of the Quorum-Sensing Receptor LasR Reveals Interactions that Govern Activation and Inhibition by Nonlactone Ligands

SummaryGram-negative bacteria use N-acyl L-homoserine lactone (AHL) quorum-sensing (QS) signals to regulate the expression of myriad phenotypes. Non-native AHL analogs can strongly attenuate QS receptor activity and thereby QS signaling; however, we currently lack a molecular understanding of the mechanisms by which most of these compounds elicit their agonistic or antagonistic profiles. In this study, we investigated the origins of striking activity profile switches (i.e., receptor activator to inhibitor, and vice versa) observed upon alteration of the lactone head group in certain AHL analogs. Reporter gene assays of mutant versions of the Pseudomonas aeruginosa QS receptor LasR revealed that interactions between the ligands and Trp60, Tyr56, and Ser129 govern whether these ligands behave as LasR activators or inhibitors. Using this knowledge, we propose a model for the modulation of LasR by AHL analogs—encompassing a subtly different interaction with the binding pocket to a global change in LasR conformation

Arnol'd Tongues and Quantum Accelerator Modes

The stable periodic orbits of an area-preserving map on the 2-torus, which is formally a variant of the Standard Map, have been shown to explain the quantum accelerator modes that were discovered in experiments with laser-cooled atoms. We show that their parametric dependence exhibits Arnol'd-like tongues and perform a perturbative analysis of such structures. We thus explain the arithmetical organisation of the accelerator modes and discuss experimental implications thereof.Comment: 20 pages, 6 encapsulated postscript figure