3,856 research outputs found
Iterated Binomial Sums and their Associated Iterated Integrals
We consider finite iterated generalized harmonic sums weighted by the
binomial in numerators and denominators. A large class of these
functions emerges in the calculation of massive Feynman diagrams with local
operator insertions starting at 3-loop order in the coupling constant and
extends the classes of the nested harmonic, generalized harmonic and cyclotomic
sums. The binomially weighted sums are associated by the Mellin transform to
iterated integrals over square-root valued alphabets. The values of the sums
for and the iterated integrals at lead to new
constants, extending the set of special numbers given by the multiple zeta
values, the cyclotomic zeta values and special constants which emerge in the
limit of generalized harmonic sums. We develop
algorithms to obtain the Mellin representations of these sums in a systematic
way. They are of importance for the derivation of the asymptotic expansion of
these sums and their analytic continuation to . The
associated convolution relations are derived for real parameters and can
therefore be used in a wider context, as e.g. for multi-scale processes. We
also derive algorithms to transform iterated integrals over root-valued
alphabets into binomial sums. Using generating functions we study a few aspects
of infinite (inverse) binomial sums.Comment: 62 pages Latex, 1 style fil
Room temperature high frequency transport of Dirac fermions in epitaxially grown Sb_2Te_3 based topological insulators
We report on the observation of photogalvanic effects in epitaxially grown
Sb_2Te_3 three-dimensional (3D) topological insulators (TI). We show that
asymmetric scattering of Dirac electrons driven back and forth by the terahertz
electric field results in a dc electric current. Due to the "symmetry
filtration" the dc current is generated in the surface electrons only and
provides an opto-electronic access to probe the electric transport in TI,
surface domains orientation and details of electron scattering even in 3D TI at
room temperature where conventional surface electron transport is usually
hindered by the high carrier density in the bulk
Zero-field thermopower of a thin heterostructure membrane with a 2D electron gas
We study the low-temperature thermopower of micron sized, free-standing
membranes containing a two-dimensional electron system. Suspended membranes of
320 nm thickness including a high electron mobility structure in Hall bar
geometry of 34 {\mu}m length are prepared from GaAs/AlGaAs heterostructures
grown by molecular beam epitaxy. Joule heating on the central region of the
membrane generates a thermal gradient with respect to the suspension points
where the membrane is attached to cold reservoirs. Temperature measurements on
the membrane reveal strong thermal gradients due to the low thermal
conductivity. We measure the zero-field thermopower and find that the
phonon-drag contribution is suppressed at low temperatures up to 7 K.Comment: 5 page
Building evidence into youth health policy: a case study of the Access 3 knowledge translation forum.
BACKGROUND: Effective integration of evidence and youth perspectives into policy is crucial for supporting the future health and well-being of young people. The aim of this project was to translate evidence from the Access 3 project to support development of a new state policy on youth health and well-being within New South Wales (NSW), Australia. Ensuring the active contribution of young people within policy development was a key objective of the knowledge translation (KT) process. METHODS: The KT activity consisted of a 1-day facilitated forum with 64 purposively sampled stakeholders. Participants included eight young people, 14 policy-makers, 15 academics, 22 clinicians or managers from NSW health services, four general practitioners and one mental health service worker. Research to be translated came from the synthesized findings of the NSW Access 3 project. The design of the forum included stakeholder presentations and group workshops, guided by the 2003 Lavis et al. KT framework that was improved by the Grimshaw et al. KT framework in 2012. Members of the Access 3 research team took on the role of knowledge brokers throughout the KT process. Participant satisfaction with the workshop was evaluated using a brief self-report survey. Policy uptake was determined through examination of the subsequent NSW Youth Health Framework 2017-2024. RESULTS: A total of 25 policy recommendations were established through the workshop, and these were grouped into six themes that broadly aligned with the synthesized findings from the Access 3 project. The six policy themes were (1) technology solutions, (2) integrated care and investment to build capacity, (3) adolescent health checks, (4) workforce, (5) youth participation and (6) youth health indicators. Forum members were asked to vote on the importance of individual recommendations. These policy recommendations were subsequently presented to the NSW Ministry of Health, with some evidence of policy uptake identified. The majority of participants rated the forum positively. CONCLUSIONS: The utilization of KT theories and active youth engagement led to the successful translation of research evidence and youth perspectives into NSW youth health policy. Future research should examine the implementation of policy arising from these KT efforts
Mesoscopic mean-field theory for spin-boson chains in quantum optical systems
We present a theoretical description of a system of many spins strongly coupled to a bosonic chain. We rely on the use of a spin-wave theory describing the Gaussian fluctuations around the mean-field solution, and focus on spin-boson chains arising as a generalization of the Dicke Hamiltonian. Our model is motivated by experimental setups such as trapped ions, or atoms/qubits coupled to cavity arrays. This situation corresponds to the cooperative (E⊗β) Jahn-Teller distortion studied in solid-state physics. However, the ability to tune the parameters of the model in quantum optical setups opens up a variety of novel intriguing situations. The main focus of this paper is to review the spin-wave theoretical description of this problem as well as to test the validity of mean-field theory. Our main result is that deviations from mean-field effects are determined by the interplay between magnetic order and mesoscopic cooperativity effects, being the latter strongly size-dependent
Evidence for a Two-stage Melting Transition of the Vortex Matter in Bi2Sr2Ca1Cu2O8+d Single Crystals obtained by Muon Spin Rotation
From muon spin rotation measurements on under- to overdoped Bi-2212 crystals
we obtain evidence for a two-stage transition of the vortex matter as a
function of temperature. The first transition is well known and related to the
irreversibility line (IL). The second one is located below the IL and has not
been previously observed. It occurs for all three sets of crystals and is
unrelated to the vortex mobility. Our data are consistent with a two-stage
melting scenario where the intra-planar melting of the vortex lattice and the
inter-planar decoupling of the vortex lines occur independently.Comment: 9 pages and 3 figure
Encoded Recoupling and Decoupling: An Alternative to Quantum Error Correcting Codes, Applied to Trapped Ion Quantum Computation
A recently developed theory for eliminating decoherence and design
constraints in quantum computers, ``encoded recoupling and decoupling'', is
shown to be fully compatible with a promising proposal for an architecture
enabling scalable ion-trap quantum computation [D. Kielpinski et al., Nature
417, 709 (2002)]. Logical qubits are encoded into pairs of ions. Logic gates
are implemented using the Sorensen-Molmer (SM) scheme applied to pairs of ions
at a time. The encoding offers continuous protection against collective
dephasing. Decoupling pulses, that are also implemented using the SM scheme
directly to the encoded qubits, are capable of further reducing various other
sources of qubit decoherence, such as due to differential dephasing and due to
decohered vibrational modes. The feasibility of using the relatively slow SM
pulses in a decoupling scheme quenching the latter source of decoherence
follows from the observed 1/f spectrum of the vibrational bath.Comment: 12 pages, no figure
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