Broadly tunable dual-wavelength light source for coherent anti-Stokes Raman scattering microscopy

The signal and idler beams from a picosecond, synchronously pumped optical parametric oscillator (OPO) provide the two colors necessary for coherent anti-Stokes Raman scattering (CARS) microscopy. The OPO provides a continuously tunable frequency difference between the two beams over a broad range of Raman shifts (100-3700 cm(-1)) by varying the temperature of a single nonlinear crystal. The near-infrared output (900-1300 nm) allows for deep penetration into thick samples and reduced nonlinear photodamage. Applications of this light source to in vivo cell and ex vivo tissue imaging are demonstrated.     

Enhanced downconversion of UV light by resonant scattering of aluminum nanoparticles

Metallic nanoparticles are known to enhance nonlinear optical processes due to a local enhancement of the optical field. This strategy has been proposed to enhance downconversion in thin film solar cells, but has various disadvantages, among which is the fact that the enhancement occurs only in a tiny volume close to the particles. We report on a very different physical mechanism that can lead to significant downconversion enhancement, namely, that of resonant light scattering, and which is a large volume effect. We show that only a tiny amount of resonantly scattering metallic (aluminum) nanoparticles is enough to create a significant enhancement of the fluorescence of dye molecules in the visible wavelength range. The strategy can be applied in general to increase the emission of UV-absorbing constituents, and is of particular use for solar energy.     

k-Cosymplectic Classical Field Theories: Tulczyjew and Skinner–Rusk Formulations

The k-cosymplectic Lagrangian and Hamiltonian formalisms of first-order classical field theories are reviewed and completed. In particular, they are stated for singular and almost-regular systems. Subsequently, several alternative formulations for k-cosymplectic first-order field theories are developed: First, generalizing the construction of Tulczyjew for mechanics, we give a new interpretation of the classical field equations. Second, the Lagrangian and Hamiltonian formalisms are unified by giving an extension of the Skinner–Rusk formulation on classical mechanics.     

Analysis of confiscated fireworks using Raman spectroscopy assisted with SEM‐EDS and FTIR

A forensic analysis of several samples of pyrotechnic artefacts was performed by Raman spectroscopy assisted by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy (SEM‐EDS) and Fourier transform infrared (FTIR) analysis. Among the components, several nitrates, ammonium perchlorate, nitrocellulose, metallic titanium particles and shellac were detected. The combination of Raman spectroscopy and SEM‐EDS showed very useful performance. All components were detected by Raman spectroscopy except for shellac, kaolinite and titanium particles, which were not conclusive enough and had to be determined by FTIR and EDS. In contrast, many compounds were not detected by FTIR. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation of the possible origins of sulfur in 19th century salted paper photographs by x‐ray fluorescence spectroscopy

An X‐ray fluorescence method to determine whether sulfur is present in 19th century photographs due to intentional toning or to environmental deterioration is proposed. In the 19th century salted paper print photographic process, AgCl formed on the surface of a sheet of paper was exposed to sunlight in contact with a negative, leading to the printing out of a Ag image that was fixed by immersing it in a sodium thiosulfate solution or hypo. The improper execution of the fixing in these photographs may result in the presence of sulfur, mostly manifested in image fading, irregular staining, and discoloration. Also, 19th century artists produced salted paper prints with a variety of image tonalities, for example, by using an artificially aged thiosulfate bath. The presence of sulfur in photographs may also be due to sulfur‐containing environmental pollutants. Therefore, knowledge about the location and amounts of sulfur is important to understand the artistic technique and/or the deterioration processes. In this study, the amounts of sulfur and the silver to sulfur signal ratios were determined for a salted paper print made in the laboratory following a 19th century procedure and for two artistic salted paper photographs using X‐ray fluorescence and standards prepared with different amounts of retained hypo and quantified by inductively coupled plasma atomic emission spectroscopy. The amounts of sulfur and the normalized silver to sulfur ratios for the artistic photographs were evaluated based on the results obtained in the samples prepared in the laboratory and in the context of the 19th century practices. Copyright © 2016 John Wiley & Sons, Ltd.     

Changes in cerebral activity after decreased upper-limb hypertonus: an EMG-fMRI study

Objective

Whereas several studies have used functional magnetic resonance imaging (fMRI) to investigate motor recovery, whether therapy to decrease post-stroke hypertonus alters central motor patterns remains unclear. In this study, we used continuous electromyography (EMG)-fMRI to investigate possible changes in movement-related brain activation in patients receiving Botulinum toxin (BoNT-A) for hand-muscle hypertonus after chronic stroke.

Methods

We studied eight stroke patients all of whom had hemiparesis and associated upper-limb hypertonus. All patients underwent an fMRI-EMG recording and clinical-neurological assessment before BoNT-A and 5 weeks thereafter. The handgrip motor task during imaging was fixed across both patients and controls. The movements were metronome paced, movement amplitude and force were controlled with a plastic orthosis, dynamometer and EMG recording. An age-matched control group was recruited from among healthy volunteers underwent the same fMRI-EMG recording.

Results

Before BoNT-A, while patients moved the paretic hand, fMRI detected wide bilateral activation in the sensorymotor areas (SM1), in the supplementary motor area (SMA) and cerebellum. After BoNT-A blood oxygenation level-dependent (BOLD) activation decreased in ipsilateral and contralateral motor areas and became more lateralized. BOLD activation decreased also in ipsilateral cerebellar regions and in the SMA.

Conclusion

Changes in peripheral upper-limb hypertonus after BoNT-A were associated to an improvement in active movements and more lateralized and focalized activation of motor areas. The clinical and EMG-fMRI coregistration technique we used to study hand-muscle hypertonus in patients receiving BoNT-A after chronic stroke should be useful in future studies seeking improved strategies for post-stroke neurorehabilitation.     

Characterization of Al(III) complexes with hematein in artistic alum logwood inks

The complexes between Al(III) and hematein, the main coloring matter in alum logwood inks, were characterized by Raman and ²⁷Al NMR (nuclear magnetic resonance) spectroscopies. Raman spectra of the crystallized complexes and of the compounds applied on a paper substrate are presented and assigned based on published data for the parent compounds. These Raman spectra show that the coordination of the hematein to the Al(III) ions takes place in both cases through the carbonyl and hydroxyl groups in the molecule, and that the aromatic rings are also involved in the interaction. The Raman spectra of the pure hematein–Al(III) complexes were found to be consistent with those recorded for a logwood ink prepared following a late 19th century recipe, using logwood chips instead of pure hematein, and applied on a paper substrate. These spectra can be used as references for the noninvasive identification of the compounds in works of art. ²⁷Al solid‐state NMR showed that the coordination of the Al(III) atoms in the crystallized powder is predominantly octahedral, while when applied on a paper substrate the colorant is present mainly as a tetrahedral complex, with an octahedral coordination also present in a smaller proportion. The fact that the predominant coordinations for the complexes in the crystallized material and for the ones present on the paper substrate are different is relevant for the study of the lightfastness and thermal stability of works of art bearing these media. Copyright © 2009 John Wiley & Sons, Ltd.     

Accurate sensitivity in optically preamplified direct detection

We present a novel model for calculating the bit error rate in optical communication systems in the case of on-off keying intensity modulation and optically preamplified direct detection. The model accounts for the intersymbol interference and is based on the Laguerre photon-count probability distribution predicted by photodetection theory. For a non-return-to-zero modulation format an accurate value of the sensitivity for a quantum-limited receiver of 33.9 photons/bit is obtained.     

AFM, SEM and GIXRD studies of thin films of red polycarbazolyldiacetylenes

In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings.