Wide bandgap conjugated polymer donors based on alkyloxime substituted thiophene for organic solar cells

Remarkable progress has been made for non-fullerene based organic solar cells (OSCs), with a power conversion efficiency (PCE) of over 18% having been achieved. Conjugated polymer donors consisting of alternating donor and acceptor units can form complementary light absorption and suitable energy levels with non-fullerene acceptors. Thus, rational design and matching of the conjugated polymer donor with narrow bandgap non-fullerene acceptors (NFAs) is essential for breakthroughs in OSC performance. By incorporating the thiophene unit as a π bridge between the donor unit (BDT) and the acceptor unit (oxime substituted thiophene (TO)), a new wide bandgap polymer donor TTOT was designed, synthesized, and characterized. It exhibited wide optical bandgap of 1.98 eV, and the energy of the highest occupied molecular orbital (EHOMO) of TTOT was -5.33 eV. In addition, TTOT polymer neat film showed a high hole mobility of up to 3.36 × 10-3 cm2V-1s-1. By matching with the non-fullerene acceptor Y6, the as-cast TTOT-based OSC achieved a PCE of 7.65%, JSC of 23.58 mA/cm2, VOC of 0.62 V, and FF of 0.52. However, the incorporation of electron-donating thiophene spaces led to a rise in EHOMO to -5.33 eV, which resulted in the relatively low VOC of the OSCs. To further improve the VOC of TTOT-based OSC, a halogenation strategy was adopted to downshift the EHOMO of TTOT. Two new wide bandgap polymer donors TTOTF and TTOTCl were designed and synthesized by substituting BDT with fluorinated BDTTDFSn and chlorinated BDTTDClSn, respectively. Both polymers have wide optical bandgaps of over 1.97 eV, with EHOMO’s of -5.46 eV (TTOTF) and -5.48 eV (TTOTCl). Then Y6 was chosen as the acceptor to investigate the photovoltaic performance. The best TTOTF-based OSC device showed good device performance with a JSC of 27.61 mA/cm2, improved VOC of 0.72 V and FF of 0.69, resulting in an almost two-fold higher PCE of 13.57% when comparing with TTOT based OSCs. Furthermore, the optimized TTOTCl-based OSC device showed an even higher PCE of 14.91%, VOC of 0.70 V, FF of 0.68 and a record-high JSC of 31.03 mA/cm2 among non-fullerene OSCs. The largely increased FF and JSC are the results of the considerably improved SCLC hole mobility of TTOTF and TTOTCl in OSCs. In addition, the optimized TTOTF and TTOTCl-based OSC devices demonstrated excellent long-term air stability, retaining nearly 80% PCE after 2 months without encapsulation. Lastly, to further improve the device performance of TTOTCl-based OSCs, some future directions are proposed. The first approach is to match TTOTCl with non-fullerene acceptors that have higher EHOMO’s than Y6. As a result, the HOMO offset between donor and acceptor can be reduced, resulting in a lower energy loss and higher device performance. The second approach is to optimize TTOTCl-based OSC through incorporating LiTFSI as a hole transport enhancement layer. The OSCs with a thin LiTFSI layer achieved an excellent PCE of 15.96%, with an enhanced VOC of 0.72 V and FF of 0.71. Further investigations are needed to fully understand the effect and improve the film quality of the LiTFSI layer. This thesis demonstrated the use of thiophene π spacers with fluorine or chlorine substitutions are highly effective for reducing energy loss, enhancing charge carrier mobility, and improving film morphology in OSCs. In addition, the TO-based polymer TTOTCl is a very promising donor material for fabricating highly efficient and air stable OSCs

