Fresnel-type Solid Immersion Lens for efficient light collection from quantum defects in diamond

Quantum defects in diamonds have been studied as a promising resource for quantum science. The subtractive fabrication process for improving photon collection efficiency often require excessive milling time that can adversely affect the fabrication accuracy. We designed and fabricated a Fresnel-type solid immersion lens using the focused ion beam. For a 5.8 um-deep Nitrogen-vacancy (NV-) center, the milling time was highly reduced (1/3 compared to a hemispherical structure), while retaining high photon collection efficiency (> 2.24 compared to a flat surface). In numerical simulation, this benefit of the proposed structure is expected for a wide range of milling depths.Comment: 16 pages, 9 figure

Gadolinium added uranium mononitride fuels for light water reactor applications: fabrication and thermophysical property measurements

Department of Nuclear EngineeringThe uranium mononitride (UN) has superior thermophysical properties such as high thermal conductivity, melting point, and fissile atom density than traditional uranium dioxide (UO2) fuels. The use of UN fuel, however, has not been considered economically feasible because extremely high temperature is required to obtain high-density pellets by conventional sintering method. The spark plasma sintering (SPS) has thus been proposed for UN fuel fabrication since this technique has the capability of rapid densification at relatively low temperatures. However, the SPS behavior of UN fuel has not yet been sufficiently studied, for both pure and gadolinium added pellets, two representative types of light water reactor (LWR) fuels. Densification and grain growth behavior of the pure UN powder during SPS were investigated in a wide range of temperatures (from 1500 to 1800 ??C) and times (from 5 to 180 min) under uniaxial pressure of 70 MPa. The hydride-nitride process was employed to synthesize the UN powder with an average particle size of 6.0 ?? 4.9 ??m. The thermal etching technique was used to reveal the grain boundaries of the pellets. The crystallographic and microstructural characterizations were completed by using X-ray diffraction (XRD) and scanning electron microscope (SEM). Collected data presented in the grain size-density trajectory revealed two distinct stages of the SPS process in accordance with sintering temperature: at temperatures below 1700 ??C, the pellet density increased until it reached the maximum value (~97 %TD) as temperature increased, while the grain growth was not significant (average grain size 8 ??m) was followed with continued heating time (up to 180 min). Phase stability of UN/GdN and UN/Gd2O3 composite pellets was investigated for various compositions of GdN (3.5, 7.0, 10.7, 14.5, and 38.4 wt%) and Gd2O3 (5, 10, and 15 wt%). The SPS temperature and time were respectively varied from 1800 to 2000 ??C and from 10 to 60 min. The XRD analysis confirmed two separate phase formation in UN/Gd2O3 pellets for all SPS conditions. In case of UN/GdN, however, solid-solution (U1-x,Gdx)N phase formation was observed from high temperature (2000 ??C) SPSed pellets. The thermal conductivity of the SPSed UN/GdN and UN/Gd2O3 composite pellets was measured from 25 to 1000 ??C by using laser flash analysis (LFA). Throughout the temperature range measured, the thermal conductivity of both composite pellets decreased with increasing Gd compositions. The non-solid-solution UN/GdN pellets exhibited 14???25% higher thermal conductivity than the solid-solution (U1-x,Gdx)N pelletsand even these solid-solution pellets showed 20???65% higher thermal conductivity than the UN/Gd2O3 pellets. These results may indicate that relatively higher thermal conductivity of UN/GdN composite as burnable absorber fuel could be further enhanced with an optimized microstructure obtainable from relatively low (< 1800 ??C) SPS temperature.ope

Cu2Se-based thermoelectric cellular architectures for efficient and durable power generation

Thermoelectric power generation offers a promising way to recover waste heat. The geometrical design of thermoelectric legs in modules is important to ensure sustainable power generation but cannot be easily achieved by traditional fabrication processes. Herein, we propose the design of cellular thermoelectric architectures for efficient and durable power generation, realized by the extrusion-based 3D printing process of Cu2Se thermoelectric materials. We design the optimum aspect ratio of a cuboid thermoelectric leg to maximize the power output and extend this design to the mechanically stiff cellular architectures of hollow hexagonal column- and honeycomb-based thermoelectric legs. Moreover, we develop organic binder-free Cu2Se-based 3D-printing inks with desirable viscoelasticity, tailored with an additive of inorganic Se-8(2-) polyanion, fabricating the designed topologies. The computational simulation and experimental measurement demonstrate the superior power output and mechanical stiffness of the proposed cellular thermoelectric architectures to other designs, unveiling the importance of topological designs of thermoelectric legs toward higher power and longer durability

Endotracheal intubation in rabbits using a video laryngoscope with a modified blade

