Moderate Field Strengths Research Articles

Die Übertragung der LCAO-Interpolationsmethode auf Gitterelektronen im Magnetfeld / The LCAO Interpolation Method Applied to Crystal Electrons in a Magnetic Field

The splitting of the energy levels of crystal electrons in homogeneous magnetic fields of moderate strength is described in terms of the matrix elements of the LCAO method. The matrix elements are regarded as adjustable parameters connected with the energy structure of the crystal electron without magnetic field. The translational symmetry of the crystal in a magnetic field is exactly taken into account, and the matrix elements contain the symmetry of the point group of the material. The resulting eigenvalue equation is a system of linear difference equations. In analogy to the treatment of a similar one-dimensional difference equation for the differential equation of Mathieu type the eigenvalues result from an investigation of a vector recursion formula. In connection with this method the limiting cases magnetic field and crystal potential approaching zero are discussed in short

Effect of electric fields on the daytime high-latitudeEandFregions

We have obtained solutions of the coupled continuity, momentum, and energy equations for NO+, O2+, and O+ ions for conditions appropriate to the daytime high-latitude E and F regions. Owing to the rapid increase of the reaction O+ + N2 → NO+ + N with ion energy, high-latitude electric fields and consequent E⊥ × B drifts deplete O+ in favor of NO+. For electric field strengths less than about 10 mV m−1 the depletion of O+ is small, and the altitude profiles of ion density are similar to those found at mid-latitudes. However, for moderate electric field strengths (∼50 mV m−1), NO+ is substantially increased in relation to O+ and becomes an important ion throughout the F region. For these conditions the electron density has a tendency to become nearly constant with altitude in the range 160–360 km. For large electric fields (∼200 mV m−1), NO+ completely dominates the ion composition to at least 600 km, decreasing at high altitudes with a diffusive equilibrium scale height. Since the overall F region electron density decreases markedly with increasing electric field strength, it appears that high-latitude, daytime electron density troughs are directly related to the presence of ionospheric electric fields. In addition, since increases in the N2 density or the N2 vibrational temperature also affect ion composition and electron densities in a manner similar to that of electric fields, the observed daytime troughs may arise from both processes acting simultaneously.

Possible mechanisms of corona discharge involved in biogenesis.

ELECTRIC discharges are very efficient1 in synthesising amino acids and other organic compounds in conditions which simulate the atmosphere of the primitive Earth. Consequently, they may have been of considerable importance in the origin of life. Corona emission from pointed objects is probably1 the most effective form of electric discharge involved in prebiotic synthesis. Clearly, coronae occurring in the vicinity of the oceans would be of particular importance, but even though land surfaces generally possess features of sufficient irregularity to permit corona emission in naturally occurring electric fields of moderate strength, it is not obvious that suitable protuberances exist at the ocean surface.

Switching of optical rotatory power in ferroelectric 5pbo 3Ge02 single crystal

An enantiomorphic transition was observed for the first time by observing Airy's spirals of the oppositely polarized ferroelectric 5PbO 3GeO2 single crystals, which were grown by the Czochralski method. Switching time follows an exponential law at moderate field strengths and a power law at higher field strengths.

Impact ionization in p-type InSb

Impact ionization in p-InSb is shown to be initiated by injected electrons. At sufficiently high average electric field strength. 1 kV/cm, impact ionization begins next to the cathode. An impact ionization wavefront forms there and propagates along the sample with a velocity ν ii =3·2×10 8 cm/sec at 77 K. At moderate field strengths an impact ionization wavefront is initiated at some plane between the cathode and anode. Before its initiation in such a case, injected electrons exclusively propagate in a well defined front at 10 7 cm/sec, then when the field ahead of the injected front reaches ∼490 V/cm, impact ionization is initiated and the impact ionization wavefront propagates to the anode with ν ii . After the impact ionization wavefront reaches the anode, carrier density grows exponentially to a steady-state magnitude. The growth rate dependence on field strength is best expressed by g(E) φ exp (0·8×10 6/ E 2). Thus the energy dependence of the electrons during impact ionization in p-InSb at 77 K appears to be Maxwellian.

