Mixed 2D molecular systems: Mechanic, thermodynamic and dielectric properties

Study of Langmuir monolayers consisting of stearic acid (SA) and dipalmitoylphosphatidylcholine (DPPC) molecules was done by surface pressure-area isotherms (π-A), the Maxwell displacement current (MDC) measurement, X-ray reflectivity (XRR) and atomic force microscopy (AFM) to investigate the selected mechanic, thermodynamic and dielectric properties based on orientational structure of monolayers. On the base of π-A isotherms analysis we explain the creation of stable structures and found optimal monolayer composition. The dielectric properties represented by MDC generated monolayers were analyzed in terms of excess dipole moment, proposing the effect of dipole-dipole interaction. XRR and AFM results illustrate deposited film structure and molecular ordering.     

Comparison of phase behavior between water soluble and insoluble surfactants at the air-water interface

The surface phase behavior of 2-hydroxyethyl myristate (2-HEM) has been studied in Langmuir monolayers by measuring surface pressure (π)-area (A) isotherms with a film balance and observing monolayer morphology with a Brewster angle microscope (BAM). These results are compared with the phase behavior of 2-hydroxyethyl laurate (2-HEL) in Gibbs monolayers studied by measuring π-time (t) curves and observing monolayer morphology. The π-A isotherms of 2-HEM show a first-order phase transition from a liquid expanded (LE) phase to a liquid condensed (LC) phase in the temperature range between 5 and 35 °C whereas the π-t curves of 2-HEL represent a similar phase transition in the temperature range between 2 and 25 °C. The critical surface pressure, π_c necessary for the phase transitions increases with increasing temperature in both the cases. The LC domains formed in 2-HEM show circular shapes, which are independent of the temperature. In contrast, the circular domains having stripe texture formed at lower temperatures show a shape transition to fingering domains with uniform brightness at 15 °C. The amphiphile, 2-HEM having 13-carbon chain has higher line tension than 2-HEL that has 11-carbon chain as tail. Thus, for 2-HEM, this high line tension always dominates over other factors giving rise to circular domains at the all studied temperatures.     

Effects of surface concentration on the porphine monolayers: Molecular simulations at the nanoscale water-gas interface

The effect of surface concentration on the structure and stability of porphine (PH₂) monolayers at the water-gas interface was studied by using molecular dynamics simulation. Five monolayer systems having different surface concentrations were investigated in order to cover a full range of the experimental π-A isotherm. The simulation results show that increment of a number of the PH₂ molecules not only affects the significantly decreasing water density at the interface but also the monolayer surface tensions. The calculated surface tensions of the five systems indicate that the monolayer phase transfer corresponding to gaseous, expanded, condensed, and collapsed phases are observed. The hydrogen bonding between water and the PH₂ molecules at the interface plays an important role on the monolayer film formation, especially at the lower surface concentrations. The PH₂ orientations for all surface concentrations, except the highest one, are favored to be the β-structure as observed in the copper porphyrazine (CuPz) monolayer.     

Studies on behaviors of dipalmitoylposphatidylcholine and bilirubin in mixed monolayer at the air/water interface

Mixed monolayers of dipalmitoylposphatidylcholine (DPPC) and bilirubin (BR) were prepared on different subphases. The properties of DPPC/BR monolayer, such as collapse pressure (π_coll), limiting area per molecule (A_lim), surface compressibility modulus, free energy (ΔG_mix) and excess free energy (ΔG_ex), were investigated based on the analysis of the surface pressure-area isotherms on pure water. The results showed that DPPC and BR were miscible and formed non-ideal mixed monolayers at the air/water interface. With the molar fraction of BR (X_BR) increasing, the LE-LC coexistence region of DPPC monolayer was eliminated gradually. The DPPC/BR complex (M_D-B) of 1:2 stoichiometry formed as a result of the strong hydrogen bonds between the polar groups of DPPC and BR. The studies of effects of pH values and calcium ions in subphase on the DPPC/BR monolayers showed that the mixed monolayer became expanded on alkali aqueous solution and on 1 mmol/L CaCl₂ aqueous solution. The orientation of DPPC and BR at air/water interface was also discussed.     

