Publications (55)29.12 Total impact
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Article: Massive Quiescent Cores in Orion: Dynamical State Revealed by High-Resolution Ammonia Maps
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ABSTRACT: We present combined VLA and Green Bank Telescope images of \ammonia\ inversion transitions (1,1) and (2,2) toward OMC2 and OMC3. We focus on the relatively quiescent Orion cores, which are away from the Trapezium cluster and have no sign of massive protostars nor evolved star formation, such as IRAS source, water maser, and methanol maser. The 5\arcsec\ angular resolution and $0.6 \rm{}km\,s^{-1}$ velocity resolution of these data enable us to study the thermal and dynamic state of these cores at $\sim{}0.02 \rm{}pc$ scales, comparable to or smaller than those of the current dust continuum surveys. We measure temperatures for a total of 30 cores, with average masses of $11\,\Ms$, radii of $0.039 \rm{}pc$, virial mass ratio $\bar{R_{vir}}$ = 3.9, and critical mass ratio $\bar{R_{C}}$ = 1.5. Twelve sources contain \textit{Spitzer} protostars. The thus defined starless and protostellar subsamples have similar temperature, line width, but different masses, with an average of $7.3\,\Ms$ for the former and $16\,\Ms$ for the latter. Compared to others Gould Belt dense cores, mores Orion cores have a high gravitational-to kinetic energy ratio and more cores have a larger thant unity critical mass ratio. Orion dense cores have velocity dispersion similar to those of cores in low-mass star-forming regions but larger masses for fiven size. Some cores appear to have truly supercritical gravitational-to-kinetic energy ratios, even when considering significant observational uncertainties: thermal and non-thermal gas mothins alone cannot prevent collapse.07/2012; -
Article: A compensation method for the disturbance in the temperature field caused by subsurface thermocouples
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ABSTRACT: The presence of a subsurface thermocouple hole can lead to a local disturbance of the temperature field in a sample and to a discrepancy between the thermal history measured by the thermocouple and the thermal history in an area without a thermocouple. This phenomenon also leads to errors in the surface heat flux calculated using an inverse heat conduction model, which relies on the acquired thermal history data. This article analyzes the factors that influence the temperature discrepancy caused by a subsurface thermocouple hole. A technique called the “equivalent depth” technique is proposed to compensate for the disturbance of the temperature field due to the presence of a thermocouple hole. This technique involves off-setting the location of the thermocouple position based on the radius of the thermocouple hole. A verification of this technique for the calculation of the surface heat flux using an inverse heat conduction model with measured thermal history data is presented.Metallurgical and Materials Transactions B 04/2012; 37(3):475-483. · 0.90 Impact Factor -
Article: A comparison study of microstructure and mechanical properties of Ti-24Al-14Nb-3V-0.5Mo with and without Si
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ABSTRACT: A comparative study has been made of the room- and elevated-temperature properties, room-temperature fracture toughness, fatigue-crack propagation rates, and 650 °C creep properties of Ti-24Al-14Nb-3V-0.5Mo with and without 0.9 at. pct Si. Both alloys have microstructures consisting of the α 2, B2, and the orthorhombic O phase, with different proportions of the α 2 phase relative to the (O + B2) mixtures, depending on solution-treatment temperature. The alloy with a Si addition contains additional primary ζ-Ti5Si3 particles distributed in the (O + B2) matrix. Tests of mechanical properties showed that the incorporation of a small fraction (about 0.03 by volume) of the Ti5Si3 phase leads to greater room-temperature and elevated-temperature strengths, but lower room-temperature elongations and fracture toughness as compared with the base alloy. Alloys containing greater volume fractions of the α 2 phase exhibited better tensile ductility, and this was attributed to the concurrent stabilization of the B2 phase. Examination of tensile-tested and fatigued specimens indicates that the primary failure mode of the alloys, regardless of Si addition, was due to the brittleness of the α 2 phase; the silicide particles that debonded from the matrix also contribute to cracking in the monotonic loading mode. Up to a 20 pct improvement in creep-rupture life was observed in the Si-containing alloys, and this was interpreted in terms of the solute-strengthening effect of Si. While the incorporated Ti5Si3 phase has an unfavorable effect on ductility and room-temperature fracture toughness, the difference in fatigue-crack propagation rates between the alloys with and without Si is minimal. It is concluded that the controlling factor for the fatigue failure in orthorhombic alloys is related to the (α 2 + O + B2) microstructure, instead of the Ti5Si3 particles.Metallurgical and Materials Transactions A 04/2012; 31(9):2205-2217. · 1.54 Impact Factor -
