218 research outputs found
Thermal melting of density waves on the square lattice
We present the theory of the effect of thermal fluctuations on commensurate
"p x p" density wave ordering on the square lattice (p >= 3, integer). For the
case in which this order is lost by a second order transition, we argue that
the adjacent state is generically an incommensurate striped state, with
commensurate p-periodic long range order along one direction, and
incommensurate quasi-long-range order along the orthogonal direction. We also
present the routes by which the fully disordered high temperature state can be
reached. For p=4, and at special commensurate densities, the "4 x 4"
commensurate state can melt directly into the disordered state via a self-dual
critical point with non-universal exponents.Comment: 12 pages, 5 figure
Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements
We have measured the low-temperature specific heat of the geometrically
frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic
field. The specific heat is found to drop exponentially below approximately 350
mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy
resulting from single ion effects and long-range dipolar interactions. The data
are well fitted by linear spin-wave theory, ruling out unconventional low
energy magnetic excitations in this system, and allowing a determination of the
pertinent exchange interactions in this material
Quantum spin fluctuations in the dipolar Heisenberg-like rare earth pyrochlores
The magnetic pyrochlore oxide materials of general chemical formula R2Ti2O7
and R2Sn2O7 (R = rare earth) display a host of interesting physical behaviours
depending on the flavour of rare earth ion. These properties depend on the
value of the total magnetic moment, the crystal field interactions at each rare
earth site and the complex interplay between magnetic exchange and long-range
dipole-dipole interactions. This work focuses on the low temperature physics of
the dipolar isotropic frustrated antiferromagnetic pyrochlore materials.
Candidate magnetic ground states are numerically determined at zero temperature
and the role of quantum spin fluctuations around these states are studied using
a Holstein-Primakoff spin wave expansion to order 1/S. The results indicate the
strong stability of the proposed classical ground states against quantum
fluctuations. The inclusion of long range dipole interactions causes a
restoration of symmetry and a suppression of the observed anisotropy gap
leading to an increase in quantum fluctuations in the ground state when
compared to a model with truncated dipole interactions. The system retains most
of its classical character and there is little deviation from the fully ordered
moment at zero temperature.Comment: Latex2e, 18 pages, 4 figures, IOP forma
Heat in optical tweezers
Laser-induced thermal effects in optically trapped microspheres and single cells have been investigated by Luminescence Thermometry. Thermal spectroscopy has revealed a non-localized temperature distribution around the trap that extends over tens of microns, in agreement with previous theoretical models. Solvent absorption has been identified as the key parameter to determine laser-induced heating, which can be reduced by establishing a continuous fluid flow of the sample. Our experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping wavelength exists for biological applications close to 820 nm. This has been corroborated by a simultaneous analysis of the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. Minimum intracellular heating, well below the cytotoxic level (43 °C), has been demonstrated to occur for optical trapping with 820 nm laser radiation, thus avoiding cell damage
The Spin Liquid State of the Tb2Ti2O7 Pyrochlore Antiferromagnet: A Puzzling State of Affairs
The pyrochlore antiferromagnet Tb2Ti2O7 has proven to be an enigma to
experimentalists and theorists working on frustrated magnetic systems. The
experimentally determined energy level structure suggests a local Ising
antiferromagnet at low temperatures, T < 10 K. An appropriate model then
predicts a long-range ordered Q = 0 state below approximately 2 K. However,
muon spin resonance experiments reveal a paramagnetic structure down to tens of
milli-Kelvin. The importance of fluctuations out of the ground state effective
Ising doublet has been recently understood, for the measured paramagnetic
correlations can not be described without including the higher crystal field
states. However, these fluctuations treated within the random phase
approximation (RPA) fail to account for the lack of ordering in this system
below 2 K. In this work, we briefly review the experimental evidence for the
collective paramagnetic state of Tb2Ti2O7. The basic theoretical picture for
this system is discussed, where results from classical spin models are used to
motivate the investigation of quantum effects to lowest order via the RPA.
