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• Assessing feasibility of inferring key track condition parameters using micro-electro-mechanical-system (MEMS) accelerometers. • Prototype of onboard data acquisition system designed and installed on a track recording car (TRC) and comparison of accelerometer-based results vs TRC recordings. • Accelerometers on the bogie are the best compromise between proximity to source and insensitivity to impulsive noise. • Two bogie accelerometers with two measurement axes can provide quantitative estimates of vertical alignment and trends in geographical distribution of horizontal alignment. • Frequency analysis of vertical/horizontal alignment formulas to justify choice of filtering parameters. The main objective of this paper is to assess the estimation of track condition parameters using onboard micro-electro-mechanical-system (MEMS) accelerometers. A prototype of an onboard data acquisition system was designed and installed on a track recording car (TRC) and a measurement campaign was conducted on an extensive portion of the Brisbane Suburban railway network. Comparison of the accelerometer-based results vs TRC recordings have shown that accelerometers installed on the bogie are the best compromise between proximity to the source and insensitivity to impulsive noise. It was found that two vertical bogie accelerometers (left and right) provide a good quantitative estimate of vertical alignment and that strong correlations with TRC measurements exist for lateral MEMS accelerometer measurements (horizontal alignment). These findings suggest that two bogie MEMS accelerometers with vertical and lateral measurement axes are effective in estimating geographical distributions of vertical/horizontal alignment. [ABSTRACT FROM AUTHOR]

Self-powered vibration sensors have the potential to greatly improve vibration monitoring of remote and hard-to-access structures by providing cost-effective and energy-efficient solutions. One promising type of sensors based on the triboelectric generator mechanism has shown significant advantages over other self-powered sensors, including better energy conversion efficiency and high output voltage. However, the majority of the recently reported triboelectric powered sensors exhibit strong frequency dependence, being mostly effective under low frequency vibrations. To address these issues, herein we present a novel design of self-powered vibration sensors based on the clapping mode of a triboelectric nanogenerator (TENG). The sensor, consisting of two tribo-layers made of regular copy paper and PTFE that are clamped together by springs, is able to achieve a high sensitivity of 10.8 mV/g and a broad frequency range from 50 to 8000 Hz with a flat frequency response of ±5 dB, regardless of the inclination angle between the contacting surfaces and gravity. The sensor exhibits high linearity (0.9999) and stability over six days and 400,000 cycles. Furthermore, computational modelling has been conducted to understand the nonlinear clapping phenomenon and the influence of clamping force, proof mass and spring stiffness on the sensor's performance. The potential of the clapping TENG sensor is demonstrated through two different applications such as music recording and diagnosis of the loosing of bolts in a rotating machine. Its superior performances, along with low cost, compact design, and electromagnetic shielding, make it a promising candidate for battery-free high-frequency vibration sensors in practical vibration measurement applications. [Display omitted] • The sensor is capable of a high sensitivity of 10.8 mV/g. • A flat frequency response of ± 5 dB between 50 and 8000 Hz. • Performance is insensitive to the inclination angle with gravity. • High stability of 400,000 cycles and six days with varying humidity. • Made of low-cost materials and shielded from electromagnetic interference. [ABSTRACT FROM AUTHOR]

• The two-dimensional temperature field of the tensile process was investigated based on Digital Image Correlation (DIC) technology and cooling heat transfer model. • The reconstructed temperature field is in good agreement with the temperature rise in the tensile process. • The observed trend of increased martensite production is consistent with the simulated predictions. To better understand the tensile fracture behavior and temperature variation during the tension testing of the 316LN at cryogenic temperatures, a two-dimensional temperature field solution method is developed based on two-dimensional strain field measured by the digital image correlation technology combined with the Taylor Quinney coefficient model and the intrinsic model of strain-induced martensitic phase transformation. The method allows for visualization of the strain field and temperature variation of the 316LN austenitic stainless steel at cryogenic temperature. By numerical simulation, the localized temperature elevation of the 316LN is determined to be 13.3 K during the tensile test at 77 K, which is in good agreement with the experimental result of 10.2 K. This model reconstructed the two-dimensional temperature field variation throughout the entire tensile test, which is beneficial for facilitating the analysis of the mutual relation between the mechanical properties and microstructural evolution of the 316LN and other metastable austenitic stainless steels in cryogenic temperatures. [ABSTRACT FROM AUTHOR]

