Choice For Potential Research Articles

A comprehensive analytical and computational assessment of soil water characteristics curves in Atlantic Canada: Application of a novel SelectKbestbased GEP model

For sustainable agriculture, irrigation is one of the most important management practices in a semi-arid climate. Determining the site-specific soil type-based irrigation water requirements requires the development of a soil water characteristics curve (SWCC). This study focuses on exploring the suitability of analytical SWCC models based on the observed data of SWCC developed using the pressure membrane apparatus. A novel SelectKbest gene expression programming (GEP) model is used to create the generalized machine learning SWCC model for Atlantic Canadian soils. The composite soil samples with representative soil textures of loamy sand, loam, and sandy loam are collected from the selected locations in Prince Edward Island and New Brunswick provinces of Canada. The suitability of models at three regions shows that at all sites, including PEI-1 (loam soil) 1, PEI-2 (loamy sand), and NB-3 (sandy loam) if SWCC data has four measured suction potential levels, then McBee & Bomb and Tani exponential models may be selected. Van Genuchten, double exponential, Ruso, Kosuki, and Gardner's four parameters models should be a good choice for five-section potential. Similarly, for six measured suction potential values, the Fredlund & Xing, Omuto, and Van Genuchten models having parameters should be selected for determining the optimum soil hydraulic parameters. The HydroMe program with Brooks and Corey, four, and five parameters Van Genuchten models performed well. The HydroMe program is calibrated and validated with standard RETC for selected regions of Atlantic Canada, which suggests that the HydroMe program is flexible in developing efficient agricultural water management algorithms. Various performance metrics like R2 and RMSE are employed to assess the robustness of the model. A generalized SWCC model (R2=0.976 and RMSE=0.04) is developed using a novel SelectKbest-based GEP modeling approach for Atlantic Canadian soils. These novel approaches can significantly improve site-specific agricultural water management and decision support systems.

Nuclear matter within the continuous choice in the full Dirac space

The relativistic Brueckner-Hartree-Fock equations are solved self-consistently for symmetric nuclear matter in the full Dirac space within the continuous choice for the single-particle potential. Inspired from the nucleon-nucleon scattering in the free space, the energy denominator of the scattering equation in the nuclear medium is rewritten and a complex Thompson equation for the effective interaction $G$ matrix is derived. By decomposing the matrix elements of the single-particle potential operator in the full Dirac space, both the real and the imaginary parts of the single-particle potential are determined uniquely. The single-particle energy and Dirac mass behave continuously through the Fermi surface as expected. By comparing the equation of state obtained within the continuous choice with that obtained within the gap choice and in-between choice, the convergence of the hole-line expansion is discussed.

Coarse-graining strategy for modeling effective, highly diffusive fluids with reduced polydispersity: A dynamical study.

We present a coarse-graining strategy for reducing the number of particle species in mixtures to achieve a simpler system with higher diffusion while preserving the total particle number and characteristic dynamic features. As a system of application, we chose the bidisperse Lennard-Jones-like mixture, discovered by Kob and Andersen [Phys. Rev. Lett. 73, 1376 (1994)], possessing a slow dynamics due to the fluid's multi-component character with its apparently unconventional choice for the pair potential of the type-A-type-B arrangement. We further established in a so-formed coarse-grained and temperature-independent monodisperse system an equilibrium structure with a radial distribution function resembling its mixture counterpart. This one-component system further possesses similar dynamic features such as glass transition temperature and critical exponents while subjected to Newtonian mechanics. This strategy may finally lead to the manufacturing of new nanoparticle/colloidal fluids by experimentally modeling only the outcoming effective pair potential(s) and no other macroscopic quantity.

