Anomalies of upper critical field in the spinel superconductor LiTi2_2O4−δ_{4-\delta}

High-field electrical transport and point-contact tunneling spectroscopy were used to investigate superconducting properties of the unique spinel oxide, LiTi$_2$O$_{4-\delta}$ films with various oxygen content. We find that the upper critical field $B_\mathrm{c2}$ gradually increases as more oxygen impurities are brought into the samples by carefully tuning the deposition atmosphere. It is striking that although the superconducting transition temperature and energy gap are almost unchanged, an astonishing isotropic $B_\mathrm{c2}$ up to $\sim$ 26 Tesla is observed in oxygen-rich sample, which is doubled compared to the anoxic sample and breaks the Pauli limit. Such anomalies of $B_\mathrm{c2}$ were rarely reported in other three dimensional superconductors. Combined with all the anomalies, three dimensional spin-orbit interaction induced by tiny oxygen impurities is naturally proposed to account for the remarkable enhancement of $B_\mathrm{c2}$ in oxygen-rich LiTi$_2$O$_{4-\delta}$ films. Such mechanism could be general and therefore provides ideas for optimizing practical superconductors with higher $B_\mathrm{c2}$

Anomalies of upper critical field in the spinel superconductor LiTi2 O4-δ

© 2019 American Physical Society. High-field electrical transport and point-contact tunneling spectroscopy are used to investigate superconducting properties of spinel oxide LiTi2O4-δ films with various oxygen contents. It is striking that although the superconducting transition temperature and energy gap are almost unchanged, an isotropic upper critical field Bc2 up to 26.0 T is observed in the oxygen-rich sample, which is more than twice the Bc2 of 11.3 T in the anoxic one. The change of the dominating pair-breaking mechanism from the orbital effect to the spin flip at Bc2 is achieved by tuning oxygen contents, which can be explained by the appearance of small Fermi pockets due to extra oxygen. Our paper provides deep understanding of the intrinsic relation between Bc2 and the complex Fermi surface, and contributes a promising way to enhance Bc2 for practical superconductors

Developing competitive advantages in political risk management for international construction enterprises

International construction projects invariably involve political risks. This has been a persistent and pernicious problem encountered by international contractors. Various sets of variables have been suggested in the literature focusing on different aspects of political risk management (PRM) for international construction enterprises (ICEs). It is crucial to identify the relative importance and groupings of these variables. This paper aims to identify critical variables associated with PRM in international construction projects, and to analyze their rankings and underlying relationships. A total of 17 variables were identified through a literature review and consolidated by pilot studies with professionals in the international construction industry. Questionnaire instruments containing the 17 variables were sent out to the practitioners and academics, and 138 completed questionnaires were received. The top five ranked variables for PRM were (1) relationship with governments, (2) misconduct of contractors, (3) experiential knowledge of political risks, (4) relations with power groups, and (5) localization. Factor analysis was used as the data reduction tool and these 17 variables were further grouped into four resource dimensions, as follows: (1) relations, experience, acceptance, and localization; (2) recourse, organization, operation, and technology; (3) growth, ownership, leverage, and diversification; and (4) sustainability, opportunity, integration, and long-term. A management framework with both theoretical and practical meanings was finally developed for successful PRM in international construction projects. The findings would help the ICEs to clarify the highly prioritized variables and underlying factors which could be used as an assessment tool to evaluate the performance of PRM. Successful PRM would provide competitive advantages for the ICEs to survive and prosper in the host construction market, especially in those locations characterized by highly political risks

Entry mode taxonomy and choice of Chinese international construction companies

Along with China’s national strategy “One Belt, One Road,” an increasing number of Chinese construction companies has ventured or will venture into the global market. The choice of entry mode is crucial for companies when going abroad. The objectives of this study are to (1) establish a systematic classification of the entry modes used in the international engineering field, and (2) identify and analyze the factors that influence the entry-mode choices of Chinese international construction companies (ICCs). Based on a literature review and a survey of 264 cases, a two-dimensional (2D) taxonomy model of the entry modes was established, and six factors significantly impact the choice of entry mode for Chinese ICCs were identified. The findings may help Chinese ICCs learn more about the choices available to them, the factors that influence these choices, and the way these factors influence their choices when venturing abroad

Preparation of open-cell alumina ceramic foam with uniform cell structure using plant seed template

Open-cell Al O ceramic foams with uniform cell structures and dense cell struts were fabricated by centrifugal slip casting using the plant seeds as the templates. The rheological characteristic of Al O slurries with up to 50 vol.% solid content was investigated. The shrinkage matching between the Al O green compact and the plant seeds during drying was studied. The effect of solid contents of slurries on change of green density of cell struts along the height of compacts was analyzed. The drying and sintering schedule of Al O green cakes were studied. The results indicated mass segregation of Al O particles with different sizes during centrifugal process was negligible for slurries with high solid loadings with 50 vol. %. The cell struts of green bodies had high density of 63.8% TD. After sintered at 1500 °C for 2 h, the final products had dense cell struts with high sintered density of 98.9%TD and homogeneous microstructure. The porosity and compressive strength ofsintered products was 66.5% and 5.26 MPa, respectively

