Pressure inactivation of fungal spores in aqueous model solutions and in real food systems

Abstract

Conidiospores from Penicillium expansum and ascospores from Eurotium repens were exposed to high hydrostatic pressure in isotonic salt solution, apple and broccoli juice. Kinetic measurements were done at 4,25 and 40 or 45°C. The shape of the inactivation curves was strongly dependent on the temperature. Asco- and conidiospores were found to behave in a contrary way. The fastest reduction for conidiospores was found at 4°C, for ascospores best inactivation was achieved at 45°C. High pressure inactivation of spores in apple or broccoli juice was nearly the same as in isotonic salt solution.     

First-order optical systems with real eigenvalues

It is shown that a lossless first-order optical system whose real symplectic ray transformation matrix can be diagonalized and has only real eigenvalues, is similar to a separable hyperbolic expander in the sense that the respective ray transformation matrices are related by means of a similarity transformation. Moreover, it is shown how eigenfunctions of such a system can be determined, based on the fact that simple powers are eigenfunctions of a separable magnifier. As an example, a set of eigenfunctions of a hyperbolic expander is determined and the resemblance between these functions and the well-known Hermite-Gauss modes is exploited.     

Variational real space renormalization group and its application to frustrated systems

We propose an improved variational version of the Migdal-Kadonoff approximation. We test this method on the two-dimensional triangular lattice Ising model in the ferromagnetic, antiferromagnetic (fully frustrated) and spin glass (randomly frustrated) cases.     

Irreducible second order SUSY transformations between real and complex potentials

Second order SUSY transformations between real and complex potentials for three important from physical point of view Sturm–Liouville problems, namely, problems with the Dirichlet boundary conditions for a finite interval, for a half axis and for the whole real line are analyzed. For every problem conditions on transformation functions are formulated when transformations are irreducible.     

A multi-orbital iterated perturbation theory for model Hamiltonians and real material-specific calculations of correlated systems

The dynamical mean field theory (DMFT) has emerged as one of the most importantframeworks for theoretical investigations of strongly correlated lattice models and realmaterial systems. Within DMFT, a lattice model can be mapped onto the problem of amagnetic impurity embedded in a self-consistently determined bath. The solution of thisimpurity problem is the most challenging step in this framework. The available numericallyexact methods such as quantum Monte Carlo, numerical renormalization group or exactdiagonalization are naturally unbiased and accurate, but are computationally expensive.Thus, approximate methods, based e.g. on diagrammatic perturbation theory have gainedsubstantial importance. Although such methods are not always reliable in various parameterregimes such as in the proximity of phase transitions or for strong coupling, theadvantages they offer, in terms of being computationally inexpensive, with real frequencyoutput at zero and finite temperatures, compensate for their deficiencies and offer aquick, qualitative analysis of the system behavior. In this work, we have developed such amethod, that can be classified as a multi-orbital iterated perturbation theory (MO-IPT) tostudy N-folddegenerate and non degenerate Anderson impurity models. As applications of the solver, wehave embedded the MO-IPT within DMFT and explored lattice models like the single orbitalHubbard model, covalent band insulator and the multi-orbital Hubbard model fordensity-density type interactions in different parameter regimes. The Hund’s couplingeffects in case of multiple orbitals is also studied. The limitations and quality ofresults are gauged through extensive comparison with data from the numerically exactcontinuous time quantum Monte Carlo method (CTQMC). In the case of the single orbitalHubbard model, covalent band insulators and non degenerate multi-orbital Hubbard models,we obtained an excellent agreement between the Matsubara self-energies of MO-IPT andCTQMC. But for the degenerate multi-orbital Hubbard model, we observe that the agreementwith CTQMC results gets better as we move away from particle-hole symmetry. We have alsointegrated MO-IPT+DMFT with density functional theory based electronic structure methodsto study real material systems. As a test case, we have studied the classic, stronglycorrelated electronic material, SrVO₃. A comparison of density of states and photo emissionspectrum (PES) with results obtained from different impurity solvers and experimentsyields good agreement.     

An effective action approach to spin potentials for heavy quark systems

The spin-dependent terms of an approximate, Breit-Fermi-type Hamiltonian for heavy quark-antiquark pairs are obtained by the use of an effective-action approach to QCD statics. As an introduction, a review of the effective action method and the related confinement mechanism is given. The method is extended to include spin-spin effects and the spin-orbit terms are derived from the spin-spin potential in a natural way. The quantitative functional form of the spin potential is given in terms of the solutions to numerical problems that are formulated but not solved. The solution of these problems will be reported in a subsequent paper.     

