Intermediate Wavelength Research Articles

Non-neutral plasma compression to ultrahigh density

Oscillations of a cold, homogeneous, non-neutral plasma spheroid are considered. A new class of purely compressional, large-amplitude, nonlinear oscillations is found. With a periodically time-varying external electrostatic quadrupole and a static magnetic field, such oscillations periodically can produce arbitrarily large plasma densities with only a modest swing in the applied quadrupole. In limiting cases, one- to three-dimensional plasma oscillations are true normal modes, requiring no variation of the applied quadrupole. For appropriate parameters, peak density is associated with a very ‘‘soft core,’’ so that an extremely high density is associated with a very modest size at minimum density. Further, cold-plasma stability is examined for these cases. For three-dimensional oscillations, all modes are stable. For two-dimensional oscillations, modes with intermediate axial wavelengths are not examined in detail. Long-axial-wavelength modes are found to be unstable only for small oscillation amplitudes. These modes are stable at sufficiently large oscillation amplitude. Those modes with a very short axial wavelength are always stable. Thus, it is very likely that extremely high densities may be produced in a compact system.

Ultrafast energy transfer in LHC-II trimers from the Chl a/b light-harvesting antenna of Photosystem II

Time-resolved absorption difference profiles were obtained for LHC-II trimers, isolated from Photosystem II in spinach with n-dodecyl β- d-maltoside, using one-color and two-color pump-probe techniques. The one-color isotropic signals are predominantly excited state absorption at 640 nm, and a combination of photobleaching and stimulated emission at wavelengths ≥ 665nm. At intermediate wavelengths, dynamic red-shifting due to downhill energy transfer among the chlorophyll (Chl) spectral forms produces a bipolar signal, in which prompt photo-bleaching/stimulated emission is superseded at later times by excited state absorption. Triexponential analyses of these profiles yield the lifetime components 2–6 ps (associated with the spectral shifting), 14–36 ps (possibly due to energy transfer between LHC-II monomers), and several hundred picoseconds. The one-color anisotropy decays are resolvable at 665–675 nm, with lifetimes of 4.3 to 6.3 ps. They are unresolvably fast (i.e., exhibit subpicosecond lifetimes) at 640–650 nm. The two-color isotropic absorption difference signals show clear spectral evolution arising from equilibration among the LHC-II spectral components for excitation wavelengths shorter than 670 nm. However, most of this spectral evolution occurs within less than 2.5 ps. No resolvable anisotropy decay was observed in the two-color experiments. Taken together, the one-color and two-color experiments indicate that both picosecond and subpicosecond energy transfer steps occur in this antenna. The faster processes appear to dominate the spectral equilibration; slower processes occur in isoenergetic energy transfers among the longer-wavelength Chl a spectral forms that absorb between 665 and 675 nm. The values of the long-time anisotropic r( x), measured in the one-color and two-color experiments, are qualitatively consistent with static linear dichroism spectra of these preparations.

The coupling of interfacial instabilities and the stabilization of two-layer annular flows

In this paper the stability of annular pressure-driven parallel flows of two liquids sandwiching a free cylindrical interface is considered. For small to moderate Reynolds numbers, the interface is susceptible to capillary and interfacial wave instabilities, the latter instability caused by a jump in viscosity at the interface. It is shown that favorable velocity profiles in both liquids may stabilize capillary breakup of the interface and suppress the axisymmetric interfacial wave instability. A long-wave analysis leads to the physical mechanism responsible for stabilization of capillary breakup. This physical mechanism is a generalization of that by which capillary breakup is stabilized by interfacial shear in an annular film of a single liquid. Stabilization of intermediate wavelengths is studied with a mechanical energy analysis, which leads to a description of the energetic processes at work.

