Scientific Bulletin. Physics / Lodz University of Technology
It is shown that the experimental data contradicts the theoretical Turnbull-Fisher equation G(T) if the values of free activation energy αEA and αFG calculated with traditional method are applied. The correctly calculated values of these energies are about doubled, compared to the old values. The new values assure conformity of the G(T) equation with the experiment.
In the present paper, recent results of computer simulations of two-dimensional arrays of vertical-cavity surface-emitting lasers (VCSELs), transverse modes in gain-guided VCSELs as well as double-heterostructure and quantum-well nitride VCSELs are presented. As expected, the simulations enable us to propose essential design modifications of the devices under consideration.
Using the self-consistent phonon theory based on the thermodynamic double-time Green's function method the thermodynamical and dynamical stability conditions of f.c.c. crystal lattice are investigated. The results of calculations of the pressure variations of the limiting temperature of stability and selected thermodynamic properties of solid neon near the limit of stability obtained with the help...
The extinction coefficient of various silicon oils useful in measurements of electrooptic properties of crystals is investigated The temperature dependence of refractive indices of the oils is also determined.
Values of the Kerr constant B and changes in B with temperature in some silicon oils are determined. The measurements show that B is close to 1 · 10-15 m/V² and (l/B)(∂B/∂T) is about 10-3 deg-1. The results obtained indicate that these liquid dielectrics can be useful in measurements of the quadratic electrooptic coefficients in crystals.
In this work the new method of calculation of polarizability tensor components and (α II - α ⊥) is introduced and applied to four liquid crystals: cholesteryl propionate, nonanoate, decanoate and myristate. Polarizability tensor components of α II and α ⊥ seems to be non-linear function of temperature. Result of subtraction of (α II - α ⊥) for all four liquid crystal are nearly constant in all of...
The polarizability tensor components α II, α ⊥, polarizability anisotropy (α II - α ⊥) and (ne+no) / d of five liquid crystals CB 6, CB 7, CB 8, MBBA and EBBA are investigated in order to check how the addition of CH2 group to the molecule influence on the values of its polarizability anisotropy (α II - α ⊥) and (ne+no)/d. Obtained results show that the addition of CH2 group change mentioned above...
A detailed threshold simulation of a room-temperature operation of possible GaN/AlGaN/AlN vertical-cavity surface-emitting lasers (VCSELs) is developed in an analytical form to compare usabilities of their various designs. Multiple-quantum-wen VCSEL configurations are proved to be the best suited for this application. Their optimal number of quantum wells is found to be proportional to all optical...
The elastic properties of f.c.c. 20Ne are computed using the reduced second-order self-consistent phonon approximation. The results of calculations of the temperature and pressure variations of the isothermal bulk modulus, elastic constants and coefficients of anisotropy obtained with the help of the (exp.m) Buckingham, (exp, exp) Morse and (n, m) Lennard-Jones self-consistent potentials are given...
Dielectric investigations of ferroelectric liquid crystals in the frequency range 10-2Hz-5· 10 5 Hz enable to detect four loss processes. One of them (Goldstone mode) results from collective movements of molecules. The other ones may result from ionic conduction, from inhomogenity of sample (Maxwell-Wagner effect) or from the influence of electrodes (conducting ITO layers).It turns out that all the...
Two phenomena influence the temperature dependence of components of polarizability tensor. The first one is the change of distance between electrons and protons with temperature. The second is the conformation change of molecule. From the two reasons mentioned above the electron proton distance change is only the linear Junction of temperature. It gives the possibility of separation of two part of...
The temperature dependence of the polarizability anisotropy (αII-α⊥) and polarizabilily tensor components αII and α⊥ were investigated for homoloque of CH3CH2OC6H4N:N-C6H4OC(:O)(CH2)nCH3 liquid crystals, (series of nematogenic 4-ethoxy-4'-n-alkanoyl-oxyazobenzenes), whose molecules differ by the number of CH2 group in the alkyl chain. It was found that: (1) a change in the number of CH2 group in the...
The traditional crystallization parameters growth rate and nucleation rate can be difficult to measure in direct way. They can be calculate instead using formulae, which combine these parameters with the crystallization time and the granularity. These formulae are presented in the paper. They were also verified experimentally and with computer simulation test.
On the basis of the reduced second order self-consistent phonon approximation the dynamic, thermodynamic and elastic functions of solid helium are computed and compared with available experimental data. The system of self-consistent equations is solved for the (exp,m) Buckingham, (n,m) Lennard-Jones and the (exp,exp) Morse interatomic potentials.
As the result of the changes of temperature on the surface of the sample illuminated with the light beam of modulated intensity the acoustic wave propagates from the boundary between the sample and the surrounding gas. From the examinations of the intensity of this wave for the samples of steel the thermal diffusion length and the coefficient of thermal diffusion were determined.
Dielectric investigations of ferroelectric liquid crystals in the low frequency range enable to detect two kinds of collective molecular motions including Goldstone mode. Recently synthesised ferroelectric liquid crystal MHPFOBC with broad temperature range of SmC* phase was chosen for investigation of Goldstone mode.
The extinction coefficient and the temperature dependence of the refractive index of some mineral oils are determined. Measurements were also made of temperature changes in the Kerr constants of the oils. The results obtained confirm that these liquid dielectrics can be useful in measurements of quadratic electrooptic coefficients in crystals.
Lightning is a discharge connected with a large difference of potentials. Although it is a common phenomenon in nature, it is not quite understood up to now. The article is devoted to the explanation of the cloud electrification based on the novel theory of electrification by friction. The author studying the polarizability tensor of liquid crystal molecules confirmed that the two kinds of atoms could...
The porosity is one of the parameters of the three-dimensional structure of certain materials, also of the biological origin. The work briefly presents different methods of porosity evaluation, especially the so called point method and connected with the application of the Scanning Electron Microscope (SEM). The results obtained for several samples of hydrated calcium sulphate (natural gypsum) agree...
Two phenomenon influence on the temperature dependence of component of polarizability tensor. First one is the change of distance between electrons and protons with temperature. The second is the conformation change of molecule. From the two reasons mentioned above the electron proton distance change is only the linear function of temperature. It gives the possibility of separation of two part of...