Temperature Dependence Of Position Research Articles

Building a Hofmeister-like series for the maximum in density temperature of aqueous electrolyte solutions

The temperature of the maximum in density (TMD) at room pressure is experimentally evaluated for aqueous solutions of a set of halides containing F−, Cl−, Br−, I−, Li+, Na+, K+, Rb+, Cs+ and Mg2+ at a 1 m concentration. The measurements were performed by monitoring the density-temperature profiles and tracking the temperature-dependent position of the meniscus, in a capillary glass tube. Adding salts diminishes the TMD of the solutions with respect to pure water, being the magnitude of the change dependent on the nature of the electrolyte. The experimental values of the shift in the TMD can be split into individual ion contributions. From this information we were able to establish a rank of ions (i.e., a Hofmeister-like series) according to their efficiency in shifting down the TMD. The experimental results are also compared to simulation values obtained via Molecular Dynamics using the Madrid-2019 force field that assigns non-integer charges for the ions and is parametrized for the TIP4P/2005 water model. Finally, since the TMD is a fingerprint property of water, we will discuss the impact of ions on this maximum in relation with the way different ions modify the structure of water.

Inhomogeneous broadening of optical transitions of 87Rb atoms in an optical nanofiber trap

We experimentally demonstrate optical trapping of atoms using a two-color evanescent field around an optical nanofiber. In our trapping geometry, a blue-detuned traveling wave whose polarization is nearly parallel to the polarization of a red-detuned standing wave produces significant vector light shifts that lead to broadening of the absorption profile of a near-resonant beam at the trapping site. A model that includes scalar, vector, and tensor light shifts of the probe transition - from the trapping beams, weighted by the temperature-dependent position of the atoms in the trap, qualitatively describes the observed asymmetric profile and explains differences with previous experiments that used Cs atoms. The model provides a consistent way to extract the number of atoms in the trap.

Thermal transformations in ultrafine plasmochemical zirconium dioxide powders

The methods of thermal analysis and X-ray diffraction are used to investigate polymorphic transformations taking place under heating and cooling in nonstabilized ultrafine ZrO2 powders (ZrO2 UFP) synthesized in a plasmochemical process. It is found out that ZrO2 UFP is characterized by an increased content (up to 55 mass%) of tetragonal-phase particles, which is associated with the size effect of its stabilization. Heating of UFP within T = (25–700) °C, which is followed by the release of H2O, CH2O, and CO2, does not result in a change in its structural-phase state, while annealing within the temperature interval T = (700–1,000) °C gives rise to an increased growth of the size of t-ZrO2 crystallites and results in an elevated tetragonality of the crystal lattice (c/a). A complete t-ZrO2 → m-ZrO2 transition occurs as a result of heating the powder up to T = 1,300 °C. The effect of the dimensional factor on temperature characteristics of polymorphic m ↔ t transitions and the value of their temperature hysteresis is established. It is shown that the powder particle size exerts the most pronounced influence on the temperature-dependent position of the point of martensitic transformation Ms. As this influence is increased, Ms is shifted toward the region of higher temperatures. This is followed by a decreased temperature hysteresis of the m ↔ t martensitic transformations.

All-space existence and dispersion of athermal directions in monoclinic KY(WO4)2

The analytical expressions for thermo-optic coefficients, dn/dT, for “fast” and “slow” light waves propagating along the arbitrary direction in a biaxial crystal are derived. On the basis of these expressions, the all-space analysis of existence of athermal directions is performed for monoclinic and biaxial KY(WO4)2 at 1.03μm. The calculations are performed for an arbitrary light propagation direction and polarization (not restricted to the principal planes). The appearance of directions that can be athermal for both “fast” and “slow” waves is predicted. The dispersion of athermal directions is analyzed for visible and near-IR. The existence of upper and lower dispersion limits for athermal behavior of KY(WO4)2 is shown. It is shown that the optical indicatrix axes can be athermal itself at some light wavelengths. Wavelength- and temperature-dependent position of the optical axes of KY(WO4)2 is also determined.

