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Spectral Characteristics (spectral + characteristic)
Selected AbstractsChemInform Abstract: Synthesis and Spectral Characteristics of 4-(10,10-Dimethyl-8-oxo-7,8,9,10,11,12-hexahydrobenzo [c]acridin-7-yl)-2-methoxy(ethoxy)phenyl Carboxylates.CHEMINFORM, Issue 14 2008V. V. Skatetskii Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Stepwise Synthesis and Spectral Characteristics of meso-trans-Diphenyldi(1-naphthyl)tetrabenzoporphin (I) and Its Zinc Complex.CHEMINFORM, Issue 14 2005N. E. Galanin No abstract is available for this article. [source] Synthesis and Spectral Characteristics of Unsymmetrical Porphirazines with Triphenylmethyl Groups.CHEMINFORM, Issue 47 2004N. E. Galanin No abstract is available for this article. [source] Solvatochromism of carbenium,arene EDA (electrondonor,acceptor) complexes and their behaviour on silicaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2001Stefan Spange Abstract Spectral characteristics of two different types of electron donor,acceptor (EDA) complexes with charged components (arene,carbenium and anion,, acceptor) are presented. The UV,Vis absorption maxima of the charge-transfer (CT) band (,max,CT) of the EDA complexes were measured in various solvents and after adsorption on silica. Tropylium, triarylmethylium and diarylmethylium ions in combination with aromatic , donors, e.g. pyrene, acenaphthene and methoxy-substituted benzene derivatives and also the tetraethylammonium iodide,1,3,5-trinitrobenzene complex have been investigated by means of a special UV,Vis technique in transparent slurries of silica nanoparticles in 1,2-dichloroethane. Multiple linear regression analyses of the ,max,CT values of the EDA complexes in various solvents and on silica with the Kamlet,Taft solvent parameters and structure,reactivity terms of the complex components, e.g. the oxidation potential of the arene component or the Hammett substituent constant, ,p+, of the arylmethyl component, show their related properties to the solution complexes. The influence of the electron-pair donating capacity of a solvent on ,max,CT of carbenium/arene complexes was compared with the property of the silica surface in order to link EDA complexes. For the diarylmethyl carbenium ion,pyrene complexes on silica, the presence of a ,-like structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Multimode fiber lasers based on Bragg gratings and double-clad Yb-doped fibersLASER PHYSICS LETTERS, Issue 9 2004A. S. Kurkov Abstract We have realized a set of multimode lasers based on a double-clad Yb-doped fiber and Bragg gratings written on a graded-index multimode fiber. Efficient laser operation in the spectral range of 1.03-1.09 ,m has been observed. Spectral characteristics of the laser emission have been investigated. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Characterization of the Photochromic Pigments in Red Fluorescent Proteins Purified from the Gut Juice of the Silkworm Bombyx mori L.PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2008Santosh G. Sunagar Multiple forms of red fluorescent proteins (RFPs) were observed in the gut juice of the silkworm, Bombyx mori L. It is to be noted that only one RFP band is reported in the literature so far. However, we report here three electrophoretically separated RFPs (A, B and C) found to be heterogeneous with respect to their components, namely the protein part and the fluorescent tetrapyrrole pigment moiety. Of the three RFPs, band C was found to be a glycoprotein. The absorption extinction coefficients and fluorescence quantum yields of the three RFPs were estimated. Further, this is the first communication demonstrating the presence of three different chlorophyll derivatives associated with the three different RFPs. The pigments were analyzed by thin layer chromatography followed by their elution to characterize the pigments by spectrophotometric and spectrofluorometric methods. Spectral characteristics have led to the identification of monovinyl chlorophyllide a, divinyl protochlorophyllide a and monovinyl pheophytin a as being associated with RFP bands A, B and C, respectively. These three purified RFPs can serve as the source of the three pigments as the standards. [source] Spectral characteristics of single InAs/InGaAs quantum dots in a quantum wellPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003L. Worschech Abstract Self assembled InAs quantum dots embedded in an InGaAs quantum well were grown by molecular beam epitaxy. At room temperature these dots in a well (DWELLS) have an emission wavelength of 1.3,,m. Small mesas with lateral sizes down to 200 × 200 nm2 were fabricated by electron beam lithography and etching techniques. By photoluminescence spectroscopy at low temperatures