Rabbits are being increasingly used as companion animals, and in research; thus, the need for proper veterinary care for rabbits has increased. Surgical access is more challenging in rabbits under inhalation anesthesia compared to other animals, such as dogs and cats. Rabbits have a very narrow and deep oral cavity, large incisors, and a large tongue. Moreover, their temporomandibular joint has limited mobility, making it more difficult to approach the larynx. Various methods have been proposed to overcome this difficulty. The video laryngoscope was introduced in 1999 and is useful when airway intubation is unsuccessful using a conventional laryngoscope. We postulated that a video laryngoscope with a modified size 1 Macintosh blade (McGrath MAC Video Laryngoscope, Medtronic, USA) would facilitate the intubation of New Zealand White rabbits. Sixteen specific-pathogen-free male New Zealand White rabbits weighing 3.45–4.70 kg were studied. All rabbits were intubated using the video laryngoscope. Typically, a 3.0 mm endotracheal tube was used for rabbits weighing  4 kg. During surgery, anesthesia was well maintained, and there were no major abnormalities in the animals’ conditions. No rabbit developed breathing difficulties or anorexia after recovering from anesthesia. We established an intubation method using a video laryngoscope with a modified blade and stylet in the supine (ventrodorsal) position and successfully applied it in 16 rabbits. It is useful for training novices and for treating rabbits in veterinary hospitals with few staff members and animal research facilities where there are insufficient human resources

Thermal conductivity of gadolinium added uranium mononitride fuel pellets sintered by spark plasma sintering

Thermal conductivity of spark plasma sintered UN/Gd2O3 and UN/GdN composite pellets with various compositions of Gd2O3 (5.0 to 15.0 wt%) and GdN (3.5 to 38.4 wt%) was measured from 25 degrees C to 1000 degrees C using laser flash analyzer (LFA). Overall thermal conductivity of both composite pellets decreases with increasing Gd compositions for the entire temperature range measured. The UN/GdN pellets sintered at high temperature (2000 degrees C) contained solid-solution (U1-x,Gd-x)N phase and exhibited 20-65 % higher thermal conductivity than the UN/Gd2O3 pellets. We also confirmed a two-phase structure in low temperature (1800 degrees C) sintered UN/GdN pellets, which exhibited 14-25 % higher thermal conductivity than solid-solution UN/GdN pellets. This result may indicate that relatively higher thermal conductivity of UN/GdN composite as burnable absorber fuel could be further enhanced with an optimized microstructure. (C) 2021 Elsevier B.V. All rights reserved

Thermal conductivity measurement of non-stoichiometric UO2 pellet for advanced nuclear material accountancy

Currently, the IAEA utilizes thermogravimetric analysis (TGA) to identify UO2 fuel stoichiometry or O/U ratio; however, the method is unfit for on-site inspection, since it requires a large heating device to achieve high temperature (900 ??C) to fully oxidize UO2??x to U3O8. In order to enable the development of a hand-carry device for this matter, we suggest the utilization of UO2 thermal conductivity which sensitively varies with the fuel stoichiometry at low temperature (&lt; 300 ??C). In this study, various hyper-stoichiometric UO2+x pellets (0 &lt; x &lt; 0.025) were sintered under mixed gas of CO/CO2 and H2/Ar, referring to the equilibrium oxygen potential of constitutional U-O phase diagram. The stoichiometry of fabricated pellets was reaffirmed following the standard TGA method, which appears to be matched with intended stoichiometry. The thermal conductivity of fabricated UO2+x pellets was measured from 25 ??C to 300 ??C using laser flash analyzer (LFA) and compensated to 96 % theoretical density (TD) considering various sintered pellet density from 89 to 92 %TD. LFA-measured fuel thermal conductivity show 8% decrease at room temperature over 0.004 stoichiometry deviation from 2.007 to 2.011, which indicates clear potential of LFA method for advanced material accountancy of commercial nuclear fuel

Grain growth and densification of uranium mononitride during spark plasma sintering

With the aim of investigating the spark plasma sintering behavior of uranium mononitride synthesized by the hydride-nitride process, several pellets were prepared using a wide range of fabrication temperatures (1500-1800 degrees C) and dwell times (5-180 min) under 70 MPa. The collected data in the grain size-density trajectory revealed that the spark plasma sintering process of uranium mononitride was divided into two regimes according to the sintering temperature. In particular, at low temperatures up to 1700 degrees C, the pellet density increased with increasing temperatures until it reached a maximum value (similar to 97 %TD), while the grain growth was not significant (average grain size &lt; 3.5 mu m). In contrast, at a temperature of 1800 degrees C, the maximum density was rapidly achieved (&lt;5 min) with a slightly larger average grain size (4.3 mu m), and a significant grain growth (up to 8 mu m) continued for 180-min dwell time