Article: Influence of surface morphology, water flow rate, and sample thermal history on the boiling-water heat transfer during direct-chill casting of commercial aluminum alloys
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ABSTRACT: An experimental investigation has been conducted on as-cast samples from three commercially significant aluminum alloys (AA1050, AA3004, and AA5182) to quantify the influence of surface morphology, water flow rate, and sample thermal history on the boiling-water heat transfer under conditions similar to those experienced in the direct-chill (DC) casting process. The study involved characterization of the as-cast surface morphology using a laser profilometer and quantification of the sample surface temperature and heat extraction to the cooling water using a DC casting simulator in combination with an inverse heat-conduction (IHC) analysis. The results from the study indicate that alloy’s thermal conductivity, surface morphology, and sample initial temperature all dramatically influence the calculated “boiling curve.” The intensity of the heat extraction was found to be enhanced at high heat fluxes in the nucleate boiling regime as the thermal conductivity was increased and was also found to increase as the surface of the sample became rougher, presumably through promotion of nucleation, growth, and/or detachment of bubbles. The heat transfer was also found to increase with increasing sample starting temperature, resulting in a series of boiling curves dependent on initial sample temperature. Finally, the effect of the water flow rate on heat transfer was found to be comparatively moderate and was limited to the sample with the smooth (machined) surface.Metallurgical and Materials Transactions B 04/2012; 32(5):929-939. · 0.90 Impact Factor -
Article: Thermoelectric Properties of Co-Doped TiS2
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ABSTRACT: The thermoelectric properties of cobalt-doped compounds Co x Ti1−x S2 (0≤x≤ 0.3) prepared by solid-state reaction were investigated from 5K to 310K. It was found that the electric resistivity ρ and absolute thermopower |S| for all the doped compounds decreased significantly with increasing Co content over the whole temperature range investigated. The increased lattice thermal conductivity of the doped compounds would imply enhancement of the acoustic velocity. Moreover, the ZT value of the doped compounds was improved over the whole temperature range investigated, and specifically reached 0.03 at 310K for Co0.3Ti0.7S2, being about 66% larger than that of TiS2. KeywordsThermoelectric–thermal conductivity–resistivity–TiS2Journal of Electronic Materials 04/2012; 40(5):980-986. · 1.47 Impact Factor -
Article: Measurements of liquidus temperatures in the Cu-Nb and Cu-Cr systems
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ABSTRACT: The Cu-Nb and Cu-Cr alloys at compositions ranging from 5 to 86 wt% Nb (89 wt% Cr) were processed in a clean environment and solidified at relatively low cooling rates of 50 to 75 °C/s to determine liquidus temperatures. In this study, both temperature measurements and microstructural observations confirmed the equilibrium phase diagram having an S-shaped, nearly flat liquidus, rather than that with a monotectic reaction in the liquid state. However, a metastable liquid miscibility gap exists in the two systems.Journal of Phase Equilibria 04/2012; 21(2):136-140. -
Article: Multi-line detection of O2 toward rho Oph A
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ABSTRACT: Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. Contrary to expectation, the space missions SWAS and Odin found only very small amounts of water vapour and essentially no O2 in the dense star-forming interstellar medium. Only toward rho Oph A did Odin detect a weak line of O2 at 119 GHz in a beam size of 10 arcmin. A larger telescope aperture such as that of the Herschel Space Observatory is required to resolve the O2 emission and to pinpoint its origin. We use the Heterodyne Instrument for the Far Infrared aboard Herschel to obtain high resolution O2 spectra toward selected positions in rho Oph A. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. The 487.2GHz line was clearly detected toward all three observed positions in rho Oph A. In addition, an oversampled map of the 773.8GHz transition revealed the detection of the line in only half of the observed area. Based on their ratios, the temperature of the O2 emitting gas appears to vary quite substantially, with warm gas (> 50 K) adjacent to a much colder region, where temperatures are below 30 K. The exploited models predict O2 column densities to be sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these model, the observationally determined O2 column densities seem not to depend strongly on the derived gas temperatures, but fall into the range N(O2) = (3 to >6)e15/cm^2. Beam averaged O2 abundances are about 5e-8 relative to H2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz of about 4 - 5 arcmin, encompassing the entire rho Oph A core.02/2012; -
