Silicon Burning II: Quasi-Equilibrium and Explosive Burning

Having examined the application of quasi-equilibrium to hydrostatic silicon burning in Paper I of this series, Hix & Thielemann (1996), we now turn our attention to explosive silicon burning. Previous authors have shown that for material which is heated to high temperature by a passing shock and then cooled by adiabatic expansion, the results can be divided into three broad categories; \emph{incomplete burning}, \emph{normal freezeout} and \emph{$\alpha$-rich freezeout}, with the outcome depending on the temperature, density and cooling timescale. In all three cases, we find that the important abundances obey quasi-equilibrium for temperatures greater than approximately 3 GK, with relatively little nucleosynthesis occurring following the breakdown of quasi-equilibrium. We will show that quasi-equilibrium provides better abundance estimates than global nuclear statistical equilibrium, even for normal freezeout and particularly for $\alpha$-rich freezeout. We will also examine the accuracy with which the final nuclear abundances can be estimated from quasi-equilibrium.Comment: 27 pages, including 15 inline figures. LaTeX 2e with aaspp4 and graphicx packages. Accepted to Ap

Organizational Satisfaction And Participation: Findings from a Study Of ACE Members

Organizations which serve information professionals, such as Agricultural Communicators in Education, must continue to respond to the needs of members through relevant programs and professional opportunities. The study reported here examines satisfaction and participation within the organization. Overall, the study found broad-based member satisfaction. But while there is widespread support, there are segments of the membership which need attention. Findings also identify organizational areas which can be improved, particularly in the conduct of the Critique and Awards Program and in meeting the expectations of members involved in Special Interest Groups (SIG). Specific questions that may have organizational policy implications are raised. The study\u27s finding that member participation positively is related to overall satisfaction with ACE is encouraging. One important goal for ACE, then, would be to encourage increased participation. And, because newer members tend to be the most dissatisfied with ACE, emphasis should be placed on immediately getting them more involved in ACE activities

On gravitational-wave spectroscopy of massive black holes with the space interferometer LISA

Newly formed black holes are expected to emit characteristic radiation in the form of quasi-normal modes, called ringdown waves, with discrete frequencies. LISA should be able to detect the ringdown waves emitted by oscillating supermassive black holes throughout the observable Universe. We develop a multi-mode formalism, applicable to any interferometric detectors, for detecting ringdown signals, for estimating black hole parameters from those signals, and for testing the no-hair theorem of general relativity. Focusing on LISA, we use current models of its sensitivity to compute the expected signal-to-noise ratio for ringdown events, the relative parameter estimation accuracy, and the resolvability of different modes. We also discuss the extent to which uncertainties on physical parameters, such as the black hole spin and the energy emitted in each mode, will affect our ability to do black hole spectroscopy.Comment: 44 pages, 21 figures, 10 tables. Minor changes to match version in press in Phys. Rev.

Selective deletion of cochlear hair cells causes rapid age-dependent changes in spiral ganglion and cochlear nucleus neurons

During nervous system development, critical periods are usually defined as early periods during which manipulations dramatically change neuronal structure or function, whereas the same manipulations in mature animals have little or no effect on the same property. Neurons in the ventral cochlear nucleus (CN) are dependent on excitatory afferent input for survival during a critical period of development. Cochlear removal in young mammals and birds results in rapid death of target neurons in the CN. Cochlear removal in older animals results in little or no neuron death. However, the extent to which hair-cell-specific afferent activity prevents neuronal death in the neonatal brain is unknown. We further explore this phenomenon using a new mouse model that allows temporal control of cochlear hair cell deletion. Hair cells express the human diphtheria toxin (DT) receptor behind the Pou4f3 promoter. Injections of DT resulted in nearly complete loss of organ of Corti hair cells within 1 week of injection regardless of the age of injection. Injection of DT did not influence surrounding supporting cells directly in the sensory epithelium or spiral ganglion neurons (SGNs). Loss of hair cells in neonates resulted in rapid and profound neuronal loss in the ventral CN, but not when hair cells were eliminated at a more mature age. In addition, normal survival of SGNs was dependent on hair cell integrity early in development and less so in mature animals. This defines a previously undocumented critical period for SGN survival

