7,571 research outputs found
Discovery of Two New Class II Methanol Maser Transitions in G345.01+1.79
We have used the Swedish ESO Submillimetre Telescope (SEST) to search for new
class II methanol maser transitions towards the southern source G345.01+1.79.
Over a period of 5 days we observed 11 known or predicted class II methanol
maser transitions. Emission with the narrow line width and characteristic
velocity of class II methanol masers (in this source) was detected in 8 of
these transitions, two of which have not previously been reported as masers.
The new class II methanol maser transitions are the 13(-3)-12(-4)E transition
at 104.1 GHz and the 5(1)-4(2)E transition at 216.9 GHz. Both of these are from
transition series for which there are no previous known class II methanol maser
transitions. This takes the total number of known class II methanol maser
series to 10, and the total number of transitions (or transition groups) to 18.
The observed 104.1 GHz maser suggests the presence of two or more regions of
masing gas with similar line of sight velocities, but quite different physical
conditions. Although these newly discovered transitions are likely to be
relatively rare, where they are observed combined studies using the Australia
Telescope Compact Array and the Atacama Large Millimeter Array offer the
prospect to be able to undertake multi-transition methanol maser studies with
unprecedented detail.Comment: 8 pages, 3 figures, accepted for publication in ApJ Letter
A Search for Biomolecules in Sagittarius B2 (LMH) with the ATCA
We have used the Australia Telescope Compact Array to conduct a search for
the simplest amino acid, glycine (conformers I and II), and the simple chiral
molecule propylene oxide at 3-mm in the Sgr B2 LMH. We searched 15 portions of
spectrum between 85 and 91 GHz, each of 64 MHz bandwidth, and detected 58
emission features and 21 absorption features, giving a line density of 75
emission lines and 25 absorption lines per GHz stronger than the 5 sigma level
of 110 mJy. Of these, 19 are transitions previously detected in the
interstellar medium, and we have made tentative assignments of a further 23
features to molecular transitions. However, as many of these involve molecules
not previously detected in the ISM, these assignments cannot be regarded with
confidence. Given the median line width of 6.5 km/s in Sgr B2 LMH, we find that
the spectra have reached a level where there is line confusion, with about 1/5
of the band being covered with lines. Although we did not confidently detect
either glycine or propylene oxide, we can set 3 sigma upper limits for most
transitions searched. We also show that if glycine is present in the Sgr B2 LMH
at the level of N = 4 x 10^{14} cm^{-2} found by Kuan et al. (2003) in their
reported detection of glycine, it should have been easily detected with the
ATCA synthesized beam size of 17.0 x 3.4 arcsec^{2}, if it were confined to the
scale of the LMH continuum source (< 5 arcsec). This thus puts a strong upper
limit on any small-scale glycine emission in Sgr B2, for both of conformers I
and II.Comment: 12 pages, 2 figures, 5 tables, accepted by MNRA
Fretting wear of Ti(CxNy) PVD coatings under variable environmental conditions
Fretting wear as a specific type of degradation is defined as an oscillatory motion at small amplitude between two nominally stationary solid bodies in mutual contact. Under external stresses the interface is being damaged by debris generation and its successive ejections outside the contact area. A potential protection against fretting damage by means of hard coatings is being offered by different surface engineering techniques. For this study TiC, TiN and TiCN hard coatings manufactured by a PVD method have been selected and tested against smooth polycrystalline alumina ball. A fretting test programme has been carried out at the frequency of 5Hz, 100N normal load, 100µm displacement amplitude and at three values of a relative humidity: 10, 50 and 90% at 295-298K temperature. It turned out that the intensity of wear process was depending not only on loading conditions but on environmental ones as well. A significant impact of RH on wear rate and friction behaviour of the coatings under investigation has been observed. Two different damage mechanisms have been identified and related to the phenomena of debris oxidation and debris adhesion to the counterbody surface. In the latter case the debris deposited onto the surface of the alumina ball lead to a change of stress distribution at the interface and as a result to accelerated wear. In this work experiments with variable relative humidity increasing from 10% to 90% within 1 a single fretting test have been completed. It follows from these experiments that there exists an intermediate value of the RH at which the friction coefficient changes rapidly. Finally a dissipated energy approach has been applied in the work in order to quantify and compare fretting wear rates of different hard coatings
The Effect of a Magnetic Field on the Acoustoelectric current in a Narrow Channel
The effect of a perpendicular magnetic field on the quantized current induced
by a surface acoustic wave in a quasi-1D channel is studied. The channel has
been produced experimentally in a GaAs heterostructure by shallow etching
techniques and by the application of a negative gate voltage to Schottky split
gates. Commensurability oscillations of the quantized current in this
constriction have been observed in the interval of current between quantized
plateaus. The results can be understood in terms of a moving quantum dot with
the electron in the dot tunneling into the adjacent two-dimensional region. The
goal is to explain qualitatively the mechanism for the steplike nature of the
acoustoelectric current as a function of gate voltage and the oscillations when
a magnetic field is applied. A transfer Hamiltonian formalism is employed.Comment: 5 pages, 2 figure
Class II methanol maser candidates
Model spectra are presented for Class II methanol masers under a variety of conditions. The model is that of Sobolev & Deguchi, which includes pumping through levels of the second and first torsionally excited states. All the currently identified Class II methanol masers appear as strong masers in one or more of the model regimes, and a number of new maser candidates are identified. © 1997 RAS
Literature review: Impact of inspections on the improvement of schools and of networks of schools
Models of class II methanol masers based on improved molecular data
The class II masers of methanol are associated with the early stages of
formation of high-mass stars. Modelling of these dense, dusty environments has
demonstrated that pumping by infrared radiation can account for the observed
masers. Collisions with other molecules in the ambient gas also play a
significant role, but have not been well modelled in the past. Here we examine
the effects on the maser models of newly available collision rate coefficients
for methanol. The new collision data does not alter which transitions become
masers in the models, but does influence their brightness and the conditions
under which they switch on and off. At gas temperatures above 100 K the effects
are broadly consistent with a reduction in the overall collision cross-section.
This means, for example, that a slightly higher gas density than identified
previously can account for most of the observed masers in W3(OH). We have also
examined the effects of including more excited state energy levels in the
models, and find that these play a significant role only at dust temperatures
above 300 K. An updated list of class II methanol maser candidates is
presented.Comment: 14 pages, 4 figures, Accepted for publication in MNRA
Quartz crystal microbalance use in biological studies
Design, development, and applications of quartz crystal microbalance are discussed. Two types of crystals are used. One serves as reference and other senses changes in mass. Specific application to study of bacterial spores is described
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