Chapter: Monitoring of Meniscus Thermal Phenomena with Thermocouples in Continuous Casting of Steel
04/2011: pages 119 - 126; , ISBN: 9781118061800 -
Article: GLOBAL SUPPLY CHAIN MANAGEMENT UNDER THE CARBON EMISSION TRADING PROGRAM USING MIXED INTEGER PROGRAMMING AND GENETIC …
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ABSTRACT: In this paper, the transportation problem under the carbon emission trading program is modelled by mathematical programming and genetic algorithm. Since green supply chain issues become important and new legislations are taken into account, carbon emissions costs are included in the total costs of the supply chain. The optimisation model has the ability to minimise the total costs and provides the best solutions, which are both cost-effective and environmentally friendly. Moreover, a mathematical model and genetic algorithm are used to simulate the developments when carbon emission costs are changed and when companies are committed penalty charge. Finally, the result is shown the genetic algorithm technique is feasible in transportation network planning.IJE Transactions B: Applications. 03/2011; 24. -
Article: Annihilator Conditions Relative to a Class of Modules
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ABSTRACT: Annihilator conditions relative to a class of modules are studied and used to characterize the relative extending modules. In particular, dual rings relative to the class of all small right ideals, called right small-dual rings, are investigated and some known results on the dual rings are generalized to the case of small-dual rings.Thai Journal of Mathematics Volume. 01/2011; 9(1):1-9. -
Article: [CII] observations of H$_2$ molecular layers in transition clouds
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ABSTRACT: We present the first results on the diffuse transition clouds observed in [CII] line emission at 158 microns (1.9 THz) towards Galactic longitudes near 340deg (5 LOSs) and 20deg (11 LOSs) as part of the GOT C+ survey. Out of the total 146 [CII] velocity components detected by profile fitting we identify 53 as diffuse molecular clouds with associated $^{12}$CO emission but without $^{13}$CO emission and characterized by A$_V$ < 5 mag. We estimate the fraction of the [CII] emission in the diffuse HI layer in each cloud and then determine the [CII] emitted from the molecular layers in the cloud. We show that the excess [CII] intensities detected in a few clouds is indicative of a thick H$_2$ layer around the CO core. The wide range of clouds in our sample with thin to thick H$_2$ layers suggests that these are at various evolutionary states characterized by the formation of H$_2$ and CO layers from HI and C$^+$, respectively. In about 30% of the clouds the H$_2$ column densities (''dark gas'') traced by the [CII] is 50% or more than that traced by $^{12}$CO emission. On the average about 25% of the total H$_2$ in these clouds is in an H$_2$ layer which is not traced by CO. We use the HI, [CII], and $^{12}$CO intensities in each cloud along with simple chemical models to obtain constraints on the FUV fields and cosmic ray ionization rates. Comment: To be published in HIFI A&A special edition07/2010; -
Article: C$^+$ detection of warm dark gas in diffuse clouds
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ABSTRACT: We present the first results of the Herschel open time key program, Galactic Observations of Terahertz C$^+$ (GOT C+) survey of the [CII] fine-structure line at 1.9 THz (158 microns) using the HIFI instrument on Herschel. We detected 146 interstellar clouds along sixteen lines-of-sight towards the inner Galaxy. We also acquired HI and CO isotopologue data along each line-of-sight for analysis of the physical conditions in these clouds. Here we analyze 29 diffuse clouds (A$_{V}$ < 1.3 mag.) in this sample characterized by having [CII] and HI emission, but no detectable CO. We find that [CII] emission is generally stronger than expected for diffuse atomic clouds, and in a number of sources is much stronger than anticipated based on their HI column density. We show that excess [CII] emission in these clouds is best explained by the presence of a significant diffuse warm H$_2$, dark gas, component. This first [CII] 158 micron detection of warm dark gas demonstrates the value of this tracer for mapping this gas throughout the Milky Way and in galaxies. Comment: To be published in A&A HIFI Special Edition07/2010; -
