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1 V AC-DC difference of a thermal transfer standard measured with a pulsed Josephson standard unloaded by a transconductance amplifier
No full textA transconductance amplifier (TCA) with a negative admittance has been used in parallel with a commercial thermal transfer standard (TTS) to unload the voltage source, a pulse-driven AC Josephson Voltage Standard (also known as Josephson Arbitrary Waveform Synthesizer or JAWS). AC-DC difference measurements at 1 V and at frequencies from 10 Hz to 10 kHz show excellent agreement with the values obtained by a conventional method. Expanded uncertainties between 0.28 \ub5V/V and 0.39 \ub5V/V (k=2), depending on the frequency, have been achieved.Peer reviewed: YesNRC publication: Ye
Calibration of gigahertz microwave generator for the programmable Josephson voltage standard at NRC
No full textA frequency calibration method is developed to characterize the frequency accuracy of the commercial microwave generator (MWG) used in the programmable Josephson voltage standard at the National Research Council Canada. The approach allows the evaluation of the MWG performance at 9.2 and 18.4 GHz with fractional frequency uncertainty at 10\ub9\u2074. The method also validates the MWG frequency resolution and setting accuracy from millihertz to megahertz to gigahertz.yesPeer reviewed: YesNRC publication: Ye
Antigen recognition by single-domain antibodies: structural latitudes and constraints
No full textSingle-domain antibodies (sdAbs), the autonomous variable domains of heavy chain-only antibodies produced naturally by camelid ungulates and cartilaginous fishes, have evolved to bind antigen using only three complementarity-determining region (CDR) loops rather than the six present in conventional VH:VL antibodies. It has been suggested, based on limited evidence, that sdAbs may adopt paratope structures that predispose them to preferential recognition of recessed protein epitopes, but poor or non-recognition of protuberant epitopes and small molecules. Here, we comprehensively surveyed the evidence in support of this hypothesis. We found some support for a global structural difference in the paratope shapes of sdAbs compared with those of conventional antibodies: sdAb paratopes have smaller molecular surface areas and diameters, more commonly have non-canonical CDR1 and CDR2 structures, and have elongated CDR3 length distributions, but have similar amino acid compositions and are no more extended (interatomic distance measured from CDR base to tip) than conventional antibody paratopes. Comparison of X-ray crystal structures of sdAbs and conventional antibodies in complex with cognate antigens showed that sdAbs and conventional antibodies bury similar solvent-exposed surface areas on proteins and form similar types of non-covalent interactions, although these are more concentrated in the compact sdAb paratope. Thus, sdAbs likely have privileged access to distinct antigenic regions on proteins, but only owing to their small molecular size and not to general differences in molecular recognition mechanism. The evidence surrounding the purported inability of sdAbs to bind small molecules was less clear. The available data provide a structural framework for understanding the evolutionary emergence and function of autonomous heavy chain-only antibodies.gold accessPeer reviewed: YesNRC publication: Ye
Athermal echelle grating filter in silicon-on-insulator using a temperature-synchronized input
No full textAthermal design of integrated photonic devices can reduce the need for active temperature stabilization and consequently the energy required to operate photonic integrated circuits. For silicon photonic filters such as AWGs which employ wire or ridge waveguides, temperature insensitivity can be achieved using cladding materials with negative thermo-optic coefficients. On the other hand, in echelle grating filters the inteference takes place in the slab free-propagation region, and therefore the modal overlap with the cladding is small, rendering this method ineffective. In this work we present an approach to design an athermal echelle grating filter exploiting a temperature-synchronized Mach-Zehnder interferometer as input. This reduces the spectral shift over a temperature range of 20 K to less than \ub145 pm compared to the 1.6 nm shift for the same echelle grating with a conventional waveguide input. Furthermore, the proposed design relies exclusively on a standard fabrication process for silicon-on-insulator photonic devices and exhibits a good tolerance to fabrication uncertainties.Peer reviewed: YesNRC publication: Ye
Automated fatigue testing device for assessing performance of sealant jointing products
No full textA description of the sealant jointing product test device is given herein that includes information on its operation and results from its use in subjecting sealant products to fatigue resistance tests. In the first instance, a novel benchtop sealant test device was developed that permits assessing the expected long-term performance of joint sealant products. This sealant test device can be used to conduct bench-scale testing indoors in a laboratory setting or outdoors whereby sealant products are exposed to weathering effects while undergoing movement. The device also includes a load cell that permits monitoring the load imposed on the products while undergoing movement; thus, changes in the resistance to movement can be monitored over time. Cyclic movement programs can be run once input to the device, and the rate of movement can be set at predetermined levels. In a subsequent development stage, the durability of sealed joints was verified with the use of the testing device. The effect of the curing condition and stress relaxation of sealants during joint movement were continuously monitored over the course of a daily cycle or a 12-s cycle of compression-tension with the device's load cell. Results showed that over the curing period the sealant joint was damaged, as evident from changes in the cross-section of the sealed joint and reduction in stress of the jointing product. It is likely that this would influence the fatigue resistance of the sealed joint. In addition, in respect to the stress relaxation of sealants, the rate of decrease in the compressive load compared with the initial load is larger than that of the decrease on tensile load; as such, to properly evaluate the fatigue resistance of sealed joints, it is desirable to carry out a program of cyclic joint movement.Peer reviewed: YesNRC publication: Ye
Dispersion, stability and size measurements for cellulose nanocrystals by static multiple light scattering
