Ultra-small Space Research Articles

Preliminary analysis of in-orbit operation accidents for an ultra-small Lithium-cooled space reactor power system

To study the safety characteristics of an ultra-small (5.2 MWt) lithium-cooled space reactor power system (ULCR) under postulated accidents, a transient analysis code for the ultra-small space reactor coupled with a closed Brayton cycle dynamic conversion and heat pipe radiator was established. A preliminary analysis of four typical postulated accidents occurring at 100 percent power in-orbit operation of the ULCR system was conducted to define postulated problem areas and establish safety requirements. The postulated accidents mainly include (1) reactivity insertions, (2) coolant partial flow loss, (3) turbomachinery failure, and (4) radiator partial failure. The results showed that: a) since the ULCR system was designed to operate at high-temperature conditions (coolant temperature greater than 1500 K), the safety margin of the ULCR system was small. Emergency shutdown control or reduced power operation action should be taken proactively to ensure ULCR's safety in different accidents. b) When the control rod was misoperated and large reactivity was inserted, the maximum temperature of the lithium coolant was very close to the saturation temperature (the difference was 24 K), and the system was operated at extremely high temperatures (the average temperature of the core coolant was 1750 K); c) In coolant flow loss accident, when the coolant flow of the system dropped below 40% of the rated mass flow, the lithium coolant boiling would occur in the primary loop system, and the emergency shutdown control action was required to ensure the safety of the system.

Non-Fourier Heat Conduction of Nano-Films under Ultra-Fast Laser.

The ultra-fast laser heating process of nano-films is characterized by an ultra-short duration and ultra-small space size, in which the classical Fourier law based on the hypothesis of local equilibrium is no longer applicable. Based on the Cattaneo-Vernotte (CV) model and the dual-phase-lag (DPL) model, the two-dimensional analytical solutions of heat conduction in nano-films under ultra-fast laser are obtained using the integral transformation method. The results show that there is a thermal wave phenomenon inside the film, which becomes increasingly evident as the elapse of the lag time of the temperature gradient. Moreover, the wave amplitude in the vertical direction is much larger than that in the horizontal direction of the nano-film. By comparing the numerical result of the two models, it is found that the temperature distribution inside the nano-film based on the DPL model is gentler than that of the CV model. Additionally, the temperature distribution in the two-dimensional solution is lower than that in the one-dimensional solution under the same Knudsen number. In the comparison results of the CV model, the maximum peak difference in the thermal wave reaches 75.08 K when the Knudsen number is 1.0. This demonstrates that the horizontal energy carried by the laser source significantly impacts the temperature distribution within the film.

Dynamic Response of the Cross Tunnel with Ultra-Small Spacing Under Various Seismic Motions Using a Shaking Table Model Test

ABSTRACT Different from a single tunnel, the cross tunnel with ultra-small spacing is characterized by high crossing risk, significant coupling of multiple effects, and difficulty in controlling stability. A shaking table model test was carried out to study the failure process and dynamic response of the cross tunnel with ultra-small spacing under seismic motions with various types and peak accelerations. The results show that the seismic damage of the cross tunnel model has significant failure stages. The deformation of the upper-span tunnel lining is cumulative progressive damage from the left wall to the invert, while the under-crossing tunnel lining is cumulative progressive damage from the left wall to the crown. The acceleration response of the model when inputting Wenchuan seismic motions is greater than that of El-Centro seismic motions, and the Wenchuan seismic motions may cause a peak lag in the acceleration response of the model. Compared with inputting El-Centro seismic motions, the 1st predominant frequency of the model increases while the 2nd predominant frequency decreases when inputting Wenchuan seismic motions. Additionally, the 2nd predominant frequency components are significantly amplified in the propagation of seismic motions from bottom to top through the lining structure. Although the energy ratio of the wavelet packet frequency components gradually tends from low-frequency bands to relatively high-frequency bands, the low-frequency bands still play a dominant role in the failure of the model.

