Intrinsic Turnover Research Articles

Young faculty job perceptions in the midst of Chinese higher education reform: the case of Zhejiang University

Chinese higher education is undergoing fundamental changes to meet the demand of producing high quantity and quality college students. These changes have significantly impacted the work lives of Chinese faculty members. This study investigated Chinese young faculty's job perceptions using four variables: intrinsic motivation, job burnout, job satisfaction, and turnover. The findings revealed that surveyed faculties had high intrinsic motivation, relatively high professional efficacy, and low turnover. However, they showed job burnout as indicated by emotional exhaustion and they demonstrated moderate intrinsic satisfaction and low extrinsic satisfaction. The study proposed that a healthy academic environment is needed for sustainable scholarship development.

Multi-product steady-state isotopic transient kinetic analysis of CO hydrogenation over supported molybdenum carbide

Isotopic transient analysis of steady state of CO hydrogenation catalyzed by alumina-supported Mo2C nanoclusters was performed at 573K, 1.2bar syngas with H2/CO=1. An isotope switch from 12CO to 13CO during the steady-state reaction produced a rapid transient associated with CO hydrogenation and a very slow transient associated with turnover of ineffective catalytic sites or exchange of carbidic carbon with reaction intermediates. Although the intrinsic turnover frequency for hydrocarbon formation was similar to that observed on late transition metals, the coverage of reaction intermediates on the Mo2C clusters was very low (≪1%), which accounts for the overall low activity of Mo2C. Promotion of Mo2C with Rb2CO3 lowered the coverage of intermediates even further, but increased the selectivity toward alcohols. Very strong interaction of the alcohols with the promoter suggests that Rb may form alkoxides at reaction conditions.

Suppression of particle dispersion by sweeping effects in synthetic turbulence

Synthetic models of Eulerian turbulence like so-called kinematic simulations (KS) are often used as computational shortcuts for studying Lagrangian properties of turbulence. These models have been criticized by Thomson and Devenish (2005), who argued on physical grounds that sweeping decorrelation effects suppress pair dispersion in such models. We derive analytical results for Eulerian turbulence modeled by Gaussian random fields, in particular for the case with zero mean velocity. Our starting point is an exact integrodifferential equation for the particle pair separation distribution obtained from the Gaussian integration-by-parts identity. When memory times of particle locations are short, a Markovian approximation leads to a Richardson-type diffusion model. We obtain a time-dependent pair diffusivity tensor of the form K(ij)(r,t)=S(ij)(r)τ(r,t), where S(ij)(r) is the structure-function tensor and τ(r,t) is an effective correlation time of velocity increments. Crucially, this is found to be the minimum value of three times: the intrinsic turnover time τ(eddy)(r) at separation r, the overall evolution time t, and the sweeping time r/v(0) with v(0) the rms velocity. We study the diffusion model numerically by a Monte Carlo method. With inertial ranges like the largest achieved in most current KS (about 6 decades long), our model is found to reproduce the t(9/2) power law for pair dispersion predicted by Thomson and Devenish and observed in the KS. However, for much longer ranges, our model exhibits three distinct pair-dispersion laws in the inertial range: a Batchelor t(2) regime, followed by a Kraichnan-model-like t(1) diffusive regime, and then a t(6) regime. Finally, outside the inertial range, there is another t(1) regime with particles undergoing independent Taylor diffusion. These scalings are exactly the same as those predicted by Thomson and Devenish for KS with large mean velocities, which we argue hold also for KS with zero mean velocity. Our results support the basic conclusion of Thomson and Devenish (2005) that sweeping effects make Lagrangian properties of KS fundamentally differ from those of hydrodynamic turbulence for very extended inertial ranges.

Separating soil CO2 efflux into C-pool-specific decay rates via inverse analysis of soil incubation data

Soil organic matter (SOM) is heterogeneous in structure and has been considered to consist of various pools with different intrinsic turnover rates. Although those pools have been conceptually expressed in models and analyzed according to soil physical and chemical properties, separation of SOM into component pools is still challenging. In this study, we conducted inverse analyses with data from a long-term (385 days) incubation experiment with two types of soil (from plant interspace and from underneath plants) to deconvolute soil carbon (C) efflux into different source pools. We analyzed the two datasets with one-, two- and three-pool models and used probability density functions as a criterion to judge the best model to fit the datasets. Our results indicated that soil C release trajectories over the 385 days of the incubation study were best modeled with a two-pool C model. For both soil types, released C within the first 10 days of the incubation study originated from the labile pool. Decomposition of C in the recalcitrant pool was modeled to contribute to the total CO2 efflux by 9-11 % at the beginning of the incubation. At the end of the experiment, 75-85 % of the initial soil organic carbon (SOC) was modeled to be released over the incubation period. Our modeling analysis also indicated that the labile C-pool in the soil underneath plants was larger than that in soil from interspace. This deconvolution analysis was based on information contained in incubation data to separate carbon pools and can facilitate integration of results from incubation experiments into ecosystem models with improved parameterization.