Crack initiation and propagation behaviour under high-temperature very-high-cycle fatigue: Directionally solidified columnar-grained vs. single-crystal superalloys

Role of oxidation and recrystallisation on very-high-cycle fatigue of columnar-grained DZ125 and single-crystal DD6 superalloys are investigated. With the temperature increase from 850 to 1000 °C for DZ125 while from 1000 to 1100 °C for DD6, the Mode-I cracking tendency increases due to internal oxide penetration. Recrystallisation can occur for both the electrolytically and mechanically polished surface conditions, controlled primarily by temperature and test duration. Its presence can lead to strain localisation at subsurface, but the surface recrystallisation does not necessarily determine the oxide penetration. By comparison with the single-crystal DD6 that shows the pure Stage I at 1000 °C, the columnar-grained DZ125 exhibits the distinctive Stage I cracking followed by Mode I propagation. This fracture characteristics in DZ125 can be attributed to the combined effect of the high-angle grain boundaries and far-field stress. The microstructure-related factor plays a vital role when the crack length is small, whereas the role of stress becomes predominant when the crack length is comparable to a couple of grains, ultimately leading to the shift from the crystallographic Stage I to Mode I propagation

Modeling and analysis of compressive properties of porous NiTi shape memory alloy using artificial neural network

Artificial neural network (ANN) is an intriguing data processing technique. Over the last decade, it was applied widely in the chemistry field, but there were few applications in the porous NiTi shape memory alloy (SMA). In this paper, 32 sets of samples from thermal explosion experiments were used to build a three-layer BP (back propagation) neural network model. According to the registered BP model, the effect of process parameters including heating rate (v), green density(D) and particle size of Ti ( d ) on compressive properties of reacted products including ultimate compressive strength (σ ) and ultimate compressive strain (ε ) was analyzed. The predicted results agree with the actual data within reasonable experimental error, which shows that the BP model is a practically very useful tool in the properties analysis and process parameters design of the porous NiTi SMA prepared by thermal explosion method

Transition from internal to surface crack initiation of a single-crystal superalloy in the very-high-cycle fatigue regime at 1100 °C

Transition from internal to surface crack initiation is controlled by oxidation assisted fatigue-crack process in the very-high-cycle fatigue regime. Between 760 and 1000 °C, single crack initiation site is associated with internal casting defect, followed by a crystallographic Stage I propagation. By contrast, multiple surface crack initiation sites appear at 1100 °C, as the consequence of internal oxide penetration. The fatal crack follows a Mode I propagation and oxygen can diffuse into the material along the crack path. γ′-phase depletion appears surrounding the oxidised and cracked regions, while localised rafting can occur close to the crack tip

GMRE-iUnet: Isomorphic Unet Fusion Model for PET and CT Lung Tumor Images

Lung tumor PET and CT image fusion is a key technology in clinical diagnosis. However, the existing fusion methods are difficult to obtain fused images with high contrast, prominent morphological features, and accurate spatial localization. In this paper, an isomorphic Unet fusion model (GMRE-iUnet) for lung tumor PET and CT images is proposed to address the above problems. The main idea of this network is as following: Firstly, this paper constructs an isomorphic Unet fusion network, which contains two independent multiscale dual encoders Unet, it can capture the features of the lesion region, spatial localization, and enrich the morphological information. Secondly, a Hybrid CNN-Transformer feature extraction module (HCTrans) is constructed to effectively integrate local lesion features and global contextual information. In addition, the residual axial attention feature compensation module (RAAFC) is embedded into the Unet to capture fine-grained information as compensation features, which makes the model focus on local connections in neighboring pixels. Thirdly, a hybrid attentional feature fusion module (HAFF) is designed for multiscale feature information fusion, it aggregates edge information and detail representations using local entropy and Gaussian filtering. Finally, the experiment results on the multimodal lung tumor medical image dataset show that the model in this paper can achieve excellent fusion performance compared with other eight fusion models. In CT mediastinal window images and PET images comparison experiment, AG, EI, QAB/F, SF, SD, and IE indexes are improved by 16.19%, 26%, 3.81%, 1.65%, 3.91% and 8.01%, respectively. GMRE-iUnet can highlight the information and morphological features of the lesion areas and provide practical help for the aided diagnosis of lung tumors. </p

Receive Quadrature Reflecting Modulation for RIS-Empowered Wireless Communications

In this paper, we propose a novel reconfigurable intelligent surface (RIS)-based modulation scheme, named RIS-aided receive quadrature reflecting modulation (RIS-RQRM), by resorting to the concept of spatial modulation. In RIS-RQRM, the whole RIS is virtually partitioned into two halves to create signals with only in-phase (I-) and quadrature (Q-) components, respectively, and each half forms a beam to a receive antenna whose index carries the bit information. Furthermore, we design a low-complexity and non-coherent detector for RIS-RQRM, which measures the maximum power and polarities of the I- and Q- components of the received signals. Approximate bit error rate (BER) expressions are derived for RIS-RQRM over Rician fading channels. Simulation results show that RIS-RQRM outperforms the existing counterpart without I/Q index modulation in terms of BER in the low signal-to-noise ratio region