Temperature Behavior Of Specific Heat Research Articles

On the Possible Nature of Armchair-Zigzag Structure Formation and Heat Capacity Decrease in MWCNTs.

Structural disorder and temperature behavior of specific heat in multi walled carbon nanotubes (MWCNTs) have been investigated. The results of X-ray diffractometry, Raman spectroscopy, and transmission electron microscopy (TEM) images are analyzed. The thermodynamic theory of the zigzag-armchair domain structure formation during nanotube synthesis is developed. The influence of structural disorder on the temperature behavior of specific heat is investigated. The size of domains was estimated at ~40 nm. A decrease in heat capacity is due to this size effect. The revealed dependence of the heat capacity of MWCNTs on the structural disorder allows control over thermal properties of nanotubes and can be useful for the development of thermoelectric, thermal interface materials and nanofluids based on them.

The quasi-low temperature behaviour of specific heat.

A new mathematical approach to condensed matter physics, based on the finite temperature field theory, was recently proposed. The field theory is a scale-free formalism; thus, it denies absolute values of thermodynamic temperature and uses dimensionless thermal variables, which are obtained with the group velocities of sound and the interatomic distance. This formalism was previously applied to the specific heat of condensed matter and predicted its fourth power of temperature behaviour at sufficiently low temperatures, which was tested by experimental data for diamond lattice materials. The range of temperatures with the quartic law varies for different materials; therefore, it is called the quasi-low temperature regime. The quasi-low temperature behaviour of specific heat is verified here with experimental data for the fcc lattice materials, silver chloride and lithium iodide. The conjecture that the fourth order behaviour is universal for all condensed matter systems has also supported the data for glassy matter: vitreous silica. This law is long known to hold for the bcc solid helium-4. The characteristic temperatures of the threshold of the quasi-low temperature regime are found for the studied materials. The scaling in the specific heat of condensed matter is expressed by the dimensionless parameter, which is explored with the data for several glasses. The explanation of the correlation of the ‘boson peak’ temperature with the shear velocity is proposed. The critique of the Debye theory of specific heat and the Born–von Karman model of the lattice dynamics is given.

Multicanonical sampling of the space of states of ℋ(2, n)-vector models

Problems of temperature behavior of specific heat are solved by the entropy simulation method for Ising models on a simple square lattice and a square spin ice (SSI) lattice with nearest neighbor interaction, models of hexagonal lattices with short-range (SR) dipole interaction, as well as with long-range (LR) dipole interaction and free boundary conditions, and models of spin quasilattices with finite interaction radius. It is established that systems of a finite number of Ising spins with LR dipole interaction can have unusual thermodynamic properties characterized by several specific-heat peaks in the absence of an external magnetic field. For a parallel multicanonical sampling method, optimal schemes are found empirically for partitioning the space of states into energy bands for Ising and SSI models, methods of concatenation and renormalization of histograms are discussed, and a flatness criterion of histograms is proposed. It is established that there is no phase transition in a model with nearest neighbor interaction on a hexagonal lattice, while the temperature behavior of specific heat exhibits singularity in the same model, in case of LR interaction. A spin quasilattice is found that exhibits a nonzero value of residual entropy.

Thermodynamics of single-stranded RNA with random sequence: Constrained annealing approach

The effect of sequence disorder on thermodynamics of ssRNA is studied on the basis of constrained annealing approach. A random sequence with bimodal disorder is considered. The temperature behavior of specific heat and helicity degree is examined. A reasonable agreement with numerical results is obtained. In the presence of competing interactions the model exhibits not only partial high-temperature melting, but also partial cold denaturation.

Lattice dynamics study and specific heat ofCsH2PO4andCsD2PO4

This paper reports the results of lattice dynamics simulation of ${\mathrm{CsH}}_{2}{\mathrm{PO}}_{4}$ and ${\mathrm{CsD}}_{2}{\mathrm{PO}}_{4}$ crystals in paraelectric and ferroelectric phase using a semiempirical atomistic model based on the Coulomb, short range, covalent, and van der Waals interactions. The peculiarity of the two types of hydrogen bonds is taken into consideration too. The tunneling of protons (deuterons) on the one type of hydrogen bonds above the phase transition point was simplified through keeping the $H(D)$ atom position at the middle in hydrogen bonds. Phonon density of states, partial density of states, isotropic temperature factors, and specific heat were calculated. The computed phonon frequencies are particularly useful in interpreting the complicated Raman and IR spectra of these hydrogen-bonded crystals. The specific heat experimental data, reported by two groups of authors, contradict each other. The results of the given simulation may be helpful in establishing the real temperature behavior of specific heat.

Dynamics of Random One-Dimensional ±J Systems

Finite chains of a two-state random Potts spin model with periodic boundary conditions are studied within Glauber dynamics. The spin exchange is assumed random with frustration between ferro and antiferromagnetic values (±J). Time-dependent fluctuations are induced by periodic temperature oscillations. Master type differential equations for spin correlation functions are solved within linear response theory. The spectrum of relaxation times are calculated at different temperatures. The ±J Potts glass chains undergo a zero temperature phase transition. The barriers against inversion of the spin chain take only two values; 0 and 2|J|. The temperature behaviour of specific heat is characterized by rounded peaks. The frequency dependence displays two plateaus for the real part of specific heat and two corresponding peaks for the imaginary part. The dynamic specific heat is not affected by the longest relaxing mode like susceptibility. The time separation of the modes is demonstrated by the Cole-Cole plots.