Change In Decay Rate Research Articles

Mechanism of Electrolyte-Induced Brightening in Single-Wall Carbon Nanotubes

While addition of electrolyte to sodium dodecyl sulfate suspensions of single-wall carbon nanotubes has been demonstrated to result in significant brightening of the nanotube photoluminescence (PL), the brightening mechanism has remained unresolved. Here, we probe this mechanism using time-resolved PL decay measurements. We find that PL decay times increase by a factor of 2 on addition of CsCl as the electrolyte. Such an increase directly parallels an observed near-doubling of PL intensity, indicating the brightening results primarily from changes in nonradiative decay rates associated with exciton diffusion to quenching sites. Our findings indicate that a reduced number of these sites results from electrolyte-induced reorientation of the surfactant surface structure that partially removes pockets of water from the tube surface where excitons can dissociate, and thus underscores the contribution of interfacial water in exciton recombination processes.

Cost-Effective Spatial and Dynamic Management of a Eutrophied Baltic Sea

The purpose of this article is to calculate cost-effective spatial and dynamic allocations of nutrient abatement for reaching targets in a large sea with different and interlinked marine basins. A discrete dynamic model was constructed to account for measures affecting both nitrogen and phosphorus and heterogeneous and coupled marine basins within the sea. Theoretical results revealed that positive decay rates of nutrient pools in the marine basins reduce abatement costs by delaying abatement over time. The results also showed that simultaneous management of both nutrients reduces overall abatement costs as compared with separate management. An empirical application to the intergovernmental agreement on nutrient pool targets in the Baltic Sea was made by combining results from an oceanographic model with an economic model of abatement costs. The results indicate that modest changes in decay rates make a significant impact on abatement costs and that simultaneous implementation of targets for both nutrients can reduce total cost by approximately 15% compared with separate treatment. A robust result is the finding that one country, Poland, faces much higher abatement costs than the other eight riparian countries because of its relatively large discharges into a marine basin with a stringent phosphorus target and slow response to load changes.

Stochastic Modeling of Expression Kinetics Identifies Messenger Half-Lives and Reveals Sequential Waves of Co-ordinated Transcription and Decay

The transcriptome in a cell is finely regulated by a large number of molecular mechanisms able to control the balance between mRNA production and degradation. Recent experimental findings have evidenced that fine and specific regulation of degradation is needed for proper orchestration of a global cell response to environmental conditions. We developed a computational technique based on stochastic modeling, to infer condition-specific individual mRNA half-lives directly from gene expression time-courses. Predictions from our method were validated by experimentally measured mRNA decay rates during the intraerythrocytic developmental cycle of Plasmodium falciparum. We then applied our methodology to publicly available data on the reproductive and metabolic cycle of budding yeast. Strikingly, our analysis revealed, in all cases, the presence of periodic changes in decay rates of sequentially induced genes and co-ordination strategies between transcription and degradation, thus suggesting a general principle for the proper coordination of transcription and degradation machinery in response to internal and/or external stimuli.

Computed diffusion contribution in the complex blood oxygenation-level dependent fMRI signal

Diffusion is a ubiquitous phenomenon in blood oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI), but it cannot be completely separated out from BOLD signals experimentally or theoretically. Nevertheless, it is possible to numerically characterize the diffusion-only contribution by Monte Carlo simulation and signal analysis. The simulation was carried out for a variety of parameter settings of cortical vasculature (vessel radii = [2, 16] micron) and field strength (B0 = [0.18, 12.9] T). A cortical voxel was simulated in a cube of size 320 × 320 × 320 micron3 filled with a random vascular network. Diffusion-present and diffusion-absent signals were calculated by intravoxel dephasing (via switching on and off the diffusion coefficients) for a range of echo times TE = [0, 60] ms. Given a pair of diffusion-present and diffusion-absent complex signals, the diffusion-only contribution was calculated by two signal analysis models: multiplication and addition. Statistics were rendered through multiple random realizations for each vasculature setting. Simulations suggest that diffusion contributes to BOLD signal (for setting of vessel radius = 3 micron, B0 = 3 T, TE = 30 ms) by a signal amplitude decay rate change of 0.8 Hz (multiplication model) or by a signal amplitude change percentage of 5% (addition model). Overall, this contribution is maximal amid a large range of field strengths, diminishing toward low and high fields. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part A 40A: 128–145, 2012.

