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Decay Profiles (decay + profile)
Selected AbstractsTime-Resolved and Steady-State Fluorescence Spectroscopy of Eumelanin and Indolic PolymersPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2007Stephen P. Nighswander-Rempel Eumelanin plays a variety of important physiological roles in human skin. However, its structure and fundamental properties still remain poorly understood. Although the absorbance of eumelanin is broad and reveals little about its structure, a variety of techniques have revealed the presence of a disordered array of chromophores within the melanin compound. In order to examine the fluorescence decay dynamics of these chromophores, time-resolved spectroscopy was applied to solutions of synthetic eumelanin and a melanin-like polymer of N-methyl,5-hydroxy,6-methoxyindole (N-Me-5H6MI). Solutions were excited with 80 fs laser pulses at 355, 370, 390 and 400 nm, and decay time courses were acquired at 20 nm intervals between 400 and 600 nm for each excitation wavelength. Decay profiles for both eumelanin and the polymer exhibited a characteristic multiexponential behavior with decay times between 0.5 and 15 ns, although steady-state spectra for the polymer exhibited only two peaks. The long-decay component in the polymer showed a significant decrease in both amplitude (30,5%) and decay time (14,6 ns) with increasing emission wavelength. In contrast, the amplitude and decay time in melanin increased slightly (10,15% and 7,10 ns, respectively) from 400 to 520 nm emission, at which point they leveled off. These trends were consistent for all excitation wavelengths. These results suggest that the multiexponential behavior of melanin fluorescence is characteristic of each oligomer within the eumelanin compound, and is consistent with the assertion that the diversity of constituents within eumelanin provides it with a robustness in spectral properties. [source] Narrowing of exciton linewidth of a quantum dot with increasing temperaturePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Kazuki Bando Abstract Spectral narrowing of exciton luminescence at the elevated temperature was observed in a semiconductor quantum dot (QD). The Fourier spectroscopy was used for the study of decoherence processes of excitons in the single QD. High resolution spectra of the excitons were obtained from the Fourier transform of the decay profile of the exciton decoherence. We found that the exciton linewidth in the QD at low temperature was predominated by spectral diffusion due to carriers trapped at localized sites around the QD and the narrowing of the exciton line was induced by thermally activated escape processes of the carriers from the trap sites. The narrowing of the exciton line also indicates that the exciton decoherence in the semiconductor quantum dots is predominated by environmental fluctuation rather than the exciton-phonon interaction at low temperature. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Platinum pharmacokinetics in sulphur-crested cockatoos (Cacatua galerita) following single-dose cisplatin infusionAUSTRALIAN VETERINARY JOURNAL, Issue 6 2000LJ FILIPPICH Objective To determine the pharmacokinetics of platinum (Pt) in cockatoos. Design A pharmacokinetic study of Pt, following a single IV infusion of cisplatin, was done in six healthy sulphur-crested cockatoos (Cacatua galerita). Procedure Birds were hydrated for 1 h before and 2 h after a 1-h cisplatin infusion (1 mg/kg, IV). Serial blood samples were collected for 96 h after initiation of the infusion and urine was collected for 2 h during the hydration period after cisplatin administration. Tissue samples from 10 organs were obtained at necropsy, 96 h after cisplatin infusion. Total Pt and filterable Pt in plasma, urinary Pt and tissue Pt concentrations were assayed by inductively coupled plasma-mass spectrometry. A noncompartmental pharmacokinetic analysis was performed on the plasma and urine data. Results For total Pt and filterable Pt, the respective mean systemic clearances were 0.373 and 0.699 L/kg hourly, the steady state volumes of distribution were 4.19 and 0.356 L/kg, and the mean residence times were 111 and 0.512 h. Total plasma Pt displayed a bi-exponential decay profile with average half-lives of 0.398 and 79.0 h, while filterable Pt had a monoexponential decay with mean half-life of 0.413 h. The renal clearance during the 2-h postinfusion period was 0.167 L/kg hourly. The kidneys had the highest Pt accumulation (4.54 u.g/g DM). Conclusions and Clinical Relevance Cisplatin infusion in cockatoos was well tolerated and Pt plasma concentrations were similar to those measured during treatment of solid tumours in human patients. Despite anatomical, physiological and biochemical differences among animal species, the pharmacokinetic disposition of Pt in the cockatoo shares some features with the kinetics reported previously in rodents, dogs and human beings. [source] Intraoperative decay profile of intact (1,84) parathyroid hormone in surgery for secondary hyperparathyroidism in a consecutive series of 50 patients on haemodialysisBRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 9 2000J. Lokey Background The usefulness of rapid intraoperative monitoring