Shift Of Critical Temperature Research Articles

Seasonal changes in heat balance of dogs acclimatized to outdoor climate.

Heat production (M), dry heat loss (R+C), evaporative heat loss (E) and rectal temperature (Tre) were measured in a direct calorimeter in female mongrel dogs acclimatized to outdoor climate at Kanazawa (latitude; 36 degrees 35" N), Japan. M and total dry and evaporative heat losses (HL) were minimum at calorimeter wall temperatures (TW) of 26-29 degrees C in summer and 22-26 degrees C in winter (thermoneutral temperature; TNT). The seasonal shift of the lower critical temperature was confirmed. At TW below TNT, the values of M and HL were significantly higher in summer. At TW above TNT, these values increased. A TNT and above, M and HL were significantly higher in winter. (R+C) decreased linearly with increasing TW in both seasons. AT TW below 26 degrees C, (R+C) were significantly higher in summer. At TW above 26 degrees C, E increased greatly. The values of E were significantly higher in winter at TW 29-32 degrees C. Tre remained nearly constant at TNT and below, and increased at TW above TNT in both seasons. Mean body surface temperature (Tsf) decreased with decreasing TW. Body thermal conductance (K) was minimum at TW below 26 degrees C in summer and at TW below 22 degrees C in winter. At TW above these temperatures, K increased significantly. Whole body insulation (I) was significantly higher in winter, particularly at TW 18 degrees C. These results suggest that the dogs reared outdoors in winter acclimatized to cold in two ways; by increasing the insulating effect of the fur coat and by elevating resting heat production.

Effect of three-body interactions on the ordering of bcc binary alloys

The composition dependence of the order---disorder critical temperature is investigated for a model binary alloy equivalent to an Ising system with both the nearest-neighbor interactions ($J$) and the three-particle interactions ($P$) present. Using a real-space renormalization-group method for calculating the phase diagram, we find that for small three-body forces, the maximum critical temperature shifts from the 50-50 atomic percent composition proportionally to $\frac{P}{J}$. The proportionality constant is determined both from the renormalization-group method and from Griffith's smoothness postulate. The results of the two calculations agree with each other, and they are used to estimate the relative strength of the three-body potentials in iron cobalt. The estimate $\frac{P}{J}=0.11\ifmmode\pm\else\textpm\fi{}0.06$ indicates that three-body forces are small, so that the nearest-neighbor Ising model is a good first approximation for the description of ordering in FeCo.

Critical temperature of a compressible ising magnet

AbstractThe shift in critical temperature due to spin‐phonon interaction in a two‐dimensional compressible Ising magnet under zero pressure is obtained using a self‐consistent field approach. Fluctuations near the shifted critical temperature are also discussed. The observed shift in critical temperature is compared with that of Matsudaira.

Series-expansion analysis of critical-temperature shifts of finite Ising lattices with "self-consistent" boundary conditions

Finite Ising $N\ifmmode\times\else\texttimes\fi{}N$ ($N=1\ensuremath{-}5$) and $N\ifmmode\times\else\texttimes\fi{}\ensuremath{\infty}$ ($N=1\ensuremath{-}8$) systems with one of the three self-consistent extended mean-field boundary conditions all around and on both sides, respectively, are studied. The boundary conditions used are: ($a$) extended mean-field boundary condition using average, abbreviated EA (in which each boundary spin takes some average value); ($b$) extended mean-field boundary condition using probability, abbreviated EP (in which each boundary spin takes the values \ifmmode\pm\else\textpm\fi{}1 with certain probabilities) and ($c$) extended Bethe-Peierls, EBP (in which each boundary spin is assumed to be acted on by some effective field). The self-consistent equations are then derived by letting the average magnetization of the internal spins of the system be equal to that of the boundary spins. The finite systems considered therefore represent some high-order systematic generalization of the familiar molecular-field and Bethe-Peierls approximations. The equations for the critical temperature are formulated graphically in terms of some high-temperature expansion series which are calculated to the ninth and tenth orders. Two of the series in the equations of $N\ifmmode\times\else\texttimes\fi{}\ensuremath{\infty}$ for $N\ensuremath{\rightarrow}\ensuremath{\infty}$ are directly related to the layer and local susceptibilities considered by Binder and Hohenberg for the Ising infinite half plane. Critical temperatures obtained numerically with the use of truncation and extrapolation techniques. Results on the systems with EA and EP indicate that the shifts of their critical temperatures can be described by a power law ${N}^{\ensuremath{-}\ensuremath{\lambda}}$ where $\ensuremath{\lambda}=\frac{1}{{\ensuremath{\gamma}}_{1}}$ and ${\ensuremath{\gamma}}_{1}(\ensuremath{\approx}\frac{11}{8})$ is the critical exponent of the layer susceptibility. This is different from the value $\ensuremath{\lambda}=1$ which is believed true for two-dimensional finite systems with periodic or free boundary conditions. No conclusive remark can be made to systems with EBP through they suggest some even higher value (\ensuremath{\ge} 2).

Critical temperature shifts for finite slabs in the ε-expansion

The critical temperature Tc(b) of a d-dimensional system with finite thickness b in one of its dimensions approaches its bulk limit as b to infinity according to Tc( infinity )-Tc(b) varies as b- lambda . To first order in epsilon =4-d the shift exponent lambda is found to be given by lambda =2-((n+2)/(n+8)) epsilon +O( epsilon 2), and thus satisfies the scaling relation lambda = nu d-1, where nu d is the correlation length exponent of the bulk system and n is the order parameter dimensionality.

Critical temperature shifts for layered periodic systems in 1/n expansion

A classical n-vector model is considered which is infinitely extended in d-1 dimensions and periodic of period b in the dth dimension. Asymptotically for large values of b the critical temperature is expected to obey a scaling law Tc(b)-Tc( infinity ) approximately Ab- lambda . The authors have calculated the shift exponent lambda to first order in a 1/n expansion for dimensions between three and four. To this order the result is consistent with the assertion lambda = nu d-1 where nu d is the correlation length exponent of the infinitely extended d-dimensional system. From the equivalence between this model and (d-1)-dimensional quantum mechanical systems the behaviour of critical lines near the displacive limit (Tc=0) can be derived.

Spherical model of ferromagnetic films

The n to infinity limit of the n-vectorial model of a film is studied. It is found that the phase transition keeps the essential features of the Berlin-Kac mechanism for bulk systems. However, in the ferromagnetic phase, the specific heat is not constant; this is related to the appearance of a generalized sticking phenomenon. The index lambda of the relative shift of the critical temperature satisfies the relation lambda =1/ nu , nu being the index of the bulk correlation length.

Superconducting phase transitions in granular systems

We consider a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers. We obtain systematically the various critical regions, critical temperature shifts, and crossover regions between zero- and three-dimensional behavior as functions of measurable sample parameters. The qualitative behavior of the system in the various regimes is analyzed and results for the specific heat and fluctuation conductivity in the Gaussian region above ${T}_{c}$ are obtained. The possibility of obtaining large critical regions is emphasized. The conditions for observing the phase-locking transition distinct from quasiordering within the grains are found. Theoretical predictions are compared with existing experimental results.