Frequency V0 Research Articles

Properties of antiferromagnetic resonance in GdB6

Antiferromagnetic resonance in GdB6 exhibits a series of anomalous features such as jump of the resonance position at TN = 15.5 K and resonance evolution to four line structure with further temperature decrease. Here we report the study of temperature behaviour of antiferromagnetic resonance modes v(H0) in AFM phase. We analyzed v(H0) dependencies at several temperatures T < TN within the model of an antiferromagnet with easy anisotropy axis. In the result we have demonstrated that AFMR behaviour is determined by two following factors: (i) abrupt change of the gyromagnetic ratio γ at TN, which remains constant (corresponding to g-factor g = 1.27) in AFM phase and (ii) jump of zero field frequency v0 (from v0 ≈ 0 to v0 ≈ 20 GHz at TN with its further growth to v0 ≈ 35 GHz at T = 1.9 K.

Ionic conduction and vibrational characteristics of Al3+ modified monoclinic LiZr2(PO4)3

Effects of Al3+ substitution for Zr4+ in LiZr2(PO4)3 on its structure and lithium ion conduction are investigated. Li1+xZr2-xAlx(PO4)3 samples prepared via a sol-gel route and calcined at 900 °C crystallize in monoclinic structure with P21/n space group and show a reduction in cell volume with an increase in x. Raman spectra showed an increase in broadening of higher frequency v1 &v3 vibrational modes and a spectral weight transfer between v2 &v4 bending modes of PO4 tetrahedra with the increase in Al3+ doping. Analysis of Raman spectra further suggested that the renormalization of the mode frequencies in doped samples is controlled by Li-ion motion via strongly interacting with internal bending modes of PO4 tetrahedra. A significant improvement in ionic conductivity was observed in Al-doped samples, and the highest conductivity of 1.83 × 10−4 Ω−1m−1 and lithium diffusion coefficient of about 5.7 × 10−19 m2s−1 was observed for Li1.25Zr1.75Al0.25(PO4)3 at room temperature. Li transference number suggested that the conductivity in Li1.25Zr1.75Al0.25(PO4)3 is predominantly ionic. Activation energy was found to decrease from 0.58 eV for LiZr2(PO4)3 to 0.47 eV for Li1.25Zr1.75Al0.25(PO4)3.

A study on the electrical properties of Mn-Co-Ni-O thin films grown by radio frequency magnetron sputtering with different thicknesses

This study provides an insight to understanding the role of thickness on the hopping frequency (v0) of electrons between Mn3+ and Mn4+, the temperature coefficient of resistance (αT) and the characteristic temperature (T0) in Mn-Co-Ni-O spinel films. A remarkable decrease in the Mn3+/Mn4+ ratio of films from 265 to 693nm and an increase in the range of 693–887nm can be probed by x-ray photoelectron spectroscopy. From the analysis of the Hall measurements, it is found that both the 1/v0 and αT =303K increase with the thickness below 693nm, and then decrease above 693nm. Such a feature is attributed to the change in the distribution of Mn cation. The T0 are 3675, 3352, 3087, 3366 and 3816K for films with thicknesses from 265 to 887nm. It reveals that the ratio of Mn3+/Mn4+ should also be responsible for T0, which can result in significantly different electrical properties of Mn-Co-Ni-O films with increasing thickness. The present result will open a way to design a desired negative temperature coefficient thermistor by adjusting the thickness of films.

Pressure effect on the Fermi resonance doublets of ν1 ∼ ν12 and ν1+ν6 ∼ ν8 in pyridine

Raman spectra of pure pyridine, pyridine aqueous solution, and pyridine in methanol under high pressure were measured separately. Behaviors of two Fermi doublets, v1 and v12, v1+v6 and v8, occurred simultaneously in one pyridine molecule are analyzed according to their spectra, which indicates that the v1 Raman activity decreased with increasing pressure and disappeared eventually, which induced weakness and even disappearance of the Fermi resonance between v1 and v12, while the v1 Raman intensity variation had no effect on the presence of the Fermi resonance between v1+v6 and v8 as well as its variation law with increasing pressure. Those phenomena were interpreted by group theory in this article. It also indicates experimentally that all Raman bands of pyridine appeared blueshift with increasing pressure except that OH group appeared redshift. Moreover, frequency v1 shifted more quickly with increasing pressure than their counterparts did in neat liquid, so did its Raman intensity variation.

