3,377 research outputs found

    SU(3) Chiral Symmetry in Non-Relativistic Field Theory

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    Applications imposing SU(3) chiral symmetry on non-relativistic field theory are considered. The first example is a calculation of the self-energy shifts of the spin-3/2 decuplet baryons in nuclear matter, from the chiral effective Lagrangian coupling octet and decuplet baryon fields. Special attention is paid to the self-energy of the delta baryon near the saturation density of nuclear matter. We find contributions to the mass shifts from contact terms in the effective Lagrangian with coefficients of unknown value. As a second application, we formulate an effecive field theory with manifest SU(2) chiral symmetry for the interactions of K and eta mesons with pions at low energy. SU(3) chiral symmetry is imposed on the effective field theory by a matching calculation onto three-flavor chiral perturbation theory. The effective Lagrangian for the pi-K and pi-eta sectors is worked out to order Q^4; the effective Lagrangian for the K-K sector is worked out to order Q^2 with contact interactions to order Q^4. As an application of the method, we calculate the KK s-wave scattering phase shift at leading order and compare with chiral perturbation theory. We conclude with a discussion of the limitations of the approach and propose new directions for work where the matching calculation may be useful.Comment: 85 pages, Ph.D. Thesi

    Micro-Structured Ferromagnetic Tubes for Spin Wave Excitation

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    Micron scale ferromagnetic tubes placed on the ends of ferromagnetic CoTaZr spin waveguides are explored in order to enhance the excitation of Backward Volume Magnetostatic Spin Waves. The tubes produce a closed magnetic circuit about the signal line of the coplanar waveguide and are, at the same time, magnetically contiguous with the spin waveguide. This results in a 10 fold increase in spin wave amplitude. However, the tube geometry distorts the magnetic field near the spin waveguide and relatively high biasing magnetic fields are required to establish well defined spin waves. Only the lowest (uniform) spin wave mode is excited.Comment: 3 pages, 3 figure

    A ssDNA Aptamer That Blocks the Function of the Anti-FLAG M2 Antibody

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    Using SELEX (systematic evolution of ligands by exponential enrichment), we serendipitously discovered a ssDNA aptamer that binds selectively to the anti-FLAG M2 antibody. The aptamer consisted of two motifs (CCTTA and TGTCTWCC) separated by 2-3 bases, and the elimination of one or the other motif abrogated binding. The DNA aptamer and FLAG peptide competed for binding to the antigen-binding pocket of the M2 antibody. In addition, the aptamer eluted FLAG-tagged proteins from the antibody, suggesting a commercial application in protein purification. These findings demonstrate the feasibility of using SELEX to develop ssDNA aptamers that block the function of a specific antibody, a capability that could lead to the development of novel therapeutic modalities for patients with systemic lupus erythematosus, rheumatoid arthritis, and other autoimmune diseases

    First Evidence of Circumstellar Disks around Blue Straggler Stars

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    We present an analysis of optical HST/STIS and HST/FOS spectroscopy of 6 blue stragglers found in the globular clusters M3, NGC6752 and NGC6397. These stars are a subsample of a set of ~50 blue stragglers and stars above the main sequence turn-off in four globular clusters which will be presented in an forthcoming paper. All but the 6 stars presented here can be well fitted with non-LTE model atmospheres. The 6 misfits, on the other hand, possess Balmer jumps which are too large for the effective temperatures implied by their Paschen continua. We find that our data for these stars are consistent with models only if we account for extra absorption of stellar Balmer photons by an ionized circumstellar disk. Column densities of HI and CaII are derived as are the the disks' thicknesses. This is the first time that a circumstellar disk is detected around blue stragglers. The presence of magnetically-locked disks attached to the stars has been suggested as a mechanism to lose the large angular momentum imparted by the collision event at the birth of these stars. The disks implied by our study might not be massive enough to constitute such an angular momentum sink, but they could be the leftovers of once larger disks.Comment: Accepted by ApJ Letters 10 pages, 2 figure

    Lagrangian Structure Functions in Turbulence: A Quantitative Comparison between Experiment and Direct Numerical Simulation

