A Two-Sided Quaternion Higher-Order Singular Value Decomposition

Higher-order singular value decomposition (HOSVD) is one of the most celebrated tensor decompositions that generalizes matrix SVD to higher-order tensors. It was recently extended to the quaternion domain \cite{miao2023quat} (we refer to it as L-QHOSVD in this work). However, due to the non-commutativity of quaternion multiplications, L-QHOSVD is not consistent with matrix SVD when the order of the quaternion tensor reduces to $2$; moreover, theoretical guaranteed truncated L-QHOSVD was not investigated. To derive a more natural higher-order generalization of the quaternion matrix SVD, we first utilize the feature that left and right multiplications of quaternions are inconsistent to define left and right quaternion tensor unfoldings and left and right mode-$k$ products. Then, by using these basic tools, we propose a two-sided quaternion higher-order singular value decomposition (TS-QHOSVD). TS-QHOSVD has the following two main features: 1) it computes two factor matrices at a time from SVDs of left and right unfoldings, inheriting certain parallel properties of the original HOSVD; 2) it is consistent with matrix SVD when the order of the tensor is $2$. In addition, we study truncated TS-QHOSVD and establish its error bound measured by the tail energy; correspondingly, we also present truncated L-QHOSVD and its error bound. Deriving the error bounds is nontrivial, as the proofs are more complicated than their real counterparts, again due to the non-commutativity of quaternion multiplications. %Numerical experiments on synthetic and color video data show the efficacy of the proposed TS-QHOSVD. Finally, we illustrate the derived properties of TS-QHOSVD and its efficacy via some numerical examples

Low-dissipation model of three-terminal refrigerator: performance bounds and comparative analyses

[EN]In the present paper, a general non-combined model of three-terminal refrigerator beyond specific heat transfer mechanisms is established based on the low-dissipation assumption. The relation between the optimized cooling power and the corresponding coefficient of performance (COP) is analytically derived, according to which the COP at maximum cooling power (CMP) can be further determined. At two dissipation asymmetry limits, upper and lower bounds of CMP are obtained and found to be in good agreement with experimental and simulated results. Additionally, comparison of the obtained bounds with previous combined model is presented. In particular it is found that the upper bounds are the same, whereas the lower bounds are quite different. This feature indicates that the claimed universal equivalence for the combined and non-combined models under endoreversible assumption is invalid within the frame of low-dissipation assumption. Then, the equivalence between various finite-time thermodynamic models needs to be reevaluated regarding multi-terminal systems. Moreover, the correlation between the combined and non-combined models is further revealed by the derivation of the equivalentJGA thanks financial support for a postdoctoral contract from University of Salamanca under Program I

A novel electrochemical system with adiabatic pre-charging and pre-discharging processes for efficient refrigeration

[EN]The extraordinary thermal-to-electricity conversion efficiency of thermally regenerative electrochemical cycle triggers interest in its reverse counterpart, namely thermally regenerative electrochemical refrigerator (TRER), a promising alternative to conventional cooling devices. Nevertheless, due to three fundamental obstacles, the practically feasible TRER model is still absent, which hinders the development of follow-up research. To break this bottleneck, heating by discharging and cooling by charging effects are innovatively utilized to construct TRER models where the electrochemical counterparts of traditional adiabatic compression and expansion processes, namely adiabatic pre-charging and pre-discharging processes, are proposed and introduced. Significantly, the maximum coefficient of performance (COP) and the COP at maximum cooling power are predicted to achieve up to 40% and 5% of Carnot COP, respectively for the given values of parameters. Moreover, the great potential for efficient refrigeration is highlighted by comparing the obtained results with various refrigeration systems. This work lays the foundation for further experimental investigations and opens a new avenue for constructing other novel electrochemical cycles

The equivalent low-dissipation combined cycle system and optimal analyses of a class of thermally driven heat pumps

