Μm Radius Research Articles

Burnup computation for HTR-10 using MCNPX as the function of radius and fuel enrichment

The HTR-10 is a gas-cooled high-temperature reactor with spherical fuel and moderator called pebble bed and operated on 10 MW thermal power. Until now, a lot of research and development on the HTR-10 in terms of neutronic computational modeling has been carried out, one of which is burnup analysis. Fuel depletion or burnup analysis is an analysis related to fuel control and reactor output power. This analysis is needed because changes in fuel composition will affect the neutronic parameter values of a reactor. The 10 MW HTR fuel depletion study has been conducted by modeling the reactor using MCNPX (Monte Carlo N-Particle e-Xtended) to analyze the effect of radius and enrichment of reactor fuel to the left value and the burnup rate. The study is conducted by modeling a 10 MW HTR with three sorts of fuel kernel radiuses using MCNPX. First, 250 μm radius, second, 275 μm radius, third, 300 μm radius and all radiuses are variated with 10-15% fuel enrichment. TRISO particles are dispersed using simple cubic (SC) lattice in the fuel zone. The fuel balls are allocated in the reactor core along with moderator balls using a body-centered cubic. To perform all the calculations, MCNPX utilizes continuous energy data library ENDF/B-VI. From the calculation result using MCNPX can be concluded that the kernels with the radius of 275 μm and 300 μm at 14% and 13% fuel enrichment respectively were more able to maintain a critical condition within a year of operation than the kernels a 250 μm radius and the fuel with 250 μm radius has the highest burnup rate that is 52,07 GWd/MTU.

Development of the TIP-HOLE gas avalanche structure for nuclear physics/astrophysics applications with radioactive isotope beams: preliminary results.

We discuss the operational principle and performance of new micro-pattern gaseous detectors based on the multi-layer Thick Gaseous Electron Multiplier (M-THGEM) concept coupled to a needle-like anode. The new gas avalanche structure aims at high-gain operation in nuclear physics and nuclear astrophysics applications with radioactive isotope beams. It is thereafter named TIP-HOLE gas amplifier, and consists of a THGEM or a two-layers M-THGEM mounted in a WELL configuration. The avalanche electrodes are collected by thin conductive needles (with up to a few ten μm radius and a height of 100 μm), located at the center of the hole and acting as a point-like anode. The bottom area of the needle could be surrounded by a cylindrical cathode strip in order to increase the electron collection efficiency. The electric field lines from the drift region above the M-THGEM are focused into the holes, and then forced to converge on the needle tip. An extremely high field is reached at the top of the needle, creating a point-like avalanche process. Stable, high-gain operations in a wide range of pressures can be achieved at relatively low operational voltage, even in pure quencher gas at atmospheric pressure (e.g. pure isobutene). The TIP-HOLE structure may be produced by the innovative scalable additive manufacturing technology for large-area, multiple-layer printed circuit boards, recently developed by the UHV technology company (USA) and discussed for the first time in this work.

Streaked optical pyrometer for proton-driven isochoric heating experiments of solid and foam targets

We have designed, built, and calibrated an ultrafast streaked optical pyrometer (SOP) with ∼5 ps resolution for measuring the time-resolved surface blackbody temperature of an isochorically heated plasma. The pyrometer is calibrated to measure temperatures from 0.5 eV to 25 eV, with the option of adding calibrated neutral density filters to observe hotter plasmas. We demonstrated the use of this pyrometer on isochoric heating experiments using laser-accelerated proton beams as an energy source at the f/40 beamline of the Texas Petawatt Laser. We used the large focal spot size (∼80 μm radius) of the f/40 pulses to accelerate high numbers of ∼MeV protons off 5 μm thick solid gold targets. During our experimental campaign, we heated 10 µm thick aluminum foil targets to 1–10 eV over a duration of 50 ps and also observed heating to ∼2 eV in 100 µm thick 60 mg/cm3 carbon foams using the SOP to measure both the temperature and heating timescale.