Decay rates modification through coupling of degenerate surface plasmon modes

We measured the decay rates of two degenerate surface plasmon modes in Au nanohole arrays with different hole sizes by angle-resolved reflectivity spectroscopy. For each hole size, at the spectral region where resonant coupling occurs, we observed a large modification in decay rates, leading to the formation of dark and bright modes. The change in decay rates is well explained by temporal coupled mode theory. The deduced coupling constant is found to increase with increasing hole diameter. This study provides us a simple and effective means to control the decay rates of dark and bright modes, which are useful in plasmonic applications.

Decomposition of black locust and black pine leaf litter in two coeval forest stands on Mount Vesuvius and dynamics of organic components assessed through proximate analysis and NMR spectroscopy

Litter quality is an important determinant of soil organic matter formation. Changes of organic components were investigated along decomposition of black locust (Robinia pseudoacacia L.) leaf litter and black pine (Pinus nigra Arn.) needle litter in the native adjacent coeval forest stands. To this purpose, data from proximate analyses were compared with those from CPMAS 13C NMR. Newly shed leaf litter of black locust had significantly higher concentrations of ADSS (acid detergent soluble substances) as well as lower concentrations of cellulose and AUR (acid unhydrolyzable residues that include lignin) and higher AUR-to-Cellulose ratio than that of black pine. The 13C CPMAS NMR spectra of newly shed leaf litter of black locust and black pine revealed that O-Alkyl-C components (including cellulose and hemicelluloses) accounted, respectively, for 53.8% and 61.4% of the total area of the spectra. All other C fractions were relatively more abundant in black locust than in black pine. Within individual sampling periods, relationships between residual litter mass and concentrations of ADSS, cellulose and AUR were examined, as were relationships between residual litter C and NMR fractions. Four periods were defined based on the slopes of the decomposition curve, with the length of period I defined by the start of a net decrease of AUR. Proximate analyses and NMR data showed changes in chemical composition over the decomposition process, as well as changes in decay rates of the residues, following different paths in the two litters. ADSS decayed faster in black locust litter; in contrast cellulose and AUR decayed faster in that of black pine. AUR concentration increased in both litters during decomposition; however, compared to black pine, the remaining litter of black locust was richer in AUR, despite the lower initial concentration, and had a higher AUR-to-Cellulose ratio. Phenol-C and Aryl-C decayed faster in black locust litter, while Alkyl-C decayed faster in that of black pine. In both litters, mass loss in periods was negatively correlated to concentration of AUR at the start of the periods. C loss in periods was negatively correlated to the concentration at the start of the periods of MC-to-PC (an index of lignin content) in black locust litter and positively correlated to Alkyl-C and O-Alkyl-C in that of black pine. Phenol-C, O-Alkyl-C and Aryl-C were the most decomposable C fractions in black locust. O-Alkyl-C and Alkyl-C were the most decomposable C fractions in black pine. Limit value was lower in black pine than in black locust. Consequently the different pattern of litter decomposition can affect the size of C sequestration in the forest floor and the quality of accumulated organic carbon.

Piecewise mixed-effects models with skew distributions for evaluating viral load changes: A Bayesian approach

Studies of human immunodeficiency virus dynamics in acquired immuno deficiency syndrome (AIDS) research are very important in evaluating the effectiveness of antiretroviral (ARV) therapies. The potency of ARV agents in AIDS clinical trials can be assessed on the basis of a viral response such as viral decay rate or viral load change in plasma. Following ARV treatment, the profile of each subject's viral load tends to follow a 'broken stick'-like dynamic trajectory, indicating multiple phases of decline and increase in viral loads. Such multiple-phases (change-points) can be described by a random change-point model with random subject-specific parameters. One usually assumes a normal distribution for model error. However, this assumption may be unrealistic, obscuring important features of within- and among-subject variations. In this article, we propose piecewise linear mixed-effects models with skew-elliptical distributions to describe the time trend of a response variable under a Bayesian framework. This methodology can be widely applied to real problems for longitudinal studies. A real data analysis, using viral load data from an AIDS study, is carried out to illustrate the proposed method by comparing various candidate models. Biologically important findings are reported, and these findings also suggest that it is very important to assume a model with skew distribution in order to achieve reliable results, in particular, when the data exhibit skewness.