[EN]The performance characteristics, operation, and design strategies of a class of thermally driven heat pumps are investigated due to their important roles in the efficient utilization of low-grade thermal energy. In order to establish a more generic thermodynamic model of thermally driven heat pumps mainly including absorption, adsorption, and ejector heat pumps, low-dissipation assumption is adopted. Accordingly, the associated dissipation parameters accounting for the specific information on the irreversibilities in each heat-transfer process are introduced rather than specifying heat-transfer law. Based on the proposed model, the theoretical results of the coefficient of performance and heat load are derived with regard to two key parameters denoting the size ratio of the two involved subsystems and the matching deviation from reversible limit. The performance characteristics and the optimally operating regions of the whole system are determined and the differences between thermally driven heat pump and refrigerator are highlighted. The proposed model and obtained results further develop the low-dissipation mode

Thermally driven refrigerators: Equivalent low-dissipation three-heat-source model and comparison with experimental and simulated results

[EN]In order to investigate the performance of a class of thermally driven refrigerators, usually driven by low-grade thermal energy, a generic thermodynamic model of three-heat-source refrigerator without involving any specific heat-transfer law is put forward by adopting low-dissipation assumptions. Based on the proposed model, the analytical expressions for the coefficient of performance (COP) and cooling power of the system are derived in terms of well-defined dissipation parameters and contact time durations between the system and heat reservoirs. One essential parameter accounting for the size ratio of the two coupled subsystems inside the overall system is introduced in light of the practical meaning of the reversible entropy change. With the help of the aforementioned parameter, the optimal relation between the COP and cooling power is obtained. The optimal operation region and optimal construction of the overall system are further determined for the first time. In addition, the influences of the dissipation and temporal symmetries are discussed in detail, according to which the upper and lower bounds of the COP at maximum cooling power are firstly obtained under two extreme situations. Experimental and simulated data from previous reported works are collected to illustrate the validity and practical significance of the proposed model and associated results. A limit case is presented to highlight the generality of the model.National Natural Science Foundation of China ; Junta de Castilla y León of Spain ; University of Salamanca contract 2017/X005/1

Interface-engineered ferroelectricity of epitaxial Hf\u3csub\u3e0.5\u3c/sub\u3eZr\u3csub\u3e0.5\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e thin films

Ferroelectric hafnia-based thin films have attracted intense attention due to their compatibility with complementary metal-oxide-semiconductor technology. However, the ferroelectric orthorhombic phase is thermodynamically metastable. Various efforts have been made to stabilize the ferroelectric orthorhombic phase of hafnia-based films such as controlling the growth kinetics and mechanical confinement. Here, we demonstrate a key interface engineering strategy to stabilize and enhance the ferroelectric orthorhombic phase of the Hf0.5Zr0.5O2 thin film by deliberately controlling the termination of the bottom La0.67Sr0.33MnO3 layer. We find that the Hf0.5Zr0.5O2 films on the MnO2-terminated La0.67Sr0.33MnO3 have more ferroelectric orthorhombic phase than those on the LaSrO-terminated La0.67Sr0.33MnO3, while with no wake-up effect. Even though the Hf0.5Zr0.5O2 thickness is as thin as 1.5nm, the clear ferroelectric orthorhombic (111) orientation is observed on the MnO2 termination. Our transmission electron microscopy characterization and theoretical modelling reveal that reconstruction at the Hf0.5Zr0.5O2/ La0.67Sr0.33MnO3 interface and hole doping of the Hf0.5Zr0.5O2 layer resulting from theMnO2 interface termination are responsible for the stabilization of the metastable ferroelectric phase of Hf0.5Zr0.5O2. We anticipate that these results will inspire further studies of interface-engineered hafnia-based systems

Case Report: Recurrent Autoimmune Hypoglycemia Induced by Non-Hypoglycemic Medications

We present a case of recurrent autoimmune hypoglycemia induced by non-hypoglycemic agents. We review reported cases of autoimmune hypoglycemia related to non-hypoglycemic agents, and discuss the effects of different detection methods for insulin autoantibodies on the results obtained. We aim to provide information for clinicians and a warning for medication usage. Considering the increasing number of clopidogrel-induced AIH cases and the hypoglycemia-induced increase in the risk of cardiovascular events, we recommend that cardiovascular disease patients being treated with clopidogrel be informed of this rare side effect and that clinicians be vigilant for the possibility of autoimmune hypoglycemia in this patient population

