140 research outputs found
Electric field control of a quantum spin liquid in weak Mott insulators
The triangular lattice Hubbard model at strong coupling, whose effective spin
model contains both Heisenberg and ring exchange interactions, exhibits a rich
phase diagram as the ratio of the hopping to onsite Coulomb repulsion
is tuned. This includes a chiral spin liquid (CSL) phase. Nevertheless, this
exotic phase remains challenging to realize experimentally because a given
material has a fixed value of that can difficultly be tuned with external
stimuli. One approach to address this problem is applying a DC electric field,
which renormalizes the exchange interactions as electrons undergo virtual
hopping processes; in addition to creating virtual doubly occupied sites,
electrons must overcome electric potential energy differences. Performing a
small expansion to fourth order, we derive the ring exchange model in the
presence of an electric field and find that it not only introduces spatial
anisotropy but also tends to enhance the ring exchange term compared to the
dominant nearest-neighbor Heisenberg interaction. Thus, increasing the electric
field serves as a way to increase the importance of the ring exchange at
constant . Through density matrix renormalization group calculations, we
compute the ground state phase diagram of the ring exchange model for two
different electric field directions. In both cases, we find that the electric
field shifts the phase boundary of the CSL towards a smaller ratio of .
Therefore, the electric field can drive a magnetically ordered state into the
CSL. This explicit demonstration opens the door to tuning other quantum spin
systems into spin liquid phases via the application of an electric field.Comment: 9 + 17 pages, 10 + 13 figure
Genetically modified mice- Methods, applications and outlook
Background & Aim: Transgenic mice, of tengenerated by random integration of foreign
genes into the mouse genome or by targeted mutation in a particular gene, have demonstrated
to be a very effective tool for studying gene function in living things. In this review article, we
discussed on the current methods of generating genetically-modified mice and their related
problems and then investigated the new methods developed to overcome these problems.
Finally, we discussed future prospects on the gene targeting.
Methods & Materials: This is a review article, which has been written after searching
Pubmed, Scopus, Google Scholar, Springer, Elsevier and Magiran databases by using
keywords of transgenic mice, functional genetics, genetargeting, and homologous
recombination.
Results: This study dealt with genetic variations in a wide range, differential processing and
inactivation of gene-specific isoforms, local and induced genetic changes, Cre/loxP system
and some future perspectives.
Conclusion: Success rate in genetic modification of mouse genome has increased
dramatically, and use of knockout mice has resulted in increased knowledge of human
biology and diseases
Topology and Fragility in Cosmology
We introduce the notion of topological fragility and briefly discuss some
examples from the literature. An important example of this type of fragility is
the way globally anisotropic Bianchi V generalisations of the FLRW model
result in a radical restriction on the allowed topology of spatial sections,
thereby excluding compact cosmological models with negatively curved
three-sections with anisotropy. An outcome of this is to exclude chaotic mixing
in such models, which may be relevant, given the many recent attempts at
employing compact FLRW models to produce chaotic mixing in the cosmic
microwave background radiation, if the Universe turns out to be globally
anisotropic.Comment: 12 pages, LaTex file, to appear in Gen. Rel. Grav. (1998
Magnetoplasmonic design rules for active magneto-optics
Light polarization rotators and non-reciprocal optical isolators are
essential building blocks in photonics technology. These macroscopic passive
devices are commonly based on magneto-optical Faraday and Kerr polarization
rotation. Magnetoplasmonics - the combination of magnetism and plasmonics - is
a promising route to bring these devices to the nanoscale. We introduce design
rules for highly tunable active magnetoplasmonic elements in which we can
tailor the amplitude and sign of the Kerr response over a broad spectral range
Early Universe Dynamics in Semi-Classical Loop Quantum Cosmology
Within the framework of loop quantum cosmology, there exists a semi-classical
regime where spacetime may be approximated in terms of a continuous manifold,
but where the standard Friedmann equations of classical Einstein gravity
receive non-perturbative quantum corrections. An approximate, analytical
approach to studying cosmic dynamics in this regime is developed for both
spatially flat and positively-curved isotropic universes sourced by a
self-interacting scalar field. In the former case, a direct correspondence
between the classical and semi-classical field equations can be established
together with a scale factor duality that directly relates different expanding
and contracting universes. Some examples of non-singular, bouncing cosmologies
are presented together with a scaling, power-law solution.Comment: 14 pages, In Press, JCA
“For most of us Africans, we don’t just speak”: a qualitative investigation into collaborative heterogeneous PBL group learning
