Temporal compression of nanosecond laser pulses using coherent control

We present a study of the temporal compression of nanosecond laser pulses resulting from the coherent control peculiarities of the propagation dynamics in a regime of electromagnetically induced transparency. We describe the general theoretical framework and discuss the crucial conditions required in order to experimentally realize such a temporal compression scheme. A proof-of-concept experimental realization of a scheme of this type in a sample of hot sodium vapors is currently being implemented: we describe in detail the experimental setup designed for this purpose.     

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Ohne Zusammenfassung     

Studies about the adsorption on lichen Evernia prunastri by enthalpimetric measurements

Lichens are bioaccumulators of divalent metal ions and the interaction between the lichens and five heavy metals was studied. In order to have a better understanding of the metal-uptake process by the lichens, data from atomic absorption spectroscopy were used to calculate the apparent coordination constants of the lichen–metal ion interactions by means of the Langmuir elaboration and microcalorimetric measurements to obtain enthalpimetric information. The results showed a correlation between the Langmuir constants and enthalpimetric measurements.     

Mixing method influence on compatibility and polymorphism studies by DSC and statistical analysis

Most of the pharmaceutical products are formulated as solid dosage form, which may present drug–excipient interactions that lead to changes in the chemical nature of the drug, such as solubility and bioavailability and may compromise its safety and effectiveness. Differential scanning calorimetry (DSC) is a widely used method for the rapid evaluation of the drug-excipient compatibility and the stability of the mixture formed; however, there is no consensus on the preparation methods of the drug–excipient mixtures. The aim of this study was to investigate the influence of the mixing method on the drug–excipient compatibility studies by means of DSC analysis, using tenofovir disoproxil fumarate as a drug model. Statistical analysis revealed significant differences in the heat of fusion of the drug in the mixtures prepared by several mixing methods. Vortex Mixer with a Pop-Off Cup used for 3 min proved to be very satisfactory for these studies. A polymorphic transition was observed in the mixture prepared with the mortar and pestle. Therefore, this method should be avoided since it may induce errors in the interpretation of DSC results. In this way, the mixing method used to prepare a mixture for studies of interactions between the API and the excipients in a pharmaceutical formulation has a great influence on the results and it must be chosen carefully.     

Controlling the propagation of broadband light pulses by Electromagnetically Induced Transparency

We present an experimental and theoretical investigation, performed on hot sodium atoms in a ladder scheme, showing the control of the absorption and of the propagation velocity of a probe light pulse with a spectral bandwidth as large as 1.8 GHz. The predictions of the theoretical model compare favorably with the experimental results.     

Investigation on the surface orientation of cylindrical microdomains in styrene-butadiene-styrene triblock copolymers by scanning force microscopy/transmission electron microscopy

The orientation of the microdomains at the free surface of solvent-cast films of a polystyrene-block-polybutadiene-block-polystyrene triblock copolymer with cyclindrical morphology was studied by coupling transmission electron and scanning force microscopies (SFM-TEM). It was found that the cylinders of polystyrene, which are assembled in grains randomly oriented in the bulk, tend to reorient with the main axis perpendicular to the surface. SFM investigation indicates that the hexagonal symmetry of the cylinders is also maintained at the free surface which is characterized by protrusions and corrugation with size and characteristic distances closely related to the cylindrical morphology visible in the bulk. Good quantitative agreement between TEM and SFM measurements is observed.     

Spin densities in some diazine and naphthyridine anions

The E.S.R. spectra of a number of diazine and naphthyridine anions are interpreted using molecular orbital theory. Results obtained with different theoretical procedures are compared and discussed.     

Generation and propagation of a picosecond acoustic pulse at a buried interface: time-resolved x-ray diffraction measurements

We report on the propagation of coherent acoustic wave packets in (001) surface oriented Al0.3Ga0.7As/GaAs heterostructure, generated through localized femtosecond photoexcitation of the GaAs. Transient structural changes in both the substrate and film are measured with picosecond time-resolved x-ray diffraction. The data indicate an elastic response consisting of unipolar compression pulses of a few hundred picosecond duration traveling along [001] and [001] directions that are produced by predominately impulsive stress. The transmission and reflection of the strain pulses are in agreement with an acoustic mismatch model of the heterostructure and free-space interfaces.