Extended phonon collapse and the origin of the charge-density wave in 2H-NbSe2.

We report inelastic x-ray scattering measurements of the temperature dependence of phonon dispersion in the prototypical charge-density-wave (CDW) compound 2H-NbSe2. Surprisingly, acoustic phonons soften to zero frequency and become overdamped over an extended region around the CDW wave vector. This extended phonon collapse is dramatically different from the sharp cusp in the phonon dispersion expected from Fermi surface nesting. Instead, our experiments, combined with ab initio calculations, show that it is the wave vector dependence of the electron-phonon coupling that drives the CDW formation in 2H-NbSe2 and determines its periodicity. This mechanism explains the so far enigmatic behavior of CDW in 2H-NbSe2 and may provide a new approach to other strongly correlated systems where electron-phonon coupling is important.

Electron-phonon coupling and the soft phonon mode in TiSe2.

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe(2). We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5, 0, 0.5), at T≈T(CDW). Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe(2) are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3, 0, 0.5)≤q≤(0.5, 0, 0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe(2) although other mechanisms might further boost the transition temperature.

Gammasubdurography in the diagnosis of chronic subdural bilateral and communicating effusion in infants.

The results obtained by means of Gammasubdurography (G.S.G.) in 37 infants having chronic subdural bilateral effusions, are presented. The use of this procedure, which consists of unilateral injection of Radioiodinated Human Sero Albumin (RIHSA-I 131), into the subdural effusion, is suggested for the determination of a communication between the two cavities. At the same time it is possible to get valuable information about their exact localization and extension. Once the communication is diagnosed, the treatment proposed is internal or external unilateral drainage. The method is safe and is performed in a short time which permits its use in the screening of these patients, especially in conjunction with Gammaencephalography (G.E.G.) and Computer Tomography (CT), patients to it. The test (G.S.G.) has been used by us since 1979. All our cases are included in this series. All of them had been diagnosed by subdural puncture, transillumination, G.E.G. and or CT Scan, as having bilateral subdural collections. All the patients received a saturated iodine solution, 24 hours in advance and for 10 days, as a thyroid blocking agent, which was administered in the usual oral dosage. The radiopharmaceutical administration was performed through a unilateral subdural puncture in a dose of 50 to 80 microcurie of RIHSA-I 131 with a high specific activity. Immediately after this, sequential analog images were obtained with the patient supine and in anterior and lateral head projections. This was accomplished by using a PICKER DYNA 4 Gammacamera equipped with a medium energy parallel hole collimator. The interval between the images was determined during the test in agreement with the findings.

Gamaencefalografia con Tc - 99m DTPA en el diagnostico de la ventriculitis / Gammaencephalography with Tc - 99m DTPA in the diagnosis of ventriculitis

Se destaca la importancia del diagnostico precoz de la ventriculitis. Es igualmente imperativo contar con medios que permitan seguir la evolucion bajo tratamiento, asi como certificar la curacion, total o parcial, de este cuadro. Se presenta una serie preliminar de gamaencefalografia con Tc - DTPA que se ha mostrado muy alentadora en estos aspectos. Se destaca la inocuidad, rapidez y economia del metodo

Utilidad de la gamaencefalografia en el diagnostico y seguimento de los infartos cerebrales. / Utility of the gamaencephalography in the diagnosis and follow-up of cerebral infarction

Se revisan los examenes gamaencefalograficos realizados en el Servicio de Medicina Nuclear del Instituto de Neurocirurgia de Santiago entre abril de 1977 y septiembre de 1981. Se seleccionan de alli 114 casos con el diagnostico de AVE y con suficiente material clinico para su analisis. Se muestra su distribucion por sexo y edades y se analiza la positividad de la GEG, como su correlacion con otros recursos diagnosticos. Se demuestra la necesidad de efectuar rutinariamente la angiografia isotopica al comienzo de cada examen como tambien GEG de control, para aumentar la positividad del metodo. Se destaca tambien la necesidad de tener en cuenta el periodo de evolucion del cuadro para alcanzar el mayor rendimiento del procedimiento

La gamasubdurografia en la determinacion de comunicacion entre colecciones subdurales cronicas bilaterales del lactante.Su utilidad diagnostica y terapeutica. / The gammasubdurography in the determination of comminication among bilateral chronic subdural collections in infant.Its diagnostic and therapeutic usefulness

Se presentan los resultados obtenidos en el estudio mediante gamasubdurografia en 10 lactantes portadores de coleccion subdural bilateral. Se propone el empleo de este examen unilateral, con RISA I-131 en estos pacientes para determinar la existencia de comunicacion entre ambas cavidades.Proporciona simultaneamente valiosa informacion respecto a la extension y ubicacion exata de las lesiones.Demostrada la comunicacion mediante el drenaje, interno o externo,unilateral.La inocuidad y rapidez del metodo permite proponerlo como parte del estudio rutinario de estos pacientes, en especial, como complemento de la gamaencefalografia y de la tomografia axial computarizada