Collaborative approaches such as Problem Based Learning (PBL) may provide the opportunity to bring together diverse students but their efficacy in practice and the complications that arise due to the mixed ethnicity needs further investigation. This study explores the key advantages and problems of heterogeneous PBL groups from the students’ and teachers’ opinions. Focus groups were conducted with a stratified sample of second year medical students and their PBL teachers. We found that students working in heterogeneous groupings interact with students with whom they don’t normally interact with, learn a lot more from each other because of their differences in language and academic preparedness and become better prepared for their future professions in multicultural societies. On the other hand we found students segregating in the tutorials along racial lines and that status factors disempowered students and subsequently their productivity. Among the challenges was also that academic and language diversity hindered student learning. In light of these the recommendations were that teachers need special diversity training to deal with heterogeneous groups and the tensions that arise. Attention should be given to create ‘the right mix’ for group learning in diverse student populations. The findings demonstrate that collaborative heterogeneous learning has two sides that need to be balanced. On the positive end we have the ‘ideology’ behind mixing diverse students and on the negative the ‘practice’ behind mixing students. More research is needed to explore these variations and their efficacy in more detail
Designer Magnetoplasmonics with Nickel Nanoferromagnets
We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light’s polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing. © 2011 American Chemical Society.A.D. and Z.P. acknowledge support from the Swedish Research Council and Swedish Foundation for Strategic Research (Framework program Functional Electromagnetic Metamaterials,
project RMA08). J.Å. acknowledges support from the Swedish Research Council, the Swedish Foundation for Strategic Research (Future Research Leader Programme), and the G€oran Gustafsson Foundation. J.Å. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. V.B. acknowledges the G€oran Gustafsson Foundation and the Blanceflor Boncompagni-Ludovisi Foundation. P.V. acknowledges funding from the Basque Government
through the ETORGAI Program, Project No. ER-
2010/00032 and Program No. PI2009-17, the Spanish Ministry of Science and Education under Projects No. CSD2006-53 and No. MAT2009-07980. J.N. acknowledges funding for the Generalitat de Catalunya and the Spanish Ministry of Science and
Education through No. 2009-SGR-1292 and No. MAT2010-20616-C02 projects.Peer Reviewe
Self-rated health is associated with the length of stay at the intensive care unit and hospital following cardiac surgery
Nonminimal Inflation and the Running Spectral Index
We study a class of models in which the inflaton is minimally coupled to
gravity with a term f(R)\vp^2. We focus in particular on the case when , the expansion of the scale factor is driven by the usual potential
energy, while the rolling of the inflaton is driven by the nonminial coupling.
We show that the power spectrum is in general blue, and the problem of getting
a running spectral index is eased. However, the inflaton potential must have a
large second derivative in order to get a large running.Comment: 9 pages, harvma
The Autoimmune Manifestations in Patients with Genetic Defects in the B Cell Development and Differentiation Stages
Purpose: Primary B cell defects manifesting as predominantly antibody deficiencies result from variable inborn errors of the B cell lineage and their development, including impairments in early bone marrow development, class switch recombination (CSR), or terminal B cell differentiation. In this study, we aimed to investigate autoimmunity in monogenic patients with B cell development and differentiation defects.
Methods: Patients with known genetic defects in the B cell development and differentiation were recruited from the Iranian inborn errors of immunity registry.
Results: A total of 393 patients with a known genetic defect in the B cell development and differentiation (257 males; 65.4%) with a median age of 12 (6-20) years were enrolled in this study. After categorizing patients, 109 patients had intrinsic B cell defects. More than half of the patients had defects in one of the ATM (85 patients), BTK (76 patients), LRBA (34 patients), and DOCK8 (33 patients) genes. Fifteen patients (3.8%) showed autoimmune complications as their first manifestation. During the course of the disease, autoimmunity was reported in 81 (20.6%) patients at a median age of 4 (2-7) years, among which 65 patients had mixed intrinsic and extrinsic and 16 had intrinsic B cell defects. The comparison between patients with the mentioned four main gene defects showed that the patient group with LRBA defect had a significantly higher frequency of autoimmunity compared to those with other gene defects. Based on the B cell defect stage, 13% of patients with early B cell defect, 17% of patients with CSR defect, and 40% of patients who had terminal B cell defect presented at least one type of autoimmunity.
Conclusion: Our results demonstrated that gene mutations involved in human B cell terminal stage development mainly LRBA gene defect have the highest association with autoimmunity
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