A New Non-Invasive Air-Based Actuator for Characterizing and Testing MEMS Devices

This research explores a new ATE (Automatic Testing Equipment) method for Micro Electro Mechanical Systems (MEMS) devices. In this method, microscale aerodynamic drag force is generated on a movable part of a MEMS sensor from a micronozzle hole located a specific distance above the chip that will result in a measurable change in output. This approach has the potential to be generalized for the characterization of every MEMS device in mass production lines to test the functionality of devices rapidly and characterize important mechanical properties. The most important testing properties include the simultaneous application of controllable and non-invasive manipulative force, a single handler for multi-sensor, and non-contact characterization, which are relatively difficult to find with other contemporary approaches. Here we propose a custom-made sensing platform consisting of a microcantilever array interconnected to a data acquisition device to read the capacitive effects of each cantilever’s deflection caused by air drag force. This platform allows us to empirically prove the functionality and applicability of the proposed characterization method using airflow force stimuli. The results, stimulatingly, exhibited that air force from a hole of 5 µm radii located 25 µm above a 200 × 200 µm2 surface could be focused on a circular spot with radii of approximately 5 µm with surface sweep accuracy of <8 µm. This micro-size airflow jet can be specifically designed to apply airflow force on the MEMS movable component surface. Furthermore, it was shown that the generated air force range could be controlled from 20 nN to 60 nN, approximately, with a linear dependency on airflow ranging from 5 m/s to 20 m/s, which is from a 5 µm radius microhole air jet placed 400 µm above the chip. In this case-study chip, for a microcantilever with a length of 400 µm, the capacitance curve increased linearly from 28.2 pF to 30.5 pF with airflow variation from 5 m/s to 21 m/s from a hole. The resultant curve is representative of a standard curve for testing of the further similar die. Based on these results, this paper paves the way towards the development of a new non-contact, non-invasive, easy-to-operate, reliable, and relatively cheap air-based method for characterizing and testing MEMS sensors.

Pore structure and physical properties of sandy conglomerate reservoirs in the Xujiaweizi depression, northern Songliao Basin, China

Pore structure analysis is the basis of reservoir classification and exploitation, especially for tight reservoirs with complex pore throat systems. The sandy conglomerates in the Lower Cretaceous strata in northeastern China have attracted little attention from explorers in the past 50 years, but prospecting of promising tight gas reservoirs has recently begun in this area. Here, we report on the pore structure and physical properties of samples from the Shahezi Formation in the Xujiaweizi depression. Pore throat structure was investigated using thin section observations, scanning electron microscopy (SEM), high-pressure mercury injection (HPMI), and nuclear magnetic resonance (NMR). Regression analysis was used to analyze the correlation between the various pore structure parameters and the reservoir's physical properties. The results show that the pore types in the Shahezi sandy conglomerates are primarily dissolution pores with few inter-particle pores and micro-cracks. The pores are mostly less than 1 μm in radius, and the large pores are generally connected by tiny throats with radii of less than 0.1 μm. The Porapex and Porem values, which reveal the connected pore volume, were derived from the HPMI capillary pressure curve and the NMR T2 spectrum, respectively. The Porapex and Porem values are more strongly correlated with the reservoir's permeability than the other pore structure parameters, including the max throat radius (Rmax), the median radius (R50), the homogeneity coefficient (ϕ), the sorting parameter (Sp), the displacement pressure (Pd), and the mercury removal efficiency (Ew). Porapex and Porem account for only a small portion of the total pore volume (average of 37.1%) but contribute (average of 81.7%) to the permeability. By studying the microscopic and macroscopic characteristics, three typical pore structures were identified mainly based on Porapex and Porem. Type I reservoirs are characterized by relatively well connected inter-dissolution pores and high Porapex(>2.0), Porem(>2.0), and total porosity(>5.5%). Type III reservoirs show poor physical properties with some intercrystalline pores and small Porapex(<1.0), Porem(<1.0), and total porosity(<3.5%). Type II reservoirs are between type I and type III reservoirs. Favorable reservoirs (Type I and Type II) are located in the strata shallower than 4200 m.

