Complete analysis of ensemble inequivalence in the Blume-Emery-Griffiths model.

We study inequivalence of canonical and microcanonical ensembles in the mean-field Blume-Emery-Griffiths model. This generalizes previous results obtained for the Blume-Capel model. The phase diagram strongly depends on the value of the biquadratic exchange interaction K, the additional feature present in the Blume-Emery-Griffiths model. At small values of K, as for the Blume-Capel model, lines of first- and second-order phase transitions between a ferromagnetic and a paramagnetic phase are present, separated by a tricritical point whose location is different in the two ensembles. At higher values of K the phase diagram changes substantially, with the appearance of a triple point in the canonical ensemble, which does not find any correspondence in the microcanonical ensemble. Moreover, one of the first-order lines that starts from the triple point ends in a critical point, whose position in the phase diagram is different in the two ensembles. This line separates two paramagnetic phases characterized by a different value of the quadrupole moment. These features were not previously studied for other models and substantially enrich the landscape of ensemble inequivalence, identifying new aspects that had been discussed in a classification of phase transitions based on singularity theory. Finally, we discuss ergodicity breaking, which is highlighted by the presence of gaps in the accessible values of magnetization at low energies: it also displays new interesting patterns that are not present in the Blume-Capel model.

The effects of retail concentration on retail dairy product prices in the United States.

This study provides an empirical investigation of the relationship between grocery retail concentration and retail dairy product prices in the United States. The analysis was performed based on a unique data set on store-level retail prices provided by the Information Resources Inc. Further, alternative measures of retail concentration were considered, which included revenue and store selling space-based Herfindahl-Hirschman Index that were computed based on a Nielsen TDLinx data set on store characteristics. Results from a reduced-form empirical framework estimated via panel data techniques indicated that grocery retail concentration had a positive statistically significant effect on retail dairy product prices in the analyzed locations during the analyzed period of time. Specifically, a 10% increase in concentration was found to lead to a 0.46% rise in retail dairy product prices. This central result was robust to the way in which retail concentration was measured and was consistent with broader empirical evidence in the literature on retail market power.

Exactly solvable spin-1 Ising-Heisenberg diamond chain with the second-neighbor interaction between nodal spins.

The spin-1 Ising-Heisenberg diamond chain with the second-neighbor interaction between nodal spins is rigorously solved using the transfer-matrix method. In particular, exact results for the ground state, magnetization process and specific heat are presented and discussed. It is shown that further-neighbor interaction between nodal spins gives rise to three novel ground states with a translationally broken symmetry, but at the same time, does not increases the total number of intermediate plateaus in a zero-temperature magnetization curve compared with the simplified model without this interaction term. The zero-field specific heat displays interesting thermal dependencies with a single- or double-peak structure.

Photo-induced processes in collagen-hypericin system revealed by fluorescence spectroscopy and multiphoton microscopy.

Collagen is the main structural protein and the key determinant of mechanical and functional properties of tissues and organs. Proper balance between synthesis and degradation of collagen molecules is critical for maintaining normal physiological functions. In addition, collagen influences tumor development and drug delivery, which makes it a potential cancer therapy target. Using second harmonic generation, two-photon excited fluorescence microscopy, and spectrofluorimetry, we show that the natural pigment hypericin induces photosensitized destruction of collagen-based tissues. We demonstrate that hypericin-mediated processes in collagen fibers are irreversible and may be used for the treatment of cancer and collagen-related disorders.

Thermally induced irreversible conformational changes in collagen probed by optical second harmonic generation and laser-induced fluorescence.

Irreversible thermal conformational changes induced to collagen have been studied by optical methods. More specifically, second harmonic generation (SHG) from incident nanosecond Ng:YAG 1064 nm radiation and laser-induced fluorescence by 337 nm, pulsed nanosecond nitrogen laser excitation, at 405, 410 and 415 nm emission wavelengths were registered at eight temperatures (40 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees and 80 degrees C) and normalised with respect to the corresponding values at the ambient temperature of 30 degrees C. The heating protocol used in this work, was selected to monitor only permanent changes reflecting in the optical properties of the samples under investigation. In this context, the SHG, directly related to the collagen fibril population in triple helix conformation, indicated on irreversible phase transition around 64 degrees C. On the other hand fluorescence related to the destruction of cross-linked chromophores in collagen, some of which are related to the triple helix tertiary structure, also indicated a permanent phase transition around 63 degrees C. These results are in agreement with previous results from studies with differential scanning calorimetry. However SHG and fluorescence, being non-invasive optical methods are expected to have a significant impact in the fields of laser ablative surgery and laser tissue welding.

Visual observation of infrared laser speckle patterns at half their fundamental wavelength.

In the course of work aimed to examine second harmonic generation in biological macromolecules, it was discovered that 1064 nm pulsed nanosecond infrared laser radiation, after scattering on the optically rough sample surface, was perceived as double the fundamental frequency green speckle pattern by the unaided eye. The threshold of this arresting phenomenon was found to be around 60 mJ/cm2 on hyaluronic acid potassium salt in dark ambient conditions. This effect is of a second order non-linear nature. After experiments with nearsighted, farsighted and normal vision observers in combination with second harmonic generation experiments on various lamb eye tissues, the effect was mainly attributed to second harmonic generation in the cornea arising from phase interference of the incident infrared radiation. The current work could possibly have implications in the fields of speckle interferometry and biomedicine.

Photochemical effects and hypericin photosensitized processes in collagen.

Emission and excitation spectra of collagen were recorded in the ultraviolet and visible regions. The existence of several types of chromophores absorbing and emitting throughout these spectral regions was observed. It was shown that laser irradiation at 355 and 532 nm caused collagen fluorescence photobleaching by 30%, when the delivered light doses were 9 and 18 J/cm2, respectively. This process of collagen fluorophores photodestruction was found to be a one-photon effect. The effect of hypericin (HYP), a polycyclic quinone, photosensitization on collagen was also studied. Addition of HYP aqueous solution to collagen produced quenching, redshift of the maximum, and broadening of the spectral form of its fluorescence. These effects became more prominent with increasing HYP concentration. The fluorescence of HYP sensitized collagen decreased in a spectrally nonproportional manner during laser irradiation at both 355 and 532 nm.