The apparent change of activity with temperature in a 226Ra decay chain

Radioactive decay rates are to a large extent believed to be independent of the chemical environment. This is the physics basis implicitly assumed in applications such as radioisotope dating. While this statement is a good approximation for most radioactive decays, there are cases where a slight variation of 0.5% or more can be observed, as in the electron capture type of decay. There are renewed interests in possible decay-rate changes with external parameters such as temperature, with controversy as to the phenomenon’s authenticity. In this paper, we study the variation of radioactivity counts that significantly change (up to 50% or more) with temperature. We carefully studied the characteristics of the change and found that the presence of a gaseous decay daughter can pose a serious challenge to a bona fide account of the intrinsic nuclear decay rate. After a careful solution to rate equations of the relevant isotopes under our experimental conditions, we found that most of the radioactivity change could be accounted for by the diffusion and loss of gaseous daughters under the heat, without a supposed change in the intrinsic nuclear decay rate. We hence demonstrate that an accurate determination of the decay constant has to consider the possible diffusion of volatile components in the decay chain. This is especially important in cases involving significant temperature change.

Ultrafast photoluminescence spectroscopy of H- and O-terminated nanocrystalline diamond films

We use femtosecond photoluminescence spectroscopy to study the light-induced changes in the sub-gap energy states of nanocrystalline diamond samples (thickness ~ 500 and 1000 nm) prepared on a spectral-grade fused silica substrate by microwave plasma enhanced chemical vapour deposition technique. The decay of photoluminescence in the visible spectral interval excited by blue femtosecond light pulses (405 nm,70 fs) shows that photoexcited charge carrier dynamics depend strongly on the ambient air pressure and on the light irradiation by the laser pulses. Specifically, at lower ambient air pressure (0.5–300 Pa) the irradiation leads to the peak photoluminescence intensity increase and to its faster decay. At higher air pressures (> 600 Pa) the photoluminescence intensity slightly decreases with no change in decay rates. O- and H-termination of nanocrystalline diamond films had negligible effect on their photoluminescence dynamics. The photoluminescence decay curves are described very well by the power-law decay reflecting the importance of the carrier trapping in the dynamics. Based on our results we propose a model of surface and sub-surface structure of nanodiamond films.

Uncertainty of 21st century growing stocks and GHG balance of forests in British Columbia, Canada resulting from potential climate change impacts on ecosystem processes

Over the coming decades, climate change will increasingly affect forest ecosystem processes, but the future magnitude and direction of these responses is uncertain. We designed 12 scenarios combining possible changes in tree growth rates, decay rates, and area burned by wildfire with forecasts of future harvest to quantify the uncertainty of future (2010–2080), timber growing stock, ecosystem C stock, and greenhouse gas (GHG) balance for 67 million ha of forest in British Columbia, Canada. Each scenario was simulated 100 times with the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3). Depending on the scenario, timber growing stock over the entire land-base may increase by 14% or decrease by 9% by 2080 (a range of 2.8 billion m 3), relative to 2010. However, timber growing stock available for harvest was forecast to decline in all scenarios by 26–62% relative to 2010 (a range of 1.2 billion m 3). Forests were an annual GHG source in 2010 due to an ongoing insect outbreak. If half of the C in harvested wood was assumed to be immediately emitted, then 0–95% of simulations returned to annual net sinks by 2040, depending on scenario, and the cumulative (2010–2080) GHG balance ranged from a sink of −4.5 Pg CO 2e (−67 Mg CO 2e ha −1) for the most optimistic scenario, to a source of 4.5 Pg CO 2e (67 Mg CO 2e ha −1) for the most pessimistic. The difference in total ecosystem carbon stocks between the most optimistic and pessimistic scenarios in 2080 was 2.4 Pg C (36 Mg C ha −1), an average difference of 126 Tg CO 2e yr −1 (2 Mg CO 2e yr −1 ha −1) over the 70-year simulation period, approximately double the total reported anthropogenic GHG emissions in British Columbia in 2008. Forests risk having reduced growing stock and being GHG sources under many foreseeable scenarios, thus providing further feedback to climate change. These results indicate the need for continued monitoring of forest responses to climatic and global change, the development of mitigation and adaptation strategies by forest managers, and global efforts to minimize climate change impacts on forests.

