Field-dependent Terms Research Articles

Field-enhanced Si–Si bond-breakage mechanism for time-dependent dielectric breakdown in thin-film SiO2 dielectrics

A field-enhanced Si–Si bond-breakage mechanism is presented which accurately describes the time-dependent dielectric breakdown behavior recently reported for thin-film SiO2 dielectrics over a wide range of fields and temperatures. The breakdown kinetics (both the field and temperature dependence) are shown to be consistent with a field-dependent dipolar energy term associated with an oxygen vacancy which serves to reduce the activation energy required for Si–Si bond breakage.

Field dependence of the soliton contribution to the dynamic correlation function of a classical Heisenberg antiferromagnet

Recent theoretical and experimental work confirm the existence of solitons in the nearly classical two-dimensional (2D) Heisenberg antiferromagnet. Previous ac susceptibility measurements on (n-propyl ammonium)2MnCl4 or (PAMC), a 2D spin 5/2 antiferromagnet AFM shows that the susceptibility is strongly dependent on a weak magnetic field (≈0.2 Oe) at temperatures below TC. These data provided the motivation for a calculation of the field dependence of the static soliton structure factor. This is done by assuming the small field dependent term as a perturbation around the static soliton solution. The dynamic part of the correlation function is assumed to result from soliton–magnon scattering in the Born approximation. These field-dependent and dynamic results are combined to obtain the dynamic field-dependent correlation function.

A review of spin Hamiltonian forms for various point-group site symmetries

A review has been made of the spin Hamiltonian forms for all the 32 point groups, including linear magnetic field-dependent terms in spin operators\(\hat O_1^m \),\(\hat O_3^m \),\(\hat O_5^m \),\(\hat O_1^m \),\(\hat O_3^m \), and\(\hat O_5^m \). All spin operators, as well as their matrix elements, to be used in constructing spin Hamiltonian matrices, have been listed. The various point group aggregates for distinct spin-Hamiltonian forms have been classified. In addition, descent of symmetry point groups, useful for studying structural phase transitions, have been indicated.

Noble-gas-like mechanism of localized field ionization of nitrogen as detected by field ion appearance energy spectroscopy

A local (probe-hole) mass-to-charge resolved retarding potential analysis of N 2 + emitted from a few surface sites of the apex plane of a [111]-oriented W tip is carried out and corresponding field ion appearance energies are obtained. A comparison of the results of N 2 + W(111) field ion appearance energy spectroscopy with independently obtained field-free nitrogen adsorption data reveals a noble-gas-like mechanism for the localized field ionization of N 2, supplied as imaging gas in the field ion microscope. The differences in the physical nature of the field-dependent terms of the appearance energy of N 2 + and CO + field ions are discussed in relation to the peculiarities of the high-field modified interaction of nitrogen and carbon monoxide with the tungsten surface.

Logarithmic Correction Terms of the Magnetic Susceptibility in Highly Correlated Electron Systems

The logarithmic correction terms in the repulsive Hubbard chain is investigated by using the Bethe Ansatz . The magnetic susceptibility χ of this model has a field dependent logarithmic correction term in small magnetic field at zero-temperature. This term causes ∂χ/∂ h ∣ h =0 =∞ . In arbitrary n and U the existence of the logarithmic correction term is shown for the susceptibility. We consider how this term depends on n and U . We also discuss the logarithmic correction term of the super-symmetric t-J model.

Poisson-Lie Structure of O(3)-σ Model in Terms of Moving Local Frame11The project partly supported by National Natural Science Foundation of China

We discuss the Poisson-Lie structure of the integrable nonlinear O(3)-σ model in terms of moving local frame. The corresponding r, s matrices are given out explicitly. The field-dependent terms in r, s matrices appear to be associated with the Riemannian connection of the target manifold.