Morphology of Thin Film Composite Membranes Explored by Small-Angle Neutron Scattering and Positron-Annihilation Lifetime Spectroscopy.

The morphology of thin film composite (TFC) membranes used in reverse osmosis (RO) and nanofiltration (NF) water treatment was explored with small-angle neutron scattering (SANS) and positron-annihilation lifetime spectroscopy (PALS). The combination of both methods allowed the characterization of the bulk porous structure from a few Å to µm in radius. PALS shows pores of ~4.5 Å average radius in a surface layer of about 4 μm thickness, which become ~40% smaller at the free surface of the membranes. This observation may correlate with the glass state of the involved polymer. Pores of similar size appear in SANS as closely packed pores of ~6 Å radius distributed with an average distance of ~30 Å. The main effort of SANS was the characterization of the morphology of the porous polysulfone support layer as well as the fibers of the nonwoven fabric layer. Contrast variation using the media H2O/D2O and supercritical CO2 and CD4 identified the polymers of the support layers as well as internal heterogeneities.

High frequency acoustic emission monitoring in nano-impact of alumina and partially stabilised zirconia

High frequency acoustic emission monitoring is proving a useful technique in improving the understanding of deformation processes occurring in nano- and micro-scale mechanical contacts. In this study AE monitoring has been used to investigate the fracture of alumina and MgO-partially stabilised zirconia (PSZ) at high strain rate in repetitive nano-impact tests with cube-corner and 5 μm radius spherical diamond indenters. Focussed ion beam milling of impact craters revealed sub-surface intergranular cracking on alumina and sub-surface transgranular cracking on PSZ. The evolution of AE through the test was strongly dependent on the geometry of the indenter used to create the impacts. AE energy was generally much higher when impacts cause rapid increases in penetration depth, with single high energy hits observed on abrupt depth bursts in tests with the cube corner indenter. The damage progression in tests with the spherical indenter differed between the ceramics, with more AE events near the start of the test on alumina and later in the test for PSZ. Reasons for these differences are discussed.

A versatile Johansson-type tender x-ray emission spectrometer.

We present a high energy resolution x-ray spectrometer for the tender x-ray regime (1.6-5.0 keV) that was designed and operated at Stanford Synchrotron Radiation Lightsource. The instrument is developed on a Rowland geometry (500 mm of radius) using cylindrically bent Johansson analyzers and a position sensitive detector. By placing the sample inside the Rowland circle, the spectrometer operates in an energy-dispersive mode with a subnatural line-width energy resolution (∼0.32 eV at 2400 eV), even when an extended incident x-ray beam is used across a wide range of diffraction angles (∼30° to 65°). The spectrometer is enclosed in a vacuum chamber, and a sample chamber with independent ambient conditions is introduced to enable a versatile and fast-access sample environment (e.g., solid/gas/liquid samples, in situ cells, and radioactive materials). The design, capabilities, and performance are presented and discussed.

Ultrasonic backscattering and microstructure in sheared concentrated suspensions.

Quantitative ultrasound techniques based on the parametrization of the backscatter coefficient (BSC) are used to characterize concentrated particle suspensions. Specifically, a scattering model is fit to the measured BSC and the fit parameters can provide local suspension properties. The scattering models generally assume an isotropic microstructure (i.e., spatial organization) of the scatterers, whereas the sheared concentrated suspensions can develop an anisotropic microstructure. This paper studied the influence of the shear-induced anisotropic microstructure of concentrated suspensions on the ultrasonic backscattering. Experiments were conducted on suspensions of polymethylmetacrylate spheres (5.8 μm in radius) sheared in a Couette flow device to obtain anisotropic microstructure and then mixed by hand to obtain isotropic microstructure. Experimental structure factors that are related to the spatial distribution of sphere positions were obtained by comparing the BSCs of one concentrated and one diluted suspension. Finally, Stokesian dynamics numerical simulations of sheared concentrated suspensions are used to determine the pair correlation function, which is linked to the Fourier transform of the structure factor. The experimental structure factors are found to be in good agreement with numerical simulations. The numerical simulation demonstrates that the angular-dependent BSCs and structure factors are caused by the shear-induced anisotropic microstructure within the suspension.