Article: Herschel/HIFI discovery of interstellar chloronium (H$_2$Cl$^+$)
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ABSTRACT: We report the first detection of chloronium, H$_2$Cl$^+$, in the interstellar medium, using the HIFI instrument aboard the \emph{Herschel} Space Observatory. The $2_{12}-1_{01}$ lines of ortho-H$_2^{35}$Cl$^+$ and ortho-H$_2^{37}$Cl$^+$ are detected in absorption towards NGC~6334I, and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ is detected in absorption towards NGC~6334I and Sgr~B2(S). The H$_2$Cl$^+$ column densities are compared to those of the chemically-related species HCl. The derived HCl/H$_2$Cl$^+$ column density ratios, $\sim$1--10, are within the range predicted by models of diffuse and dense Photon Dominated Regions (PDRs). However, the observed H$_2$Cl$^+$ column densities, in excess of $10^{13}$~cm$^{-2}$, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models. Comment: Accepted for publication in A&A, HIFI Special Issue; 4 pages, 2 figures, 1 table07/2010; -
Article: Large Annihilator Conditions Relative to Modules Classes
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ABSTRACT: Annihilator conditions relative to modules classes are studied, and used to characterize the relative extending modules. In particular, dual rings relative to the class of all small right ideals, called right small-dual rings, are investigated, and some known results on the dual rings are generalized to the case of small-dual rings.Thai Journal of Mathematics Volume. 01/2010; 8(2):275-284. -
Article: Tentative Detection of Molecular Oxygen in the ρ Ophiuchi Cloud
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ABSTRACT: We report the tentative detection of molecular oxygen in the interstellar medium. Deep integrations using the Submillimeter Wave Astronomy (SWAS) satellite of the ρ Oph A cloud have resulted in a detection of an emission feature consistent with the NJ = 33 → 12 transition of O2 at a local standard of rest velocity of 6.0 km s-1. The line width and velocity are suggestive of the redshifted wing emission seen in species that trace the molecular outflows seen in this region. The fractional abundance of O2 relative to H2 in this high-velocity gas is approximately 10-5. The fractional abundance of ortho-H2O in this material is 8 × 10-8, somewhat higher than found in quiescent material by earlier SWAS observations but less than that found in younger outflows. We suggest a unified scenario that explains the low O2 abundance in cloud cores previously reported [X(O2) ≤ few × 10-7], along with the much enhanced abundance in the outflow region. In this picture, quiescent clouds are characterized by significant depletion of gas-phase oxygen, which ends up largely as water ice on the dust grains. A shock associated with the outflow results in almost all oxygen being processed into gas-phase water. In the cool postshock gas, the standard gas-phase chemistry reasserts itself, and after an elapsed time of a few times 105 yr, the O2 abundance has increased to the point that this species is one of the main repositories of oxygen atoms. At the same time, the gas-phase water abundance drops drastically, in agreement with the SWAS observations that we report here. On a somewhat longer timescale, depletion again dominates and the gas-phase abundance of O2 drops by several orders of magnitude, with a significant fraction of oxygen remaining in atomic form.The Astrophysical Journal 12/2008; 576(2):814. · 6.02 Impact Factor -
Article: Effect of Sample Start Temperature during Transient Boiling Water Heat Transfer
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ABSTRACT: The influence of the initial sample start temperature (400°C to 1000°C) on the boiling water heat-transfer behavior during quenching of AISI 316 stainless steel plates has been examined. The study involved instrumenting 280-mm-diameter, 12.7-mm- (0.5- in.-) thick plates with seven subsurface thermocouples (TCs) placed at various locations across the diameter and spraying water onto the surface using a circular cone spray nozzle placed directly above the plate surface. The measured temperature-time history at each location was then input to a two-dimensional (2-D) axisymmetric inverse heat conduction (IHC) model so that the boiling curves for each test condition could be determined. The study has demonstrated that the initial sample temperature has a significant effect on the shape and magnitude of the boiling curve during transient cooling conditions. A simple method is proposed to approximately capture the influence of sample start temperature on transient boiling water behavior that alleviates the need to conduct multiple measurements.Metallurgical and Materials Transactions B 11/2007; 38(6):901-910. · 0.90 Impact Factor -
