A comparison of 3 optical systems for the detection of broadband ultrasound

There are many applications of ultrasound in the field of material properties' evaluation and structural health monitoring. Here we will consider the detection of broadband laser generated ultrasound taking as an example acoustic emission as simulated by the pencil break test. In this paper three optical methods of detecting these ultrasound signals are compared; these are polarimetry, fibre Bragg gratings and vibrometery. Of these, the first two involve the bonding of a fibre sensor to the sample, whilst the vibrometer is a non-contact instrument that measures out-of-plane displacements. FBGs respond to the inplane strains associated with an ultrasound wave whilst the polarimeter detects birefringence produced by pressure waves acting normal to the fibre. The sensitivities of the systems are compared and their relative merits are discussed. It will also be shown that the polarimetric responses of symmetric and antisymmetric Lamb waves differ, which opens up the possibility of learning more about the nature of an acoustic signal using this technique than can be determined simply from the measurement of in-plane or out-of plane displacements alone

Laser ultrasound measurement of diaphragm thickness, Young’s modulus and Poisson’s ratio in a MEMS device

Laser-generated Lamb waves, coupled with a large bandwidth Michelson interferometer, have been demonstrated to accurately measure the thickness of a MEMS pressure sensor diaphragm in the [110] direction of a silicon wafer. Using the reassigned Gabor time-frequency method to produce group velocity dispersion curves, the technique facilitates the measurement of thickness, Young’s modulus and Poisson’s ratio from just one non-contact measurement. In this investigation, thickness was determined to be 35.01 μm ± 0.18 μm. For comparison, the thickness was measured using an independent optical technique; obtaining a value of 34.60 μm ± 0.27 μm. Values for Young’s modulus and Poisson’s ratio were also determined to be 163 GPa ± 11.7 GPa and 0.351 respectively and these are in good agreement with values found in the literature

Evaporation and condensation of spherical interstellar clouds. Self-consistent models with saturated heat conduction and cooling

Shortened version: The fate of IS clouds embedded in a hot tenuous medium depends on whether the clouds suffer from evaporation or whether material condensates onto them. Analytical solutions for the rate of evaporative mass loss from an isolated spherical cloud embedded in a hot tenuous gas are deduced by Cowie & McKee (1977). In order to test the validity of the analytical results for more realistic IS conditions the full hydrodynamical equations must be treated. Therefore, 2D numerical simulations of the evolution of IS clouds %are performed with different internal density structures and surrounded by a hot plasma reservoir. Self-gravity, interstellar heating and cooling effects and heat conduction by electrons are added. Classical thermal conductivity of a fully ionized hydrogen plasma and saturated heat flux are considered. Using pure hydrodynamics and classical heat flux we can reproduce the analytical results. Heat flux saturation reduces the evaporation rate by one order of magnitude below the analytical value. The evolution changes totally for more realistic conditions when interstellar heating and cooling effects stabilize the self-gravity. Evaporation then turns into condensation, because the additional energy by heat conduction can be transported away from the interface and radiated off efficiently from the cloud's inner parts. I.e. that the saturated heat flux consideration is inevitable for IS clouds embedded in hot tenuous gas. Various consequences are discussed in the paper.Comment: 16 pages, 24 figures, accepted in Astronomy and Astrophysic

Review of the effectiveness of current community ownership mechanisms and of options for supporting the expansion of community ownership in Scotland

This report presents the findings of research commissioned by the Scottish Land Commission to review the effectiveness of community ownership mechanisms and options for simplifying or improving these mechanisms to enable and support the expansion of community ownership in Scotland. This included reviewing processes relating to negotiated sales or transfers of land and/or assets to communities, as well as legislative mechanisms including the Community Right to Buy (CRtB), Crofting Community Right to Buy, the Transfer of Crofting Estates (Scotland) Act 1997 and Asset Transfer measures under the Community Empowerment (Scotland) Act 2015

