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Thermo-mechanical fatigue testing of welded tubes for exhaust applications
No full textSelected ferritic stainless steel sheets for exhaust applications were tested under thermo-mechanical fatigue (TMF) condition in the temperature range of 400-800 \ub0C with partial constraint. Straight welded tubes were used as the testing coupons to withstand large compression without buckling, and to understand the effect of welding as well. Repeated tests confirmed the observed failure scenario for each material type. The hysteresis loop behaviors were also simulated using the mechanism-based integrated creep and fatigue theory (ICFT) model. Although more development work is needed, for quick material screening purpose this type of testing could be a very cost effective solution for materials and tube weld development for exhaust applications.Peer reviewed: YesNRC publication: Ye
A deeper look at the GD1 stream: density variations and wiggles
No full textUsing deep photometric data from Canada\u2013France\u2013Hawaii Telescope/Megacam, we study the morphology and density of the GD-1 stream, one of the longest and coldest stellar streams in the Milky Way. Our deep data recovers the lower main sequence of the stream with unprecedented quality, clearly separating it from Milky Way foreground and background stars. An analysis of the distance to different parts of the stream shows that GD-1 lies at a heliocentric distance between 8 and 10\u2009kpc, with only a shallow gradient across 45\ub0 on the sky. Matched filter maps of the stream density show clear density variations, such as deviations from a single orbital track and tentative evidence for stream fanning. We also detect a clear underdensity in the middle of the stream track at \u3c61 = 1245\ub0 surrounded by overdense stream segments on either side. This location is a promising candidate for the elusive missing progenitor of the GD-1 stream. We conclude that the GD-1 stream has clearly been disturbed by interactions with the Milky Way disc or other subhaloes.Peer reviewed: YesNRC publication: Ye
A massive core for a cluster of galaxies at a redshift of 4.3
No full textMassive galaxy clusters have been found that date to times as early as three billion years after the Big Bang, containing stars that formed at even earlier epochs1,2,3. The high-redshift progenitors of these galaxy clusters\u2014termed \u2018protoclusters\u2019\u2014can be identified in cosmological simulations that have the highest overdensities (greater-than-average densities) of dark matter4,5,6. Protoclusters are expected to contain extremely massive galaxies that can be observed as luminous starbursts7. However, recent detections of possible protoclusters hosting such starbursts8,9,10,11 do not support the kind of rapid cluster-core formation expected from simulations12: the structures observed contain only a handful of starbursting galaxies spread throughout a broad region, with poor evidence for eventual collapse into a protocluster. Here we report observations of carbon monoxide and ionized carbon emission from the source SPT2349-56. We find that this source consists of at least 14 gas-rich galaxies, all lying at redshifts of 4.31. We demonstrate that each of these galaxies is forming stars between 50 and 1,000 times more quickly than our own Milky Way, and that all are located within a projected region that is only around 130 kiloparsecs in diameter. This galaxy surface density is more than ten times the average blank-field value (integrated over all redshifts), and more than 1,000 times the average field volume density. The velocity dispersion (approximately 410 kilometres per second) of these galaxies and the enormous gas and star-formation densities suggest that this system represents the core of a cluster of galaxies that was already at an advanced stage of formation when the Universe was only 1.4 billion years old. A comparison with other known protoclusters at high redshifts shows that SPT2349-56 could be building one of the most massive structures in the Universe today.Peer reviewed: YesNRC publication: Ye
A numerical investigation on NO2 formation in a natural gas\u2013diesel dual fuel engine
No full textThis research numerically simulates the formation and destruction of nitrogen dioxide (NO2) in a natural gas (NG)\u2013diesel dual fuel engine using commercial CFD software converge coupled with a reduced primary reference fuel (PRF) mechanism consisting of 45 species and 142 reactions. The model was validated by comparing the simulated cylinder pressure, heat release rate (HRR), and nitrogen oxide (NOx) emissions with experimental data. The validated model was used to simulate the formation and destruction of NO2 in a NG\u2013diesel dual fuel engine. The formation of NO2 and its correlation with the local concentration of nitric oxide (NO), methane, and temperature were examined and discussed. It was revealed that NO2 was mainly formed in the interface region between the hot