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The attainment and maintenance of a low temperature environment is essential for aerospace cryogenic detectors to achieve their required performance. Developing cryocoolers with features of high efficiency, compact structure, and long lifetime is the main challenge for cryogenic detector cooling. In this paper, a high efficiency thermally-coupled two-stage Stirling type pulse tube cryocooler working at 35 K for HgCdTe long wave infrared detector cooling is designed and tested. The thermally-coupled type avoids gas distribution at cold side which minimizes the inter-stage influence. The whole cryocooler is driven by one linear compressor which enables compact structure. The influence of operation frequency and mean pressure is studied by numerical calculation and experiments to determine the optimum operation condition. Acoustic impedance characteristics of both stages and the whole cold finger are also analyzed by comparing performance of cryocooler with different frequency, mean pressure and structure dimensions. The distributions of acoustic power and phase angle are presented to study the relation between impedance characteristic and the cooling performance. Impedance match between compressor and cold finger is also discussed by analyzing the efficiency of the linear compressor and the performance of cryocooler with different pulse tubes. Under optimum impedance match and operation condition of a working frequency of 39.2 Hz and a mean pressure of 2.45 MPa, the cryocooler provides a cooling power of 1 W at 35.1 K with an input electrical power of 150 W, which indicates a relative Carnot efficiency of 5%. This is a rather high efficiency for developed Stirling type multi-stage pulse tube cryocooler working at 35 K with only inertance tubes as phase shifter. The development of this cryocooler lays a solid base for the further optimization to realize a competitive candidate for aerospace cooling requirements.

For the first time, a group of CaB6-typed cubic rare earth high-entropy hexaborides have been successfully fabricated into dense bulk pellets (>98.5 % in relative densities). The specimens are prepared from elemental precursors via in-situ metal-boron reactive spark plasma sintering. The sintered bulk pellets are determined to be single-phase without any detectable oxides or other secondary phases. The homogenous elemental distributions have been confirmed at both microscale and nanoscale. The Vickers microhardness are measured to be 16−18 GPa at a standard indentation load of 9.8 N. The nanoindentation hardness and Young’s moduli have been measured to be 19−22 GPa and 190−250 GPa, respectively, by nanoindentation test using a maximum load of 500 mN. The material work functions are determined to be 3.7–4.0 eV by ultraviolet photoelectron spectroscopy characterizations, which are significantly higher than that of LaB6.

Single-phase high-entropy monoborides (HEMBs) of the CrB prototype structure have been synthesized for the first time. Reactive spark plasma sintering of ball milled mixtures of elemental precursor powders produced bulk (V0.2Cr0.2Nb0.2Mo0.2Ta0.2)B, (V0.2Cr0.2Nb0.2Mo0.2W0.2)B, and (V0.2Cr0.2Nb0.2Ta0.2W0.2)B HEMB specimens of ~98.3–99.5% relative densities. Vickers hardness was measured to be ~22–26 GPa at an indentation load of 9.8 N and ~32–37 GPa at 0.98 N. In particular, the load-dependent hardness of (V0.2Cr0.2Nb0.2Ta0.2W0.2)B is higher than those of ternary (Ta0.5W0.5)B (already considered as superhard) and hardest reported high-entropy metal diborides, and on a par with the classical superhard boride WB4.

A novel non-equiatomic NbTaTi-based refractory complex concentrated alloy (RCCA) capable of being cold-rolled up to a reduction in thickness of over 90% directly from the as-cast state is studied. Instead of conventional heat-treatment at temperatures greater than 0.8Tm for long durations, the excellent cold-workability in this RCCA allows for tunable microstructural features, including fine-grained, coarse-grained, and heterogeneous lamella (HL) structures, through proper heat-treatment at relatively lower temperatures for shorter duration. By tailoring microstructures, balanced tensile properties are achieved in this RCCA, through back-stress strengthening of HL structures. This study demonstrates an energy-saving and efficient way to fabricate high-performance RCCAs.