Article: Massive Quiescent Cores in Orion. -- II. Core Mass Function
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ABSTRACT: We have surveyed submillimeter continuum emission from relatively quiescent regions in the Orion molecular cloud to determine how the core mass function in a high mass star forming region compares to the stellar initial mass function. Such studies are important for understanding the evolution of cores to stars, and for comparison to formation processes in high and low mass star forming regions. We used the SHARC II camera on the Caltech Submillimeter Observatory telescope to obtain 350 \micron data having angular resolution of about 9 arcsec, which corresponds to 0.02 pc at the distance of Orion. Our analysis combining dust continuum and spectral line data defines a sample of 51 Orion molecular cores with masses ranging from 0.1 \Ms to 46 \Ms and a mean mass of 9.8 \Ms, which is one order of magnitude higher than the value found in typical low mass star forming regions, such as Taurus. The majority of these cores cannot be supported by thermal pressure or turbulence, and are probably supercritical.They are thus likely precursors of protostars. The core mass function for the Orion quiescent cores can be fitted by a power law with an index equal to -0.85$\pm$0.21. This is significantly flatter than the Salpeter initial mass function and is also flatter than the core mass function found in low and intermediate star forming regions. Thus, it is likely that environmental processes play a role in shaping the stellar IMF later in the evolution of dense cores and the formation of stars in such regions.11/2006; -
Article: Thermal time–concepts and utility
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ABSTRACT: This paper (i) reviews temperature/development rate relationships in plants and poikilothermic invertebrates, (ii) argues that the relationship is often linear over much of the range up to the thermal optimum (T o) and provides a possible mechanism, (iii) provides evidence of a trade-off between the base temperature (T b) and the thermal constant (DD) that enables each species to adapt to its thermal environment, and (iv) indicates some of the practical and ecological implications. Where a linear relationship has been characterised it is possible to estimate the base temperature for development (T b , expressed in °C) and the thermal constant for development (DD, the reciprocal of the temperature coefficient (a), expressed in degree [°C] days accumulated above T b). A possible basis for the linear relationship between rate and temperature is proposed based on the Arrhenius and Sharpe-Schoolfield equations involving activation enthalpy and progressive inactivation of the reactant molecules at both low and high temperatures. Knowledge of T b and DD enables rates of development of organisms/ processes to be calculated and compared at any given temperature between T b and T o . An analysis of published results for differentiation processes (differentiation = a change of state) in species of insects, Collembola, spiders, nematodes and plants showed that T b tended to vary with the temperature of the niche to which the organism is adapted, and that there was a trade-off between T b and DD. Tropical species had higher values of T b than temperate and DD decreased as T b increased (and vice versa). This conferred a competitive advantage on each species in the thermal environment to which it was adapted. The decrease in DD tended to be relatively greater than the increase in T b, further favouring a high T b in tropical species. A mechanism for the trade-off is suggested whereby DD and T b were shown to be correlated (P < 0.01) with the activation enthalpy (H A) of an assumed, rate-limiting enzyme. Thermal time can also be applied to processes involving growth (= an increase in dry weight) when the DD requirement for development to maturity is the sum of the requirements for differentiation and growth. Rates of both differentiation and growth can vary greatly between species, depending upon the niche they inhabit, and the implications of such differences for resource requirements are considered. In insects and nematodes, but not in annual plants, development is usually coupled to growth. Consequently, when resources are inadequate, mature size in these animals varies less than in plants. Thermal time is shown to provide insight into the life strategies of species within their communities and to have practical implications.Annals of Applied Biology 01/2005; 146:1-14. · 2.18 Impact Factor -