Assessment of an Elekta Versa HD linear accelerator for stereotactic radiosurgery with circular cone collimators.

Versa HD linear accelerators (linacs) are used for stereotactic radiosurgery treatment. However, the mechanical accuracy of such systems remains a concern. The purpose of this study was to evaluate the accuracy of an Elekta Versa HD linac. We performed measurements with a ball bearing phantom to calculate the rotational isocenter radii of the linac's gantry, collimator, and table, and determine the relative locations of those isocenters. We evaluated the accuracy of the cone-beam computed tomography (CBCT) guidance with a film-embedding head phantom and circular cone-collimated radiation beams. We also performed dosimetric simulations to study the effects of the linac mechanical uncertainties on non-coplanar cone arc delivery. The mechanical uncertainty of the linac gantry rotation was 0.78 mm in radius, whereas that of the collimator and the table was <0.1 mm and 0.33 mm, respectively. The axes of rotation of the collimator and the table were coinciding with and 0.13 mm away from the gantry isocenter, respectively. Experiments with test plans demonstrated the limited dosimetric consequences on the circular arc delivery given the aforementioned mechanical uncertainties. End-to-end measurements determined that the uncertainty of the CBCT guidance was≤1 mm in each direction with respect to the reference CT image. In arc delivery, the mechanical uncertainties associated with the gantry and the table do not require remarkable increases in geometric margins. If large enough, the residual setup errors following CBCT guidance will dominate the overall dosimetric consequence. Therefore, the Versa HD linac is a valid system for stereotactic radiosurgery using non-coplanar arc delivery.

Design and analysis of MEMS based electrospray thruster

This paper presents a design of MEMS based Electrospray thruster with high throughput, low volume and high output velocities. The performance of thruster can be improved by choosing best possible dimensions of cone height, half angle, propellant height and its radius. The most effective outcomes of the design have been observed through various analysis, which are suggested that propellant height should be > 280 μm, also propellant radius varied between 50 and 125 μm, tip angle with 44°, operating voltage between 1.5 and 3 kV. The elements of the device are designed in micro scale using COMSOL multiphysics tool in Laminar flow environment. Propellant within the emitter usually has ionic liquid, in this design EMI-BF4 is used as propellant. The output velocity is analyzed for input voltages 1.5 kV to 3 kV by varying height and half angle of cone, height and radius of propellant. The optimum outcomes producing the higher efficiencies for the device are achieved for cone angle of 44° with cone height 124 μm and cone bottom radius of 125 μm along with propellant radius of 125 μm and propellant height of 360 μm, the output velocities are of the order 106.

A Closed-Loop Optogenetic Stimulation Device

Closed-loop optogenetic stimulation devices deliver optical stimulations based on real-time measurement and analysis of neural responses to stimulations. However, the use of large bench-top and tethered devices hinders the naturalistic test environment, which is crucial in pre-clinical neuroscience studies involving small rodent subjects. This paper presents a tetherless, lightweight and miniaturized head-mountable closed-loop optogenetic stimulation device. The device consists of three hardware modules: a hybrid electrode, an action potential detector, and an optogenetic stimulator. In addition, the device includes three software modules: a feature extractor, a control algorithm, and a pulse generator. The details of the design, implementation, and bench-testing of the device are presented. Furthermore, an in vitro test environment is formed using synthetic neural signals, wherein the device is validated for its closed-loop performance. During the in vitro validation, the device was able to identify abnormal neural signals, and trigger optical stimulation. On the other hand, it was able to also distinguish normal neural signals and inhibit optical stimulation. The overall power consumption of the device is 24 mW. The device measures 6 mm in radius and weighs 0.44 g excluding the power source.

UV-O3 treated annealing-free cerium oxide as electron transport layers in flexible planar perovskite solar cells.

