Thymine adsorption on two-dimensional boron nitride structures: first-principles studies.

First-principles total-energy calculations were performed to investigate the structural and electronic properties of thymine (T) adsorption on pristine and Al-doped two-dimensional hexagonal boron nitride (2D-hBN) surfaces. Periodic density functional theory, as developed in the PWscf code of the quantum espresso package, was applied. The pseudopotential theory was used to deal with electron-ion interactions. The generalized gradient approximation was applied to treat the exchange-correlation energies. Van der Waals interactions were incorporated in the calculations. Considering T as an elongated molecule and the interactions through one oxygen atom of the molecule ring, two geometries were explored in pristine and Al-doped systems: in (1) the ring side O interacts with B, and (2) the O at the molecule end interacting with the B. The pristine case yields (4 × 4-a), (5 × 5-b) and (6 × 6-b) as the ground states, , while the doped system shows (4 × 4-a), (5 × 5-a) and (6 × 6-a) as the ground states. Calculations of the adsorption energies indicate chemisorption. Doping enhances the surface reactivity, inducing larger binding energies. The total density of states (DOS) was calculated and interpreted with the aid of the projected DOS. Below the Fermi energy, the DOS graphs indicate that p orbitals make the largest contributions. Above the Fermi level, the DOS is formed mainly by -s and H-s orbitals. The DOS graphs indicate that the structures have non-semiconductor behavior.

Chiral atomically thin films.

Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg µm(-1)) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra.

Circular polarization interferometry: circularly polarized modes of cholesteric liquid crystals.

We describe a novel polarization interferometer which permits the determination of the refractive indices for circularly-polarized light. It is based on a Jamin-Lebedeff interferometer, modified with waveplates, and permits us to experimentally determine the refractive indices nL and nR of the respectively left- and right-circularly polarized modes in a cholesteric liquid crystal. Whereas optical rotation measurements only determine the circular birefringence, i.e. the difference (nL - nR), the interferometer also permits the determination of their absolute values. We report refractive indices of a cholesteric liquid crystal in the region of selective (Bragg) reflection as a function of temperature.

Orientational order parameters of a de Vries-type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction.

The orientational order parameters (P{2}) and (P{4}) of the ferroelectric, de Vries-type liquid crystal 9HL have been determined in the SmA and SmC phases by means of polarized Raman spectroscopy, and in the SmA phase using x-ray diffraction. Quantum density functional theory predicts Raman spectra for 9HL that are in good agreement with the observations and indicates that the strong Raman band probed in the experiment corresponds to the uniaxial, coupled vibration of the three phenyl rings along the molecular long axis. The magnitudes of the orientational order parameters obtained in the Raman and x-ray experiments differ dramatically from each other, a discrepancy that is resolved by considering that the two techniques probe the orientational distributions of different molecular axes. We have developed a systematic procedure in which we calculate the angle between these axes and rescale the orientational order parameters obtained from x-ray scattering with results that are then in good agreement with the Raman data. At least in the case of 9HL, the results obtained by both techniques support a "sugar loaf" orientational distribution in the SmA phase with no qualitative difference to conventional smectics A. The role of individual molecular fragments in promoting de Vries-type behavior is considered.

Isosorbide dinitrate sublingual therapy for inferior myocardial infarction: randomized trial to assess infarct size limitation.

To assess the potential of isosorbide dinitrate sublingual therapy for limiting myocardial infarct size, 41 patients with inferior acute myocardial infarction (AMI) were studied. Twenty patients were randomly assigned to the control group and 21 to the treatment group. Patients in the treatment group received 10 mg of isosorbide dinitrate every 2 hours for 72 hours. To estimate infarct size, QRS scoring, peak creatine kinase (CK) serum levels and CK curves were used. There were no significant differences between the 2 groups in maximal or cumulative activity of CK or QRS score (percent of left ventricle infarcted: 16% in the control group, 17% in the treatment group). In both groups the QRS score increased significantly by 13 hours after AMI, and the increase was highly significant by 19 to 23 hours. Thus, sublingual isosorbide dinitrate at the dosage given did not reduce infarct size in patients with inferior AMI.

[Permanent endocardial pacemaker. Review of 116 implantations (author's transl)]. / Marcapaso endocavitario permanente. A propósito de 116 implantaciones.

A retrospective study on the results of 116 permanent ventricular pacemaker implantations performed in the Service of Cardiology of the Hospital Clinico Universitario in Salamanca is reported. In the majority of cases the indication for a pacemaker was a complete atrioventricular block (53 cases). Sixteen cases had a "sick-sinus syndrome". An apparent cardiopathy was not found in 84 percent of the cases. In the group of patients with cardiopathy that of ischemic type was the most common. The technique of endocardiac catheter pacing was employed in all cases. An 18 percent of global complications occurred, but in no case an early electrode displacement was registered. Complications appeared at a later time included erosion of the pacemaker in ten cases, and displacement and/or deinsertion in seven. The mean life for 18 displaced generators was 41.3 months. A sudden equipment malfunction occurred in two cases, and an inhibition by potentials of the pectoralis major muscle in another. Morbidity rate was lower to that of other published series, may be due to the use of modern generators with a progressive reduction of its diameter and weight and more flexible electrodes which allow a better implantation. The mortality rate was zero.

[Chromosomal in study patients treated with anticonvulsant drugs]. / Estudio cromosómico en pacientes tratados con farmacos anticonvulsivantes.

Selected at random from a special consultation in a general teaching hospital in the City of La Habana, 10 epileptic patients were studied. They were clinically, as well as electroencephalographically diagnosed; followed by treatment with different anticonvulsant drugs for a period not less than 3 months and not greater than 5 years. 100 metaphases of each one of the patients were analyzed without finding any deviation in the normal diploidy number of chromosomes (2n = 46), nor alterations in the morphology of the same. We consider this work a preliminary report which does not permit us to arrive at definite conclusions at this moment; but in subsequent work, which we are already carrying out, we hope to issue some considerations with respect to the use of anticonvulsant drugs and their effects in the human chromosomes.