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

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

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

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

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,

Magnetic domain wall propagation in a submicron spin-valve stripe: influence of the pinned layer

The propagation of a domain wall in a submicron ferromagnetic spin-valve stripe is investigated using giant magnetoresistance. A notch in the stripe efficiently traps an injected wall stopping the domain propagation. The authors show that the magnetic field at which the wall is depinned displays a stochastic nature. Moreover, the depinning statistics are significantly different for head to head and tail-to-tail domain walls. This is attributed to the dipolar field generated in the vicinity of the notch by the pinned layer of the spin-valve

Modeling the Impact of Drought on South Carolina Blue Crabs Using a Spatially-Explicit Individual-Based Population Model

2010 S.C. Water Resources Conferences - Science and Policy Challenges for a Sustainable Futur

The development and application of aninolevulinic acid dehydratase and zinc protoporphyrin assays in dairy cattle for lead poisoning

Normal whole blood values of aminolevullnic acid dehydratase (ALAD) activity and zinc protoporphyrin (ZPP) concentrations were described in four groups of cattle according to age; C-I) 1 to 16 weeks of age (n=69); C-II) 9 months of age (n=10); C-III) 2 years of age (n=30); C-IV) 10 years of age (n=12). Group C-I was further subdivided by weekly age. All 121 animals had whole blood lead con-centrations less than 10 μg Pb/dl. Hemoglobin, total erythrocytes and leukocytes, MCH, MCHC, MCV, and PCV were measured to assess any possible influence on ALAD activity and ZPP concentrations. Twenty-nine calves from Group C-I were selected to measure the effect of lead on ALAD activity, and 12 animals to measure the effect of lead on ZPP concentration. Four treatment groups were established: L-I) control calves receiving no lead (n=8); L-II) calves receiving 2.7 mg Pb/Kg body wt. for 20 days (n=5); L-III) calves receiving 5.0 mg Pb/Kg body wt. for 4 days and followed for additional 10 days. Treatment Group L-II was not included in the measurement of ZPP concentrations. The lead was given per os in the acetate form dissolved in water daily as a single bolus, with lead dose calculated only as the lead portion. In Group C-I ALAD activity was shown to increase with age through nine weeks (851 nM PBG/ml RBC/hr) at which time the level of activity began to decrease through 16 weeks of age. Calves in C-I (548 nM PBG/ml RBC/hr) had a significantly higher (P \u3c .05) activity than the calves 3 weeks of age or less. The range within Group C-I was 113-1873 nM PBG/ml RBC/hr. Mean ZPP concentrations measured by the hematofluorometer were significantly greater (p \u3c .05) in Group C-IV (3.2 μg ZPP/g Hb) than Groups C-I, C-II, or C-III. The mean ZPP concentration of the com-bined Groups C-I, C-II, and C-III was 2.2 μg ZPP/g Hb. No signifi cant difference was observed between Groups C-I, C-II, or C-III. The effects of lead on ALAD activity and ZPP concentrations were quite evident in all groups. The ALAD activity of Treatment Group L-2 was significantly higher (p \u3c .05) than Treatment Groups L-3 or L-4 but significantly less (p \u3c .05) than the initial measurement of ALAD activity in Group L-2. A negative correlation coefficient of -0.80 was observed between the log ALAD and log blood lead in Treatment Groups L-3 and L-4. In these two treatment groups ALAD activity had dropped from a mean of 548 to 110 nM PBC/ml RBC/hr within 6 hours after the initial dose. By 24 hours, ALAD activity had dropped below 60 nM PBC/ml RBC/hr. During the same time interval, whole blood lead con-centration had increased to a mean of 80 μg Pb/dl. ALAD activity continued to drop after daily doses of lead; however, the blood lead concentrations stayed relatively the same. No significant dif-ference in blood lead concentration or ALAD activity was observed between Treatment Groups L-3 and L-4. Mean ZPP concentration increased from 2.2 μg/g Hb to 7.3 μg/g Hb in Treatment Groups L-3 and L-4. No differences were observed between Treatment Groups L-3 and L-4. No significant correlation between ZPP and blood lead concentrations or between ZPP concentrations and ALAD activity was observed in Treatment Groups L-3 and L-4. Normal hematological parameters were noted during the measure-ment of ALAD activity and ZPP concentrations. Lead did not effect total erythrocyte and leukoctye counts, hemoglobin, MCH, MCHC, MCV, and PCV

Analyzing the Reported Professional Learning of Ninth-Grade Teachers Participating in an Interdisciplinary Team

Interdisciplinary teaming has been a hallmark of the middle school philosophy for over 30 years and consists of a multitude of benefits for teachers, ranging from job satisfaction to communal support. Yet, interestingly, there is little research on the benefits of interdisciplinary teaming at the high school level, even with an increased focus on teacher collaboration and Professional Learning Communities (PLCs). Thus, the purpose of this practitioner action research study was to examine the reported professional learning of ninth-grade teachers participating in an interdisciplinary team. The interdisciplinary team consisted of seven secondary level English, science, math, and social studies teachers, including me. During this two-year study (2017–2019), the interdisciplinary team functioned as a PLC and met twice a month: once for the required PLC time and a second time in a voluntary format. Two research questions guided my study: How do we create space for an interdisciplinary team at the high school level? What types of teacher learning and student support may result from creating space for high school teachers to work in an interdisciplinary team setting? Throughout my two findings chapters, I utilized the “Grammar of Schooling” by Tyack and Tobin (1994) as a conceptual framework and Social Learning Theory by Brown and Adler (2008) as a theoretical framework. Both of these frameworks provided useful lenses in understanding the archaic structures of schooling and the organic and innovative collaborative practices of people working in groups. Initially, I found it difficult to replicate a traditional interdisciplinary team model. But despite the institutional barriers, the interdisciplinary team collectively learned from one another, contributed to conversations, offered suggestions and resources, and, most importantly, advocated for ninth-grade students