499 research outputs found
Elastic and magnetic effects on the infrared phonon spectra of MnF2
We measured the temperature dependent infrared reflectivity spectra of MnF2
between 4 K and room temperature. We show that the phonon spectrum undergoes a
strong renormalization at TN. The ab-initio calculation we performed on this
compound accurately predict the magnitude and the direction of the phonon
parameters changes across the antiferromagnetic transition, showing that they
are mainly induced by the magnetic order. In this material, we found that the
dielectric constant is mostly from phonon origin. The large change in the
lattice parameters with temperature seen by X-ray diffraction as well as the
A2u phonon softening below TN indicate that magnetic order induced distortions
in MnF2 are compatible with the ferroelectric instabilities observed in TiO2,
FeF2 and other rutile-type fluorides. This study also shows the anomalous
temperature evolution of the lower energy Eu mode in the paramagnetic phase,
which can be compared to that of the B1g one seen by Raman spectroscopy in many
isostructural materials. This was interpreted as being a precursor of a phase
transition from rutile to CaCl2 structure which was observed under pressure in
ZnF2.Comment: 8 pages, 8 figures, updated version accepted in PR
Gupta-Bleuler quantization for minimally coupled scalar fields in de Sitter space
We present in this paper a fully covariant quantization of the
minimally-coupled massless field on de Sitter space. We thus obtain a formalism
free of any infrared (e.g logarithmic) divergence. Our method is based on a
rigorous group theoretical approach combined with a suitable adaptation (Krein
spaces) of the Wightman-G\"{a}rding axiomatic for massless fields
(Gupta-Bleuler scheme). We make explicit the correspondence between unitary
irreducible representations of the de Sitter group and the field theory on de
Sitter space-time. The minimally-coupled massless field is associated with a
representation which is the lowest term of the discrete series of unitary
representations of the de Sitter group. In spite of the presence of negative
norm modes in the theory, no negative energy can be measured: expressions as
\le n_{k_1}n_{k_2}...|T_{00}|n_{k_1}n_{k_2}...\re are always positive.Comment: 20 pages, appear in class. quantum gra
The impact of automated eGFR reporting and education on nephrology service referrals
Background. Serum creatinine concentration is an unreliable and insensitive marker of chronic kidney disease (CKD). To improve CKD detection, the Australasian Creatinine Consensus Working Committee recommended reporting of estimated glomerular filtration rate (eGFR) using the four-variable Modification of Diet in Renal Disease (MDRD) formula with every request for serum creatinine concentration. The aim of this study was to evaluate the impact of automated laboratory reporting of eGFR on the quantity and quality of referrals to nephrology services in Southeast Queensland, Australia
Robotic-assisted radical cystectomy: the first multicentric Brazilian experience
The objective of this study is to report the first multicentric Brazilian series and learning curve of robotic radical cystectomy (RARC) with related intra- and postoperative outcomes. We retrospectively analyzed 37 RARC prospectively collected at four different centers in Brazil, from 2013 to 2019. We analyzed the patient’s demographics, pathological tumor, and nodal status, as well as intra- and postoperative outcomes. Statistical analysis was performed with the IBM (SPSS version 25) software. Overall, 86% were male, and the median age was 69 years. 83% had muscle-invasive bladder cancer, and 17% a high-grade, recurrent non-muscle-invasive tumor. The median operative time was 420 min with 300 min as console time. Median blood loss was 350 ml and transfusion rate was 10%. In 68% of the cases, we performed an intracorporeal Bricker urinary diversion, 24% intracorporeal neobladder, and 8% ureterostomy. Six patients (16%) had a Clavien 1–2, 8% had Clavien 3, 2.5% had a Clavien 4, and 5% had Clavien 5. The median length of hospital stay was 7 days. The final pathological exam pointed out pT0 in 16%, pT1 in 8%, pT2 in 32%, ≥ pT3 in 27%, and 16% pTis. 95% had negative surgical margins. The survival at 30, 90, and 180 days was 98%, 95%, and 95%, respectively. To our knowledge, this is the first multicentric series of RARC reporting the learning curve in Brazil; even if still representing a challenging procedure, RARC could be safely and effectively faced by experienced surgeons at centers with high volumes of robotic surgery
Magnetoresistance through a single molecule
The use of single molecules to design electronic devices is an extremely
challenging and fundamentally different approach to further downsizing
electronic circuits. Two-terminal molecular devices such as diodes were first
predicted [1] and, more recently, measured experimentally [2]. The addition of
a gate then enabled the study of molecular transistors [3-5]. In general terms,
in order to increase data processing capabilities, one may not only consider
the electron's charge but also its spin [6,7]. This concept has been pioneered
in giant magnetoresistance (GMR) junctions that consist of thin metallic films
[8,9]. Spin transport across molecules, i.e. Molecular Spintronics remains,
however, a challenging endeavor. As an important first step in this field, we
have performed an experimental and theoretical study on spin transport across a
molecular GMR junction consisting of two ferromagnetic electrodes bridged by a
single hydrogen phthalocyanine (H2Pc) molecule. We observe that even though
H2Pc in itself is nonmagnetic, incorporating it into a molecular junction can
enhance the magnetoresistance by one order of magnitude to 52%.Comment: To appear in Nature Nanotechnology. Present version is the first
submission to Nature Nanotechnology, from May 18th, 201
Thoughts on Tachyon Cosmology
After a pedagogical review of elementary cosmology, I go on to discuss some
obstacles to obtaining inflationary or accelerating universes in M/String
Theory. In particular, I give an account of an old No-Go Theorem to this
effect. I then describe some recent ideas about the possible r\^ole of the
tachyon in cosmology. I stress that there are many objections to a naive
inflationary model based on the tachyon, but there remains the possiblity that
the tachyon was important in a possible pre-inflationary Open-String Era
preceding our present Closed String Era.Comment: 34 pages, no figures. This is the written version of a lecture
delivered at the Workshop on the Quantum Structure of Spacetime and the
Geometric Nature of Fundamental Interactions held in Leuven from Sept 13th to
Sept 19th(2002) which is to appear in the Proceedings in a special issue of
Quantum and Classical Gravit
Stages of change in physical activity-related behavior in adolescents from a Brazilian state capital
Brevianes Revisited
Breviones are a new family of secondary metabolites that were originally isolated from the New Zealand endemic fungus Penicillium brevicompactum var. Dierckx. These compounds are generally characterized by a new carbon skeleton, known as breviane, which that has three possible structural variations, such as breviane, abeo-breviane, and abeo-norbreviane. Brevianes present a basic diterpenic tricyclic core that is mevalonic in origin and is similar to that of perhydrophenanthrene. The core bears four methyl groups at positions C4, C8, C10, and C13 and has defined stereochemistry at positions C5, C8, C9, C10, and C14. The C1'-C7' side chain has been proposed to have a polyketide biosynthetic origin and is joined to the diterpenic moiety through carbons C2'-C15'. The cyclization and lactonization of this part of the molecule leads to the characteristic breviane spiranic ring fused to the α-pyrone
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