A Joint Replication-Migration-based Routing in Delay Tolerant Networks

Abstract—Delay tolerant networks (DTNs) use mobility-assisted routing, where nodes carry, store, and forward data to each other in order to overcome the intermittent connectivity and limited network capacity of this type of network. In this paper, we propose a routing protocol that includes two mechanisms: message replication and message migration. Each mechanism has two steps: message selection and node selection. In message repli-cation, we choose the smallest hop-count message to replicate. The hop-count threshold is used to control the replication speed. We propose a metric called 2-hop activity level to measure the relay node’s transmission capacity, which is used in node selection. Our protocol includes a novel message migration policy that is used to overcome the limited buffer space and bandwidth of DTN nodes. We validate our protocol via extensive simulation experiments; we use a combination of synthetic and real mobility traces. Index Terms—Buffer management, delay tolerant networks (DTNs), message migration, message replication, routing. I

A predictive scoring system for proximal junctional kyphosis after posterior internal fixation in elderly patients with chronic osteoporotic vertebral fracture: A single-center diagnostic study

ObjectiveTo establish a predictive scoring system for proximal junctional kyphosis (PJK) after posterior internal fixation in elderly patients with chronic osteoporotic vertebral fracture (COVF).Materials and methodsThe medical records of 88 patients who were diagnosed with COVF and underwent posterior internal fixation in our hospital from January 2013 to December 2017 were retrospectively analyzed. The included patients were divided into two groups according to whether they suffered PJK after surgery, namely, the PJK group (25 cases) and non-PJK group (63 cases). The following clinical characteristics were recorded and analyzed: age, gender, body mass index (BMI), bone mineral density (BMD), smoking history, fracture segment, proximal junction angle, sagittal vertebral axis, pelvic incidence (PI)–lumbar lordosis (LL), pelvic tilt (PT), sacral slope (SS), posterior ligamentous complex (PLC) injury, upper instrumented vertebra, lower instrumented vertebra, and the number of fixed segments. The prevalence of these clinical characteristics in the PJK group was evaluated, and the scoring system was established using logistic regression analysis. The performance of the scoring system was also prospectively validated.ResultsThe predictive scoring system was established based on five clinical characteristics confirmed as significant predictors of PJK, namely, age > 70 years, BMI > 28 kg/m2, BMD < −3.5 SD, preoperative PI-LL > 20°, and PLC injury. PJK showed a significantly higher score than non-PJK (7.80 points vs. 2.83 points, t=9.556, P<0.001), and the optimal cutoff value for the scoring system was 5 points. The sensitivity and specificity of the scoring system for predicting postoperative PJK were 80.00% and 88.89%, respectively, in the derivation set and 75.00% and 80.00% in the validation set.ConclusionThe predictive scoring system was confirmed with satisfactory sensitivity and specificity in predicting PJK after posterior internal fixation in elderly COVF patients. The risk of postoperative PJK in patients with a score of 6–11 is high, while the score of 0–5 is low

Can we early diagnose metabolic syndrome using brachial-ankle pulse wave velocity in community population

BACKGROUND: The prevalence of metabolic syndrome (MetS) increased recently and there was still not a screening index to predict MetS. The aim of this study was to estimate whether brachial-ankle pulse wave velocity (baPWV), a novel marker for systemic arterial stiffness, could predict MetS in Chinese community population. METHODS: A total of 2 191 participants were recruited and underwent medical examination including 1 455 men and 756 women from June 2011 to January 2012. MetS was diagnosed according to the criteria of the International Diabetes Federation (IDF). Multiple Logistic regressions were conducted to explore the risk factors of MetS. Receiver operating characteristic (ROC) curve was performed to estimate the ideal diagnostic cutoff point of baPWV to predict MetS. RESULTS: The mean age was (45.35+/-8.27) years old. In multiple Logistic regression analysis, the gender, baPWV and smoking status were risk factors to MetS after adjusting age, gender, baPWV, walk time and sleeping time. The prevalence of MetS was 17.48% in 30-year age population in Shanghai. There were significant differences (chi(2) = 96.46, P \u3c 0.05) between male and female participants on MetS prevalence. According to the ROC analyses, the ideal cutoff point of baPWV was 1 358.50 cm/s (AUC = 60.20%) to predict MetS among male group and 1 350.00 cm/s (AUC = 70.90%) among female group. CONCLUSION: BaPWV may be considered as a screening marker to predict MetS in community Chinese population and the diagnostic value of 1 350.00 cm/s was more significant for the female group