FIELD-ASSISTED REEMISSION OF CHARGE CARRIERS FROM SHALLOW IMPURITY CENTERS IN GERMANIUM

Field-assisted reemission has been observed at low temperatures for charge carriers captured by shallow ionized donor and acceptor states in germanium. The observed behavior is well explained by the three-dimensional Poole-Frenkel theory at moderate field strength (400–1000 V cm−1); at higher fields, other effects dominate the reemission process.

Theory of Magnetized Solid Helium Three

Experiments on the thermodynamic properties of magnetized solid ${\mathrm{He}}^{3}$ at accessible temperatures and fields are shown to be a conveneint and powerful method of studying the nature and form of the nuclear spin interaction in solid ${\mathrm{He}}^{3}$. In particular, it should be possible to determine whether these properties are described in a satisfactory way by an exchange-interaction model assumed to be proportional to the scalar product of nuclear spin vectors of nearest-neighbor atoms of the solid. Independently of this model, it is shown that measurements of the magnetic modification of the melting pressure, at low but readily accessible temperatures and moderate field strengths, correspond to almost absolute measurements, of good accuracy, of the nuclear paramagnetic susceptibility of the solid at melting. The entropy diagram of the magnetized model solid enables one to describe with precision the isothermal magnetization and adiabatic demagnetization processes, which should contribute to the verification of the model through their experimental investigation. The increase in the heat capacity on magnetization is large enough to be maesured accurately and to test the validity of the model. An interesting effect is that the thermally anomalous unmagnetized solid becomes normal on magnetization, over a finite and low but accessible temperature range, and at intermediate field strengths. Experimental investigations of various equilibrium thermal properites of magnetized solid ${\mathrm{He}}^{3}$ could thus contribute significantly toward the elucidation of the behavior of its nuclear spin system which alone determines its thermal properties over the currently accessible low temperatures.

Drift Velocity and Energy of Electrons in Liquid Argon

Measurements are reported of the energy required for injection of an electron into liquid argon and of the drift velocity of electrons in liquid argon at moderate field strength. It is found that the barrier to electron injection is ---0.33 eV, in moderately good agreement with a theoretical estimate of ---0.45 eV. The observed field dependence of the drift velocity is in good agreement with the recent calculations of Lekner.

Gas content and cathode emission changes in cutoff electron tubes

This work studies the effect of pulsed electric field (PEF) treatment at moderate and high field strengths (E = 0.8 kV/cm & 5 kV/cm) prior and during alcoholic fermentation (AF) of red grapes on improving different parameters of pre-treated extracts: pH, °Brix, colour intensity (CI), total polyphenols content (TPI) of Cabernet Sauvignon red wine. Similar trends were observed for treating grapes using moderate and high electric field strength on the enhancement of CI and TPI of the wine after AF. The application of PEF using moderate strengths at different times during cold maceration (CM) (0, 2 and 4 days) was more efficient for treatment during CM. The treatment during AF showed lower extraction rate compared to treating during CM and prior to AF. Our results clearly show that the best time for applying the PEF-treatment through the red fermentation is during the CM step.

Mass telespectrometry: M. De Rossi, Ricerca Sci., 3 (IIA), (1963), 497

This work studies the effect of pulsed electric field (PEF) treatment at moderate and high field strengths (E = 0.8 kV/cm & 5 kV/cm) prior and during alcoholic fermentation (AF) of red grapes on improving different parameters of pre-treated extracts: pH, °Brix, colour intensity (CI), total polyphenols content (TPI) of Cabernet Sauvignon red wine. Similar trends were observed for treating grapes using moderate and high electric field strength on the enhancement of CI and TPI of the wine after AF. The application of PEF using moderate strengths at different times during cold maceration (CM) (0, 2 and 4 days) was more efficient for treatment during CM. The treatment during AF showed lower extraction rate compared to treating during CM and prior to AF. Our results clearly show that the best time for applying the PEF-treatment through the red fermentation is during the CM step.