Zero-phonon lines of systems with different dimensions and unconventional vibronic interactions

The standard theory of the optical spectra of impurity centres in solids predicts the Lorentzian shape of the zero-phonon lines to have temperature-dependent position and width. However, in recent years different systems, including ones of reduced dimension, have been found, in which remarkable deviations from the standard laws have been observed. Generalizations of the theory to these systems are presented. Among other things, the quantum liquid 3He doped by optical centres is considered.

Electron paramagnetic resonance of Cr3+ ions in ferroelastic CsLiSO4

The X-band EPR studies of Cr3+-doped LCS have been performed. The values of the spin-Hamiltonian parameters for Cr3+ ions have been estimated at room temperature. The effect of crystal twinning on the EPR spectra has also been described. The temperature behaviour of EPR lines originated from two structurally different chromium complexes has been studied close to the ferroelastic phase transition. From the temperature dependence of positions of the split resonance lines a value of the critical exponent β of the order parameter was found to be β = 0.25.

Photonic Liquid Crystal Fibers for Sensing Applications

The paper presents our latest experimental results on the influence of temperature, an external electric field, and hydrostatic pressure on propagation properties of the photonic crystal fibers infiltrated with liquid crystals of low and medium material anisotropies. Measurand-induced shifts of the photonic bandgap wavelengths give information about the value of temperature, voltage, and pressure. Moreover, temperature-dependent positions of the photonic bandgap wavelengths in the transmission spectrum can serve to determine the thermal characteristics of the liquid crystal ordinary refractive index.

Spin Quantum Tunneling in Single Molecular Magnets: Fingerprints in Transport Spectroscopy of Current and Noise

We demonstrate that transport spectroscopy of single molecular magnets shows signatures of quantum tunneling at low temperatures. We find current and noise oscillations as a function of bias voltage due to a weak violation of spin-selection rules by quantum tunneling processes. The interplay with Boltzmann suppression factors leads to fake resonances with temperature-dependent position which do not correspond to any charge excitation energy. Furthermore, we find that quantum tunneling can completely suppress transport if the transverse anisotropy has a high symmetry.

Phonon-assisted changes in charge states of deep level defects in germanium

Electronic processes associated with changes in the charge states of the vacancy–oxygen center (VO or A center) and vacancy–group-V-impurity atom (P, As, Sb or Bi) pairs (E centers) in irradiated germanium crystals have been studied using deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS and Hall effect measurements. It is found that the electron emission and capture processes related to transitions between the doubly and the singly negatively charged states of the A center and the E centers in Ge are phonon-assisted, i.e., they are accompanied by significant vibrations and re-arrangements of atoms in the vicinity of the defects. Manifestations of the phonon involvements are: (i) temperature-dependent electron capture cross-sections which are well described in the frame of the multi-phonon-assisted capture model; (ii) large changes in entropy related to the ionization of the defects and, associated with these, temperature-dependent positions of energy levels; and (iii) electron emission via phonon-assisted tunneling upon the application of electric field. These effects have been considered in detail for the vacancy–oxygen and the vacancy–donor complexes. On the basis of a combined analysis of the electronic processes a configuration-coordinate diagram of the acceptor states of the A and E centers is plotted. It is found that changes in the entropy of ionization and the energy for electron emission for these traps follow the empirical Meyer–Neldel rule. A model based on multi-phonon-assisted carrier emission from defects is adapted for the explanation of the origin of this rule for the case of electronic processes in Ge.

Tunneling spectroscopy of YBa 2Cu 3O 7− δ 45° asymmetrical bicrystals grown by liquid phase epitaxy

We report on the study of tunneling characteristics of 45° asymmetrical grain boundaries fabricated in YBa 2Cu 3O 7− δ films grown by the liquid phase epitaxy. A well defined conductance peak has been observed in the conductance vs voltage curves at various temperatures below T c. Magnetic field and temperature dependence of position and amplitude of this peak strongly suggests its superconducting origin. The estimated gap value is about 45 meV at T=5 K and decreases to zero near T c.