of intact (1,84) parathyroid hormone (PTH) is not clearly defined in the surgical management of secondary HPT in the patients on haemodialysis. The aim of this study was to define the normal pattern of decay during surgery for secondary HPT using the rapid intact (1,84) PTH assay during operation. Methods Fifty patients on haemodialysis underwent neck exploration for secondary HPT. The therapeutic goal in all patients was the subtotal resection of four or more glands and bilateral transcervical thymectomy. PTH levels were monitored using a rapid immunochemiluminometric assay. Peripheral blood samples were assayed at induction of anaesthesia, after dissection but before resection, and 20 and 40 min after resection in all patients. All patients were followed up for at least 6 months. PTH levels were expressed as absolute values, as multiples of the upper limit of normal and as the percentage decline from pre-excision values. Results Forty-eight patients (96 per cent) were considered cured after surgery. Twenty patients (40 per cent) had a PTH level less than twice normal and 20 patients (40 per cent) had a PTH level between two and four times normal at 20 min. At late follow-up, all these patients were cured. Ten patients (20 per cent) had a PTH level greater than four times normal at 20 min. Eight of these patients were cured. Seven of these eight had a PTH level at 20 min, while not less than four times normal, less than 40 per cent of the original value. In contrast, the two failures had neither a decline to less than four times normal nor a decay to less than 40 per cent of the original value. One has been reoperated with resection of a fifth gland and one awaits reoperation. Conclusion The intraoperative decay of PTH during surgery for secondary HPT in patients on haemodialysis is slower than that in patients with normal renal function. However, 20 min after resection, a decline to less than four times the upper limit of normal is predictive of cure. Variability of decay slopes in individual patients may reflect molecular heterogeneity or biphasic metabolism of the hormone. © 2000 British Journal of Surgery Society Ltd [source] Highly Fluorescent Mesostructured Films that consist of Oligo(phenylenevinylene),Silica Hybrid Frameworks,ADVANCED FUNCTIONAL MATERIALS, Issue 22 2008Norihiro Mizoshita Abstract Highly fluorescent and visible-light-responsive mesostructured organosilica films are successfully obtained by acidic sol,gel polycondensation of oligo(phenylenevinylene) (OPV)-bridged organosilane and tetraethoxysilane precursors in the presence of a template surfactant. The OPV-bridged organosilane precursors with different lateral alkoxy substituents, hexyloxy and 2-ethylhexyloxy, and no substituent, are synthesized by Rh-catalyzed silylation of corresponding aromatic iodides. From the organosilane precursors, three kinds of mesostructured OPV,silica hybrid films are prepared by spin-casting using evaporation-induced self-assembly. UV-vis absorption and fluorescence behavior of the OPV,silica hybrid films show that the optical properties and intermolecular interactions of the OPV moieties embedded within the organosilica frameworks strongly depend on the lateral alkoxy substituents in the precursors. The hexyloxy and 2-ethylhexyloxy substituents prevent aggregation of the OPV units in the organosilica frameworks; this result leads to high fluorescence quantum yields of 0.48,0.61 and 0.63,0.66, respectively, while non-substitution leads to lower fluorescence quantum yields of 0.25,0.34. Fluorescence decay profiles of the organosilica hybrid films also confirm a suppression of the aggregation of OPV moieties by the lateral substituents. These mesostructured organosilica films with significant optical properties in the visible-light region are promising as a new class of phosphor materials. [source] Modeling complex decay profiles of hepatitis B virus during antiviral therapy,,HEPATOLOGY, Issue 1 2009Harel Dahari Typically, hepatitis B virus (HBV) decays in patients under therapy in a biphasic manner. However, more complex decay profiles of HBV DNA (e.g., flat partial response, triphasic, and stepwise), for which we have no clear understanding, have also been observed in some treated patients. We recently introduced the notion of a critical drug efficacy, ,c, such that if overall drug efficacy, ,tot, is higher than the critical drug efficacy (i.e., ,tot > ,c) then viral levels will continually decline on therapy, while if ,tot < ,c, then viral loads will initially decline but will ultimately stabilize at a new set point, as seen in flat partial responders. Using the idea of critical efficacy and including hepatocyte proliferation in a viral kinetic model, we can account for these complex HBV DNA decay profiles. The model predicts that complex profiles such as those exhibiting a plateau or shoulder phase, as well as a class of stepwise declines, occur only in patients in whom the majority of hepatocytes are infected before therapy. Conclusion: We show via kinetic modeling how a variety of HBV DNA decay profiles can arise in treated patients. (HEPATOLOGY 2009;49:32-38.) [source] Viral dynamics and response differences in HCV-infected African American and white patients treated with IFN and