634 research outputs found

    Perspective on Reversible to Irreversible Transitions in Periodic Driven Many Body Systems and Future Directions For Classical and Quantum Systems

    Full text link
    Reversible to irreversible (R-IR) transitions arise in numerous periodically driven collectively interacting systems that, after a certain number of driving cycles, organize into a reversible state where the particle trajectories repeat, or remain irreversible with chaotic motion. R-IR transitions were first systematically studied for periodically sheared dilute colloids, and appear in a wide variety of both soft and hard matter systems, including amorphous solids, crystals, vortices in type-II superconductors, and magnetic textures. In some cases, the reversible transition is an absorbing phase transition with a critical divergence in the organization time scale. R-IR systems can store multiple memories and exhibit return point memory. We give an overview of R-IR transitions including recent advances in the field, and discuss how the general framework of R-IR transitions could be applied to a much broader class of periodically driven nonequilibrium systems, including soft and hard condensed matter systems, astrophysics, biological systems, and social systems. Some likely candidate systems are commensurate-incommensurate states, systems exhibiting hysteresis or avalanches, and nonequilibrium pattern forming states. Periodic driving could be applied to hard condensed matter systems to see if R-IR transitions occur in metal-insulator transitions, semiconductors, electron glasses, electron nematics, cold atom systems, or Bose-Einstein condensates. R-IR transitions could also be examined in dynamical systems where synchronization or phase locking occurs. We discuss the use of complex periodic driving such as changing drive directions or multiple frequencies as a method to retain complex multiple memories. Finally, we describe features of classical and quantum time crystals that could suggest the occurrence of R-IR transitions in these systems.Comment: 25 pages, 27 figure

    Phase diagram of multiferroic KCu3_3As2_2O7_7(OD)3_3

    Full text link
    The layered compound KCu3_3As2_2O7_7(OD)3_3, comprising distorted kagome planes of S=1/2S=1/2 Cu2+^{2+} ions, is a recent addition to the family of type-II multiferroics. Previous zero field neutron diffraction work has found two helically ordered regimes in \kns, each showing a distinct coupling between the magnetic and ferroelectric order parameters. Here, we extend this work to magnetic fields up to 2020~T using neutron powder diffraction, capacitance, polarization, and high-field magnetization measurements, hence determining the H−TH-T phase diagram. We find metamagnetic transitions in both low temperatures phases around μ0Hc∼3.7\mu_0 H_c \sim 3.7~T, which neutron powder diffraction reveals to correspond to a rotation of the helix plane away from the easy plane, as well as a small change in the propagation vector. Furthermore, we show that the sign of the ferroelectric polarization is reversible in a magnetic field, although no change is observed (or expected on the basis of the magnetic structure) due to the transition at 3.73.7~T. We finally justify the temperature dependence of the polarization in both zero-field ordered phases by a symmetry analysis of the free energy expansion

    Recovery from severe mental health problems: a systematic review of service user and informal caregiver perspectives

    Get PDF
    Introduction: The recovery approach aims to have users' perspectives at the heart of service development and research; it is a holistic perspective that considers social needs, personal growth and inclusion. In the last decade recovery-oriented research and practice has increased greatly, however, a comprehensive model of recovery considering exclusively the perspectives of people with lived experience has not been devised. Aims: This review aimed to develop a framework and contextualize service users' and informal caregivers' understanding of recovery from severe mental health problems. Methods: We systematically searched 6 databases including key terms related to knowledge, experience and narratives AND mental health AND personal recovery. The search was supplemented with reference sourcing through gray literature, reference tracking and expert consultation. Data analysis consisted of a qualitative meta-synthesis using constant comparative methods. Results: Sixty-two studies were analyzed. A pattern emerged regarding the recovery paradigms that the studies used to frame their findings. The resulting recovery framework included the domains Social recovery; Prosperity (Legal, political, and economic recovery); Individual Recovery; and Clinical Recovery Experience (SPICE). Service users' definitions of recovery tended to prioritize social aspects, particularly being accepted and connecting with others, while caregivers focused instead on clinical definitions of recovery such as symptom remission. Both groups emphasized individual aspects such as becoming self-sufficient and achieving personal goals, which was strongly linked with having economic means for independence. Conclusions: The recovery model provided by this review offers a template for further research in the field and a guide for policy and practice. Predominant definitions of recovery currently reflect understandings of mental health which focus on an individual perspective, while this review found an important emphasis on socio-political aspects. At the same time, only a small number of studies took place in low-income countries, focused on minoritized populations, or included caregivers' perspectives. These are important gaps in the literature that require further attention. Systematic Review Registration: The review protocol was registered on PROSPERO (CRD42017076450); https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=76450

