Dispersion of Ordered Stripe Phases in the Cuprates

A phase separation model is presented for the stripe phase of the cuprates, which allows the doping dependence of the photoemission spectra to be calculated. The idealized limit of a well-ordered array of magnetic and charged stripes is analyzed, including effects of long-range Coulomb repulsion. Remarkably, down to the limit of two-cell wide stripes, the dispersion can be interpreted as essentially a superposition of the two end-phase dispersions, with superposed minigaps associated with the lattice periodicity. The largest minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk) Van Hove singularity. The calculated spectra are dominated by two features -- this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a strong correlation between these two features and the experimental photoemission results of a two-peak dispersion in La$_{2-x}$Sr$_x$CuO$_4$, and the peak-dip-hump spectra in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The differences are suggestive of the role of increasing stripe fluctuations. The 1/8 anomaly is associated with a quantum critical point, here expressed as a percolation-like crossover. A model is proposed for the limiting minority magnetic phase as an isolated two-leg ladder.Comment: 24 pages, 26 PS figure

Neurofibromatosis type 1 gene product (neurofibromin) associates with microtubules

The neurofibromatosis type 1 (NF1) gene was recently identified by positional cloning and found to encode a protein with structural and functional homology to mammalian and yeast GTPase-activating proteins (GAPs). Using antibodies directed against the NF1 gene product, a protein of ∼250kDa was identified and termed neurofibromin. Double-indirect immunofluorescent labeling with anti-neurofibromin and anti-tubulin antibodies demonstrates that neurofibromin associates with cytoplasmic microtubules. Immunoblotting of microtubule-enriched cytoplasmic fractions, using antibodies generated against neurofibromin, shows that neurofibromin copurifies with microtubules. When portions of neurofibromin are expressed in Sf9 insect cells they associate with polymerized microtubules; furthermore, the critical residues for this interaction reside within the GAP-related domain of neurofibromin. The unexpected association of neurofibromin with microtubules suggests that neurofibromin is involved in microtubule-mediated intracellullar signal transduction pathways.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45544/1/11188_2005_Article_BF01233074.pd

Self-regulation of Exercise Intensity in Cardiac Rehabilitation Participants

Purpose The purpose of this study was to determine if Phase III‐IV cardiac rehabilitation participants could accurately self‐monitor exercise intensity through the use of the heart rate (HR) palpation technique and the rating of perceived exertion scale (RPE) during their typical exercise routine and to determine if participants were exercising within their prescribed target heart rate (THR) range.Methods One hundred and sixty‐one (119 men, 42 women) cardiac rehabilitation participants (age = 64.8 ± 9.2 years) each performed their usual exercise routine on aerobic equipment for 20 min, while wearing a HR monitor. At 10 and 15min of exercise, participants reported their 10‐s palpated HR and RPE rating.Results No significant differences were found between mean palpated HRmin10 (100.8 ±18.6 beats per minute (BPM) and mean actual HRmin10 (102.7 ± 17.1 BPM) or mean palpated HRmin15 (105.9 ±19.2 BPM) and mean actual HRmin15 (106.4 ± 18.4 BPM). The correlations between actual HR and palpated HR at 10 and 15 min of exercise was 0.73 (p \u3c 0.0001, (Standard error of the estimate) SEE = 11.7 BPM) and 0.83 (p \u3c 0.0001, SEE = 10.3 BPM), respectively. When actual HR was compared with THR, 16 participants exceeded their prescribed THR (11–20 BPM), 82 participants fell below their THR (15–26 BPM), and 25 participants exercised within their THR, even though all reported a similar RPE (11–12).Conclusions The results of this study suggest that Phase III‐IV cardiac rehabilitation participants can accurately palpate their exercise pulse rates but their RPE did not appropriately reflect the intensity of their physical effort. Additionally, the majority of participants did not exercise within their prescribed THR range