The Fermi–Pasta–Ulam System as a Model for Glasses

We show that the standard Fermi–Pasta–Ulam system, with a suitable choice for the interparticle potential, constitutes a model for glasses, and indeed an extremely simple and manageable one. Indeed, it allows one to describe the landscape of the minima of the potential energy and to deal concretely with any one of them, determining the spectrum of frequencies and the normal modes. A relevant role is played by the harmonic energy \(\mathcal {E}\) relative to a given minimum, i.e., the expansion of the Hamiltonian about the minimum up to second order. Indeed we find that there exists an energy threshold in \(\mathcal {E}\) such that below it the harmonic energy \(\mathcal {E}\) appears to be an approximate integral of motion for the whole observation time. Consequently, the system remains trapped near the minimum, in what may be called a vitreous or glassy state. Instead, for larger values of \(\mathcal {E}\) the system rather quickly relaxes to a final equilibrium state. Moreover we find that the vitreous states present peculiar statistical behaviors, still involving the harmonic energy \(\mathcal {E}\). Indeed, the vitreous states are described by a Gibbs distribution with an effective Hamiltonian close to \(\mathcal {E}\) and with a suitable effective inverse temperature. The final equilibrium state presents instead statistical properties which are in very good agreement with the Gibbs distribution relative to the full Hamiltonian of the system.

Current Applications of Human Pluripotent Stem Cells: Possibilities and Challenges

Stem cells are self-renewable cells with the differentiation capacity to develop into somatic cells with biological functions. This ability to sustain a renewable source of multi- and/or pluripotential differentiation has brought new hope to the field of regenerative medicine in terms of cell therapy and tissue engineering. Moreover, stem cells are invaluable tools as in vitro models for studying diverse fields, from basic scientific questions such as developmental processes and lineage commitment, to practical application including drug screening and testing. The stem cells with widest differentiation potential are pluripotent stem cells (PSCs), which are rare cells with the ability to generate somatic cells from all three germ layers. PSCs are considered the most optimal choice for therapeutic potential of stem cells, bringing new impetus to the field of regenerative medicine. In this article, we discuss the therapeutic potential of human PSCs (hPSCs) including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), reviewing the current preclinical and clinical data using these stem cells. We describe the classification of different sources of hPSCs, ongoing research, and currently encountered clinical obstacles of these novel and versatile human stem cells.

A thermodynamic framework to develop rate-type models for fluids without instantaneous elasticity

In this paper, we apply the thermodynamic framework recently put into place by Rajagopal and co-workers, to develop rate-type models for viscoelastic fluids which do not possess instantaneous elasticity. To illustrate the capabilities of such models we make a specific choice for the specific Helmholtz potential and the rate of dissipation and consider the creep and stress relaxation response associated with the model. Given specific forms for the Helmholtz potential and the rate of dissipation, the rate of dissipation is maximized with the constraint that the difference between the stress power and the rate of change of Helmholtz potential is equal to the rate of dissipation and any other constraint that may be applicable such as incompressibility. We show that the model that is developed exhibits fluid-like characteristics and is incapable of instantaneous elastic response. It also includes Maxwell-like and Kelvin-Voigt-like viscoelastic materials (when certain material moduli take special values).

Density profiles of Ar adsorbed in slits of CO2: Spontaneous symmetry breaking revisited

A recently reported symmetry breaking of density profiles of fluid argon confined by two parallel solid walls of carbon dioxide is studied. The calculations are performed in the framework of a nonlocal density functional theory. It is shown that the existence of such asymmetrical solutions is restricted to a special choice for the adsorption potential, where the attraction of the solid-fluid interaction is reduced by the introduction of a hard-wall repulsion. The behavior as a function of the slit's width is also discussed. All the results are placed in the context of the current knowledge on this matter.

Spin–orbit and tensor interactions in homogeneous matter of nucleons: accuracy of modern many-body theories

We study the energy per particle of symmetric nuclear matter and pure neutron matter using realistic nucleon–nucleon potentials having noncentral tensor and spin–orbit components, up to three times the empirical nuclear matter saturation density, ρ0=0.16 fm−3. The calculations are carried out within the frameworks of the Brueckner–Bethe–Goldstone (BBG) and correlated basis functions (CBF) formalisms, in order to ascertain the accuracy of the methods. The two hole-line approximation, with the continuous choice for the single particle auxiliary potential, is adopted for the BBG approach, whereas the variational Fermi hypernetted chain/single operator chain theory, corrected at the second order perturbative expansion level, is used in the CBF one. The energies are then compared with the available quantum and variational Monte Carlo results in neutron matter and with the BBG, up to the three hole-line diagrams. For neutron matter and potentials without spin–orbit components all methods, but perturbative CBF, are in reasonable agreement up to ρ∼3ρ0. After the inclusion of the LS interactions, we still find agreement around ρ0, whereas it is spoiled at larger densities. The spin–orbit potential lowers the energy of neutron matter at ρ0 by ∼3–4 MeV per nucleon. In symmetric nuclear matter, the BBG and the variational results are in agreement up to ∼1.5ρ0. Beyond this density, and in contrast with neutron matter, we find good agreement only for the potential having spin–orbit components.

