763 research outputs found
A Technique for Photometric Detection and Measurement of Unresolved Binary Systems
A technique is described for the detection and measurement of close binary
systems whose images are unresolved. The method is based on analysis of the
moment of inertia tensor of the image, from which the product of the binary
flux ratio and square of the angular separation may be determined. Intrinsic
asymmetries of the point-spread function are removed by comparison with the
image of a reference star. Multiple exposures may be used to increase the
signal-to-noise ratio without need of image alignment. An example is given of a
simulated measurement of the dwarf carbon star system G77-61.Comment: PASP, in press. 17 pages including 2 figure
Analysis of a Very Massive DA White Dwarf via the Trigonometric Parallax and Spectroscopic Methods
By two different methods, we show that LHS 4033 is an extremely massive white
dwarf near its likely upper mass limit for destruction by unstable electron
captures. From the accurate trigonometric parallax reported herein, the
effective temperature (T=10,900 K) and the stellar radius (R=0.00368 R_sun) are
directly determined from the broad-band spectral energy distribution -- the
parallax method. The effective temperature and surface gravity are also
estimated independently from the simultaneous fitting of the observed Balmer
line profiles with those predicted from pure-hydrogen model atmospheres -- the
spectroscopic method (T=10,760 K, log g=9.46). The mass of LHS 4033 is then
inferred from theoretical mass-radius relations appropriate for white dwarfs.
The parallax method yields a mass estimate of 1.310--1.330 M_sun, for interior
compositions ranging from pure magnesium to pure carbon, respectively, while
the spectroscopic method yields an estimate of 1.318--1.335 M_sun for the same
core compositions. This star is the most massive white dwarf for which a robust
comparison of the two techniques has been made.Comment: 17 pages, including 4 figures, Accepted for Ap.
Intercalation of Poly(bis-(methoxyethoxyethoxy)phosphazene) into Lithium Hectorite
Poly(bis-(methoxyethoxyethoxy)phosphazene) (MEEP) intercalated into lithium hectorite was investigated for its potential application as a solid polymer electrolyte in lithium-ion polymer batteries. Varying amounts of MEEP were intercalated into lithium hectorite, and the physical properties of the nanocomposites were monitored using powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and attenuated total reflectance spectroscopy. Alternating current (AC) impedance spectroscopy was used to determine the ionic conductivity of the nanocomposites when complexed with lithium triflate salt
Intercalation of Poly[Oligo(Ethylene Glycol) Oxalate] into Vanadium Pentoxide Xerogel: Preparation, Characterization and Conductivity Properties
We report, for the first time, the intercalation of poly[oligo(ethylene glycol) oxalate] (POEGO) and POEGO lithium salt (LiCF3SO3) complex (POEGO-LiCF3SO3) into vanadium pentoxide xerogel (V2O5nH2O). The effect of changing the polymer concentration on the interlayer expansion of the layered host was studied, and the optimal intercalation ratio was determined to be 1:2. The intercalates were characterized by powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and AC impedance spectroscopy
Scanning Tunneling Microscopy Studies of Chloroplasts in Solution
Previous work has shown that it is possible to image whole uncoated chloroplasts using scanning tunneling microscopy (STM), provided this is done in solution using tunnelling currents below about 100 pA.
More recent images include some which suggest that the STM is sensitive to dynamic processes occurring on chloroplast surfaces. Current-versus-distance curves and dI/ds measurements are consistent with tunnelling between the tip and sample surface, and relatively small deformations of the sample surface due to tip-sample forces. Attempts to use the same imaging conditions on bacteria were unsuccessful
Persistenz bodenphysikalischer Wirkungen perennierender Futterpflanzen mit Pfahlwurzelsystemen
Taprooted crops create large sized biopores in the subsoil which in turn facilitate root growth of following crops. To date it was unclear, over which periods of time biopores
created by taproots remain stable. This study based on a long-term field experiment provides evidence that soil physical effects of taprooted chicory are persistent even 6 years after cultivation. Moreover, repeated cultivation of taprooted crops probably has cumulative beneficial effects on soil structure
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