FeAl-based Metallic-Intermetallic Laminate (MIL) composites exhibit enhanced strength and ductility compared to previously studied MIL composites. The deformation and fracture evolution of the FeAl-based MIL composites are investigated here via incremental compression testing. Microstructure assessment via electron backscatter diffraction suggests that deformation proceeds in a fairly homogeneous manner across gradients in the microstructure. Eventual failure is mainly induced by normal stresses, whereas other MIL composites typically fail by shear induced localizations. Geometrically necessary dislocation analysis indicates the FeAl regions deform in similar manners for the three MIL composites (Fe-FeAl-MIL, 430SS-FeAl-MIL, and 304SS-FeAl-MIL), and each fails in a similar mode. While the FeAl phase is the majority constituent of the composites, the mechanical properties are significantly influenced by the softer metal layers. The transition layer formed between the Fe-based metal layers and FeAl regions is the most critical constituent of the composites. Although the volume fraction of the transition layer is only ∼15%, a stronger transition layer can improve the work hardening behavior of the FeAl phase, increasing MIL composite strength by as much as 1 GPa. The findings can guide the design of the MIL composites to achieve even better mechanical properties.

The electromigration effect in spark plasma sintering (SPS) (a.k.a. field assisted sintering) is quantitively analyzed in the Fe-Al diffusion couple system. In SPS, the samples are heated by a high applied voltage and electric current, which can lead to an electromigration effect. Finite element analysis is utilized to determine the voltage applied to the Fe-Al diffusion couple, which is found to be order of magnitudes smaller than the overall system voltage, indicating the electron wind force would be the dominant mechanism for electromigration in SPS. Additionally, the simulation suggests the temperature and current density distribution is uniform across the metallic diffusion couple, which makes quantitative measurement feasible. A mathematic algorithm that allows diffusivity and electromigration coefficients to be solved, is developed for the Fe-Al, where multiple intermetallic phases coexist. At temperatures below aluminum melting, Fe2Al5 is the single intermetallic phases formed in Fe-Al system, for which electromigration is negligible. At temperatures above aluminum melting, FeAl2, FeAl and α-Fe solid solution phases coexist. Among them, the electromigration effect is noticeable in FeAl phase and is significant in the FeAl2 phase. The corresponding electromigration enhancement constants are calculated.

Fitting conics from images is a preliminary step for its plentiful applications. It is a common sense that geometric distance based fitting methods are better than algebraic distance based ones. However, for a long time, there has not been a geometric distance between a point and a general conic that allows easy computation and achieves high accuracy simultaneously. Though Sampson distance is widely accepted, it is only a first-order approximation. For other geometric distances, the computations are too complex to be popular in practice. In this paper, we derive a new geometric distance between a point and a general conic, called Polar-N-Direction distance. The distance can be adapted to a projective transformation because it is computed along the normal direction of the polar line of the point, making conic fitting more robust. Moreover, Polar-N-Direction distance is accurate and simultaneously still analytical in an explicit representation, which is quite easy to be implemented. Then, based on the distance, a new cost function is constructed. The conic fitting optimization by minimizing this cost function has all the merits of the geometric distance based methods and simultaneously avoids their limitations. Experiments show that the conic fitting method is greatly efficient.

The electrocardiogram (ECG) is an important tool for detecting arrhythmia. To solve the limitations of visual inspection, computer-aided diagnosis appears and grows rapidly. Most of the reported researches for heartbeat classification were based on intra-patient dataset. Moreover, existing inter-patient researches were usually conducted for superclasses of arrhythmia. To classify specific types of arrhythmia, this study proposed an inter-patient heartbeat classification method based on region feature extraction and ensemble classifier. The proposed method is composed of four stages. In preprocessing stage, the ECG signal is filtered and proportionally segmented. Afterwards, heartbeats are divided into three regions and region features are extracted. Subsequently, the dimension of features is reduced and all the features are fused and normalized. Eventually, an ensemble classifier is employed for the classification of Normal (N), Left Bundle Branch Block (LBBB), Right Bundle Branch Block (RBBB), Atrial Premature Contraction (APC) and Ventricular Premature Contraction (VPC). The method was applied to a new dataset divided from MIT-BIH arrhythmia database. The obtained sensitivities for Normal, LBBB, RBBB, APV and VPC were 95.0%, 27.9%, 79.6%, 81.8% and 88.1%. A comparative experiment demonstrated that the proposed region feature extraction method improves the accuracy of arrhythmia classification. The new division of MIT-BIH arrhythmia database is also advised to other researchers.