Fabricating electron transport layers at low temperatures is challenging but highly desired in the field of flexible perovskite solar cells (f-PSCs). In this study, highly uniform cerium oxide (CeOx) films prepared by the UV–O3 treatment have been successfully applied as the electron transport layer (ETL) in methylammonium lead halide (CH3NH3PbI3) perovskite-based f-PSCs. Under AM 1.5 G sunlight with 100 mW cm−2, these cells exhibited an open-circuit voltage (Voc) of 0.98 V, a short-circuit current density (Jsc) of 19.42 mA cm−2, a fill factor (FF) of 0.72 and power conversion efficiency (PCE) of 14.63%. The PCE was much higher than that of the control planar CeOx ETL (PCE ∼ 9.08%) prepared at a low temperature (80 °C) without the UV–O3 treatment, and this was ascribed to the improved CeOx film, enhanced light absorption and suppressed charge recombination. The cells that bend at 15 mm of radius showed excellent stability with less than 10% reduction in PCE after 500 cycles of repeated bending at ambient temperature. The charge-transmission kinetic parameters and long-term stability of the CeOx-based f-PSCs were analyzed as well.

Liquid Heating During the Collapse of a Single Cavitation Bubble

This paper presents the results of a numerical study of the liquid heating process during collapse of a single spherical cavitation bubble in water at a liquid pressure of 10 bar, temperature of 20°C, and an initial bubble radius of 500 μm. The simulation of this phenomenon took into account the thermal conductivity of the vapor in the bubble and the surrounding liquid, heat transfer and evaporation/condensation on the surface of the bubble, and the effects of viscosity and compressibility of the liquid. It is shown that, as a result of bubble collapse, the liquid heats up in a region of about 60 μm radius. The temperature in the center of this region is about 50°C higher than in the surrounding liquid. The thermal energy expended on heating the liquid in this region is approximately equal to 25 μJ.

Deterministic polishing of micro geometries

Ultraprecision polishing of miniature components and features with small curvature radii is limited by surface accessibility, availability of suitable tools and the capability to control material removal with sufficient spatial resolution. This paper presents the development of an approach for the application of nearly deterministic micro polishing using miniature tools with 400 μm radius. To enable implementation of the proposed approach, the effect of tool wear and polymer relaxation on the control of local contact pressure is characterized and compensation of tool wear along the tool path is introduced. The process is experimentally validated by application to features in nickel phosphor with lateral dimensions down to 2 mm, yielding roughness down to less than Sa 1 nm and profile accuracy better than 10 nm P-V.

Parametric optimization of roll-hemming process in oblique planes with linear and non-linear trajectories

The present work focuses on the optimization of geometric parameters for Roll Hemming process, considering linear and nonlinear trajectories on two oblique planes (3D). Here, the optimization parameters of interest are the roller radius, pre-hemming angle, fillet radius, and fillet height. The main aim of this work is to improve the quality parameters of the 3D process: roll-in, roll-out and wrinkle. Furthermore, a comparison is presented between numerical (Finite Element Method) and experimental data with optimal and non-optimal parameters for four different rollers (10, 15, 20 and 25 mm in radius). The experimental testing was performed using a 6 degree° of freedom (DoF) NACHI® SRA210 industrial manipulator, with a self-developed end effector. The parameters estimated through simulations were used to build the four rollers for experimental testing. Multiple roll hemming tests were performed on several U-shaped aluminum 6011 sheets (31,194 mm2), with a thickness of 0.9 mm. After a detailed analysis of numerical and experimental data, it was observed that the optimum parameters for the roller with 15 mm in radius generated the best quality in hemmed samples.

