Second harmonic generation in anisotropic stratified media: a generalization of the Berreman method and its application to photonic materials.

We have developed a numerical method for calculating the second-harmonic generation (SHG) generated by an anisotropic material whose optical properties present an arbitrary modulation in one dimension. The method is based on the Berreman 4 × 4 matrix formalism, which is generalized to include nonlinear optical phenomena. It can be used under oblique incidences of the input beam, and is valid even when the SHG frequency is close to photonic bands, where the usual slowly-varying-amplitude approximation breaks down. As an example of application, we have studied the SHG performance of ferroelectric and helielectric fluids. The obtained results indicate that the present procedure may contribute to improving the structural design and enlarging the variety of nonlinear optical materials for application in optical devices.

Kinetic behavior of light emission in cholesteric liquid crystal lasers: An experimental study.

Some dynamical aspects of fluorescence and lasing have been studied in a dye-doped cholesteric liquid crystal by measuring the response of the material to nanosecond optical pumping. It has been found that as the pumping energy is increased the fluorescence pulse duration decreases, reaching a minimum at the lasing threshold. Above the threshold the temporal profiles are irregular and consist of a set of narrow pulses whose measured duration is limited by the detector risetime (1 ns). The results are interpreted in terms of a recently proposed model [JETP, 118, 822 (2014)] that makes use of rate equations to account for the laser generation in cholesteric liquid crystals. The prediction of such equations for an experimental configuration appropriate for fluorescence lifetime measurements is analyzed.

Scenario-targeted toxicity assessment through multiple endpoint bioassays in a soil posing unacceptable environmental risk according to regulatory screening values.

Lanestosa is a chronically polluted site (derelict mine) where the soil (Lanestosa (LA) soil) exceeds screening values (SVs) of regulatory policies in force (Basque Country; Europe) for Zn, Pb and Cd. A scenario-targeted toxicity assessment was carried out on the basis of a multi-endpoint bioassay approach. Acute and chronic toxicity bioassays were conducted with selected test species (Vibrio fischeri, Dictyostelium discoideum, Lactuca sativa, Raphanus sativus and Eisenia fetida) in combination with chemical analysis of soils and elutriates and with bioaccumulation studies in earthworms. Besides, the toxicity profile was compared with that of the mine runoff (RO) soil and of a fresh artificially polluted soil (LAAPS) resembling LA soil pollutant profile. Extractability studies in LA soil revealed that Pb, Zn and Cd were highly available for exchange and/or release into the environment. Indeed, Pb and Zn were accumulated in earthworms and LA soil resulted to be toxic. Soil respiration, V. fischeri, vegetative and developmental cycles of D. discoideum and survival and juvenile production of E. fetida were severely affected. These results confirmed that LA soil had unacceptable environmental risk and demanded intervention. In contrast, although Pb and Zn concentrations in RO soil revealed also unacceptable risk, both metal extractability and toxicity were much lower than in LA soil. Thus, within the polluted site, the need for intervention varied between areas that posed dissimilar risk. Besides, since LAAPS, with a high exchangeable metal fraction, was the most toxic, ageing under in situ natural conditions seemingly contributed to attenuate LA soil risk. As a whole, combining multi-endpoint bioassays with scenario-targeted analysis (including leaching and ageing) provides reliable risk assessment in soils posing unacceptable environmental risk according to SVs, which is useful to optimise the required intervention measures.

Thermally induced light-scattering effects as responsible for the degradation of cholesteric liquid crystal lasers.

We have studied the degradation process of the laser emission in a cholesteric liquid crystal laser. We have found that there exists a negative correlation between the laser efficiency and the amount of light scattered by the liquid-crystal sample in the illuminated area. The growth of scattering is attributed to the appearance of small imperfections generated in the sample as a result of certain thermal processes that involve the dye molecules. The scattering implies an increase of the coefficient of distributed losses, which is the main response of the rise of the laser threshold.

Spontaneous and field-induced mesomorphism of a silyl-terminated bent-core liquid crystal as determined from second-harmonic generation and resonant X-ray scattering.