The mechanism of self-sustainment in collisional drift wave turbulence

Although collisional drift waves in a sheared slab configuration are linearly damped, the corresponding turbulence is self-sustaining if initialized at an electrostatic potential fluctuation amplitude of eφ/T≳0.3ρs/Ln, much less than that of observed fluctuations. Within the context of two-dimensional sheared slab magnetic geometry, computational investigations into the amplitude threshhold and the nonlinear mode structure reveal the shear-induced self-organization that is responsible for efficiently tapping the free energy in the temperature and density gradients. They also show that the turbulence is nondiffusive in character, since the important assumptions behind turbulence-as-diffusion are all violated. Many important features of experimentally observed tokamak edge fluctuations are reproduced by these single resonant surface nonlinear dynamics, suggesting that model components not treated may have an effect more additive than qualitative. The ingredients giving rise to self-organized turbulence, shear-localized long-wavelength modes of some width Δ0<λ, and isotropic intermediate wavelength modes with λ∼Δ0, in direct, coherent interaction, are at least potentially shared by most of the viable candidates for anomalous tokamak transport. Consequently, such transport is unlikely to bear much resemblance to the simpler models currently in use.

Nonlinear kink mode dynamics in circular and noncircular pinches

It is shown that the global (free-boundary) m=1 kink instability of the ideal, magnetohydrodynamic (MHD) sharp boundary (surface current) pinch is stabilized by nonlinear effects, provided Be≲1 and βp<1, where βp=1+B2e−B2i and Bi and Be denote, respectively, the internal and external axial magnetic fields of the pinch, normalized to the poloidal magnetic field. The stabilization has to do with the bending of the interior, ‘‘frozen’’ field lines and associated volume currents induced in the pinch, and does not occur in a pure surface current model, which neglects these currents and only conserves the total magnetic flux through the pinch. It is suggested that the global, helical m=1 structures observed in various pinch experiments may have to do with the stabilizing mechanism above. The nonlinear stability has been calculated by means of a new approach to the bifurcated equilibria of the helical m=1 mode, and the method should also be useful in connection with other nonlinear, ideal MHD phenomena. The regime of nonlinear stability above corresponds to intermediate or short wavelengths of the marginal mode (ka≳1). In the opposite, long-wavelength regime, the ideal MHD model and the pure surface current model give similar results, predicting nonlinear instability for, e.g., the nearly marginal Kruskal–Shafranov mode in tokamaks, in agreement with previous theories. Effects of mode rotation as well as of a noncircular cross section of the pinch, modeling the Extrap [Fusion Technol. 16, 7 (1989)] configuration, have also been considered, extending the results of a previous, linear investigation [Phys. Fluids B 2, 1601 (1990)] to the nonlinear regime.

Propagation properties in short lengths of rectangular epoxy waveguides

The propagation loss and beam spreading in large-core epoxy ridge waveguides on a glass substrate at wavelengths ranging from 630 to 1550 nm have been measured. At the intermediate wavelengths, a loss floor of 1.2 dB/cm is observed which is caused by inclusions and wall imperfections. The theoretical and experimentally determined equilibrium numerical aperture is 0.65 and 0.29 and the modal dispersion is 5.1 and 1.0 ps/cm, respectively. The discrepancy is due to strong scattering. The scattering does not give rise to any noticeable mode mixing. The epoxy waveguides also provide a rapid filling of the modes which is attractive for modal noise suppression.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The two-dimensional tricritical Ising model in restricted domains with free boundaries

Using conformal field theory, we derive the connected two-point functions for all Z 2-even and odd operators with Kac indices ( p, q)=(1, 2) in the unitary minimal series, constrained to restricted domains with free boundaries (semi-infinite plane, infinite strip, disc, rectangle). Applying the result to the two-dimensional tricritical Ising model, we obtain the exact correlation functions for the energy density and the subleading magnetisation in the corresponding domains. This allows for a detailed analysis of finite-size and boundary effects on tricritical correlation lengths, structure factors, the specific heat and the subleading magnetic susceptibility in circular and rectangular geometries with free boundaries. Our results for the structure factors reveal an unexpectedly slow crossover from the apparent power-law behaviour at intermediate wavelengths to the bulk behaviour at small wavelengths.