ribavirinHEPATOLOGY, Issue 6 2003Jennifer E. Layden-Almer Studies have suggested that African American patients infected with hepatitis C virus (HCV) do not respond as well to treatment with interferon (IFN) as white patients. Here we analyzed the difference in the viral kinetic response between genotype 1 HCV-infected African American patients (n = 19) and white patients (n = 16). Patients were treated with 10 mIU IFN-,2b daily with or without ribavirin for 1 month followed by 3 mIU IFN-,2b 3 times a week with ribavirin. The kinetic parameters (,, treatment effectiveness at inhibiting virion production; ,, loss rate of virus-producing cells; c, clearance rate of free virions; ,, delay until viral decline starts) were estimated from the viral load decay profiles using a previously described mathematical model. Differences in early kinetic parameters and viral negativity frequencies at weeks 4, 12, and 48 were compared. Ribavirin did not appear to enhance any of the viral kinetic parameters, although this may have been due to the high dose of IFN used. African American patients exhibited significantly (P = .005) lower drug effectiveness (88.6% vs. 98.2%) compared with white patients, accounting for a 0.8 log lower HCV RNA decrease in the first 24 hours of treatment. Significant differences (P = .006) were also noted for ,. There was no correlation between any of the viral kinetic parameters and either age, body mass index (BMI), or genotype 1 subtype. No patient achieved viral negativity at weeks 4, 12, or 48 without an , greater than 90%. The mean viral decline and viral negativity rates were statistically different between the two races; however, when controlling for treatment effectiveness, these differences were no longer apparent. In conclusion, the failure of IFN response in African American patients infected with genotype 1 HCV is in part due to an impaired ability to inhibit viral production. [source] Analysis of hepatitis B viral load decline under potent therapy: Complex decay profiles observedHEPATOLOGY, Issue 5 2001Sharon R. Lewin We used a new real-time polymerase chain reaction (PCR)-based assay that is sensitive, has a wide dynamic linear range, and is highly reproducible to quantify hepatitis B virus (HBV) DNA in the serum of infected individuals undergoing potent antiviral therapy. In addition, we made frequent measurements of viral load after initiation of treatment and maintained follow-up to about 12 weeks. To analyze the data we used a new model of HBV decay, which takes into account that existing drug treatments do not completely block de novo infection and the possibility of noncytolytic loss of infected cells. On initiation of therapy, there was a mean delay of 1.6 days followed by a biphasic or muliphasic decay of plasma HBV DNA. The slope of the first phase varied considerably, with one individual having rapid decay, corresponding to a virion half-life of 1 hour, but others showing half-lives of up to 92 hours. Individuals either had a slow second-phase decline (t˝ = 7.2 ± 1.2 days) or a flat second phase. Some individuals exhibited a complex "staircase pattern" of decay, with further phases of viral DNA decline and phases with little change in viral load. [source] Temporally and spectrally resolved fluorescence spectroscopy for the detection of high grade dysplasia in Barrett's esophagusLASERS IN SURGERY AND MEDICINE, Issue 1 2003T. Joshua Pfefer PhD Abstract Background and Objectives Temporal and spectral fluorescence spectroscopy can identify adenomatous colonic polyps accurately. In this study, these techniques were examined as a potential means of improving the surveillance of high grade dysplasia (HGD) in Barrett's esophagus (BE). Study Design/Materials and Methods Using excitation wavelengths of 337 and 400 nm, 148 fluorescence spectra, and 108 transient decay profiles (at 550,±,20 nm) were obtained endoscopically in 37 patients. Corresponding biopsies were collected and classified as carcinoma, HGD, or low risk tissue (LRT) [non-dysplastic BE, indefinite for dysplasia (IFD), and low grade dysplasia (LGD)]. Diagnostic algorithms were developed retrospectively using linear discriminant analysis (LDA) to separate LRT from HGD. Results LDA produced diagnostic algorithms based solely on spectral data. Moderate levels of sensitivity (Se) and specificity (Sp) were obtained for both 337 nm (Se,=,74%, Sp,=,67%) and 400 nm (Se,=,74%, Sp,=,85%) excitation. Conclusions In the diagnosis of HGD in BE, steady-state fluorescence was more effective than time-resolved data, and excitation at 400 nm excitation was more effective than 337 nm. While fluorescence-targeted biopsy is approaching clinical usefulness, increased sensitivity to dysplastic changes,possibly through modification of system parameters,is needed to improve accuracy levels. Lasers Surg. Med. 32:10,16,2003. © 2003 Wiley-Liss, Inc. [source] Synthesis, characterization, and its PL dynamics of colloidal type II CdTe/CdSe nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Masaru Oda Abstract We describe our improved synthesis and optical properties of high quality type II CdTe/CdSe nanocrystals (NCs). Specifically, clear shell-thickness dependences have been observed in the absorption and photoluminescence (PL) spectra and PL decay