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    A detailed comparison between data from experimental measurements and numerical simulations of Lagrangian velocity structure functions in turbulence is presented. By integrating information from experiments and numerics, a quantitative understanding of the velocity scaling properties over a wide range of time scales and Reynolds numbers is achieved. The local scaling properties of the Lagrangian velocity increments for the experimental and numerical data are in good quantitative agreement for all time lags. The degree of intermittency changes when measured close to the Kolmogorov time scales or at larger time lags. This study resolves apparent disagreements between experiment and numerics.Comment: 13 RevTeX pages (2 columns) + 8 figures include

    A versatile wavelength-dependent spectrophotometer for efficiency measurements of CCD and cryogenic gratings

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    A user-friendly and automatic illuminator with adjustable wavelength and optical power has been developed to obtain precision quantum efficiency (QE) curves of astronomical CCD as well as optical transmission measurements for cryogenic holographic gratings and other optical components. Integrating commercial components with custom mechanical parts and control software, this equipment is able to illuminate a target with light of controlled intensity and wavelength. This facility is primarily intended for testing of Volume Phase Holographic (VPH) gratings at low temperature as well as obtaining CCD quantum efficiencies. A Labview control application runs on a desktop computer allowing full automation of the spectrophotometer. The apparatus includes a Quartz-Tungsten light source, neutral density filters, a monochromator, visible and near-infrared power meters, as well as collimating and focusing optics. Rotation mechanisms allow the characterization of gratings for all angles of diffractions. For CCD testing, network commands allow the facility to get raw images, compute and record QE curves for further detector characterization

    MR Spectroscopic Imaging of Peripheral Zone in Prostate Cancer Using a 3T MRI Scanner: Endorectal versus External Phased Array Coils.

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    Magnetic resonance spectroscopic imaging (MRSI) detects alterations in major prostate metabolites, such as citrate (Cit), creatine (Cr), and choline (Ch). We evaluated the sensitivity and accuracy of three-dimensional MRSI of prostate using an endorectal compared to an external phased array "receive" coil on a 3T MRI scanner. Eighteen patients with prostate cancer (PCa) who underwent endorectal MR imaging and proton (1H) MRSI were included in this study. Immediately after the endorectal MRSI scan, the PCa patients were scanned with the external phased array coil. The endorectal coil-detected metabolite ratio [(Ch+Cr)/Cit] was significantly higher in cancer locations (1.667 ± 0.663) compared to non-cancer locations (0.978 ± 0.420) (P < 0.001). Similarly, for the external phased array, the ratio was significantly higher in cancer locations (1.070 ± 0.525) compared to non-cancer locations (0.521 ± 0.310) (P < 0.001). The sensitivity and accuracy of cancer detection were 81% and 78% using the endorectal 'receive' coil, and 69% and 75%, respectively using the external phased array 'receive' coil

    Do Complexity Measures of Frontal EEG Distinguish Loss of Consciousness in Geriatric Patients Under Anesthesia?

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    While geriatric patients have a high likelihood of requiring anesthesia, they carry an increased risk for adverse cognitive outcomes from its use. Previous work suggests this could be mitigated by better intraoperative monitoring using indexes defined by several processed electroencephalogram (EEG) measures. Unfortunately, inconsistencies between patients and anesthetic agents in current analysis techniques have limited the adoption of EEG as standard of care. In attempts to identify new analyses that discriminate clinically-relevant anesthesia timepoints, we tested 1/f frequency scaling as well as measures of complexity from nonlinear dynamics. Specifically, we tested whether analyses that characterize time-delayed embeddings, correlation dimension (CD), phase-space geometric analysis, and multiscale entropy (MSE) capture loss-of-consciousness changes in EEG activity. We performed these analyses on EEG activity collected from a traditionally hard-to-monitor patient population: geriatric patients on beta-adrenergic blockade who were anesthetized using a combination of fentanyl and propofol. We compared these analyses to traditional frequency-derived measures to test how well they discriminated EEG states before and after loss of response to verbal stimuli. We found spectral changes similar to those reported previously during loss of response. We also found significant changes in 1/f frequency scaling. Additionally, we found that our phase-space geometric characterization of time-delayed embeddings showed significant differences before and after loss of response, as did measures of MSE. Our results suggest that our new spectral and complexity measures are capable of capturing subtle differences in EEG activity with anesthesia administration-differences which future work may reveal to improve geriatric patient monitoring
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