When hot water freezes before cold

I suggest that the origin of the Mpemba effect (the freezing of hot water before cold) is freezing-point depression by solutes, either gaseous or solid, whose solubility decreases with increasing temperature so that they are removed when water is heated. They are concentrated ahead of the freezing front by zone refining in water that has not been heated, reduce the temperature of the freezing front, and thereby reduce the temperature gradient and heat flux, slowing the progress of the front. I present a simple calculation of this effect, and suggest experiments to test this hypothesis.Comment: 7 pages, 1 figur

Calculation of Screening Masses in a Chiral Quark Model

We consider a simple model for the coordinate-space vacuum polarization function which is often parametrized in terms of a screening mass. We discuss the circumstances in which the standard result for the screening mass, $m_{sc}=\pi T$, is obtained. In the model considered here, that result is obtained when the momenta in the relevant vacuum polarization integral are small with respect to the first Matsubara frequency.Comment: 6 pages, 2 figure

The heat capacity of nitrogen chains in grooves of single-walled carbon nanotube bundles

The heat capacity of bundles of closed-cap single-walled carbon nanotubes (SWNT) with one-dimensional chains of nitrogen molecules adsorbed in the grooves has been first experimentally studied at temperatures from 2K to 40K using an adiabatic calorimeter. The contribution of nitrogen C(T) to the total heat capacity has been separated. In the region 2-8K the behaviour of the curve C(T) is qualitatively similar to the theoretical prediction of the phonon heat capacity of 1D chains of krypton (Kr) atoms localized in the grooves of SWNT bundles. Below 3K the dependence C(T) is linear. Above 8K the dependence C(T) becomes steeper in comparison with the case of Kr atoms. This behaviour of the heat capacity C(T) is due to the contribution of the rotational degrees of freedom of the nitrogen molecules.Comment: 15 pages, 4 figure

Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures

The linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles in an interval of 2.2 - 120K. The measurement was performed using a dilatometer with a sensitivity of 2*10-9 cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5-30 um.Comment: 4 pages, 1 figur

Anomalous Thermal Stability of Metastable C_20 Fullerene

The results of computer simulation of the dynamics of fullerene C_20 at different temperatures are presented. It is shown that, although it is metastable, this isomer is very stable with respect to the transition to a lower energy configuration and retains its chemical structure under heating to very high temperatures, T ~ 3000 K. Its decay activation energy is found to be E_a ~ 7 eV. Possible decay channels are studied, and the height of the minimum potential barrier to decay is determined to be U = 5.0 eV. The results obtained make it possible to understand the reasons for the anomalous stability of fullerene C_20 under normal conditions.Comment: Slightly corrected version of the paper submitted to Phys. Solid Stat

Decay and fusion as two different mechanisms of stability loss for the (C_20)_2 cluster dimer

The thermal stability of the (C_20)_2 cluster dimer consisting of two C_20 fullerenes is examined using a tight-binding approach. Molecular dynamics simulations of the (C_20)_2 dimer at temperatures T = 2000 - 3500 K show that the finite lifetime \tau of this metastable system is determined by two fundamentally different processes, the decay of one of the C_20 fullerenes and the fusion of two C_20 fullerenes into the C_40 cluster. The activation energies for these processes Ea = 3.4 and 2.7 eV, respectively, as well as their frequency factors, have been determined by analyzing the dependence of \tau on T.Comment: Slightly modified version of the paper to appear in JETP Let

High orders of the perturbation theory for hydrogen atom in magnetic field

The states of hydrogen atom with principal quantum number $n\le3$ and zero magnetic quantum number in constant homogeneous magnetic field ${\cal H}$ are considered. The coefficients of energy eigenvalues expansion up to 75th order in powers of ${\cal H}^2$ are obtained for these states. The series for energy eigenvalues and wave functions are summed up to ${\cal H}$ values of the order of atomic magnetic field. The calculations are based on generalization of the moment method, which may be used in other cases of the hydrogen atom perturbation by a polynomial in coordinates potential.Comment: 16 pages, LaTeX, 6 figures (ps, eps

Meson Correlation Function and Screening Mass in Thermal QCD

Analytical results for the spatial dependence of the correlation functions for all meson excitations in perturbative Quantum Chromodynamics, the lowest order, are calculated. The meson screening mass is obtained as a large distance limit of the correlation function. Our analysis leads to a better understanding of the excitations of Quark Gluon Plasma at sufficiently large temperatures and may be of relevance for future numerical calculations with fully interacting Quantum Chromodynamics.Comment: 11 page

CHIRAL SYMMETRY AND UA(1)U_A(1) ANOMALY IN AN EFFECTIVE THEORY OF QCD

We show on the basis of an effective theory of QCD that a wide variety of observables in the hadron world is governed by the chiral symmetry together with an interplay between the axial anomaly and the explicit symmetry breaking due to the current quark mass. We also discuss the nature of the chiral transition at finite temperature and related dynamical phenomena using the effective Lagrangian. Some phenomenological implications of the small vector coupling (``vector limit'') at high temperatures are suggested.Comment: 8 pages, LATEX(macros are included). Invited talk presented at Int. RCNP Workshop on Color Confinement and Hadrons, March 22 - 24, RCNP, Osaka, Japa

1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-

Using a known result by Falk et al. for the 1/m_b^2 correction to the dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry in this decay. Employing an up-to-date range of values for the non-perturbative parameter \lambda_1, we find that the correction is much smaller than it should have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear in Physical Review D. The complete postscript file is also available from URL ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g