The polarity and structure of the phases of a liquid crystal constituted by thiophene-based bent-core molecules is investigated by means of optical second-harmonic generation (SHG), and resonant and conventional X-ray diffraction. The material studied is representative of a wide family of mesogens that contain silyl groups at the ends of the chains. These bulky terminal groups have been reported to give rise to smectic phases showing ferroelectric switching. However, the analysis of the SHG signal before and after application of electric fields has allowed us to establish unambiguously that the reported ferroelectricity is not intrinsic to the material but stabilized by the cell substrates once an electric field has been applied. In addition, the results obtained from resonant X-ray diffraction indicate that virgin samples have antiferroelectric undulated synclinic smectic structures.

Tear proteome and protein network analyses reveal a novel pentamarker panel for tear film characterization in dry eye and meibomian gland dysfunction.

Dry eye and meibomian gland dysfunction are common ocular surface disorders. Discrimination of both conditions often may be difficult given the overlapping of signs and symptoms, and the lack of correlation with clinical parameters. A total of 144 individuals were included in this study. To search for proteome differences, tear proteins were collected by Merocel sponge and analyzed using 2D-PAGE. Comparative tear protein profile analysis indicated changes in the expression levels of fifteen proteins. Subsequent to MALDI-TOF/TOF protein identification, network analysis revealed expression/interaction connections with other proteins, thereby identifying additional putative markers. A screening validation assay demonstrated the discriminative power of six candidate biomarkers. A further validation study using multiplexed-like ELISA assays in tear samples collected with both sponge and capillary confirmed the high discriminatory power of five biomarkers: S100A6, annexin A1 (ANXA1), annexin A11 (ANXA11), cystatin-S (CST4), and phospholipase A2-activating protein (PLAA) with an area under ROC curve (AUC)≥ 97.9% (sensitivity ≥ 94.3%; specificity ≥ 97.6%) when comparing dry eye and control individuals. This panel also discriminated between dry eye, meibomian gland dysfunction and control individuals, with a global correct assignment (CA) of 73.2% between all groups. Correct assignment was not found to be significantly dependent on the tear collection method.

Second-harmonic generation in a laterally azo-bridged trimer ferroelectric liquid crystal: phase matching in the presence of a helicoidal structure.

Optical second-harmonic generation (SHG) has been studied in a trimer smectic C* liquid crystal especially designed for nonlinear optical applications. The molecule has a long conjugated donor-acceptor unit that transversally links three parallel rod-shaped moieties. A strong SHG signal has been observed at a fundamental wavelength of 1369 nm even in the presence of the spontaneous helicoidal structure of the smectic C* phase. This unusual behavior has been interpreted as due to the existence of phase matching, in which the wave vector mismatch is compensated by the wave vector of the helix. This point has been confirmed by the study of the SHG intensity versus sample thickness and light polarization characteristics. The main coefficient of the second-order susceptibility tensor of the material has been estimated to be d(22) = 28 pm/V.

Electric-field-induced phase transitions in bent-core mesogens determined by x-ray diffraction.

The changes in the x-ray diffraction diagram induced by an electric field have been studied in four bent-core liquid crystals. Two of the compounds present columnar B1 phases and the other two show dark conglomerate (DC) structures. In the B1 materials the electric field gives rise to switchable phases whose diffraction pattern is that of the smectic C polar (SmCP) phase. In the DC structures the positions of the Bragg reflections remain essentially unaltered, but in one of the compounds the peaks become narrower under field, indicating that the correlation length of the smectic order increases. A slight enhancement of the smectic spacing is found in the DC phases upon field application.

Polarization periodicity in the B(1) columnar phase determined by resonant x-ray scattering.

We report structural results that evidence the polarization distribution of the blocks in the columnar phase of an achiral bent-core liquid crystal. The study was performed using resonant x-ray diffraction at the sulfur K edge on oriented samples aligned on substrates. The extra periodicity is revealed through the violation of the systematic extinction rule of the structural symmetry group along the experimentally accessible diffraction direction. Further data obtained from the polarization analysis of a resonant reflection give information concerning the transition mechanism between B(1) and B(2) phases.

