120 research outputs found
Dimensionality Control of Electronic Phase Transitions in Nickel-Oxide Superlattices
The competition between collective quantum phases in materials with strongly
correlated electrons depends sensitively on the dimensionality of the electron
system, which is difficult to control by standard solid-state chemistry. We
have fabricated superlattices of the paramagnetic metal LaNiO3 and the wide-gap
insulator LaAlO3 with atomically precise layer sequences. Using optical
ellipsometry and low-energy muon spin rotation, superlattices with LaNiO3 as
thin as two unit cells are shown to undergo a sequence of collective
metalinsulator and antiferromagnetic transitions as a function of decreasing
temperature, whereas samples with thicker LaNiO3 layers remain metallic and
paramagnetic at all temperatures. Metal-oxide superlattices thus allow control
of the dimensionality and collective phase behavior of correlated-electron
systems
Rare earth magnetism in CeFeAsO: A single crystal study
Single crystals of CeFeAsO, large enough to study the anisotropy of the
magnetic properties, were grown by an optimized Sn-flux technique. The high
quality of our single crystals is apparent from the highest residual
resistivity ratio, RRR = 12, reported among undoped RFeAsO compounds (R=rare
earth) as well as sharp anomalies in resistivity, specific heat, C(T), and
thermal expansion at the different phase transitions. The magnetic
susceptibility chi(T) presents a large easy-plane anisotropy consistent with
the lowest crystal electric field doublet having a dominant Gamma_6 character.
Curie-Weiss like susceptibilities for magnetic field parallel and perpendicular
to the crystallographic c-axis do not reveal an influence of a staggered field
on the Ce site induced by magnetic ordering of the Fe. Furthermore, the
standard signatures for antiferromagnetic order of Ce at T_N = 3.7 K observed
in chi(T) and C(T) are incompatible with a Zeeman splitting Delta = 10 K of the
CEF ground state doublet at low temperature due to the Fe-magnetic order as
previously proposed. Our results can be reconciled with the earlier observation
by assuming a comparatively stronger effect of the Ce-Ce exchange leading to a
reduction of this Zeeman splitting below 15 K.Comment: 15 pages, 6 figures, added section on magn. susceptibilit
Specific-heat study of superconducting and normal states in FeSe1-xTex (0.6<=x<=1) single crystals: Strong-coupling superconductivity, strong electron-correlation, and inhomogeneity
The electronic specific heat of as-grown and annealed single-crystals of
FeSe1-xTex (0.6<=x<=1) has been investigated. It has been found that annealed
single-crystals with x=0.6-0.9 exhibit bulk superconductivity with a clear
specific-heat jump at the superconducting (SC) transition temperature, Tc. Both
2Delta_0/kBTc [Delta_0: the SC gap at 0 K estimated using the single-band BCS
s-wave model] and Delta C/(gamma_n-gamma_0)Tc [Delta C$: the specific-heat jump
at Tc, gamma_n: the electronic specific-heat coefficient in the normal state,
gamma_0: the residual electronic specific-heat coefficient at 0 K in the SC
state] are largest in the well-annealed single-crystal with x=0.7, i.e., 4.29
and 2.76, respectively, indicating that the superconductivity is of the strong
coupling. The thermodynamic critical field has also been estimated. gamma_n has
been found to be one order of magnitude larger than those estimated from the
band calculations and increases with increasing x at x=0.6-0.9, which is
surmised to be due to the increase in the electronic effective mass, namely,
the enhancement of the electron correlation. It has been found that there
remains a finite value of gamma_0 in the SC state even in the well-annealed
single-crystals with x=0.8-0.9, suggesting an inhomogeneous electronic state in
real space and/or momentum space.Comment: 22 pages, 1 table, 6 figures, Version 2 has been accepted for
publication in J. Phys. Soc. Jp
Hybrid Equation/Agent-Based Model of Ischemia-Induced Hyperemia and Pressure Ulcer Formation Predicts Greater Propensity to Ulcerate in Subjects with Spinal Cord Injury
Pressure ulcers are costly and life-threatening complications for people with spinal cord injury (SCI). People with SCI also exhibit differential blood flow properties in non-ulcerated skin. We hypothesized that a computer simulation of the pressure ulcer formation process, informed by data regarding skin blood flow and reactive hyperemia in response to pressure, could provide insights into the pathogenesis and effective treatment of post-SCI pressure ulcers. Agent-Based Models (ABM) are useful in settings such as pressure ulcers, in which spatial realism is important. Ordinary Differential Equation-based (ODE) models are useful when modeling physiological phenomena such as reactive hyperemia. Accordingly, we constructed a hybrid model that combines ODEs related to blood flow along with an ABM of skin injury, inflammation, and ulcer formation. The relationship between pressure and the course of ulcer formation, as well as several other important characteristic patterns of pressure ulcer formation, was demonstrated in this model. The ODE portion of this model was calibrated to data related to blood flow following experimental pressure responses in non-injured human subjects or to data from people with SCI. This model predicted a higher propensity to form ulcers in response to pressure in people with SCI vs. non-injured control subjects, and thus may serve as novel diagnostic platform for post-SCI ulcer formation. © 2013 Solovyev et al