    Strong quantum fluctuation of vortices in the new superconductor MgB2MgB_2

    Full text link
    By using transport and magnetic measurement, the upper critical field Hc2(T)H_{c2}(T) and the irreversibility line Hirr(T)H_{irr}(T) has been determined. A big separation between Hc2(0)H_{c2}(0) and Hirr(0)H_{irr}(0) has been found showing the existence of a quantum vortex liquid state induced by quantum fluctuation of vortices in the new superconductor MgB2MgB_2. Further investigation on the magnetic relaxation shows that both the quantum tunneling and the thermally activated flux creep weakly depends on temperature. But when the melting field HirrH_{irr} is approached, a drastic rising of the relaxation rate is observed. This may imply that the melting of the vortex matter at a finite temperature is also induced by the quantum fluctuation of vortices.Comment: 4 pages, 4 figure

    Non-overlapping Distributed Tracking System Utilizing Particle Filter

    Get PDF
    Tracking people across multiple cameras is a challenging research area in visual computing, especially when these cameras have non-overlapping field of views. The important task is to associate a current subject with other prior appearances of the same subject across time and space in a camera network. Several known techniques rely on Bayesian approaches to perform the matching task. However, these approaches do not scale well when the dimension of the problem increases; e.g. when the number of subject or possible path increases. The aim of this paper is to propose a unified tracking framework using particle filters to efficiently switch between visual tracking (field of view tracking) and track prediction (non-overlapping region tracking). The particle filter tracking system utilizes a map (known environment) to assist the tracking process when targets leave the field of view of any camera. We implemented and tested this tracking approach in an in-house multiple cameras system as well as using on-line data. Promising results were obtained which suggested the feasibility of such an approach

    Nucleation of Stable Superconductivity in YBCO-Films

    Full text link
    By means of the linear dynamic conductivity, inductively measured on epitaxial films between 30mHz and 30 MHz, the transition line Tg(B)T_g (B) to generic superconductivity is studied in fields between B=0 and 19T. It follows closely the melting line Tm(B)T_m (B) described recently in terms of a blowout of thermal vortex loops in clean materials. The critical exponents of the correlation length and time near Tg(B)T_g (B), however, seem to be dominated by some intrinsic disorder. Columnar defects produced by heavy-ion irradiation up to field-equivalent-doses of Bϕ=10TB_{\phi} = 10T lead to a disappointing reduction of Tg(B→0)T_g (B \to 0) while for B>BϕB>B_{\phi} the generic line of the pristine film is recovered. These novel results are also discussed in terms of a loop-driven destruction of generic superconductivity.Comment: 11 pages including 7 EPS figures, accepted for publication in the Proceedings of the Spring Meeting of the German Physical Society, Muenster 1999,Festkoerperprobleme/Advances in Solid State Physics 199

