Magnetic properties and Spin dynamics in magnetic Molecular Rings

Molecular nanomagnets are spin clusters whose topology and magnetic interactions can be modulated at the level of the chemical synthesis. They are formed by a small number of transition metal ions coupled by the Heisenberg's exchange interactions. Each cluster is magnetically isolated from its neighbors by organic ligands, making each unit not interacting with the others. Therefore, we can investigate the magnetic properties of an isolated molecular nanomagnet by bulk measurements. The present thesis has been mostly devoted to the experimental investigation of the magnetic properties and spin dynamics of different classes of antiferromagnetic (AF) molecular rings. This study has been exploiting various techniques of investigations, such as Nuclear Magnetic Resonance (NMR), muon spin relaxation (muSR) and SQUiD magnetometry. We investigate the magnetic properties and the phonon-induced relaxation dynamics of the first regular Cr9 antiferromagnetic (AF) ring, which represents a prototype frustrated AF ring. The magnetically-open AF rings like Cr8Cd are model systems for the study of the microscopic magnetic behaviour of finite AF Heisenberg chains. In this type of system the different magnetic behaviour depends length and on the parity of the chain (odd or even). In order to study the local spin densities on the Cr sites, the Cr-NMR spectra was collected at low temperature. The experimental result confirm the theoretical predictions for the spin configuration. Finally, the study of Dy6, the first rare-earth based ring that has been ever synthesized, has been performed by AC-SQuID and muSR measurements. We found that the dynamics is characterized by more than one characteristic correlation time, whose values depend strongly on the applied field.

Fiber Bragg grating structures inscribed using 800nm femtosecond laser in single- and multi-core mid-IR glass fibers with their spectral, thermal and strain properties

Single- and multi-core passive and active germanate and tellurite glass fibers represent a new class of fiber host for in-fiber photonics devices and applications in mid-IR wavelength range, which are in increasing demand. Fiber Bragg grating (FBG) structures have been proven as one of the most functional in-fiber devices and have been mass-produced in silicate fibers by UV-inscription for almost countless laser and sensor applications. However, because of the strong UV absorption in germanate and tellurite fibers, FBG structures cannot be produced by UVinscription. In recent years femtosecond (fs) lasers have been developed for laser machining and microstructuring in a variety of glass fibers and planar substrates. A number of papers have been reported on fabrication of FBGs and long-period gratings in optical fibers and also on the photosensitivity mechanism using 800nm fs lasers. In this paper, we demonstrate for the first time the fabrication of FBG structures created in passive and active single- and three-core germanate and tellurite glass fibers by using 800nm fs-inscription and phase mask technique. With a fs peak power intensity in the order of 1011W/cm2, the FBG spectra with 2nd and 3rd order resonances at 1540nm and 1033nm in a single-core germanate glass fiber and 2nd order resonances between ~1694nm and ~1677nm with strengths up to 14dB in all three cores of three-core passive and active tellurite fibers were observed. Thermal and strain properties of the FBGs made in these mid-IR glass fibers were characterized, showing an average temperature responsivity of ~20pm/°C and a strain sensitivity of 1.219±0.003pm/µe.

Turbulent broadening of optical spectra in ultralong Raman fiber lasers

We study the properties of radiation generated in ultralong fiber lasers and find an interesting link between these optical systems and the theory of weak wave turbulence. Experimental observations strongly suggest that turbulentlike weak interactions between the multitude of laser cavity modes are responsible for practical characteristics of ultralong fiber lasers such as spectra of the output radiation.

