Regularly alternating spin-1/2 anisotropic XY chains: The ground-state and thermodynamic properties

Using the Jordan-Wigner transformation and continued fractions we calculate rigorously the thermodynamic quantities for the spin-1/2 transverse Ising chain with periodically varying intersite interactions and/or on-site fields. We consider in detail the properties of the chains having a period of the transverse field modulation equal to 3. The regularly alternating transverse Ising chain exhibits several quantum phase transition points, where the number of transition points for a given period of alternation strongly depends on the specific set of the Hamiltonian parameters. The critical behavior in most cases is the same as for the uniform chain. However, for certain sets of the Hamiltonian parameters the critical behavior may be changed and weak singularities in the ground-state quantities appear. Due to the regular alternation of the Hamiltonian parameters the transverse Ising chain may exhibit plateau-like steps in the zero-temperature dependence of the transverse magnetization vs. transverse field and many-peak temperature profiles of the specific heat. We compare the ground-state properties of regularly alternating transverse Ising and transverse XX chains and of regularly alternating quantum and classical chains. Making use of the corresponding unitary transformations we extend the elaborated approach to the study of thermodynamics of regularly alternating spin-1/2 anisotropic XY chains without field. We use the exact expression for the ground-state energy of such a chain of period 2 to discuss how the exchange interaction anisotropy destroys the spin-Peierls dimerized phase

Emergent Ising degrees of freedom in frustrated two-leg ladder and bilayer s=1/2s=1/2 Heisenberg antiferromagnets

Based on exact diagonalization data for finite quantum Heisenberg antiferromagnets on two frustrated lattices (two-leg ladder and bilayer) and analytical arguments we map low-energy degrees of freedom of the spin models in a magnetic field on classical lattice-gas models. Further we use transfer-matrix calculations and classical Monte Carlo simulations to give a quantitative description of low-temperature thermodynamics of the quantum spin models. The classical lattice-gas model yields an excellent description of the quantum spin models up to quite large temperatures. The main peculiarity of the considered frustrated bilayer is a phase transition which occurs at low temperatures for a wide range of magnetic fields below the saturation magnetic field and belongs to the two-dimensional Ising model universality class.Comment: 17 pages, 8 figure

Metrizability of Clifford topological semigroups

We prove that a topological Clifford semigroup $S$ is metrizable if and only if $S$ is an $M$-space and the set $E=\{e\in S:ee=e\}$ of idempotents of $S$ is a metrizable $G_\delta$-set in $S$. The same metrization criterion holds also for any countably compact Clifford topological semigroup $S$.Comment: 4 page

Serous Pigment Epithelium Detachment Associated with Age-Related Macular Degeneration: A Possible Treatment Approach

To evaluate the effects of intravitreal triamcinolone acetonide (TA) as a monotherapy of serous Pigment Epithelial Detachment (PED) associated with AMD (Age-Related Macular Degeneration), this study has been performed. Seventeen patients (19 eyes) with serous PED associated with AMD were observed. All patients received 0.1ml (4mg) of intravitreal TA. The mean follow-up period was 18 months. Re-attachment of serous PED was observed in 37% of cases to the end of follow-up. In other cases, the height and length of serous PED significantly decreased. Visual acuity remained stable in all cases. No evidence of RPE tear or CNV development were noted. Before TA administration, intraocular pressure (IOP) was 20.18 ± 2.58 mmHg however, after intravitreal TA, IOP increased gradually and reached its maximum of all period of observation (23.25±1.85mmHg) six months after injection (P=0.031). In 7 (37%) of the cases, progression to cataract was observed after treatment. After surgery, the visual acuity in all cases increased by 0.2 to 0.5. As a conclusion, intravitreal TA decreases of both the height and length of serous PED associated with AMD after 18 months follow-up in most cases. The presented data provides support for the hypothesis regarding the possibility of monotherapy of serous PED with intravitreal TA

Serous Pigment Epithelium Detachment Associated with Age-Related Macular Degeneration: A Possible Treatment Approach

oai:www.mehdijournal.com:article/50To evaluate the effects of intravitreal triamcinolone acetonide (TA) as a monotherapy of serous Pigment Epithelial Detachment (PED) associated with AMD (Age-Related Macular Degeneration), this study has been performed. Seventeen patients (19 eyes) with serous PED associated with AMD were observed. All patients received 0.1ml (4mg) of intravitreal TA. The mean follow-up period was 18 months. Re-attachment of serous PED was observed in 37% of cases to the end of follow-up. In other cases, the height and length of serous PED significantly decreased. Visual acuity remained stable in all cases. No evidence of RPE tear or CNV development were noted. Before TA administration, intraocular pressure (IOP) was 20.18 ± 2.58 mmHg however, after intravitreal TA, IOP increased gradually and reached its maximum of all period of observation (23.25±1.85mmHg) six months after injection (P=0.031). In 7 (37%) of the cases, progression to cataract was observed after treatment. After surgery, the visual acuity in all cases increased by 0.2 to 0.5. As a conclusion, intravitreal TA decreases of both the height and length of serous PED associated with AMD after 18 months follow-up in most cases. The presented data provides support for the hypothesis regarding the possibility of monotherapy of serous PED with intravitreal TA