No full textStatic multiple light scattering (SMLS) is used to provide qualitative information on cellulose nanocrystal (CNC) suspensions as a function of the methods used to disperse the dry CNCs and, in some cases, to estimate the equivalent size for primary particles and their aggregates. The methods were validated by measuring the mean diameter of several sizes and concentrations of silica particles which are approximately monodisperse and spherical, both of which significantly simplify the analysis of SMLS data. The results indicate that uncertainty in the silica density contributes to differences between the estimated SMLS diameters and those determined by dynamic light scattering. Suspension stability, sedimentation kinetics, and particle size as a function of dispersion method were evaluated for CNC suspensions by measuring the intensity profiles of light transmitted through the sample as a function of time, and applying sedimentation or light scattering theories. The results demonstrate that SMLS is a useful method for monitoring CNC dispersion for samples that are too concentrated to study by DLS. The sedimentation analysis provides qualitative information on the presence and size (equivalent diameter) of CNC aggregates/agglomerates and evidence for formation of a stable phase that forms during concurrent sedimentation and dispersion of CNC aggregates for unsonicated suspensions and is hypothesized to be a gel phase.Peer reviewed: YesNRC publication: Ye
Contrail flight data for a variety of jet fuels
No full textIn 2017/18, the NRC undertook biofuel contrail flight research from a number of jet transport aircraft and jet fuels, including petroleum JetA1, JP-5, HEFA and ethanol-derived ATJ biofuels. The flight contrail data, consisting of derived ice particle number, size, spherical mass, and the FSSP-100 optical properties of effective size, extinction coefficient, optical depth and laterally-integrated optical depth, was obtained and compared for JetA1, JP-5 and biofuels (43% HEFA-SPK blend with Jet A1 and 92% ethanol-derived ATJ-SPK blend with aromatics). Contrail conditions covered sublimating to persistent. Contrail properties were compared with aerosol and non-volatile particulate emissions, and with previous soot modeling of young contrails. Results showed progressive reductions in persistent contrail ice particle number with biofuel blend percentage, almost log-linear reductions with non-volatile aerosol emissions, a slight increase in ice particle size with 92% ATJ-SPK. The lateral integrands of optical depth showed 30-50% reductions for the 92% blend ATJ-SPK, compared to Jet A1.Peer reviewed: YesNRC publication: Ye
Effect of venting range hood flow rate on size-resolved ultrafine particle concentrations from gas stove cooking
No full textCooking is the main source of ultrafine particles (UFP) in homes. This study investigated the effect of venting range hood flow rate on size-resolved UFP concentrations from gas stove cooking. The same cooking protocol was conducted 60 times using three venting range hoods operated at six flow rates in twin research houses. Size-resolved particle (10\u2013420\u2009nm) concentrations were monitored using a NanoScan scanning mobility particle sizer (SMPS) from 15\u2009min before cooking to 3\u2009h after the cooking had stopped. Cooking increased the background total UFP number concentrations to 1.3\u2009
7\u2009103 particles/cm3 on average, with a mean exposure-relevant source strength of 1.8\u2009
7\u20091012 particles/min. Total particle peak reductions ranged from 25% at the lowest fan flow rate of 36\u2009L/s to 98% at the highest rate of 146\u2009L/s. During the operation of a venting range hood, particle removal by deposition was less significant compared to the increasing air exchange rate driven by exhaust ventilation. Exposure to total particles due to cooking varied from 0.9 to 5.8\u2009
7\u2009104 particles/cm3\ub7h, 3\u2009h after cooking ended. Compared to the 36\u2009L/s range hood, higher flow rates of 120 and 146\u2009L/s reduced the first-hour post-cooking exposure by 76% and 85%, respectively.Peer reviewed: YesNRC publication: Ye
Engineered nanomaterials and human health: Part 2. Applications and nanotoxicology (IUPAC Technical Report)
No full textResearch on engineered nanomaterials (ENM) has progressed rapidly from the very early stages of studying their unique, size-dependent physicochemical properties and commercial exploration to the development of products that influence our everyday lives. We have previously reviewed various methods for synthesis, surface functionalization, and analytical characterization of ENM in a publication titled \u2018Engineered Nanomaterials: Preparation, Functionalization and Characterization\u2019. In this second, inter-linked document, we first provide an overview of important applications of ENM in products relevant to human healthcare and consumer goods, such as food, textiles, and cosmetics. We then highlight the challenges for the design and development of new ENM for bio-applications, particularly in the rapidly developing nanomedicine sector. The second part of this document is dedicated to nanotoxicology studies of ENM in consumer products. We describe the various biological targets where toxicity may occur, summarize the four nanotoxicology principles, and discuss the need for careful consideration of the biodistribution, degradation, and elimination routes of nanosized materials before they can be safely used. Finally, we review expert opinions on the risk, regulation, and ethical aspects of using engineered nanomaterials in applications that may have direct or indirect impact on human health or our environment.Peer reviewed: YesNRC publication: Ye
Experimental and theoretical investigation of a multimode cooling scheme using multiple electromagnetically-induced-transparency resonances
No full textWe introduce and demonstrate double-bright electromagnetically-induced-transparency (D-EIT) cooling as an extension to EIT cooling. By involving an additional ground state, two bright states can be shifted individually into resonance for cooling of motional modes of frequencies that may be separated by more than the width of a single EIT cooling resonance. This allows three-dimensional ground-state cooling of a 40Ca+ ion trapped in a linear Paul trap with a single cooling pulse. Measured cooling rates and steady-state mean motional quantum numbers for this D-EIT cooling are compared with those of standard EIT cooling as well as concatenated standard EIT cooling pulses for multimode cooling. Experimental results are compared to full-density matrix calculations. We observe a failure of the theoretical description within the Lamb-Dicke regime that can be overcome by a time-dependent rate theory. Limitations of the different cooling techniques and possible extensions to multi-ion crystals are discussed.Peer reviewed: YesNRC publication: Ye