NO-containing combustion products and the relatively cool unburnt methane\u2013air mixture. The NO2 formed at the early combustion stage is usually destructed to NO after the complete oxidation of methane and n-heptane, while NO2 formed during the postcombustion process survives through the expansion process and exits the engine. The increased NO2 emissions from NG\u2013diesel dual fuel engines was formed during the post combustion process due to higher concentration of HO2 produced during the oxidation process of the unburned methane at low temperature. A detailed analysis of the chemical reactions occurring in the NO2 containing zone consisting of NO2, NO, O2, methane, etc., was conducted using a quasi-homogeneous constant volume (QHCV) model to identify the key reactions and species dominating NO2 formation and destruction. The HO2 produced during the postcombustion process of methane was identified as the primary species dominating the formation of NO2 during the post combustion expansion process. The simulation revealed the key reaction path for the formation of HO2 noted as CH4 \u2192 CH3 \u2192 CH2O \u2192 HCO \u2192 HO2, with conversion ratios of 98%, 74%, 90%, 98%, accordingly. The backward reaction of OH\u2009+\u2009NO2 =\u2009NO\u2009+\u2009HO2 consumed 34% of HO2 for the production of NO2.Peer reviewed: YesNRC publication: Ye
A numerical study on the chemical kinetics process during auto-ignition of n-heptane in a direct injection compression ignition engine
No full textThis paper presents a numerical analysis of the ignition process of an n-heptane spray in a compression ignition engine using a post-processing tool developed by West Virginia University. Such a tool is able to process the CFD simulation data for the examination of chemical reaction process without revising the CFD source code. The main functions of the post-processing tool include: (1) The calculation of the instantaneous rate of production (ROP) using CHEMKIN with the temperature, pressure and species concentration in each cell simulated using CFD; (2) the development of the representative destruction reaction (RDR) and destruction pathway of the key species involved in a specific area; and (3) the visualization of the analysis results. Such a tool was applied to examine the chemical reaction process during ignition delay of the n-heptane spray in a direct injection compression ignition engine. The H abstraction of n-heptane by O2, OH, HO2, and H radical during ignition period was further examined. The destruction pathway of key species in RDROH/RDRHO2 region and their development leading to the autoignition of n-heptane were studied. It is found that both the n-heptane/air mixture and bulk gas movement play an important role in the formation of RDRHO2 region. The RDRHO2 region featured with medium temperature (around 1000\u202fK) produces more H2O2/HO2 radical before the auto-ignition of n-heptane than low-temperature combustion. The rapid dissociation of H2O2 provides a large amount of OH radical that enhances the chain branching reaction as well as heat release process which then initiates the autoignition of n-heptane. The reaction rates of nC7H16\u202f+\u202fOH\u202f=\u202fC7H15\u202f+\u202fH2O and nC7H16\u202f+\u202fHO2\u202f=\u202fC7H15\u202f+\u202fH2O2 were examined to reveal their competition in destructing n-heptane. The H atom is also found to promote the chain branching during auto-ignition. Such a tool provides the convenience for commercial CFD research community to conveniently elaborate the CFD simulation results for better understanding of the fundamental aspects of the combustion and emissions phenomenon observed using CFD code.Peer reviewed: YesNRC publication: Ye
All-electronic nanosecond-resolved scanning tunneling microscopy: facilitating the investigation of single dopant charge dynamics
No full textThe miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new techniques capable of characterizing their dynamics. Investigating single dopants requires sub-nanometer spatial resolution, which motivates the use of scanning tunneling microscopy (STM). However, conventional STM is limited to millisecond temporal resolution. Several methods have been developed to overcome this shortcoming, including all-electronic time-resolved STM, which is used in this study to examine dopant dynamics in silicon with nanosecond resolution. The methods presented here are widely accessible and allow for local measurement of a wide variety of dynamics at the atomic scale. A novel time-resolved scanning tunneling spectroscopy technique is presented and used to efficiently search for dynamics.Peer reviewed: YesNRC publication: Ye
An experimental and computational study of CO2 adsorption in the sodalite-type M-BTT (M = Cr, Mn, Fe, Cu) metal\u2013organic frameworks featuring open metal sites