we observe narrow lines, which we attribute to excitons and excitonic molecules. Biexciton binding energies ranging between 3.5,5,meV are found. [source] Gamma activity and reactivity in human thalamic local field potentialsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2009Florian Kempf Abstract Depth recordings in patients with Parkinson's disease on dopaminergic therapy have revealed a tendency for oscillatory activity in the basal ganglia that is sharply tuned to frequencies of ,70 Hz and increases with voluntary movement. It is unclear whether this activity is essentially physiological and whether it might be involved in arousal processes. Here we demonstrate an oscillatory activity with similar spectral characteristics and motor reactivity in the human thalamus. Depth signals were recorded in 29 patients in whom the ventral intermediate or centromedian nucleus were surgically targeted for deep brain stimulation. Thirteen patients with four different pathologies showed sharply tuned activity centred at ,70 Hz in spectra of thalamic local field potential (LFP) recordings. This activity was modulated by movement and, critically, varied over the sleep,wake cycle, being suppressed during slow wave sleep and re-emergent during rapid eye movement sleep, which physiologically bears strong similarities with the waking state. It was enhanced by startle-eliciting stimuli, also consistent with modulation by arousal state. The link between this pattern of thalamic activity and that of similar frequency in the basal ganglia was strengthened by the finding that fast thalamic oscillations were lost in untreated parkinsonian patients, paralleling the behaviour of this activity in the basal ganglia. Furthermore, there was sharply tuned coherence between thalamic and pallidal LFP activity at ,70 Hz in eight out of the 11 patients in whom globus pallidus and thalamus were simultaneously implanted. Subcortical oscillatory activity at ,70 Hz may be involved in movement and arousal. [source] Synthesis, NMR, and Conformational Studies of Cyclic Oligo-(1,6)-,- D -Glucosamines,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2010Marina L. Gening Abstract The first synthesis of a series of homologous cyclic oligo-(1,6)-,- D -glucosamines consisting of two to seven residues and representing a new type of functionalized cyclic oligosaccharides is reported. Remarkably high yields of the studied macrocyclization reaction irrespective of the length of the acyclic precursors were observed. In the case of compounds constituted of four to seven glucosamine units ,-stereoisomers formed as side products despite the presence of a strongly participating 2- N -phthaloyl group to control ,-glycosylation. Both phenomena may be accounted for by conformational features of the linear bifunctional precursors. According to computer modeling and NMR conformational studies, the described linear (1,6)-,-linked oligoglucosamines exist in a right-handed helix-like conformation, in which the glycosyl donor and acceptor moieties are prearranged in a way that facilitates intramolecular glycosylation from the ,-side. Prepared cyclo-oligoglucosamines differ in their conformational flexibilities, as illustrated by their spectral characteristics and calculated asphericity distributions. Moreover, the obtained compounds do not possess a distinct hydrophobic cavity, which is in contrast to the well-known cyclodextrins. All these characteristics provide an excellent basis for the use of these novel cyclic oligosaccharides as scaffolds for the construction of biomolecular conjugates. [source] Synthesisation of pulse shaping waveforms for spectral efficient digital modulations: some practical approachesEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2006Hsiao-Hwa Chen Bandwidth efficiency of all digital modulations is associated closely with baseband pulse shaping waveforms (PSW's) before carrier modulation. Traditional PSW designing approaches usually work in a way such that the design of PSW's in the time domain hardly reveals a direct connection with their spectral characteristics. In other words, designing process of the PSW's offers too little degree-of-freedom to control spectral properties of the resultant signals. This paper will present a methodology, based on which several new PSW synthesising approaches, including time-domain convolution (TDC), steepest sidelobe roll-off (SSR) and zero-point insertion (ZPI) methods, will be proposed to design different PSW's with controllable spectral characteristics, such as sidelobe roll-off rate, main lobe width and null positions in their power spectral density functions. In particular, the SSR and ZPI methods are based on a truncated cosine function series, which can be further generalised to use other