Isotopic transient analysis of the ethanol coupling reaction over magnesia

Isotopic transient analysis of ethanol coupling to butanol over MgO in a fixed-bed reactor at 673K revealed a surface coverage of adsorbed ethanol equivalent to about 50% of the exposed MgO atomic pairs. DRIFTS of ethanol reaction at 673K confirmed that the surface was populated primarily with adsorbed ethoxide and hydroxide, presumably from the dissociative adsorption of ethanol. The coverage of reactive intermediates leading to butanol was an order of magnitude lower than that of adsorbed ethanol, and about half the surface base sites counted by adsorption of CO2. The intrinsic turnover frequency for the coupling reaction at 673K determined by isotopic transient analysis was 0.04s−1, which is independent of any assumptions about the nature of the active sites. Although the ethanol coupling reaction appears to involve aldol condensation of an aldehyde intermediate, the high coverage of ethanol under steady-state conditions apparently inhibits unproductive CC coupling reactions that deactivate the catalyst at high temperature.

Comparison of different precious metals in activated carbon-supported catalysts for the gas-phase hydrodechlorination of chloromethanes

Four precious metals supported on activated carbon are compared as catalysts in the gas-phase hydrodechlorination (HDC) of chloromethanes. The intrinsic activity or turnover frequency (TOF) of the catalysts follows the order Pd/C>Rh/C>Pt/C>Ru/C in the HDC of dichloromethane (DCM) while the sequence Pd/C>Pt/C>Rh/C>Ru/C was found for the HDC of chloroform (TCM). High selectivities to non-chlorinated products were obtained in all cases except for the HDC of TCM with Rh/C and Ru/C where the selectivity to DCM greatly depends on the operating conditions. A wider diversity of non-chlorinated hydrocarbons was obtained as reaction products with these two catalysts, especially in the HDC of TCM, favoring the formation of carbonaceous deposits which provoked a marked deactivation of the catalysts. In contrast, CH4 was the only non-chlorinated product obtained with the Pt/C catalysts which showed by far the highest stability. Different reaction pathways were found depending on the catalyst and the starting chloromethane. The different reactivity of the metals is explained in terms of their different electronic structure and the physicochemical properties of the catalysts.

Progenitor and Terminal Subsets of CD8 + T Cells Cooperate to Contain Chronic Viral Infection

Chronic infections strain the regenerative capacity of antiviral T lymphocyte populations, leading to failure in long-term immunity. The cellular and molecular events controlling this regenerative capacity, however, are unknown. We found that two distinct states of virus-specific CD8(+) T cells exist in chronically infected mice and humans. Differential expression of the T-box transcription factors T-bet and Eomesodermin (Eomes) facilitated the cooperative maintenance of the pool of antiviral CD8(+) T cells during chronic viral infection. T-bet(hi) cells displayed low intrinsic turnover but proliferated in response to persisting antigen, giving rise to Eomes(hi) terminal progeny. Genetic elimination of either subset resulted in failure to control chronic infection, which suggests that an imbalance in differentiation and renewal could underlie the collapse of immunity in humans with chronic infections.

Facile hydrogenation of carbon-carbon double bonds using catalytic noble nanoparticles immobilized in microfluidic reactors

Abstract Facile hydrogenation of carbon-carbon double bonds was achieved in a poly(dimethylsiloxane) (PDMS) microfluidic reactor with immobilized noble nanoparticles, using the conversion of 6-bromo-1-hexene to 1-bromo-hexane as a model reaction. The microreactor was used to measure the intrinsic catalytic activity and turnover frequencies (TOF) of palladium (Pd), platinum (Pt) and ruthenium (Ru) nanocatalysts. The TOF of reactions run with immobilized nanocatalysts in the microfluidic reactor were hundreds of times larger than those measured in identical reactions in batch reactors. The combination of well-defined nanocatalysts and microfluidics significantly enhances hydrogen diffusion to catalytic sites, thus eliminating mass transfer limitations and enabling evaluation of the intrinsic catalytic activity. The system provides an excellent platform for high throughput screening of catalysts, and for conducting mechanistic studies of reaction kinetics.

