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Decay Curve (decay + curve)
Kinds of Decay Curve Selected AbstractsProton T2 relaxation of cerebral metabolites of normal human brain over large TE rangeNMR IN BIOMEDICINE, Issue 1 2005E. E. Brief Abstract T2 of NAA, creatine and choline-containing compounds were measured in posterior frontal white matter and occipital grey matter in 10 healthy human volunteers. Decay curves comprised signals from eight TE times ranging from 30 to 800,ms with TR 2000,ms acquired with a PRESS sequence on a 1.5,T clinical scanner. Simulations were conducted to assess the precision of T2 estimates from decay curves comprising varying numbers and ranges of TE points. Mean and standard errors for T2s of NAA, creatine and choline-containing compounds were 300(8), 169(3) and 239(4) ms in posterior frontal white matter and 256(6), 159(8) and 249(8) ms in occipital grey matter. In vivoT2s found for choline and NAA were shorter than the T2s in the literature. The elevation of literature T2s is accounted for by the simulation results, which demonstrated that there is a bias towards lengthened T2s when T2 is measured with a maximum TE , T2. Concentration estimates are at risk of being underestimated if previously reported T2 corrections are used. Copyright © 2004 John Wiley & Sons, Ltd. [source] Fast transient fluorescence technique for studying swelling of gels made at various crosslinker contents and exposed to organic vapourPOLYMER INTERNATIONAL, Issue 9 2002M Erdo Abstract Fast transient fluorescence technique (FTRF) was employed for studying swelling of disc-shaped poly(methyl methacrylate) (PMMA) gels, which were prepared by free radical copolymerization of methyl methacrylate (MMA) using various ethylene glycol dimethacrylate (EGDM) contents at 60,°C. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P-doped PMMA gels under chloroform vapor. Decay curves of P were measured during in situ swelling experiments. Exponential fits were performed to measure pyrene lifetimes, ,, inside the PMMA gels. It was observed that , values decreased as swelling proceeded. An equation is derived for low quenching efficiencies to interpret the behaviour of P lifetimes during swelling. The Li,Tanaka equation was used to determine the cooperative diffusion coefficients, Dc, for the gels made at various crosslinker contents. It is observed that Dc values decrease as the crosslinker content is increased. © 2002 Society of Chemical Industry [source] A model of non-isothermal degradation of nutrients, pigments and enzymesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2004Maria G Corradini Abstract Published isothermal degradation curves for chlorophyll A and thiamine in the range 100,150 °C and the inactivation curves of polyphenol oxidase (PPO) in the range 50,80 °C could be described by the model C(t)/C0 = exp[,b(T)tn] where C(t) and C0 are the momentary and initial concentrations, respectively, b(T) a temperature dependent ,rate parameter' and n, a constant. This suggested that the temporal degradation/inactivation events of all three had a Weibull distribution with a practically constant shape factor. The temperature dependence of the ,rate parameter' could be described by the log logistic model, b(T) = loge[1 + exp[k(T , Tc)], where Tc is a marker of the temperature level where the degradation/inactivation occurs at a significant rate and k the steepness of the b(T) increase once this temperature range has been exceeded. These two models were combined to produce a non-isothermal degradation/inactivation model, similar to one recently developed for microbial inactivation. It is based on the assumption that the local slope of the non-isothermal decay curve, ie the momentary decay rate, is the slope of the isothermal curve at the momentary temperature at a time that corresponds to the momentary concentration of the still intact or active molecules. This model, in the form of a differential equation, was solved numerically to produce degradation/inactivation curves under temperature profiles that included heating and cooling and oscillating temperatures. Such simulations can be used to assess the impact of planned commercial heat processes on the stability of compounds of nutritional and quality concerns and the efficacy of methods to inactivate enzymes. Simulated decay curves on which a random noise was superimposed were used to demonstrate that the degradation/inactivation parameters, k and Tc, can be calculated directly from