seed functions. The results show that the approaches can help us to generate a PSW database containing a wide collection of promising PSW's to suit for diverse wireless applications, such as traditional digital modems as well as emerging ultra-wideband systems. Copyright © 2005 AEIT. [source] Conformational stability and multistate unfolding of poly(A)-specific ribonucleaseFEBS JOURNAL, Issue 10 2009Guang-Jun He Poly(A)-specific ribonuclease (PARN) specifically catalyzes the degradation of the poly(A) tails of single-stranded mRNAs in a highly processive mode. PARN participates in diverse and important intracellular processes by acting as a regulator of mRNA stability and translational efficiency. In this article, the equilibrium unfolding of PARN was studied using both guanidine hydrochloride and urea as chemical denaturants. The unfolding of PARN was characterized as a multistate process, but involving dissimilar equilibrium intermediates when denatured by the two denaturants. A comparison of the spectral characteristics of these intermediates indicated that the conformational changes at low concentrations of the chemical denaturants were more likely to be rearrangements of the tertiary and quaternary structures. In particular, an inactive molten globule-like intermediate was identified to exist as soluble non-native oligomers, and the formation of the oligomers was modulated by electrostatic interactions. An active dimeric intermediate unique to urea-induced unfolding was characterized to have increased regular secondary structures and modified tertiary structures, implying that additional regular structures could be induced by environmental stresses. The dissimilarity in the unfolding pathways induced by guanidine hydrochloride and urea suggest that electrostatic interactions play an important role in PARN stability and regulation. The appearance of multiple intermediates with distinct properties provides the structural basis for the multilevel regulation of PARN by conformational changes. [source] Fluorescent proteins for single-molecule fluorescence applicationsJOURNAL OF BIOPHOTONICS, Issue 1 2008Britta Seefeldt Abstract We present single-molecule fluorescence data of fluorescent proteins GFP, YFP, DsRed, and mCherry, a new derivative of DsRed. Ensemble and single-molecule fluorescence experiments proved mCherry as an ideally suited fluorophore for single-molecule applications, demonstrated by high photostability and rare fluorescence-intensity fluctuations. Although mCherry exhibits the lowest fluorescence quantum yield among the fluorescent proteins investigated, its superior photophysical characteristics suggest mCherry as an ideal alternative in single-molecule fluorescence experiments. Due to its spectral characteristics and short fluorescence lifetime of 1.46 ns, mCherry complements other existing fluorescent proteins and is recommended for tracking and localization of target molecules with high accuracy, fluorescence resonance energy transfer (FRET), fluorescence lifetime imaging microscopy (FLIM), or multicolor applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Moult speed affects structural feather ornaments in the blue titJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2009M. GRIGGIO Abstract Growing evidence suggests that structural feather colours honestly reflect individual quality or body condition but, contrary to pigment-based colours, it is not clear what mechanism links condition to reflectance in structural feather colours. We experimentally accelerated the moult speed of a group of blue tits (Cyanistes caeruleus) by exposing them to a rapidly decreasing photoperiod and compared the spectral characteristics of their structural feather colours with those of control birds. Blue tits were sexually dimorphic on the UV/blue crown and on the white cheek feathers. Moult speed, however, dramatically reduced brightness and the saturation only on the UV/blue crown feathers, whereas structural white on the cheek feathers was basically unaffected by moult speed. Given that the time available for moulting is usually confined to the period between the end of the breeding season and migration or wintering, UV/blue colours, but not structural white, may convey long-term information about an individual's performance during the previous breeding season. The trade-off between fast moulting and structural colour expression may represent a previously unrecognized selective advantage for early-breeding birds. [source] Moult speed constrains the expression of a carotenoid-based sexual ornamentJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2007L. SERRA Abstract We investigated the effect of moult speed on the expression of a sexually selected, carotenoid-based feather ornament in the rock sparrow (Petronia petronia). We experimentally accelerated the moult speed of a group of birds by exposing them to a rapidly decreasing photoperiod and compared the area and the spectral characteristics of their ornaments with those of control birds. Birds with accelerated moulting rate showed a smaller yellow patch with lower yellow reflectance compared to their slow-moulting counterparts. Considering that the time available for moulting is usually constrained between the end of the breeding season and migration or wintering, carotenoid feather ornaments, whose expression is mediated by moult speed, may convey long term information about an individual's condition, potentially encompassing the previous breeding season. Furthermore, the observed trade-off between moult speed and ornament expression may represent a previously unrecognized selective advantage for early breeding birds. [source] Phenothiazine photosensitizers for onium salt photoinitiated cationic polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2001Zaza Gomurashvili Abstract Phenothiazine compounds bearing a wide range of different substituents are excellent photosensitizers for onium salt cationic photoinitiators. These photosensitizers are generally operative in the mid- and long-range regions of the UV spectrum and are especially useful for enhancing the rate of photoinitiated cationic polymerization carried out utilizing both filtered and broadband UV emission sources. In this article, the syntheses of several different substituted phenothiazines are described and the ability of these compounds to photosensitize the photolysis of different onium salt photoinitiators is evaluated. Attempts were made to correlate the structure and spectral characteristics of the phenothiazines with their efficiency of photosensitization in the cationic photopolymerizations of several typical epoxide and vinyl ether monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1187,1197, 2001 [source] Towards a specific characterisation of components on a cell surface,combined TERS-investigations of lipids and human cellsJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2009R. Böhme Abstract Supported lipid structures and human cells (human dermal derived keratinocyte, HaCaT) were investigated using tip-enhanced Raman spectroscopy (TERS) to use the high spatial resolution capabilities of TERS, which is assumed to be less than 10 nm, to determine specific components on the cell surface. As lipids are a main component of cellular membranes, the correlation of spectral properties of pure lipids with respect to the complex biological sample was investigated. Induced by dynamic structural changes as well as nanoscale effects, a particular spectral feature of the lipid TERS spectra is found to vary, and a similar spectral deviation appears among the TERS spectra measured on the cell. Modifications of the cell surface alone cannot cause such behaviour. In contrast to soft lipid agglomerates, the cells were fixed and therefore hampered for intrinsic structural changes. Hence, the main contribution for the cell TERS spectra variation results from nanoscale effects, determined by different spectral characteristics compared to conventional Raman spectroscopy. The present results demonstrate the capability of TERS to provide a detailed and fast insight into the composition of the cell surface, even allowing the detection of single components. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effects of Alcohol on Sleep and the Sleep Electroencephalogram in Healthy Young WomenALCOHOLISM, Issue 6 2006Eliza Van Reen Background: Although the association between sleep and alcohol has been of interest to scientists for decades, the effects of alcohol on sleep and sleep electroencephalogram (EEG) have not been extensively studied in women. Our specific aim was to determine whether sleep stage variables and/or spectral characteristics of the sleep EEG are altered by alcohol administration in women. Methods: Changes of sleep and the sleep EEG were investigated after administration of a moderate dose of alcohol (0.49 g/kg) in the hour before bedtime compared with placebo in young healthy women. After approximately 2 weeks at home on a fixed 8.5- or 9-hour stabilization sleep schedule, sleep was continuously recorded by polysomnography for 3 consecutive nights [adaptation, placebo, alcohol (mean breath alcohol concentration 0.043 g/% before bedtime)] in the laboratory in 7 women (ages 22,25, mean=23.5, SD=1 year). Sleep stages were scored according to conventional criteria. Electroencephalogram power spectra of the bipolar derivations Fz/Cz (anterior) and Pz/Oz (posterior) were calculated using a fast Fourier transform routine. Results: Only few changes in sleep and the sleep EEG were