A modal model for diffraction gratings

A description of an algorithm for a rather general modal grating calculation is presented. Arbitrary profiles, depth, and permittivity are allowed. Gratings built up from sub-gratings are allowed, as are coatings on the sidewalls of lines, and arbitrary complex structure. Conical angles and good conductors are supported

Contrasting alterations to synaptic and intrinsic properties in upper-cervical superficial dorsal horn neurons following acute neck muscle inflammation

Background: Acute and chronic pain in axial structures, like the back and neck, are difficult to treat, and have incidence as high as 15%. Surprisingly, most preclinical work on pain mechanisms focuses on cutaneous structures in the limbs and animal models of axial pain are not widely available. Accordingly, we developed a mouse model of acute cervical muscle inflammation and assessed the functional properties of superficial dorsal horn (SDH) neurons.<p></p> Results: Male C57/Bl6 mice (P24-P40) were deeply anaesthetised (urethane 2.2?g/kg i.p) and the rectus capitis major muscle (RCM) injected with 40??l of 2% carrageenan. Sham animals received vehicle injection and controls remained anaesthetised for 2?hrs. Mice in each group were sacrificed at 2?hrs for analysis. c-Fos staining was used to determine the location of activated neurons. c-Fos labelling in carrageenan-injected mice was concentrated within ipsilateral (87% and 63% of labelled neurons in C1 and C2 segments, respectively) and contralateral laminae I - II with some expression in lateral lamina V. c-Fos expression remained below detectable levels in control and sham animals. In additional experiments, whole cell recordings were obtained from visualised SDH neurons in transverse slices in the ipsilateral C1 and C2 spinal segments. Resting membrane potential and input resistance were not altered. Mean spontaneous EPSC amplitude was reduced by ~20% in neurons from carrageenan-injected mice versus control and sham animals (20.63???1.05 vs. 24.64???0.91 and 25.87???1.32 pA, respectively). The amplitude (238???33 vs. 494???96 and 593???167 pA) and inactivation time constant (12.9???1.5 vs. 22.1???3.6 and 15.3???1.4?ms) of the rapid A type potassium current (IAr), the dominant subthreshold current in SDH neurons, were reduced in carrageenan-injected mice.<p></p> Conclusions: Excitatory synaptic drive onto, and important intrinsic properties (i.e., IAr) within SDH neurons are reduced two hours after acute muscle inflammation. We propose this time point represents an important transition period between peripheral and central sensitisation with reduced excitatory drive providing an initial neuroprotective mechanism during the early stages of the progression towards central sensitisation

The Power Spectrum of the PSC Redshift Survey

We measure the redshift-space power spectrum P(k) for the recently completed IRAS Point Source Catalogue (PSC) redshift survey, which contains 14500 galaxies over 84% of the sky with 60 micron flux >= 0.6 Jansky. Comparison with simulations shows that our estimated errors on P(k) are realistic, and that systematic errors due to the finite survey volume are small for wavenumbers k >~ 0.03 h Mpc^-1. At large scales our power spectrum is intermediate between those of the earlier QDOT and 1.2 Jansky surveys, but with considerably smaller error bars; it falls slightly more steeply to smaller scales. We have fitted families of CDM-like models using the Peacock-Dodds formula for non-linear evolution; the results are somewhat sensitive to the assumed small-scale velocity dispersion \sigma_V. Assuming a realistic \sigma_V \approx 300 km/s yields a shape parameter \Gamma ~ 0.25 and normalisation b \sigma_8 ~ 0.75; if \sigma_V is as high as 600 km/s then \Gamma = 0.5 is only marginally excluded. There is little evidence for any `preferred scale' in the power spectrum or non-Gaussian behaviour in the distribution of large-scale power.Comment: Latex, uses mn.sty, 14 pages including 11 Postscript figures. Accepted by MNRA

Quantitative magnetic resonance imaging of meniscal pathology ex vivo

OBJECTIVE To determine the ability of conventional spin echo (SE) T2 and ultrashort echo time (UTE) T2* relaxation times to characterize pathology in cadaveric meniscus samples. MATERIALS AND METHODS From 10 human donors, 54 triangular (radially cut) meniscus samples were harvested. Meniscal pathology was classified as normal (n = 17), intrasubstance degenerated (n = 33), or torn (n = 4) using a modified arthroscopic grading system. Using a 3-T MR system, SE T2 and UTE T2* values of the menisci were determined, followed by histopathology. Effect of meniscal pathology on relaxation times and histology scores were determined, along with correlation between relaxation times and histology scores. RESULTS Mean ± standard deviation UTE T2* values for normal, degenerated, and torn menisci were 3.6 ± 1.3 ms, 7.4 ± 2.5 ms, and 9.8 ± 5.7 ms, respectively, being significantly higher in degenerated (p  0.14). In terms of histology, we found significant group-wise differences (each p < 0.05) in fiber organization and inner-tip surface integrity sub-scores, as well as the total score. Finally, we found a significant weak correlation between UTE T2* and histology total score (p = 0.007, R$_{s}$$^{2}$ = 0.19), unlike the correlation between SE T2 and histology (p = 0.09, R$_{s}$$^{2}$ = 0.05). CONCLUSION UTE T2* values were found to distinguish normal from both degenerated and torn menisci and correlated significantly with histopathology

