In this paper a new vector hysteresis model is constructed on the basis of a scalar hysteresis model. The advantages of the scalar model are its easy identification, past memory representation and numerical simplicity. The accommodation property of the model comes from the construction philosophy of the model. The feasibility of the extrapolation is defined by the turning points. The convenience of this model is its efficiency in reduction of the calculation time. The model parameters, the modification vector fields, derived from the permeability vector can be determined from the measured data points. The vector model can approximate the behavior of the vector hysteresis characteristics of ferromagnetic materials. In this paper the main question of the vector model, the definition of the initial values of components in the selected directions is solved.
Authors:S. Hayami, T. Kawahara, G. Juhász, K. Kawamura, K. Uehashi, O. Sato, and Y. Maeda
The magnetic properties of the spin-crossover compound, [Fe(qsal)2]NCSe·2DMSO (N-(8-quinolyl)-salicyladimine) (1), have been measured. We have discovered that the compound 1 exhibits a wide "thermal hysteresis loop" of 115 K (T1/2
= 324 K and T1/2
= 209 K) in the first cycle. Thermogravimetric analysis shows that solvent molecules of the compound 1 are removed at around 324 K. This means that the hysteresis loop observed for the first cycle is only an apparent one. Following the first loop, the compound 1 shows a spin-crossover in warming mode. The spin transition occurs at T1/2
= 285 K and T1/2
= 209 K and the hysteresis width can be estimated to be 76 K, which is one of the largest values reported so far for spin-crossover compounds. It is thought that the cooperativity produced in the compound mainly arises from the intermolecular interactions between the quinoline and the phenyl rings.
The CISORP Water Sorption Analyser has been used to characterise a selection of solid samples at relative humidities from
0 to 100% and at ambient pressure. The analysis reveals many interesting features about the samples and shows the scope of
Hysteresis due to porosity and differences in the physical properties of similar chemical samples show up clearly in isotherm
curves. Kinetic curves reveal features such as the level of stability of dehydrated food products, changes in the hydration
states of salts, and the effect of adding powdered excipient on the water sorption behaviour of a pharmaceutical compound.
Kinetic curves were also used to compare the water sorption behaviour of two types of wood found inside a pine cone, and to
determine equilibrium moisture sorption by calculation.
It was shown that many samples take up moisture irreversibly under the experimental conditions such as amorphous sucrose and
other freeze-dried samples, as well as unstable crystalline forms of compounds. Wet samples such as soaked brick and archaeological
wood from a well dry out irreversibly even at 100% RH.
Recording isotherms at different temperatures allows the calculation of enthalpies of water sorption. If these are compared
with the enthalpy of water condensation the two processes can be compared quantitatively.
Authors:A. Raemy, C. Appolonia Nouzille, P. Frossard, L. Sagalowicz, and M.-E. Leser
Summary Emulsifiers are often used in the food industry to stabilize interfaces in emulsions and foams, for example. When added to an aqueous phase, emulsifiers form spontaneously self-assembly structures. Such structured fluids can be used for active ingredients encapsulation or as micro-reactors for flavour formation. In the present paper we describe the potentialities of DSC, mainly micro-DSC, to study phase transitions of emulsifiers alone and with addition of water. The main role of the calorimetric techniques will probably be to precisely determine melting and crystallization zones, to inform about polymorphism and hysteresis due to undercooling, and especially to follow the effects of guest molecules on the weak liquid crystal transitions. Micro-DSC, when compared to other techniques, generally allows measurements over an extended temperature range.
Temperature-modulated calorimetry (TMC) allows the experimental evaluation of the kinetic parameters of the glass transition
from quasi-isothermal experiments. In this paper, model calculations based on experimental data are presented for the total
and reversing apparent heat capacities on heating and cooling through the glass transition region as a function of heating
rate and modulation frequency for the modulated differential scanning calorimeter (MDSC). Amorphous poly(ethylene terephthalate)
(PET) is used as the example polymer and a simple first-order kinetics is fitted to the data. The total heat flow carries
the hysteresis information (enthalpy relaxation, thermal history) and indications of changes in modulation frequency due to
the glass transition. The reversing heat flow permits the assessment of the first and higher harmonics of the apparent heat
capacities. The computations are carried out by numerical integrations with up to 5000 steps. Comparisons of the calculations
with experiments are possible. As one moves further from equilibrium, i.e. the liquid state, cooperative kinetics must be
used to match model and experiment.