We consider low-energy nucleons at next-to-next-to-leading order in lattice chiral effective field theory. Three-body interactions
first appear at this order, and we discuss several methods for determining three-body interaction coefficients on the lattice.
We compute the energy of the triton and low-energy neutron-deuteron scattering phase shifts in the spin-doublet and spin-quartet
channels using Lüscher’s finite-volume method. In the four-nucleon system we calculate the energy of the -particle using auxiliary fields and projection Monte Carlo. 相似文献
Particulate gels are known to be formed by bovine β-lactoglobulin near the isoelectric point when partial unfolding is allowed
to occur under heating. The aggregation process of the protein has been investigated within the context of a nucleation and
growth process by preparing gels under precisely controlled thermal histories. This was achieved using a Differential Scanning
Calorimeter (DSC) to provide controlled heating rates, and known final temperatures and incubation times. The resulting particulate
gels were characterized by their particle size and polydispersity using Environmental Scanning Electron Microscopy (ESEM),
which permits hydrated samples to be observed. Particle size was found to decrease with increasing final temperature, with
the aggregation taking longer to reach completion for lower temperatures. Particle size was also found to decrease with increasing
heating rate. This system could be modelled as evolving via nucleation and growth by taking into account the fact that the
concentration of the aggregating species was varying as a function of temperature as well as time. The intrinsic tryptophan
fluorescence as a function of temperature was used as a guide to the fraction of unfolded protein in solution, thereby permitting
successful comparisons between the model predictions and the particle sizes to be made.-1 相似文献
Based on the preformed cluster model (PCM), we have extended our earlier study on cluster decays of heavy parent nuclei to analyze the effects of different nuclear proximity potentials in the ground-state clusterization of superheavy nuclei with Z = 113, 115 and 117. In order to look for the possible role of deformations, calculations are performed for spherical as well as β2-deformed choices of fragmentation. The relevance of “hot compact” over “cold elongated” configurations due to orientations is also explored, in addition to the role of Q value and angular momentum ℓ effects. As the PCM is based on collective clusterization picture, the preformation and penetration probabilities get modified considerably, and hence do so the decay constants and half-lives of the clusters, with the use of different nuclear proximity potentials. The comparative importance of nuclear proximity potentials Prox-1977 and Prox-2000 is analyzed and the calculated decay half-lives in the framework of PCM are compared with the recent predictions of the analytical super-asymmetric fission model (ASAFM). The possible role of shell corrections is also investigated for understanding the dynamics of heavy particle radioactivity. Finally, the potential energy surfaces are compared for different proton and neutron magic numbers in superheavy mass region.
α-Ketoglutarate (αKG)-dependent nonheme iron enzymes utilize a high-spin (HS) ferrous center to couple the activation of oxygen to the decarboxylation of the cosubstrate αKG to yield succinate and CO(2), and to generate a high-valent ferryl species that then acts as an oxidant to functionalize the target C-H bond. Herein a detailed analysis of the electronic-structure changes that occur in the oxygen activation by this enzyme was performed. The rate-limiting step, which is identical on the septet and quintet surfaces, is the nucleophilic attack of the distal O atom of the O(2) adduct on the carbonyl group in αKG through a bicyclic transition state ((5, 7) TS1). Due to the different electronic structures in (5, 7) TS1, the decay of (7)TS1 leads to a ferric oxyl species, which undergoes a rapid intersystem crossing to form the ferryl intermediate. By contrast, a HS ferrous center ligated by a peroxosuccinate is obtained on the quintet surface following (5)TS1. Thus, additional two single-electron transfer steps are required to afford the same Fe(IV)-oxo species. However, the triplet reaction channel is catalytically irrelevant. The biological role of αKG played in the oxygen-activation reaction is dual. The αKG LUMO (C=O π*) serves as an electron acceptor for the nucleophilic attack of the superoxide monoanion. On the other hand, the αKG HOMO (C1-C2 σ) provides the second and third electrons for the further reduction of the superoxide. In addition to density functional theory, high-level ab initio calculations have been used to calculate the accurate energies of the critical points on the alternative potential-energy surfaces. Overall, the results delivered by the ab initio calculations are largely parallel to those obtained with the B3LYP density functional, thus lending credence to our conclusions. 相似文献
Generalizing the idea of the Lovász extension of a set function and the discrete Choquet integral, we introduce a combinatorial model that allows us to define and analyze matroid-type greedy algorithms. The model is based on a real-valued function v on a (finite) family of sets which yields the constraints of a combinatorial linear program. Moreover, v gives rise to a ranking and selection procedure for the elements of the ground set N and thus implies a greedy algorithm for the linear program. It is proved that the greedy algorithm is guaranteed to produce primal and dual optimal solutions if and only if an associated functional on ${\mathbb{R}^N}$ is concave. Previous matroid-type greedy models are shown to fit into the present general context. In particular, a general model for combinatorial optimization under supermodular constraints is presented which guarantees the greedy algorithm to work. 相似文献
The nuclear spin alignments of the β-emitting fragments 12B(Iπ=1+, T1/2=20.2 ms) and 13B(Iπ=3/2−, T1/2=17.4 ms) produced in the 100A-MeV 13C, 15N + 9Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By
means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO2, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for
P and A are almost the same, there may be some depolarization mechanism in the collision process itself.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
We show that a maximal partial plane of order 6 with 31 lines and a maximal pure partial plane of order 6 with 25 lines can
be constructed from the icosahedron and the Petersen graph.
To Daniel R. Hughes, to commemorate his 80th birthday, August 7th, 2007. 相似文献