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We observed Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the +50 km s−1 cloud (M−0.02−0.07), the circumnuclear disk (CND) and the +20 km s−1 (M−0.13−0.08) cloud in the Sgr A complex with the VLA, Odin and SEST. Strong OH absorption, H2O emission and absorption lines were seen at all three positions. Strong C18O emissions were seen towards the +50 and +20 km s−1 clouds. The CND is rich in H2O and OH, and these abundances are considerably higher than in the surrounding clouds, indicating that shocks, star formation and clump collisions prevail in those objects. A comparison with the literature reveals that it is likely that PDR chemistry including grain surface reactions, and perhaps also the influences of shocks has led to the observed abundances of the observed molecular species studied here. In the redward high-velocity line wings of both the +50 and +20 km s−1 clouds and the CND, the very high H2O abundances are suggested to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry. Only three of the molecules are briefly discussed here. For OH and H2O three of the nine observed positions are shown, while a map of the C18O emission is provided. An extensive paper was recently published with Open Access (Karlsson et al. 2013, A&A 554, A141).
It is well known that signs of respiratory distress or disease (RD), such as high breathing frequency, chest wall retractions, grunting, and cyanosis, are common in newborn infants. The signs may be very transient or develop into a potentially life-threatening condition. When they are first observed, they often have a very ambiguous prognostic significance.
A spectral line survey of Orion KL has been performed over the frequency range of 486–492 GHz and 541–577 GHz using the Odin satellite. Over 1000 lines have been identified from 40 different molecular species, including several organic compounds such as methyl cyanide (CH3CN), methanol (CH3OH, 13CH3OH), and dimethyl ether (CH3OCH3).
The processes by which methanol, one of the most abundant interstellar organics, is formed in the interstellar medium are not yet accurately known. Pure gas-phase chemistry models fail to reproduce observed abundances by orders of magnitude, pointing to formation on grains and subsequent desorption.
Observations of methanol and its isotopologue 13CH3OH in several sources have been used to trace the origin, and thus the formation routes of methanol on interstellar grains, by means of isotope labelling a posteriori.
In this paper we describe a unified, hierarchical computational approach to aging and reliability problems caused by materials changes in the oxide layers of Si-based microelectronic devices. We apply this method to a particular low-dose-rate radiation effects problem.
We present calculations of the specific contact resistance for metals to GaN. Our calculations include a correct determination of the Fermi level taking into account the effect of the degenerate doping levels, required in creating tunneling ohmic contacts. Using a recently reported improved WKB approximation suitable in representing the depletion width at the metal-semiconductor interface, and a two band k-p model for the effective masses, specific contact resistance was determined as a function of doping concentration. The specific contact resistance was calculated using the best data available for barrier heights, effective masses and dielectric coefficients for GaN. Because the barrier height at the metal-semiconductor interface has a very large effect on the contact resistance and the available data is sketchy or uncertain, the effect of varying the barrier height on the calculated specific contact resistance was investigated. Further, since the III-V nitrides are being considered for high temperature device applications, the specific contact resistance was also determined as a function of temperature.
We report on results from an ongoing spectral scan of four nearby positions in the Sgr B2 molecular cloud using SEST (Swedish-ESO Submillimeter Telescope). The antenna beam size is approximately 22″ in the frequency range 226-245 GHz presently covered. This high angular resolution allows detailed studies of the physical and chemical conditions in the warm and compact cores discovered (Vogel et al. 1987, Goldsmith et al. 1987) inside the region previously surveyed in the 3 mm band with lower angular resolution (Cummins et al. 1986, Turner 1989, beam sizes of 1.5-2.9′ and 1-2′, respectively). The Sgr B2(OH) position used by these investigators is located about 30″ south of our M position, and hence the cores M and N will contribute to the observed spectral line emissions to a larger or lesser extent.
M51, M101 and IC342 were all observed in the CO(1-0) line with the Onsala 20 m antenna. “The average pointing error for a 20 minute run is less than 5”, usually considerably less, and the receivers are stable. The error lobe is considerable with an efficiency of about 40%. With a width of about 20′ it is of little importance compared to an emission region of 2′ to 3′ however. Of more concern is an upper and a lower sidelobe with a combined efficiency of about 14%.