profiles as well. The magnitude of the lowest absorption band decreases drastically with large redshift as the shell thickness increases. The origin will be discussed on the bases of the model where the spatial configuration of the lowest electron-hole pair in the NCs changes from that of type I to type II as the shell thickness increases. As for the PL lifetime of the lowest electron-hole excitations, substantial increase is observed with increasing shell thickness. This can also be understood by considering the spatial configuration; spatial overlap between electron and hole wavefunctions decreases with increasing shell thickness, thus the lifetime increases. As for the NCs with extremely thin shell (,1 ML; 1 ML = 0.35 nm), the PL lifetime seems much longer than expected. This suggests that the thin shells seem imperfect and work rather a kind of trap sites than layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temporal profiles of excitons in surface-modified CdS and CdMnS quantum dots prepared by a reverse-micelle methodPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004D. Kim Abstract We have investigated surface-modification effects on photoluminescence properties of CdS and CdMnS quantum dots (QDs) prepared by a reverse-micelle method from the viewpoint of photoluminescence dynamics. By the surface modification, the band-edge luminescence intensity is markedly increased in CdS QDs. The surface modification also causes drastic changes of decay profiles of the band-edge luminescence. The Mn2+ luminescence originated from the intra-3d shell transition of Mn2+ is clearly observed in CdMnS QDs, and its intensity is also increased by the surface modification. Furthermore, the decay time of the band-edge luminescence in surface-modified CdMnS QDs is faster than that in CdS QDs, which is due to the energy transfer from excitons to Mn2+. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ortho-aminobenzoic acid-labeled bradykinins in interaction with lipid vesicles: Fluorescence studyBIOPOLYMERS, Issue 5 2002R. F. Turchiello Abstract The peptide hormone bradykinin (BK) (Arg1 -Pro2 -Pro3 -Gly4 -Phe5 -Ser6 -Pro7 -Phe8 -Arg9) and its shorter homolog BK1,5 (Arg1 -Pro2 -Pro3 -Gly4 -Phe5) were labeled with the extrinsic fluorescent probe ortho -aminobenzoic acid (Abz) bound to the N-terminal and amidated in the C-terminal carboxyl group (Abz-BK-NH2 and Abz-BK1,5 -NH2). The fragment des-Arg9 -BK was synthesized with the Abz fluorescent probe attached to the 3-amino group of 2,3-amino propionic acid (DAP), which positioned the Abz group at the C-terminal side of BK sequence, constituting the peptide des-Arg9 -BK-DAP(Abz)-NH2. The spectral characteristics of the probe were similar in the three peptides, and their fluorescent properties were monitored to study the interaction of the peptides with anionic vesicles of dimyristoylphosphatidylglycerol (DMPG). Time-resolved fluorescence experiments showed that the fluorescence decay of the peptides was best described by double-exponential kinetics, with mean lifetimes values around 8.0 ns in buffer pH 7.4 that increased about 10% in the presence of DMPG vesicles. About a 10-fold increase, compared with the values in aqueous solution, was observed in the steady-state anisotropy in the presence of vesicles. A similar increase was also observed for the rotational correlation times obtained from time-resolved anisotropy decay profiles, and related to the overall tumbling of the peptides. Equilibrium binding constants for the peptide,lipid interaction were examined monitoring anisotropy values in titration experiments and the electrostatic effects were evaluated through Gouy,Chapman potential calculations. Without corrections for electrostatic effects, the labeled fragment Abz-BK1,5 -NH2 presented the major affinity for DMPG vesicles. Corrections for the changes in peptide concentration due to electrostatic interactions suggested higher affinity of the BK fragments to the hydrophobic phase of the bilayer. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 336,346, 2002 [source] Layer-by-Layer Deposition of Rhenium-Containing Hyperbranched Polymers and Fabrication of Photovoltaic CellsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007Chui Wan Tse Abstract Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 ,,A,cm,2, 0.19, and 6.1×10,3,%, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film. [source] Enhancement of Förster Energy Transfer within a Microspherical CavityCHEMPHYSCHEM, Issue 11 2005Hideki Fujiwara Dr. Abstract Energy transfer from pyrene to perylene molecules co-doped within a poly(methyl methacrylate) latex microsphere was drastically accelerated relative to free space. Fluorescence spectra of the microspheres showed that the relative emission intensities of pyrene and perylene changed with the sphere diameter. Analyses of emission decay profiles clarified that Förster-type energy-transfer processes were induced and that the transfer rates increased within the microspherical cavity. This enhancement can be ascribed not only to the quantum electrodynamic effects on the pyrene emission rate, but also the cavity effect of increasing the overlapping factor between donor emission and acceptor absorption spectra. [source] | |||||||||||||