Characterization of optical diffraction by single nanochannel for aL–fL sample detection in nanofluidics

Nanofluidics which integrates analytical systems in 101–103 nm space provides ultra-sensitive analyses at a single-cell and single-molecule level. One of the key technologies for nanofluidics is the ultra-sensitive detection method; however, the ultra-small volume at aL–fL scale makes it challenging. Recently, we have developed a non-fluorescent molecule detection method for nanofluidics called photo-thermal optical diffraction (POD) which utilizes the photo-thermal effect of target molecules and optical diffraction by a single nanochannel. To improve the performance of such diffraction-based detection methods, the design and optimization of optical diffraction are essential. However, it is unknown whether the optical diffraction by a single nanochannel follows general diffraction theory because liquid properties change in the ultra-small space. In this study, we elucidated optical diffraction by a single nanochannel from theoretical calculations and experiments. Our experiments revealed the effect of channel size, channel position, and solvents in the nanochannel, which showed good agreement with proposed theoretical calculations. We also revealed no or little change of refractive index of water in the nanochannel compared with that in the bulk. Finally, we confirmed that the POD signal was proportional to the diffracted light intensity, and the calculated limit of detection of POD was 7.0 × 10–7 RIU in a detection volume of 0.23 fL. Our theoretical calculations and experimental results can be widely applied to the design and optimization of detection methods using optical diffraction by nanochannels and nanostructures.

Studies of the ionosphere using radiophysical methods on ultra-small spacecrafts

The principal possibility to measure the plasma density and its fluctuations in the ionosphere on ultra-small space vehicles using radiophysical methods is shown. These methods allow us to determine the characteristics of the medium by the properties of the received radiation. It is assumed that each small spacecraft has a satellite navigation receiver as well as a device for emitting and detecting a signal at two multiple frequencies in the radio band. In this approach, information on plasma density is contained in the received phase difference. Radio receivers and radio transmitters on satellites constantly exchange radio signals and then it is possible to determine the plasma density and its fluctuations from the phase shift. Numerical estimates are also made to determine the maximum distance between satellites where one can reliably receive a radio signal.

Normalized Lithium Growth from the Nucleation Stage for Dendrite-Free Lithium Metal Anodes.

Inducing uniform deposition of lithium from the stage of metal crystallization nucleation is of vital importance to achieve dendrite-free lithium anodes. Herein, using experiments and simulation, homogenization of Li nucleation and normalization of Li growth can be achieved on PNIPAM polymer brushes with lithiophilic functional groups modified Cu substrates. The lithiophilic functional groups of amide O can homogenize ion mass transfer and induce the uniform distribution of Li nucleation sites. What is more, the ultra-small space between each brush can act as the channels for Li transportation and normalization growth. Owing to the synergistic effect of homogenization and normalization of electrodeposited Li, the obtained planar columnar Li anode exhibits excellent cycle stability at an ultra-high current density of 20 mA cm-2 .

Nonfluorescent Molecule Detection in 102 nm Nanofluidic Channels by Photothermal Optical Diffraction.

Integrating analytical systems in 101-103 nm spaces provides ultrasensitive analytical devices at the single cell and the single molecule levels due to the ultrasmall space, and fundamental technologies for nanofluidics are developed. A simple and ultrasensitive detection method is one of the essential technologies for nanofluidics; however, it is still challenging due to the ultrasmall volume at the attoliter to femtoliter scale. In this study, we report a new photothermal detection method of nonfluorescent molecules for a 102 nm space, photothermal optical diffraction (POD), which utilizes light absorption and heat generation by an analyte and optical diffraction by a nanochannel after heat diffusion. Concentration determination of nonfluorescent molecules in a 400 nm channel was successfully demonstrated, and a limit of detection (LOD) of 5.0 μM was achieved, corresponding to 500 molecules (0.84 zmol) in a detection volume of 230 aL. Also, detection in a 200 nm channel was successfully demonstrated without degradation of the LOD. Our method can be widely used for chemical and biological analyses in 102-103 nm nanofluidics.

