Experimental Study on Hybrid Organic Phase Change Materials Used for Solar Energy Storage

The solar energy utilization in built environment has been limited due to its low heat flux, uneven distribution in time and space and temporal difference in day and night. The phase change materials have been used to collect the fluctuant solar energy to form a stable energy source for the terminal equipment of the buildings. In this study, the hybrid organic phase change materials was prepared for the capillary radiant heating system which formed a cascade utilization of solar energy. Firstly, lauric acid and stearic acid were selected as the basic organic phase change materials and the binary equilibrium phase diagram was completed based on the method of step cooling curve according to the experimental tests data. The results showed that the phase transition temperature of the mixed acid at the lowest eutectic point was 31.2℃ and the latent heat value was 264.3 kJ/kg when the mass mixing ratio was 70% for lauric acid and 30% for stearic acid. Secondly, the expanded graphite was used as an additive to enwrap the mixed acid and enhance the heat conductivity. The experimental results showed that when the mass proportion of expanded graphite in the mixed acid was 10%, the mixed acid could be completely enclosed by expanded graphite and the stability of melting and solidification was optimal. Additionally, the phase transition temperature of the hybrid phase change material was 31.5℃ and the latent heat value was 217.4 kJ/kg. The novel hybrid phase change material has a lower eutectic point and a higher latent heat of phase change, so it has a large application space and is quite suitable for the cascade utilization of solar energy with capillary network heating system.     

Cross-linked polyvinyl amidoxime fiber: a highly selective and recyclable adsorbent of gallium from Bayer liquor

Gallium, a scarce metal produced mainly from Bayer liquor, is widely used in semiconductors. Ion-exchange method is currently considered as the most effective method to recover gallium from Bayer liquor. In this article, fibrous amidoxime adsorbents are introduced to recover gallium from Bayer liquor. In addition, hydrazine cross-linked polyvinyl amidoxime (HPAO) fibers have been prepared. The structure of the as-prepared fibers was ascertained by FTIR, elemental analysis and weight gain rate. The adsorption kinetics, adsorption isotherm and recycling performance were investigated by batch method. Cross-linking duration was studied and it turned out to be an important factor to optimize the adsorption capacity and recycling performance. After 1.5 h cross-linking time, the fiber showed the highest gallium adsorption capacity of 14.83 mg/g in Bayer liquor. After 3 h cross-linking time, the fiber showed the best recycling performance, which retained 82.9% of the initial adsorption ability after four cycles. Adsorption capacity of vanadium was lower than 1 mg/g for all samples. HPAO displayed very fast adsorption kinetics with an equilibrium at 60 min. The EDS results confirmed the low extraction of aluminum and vanadium provided by HPAO fibers. The gallium-loaded fiber could be effectively eluted by acidified thiourea. With proper control of the cross-linking duration by hydrazine, HPAO fiber with high selectivity towards gallium, high adsorption capacity and good recycle performance could be obtained, which is promising for recovering gallium needed for industrial applications.     

Path Representation in Circuit Netlists Using Linear-Sized ZDDs with Optimal Variable Ordering

The efficient representation and manipulation of a large number of paths in a Directed Acyclic Graph (DAG) requires the usage of special data structures that may become of exponential size with respect to the size of the graph. Several methodologies targeting Electronic Design Automation problems such as timing analysis, physical design, verification and testing involve path representation and necessary manipulation. Previous works proposed an encoding using Zero-suppressed Binary Decision Diagrams (ZDDs), which has been shown experimentally to cope well when representing structural or logical paths in VLSI circuits. However, it is well known that the ordering of the variables in a ZDD highly affects its size and, therefore, the efficiency of the methodologies utilizing these data structures. In this work, we show that using a reverse topological order for the ZDD variables bounds the number of nodes in the ZDD representing structural paths to the number of edges in the DAG considered, hence, making the ZDD size linear to the DAG’s size. This result, supported here both theoretically and experimentally, is very important as it can render methodologies with questionable scalability applicable to larger industrial designs. We demonstrate the applicability of the proposed variable ordering in one such methodology which utilizes ZDDs to grade the Path Delay Fault coverage of a given test set.     

Robust Encryption

We provide a provable-security treatment of “robust” encryption. Robustness means it is hard to produce a ciphertext that is valid for two different users. Robustness makes explicit a property that has been implicitly assumed in the past. We argue that it is an essential conjunct of anonymous encryption. We show that natural anonymity-preserving ways to achieve it, such as adding recipient identification information before encrypting, fail. We provide transforms that do achieve it, efficiently and provably. We assess the robustness of specific encryption schemes in the literature, providing simple patches for some that lack the property. We explain that robustness of the underlying anonymous IBE scheme is essential for public-key encryption with keyword search (PEKS) to be consistent (meaning, not have false positives), and our work provides the first generic conversions of anonymous IBE schemes to consistent (and secure) PEKS schemes. Overall, our work enables safer and simpler use of encryption.     

A minimum projected-distance test for parametric single-index Berkson models

In this paper, we propose a minimum projected-distance test for parametric single-index regression models when the predictors are measured with Berkson errors. This test asymptotically behaves like a locally smoothing test as if the null model were with one-dimensional predictor, and is omnibus to detect all global alternative models. The test can also detect local alternative models that converge to the null model at the fastest rate that the existing locally smoothing tests with one-dimensional predictor can achieve. Therefore, the proposed test has potential for alleviating the curse of dimensionality in this field. We also give two bias-correction methods to center the test statistic. Numerical studies are conducted to examine the performance of the proposed test.     

Recent advances in finite element modeling of the human cervical spine

The human cervical spine is a complex structure that is the most frequently injured site among all spinal injuries. Therefore, understanding of the cervical spine injury and dysfunction, and also biomechanical response to external stimuli is important. Finite element (FE) modeling can help researchers to access the internal stresses and strains in the bones, ligaments and soft tissues more realistically, and it has been widely adopted for spine biomechanics research. Although in recent years numerous techniques have been developed, there are no recent literature reviews on FE models of the cervical spine. Our objective was to present recent advances in FE modeling of the human cervical spine in terms of component modeling, material properties, and validation procedures. Model applications and further development are also discussed. The integration of new technologies will allow us to generate more accurate and comprehensive model of the cervical spine, which can increase efficiency and model applicability. Finally, the FE modeling can help to facilitate diagnosis, treatment, and prevention technologies for cervical spine injuries.