Avenues for future experimental and theoretical work on Tb2Ti2O7 are presented.Comment: Latex2e,6 pages, IOP format, introduction shortened and other minor
corrections, replaced with published version in the Proceedings of the Highly
Frustrated Magnetism 2003 Conference, Grenobl
Profibrotic role of inducible heat shock protein 90α isoform in systemic sclerosis
Systemic sclerosis (SSc) is an autoimmune disease that affects skin and multiple internal organs. TGF-β, a central trigger of cutaneous fibrosis, activates fibroblasts with the involvement of the stress-inducible chaperone heat shock protein 90 isoform α (Hsp90α). Available evidence supports overexpression and secretion of Hsp90α as a feature in profibrotic pathological conditions. The aim of this work is to investigate the expression and function of Hsp90α in experimental models of skin fibrosis such as human fibroblasts, C57BL/6 mice, and in human SSc. For this purpose, we generated a new experimental model based on doxorubicin administration with improved characteristics with respect to the bleomycin model. We visualized disease progression in vivo by fluorescence imaging. In this work, we obtained Hsp90α mRNA overexpression in human skin fibroblasts, in bleomycin- and doxorubicin-induced mouse fibrotic skin, and in lungs of bleomycin- and doxorubicin-treated mice. Hsp90α-deficient mice showed significantly decreased skin thickness compared with wild-type mice in both animal models. In SSc patients, serum Hsp90α levels were increased in patients with lung involvement and in patients with the diffuse form of SSc (dSSc) compared with patients with the limited form of SSc. The serum Hsp90α levels of patients dSSc were correlated with the Rodnan score and the forced vital capacity variable. These results provide new supportive evidence of the contribution of the Hsp90α isoform in the development of skin fibrosis. In SSc, these results indicated that higher serum levels were associated with dSSc and lung fibrosis.This work was supported by Spanish Ministerio de Economía, Industria y Competitividad, Gobierno de España Grant RTI2018-095214-B-I00, as well as by the Instituto de Formación e Investigación Marqués de Valdecilla IDIVAL (InnVal 17/22; InnVal 20/34), 2020UCI22-PUB-0003 Gobierno de Cantabria (to A.V.V.), SAF2016-75195-R (to J.M.), SAF2017-82905-R (to R.M.), and (NextVal 18/14) to A.P
Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment
In this paper, we review theoretical and experimental research on rare region
effects at quantum phase transitions in disordered itinerant electron systems.
After summarizing a few basic concepts about phase transitions in the presence
of quenched randomness, we introduce the idea of rare regions and discuss their
importance. We then analyze in detail the different phenomena that can arise at
magnetic quantum phase transitions in disordered metals, including quantum
Griffiths singularities, smeared phase transitions, and cluster-glass
formation. For each scenario, we discuss the resulting phase diagram and
summarize the behavior of various observables. We then review several recent
experiments that provide examples of these rare region phenomena. We conclude
by discussing limitations of current approaches and open questions.Comment: 31 pages, 7 eps figures included, v2: discussion of the dissipative
Ising chain fixed, references added, v3: final version as publishe
Frequent expression loss of Inter-alpha-trypsin inhibitor heavy chain (ITIH) genes in multiple human solid tumors: A systematic expression analysis
<p>Abstract</p> <p>Background</p> <p>The inter-alpha-trypsin inhibitors (ITI) are a family of plasma protease inhibitors, assembled from a light chain – bikunin, encoded by <it>AMBP </it>– and five homologous heavy chains (encoded by <it>ITIH1</it>, <it>ITIH2</it>, <it>ITIH3</it>, <it>ITIH4</it>, and <it>ITIH5</it>), contributing to extracellular matrix stability by covalent linkage to hyaluronan. So far, ITIH molecules have been shown to play a particularly important role in inflammation and carcinogenesis.</p> <p>Methods</p> <p>We systematically investigated differential gene expression of the <it>ITIH </it>gene family, as well as <it>AMBP </it>and the interacting partner <it>TNFAIP6 </it>in 13 different human tumor entities (of breast, endometrium, ovary, cervix, stomach, small intestine, colon, rectum, lung, thyroid, prostate, kidney, and pancreas) using cDNA dot blot analysis (Cancer Profiling Array, CPA), semiquantitative RT-PCR and immunohistochemistry.</p> <p>Results</p> <p>We found that <it>ITIH </it>genes are clearly downregulated in multiple human solid tumors, including breast, colon and lung cancer. Thus, <it>ITIH </it>genes may represent a family of putative tumor suppressor genes that should be analyzed in greater detail in the future. For an initial detailed analysis we chose <it>ITIH2 </it>expression in human breast cancer. Loss of <it>ITIH2 </it>expression in 70% of cases (n = 50, CPA) could be confirmed by real-time PCR in an additional set of breast cancers (n = 36). Next we studied ITIH2 expression on the protein level by analyzing a comprehensive tissue micro array including 185 invasive breast cancer specimens. We found a strong correlation (p < 0.001) between ITIH2 expression and estrogen receptor (ER) expression indicating that ER may be involved in the regulation of this ECM molecule.</p> <p>Conclusion</p> <p>Altogether, this is the first systematic analysis on the differential expression of <it>ITIH </it>genes in human cancer, showing frequent downregulation that may be associated with initiation and/or progression of these malignancies.</p
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