Use of ultra-small space vehicles for studying near-Earth plasma by radiophysical methods

The paper shows the possibility to measure plasma density and its fluctuations in the ionosphere on ultra-small space spacecraft using radiophysical methods that allow determining the characteristics of the medium through which radiation is transmitted. It is assumed that each spacecraft will have a navigational satellite receiver, as well as a device for emitting and detecting a signal at two multiple frequencies in the radio band. With this approach, information on plasma density is contained in the received phase difference. Radio receivers and radio transmitters on satellites constantly exchange radio signals and then it is possible to determine the electron concentration and its fluctuations from the phase shift. The authors obtained numerical estimates of the resulting phase difference for different frequencies from 10 MHz to 10 GHz with typical ionospheric parameters depending on the distance between the satellites. Calculations were also made to determine the maximum distance between satellites at which it is possible to receive a signal, provided that the transmitter power is 2 watts.

Detachable glass micro/nanofluidic device.

Glass is one of the most ideal materials for micro/nanofluidic devices due to its excellent optical transparency, resistance to a wide range of solvents and reagents, and easy to modify surfaces by silane-coupling reagents. From a practical point of view, glass is a hard material and is suitable for real applications. One of the advantages of glass is its reusability; however, this reusability is difficult to realize in certain conditions. Washing or re-modification of micro/nanofluidic channels is sometimes difficult due to the ultrasmall space in these channels. If the glass devices are detachable, it is easy to access the channel surface, and the channels can be cleaned and re-modified. When the substrates are bonded again, the devices are fabricated easily without repeating laborious and expensive micro/nano-fabrication processes. This technology gives researchers and users a choice of glass substrates in fundamental research studies and real-time applications. In this study, we propose a detachable glass micro/nanofluidic device by our low temperature bonding method. The surface bonding energy is controlled to realize both high pressure capacity for micro/nanofluidics and easy separation of glass substrates without fracturing. As a result, at least four times detaching and bonding is confirmed.

Confined whispering-gallery mode in silica double-toroid microcavities for optical sensing and trapping

Abstract We propose and theoretically study a silica double-toroid microcavity to confine the whispering-gallery mode (WGM) in an ultra-small space, which consists of two toroid-to-toroid coupled cavities separated by a nanoscale gap region with low refractive index, such as the air gap. Benefitting from the strong field localization of the “slot” effect, power enhancement of symmetric WGMs in the gap results in the ultra-small mode volume of 4. 8 μ m which is quite smaller than the conventional toroidal microcavity with mode volume of about hundreds of cubic micrometers. The confined modes hold the potential advantages over conventional photonic devices, especially in the applications of the sensing and optical trapping. In the application of refractometer, a high refractive index sensitivity of up to 468 nm per refractive index unit (nm/RIU) can be obtained in the 1000 nm wavelength band. In the optical trapping application, the double-toroid microcavity enables a significant field enhancement in the confined WGM, and the gradient force could reach as high as 22 pN/W for a single nanoparticle with the radius of 5 nm. As the potential advantages, this study of silica double-toroid microcavity provides a good reference for realizing the high-efficient photonic applications such as optical sensing and trapping.

Miniaturized fiber-taper-based Fabry-Perot interferometer for high-temperature sensing.

A microminiaturized all-fiber Fabry-Perot interferometer (FPI) for high-temperature sensing has been proposed and experimentally demonstrated. The FPI is composed of a micro-air bubble and a taper probe with a tip less than 2 μm in diameter as reflected interfaces. A temperature sensitivity of 14.68 pm/°C near the wavelength of 1550 nm is obtained. The sensor, with its miniature size, can work in an ultra-small space with a large range of temperature variation.

