Marc L. Fischer

Estimating species-area relationships from plot to landscape scale using species spatial-turnover data

Vegetation census data from montane meadow plots are used to test a predicted connection between the species-area relationship, S = cA z , and the dependence of interpatch species turnover on patch area A, interpatch distance D, and the species-area exponent z. At small spatial scales, from D 1-10 m, where species-area parameters can be independently estimated, the prediction is confirmed; at larger scales, from D 1-10 4 m, the scale-dependence of z is deduced. A predicted dependence of species richness on the shape of censused patches is also confirmed. Our results indicate that readily obtainable species-turnover data between distant small patches can be used to estimate species-area exponents at landscape scales where census data for nested areas are generally not available, thereby improving our ability to estimate landscape-scale species richness and rarity.

A bolometric millimeter-wave system for observations of anisotropy in the cosmic microwave background radiation on medium angular scales

We report the performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0 deg 3 min to 3 deg. The system represents a collaborative effort combining a low-background 1 m diameter balloon-borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four-channel bolometric receiver with passbands centered near frequencies of 3 (90), 6 (180), 9 (270), and 12 (360) cm(exp -1) (GHz). The telescope was flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of Delta(T)/T(sub CMB) is approximately equal to 10(exp -5) with detectors operated at T = 0.3 K.

A degree scale anisotropy measurement of the cosmic microwave background near the star Gamma Ursae Minoris

Results from a search for anisotropy in the cosmic microwave background (CMB) are presented from the third flight of the Millimeter-wave Anisotropy experiment. The CMB observation occurred over 1.37 hours and covered a 6.24 sq deg area of the sky where very little foreground emission is expected. Significant correlated structure is observed at 6 and 9/cm. At 12/cm we place an upper limit on the structure. The relative amplitudes at 6, 9, and 12/cm are consistent with a CMB spectrum. The spectrum of the structure is inconsistent with thermal emission from known forms of interstellar dust. Synchrotron and free-free emission would both require unusually flat spectral indices at cm wavelengths in order to account for the amplitude of the observed structure. Although known systematic errors are not expected to contribute significantly to any of the three optical channels, excess sidelobe contamination cannot be definitively ruled out. If all the structure is attributed to CMB anisotropy, a value of the weighted rms of the 6 and 9/cm channels of Delta T/T(CMB) = 4.7 +/- 0.8 x 10 exp -5 (+/- 1 sigma) was measured. If the CMB anisotropy is assumed to have a Gaussian autocorrelation function with a coherence angle of 25 arcmin, then the most probable value is Delta T/T(CMB) = 4.2 +1.7 or -1.1 x 10 exp -5, where the +/- refers to the 95 percent confidence limits.

A search for anisotrophy in the cosmic microwave background on intermediate angular scales

The results of a search for anisotropy in the cosmic microwave background on angular scales near 1 deg are presented. Observations were simultaneously performed in bands centered at frequencies of 6, 9, and 12 per cm with a multifrequency bolometric receiver mounted on a balloon-borne telescope. The statistical sensitivity of the data is the highest reported to date at this angular scale, which is of critical importance for understanding the formation of structure in the universe. Signals in excess of random were observed in the data. The experiment, data analysis, and interpretation are described.

Evaluation of LCD monitors for deflectometric measurement systems

With deflectometric measurement methods there are powerful systems available today that are capable of measuring the geometry of specular surfaces or the power distribution of refractive optics in a fast and flexible manner without influencing the measurement object by tactile probing. They are based on the general principle to image a known spatially coded reference structure via the unknown measurement object onto an optically calibrated camera. As a representation of the reference structure LC-displays are very suitable as they provide a high flexibility in the generation of spatial coding patterns like sinusoidal fringes. As the characteristics of the reference structure have a huge impact on the resolution, the accuracy and the measurement range of the whole system, in this work two displays with different LCD technologies are analysed, compared and evaluated especially for deflectometric applications. The main focus is on the quality of gray-value rendering and the dependency between the characteristic curve and the observation angle. The experimental results corroborate the theoretical finding that IPS-technology is superior to TN- and MVA-displays in terms of an observation-angle independent shape of the grayscale-characteristic curve. So IPS should be the technologyof- choice when selecting a LC-display for a deflectometric measurement system.

Three-dimensional shape measurement of aspheric refractive optics by pattern transmission photogrammetry

For fast, accurate and robust shape measurement of specular surfaces there are several powerful measurement techniques based on deflectometry. For boundary surfaces of transparent objects like refractive optics, on the contrary, deflectometry is so far limited to the measurement of only one surface in reflection. This is unsatisfying from a metrological point of view as the geometrical relation between both surfaces, which substantially defines the optical function, is lost. In this work a new deflectometric approach is presented that works in transmission and allows the simultaneous measurement of both surfaces of refractive optics. The basic idea of the approach is calculating the unknown surface geometry of a transparent object by iteratively adapting a surface model to the observed light ray deflections. The main problem in this case is the ambiguity of the refraction at the two boundary surfaces of a lens, as there are multiple possible solutions that produce the same measurement results. This is solved by combining four different views on the object under test, which allows to find an unambiguous solution. An experimental measurement setup is presented and results of different simulations and tests are discussed in this paper.

A millimeter‐wave anisotropy experiment (MAX) to search for anisotropy in the cosmic background radiation on medium angular scales

We report preliminary results from two balloon flights of a millimeter‐wave telescope designed to measure anisotropy in the cosmic microwave background (CMB) on angular scales from 0.3 to 3 degrees. The receiver used in the first flight, in November 1989, was a dichroic, 3He‐cooled bolometric photometer with passbands centered at 3, 6, 9, and 12 cm−1. During this flight we measured the spectrum of the brightness of the galactic plane at a galactic longitude of lII=24 degrees and searched for CMB anisotropy at nine points centered near the north celestial pole (NCP). The noise in the 6 cm−1 band integrated down to one sigma errors of 140 μK per point over the 40 minute observation near th NCP. After further analysis these data will set an upper limit on CMB anisotropy of ΔT/T<1–2×10−4 (95% CL) for Gaussian correlation functions with a correlation length of 0.5 degree. The second flight, in July 1990, employed improved bolometric detectors. The 3 cm−1 band was removed in order to increase the efficiency of ...

100-mK bolometric receiver for low-background astronomy

The design and construction of 100 mK composite bolometers for low background submillimeter and millimeter-wave astronomy are discussed. The bolometers are cooled to 100 mK using an adiabatic demagnetization refrigerator. The bolometers consist of a silicon substrate suspended by nylon fibers, a bismuth film absorber, a neutron transmutation doped germanium thermometer with graphite fiber electrical leads, and a brass wire thermal strap. Heated JFET amplifiers located on the 1.5 K cold plate are used to read out the bolometer signals. Electrically measured noise equivalent powers as low as 2 X 10-17 W/(root)Hz have been achieved.