Three hole-line contribution in nuclear matter revisited

Abstract The three-hole line contribution to the Equation of State of symmetric nuclear matter is calculated by solving the Bethe-Fadeev equations within the standard choice for the single particle auxiliary potential. The results, given up to the Fermi momentum k F = 1.8 fm −1 , show satisfactory agreement with the only previous calculation, performed by Day. The corresponding Brueckner-Hartree-Fock calculation, within the continuous choice for the single particle potential, appears to be very close to the full Equation of State which includes also an estimate of the four-hole line contribution.

Dynamic correlation effects in K-shell hole production by fast protons

There is a marked disagreement between the universal cross sections extracted from experiment by Paul (1989) for K-vacancy production produced by fast protons incident on light atoms, and theoretically calculated cross sections for the same processes. The authors address this discrepancy by examining the corrections to the theory due to the neglect of dynamic correlation. They find that these corrections are important, though they can be significantly reduced by a better choice for the single-particle potential to be used in an independent particle model. The inclusion of dynamic correlation in the theory reduces the Paul discrepancy but some disagreement still remains.

Nuclear matter within the continuous choice.

The saturation curve of symmetric nuclear matter is calculated at the Brueckner-Hartree-Fock level of approximation within the continuous choice for the single-particle potential. The realistic local Argonne ${\mathit{v}}_{14}$ potential is used and the results are compared with similar calculations presented in the literature. The binding energies per nucleon around saturation agree closely with previous results obtained with separable versions of the same potential as well as of the Paris potential.

The Spherical Crystal Potential and Physical Properties of Ions in Crystals. A HF‐Calculation for the 10, 18, and 36 Electron Closed Shell Ions of X‐Ray Scattering Factors, Diamagnetic Susceptibilities, and Dipole Polarizabilities

AbstractThe diamagnetic susceptibilities χd, the dipole polarizabilities αD, and the atomic form factors f are calculated for 10, 18, and 36 electron closed shell ions (Na⊕, Mg2⊕, Al3⊕, N3⊖, O2⊖, F⊖, K⊕, Ca2⊕, P3⊖, S2⊖, Cl⊖, Rb⊕, Sr2⊕, Br⊖). Three effects on the physical properties are studied the quantum mechanical method to calculate the wave functions; the influence of the spherical crystal potential on the wave functions and the inclusion of self consistency in deriving αD from the wave functions. The investigation of the polarizability shows that the best choice for the crystal potential is to adjust the charged compensating sphere to the Madelung potential; thereby agreement between experimental and theoretical data is good. — Deviations of atomic form factors for crystal ions from free ion values are high; for soft ions such as N3⊖, O2⊖, and S2⊖ f is changed up to 18% (N3⊖) near sin ϑ/λ = 0.1 Å−1 compared to the quasi free ion value. From the crystal ion atomic scattering factors ffree ion is deduced by extrapolation for the unstable free ions N3⊖, O2⊖, and S2⊖.

Density functionals in unresticted Hartree–Fock theory

The Hohenberg–Kohn theorem is generalized to unrestricted Hartree–Fock (UHF) wave functions. It is postulated that each N-electron density can be expanded in many sets of orbitals, and these orbital sets are continuously deformable into one another. Subject to these postulates several conclusions follow: The UHF wave function functional ψ[ρ] exists for all such densities. It consists of those orbitals which minimize the sum of kinetic and exchange energies, and it can always be chosen to be a ground state wave function. The exact exchange energy, including self-repulsion, is also a functional of the electron density. It is implicitly defined as the expectation value of exchange energy for the wave function functional ψ[ρ]. This work also addresses some general properties of local exchange potentials. A local exchange potential is a multiplicative potential which replaces the exchange operator in the UHF equations. Every method which employs a local exchange potential is variationally equivalent to minimization of kinetic energy alone, subject to constant density constraint. Many ad hoc local exchange potentials are currently in use, but it is here shown that the functional derivative of exchange energy δK/δρ (r) is the optimal choice for a local exchange potential. This choice is best because the resultant orbitals reproduce the correct UHF ground state energy and electron density.