The high-mass disk candidates NGC7538IRS1 and NGC7538S

Context: The nature of embedded accretion disks around forming high-mass stars is one of the missing puzzle pieces for a general understanding of the formation of the most massive and luminous stars. Methods: Using the Plateau de Bure Interferometer at 1.36mm wavelengths in its most extended configuration we probe the dust and gas emission at ~0.3",corresponding to linear resolution elements of ~800AU. Results: NGC7538IRS1 remains a single compact and massive gas core with extraordinarily high column densities, corresponding to visual extinctions on the order of 10^5mag, and average densities within the central 2000AU of ~2.1x10^9cm^-3 that have not been measured before. We identify a velocity gradient across in northeast-southwest direction that is consistent with the mid-infrared emission, but we do not find a gradient that corresponds to the proposed CH3OH maser disk. The spectral line data toward NGC7538IRS1 reveal strong blue- and red-shifted absorption toward the mm continuum peak position. The red-shifted absorption allows us to estimate high infall rates on the order of 10^-2 Msun/yr. Although we cannot prove that the gas will be accreted in the end, the data are consistent with ongoing star formation activity in a scaled-up low-mass star formation scenario. Compared to that, NGC7538S fragments in a hierarchical fashion into several sub-sources. While the kinematics of the main mm peak are dominated by the accompanying jet, we find rotational signatures from a secondary peak. Furthermore, strong spectral line differences exist between the sub-sources which is indicative of different evolutionary stages within the same large-scale gas clump.Comment: 15 pages, 12 figures, accepted for A&

Near-Infrared Photometry and Radio Continuum Study of the Massive Star Forming Regions IRAS 21413+5442 and IRAS 21407+5441

IRAS 21413+5442 and IRAS 21407+5441 are two massive star forming regions of high luminosity, likely associated with each other. Near-infrared photometry on these two IRAS sources was performed at UKIRT using the UFTI under excellent seeing conditions yielding an angular resolution of $\sim$ 0.5 arcsec. Our results reveal details of stellar content to a completeness limit (90%) of J = 18.5, H = 18.0, and K = 17.5 mag in the two regions. In IRAS 21413+5442, we identify a late O type star, having large (H-K) color, to be near the centre of the CO jets observed by earlier authors. The UKIRT images reveal in IRAS 21407+5441, a faint but clear compact HII region around a central high - intermediate mass star cluster. We have detected a number of sources with large (H-K) color which are not detected in J band. We also present the GMRT radio continuum map at 1.28 GHz covering the entire region surrounding the two star forming clouds. The radio continuum fluxes are used to estimate the properties of HII regions which seem to support our near-IR photometric results. Based on our radio continuum map and the archival MSX 8.2 $\mu$m image, we show that the two IRAS sources likely belong to the same parent molecular cloud and conjecture that a high mass star of large IR colors, present in between the two sources, might have triggered star formation in this region. However one can not rule out the alternative possibility that Star A could be a nearby foreground star.Comment: 12 pages, 7 figures, accepted for publication in MNRA

The RMS Survey: Mid-Infrared Observations of Candidate Massive YSOs in the Southern Hemisphere

Abridged abstract: The Red MSX Source (RMS) survey is an ongoing effort to return a large, well-selected sample of massive young stellar objects (MYSOs) within our Galaxy. A series of ground-based follow-up observations are being undertaken in order to remove contaminant objects from our list of 2000 candidates, and to begin characterising these MYSOs. As a part of these follow-up observations, high resolution (~1") mid-IR imaging aids the identification of contaminant objects which are resolved (UCHII regions, PN) as opposed to those which are unresolved (YSOs, evolved stars) as well as identifying YSOs near UCHII regions and other multiple sources. We present 10.4 micron imaging observations for 346 candidate MYSOs in the RMS survey in the Southern Hemisphere, primarily outside the region covered by the GLIMPSE Spitzer Legacy Survey. These were obtained using TIMMI2 on the ESO 3.6m telescope in La Silla, Chile. Our photometric accuracy is of order 0.05Jy, and our astrometric accuracy is 0.8", which is an improvement over the nominal 2" accuracy of the MSX PSC.Comment: 9 page paper accepted to A&A. Online data for table 2 and figure 1 will be available in the published online version of this paper via A&A. The paper contains 7 figures and 3 table