Rate-Limiting Domain and Loop Motions in Arginine Kinase

Arginine kinase catalyzes the reversible transfer of a phosphoryl group between ATP and arginine. It is the arthropod homologue of creatine kinase, buffering cellular ATP levels. Crystal structures of arginine kinase, in substrate-free and substrate-bound forms, have revealed large conformational changes associated with the catalytic cycle. Recent nuclear magnetic resonance identified movements of the N-terminal domain and a loop comprising residues I182--G209 with conformational exchange rates in the substrate-free enzyme similar to the turnover rate. Here, to understand whether these motions might be rate-limiting, we determined activation barriers for both the intrinsic dynamics and enzyme turnover using measurements over a temperature range of 15-30 °C. (15)N transverse relaxation dispersion yields activation barriers of 46 ± 8 and 34 ± 12 kJ/mol for the N-terminal domain and I182--G209 loop, respectively. An activation barrier of 34 ± 13 kJ/mol was obtained for enzyme turnover from steady-state kinetics. The similarity between the activation barriers is indeed consistent with turnover being limited by backbone conformational dynamics and pinpoints the locations of potentially rate-limiting motions.

Intrinsic Motivation, Job Autonomy and Turnover Intention in the Italian Healthcare: The mediating role of Affective Commitment

Drawing on Self-Determination and Work Characteristics theories, we hypothesized that job autonomy and intrinsic motivation were key exogenous variables positively related to affective commitment, which in turn is negatively related to turnover intention, by performing a mediating role. A sample of 442 nurses has been involved in this research. Through the cross-validation technique, the results showed that the hypotheses of this study were supported and affective commitment completely mediated the relationships between job autonomy, intrinsic work motivation and turnover intention. These findings have important implications for healthcare organizations by helping to promote effective work environments and major opportunities of responsibility to workers to develop their own activity. Conclusions were examined considering practical implications for organizations, employees and the need for further researches.

Transferability of Research on Persistent Risks in Supplier Engagement and Contract Administration

Drawing on Self-Determination and Work Characteristics theories, we hypothesized that job autonomy and intrinsic motivation were key exogenous variables positively related to affective commitment, which in turn is negatively related to turnover intention, by performing a mediating role. A sample of 442 nurses has been involved in this research. Through the cross-validation technique, the results showed that the hypotheses of this study were supported and affective commitment completely mediated the relationships between job autonomy, intrinsic work motivation and turnover intention. These findings have important implications for healthcare organizations by helping to promote effective work environments and major opportunities of responsibility to workers to develop their own activity. Conclusions were examined considering practical implications for organizations, employees and the need for further researches.

Chemical Screens against a Reconstituted Multiprotein Complex: Myricetin Blocks DnaJ Regulation of DnaK through an Allosteric Mechanism

DnaK is a molecular chaperone responsible for multiple aspects of bacterial proteostasis. The intrinsically slow ATPase activity of DnaK is stimulated by its co-chaperone, DnaJ, and these proteins often work in concert. To identify inhibitors we screened plant-derived extracts against a reconstituted mixture of DnaK and DnaJ. This approach resulted in the identification of flavonoids, including myricetin, which inhibited activity by up to 75%. Interestingly, myricetin prevented DnaJ-mediated stimulation of ATPase activity, with minimal impact on either DnaK's intrinsic turnover rate or its stimulation by another co-chaperone, GrpE. Using NMR, we found that myricetin binds DnaK at an unanticipated site between the IB and IIB subdomains and that it allosterically blocked binding of DnaK to DnaJ. Together, these results highlight a "gray box" screening approach, which might facilitate the identification of inhibitors of other protein-protein interactions.

Structural effects of Na promotion for high water gas shift activity on Pt–Na/TiO 2

Sodium (1–10 wt.%)-promoted 1 wt.% Pt/TiO 2 catalysts were prepared by a co-impregnation method and tested for the water gas shift (WGS) reaction under differential reaction conditions. Significantly higher intrinsic activity is achieved with 2–4 wt.% Na addition, when 2–4 layers of NaO x are deposited on the support and the Pt particles are partially covered by NaO x , with moderate surface basicity and exposed Pt surface areas. In addition to the physical coverage, XPS data suggest that interactions between Pt and NaO x may occur by Pt electron donation to O in NaO x through Pt–O–Na. The strong metal–promoter interactions provide highly active sites for the WGS reaction at the periphery of the Pt–NaO x interface and also inhibit Pt particles from sintering. Optimal 4 wt.% Na (Na/Pt = 34) improves the intrinsic reaction rate and turnover frequency of Pt/TiO 2 at 300 °C by 8 and 11 times, respectively, and appears to be significantly higher than reported in the literature. The catalysts were characterized by X-ray diffraction, N 2 adsorption, CO chemisorption, transmission electron microscopy, H 2 temperature-programmed reduction, CO 2 temperature-programmed desorption, and X-ray photoelectron spectroscopy.

