Ages of Type Ia Supernovae Over Cosmic Time

We derive empirical models for galaxy mass assembly histories, and convolve these with theoretical delay time distribution (DTD) models for Type Ia supernovae (SNe Ia) to derive the distribution of progenitor ages for all SNe Ia occurring at a given epoch of cosmic time. In actively star-forming galaxies, the progression of the star formation rate is shallower than a $t^{-1}$ SN Ia DTD, so mean SN Ia ages peak at the DTD peak in all star-forming galaxies at all epochs of cosmic history. In passive galaxies which have ceased star formation through some quenching process, the SN Ia age distribution peaks at the quenching epoch, which in passive galaxies evolves in redshift to track the past epoch of major star formation. Our models reproduce the SN Ia rate evolution in redshift, the relationship between SN Ia stretch and host mass, and the distribution of SN Ia host masses in a manner qualitatively consistent with observations. Our model naturally predicts that low-mass galaxies tend to be actively star-forming while massive galaxies are generally passive, consistent with observations of galaxy "downsizing". Consequently, the mean ages of SNe Ia undergo a sharp transition from young ages at low host mass to old ages at high host mass, qualitatively similar to the transition of mean SN Ia Hubble residuals with host mass. The age discrepancy evolves with redshift in a manner currently not accounted for in SN Ia cosmology analyses. We thus suggest that SNe Ia selected only from actively star-forming galaxies will yield the most cosmologically uniform sample, due to the homogeneity of young SN Ia progenitor ages at all cosmological epochs.Comment: 15 pages, 15 figures, accepted for publication in MNRA

IMMOVABLE PROPERTY MARKETS IN METROPOLITAN TIRANA, ALBANIA

This paper uses information from three empirical studies to describe, after seven years of privatization and real estate market transactions, how the physical space of the city of Tirana is presently organized, and how active real estate markets have been. The first empirical study, fielded in December 1997 (completed in January 1998), was based on an "area sample" of the city of Tirana. One-hectare grid squares were overlaid on the city's 3,060 hectares within the municipal boundary, and a random sample was taken of these grids. Eighteen grid squares within the ring roads (an area of 340 hectares) and 14 grid squares between the ring roads and the outer municipal boundary (an area of 2,720 hectares) were randomly selected. Within the selected grid squares of 1 hectare each, research teams visited each property and questioned the holders about its use, who owned it, when it was constructed, and other characteristics of the property. The sample values obtained from the questionnaires were then "expanded" by the sampling ratio to describe the physical space of Tirana within the city's municipal boundaries. The second study of the transactions recorded in the Hipoteka Office of Tirana was done in early 1998. All documents from 1993 through 1997 were classified according to type of property involved, and the number of transactions were tabulated. The third study of real estate prices from 1993 to 1997 was done based on the data of one real estate agency in February 1998. This database represents approximately 70 percent of all offerings of real estate for sale done through real estate agencies in Tirana.Real property--Prices--Albania--Tirana, Land use, Urban--Albania--Tirana, Land titles--Registration and transfer--Albania--Tirana, Real estate development--Albania--Tirana, Land markets--Albania--Tirana, Land tenure, Urban--Albania--Tirana, Land Economics/Use,

Continuous breakdown of Purcell's scallop theorem with inertia

Purcell's scallop theorem defines the type of motions of a solid body - reciprocal motions - which cannot propel the body in a viscous fluid with zero Reynolds number. For example, the flapping of a wing is reciprocal and, as was recently shown, can lead to directed motion only if its frequency Reynolds number, Re_f, is above a critical value of order one. Using elementary examples, we show the existence of oscillatory reciprocal motions which are effective for all arbitrarily small values of the frequency Reynolds number and induce net velocities scaling as (Re_f)^\alpha (alpha > 0). This demonstrates a continuous breakdown of the scallop theorem with inertia.Comment: 6 pages, 1 figur

Narrow frequency-band laser with optical feedback

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 24).In this paper we discuss the construction of a narrow frequency-band laser with optical feedback. We use a distributed Bragg reflector (DBR) laser diode centered at the cesium D₂ transition wavelength, [gamma] = 852 nm. The linewidth of this diode is reduced by several orders of magnitude by means of optical feedback from an external cavity. The system is further stabilized by locking the path length between diode and cavity to optimize coupling between them. The absolute frequency of our laser is fixed by means of a delay line lock system that uses the beat note between our laser and a fixed reference laser to set our laser's frequency. We present both the theory behind these systems and data from our own setup. We then finally discuss potential uses of the narrow laser in atomic physics experiments, including detection of a single atom in an optical cavity.by Michael J. Childress.S.B

Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal

We have developed a self-aligned, high-yield process to fabricate CPP (current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions. A pinned synthetic antiferromagnet (SAF) is used as the reference layer which minimizes dipole coupling to the free layer and field induced rotation of the reference layer. We find that the critical currents for spin transfer induced magnetization reversal of the free layer vary dramatically with relatively small changes the in-plane magnetic field, in contrast to theoretical predictions based on stability analysis of the Gilbert equations of magnetization dynamics including Slonczewski-type spin-torque terms. The discrepancy is believed due to thermal fluctuations over the time scale of the measurements. Once thermal fluctuations are taken into account, we find good quantitative agreement between our experimental results and numerical simulations.Comment: 14 pages, 4 figures, Submitted to Appl. Phys. Lett., Comparison of some of these results with a model described by N. Smith in cond-mat/040648

Anomalous exponents at the onset of an instability

Critical exponents are calculated exactly at the onset of an instability, using asymptotic expansiontechniques. When the unstable mode is subject to multiplicative noise whose spectrum at zero frequency vanishes, we show that the critical behavior can be anomalous, i.e. the mode amplitude X scales with departure from onset \mu as $~ \mu^\beta$ with an exponent $\beta$ different from its deterministic value. This behavior is observed in a direct numerical simulation of the dynamo instability and our results provide a possible explanation to recent experimental observations

The Oprah Effect : A Content Analysis of Media Coverage of Toni Morrison and How the Coverage Changed Post-Oprah.

The present study analyzes the way in which Toni Morrison, an established author, was covered by U.S. newspapers in the year before and year following her selection for Opraha\u27s Book Club. The content analysis method was used in the research, and the results were used to test 6 hypotheses and 6 research questions. The results indicated that there was a significant increase in the total number of mentions of Toni Morrison in the year after her inclusion in Opraha\u27s Book Club. The overwhelming trend that was seen in all variable comparisons was that while there were obviously more mentions of Toni Morrison post-Book Club, there were also increases and changes in the tone, page placement, and story placement of the mentions of Toni Morrison

Going with the flow: Forecasting the impact of climate change on blue crabs

2014 S.C. Water Resources Conference - Informing Strategic Water Planning to Address Natural Resource, Community and Economic Challenge

Suppression of spin-torque in current perpendicular to the plane spin-valves by addition of Dy cap layers

We demonstrate that the addition of Dy capping layers in current perpendicular to the plane giant magneto-resistive spin-valves can increase the critical current density beyond which spin-torque induced instabilities are observed by about a factor of three. Current densities as high as 5e7 A/cm2 are measured provided that the electron current flows from the free to the reference layer. While Dy capped samples exhibit nonmagnetic 1/f noise, it is sufficiently small to be unimportant for read head operation at practical data rates.Comment: 13 pages (manuscript form), with 5 figures. Submitted for publicatio