In this work, the microstructure evolution and magnetic properties of the 316LN austenitic stainless steels under high-cycle-fatigue loading at liquid helium temperature (4.2 K) were assessed by using the X-ray diffractometer (XRD), electron microscopy and magnetic measurements. The microstructure was composed of a single face-centered cubic (FCC) phase, and the high local misorientation was found near the grain boundaries. Observations through the high-resolution transmission electron microscopy reveals that the deformation was dominated by the dislocation and stacking faults. The magnetic susceptibility varies slightly after cyclic loading test at 4.2 K. [Display omitted] [ABSTRACT FROM AUTHOR]

Follicular helper T (Tfh) cells promote, whereas follicular regulatory T (Tfr) cells restrain, germinal center (GC) reactions. However, the precise roles of these cells in the complex GC reaction remain poorly understood. Here, we perturb Tfh or Tfr cells after SARS-CoV-2 spike protein vaccination in mice. We find that Tfh cells promote the frequency and somatic hypermutation (SHM) of Spike-specific GC B cells and regulate clonal diversity. Tfr cells similarly control SHM and clonal diversity in the GC but do so by limiting clonal competition. In addition, deletion of Tfh or Tfr cells during primary vaccination results in changes in SHM after vaccine boosting. Aged mice, which have altered Tfh and Tfr cells, have lower GC responses, presenting a bimodal distribution of SHM. Together, these data demonstrate that GC responses to SARS-CoV-2 spike protein vaccines require a fine balance of positive and negative follicular T cell help to optimize humoral immunity. [Display omitted] • Tfh and Tfr cells are required for affinity maturation of GC B cells • Tfh and Tfr cells optimize antibody responses to SARS-CoV-2 vaccines • Aged mice have defective GC responses leading to bimodal antibody responses • Tfh/Tfr help balance affinity maturation with clonal diversity in germinal centers Cavazzoni et al. show that both Tfh and Tfr cells are essential for optimization of germinal center responses to SARS-CoV-2 vaccines. Limiting Tfh cells results in fewer SARS-CoV-2 GC responses and lower affinity maturation, whereas limiting Tfr cells promotes non-antigen-specific GC responses, leading to lower-affinity maturation. Altered Tfh/Tfr responses in aging result in unique bimodal antibody responses. [ABSTRACT FROM AUTHOR]

• A Ne-liquefaction system cooled by a G-M cryocooler was developed and the refractive index and transmission of 940 nm infrared in liquid neon were also measured. • The neon gas was liquefied while the condenser chamber temperature was cooled down to 26.7 K and the production rate of liquid neon was 0.52 L/h. • The refractive index and transmittance of 940 nm infrared in liquid neon are 1.103 and 99.85%, respectively. A Ne-liquefaction system cooled by a G-M cryocooler was developed. The heat load and liquefied rate of the system were analyzed theoretically. The neon gas was liquefied over 340 min while the condenser chamber was cooled down to 26.7 K. The gas pressures of the heat exchanger inlet and condenser are directly proportional to its absolute temperature, which decreased with the reduction of cryostat system temperature. The pressure of the heat exchanger inlet decreased from 105 kPa to 100.4 kPa with the pressure of the condenser decreased from 101 kPa to 100.1 kPa. Neon gas with a purity of 99.999% was used in liquefaction and the mass flow is set to 0.173 g/s. The production rate of liquid neon is determined to be 0.52 L/h. The liquid neon was collected in a glass vacuum dewar with a transparent window, which allows to observe the liquid level and conduct the optical tests. The refractive index and transmittance of the 940 nm infrared in liquid neon are 1.103 and 99.85%, respectively. The parameters will provide a valuable database on infrared equipment with liquid neon as a cryogen. [ABSTRACT FROM AUTHOR]

• The sound welded joint was obtained with Ni interlayer for 316L/Cu dissimilar laser welding joint. • No welding defects and spherical particles were formed in the fusion zone. • The average tensile strength of dissimilar welded joint is 408 MPa at 77 K. To improve the quality of welded joints between copper and 316L stainless steel, laser welding with Ni interlayer was carried out. A sound welded joint was obtained and the microstructures as well as mechanical properties were investigated. Results indicate that no welding defects or spherical particles were formed in the fusion zone. The microstructures in the fusion zone were characterized as dendritic grains, and no macroscopic segregation was observed. The welded joint failed at copper base material with an average tensile strength of 408 MPa at 77 K, and ductile fracture mode with dimples on the fracture surface were presented. Moreover, the addition of Ni interlayer prevents formation of welding defects and spherical particles and improves mechanical properties of the joint. [ABSTRACT FROM AUTHOR]