The B2 structure based MIL composites was fabricated by a two-step processing: the stacked Al and Fe foils were firstly hot pressed under eutectic reaction to form the Al-rich intermetallic phase(Fe2Al5) layer by consuming all the Al foils. And then, for forming the Fe-rich intermetallic phase (FeAl with B2 structure), three kinds of experiments were carried out to transfer the Al-rich phase layer to B2 structure: annealing at eutectic temperature for a long time; hot pressing or Spark plasma sintering (SPS) at higher temperature (1000 °C). The EDS, EBSD, XRD, micro-hardness tests and quasi-static compression are applied to study microstructure evolution, phase transformation and identification during fabricating the B2 structure based MIL composites. Mechanical properties of the B2 structure based MIL composites has proved the reduction of the stress concentration on the interface.

In this paper, the Co/Al2O3 catalyst was prepared by incipient wetness impregnation method, and different post treatment methods were used to promote its dehydrogenation properties. Interestingly, we found that Co/Al2O3 catalysts with different post treatment protocols exhibited totally different catalytic behaviors in propane dehydrogenation. Fresh catalyst showed an induction period and was highly active for pyrolysis and coking at 10–30 min of reaction. The pre-reduction led to complete pyrolysis and coking at the beginning of reaction. However, the re-oxidation treatment gave a high selectivity (∼93.0%) to propylene at the whole process. XRD, H2-TPR, XPS, TEM and hydrogen chemisorption investigations showed that the post treatment has a great impact on the state of cobalt species and the performance of propane dehydrogenation over Co/Al2O3 catalysts. Specifically, the poorly dispersed metal Co led to pyrolysis and coking, while highly dispersed metal Co were responsible for the dehydrogenation of propane. The large Co3O4 particles (DFresh = 33.68 nm) result in the large metal Co grains (DPre-reduced = 24.90 nm) after the reduction or reaction process. While during the re-oxidization process, the surface metal Co was re-oxidized in a mild environment and got re-dispersion (DRe-oxidized = 6.07 nm). And the surface cobalt oxides layer is more readily to be reduced to metal Co during the reaction thus leading to the shortened induction period.

Pure nickel and Nickel Alloy-X based Metallic-Intermetallic Laminate (MIL) composites were fabricated and investigated for their microstructure evolution, growth kinetics and microhardness distribution across the intermetallic/metal interfaces. Multi-phase layer structure with parabolic growth kinetics is shown in the nickel-based MIL composites. A two-phase eutectic layer along with a uniform layer form in the Alloy-X based MIL composites, which shows a mixed growth kinetic mechanism. The microhardness distribution across the intermetallic/metal interface of the two MIL composites was investigate with respect to the effects of texture and microstructure of the intermetallic phases. A simple intermetallic growth model is developed and validated for predicting the phase formation in binary or ternary reactions for synthesis of these MIL composites.

Different with Wang et. al.’s study, we found that polymeric Si–O–Sn 2+ rather than Ni-Sn alloy and metallic Sn are active species in silica-supported tin oxide catalysts for dehydrogenation of propane. The results showed that high surface area of mesoporous silica brought about high dispersion of tin oxide species, as a result, catalytic activity and stability were both improved. DRUV–vis, XPS, TPR and XRD studies of fresh and reduced catalysts indicated that the deactivation was related to the reduction of active species rather than the coke formation since active tin species cannot maintain its oxidation state at reaction conditions (high temperature and reducing atmosphere). The formed Ni 3 Sn 2 alloy after reduction just functioned as promoter which accelerated the desorption of H 2 and regeneration of active site. A synergy effect between active tin species and Ni 3 Sn 2 alloy were observed.