Optimal forwarding ratio on dynamical networks with heterogeneous mobility

Since the discovery of non-Poisson statistics of human mobility trajectories, more attention has been paid to understand the role of these patterns in different dynamics. In this study, we first introduce the heterogeneous mobility of mobile agents into dynamical networks, and then investigate packet forwarding strategy on the heterogeneous dynamical networks. We find that the faster speed and the higher proportion of high-speed agents can enhance the network throughput and reduce the mean traveling time in random forwarding. A hierarchical structure in the dependence of high-speed is observed: the network throughput remains unchanged at small and large high-speed value. It is also interesting to find that a slightly preferential forwarding to high-speed agents can maximize the network capacity. Through theoretical analysis and numerical simulations, we show that the optimal forwarding ratio stems from the local structural heterogeneity of low-speed agents

Prediction of the Factors Influencing the Shengjing Classification of Portal Vein Thrombosis after Splenectomy for Portal Hypertension in Cirrhosis: A Single-Center Retrospective Case-Control Study

Objective. To compare the survival time of patients with portal vein thrombosis after splenectomy for portal hypertension in cirrhosis and explore the influencing factors of the Shengjing classification. Methods. Clinical data of 108 patients with portal vein thrombosis after splenectomy in the department of general surgery of our hospital from November 2011 to December 2018 were selected, and a retrospective analysis was performed. Results. Among 108 patients with postoperative PVST formation, 9 had type Ia, 32 type Ib, 39 type IIa, 20 type IIb, 5 type IIIa, 3 type IIIb, and 0 type IV. Survival analysis showed that the difference in survival time distribution among the Shengjing typing groups was statistically significant (P<0.05). The higher the classification level, the shorter the survival time and the higher the risk of death. The results of a single-factor analysis showed that there were statistically significant differences in the PVST Shengjing typing groups between the preoperative group with or without hepatitis, preoperative d-dimer level, and postoperative day 14 fibrinogen (FIB) level (P<0.05). Multivariate logistic regression analysis showed that the OR value of higher PVST Shengjing typing in patients with hepatitis was 4.634 times higher than that in patients without hepatitis (95% CI: 1.593-13.478, χ2=7.922, P=0.005<0.05). Preoperative d-dimer volume increased by 1 μg/L; the OR value of higher grade PVST Shengjing typing was 1.001 times higher (95% CI: 1.000-1.002) than that of lower grade PVST Shengjing typing (χ2=8.369, P=0.004<0.05). Conclusions. The survival time of patients with portal vein system thrombosis after splenectomy was significantly different among Shengjing typing groups, and the higher the classification level, the shorter the survival time and the higher the risk of death. In patients with portal hypertension in cirrhosis and PVST formation after splenectomy, if the preoperative d-dimer level is high or accompanied by hepatitis virus, the formation of PVST will involve a wide range, the disease is more serious, and the prognosis is also poor, so corresponding preventive measures should be taken to avoid the aggravation of PVST

Comparative Assessment of Various Low-Dissipation Combined Models for Three-Terminal Heat Pump Systems

Thermally driven heat pump systems play important roles in the utilization of low-grade thermal energy. In order to evaluate and compare the performances of three different constructions of thermally driven heat pump and heat transformer, the low-dissipation assumption has been adopted to establish the irreversible thermodynamic models of them in the present paper. By means of the proposed models, the heating loads, the coefficients of performance (COPs) and the optimal relations between them for various constructions are derived and discussed. The performances of different constructions are numerically assessed. More importantly, according to the results obtained, the upper and lower bounds of the COP at maximum heating load for different constructions are generated and compared by the introduction of a parameter measuring the deviation from the reversible limit of the system. Accordingly, the optimal constructions for the low-dissipation three-terminal heat pump and heat transformer are determined within the frame of low-dissipation assumption, respectively. The optimal constructions in accord with previous research and engineering practices for various three-terminal devices are obtained, which confirms the compatibility between the low-dissipation model and endoreversible model and highlights the validity of the application of low-dissipation model for multi-terminal thermodynamic devices. The proposed models and the significant results obtained enrich the theoretical thermodynamic model of thermally driven heat pump systems and may provide some useful guidelines for the design and operation of realistic thermally driven heat pump systems