Attempt at the Change of Decay Rate of Gold-198 by Using Weak-Interaction Field in Electrochemical Neutrino Detector

Attempt at the Change of Decay Rate of Gold-198 by Using Weak-Interaction Field in Electrochemical Neutrino Detector

Geometric measure of quantum discord under decoherence

The dynamics of a geometric measure of the quantum discord (GMQD) under decoherence is investigated. We show that the GMQD of a two-qubit state can be alternatively obtained through the singular values of a $3\times4$ matrix whose elements are the expectation values of Pauli matrices of the two qubits. By using Heisenberg picture, the analytic results of the GMQD is obtained for three typical kinds of the quantum decoherence channels. We compare the dynamics of the GMQD with that of the quantum discord and of entanglement. We show that a sudden change in the decay rate of the GMQD does not always imply that of the quantum discord, and vice versa. We also give a general analysis on the sudden change in behavior and find that at least for the Bell diagonal states, the sudden changes in decay rates of the GMQD and that of the quantum discord occur simultaneously.

Fluorescence quenching of rhodamine-6G in Au nanocomposite polymers

Nanocomposite polymers are gaining interest because of their ease of preparation and device applications. In this report, synthesis of Au-polyvinyl alcohol nanocomposite and rhodamine-6G doped Au-polyvinyl alcohol nanocomposite polymer films which are prepared at room temperature have been reported. The role of nanosized gold on fluorescence properties of rhodamine-6G has been analyzed. Steady state fluorescence studies show that the nanoparticles quench the fluorescence of rhodamine-6G. Fluoresence quenching were analyzed using all possible mechanisms like Förster resonant energy transfer, nanometal surface energy transfer and electron transfer to metallic conduction bands. Time resolved fluorescence studies reveal that the decay rate changes because of the addition of Au nanoparticles and also depends on the size of the nanoparticles.

ChemInform Abstract: Electronic Relaxation in Long Polyenes

A series of carotenols with from 7 to 11 conjugated double bonds have been synthesized and purified by using HPLC techniques. Absorption, fluorescence, and fluorescence excitation spectra have been obtained in 77 K glasses. The shorter members of this series exhibit the Stokes-shifted, S{sub 1} {yields} S{sub 0} emissions seen in previous studies of model polyenes. For carotenols with more than eight conjugated double bonds, however, the fluorescence is dominated by anti-Kasha, S{sub 2} {yields} S{sub 0} fluorescence. these findings in part can be attributed to a larger S{sub 2}-S{sub 1} energy difference and the resultant decrease in S{sub 2} {yields} S{sub 1} radiationless decay rates in longer polyenes. The precipitous crossover from S{sub 1} {yields} S{sub 0} to S{sub 2} {yields} S{sub 0} emission, however, cannot be fully accounted for by the energy gap law, which predicts only modest changes in radiative and nonradiative decay rates with increasing polyene length. The implications of large S{sub 2}-S{sub 1} energy gaps for the spectroscopy and photochemistry of {beta}-carotene and other long polyenes also are discussed.

Diesel exhaust particle exposure exacerbates contractile dysfunction in diabetic‐like cardiomyocytes

Diesel particulate matter (DEP) pollution and diabetes mellitus (DM) are two key contributors to heart disease in modern cities. The purpose of the present study was to evaluate contractile function, calcium signaling and reactive oxygen species (ROS) formation in adult rat ventricular myocytes exposed to DEP (1 μM) and/or DM simulation media (HG, 25.5mM glucose) overnight. Ventricular myocytes were isolated from adult male Sprague‐Dawley rats and sarcomeric contractile properties were evaluated using an IonOptix Field‐Stimulator system, including: peak shortening normalized to baseline (PS), maximal velocities of shortening/relengthening (±dL/dt), time‐to‐90% peak (TPS90,), time‐to‐ 90% relengthening (TR90), change in fura fluorescence intensity (FFI) and fluorescence decay rate (tau). Intracellular ROS formation was assessed using dihydroethidium. We found that DEP exposure significantly decreased PS, ±dL/dt and increased time‐to‐ 90% relengthening (TR90), tau and intracellular ROS formation in diabetic‐like cells. Further studies indicated that antioxidant co‐culture (0.25 mM Tiron and 0.5 mM N‐Acetyl‐L‐cysteine) completely restored contractile function in DEP‐treated diabetic‐like myocytes. Our final data confirm that DEP exacerbates myocardial dysfunction in diabetic cardiomyocytes, which is mediated by ROS production.