non-isothermal decay curves, provided that the validity of the Weibullian and log logistic models and the constancy of the shape factor n could be assumed. Copyright © 2004 Society of Chemical Industry [source] A multicenter pharmacokinetic study of the B-domain deleted recombinant factor VIII concentrate using different assays and standardsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 11 2003M. Morfini Summary., When the one-stage clotting assay is used in comparison with the chromogenic and immunological assays, plasma levels of factor (F)VIII are underestimated by 40,50% after infusion of B-domain deleted recombinant FVIII (BDD-rFVIII) in patients with hemophilia. A possible way to counteract the underestimation of FVIII levels by the one-stage assay is the adoption of a recombinant FVIII reference standard instead of a plasma standard. To evaluate the usefulness of such a standard [ReFacto® Laboratory Standard (RLS)], the pharmacokinetic parameters of a single dose of BDD-rFVIII (25 U kg,1) were evaluated in a multicenter study carried out in 18 patients with severe hemophilia A. The very low in vivo recovery, obtained with the combination of the one-stage assay and plasma reference standard, was increased up to the values obtained by the chromogenic assay when the results were expressed in terms of RLS. When the plasma standard was used, the one-stage/chromogenic ratio was 0.82 ± 0.12 for FVIII levels above 25 U dL,1 and 1.42 ± 0.99 for FVIII levels below 25 U dL,1. Using the RLS, the one-stage/chromogenic ratio increased to 1.01 ± 0.19 at FVIII levels above 25 U dL,1, as a consequence of a complete overlap of the two decays; however, at FVIII levels below 25 U dL,1, the one-stage/chromogenic ratio was still 1.6 ± 0.85. After the twelfth hour, FVIII concentrations obtained by chromogenic assay were always lower than those resulting from the one-stage clotting assay, independently of the standard used. Results obtained by chromogenic assay were not affected by the type of standard used. Compared with those obtained by the one-stage assay, higher values of clearance, lower volume of distribution area and shorter plasma half-life or mean residence time were obtained by chromogenic assay because of a shape change of the decay curve due to a shift to higher values in the first part (time interval 0,12 h) and to lower values in the second part of the decay curve (time interval 12,48 h). As a consequence, the slope of the decay curve obtained by means of chromogenic assay was steeper. In conclusion, the more homogeneous results of in vivo recovery and pharmacokinetic analysis, due to the decrease of discrepancy between the two methods when RLS was used, make the cheaper and more widely used one-stage assay preferable to the more expensive chromogenic assay, on condition that the ReFacto specific standard has used. [source] The effect of experimental conditions on the detection of spermine in cell extracts and tissuesNMR IN BIOMEDICINE, Issue 2 2010Nicholas G. Spencer Abstract The aim of this work was to investigate the effect of experimental conditions on the visibility of polyamines. In solution the chemical shift of the three groups of peaks (at approximately 1.8, 2.1 and 3.1,ppm) were found to be pH dependent. Relaxation times in aqueous solution at pH 7.0, 298,K and 11.74,T were measured to be: putrescine (T1,=,2.49,s, T2,=,2.07,s), spermidine (T1,=,1.27,s, T2,=,1.05,s) and spermine (T1,=,1.02,s, T2,=,0.82,s). Simple spin-echo sequences could not be used to measure T2 as the spins also experience phase evolution from homonuclear coupling which imposes a modulation on the T2 decay curve. This modulation is eliminated by using CPMG sequences with an echo spacing of <500,µs. Relaxation times for spermine in solution in presence of metal ions and protein showed that metal ions had little effect on T2; however, addition of 15,mg/ml bovine serum albumin reduced T2 of spermine (0.41,s at 298,K and 0.19,s at 277,K) but was not as short as the T2 of the polyamine peak in prostatic tissue (0.03,s at 277,K). The MR visibility of polyamines in prostate cell extracts, PC-3 xenograft (intact as well as extracted) and intact human prostatic tissues were investigated. Polyamines were not detected in methanol/chloroform extracts, but were visible in perchloric acid extracts of prostate tumour cells. No polyamines were detected in the HR MAS spectra of three samples of whole PC-3 xenograft tissue studied. In summary, the chemical shift of polyamine