676 research outputs found
Эндопротезирование плечевого сустава при опухолях проксимального отдела плечевой кости
У 25 хворих з ураженням пухлинами проксимального відділу плечової кістки
вивчені функціональні результати ендопротезування плечового суглоба залежно
від збереження або резекції нервово- м’язового механізму відведення і згинання
плеча. Ендопротезування при збереженому механізмі відведення плеча дає
високий функціональний результат (85.5±1.65%) і виконує переважно косметичну
функцію, коли механізм відведення плеча не зберігається (функція відповідає
63.7±1.28%).Functional results of humoral joints endoprosthetics in 25 patients with upper extremity
bones tumours subject to saving or resection of shoulder drawing aside and flection
neuromuscular mechanism are studied. Endoprosthetics in the case of shoulder
drawing aside mechanism saving gives a high functional result (85.5±1.65%), but it
executing mainly cosmetic function, in the case when mechanism of shoulder drawing
aside is not saved (such function corresponds to 63.7±1.28% from a due size)
Coupled quantum wires
We study a set of crossed 1D systems, which are coupled with each other via
tunnelling at the crossings. We begin with the simplest case with no
electron-electron interactions and find that besides the expected level
splitting, bound states can emerge. Next, we include an external potential and
electron-electron interactions, which are treated within the Hartree
approximation. Then, we write down a formal general solution to the problem,
giving additional details for the case of a symmetric external potential.
Concentrating on the case of a single crossing, we were able to explain recent
experinents on crossed metallic and semiconducting nanotubes [J. W. Janssen, S.
G. Lemay, L. P. Kouwenhoven, and C. Dekker, Phys. Rev. B 65, 115423 (2002)],
which showed the presence of localized states in the region of crossing.Comment: 11 pages, 10 figure
The influence of a weak magnetic field in the Renormalization-Group functions of (2+1)-dimensional Dirac systems
The experimental observation of the renormalization of the Fermi velocity
as a function of doping has been a landmark for confirming the
importance of electronic interactions in graphene. Although the experiments
were performed in the presence of a perpendicular magnetic field , the
measurements are well described by a renormalization-group (RG) theory that did
not include it. Here we clarify this issue, for both massive and massless Dirac
systems, and show that for the weak magnetic fields at which the experiments
are performed, there is no change in the renormalization-group functions. Our
calculations are carried out in the framework of the Pseudo-quantum
electrodynamics (PQED) formalism, which accounts for dynamical interactions. We
include only the linear dependence in , and solve the problem using two
different parametrizations, the Feynman and the Schwinger one. We confirm the
results obtained earlier within the RG procedure and show that, within linear
order in the magnetic field, the only contribution to the renormalization of
the Fermi velocity arises due to interactions. In addition, for gapped systems,
we observe a running of the mass parameter.Comment: Discussion about the fermionic mass has been added to the previous
versio
Interaction Induced Quantum Valley Hall Effect in Graphene
We use Pseudo Quantum Electrodynamics (PQED) in order to describe the full electromagnetic interaction of the p-electrons of graphene in a consistent 2D formulation. We first consider the effect of this interaction in the vacuum polarization tensor or, equivalently, in the current correlator. This allows us to obtain the dc conductivity after a smooth zero-frequency limit is taken in Kubo's formula.Thereby, we obtain the usual expression for the minimal conductivity plus corrections due to the interaction that bring it closer to the experimental value. We then predict the onset of an interaction-driven spontaneous Quantum Valley Hall effect (QVHE) below a critical temperature of the order of K. The transverse (Hall) valley conductivity is evaluated exactly and shown to coincide with the one in the usual Quantum Hall effect. Finally, by considering the effects of PQED, we show that the electron self-energy is such that a set of P- and T- symmetric gapped electron energy eigenstates are dynamically generated, in association with the QVHE
Flux noise in high-temperature superconductors
Spontaneously created vortex-antivortex pairs are the predominant source of
flux noise in high-temperature superconductors. In principle, flux noise
measurements allow to check theoretical predictions for both the distribution
of vortex-pair sizes and for the vortex diffusivity. In this paper the
flux-noise power spectrum is calculated for the highly anisotropic
high-temperature superconductor Bi-2212, both for bulk crystals and for
ultra-thin films. The spectrum is basically given by the Fourier transform of
the temporal magnetic-field correlation function. We start from a
Berezinskii-Kosterlitz-Thouless type theory and incorporate vortex diffusion,
intra-pair vortex interaction, and annihilation of pairs by means of a
Fokker-Planck equation to determine the noise spectrum below and above the
superconducting transition temperature. We find white noise at low frequencies
omega and a spectrum proportional to 1/omega^(3/2) at high frequencies. The
cross-over frequency between these regimes strongly depends on temperature. The
results are compared with earlier results of computer simulations.Comment: 9 pages, 4 PostScript figures, to be published in Phys. Rev.
