Independent responsive behaviour and communication in hydrogel objects

In this work, we show the fabrication of soft hydrogel alginate-based objects, namely fibres and beads, that have an individually programmed time delay in their response to a shared environmental stimulus. We utilize the enzyme urease to programme a self-regulated change in pH, which in turn activates the designed response of gel fibre disintegration or a change in gel bead colour. This design allows for independent response behaviour of a collection of bodies in a single closed system, as well as inter-material communication on shorter length scales. The incorporation of responsive time control directly into soft matter objects demonstrates an advance in the field of autonomous materials

An ASCA Study of the W51 Complex

We present the analysis of ASCA archival data from the Galactic source W51. The ASCA spectra show that the soft (kT<= 2.5 keV) X-rays are of thermal origin and are compatible with W51C being a single, isothermal (kT~0.3 keV) supernova remnant at the far-side of the Sagittarius arm. The ASCA images reveal hard (kT>=2.5 keV) X-ray sources which were not seen in previous X-ray observations. Some of these sources are coincident with massive star-forming regions and the spectra are used to derive X-ray parameters. By comparing the X-ray absorbing column density with atomic hydrogen column density, we infer the location of star-forming regions relative to molecular clouds. There are unidentified hard X-ray sources superposed on the supernova remnant and we discuss the possibility of their association.Comment: 13 pages, 11 figures, to be published in Astronomical Journa

Faint HI 21-cm Emission Line Wings at Forbidden-Velocities

We present the results of a search for faint HI 21-cm emission line wings at velocities forbidden by Galactic rotation in the Galactic plane using the Leiden/Dwingeloo HI Survey data and the HI Southern Galactic Plane Survey data. These ``forbidden-velocity wings (FVWs)'' appear as protruding excessive emission in comparison with their surroundings in limited (< 2 deg) spatial regions over velocity extent more than ~20 km/s in large-scale (l-v) diagrams. Their high-velocities imply that there should be some dynamical phenomena associated. We have identified 87 FVWs. We present their catalog, and discuss their distribution and statistical properties. We found that 85% of FVWs are not coincident with known supernova remnants (SNRs), galaxies, or high-velocity clouds. Their natures are currently unknown. We suspect that many of them are fast-moving HI shells and filaments associated with the oldest SNRs that are essentially invisible except via their HI line emission. We discuss other possible origins.Comment: 41 pages, 14 figures, to be published in apj

Shocked Molecular Gas in the Supernova Remnant HB 21

We report the discovery of the shocked molecular gas in the supernova remnant HB 21. We derive the physical parameters of the shocked gas from CO J=1-0 and J=2-1 line observations. We discuss the correlation of the shocked molecular gas with the previously detected, shocked atomic gas and the associated infrared emission.Comment: 24 pages, 10 figures, To appear in the ApJ, scheduled for the April 10, 2001 issue (v551

A "Missing" Supernova Remnant revealed by the 21-cm Line of Atomic Hydrogen

Although some 20--30,000 supernova remnants (SNRs) are expected to exist in the Milky Way, only about 230 are presently known. This implies that most SNRs are ``missing''. Recently, we proposed that small (\simlt 1^\circ), faint, high-velocity features seen in large-scale 21-cm line surveys of atomic hydrogen ({\sc Hi}) in the Galactic plane could be examples of such {\it missing} old SNRs. Here we report on high-resolution \schi observations of one such candidate, FVW 190.2+1.1, which is revealed to be a rapidly expanding ($\sim 80$ \kms) shell. The parameters of this shell seem only consistent with FVW 190.2+1.1 being the remnant of a SN explosion that occurred in the outermost fringes of the Galaxy some $\sim 3\times 10^5$ yr ago. This shell is not seen in any other wave band suggesting that it represents the oldest type of SNR, that which is essentially invisible except via its \schi line emission. FVW 190.2+1.1 is one of a hundred "forbidden-velocity wings" (FVWs) recently identified in the Galactic plane, and our discovery suggests that many of these are likely to be among the oldest SNRs. We discuss the possible link between FVWs and fast-moving atomic clouds in the Galaxy.Comment: 12 pages, 3 figures, To appear in The Astrophysical Journal Letter