species is pH dependent, while protein binding causes peak broadening and reduction in T2. Perchloric acid extraction improves visibility of intracellular polyamines, but whole tissue polyamines are not seen in xenografts without epithelial/ ductal structure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ultraweak and Induced Photon Emission After Wounding of PlantsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009R. Winkler The ultraweak and induced photon emission were measured by a single photon counting equipment (Photomultiplier Hamamatsu R562) on Cucurbita pepo variaca styriacae after wounding. Wounding significantly changes the emission from a stationary to a nonstationary state and the shape of the decay curve obtained after light illumination. The rise in the ultraweak photon emission depends on the kind of wounding and its localization on the plant. The decay curves obtained after wounding could be better fit by an exponential function than by a hyperbolic one. So the biophoton emission correlates with physiological and bioelectrical changes like membrane depolarizations as they also depend on the kind of injury. [source] Time-resolved spectroscopy in an undoped GaN (1-101)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Eunhee Kim Abstract Time-resolved photoluminescence spectroscopy was performed at 77 K in a GaN (1-101) grown on a 7 degree off-axis (001) Si substrate. The sample was grown by metal-organic-vapour-phase-epitaxy (MOVPE) and was un-intentionally doped with O, C and Si. By using photoluminescence intensity correlation method, the energy relaxation process of the photogenerated carriers near the band edge was investigated in pico-second regime. The correlation signal was represented by a single exponential decay curve and the energy relaxation time was determined, which depended strongly on the kinetic energy of the excess carriers. At low energies, the relaxation time was around 700 ps, while it was as short as a few ps at the highest energy under study. The correlation signals obtained for carriers of which kinetic energy was less than 80 meV showed an anti-correlation behaviour suggesting the occurrence of carrier accumulation. The time constants for the accumulation were of several picoseconds depending on the kinetic energy, which was nearly equal to the decay time constants determined at high energies. This fact shows that the energy relaxation at high energies is controlled by the emission of an LO phonon. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Should fimbriae be included in pertussis vaccines?APMIS, Issue 9 2009Studies on ELISA IgG anti-Fim2/3 antibodies after vaccination, infection The anti-Fim response and long-term persistence after vaccination and infection may be of importance in understanding population immunity. Longitudinal serum samples (n = 1330) from 542 non-infected children related to a Swedish vaccine trial showed that the post vaccination (DTPa5) antibody decay curve for pertussis ELISA IgG anti-fimbriae2/3 (anti-Fim2/3) was bi-phasic. A slower one followed an initial rapid decay approximately 5,6 months after the third dose at 12 months of age. After 71 months, however, 60% still had concentrations above ,5 EU/ml, a level that had been shown to correlate with decreased risk of disease. Booster responses after re-vaccination with DTPa5 at 4, 5 and 6 years of age were strong and appeared within 1 week after vaccination, indicating immune memory. Ninety-six young children with verified pertussis infection, for whom we had serum samples both before, during and after the infection, showed a high response if they had been primed with fimbriae (either DTPa5 or DTPwc). In contrast, 76% of infected children not primed with fimbriae (a DTPa2 or DT group) only had concentrations below the minimum level of detection in all samples taken during and after the infection. In two Swedish seroepidemiological surveys, one from 1997 just after reintroduction of universal childhood vaccination against pertussis and one from 2007, the proportion of children 2,3 years with anti-Fim2/3 concentrations <5 EU/ml was similar and above 90%. This reflects that the two- or three-component pertussis vaccines (DTPa2 and DTPa3) that were introduced in Sweden in 1996 do not induce anti-Fim2/3 antibodies. In previous studies it was shown in multivariate analyses that levels of IgG anti-Fim2/3 ,5 EU/ml reduced short-term risk of pertussis in small children. As the antibody response to Fim2/3 after