Extended-Nanofluidic Devices and the Unique Liquid Properties - Invited Paper

Microfluidic devices are downscaling to 10-100 nm space, which we call extended-nano space. Because the extended-nano space is a space to bridge isolated molecules and normal bulk fluid, new solution chemistry can be expected. However, it was difficult to investigate due to the ultra-small space. Our group developed fundamental technologies for the extended-nano fluidics such as nanofabrication and bonding for glass substrates, aL-fL pressure driven fluidic control, partial surface modification, and single molecule detection. Based on these technologies, many unique liquid properties were found such as viscosity increase, enhanced proton mobility, lower dielectric constant. In addition, the liquid property changes depended on channel size, channel shape, and kinds of liquid. New analytical and energy devices are created utilizing the unique properties in the extended-nano space. In this talk, fundamental technologies and unique liquid properties found in this space are mainly presented, which would have impact not only on chemistry and biology but also on semiconductor industry.

Thermo-molecular gas-film lubrication dynamics considering boundary temperature and ambient gas (2-DOF numerical analysis by t-MGL equation)

The static and dynamic flying characteristics of a slider in a hard disk drive have become an important consideration owing to recent increases in recording density. In the present paper, the characteristics of a plane inclined slider (Case 1) and a step slider flying in either air or He (Case 2) over a running boundary wall with local temperature distributions are analyzed using the thermo-molecular gas-film lubrication (t-MGL) equation. For a plane inclined slider (Case 1), the fundamental static and dynamic characteristics are analyzed numerically and are examined through two limiting approximations: the approximation for infinite bearing number and the incompressible short bearing approximation. For a step slider (Case 2), the decreases in the minimum spacing for a slider flying in He are significant because the mean free path of He, ?He, is approximately three times that of air, ?air. The increases in the minimum spacing due to laser heating are negligible in both air and He because the heat spot size is very small. Moreover, the decrease in the minimum spacing produced by thermal deformation (projection height, dmax) by laser heating in the thermal fly-height control slider is reduced by the total additional pressure of (1) MGL pressures produced by the air-film wedge effect, (2) t-MGL pressures produced by the applied temperature distribution, and (3) van der Waals attractive pressure due to the ultra-small spacing. The spacing fluctuation in He caused by a running wavy disk is smaller than that in air, because the inlet-to-outlet spacing ratio (h1/h0) in He is larger than that in air.

地球周回軌道に投入された超小型衛星の月への移動手法

When we develop a space probe, are needed to carry out its orbit analysis. Space industries and space agencies they have been using the System Tool Kit (STK) for these orbit analysis. Most of satellite projects were used this software. An allowable mass demand of a rocket to an ultra-small space probe is very severe, for this reason a throughput and a number of a microcomputer are restricted. Since this probe cruises deep space, advanced autonomous control capability is required. It is important that an orbital prediction method as highly precise as possibly simple is built. An analyzed result by this new method is agreement with an analysis result by this STK. This may use be utilized for an autonomous control type ultra-small probe. This paper shows an outline of this new orbital prediction method.

Wavelength Resource Sharing in Bidirectional Optical Mobile Fronthaul

In this paper, we propose high-capacity spectrally-efficient optical mobile fronthaul (MFH) architectures featuring wavelength resource sharing, where multiple cell sites share one dense wavelength division multiplexing (DWDM) channel instead of occupying a number of separated DWDM channels. In the downlink (DL), subcarrier multiplexing (SCM) is integrated with DWDM passive optical network. The key technical innovation lies in the reception of uplink (UL) signals being optically aggregated with ultrasmall spacing. We introduce two novel schemes for spectrally-efficient and low-complexity upstream transmissions. The first method is based on SCM in remote radio heads (RRHs) and coherent detection in baseband units (BBUs), achieving channel spacing of as small as 100 MHz. For the first time, successful coherent reception of LTE signal, whose symbol rate (15 ksps) is much smaller than the laser linewidth, is achieved by pairing a radio frequency pilot tone from each RRH. Bidirectional transmission of four 20-MHz 16-QAM-OFDM LTE-like signals with 100-MHz spacing aggregated on one wavelength is demonstrated. For the second proposed UL scheme, we report a low-complexity ultradense WDM over DWDM allocation with 1-GHz wavelength spacing and novel phase-noise-insensitive heterodyne detection using MHz-linewidth lasers and an off-the-shelf envelope detector. We experimentally demonstrate the transmission and simple detection of multichannel 100/200 Mb/s OOK or 200 Mb/s 16-QAM-OFDM signals with 1-GHz spacing over 30-km standard single mode fiber using 5-MHz-linewidth lasers. By enabling ultrahigh spectral efficiency, high receiver sensitivity, and low-complexity, the proposed approach achieves a significant breakthrough for future high-capacity mobile fronthaul systems.