Gravity modulation study on opposed flame spread over thin solid fuels

In this work a numerical investigation has been carried out to study the effect of g-jitter on zero-gravity (0g_e) opposed flow spreading flame over thin solid fuels. For comparison simulations have also been carried out for normal gravity (1g_e) downward spreading flames. G-jitter is emulated by gravity modulation of sinusoidal (A_ge sin(2πt/T_ge)) gravity perturbation (g-perturbation) of a particular time-period (T_ge) and amplitude (A_ge) over a selected base gravity level (0g_e or 1g_e). The response of flames at 0g_e base gravity and at 1g_e base gravity was different to the imposed g-perturbation. While at 0g_e the mean and the amplitude of the oscillatory flame spread rate (FSR) magnified with increase in the time period of g-perturbation, interestingly for the 1g_e flame a maximum mean FSR and oscillation amplitude occurs at certain perturbation time period. Further, at very small perturbation time-periods (T_ge) the FSR at 1g_e was lower than the steady state FSR. The amplitude of oscillatory FSR increased with increase in perturbation amplitude (A_ge). However, the 0g_e flame which is little affected (compared to 1g_e flame) at small perturbation amplitude (A_ge) is affected severely at large perturbation amplitude (A_ge). Both the gas phase and fuel pyrolysis (or fuel response) follow perturbation signal with a lag but fuel pyrolysis is more sluggish and lags behind gas phase. The phase lag between fuel pyrolysis and gas increases at smaller time-periods (T_ge) and tends to enhance the effect of external perturbation whereas at larger time-periods (T_ge) this lag inhibits the effect of external perturbation.     

Diffuse reflectance spectrum of Co3+-N-acetylacetone-anthralinic acid complex

Diffuse reflectance spectrum of Co³⁺-N-Acetylacetone-anthranilic acid complex is reported between 50.000-10.000 cm^?1. Two absorption peaks have been observed at 34.310 and 20.000 cm^?. They have been assigned to ¹T_2g ? ¹A_1g and ¹T_1g ? ¹A_1g transitions.     

Concurrent changes of crystallographic and Mössbauer effect parameters at the high-spin(5T2) ⤥ low-spin(1A1) transition in compounds of iron (II)

Distinct and different X-ray diffraction patterns are found for the ⁵T₂ and ¹A₁ phases at the high-spin(⁵T₂) ? low-spin(¹A₁) transition in Fe(bt)₂(NCS)₂ (I) and Fe(phy)₂(ClO₄)₂ (II) (bt = 2,2′-bi-2-thiazoline; phy = 1,10-phenanthroline-2-carbaldehydephenylhydrazone). The peak profiles show the same temperature dependence and the same hysteresis behaviour as the ⁵T₂ and ¹A₁ fractions determined on the basis of Mössbauer effect or magnetism. At the transition temperature T_c, both phases are coexistent.     

Temperature dependence of the emission spectra of p-benzoquinone in a p-dichlorobenzene matrix

Emission and excitation spectra of p-benzoquinone have been measured in a partially translucent p-dichlorobenzene host matrix at different temperatures from 77 up to 323 K. Successive occurrence of the T₁(n,π^?) and T₂(n,π^?) phosphorescence and S₁(n,π^?) fluorescence has been observed for p-benzoquinone upon increasing temperature. The S₁–T₂ and T₂–T₁ energy separations determined from the temperature dependence of the emission intensities agreed well with those obtained from the locations of the T₁ and T₂ phosphorescence and S₁ fluorescence origins. Occurrence of the emission from S₁ and T₂ is brought by the thermal population from the T₁ state. The symmetries of the T₁ and T₂ states were determined to be B_1g and A_u, respectively, based on the spectral data.     