• An emissivity measurement system based on radiometric method was designed and built. • The radiation power signal received by detector can be switched by a stepping motor. • The emissivity of the blackbody coating (Nextel 811–21), 304 stainless steel and G10 were measured and discussed. Thermal radiation is a major part of heat transfer in cryogenic systems, especially in vacuum environment. The emissivity of materials is an essential factor of thermal radiation, which is difficult to be precisely predicted by theoretical calculation. Thus, the direct experimental measurement becomes an inevitable, reliable method. In this paper, a preliminary emissivity measurement system using the direct radiometric method was designed and built with a G-M (Gifford-McMahon) cryocooler as the cold source. The sample plate in the apparatus can be cooled to 9.2 K, while the sample thermal radiation shield and the optical path cover can respectively reach 46.7 K and 46.9 K. At present stage, MCT (HgCdTe) detector with an effective bandwidth 2–12 μm was used in this system, which achieved the measurements of emissivities of coating Nextel 811–21, 304 stainless steel and G10 composite from 240 K to 300 K. The reliability of the system was verified by comparing the measurement results with the data already published, and the dependence of the emissivities of these materials on temperature are analyzed. [ABSTRACT FROM AUTHOR]

• Mechanical properties of superconducting magnet insulation materials after reheat. • Strain responses during second Vacuum Pressure Impregnation process. • Monitoring by Fiber Bragg Grating sensors embedded in the insulation layers. • Additional strain introduced by the new added epoxy resin. In large-scale, high-field superconducting magnets used for magnetic confinement fusion, high energy accelerators, and magnetic resonance imaging, the insulating system made from glass fiber reinforced resin-based composites is the key component, which mainly plays the role of mechanical support, fixing and protecting superconducting conductors, as well as electrical insulation. Vacuum Pressure Impregnation (VPI) approach is widely used in the manufacturing of the insulation system. The second curing cycle is generally required after the first VPI and curing process. For example, after the superconducting coil is cured in the mold, the de-molding process requires the superconducting coil to be reheated according the curing temperature. Moreover, for large-scale superconducting magnets, the superconducting coil needs to undergo a second VPI process after the first VPI process to fix the coil in the coil case. In this work, the tensile and shear properties of pure epoxy resin and the glass fiber reinforced resin-based composite, were investigated at both room and cryogenic temperatures and the effect of the second curing cycle on the mechanical properties was analyzed. Additionally, the strain evolution of the Nb-Ti superconducting coil during the second curing cycle was measured using the Fiber Bragg Grating (FBG) sensors embedded in the composite. The results indicate that the second curing cycle will not introduce additional strain to the previously cured resin matrix, but the defective or weak parts of the resin matrix may be affected by the new added epoxy resin and a little extra strain has been observed. [ABSTRACT FROM AUTHOR]

• A model coupling shaft torsional vibration and advanced injection angle is built to predict engine block vibration. • Formulas of block vibration excitation forces are analyzed and derived by taking in to account the coupling model. • An optimization method for block vibration mitigation by adjusting advanced injection angle is proved. Engine body vibration is an important safety concern for diesel engines as it can lead to severe engine damages and even catastrophic failures. Traditional methods for excitation computation assume that the rotational speed and the cylinder pressure remain stable under each working cycle, which makes it impossible to precisely predict vibration peaks at certain frequencies. But in practice, the existence of shafting torsional vibration will lead to the fluctuation of rotational speed and cylinder pressure. To predict engine block vibration more accurately, this paper proposes a novel method considering the instantaneous variations in rotational speed and cylinder pressure. It is implemented by two steps. Firstly, an innovative model considering the coupling effect between shaft torsional vibration and advanced injection angle is proposed, it particularly explains how the cylinder pressure and instantaneous rotational speed vary due to the coupling effects. Secondly, the excitation forces that cause block vibration are analyzed and their computational formulas are improved. This method also considers the offset of excitation loading position caused by torsional vibration. The coupling model is experimentally verified and the excitations are loaded into a finite element model of the diesel engine for vibration response prediction. The results reveal that the coupled model can predict vibration peaks at sideband frequencies and thus makes the frequency spectrum much richer than that of the traditional method. Furthermore, it shows that the acceleration results obtained by the coupled model have better prediction accuracy than those obtained from traditional methods, with the deviation percentage reducing from 6.31% and 8.41% to 0.64% and 0.32% in the X and Z direction. It indicates that the coupled model is more reliable in predicting the vibration response of the engine block. Finally, the effect of advanced injection angle on engine block vibration is investigated and the optimal value of the advanced injection angle is determined to be 29 CA, which makes the engine block vibration reduced by 3.60%, 2.72%, and 3.16% in the X, Y, and Z direction comparing to the original advanced injection angle. Overall, this study presents an improved approach for predicting engine block vibrations and offers valuable insights for the design of shafting structures and fuel injection parameters in marine diesel engines. [ABSTRACT FROM AUTHOR]

