Photoabsorption cross sections necessary for calculations of the equilibrium conditions in the stratosphere fall into two distinct classes: cross sections for molecular oxygen and ozone, which control the transmission of solar radiation; cross sections for minor atmospheric species which are optically thin to solar radiation, and which are needed to calculate their rates of dissociation.The principal absorption features of molecular oxygen are absorption bands of the Schumann-Runge system between 175 and 200 nm and a weak dissociation continuun~ which extends from 175 to 260 nnl. The band structure consists of many sharp rotational lines, and it is necessary to calculate cross sections using measured band parameters. Two measurements of the line widths for these bands have obtained large line widths (-1 cm-') indicating predissociation. The agreement between the two sets of data is good for only a few I~nes. This has in~plications in the calculation of the transmission of solar radiation to the lower stratosphere. The continua have been measured by four groups. The results agree, within the respective experimental errors, near 220 nm, but disagree near 250 nm.Ozone has a continuous absorption spectrum between 175 and 300 nm with band structure above 300 nm. Four sets of data are available which agree within *2%. The cross section above 300 nni is temperature dependent. The cross sections for the minor species are in general not as well known. In nitric oxide, carbon monoxide, ammonia, and sulfur dioxide, band structure dominates the absorption spectrum, and cross sections have been measured at insufficient spectral resolution. Other species, such as nitric acid, hydrogen peroxide, water vapor, carbon dioxide, nitrous oxide, and nitrogen dioxide, have continua over the entire spectra range from 175 to 300 nm. Cross sections for these species have been measured; however, cross sections for many molecules, e.g., NzO;, NO,, etc., have not been studied.Ides coupes de photoabsorption ntcessaires pour les calculs des conditions d'tquilibre dans la stratosphtre se rtpartissent en deux classes distinctes: les coupes de l'oxygtne et I'ozone moltculaires qui contr6lent la transmission des radiations solaires; les coupes d'esptces atmosphtriques secondaires qui sont optiquement poreuses aux radiations solaires et qui sont ntcessaires pour le calcul cle leur vitesse cle dissociation.Les principales caracttristiques d'absorption de l'oxygbne molCculaire sont cles bandes d'absorption du systtme Schumann-Runge entre 175 et 200 nm et une faible dissociation continu qui s'ttend de 175 h 260 nm. La structure de bandes consiste en plusieurs lignes fines de rotation et il est ntcessaire de calculer les sections droites en utilisant les paramttres de bandes mesurts. Deux mesures de largeurs des lignes de ces bandes montrent d'importantes largeurs des lignes (-1 cm-') indiquant une prtdissociation. L'accord entre les deux stries de donntes est bon pour quelques lignes seulement. Ceci comporte des implications dans le calcul de la tran...

The conventional XRAM (MARX spelled backwards) current multiplier circuit is similar in concept to the better known MARX voltage multiplier circuit. In the MARX circuit, capacitors charged in parallel from a voltage source are switched to discharge in series producing an output voltage approximately equal to the sum of individual capacitor voltages. In the XRAM circuit, inductors energized in series from a current source (battery, homopolar generator, other) are switched to discharge in parallel, producing an output current which is the sum of the individual inductor currents. In high energy pulsed power systems these multiplier techniques simplitj primary power design at the expense of more complex switching. circuit described in this paper minimizes switching requirements while retaining the positive benefits of the conventional XRAM circuit. It also provides a smooth rising current waveform which is useful for EM and ET gun research. The tradeoff for these benefits is that, during switching, approximately 50% of total system energy is stored in a capacitor bank of simple design.In addition to simplified switching, the hybrid concept offers other advantages over either an all capacitive or all inductive system. As a laboratory power supply at 2-3 MA current and 10-20 MJ stored energy, it doubles energy which would by, available from a capacitive system while offering the current stifhas" available from an inductive system. Less obvious but potentially of greater interest, the concept appears to scale to high energy (10's to 100's of MJ) for either a distributed energy or multi shot power supply. This paper outlines two XRAM circuit concepts, and discusses the distributed energy and multi-shot aspects of the hybrid concept. It also describes a more detailed study of a battery powered hybrid XRAM current doubler design being considered for use as a general purpose laboratory inductive energy supply, operating at up to 2.5 MA with as much as 10 MJ of electrical energy stored. The circuit described is modeled using known values from existing circuit components. Resulting waveforms are shown and benefits derived from the use of this circuit are compared to those from a conventional XRAM current doubler as well as from a direct, inductive store, system design. The hybrid I. ~NTRODUCITONAs EML research moves to higher energy and higher rojectile velocity systems, stored energy per shot is typicalfy 5 -10 UT and desired peak current is at least 1 -2 MA.In experiments where multi-shot firing capability is desired, the stored energy requirements are often increased in proportion to the number of shots desired in a burst. One system presently being designed [ 11 will store more than 500 UT and w i l l deliver peak current of up to 5 MA. Present technology utilizes either capacitive energy storage with closing switches or inductive storage with opening switches to meet these needs. Both types of systems become very Thin work was supported in part by Wright Laboratory and SDIO under Contract No. FO8635-914-OOO1.expensive an...