Collective Behavior in Solid-State Plasmas

The conditions for the existence of plasma wave instabilities in the plasma formed by the electrons and holes in semiconductors are discussed. The dispersion relations for both the high-frequency optical mode in which electrons and holes move out of phase, and the low-frequency acoustic mode in which electrons and holes move in phase are calculated. Growing acoustic waves are shown to occur for a sufficiently large relative drift velocity of the electrons and holes, and the boundary between growing and damped waves is determined for various electron-hole temperature ratios. Growth rates are calculated for several cases of interest; when the influence of impurity and phonon scattering on the electron-hole behavior is taken into account it is concluded that InSb is perhaps the most promising semiconductor in which to observe such instabilities. An investigation of the hole and electron temperatures and the relative electron-hole drift velocity as a function of field strength is carried out for InSb. It is shown that moderate field strengths (\ensuremath{\sim}100 v/cm) suffice to produce electron-hole drifts of the required order of magnitude for the observation of plasma wave instability; however, the scattering mechanisms present are sufficiently effective that it appears marginal whether the other condition (long hole relaxation times) necessary for the observation of the plasma wave instability is achievable in practice. In an Appendix the conditions for the occurrence of similar plasma wave instabilities in semimetals are analyzed briefly.

Nonlinear Behavior of the Electrical Conductivity of a Slightly Ionized Gas

Attention is directed to the nonlinear relationship between the current density and field strength of an applied oscillating electromagnetic field. It is pointed out that the general solution of this problem obtained by Margenau is too complex for use in further analyses except for the limiting case of vanishing field strength. A further approximation is introduced which yields a relatively simple expression for the current-field strength relationship, valid for large frequencies and moderate field strengths. It is found that significant nonlinear effects may occur even at small field strengths if the gas density is sufficiently low. The effect of the nonlinearity is to increase that part of the current in phase with the applied field.

A shallow-liquid theory in magnetohydrodynamics

The non-linear and linear ‘shallow-water’ theories, which describe long gravity waves on the free surface of an inviscid liquid, are extended to the case of an electrically conducting liquid on a horizontal bottom, in the presence of a vertical magnetic field. The dish holding the liquid, and the medium outside it, are assumed to be non-conducting. The approximate equations are based on a small ratio of depth to wavelength, on the properties of mercury, and on a moderate magnetic field strength. These equations have a ‘magneto-hydraulic’ character, for in the shallow liquid layer the horizontal fluid velocity and current density are independent of the vertical co-ordinate.Some explicit solutions of the linear equations are obtained for plane flows and for axi-symmetric flows in which the velocity vector lies in a vertical, meridional plane. The amplitudes of waves in a dish, and the amplitudes behind wave fronts progressing into undisturbed liquid, are found to be exponentially damped, the mechanical energy associated with a disturbance being dissipated by Joule heating.The approximate non-linear equations for plane flow are studied by means of characteristic variables, and it appears that, because of the magnetic damping effect, there is less qualitative difference between solutions of the non-linear and linear approximate equations at large times than is the case when the magnetic field is absent. In particular, the characteristic curves depart only a finite distance from their ‘undisturbed positions’.

Zeeman Effect for PerturbedN2+Terms

The Zeeman effects for the perturbed terms in the $v=1 \mathrm{and} 3$ levels of the upper $^{2}\ensuremath{\Sigma}$ state of ${\mathrm{N}}_{2}^{+}$ have been investigated at various field strengths up to 27,000 gauss. At the points of maximum perturbation the Zeeman patterns are doublets for the moderate and high field strengths. At high field strengths the unperturbed lines, of the same $K$ value as the most perturbed lines, also become doublets under the influence of the magnetic field. This is attributed to a Paschen-Back effect. For $K$ values greater than those of the maximum perturbation point, all the lines exhibit an asymmetric broadening in the field. A consideration of the interactions with the perturbing $^{2}\ensuremath{\Pi}$ state gives an explanation of the patterns observed.