Room Temperature Organic Superconductor?

The electron--phonon coupling in fullerene C28 has been calculated from first principles. The value of the associated coupling constant lambda/N(0) is found to be a factor three larger than that associated with C60. Assuming similar values of the density of levels at the Fermi surface N(0) and of the Coulomb pseudopotential for C28-based solids as those associated with alkali-doped fullerides A3C60, one obtains Tc(C28) \approx 8 Tc(C60).Comment: 10 pages, 2 figure

Sirolimus Therapy for Patients With Lymphangioleiomyomatosis Leads to Loss of Chylous Ascites and Circulating LAM Cells

A young woman received a diagnosis of abdominal, sporadic lymphangioleiomyomatosis (LAM) and multiple abdominal lymphangioleiomyomas and was referred for recurrent chylous ascites responding only to a fat-free diet. On admission, pulmonary function test (PFT) results showed a moderate reduction in the transfer factor for carbon monoxide with normal exercise performance. The serum vascular endothelial growth factor D (VEGF-D) level was 2,209 pg/mL. DNA sequences, amplified at loci kg8, D16S3395, D16S3024, D16S521, and D16S291 on chromosome 16p13.3, showed a loss of heterozygosity (LOH) only for kg8. Fat-free total parenteral nutrition in association with sirolimus (2 mg po daily) was initiated. Serum sirolimus levels were maintained at concentrations between 5 and 15 ng/mL. After 1 month, reintroduction of a low-fat oral feeding was achieved without recurrence of ascites. PFT results were stable. Interestingly, clinical improvement was associated with a reduction in the VEGF-D serum level (1,558 pg/mL). LOH at the kg8 biomarker in blood LAM cells was no longer detected

Mini bobina de Tesla para el proceso de enseñanza - aprendizaje y/o la demostración en el aula

Con este trabajo se busca favorecer al proceso enseñanza-aprendizaje del electromagnetismo o bien la demostración de algunos fenómenos físicos tales como el principio de conservación de la energía entre otros. El primero de los objetivos se puede alcanzar por medio del seguimiento detallado del diseño, construcción y funcionamiento de la bobina de Tesla. La investigación, el desarrollo y la construcción son piezas claves para el proceso aprendizaje de los estudiantes, permitiendoles la capacidad de lograr que la teoría pueda ser aplicada de una u otra forma en un sentido práctico, ya sea orientado a la tecnología o bien a la ciencia básica que tienen como finalidad el conocimiento, el cual también puede incluir la educación. El segundo de los objetivos, por ser puramente demostrativo, parece más sencillo de lograr pero requiere un agudo sentido del oportunismo acompañado de las explicaciones y ejemplificaciones apropiadas. Lo que implica un conocimiento cabal de los fenómenos físicos que ocurren en esta mini-bobina de Tesla por parte del docente.

Deriving amino acid contact potentials from their frequencies of occurence in proteins: a lattice model study

The possibility of deriving the contact potentials between amino acids from their frequencies of occurence in proteins is discussed in evolutionary terms. This approach allows the use of traditional thermodynamics to describe such frequencies and, consequently, to develop a strategy to include in the calculations correlations due to the spatial proximity of the amino acids and to their overall tendency of being conserved in proteins. Making use of a lattice model to describe protein chains and defining a "true" potential, we test these strategies by selecting a database of folding model sequences, deriving the contact potentials from such sequences and comparing them with the "true" potential. Taking into account correlations allows for a markedly better prediction of the interaction potentials

Simple models of protein folding and of non--conventional drug design

While all the information required for the folding of a protein is contained in its amino acid sequence, one has not yet learned how to extract this information to predict the three--dimensional, biologically active, native conformation of a protein whose sequence is known. Using insight obtained from simple model simulations of the folding of proteins, in particular of the fact that this phenomenon is essentially controlled by conserved (native) contacts among (few) strongly interacting ("hot"), as a rule hydrophobic, amino acids, which also stabilize local elementary structures (LES, hidden, incipient secondary structures like $\alpha$--helices and $\beta$--sheets) formed early in the folding process and leading to the postcritical folding nucleus (i.e., the minimum set of native contacts which bring the system pass beyond the highest free--energy barrier found in the whole folding process) it is possible to work out a succesful strategy for reading the native structure of designed proteins from the knowledge of only their amino acid sequence and of the contact energies among the amino acids. Because LES have undergone millions of years of evolution to selectively dock to their complementary structures, small peptides made out of the same amino acids as the LES are expected to selectively attach to the newly expressed (unfolded) protein and inhibit its folding, or to the native (fluctuating) native conformation and denaturate it. These peptides, or their mimetic molecules, can thus be used as effective non--conventional drugs to those already existing (and directed at neutralizing the active site of enzymes), displaying the advantage of not suffering from the uprise of resistance

