57949 research outputs found
Sort by
Hole free phase plate tomography for materials sciences samples
No full textWe report, for the first time, the three dimensional reconstruction (3D) of a transistor from a microprocessor chip and roughness of molecular electronic junction obtained by electron tomography with Hole Free Phase Plate (HFPP) imaging. The HFPP appears to enhance contrast between inorganic materials and also increase the visibility of interfaces between different materials. We demonstrate that the degree of enhancement varies depending on material and thickness of the samples using experimental and simulation data.Peer reviewed: YesNRC publication: Ye
The He2-OCS complex: comparison between theory and experiment
No full textOCS is an ideal probe for quantum solvation effects in cold helium clusters. He2-OCS is the \u201csecond step\u201d in going from a single OCS molecule to a large doped superfluid helium cluster. Here assignment of the spectrum of He2-OCS is significantly extended to higher values of J, K, and vt (the low frequency torsional vibration). The observation of a new infrared band, OCS \u3bd1\u202f+\u202f\u3bd3, taken together with the known \u3bd1 band, enables assignments to be verified by comparing ground state combination differences. Relatively straightforward scaling of previously calculated theoretical energy levels gives a remarkably good fit to experiment.Peer reviewed: YesNRC publication: Ye
Trace metals in soot and PM2.5 from heavy-fuel-oil combustion in a marine engine
No full textHeavy fuel oil (HFO) particulate matter (PM) emitted by marine engines is known to contain toxic heavy metals, including vanadium (V) and nickel (Ni). The toxicity of such metals will depend on the their chemical state, size distribution, and mixing state. Using online soot-particle aerosol mass spectrometry (SP-AMS), we quantified the mass of five metals (V, Ni, Fe, Na, and Ba) in HFO-PM soot particles produced by a marine diesel research engine. The in-soot metal concentrations were compared to in-PM2.5 measurements by inductively coupled plasma-optical emission spectroscopy (ICP-OES). We found that <3% of total PM2.5 metals was associated with soot particles, which may still be sufficient to influence in-cylinder soot burnout rates. Since these metals were most likely present as oxides, whereas studies on lower-temperature boilers report a predominance of sulfates, this result implies that the toxicity of HFO PM depends on its combustion conditions. Finally, we observed a 4-to-25-fold enhancement in the ratio V:Ni in soot particles versus PM2.5, indicating an enrichment of V in soot due to its lower nucleation/condensation temperature. As this enrichment mechanism is not dependent on soot formation, V is expected to be generally enriched within smaller HFO-PM particles from marine engines, enhancing its toxicity.Peer reviewed: YesNRC publication: Ye
Where is OH and does it trace the dark molecular gas (DMG)?
No full textHydroxyl (OH) is expected to be abundant in diffuse interstellar molecular gas because it forms along with H2 under similar conditions and forms within a similar extinction range. We have analyzed absorption measurements of OH at 1665 MHz and 1667 MHz toward 44 extragalactic continuum sources, together with the J = 1\u20130 transitions of 12CO, 13CO, and C18O, and the J = 2\u20131 transition of 12CO...Peer reviewed: YesNRC publication: Ye
Application of the hot stamping process to aluminum alloy structural components
No full textIt has long been accepted that one primary way to achieve vehicle lightweighting is to incorporate aluminum alloys wherever possible. As such, panel-type components have since been produced using these alloys. Structural components, however, still present a challenge for the aluminum hot forming field. In order to help bridge this knowledge gap, the National Research Council Canada (NRC) explored the applicability of subjecting two heat-treatable aluminum alloys, namely a medium strength 6082 and a high strength 7021, to a rapid hot forming process, notably hot stamping, in order to simultaneously form and quench a part destined for structural applications. A full-scale structural part was hot stamped in ~30 s, which is in very good agreement with the time constraints reported in the literature. Differential scanning calorimetry was used to optimize blank soaking conditions. Finally, artificial aging tests were carried out to restore the T6-temper strength of the initial as-received sheet.Peer reviewed: YesNRC publication: Ye
Beyond k-NN: combining cluster analysis and classification for recommender systems
No full textRecommendation systems have a wide application in e-business and have been successful in guiding users in their online purchases. The use of data mining techniques, to aid recommendation systems in their goal to learn the correct user profiles, is an active area of research. In most recent works, recommendations are obtained by applying a supervised learning method, notably the k-nearest neighbour (k-NN) algorithm. However, classification algorithms require a class label, and in many applications, such labels are not available, leading to extensive domain expert labelling. In addition, recommendation systems suffer from a data sparsity problem, i.e. the number of items purchased by a customer is typically a small subset of all \u109vailable products. One solution to overcome the labelling and data sparsity problems is to apply cluster analysis techniques prior to classification. Cluster analysis allows one to learn the natural groupings, i.e. similar customer profiles. In this paper, we s tudy the value of applying cluster analysis techniques to customer ratings prior to applying classification models. Our HCC-Learn framework combines content-based analysis in the cluster analysis stage, with collaborative filtering in the recommending stage. Our experimental results show the value of combining cluster analysis and classification against two real-world data sets.Peer reviewed: YesNRC publication: Ye
pH-switchable water-soluble boron nitride nanotubes
No full textThe first example of aqueous solutions of boron nitride nanotubes (BNNTs) with switchable stability and without use of surfactants is demonstrated. The as\u2010produced boron nitride nanotubes are both purified and solubilized through an environmentally friendly and scalable approach using water extraction and liquid bromine treatment. This treatment effectively removes elemental boron particles and excess bromine reacts with BNNTs, inducing B 12N bond cleavage on the BNNT surface to yield hydroxyl (OH) and amino (NH2) functionalized BNNTs. The resulting functionalized BNNTs form stable aqueous solutions around neutral pH (4 < pH < 8), but readily precipitate in other pH ranges. This switchable solubility is explained in terms of the capability of the functional groups (OH and NH2) to form hydrogen\u2010bonding networks in water. Further, the solubility differences in selected polar organic solvents have been utilized to prepare functionalized BNNTs with higher purity.Peer reviewed: YesNRC publication: Ye
Theory of atomic scale quantum dots in silicon: dangling bond quantum dots on silicon surface
No full textWe present here a theory and a computational tool, Silicon-{\sc Qnano}, to describe atomic scale quantum dots in Silicon. The methodology is applied to model dangling bond quantum dots (DBQDs) created on a passivated H:Si-(100)-(2
7 1) surface by removal of a Hydrogen atom. The electronic properties of DBQD are computed by embedding it in a computational box of Silicon atoms. The surfaces of the computational box were constructed by using DFT as implemented in {\sc Abinit} program. The top layer was reconstructed by the formation of Si dimers passivated with H atoms while the bottom layer remained unreconstructed and fully saturated with H atoms. The computational box Hamiltonian was approximated by a tight-binding (TB) Hamiltonian by expanding the electron wave functions as a Linear Combination of Atomic Orbitals and fitting the bandstructure to {\it ab-initio} results. The parametrized TB Hamiltonian was used to model large finite Si(100) boxes (slabs) with number of atoms exceeding present capabilities of {\it ab-initio} calculations. The removal of one hydrogen atom from the reconstructed surface resulted in a DBQD state with wave function strongly localized around the Si atom and energy in the silicon bandgap. The DBQD could be charged with zero, one and two electrons. The Coulomb matrix elements were calculated and the charging energy of a two electron complex in a DBQD obtained.Peer reviewed: NoNRC publication: Ye