Radiative Transfer Effects in He I Emission Lines

We consider the effect of optical depth of the 2 ^{3}S level on the nebular recombination spectrum of He I for a spherically symmetric nebula with no systematic velocity gradients. These calculations, using many improvements in atomic data, can be used in place of the earlier calculations of Robbins. We give representative Case B line fluxes for UV, optical, and IR emission lines over a range of physical conditions: T=5000-20000 K, n_{e}=1-10^{8} cm^{-3}, and tau_{3889}=0-100. A FORTRAN program for calculating emissivities for all lines arising from quantum levels with n < 11 is also available from the authors. We present a special set of fitting formulae for the physical conditions relevant to low metallicity extragalactic H II regions: T=12,000-20,000 K, n_{e}=1-300 cm^{-3}, and tau_{3889} < 2.0. For this range of physical conditions, the Case B line fluxes of the bright optical lines 4471 A, 5876 A, and 6678 A, are changed less than 1%, in agreement with previous studies. However, the 7065 A corrections are much smaller than those calculated by Izotov & Thuan based on the earlier calculations by Robbins. This means that the 7065 A line is a better density diagnostic than previously thought. Two corrections to the fitting functions calculated in our previous work are also given.Comment: To be published in 10 April 2002 ApJ; relevant code available at ftp://wisp.physics.wisc.edu/pub/benjamin/Heliu

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The distribution of aneurinpyrophosphate between the nucleus and the cytoplasm of chicken erythrocytes

The nuclei of chicken erythrocytes contain about 20 times as much aneurinpyrophosphate per unit volume as the cytoplasm

The conversion of aneurin into aneurinpryrophosphate by blood corpuscles

1. The in vitro synthesis of aneurinpyrophosphate from added aneurin by the white and red cells of the blood of the rat and of man was studied. Though the synthesis is by no means negligible in human blood it is much higher in rat blood. 2. An average rat leukocyte contains about 160 times as much aneuripyrophosphate as an average rat erythrocyte. This ratio is increased to about 550 upon incubation of the blood with 1 mg aneurin per ml. 3. The synthesis in inhibited by oxalate, monoiodoacetate, fluoride and cyanide. 4. The synthesis by the red cells is preferentially inhibited by oxalate, the synthesis by the white cells by cyanide. This proves that the energy required for the synthesis of aneurinpyrophosphate from aneurin is mainly provided by glycolysis in the red cells and by respiration in the white cells. 5. Upon incubation of the blood with a small amount of aneurin a higher percentage is converted into aneurinpyrophosphate than with a large amount of aneurin. However, even from 0.1 gamma-aneurin added to 1 ml of blood only 26% is phosphorylated (from 1 mg added about 0.25% is phosphorylated). 6. During incubation of rat blood with aneurin at 39°C aneurin is not destroyed, nor are substances formed inhibiting aneurin pyrophosphate synthesis. 7. The synthesis of aneurinpyrophosphate by the erythrocytes depends upon the concentration of glucose present. It is decreased when the glucose concentration is below normal or extremely high. 8. The enzym system responsible for the synthesis of aneurinpyrophosphate from aneurin is badly damaged by incubating the blood at 39°C for some hours. 9. Attention is called to the fact that process producing energy are necessary for the conversion of a certain vitamin into its physiologically active form. As other vitamins form part of various enzymes connected with energy production insight into the interrelationship of various avitaminoses may be gained from investigations on the influence of the lack or one vitamin in the food on the conversion of another vitamin into its physiologically active form

Defining adaptation in a generic multi layer model : CAM: the GRAPPLE conceptual adaptation model

Authoring of Adaptive Hypermedia is a difficult and time consuming task. Reference models like LAOS and AHAM separate adaptation and content in different layers. Systems like AHA! offer graphical tools based on these models to allow authors to define adaptation without knowing any adaptation language. The adaptation that can be defined using such tools is still limited. Authoring systems like MOT are more flexible, but usability of adaptation specification is low. This paper proposes a more generic model which allows the adaptation to be defined in an arbitrary number of layers, where adaptation is expressed in terms of relationships between concepts. This model allows the creation of more powerful yet easier to use graphical authoring tools. This paper presents the structure of the Conceptual Adaptation Models used in adaptive applications created within the GRAPPLE adaptive learning environment, and their representation in a graphical authoring tool

Defining adaptation in a generic multi layer model : CAM: the GRAPPLE conceptual adaptation model

Authoring of Adaptive Hypermedia is a difficult and time consuming task. Reference models like LAOS and AHAM separate adaptation and content in different layers. Systems like AHA! offer graphical tools based on these models to allow authors to define adaptation without knowing any adaptation language. The adaptation that can be defined using such tools is still limited. Authoring systems like MOT are more flexible, but usability of adaptation specification is low. This paper proposes a more generic model which allows the adaptation to be defined in an arbitrary number of layers, where adaptation is expressed in terms of relationships between concepts. This model allows the creation of more powerful yet easier to use graphical authoring tools. This paper presents the structure of the Conceptual Adaptation Models used in adaptive applications created within the GRAPPLE adaptive learning environment, and their representation in a graphical authoring tool

The Primordial Abundance of He4: An Update

We include new data in an updated analysis of helium in low metallicity extragalactic HII regions with the goal of deriving the primordial abundance of He4 (Y_P). We show that the new observations of Izotov et al (ITL) are consistent with previous data. However they should not be taken in isolation to determine (Y_P) due to the lack of sufficiently low metallicity points. We use the extant data in a semi-empirical approach to bounding the size of possible systematic uncertainties in the determination of (Y_P). Our best estimate for the primordial abundance of He4 assuming a linear relation between He4 and O/H is Y_P = 0.230 \pm 0.003 (stat) based on the subset of HII regions with the lowest metallicity; for our full data set we find Y_P = 0.234 \pm 0.002 (stat). Both values are entirely consistent with our previous results. We discuss the implications of these values for standard big bang nucleosynthesis (SBBN), particularly in the context of recent measurements of deuterium in high redshift, low metallicity QSO absorption-line systems.Comment: 26 pages, latex, 6 ps figure