Derivation of a tangent function using an integrated circuit four-quadrant multiplier

A tangent function generator is provided which utilizes input signals proportionate to the sine and cosine of a given angle. The equipment accomplishes a trigonometric manipulation which forms an output signal substantially independent of the input reference voltage but proportional to the tangent of the angle. The device uses a multiplier and operational amplifier

On the Self-Affine Roughness of a Crack Front in Heterogeneous Media

The long-ranged elastic model, which is believed to describe the evolution of a self-affine rough crack-front, is analyzed to linear and non-linear orders. It is shown that the nonlinear terms, while important in changing the front dynamics, are not changing the scaling exponent which characterizes the roughness of the front. The scaling exponent thus predicted by the model is much smaller than the one observed experimentally. The inevitable conclusion is that the gap between the results of experiments and the model that is supposed to describe them is too large, and some new physics has to be invoked for another model.Comment: 4 pages, 4 figure

Key aspects of stratospheric tracer modeling using assimilated winds

International audienceThis study describes key aspects of global chemistry-transport models and their impact on stratospheric tracer transport. We concentrate on global models that use assimilated winds from numerical weather predictions, but the results also apply to tracer transport in general circulation models. We examined grid resolution, numerical diffusion, air parcel dispersion, the wind or mass flux update frequency, and time interpolation. The evaluation is performed with assimilated meteorology from the "operational analyses or operational data" (OD) from the European Centre for Medium-Range Weather Forecasts (ECMWF). We also show the effect of the mass flux update frequency using the ECMWF 40-year re-analyses (ERA40). We applied the three-dimensional chemistry-transport Tracer Model version 5 (TM5) and a trajectory model and performed several diagnoses focusing on different transport regimes. Covering different time and spatial scales, we examined (1) polar vortex dynamics during the Arctic winter, (2) the large-scale stratospheric meridional circulation, and (3) air parcel dispersion in the tropical lower stratosphere. Tracer distributions inside the Arctic polar vortex show considerably worse agreement with observations when the model grid resolution in the polar region is reduced to avoid numerical instability. The results are sensitive to the diffusivity of the advection. Nevertheless, the use of a computational cheaper but diffusive advection scheme is feasible for tracer transport when the horizontal grid resolution is equal or smaller than 1 degree. The use of time interpolated winds improves the tracer distributions, particularly in the middle and upper stratosphere. Considerable improvement is found both in the large-scale tracer distribution and in the polar regions when the update frequency of the assimilated winds is increased from 6 to 3 h. It considerably reduces the vertical dispersion of air parcels in the tropical lower stratosphere. Strong horizontal dispersion is not necessarily an indication of poor wind quality, as observations indicate. Moreover, the generally applied air parcel dispersion calculations should be interpreted with care, given the strong sensitivity of dispersion with altitude. The results in this study provide a guideline for stratospheric tracer modeling using assimilated winds. They further demonstrate significant progress in the use of assimilated meteorology in chemistry-transport models, relevant for both short- and long-term integrations

The Closest Damped Lyman Alpha System

A difficulty of studying damped Lyman alpha systems is that they are distant, so one knows little about the interstellar medium of the galaxy. Here we report upon a damped Lyman alpha system in the nearby galaxy NGC 4203, which is so close (v_helio = 1117 km/s) and bright (B_o = 11.62) that its HI disk has been mapped. The absorption lines are detected against Ton 1480, which lies only 1.9' (12 h_50 kpc) from the center of NGC 4203. Observations were obtained with the Faint Object Spectrograph on HST (G270H grating) over the 2222-3277 Angstrom region with 200 km/s resolution. Low ionization lines of Fe, Mn, and Mg were detected, leading to metallicities of -2.29, -2.4, which are typical of other damped Lyman alpha systems, but well below the stellar metallicity of this type of galaxy. Most notably, the velocity of the lines is 1160 +- 10 km/s, which is identical to the HI rotational velocity of 1170 km/s at that location in NGC 4203, supporting the view that these absorption line systems can be associated with the rotating disks of galaxies. In addition, the line widths of the Mg lines give an upper limit to the velocity dispersion of 167 km/s, to the 99% confidence level.Comment: 4 pages LaTeX, including 1 figure and 1 table, uses emulateapj.sty. Accepted for publication by Astrophysical Journal Letter