The French program of circumterrestrial magnetic surveys using stratospheric balloons

The riddle propounded by numerous reports of sightings of silver and circular “unidentified flying objects” hanging in the sky of South Africa in northwest Pretoria was answered in the November 26, 1988, issue of the Pretoria News. UFO spotters had been watching two Infrared Montgolfiers (IRM) launched a few days earlier by the Centre National d'Etudes Spatiales (CNES) of France. Due to unexpectedly quiet weather conditions, the vehicles wandered for several days above South Africa before beginning their journeys across the Atlantic and Pacific oceans driven by zonal westward stratospheric winds near 25‐km altitude.One of these balloons was carrying a magnetometer payload in a first attempt at performing a quasi‐circumterrestrial continuous magnetic anomaly profile. This experiment formed part of a program initiated in 1984 by the Département de Géomagnétisme of the Institut de Physique du Globe de Paris to determine the intermediate wavelength (50–1000 km) magnetic anomaly field of crustal and lithospheric origin.

Baroclinic instability in a two-layer, vertically semi-infinite domain

A quasi-geostrophic two-layer system with uniform, but different, shears and stratifications in two layers is examined for the occurrence of baroclinic instability. A derived necessary condition for instability requires that the shear in the upper, semi-infinite layer does not exceed a certain value (related to the stratification). For each configuration of the basic flow, there appear two short and two long neutral modes as well as a decaying and a growing mode at intermediate wavelengths. The short neutral modes are bound to either the surface or the interface, the long neutral modes to one or other of the layers. Instability appears if the foregoing modes propagate at a similar velocity. The depth of the waves is shown to be of less importance in the framework of potential vorticity dynamics. For some configurations, the growth rates surpass those of the classical Eady problem. Finally some consideration is given to the linkage between these results and the formation of polar lows. DOI: 10.1034/j.1600-0870.1991.t01-4-00003.x

Influences of artificial lighting on the seaward orientation of hatchling loggerhead turtles Caretta caretta

The seaward orientation behavior of hatchling loggerhead turtles Caretta caretta when exposed to five different artificial light sources (high-pressure) and low-pressure sodium vapor, and yellow, red, and white incandescent lamps) was examined. Each light source affected hatchling sea-finding performance either in direction of orientation or width of dispersion. Hatchlings were attracted to light sources emitting short-wavelength visible light and long-wavelength sources that excluded intermediate wavelengths. A negative response was observed toward sources emitting predominately yellow light. For this reason, low-pressure sodium vapor (LPS) luminaires, which emit only yellow light, are expected to affect loggerhead hatchling sea-finding minimally, if positioned behind the primary dune. LPS luminaires positioned between emerging hatchlings and the ocean, however, will disrupt hatchling orientation.

A local stability analysis of astronomical disks

Abstract A fifth-order dispersion relation describing the local stability of a differentially rotating flow against small perturbations is derived. Finite viscosity and conductivity and both vertical (parallel to the rotation axis) and radial gradients in density, temperature and pressure are included. A general form is assumed for the equation of state, although this is not exploited in the paper. A number of special cases are studied: with negligible viscosity and conductivity, it is shown that modes can often be separated into two high frequency (modified acoustic), two intermediate frequency (combined inertial and internal waves) and a low frequency mode. In convectively unstable situations the intermediate frequency modes may be replaced by a damped/growing pair of instablities. Various criteria for mode excitation are given. It is shown that viscosity always inhibits instability at very short wavelengths, while non-zero conductivity may destabilize the flow. At intermediate wavelengths viscosity cou...