Pulsed cathodoluminescence of two-alkali sodium potassium silicate glasses

Alkali silicate glasses of variable composition 22xNa2O · 22(1−x)K2O · 3CaO · 75SiO2 with equimolecular replacement of sodium ions by potassium ions are investigated using pulsed cathodoluminescence. It is revealed that localized electronic states interact with vibrations of two types, namely, polarization vibrations of the silicon-oxygen network with the frequency v0 = 820 cm−1 and bending vibrations of the modifier sublattice. At low concentrations of one of the alkali components (x < 0.1), bending vibrations are observed at two frequencies. These frequencies coincide with those of the corresponding vibrations in one-alkali systems containing Na (530 cm−1) and K (520 cm−1). At higher concentrations (x in the range ∼0.14–0.86), there occur bending vibrations of the cationic sublattice with a frequency of 420 cm−1. This can be interpreted as a luminescence analog of two-alkali (mixed-alkali) effect.

Some Conclusions on the MHD Alfvén Wave Oscillation Model of kHz QPO

MHD Alfven wave oscillation for the interpretation of the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) is proposed, and the upper kHz QPO frequency coincides with the Keplerian frequency. The model concludes that the kHz QPO frequencies inversely depend on the disk radius, and the theoretical relation between the upper frequency (v2) and the lower frequency (v1) is v1 ~ v22, which is similar to the measured empirical relation. The separation between the twin frequencies decreases (increases) with increasing the kHz QPO frequency if the lower kHz frequency is more (less) than ~ 400 Hz.

Positiver Kontrast zum Nachweis magnetisch markierter Zellen in der MRT – in-vitro Experimente / Positive contrast in the detection of magnetically labeled cells by MRI – in vitro experiments

Magnetically labeled cells (MLC) cause local field inhomogenities within the single voxels as well as on a macroscopic scale. The related Larmor frequency shift near MLC was exploited to obtain bright visualization applying spectral selective saturation (SSS). SK-Mel28 cells were labeled with the superparamagnetic iron oxide contrast agent SHU 555A. Low cell concentrations (0, 5, 20, 30, 50, 75, and 150 MLC/microl) and high cell concentrations (10 x 10(3), 30 x 10(3), 60 x 10(3), and 100 x 10(3) MLC/10 microl) were examined at 3 Tesla. Shimming and frequency adjustment to spectrometer reference frequency v0 was performed with the built in routine of the scanner. A 2D spin echo sequence with broadband excitation and refocusing pulses was used (BWex = 1.000 Hz). Prior to each TR, a non-selective saturation sinc pulse centred at v0 was applied. Bandwidth (BWsat) of this pulse was varied from 100 Hz to 800 Hz in logarithmic steps. Without SSS the highest value of Crel (i.e. relative MR contrast between labeled to unlabeled samples) was found for 150 MLC/microl and was given by 10%. Applying SSS led to positive contrast of the complete labeled volumes and to remarkable improvements in Crel. With increasing cell concentrations Crel raised to maximum, that was given by 52% (BWsat=100 Hz) and 28% (BWsat = 200 Hz) found for 75 MLC/microl. For 150 MLC/microl Crel decreased. A contrast clarification could also be detected near cell aggregations despite saturation. Using SSS positive contrast can be achieved for voxels containing MLC and voxels close to cell clusters. Under in vitro conditions positive contrast improved the sensitivity to detect MLC as compared to negative contrast imaging techniques. It seems reasonable, that positive contrast approaches can be applied in vivo as the underlying physical mechanism are comparable.

Antisymmetric polarizabilities of rotational sublevels for linear molecules with a non-degenerate ground electronic state