Single-phase intermetallic FeAl layered material is synthesized using a layered foil approach to study the fracture mechanisms of FeAl-based metallic-intermetallic laminate (MIL) composites containing a similarly fabricated structure. The mechanical properties and crack evolution of the single-phase FeAl are investigated via incremental compression testing. Microstructure and composition assessment confirm a similar intermetallic layer laminate microstructure of single-phase FeAl and FeAl-based MIL composites. When compressed perpendicular to the layers, both materials fail by the axial splitting of the FeAl phase along the loading direction. Mesoscale hetero-deformation induced (HDI) stress, which is tensile on the FeAl layers of MIL composites, accelerates crack nucleation and crack propagation, eventually inducing failure. The HDI stress evaluated via finite element analysis (FEA) simulation provides an explanation for the difference between 430SS-FeAl and 304SS-FeAl MIL composites, which posses similar microstructure and composition, but very different strengths. When compressed parallel to the layers, mesoscale HDI stress is expected to be negligible, whereas the geometrically necessary dislocation (GND) pile-up induced HDI stress can enhance the performance of the composites. Fracture toughness is characterized via four-point bend testing, and the results demonstrate improvement of the FeAl-based MIL composites over the single-phase FeAl material.

Liquid natural gas and liquid hydrogen are promising and economical clean energy sources for reducing CO2 emissions and slowing global warming. Characterization and monitoring of the vacuum pressure inside tank containers with multilayer insulation (MLI) are essential for the safe storage and convenient transportation of these cryogenic fuels. Herein, a new method for characterizing the vacuum pressure of tank containers with MLI is proposed. A theoretical analysis revealed that the temperature of the outer surface of the MLI material (To) is a good indicator of the vacuum pressure inside the tanks. Experimental verification was conducted using an MLI performance-testing apparatus, To was measured under 10 different vacuum pressures. The results showed that when the vacuum pressure was 1 Pa, To decreased sharply with the increase of vacuum pressure. The mechanism of the proposed method was also discussed based on the thermal analysis of the experimental system at different vacuum pressures. This study provides a simple and reliable method for vacuum pressure monitoring of tank containers with MLI, which allows the large-scale and safe utilization of clean energy with a low boiling temperature.

BiOX/NaBiO3 (X = Cl, Br, I) heterostructures were synthesized by a simple chemical etching method using haloid acid as etching agents to react with NaBiO3. Several characterization tools including X-ray powder diffraction (XRD), scanning electron microscope (SEM) and UV–vis diffuse reflectance spectra (UV–vis DRS) were employed for structural and composition analyses of the samples. The as-prepared heterogeneous samples exhibited more efficient photocatalytic activities than pure NaBiO3 and BiOX (X = Cl, Br, I) for the degradation of Rhodamine B (RhB) under visible light (or UV light) irradiation, which could be attributed to the formation of the p–n junction between p-BiOX (X = Cl, Br, I) and n-NaBiO3, which effectively suppresses the recombination of photo-generated electron-hole pairs. Terephthalic acid photoluminescence (TA-PL) probing test and trapping agents experiments demonstrated that OH (or h+) was the dominant reactive species depend on the different band gap structure of the p–n heterojunctions. Possible transfer processes of photo-generated charge carriers were proposed based on the band structures of BiOX/NaBiO3 (X = Cl, Br, I) and the experimental results.