Ac susceptibility and transport critical-current density of polycrystalline c-axis-orientedYBa2Cu3O7−δnfilms:fJosephson tunneling and d-wave pairing

We determined the intergranular critical-current density ${\mathrm{j}}_{\mathrm{cJ}}$(T) of thin films of polycrystalline c-axis-oriented ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ by measuring the isothermal ac susceptibility \ensuremath{\chi}(${\mathrm{h}}_{\mathrm{ac}}$) at zero dc magnetic field. The temperature dependence of ${\mathrm{j}}_{\mathrm{cJ}}$ was obtained from the temperature-dependent position of the intergrain peak in ${\mathrm{\ensuremath{\chi}}}^{|\mathrm{I}\mathrm{J}}$(${\mathrm{h}}_{\mathrm{ac}}$). We confirmed our results by measurements of the transport critical current performed under self-field conditions. The observed temperature dependence of the critical current was compared with calculations of the Josephson critical current across rough interfaces. The experimental data can be explained by either assuming d-wave symmetry of the superconducting order parameter or, alternatively, by assuming s-wave symmetry and unusually strong pair breaking at the grain boundaries. The calculated critical currents show temperature dependences significantly different from the Ambegaokar-Baratoff formula, and agree well with recent measurements on single grain boundary junctions.

Triplet-singlet difference spectra of Rps. viridis recorded with magneto-optical difference spectroscopy at 1.2–286 K. Temperature dependence of position and width of the long-wavelength absorption band

Abstract The long-wavelength absorption band of Rps. viridis has been monitored by magneto-optical difference spectroscopy at temperatures between 1.5 and 286 K. Clear evidence is obtained for two components whose relative contribution is strongly temperature dependent. Plots of linewidth and peak position of the two components (determined by Gaussian fits) as a function of temperature could be well fitted with the standard theory of vibrational broadening, yielding a Huang-Rhys factor S = 4–5 and average mode frequencies of about 70 cm −1 . Unlike the values obtained treating the long-wavelength band as a single component, the present parameter values compare well with those derived from holeburning spectroscopy.

PtP242. Fluctuations of incommensurate wave near faraelectric-modulated phase transition in Rb2ZnCl4

Abstract The ESR spectra of Mn2+ probe have been investigated in the temperature interval including paraelectric-incommensurate phase transition point Ti of Rb2ZnCl4. Near below Ti we have measured the temperature dependence of position of the inhomogeneously broaden ESR line. On the basis of the simple model - it is shown that ESR spectrum is influenced by phase and amplitude fluctuations of modulation wave.

Temperature-dependent infrared band structure and dynamics of the CH choromophore in C 4F 9CCH

High-resolution IR-spectra of 4.4.4-trifluoro-3.3-bis(trifluoromethyl) butyne. (CF 3) 3CCCH are reported. The temperature-dependent positions and vibrational widths are interpreted in terms of homogeneous and inhomogeneous contributions and in terms of intramolecular dynamics on the picosecond time scale. The results are also important for understanding the mechanism of IR photochemistry.

Dielectric principal relaxation above and near the glass transition

A theoretical interpretation of the temperature dependence of position and shape of the relaxation-frequeney-spectrum is given for the dielectric principal relaxation of amorphous polymers. Assuming the spectrum obeys the HAVRILIAK-NEGAMI-formula, its change versus temperature (above Tg) can be described quantitatively by three WLF-like equations differing mutually in the value of one constant only.

Ultrasonic relaxation of rotational-isomeric equilibria in polymer solutions

The sound absorption per wavelength µ in solutions of polystyrene in benzene and carbon tetrachloride deviates from proportionality with frequency in the low MHz range. This could be accounted for with good agreement by an additional, Debye-shaped excess absorption. Various models for the relevant relaxation process are discussed; the most probable one is the thermal relaxation of a rotational-isomeric equilibrium within the polymer chain, consisting of a rotation of a single monomer unit. Under that assumption, from the temperature dependence of position and amount of the absorption maximum the following data of the rotational potential were calculated: separation of the equilibrium energies ΔH= 0.9 kcal/mol, activation energy ΔH12= 7.5 kcal/mol, frequency factor ν= 1.4 × 1012 s–1.