Dielectric and electro-optical properties of some cyanobiphenyl liquid-crystals

A variety of methods have been reviewed for obtaining parallel or perpendicular alignment in liquid-crystal cells. Some of these methods have been selected and developed and were used in polarised spectroscopy, dielectric and electro-optic studies. Also, novel dielectric and electro-optic cells were constructed for use over a range of temperature. Dielectric response of thin layers of E7 and E8 (eutectic mixture liquid-crystals) have been measured in the frequency range (12 Hz-100 kHz) and over a range of temperature (183-337K). Dielectric spectra were also obtained for supercooled E7 and E8 in the Hz and kHz range. When the measuring electric field was parallel to the nematic director, one loss peak (low-frequency relaxation process) was observed for E7 and for E8, that exhibits a Debye-type behaviour in the supercooled systems. When the measuring electric field was perpendicular to the nematic director, two resolved dielectric processes have been observed. The phase transitions, effective molecular polarisabilities, anisotropy of polarisabilities and order parameters of three liquid crystal homologs (5CB, 6CB, and 7CB), 60CB and three eutectic nematic mixtures E7, E8, and E607 were calculated using optical and density data measured at several temperatures. The order parameters calculated using the different methods of Vuks, Neugebauer, Saupe-Maier, and Palffy-Muhoray are nearly the same for the liquid crystals considered in the present study. Also, the interrelationship between density and refractive index and the molecular structure of these liquid crystals were established. Accurate dielectric and dipole results of a range of liquid-crystal forming molecules at several temperatures have reported. The role of the cyano-end group, biphenyl core, and flexible tail in molecular association, were investigated using the dielectric method for some molecules which have a structural relationship to the nematogens. Analysis of the dielectric data for solution of the liquid-crystals indicated a high molecular association, comparable to that observed in the nematic or isotropic phases. Electro-optic Kerr effect were investigated for some alkyl cyanobiphenyls, their nematic mixtures and the eutectic mixture liquid-crystals E7 and E8 in the isotropic phase and solution. The Kerr constant of these liquid crystals found to be very high at the nematic-isotropic transition temperatures as the molecules are expected to be highly ordered close to phase transition temperatures. Dynamic Kerr effect behaviour and transient molecular reorientation were also observed in thin layers of some alkyl cyanobiphenyls. Dichroic ratio R and order parameters of solutions containing some azo and anthraquinone dyes in the nematic solvent (E7 and E8), were investigated by the measurement of the intensity of the absorption bands in the visible region of parallel aligned samples. The effective factors on the dichroic ratio of the dyes dissolved in the nematic solvents were determined and discussed.

The synthesis and properties of some hydrazines

A new synthetic method, applicable to the preparation of a wide range of hydrazine derivatives, is described. This involves the diborane reduction of a hydrazone, or, more conveniently, the reductive-condensation of a hydrazine and the appropriate aldehyde (or ketone). The method gives high yields and provides a particularly simple route to the relatively inaccessible 1,2-disubstituted hydrazines bearing a different group on each nitrogen. The new method has also been applied to the preparation of 1,2-disubstituted hydrazines with the same group on both nitrogens (via the azine), the very rare 1 ,2-disubstituted hydrazines bearing a tert-butyl group, trisubstituted hydrazines and monosubstituted hydrazines. Application of the reaction to the preparation of diaziridines has also been investigated. A mechanism for the reduction, supported by the isolation of a boron-containing intermediate, is suggested. Some limitations of the procedure are discussed. A general i.r. method of distinguishing the isomeric disubstituted hydrazines, as stable salts, has been developed. This has the advantages of speed and simplicity over previous methods. The mass spectra of a series of monosubstituted hydrazines, a series of 1,2-disubstituted hydrazines and some 1-benzoyl 2-alkylhydrazines have been examined in detail. The spectra are generally dominated byα -cleavage processes and the compounds show a variety of interesting rearrangement reactions. The mass spectra of some 1, 1-disubstituted hydrazines and some trisubstituted hydrazines have also been examined. Rearrangement processes occurring in the mass spectrum of tropylium fluoroborate have been examined. Similar rearrangements have been found in the spectrum of trityl fluoroborate and may be of general occurrence in the mass spectra of aromatic fluoroborates. Chemical shift values for some groups on hydrazine nitrogen are recorded and the results of tumour inhibitory tests on some hydrazines are also given.