Two and three pion-cut contributions to nucleon-nucleon scattering

Examining information from NN forward scattering in terms of discrepancy functions, we show that the 2π cut contributions as calculated via dispersion methods from πN scattering are in perfect agreement with NN scattering. Furthermore, we demonstrate the need for 3π cut contributions which are quantitatively well described by a nucleon exchange model. Finally, in addition to the 2π and 3π cut contributions, we determine the coupling constants of the ω and A₁ to be: g_Vω²/4π = 8.1 ± 1.5, g_Tω/g_Vω = 0.14 ± 0.20 and g_A1²/4π = 7.3 ± 3.0. The coupling of the η turns out to be zero.     

Hysteresis phenomena in charging of Si Mosfet in quantizing magnetic field

We report the observation of nonequilibrium processes of charging in 2D electron layer in Si MOSFET. There were investigated the hysteresis variations of a 2D-layer charge Q_S with a gate voltage V_g or with a magnetic field H, and the hysteresis of a gate potential U_g vs magnetic field at Q_S = Const. At sufficiently low temperature T < 1K the relaxation time of a nonequilibrium state is much higher than 10³ sec. The observed phenomena may be explained qualitatively in frame of a surface potential randomness conception.     

High-pT pion production in ππ interactions

Charged pion production in high energy π^-π^- interactions is studied in the p_T region of 1–2 GeV/c. The characteristics of pion production in π^-π^- interactions are compared with those in π^-p and pp interactions. The p_T dependence of pion production in these reactions follows a systematic trend which indicates that high-p_T pion production for ππ interactions as well as for πp and pp interactions proceeds via quark-quark scattering as predicted by QCD.     

Current algebra calculation of e+e-→4π± and determination of ϱ′(1600) parameters

A current algebra calculation of e⁺e^-→4π^± cross section is carried out using the axial current matrix element obtained from τ→π?ν. Assuming ?′→?+2π(I=0, l=0), the following results are obtained: for the A₁ resonance, 1.05?m_A ?1.15 GeV; for ?′, Γ?′(total)≈0.23 GeV, M_?′≈1.5 GeV, Γ(?′→e⁺e^-)≈0.4 keV×B^?1(?′→?′ →?π⁺π).     

Direct observation of the relaxation time of the symmetric molecular CO2-3 vibration of calcite

The relaxation of the internal A_1g-mode of the CO^2-₃ group (? = 1086 cm^-1) is investigated with picosecond pulses. The measured decay times are 4.4 psec and 8.7 psec at 295 K and 90 K, respectively. Our values are in agreement with spontaneous Raman data. Possible relaxation processes are discussed.     

Phase transition and ferroelastic property studied by using the Cs nuclear magnetic resonance in a CsHSO4 single crystal

The ¹³³Cs spin-lattice relaxation time in a CsHSO₄ single crystal was measured in the temperature range from 300 to 450 K. The changes in the ¹³³Cs spin-lattice relaxation rate near T_c1 (=333 K) and T_c2 (=415 K) correspond to phase transitions in the crystal. The small change in the spin-lattice relaxation time across the phase transition from II to III is due to the fact that during the phase transition, the crystal lattice does not change very much; thus, this transition is a second-order phase transition. The abrupt change of T₁ around T_c2 (II-I phase transition) is due to a structural phase transition from the monoclinic to the tetragonal phase; this transition is a first-order transition. The temperature dependences of the relaxation rates in phases I, II, and III are indicative of a single-phonon process and can be represented by T₁⁻¹=A+BT. In addition, from the stress-strain hysteresis loop and the ¹³³Cs nuclear magnetic resonance, we know that the CsHSO₄ crystal has ferroelastic characteristics in phases II and III.     

Nuclearg-factors of theJ π=21/2+isomer in112In and theJ π=6+ 112Sn

Theg-factor of theJ ^π=21/2⁺ isomeric state in¹¹¹In (T _1/2=13.3 ns) and of theJ ^π=6⁺ isomeric state in¹¹²Sn (T _1/2=13.7 ns) were measured using the spin rotation method. The result obtained for theJ ^π=21/2⁺ level in¹¹¹In,g=+0.47 (2), indicates that this state has an almost pure ((πg _9/2)^?1 νg _7/2 νd _5/2) shell model configuration. The experimental valueg=+0.04 (3) for theJ ^π=6⁺ isomer in¹¹²Sn agrees with the theoretical value calculated within the frame of the BCS model.     