Glucosamine-induced endoplasmic reticulum stress attenuates apolipoprotein B100 synthesis via PERK signaling

Glucosamine impairs hepatic apolipoprotein B100 (apoB100) production by inducing endoplasmic reticulum (ER) stress and enhancing cotranslational and posttranslational apoB100 degradation (Qiu, W., R. K. Avramoglu, A. C. Rutledge, J. Tsai, and K. Adeli. Mechanisms of glucosamine-induced suppression of the hepatic assembly and secretion of apolipoprotein B-100-containing lipoproteins. J. Lipid Res. 2006. 47: 1749-1761). Here, we report that glucosamine also regulates apoB100 protein synthesis via ER-stress-induced PERK activation. Short-term (4 h) glucosamine treatment of HepG2 cells reduced both cellular (by 62%) and secreted apoB100 (by 43%) without altering apoB100 mRNA. Treatment with proteasomal inhibitors only partially prevented the suppressive effects of glucosamine, suggesting that mechanisms other than proteasomal degradation may also be involved. Glucosamine-induced ER stress was associated with a significantly reduced apoB100 synthesis with no significant change in posttranslational decay rates, suggesting that glucosamine exerted its effect early during apoB biosynthesis. The role of PERK and its substrate, alpha-subunit of eukaryotic initiation factor 2 (eIF2alpha), in the suppressive effects of glucosamine on apoB synthesis was then investigated. Coexpression of apoB15 (normally resistant to intracellular degradation) with wild-type double stranded (ds) RNA activated protein kinase (PKR)-like endoplasmic reticulum kinase (PERK) in COS-7 cells resulted in a dramatic reduction in the levels of newly synthesized apoB15. Interestingly, cotransfection with apoB15 and a kinase inactive PERK mutant (K618A) increased apoB15 expression. In addition, short-term glucosamine treatment stimulated an increase in phosphorylation of PERK and eIF2alpha. Taken together, these data suggest that in addition to the induction of ER-associated degradation and other degradative pathways, ER stress is associated with suppression of apoB synthesis via a PERK-dependent mechanism.

Poincaré's inequality and diffusive evolution equations

This paper addresses the question of change of decay rate from exponential to algebraic for diffusive evolution equations. We show how the behaviour of the spectrum of the Dirichlet Laplacian yields the passage from exponential decay in bounded domains to algebraic decay or no decay at all in the case of unbounded domains. It is well known that such rates of decay exist. The purpose of this paper is to explain what makes the change in decay happen. We also discuss what kind of data is needed to obtain various decay rates.

Signaling control of SOS1 mRNA stability

Regulation of mRNA decay rates appears to be an important control point in determining the abundance of gene transcripts. Rapid change in decay rates of mRNAs could provide prompt responses of the plants to environmental fluctuations. SOS1 is a plasma-membrane Na+/H+ antiporter crucial for salt tolerance in Arabidopsis. In our recent paper in Plant Journal, we have shown that SOS1 mRNA is inherently instable at normal growth conditions, but its stability is substantially elevated by salt and oxidative stress treatments. Salt stress-induced SOS1 mRNA stability is mediated by reactive oxygen species (ROS) produced, at least in part, through NADPH oxidases. We proposed a hypothetical model for the signaling pathway controlling SOS1 mRNA stability. In this addendum, we discuss the possible involvement of other components in conferring inherent instability and stress-induced stability of SOS1 mRNA.

Litter decomposition promotes differential feedbacks in an oligotrophic southern Everglades wetland

The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P), nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr−1). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands, and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands (r 2 = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems. Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization, further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state.

Synergistic Evaluation of Ozone and UV at the Coquitlam Source for Enhanced DBP Control and Cryptosporidium Inactivation

A study was performed for the GVRD to select the ozone dose that results in a higher UVT (UV Transmittance) and reduced DBP formation potential, at the most economical life cycle costs of ozone and UV treatment. The GVRD treats its Coquitlam source with ozone, to meet Giardia and virus inactivation requirements. Currently, the Coquitlam Facility does not meet Cryptosporidium inactivation requirements (3-log). Because the ozone dosage required for Cryptosporidium inactivation is cost prohibitive, UV treatment was selected to provide for adequate log inactivation. Based on pilot and full-scale test results, a model was developed to predict the ozone treated water UVT, which was applied to historical water quality data to evaluate life cycle costs of ozone and UV treatment. In addition, the dosage necessary for control of DBPs, the change in ozone decay rate with increases in pH, and the impact of three quenching chemicals on treated water UVT were evaluated.