Magnetolocalization in disordered quantum wires

The magnetic field dependent localization in a disordered quantum wire is considered nonperturbatively. An increase of an averaged localization length with the magnetic field is found, saturating at twice its value without magnetic field. The crossover behavior is shown to be governed both in the weak and strong localization regime by the magnetic diffusion length L_B. This function is derived analytically in closed form as a function of the ratio of the mean free path l, the wire thickness W, and the magnetic length l_B for a two-dimensional wire with specular boundary conditions, as well as for a parabolic wire. The applicability of the analytical formulas to resistance measurements in the strong localization regime is discussed. A comparison with recent experimental results on magnetolocalization is included.Comment: 22 pages, RevTe

The Hidden Curriculum of Veterinary Education: Mediators and Moderators of Its Effects

The “hidden curriculum” has long been supposed to have an effect on students' learning during their clinical education, and in particular in shaping their ideas of what it means to be a professional. Despite this, there has been little evidence linking specific changes in professional attitudes to the individual components of the hidden curriculum. This study aimed to recognize those components that led to a change in students' professional attitudes at a UK veterinary school, as well as to identify the attitudes most affected. Observations were made of 11 student groups across five clinical rotations, followed by semi-structured interviews with 23 students at the end of their rotation experience. Data were combined and analyzed thematically, taking both an inductive and deductive approach. Views about the importance of technical competence and communication skills were promoted as a result of students' interaction with the hidden curriculum, and tensions were revealed in relation to their attitudes toward compassion and empathy, autonomy and responsibility, and lifestyle ethic. The assessment processes of rotations and the clinical service organization served to communicate the messages of the hidden curriculum, bringing about changes in student professional attitudes, while student-selected role models and the student rotation groups moderated the effects of these influences

Level and Eigenfunction Statistics in Billiards with Surface Scattering

Statistical properties of billiards with diffusive boundary scattering are investigated by means of the supersymmetric sigma-model in a formulation appropriate for chaotic ballistic systems. We study level statistics, parametric level statistics, and properties of electron wavefunctions. In the universal regime, our results reproduce conclusions of the random matrix theory, while beyond this regime we obtain a variety of system-specific results determined by the classical dynamics in the billiard. Most notably, we find that level correlations do not vanish at arbitrary separation between energy levels, or if measured at arbitrarily large difference of magnetic fields. Saturation of the level number variance indicates strong rigidity of the spectrum. To study spatial correlations of wavefunction amplitudes, we reanalyze and refine derivation of the ballistic version of the sigma-model. This allows us to obtain a proper matching of universal short-scale correlations with system-specific ones.Comment: 19 pages, 5 figures included. Minor corrections, references adde

The nonlinear Schroedinger equation for the delta-comb potential: quasi-classical chaos and bifurcations of periodic stationary solutions

The nonlinear Schroedinger equation is studied for a periodic sequence of delta-potentials (a delta-comb) or narrow Gaussian potentials. For the delta-comb the time-independent nonlinear Schroedinger equation can be solved analytically in terms of Jacobi elliptic functions and thus provides useful insight into the features of nonlinear stationary states of periodic potentials. Phenomena well-known from classical chaos are found, such as a bifurcation of periodic stationary states and a transition to spatial chaos. The relation of new features of nonlinear Bloch bands, such as looped and period doubled bands, are analyzed in detail. An analytic expression for the critical nonlinearity for the emergence of looped bands is derived. The results for the delta-comb are generalized to a more realistic potential consisting of a periodic sequence of narrow Gaussian peaks and the dynamical stability of periodic solutions in a Gaussian comb is discussed.Comment: Enhanced and revised version, to appear in J. Nonlin. Math. Phy

Making connections: technological interventions to support students in using, and tutors in creating, assessment feedback

This paper explores the potential of technology to enhance the assessment and feedback process for both staff and students. The ‘Making Connections’ project aimed to better understand the connections that students make between the feedback that they receive and future assignments, and explored whether technology can help them in this activity. The project interviewed 10 tutors and 20 students, using a semi-structured approach. Data were analysed using a thematic approach, and the findings have identified a number of areas in which improvements could be made to the assessment and feedback process through the use of technology. The findings of the study cover each stage of the assessment process from the perspective of both staff and students. The findings are discussed in the context of current literature, and special attention is given to projects from the UK higher education sector intended to address the same issues. Keywords: feed-forward; assessment; practices; technology; technology-enhanced learnin