Relaxation times and low-temperature specific heat of the quadrupolar glass

Computer simulations of a simplified model for molecular orientational order in certain solids provide results consistent with glass-like linear specific heat c_v at low temperatures. The temperature dependence of the quadrupolar relaxation time is found to be well described by the expression 1/τ～exp [-A/(T?T₀)], with T₀ well below the onset of the linear c_v regime. The relationship to experiments on solid hydrogen is discussed.     

Measurement of complex susceptibility on a metallic spin glass with broad relaxation spectrum

AC susceptibility measurements (0.625 H_z?_v?625 H_z) have been performed in a SQUID magnetometer on the amorphous metallic spin glass (Fe_0.06Ni_0.94)₇₅P₁₆B₆Al₃. The in-phase component of the susceptibility (x') shows a sharp peak at the spin glass freezing temperature T_g≈8 K with a frequency dependence of ?T_g/T_g≈0.015 per decade of frequency increase. The out-of-phase component (x″) exhibits a small anomaly at the spin glass transition with the magnitude of the anomaly almost independent of frequency. In particular we find the relation x″=(π;/2)?x'/? lnω to be valid in the vicinity of T_g. This relation and a frequency independence of x″ are fundamental characteristics of a spin glass having a broad spectrum of relaxation times. We argue that similar results from ac susceptibility measurements should be found in many spin glass systems, metallic as well as non-metallic.     

Influence of temperature on raman spectra of the FeS2 single crystal with pyrite structure

Raman scattering in a natural FeS₂ single crystal with the pyrite structure was investigated in the temperature range of 80–300 K. All five Raman-active modes E _g , T _g (1), T _g (2), A _g , and T _g (3) were observed under normal conditions (T = 23°C). The influence of temperature on the Raman spectra was studied in the HH configurations (polarizations of the incident and scattered radiations are parallel), which made it possible to detect the strongest spectral lines A _g and E _g . Widths of modes E _g and A _g were substantially smaller than those given in previous publications. It was found that the temperature dependences of frequencies and widths (FWHM) of modes A _g and E _g are approximated well by the Klemens model, which describes the three-phonon scattering mechanism.     

TSC study of deuteration of polystyrene

A comparative study of natural and deuterated polysterene has been performed by thermally stimulated currents (TSC). Around the glass-rubber transition temperature (T_g a TSC peak is observed whose relaxation times obey an Arrhenius equation. At 50° above T_g another TSC peak is observed whose relaxation time obeys a Vogel equation. Deuteration is found to increase the values of T_g.     

Nuclear magnetic resonance on oriented109In(4.2h) and110In(4.9h) after recoil implantation into Fe

Radioactive¹⁰⁹In(j ^π=9/2⁺;T _1/2=4.2h) and¹¹⁰In(j ^π=7⁺;T _1/2=4.9h) were produced via the¹⁰⁹Ag (α, xn) reactions and recoil-implanted into Fe foils. With the technique of nuclear magnetic resonance on oriented nuclei the magnetic hyperfine splittings were investigated in external magnetic fieldsB ₀=0.5...4.2 kG. The zero-field splitting were measured as 268.9(2)MHz and 147.3(3)MHz for¹⁰⁹InFe and¹¹⁰InFe, respectively. With the known hyperfine fieldB _HF(InFe)=?286.6(5) kG the nuclearg-factors are deduced asg(¹⁰⁹In)=1.231(3) andg(¹¹⁰In)=0.674(2). Our result for¹⁰⁹In shows that theπ g _9/2 g-factors vary by only ～0.1% betweenA=109 and 115. For the |π _9/2 vd _5/2〉₇₊ of¹¹⁰In the additivity relation of magnetic moments is fulfilled to on accuracy of 0.3(3)%.