Octave-tunable miniature RF resonators

The development and testing of a miniaturized, high-Q, broadly tunable resonator is described. An exemplary device, with a center frequency that is continuously tunable from 1.2 to 2.6 GHz, was tested in detail. Experimental results demonstrated a resonator Q of up to 380, and typical insertion loss of -1.9 dB for a 25 MHz 3-dB bandwidth. These resonators have been used to stabilize a broadly-tunable oscillator with phase noise of -132 dBc/Hz at 100-kHz offset, with a center frequency tunable from 1.2-2.6 GHz, and a tuning speed of 1 GHz/ms

Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics

A sample of 197 X-ray emitting clusters of galaxies is considered in the context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the gas mass, extrapolated via an assumed $\beta$ model to a fixed radius of 3 Mpc, is correlated with the gas temperature as predicted by MOND ($M_g \propto T^2$). The observed temperatures are generally consistent with the inferred mass of hot gas; no substantial quantity of additional unseen matter is required in the context of MOND. However, modified dynamics cannot resolve the strong lensing discrepancy in those clusters where this phenomenon occurs. The prediction is that additional baryonic matter may be detected in the central regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro

Observed variability in the Fraunhofer line spectrum of solar flux, 1975 - 1980

Over the five years double-pass spectrometer observations of the Sun-as-a-star revealed significant changes in line intensities. The photospheric component weakened linearly with time 0 to 2.3%. From a lack of correlation between these line weakenings and solar activity indicators like sunspots and plage, a global variation of surface properties is inferred. Model-atmosphere analysis suggests a slight reduction in the lower-photospheric temperature gradient corresponding to a 15% increase in the mixing length within the granulation layer. Chromospheric lines such as Ca II H and K, Ca II 8543 and the CN band head weaken synchronously with solar activity. Thus, the behavior of photospheric and chromospheric lines is markedly different, with the possibility of secular change for the former

Measured and predicted shock shapes and aerodynamic coefficients for blunted cones at incidence in helium at Mach 20.3

Experimental values of shock shapes (alpha = 0 degrees and 10 degrees) and static aerodynamic coefficients (alpha = -4 degrees to 12 degrees) for sharp and spherically blunted cones having cone half-angles of 30, 45, 60, and 70 degrees and nose bluntness ratios of 0, 0.25, and 0.50 are presented. Shock shapes were also measured at 0 degree angle of attack by using a flat-faced cylinder (90 degree cone) and a hemispherically blunted cylinder (sphere). All tests were conducted in helium (gamma = 5/3) at a free-stream Mach number of 20.3 and a unit free-stream Reynolds number of 22,400,000 per meter. Comparisons between measured values and predicted values were made by using several numerical and simple engineering methods

Stripes on a 6-Leg Hubbard Ladder

While DMRG calculations find stripes on doped n-leg t-J ladders, little is known about the possible formation of stripes on n-leg Hubbard ladders. Here we report results for a 7x6 Hubbard model with 4 holes. We find that a stripe forms for values of U/t ranging from 6 to 20. For U/t ~ 3-4, the system exhibits the domain wall feature of a stripe, but the hole density is very broadened.Comment: 4 pages, 5 figure

Observing the sky at extremely high energies with the Cherenkov Telescope Array: Status of the GCT project

The Cherenkov Telescope Array is the main global project of ground-based gamma-ray astronomy for the coming decades. Performance will be significantly improved relative to present instruments, allowing a new insight into the high-energy Universe [1]. The nominal CTA southern array will include a sub-array of seventy 4 m telescopes spread over a few square kilometers to study the sky at extremely high energies, with the opening of a new window in the multi-TeV energy range. The Gamma-ray Cherenkov Telescope (GCT) is one of the proposed telescope designs for that sub-array. The GCT prototype recorded its first Cherenkov light on sky in 2015. After an assessment phase in 2016, new observations have been performed successfully in 2017. The GCT collaboration plans to install its first telescopes and cameras on the CTA site in Chile in 2018-2019 and to contribute a number of telescopes to the subsequent CTA production phase.Comment: 8 pages, 7 figures, ICRC201

The effect of elevated hydrostatic pressure on the spectral absorption of deep-sea fish visual pigments

The effect of hydrostatic pressure (0.1-54 MPa, equivalent to pressures experienced by fish from the ocean's surface to depths of ca. 5400 m) on visual pigment absorption spectra was investigated for rod visual pigments extracted from the retinae of 12 species of deep-sea fish of diverse phylogeny and habitat. The wavelength of peak absorption (λmax) was shifted to longer wavelengths by an average of 1.35 nm at 40 MPa (a pressure approximately equivalent to average ocean depth) relative to measurements made at one atmosphere (ca. 0.1 MPa), but with little evidence of a change in absorbance at the λmax. We conclude that previousλ max measurements of deep-sea fish visual pigments, made at a pressure close to 0.1 MPa, provide a good indication ofλ max values at higher pressures when considering the ecology of vision in the deep-sea. Although not affecting the spectral sensitivity of the animal to any important degree, the observed shift inλ max may be of interest in the context of understanding opsin-chromophore interaction and spectral tuning of visual pigments

A simplified PERT system

Modified PERT technique processes the input data and arranges it in familiar graphic form in a booklet which is issued at periodic intervals. The tabulated data provides readily available information to management personnel concerned with monitoring the progress of a program