With the rapid development of infrared material and the serious threat of global warming and ozonosphere depletion, Stirling-type pulse tube refrigerators (PTRs) attract much attention for High Operation Temperature (HOT) infrared detectors cooling and refrigeration near ambient temperature as the advantages of oil lubrication free, compact structure, low vibration, high reliability and long life by eliminating moving parts at the cold end. A high efficiency Stirling-type PTR working above 200 K based on a detailed, time-saving hybrid design process is designed, fabricated and tested. A no-load cooling temperature of 99.8 K and a net cooling power of 181.3 W at 233 K are obtained with an input power of 500 W. The second law efficiency at 233 K and 154 K are 10.4% and 14.24% respectively, and the efficiency is about 50% higher than the conventional prediction of the PTRs at that temperature zone. The experimental results agree with the simulation well. The energy flows and losses in the PTR, the impedance matching between cold finger and compressor are discussed in detail. Numerical simulation indicates that the cooling power of the PTR will increase 30% when warm displacer is adopted as phase shifter. This work is a meaningful attempt to extend the working region of PTRs from cryogenic ( 200 K).

When fabricating Metal-Intermetallic Laminate (MIL) composites by hot pressing alternately stacked Al and Fe-based foils, the oxides on the surface of the sheets will affect the nucleation and growth kinetics of the intermetallic phases. The influence of the oxide surface layers on phase formation, growth kinetics and morphology of the intermetallic layer was studied by tracking the evolution of the initial oxide layer during interfacial reaction processing. The dominant intermetallic phase formed in the pure Fe/Al reaction was Fe2Al5 phase which preferentially grew along the dense packed direction of its unit cell ([001] direction in c-axis). In the early reaction stage, the morphology of aluminide growth is planar due to primarily two-dimensional diffusion. In the later stage of reaction, three-dimensional diffusion causes anisotropic growth of intermetallic layer with tongue-like morphology. The presence of the oxide layer also increases the growth rate of Kirkendall voids in the intermetallic phase.

Background and objective Atrial fibrillation (AF) is a type of arrhythmia with high incidence. Automatic AF detection methods have been studied in previous works. However, a model cannot be used all the time without any improvement. And updating model requires adequate data and cost. Therefore, this study aims at finding a low-cost way to choose learning samples and developing an incremental learning system for AF detection. Methods Based on transfer learning and active learning, this paper proposed a loop-locked framework integrating AF diagnose, label query, and model fine-tuning. In the pre-training stage, a novel multiple-input deep neural network (MIDNN) is pre-trained using labeled samples from an original training set. In practical application, the model can be used for AF detection. Meanwhile, continuous data is collected to form the candidate set. In the incremental learning stage, the model was fine-tuned continuously by the most informative samples in the candidate set. These samples are selected from the candidate set based on the pre-trained model and a new active learning strategy. The strategy combines the features and the uncertainty of the predicted results. Results In order to evaluate the method, the MIT-BIH atrial fibrillation database was used for pre-training and samples of the MIT-BIH arrhythmia database were taken as candidate set. The initial values of Acc, Sen, and PPV were 87.40%, 97.46%, and 81.11%. These indexes reached to the top values of 97.53%, 100.00%, and 95.29% after 14 iterations. Hence, the number of queries was saved by 90.67%. Conclusions The proposed system is able to update the model continuously and reduce the labeling cost over 90%. The comparisons demonstrated the effectiveness of MIDNN model and the suitability of novel learning strategy for AF. Moreover, this framework can be extended to other biomedical applications.

As an important arrhythmia detection method, the electrocardiogram (ECG) can directly reflect abnormalities in cardiac physiological activity. In view of the difficulty in the diagnosis of arrhythmia in different people, automatic arrhythmia detection methods have been studied in previous works. In this paper, we present a dual fully-connected neural network model for accurate classification of heartbeats. Our method is following the AAMI inter-patient standard, which includes normal beats (N), supraventricular ectopic beats (S), ventricular ectopic beats (V), fusion beats (F), and unknown beats (Q). Firstly, a total of 105 features are extracted from the preprocessed signals. Then, a two-layer classifier is introduced in the classification stage. Each layer contains two independent fully-connected neural networks, and the threshold criterion is also added in the second layer. For verification, both the MIT arrhythmia database (MITDB) and the MIT supraventricular arrhythmia database (SVDB) were adopted. The experiments demonstrate that the proposed method has high performance for arrhythmia detection. It also achieves high sensitivity for class S and V, which can easily detect potentially abnormal heartbeats. Furthermore, the proposed method can interfere with the classification effect for a certain disease and have more advantages in dataset size when comparing a convolutional neural network (CNN). Once properly trained, the proposed method can be employed as a tool to automatically detect arrhythmia from ECG.