No full textWe present a comprehensive investigation of the CO2 adsorption properties of an isostructural series of metal\u2013organic frameworks, M-BTT (M = Cr, Mn, Fe, Cu; BTT3 12 = 1,3,5-benzenetristetrazolate), which exhibit a high density of open metal sites capable of polarizing and binding guest molecules. Coupling gas adsorption measurements with in situ neutron and X-ray diffraction experiments provides molecular-level insight into the adsorption process and enables rationalization of the observed adsorption isotherms. In particular, structural data confirms that the high initial isosteric heats of CO2 adsorption for the series are directly correlated with the presence of open metal sites and further reveals the positions and orientations of as many as three additional adsorption sites. Density functional theory calculations that include van der Waals dispersion corrections quantitatively support the observed structural features associated with the primary and secondary CO2 binding sites, including CO2 positions and orientations, as well as the experimentally determined isosteric heats of CO2 adsorption.Peer reviewed: YesNRC publication: Ye
An infrared-induced terahertz imaging modality for foreign insert detection in a glass fiber-skinned lightweight honeycomb composite panel
No full textIn this paper, terahertz time-domain spectroscopy (THz-TDS) is used for the first time to detect fabricated defects in a glass fiber-skinned lightweight honeycomb composite panel. A novel amplitude polynomial regression (APR) algorithm is proposed as a pre-processing method. This method segments the amplitude-frequency curves to simulate the heating and the cooling monotonic behavior as in infrared thermography. Then, the method of empirical orthogonal function (EOF) imaging is applied on the APR pre-processed data as a post-processing algorithm. Signal-to-noise ratio analysis is performed to verify the image improvement of the proposed APR-EOF modality from a quantitative point of view. Finally, the experimental results and the physical analysis show that THz is more suitable with respect to the detection of defects in glass fiber lightweight honeycomb composites.Peer reviewed: YesNRC publication: Ye
Application of CRISPR/Cas9 genome editing technology for the improvement of crops cultivated in tropical climates: recent progress, prospects, and challenges
No full textThe world population is expected to increase from 7.3 to 9.7 billion by 2050. Pest outbreak and increased abiotic stresses due to climate change pose a high risk to tropical crop production. Although conventional breeding techniques have significantly increased crop production and yield, new approaches are required to further improve crop production in order to meet the global growing demand for food. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 (CRISPR-associated protein9) genome editing technology has shown great promise for quickly addressing emerging challenges in agriculture. It can be used to precisely modify genome sequence of any organism including plants to achieve the desired trait. Compared to other genome editing tools such as zinc finger nucleases (ZFNs) and transcriptional activator-like effector nucleases (TALENs), CRISPR/Cas9 is faster, cheaper, precise and highly efficient in editing genomes even at the multiplex level. Application of CRISPR/Cas9 technology in editing the plant genome is emerging rapidly. The CRISPR/Cas9 is becoming a user-friendly tool for development of non-transgenic genome edited crop plants to counteract harmful effects from climate change and ensure future food security of increasing population in tropical countries. This review updates current knowledge and potentials of CRISPR/Cas9 for improvement of crops cultivated in tropical climates to gain resiliency against emerging pests and abiotic stresses.Peer reviewed: YesNRC publication: Ye
Behavior of selenium hydride in heated quartz tube and dielectric barrier discharge atomizers
No full textAtomization of SeH2 in an externally heated multiple microflame quartz tube atomizer (MMQTA) as well as planar dielectric barrier discharge (DBD) atomizer was investigated using a variety of probes. Deposits of Se on inner surfaces of the atomizers were quantified and their distribution visualized by autoradiography with 75Se radiotracer. The gas phase fraction of Se transported beyond the confines of the atomizers was also determined. In the MMQTA, a 15% mass fraction of Se was deposited in a narrow zone at both colder ends of the optical arm (100\u2013400\u202f\ub0C). By contrast, a 25-40% mass fraction of Se was deposited homogeneously along the entire length of the optical arm of the DBD, depending on detection technique employed. The fraction of Se transported outside the MMQTA approached 90%, whereas it was 50\u201370% in the DBD. The presence of H2 was essential for atomization of selenium hydride in both atomizers. The gaseous effluent arising from the hydride generator as well as the atomizers was investigated by direct analysis in real time (DART) coupled to an Orbitrap-mass spectrometer, enabling identification of major gas phase species of Se.Peer reviewed: YesNRC publication: Ye