Fiber Bragg grating structures inscribed using 800nm femtosecond laser in single- and multi-core mid-IR glass fibers with their spectral, thermal and strain properties

Single- and multi-core passive and active germanate and tellurite glass fibers represent a new class of fiber host for in-fiber photonics devices and applications in mid-IR wavelength range, which are in increasing demand. Fiber Bragg grating (FBG) structures have been proven as one of the most functional in-fiber devices and have been mass-produced in silicate fibers by UV-inscription for almost countless laser and sensor applications. However, because of the strong UV absorption in germanate and tellurite fibers, FBG structures cannot be produced by UVinscription. In recent years femtosecond (fs) lasers have been developed for laser machining and microstructuring in a variety of glass fibers and planar substrates. A number of papers have been reported on fabrication of FBGs and long-period gratings in optical fibers and also on the photosensitivity mechanism using 800nm fs lasers. In this paper, we demonstrate for the first time the fabrication of FBG structures created in passive and active single- and three-core germanate and tellurite glass fibers by using 800nm fs-inscription and phase mask technique. With a fs peak power intensity in the order of 1011W/cm2, the FBG spectra with 2nd and 3rd order resonances at 1540nm and 1033nm in a single-core germanate glass fiber and 2nd order resonances between ~1694nm and ~1677nm with strengths up to 14dB in all three cores of three-core passive and active tellurite fibers were observed. Thermal and strain properties of the FBGs made in these mid-IR glass fibers were characterized, showing an average temperature responsivity of ~20pm/°C and a strain sensitivity of 1.219±0.003pm/µe.

Asymmetric reactions of organosilicon compounds and properties of novel optically active organosilanes

Partial reduction of racemic methoxysilanes by 1:1 complexes of lithium aluminium hydride with optically active cinchona and ephedra alkaloids give optically active silanes and methoxysilanes. Optical yields depend on the groups attached to silicon and the alkaloid used but in some cases approach 50%, The method has been used to prepare novel optically active organosilanes, possessing an asymmetric silicon centre, which are either inaccessible by any of the other available routes or would require a time consuming preparation. Such compounds are of use in the study of the mechanism of substitutions at silicon. Attempts have been made to rationalize the results of the asymmetric reductions in terms of differences in sterio and electronic interactions in diastereoisomeric transition states. Circular dichroism and optical rotatory dispersion spectra have been obtained for the optically active products in an attempt to elucidate the absolute configurations of the novel asymmetric organosilanes. The results from these studies provide a useful addition to the data so far accumulated for asymmetrically perturbed aromatic chromophores. Nuclear magnetic resonanoe studies of diastereoisomaric (-)-menthoxysilanes show that these compounds possess resonances extremely useful in the determination of optical purities for asymmetric organosilanes which possess an aromatic group. The effect of variable temperature on the spectra has revealed evidence for the conformational preferences in these compounds. Other diastereoisomeric alkoxysilanes have been prepared and their n.m.r.spectra studied in the hope of establishing trends. Exploratory studies for other asymmetric reactions proceeding at silicon have proved unfruitful.

Mechanical properties and the evolution of matrix molecules in PTFE upon irradiation with MeV alpha particles

