Mandala

pages 94-9

Hidden Charge 2e Boson in Doped Mott Insulators: Field Theory of Mottness

We construct the low energy theory of a doped Mott insulator, such as the high-temperature superconductors, by explicitly integrating over the degrees of freedom far away from the chemical potential. For either hole or electron doping, a charge 2e bosonic field emerges at low energy. The charge 2e boson mediates dynamical spectral weight transfer across the Mott gap and creates a new charge e excitation by binding a hole. The result is a bifurcation of the electron dispersion below the chemical potential as observed recently in angle-resolved photoemission on Pb-doped Bi_2Sr_2CaCu_2O_{8+\delta} (Pb2212).Comment: 4 pages, 2 figures: Correct version to appear in PRL. Revisions include a derivation of the electron operator at low energies which reveals a branching structure seen recently in ARPES on Pb221

Origin of the Mott Gap

We show exactly that the only charged excitations that exist in the strong-coupling limit of the half-filled Hubbard model are gapped composite excitations generated by the dynamics of the charge $2e$ boson that appears upon explicit integration of the high-energy scale. At every momentum, such excitations have non-zero spectral weight at two distinct energy scales separated by the on-site repulsion $U$. The result is a gap in the spectrum for the composite excitations accompanied by a discontinuous vanishing of the density of states at the chemical potential when $U$ exceeds the bandwidth. Consequently, we resolve the long-standing problem of the cause of the charge gap in a half-filled band in the absence of symmetry breaking.Comment: 6 pages, 2 figures: Expanded Published versio

Apply Now!: Utilizing Application Date to Predict College Enrollment

Using Perna’s (2006) college choice model as the conceptual framework, the researcher utilized two data analyses to complete this study. First, multiple regressions were performed on three groups of variables: entrance examination, core high school gpa, and cumulative high school gpa; gender, ethnicity, and residency; and first-generation status and Mississippi congressional district. Second, a chi square test was completed to discover how likely it is that a student’s application date is related to the acceptance rate (likelihood of acceptance) and yield rate (likelihood of matriculating) of the University of Mississippi freshman class

Impact of Gender on Acute Aerobic Exercise Induced Brainderived Neurotrophic Factor And Cognitive Function In Older Adults

Purpose: The purpose of this study was to examine the impact of gender on acute exercise induced BDNF and cognitive function among older individuals. The hypothesis was that exercise would increase BDNF levels and enhance cognitive processing time post exercise followed by a drop in BDNF and return cognitive processing time to baseline post-30 minutes. It was also hypothesized that women would have higher BDNF values compared to men. Methods: The subjects consisted of 18 active males (n = 9) and females (n = 9). The subjects took part in an exercise trial and a control trial. The exercise trial entailed riding either a recumbent or upright bike at 75% of their age predicted max heart rate for 30 minutes. The control trial consisted of reading. A Stroop Test was given, and blood samples were obtained before, after, and 30 minutes after exercise and control. Serum was analyzed for BDNF, testosterone, and estrogen using commercially available ELISA kits. Results: Results showed that there was a significant effect of time in Stroop testing across all subjects. There was a trend (p = 0.068) for a decrease in Stroop time from pre to immediate post timepoints, and a significant decrease (p = 0.004) in Stroop time from pre to post-30 timepoints. There was a significant main effect of exercise on BDNF levels, (p = 0.05) and females were found to have significantly higher BDNF than males (p = 0.055). Conclusion: There was statistical evidence that acute exercise affects BDNF production in both genders, but not cognitive processing speed among an older active population. Cognitive processing speed continued to improve across all timepoints. As well, women were found to have overall higher BDNF

The empathetic researcher: applying research methods from anthropology to lis

I combined semi-structured interviews and structured video auto-ethnography in an exploratory study of rural librarians’ support for cyberbullied teens. This study involved two stages: 1) librarian and teen participants engaged in individual interviews with me. Librarian questions focused on perceptions of librarian roles and support for teens, while teen questions focused on perceptions of cyberbullying and needed adult support; 2) each participant then recorded one video entry via a personal digital device (e.g. iPhone) in which they responded to provided prompts that included hypothetical scenarios that allowed participants to engage in self-reflection and self-examination. Relational theory supported interview and prompt question development. Throughout the study, I maintained a written auto-ethnography that allowed me to reflect upon interview and video prompt design; participant interactions; and capture self-reflections during data collection. This poster will present an instrumental case that reflects the data collection activities and early results to illustrate innovative LIS research

Skeletal muscle protein metabolism in the elderly: Interventions to counteract the 'anabolic resistance' of ageing

Age-related muscle wasting (sarcopenia) is accompanied by a loss of strength which can compromise the functional abilities of the elderly. Muscle proteins are in a dynamic equilibrium between their respective rates of synthesis and breakdown. It has been suggested that age-related sarcopenia is due to: i) elevated basal-fasted rates of muscle protein breakdown, ii) a reduction in basal muscle protein synthesis (MPS), or iii) a combination of the two factors. However, basal rates of muscle protein synthesis and breakdown are unchanged with advancing healthy age. Instead, it appears that the muscles of the elderly are resistant to normally robust anabolic stimuli such as amino acids and resistance exercise. Ageing muscle is less sensitive to lower doses of amino acids than the young and may require higher quantities of protein to acutely stimulate equivalent muscle protein synthesis above rest and accrue muscle proteins. With regard to dietary protein recommendations, emerging evidence suggests that the elderly may need to distribute protein intake evenly throughout the day, so as to promote an optimal per meal stimulation of MPS. The branched-chain amino acid leucine is thought to play a central role in mediating mRNA translation for MPS, and the elderly should ensure sufficient leucine is provided with dietary protein intake. With regards to physical activity, lower, than previously realized, intensity high-volume resistance exercise can stimulate a robust muscle protein synthetic response similar to traditional high-intensity low volume training, which may be beneficial for older adults. Resistance exercise combined with amino acid ingestion elicits the greatest anabolic response and may assist elderly in producing a 'youthful' muscle protein synthetic response provided sufficient protein is ingested following exercise

Exact Integration of the High Energy Scale in Doped Mott Insulators

We expand on our earlier work (cond-mat/0612130, Phys. Rev. Lett. {\bf 99}, 46404 (2007)) in which we constructed the exact low-energy theory of a doped Mott insulator by explicitly integrating (rather than projecting) out the degrees of freedom far away from the chemical potential. The exact low-energy theory contains degrees of freedom that cannot be obtained from projective schemes. In particular a new charge $\pm 2e$ bosonic field emerges at low energies that is not made out of elemental excitations. Such a field accounts for dynamical spectral weight transfer across the Mott gap. At half-filling, we show that two such excitations emerge which play a crucial role in preserving the Luttinger surface along which the single-particle Green function vanishes. In addition, the interactions with the bosonic fields defeat the artificial local SU(2) symmetry that is present in the Heisenberg model. We also apply this method to the Anderson-U impurity and show that in addition to the Kondo interaction, bosonic degrees of freedom appear as well. Finally, we show that as a result of the bosonic degree of freedom, the electron at low energies is in a linear superposition of two excitations--one arising from the standard projection into the low-energy sector and the other from the binding of a hole and the boson.Comment: Published veriso