Bound states of holes in an antiferromagnet

The formation of bound states of holes in an antiferromagnetic spin-1/2 background is studied using numerical techniques applied to the ${\rm t-J}$ Hamiltonian on clusters with up to 26 sites. An analysis of the binding energy as a function of cluster size suggests that a two hole bound state is formed for couplings larger than a ``critical'' value ${\rm J/t]_c}$. The symmetry of the bound state is \dx2y2. We also observed that its ``quasiparticle'' weight ${\rm Z_{2h}}$ (defined in the text), is finite for all values of the coupling ${\rm J/t}$. Thus, in the region ${\rm J/t \geq J/t]_c}$ the bound state of two holes behaves like a quasiparticle with charge $Q=2e$, spin $S=0$, and \dx2y2 internal symmetry. The relation with recent ideas that have suggested the possibility of d-wave pairing in the high temperature cuprate superconductors is briefly discussed.Comment: 12 pages and 3 figures (3 postscript files included), Report LPQTH-93/0

Interaction between Ionized and Molecular Gas in the Active Star-Forming Region W31

We have carried out 21 cm radio continuum, H76_\alpha radio recombination line, and various (CO, ^13CO, CS, & C^34S) molecular line observations of the W31 complex. Our radio continuum data show that W31 is composed of two extended HII regions, G10.2-0.3 and G10.3-0.1, each of which comprises an ultracompact HII region, two or more compact components, and diffuse envelope. The W31 cloud appears as an incomplete shell on the whole and consists of southern spherical and northern flat components, which are associated with G10.2-0.3 and G10.3-0.1, respectively. We detect two large and massive CS-emitting regions in the northern and southern cloud components. The large amount of dense gas may suggest that the W31 cloud has ability to form rich stellar clusters and that star formation has only recently begun. The extended envelopes of both G10.2-0.3 and G10.3-0.1 are likely to be results of the champagne flows, based on the distributions of ionized and molecular gas and the velocity gradient of H76_\alpha line emission. We find strong evidence of bipolar molecular outflows associated with the two ultracompact HII regions. In the vicinity of the ultracompact and compact HII regions in G10.3-0.1, the CO J=2-1/J=1-0 intensity ratio is high (1.4) and a small but prominent molecular gas hollow exists. These observations strongly indicate that the HII regions and their ionizing stars are interacting with the molecular cloud. Therefore, it is most likely that recently formed massive stars are actively disrupting their parental molecular cloud in the W31 complex.Comment: 26 pages, including 10 figures, accepted for publication in Ap

SRAO CO Observation of 11 Supernova Remnants in l = 70 to 190 deg

We present the results of 12CO J = 1-0 line observations of eleven Galactic supernova remnants (SNRs) obtained using the Seoul Radio Astronomy Observatory (SRAO) 6-m radio telescope. The observation was made as a part of the SRAO CO survey of SNRs between l = 70 and 190 deg, which is intended to identify SNRs interacting with molecular clouds. The mapping areas for the individual SNRs are determined to cover their full extent in the radio continuum. We used halfbeam grid spacing (60") for 9 SNRs and full-beam grid spacing (120") for the rest. We detected CO emission towards most of the remnants. In six SNRs, molecular clouds showed a good spatial relation with their radio morphology, although no direct evidence for the interaction was detected. Two SNRs are particularly interesting: G85.4+0.7, where there is a filamentary molecular cloud along the radio shell, and 3C434.1, where a large molecular cloud appears to block the western half of the remnant. We briefly summarize the results obtained for individual SNRs.Comment: Accepted for publication in Astrophysics & Space Science. 12 pages, 12 figures, and 3 table