The interstellar medium (ISM) in our Galaxy is in a complex state. The temperature and the density vary by about five and ten orders of magnitude respectively. The medium is exposed to cosmic rays and starlight and contains magnetic fields. Its average density is about 10−24 g cm−3, or about one hydrogen atom per cubic centimeter, corresponding to 0.025 M⊙ pc−3. Thus on average one solar mass of the medium is contained in 40 pc3. About 75% of the medium is hydrogen, about 25% is helium, and the remaining part (about 2%) is in heavier atoms. A large fraction of the heavier elements has condensed out as dust grains having an average density of about 0.001 M⊙ pc−3.
The local kinetic gas temperatures range from 10 K to 106 K. These temperatures correspond to energies which are much lower than those typical of cosmic rays. The lower temperatures correspond to energies which are less than those typical for starlight. Cosmic rays and starlight drive processes including ionization; hence, the ionization structure sometimes is very far from that in a gas in thermal equilibrium at the gas kinetic temperature. The energy density of cosmic rays is ≈0.5 eV cm−3, of Galactic magnetic fields ≈0.2 eV cm−3 (≈10−6G), and of diffuse starlight ≈0.5 eV cm−3. Hence there is a rough equipartition of energy among these components. The description of the interaction of matter with radiation is complicated by the huge variation of opacities for different wavelengths.
I wish to report on some results from mapping of molecular cloud distributions in galaxies and from tidal interaction modeling – work performed at Onsala Space Observatory and in the Astrophysics Group of Institute of Theoretical Physics, Chalmers University of Technology/University of Göteborg.
The DX-center model is widely used to explain data for the persistent photoconductivity (PPC) effect. An analysis of the DX-center model suggests a new experiment to test its correctness. In this experiment, photons near the threshold energy of the photoionization cross-section for the DX-center induce transitions from the partially occupied conduction band to empty DX-centers. This mechanism, which we call photocapture, competes with the usual photoionization which empties the DX-centers. The photocapture cross-section is estimated and an experimental attempt is made to detect photocapture. The significance of the null result is discussed.
The electronic properties of interface roughness in a quantum well are described. Interface roughness is shown to always produce localized bound states. Thus intrinsic roughness can explain the giant oscillator strength observed for “free” excitons in quantum wells.
We have observed transitions of methanol, methyl acetylene(1),(2) and acetaldehyde(3) in dark clouds. in methanol the 20−10 A+, 10−00 A+, 2-1−1−1 E lines and tentatively the 20−10 E line have been observed. The 10−00 E, 21−11 E and the 00−1−1 E lines were searched for but not detected. Maps of TMC1, L134N, and B335 in the 20−10 A+ and 2−1−1−1 E lines show that the methanol emission is very extended and follows the extent of the C180 J=1−0 emission well.
Results from a continuing study (Figure 1a) of the CO (J = 1-0) distribution in M51 are presented. The angular resolution (beam size 33″ = 1.5 kpc) and pointing stability (better than 4″) of the Onsala 20-m telescope have extracted a number of new features of the molecular cloud distribution and kinematics of M51 [1,2]:
Pressure dependent Deep Level Transient Spectroscopy (DLTS) experiments are used to measure the properties of the deep donors (DX-centers) responsible for the persistent photoconductivity effect in Si-doped AlGaAs. The sample dependence of the DLTS spectra shows evidence for a defect complex involved in the DX-center.