Structural Basis of Novel Interactions Between the Small-GTPase and GDI-like Domains in Prokaryotic FeoB Iron Transporter

The FeoB family proteins are widely distributed prokaryotic membrane proteins involved in Fe(2+) uptake. FeoB consists of N-terminal cytosolic and C-terminal transmembrane domains. The N-terminal region of the cytosolic domain is homologous to small GTPase (G) proteins and is considered to regulate Fe(2+) uptake. The spacer region connecting the G and TM domains reportedly functions as a GDP dissociation inhibitor (GDI)-like domain that stabilizes the GDP-binding state. However, the function of the G and GDI-like domains in iron uptake remains unclear. Here, we report the structural and functional analyses of the FeoB cytosolic domain from Thermotoga maritima. The structure-based mutational analysis indicated that the interaction between the G and GDI-like domains is important for both the GDI and Fe(2+) uptake activities. On the basis of these results, we propose a regulatory mechanism of Fe(2+) uptake.

Mechanism of action of SNS-032, a novel cyclin-dependent kinase inhibitor, in chronic lymphocytic leukemia

AbstractInhibitors of cyclin-dependent kinases (Cdks) have been reported to have activities in chronic lymphocytic leukemia cells by inhibiting Cdk7 and Cdk9, which control transcription. Here we studied the novel Cdk inhibitor SNS-032, which exhibits potent and selective inhibitory activity against Cdk2, Cdk7, and Cdk9. We hypothesized that transient inhibition of transcription by SNS-032 would decrease antiapoptotic proteins, resulting in cell death. SNS-032 effectively killed chronic lymphocytic leukemia cells in vitro regardless of prognostic indicators and treatment history. This was associated with inhibition of phosphorylation of RNA polymerase II and inhibition of RNA synthesis. Consistent with the intrinsic turnover rates of their transcripts and proteins, antiapoptotic proteins, such as Mcl-1 and X-linked inhibitor of apoptosis protein (XIAP), were rapidly reduced on exposure to SNS-032, whereas Bcl-2 protein was not affected. The initial decrease of Mcl-1 protein was the result of transcriptional inhibition rather than cleavage by caspase. Compared with flavopiridol and roscovitine, SNS-032 was more potent, both in inhibition of RNA synthesis and at induction of apoptosis. SNS-032 activity was readily reversible; removal of SNS-032 reactivated RNA polymerase II, which led to resynthesis of Mcl-1 and cell survival. Thus, these data support the clinical development of SNS-032 in diseases that require short-lived oncoproteins for survival.

Size‐Dependent Catalytic Activity of Supported Palladium Nanoparticles for Aerobic Oxidation of Alcohols

AbstractSilica‐alumina (SiO2‐Al2O3)‐supported palladium catalysts prepared by adsorption of the tetrachloropalladate anion (PdCl42−) followed by calcination and reduction with either hexanol or hydrogen were studied for the aerobic oxidation of alcohols. The mean size of the Pd particles over the SiO2‐Al2O3 support was found to depend on the Si/Al ratio, and a decrease in the Si/Al ratio resulted in a decrease in the mean size of the Pd nanoparticles. By changing the Si/Al ratio, we obtained supported Pd nanoparticles with mean sizes ranging from 2.2 to 10 nm. The interaction between the Pd precursor and the support was proposed to play a key role in tuning the mean size of the Pd nanoparticles. The Pd/SiO2‐Al2O3 catalyst with an appropriate mean size of Pd particles could catalyze the aerobic oxidation of various alcohols to the corresponding carbonyl compounds, and this catalyst was particularly efficient for the solvent‐free conversion of benzyl alcohol. The intrinsic turnover frequency per surface Pd atom depended significantly on the mean size of Pd particles and showed a maximum at a medium mean size (3.6–4.3 nm), revealing that the aerobic oxidation of benzyl alcohol catalyzed by the supported Pd nanoparticles was structure‐sensitive.