Exploring the mycobacteriophage metaproteome: Phage genomics as an educational platform
Bacteriophages are the most abundant forms of life in the biosphere and carry genomes characterized by high genetic diversity and mosaic architectures. The complete sequences of 30 mycobacteriophage genomes show them collectively to encode 101 tRNAs, three tmRNAs, and 3,357 proteins belonging to 1,536 "phamilies" of related sequences, and a statistical analysis predicts that these represent approximately 50% of the total number of phamilies in the mycobacteriophage population. These phamilies contain 2.19 proteins on average; more than half (774) of them contain just a single protein sequence. Only six phamilies have representatives in more than half of the 30 genomes, and only three - encoding tape-measure proteins, lysins, and minor tail proteins - are present in all 30 phages, although these phamilies are themselves highly modular, such that no single amino acid sequence element is present in all 30 mycobacteriophage genomes. Of the 1,536 phamilies, only 230 (15%) have amino acid sequence similarity to previously reported proteins, reflecting the enormous genetic diversity of the entire phage population. The abundance and diversity of phages, the simplicity of phage isolation, and the relatively small size of phage genomes support bacteriophage isolation and comparative genomic analysis as a highly suitable platform for discovery-based education. © 2006 Hatfull et al
Charge Transport in Manganites: Hopping Conduction, the Anomalous Hall Effect and Universal Scaling
The low-temperature Hall resistivity \rho_{xy} of La_{2/3}A_{1/3}MnO_3 single
crystals (where A stands for Ca, Pb and Ca, or Sr) can be separated into
Ordinary and Anomalous contributions, giving rise to Ordinary and Anomalous
Hall effects, respectively. However, no such decomposition is possible near the
Curie temperature which, in these systems, is close to metal-to-insulator
transition. Rather, for all of these compounds and to a good approximation, the
\rho_{xy} data at various temperatures and magnetic fields collapse (up to an
overall scale), on to a single function of the reduced magnetization
m=M/M_{sat}, the extremum of this function lying at m~0.4. A new mechanism for
the Anomalous Hall Effect in the inelastic hopping regime, which reproduces
these scaling curves, is identified. This mechanism, which is an extension of
Holstein's model for the Ordinary Hall effect in the hopping regime, arises
from the combined effects of the double-exchange-induced quantal phase in
triads of Mn ions and spin-orbit interactions. We identify processes that lead
to the Anomalous Hall Effect for localized carriers and, along the way, analyze
issues of quantum interference in the presence of phonon-assisted hopping. Our
results suggest that, near the ferromagnet-to-paramagnet transition, it is
appropriate to describe transport in manganites in terms of carrier hopping
between states that are localized due to combined effect of magnetic and
non-magnetic disorder. We attribute the qualitative variations in resistivity
characteristics across manganite compounds to the differing strengths of their
carrier self-trapping, and conclude that both disorder-induced localization and
self-trapping effects are important for transport.Comment: 29 pages, 20 figure
Patient Choice in the Post-Semashko Health Care System
The opportunity for patient choice in the health care system in CIS countries was created by the partial destruction of the referral system and the development of paid medical services. The data of two population surveys conducted in Russia in 2009 and 2011 show that patient choice of medical facility and physician is taking place in the post-Semashko health care system, and it is not restricted to the area of paid medical services. However for the majority of population the choice of medical facility and physician is not a necessity. Part of reason for patient choice is caused by the failure of the patient referral system to ensure the necessary treatment. For some Russian citizens, the choice of health care provider is a means to obtain better quality care, and in this respect the enhancement of patient choice is leading to the improved efficiency of the emerging health care system.ĐŃла ŃĐŸĐ·ĐŽĐ°ĐœĐ° ĐČĐŸĐ·ĐŒĐŸĐ¶ĐœĐŸŃŃŃ ĐŽĐ»Ń ĐČŃĐ±ĐŸŃĐ° паŃĐžĐ”ĐœŃĐ° ĐČ ŃĐžŃŃĐ”ĐŒĐ” Đ·ĐŽŃĐ°ĐČĐŸĐŸŃ
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Syndromics: A Bioinformatics Approach for Neurotrauma Research
Substantial scientific progress has been made in the past 50Â years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational âsyndromeâ produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call âsyndromicsâ, which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings
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