Central Star Formation in Pseudobulges and Classical Bulges

I use Spitzer 3.6-8.0 \mu m color profiles to compare the radial structure of star formation in pseudobulges and classical bulges. Pseudobulges are ``bulges'' which form through secular evolution, rather than mergers. In this study, pseudobulges are identified using the presence of disk-like structure in the center of the galaxy (nuclear spiral, nuclear bar, and/or high ellipticity in bulge); classical bulges are those galaxy bulges with smooth isophotes which are round compared to the outer disk, and show no disky structure in their bulge. I show that galaxies structurally identified as having pseudobulges have higher central star formation rates than those of classical bulges. Further, I also show that galaxies identified as having classical bulges have remarkably regular star formation profiles. The color profiles of galaxies with classical bulges show a star forming outer disk with a sharp change, consistent with a decline in star formation rates, toward the center of the galaxy. Classical bulges have a nearly constant inner profile (r < 1.5 kpc) that is similar to elliptical galaxies. Pseudobulges in general show no such transition in star formation properties from the outer disk to the central pseudobulge. Thus I conclude that pseudobulges and classical bulges do in fact form their stars via different mechanisms. Further, this adds to the evidence that classical bulges form most of their stars in fast episodic bursts, in a similar fashion to elliptical galaxies; whereas, pseudobulges form stars from longer lasting secular processes.Comment: accepted to ApJ Letter

Low Hubble Constant from Type Ia Supernovae by van den Bergh's Method

An interesting way to calibrate the absolute magnitudes of remote Type Ia supernovae (SNe Ia) that are well out in the Hubble flow, and thus determine the value of the Hubble constant, H_0, has been introduced by van den Bergh. His approach relies on calculations of the peak absolute magnitudes and broad--band colors for SN Ia explosion models. It does not require any corrections for extinction by interstellar dust, and no SNe Ia are excluded on grounds of peculiarity. Within the last few years distances have been determined to the parent galaxies of six SNe Ia by means of Cepheid variables. Cepheid--based distances also have become available for three other SNe Ia if one is willing to use the distance to a galaxy in the same group in lieu of the distance to the parent galaxy itself. Here we determine the value of H_0 in a way that is analogous to that of van den Bergh, but now using Cepheid--based distances instead of calculated light curves. We obtain H_0 = 55 km/s/Mpc. This value, with Lambda=0 and Omega=1, corresponds to a cosmic expansion time of 12 Gyr, which is consistent with several recent determinations of the ages of globular clusters.Comment: Latex, 4 pages, 1 table, 1 figure, Submitted to Nature March 28, 1996. PostScript version available at http://www.nhn.ou.edu/~nugent

Automorphisms of real Lie algebras of dimension five or less

The Lie algebra version of the Krull-Schmidt Theorem is formulated and proved. This leads to a method for constructing the automorphisms of a direct sum of Lie algebras from the automorphisms of its indecomposable components. For finite-dimensional Lie algebras, there is a well-known algorithm for finding such components, so the theorem considerably simplifies the problem of classifying the automorphism groups. We illustrate this by classifying the automorphisms of all indecomposable real Lie algebras of dimension five or less. Our results are presented very concisely, in tabular form

Distinct Examples of Immunologic Analysis in Molecular and Cellular Biology: Small Nuclear Ribonucleoproteins and the T Cell Receptor

Since the discovery (Tan and Kunkel, 1966; Mattioli and Peichlin, 1971; Sharp, et al., 1972) of human SLE autoantibodies directed against RNA-protein complexes in eucaryotic nuclei, a great deal of interest has been generated regarding both the relationships of antibody specificities to disease and the biological roles of the recognized antigens. These antibodies are some of the many autoantibody species which have been described in systemic lupus erythematosus (SLE) as well as other rheimatic disease conditions. A common feature of many of these reactivities is the apparent nuclear localization of antigen. Study of the antibodies as well as these antigens has led to formation of a particularly unique bridge between clinical medicine and basic science questions in cellular biology and metabolism. The spectrum of diseases which present with antibodies directed against cellular constituents is vast although certain features of these conditions imply common aspects which may, furthermore, be of some diagnostic use

The Origin of Meteorites: Space Erosion and Cosmic Radiation Ages

particles in the asteroidal belt, coupled with the fact that there is a high mass cut-off for chondrites at about 1000 kg, is sufficient to explain the absence of chondrites with radiation ages greater than 55 x 10^ years. Then if one postulates continuous creation of meteorites by asteroidal collisions, the effect of space erosion is to shift the measured ages toward lower values and to destroy a certain portion of meteorites as a function of their time in space. The total effect, as estimated with several simple but plausible erosion rates, is to duplicate quite nicely the observed shape of the radiation age spectrum. Thus space erosion is not the sole factor in determining the radiation age of a chondrite, but is a factor which grows in importance as the age increases, becoming the sole factor at 55 x 10 years. The model is in agreement with the postulate of a distinct bronzite producing collision 4 million years ago, whose effect is observed on top of the background of continuous collision* It is therefore suggested that both stone and iron meteorites are created by collisional processes in the asteroidal belt

Heuristic Spike Sorting Tuner (HSST), a framework to determine optimal parameter selection for a generic spike sorting algorithm

Extracellular microelectrodes frequently record neural activity from more than one neuron in the vicinity of the electrode. The process of labeling each recorded spike waveform with the identity of its source neuron is called spike sorting and is often approached from an abstracted statistical perspective. However, these approaches do not consider neurophysiological realities and may ignore important features that could improve the accuracy of these methods. Further, standard algorithms typically require selection of at least one free parameter, which can have significant effects on the quality of the output. We describe a Heuristic Spike Sorting Tuner (HSST) that determines the optimal choice of the free parameters for a given spike sorting algorithm based on the neurophysiological qualification of unit isolation and signal discrimination. A set of heuristic metrics are used to score the output of a spike sorting algorithm over a range of free parameters resulting in optimal sorting quality. We demonstrate that these metrics can be used to tune parameters in several spike sorting algorithms. The HSST algorithm shows robustness to variations in signal to noise ratio, number and relative size of units per channel. Moreover, the HSST algorithm is computationally efficient, operates unsupervised, and is parallelizable for batch processing

The Impact of MITF on Melanoma Development – News from Bench and Bedside

Summary In the current issue, two articles highlight the impact of MITF on melanoma development. In the first, Lister et al. (2013) reveal in vivo proof of MITF directly regulating tumor development in BRAFV600E melanomas. In the second, Sturm et al. (2013) present a clinical trial that emphasizes the importance of the recently discovered E318K MITF germline mutation in patients with multiple primary melanomas

DNA bending and the curious case of Fos/Jun

DNA bending has been implicated as an important regulatory mechanism in several processes involving protein—DNA interactions. Various methods for examining intrinsic and protein-induced DNA bending may lead to different conclusions. For the Fos and Jun transcription factors, this has resulted in controversy over whether these factors significantly bend DNA at all