Self-consistent calculation of real space renormalization group flows and effective potentials

We show how to compute real space renormalization group flows in lattice field theory by a self-consistent method which is designed to preserve the basic stability properties of a Boltzmann factor. Particular attention is paid to controlling the errors which come from truncating the action to a manageable form. In each step, the integration over the fluctuation field (high frequency components of the field) is performed by a saddle point method. The saddle point depends on the block spin. Higher powers of derivatives of the field are neglected in the actions, but no polynomial approximation in the field is made. The flow preserves a simple parameterization of the action. In the first part the method is described and numerical results are presented. In the second part we discuss an improvement of the method where the saddle point approximation is preceded by self-consistent normal ordering, i.e. solution of a gap equation. In the third part we describe a general procedure to obtain higher order corrections with the help of Schwinger-Dyson equations.In this paper we treat scalar field theories as an example. The basic limitations of the method are also discussed. They come from a possible breakdown of stability which may occur when a composite block spin or block variables for domain walls would be needed.     

Volume integrals of real part of optical potentials for light projectiles

A semi-empirical formula for the real volume integrals of the optical potentials for composite projectiles is proposed based on real volume integrals for the nucleonnucleus optical potential derived from the microscopic calculation of Jeukenne et al. which has been cast into a 5 parameter formula for energies upto 50 MeV by adding one additional term for the compositeness of the projectiles. The three parameters of this term have been obtained using the phenomenological analyses for light composite projectiles such as deuteron, triton, helium-3, alpha and lithium-6. The resultant formula describes successfully the physically meaningful volume integral per interacting nucleon-pair to an accuracy of 7% upto the projectile energies around 50 MeV per nucleon for targets over the whole periodic table.     

Moduli space of model real submanifolds

In [6], to a completely nondegenerate germ of a real submanifold of a chosen C R-type (n, K) in a complex space, we assigned a tangent polynomial model of the submanifold. In the present paper, we construct the moduli space M(n, K) of the family of polynomial models, i.e., the space parametrizing the holomorphically nonequivalent polynomial models. The space thus obtained is used to construct C R-characteristic classes. Financially supported by the RFBR grant no. 05-01-0981 and by the grant NSh-2040.2003.1.     

Next generation interatomic potentials for condensed systems

The computer simulation of condensed systems is a challenging task. While electronic structure methods like density-functional theory (DFT) usually provide a good compromise between accuracy and efficiency, they are computationally very demanding and thus applicable only to systems containing up to a few hundred atoms. Unfortunately, many interesting problems require simulations to be performed on much larger systems involving thousands of atoms or more. Consequently, more efficient methods are urgently needed, and a lot of effort has been spent on the development of a large variety of potentials enabling simulations with significantly extended time and length scales. Most commonly, these potentials are based on physically motivated functional forms and thus perform very well for the applications they have been designed for. On the other hand, they are often highly system-specific and thus cannot easily be transferred from one system to another. Moreover, their numerical accuracy is restricted by the intrinsic limitations of the imposed functional forms. In recent years, several novel types of potentials have emerged, which are not based on physical considerations. Instead, they aim to reproduce a set of reference electronic structure data as accurately as possible by using very general and flexible functional forms. In this review we will survey a number of these methods. While they differ in the choice of the employed mathematical functions, they all have in common that they provide high-quality potential-energy surfaces, while the efficiency is comparable to conventional empirical potentials. It has been demonstrated that in many cases these potentials now offer a very interesting new approach to study complex systems with hitherto unreached accuracy.     

The folding deuteron optical model potentials

In this paper we construct a kind of deuteron optical potential with the folding model. For the nucleon optical potential, we choose two kinds of forms: the phenomenological global nucleon optical potential and the microscopic nucleon optical potential based on the nuclear-matter approach. We use our folding and global deuteron optical potential to calculate the reaction cross-sections, elastic scattering angular distributions, and the values for 64 target nuclei.     

Optical potentials in relativistic meson-nucleon model

The relativistic microscopic optical potentials (RMOP) at E < 300 MeV have been derived and investigated based on Walecka's meson-nucleon model. An effective lagrangian including nucleon, σ- and ω-mesons, which is required to reproduce the nuclear matter saturation properties, has been introduced and used to calculate the self-energy of a nucleon in the nuclear medium. Systematical analyses of the scattering data are performed with the RMOP. Finally, several effects, such as the meson-nucleon vertex form factor, isovector meson exchanges, non-linear σ-model are studied.     

One-dimensional diffusion in soluble model potentials

The one-dimensional diffusion in potentials which have a finite number of jumps in their value and in their derivative is investigated. The jump conditions of the eigenfunctions of the corresponding Fokker-Planck-operator are derived. These conditions are then applied to bistable models, to a metastable model and to a periodic potential model. At least for one model in all these three cases all eigenvalues and eigenfunctions are given analytically.     

现代数字物理教学连载⑥——关于势模型问题的教学

在大学物理教学内容中,势模型的教学是特别重要的.传统教材受到数学技术上的限制,使学生实际接触到的势模型寥寥无几,而数字化教学大大丰富了势模型问题的教学,在提高教学效益与质量上发挥了巨大的作用.