A bilayer spin-1/2 Ising model consisting of two superposed Bethe lattices with antiferromagnetic/ferromagnetic interactions is studied by the use of exact recursion relations in a pairwise approach in the presence of an external staggered magnetic field. Besides the ground state phase diagrams calculated in different possible planes of the model parameters space, the thermal variations of the order-parameters and the free energy are investigated to obtain the temperature-dependent phase diagrams of the model for different values of the coordination numbers q. Our calculations reveal that depending on the strength of the model parameters, the model exhibits a variety of interesting phase transitions and therefore phase diagrams. 相似文献
A new path to zeolites: Nanofusion is a template-free, one-step process that gives mesoporous zeolite beta with tunable mesopore diameters in very short reaction times. The hierarchical materials are built from zeolite beta nanocrystals in concentrated gels. The nanocrystals can either be retrieved as individual particles in a colloidal suspension or are directly fused into mesoporous zeolitic materials (see scheme). 相似文献
The sound attenuation phenomena is investigated for a spin- 3/2 Ising model on the Bethe lattice in terms of the recursion relations by using the Onsager theory of irreversible thermodynamics. The dependencies of sound attenuation on the temperature (T), frequency (w), Onsager coefficient (γ) and external magnetic field (H) near the second-order (Tc) and first-order (Tt) phase transition temperatures are examined for given coordination numbers q on the Bethe lattice. It is assumed that the sound wave couples to the order-parameter fluctuations which decay mainly via the order-parameter relaxation process, thus two relaxation times are obtained and which are used to obtain an expression for the sound attenuation coefficient (α). Our investigations revealed that only one peak is obtained near Tt and three peaks are found near Tc when the Onsager coefficient is varied at a given constant frequency for q=3. Fixing the Onsager coefficient and varying the frequency always leads to two peaks for q=3,4 and 6 near Tc. The sound attenuation peaks are observed near Tt at lower values of external magnetic field, but as it increases the sound attenuation peaks decrease and eventually disappear. 相似文献
The effects of assuming equal or unequal crystal fields (CF) on the phase diagrams of a mixed spin-1 and spin-5/2 system are investigated in terms of the recursion relations on the Bethe lattice (BL). The equal CF case was considered for the coordination numbers q=3, 4, and 6, while for q=3 the unequal CF case was also studied. It was found that for the equal CF case, the model exhibits second-order phase transitions and two compensation temperatures for all q, the reentrant behavior for q=4 and first-order phase transitions and tricritical point (TCP) for q=6. In the unequal CF case for q=3, the system yields first- and second-order phase transitions, TCP's, and three compensation temperatures. In addition, the TCP's in a very short range are classified as the stable and unstable ones depending on their free energies. 相似文献
The thermal entanglement of a two-qutrit spin-1 anisotropic Heisenberg XXZ chain in an inhomogeneous magnetic field is studied in detail. The effects of the external magnetic field (B), a parameter b which controls the inhomogeneity of B, and the bilinear interaction parameters Jx=Jy≠Jz on the thermal variation of the negativity are studied in detail. It is found that negativity N decreases when the values of magnetic field, inhomogeneity b and temperature are increasing. In addition, N remains at higher temperatures for higher values of Jz and lower values of B and b.相似文献
A two-fold Cayley tree graph with fully q-coordinated sites is constructed and the spin-1 Ising Blume-Emery-Griffiths model on the constructed graph is solved exactly
using the exact recursion equations for the coordination number q = 3. The exact phase diagrams in (kT/J, K/J ) and (kT/J, D/J) planes are obtained for various values of constants D/J and K/J, respectively, and the tricritical behavior is found. It is observed that when the negative biquadratic exchange (K) and the positive crystal-field (D) interactions are large enough, the tricritical point disappears in the (kT/J, K/J) plane. On the other hand, the system always exhibits a tricritical behavior in the phase diagram of (kT/J, D/J) plane.
Received 8 June 2001 and Received in final form 28 September 2001 相似文献
We have introduced the concept of the so-called swivel type cruciforms as a highly flexible tool to tune the molecular properties from amorphous to highly crystalline features. Simple alkoxy substituted binaphthyl building blocks have been introduced randomly into poly(9,9-dioctylfluorene) (PFO) thereby suppressing the formation of side-chain crystallization. On the other hand the all aryl penta-thiophene based cruciform exhibited strong π–π interaction between the arms and gave one of the highest values reported to date for wet processed organic field effect transistors (OFETs) utilising oligothiophenes. 相似文献
Dodecyltrimethylammonium bromide-modified bentonite (DTMA-bentonite) was prepared and tested as an adsorbent for an acid dye (Acid Blue 193, AB193) removal from aqueous solution in comparison with Na-bentonite. The effect of various experimental parameters was investigated using a batch adsorption technique. In this manner, the adsorption isotherms, adsorption kinetics, and temperature and pH effects upon Acid Blue 193 adsorption on Na-bentonite and DTMA-bentonite were thoroughly examined. Results show that a pH value of 1.5 is favorable for the adsorption of Acid Blue 193. The isothermal data could be well described by the Freundlich equation. The dynamical data fit well with the pseudo-second-order kinetic model. The adsorption capacity of DTMA-bentonite (740.5 mg g(-1)) was found to be around 11 times higher than that of Na-bentonite (67.1 mg g(-1)) at 20 degrees C. Thermodynamic parameters such as activation energy (E(a)) and change in the free energy (DeltaG(0)), the enthalpy (DeltaH(0)), and the entropy (DeltaS(0)) were also evaluated. The overall adsorption process was exothermic but it is only spontaneous at 20 degrees C. The results indicate that Na-bentonite and DTMA-bentonite could be employed as low-cost alternatives to activated carbon in wastewater treatment for the removal of color which comes from textile dyes. 相似文献
The isothermal entropy change of spin-1 Blume-Capel (BC) is investigated on the Bethe lattice (BL) with the variations of coordination numbers (q), crystal field (D) and external magnetic field (H) in the vicinity of critical temperatures, i.e. about the second- and first-order phase transition temperatures. The calculation is carried on the BL in terms of exact recursion relations. It is found that the peaks of the isothermal entropy variation obtained for both magnetization and quadrupole moments are observed to be increasing with increasing values of H for given D and q, decreasing with the increasing q for fixed D and H and also decreasing with the increasing values of D for constant q and H. The peaks of the curves for the quadrupole moment is less sharper then the ones obtained for the magnetization.