Using the semiclassical perturbation theory, we study the antisymmetric polarizabilities of rotational sublevels, the M-dependent splittings and shifts of the sublevels and corresponding rotational spectral lines of a linear molecule induced by a right (+) or left (−) circularly polarized resonant optical field. The deduced theoretical formulas for these quantities indicate that for rotational sublevels M of linear molecules with a non-degenerate ground electronic state, the antisymmetric polarizabilities induced by a resonant polarized optical fields exist and are the same order of magnitude of the symmetric ones. Based on them, M-dependent (both size and sign of M) splitting and shifts of the sublevels and corresponding spectral lines can be produced and the degeneracy for +M and −M sublevels can be completely broken by the circularly polarized resonant optical field. As examples, we have calculated these quantities for H2 and CO molecules. For H2 molecule, the antisymmetric and symmetric polarizabilities of the rotational magnetic sublevels in the ground electronic state X1Σg+(v=0,J=1,M), which are induced by a optical field with frequency v0 resonant with the transition X1Σ+g(v=0,J=1)→B1Σu+(v′=0,J′=2), are the same order of 10 a.u.; and laser-induced M-dependent splittings and shifts for M=1,0,−1 sublevels and the corresponding resonant Rayleigh scattering lines X1Σg+(v=0,J=1,M)↔B1Σu+(v′=0,J′=2,M′) can be the order of 0.1–1 GHz when the intensity of circularly polarized optical field is 100 MW cm−2. Similarly the antisymmetric polarizabilities of CO molecule in the rotational magnetic sublevels X1Σ+(v=0,J=1,M=1) using IR field with the frequency v0 resonant with the transition X1Σ+(v=0,J=1)→X1Σ+(v′=1,J′=2) are the same order (10 a.u.) of the symmetric ones.

Raman Spectroscopy of the Kaolinite Hydroxyls at 77 K

Raman spectroscopy of two types of kaolinites has been obtained at liquid nitrogen temperature (77 K) with the use of a Raman microprobe and a thermal stage. The Raman spectrum is characterized by the combination of the frequencies of the inner hydroxyl and the inner surface hydroxyl groups. The inner hydroxyl frequency is reduced, and the outer hydroxyl frequencies move to higher frequencies upon cooling to 77 K. The inner hydroxyl frequency shifts from 3620 cm−1 at 298 K to 3615 cm−1 at 77 K. The two in-phase inner surface hydroxyl frequencies move from 3684 and 3689 cm−1 at 298 K to 3690 and 3699 cm−1 at 77 K. The two out-of-phase vibrations shift from 3650 and 3668 cm−1 to 3656 and 3675 cm−1. The bandwidth of the inner hydroxyl frequency decreases from 3.7 to 2.1 cm−1 at 77 K. The bandwidth of the inner surface hydroxyl frequency ( v1) increases upon cooling from 17.4 to 19.2 cm−1. It is proposed that the increased resolution at low temperature enabled an additional inner surface hydroxyl frequency to be observed.

The most resonant pulsation frequency of δ Scuti stars

AbstractPulsation of the Sun with a period of P0 ≈ 160 min discovered about two decades ago, is still waiting explanation. In view of the hypothesis about its cosmological origin, and attempting to find signature of this P0 periodicity among other (short‐period variable) stars, the pulsation frequencies of δ Sct stars are subjected to specific analysis. With a confidence level ≈ 3.8σ it is found that the frequency v0 = P0−1 ≈ 104 m̈Hz, within the error limits, appears indeed to be the most “resonant” one for the total sample of 318 pulsating stars of δ Sct type (the most commensurable, or “synchronizing”, period for all these stars occurs to be 162 ± 4 min). We conjecture that a) the P0 oscillation might be connected with periodic fluctuations of gravity field (metrics), and b) the primary excitation mechanism of pulsations of δ Sct stars, reffected by this “ubiquitous” P0 resonance, must be attributed perhaps to superfast rotation of their inner cores (their rates tend to be in near‐resonance with the “universal” v0 frequency). The arguments are given favouring a cosmoogical nature of the P0 oscillation.

Can a single-pulse standing wave induce chaos in atomic motion?

Time-dependent Hamiltonian dynamics exhibit a wide range of novel effects in both classical and quantum domains [1,2]. Possibly the simplest time-dependent potential is the turning on and off of an interaction, though even here our intuition is clear only for the two extreme cases of fast passage and adiabatic interactions. Since the majority of cases fall between these two limits, it is important to develop a clear understanding and simple physical pictures at intermediate time scales. We show that when the interaction is nonlinear, the mere act of turning on and off a potential in this intermediate regime can lead to classical chaos. Further, we provide a clean experimental demonstration of the classical mechanism of resonance overlap [3 ‐ 5] which leads to classically diffusive growth. This general problem is posed in the context of atom optics with ultracold atoms. The nonlinear interaction is a single pulse of a one-dimensional standing wave of light. This type of time-dependent interaction is ubiquitous and occurs, for example, whenever an atomic beam passes through a standing wave of light. The starting point for this discussion is the model of a two level atom (transition frequency v0) interacting with a standing wave of near-resonant light (frequency vL) which is turned on and off with a time-dependent function fstd. For sufficiently large detuning dL › v0 2v L(relative to the natural linewidth), the excited state amplitude can be adiabatically eliminated [6], leading to a Hamiltonian for the ground state H › p 2 y2M 2 s ¯ hVeffy8df std cos2kLx.