Detection of zeptomole quantities of nonfluorescent molecules in a 101 nm nanochannel by thermal lens microscopy

Nanofluidics in 10(1) nm space, whose scale is comparable to the electric double layer (EDL) and the size of biomolecules, promises novel functional analytical devices. However, the detection, which is indispensable to the integrated chemical system, is still challenging in such an ultra-small space. Previously, we reported a differential interference contrast thermal lens microscope (DIC-TLM) based on the photothermal interferometry principle and succeeded in detection of nonfluorescent molecules in 10(2) nm spaces. However, the thermal diffusion into substrates becomes a problem for detection in 10(1) nm spaces. The DIC-TLM signals are significantly cancelled out in spaces much smaller than the confocal length (∼10(2) nm), which makes DIC-TLM detection in 10(1) nm space quite difficult. To overcome this problem, we propose a new channel structure that benefits the thermal diffusion and sensitivity enhancement in DIC-TLM by employing TiO2 as a substrate material for compensating the signal cancellation effect. As a result, DIC-TLM detection of nonfluorescent molecules (800 molecules) was successfully demonstrated in a nanochannel with a depth of 50 nm. The developed detection method will contribute to the functional nanofluidic devices utilizing 10(1) nm spaces.

Experiment Studying of Multiwavelength Erbium-Doped Fiber Laser with Ultra-Small Wavelength Spacing

The configurations of Erbium-doped fiber laser and comb filter that work stably have been designed. The stable multiwavelength oscillation of erbium-doped fiber laser with wavelength spacing 0.20nm in 1532nm band had been obtained at liquid nitrogen temperature by optimizing length of erbium-doped fiber and loss of cavity. The experimental results show that, the erbium-doped fiber exhibits obviously different inhomogeneous gain broadening in different band.

Tuning surface plasmons in nanorod arrays with ultrasmall spacing

In this work, we first investigate the optical properties of nanorod arrays with normal inter-rod spacing (>100 nm) and realize the tuning of nanorod localized surface plasma resonance (LSPR) by changing array parameters (e.g., periodicity). Then we filter our individual colors in the visible range using nanorod arrays with ultrasmall inter-rod spacing and ultrahigh density fabricated by electron beam lithography (EBL) and ion etching. The functional nanorod arrays developed in this work are compatible with current digital light processing technique, enabling screen with ultrasmall pixels which can find extensive applications in display and imaging.

Binary Mixture Film of Perfluoropolyether Lubricants

It has become more and more difficult to find a single lubricant meeting all the requirements for ultra-small head-media spacing hard disk drives (HDDs). Therefore, an appropriate mixture of lubricants may be a feasible and promising alternative for future HDDs. In this paper, molecular dynamics (MD) simulations employing a bead-spring model were performed to examine the detailed structure, conformation, and dynamics of binary mixture lubricant nano films by extensively analyzing the anisotropic radius of gyration and the self-diffusion coefficient as a function of composition. Our simulation analysis indicates that a binary (or even a ternary) mixture monolayer can be a more suitable disk lubricant as compared to a single component lubricant. The conformation and mobility change by tuning the volume fraction was examined in conjunction with the optimal lubricant selection.

Corrected expression of the van der Waals pressure for multilayered system with application to analyses of static characteristics of flying head sliders with an ultrasmall spacing

A corrected and approximate expression of the van der Waals pressure for a multilayered system was developed. The conventional expression cannot be applied to a general multilayered system, while the corrected expression can be applied to multilayered system composed of any materials. Applying the corrected expression to the analyses of the static characteristics of an inclined flying head slider, the dependences of the static load-carrying capacity and the static limit minimum spacing on the PFPE film thickness were clarified.