CIRCULAR DICHROISM OF LIGHT-HARVESTING COMPLEXES FROM PURPLE PHOTOSYNTHETIC BACTERIA

The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of α-helix (50%) and very little 0-pleated sheet. This confirms the predictions of the group of Zuber of a high a-helical content based upon consideration of the primary structures of several antenna apoproteins. The CD spectra from the carotenoids and the bacteriochlorophylls show considerable variations depending upon the type of antenna complex. The different amplitude ratios in the CD spectrum for the bacteriochlorophyll Qy, Qx and Soret bands indicate not only different degrees of exciton coupling, but also a strong and variable hyperchromism (Scherz and Parson, 1984a, b)

Origin and evolution of halo bias in linear and non-linear regimes

We present results from a study of bias and its evolution for galaxy-size halos in a large, high-resolution simulation of a LCDM model. We consider the evolution of bias estimated using two-point correlation function (b_xi), power spectrum (b_P), and a direct correlation of smoothed halo and matter overdensity fields (b_d). We present accurate estimates of the evolution of the matter power spectrum probed deep into the stable clustering regime (k~[0.1-200]h/Mpc at z=0). The halo power spectrum evolves much slower than the power spectrum of matter and has a different shape which indicates that the bias is time- and scale-dependent. At z=0, the halo power spectrum is anti-biased with respect to the matter power spectrum at wavenumbers k~[0.15-30]h/Mpc, and provides an excellent match to the power spectrum of the APM galaxies at all probed k. In particular, it nicely matches the inflection observed in the APM power spectrum at k~0.15h/Mpc. We complement the power spectrum analysis with a direct estimate of bias using smoothed halo and matter overdensity fields and show that the evolution observed in the simulation in linear and mildly non-linear regimes can be well described by the analytical model of Mo & White (1996), if the distinction between formation redshift of halos and observation epoch is introduced into the model. We present arguments and evidence that at higher overdensities, the evolution of bias is significantly affected by dynamical friction and tidal stripping operating on the satellite halos in high-density regions of clusters and groups; we attribute the strong anti-bias observed in the halo correlation function and power spectrum to these effects. (Abridged)Comment: submitted to the Astrophys.Journal; 19 pages, 9 figures LaTeX (uses emulateapj.sty

Measuring the galaxy power spectrum with future redshift surveys

Precision measurements of the galaxy power spectrum P(k) require a data analysis pipeline that is both fast enough to be computationally feasible and accurate enough to take full advantage of high-quality data. We present a rigorous discussion of different methods of power spectrum estimation, with emphasis on the traditional Fourier method, the linear (Karhunen-Loeve; KL), and quadratic data compression schemes, showing in what approximations they give the same result. To improve speed, we show how many of the advantages of KL data compression and power spectrum estimation may be achieved with a computationally faster quadratic method. To improve accuracy, we derive analytic expressions for handling the integral constraint, since it is crucial that finite volume effects are accurately corrected for on scales comparable to the depth of the survey. We also show that for the KL and quadratic techniques, multiple constraints can be included via simple matrix operations, thereby rendering the results less sensitive to galactic extinction and mis-estimates of the radial selection function. We present a data analysis pipeline that we argue does justice to the increases in both quality and quantity of data that upcoming redshift surveys will provide. It uses three analysis techniques in conjunction: a traditional Fourier approach on small scales, a pixelized quadratic matrix method on large scales and a pixelized KL eigenmode analysis to probe anisotropic effects such as redshift-space distortions.Comment: Major revisions for clarity. Matches accepted ApJ version. 23 pages, with 2 figs included. Color figure and links at http://www.sns.ias.edu/~max/galpower.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/galpower.html (faster from Europe) or from [email protected]

An Inversion Method for Measuring Beta in Large Redshift Surveys

A precision method for determining the value of Beta= Omega_m^{0.6}/b, where b is the galaxy bias parameter, is presented. In contrast to other existing techniques that focus on estimating this quantity by measuring distortions in the redshift space galaxy-galaxy correlation function or power spectrum, this method removes the distortions by reconstructing the real space density field and determining the value of Beta that results in a symmetric signal. To remove the distortions, the method modifies the amplitudes of a Fourier plane-wave expansion of the survey data parameterized by Beta. This technique is not dependent on the small-angle/plane-parallel approximation and can make full use of large redshift survey data. It has been tested using simulations with four different cosmologies and returns the value of Beta to +/- 0.031, over a factor of two improvement over existing techniques.Comment: 16 pages including 6 figures Submitted to The Astrophysical Journa