Simple algorithm in time-window extending for magnetic relaxation in high Tc superconductors

A one to one map is established between the magnetic-hysteresis-loop (MHL) measurements and the magnetization relaxation measurements performed at the same external field, noticeably keeping no uncertainties of such factors as the microscopic attempt frequency v0 and the hopping distance lhop for pinned flux motion. By utilizing this map, we are able to construct and extend the magnetization relaxation data from the corresponding reported MHL measurements. The present algorithm proves to be reliable and simple for investigations of the U(J) behavior and relaxation effects.

3.5 hour periodic variability of WR66 (HD 134877, WN8): the first example of non-radial pulsations among Wolf-Rayet stars?

We report a first result from an extensive observing campaign for the WN8 star WR66 (HD 134877). We obtained 219 photometric observations of WR66 in a standard broadband V-filter during 61 nights, distributed in a T = 83d interval. Details of observations and data reduction can be found in Antokhin et al. (1994). The power spectra of WR66-C1, WR66-C2 and C2-C1 are shown in Fig.1. Both the WR66-C1 and WR66-C2 spectra clearly show high frequency components. The overall structure of the peaks is evidently determined by 1-day aliasing. The highest peak in both spectra has frequency v1 = 6.828 d−1 (period P = 3h.51). Inspection of the power spectra shows that C1 is a low-amplitude variable, but luckily at low frequencies only. We conclude that WR66 is significantly variable with a period of 3h.5. A phase plot of the data (WR-C2 and C2-C1) with this frequency is shown in Fig.2. Plausible scenarios which could potentially account for the observed variability are: (i) non-radial pulsations (NRP); (ii) rotational light-modulation by spots or (magnetic) loops at the stellar surface; (iii) spiral-in system (WR+c), like the massive X-ray binary Cyg X-3 (van Kerkwijk 1993).

Mixing effect in the NH3 absorption and MIR emission spectra pumped by a continuously tunable CO2 laser

By tuning a high pressure CO2 laser (HPL) around strong ammonia lines nearly coincident with CO2 lines an of-fresonant absorption is observed which can be confirmed by the superfluorescent MIR emission. This effect is related to a two frequency v1, v3 HPL emission in the regime of moderate pulling. Around a strong absorption line a mixed v4=2v1−v3 frequency is produced that is strongly absorbed

Nuclear magnetic resonance survey of hydrogen motion and electronic structure in α-phase (NbMo)-H alloys

The results of a proton nuclear magnetic resonance (NMR) survey of hydrogen motion and electronic structure in the solid solution (α) phase of niobium rich Nb1−yMoyHx alloys are reported (y ⩽ 0.2, x ⩽ 0.2). Measurements of the temperature dependence of the proton spin-lattice relaxation time T1 over the range 20 ⩽ T ⩽ 800 K were analyzed to yield values of the activation energy Ea and jump attempt frequency v0 for hydrogen diffusive hopping and of the product T1eT = Ce indicative of the electronic density-of-states at the Fermi level, N(EF), where T1e is that contribution to T1. The T1vs. T behavior shows features characteristic of hydrogen in random alloys, reflecting a distribution of Ea and v0 values. At high temperatures (~ 500 K), T1 exhibits anomalous behavior, passing through a maximum and decreasing again at higher temperatures in the same manner found in the NbH and (NbV)-H systems.

Infrared Dust Emission in Galaxies and Spectral Distortion of Microwave Background

Recent observations (Matsumoto et al., 1988) indicate that at submillimeter wavelengths the spectrum of the cosmic background radiation (CBR) deviates from that of Planckian blackbody with a temperature T0R = 2.76 K. The relative excess of the flux ζ(v) = [F(v) – F0(v)] / F0(v) (where F(v) and F0(v) are the registered flux and the flux of the blackbody radiation at the frequency of the observations) are 0.6 at a frequency v1 = 380 GHz (λ = 709 μm) and 3.4 at a frequency v2 = 624 GHz (λ = 481 μm).

