1,965 research outputs found
Thermally fluctuating superconductors in two dimensions
We describe the different regimes of finite temperature dynamics in the
vicinity of a zero temperature superconductor to insulator quantum phase
transition in two dimensions. New results are obtained for a low temperature
phase-only hydrodynamics, and for the intermediate temperature quantum-critical
region. In the latter case, we obtain a universal relationship between the
frequency-dependence of the conductivity and the value of the d.c. resistance.Comment: Presentation completely revised; 4 pages, 2 figure
Low temperature vortex liquid in
In the cuprates, the lightly-doped region is of major interest because
superconductivity, antiferromagnetism, and the pseudogap state
\cite{Timusk,Lee,Anderson} come together near a critical doping value .
These states are deeply influenced by phase fluctuations \cite{Emery} which
lead to a vortex-liquid state that surrounds the superconducting region
\cite{WangPRB01,WangPRB06}. However, many questions
\cite{Doniach,Fisher,FisherLee,Tesanovic,Sachdev} related to the nature of the
transition and vortex-liquid state at very low tempera- tures remain open
because the diamagnetic signal is difficult to resolve in this region. Here, we
report torque magnetometry results on (LSCO) which show
that superconductivity is lost at by quantum phase fluctuations. We find
that, in a magnetic field , the vortex solid-to-liquid transition occurs at
field much lower than the depairing field . The vortex liquid
exists in the large field interval , even in the limit 0.
The resulting phase diagram reveals the large fraction of the - plane
occupied by the quantum vortex liquid.Comment: 6 pages, 4 figures, submitted to Nature Physic
Single and two-particle energy gaps across the disorder-driven superconductor-insulator transition
The competition between superconductivity and localization raises profound
questions in condensed matter physics. In spite of decades of research, the
mechanism of the superconductor-insulator transition (SIT) and the nature of
the insulator are not understood. We use quantum Monte Carlo simulations that
treat, on an equal footing, inhomogeneous amplitude variations and phase
fluctuations, a major advance over previous theories. We gain new microscopic
insights and make testable predictions for local spectroscopic probes. The
energy gap in the density of states survives across the transition, but
coherence peaks exist only in the superconductor. A characteristic pseudogap
persists above the critical disorder and critical temperature, in contrast to
conventional theories. Surprisingly, the insulator has a two-particle gap scale
that vanishes at the SIT, despite a robust single-particle gap.Comment: 7 pages, 5 figures (plus supplement with 4 pages, 5 figures
Criticality in correlated quantum matter
At quantum critical points (QCP)
\cite{Pfeuty:1971,Young:1975,Hertz:1976,Chakravarty:1989,Millis:1993,Chubukov:1
994,Coleman:2005} there are quantum fluctuations on all length scales, from
microscopic to macroscopic lengths, which, remarkably, can be observed at
finite temperatures, the regime to which all experiments are necessarily
confined. A fundamental question is how high in temperature can the effects of
quantum criticality persist? That is, can physical observables be described in
terms of universal scaling functions originating from the QCPs? Here we answer
these questions by examining exact solutions of models of correlated systems
and find that the temperature can be surprisingly high. As a powerful
illustration of quantum criticality, we predict that the zero temperature
superfluid density, , and the transition temperature, , of
the cuprates are related by , where the exponent
is different at the two edges of the superconducting dome, signifying the
respective QCPs. This relationship can be tested in high quality crystals.Comment: Final accepted version not including minor stylistic correction
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State of the California current 2012-13: No such thing as an “average” year
This report reviews the state of the California Current System (CCS) between winter 2012 and spring 2013, and includes observations from Washington State to Baja California. During 2012, large-scale climate modes indicated the CCS remained in a cool, productive phase present since 2007. The upwelling season was delayed north of 42°N, but regions to the south, especially 33° to 36°N, experienced average to above average upwelling that persisted throughout the summer. Contrary to the indication of high production suggested by the climate indices, chlorophyll observed from surveys and remote sensing was below average along much of the coast. As well, some members of the forage assemblages along the coast experienced low abundances in 2012 surveys. Specifically, the concentrations of all lifestages observed directly or from egg densities of Pacific sardine, Sardinops sagax, and northern anchovy, Engraulis mordax, were less than previous years’ survey estimates. However, 2013 surveys and observations indicate an increase in abundance of northern anchovy. During winter 2011/2012, the increased presence of northern copepod species off northern California was consistent with stronger southward transport. Krill and small-fraction zooplankton abundances, where examined, were generally above average. North of 42°N, salps returned to typical abundances in 2012 after greater observed concentrations in 2010 and 2011. In contrast, salp abundance off central and southern California increased after a period of southward transport during winter 2011/2012. Reproductive success of piscivorous Brandt’s cormorant, Phalacrocorax penicillatus, was reduced while planktivorous Cassin’s auklet, Ptychoramphus aleuticus was elevated. Differences between the productivity of these two seabirds may be related to the available forage assemblage observed in the surveys. California sea lion pups from San Miguel Island were undernourished resulting in a pup mortality event perhaps in response to changes in forage availability. Limited biological data were available for spring 2013, but strong winter upwelling coastwide indicated an early spring transition, with the strong upwelling persisting into early summer
Dose-dense adjuvant chemotherapy for primary breast cancer