Stripes and holes in a two-dimensional model of spinless fermions and hardcore bosons
We consider a Hubbard-like model of strongly-interacting spinless fermions
and hardcore bosons on a square lattice, such that nearest neighbor occupation
is forbidden. Stripes (lines of holes across the lattice forming antiphase
walls between ordered domains) are a favorable way to dope this system below
half-filling. The problem of a single stripe can be mapped to a spin-1/2 chain,
which allows understanding of its elementary excitations and calculation of the
stripe's effective mass for transverse vibrations. Using Lanczos exact
diagonalization, we investigate the excitation gap and dispersion of a hole on
a stripe, and the interaction of two holes. We also study the interaction of
two, three, and four stripes, finding that they repel, and the interaction
energy decays with stripe separation as if they are hardcore particles moving
in one (transverse) direction. To determine the stability of an array of
stripes against phase separation into particle-rich phase and hole-rich liquid,
we evaluate the liquid's equation of state, finding the stripe-array is not
stable for bosons but is possibly stable for fermions.Comment: 24 pages, 18 figure
Prácticas docentes para creatividad en la universidad: estudio en Portugal y Brasil
Creativity is nowadays seen as an essential feature in higher education. Nevertheless, there is a discrepancy between the need for creativity and what higher education classrooms provide. This study assessed the perceptions of 1599 higher education students from two countries (1059 Brazilian and 540 Portuguese students), from two academic domains (Sciences and Technologies – Sc&T; Social Sciences, Arts, and Humanities – SScA&H), about the presence of creativity in their teachers’ instruction and evaluation practices. The study’s findings evidence interactive effects between the variables country and academic domain for most of the assessed factors: encouragement of new ideas, climate for the expression of ideas, and interest in students’ learning. Brazilian Sc&T students presented more negative perceptions of their classroom environments when compared to SScA&H students; Portuguese students showed opposite patterns
of results. Some hypothetical explanations are discussed and future directions for research are presented.Criatividade é atualmente tomada como aspecto essencial na Educação Superior. Há, contudo, discrepância entre a necessidade
de criatividade e o que a universidade proporciona. Este estudo avaliou percepções de 1599 alunos universitários de dois países (1059
brasileiros e 540 portugueses), de duas áreas curriculares (Ciências e Tecnologias – Sc&T; Ciências Sociais, Artes e Humanidades – SscA&H)
sobre a presença de criatividade nas práticas docentes, instrucionais e avaliativas, de que são alvo. Os resultados mostraram efeitos
interativos significativos entre as variáveis país e área curricular para a maioria dos fatores avaliados: encorajamento de novas ideias,
clima para expressão de ideias e interesse pela aprendizagem dos alunos. Os estudantes brasileiros de Sc&T mostraram percepções mais
negativas da sala de aula, comparados com os de SScA&H; os alunos portugueses obtiveram padrões opostos nos resultados. Algumas
hipóteses explicativas são discutidas e são apresentadas orientações para pesquisa futura.La creatividad está actualmente considerada como aspecto esencial en la Educación Superior. Sin embargo, existe discrepancia
entre la necesidad de creatividad y lo que la universidad ofrece. Este estudio evaluó percepciones de 1.599 estudiantes universitarios
(1.059 de Brasil y 540 de Portugal) de dos áreas curriculares (Ciencia y Tecnología – Sc&T; Ciencias Sociales, Artes y Humanidades
– SscA&T) acerca de la presencia de creatividad en las prácticas docentes, instructivas y evaluativas dirigidas a ellos. Los resultados mostraron
efectos de interacción significativos entre las variables país y área curricular para la mayoría de los factores evaluados: fomento de
nuevas ideas, entorno para la expresión de ideas e interés en el aprendizaje del estudiante. Los estudiantes brasileños de Sc&T mostraron
percepciones más negativas de la clase en comparación con los de SSCA&H; los estudiantes portugueses obtuvieron patrones opuestos en
los resultados. Algunas hipótesis explicativas se discuten y se presentan directrices para investigación futura.Thermo Scientificinfo:eu-repo/semantics/publishedVersio
Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study
The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at 80 cm–1, which is assigned to a bending of the protein amide chain
Standalone vertex finding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011
- …