Photoisomerizable metallomesogens and soft crystals based on orthopalladated complexes.

With the aim of obtaining light-responsive liquid-crystalline palladium complexes, six palladium complexes derived from an orthometalated imine, bearing one or two azocarboxylato bridges, have been synthesized: [Pd(2)(µ-SC(10)H(21))(µ-O(2)CAzo)(L(1,2))(2)] (7 and 8), [Pd(2)(µ-SC(10)H(21))(µ-O(2)CAzo3C(10))(L(1,2))(2)] (9 and 10), [Pd(µ-O(2)CAzo)L(1)](2) (11), and [Pd(µ-O(2)CAzo3C(10))L(1)](2) (12), in which L(1) = p-H(21)C(10)OC(6)H(3)CH═NC(6)H(4)OC(10)H(21)-p, L(2) = p-H(21)C(10)OC(6)H(3)CH═NC(14)H(29), AzoCO(2)(-) = p-(phenylazo)benzoate, and Azo3C(10)CO(2)(-) = p-(2',3',4'-tris-n-decyloxyphenylazo)benzoate. Three of them (7-9), as well as the precursor Azo3C(10)CO(2)H (3), are thermotropic liquid crystals displaying nematic and smectic A mesophases, while 10-12 have been identified by X-ray diffraction to give rise to "soft" crystal phases. Electronic spectroscopy and (1)H NMR show that all of them undergo a trans-cis isomerization of the azobenzene moiety at λ = 365 nm. The molecular structure determines the photoresponse in solution, which is faster and more stable when the trisubstituted azocarboxylate is present and the motion of the azo group is not hindered by the orthometalated imine. The photoresponse has also been observed in the condensed phases, which change from the ordered phase to the isotropic liquid upon irradiation, except for compound 10, a soft crystal in which a permanent photoalignment highly sensitive to light polarization is produced. The latter is a behavior with potential applications, rather unusual in low-molecular-weight compounds.

Pseudolayered structure of the columnar B1 phase of bent-core liquid crystals.

Three bent-core liquid-crystal compounds presenting the unusual columnar B1 to tilted polar smectic (Sm-CP or B2) phase transition are studied through small-angle x-ray diffraction on aligned samples. The well-established character of the smectic phase helps to characterize the structural changes during the transition. A mechanism for this transition is proposed, which accounts for the low enthalpy usually observed in this process. The B1 phase is found to possess a great degree of lamellarization, with pseudosmectic ferroelectric layers along the crystallographic (11) planes. As a consequence of these observations a distribution of the block polarizations in the columnar structure is proposed.

Supramolecular-directed chiral induction in biaryl derivatives.

A thermodynamically controlled resolution has allowed for the generation of diastereomerically enriched complexes, by chirality transfer from an enantiopure building block to a dynamically racemic biaryl derivative. A switchable sense of induction could be achieved depending on the substituents of the chiral block.

Polar structures of bent-core liquid crystals with tetrathiafulvalene units.

We report on a series of three bent-core liquid crystals containing tetrathiafulvalene units. Their characterization consisted of electro-optical observations, second-harmonic generation (SHG) analysis, and x-ray diffraction measurements. Compound I exhibits a lamellar optically isotropic phase on cooling from the isotropic liquid and undergoes a nonreversible field-induced transition to a birefringent state. The two others present two-dimensional structural periodicities, being only compound II switchable. Additionally, the electron density maps of compounds II and III have been obtained based on the analysis of the x-ray diffraction intensities. According to SHG measurements the ground state is antiferroelectric in the three compounds. A quite good SHG performance is found in compounds I and II.

