Pi excitation of the t-J model

In this paper, we present analytical and numerical calculations of the pi resonance in the t-J model. We show in detail how the pi resonance in the particle-particle channel couples to and appears in the dynamical spin correlation function in a superconducting state. The contribution of the pi resonance to the spin excitation spectrum can be estimated from general model-independent sum rules, and it agrees with our detailed calculations. The results are in overall agreement with the exact diagonalization studies of the t-J model. Earlier calculations predicted the correct doping dependence of the neutron resonance peak in the YBCO superconductor, and in this paper detailed energy and momentum dependence of the spin correlation function is presented. The microscopic equations of motion obtained within current formalism agree with that of the SO(5) nonlinear sigma model, where the pi resonance is interpreted as a pseudo Goldstone mode of the spontaneous SO(5) symmetry breaking.Comment: 33 pages, LATEX, 14 eps fig

Non-equilibrium theories of rarefied gases: internal variables and extended thermodynamics

Limits of classical constitutive laws such as Fourier and Navier-Stokes equations are discovered since decades. However, the proper extensions -- generalizations of these are not unique. They differ in the underlying physical principles and in modeling capabilities. In this paper, two different theories are discussed and compared to each other, namely the kinetic theory-based Rational Extended Thermodynamics (RET) and non-equilibrium thermodynamics with internal variables (NET-IV). First, the paper starts with the case of rigid heat conductors summarizing the result achieved so far. Then a typical example of compressible bodies is shown by presenting the first generalization for rarefied gases, called Meixner's theory. It is further extended using generalized entropy current in the framework of NET-IV. It is shown how its structure is related to RET and how the compatibility between them can be acquired

Microalgae-based Food: Consumer Perception and Willingness to Pay in Austria—a Discrete Choice Based Experiment

Algae-based foods have been gaining increasing popularity in recent years and hold tremendous potential, provided that there is greater awareness and knowledge about microalgae-based foods within both the general population and the food industry. These products not only offer health benefits for the human body but are also cost-effective and environmentally sustainable to produce. Using a discrete choice experiment (DCE), we assessed consumer perception and willingness to pay (WTP) of Austrian consumers for innovative food items made from microalgae, using algae crackers as an illustrative example. To approximate the weighting of the product attributes of origin, price, flavor, production method and packaging, we employed Choice Based Conjoint Analysis (CBCA) through an online survey (n = 301 participants). Subsequently, we approximated WTP for each product attribute based on the outcomes of the CBCA. The study reveals that, on the whole, microalgae-based food products are favorably perceived by consumers. The findings generally align with prior research in the literature, albeit with some noteworthy distinctions. For instance, there is a higher WTP for organic microalgae-based food compared to similar studies where regional production was evaluated to be of higher importance. Consequently, innovative microalgae foods seem to have significant potential in consumer food markets. Food producers should consider the expectations and perceptions of consumers in order to be able to successfully introduce novel microalgae food products in this, currently, niche market

The Difficulties in Measuring Individual Utilities of Product Attributes: A Choice Based Experiment

The study combines different theoretical approaches in the field of conjoint analysis to estimate the im-portance of product related attributes. This is of major importance in food marketing, where we still try to find a valid answer, in particular, how to measure the real willingness to pay (WTP) for specific product specifica-tions. Based on a comprehensive literature analysis, a common method was used to approximate the im-portance of several product attributes. As usually suggested in literature, we used discrete choice modeling and developed a choice based experimental design considering selected product attributes. The study object was frozen pizza, a convenience good frequently bought by most households.Up to this point, there is nothing special about the choice based experiment in comparison to direct measure-ment of the importance of product attributes. However, one of the core problems of discrete choice modeling – the approximation of individual utility functions – was then addressed by transforming the choices of con-sumers into scores. With these scores traditional conjoint measurement can be used to approximate individual utilities even in choice based experiments. The individual part-worth utilities will be compared with a usual but very complex approach to approximate individual part-worth utilities, the hierarchical Bayes method. Our ap-proach addresses methodological considerations concerning the restrictions of discrete choice modeling, namely the complexity of approximating individual utilities which is of huge importance in particular for market segmentation

Some thoughts about nonequilibrium temperature

The main objective of this paper is to show that, within the present framework of the kinetic theoretical approach to irreversible thermodynamics, there is no evidence that provides a basis to modify the ordinary Fourier equation relating the heat flux in a non-equilibrium steady state to the gradient of the local equilibrium temperature. This fact is supported, among other arguments, through the kinetic foundations of generalized hydrodynamics. Some attempts have been recently proposed asserting that, in the presence of non-linearities of the state variables, such a temperature should be replaced by the non-equilibrium temperature as defined in Extended Irreversible Thermodynamics. In the approximations used for such a temperature there is so far no evidence that sustains this proposal.Comment: 13 pages, TeX, no figures, to appear in Mol. Phy