observed. Across the entire night rapid eye movement (REM) sleep decreased, while minutes of stage 4 sleep were increased in the first 2-hour interval on alcohol nights compared with placebo nights. Spectral analysis of the EEG showed increased power in the , range (9,11 Hz) during all-night non-REM (NREM) sleep in anterior derivations after alcohol compared with placebo. Differences in spectral EEG power were also present in 2-hour intervals of NREM sleep; in particular, EEG power was increased on the alcohol night for frequency bins within the , range in anterior derivations and within the , range (3,4 Hz) in posterior derivations during the initial part of the night. Conclusions: A moderate dose of alcohol just before bedtime resulted in a short-lived increase in sleep intensity. A limitation of the study, however, was that only a single dose of alcohol was used to examine the effects of alcohol on sleep. [source] Nonparametric Tests of Change-Points with Tapered DataJOURNAL OF TIME SERIES ANALYSIS, Issue 1 2001Yves Rozenholc In this work we build two families of nonparametric tests using tapered data for the off-line detection of change-points in the spectral characteristics of a stationary Gaussian process. This is done using the Kolmogorov,Smirnov statistics based on integrated tapered periodograms. Convergence is obtained under the null hypothesis by means of a double indexed (frequency, time) process together with some extensions of Dirichlet and Fejer kernels. Consistency is proved using these statistics under the alternative. Then, using numerical simulations, we observe that the use of tapered data significantly improves the properties of the test, especially in the case of small samples. [source] Facile Synthesis of Polyaniline-Polypyrrole Nanofibers for Application in Chemical Deposition of Metal NanoparticlesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2008Ping Xu Abstract Polyaniline-polypyrrole (PANI-PPy) nanofibers with high aspect ratios have been synthesized by a one-step, surfactant-assisted chemical oxidative polymerization from mixtures of aniline (An) and pyrrole (Py) monomers. PANI-PPy nanofibers synthesized with an excess of either PANI or PPy show similar spectral (UV-vis and FT-IR) characteristics as the individual homopolymers, whereas nanofibers from an equimolar mixture of An and Py display unique spectral characteristics. PANI-PPy nanofibers undergo a spontaneous redox reaction with metal ions to produce metal nanoparticles with various morphologies and/or sizes. These findings may open new opportunities for synthesizing functional polymer nanofibers and metal nanoparticles with controllable sizes and/or morphologies. [source] Quantum chemistry investigation of electronic structure and NMR spectral characteristics for fluorides of dialkylamidosulfoxylic acids and related compoundsMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2009A. B. Rozhenko Abstract The parent (H2NSF) and N,N -dialkyl-substituted fluorides of amidosulfoxylic acid (R2NSF, RMe or R2NMorph) as well as the related compounds XSF (XCH3, OH, F, SiH3, PH2, SH, Cl) have been investigated with quantum chemical calculations at the ab initio (MP2) level of approximation. The geometries, electronic structures, molecular orbital (MO) energies and NMR chemical shift values have been calculated to evaluate the role and extent of the polarization and delocalization effects in forming of the high-field fluorine NMR resonances within the series of interest. The ,F magnitudes for all investigated fluorides of amidosulfoxylic acid as well as the ,N value calculated for Me2NSF are in the good agreement with the 19F and 14N NMR chemical shift values measured experimentally. For the parent compounds, H2NSF and H2NSO2F, the orientation of principal axes of the magnetic shielding tensors and the corresponding principal ,ii values along these axes have been qualitatively interpreted basing on the analysis of the MO interactions in the presence of the rotating magnetic field. Copyright © 2009 John Wiley & Sons, Ltd. [source] MUSES-C target asteroid (25143) 1998 SF36: A reddened ordinary chondriteMETEORITICS & PLANETARY SCIENCE, Issue 8 2001Richard P. BINZEL High signal-to-noise and relatively high-resolution (50 Å) visible and near-infrared spectroscopic measurements obtained during this asteroid's favorable 2001 apparition reveal it to have a red-sloped S(IV)-type spectrum with strong 1 and 2 ,m absorption bands analogous to those measured for ordinary chondrite meteorites. This red slope, which is the primary spectral difference between (25143) 1998 SF36 and ordinary chondrite meteorites, is well modeled by the spectrum of 0.05% nanophase iron (npFe0) proposed as a weathering mechanism by Pieters et al. (2000). Asteroid 1998 SF36 