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

The role of magnetic fields in the formation of high-mass stars is still under debate, and recent measurements of their orientation and strength by using polarized maser emissions are contributing new insights. Masers polarization, in particular of the 6.7-GHz methanol masers, are one of the best probes of the magnetic field morphologies around massive protostars. Determining the magnetic field morphology around an increasing number of massive protostars at milliarcsecond resolution by observing 6.7-GHz methanol masers is crucial to better understand the role of magnetic fields in massive star formation.The First EVN Group consists of 4 massive star-forming complexes: W51, W48, IRAS18556+0138, and W3(OH). These contain well-studied \hii ~regions from some of which molecular bipolar outflows were also detected (W51-e2, G35.20-0.74N). Nine of the European VLBI Network antennas were used to measure the linear polarization and Zeeman-splitting of the 6.7-GHz methanol masers in the star-forming regions of the First EVN Group. We detected a total of 154 CH3OH masers, one third of these towards W3(OH). Fractional linear polarization (1.2-11.5%) was detected towards 55 masers. The linear polarization vectors are well-ordered in all the massive star-forming regions. We measured significant Zeeman-splitting in 3 massive star-forming regions (W51, W48, and W3(OH)) revealing a range of separations -3.5 m/s<\Delta V_{z}<3.8 m/s with the smallest |\Delta V_{z}|=0.4m/s. We were also able to compare our magnetic field results with those obtained from submillimeter wavelength dust observation in W51 and show that the magnetic field at low and high resolutions are in perfect agreement.Comment: 15 pages, 11 figures, 5 tables, accepted by Astronomy & Astrophysic

Fluorescent Nanorods and Nanospheres for Real-Time In Vivo Probing of Nanoparticle Shape-Dependent Tumor Penetration

Shape dependent: Fluorescent quantum-dot-based nanospheres and nanorods with identical hydrodynamic size and surface properties but different aspect ratios were developed for real-time in vivo tumor imaging. The nanorods exhibited superior transport and distribution into mammary tumors in vivo versus nanospheres of similar plasma half-life.National Cancer Institute (U.S.) (Grant Number R01-CA126642)MIT-Harvard Center for Cancer Nanotechnology Excellence (1U54-CA119349)Massachusetts Institute of Technology. Dept. of Chemistry Instrumentation Facility (CHE-980806)Massachusetts Institute of Technology. Dept. of Chemistry Instrumentation Facility (DBI-9729592)ISN (W911NF-07-D-0004

Exploring morphological correlations among H2CO, 12CO, MSX and continuum mappings

There are relatively few H2CO mappings of large-area giant molecular cloud (GMCs). H2CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of the study was to identify H2CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature (CBT) data and H2CO (111-110; Nanshan 25-m radio telescope), 12CO (1--0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components on foreground clouds. We report simultaneous 6-cm H2CO absorption lines and H110\alpha radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50'\times50'), W3 (70'\times90'), DR21/W75 (60'\times90') and NGC2024/NGC2023 (50'\times100') GMCs. By superimposing H2CO and 12CO contours onto the MSX color map, we can compare correlations. The resolution for H2CO, 12CO and MSX data was about 10', 8' and 18.3", respectively. Comparison of H2CO and 12CO contours, 8.28-\mu m MSX colorscale and CBT data revealed great morphological correlation in the large area, although there are some discrepancies between 12CO and H2CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H2CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H2CO absorption lines are distributed in the intensity range from -1.0 to 0 Jy and the \Delta V range from 1.206 to 5 km/s.Comment: 18 pages, 22 figures, 5 tables. Accepted to be published in Astrophysics and Space Scienc