20 research outputs found
The Shapes of Cooperatively Rearranging Regions in Glass Forming Liquids
The shapes of cooperatively rearranging regions in glassy liquids change from
being compact at low temperatures to fractal or ``stringy'' as the dynamical
crossover temperature from activated to collisional transport is approached
from below. We present a quantitative microscopic treatment of this change of
morphology within the framework of the random first order transition theory of
glasses. We predict a correlation of the ratio of the dynamical crossover
temperature to the laboratory glass transition temperature, and the heat
capacity discontinuity at the glass transition, Delta C_p. The predicted
correlation agrees with experimental results for the 21 materials compiled by
Novikov and Sokolov.Comment: 9 pages, 6 figure
Glass transition with decreasing correlation length during cooling of Fe50Co50 superlattice and strong liquids
The glass transition GT is usually thought of as a structural arrest that
occurs during the cooling of a liquid, or sometimes a plastic crystal, trapping
a metastable state of the system before it can recrystallize to stabler forms1.
This phenomenon occurs in liquids of all classes, most recently in bulk
metallic glassformers2. Much theoretical interest has been generated by the
dynamical heterogeneity observed in cooling of fragile liquids3, 4, and many
have suggested that the slow-down is caused by a related increasing correlation
length 5-9. Here we report both kinetics and thermodynamics of arrest in a
system that disorders while in its ground state, exhibits a large !Cp on arrest
(!Cp = Cp,mobile - Cp,arrested), yet clearly is characterized by a correlation
length that is decreasing as GT is approached from above. We show that GT
kinetics in our system, the disordering superlattice Fe50Co50, satisfy the
kinetic criterion for ideally 'strong' glassformers10, and since !Cp behavior
through Tg also correlates10, we propose that very strong liquidsand very
fragile liquids exist on opposite flanks of an order-disorder transition - one
that is already known for model systems
Ressonância magnética da próstata: uma visão geral para o radiologista Magnetic resonance imaging of the prostate: an overview for radiologists
O adenocarcinoma prostático é o segundo tumor em incidência e mortalidade dentre as neoplasias malignas masculinas. Para adequada programação terapêutica é importante a distinção entre tumores confinados à próstata e aqueles com extensão extraprostática. Diferentes estudos têm demonstrado que a ressonância magnética da próstata com bobina endorretal auxilia no estadiamento local destes pacientes. Este artigo apresenta informações sobre a anatomia prostática, o aspecto tumoral à ressonância magnética, sinais de extensão tumoral extraprostática e invasão de vesÃculas seminais, sugestões de protocolo, princÃpios gerais e importância da espectroscopia de prótons, do estudo perfusional e da difusão, indicações da ressonância magnética na investigação de recidiva pós-operatória e pós-radioterapia, seu papel na detecção de lesões suspeitas em pacientes com suspeita clÃnico-laboratorial de adenocarcinoma prostático, além de apresentar os diagnósticos diferenciais e limitações do método.<br>Prostate adenocarcinoma is the second tumor in incidence and mortality among malignant neoplasms in men. The differentiation between tumors confined to the organ and those with extraprostatic extension is critical for an appropriate therapeutic planning. Different studies have demonstrated that magnetic resonance imaging of the prostate with endorectal coil is useful in the local staging of these tumors. The present article presents information on the prostate gland anatomy, the tumor aspect at magnetic resonance imaging, specific signs of extracapsular extension and seminal vesicles invasion, protocol suggestions, general principles and relevance of proton spectroscopy, perfusion and diffusion imaging, role of magnetic resonance imaging in the postoperative and post-radiotherapy detection of local tumor recurrence, and also in the detection of lesions in patients with clinical/laboratory suspicion of prostate adenocarcinoma. Additionally, the present article describes differential diagnoses and limitations of the method