infection is poor in children who have not been primed earlier in life, inclusion of immunogenic Fim2/3 in future pertussis vaccines should be considered. [source] Evaluation of Cytotoxic and Cytostatic Effects in Saccharomyces cerevisiae by Poissoner Quantitative Drop TestBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2009Nadine Paese Poletto Current assay techniques, however, typically require the use of expensive technological equipment or chemical reagents, or they lack adequate testing sensitivity. The poissoner quantitative drop test (PQDT) assay is a sensitive, inexpensive and accurate method for evaluation of cytotoxicity and/or cytostatic effects of multiple chemical compounds in a single experiment. In this study, the sensitivity of the PQDT assay was evaluated in a wild-type Saccharomyces cerevisiae strain using 4-nitroquinoline-N - oxide (4-NQO) and methyl methanesulfonate (MMS), both cytotoxic and genotoxic standard compounds, and cytostatic 5-fluorouracil, an antitumoral drug. Yeast cell colony growth was measured in culture media containing increasing concentrations of the three chemical agents. The results showed that the PQDT assay was able to clearly differentiate the cytotoxic effect of 4-NQO and MMS from the cytostatic effect of 5-fluorouracil. Interestingly, the cytostatic effect of 5-fluorouracil followed an exponential decay curve with increasing concentrations, a phenomenon not previously described for this drug. The PQDT assay, in this sense, can be applied not only for cytotoxic/cytostatic assays, but also for pharmacodynamic studies using Saccharomyces cerevisiae as a model. [source] Factors affecting ocular rigidity in normal human eyesACTA OPHTHALMOLOGICA, Issue 2009AI DASTIRIDOU Purpose To measure the ocular rigidity coefficient and evaluate its relation with axial length (AL), age and mean systemic blood pressure (SBP). Methods Sixty three patients (63 eyes) undergoing cataract surgery, with different refractive errors and no ocular or systemic pathology were enrolled in this study. An invasive, computer controlled device comprising a microdosimetric pump and a pressure sensor, is connected to the anterior chamber under topical anaesthesia with drops. The system is used to raise the intraocular pressure (IOP) from 15 to 40mmHg, by infusing the eye with a saline solution. After each 4 ul infusion step, the IOP is continuously recorded for 2 seconds. From an initial level of 40mmHg an IOP decay curve of 1 minute is obtained. SBP and pulse rate are measured during the procedure. The rigidity coefficient is calculated by an exponential fit to the pressure volume data after correction for outflow. The study was approved by the Institutional Board and performed under the patient's informed consent. Results Mean AL was 24.8 (range 21.2-32.5). Mean age and SBP was 59 (12) years and 93.7 (10.5) mmHg respectively. The mean ocular rigidity coefficient was 0.021 (0.005) ul-1. Increasing axial length is associated with a decrease in the rigidity coefficient (r=-0.61, p<0.01). A positive correlation between the rigidity coefficient and age of the patients is found (r=0.31, p=0.01), whereas similar findings were not observed for SBP (p>0.05). Conclusion This manonetric approach of measuring ocular rigidity provides a normative database of this parameter in living human eyes. Axial length and age influence ocular rigidity. These results may have implications on tonography and ocular pulse studies. [source] Use of electron spin resonance measurements on irradiated sperma lentil seeds to indicate accidental irradiationINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2003Mustafa Korkmaz Summary The results of electron spin resonance studies on ,-irradiated micro- and macrosperma lentil seeds are reported. Spectra of non-irradiated intact sperma were composed of an equally spaced sextet originating from the presence of Mn2+ ions and a single weak resonance line. Irradiation produced a linear increase in the radical signal intensity in the radiation dose range (0.5,5 kGy) studied, without affecting the Mn2+ signal. Signal intensities of both sperma followed compound exponential decay curves originating from the presence of three different radical species. Heating the sperma cause irreversible decreases in both radical and Mn2+ signal intensities. Two radical species, described in the present work, and a radical of unknown origin were used to explain the experimental results. [source] Absorption of polyethylene glycol (PEG) polymers: The effect of PEG size on permeabilityJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2009Hema Gursahani Abstract Polyethylene glycol (PEG) polymers are large amphiphilic molecules that are highly hydrated in solution. To explore the permeability properties of different sized PEG polymers across epithelial membranes in vivo, we examined the absorption of fluorescently labeled PEG conjugates sized 0.55,20 kDa from the lung, since this system provides a reservoir that limits rapid diffusion of molecules away from the site of delivery and enables permeability over longer times to be examined. Following intratracheal delivery in rats, the PEG polymers underwent absorption with first-order kinetics described by single exponential decay curves. PEG size produced a marked influence on the rate of uptake from the lung, with half-lives ranging from 2.4 to 13 h, although above a size of 5 kDa, no further change in rate was observed. PEG size likewise affected retention in alveolar macrophages and in lung tissue; whereas smaller PEG sizes (<2 kDa) were effectively cleared within 48 h, larger PEG sizes (>5 kDa) remained in lung cells and tissue for up to 7 days. These data demonstrate that PEG polymers can be absorbed across epithelial membranes and that PEG size plays a dominant role in controlling the rate and mechanism of absorption. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2847,2856, 2009 [source] Synthesis and Luminescence Properties of BaMoO4:Sm3+ PhosphorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2010Zhiguo Xia BaMoO4:Sm3+ phosphor system with a tetragonal structure was synthesized via a high-temperature solid-state method. The charge compensated behaviors, 2Ba2+,Sm3++M+, where M+ is a monovalent cation like Li+, Na+, and K+ acting as a charge compensator, were investigated in this paper. It has been found that BaMoO4:Sm3+ phosphor by doping with K+ ions show greatly enhanced reddish orange emission compared with pure BaMoO4:Sm3+ sample. Investigation on Sm3+ and K+ concentration-dependent emission spectra indicated that Ba0.84MoO4:0.08Sm3+,0.12K+ phosphor exhibited the strongest reddish orange emission with a CIE values of x=0.55 and y=0.43. After irradiation under the 402 nm ultraviolet (UV) excitation, three emission peaks centered at 561, 598, and 642 nm corresponding to the 4G5/2 to 6HJ (J=5/2, 7/2, 9/2) emission lines of Sm3+ were obviously observed, and the lifetimes of three emissions (4G5/2,6HJ=5/2, 7/2, 9/2) have been calculated based on the measured decay curves. [source] A model of non-isothermal degradation of nutrients, pigments and enzymesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2004Maria G Corradini Abstract Published isothermal degradation curves for chlorophyll A and thiamine in the range 100,150 °C and the inactivation curves of polyphenol oxidase (PPO) in the range 50,80 °C could be described by the model C(t)/C0 = exp[,b(T)tn] where C(t) and C0 are the momentary and initial concentrations, respectively, b(T) a temperature dependent ,rate parameter' and n, a constant. This suggested that the temporal degradation/inactivation events of all three had a Weibull distribution with a practically constant shape factor. The temperature dependence of the ,rate parameter' could be described by the log logistic model, b(T) = loge[1 + exp[k(T , Tc)], where Tc is a marker of the temperature level where the degradation/inactivation occurs at a significant rate and k the steepness of the b(T) increase once this temperature range has been exceeded. These two models were combined to produce a non-isothermal degradation/inactivation model, similar to one recently developed for microbial inactivation. It is based on the assumption that the local slope of the non-isothermal decay curve, ie the momentary decay rate, is the slope of the isothermal curve at the momentary temperature at a time that corresponds to the momentary concentration of the still intact or active molecules. This model, in the form of a differential equation, was solved numerically to produce degradation/inactivation curves under temperature profiles that included heating and cooling and oscillating temperatures. Such simulations can be used to assess the impact of planned commercial heat processes on the stability of compounds of nutritional and quality concerns and the efficacy of methods to inactivate enzymes. Simulated decay curves on which a random noise was superimposed were used to demonstrate that the degradation/inactivation