appears to have a surface composition corresponding to that of ordinary chondrite meteorites and is most similar in spectral characteristics and modeled olivine/pyroxene content to the LL chondrite class. [source] Absorption Spectra of Human Skin In Vivo in the Ultraviolet Wavelength Range Measured by OptoacousticsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009Merve Meinhardt Knowledge of the optical properties of human skin in the ultraviolet range is fundamental for photobiologic research. However, optical properties of human skin in the ultraviolet spectral range have so far mainly been measured ex vivo. We have determined the absorption spectra of human skin in vivo in the wavelength range from 290 to 341 nm in 3 nm steps using laser optoacoustics. In this technique, optical properties are derived from the pressure profile generated by absorbed light energy in the sample. In a study on 20 subjects belonging to phototypes I,IV, we studied the optical properties at the volar and dorsal aspect of the forearm as well as on the thenar. Analysis of the measured absorption spectra shows that comparable skin areas,like different sides of the forearm,have qualitatively similar optical characteristics. Still, the optical properties may vary substantially within the same area, probably due to the skin structure and inhomogeneities. Comparison of the spectra from different skin sites indicates that the spectral characteristics of the stratum corneum and its chromophores play an important role for the optical properties of human skin in vivo in the ultraviolet B range. [source] Photobleaching of Dissolved Organic Material from a Tidal Marsh-Estuarine System of the Chesapeake Bay,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Maria Tzortziou ABSTRACT Wetlands and tidal marshes in the Rhode River estuary of the Chesapeake Bay act as important sources of dissolved organic carbon and strongly absorbing dissolved organic matter (DOM) for adjacent estuarine waters. The effects of solar exposure on the photochemical degradation of colored DOM (CDOM) were examined for material derived from different sources (estuarine and freshwater parts of the Rhode River, sub-watershed stream, marshes) in this estuarine ecosystem. Consistent with changes in fluorescence emission, absorption loss upon exposure to different portions of the solar spectrum (i.e. different long-pass cut-off filters) occurred across the entire spectrum but the wavelength of maximum photobleaching decreased as the cut-off wavelength of the filter decreased. Our results illustrate that solar exposure can cause either an increase or a decrease in the CDOM absorption spectral slope, SCDOM, depending on the spectral quality of irradiation and, thus, on the parameters (e.g. atmospheric composition, concentration of UV-absorbing water constituents) that affect the spectral characteristics of the light to which CDOM is exposed. We derived a simple spectral model for describing the effects of solar exposure on CDOM optical quality. The model accurately, and consistently, predicted the observed dependence of CDOM photobleaching on the spectral quality of solar exposure. [source] Conformational Effects on Photophysical Characteristics of C5,C5,-linked Dihydrothymine Dimers in Solution,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2000T. Ito ABSTRACT Photophysical characteristics of N-substituted C5,C5,-linked dihydrothymine dimers (1a,b[meso], meso compounds of [5R,5,S]-bi-5,6-dihydrothymines; 1a,b[rac], racemic compounds of [5R,5,R]-bi-5,6-dihydrothymines and [5S,5,S]-bi-5,6-dihydrothymines) in aqueous solution with varying contents of less-polar aprotic solvent such as tetrahydrofuran or dioxane have been investigated by UV-absorption, and steady-state and time-resolved fluorescence spectroscopies. Among the C5,C5,-linked dimers, (5R,5,S)-bi-5,6-dihydro-1-methylthymine (1a[meso]) showed a redshifted weak UV-absorption band at 270,350 nm and excimer fluorescence emission at ,max= 370 nm with a quantum yield (,F) of ,0.1 in phosphate buffer (pH < 10) at 293 K. Racemic compound of 5,6-dihydro-1-methylthymine dimer (1a[rac]), meso and racemic compounds of 5,6-dihydro-1,3-dimethylthymine dimers (1b[meso] and 1b[rac]) in phosphate buffer were nonfluorescent under similar conditions. The UV-absorption and fluorescence spectral characteristics of 1a[meso] in aqueous solution were interpreted in terms of intramolecular stacking interactions between the dihydropyrimidine chromophores leading to a preferential "closed-shell" conformation both in the ground state and the excited singlet state. In basic solutions at pH > pKa= 11.7, the fluorescence quantum yield of 1a[meso] decreased due to a dominant "open-shell" conformation resulting from the electrostatic repulsion