Kinetics of stress fibers

Stress fibers are contractile cytoskeletal structures, tensile actomyosin bundles which allow sensing and production of force, provide cells with adjustable rigidity and participate in various processes such as wound healing. The stress fiber is possibly the best characterized and most accessible multiprotein cellular contractile machine. Here we develop a quantitative model of the structure and relaxation kinetics of stress fibers. The principal experimentally known features are incorporated. The fiber has a periodic sarcomeric structure similar to muscle fibers with myosin motor proteins exerting contractile force by pulling on actin filaments. In addition the fiber contains the giant spring-like protein titin. Actin is continuously renewed by exchange with the cytosol leading to a turnover time of several minutes. In order that steady state be possible, turnover must be regulated. Our model invokes simple turnover and regulation mechanisms: actin association and dissociation occur at filament ends, while actin filament overlap above a certain threshold in the myosin-containing regions augments depolymerization rates. We use the model to study stress fiber relaxation kinetics after stimulation, as observed in a recent experimental study where some fiber regions were contractile and others expansive. We find that two distinct episodes ensue after stimulation: the turnover–overlap system relaxes rapidly in seconds, followed by the slow relaxation of sarcomere lengths in minutes. For parameter values as they have been characterized experimentally, we find the long time relaxation of sarcomere length is set by the rate at which actin filaments can grow or shrink in response to the forces exerted by the elastic and contractile elements. Consequently, the stress fiber relaxation time scales inversely with both titin spring constant and the intrinsic actin turnover rate. The model's predicted sarcomere velocities and contraction–expansion kinetics are in good quantitative agreement with experiment.

Size dependence in solvent-free aerobic oxidation of alcohols catalyzed by zeolite-supported palladium nanoparticles

Abstract The size dependence in the palladium nanoparticle-catalyzed solvent-free aerobic oxidation of alcohols was studied. Palladium nanoparticles with tunable mean sizes in a range of 2.0–10.5 nm were prepared over NaX zeolite by ion exchange of Na + with an ionic Pd precursor followed by calcination and H 2 reduction. The calcination temperature was found to be a crucial factor in determining the mean size of Pd nanoparticles. Pd/NaX catalysts with proper mean sizes of Pd could catalyze the solvent-free aerobic oxidation of various alcohols, and were particularly efficient for the oxidation of benzylic alcohols without substituents in benzene ring. Detailed studies using the Pd/NaX catalysts with different mean sizes of Pd revealed that the solvent-free aerobic oxidation of benzyl alcohol was structure-sensitive, and the intrinsic turnover frequency (TOF) reached a maximum at a medium mean size of Pd (2.8 nm). On the other hand, for the oxidation of geraniol or 2-octanol without delocalized π-ring, the reaction was structure-insensitive, and the intrinsic TOF did not change significantly with the mean size of Pd particles.

Hierarchical Network between the Components of the Multi-tRNA Synthetase Complex

The macromolecular tRNA synthetase complex consists of nine different enzymes and three non-enzymatic factors. This complex was recently shown to be a novel signalosome, since many of its components are involved in signaling pathways in addition to their catalytic roles in protein synthesis. The structural organization and dynamic relationships of the components of the complex are not well understood. Here we performed a systematic depletion analysis to determine the effects of structural intimacy and the turnover of the components. The results showed that the stability of some components depended on their neighbors. Lysyl-tRNA synthetase was most independent of other components for its stability whereas it was most required for the stability of other components. Arginyl- and methionyl-tRNA synthetases had the opposite characteristics. Thus, the systematic depletion of the components revealed the functional reason for the complex formation and the assembly pattern of these multi-functional enzymes and their associated factors.

AW02 Tissues – From Banking to Engineering

Tissue allografts are banked either in the viable or nonviable state. The latter have certain advantages in that the most immunogenic components (e.g. cells and soluble proteins) can be removed from the tissue. This enhances incorporation of the allograft, particularly for tissues with a rapid intrinsic turnover rate (e.g. bone). For other tissues, it has been claimed that the presence of viable donor cells enhances the tissues’ performance in the short to medium term. This is true of skin, where the blood vessels in the skin enosculate with vessels in the wound bed to gain a blood circulation. However this graft is eventually rejected by the recipient. For heart valves, claims of superior performance of viable grafts and long‐term survival of donor cells, are being questioned. The failure of these grafts to re‐cellularise and incorporate has been blamed on immunological responses to immunogenic components. To overcome these problems we have evaluated methods for removing donor cells from soft tissue grafts, without adversely affecting the mechanical and biological properties of the tissue matrix. We have also developed methods for re‐cellularising these tissue matrices with recipients’ cells. For tissues with immediate biomechanical function (e.g. heart valves), bioreactors providing appropriate biomechanical and biological environments have been constructed to simulate in vivo conditions and thus ‘train’ tissue‐engineered grafts, prior to implantation. These techniques are being applied to most of the soft tissue grafts currently supplied by NBS Tissue Services.