On Variations in the Peak Luminosity of Type Ia Supernovae

We explore the idea that the observed variations in the peak luminosities of Type Ia supernovae originate in part from a scatter in metallicity of the main-sequence stars that become white dwarfs. Previous, numerical, studies have not self-consistently explored metallicities greater than solar. One-dimensional Chandrasekhar mass models of SNe Ia produce most of their 56Ni in a burn to nuclear statistical equilibrium between the mass shells 0.2 and 0.8 solar masses, for which the electron to nucleon ratio is constant during the burn. We show analytically that, under these conditions, charge and mass conservation constrain the mass of 56Ni produced to depend linearly on the original metallicity of the white dwarf progenitor. Detailed post-processing of W7-like models confirms this linear dependence. The effect that we identify is most evident at metallicities larger than solar, and is in agreement with previous self-consistent calculations over the metallicity range common to both calculations. The observed scatter in the metallicity (1/3--3 times solar) of the solar neighborhood is enough to induce a 25% variation in the mass of 56Ni ejected by Type Ia supernovae. This is sufficient to vary the peak V-band brightness by approximately 0.2. This scatter in metallicity is present out to the limiting redshifts of current observations (z < 1). Sedimentation of 22Ne can possibly amplify the variation in 56Ni mass up to 50%. Further numerical studies can determine if other metallicity-induced effects, such as a change in the mass of the 56Ni-producing region, offset or enhance this variation.Comment: 4 pages, 1 figure, to appear in ApJL. Uses emulateapj.cls (included

Crystal Structure of (E)-2-[(2- bromo-3-pyridyl)methylidene]-6-methoxy-3,4-dihydronaphthalen-1-one and 3-[(E)-(6- methoxy-3,4-dihydronaphth-2-oylidene)methyl]-1H-pyridin-2-one

The title compounds C17H14BrNO2, (I), and C17H15NO3, (II), were obtained from the reaction of 6-meth­oxy-3,4-di­hydro-2H-naphthalen-1-one and 2-bromo­nicotinaldehyde in ethanol. Compound (I) was the expected product and compound (II) was the oxidation product from air exposure. In the crystal structure of compound (I), there are no short contacts or hydrogen bonds. The structure does display [pi]-[pi] inter­actions between adjacent benzene rings and adjacent pyridyl rings. Compound (II) contains two independent mol­ecules, A and B, in the asymmetric unit; both are non-planar, the dihedral angles between the meth­oxy­benzene and 1H-pyridin-2-one mean planes being 35.07 (9)° in A and 35.28 (9)°in B. In each mol­ecule, the 1H-pyridin-2-one unit participates in inter­molecular N-H...O hydrogen bonding to another mol­ecule of the same type (A to A or B to B). The structure also displays [pi]-[pi] inter­actions between the pyridyl and the benzene rings of non-equivalent mol­ecules (viz., A to B and B to A)

Transposition and time-warp invariant algorithm for detecting repeated patterns in polyphonic music

Peer reviewe

Evaluation of patients treated with natalizumab for progressive multifocal leukoencephalopathy

Background: Progressive multifocal leukoencephalopathy (PML) was reported to have developed in three patients treated with natalizumab. We conducted an evaluation to determine whether PML had developed in any other treated patients. Methods: We invited patients who had participated in clinical trials in which they received recent or long-term treatment with natalizumab for multiple sclerosis, Crohn's disease, or rheumatoid arthritis to participate. The clinical history, physical examination, brain magnetic resonance imaging (MRI), and testing of cerebrospinal fluid for JC virus DNA were used by an expert panel to evaluate patients for PML. We estimated the risk of PML in patients who completed at least a clinical examination for PML or had an MRI. Results: Of 3417 patients who had recently received natalizumab while participating in clinical trials, 3116 (91 percent) who were exposed to a mean of 17.9 monthly doses underwent evaluation for PML. Of these, 44 patients were referred to the expert panel because of clinical findings of possible PML, abnormalities on MRI, or a high plasma viral load of JC virus. No patient had detectable JC virus DNA in the cerebrospinal fluid. PML was ruled out in 43 of the 44 patients, but it could not be ruled out in one patient who had multiple sclerosis and progression of neurologic disease because data on cerebrospinal fluid testing and follow-up MRI were not available. Only the three previously reported cases of PML were confirmed (1.0 per 1000 treated patients; 95 percent confidence interval, 0.2 to 2.8 per 1000). Conclusions: A detailed review of possible cases of PML in patients exposed to natalizumab found no new cases and suggested a risk of PML of roughly 1 in 1000 patients treated with natalizumab for a mean of 17.9 months. The risk associated with longer treatment is not known

Taub--NUT Dyons in Heterotic String Theory

Starting with the Taub--NUT solution to Einstein's equations, together with a constant dilaton, a dyonic Taub--NUT solution of low energy heterotic string theory with non--trivial dilaton, axion and $U(1)$ gauge fields is constructed by employing $O(1,1)$ transformations. The electromagnetic dual of this solution is constructed, using SL(2,\rline) transformations. By an appropriate change to scaled variables, the extremal limit of the dual solution is shown to correspond to the low energy limit of an exact conformal field theory presented previously.Comment: 16 pages (plain TEX), (Revised version has curvature singularities correctly identified), IASSNS-HEP-94/50, McGill/94-2