New critical-state model for magnetization of hard type-II superconductors

We propose a critical-state model based on the empirical fact that the critical current density Jc in high-Tc superconductors in some cases is found to decay to an essentially field independent level at large inductions B. The new critical current function, Jc(‖B‖), consists of a constant plus a field dependent term of the Kim model type. Analytical expressions for internal induction profiles and the entire shape of major magnetization loops, as well as the initial branch, are derived for the infinite slab geometry. As an illustration it is shown that the new model gives a precise overall description of a magnetization loop measured for melt processed YBa2Cu3Ox.

The Poisson-Lie structure of nonlinear O(N) sigma -model by using the moving-frame method

We discuss the Poisson-Lie structure of the integrable nonlinear O(N) sigma -model with the moving-frame method. The corresponding r- and s-matrices are given explicitly. We also perform the gauge transformation for the Lax potential and the r and s matrices. Furthermore, we discover that the field-dependent terms in our r- and s-matrices only depend on the Riemannian connection of the target manifold.

Frequency Dependence of T1and T2Relaxation Times of Water in Normal and Tumoral Lung Tissues. T2Relaxation Time Evidence of Water Different Chemical Shifts and Exchange Rates.

Abstract Water 1H relaxation times, T1 and T2, have been measured at different magnetic fields for a total of 22 samples of normal and tumoral lung tissues taken away just after surgery. Results indicate that the average T1 values increase continuously with the inverse of the square root of the resonance frequency. The opposite trend is manifested for the average T2 values, which decrease continuously with the square of the frequency. We interpret the anomalous frequency dependence of T2 by introducing in the relationship a field dependent term. This term is indicative of the presence of a minimum of two kinds of water molecular surroundings in both normal and neoplastic lung tissues. The upper limits of the exchange rates are derived in this way. The values of these exchange rates are different for normal and neoplastic tissue.

Proton nuclear magnetic resonance lineshapes and transverse relaxation in a hydrated barley protein

In many hydrated biopolymer systems proton NMR lineshapes consist of a broad component and a narrow component. It is often assumed that the narrow component arises from water and that its lineshape arises from nuclei in the motionally narrowed regime. For the model cereal protein system, C-hordein–water, the effects of magnetic field strength, magic-angle spinning and 90–90 and 90–180 pulse sequences are examined. It is shown that the narrow components contain contributions from both static dipolar interactions and field-dependent terms. It is therefore concluded that simplistic interpretations of the origins of the relaxation mechanisms in terms of motionally narrowed models are not suitable.

LOW TEMPERATURE SPECIFIC HEAT OF YBa2Cu3O7

We show specific heat data in magnetic fields to B = 8T on new polycrystals with different oxygen content and compare them with earlier results. The analysis reveals a field dependent residual linear term which is discussed within theoretical models of Bulaevskii and for a spin-glass.

Construction of anomaly functional and current algebra

An iterative method is used to construct the anomaly functional. The functional is a non-local functional of the gauge fields only. Some consequences of the functional are studied; in particular it is shown that the anomaly functional contributes to the commutators of the charge densities. in 1 + 1 dimensions, the usual Kac-Moody extension term appears, in agreement with previous results. In 3 + 1 dimensions, in addition to the gauge field dependent term, we uncover a contribution of the functional to the triple commutator of the charge densities. An infinite-dimensional Lie algebra that incorporates this contribution is proposed.

Infrared laser stark shift spectroscopy in ammonia

The Stark effect in ammonia has been theoretically and experimentally analyzed using lead salt tunable diode laser absorption spectroscopy and CO2 laser absorption spectroscopy of several absorption lines around 1050 cm−1 applied to an all-optical sensor for measuring of electric field strength. Measurements of the Stark splitting effect of theaR(5,K) ammonia lines forK=1–5 as well as for the sR(3,K) lines forK=0–3 have been made at Doppler broadening pressures and for several different electric field strengths. Theoretical electric field dependent energy levels have been evaluated by diagonalization of a 6×6 energy matrix constructed using both electric field independent and dependent terms. From the theoretical analysis the resolution can be predicted and optimized both in the Doppler broadened and in the pressure broadened regimes. The predicted resolution is 0.5% at an electric field strength of 20 kV/cm. The theoretical calculations and the experimental data recorded with the tunable diode laser system were compared with independent measurements made with a CO2 laser system. The agreement between experimentally recorded and theoretically calculated spectra is good which indicates that the theoretical model is satisfactory for our purposes. The contribution from the normally forbidden ssR(5, 3) ammonia line to the absorption at theP(12) CO2 laser line in the 9 μm band is briefly discussed.