parameters, k and Tc, can be calculated directly from non-isothermal decay curves, provided that the validity of the Weibullian and log logistic models and the constancy of the shape factor n could be assumed. Copyright © 2004 Society of Chemical Industry [source] Photon echo in ruby doped only by 53Cr isotope ionsLASER PHYSICS LETTERS, Issue 8 2008V.V. Samartsev Abstract The signals of photon echo (PE) are investigated firstly in a ruby crystal doped only by the 53Cr isotope ions in a concentration of 0.03 , 0,05 wt%. The optical experiments were performed in backward regime at the wavelength of 693.4 nm both with a low magnetic field (200 G) and without it. Since the 53Cr isotope ions have hyperfine structure of levels the special attention was paid to the study of the stimulated photon echo and primarily to the investigation of its decay kinetics. It is established that this decay has a form which is typical to the signals of longlived PE. But in contrast to the long-lived PE the decay time in our case is less than the lifetime of the excited 2E () state. The signals of primary photon echo and stimulated photon echo at a low longitudinal magnetic field and their decay curves are investigated. We observed the beats of temporal shape of these signals with a period of several tens of nanoseconds. Theoretical analysis shows that they are due to the hyperfine interaction of valence electrons of 53Cr isotope ions with their own nuclei. The obtained decay curves allow us to estimate the phase relaxation time at the presence of a magnetic field. It proves to be equal to 98 ns. The spectrum of stimulated photon echo signal in the doped ruby exposed to a magnetic field is measured. (© 2008 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Long-lasting phosphorescence properties of Mn2+ -doped Cd2Ge7O16 orange light-emitting phosphorPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008Guangbo Che Abstract A new phosphor, Cd2Ge7O16:Mn2+, which emits orange-coloured long-lasting phosphorescence upon UV light excitation, was prepared by the conventional high-temperature solid-state method and its luminescent properties were systematically investigated. X-ray diffraction, photoluminescence and thermoluminescence spectra and lifetime decay curves were used to characterize the synthesized phosphor. This phosphor is well-crystallized by calcination at 950 °C for 6 h and shows excellent performance. After irradiation under 258 nm UV light, this phosphor emits a broad band centred at 585 nm and shows obvious long-lasting phosphorescence. The colour coordinate values of this phosphor are x = 0.56, y = 0.46. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ocular rigidity in living human eyes in health and diseaseACTA OPHTHALMOLOGICA, Issue 2009IG PALLIKARIS Purpose It is known that the balance between aqueous humor secretion and outflow rate controls the steady - state average intraocular pressure (IOP). It has been also early identified that blood circulation results to IOP fluctuations practically synchronous to cardiac function. IOP is the primary mechanical load to several ocular structures including the optical nerve head. Methods In-vivo intraoperative measurement of these quantities as well as secretion/outflow coefficients in humans allowed us to quantify ocular rigidity, IOP and its fluctuations (and pulsatile blood flow) in a series of physiological and pathological eyes. Ocular rigidity, outflow facility and pulsatile ocular blood flow were measured intraoperatively in a cohort of 63 patients undergoing cataract surgery. Measurements were also performed in a series of age related macular degeneration (AMD) patients. Results The eye, is a living structure under a continuously varying mechanical load that is strongly related to ocular haemodynamics. Ocular rigidity ranged from 0.0122 to 0.0343 (mean 0.0208),l-1. Outflow facility coefficient (derived from pressure decay curves) was 0.33 (sd 0.15),l/min/mmHg. Pulsatile ocular blood flow exhibited a strong negative correlation to IOP in all subjects. The ocular rigidity coefficient was higher in wet AMD patients compared to patients with dry AMD and healthy controls. Conclusion There are indications that this mechanical load, associated also to ocular rigidity, can not only inter-modulate blood flow but also have a long-term effect on other structures in the eye. Understanding the role of these parameters may contribute to the understanding of ocular disease. [source] | |||||||||||||||||||