1,648 research outputs found
Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields
The behavior of the nonlinear susceptibility and its relation to the
spin-glass transition temperature , in the presence of random fields, are
investigated. To accomplish this task, the Sherrington-Kirkpatrick model is
studied through the replica formalism, within a one-step
replica-symmetry-breaking procedure. In addition, the dependence of the
Almeida-Thouless eigenvalue (replicon) on the random fields
is analyzed. Particularly, in absence of random fields, the temperature
can be traced by a divergence in the spin-glass susceptibility ,
which presents a term inversely proportional to the replicon . As a result of a relation between and , the
latter also presents a divergence at , which comes as a direct consequence
of at . However, our results show that, in the
presence of random fields, presents a rounded maximum at a temperature
, which does not coincide with the spin-glass transition temperature
(i.e., for a given applied random field). Thus, the maximum
value of at reflects the effects of the random fields in the
paramagnetic phase, instead of the non-trivial ergodicity breaking associated
with the spin-glass phase transition. It is also shown that still
maintains a dependence on the replicon , although in a more
complicated way, as compared with the case without random fields. These results
are discussed in view of recent observations in the LiHoYF
compound.Comment: accepted for publication in PR
Quantum Critical Point in the Spin Glass-Kondo Transition in Heavy Fermion Systems
The Kondo-Spin Glass competition is studied in a theoretical model of a Kondo
lattice with an intra-site Kondo type exchange interaction treated within the
mean field approximation, an inter-site quantum Ising exchange interaction with
random couplings among localized spins and an additional transverse field in
the x direction, which represents a simple quantum mechanism of spin flipping.
We obtain two second order transition lines from the spin-glass state to the
paramagnetic one and then to the Kondo state. For a reasonable set of the
different parameters, the two second order transition lines do not intersect
and end in two distinct QCP.Comment: 20 pages; 1 figure; to appear in Physical Review
Foster families: A systematic review of intention and retention factors
Background: Compared to residential care, family foster care is the preferable type of alternative care for neglected or abused children as it provides a familiar context that supports children’s developmental needs. New foster families are needed to care for these children. Objective: This systematic review aims to provide a critical analysis of the literature, identifying factors that explain the intention to become and to continue as a foster family. This review was performed following the PRISMA checklist and guidelines, through a search conducted in the following databases (no restrictions were made): PsycArticles, PsycInfo, Psychology and Behavioral Sciences Collection, Academic Search Complete, ERIC, Scopus, and Web of Science. Study eligibility: The review includes empirical quantitative and/or qualitative studies in English, Portuguese, and Spanish, with community and/or foster parents’ samples and explores the factors for becoming and/or retention of foster parents. Results: Forty-nine studies were included. The results revealed that the intention to become a foster parent is largely influenced by motivational factors, personal and family characteristics, individual values and beliefs, social context influences, and perceived familiarity with the child protection system. The retention of foster families is closely related to factors within the child protection system, personal or family characteristics, foster child characteristics, and placement challenges. The relationship with agencies and professional support stands out as the most important factors. Limitations and Implications: This review did not include studies focused on children with specific needs and characteristics, and future research should consider the particular challenges of fostering this group. Practice implications of these findings for the recruitment, selection, and retention of foster families will be discussed.info:eu-repo/semantics/acceptedVersio
Photoassociative ionization of Na inside a storage ring
Motivated by recent interest in low dimensional arrays of atoms, we
experimentally investigated the way cold collisional processes are affected by
the geometry of the considered atomic sample. More specifically, we studied the
case of photoassociative ionization (PAI) both in a storage ring where
collision is more unidirectional in character and in a trap with clear
undefinition of collision axis. First, creating a ring shaped trap (atomotron)
we investigated two-color PAI dependence with intensity and polarization of a
probing laser. The intensity dependence of the PAI rate was also measured in a
magneto-optical trap presenting equivalent temperature and density conditions.
Indeed, the results show that in the ring trap, the value of the PAI rate
constant is much lower and does not show evidences of saturation, unlike in the
case of the 3D-MOT. Cold atomic collisions in storage ring may represent new
possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio
Applying semantic web technologies to knowledge sharing in aerospace engineering
This paper details an integrated methodology to optimise Knowledge reuse and sharing, illustrated with a use case in the aeronautics domain. It uses Ontologies as a central modelling strategy for the Capture of Knowledge from legacy docu-ments via automated means, or directly in systems interfacing with Knowledge workers, via user-defined, web-based forms. The domain ontologies used for Knowledge Capture also guide the retrieval of the Knowledge extracted from the data using a Semantic Search System that provides support for multiple modalities during search. This approach has been applied and evaluated successfully within the aerospace domain, and is currently being extended for use in other domains on an increasingly large scale
Functionalizing self-assembled GaN quantum dot superlattices by Eu-implantation
Self-assembled GaN quantum dots (QDs) stacked in superlattices (SL) with AlN spacer layers were implanted with Europium ions to fluences of 1013, 1014, and 1015 cm−2. The damage level introduced in the QDs by the implantation stays well below that of thick GaN epilayers. For the lowest fluence, the structural properties remain unchanged after implantation and annealing while for higher fluences the implantation damage causes an expansion of the SL in the [0001] direction which increases with implantation fluence and is only partly reversed after thermal annealing at 1000 °C. Nevertheless, in all cases, the SL quality remains very good after implantation and annealing with Eu ions incorporated preferentially into near-substitutional cation sites. Eu3+ optical activation is achieved after annealing in all samples. In the sample implanted with the lowest fluence, the Eu3+ emission arises mainly from Eu incorporated inside the QDs while for the higher fluences only the emission from Eu inside the AlN-buffer, capping, and spacer layers is observed.
© 2010 American Institute of PhysicsFCT-PTDC/CTM/100756/2008program PESSOA EGIDE/GRICESFCT-SFRH/BD/45774/2008FCT-SFRH/BD/44635/200
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