Novel trapping techniques for shaping Bose-Einstein condensates

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, February 2007.Includes bibliographical references (p. 125-133).A combination of radio frequency radiation and magnetic field gradients was used to trap atoms in dressed states. In a magnetic field with a quadrupole minimum. RF fields resonant with the (I F. m)) 11. -1) -- 1, 0) transition trapped the atoms on the surface of a sphere, and gravity caused the atoms to pool at the bottom of the sphere. BECs were transferred into this dressed Zeeman trap with 100% efficiency, with lifetimes of up to 30 s, and trapping frequencies of up to 250 Hz were measured. A hard disk platter with a specially written magnetic pattern was used to generate magnetic fields to confine atoms tightly. Detrimental interactions with the surface were avoided by using an extremely thin film with a large magnetic remnant. BECs of up to 5 x 10" atoms were produced in cigar shaped traps -40 pin above the surface, and trap frequencies up to 5 kHz were measured. After evaporation, condensed clouds moved(] closer to the surface to probe imperfections in the magnetic potential, revealing defects at distances closer than 35 prn. Finally, BECs were dropped from a height of 350 pm in an attempt to achieve specular reflection. but a large amount of dispersion was observed.(cont.) Finally, BECs were loaded into a three-dimensional optical lattice, and a quantum phase transition from a superfluid to a Mott insulator was observed. Using microwave spectroscopy. the density dependent "clock shift" was was found to depend on the occupation number of the wells. The singly occupied lattice sites were then investigated as an atomic clock system with no density shift. Linewidths as small as 1 Hz FWHMI out of 6.8 GHz are comparable to current atomic frequency standards.by Micah Boyd.Ph.D

Continuous and Pulsed Quantum Zeno Effect

Continuous and pulsed quantum Zeno effects were observed using a $^{87}$Rb Bose-Einstein condensate(BEC). Oscillations between two ground hyperfine states of a magnetically trapped condensate, externally driven at a transition rate $\omega_R$, were suppressed by destructively measuring the population in one of the states with resonant light. The suppression of the transition rate in the two level system was quantified for pulsed measurements with a time interval $\delta t$ between pulses and continuous measurements with a scattering rate $\gamma$. We observe that the continuous measurements exhibit the same suppression in the transition rate as the pulsed measurements when $\gamma\delta t=3.60(0.43)$, in agreement with the predicted value of 4. Increasing the measurement rate suppressed the transition rate down to $0.005\omega_R$.Comment: 5 pages, 4 figure

Imaging the Mott Insulator Shells using Atomic Clock Shifts

Microwave spectroscopy was used to probe the superfluid-Mott Insulator transition of a Bose-Einstein condensate in a 3D optical lattice. Using density dependent transition frequency shifts we were able to spectroscopically distinguish sites with different occupation numbers, and to directly image sites with occupation number n=1 to n=5 revealing the shell structure of the Mott Insulator phase. We use this spectroscopy to determine the onsite interaction and lifetime for individual shells

Atom trapping with a thin magnetic film

We have created a $^{87}$Rb Bose-Einstein condensate in a magnetic trapping potential produced by a hard disk platter written with a periodic pattern. Cold atoms were loaded from an optical dipole trap and then cooled to BEC on the surface with radiofrequency evaporation. Fragmentation of the atomic cloud due to imperfections in the magnetic structure was observed at distances closer than 40 $\mu$m from the surface. Attempts to use the disk as an atom mirror showed dispersive effects after reflection.Comment: 4 pages, 5 figure

A Nuclear DNA Perspective on Delineating Evolutionarily Significant Lineages in Polyploids: The Case of the Endangered Shortnose Sturgeon (Acipenser brevirostrum)