Electron-phonon interaction in C70

The matrix elements of the deformation potential of C$_{70}$ are calculated by means of a simple, yet accurate solution of the electron-phonon coupling problem in fullerenes, based on a parametrization of the ground state electronic density of the system in terms of $sp^{2+x}$ hybridized orbitals. The value of the calculated dimensionless total electron-phonon coupling constant is $\lambda\approx0.1$, an order of magnitude smaller than in C$_{60}$, consistent with the lack of a superconducting phase transition in C$_{70}$A$_3$ fullerite, and in overall agreement with measurements of the broadening of Raman peaks in C$_{70}$K$_4$. We also calculate the photoemission cross section of C$_{70}^-$, which is found to display less structure than that associated with C$_{60}^-$, in overall agreement with the experimental findings.Comment: To be published in Phys. Rev.

Goniómetro adaptado para la observación de los fenómenos y medición de los parámetros que intervienen en las leyes de refracción y reflexión de bajo costo

Con este trabajo se busca favorecer el proceso enseñanza aprendizaje de algunas leyes de la óptica, en particular la refracción, reflexión y la descomposición de la luz en su espectro fundamental. El objetivo fue el diseño de una unidad didáctica autocontenida que, con material de fácil consecución y bajo costo, permita a los estudiantes la asociación de los fenómenos mencionados y que se observan en la vida cotidiana, con lo aprendido sobre conceptos fundamentales de la óptica. Esto permitirá que el estudiante construya su conocimiento a través de la observación directa del mundo real a partir de las actividades diseñadas por el docente.

Theoretical estimates of the anapole magnetizabilities of C4H4X2 cyclic molecules for X=O, S, Se, and Te

Calculations have been carried out for C4H4X2 cyclic molecules, with X=O, S, Se, and Te, characterized by the presence of magnetic-field induced toroidal electron currents and associated orbital anapole moments. The orbital anapole induced by a static nonuniform magnetic field B, with uniform curl C =∇× B, is rationalized via a second-rank anapole magnetizability tensor aαβ , defined as minus the second derivative of the second-order interaction energy with respect to the components Cα and Bβ. The average anapole magnetizability a equals −χ, the pseudoscalar obtained by spatial averaging of the dipole-quadrupole magnetizability χα,βγ . It has different sign for D and L enantiomeric systems and can therefore be used for chiral discrimination. Therefore, in an isotropic chiral medium, a homogeneous magnetic field induces an electronic anapole Aα, having the same magnitude, but opposite sign, for two enantiomorphs.Fil: Pagola, Gabriel Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Ferraro, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Provasi, Patricio Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnologica; ArgentinaFil: Pelloni, Stefano. Universidad de Modena y Reggio Emilia. Departamento de Química; ItaliaFil: Lazzeretti, Paolo. Universidad de Modena y Reggio Emilia. Departamento de Química; Italia; Itali

Cabos-eletrodos epimiocárdicos

O implante de marcapasso com cabos-eletrodos endocavitários é a técnica preferida na atualidade. Entretanto, persiste o implante de cabo-eletrodo epimiocárdico ou, simplesmente, epicárdico uma vez que nem todos os casos sao elegíveis para o implante via endocavitária. Diferentes tipos de cabos-eletrodos estao disponíveis no mercado para implante de marcapassos epicárdicos definitivos e também temporários. Apesar de muito restrito, temos ainda o uso do cabo-eletrodo epicárdico na cardioversao-desfibrilaçao. Quanto à forma de fixaçao, eles sao divididos em penetrantes e nao penetrantes. Diversos acessos cirúrgicos podem ser adotados com o objetivo de expor o local no coraçao para realizar o implante desses cabos-eletrodos. O implante epicárdico deve ser abordado de forma individualizada para cada caso