Proper Motion of Pulsar B1800-21

We report high angular resolution, multi-epoch radio observations of the young pulsar PSR B1800-21. Using two pairs of data sets, each pair spanning approximately a ten year period, we calculate the proper motion of the pulsar. We obtain a proper motion of mu_alpha=11.6 +- 1.8 mas/yr, mu_delta=14.8 +- 2.3 mas/yr, which clearly indicates a birth position at the extreme edge of the W30 supernova remnant. Although this does not definitively rule out an association of W30 and PSR B1800-21, it does not support an association.Comment: 13 pages, 1 color figure. Replaced with version accepted for publication in Astrophysical Journa

Star Formation in the Extreme Outer Galaxy: Digel Cloud 2 Clusters

As a first step for studying star formation in the extreme outer Galaxy (EOG), we obtained deep near-infrared images of two embedded clusters at the northern and southern CO peaks of Cloud 2, which is one of the most distant star forming regions in the outer Galaxy (galactic radius R_g ~ 19 kpc). With high spatial resolution (FWHM ~ 0".35) and deep imaging (K ~ 21 mag) with the IRCS imager at the Subaru telescope, we detected cluster members with a mass detection limit of < 0.1 M_{sun}, which is well into the substellar regime. These high quality data enables a comparison of EOG to those in the solar neighborhood on the same basis for the first time. Before interpreting the photometric result, we have first constructed the NIR color-color diagram (dwarf star track, classical T Tauri star (CTTS) locus, reddening law) in the Mauna Kea Observatory filter system and also for the low metallicity environment since the metallicity in EOG is much lower than those in the solar neighborhood. The estimated stellar density suggests that an ``isolated type'' star formation is ongoing in Cloud 2-N, while a ``cluster type'' star formation is ongoing in Cloud 2-S. Despite the difference of the star formation mode, other characteristics of the two clusters are found to be almost identical: (1) K-band luminosity function (KLF) of the two clusters are quite similar, as is the estimated IMF and ages (~ 0.5--1 Myr) from the KLF fitting, (2) the estimated star formation efficiencies (SFEs) for both clusters are typical compared to those of embedded clusters in the solar neighborhood (~ 10 %). The similarity of two independent clusters with a large separation (~ 25 pc) strongly suggest that their star formation activities were triggered by the same mechanism, probably the supernova remnant (GSH 138-01-94).Comment: 14pages, 11 figures; Accepted for publication in Ap

Triggered massive-star formation on the borders of Galactic HII regions. III. Star formation at the periphery of Sh2-219

Context. Massive-star formation triggered by the expansion of HII regions. Aims. To understand if sequential star formation is taking place at the periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain). Results. In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000\msol lies at the southwestern border of Sh2-219, in the HI gap. Two molecular condensations, elongated along the ionization front, probably result from the interaction between the expanding HII region and the molecular cloud. In this region of interaction there lies a cluster containing many highly reddened stars, as well as a massive star exciting an ultracompact HII region. More surprisingly, the brightest parts of the molecular cloud form a `chimney', perpendicular to the ionization front. This chimney is closed at its south-west extremity by H-alpha walls, thus forming a cavity. The whole structure is 7.5 pc long. A luminous H-alpha emission-line star, lying at one end of the chimney near the ionization front, may be responsible for this structure. Confrontation of the observations with models of HII region evolution shows that Sh2-219 is probably 10^5 yr old. The age and origin of the near-IR cluster observed on the border of Sh2-219 remain unknown.Comment: 11 pages, 10 figures. To be published in A&

Discriminating cool-water from warm-water carbonates and their diagenetic environments using element geochemistry: the Oligocene Tikorangi Formation (Taranaki Basin) and the dolomite effect

Fields portrayed within bivariate element plots have been used to distinguish between carbonates formed in warm- (tropical) water and cool- (temperate) water depositional settings. Here, element concentrations (Ca, Mg, Sr, Na, Fe, and Mn) have been determined for the carbonate fraction of bulk samples from the late Oligocene Tikorangi Formation, a subsurface, mixed dolomite-calcite, cool-water limestone sequence in Taranaki Basin, New Zealand. While the occurrence of dolomite is rare in New Zealand Cenozoic carbonates, and in cool-water carbonates more generally, the dolomite in the Tikorangi carbonates is shown to have a dramatic effect on the "traditional" positioning of cool-water limestone fields within bivariate element plots. Rare undolomitised, wholly calcitic carbonate samples in the Tikorangi Formation have the following average composition: Mg 2800 ppm; Ca 319 100 ppm; Na 800 ppm; Fe 6300 ppm; Sr 2400 ppm; and Mn 300 ppm. Tikorangi Formation dolomite-rich samples (>15% dolomite) have average values of: Mg 53 400 ppm; Ca 290 400 ppm; Na 4700 ppm; Fe 28 100 ppm; Sr 5400 ppm; and Mn 500 ppm. Element-element plots for dolomite-bearing samples show elevated Mg, Na, and Sr values compared with most other low-Mg calcite New Zealand Cenozoic limestones. The increased trace element contents are directly attributable to the trace element-enriched nature of the burial-derived dolomites, termed here the "dolomite effect". Fe levels in the Tikorangi Formation carbonates far exceed both modern and ancient cool-water and warm-water analogues, while Sr values are also higher than those in modern Tasmanian cool-water carbonates, and approach modern Bahaman warm-water carbonate values. Trace element data used in conjunction with more traditional petrographic data have aided in the diagenetic interpretation of the carbonate-dominated Tikorangi sequence. The geochemical results have been particularly useful for providing more definitive evidence for deep burial dolomitisation of the deposits under the influence of marine-modified pore fluids