First observation and analysis of the ion-pair state of Br2 by optical–optical double resonance

The technique of optical–optical double resonance has been applied to a study of the [Formula: see text] ion-pair state of Br2. Two pulsed dye lasers excite the molecules from the ground state to the [Formula: see text] ion-pair state stepwise through the [Formula: see text] state in the pump-probe scheme: [Formula: see text]. The [Formula: see text] emission identified at around 215 nm is used to detect the double resonance signals when the probe laser frequency (ν2) is scanned by fixing the pump laser frequency (v1) to appropriate [Formula: see text] transitions. The emission spectra are resolved to establish the absolute vibrational numbering of the ion-pair state in terms of the Franck–Condon calculations. The Dunham coefficients of the [Formula: see text] state obtained in a global least-squares fit analysis of 377 transitions [Formula: see text] are Y00 = 57929.724(24), Y10 = 212.227(23), Y20 = −1.5683(56), Y30 = 1.606(40) × 10−2, Y01 = 0.0465652(89), Y11 = −4.500(36) × 10−4, Y21 = 1.133(41) × 10−5, and Y02 = −9.37(94) × 10−9 for 79Br2 isotope species (all in cm−1 with 3σ in parentheses).

Hydrogen Vacancy Diffusion Parameters in ScH2-x and ScD2-x from 45Sc Spin-Lattice Relaxation Time Measurements

The temperature dependence of the nuclear spin-lattice relaxation rate R1 of 45Sc has been measured in scandium dihydrides and dideuterides. These data are satisfactorily accounted for by two contributions to R1, R1e due to conduction electrons, and R1Q due to quadrupole interaction fluctuations resulting from vacancy diffusion on the hydrogen (deuterium) sublattice. Describing these fluctuations by a Lorentzian spectral density and Arrhenius behavior for the vacancy hopping, analysis of the data yields values of the Korringa product A = T/R1e and the activation energy Ea and attempt frequency v0 for vacancy-diffusion. In contrast to v0 values based on proton measurements, the 45Sc results agree satisfactorily with the value based on inelastic neutron scattering measurements of hydrogen optic mode vibration frequencies, v0 ≅ 2 x 1014s-1. We conclude that hydrogen-hydrogen interactions are responsible for the lower v0 values derived from proton R1 measurements.

High-sensitivity high-resolution pulsed CARS spectrometer

A high-sensitivity pulsed CARS (coherent anti-Stokes Raman scattering) spectrometer with a resolution of 3 × 10−3 cm−1 is described. Spectra with a resolved rotational structure of the Q branch of the v1 vibrations of 32SF6 and 34SF6 molecules were obtained. Measurements were made of the vibrational-rotational interaction constant α and of the vibrational frequency v1.

On the relationship between refractive index and density for SiO2 polymorphs

The Gladstone-Dale law (specific refraction) and the Drude law (molecular refraction) for silica polymorphs, at “sodium light” (λ D =0.5893 μm), are derived from simple atomic properties of SiO2 complex (atomic weight, first ionization potential). The considerations are based on the Lorentz electron theory of solids. The characteristic frequency (or eigenfrequency) v 0 of elementary electron oscillators (in energy units, hv) is identified with the band gap E G of a solid; on the other hand, this E G -gap is identified with the single ionization potential $$\tilde U$$ of non-free atoms. For $$\tilde U$$ =E G =10.2 eV (energy gap of quartz, see Nitsan and Shankland 1976b) the Gladstone-Dale law, or specific refraction, is (n−1)/ρ=0.208 cm3/g, where n and ρ are the refractive index and the density of medium, respectively. According to empirical data, the average value of the specific refraction of pure SiO2 polymorphs (except stishovite-high density phase of silica) is (〈n〉−1)/ρ=0.207±0.001 (〈n〉 denotes the mean refractive index of crystal). For stishovite the Drude law (n 2−1)/ρ=0.542 cm3/g is valid under an assumption that the first ionization potential $$\tilde U$$ =E G ≈9 eV; this result is good agreement with the empirical value (〈n〉2−1)/ρ=0.536 cm3/g.