Studies of molecular clouds in nearby galaxies require high angular resolution. Ten arcseconds corresponds to 0.5 kpc at the distance of M51. Typical gigant molecular clouds (GMC:s) have a size of 5-30 pc (Solomon et al. 1985). However complexes of GMC: s (Superclouds) can be several hundred parsecs (Elmegreen 1985; Rivolo et al. 1985). The higest angular resolution achived in CO(J=1-0) line observations of external galaxies is 7” (Lo et al 1984,1985). The resolution problem can be eased by observing M31 with a distance of only ⋍ 690 kpc (10” corresponds to 34 pc), which has been done by Combes et al. 1977a,b; Boulanger et al. 1984; Ryden and Stark 1985; Stark 1985; Blitz 1985; Ichikawa et al. 1985. In M31 the CO emission is strongly concetrated to the spiral arms with a arm interarm ratio of ≥ 25 (Ryden and Stark 1985; Stark 1985). The emission is caused by many small clouds unresolved with present resolution together with some larger clouds. Streaming is observed to occur across the arms. Extragalatic studies have the advantage of being more easy to interpret in terms of arm interarm contrast, noncircular motion, and galatic structure. They also make possible studies of the mass fraction of gas as a function of radius in different morphological types of galxies. Answers to questions like “Do any relation exist between galaxy type and molecular abundance?” are very important for our understanding of galatic evolution.
We present results (partly preliminary) of an extensive map (73 positions) of CO (J=1–0) emission in M51 (Fig. 1). The spectra were obtained with the Onsala 20-m antenna (beam size 33″), equipped with a cooled mixer and a 512×1 MHz multichannel receiver. The data are not yet fully analyzed but our preliminary results are as follows:
1. A small central minimum in the CO emission is apparent (Fig. 2). The average radial CO distribution shows a maximum at ~ 15″ (corresponding to 0.7 kpc, for an assumed distance of 9.6 Mpc).
2. The above minimum results from what seems to be an oval ridge structure in the emission intensity around the center, with an extent of about 30″ by 40″ (Fig. 3). This could be the markings of an elongated hole or the beginning of the spiral arms. (The ridges are fairly well correlated with the innermost parts of the spiral arms as delineated by continuum observations by Segalowitz, 1976.)
3. It seems that a central oval velocity pattern is needed to explain a dip at 450 km s-1 in the central spectrum. (The dip is present in all and independent parts of our data.)
4. The outer parts of the galaxy have only been covered in strips (Fig. 1). Clearly there is structure in these strips, i.e. not only a radial decrease. The “on-arm” spectrum (88″, 0″) has for example a greater integrated and peak intensity than the “interarm” spectrum (77″, 0″). Such arm-interarm contrast is not always clear, though. Observations covering a larger section of an arm-interarm region, where contrast has been seen, are being planned for the next observing season.
5. We also note that the observed apparent velocity differences between CO and ionized gas, reported by Rydbeck et al. (1983), persist. A fully convincing argument on this point (taking into account the finite beam etc.) requires some further model work, however.
The pseudo Jahn-Teller effect and chemical rebonding are both considered as mechanisms that drive substitutional atoms, such as N in Si, off-center. By use of an effective Hamiltonian technique, impurities forming very deep levels, such as Si:N, are found to be susceptible to off-center displacement by the pseudo Jahn-Teller effect. Using a Hartree-Fock technique, we find two classes of N displacements which depend on the relaxation of the nearest-neighbor Si atom “cage”. For outward relaxation of the four nearest neighbors, the N displaces by 0.05 Å in the  direction and retains sp3 bonding; this mechanism appears equivalent to the pseudo Jahn-Teller effect. For inward relaxation of the “cage” by 0.45 Å the N displaces by 0.75 Å in the  direction and forms a trigonal sp2 bond; this is a chemical rebonding mechanism. Additional cluster calculations suggest that inward relaxation of the “cage” is likely. Similar calculations for 0 revealed a <100> displacement of approximately 1.1Å.
We present observations, which are part of an ongoing investigation, of the CO (J=1–0) emission in the spiral galaxy M51. The spectra were obtained in a beamswitched on-on mode with the Onsala 20 m antenna (beam size ~33″), equipped with a cooled mixer and a 512 ×1 MHz multichannel receiver, and are shown in Figure 1. The inset diagram shows the observed positions superposed on the optical outline of the galaxy. With the present signal-to-noise ratio there is no evidence for an arm-interarm intensity contrast. This is even more apparent in integrated intensity. This result agrees with the lower resolution findings of Rickard et al. (1981). We have observed 13CO in one position (22″ south of the center). The 13CO to 12CO ratio, ∼0.1, agrees with Bell results from observations with a 1:7 beam (Encrenaz et al. 1979).