    Cohort profile: the Nigerian HIV geriatric cohort study

    Get PDF
    Background: The Nigerian HIV Geriatric Cohort (NHGC) is a longitudinal cohort setup to learn how elderly people living with HIV (EPLHIV) in Nigeria fare, despite not being prioritized by the national treatment program, and to deepen knowledge for their differentiated care and achieve better outcomes. In this paper, we describe data collected on sociodemographic and clinical data from EPLHIV from the inception of Nigeria’s national HIV program to 2018. Methods: Patient-level data spanning the period 2004 to 2018, obtained from comprehensive HIV treatment hospitals, that are supported by four major PEPFAR-implementing partners in Nigeria were used. These 4 entities collaborated as member organizations of the Nigeria Implementation Science Alliance. We defined elderly as those aged 50 years and above. From deidentified treatment records, demographic and clinical data of EPLHIV ≥50-year-old at ART initiation during the review period was extracted, merged into a single REDcap® database, and described using STATA 13. Results: A total of 101,652 EPLHIV were analysed. Women accounted for 53,608 (53%), 51,037 (71%) of EPLHIV identified as married and 33,446 (51%) unemployed. Median age was 57.1 years (IQR 52–60 years) with a median duration on ART treatment of 4.1 years (IQR 1.7–7.1 years). ART profile showed that 97,586 (96%) were on 1st-line and 66,125 (65%) were on TDF-based regimens. Median body mass index (BMI) was 22.2 kg/m2 (IQR 19.5–25.4 kg/m2) with 43,012 (55%), 15,081 (19%) and 6803 (9%) showing normal (BMI 18.5 – 140 mmHg or diastolic-BP > 90 mmHg) was 16,201 (21%). EPLHIV median CD4 count was 381 cells/μL (IQR 212–577 cells/μL) and 26,687 (82%) had a viral load result showing < 1000copies/ml within one year of their last visit. As for outcomes at their last visit, 62,821 (62%) were on active-in-treatment, 28,463 (28%) were lost-to-follow-up, 6912 (7%) died and 2456 (3%) had stopped or transferred out. Poor population death records and aversion to autopsies makes it almost impossible to estimate AIDS-related deaths. Conclusions: This cohort describes the clinical and non-clinical profile of EPLHIV in Nigeria. We are following up the cohort to design and implement intervention programs, develop prognostic models to achieve better care outcomes for EPLHIV. This cohort would provide vital information for stakeholders in HIV prevention, care and treatment to understand the characteristics of EPLHIV

    Is there a vortex-glass transition in high-temperature superconductors?

    Full text link
    We show that DC voltage versus current measurements of a YBCO micro-bridge in a magnetic field can be collapsed onto scaling functions proposed by Fisher, Fisher, and Huse, as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.Comment: 4 pages, 4 figure

    Ultrametric spaces of branches on arborescent singularities

    Get PDF
    Let SS be a normal complex analytic surface singularity. We say that SS is arborescent if the dual graph of any resolution of it is a tree. Whenever A,BA,B are distinct branches on SS, we denote by A⋅BA \cdot B their intersection number in the sense of Mumford. If LL is a fixed branch, we define UL(A,B)=(L⋅A)(L⋅B)(A⋅B)−1U_L(A,B)= (L \cdot A)(L \cdot B)(A \cdot B)^{-1} when A≠BA \neq B and UL(A,A)=0U_L(A,A) =0 otherwise. We generalize a theorem of P{\l}oski concerning smooth germs of surfaces, by proving that whenever SS is arborescent, then ULU_L is an ultrametric on the set of branches of SS different from LL. We compute the maximum of ULU_L, which gives an analog of a theorem of Teissier. We show that ULU_L encodes topological information about the structure of the embedded resolutions of any finite set of branches. This generalizes a theorem of Favre and Jonsson concerning the case when both SS and LL are smooth. We generalize also from smooth germs to arbitrary arborescent ones their valuative interpretation of the dual trees of the resolutions of SS. Our proofs are based in an essential way on a determinantal identity of Eisenbud and Neumann.Comment: 37 pages, 16 figures. Compared to the first version on Arxiv, il has a new section 4.3, accompanied by 2 new figures. Several passages were clarified and the typos discovered in the meantime were correcte
    • …
    corecore