Classification of Very Red Stars Using Narrowband Colors

A classification technique for faint, very red stars is described, based on two composite colors, derived from flux measurements in six narrowbands in the visual and red parts of the spectrum. One of the composite colors, ST, is an M spectral type indicator, common to both dwarfs and giants. It can be used to predict the spectral types to within half a class. The other color, DG, is a dwarf-giant discriminator for spectral types later than about M4, and whose power increases for the later types, where most other methods fail. It reflects the differences in blanketing between the late-M type dwarfs and the giants. The method can be generalized to other, similar colors, depending on the data and task at hand. It should be useful in surveys for extreme low-mass dwarfs, or alternatively, for luminous red giants, or other kinds of objects. We illustrate the application of the method on an example of a very red star identified earlier by Blair and Long, and show it to be a distant red giant

Teaching and understanding of quantum interpretations in modern physics courses

Just as expert physicists vary in their personal stances on interpretation in quantum mechanics, instructors vary on whether and how to teach interpretations of quantum phenomena in introductory modern physics courses. In this paper, we document variations in instructional approaches with respect to interpretation in two similar modern physics courses recently taught at the University of Colorado, and examine associated impacts on student perspectives regarding quantum physics. We find students are more likely to prefer realist interpretations of quantum-mechanical systems when instructors are less explicit in addressing student ontologies. We also observe contextual variations in student beliefs about quantum systems, indicating that instructors who choose to address questions of ontology in quantum mechanics should do so explicitly across a range of topics.Comment: 18 pages, references, plus 2 pages supplemental materials. 8 figures. PACS: 01.40.Fk, 03.65.-

Hierarchical Spatial Gossip for Multiresolution Representations in Sensor Networks

In this paper we propose a lightweight algorithm for constructing multi-resolution data representations for sensor networks. At each sensor node u, we compute, O(logn) aggregates about exponentially enlarging neighborhoods centered at u. The ith aggregate is the aggregated data from nodes approximately within 2 i hops of u. We present a scheme, named the hierarchical spatial gossip algorithm, to extract and construct these aggregates, for all sensors simultaneously, with a total communication cost of O(npolylogn). The hierarchical gossip algorithm adopts atomic communication steps with each node choosing to exchange information with a node distance d away with probability ∼ 1/d 3. The attractiveness of the algorithm attributes to its simplicity, low communication cost, distributed nature and robustness to node failures and link failures. We show in addition that computing multi-resolution aggregates precisely (i.e., each aggregate uses all and only the nodes within 2 i hops) requires a communication cost of Ω(n √ n), which does not scale well with network size. An approximate range in aggregate computation like that introduced by the gossip mechanism is therefore necessary in a scalable efficient algorithm. Besides the natural applications of multi-resolution data summaries in data validation and information mining, we also demonstrate the application of the pre-computed multi-resolution data summaries in answering range queries efficiently

Vitamins A & D Inhibit the Growth of Mycobacteria in Radiometric Culture

The role of vitamins in the combat of disease is usually conceptualized as acting by modulating the immune response of an infected, eukaryotic host. We hypothesized that some vitamins may directly influence the growth of prokaryotes, particularly mycobacteria. complex).Vitamins A and D cause dose-dependent inhibition of all three mycobacterial species studied. Vitamin A is consistently more inhibitory than vitamin D. The vitamin A precursor, β-carotene, is not inhibitory, whereas three vitamin A metabolites cause inhibition. Vitamin K has no effect. Vitamin E causes negligible inhibition in a single strain.We show that vitamin A, its metabolites Retinyl acetate, Retinoic acid and 13-cis Retinoic acid and vitamin D directly inhibit mycobacterial growth in culture. These data are compatible with the hypothesis that complementing the immune response of multicellular organisms, vitamins A and D may have heretofore unproven, unrecognized, independent and probable synergistic, direct antimycobacterial inhibitory activity

Hubble Space Telescope Spectroscopy of the Balmer lines in Sirius B

Sirius B is the nearest and brightest of all white dwarfs, but it is very difficult to observe at visible wavelengths due to the overwhelming scattered light contribution from Sirius A. However, from space we can take advantage of the superb spatial resolution of the Hubble Space Telescope to resolve the A and B components. Since the closest approach in 1993, the separation between the two stars has become increasingly favourable and we have recently been able to obtain a spectrum of the complete Balmer line series for Sirius B using HST?s Space Telescope Imaging Spectrograph (STIS). The quality of the STIS spectra greatly exceed that of previous ground-based spectra, and can be used to provide an important determination of the stellar temperature (Teff = 25193K) and gravity (log g = 8.556). In addition we have obtained a new, more accurate, gravitational red-shift of 80.42 +/- 4.83 km s-1 for Sirius B. Combining these results with the photometric data and the Hipparcos parallax we obtain new determinations of the stellar mass for comparison with the theoretical mass-radius relation. However, there are some disparities between the results obtained independently from log g and the gravitational redshift which may arise from flux losses in the narrow 50x0.2arcsec slit. Combining our measurements of Teff and log g with the Wood (1995) evolutionary mass-radius relation we get a best estimate for the white dwarf mass of 0.978 M. Within the overall uncertainties, this is in agreement with a mass of 1.02 M obtained by matching our new gravitational red-shift to the theoretical M/R relation.Comment: 11 pages, 6 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Understanding light quanta: First quantization of the free electromagnetic field

The quantization of the electromagnetic field in vacuum is presented without reference to lagrangean quantum field theory. The equal time commutators of the fields are calculated from basic principles. A physical discussion of the commutators suggest that the electromagnetic fields are macroscopic emergent properties of more fundamental physical system: the photons

THERMAL RADIATION FROM MAGNETIZED NEUTRON STARS: A look at the Surface of a Neutron Star.

Surface thermal emission has been detected by ROSAT from four nearby young neutron stars. Assuming black body emission, the significant pulsations of the observed light curves can be interpreted as due to large surface temperature differences produced by the effect of the crustal magnetic field on the flow of heat from the hot interior toward the cooler surface. However, the energy dependence of the modulation observed in Geminga is incompatible with blackbody emission: this effect will give us a strong constraint on models of the neutron star surface.Comment: 10 pages. tar-compressed and uuencoded postcript file. talk given at the `Jubilee Gamow Seminar', St. Petersburg, Sept. 1994

Big Bang Nucleosynthesis Constraints on Primordial Magnetic Fields

We reanalyze the effect of magnetic fields in BBN, incorporating several features which were omitted in previous analyses. We find that the effects of coherent magnetic fields on the weak interaction rates and the electron thermodynamic functions (\rhoe, \Pe, and \drhoedt ) are unimportant in comparison to the contribution of the magnetic field energy density in BBN. In consequence the effect of including magnetic fields in BBN is well approximated numerically by treating the additional energy density as effective neutrino number. A conservative upper bound on the primordial magnetic field, parameterized as $\zeta=2eB_{rms}/(T_\nu^2)$, is $\zeta \le 2$ ($\rho_B < 0.27 \rho_\nu$). This bound can be stronger than the conventional bound coming from the Faraday rotation measures of distant quasars if the cosmological magnetic field is generated by a causal mechanism.Comment: Latex, 20 pages, 3 uuencoded figures appende