Manifestaciones oftalmológicas en tumores cerebrales pediátricos: 58 casos / Ophthalological findings in pediatric brain neoplasms: 58 cases

Objetivos: Describir las manifestaciones visuales en neoplasias neuropediátricas, relacionarlas con la localización tumoral y analizar su relevancia en el seguimiento de la enfermedad. Material y métodos: Estudio descriptivo retrospectivo que incluye pacientes menores de 14 años con neoplasias cerebrales de cualquier estirpe, registradas en nuestro centro desde 1996 hasta el 2005. Resultados: En un 44% de los pacientes con descenso en la agudeza visual, la ambliopía fue catalogada como orgánica. En el 28% de los casos, la ambliopía era secundaria al estrabismo/nistagmus producido por el tumor. El tratamiento corrector resultó efectivo en varios casos de ambliopía parcial y totalmente orgánica. Tres recidivas tumorales fueron detectadas gracias a la exploración de fondo de ojo y campimetría, antes de que las pruebas de imagen fueran concluyentes. Conclusión: El examen oftalmológico (agudeza visual, campimetría, funduscopia) es una pieza clave en el seguimiento de la patología tumoral cerebral. Las ambliopías orgánicas parciales/totales son susceptibles de tratamiento corrector

Purposes: To describe the visual manifestations of brain neoplasms, and to analyze the effect of tumor control on these. Methods: This is a descriptive retrospective study, which includes patients under 14 years of age, suffering from different brain neoplasms in our hospital between 1996 and 2005 inclusive. Results: In the group of patients with low visual acuity, 44% had organic amblyopias. In 28% of cases, the amblyopia was secondary to the strabismus/nystagmus produced by the developing tumor. Corrective treatment was successful in some cases of partial or total organic amblyopia. Ophthalmologic evaluation (including perimetry and fundoscopy) enabled detection of 3 tumor relapses. Conclusions: Visual analysis (visual acuity, perimetry, fundoscopy) should be an essential component of assessment during brain neoplasm treatment and follow-up. Corrective treatment is sometimes successful in organic amblyopias (Arch Soc Esp Oftalmol 2008; 83: 471-478)

[Ophthalmological findings in pediatric brain neoplasms: 58 cases]. / Manifestaciones oftalmológicas en tumores cerebrales pediátricos: 58 casos.

PURPOSES: To describe the visual manifestations of brain neoplasms, and to analyze the effect of tumor control on these. METHODS: This is a descriptive retrospective study, which includes patients under 14 years of age, suffering from different brain neoplasms in our hospital between 1996 and 2005 inclusive. RESULTS: In the group of patients with low visual acuity, 44% had organic amblyopias. In 28% of cases, the amblyopia was secondary to the strabismus/nystagmus produced by the developing tumor. Corrective treatment was successful in some cases of partial or total organic amblyopia. Ophthalmologic evaluation (including perimetry and fundoscopy) enabled detection of 3 tumor relapses. CONCLUSIONS: Visual analysis (visual acuity, perimetry, fundoscopy) should be an essential component of assessment during brain neoplasm treatment and follow-up. Corrective treatment is sometimes successful in organic amblyopias

[Protected penetrating keratoplasty: surgical technique and endothelial response]. / Queratoplastia penetrante protegida: técnica quirúrgica y respuesta del endotelio.

PURPOSE: To describe the technique and to evaluate the safety of protected penetrating keratoplasty (PPK). METHODS: A technique for penetrating keratoplasty is described. The postoperative endothelial cell counts of 17 eyes in which this operative technique was used were compared with those in 24 eyes in whom the standard operative technique for penetrating keratoplasty (PK) was used. The post-operative time periods were grouped as follows: 3-6 months, 7-12 months and >12 months. For statistical analysis, the Mann-Whitney U non-parametric test was employed. RESULTS: There was no case where tissue extrusion occurred during the procedure. The endothelial cell count was similar in both groups for the 3-6 month period (PK = 2,086, DS 566; PPK = 1,858, DS 671; p = 0.2702) and >12 months period (PK = 1,574, DS 745; PPK = 1,419, DS 810; p = 0.2882). There was a significant difference in the 7-12 month period (PK = 2,255, DS 831; PPK = 1,569, DS 623; p = 0.0397). CONCLUSIONS: The described technique of PPK may reduce the risk of per-operative complications. Damage to the endothelium is not increased compared with that seen following the standard PK procedure.