Limitations of the long‐wavelength components of the North American magnetic anomaly map

The magnetic anomaly map of North America and its related data set provide the opportunity not only to view the obvious short‐wavelength anomalies (&lt;300 km) in a continental context, but to isolate and analyze the longer wavelength anomalies. However, care must be used in analyzing the longer wavelengths because of the effects of noncrustal sources on these anomalies. Inversion of the anomalies into lateral variations of crustal magnetization suggests that the long‐wavelength anomalies (&gt;2600 km) are strongly affected by core field components that have not been completely removed from the North American data set. Furthermore, the piecewise matching of the magnetic anomalies of adjacent survey areas in the map compilation has contaminated the intermediate wavelength anomalies (300–2600 km).

Holocene glacial rebound and sea-level change in NW Europe

SUMMARY Observations of Late Pleistocene and Holocene sea-level change relative to the crust exhibit very considerable variations across NW Europe in consequence of the response of the Earth’s crust to the deglaciation of Fennoscandia and of the water added to the oceans from the melting of all Late Pleistocene ice sheets. Inversion of sea-level observations from a site near the centre of the Fennoscandian ice sheet and from three sites located beyond the margin of the ice sheet at the time of maximum glaciation yield a range of plausible models for the Earth’s response and for the ice models. Further constraints on this range of models is placed by a comparison of observed sea-levels with predicted values at other sites near the former ice sheet margins. The resulting mantle parameters are: upper mantle viscosity (3-5) X 10’’ Pa s; lower mantle viscosity (2-7) X loz1 Pa s; lithospheric thickness 100150 km. These values represent effective parameters that describe the response of the Earth to surface loading of short to intermediate wavelengths on a time-scale of 104yr. The lower mantle viscosity is poorly constrained but the marked increase from upper to lower mantle is a characteristic of all plausible solutions. The inversion places a constraint on the total volume of ice in the Fennoscandian ice sheet such that the equivalent sea-level rise from this contribution is about 13-14 m. A less well-determined constraint of about 10 m equivalent sea-level rise is suggested for the Barents-Kara ice sheet. The inversion also indicates that a small amount of melt-water, from ice sheets far away from Europe, continued to be added into the oceans during Late Holocene time so as to raise the equivalent sea-level by about 3 m during the past 6000 yr, consistent with similar inversions of data from sites in the Australian and Pacific regions.

Absolute spectral irradiance scale in the 700–2400 nm spectral range

An absolute spectral irradiance scale for the 700-2400 nm range has been developed. The scale is based on an absolute radiometer and a series of interference filters, which were used to determine the spectral irradiance of quartz halogen incandescent lamps at a number of discrete wavelengths. Values at intermediate wavelengths have been obtained by interpolation. This new scale was compared with NIST standards based on blackbody radiance. Both scales were found to agree within +/- 1%.

Spectral interpolation and downward continuation of marine magnetic anomaly data

A two‐ or three‐dimensional treatment of magnetic anomaly data generally requires that the data be interpolated onto a regular grid, especially when the analysis involves transforming the data into the Fourier domain. We present an algorithm for interpolation and downward continuation of magnetic anomaly data that works within a statistical framework. We assume that the magnetic anomaly is a realization of a random stationary field whose power spectral density (PSD) we can estimate; by using the PSD the algorithm produces an array incorporating as much of the information contained in the data as possible while avoiding the introduction of unnecessary complexity. The algorithm has the added advantage of estimating the uncertainty of every interpolated value. Downward continuation is a natural extension of the statistical algorithm. We apply our method to the interpolation of magnetic anomalies from the region around the 95.5°W Galapagos propagating rift onto a regular grid and also to the downward continuation of these data to a depth of 2200 m. We also note that the observed PSD of the Galapagos magnetic anomalies has a minimum at low wave numbers and discuss how this implies that intermediate wavelength (65 km &lt; λ &lt; 1500 km) magnetic anomalies are weaker than suggested by one dimensional spectral analysis of single profiles.