On the use of mass-conserving wind fields in chemistry-transport models

A new method has been developed that provides mass-conserving wind fields for global chemistry-transport models. In previous global Eulerian modeling studies a mass-imbalance was found between the model mass transport and the surface pressure tendencies. Several methods have been suggested to correct for this imbalance, but so far no satisfactory solution has been found. Our new method solves these problems by using the wind fields in a spherical harmonical form (divergence and vorticity) by mimicing the physics of the weather forecast model as closely as possible. A 3-D chemistry-transport model was used to show that the calculated ozone fields with the new processing method agree remarkably better with ozone observations in the upper troposphere and lower stratosphere. In addition, the calculated age of air in the lower stratosphere show better agreement with observations, although the air remains still too young in the extra-tropical stratosphere

The Dependence of the Soft X-ray Properties of LMXBs on the Metallicity of Their Environment

We determine the X-ray spectral properties of a sample of low-mass X-ray binaries (LMXBs) which reside in globular clusters of M31, as well as five LMXBs in Galactic globular clusters and in the Large Magellanic Cloud using the ROSAT PSPC. We find a trend in the X-ray properties of the LMXBs as a function of globular cluster metallicity. The spectra of LMXBs become progressively softer as the metallicity of its environment increases. The one M31 globular cluster LMXB in our sample which has a metallicity greater than solar has spectral properties similar to those of LMXBs in the bulge of M31, but markedly different from those which reside in low metallicity globular clusters, both in M31 and the Galaxy. The spectral properties of this high metallicity LMXB is also similar to those of X-ray faint early-type galaxies. This lends support to the claim that a majority of the X-ray emission from these X-ray faint early-type galaxies results from LMXBs and not hot gas, as is the case in their X-ray bright counterparts.Comment: 5 pages, 2 embedded Postscript figures, uses emulateapj.sty, Astrophysical Journal Letters, in pres

Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud

This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of ~100,000 to ~3,000,000 K. We measured the O VI, O VII and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p_{th}/k = 6500^{+2500}_{-2600} K cm^{-3}, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII, intensities were compared with those predicted by theoretical models. Gas which was heated to 3,000,000 K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 100,000 < T < 1,000,000 K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.Comment: 10 pages, 2 figures. Accepted for publication in the Astrophysical Journa

Multifrequency observations of the superluminal quasar 3C 345

We have investigated the continuum properties of the superluminal quasar 3C 345 with monitoring studies at radio, optical, infrared, and X-ray frequencies as well as with simultaneous multifrequency spectra extending from the radio through the X-ray bands. Variability occurs more rapidly and with greater amplitude toward shorter wavelengths in the infrared-optical region (0.4-100 μm). Radio outbursts, which appear to follow infrared-optical outbursts by about a year, occur first at the highest frequencies, as expected from optical depth effects, although the peak flux is often reached at several frequencies at once. The beginning of outbursts as defined by millimeter measurements corresponds to the appearance of the three known "superluminal" components. An increase in the X-ray flux during 1979-1980 corresponds to increased radio flux, while the infrared flux changes in the opposite sense. The multifrequency spectra show that the nearly flat radio continuum steepens at 10^(11)-10^(12) Hz and has a power-law slope of -0.91 ± 0.04 from 350 to 20 μm that steepens to -1.40 ± 0.02 at 20 μm-1200 A. A "blue bump" is detected at rest wavelengths 4000-1500 A. The X-ray emission has a flatter slope (-0.7) than the infrared-ultraviolet continuum and lies above an extrapolation of that continuum to X-ray energies. This supports the finding from variability that the X-ray emission is not simply connected to the optical emission. Although the shape of the infrared-ultraviolet continuum is generally preserved during flux variations, slope variations occur and are most common in the ultraviolet region. Most of the total power (3 x 10^(47) ergs s ^(-1)) emerges in the submillimeter-optical region but about one-sixth of the power is emitted at X-ray and radio