Queratoplastia penetrante protegida: técnica quirúrgica y respuesta del endotelio / Protected penetrating keratoplasty: surgical technique and endothelial response

Objetivo: Describir la técnica y conocer la seguridad de una cirugía de queratoplastia penetrante protegida (QPP). Métodos: Se describe una técnica de QPP. Se compara la evolución postoperatoria del endotelio corneal de 17 ojos intervenidos con esta técnica, comparándola con la de 24 ojos intervenidos con queratoplastia penetrante estándar (QP), en tres periodos de tiempo: 3-6 meses, 7-12 meses y más de 12 meses. Para el análisis estadístico se realizó el test no paramétrico de la U de Mann-Whitney. Resultados: En ninguno de los casos intervenidos con técnica de QPP se apreció extrusión de tejidos o estructuras intraoculares. El recuento endotelial no mostró diferencia estadísticas en el período de 3-6 meses (QP = 2.086 DE 566; QPP = 1.858 DE 671; p = 0,2702) y el de más de 12 meses (QP = 1.574 DE 745; QPP = 1.419 DE 810; p = 0,2882). Existió diferencia significativa en el período de 7-12 meses (QP = 2.255 DE 831; QPP = 1.569 DE 623; p = 0,0397). Conclusiones: La QPP que se describe puede reducir el riesgo de ciertas complicaciones perquirúrgicas. El endotelio no muestra un sufrimiento significativo cuando se compara con la técnica de QP estándar

Purpose: To describe the technique and to evaluate the safety of protected penetrating keratoplasty (PPK). Methods: A technique for penetrating keratoplasty is described. The postoperative endothelial cell counts of 17 eyes in which this operative technique was used were compared with those in 24 eyes in whom the standard operative technique for penetrating keratoplasty (PK) was used. The post-operative time periods were grouped as follows: 3-6 months, 7-12 months and >12 months. For statistical analysis, the Mann-Whitney U non-parametric test was employed. Results: There was no case where tissue extrusion occurred during the procedure. The endothelial cell count was similar in both groups for the 3-6 month period (PK = 2,086, DS 566; PPK = 1,858, DS 671; p = 0.2702) and >12 months period (PK = 1,574, DS 745; PPK = 1,419, DS 810; p = 0.2882). There was a significant difference in the 7-12 month period (PK = 2,255, DS 831; PPK = 1,569, DS 623; p = 0.0397). Conclusions: The described technique of PPK may reduce the risk of per-operative complications. Damage to the endothelium is not increased compared with that seen following the standard PK procedure (Arch Soc Esp Oftalmol 2008; 83: 231-236)

Bent-core liquid-crystalline derivative of tetrathiafulvalene: photoresponsivity and deracemization.

A bent-core mesogen containing a tetrathiafulvalene group is studied. The mesophase is an optically isotropic spongelike smectic phase without optical activity. The material responds to uv light in a peculiar way, showing photoconductivity and, in some circumstances, changing its mesomorphic properties. Under an electric field, large chiral domains are segregated from an initial racemic phase within a few minutes.

Quantitative analysis of the x-ray diffraction intensities of undulated smectic phases in bent-core liquid crystals.

X-ray diffraction diagrams of undulated smectic phases in bent-core liquid crystals have been theoretically studied. The intensities of the reflections have been obtained for different layer modulations, and a general expression has been deduced for orthogonal cells in terms of the different harmonics of the distortion. The case of sinusoidal modulation is especially simple and has been studied also in oblique cells. High-quality x-ray measurements of three compounds reported in the literature have been analyzed as examples. In all cases it has been deduced that the modulation is sinusoidal and its amplitude has been easily obtained by fitting the experimental intensities. Equatorial (h0) reflections have been also considered to obtain information about the structure of defects at the maxima and minima of the undulation.