Anomalous anisotropies and field dependencies of the muon Knight shift and the relaxation rate in monocrystalline Bi

The angular dependence of the muon Knight shift,Kμ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothKμ and the second moment,M2, are field dependent and involveP40(cos θ) andP43(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM2 is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution around the interstitial site.

Anomalies of the heterotic σ-model in a curved superspace of two-dimensional (1, 0) supergravity and the heterotic string effective action

The covariant (in the σ-model sense) background field method for calculating anomalies of the heterotic σ-model is developed in a curved superspace of two-dimensional (1, 0) supergravity. The results of the explicit calculation for the superconformal anomaly up to five loops are found to be in agreement with the known facts about the heterotic string effective action, though our five-loop calculation is only partial for the gauge field dependent terms. This supports Tseytlin's ansatz for the effective action to the case of the heterotic string theory and provides a straightforward way for calculating the action itself.

Brans-Dicke Cosmology with a Scalar Field Dependent Cosmological Term

Brans-Dicke Cosmology with a Scalar Field Dependent Cosmological Term

Brans-Dicke Cosmology with a Scalar Field Dependent Cosmological Term

We propose a cosmology based on the Brans-Dicke theory with a cosmological term dependent in the scalar field. It is shown the existence of a solution in a Robertson-Walker metric that does not suffer from any unnatural fine tuning in the very early Universe such as the horizon, homogeneity, isotropy and flatness problems and does not present any difficulty concerning the GUTs magnetic monopoles.

Enhancement of forbidden nuclear β-decay by low-frequency electromagnetic fields

Nuclear β-decays that are forbidden by angular momentum and/or parity selection rules can be significantly enhanced by external electromagnetic fields. The effect is largely nonperturbative in nature, with a governing intensity parameter that becomes larger at long wavelengths. FIR radiation is a focus of interest for inducing the effect. An examination is done here of the field-dependent terms which lead to forbiddenness removal in β-decay. These terms come primarily from field interaction with the initial and final nuclear charges, and from the longitudinal field interaction term for the β-particle. Relevant astrophysical environments are discussed in which the effect can occur.

Spin-lattice relaxation in Co complexes of low symmetry

Spin-lattice relaxation times for 59Co contained in several low symmetry cobalt complexes are reported. Measurements have been made at two field strengths and, in the case of one complex, in several solvents. Some complementary measurements of 14N relaxation times on the same complexes are also reported. Linewidth measurements have been made to obtain T 2 values. The relaxation mechanisms depend on the solvent. In a “weakly hydrogen bonding” solvent (acetonitrile) quadrupolar and scalar relaxation through spin coupling to 14N are the most important mechanisms. Reasonable agreements between experimental and calculated relaxation times at low magnetic field can be obtained using experimental solid state quadrupole coupling constants, spin-spin coupling constants from 15N data, 14N T 1 values, and correlation times consistent with those obtained from the Debye formula. In these cases T 1 for 59Co is greater than T 2. In hydrogen bonding solvents an additional field dependent term is necessary. Both T 1 and T 2 are affected eliminating the possibility of a chemical exchange process. The field dependent term is associated with chemical shift anisotropy involving the off diagonal (antisymmetric) terms in the chemical shielding tensor. This mechanism requires that T 1 be less than T 2. The experimental data are consistent with this prediction.

Soft gauge algebras

Gauge transformations whose algebra closes only modulo field dependent terms (soft gauge algebras) are studied in detail. The results are explicitly applied to a supersymmetric gauge theory, to gravity and to conformal gravity, all seen as gauge theories overx-space; the obvious applications to supergravity are pointed out. A consistency requirement for the gauge transformations of those fields which appear in the algebra is seen to rule out “local translations” as independent gauge transformations.