The shortnose sturgeon, Acipenser brevirostrum, oft considered a phylogenetic relic, is listed as an “endangered species threatened with extinction” in the US and “Vulnerable” on the IUCN Red List. Effective conservation of A. brevirostrum depends on understanding its diversity and evolutionary processes, yet challenges associated with the polyploid nature of its nuclear genome have heretofore limited population genetic analysis to maternally inherited haploid characters. We developed a suite of polysomic microsatellite DNA markers and characterized a sample of 561 shortnose sturgeon collected from major extant populations along the North American Atlantic coast. The 181 alleles observed at 11 loci were scored as binary loci and the data were subjected to multivariate ordination, Bayesian clustering, hierarchical partitioning of variance, and among-population distance metric tests. The methods uncovered moderately high levels of gene diversity suggesting population structuring across and within three metapopulations (Northeast, Mid-Atlantic, and Southeast) that encompass seven demographically discrete and evolutionarily distinct lineages. The predicted groups are consistent with previously described behavioral patterns, especially dispersal and migration, supporting the interpretation that A. brevirostrum exhibit adaptive differences based on watershed. Combined with results of prior genetic (mitochondrial DNA) and behavioral studies, the current work suggests that dispersal is an important factor in maintaining genetic diversity in A. brevirostrum and that the basic unit for conservation management is arguably the local population

Objective and subjective measures of exercise intensity during thermo-neutral and hot yoga.

While hot yoga has gained enormous popularity in recent years due in part to increased environmental challenge associated with exercise in the heat, it is not clear whether hot yoga is more vigorous than thermo-neutral yoga. Therefore, the aim of this study was to determine objective and subjective measures of exercise intensity during constant intensity yoga in a hot and thermo-neutral environment. Using a randomized, cross-over design, 14 participants completed two identical ~20-minute yoga sessions in a hot (35.3 ± 0.8°C; humidity: 20.5 ± 1.4%) and thermo-neutral (22.1 ± 0.2°C; humidity: 27.8 ± 1.6%) environment. Oxygen consumption (VO2) and heart rate (HR) were recorded as objective measures (%VO2max and %HRmax) and rating of perceived exertion (RPE) was recorded as a subjective measure of exercise intensity. There was no difference in exercise intensity based on %VO2max during hot vs. thermo-neutral yoga (30.9 ± 2.3 vs. 30.5 ± 1.8%, p=0.68). However, exercise intensity was significantly higher during hot vs. thermo-neutral yoga based on %HRmax (67.0 ± 2.3 vs. 60.8 ± 1.9%, p=0.01) and RPE (12 ± 1 vs. 11 ± 1, p=0.04). According to established exercise intensities, hot yoga was classified as “light-intensity” based on %VO2 but “moderate-intensity” exercise based on %HRmax and RPE while thermo-neutral yoga was classified as “light-intensity” exercise based on %VO2max, %HRmax, and RPE. Despite the added hemodynamic stress and perception that yoga is more strenuous in a hot environment, we observed similar oxygen consumption during hot vs. thermo-neutral yoga classifying both exercise modalities as “light-intensity” exercise.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Individual and Contextual Risk and Protective Factors for Suicidal Thoughts and Behaviors among Black Adolescents with Arrest Histories

Black adolescents in the United States have experienced an increase in suicidal thoughts and behaviors (STBs). Since Black adolescents are overrepresented in the youth punishment system, more research is needed to investigate correlates of STBs for this population. The purpose of this paper is to explore and establish correlates of individual, family, and community risk and protective factors and their relationship to lifetime STBs in a national sample of Black youth with arrest histories. Guided by an intersectional eco-behavioral lens, we investigated individual, family and contextual risk and protective factors for STBs among a national sample of justice-involved Black youth aged 12–17 with a history of arrest (n = 513). We used logistic regression models to test risk and protective factors for STBs. Among the sample, 9.78% endorsed suicidal ideation, and 7.17% endorsed a previous suicide attempt. Further, gender (female) and depression severity were risk factors for STBs, while positive parenting and religiosity were protective factors for STBs. School engagement was associated with lower levels of suicidal ideation. The findings suggest suicide prevention and intervention efforts should identify developmentally salient risk and protective factors to reduce mental health burden associated with STBs and concurrent alleged law-breaking activity of Black youth