Article: Modeling global emissions and residues of pesticides
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ABSTRACT: A major portion of persistent organic pollutants (POPs) is organochlorine pesticides (OCPs), in which carbon and chlorine are combined. During the last decade, a number of researches have been devoted to create emission inventories of OCPs at regional and global scales. The studies on residue inventories of OCPs, however, are sparse. In the absence of complete data and information on worldwide inventories of pesticides emissions and residues, a Simplified Gridded Pesticide Emission and Residue Model (SGPERM) has been developed to estimate the emissions and residues, and build pesticide emission and residue inventories. The SGPERM is an integration of a mathematical module, a relational database system, and a geographic information system. In this paper, a complete description of the model is given. A brief review of the models application in developing emission inventories for -HCH is introduced. The model is used to create global gridded residue inventories of -HCH on cropland with a 1 latitude by 1 longitude resolution for 1980, 1990, and 2000, the first such residue inventories for any pesticide. The total global residues of -HCH on cropland were 198 kt in 1980, 35 kt in 1990, and 1.2 kt in 2000, and the emissions from these residues were 11.8 kt in 1980, 2.3 kt in 1990, and 0.15 kt in 2000. Historical trends of -HCH concentration in agricultural soil are also estimated at some locations in China and Japan, and match the monitoring data quite well.Environmental Modeling and Assessment 12/2004; 9(4):237-243. · 0.97 Impact Factor -
Article: Microbubble lensing-induced photobleaching (µ-BLIP) with application to microflow visualization
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ABSTRACT: The curvature of gas–liquid interfaces and the step change in properties across these interfaces in microchannels are shown here to create a powerful lens/mirror effect. In a hydrophilic system, light incident on the bubble is focused into the surrounding liquid, resulting in a locally increased total light exposure. The optical phenomena leading to this are discussed, and the effect is demonstrated experimentally by imaging the increased photobleaching rate of fluorophores in the near-bubble region. Numerical simulations of the system are performed to investigate the electrical potential and flow fields resulting from the application of an axial electric field. Microbubble lensing-induced photobleaching (-BLIP) is then applied as a method to inject a negative scalar flow marker for flow visualization in microchannels. Once formed, the electrokinetic transport of this marker is analyzed to determine the cross-channel velocity profile of the liquid phase and the liquid velocity in the film. Experimental data is verified by comparison with numerical predictions and previous experimental studies. This contribution represents both a new application of microscale gas–liquid interfacial phenomena, and a new technique for microfluidic flow visualization, particularly applicable (though not limited) to the study of multiphase microchannel flows.Experiments in Fluids 07/2003; 35(2):178-187. · 1.74 Impact Factor
Top co-authors
Top Journals
Institutions
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2012
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Queen's University
- Department of Mechanical and Materials Engineering
Kingston, Ontario, Canada -
University of British Columbia
- Department of Materials Engineering
Vancouver, British Columbia, Canada
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1997–2012
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Chinese Academy of Sciences
- Key Lab of Materials Physics
Beijing, Beijing Shi, China
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2008
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National Astronomy and Ionosphere Center
Arecibo, Arecibo, Puerto Rico
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2003
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University of Toronto
Toronto, Ontario, Canada -
Lakehead University Thunder Bay Campus
Thunder Bay, Ontario, Canada
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2001
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University of West London
London, ENG, United Kingdom
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1992
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Tsinghua University
Beijing, Beijing Shi, China
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