Water trees in polyethylene insulated power cables: Approach to water trees initiation mechanism

Water trees occurring in polyethylene (PE) insulated power cables at defects exist on the inner or outer semiconductor layers or in PE insulation medium. Water trees start with the existence of water source and penetration under the action of high electric fields. The inevitable micro air voids (1 μm radius) in PE medium with an internal pressure 4450 Torr, and 2.3 dielectric constant, will lead to an electric field (E) of 1.08 MV/cm which can be called tree inception field (Ei). For a protrusion defect of 200 μm tip radius and 2.5 mm insulation thickness, the minimum required breakdown field in PE is 0.417 MV/cm at 2.5 per unit (pu) over voltages. In this paper a new breakdown equation has been introduced related to the injected energy (U), electric field (E) and air void radius (r) with the so called breakdown index (n) under two cases: First case, for n<25, the air void radius increases till 5 μm diameter (water bouquet value). But for the second case, n≥ 25, the air void will crack to many branches in free space and these assume 25 cracks at n=25. The crack length (Lcr) differs according to the mechanical strength (Pm) of PE insulation. According to the new introduced equations Lcr equal 197 μm, 248 μm, and 332 μm for Pm12 N/mm2 low density polyethylene (LDPE), 15 N/mm2 high density polyethylene (HDPE), and 20 N/mm2 cross-linked polyethylene (XLPE) respectively. The water will penetrate these cracks and the progress of water trees starts.

High-performance compact spectrometer based on multimode interference in a tapered spiral-shaped waveguide.

Multimode interference patterns are strongly dependent on spectral components and can be used as fingerprints to reconstruct a spectrum with random amplitudes. Motivated by this concept, we designed and realized a high-performance compact spectrometer based on a tapered spiral-shaped waveguide with a detector array integrated directly on top. The device relies on imaging the multimode interference from leaky modes, resulting in a resolution of 20 pm in the visible range and a bandwidth from 545 to 725 nm with a 250 µm radius structure. Spectra of multiple narrow lines and synthesized broadband are well reconstructed. The ability to achieve such high resolution and broad bandwidth in a compact footprint is expected to have a significant role in low-cost and multifunctional integrated systems.

Binaural Sonar System for Simultaneous Sensing of Distance and Direction of Extended Barriers

Bat navigation via echolocation has inspired numerous acoustic-based obstacle sensing techniques. In this paper, we use a low-cost, small size, single frequency active binaural system for simultaneous detection of distance and direction of extended obstacles using the time of flight cue. For a binaural system and given size of the transducer, the minimum tolerable separation distance between the emitter and receiver as well as best frequency range for effectively sensing a barrier of any orientation will be assessed by simulation. With the given size of transducers of 6.30 mm in radius and for a working distance of 1 m, the minimum separation distance between the emitter and receiver should not be less than 5 cm and the emitter frequency should not exceed higher than 20 kHz. It will be shown in this article that higher frequency limits the lateral distance detection ability of the system. We experimentally verified the technique for detecting a wall of any orientation with respect to the system’s axis. The approach developed in this paper could be useful for mobile robotics, indoor navigation, and personalized navigation, where a compact configuration is of interest.

Numerical Characterization of a High Flux Solar Simulator Using Forward and Inverse Methods

Abstract The numerical characterization of a 10 kWe xenon arc high flux solar simulator is thoroughly presented and performed using two approaches: a forward Monte Carlo ray tracing (MCRT) method and an inverse ray tracing method. Experimental characterization was previously performed for the solar simulator using an indirect flux mapping technique, where the experimental heat flux distribution was obtained at the focal plane and additional 12 planes away from the simulator. For the first numerical characterization method, an in-house MCRT code was used to determine the shape of the xenon arc to best model the simulator. It was determined that an isotropic volumetric source consisting of a hemisphere of 1 mm radius that is attached to a cylinder of 1 mm in radius and 10 mm in length well described the experimental results obtained. The in-house code was then used to generate heat flux maps similar to that obtained experimentally and determine the intensity at the focal plane to be used by the inverse ray tracing method presented for its validation. For the inverse method, intensity interpolation schemes of zeroth and first-order were examined in addition to different solution strategies. It is shown that a first-order interpolation scheme unnecessary complicates the inverse problem, leading to larger errors. In addition, a new approach of constraining the formulated system of equations with an equality constraint that works by eliminating intensity values not tracing back to the ellipsoidal reflector is proposed. This new approach provided intensity values with reduced percentage errors.