Given the high cost and environmental problems of Pt and Cr2O3-based catalysts in current dehydrogenation technologies, the cost-effective and environment-friendly Sn/SiO2 catalyst, exhibiting comparable dehydrogenation performance to PtSn-based catalyst, provides an outstanding alternative for catalytic dehydrogenation of propane. Sn is demonstrated to play a leading role in dehydrogenation as a highly active component, profoundly updating people’s conventional understanding that Sn was only a promoter. Further, to address the deactivation problem of Sn/SiO2 catalyst due to coke deposition and mobility of Sn species during a long-term run, Pd has been introduced into the catalyst and its effect has been validated.

Tin oxide supported on silica (SnO2/SiO2) were prepared by incipient-wetness impregnation method and examined for propane dehydrogenation at 600 °C. The physicochemical properties of SnO2/SiO2 were characterized by N2-physisorption, XRD, UV–vis-DRS and H2-TPR. The results indicate that, at Sn loading ≤ 1.78 wt%, SiO2 contains a uniform distribution of Sn as isolated species in tetrahedral coordination, while crystalline SnO2 together with isolated Sn species are found for the higher Sn loadings. The reducibility of various Sn species was studied by a combination of XPS, H2-TPR, and reduction-reoxidation-TPR techniques. The results reveal that after high-temperature H2 reduction, crystalline SnO2 is fully reduced to metallic Sn, whereas isolated Sn are stabilized in the Sn2+ state with high dispersion due to a strong interaction between isolated Sn and support. Catalytic activity tests showed that these Sn2+ species exhibits both high activity and stability for propane dehydrogenation.

Three conventional complexing agents, including lactic acid, citric acid and EDTA, are applied in the electrodeposition of microcrystalline cuprous oxide (Cu2O) film on indium tin oxide glass substrate. Both scanning electron microscopy and X-ray diffraction have been performed to characterize the morphology and texture of microcrystalline Cu2O film. It is found that the stability constant of copper-based complex compound can obviously influence the deposition overpotential of Cu2O, and the overpotential can significantly alter the growth priority of different planes, which results in oriented growth of Cu2O grains. The quantitative relationships between the stability constant and the deposition overpotential of different complexing agents, as well as the relationship between the overpotential and the formation energy of microcrystalline cuprous oxide's (1 1 0), (1 1 1) and (2 0 0) planes are calculated, respectively.

Menin is a tumor suppressor that is mutated in patients with multiple endocrine neoplasia type I (MEN1), an inherited tumor-prone syndrome. Since there is no obvious conserved structural domain in menin that suggests a function, little is known as to how menin suppresses tumorigenisis. Although menin interacts with a variety of nuclear proteins including transcription factors, it is unknown whether menin itself can directly bind DNA. Here we show that menin directly binds to double stranded DNA in a sequence-independent manner. It also binds a variety of DNA structures, including Y-structures, branched structures, and 4-way junction structures. The C-terminus of menin mediates binding to DNA, but MEN1 disease-derived mutations in the C-terminus abolish the ability of menin to bind DNA. Importantly, these MEN1 disease-related menin mutants also fail to repress cell proliferation as well as cell cycle progression at G2/M phase. Furthermore, detailed mutagenesis studies indicate that positively charged residues in two nuclear localization signals mediate direct DNA binding as well as repression of cell proliferation. Collectively, these results demonstrate, for the first time, a novel biochemical activity of menin, binding to DNA, and link its DNA binding to the regulation of cell proliferation.