The morphology, chemical composition, and mechanical properties in the surface region of α-irradiated polytetrafluoroethylene (PTFE) have been examined and compared to unirradiated specimens. Samples were irradiated with 5.5 MeV 4He2+ ions from a tandem accelerator to doses between 1 × 106 and 5 × 1010 Rad. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS), using a 20 keV C60+ source, was employed to probe chemical changes as a function of a dose. Chemical images and high resolution spectra were collected and analyzed to reveal the effects of a particle radiation on the chemical structure. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Scanning electron microscopy (SEM) was used to observe the morphological variation of samples with increasing a particle dose, and nanoindentation was engaged to determine the hardness and elastic modulus as a function of a dose. The data show that PTFE nominally retains its innate chemical structure and morphology at a doses <109 Rad. At α doses ≥109 Rad the polymer matrix experiences increased chemical degradation and morphological roughening which are accompanied by increased hardness and declining elasticity. At  α doses >1010 Rad the polymer matrix suffers severe chemical degradation and material loss. Chemical degradation is observed in ToF-SIMS by detection of ions that are indicative of fragmentation, unsaturation, and functionalization of molecules in the PTFE matrix. The mass spectra also expose the subtle trends of crosslinking within the α-irradiated polymer matrix. ToF-SIMS images support the assertion that chemical degradation is the result of a particle irradiation and show morphological roughening of the sample with increased a dose. High resolution SEM images more clearly illustrate the morphological roughening and the mass loss that accompanies high doses of a particles. RGA confirms the supposition that the outcome of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss. Finally, we reveal and discuss relationships between chemical structure and mechanical properties such as hardness and elastic modulus.

Computational model of bladder tissue based on its measured optical properties

Urinary bladder diseases are a common problem throughout the world and often difficult to accurately diagnose. Furthermore, they pose a heavy financial burden on health services. Urinary bladder tissue from male pigs was spectrophotometrically measured and the resulting data used to calculate the absorption, transmission, and reflectance parameters, along with the derived coefficients of scattering and absorption. These were employed to create a "generic" computational bladder model based on optical properties, simulating the propagation of photons through the tissue at different wavelengths. Using the Monte-Carlo method and fluorescence spectra of UV and blue excited wavelength, diagnostically important biomarkers were modeled. Additionally, the multifunctional noninvasive diagnostics system "LAKK-M" was used to gather fluorescence data to further provide essential comparisons. The ultimate goal of the study was to successfully simulate the effects of varying excited radiation wavelengths on bladder tissue to determine the effectiveness of photonics diagnostic devices. With increased accuracy, this model could be used to reliably aid in differentiating healthy and pathological tissues within the bladder and potentially other hollow organs.

Effects of substituents in polyvinylcarbazole structures on their optical properties

Absorption, photoluminescence, and photoluminescence excitation spectra of solutions and thin films of N-vinylcarbazole polymers and copolymers with various substituents directly on the carbazole moiety and on the polymer chain were studied comprehensively. Polymers that were used previously to develop polymer composites with polymethine dyes having photosensitivity over a broad spectral range including the visible and near-IR regions were selected for the studies.

Properties of seawater and particulate matter from a WETLabs AC-S spectrophotometer and a WETLabs chlorophyll fluorometer mounted on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) was a global survey of ocean ecosystems aboard the Sailing Vessel Tara. It carried out extensive measurements of evironmental conditions and collected plankton (viruses, bacteria, protists and metazoans) for later analysis using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data publication provides permanent links to original and updated versions of validated data files containing measurements from the Continuous Surface Sampling System [CSSS]. Water was pumped at the front of the vessel from ~2m depth, then de-bubbled and circulated to a WETLabs AC-S spectrophotometer and a WETLabs chlorophyll fluorometer. Systems maintenance (instrument cleaning, flushing) was done approximately once a week and in port between successive legs. All data were stamped with a GPS.

Peptide-induced coalescence of bicellar lipid assemblies: sensitivity to anionic lipid and peptide properties