The nonlinear theory of thermal instability - The intermediate- and short-wavelength limits

The nonlinear evolution of thermally unstable disturbances in a plasma is investigated within the framework of one-dimensional fluid equations. The processes of heating and radiative cooling of the optically thin plasma are taken into account. The limits of intermediate and short wavelengths are considered. In these cases, the characteristic time scale of thermal processes is considerably longer than the acoustic time scale, so that unstable density and temperature perturbations grow in pressure equilibrium with their surroundings. This fact makes it possible to simplify the set of equations describing the instability, and, by using Lagrangian coordinates, to investigate the nonlinear dynamics of the instability analytically. The case of the intermediate-wavelength limit, where the linear theory of Field predicts the maximum growth rate, which presents the most important (and the simplest) case, is investigated in detail.

A theory for triple point spacing in overdriven detonation waves

Overdriven detonations for which the chemistry is modeled by one-step Arrhenius kinetics are examined in the asymptotic limit θ → ∞ where θ is the activation energy. A stability analysis is carried out in which the disturbances have a wavelength ∼ θδ and evolve on the time scale θδ u f , where δ is the detonation wave thickness and u f its speed. Instability is identified in which the growth rate is a monotonically decreasing function of wavenumber. A similar analysis carried out previously for wavelengths ∼θδ predicts a growth rate that is a monotonically increasing function of wavenumber. It follows that there is an intermediate wavelength for which the growth rate is a maximum, and it is shown that this has magnitude ∼θ 2 3 δ . It is argued that this wavelength will be selected from the continuum of values present in an arbitrary initial disturbance and will define the initial spacing of the triple points characteristic of unstable detonations.

Extension of Landau-Ginzburg free-energy functionals to high-gradient domains.

The Landau-Ginzburg (LG) free-energy-gradient theory is extended to account for domains of intermediate wavelengths. The extension is nonlocal but preserves the universal features of the LG theory, has the same level of complexity, and reduces to it in the small-gradient limit. It also enables one to gain a meaningful insight into the microstructure of a system.

Excited state properties of the N-(deoxyguanosin-8-yl)-2-aminofluorene adducts.

The spectroscopic characteristics of adducts derived from the covalent binding of the carcinogen 2-aminofluorene to the C8 position of deoxyguanosine [N-(deoxyguanosin-8-yl)-2-amino-fluorene, dGuo-C8-AF], and from an adduct of similar structure formed with the synthetic polynucleotide poly(dG-dC).poly(dG-dC), were investigated. At 77 K both adducts are characterized by well-defined and rather narrow fluorescence emission spectra with maxima at 370 and 390 nm characteristic of the aromatic, monomolecular 2-aminofluorene (AF) residue. In contrast, at room temperature, the fluorescence is characterized by a broad, structureless emission band with a maximum at 460 nm in aqueous mixtures, shifting to 415 nm in solvents of lower polarity (100% propanol); the maxima are located at intermediate wavelengths in solutions of different propanol/water compositions, and this emission is attributed to an excited state complex (exciplex). The fluorescence quantum yield decreases when either the solvent polarity or the temperature are increased, varying from 5.4% (100% propanol) to 0.04-0.05% (100% H2O). The fluorescence decay profiles of dGuo-C8-AF adducts (measured at the National Synchrotron Light Source facility at the Brookhaven National Laboratory) can be roughly, but not exactly, modeled in terms of two exponential decay components in the range of about 0.3-1.0 ns with the propanol concentration greater than 60%; at lower propanol concentrations, a single short lifetime is observed and in 100% water solutions its value is 0.08 ns. The shorter lifetime, favored in solvent mixtures of higher polarities, is attributed to an exciplex with significant charge-transfer character.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffusion effects in calcium-regulated strain fields

The Goodwin-Trainor equations for cellular morphogenesis, based on calcium ion regulation of the visco-elastic properties of the cellular cortex, are generalized to the situation where the concentration of calcium ions (free plus bound) is allowed to change locally. A stability analysis is presented which shows that the generalized equations are also stable against perturbations at low and high wave lengths and may, for certain parameter values, develop instabilities at intermediate wave lengths.