516 research outputs found
From UV to NIR: A Full-Spectrum Metal-Free Photocatalyst for Efficient Polymer Synthesis in Aqueous Conditions
Photoāmediation offers unparalleled spatiotemporal control over controlled radical polymerizations (CRP). Photoāinduced electron/energy transfer reversible additionāfragmentation chain transfer (PETāRAFT) polymerization is particularly versatile owing to its oxygen tolerance and wide range of compatible photocatalysts. In recent years, broadbandā and nearāinfrared (NIR)āmediated polymerizations have been of particular interest owing to their potential for solarādriven chemistry and biomedical applications. In this work, we present the first example of a novel photocatalyst for both full broadbandā and NIRāmediated CRP in aqueous conditions. Wellādefined polymers were synthesized in water under blue, green, red, and NIR light irradiation. Exploiting the oxygen tolerant and aqueous nature of our system, we also report PETāRAFT polymerization at the microliter scale in a mammalian cell culture medium
Progress and Perspectives Beyond Traditional RAFT Polymerization.
The development of advanced materials based on well-defined polymeric architectures is proving to be a highly prosperous research direction across both industry and academia. Controlled radical polymerization techniques are receiving unprecedented attention, with reversible-deactivation chain growth procedures now routinely leveraged to prepare exquisitely precise polymer products. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a powerful protocol within this domain, where the unique chemistry of thiocarbonylthio (TCT) compounds can be harnessed to control radical chain growth of vinyl polymers. With the intense recent focus on RAFT, new strategies for initiation and external control have emerged that are paving the way for preparing well-defined polymers for demanding applications. In this work, the cutting-edge innovations in RAFT that are opening up this technique to a broader suite of materials researchers are explored. Emerging strategies for activating TCTs are surveyed, which are providing access into traditionally challenging environments for reversible-deactivation radical polymerization. The latest advances and future perspectives in applying RAFT-derived polymers are also shared, with the goal to convey the rich potential of RAFT for an ever-expanding range of high-performance applications
Wettability effects on Bandera Gray Sandstone using biosurfactants
Despite the growing demand for sustainable technologies that enhance residual oil recovery, the environmental and cost benefits of Microbial Enhanced Oil Recovery (MEOR) have favoured an increased research that is utilising a biosurfactant for oil recovery. In this study, three produced biosurfactants were investigated, and compared, which resulted in different impacts on the IFT and wettability. A secreted, extracellular biosurfactant produced by BS 2 reduced the IFT from 56.95 to 4.49 mN/m, BS 3 to 6.69 mN/m and BS 1 to 10.94 mN/m. The spent culture medium changed the wettability of the grains to both water-wet and intermediate-wet state. The findings prove the suitability of the biosurfactants for an effective EOR and as a biosurfactant preference in sandstone reservoirs
Organism-sediment interactions govern post-hypoxia recovery of ecosystem functioning
Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.
Measurement of the hadronic photon structure function F_{2}^{Ī³} at LEP2
The hadronic structure function of the photon F_{2}^{Ī³} (x, QĀ²) is measured as a function of Bjorken x and of the photon virtuality QĀ² using deep-inelastic scattering data taken by the OPAL detector at LEP at eāŗeā» centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F_{2}^{Ī³} are extended to an average QĀ² of ćQĀ²ć=780 GeVĀ² using data in the kinematic range 0.15<x<0.98. The QĀ² evolution of F_{2}^{Ī³} is studied for 12.1<ćQĀ²ć<780 GeVĀ² using three ranges of x. As predicted by QCD, the data show positive scaling violations in F_{2}^{Ī³} with F_{2}^{Ī³} (QĀ²)/Ī± = (0.08Ā±0.02āŗā°Ā·ā°āµ_ā.āā) + (0.13Ā±0.01āŗā°Ā·ā°Ā¹_ā.āā) lnQĀ², where QĀ² is in GeVĀ², for the central x region 0.10ā0.60. Several parameterisations of F_{2}^{Ī³} are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data
Measurement of the charm structure function F_{2,c)^{Ī³} of the photon at LEP
The production of charm quarks is studied in deep-inelastic electronāphoton scattering using data recorded by the OPAL detector at LEP at nominal eāŗeā» centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D* mesons using their decays into Dā°Ļ with the Dā° observed in two decay modes with charged particle final states, KĻ and KĻĻĻ. The cross-section Ļ^{D*} for production of charged D* in the reaction eāŗeā»āeāŗeā»D*Ī§ is measured in a restricted kinematical region using two bins in Bjorken x, 0.00140.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x<0.1 the measured cross-section is 43.8Ā±14.3Ā±6.3Ā±2.8 pb with a next-to-leading order prediction of 17.0āŗĀ²Ā·ā¹_ā.ā pb
Measurement of triple gauge boson couplings from WāŗWā» production at LEP energies up to 189 GeV
A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pbā»Ā¹. After combining with our previous measurements at centre-of-mass energies of 161ā183 GeV we obtain Īŗ = 0.97_{-0.16}^{+0.20}, g_{1}^{z} = 0.991_{-0.057}^{+0.060} and Ī» = -0.110_{-0.055}^{+0.058}, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their Standard Model values. These results are consistent with the Standard Model expectations
A Measurement of Rb using a Double Tagging Method
The fraction of Z to bbbar events in hadronic Z decays has been measured by
the OPAL experiment using the data collected at LEP between 1992 and 1995. The
Z to bbbar decays were tagged using displaced secondary vertices, and high
momentum electrons and muons. Systematic uncertainties were reduced by
measuring the b-tagging efficiency using a double tagging technique. Efficiency
correlations between opposite hemispheres of an event are small, and are well
understood through comparisons between real and simulated data samples. A value
of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is
statistical and the second systematic. The uncertainty on Rc, the fraction of Z
to ccbar events in hadronic Z decays, is not included in the errors. The
dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the
deviation of Rc from the value 0.172 predicted by the Standard Model. The
result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the
Standard Model.Comment: 42 pages, LaTeX, 14 eps figures included, submitted to European
Physical Journal
Measurement of the B+ and B-0 lifetimes and search for CP(T) violation using reconstructed secondary vertices
The lifetimes of the B+ and B-0 mesons, and their ratio, have been measured in the OPAL experiment using 2.4 million hadronic Z(0) decays recorded at LEP. Z(0) --> b (b) over bar decays were tagged using displaced secondary vertices and high momentum electrons and muons. The lifetimes were then measured using well-reconstructed charged and neutral secondary vertices selected in this tagged data sample. The results aretau(B+) = 1.643 +/- 0.037 +/- 0.025 pstau(Bo) = 1.523 +/- 0.057 +/- 0.053 pstau(B+)/tau(Bo) = 1.079 +/- 0.064 +/- 0.041,where in each case the first error is statistical and the second systematic.A larger data sample of 3.1 million hadronic Z(o) decays has been used to search for CP and CPT violating effects by comparison of inclusive b and (b) over bar hadron decays, No evidence fur such effects is seen. The CP violation parameter Re(epsilon(B)) is measured to be Re(epsilon(B)) = 0.001 +/- 0.014 +/- 0.003and the fractional difference between b and (b) over bar hadron lifetimes is measured to(Delta tau/tau)(b) = tau(b hadron) - tau((b) over bar hadron)/tau(average) = -0.001 +/- 0.012 +/- 0.008
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