Photon Flux Ratio Research Articles

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes.

Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.

Radiant refrigeration by semiconductor diodes

Dousmanis et al. [Phys. Rev. 133, A316 (1964)] demonstrated that GaAs light-emitting diodes could produce a cooling effect if the quantum efficiency (ratio of photon flux to junction current) is very close to unity (e.g., >0.97). Here, it is pointed out that for narrow-bandgap semiconductors, the quantum efficiency need not be so high to produce cooling. Also, for narrow-bandgap semiconductors there is an additional cooling mode in which the reverse-biased diode cools its radiant environment by absorbing infrared radiation. Maximum cooling rates per unit of junction area are on the order of n2σT4, where n is the index of refraction, σ is the Stefan–Boltzmann constant, and T is the temperature. For small cooling rates the efficiency for cooling can approach the limit imposed by the second law of thermodynamics.

X-ray lines of helium-like oxygen and neon in the solar corona

Line ratios from the helium-like ions O vii and Ne ix are useful as plasma diagnostics for both flaring and nonflaring solar coronal active regions. The photon flux ratio, R, of the forbidden 1s/sup 2/ /sup 1/S/sub 0/-1s2s /sup 3/S/sub 1/ line to the intercombination 1s/sup 2/ /sup 1/S/sub 0/-1s2p /sup 3/P/sub 1/ line in O vii is useful as a density diagnostic at coronal temperatures of approx.2 x 10/sup 6/ K. If the electron density n/sub e/ is less than n/sub e/*roughly-equal3 x 10/sup 9/ cm/sup -3/, Rroughly-equalR/sub 0/ (where R/sub 0/ is the low-density limit), and R decreases with increasing density. Uncertainties in R and R/sub 0/ both contribute to uncertainties in n/sub e/. R/sub 0/ uncertainties are especially important for nonflaring plasmas having n/sub e/roughly-equaln/sub e/*. We analyzed 29 nonflare X-ray spectra, each a sum of approx.10 scans by the SOLEX B spectrometer on the USAF P78-1 satellite, to conclude that R/sub 0/ is in the range 3.7--4.1 G, the photon flux ratio of the forbidden plus intercombination line to the resonance 1s/sup 2/ /sup 1/S/sub 0/-1s2p /sup 1/P/sub 1/ line, can be used as an indicator of whether or not the emitting plasma is in amore » state of ionization equilibrium. For both O vii and Ne ix, G is modified by resonance scattering in the solar atmosphere, which lowers the resonance line flux. This scattering allows us to estimate the column densities of O vii and Ne ix in the corona above the active region source. We also estimate the value of G in the absence of resonance scattering.« less

Extreme ultraviolet spectrum of the solar flare of 2114 UT March 27, 1967

Scanning spectrometer measurements in the range 1310–270 A, observed from the satellite OSO 3, are reported for the solar flare of 2114 UT March 27, 1967. This flare was a long lasting sequence of bursts with EUV spectra consisting of enhanced lines and recombination continua normally emitted from the chromosphere and chromosphere-corona transition region, with unusually small increases in lines normally emited from the corona. An EUV flare spectrum is presented and suggested as one example for interpreting broadband observations of EUV bursts. Any broadband continuum other than known recombination continua contributed less than 6 % of the meassured line and hydrogen recombination continua in the range 270–1310 A. The ratio of photon flux of Ciii 1176 A to that of Ciii 977 A was 0.86, which suggests an ambient density in the region of emission greater than 1012 cm-3 at temperatures near 60000 K.

Experimental investigation of radiation fronts

The dynamical properties of plane radiation fronts are investigated. Five types of steady radiation fronts are possible, depending on the ratio of photon flux to absorber density. In an associated experiment unsteady dissociation fronts are produced. The measurements are compared with calculations based on a modified method of characteristics.