Bicellar lipid mixture dispersions progressively coalesce to larger structures on warming. This phase behaviour is particularly sensitive to interactions that perturb bilayer properties. In this study, ²H NMR was used to study the perturbation of bicellar lipid mixtures by two peptides (SP-B₆₃₋₇₈, a lung surfactant protein fragment and Magainin 2, an antimicrobial peptide) which are structurally similar. Particular attention was paid to the relation between peptide-induced perturbation and lipid composition. In bicellar dispersions containing only zwitterionic lipids (DMPC-d₅₄/DMPC/DHPC (3:1:1)) both peptides had little to no effect on the temperature at which coalescence to larger structures occurred. Conversely, in mixtures containing anionic lipids (DMPC-d₅₄/DMPG/DHPC (3:1:1)), both peptides modified bicellar phase behaviour. In mixtures containing SP-B₆₃₋₇₈, the presence of peptide decreased the temperature of the ribbon-like to extended lamellar phase transition. The addition of Magainin 2 to DMPCd₅₄/ DMPG/DHPC (3:1:1) mixtures, in contrast, increased the temperature of this transition and yielded a series of spectra resembling DMPC/DHPC (4:1) mixtures. Additional studies of lipid dispersions containing deuterated anionic lipids were done to determine whether the observed perturbation involved a peptide-induced separation of zwitterionic and anionic lipids. Comparison of DMPC/DMPG-d₅₄/DHPC (3:1:1) and DMPC-d₅₄/DMPG/DHPC (3:1:1) mixtures showed that DMPC and DMPG occupy similar environments in the presence of SP-B₆₃₋₇₈, but different lipid environments in the presence of Magainin 2. This might reflect the promotion of anionic lipid clustering by Magainin 2. These results demonstrate the variability of mechanisms of peptide-induced perturbation and suggest that lipid composition is an important factor in the peptide-induced perturbation of lipid structures.

The AGN, star-forming, and morphological properties of luminous ir-bright/optically-faint galaxies

We present the active galactic nucleus (AGN), star-forming, and morphological properties of a sample of 13 MIR-luminous (∫_24 700 μJy) IR-bright/optically-faint galaxies (IRBGs, ∫_24/f_R≲ 1000). While these z ∼ 2 sources were drawn from deep Chandra fields with >200 ks X-ray coverage, only seven are formally detected in the X-ray and four lack X-ray emission at even the 2σ level. Spitzer InfraRed Spectrograph (IRS) spectra, however, confirm that all of the sources are AGN-dominated in the mid-IR, although half have detectable polycyclic aromatic hydrocarbon (PAH) emission responsible for ∼25% of their mid-infrared flux density. When combined with other samples, this indicates that at least 30%–40% of luminous IRBGs have star formation rates in the ultraluminous infrared galaxy (ULIRG) range (∼100–2000 M_⨀ yr^−1). X-ray hardness ratios and MIR to X-ray luminosity ratios indicate that all members of the sample contain heavily X-ray obscured AGNs, 80% of which are candidates to be Compton thick. Furthermore, the mean X-ray luminosity of the sample, log L_2–10 keV(erg s^−1) ∼44.6, indicates that these IRBGs are Type 2 QSOs, at least from the X-ray perspective. While those sources most heavily obscured in the X-ray are also those most likely to display strong silicate absorption in the mid-IR, silicate absorption does not always accompany X-ray obscuration. Finally, ∼70% of the IRBGs are merger candidates, a rate consistent with that of sub-mm galaxies (SMGs), although SMGs appear to be physically larger than IRBGs. These characteristics are consistent with the proposal that these objects represent a later, AGN-dominated, and more relaxed evolutionary stage following soon after the star-formation-dominated one represented by the SMGs.

The D(D-3)-anyon chain: integrable boundary conditions and excitation spectra

Chains of interacting non-Abelian anyons with local interactions invariant under the action of the Drinfeld double of the dihedral group D-3 are constructed. Formulated as a spin chain the Hamiltonians are generated from commuting transfer matrices of an integrable vertex model for periodic and braided as well as open boundaries. A different anyonic model with the same local Hamiltonian is obtained within the fusion path formulation. This model is shown to be related to an integrable fusion interaction round the face model. Bulk and surface properties of the anyon chain are computed from the Bethe equations for the spin chain. The low-energy effective theories and operator content of the models (in both the spin chain and fusion path formulation) are identified from analytical and numerical studies of the finite-size spectra. For all boundary conditions considered the continuum theory is found to be a product of two conformal field theories. Depending on the coupling constants the factors can be a Z(4) parafermion or a M-(5,M-6) minimal model.