between the deprotonated dihydrothymine chromophores of 1a[meso] in a dianion form. [source] Light emission from different ZnO junctions and nanostructuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009M. Willander Abstract We will discuss our experimental results for optical spectra produced by hole-injection from different p-type organic and inorganic materials into n-type ZnO nanowires. The influence of different growth techniques and conditions on the nanowires and their emission spectral characteristics will then be analyzed and discussed. The latest findings on the mixture of the green emission band responsible for visible light emission from ZnO and the blue light emission from the organic polymer will be presented. Different high brightness light emitting diodes (HB-LEDs) from our grown ZnO nanowires are demonstrated. The p-type multi layer organic structures contain PEDOT:PSS as hole injectors combined with a hole transporting layer, and in some structures, a final top electron blocking/hole barrier stepping layer is placed. The purpose of this layer is to adjust the hole and electron emission from the corresponding junction side to optimize the LED performance. Structural scanning electron microscopy (SEM), electrical (I ,V characteristics), photoluminescence (PL) and electroluminescence (EL) characteristics of these devices are displayed. Theoretically, we study the superfluidity of a two-dimensional system of excitonic polaritons in an optical microcavity with an embedded quantum well. Using the effective low-energy action for thermodynamic phase fluctuations, we obtain an expression for the analogue of the superfluid density in the system in terms of the "current,current" correlation function. The Kosterlits,Thouless transition temperature to the superfluid state as a function of the controlling parameters is calculated. Two methods are considered for producing traps for a polariton system in an optical microcavity. The behaviour of a two-component Bose condensate of photons and excitons is analyzed theoretically for both types of the trap. The Bose condensate is described by the coupled system of equations of the Gross,Pitaevskii type. The approximate wave functions and the spatial profiles of coupled photon and exciton condensates are obtained. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AFM and SNOM characterization of ordinary chondrites: A contribution to solving the problem of asteroid reddeningPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Giuliano Pompeo Abstract Space weathering (SW) is an ensemble of processes that act on a body exposed to the space environment. Typically, the exposure to SW results in the accumulation, at the surface, of nanoparticles, that are thought to be produced through a vaporization and subsequent cooling of the metallo-silicaceous components exposed to the space environment. The presence of such nanoparticles is responsible for the so-called reddening of the asteroids' reflectance spectra (i.e., the increase in Vis,NIR reflectance with increase in wavelength) observed by remote-sensing measurements. To investigate the mechanism of formation of these nanoparticles, we have employed atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) to morphologically and optically characterize ordinary chondrites (OC), the most abundant class of meteorites collected on Earth and whose parent bodies are the S-type asteroids. The AFM study reveals the occurrence of a diffuse nanophase (martensite) in the meteorite's metal inclusions. Since the same areas show a reddening of the reflectivity spectra, this suggests that such spectral modification is based on a shock-induced phase transformation of the metal components of the extraterrestrial body. To gain more insight into this nanophase and on its role in the SW of the asteroids, an optical characterization by SNOM has been performed on OCs. In this work we exploited the peculiarity of this technique to search for a correlation between the topography on the nanoscale and the spectral characteristics, at different wavelengths in the red-NIR range, of the observed nanophase. Indeed, a high-resolution mapping of the optical properties of the meteorite provides an interesting method to discriminate between martensite-based and Fe-silicaceous nanoparticles. [source] Confinement factor, near and far field patterns in InGaN MQW laser diodesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005J. Martín Abstract In this work the influence of the QW number in the active region on spectral characteristics in InGaN multi quamtun well lasers is analyzed. A comparison between the abrupt index step structure (Step) and a graded-index structure (GRIN) is done. The effect of the introduction of a p-AlxGa1,xN electron blocking layer, placed above the last InGaN barrier in the Step structure is also analyzed. Calculations of the confinement factor, near and far field patterns were carried out. We found that with the adequate aluminum content in this layer, the confinement factor, near and far field patterns are improved, and values similar to those obtained with GRIN structure can be reached. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] PV thermal systems: PV panels supplying renewable electricity and heatPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2004Dr. Wim G. J. van Helden Abstract With PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat-collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set-up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost-effective manner than separate PV and solar thermal systems and thus contribute to the long-term international targets on implementation of renewable energy in the built environment. Copyright © 2004 John Wiley & Sons, Ltd. [source] Structural characterization of constituents with molecular diversity in fractions from Lysidice brevicalyx by liquid chromatography/diode-array detection/electrospray ionization tandem mass spectrometry and liquid chromatography/nuclear magnetic resonance,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2008Jing Qu A combination of electrospray ionization tandem mass spectrometry with high-performance liquid chromatography (HPLC/ESI-MSn), and hyphenation of liquid chromatography to nuclear magnetic resonance spectroscopy (HPLC/NMR), have been extensively utilized for on-line analysis of natural products, analyzing metabolite and drug impurity. In our last paper, we reported an on-line analytical method for structural identification of trace alkaloids in the same class. However, the structural types of the constituents in plants were various, such as flavanoids, terpenoids and steroids. It is important to establish an effective analytical method for on-line structural identification of constituents with molecular diversity in extracts of plants. So, in the present study, the fragmentation patterns of some isolated stilbenes, phloroglucinols and flavanoids from Lysidice rhodostegia were investigated by ESI-MSn. Their fragmentation rules and UV characteristics are summarized, and the relationship between the spectral characteristics, rules and the structures is described. According to the fragmentation rules, NMR and UV spectral characteristics, 24 constituents of different types in the fractions from L. brevicalyx of the same genus were structurally characterized on the basis of HPLC/HRMS, HPLC-UV/ESI-MSn, HPLC/1H NMR and HPLC/1H- 1H COSY rapidly. Of these, six (10, 13, 14, 16, 17 and 23) are new compounds and all of them are reported from L. brevicalyx for the first time. The aim is to develop an effective analytical method for on-line structural identification of natural products with molecular diversity in plants, and to guide the rapid and direct isolation of novel compounds by chemical screening. Copyright © 2008 John Wiley & Sons, Ltd. [source] Regulation of the epididymal receptor tyrosine kinase ros by the protein tyrosine phosphatase SHP-1AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 3 2002Rico Pusch The SH2 domain PTP SHP-1 was recently identified as a potent negative regulator of the orphan receptor tyrosine kinase Ros, an important regulator of epidimys differentiation (Keilhack et al. J Cell Biol 2001; 152:325,334). Phosphorylated Ros strongly and directly associates with SHP-1 in yeast-two-hybrid, GST pull-down, and coimmunoprecipitation experiments. Catalytically inactive SHP-1C455S exhibits greatly elevated binding to phosphorylated Ros. Direct Ros,SHP-1 interaction is mediated by the SHP-1 N-terminal SH2 domain and Ros phosphotyrosine 2267. Overexpression of SHP-1 results in Ros dephosphorylation and effectively down-regulates Ros-dependent proliferation and transformation. Elevated phosphorylation of Ros in ,viable motheaten (me-v)' mice which, have strongly reduced SHP-1 activity, suggests that Ros signaling is under control of SHP-1 in vivo. Thus sterility of male me-v mice seems to be related to dysregulation of Ros. A synthetic phosphopeptide derived from the Ros sequence around Y2267 potently activates recombinant SHP-1 in vitro but is not a good substrate for SHP-1. In contrast, phosphorylation sites in the activation loop of Ros are effectively dephosphorylated. Based on these observations we propose a mechanistic model of Ros,SHP-1 interaction. Using fusion proteins of SHP-1 variants and of Ros with GFP-proteins of different spectral characteristics the interaction of Ros and SHP-1 can be visualized in intact cells by different microscopic techniques. [source] | |||||||||||||||||||||||||||||||||||||