Atypical radio pulsations from magnetar SGR 1935+2154

Magnetars are neutron stars with extremely strong magnetic fields, frequently powering high-energy activity in X-rays. Pulsed radio emission following some X-ray outbursts have been detected, albeit its physical origin is unclear. It has long been speculated that the origin of magnetars' radio signals is different from those from canonical pulsars, although convincing evidence is still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and its associated Fast Radio Burst (FRB) 20200428, a radio pulsar phase was discovered. Here we report the discovery of X-ray spectral hardening associated with the emergence of periodic radio pulsations from SGR 1935+2154 and a detailed analysis of the properties of the radio pulses. The complex radio pulse morphology, which contains both narrow-band emission and frequency drifts, has not been seen before in other magnetars, but is similar to those of repeating FRBs - even though the luminosities are many orders of magnitude different. The observations suggest that radio emission originates from the outer magnetosphere of the magnetar, and the surface heating due to the bombardment of inward-going particles from the radio emission region is responsible for the observed X-ray spectral hardening.Comment: 47 pages, 11 figure

Deciphering the origin of the Cenozoic intracontinental rifting and volcanism in eastern China using integrated evidence from the Jianghan Basin

Intracontinental rifting and low-volume volcanism are a globally common phenomenon, yet the underlying driving mechanisms and whether they can be explained through classic plate tectonic concepts, remain hotly debated. A prominent example is the Cenozoic rift and volcanic province in eastern China. Using an integration of geological, geophysical and geochemical data, we unravel the spatial and temporal variations of the rifting and volcanism in the Jianghan Basin. Both rifting and volcanism in the Jianghan Basin show two intense-to-weak cycles (65–50 Ma and 50–26 Ma, respectively) with significant enhancement in activity during the late rift phase. Moreover, rifting and depocentres progressively migrated eastward. The Jianghan basalts all share an asthenospheric origin while the source of the late phase basalts is slightly more enriched and heterogenous in Nd-Hf isotopes than that of the early phase basalts. The late phase basalts also display a smaller extent of partial melting even under a thinner lithosphere, likely indicating a significant decrease of volatile content in the mantle source. Based on regional tectonic correlations, the main stages of tectonic evolution of the Jianghan Basin and eastern China are not synchronous with changes in Pacific plate motion, while they are coincident with India-Asia collision processes. These observations lead us to propose that the asthenospheric flow driven by India-Asia collision rather than the rollback of the subducted Pacific slab has caused the widespread rifting and volcanism in eastern China. The variations of rifting and volcanism in the Jianghan Basin suggest a multiphase and eastward asthenospheric flow beneath eastern China driven by India-Asia collision, with an intense upwelling when passing through the North-South Gravity Lineament (NSGL). The much more intense rifting and volcanism during the late rift phase may indicate a much larger scale of volatile-poor asthenospheric flow than the early rift phase which could result in a more intense erosion of ancient enriched lithospheric mantle and the volatile content in the mantle source dropping sharply. This study provides an improved model based on our multidisciplinary observations for asthenospheric flow which may be an alternative driving mechanism for intracontinental rifting and low-volume volcanism in the regions where there are step changes in lithospheric thickness globally

Fast and Effective Image Segmentation via Superpixels and Adaptive Thresholding

This paper proposes a fast and effective image segmentation algorithm by firstly clustering image pixels into a small number of superpixels and then merging these superpixels whose distances are below an adaptive threshold together to get the final segmented fields. The adoption of superpixels dramatically decreases the computation cost, while the adaptive thresholding aims to select a reasonable segmentation from a set of possible segmentations with hierarchical scales. The adaptive threshold can be calculated with a fast sequential procedure. Experiments on Berkeley Segmentation Data Set (BSDS500) demonstrate that our proposed algorithm is competitive to other state-of-the-art segmentation methods. Moreover, this segmentation framework can be improved to excellent performance by using more elaborate superpixel algorithms.EICPCI-S(ISTP)