Metal-ion assisted, gamma-radiation-induced B-Z conformation changes have been observed with UV and circular dichroism spectroscopy for poly (dGdC), calf thymus and herring testis DNA. These conformational changes are similar to those induced by increasing multivalent metal ion concentrations in DNA containing alternating purine and pyrimidine base sequences. In both the metal-ion-induced and the metal-ion-assisted, radiation-induced conformation changes, the conversions were from the right-handed B-DNA to the left-handed Z-DNA conformation. It is proposed that radiation-induced DNA strand breaks markedly reduce the high activation energy barrier in the metal ion-driven B-Z conformation conversion and allow much smaller metal ion concentrations to induce this conversion than in the absence of strand breaks. The biological importance of such radiation-induced conformational changes is discussed in terms of the potential significance of the Z-DNA conformation in the control of the DNA transcription process.

Ultraviolet difference spectra of gamma-irradiated, air-saturated aqueous solutions of DNA bases vs. unirradiated solutions of the same bases are shown to be a very sensitive supplemental tool with which to investigate the yields, postirradiation kinetics, and general nature of DNA base radiation products. Irradiated pyrimidines yield difference spectra which are approximately negative mirror-images of the base absorption spectra in the near-UV, indicating loss of ring conjugation. Difference spectra of irradiated purines yield a more complex pattern containing a positive long-wavelength peak, interpreted as radiation-induced extension of conjugation of the pi electron system beyond that of the unirradiated purine. On the basis of the spectroscopic evidence from these studies, 8-hydroxyguanine appears to be the dominant UV-absorbing radiation product in air-saturated guanine solutions with a G-value of 0.3 molec (100 eV)-1. Difference spectral studies provide isosbestic points which can be used in testing proposed radiation products and their yields. Such spectral studies are a rapid, non-invasive, supplemental tool which can be employed in conjunction with other analytical techniques in radiation-chemical studies, and which is one of the few tools able to detect short-lived chemical intermediates observed in oxygenated solutions of irradiated purines.

Continuous absorption and line absorption of radiation in calcium vapour has been measured from the 4 s 4 s 1 S 0 → 4 snp 1 P 1 series limit at 2028 to 1080 Å. Two perturbed series of auto-ionization lines (4 s 4 s 1 S 0 → 3 dnp 1 P 1 and → 3 dnp 3 P 1 ) are recorded and analyzed. A second series limit is observed at 1589 Å. This is probably two unresolved limits corresponding to the two series of auto-ionization lines. No absorption lines are observed on the short wavelength side of 1589 Å. The f -values of the lines vary from 2.4 x 10 -2 to 6 x 10 -5 and the half-lives (calculated from measurements of the half-widths of the lines) vary from 30 to 260 x 10- 15 s. The f -value for the 4 s 4 s 1 S 0 → 4 snp 1 P 1 continuum is estimated to be 0.012 (including an allowance for a portion below 1589 Å) and the f -value for the continua from wavelength 1589 to 1080 Å corresponding to the two series of auto-ionization lines is estimated to be 0.003. The measured value of the absorption near 2028 Å is about one-fiftieth of the theoretical value which has been used in astrophysical calculations.