• Mechanical properties of 316LN stainless steel with cryogenic pre-strain were studied at different temperatures (RT, 77 K and 4.2 K). • The pre-strained samples stretched at cryogenic temperature obtain higher mechanical strength. • The samples stretched at 77 K possess higher elongation and hardness than RT and 4.2 K, the mechanism was explained. • The results are attributed to the changes in dislocation density and martensite transformation due to temperature and cryogenic pre-strain. The 316LN stainless steel (SS) used for TF conduits in the ITER must undergo a series of pre-deformation during the fabrication. In order to investigate the variation of mechanical properties of 316LN SS with different temperature and cryogenic pre-strain, the cryogenic pre-strained samples with 0%, 15%, 25%, and 35% pre-strain were prepared and stretched at room temperature (RT), 77 K and 4.2 K, respectively. The yield strength (YS), ultimate tensile strength (UTS), elongation and microhardness of the samples were measured. Besides, the Scanning Electronic Microscopy (SEM) and Transmission Electronic Microscopy (TEM) were applied to observe the microstructure of 316LN SS. The magnetic measurements for the samples were carried out to investigate the volume percent of phase transformation. The results indicate that the YS, UTS and microhardness of 316LN SS are improved by means of cryogenic pre-strain and the decrease of elongation of pre-strained samples is different at different temperatures. All 316LN samples show the ductile fracture. The dislocation of samples promotes by cryogenic pre-strain and hinders by cryogenic temperatures. The martensitic transformation occurs after all pre-strained samples were stretched. The volume percent of α' martensite is minimal at RT and increases dramatically at cryogenic temperatures (77 K and 4.2 K). The combination of dislocation density and martensitic transformation results in changes in the 316LN SS mechanical properties. [ABSTRACT FROM AUTHOR]

• A cryogenic system for measuring electrical properties of insulation materials has been established. • The thermal switch in the cryostat shortens the time of precooling and saves a lot of helium gas. • Two modes in the cryogenic system: 4.2 K mode and 1.65 K mode. • The cryogenic system realizes the coupling of low temperature and high voltage. A cryogenic system has been established to measure electrical properties of insulation materials. The cryostat in the system contains two operating modes: 4.2 K and 1.65 K. A G-M cryocooler is used as cold source in these two modes. In 4.2 K mode, samples were directly cooled by the copper plates connected to the second stage of the cryocooler. In the 1.65 K mode, the helium gas is liquefied. The superfluid 4He (He-Ⅱ) of 1.65 K was obtained by throttling and depressurizing the liquid 4He (He-Ⅰ). The thermal switch in the 1.65 K mode can reduce the precooling time by 11.6 h and saved 22.5 L of helium. The transforming of the two modes is controlled by four threaded rods which are connected to the first and the second stage flange. The electrical test unit is designed, including the breakdown strength test and the flashover characteristics test with the voltage from 0 to 100 kV, which realizes the coupling of low temperature and high voltage. [ABSTRACT FROM AUTHOR]

• The system can quantitatively detect internal and external leakage within a wide range of operating temperatures (20–300 K). • This system using the GM cryocooler instead of cryogen is a benefit for its low operating cost, simple structure, and safe handling. • Five sample valves can be cooled simultaneously and tested in sequence to improve efficiency. • The helium mass spectrometry leak detector was used for its sensitive response and high precision. • The external leakage of the sample valves was detected at LH 2 temperature for the first time. Sealing performance under cryogenic temperatures should be a consideration in the development of a cryogenic valve for use in cryogenic engineering. In the present work, a cryogen-free leak detection system at 20 K to conduct leakage testing of cryogenic valves was developed. The experimental system was composed of a cooling system, a leak detection system, and a PLC (Programmable Logic Controller) system. Compared with the traditional cryogenic leak detection systems, this system using the GM cryocooler instead of cryogen is beneficial for the application for its low operating cost, simple structure, and safe handling. Five valves can be installed simultaneously and tested in sequence. The helium mass spectrometer leak detector is used for its sensitive response and high precision. The reliability of this system was verified by testing the leak rate of the system itself. Three high-pressure cryogenic solenoid valves were tested using helium gas under the pressure varied from approximately 2.5 bar to 80 bar and at both room temperature (300 K) and liquid hydrogen temperature (20 K). The tested valves can be cooled from room temperature to 18 K within 6 h. The test results of the internal leakage rate and the external leakage rate of the samples were discussed. This system will aid in the inspection of many critical cryogenic components such as liquid oxygen and liquid hydrogen valve assemblies for which leakage may lead to serious consequences. [ABSTRACT FROM AUTHOR]