Solitons, solitonic vortices, and vortex rings in a confined Bose-Einstein condensate

Quasi-one-dimensional solitons that may occur in an elongated Bose-Einstein condensate become unstable at high particle density. We study two basic modes of instability and the corresponding bifurcations to genuinely three-dimensional solitary waves such as axisymmetric vortex rings and non-axisymmetric solitonic vortices. We calculate the profiles of the above structures and examine their dependence on the velocity of propagation along a cylindrical trap. At sufficiently high velocity, both the vortex ring and the solitonic vortex transform into an axisymmetric soliton. We also calculate the energy-momentum dispersions and show that a Lieb-type mode appears in the excitation spectrum for all particle densities.Comment: RevTeX 9 pages, 9 figure

On the Relative Sensitivity of Mass-sensitive Chemical Microsensors

In this work, the chemical sensitivity of mass-sensitive chemical microsensors with a uniform layer sandwich structure vibrating in their lateral or in-plane flexural modes is investigated. It is experimentally verified that the relative chemical sensitivity of such resonant microsensors is -to a first order- independent of the microstructure\u27s in-plane dimensions and the flexural eigenmode used, and only depends on the layer thicknesses and densities as well as the sorption properties of the sensing film. Important implications for the design of mass-sensitive chemical microsensors are discussed, whereby the designer can focus on the layer stack to optimize the chemical sensitivity and on the in-plane dimensions and mode shape to optimize the resonator\u27s frequency stability

Analytical Modeling of a Novel High-\u3cem\u3eQ\u3c/em\u3e Disk Resonator for Liquid-Phase Applications

To overcome the detrimental effects of liquid environments on microelectromechanical systems resonator performance, the in-fluid vibration of a novel disk resonator supported by two electrothermally driven legs is investigated through analytical modeling and the effects of the system’s geometric/material parameters on the dynamic response are explored. The all-shear interaction device (ASID) is based on engaging the surrounding fluid primarily through shearing action. The theory comprises a continuous-system, multimodal model, and a single-degree-of-freedom model, the latter yielding simple formulas for the fundamental-mode resonant characteristics that often furnish excellent estimates to the results based on the more general model. Comparisons between theoretical predictions and previously published liquid-phase quality factor (Q) data (silicon devices in heptane) show that the theoretical results capture the observed trends and also give very good quantitative estimates, particularly for the highest Q devices. Moreover, the highest Q value measured in the earlier study (304) corresponded to a specimen whose disk radius-to-thickness ratio was 2.5, a value that compares well with the optimal value of 2.3 predicted by the present model. The insight furnished by the proposed theory is expected to lead to further improvements in ASID design to achieve unprecedented levels of performance for a wide variety of liquid-phase resonator applications

A downward revision to the distance of the 1806-20 cluster and associated magnetar from Gemini near-Infrared spectroscopy

We present H- and K-band spectroscopy of OB and Wolf-Rayet (WR) members of the Milky Way cluster 1806-20 (G10.0-0.3), to obtain a revised cluster distance of relevance to the 2004 giant flare from the SGR 1806-20 magnetar. From GNIRS spectroscopy obtained with Gemini South, four candidate OB stars are confirmed as late O/early B supergiants, while we support previous mid WN and late WC classifications for two WR stars. Based upon an absolute Ks-band magnitude calibration for B supergiants and WR stars, and near-IR photometry from NIRI at Gemini North plus archival VLT/ISAAC datasets, we obtain a cluster distance modulus of 14.7+/-0.35 mag. The known stellar content of the 1806-20 cluster suggests an age of 3-5 Myr, from which theoretical isochrone fits infer a distance modulus of 14.7+/-0.7 mag. Together, our results favour a distance modulus of 14.7+/-0.4 mag (8.7^+1.8_-1.5 kpc) to the 1806-20 cluster, which is significantly lower than the nominal 15 kpc distance to the magnetar. For our preferred distance, the peak luminosity of the December 2004 giant flare is reduced by a factor of three to 7 X 10^46 erg/s, such that the contamination of BATSE short gamma ray bursts (GRB's) from giant flares of extragalactic magnetars is reduced to a few percent. We infer a magnetar progenitor mass of ~48^+20_-8 Msun, in close agreement with that obtained recently for the magnetar in Westerlund 1.Comment: 6 pages, 4 figures, accepted for MNRAS Letter

Is there something of the MCT in orientationally disordered crystals ?

Molecular Dynamics simulations have been performed on the orientationally disordered crystal chloroadamantane: a model system where dynamics are almost completely controlled by rotations. A critical temperature T_c = 225 K as predicted by the Mode Coupling Theory can be clearly determined both in the alpha and beta dynamical regimes. This investigation also shows the existence of a second remarkable dynamical crossover at the temperature T_x > T_c consistent with a previous NMR and MD study [1]. This allows us to confirm clearly the existence of a 'landscape-influenced' regime occurring in the temperature range [T_c-T_x] as recently proposed [2,3].Comment: 4 pages, 5 figures, REVTEX