Are Galaxies Optically Thin to Their Own Lyman Continuum Radiation? II. NGC 6822

Halpha and UBV photometry of NGC 6822 are used to study the distribution of OB stars and HII regions in the galaxy and to determine whether individual regions of the galaxy are in a state of ionization balance. Four distinct components of the Halpha emission (bright, halo, diffuse and field) differentiated by their surface brightnesses are identified. We find that approximately 1/2 of all OB stars in NGC 6822 are located in the field while only 1/4 are found in the combined bright and halo regions, suggesting that OB stars spend roughly 3/4 of their lifetimes outside ``classical'' H II regions. Comparing the observed Halpha emission with that predicted from stellar ionizing flux models, we find that although the bright, halo and diffuse regions are probably in ionization balance, the field region is producing at least 6 times as much ionizing flux as is observed. The ionization balance results in NGC 6822 suggest that star formation rates obtained from Halpha luminosities must underestimate the true star formation rate in this galaxy by about 50%. Comparing our results for NGC 6822 with previous results for the spiral galaxy M33, we find that the inner kiloparsec of M33 is in a more serious state of ionization imbalance, perhaps due to its higher surface density of blue stars.Comment: Replaced version should now compile with standard aastex style files. 28 pages, aastex preprint format. Accepted in ApJ. Hardcopies of figures available on request to [email protected]

Arithmetic Operations in Multi-Valued Logic

This paper presents arithmetic operations like addition, subtraction and multiplications in Modulo-4 arithmetic, and also addition, multiplication in Galois field, using multi-valued logic (MVL). Quaternary to binary and binary to quaternary converters are designed using down literal circuits. Negation in modular arithmetic is designed with only one gate. Logic design of each operation is achieved by reducing the terms using Karnaugh diagrams, keeping minimum number of gates and depth of net in to consideration. Quaternary multiplier circuit is proposed to achieve required optimization. Simulation result of each operation is shown separately using Hspice.Comment: 12 Pages, VLSICS Journal 201

Predicting Axonal Response to Molecular Gradients with a Computational Model of Filopodial Dynamics

Axons are often guided to their targets in the developing nervous system by attractive or repulsive molecular concentration gradients. We propose a computational model for gradient sensing and directed movement of the growth cone mediated by filopodia. We show that relatively simple mechanisms are sufficient to generate realistic rajectories for both the short-term response of axons to steep gradients and the long-term response of axons to shallow gradients. The model makes testable predictions for axonal response to attractive and repulsive gradients of different concentrations and steepness, the size of the intracellular amplification of the gradient signal, and the differences in intracellular signaling required for repulsive versus attractive turning

Hepcidin secretion was not directly proportional to intracellular iron-loading in recombinant-TfR1 HepG2 cells: short communication

Hepcidin is the master regulator of systemic iron homeostasis and its dysregulation is observed in several chronic liver diseases. Unlike the extracellular iron-sensing mechanisms, the intracellular iron-sensing mechanisms in the hepatocytes that lead to hepcidin induction and secretion are incompletely understood. Here, we aimed to understand the direct role of intracellular iron-loading on hepcidin mRNA and peptide secretion using our previously characterised recombinant HepG2 cells that over-express the cell-surface iron-importer protein transferrin receptor-1. Gene expression of hepcidin (HAMP) was determined by real-time PCR. Intracellular iron levels and secreted hepcidin peptide levels were measured by ferrozine assay and immunoassay, respectively. These measurements were compared in the recombinant and wild-type HepG2 cells under basal conditions at 30 min, 2 h, 4 h and 24 h. Data showed that in the recombinant cells, intracellular iron content was higher than wild-type cells at 30 min (3.1-fold, p<0.01), 2 h (4.6-fold, p<0.01), 4 h (4.6-fold, p<0.01) and 24 h (1.9-fold, p<0.01). Hepcidin (HAMP) mRNA expression was higher than wild-type cells at 30 min (5.9-fold; p=0.05) and 24 h (6.1-fold; p<0.03), but at 4 h, the expression was lower than that in wild-type cells (p<0.05). However, hepcidin secretion levels in the recombinant cells were similar to those in wild-type cells at all time-points, except at 4 h, when the level was lower than wild-type cells (p<0.01). High intracellular iron in recombinant HepG2 cells did not proportionally increase hepcidin peptide secretion. This suggests a limited role of elevated intracellular iron in hepcidin secretio

Theoretical face pressure and drag characteristics of forward-facing steps in supersonic turbulent boundary layers

A theoretical investigation of the pressure distributions and drag characteristics was made for forward facing steps in turbulent flow at supersonic speeds. An approximate solution technique proposed by Uebelhack has been modified and extended to obtain a more consistent numerical procedure. A comparison of theoretical calculations with experimental data generally indicated good agreement over the experimentally available range of ratios of step height to boundary layer thickness from 7 to 0.05