Quantum phase transitions constitute a topical problem in condensed matter physics. Exact results, also for simplified but still nontrivial models, appear particularly relevant especially in view to ...explore, as a next step, complex and random systems. Within this context, we analyze the critical properties for a wide class of quantum models allowing an exact solution in the thermodynamic limit.
The thermodynamic properties of a classical
d-dimensional spin-
S Heisenberg ferromagnet, with long-range interactions decaying as
r
−
p
and in the presence of an external magnetic field, is ...investigated by means of the spectral density method in the framework of classical statistical mechanics. We find that long-range order exists at finite temperature for
d<
p<2
d with
d⩽2 and for
p>
d with
d>2, consistently with known theorems. Besides, the related critical temperature is determined and a study of the critical properties is performed.
The two-time retarded and advanced Green's function technique is formulated in nonextensive classical statistical mechanics within the optimal Lagrange multiplier framework. The main spectral ...properties are presented and a spectral decomposition for the spectral density is obtained. Finally, the nonextensive version of the spectral density method is given and its effectiveness is tested by exploring the equilibrium properties of a classical ferromagnetic spin chain.
The thermodynamic properties of a classical spin-
S Heisenberg ferromagnetic chain with long-range interactions decaying as
r
−
α
and in the presence of an external magnetic field, are investigated ...by means of the spectral density method. In particular, we find that long-range order exists at finite temperature for 1<
α<2, consistently with known theorems. Our results appear in a reasonable agreement with available exact ones and Monte Carlo calculations.
The two-time Green function technique is formulated in nonextensive classical statistical mechanics within the optimal Lagrange multiplier framework. We introduce also the nonextensive classical ...version of the spectral density method, for a direct calculation of the Green functions, and its effectiveness is tested exploring the equilibrium properties of the classical ferromagnetic Heisenberg spin chain.
Extracts from pods and leaves of carob (
Ceratonia siliqua L
.) were tested for their ability to inhibit cell proliferation of mouse hepatocellular carcinoma cell line (T1). The two extracts showed a ...marked alteration of T1 cell proliferation in a dose-related fashion reaching the maximal effect at 1 mg/ml. Moreover, we demonstrated that leaf and pod extracts were able to induce apoptosis in T1 cell lines after 24-h treatment mediating a direct activation of the caspase 3 pathway. HPLC analysis revealed the presence of gallic acid, (−) epigallocatechin-3-gallate and (−) epicatechin-3-gallate in pod and leaf extracts, compounds well known to exert antiproliferative effects. Their concentration reached 6.28 mg/g in carob leaves and 1.36 mg/g in carob pods extract. The discovery that carob pod and leaf extracts contained antiproliferative agents could be of practical importance in the development of functional foods and/or chemopreventive drugs.
A nonperturbative calculation of the vertex corrections for the electron–phonon Fröhlich model beyond the Migdal regime is performed within a modified version of the conventional gauge technique. We ...find that they show tendency to depress the critical temperature and other relevant quantities increasing the Migdal parameter
m. Moreover, a comparison with the results recently obtained for the BCS pairing model using the same method suggests that, varying the coupling constant
λ at fixed
m, the sign of the vertex corrections may depend sensibly on the effective pairing interaction between the charge carriers.
We extend the formalism of the thermodynamic two-time Green's functions to nonextensive quantum statistical mechanics. Working in the optimal Lagrangian multiplier representation, the q -spectral ...properties and the methods for a direct calculation of the two-time q Green's functions and the related q -spectral density ( q measures the nonextensivity degree) for two generic operators are presented in strict analogy with the extensive (q=1) counterpart. Some emphasis is devoted to the nonextensive version of the less known spectral density method whose effectiveness in exploring equilibrium and transport properties of a wide variety of systems has been well established in conventional classical and quantum many-body physics. To check how both the equations of motion and the spectral density methods work to study the q -induced nonextensivity effects in nontrivial many-body problems, we focus on the equilibrium properties of a second-quantized model for a high-density Bose gas with strong attraction between particles for which exact results exist in extensive conditions. Remarkably, the contributions to several thermodynamic quantities of the q -induced nonextensivity close to the extensive regime are explicitly calculated in the low-temperature regime by overcoming the calculation of the q grand-partition function.
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