76 research outputs found
Quantum Phase Diagram of Bosons in Optical Lattices
We work out two different analytical methods for calculating the boundary of
the Mott-insulator-superfluid (MI-SF) quantum phase transition for scalar
bosons in cubic optical lattices of arbitrary dimension at zero temperature
which improve upon the seminal mean-field result. The first one is a
variational method, which is inspired by variational perturbation theory,
whereas the second one is based on the field-theoretic concept of effective
potential. Within both analytical approaches we achieve a considerable
improvement of the location of the MI-SF quantum phase transition for the first
Mott lobe in excellent agreement with recent numerical results from Quantum
Monte-Carlo simulations in two and three dimensions. Thus, our analytical
results for the whole quantum phase diagram can be regarded as being
essentially exact for all practical purposes
Effective Action Approach for Quantum Phase Transitions in Bosonic Lattices
Based on standard field-theoretic considerations, we develop an effective
action approach for investigating quantum phase transitions in lattice Bose
systems at arbitrary temperature. We begin by adding to the Hamiltonian of
interest a symmetry breaking source term. Using time-dependent perturbation
theory, we then expand the grand-canonical free energy as a double power series
in both the tunneling and the source term. From here, an order parameter field
is introduced in the standard way, and the underlying effective action is
derived via a Legendre transformation. Determining the Ginzburg-Landau
expansion to first order in the tunneling term, expressions for the Mott
insulator-superfluid phase boundary, condensate density, average particle
number, and compressibility are derived and analyzed in detail. Additionally,
excitation spectra in the ordered phase are found by considering both
longitudinal and transverse variations of the order parameter. Finally, these
results are applied to the concrete case of the Bose-Hubbard Hamiltonian on a
three dimensional cubic lattice, and compared with the corresponding results
from mean-field theory. Although both approaches yield the same Mott insulator
- superfluid phase boundary to first order in the tunneling, the predictions of
our effective action theory turn out to be superior to the mean-field results
deeper into the superfluid phase
Symmetry and topology in antiferromagnetic spintronics
Antiferromagnetic spintronics focuses on investigating and using
antiferromagnets as active elements in spintronics structures. Last decade
advances in relativistic spintronics led to the discovery of the staggered,
current-induced field in antiferromagnets. The corresponding N\'{e}el
spin-orbit torque allowed for efficient electrical switching of
antiferromagnetic moments and, in combination with electrical readout, for the
demonstration of experimental antiferromagnetic memory devices. In parallel,
the anomalous Hall effect was predicted and subsequently observed in
antiferromagnets. A new field of spintronics based on antiferromagnets has
emerged. We will focus here on the introduction into the most significant
discoveries which shaped the field together with a more recent spin-off
focusing on combining antiferromagnetic spintronics with topological effects,
such as antiferromagnetic topological semimetals and insulators, and the
interplay of antiferromagnetism, topology, and superconductivity in
heterostructures.Comment: Book chapte
An evaluation of the factors that affect the health-related quality of life of children following myelosuppressive chemotherapy
PurposeThe purposes of this study, in children who were assessed 1 week after the administration of myelosuppressive chemotherapy were: to compare the total and subscale scores on a generic measure of health-related quality of life (HRQOL) to normative data from healthy children and describe the relationships between demographic, clinical, and symptom characteristics of children with cancer and generic and disease-specific dimensions of HRQOL.MethodsPatients (n = 61) were predominantly male (52.5%), minority (63.9%), and 14.7 years of age. Children completed the Memorial Symptom Assessment Scale for 10- to 18-year olds, the PedsQL™ Generic and Cancer Modules, and the Karnofsky Performance Status (KPS) scale 1 week after the start of a chemotherapy cycle.ResultsThe mean number of symptoms per patient was 10.6. Compared with the normative sample, children with cancer reported significantly lower scores for the total scale and all of the subscales except emotional and social functioning. No significant differences were found between any demographic characteristics and total or subscale scores on the generic or disease-specific measures of HRQOL. Lower KPS scores were associated with poorer generic and disease-specific HRQOL scores. In addition, a higher number of symptoms was associated with poorer generic and disease-specific HRQOL scores. Finally, higher symptom distress scores were associated with poorer generic and disease-specific HRQOL scores.ConclusionAmong the demographic, clinical, and symptom characteristics studied, poorer functional status and higher symptom burden were associated with significant decreases in HRQOL in children who received myelosuppressive chemotherapy
Spectral sum rules and magneto-roton as emergent graviton in fractional quantum Hall effect
Holographic spontaneous parity breaking and emergent hall viscosity and angular momentum
Escala de avaliação de qualidade de vida: (AUQEI - Autoquestionnaire Qualité de Vie Enfant Imagé) validade e confiabilidade de uma escala para qualidade de vida em crianças de 4 a 12 anos
O impacto da saúde bucal na qualidade de vida de crianças infectadas pelo HIV: revisão de literatura
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