ON THE CONVERGENCE OF THE PARABOLIC APPROXIMATION OF A CONSERVATION LAW IN SEVERAL SPACE DIMENSIONS

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Scaling laws for plasma armatures in railguns

A methodology for deriving the electrical and thermodynamic properties of plasma armatures in railgun launchers is presented. The methodology is based on the solution to the one-dimensional, quasi-steady equations for the plasma armature. It is shown that the thermodynamic and transport properties for typical armature materials can be adequately represented by power-law curve fits in the temperature and pressure regimes of interest. To illustrate the methodology, detailed computations for both copper and aluminum armatures are performed. Some discussion is also presented for hydrogen armatures. It is shown that the armature properties predicted by the scaling laws agree very well with those derived from more detailed numerical solutions to the governing differential equations. It is shown that, for both aluminum and copper armatures, the electrical conductivity is a strong function of the current per unit rail height and a weak function of launcher geometry. This dependence is shown to be in reasonable agreement with experimental data compiled over a wide range of gun bore dimensions and operating conditions     

ON LACUNARY STATISTICAL CONVERGENCE OF ORDER α

In this article, we introduce the concept of lacunary statistical convergence of order α of real number sequences and give some inclusion relations between the sets of lacunary statistical convergence of order α and strong Nαθ(p)-summability. Furthermore, some relations between the spaces Nαθ(p) and Sαθare examined.     

Biexciton quantum coherence in a single quantum dot

Nondegenerate (two-wavelength) two-photon absorption using coherent optical fields is used to show that there are two different quantum mechanical pathways leading to formation of the biexciton in a single quantum dot. Of specific importance to quantum information applications is the resulting coherent dynamics between the ground state and the biexciton from the pathway involving only optically induced exciton/biexciton quantum coherence. The data provide a direct measure of the biexciton decoherence rate which is equivalent to the decoherence of the Bell state in this system, as well as other critical optical parameters.     

Scaling study for the performance of railgun armatures

A model is developed for investigating the performance of solid, plasma, hybrid, and transitioning armatures as a function of railgun geometry and gun operating conditions. The two figures of merit used in the calculation are the armature efficiency and the maximum velocity. Effects investigated include armature parasitic mass, armature resistance, friction, ablation drag, and, for the hybrid armature, gap growth. The model is applied to study how armature performance scales with projectile mass, or correspondingly bore dimension, and with gun current per unit rail height in the hypervelocity regime from 7 to 15 km/s. The model indicates that armature efficiency generally increases with projectile mass, whereas the maximum velocity for plasma and transitioning armatures is relatively insensitive to projectile mass. Calculations are also performed to determine the sensitivity of the model's predictions to uncertainty in key parameters, such as the ablation entrainment fraction, the skin friction coefficient, and the contact potential     

Two Dimensional Generalization of Raizer's Analysis for the Subsonic Propagation of Laser Sparks

An extension to two dimensions of Raizer's analysis for the steady state, subsonic propagation of laser sparks is presented. A solution in closed form is obtained for a simplified, two dimensional energy equation, yielding both axial and radial temperature profiles as well as the relationship between incident laser intensity, laser radius and propagation velocity. The propagation mechanism is assumed to be thermal conduction and radiation losses are included in a phenomenological manner. The solution is obtained for a laser spark propagating in a channel and therefore can be used to investigate the effect of a boundary on spark propagation. The solution also allows calculation of the radial heat conduction parameter A introduced by Raizer for use in one dimensional approximations. Sample calculations are presented for air sparks of .15 and .50 cm radius.     

Thermodynamic and electrical properties of railgun plasma armatures

A model including the nonideal effects is presented that describes the plasma composition, equation of state, internal energy, and electrical conductivity for a very dense and relatively cool plasma like that which exists in a railgun plasma armature. Results are presented for four elements of specific interest for plasma armatures-hydrogen, lithium, aluminum, and copper-for pressures ranging from 1 to 1000 atm and temperatures ranging from 10000 to 50000 K. The results are presented in a graphical format which should prove useful to modelers and experimentalists investigating plasma armatures     

How does cold constrain life cycles of terrestrial plants and animals?

Short summer seasons with low thermal energy input characterise polar ecosystems. Climatic variables and physical isolation of terrestrial habitats act as selective filters which must be passed to allow colonisation, establishment and survival in these extreme environments. Life history studies of the terrestrial biota of such ecosystems give little evidence of adaptive responses to low temperatures having evolved in situ, even though behavioural, ecophysiological and biochemical features allowing tolerance of the likely extremes are well-developed. Observed life history strategies are often consistent with the general predictions of adversity (A) or stress (S) selection. However, biota successful in these extreme environments may be better-grouped by the lack of particular life history features, rather than common possession.     

SOME GEOMETRIC PROPERTIES OF A NEW DIFFERENCE SEQUENCE SPACE INVOLVING LACUNARY SEQUENCES

In this paper, we define a new generalized difference sequence space involving lacunary sequence. Then, we examine k-NUC property and property （β） for this space and also show that it is not rotund where p = （pr） is a bounded sequence of positive real numbers with pr ≥ 1 for all r ∈ N.