Adjuvant chemotherapy has been proven to reduce significantly the risk for relapse and death in women with operable breast cancer. Nevertheless, the prognosis for patients presenting with extensive axillary lymph node involvement remains suboptimal. In an attempt to improve on the efficacy of existing chemotherapy, a phase III intergroup trial led by the Cancer and Leukemia Group B (CALGB 97-41) was designed, which tested a mathematical model of tumor growth based on the Norton–Simon hypothesis. This hypothesis, developed about 3 decades ago, and the kinetic model derived from it, created the basis of the concepts of dose density and sequential therapy, both of which were tested in CALGB 97-41. This large prospective randomized trial demonstrated that shortening the time interval between each chemotherapy cycle while maintaining the same dose size resulted in significant improvements in disease-free and overall survival in patients with node-positive breast carcinoma. This finding is highly relevant and has immediate implications for clinical practice
Quantum critical behaviour in the superfluid density of strongly underdoped ultrathin cuprate films
A central issue in the physics of high temperature superconductors is to
understand superconductivity within a single copper-oxide layer or bilayer, the
fundamental structural unit in the cuprates, and how it is lost with
underdoping. As mobile holes are removed from the CuO_2 planes, the transition
temperature T_C and superfluid density n_S decrease in a surprisingly
correlated fashion in crystals and thick films. We seek to elucidate the
intrinsic physics of bilayers in the strongly underdoped regime, near the
critical doping level where superconductivity disappears. We report
measurements of n_S(T) in films of Y_{1-x}Ca_xBa_2Cu_3O_{7-\delta} as thin as
two copper-oxide bilayers with T_C's as low as 3 K. In addition to seeing the
two-dimensional (2D) Kosterlitz-Thouless-Berezinski transition at T_C, we
observe a remarkable scaling of T_C with n_S(0) that demonstrates that the
disappearance of superconductivity with underdoping is due to quantum
fluctuations near a T = 0 2D quantum critical point.Comment: 13 pages, 2 figur
A Dominant Language Constellations case-study on language use and the affective domain
Globalisation, international mobility, and new technologies make current multilingualism qualitatively different to not only mono- and bi-lingualism but also to any of its historical incarnations. As a new linguistic dispensation (Aronin & Singleton, 2008, 2012; Aronin, 2015), current multilingualism is understood to be complex, suffusive, liminal, and super-diverse; four essential properties which necessitate alternative foci in multilingual research. From this view, multilinguals are the ‘glue’ that binds cultures and societies, it is therefore essential to focus on their socioculturally-situated multilingual practices if we are to better understand the protagonists of this considerable social responsibility. In this regard, two concepts of profound interest are multilinguality (Aronin & Ó Laoire, 2004) and, its expression/realisation in concrete time-frames and socio-cultural contexts, dominant language constellations (DLC - Aronin, 2006; 2016). With this in mind, the current study examines the individual DLC of a Moroccan immigrant living in the Valencian Community in Spain. In line with earlier research calling for more varied self-report data (Todeva & Cenoz, 2009; Canagarajah & Wurr, 2011; Gorter & Cenoz, 2011), the study uses semi-structured interviews to investigate relationships between the DLC and the affective domain; specifically, attitudes, emotion, and identity. The resulting qualitative data explores the following questions: How does a multilingual speaker use their DLC to navigate specific sociolinguistic contexts? What influence does the DLC have on the expression of identity and emotions in concrete daily situations? What role does the DLC play in the formation of language attitudes? Moreover, these issues are framed within an acculturation context to articulate what Canagarajah and Wurr (2011) call ‘voices from the periphery’. While accepting that a case-study limits any attempt at generalisation, it is hoped that this research focus may contribute by providing another small piece to the overall puzzle of multilingual practices realised in concrete social and cultural contexts
Brief evidence-based interventions for universal child health services: a restricted evidence assessment of the literature
Background
Universal child health services (UCHS) provide an important pragmatic platform for the delivery of universal and targeted interventions to support families and optimize child health outcomes. We aimed to identify brief, evidence-based interventions for common health and developmental problems that could be potentially implemented in UCHS.
Methods
A restricted evidence assessment (REA) of electronic databases and grey literature was undertaken covering January 2006 to August 2019. Studies were eligible if (i) outcomes related to one or more of four areas: child social and emotional wellbeing (SEWB), infant sleep, home learning environment or parent mental health, (ii) a comparison group was used, (iii) universal or targeted intervention were delivered in non-tertiary settings, (iv) interventions did not last more than 4 sessions, and (v) children were aged between 2 weeks postpartum and 5 years at baseline.
Results
Seventeen studies met the eligibility criteria. Of these, three interventions could possibly be implemented at scale within UCHS platforms: (1) a universal child behavioural intervention which did not affect its primary outcome of infant sleep but improved parental mental health, (2) a universal screening programme which improved maternal mental health, and (3) a targeted child behavioural intervention which improved parent-reported infant sleep problems and parental mental health. Key lessons learnt include: (1) Interventions should impart the maximal amount of information within an initial session with future sessions reinforcing key messages, (2) Interventions should see the family as a holistic unit by considering the needs of parents with an emphasis on identification, triage and referral, and (3) Brief interventions may be more acceptable for stigmatized topics, but still entail considerable barriers that deter the most vulnerable.
Conclusions
Delivery and evaluation of brief evidence-based interventions from a UCHS could lead to improved maternal and child health outcomes through a more responsive and equitable service. We recommend three interventions that meet our criteria of “best bet” interventions
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