Deep Fourier Ranking Quantization for Semi-Supervised Image Retrieval.

To reduce the extreme label dependence of supervised product quantization methods, the semi-supervised paradigm usually employs massive unlabeled data to assist in regularizing deep networks, thereby improving model performance. However, the existing method focuses on the overall distribution consistency between unlabeled data and class prototypes, while ignoring subtle individual variances between unlabeled instances. Therefore, the local neighborhood structure is not fully explored, which will cause the model to easily overfit in the training set. In this paper, we introduce a new Fourier perspective to alleviate this issue by exploring the semantic relations between unlabeled instances in a self-supervised manner. Specifically, based on Fourier Transform, we first design a Phase Mixing (PM) strategy, which can manipulate the mixing area and values of the phase component between two images to control the proportion of semantic information. In this way, we can construct multi-level similarity neighbors naturally for unlabeled data. Then, a ranking quantization loss is formulated to perceive multi-level semantic variances in neighbor instances, which improves the robustness and generalization of the model. Extensive experiments in three different semi-supervised settings show that our method outperforms existing state-of-the-art methods by averaged 3.95% improvement on four datasets.

3D Nanoscale Morphology Characterization of Ternary Organic Solar Cells.

It is highly desired to develop advanced characterization techniques to explore the 3D nanoscale morphology of the complicated blend film of ternary organic solar cells (OSCs). Here, ternary OSCs are constructed by incorporating the nonfullerene acceptor perylenediimide (PDI)-diketopyrrolopyrrole (DPP)-PDI and their morphology is characterized in depth to understand the performance variation. In particular, photoinduced force microscopy (PiFM) coupled with infrared laser spectroscopy is conducted to qualitatively study the distribution of donor and acceptors in the blend film by chemical identification and to quantitatively probe the segmentation of domains and the domain size distribution after PDI-DPP-PDI acceptor incorporation by PiFM imaging and data processing. In addition, the energy-filtered transmission electron microscopy with energy loss spectra is utilized to visualize the nanoscale morphology of ultrathin cross-sections in the configuration of the real ternary device for the first time in the field of photovoltaics. These measurements allow to "view" the surface and cross-sectional morphology and provide strong evidence that the PDI-DPP-PDI acceptor can suppress the aggregation of the fullerene molecules and generate the homogenous morphology with a higher-level of the molecularly mixed phase, which can prevent the charge recombination and stabilize the morphology of photoactive layer.

Synergistic Effect of Dielectric Property and Energy Transfer on Charge Separation in Non-Fullerene-Based Solar Cells.

In non-fullerene-based photovoltaic devices, it is unclear how excitons efficiently dissociate into charge carriers under small driving force. Here, we developed a modified method to estimate dielectric constants of PM6 donor and non-fullerene acceptors. Surprisingly, most non-fullerene acceptors and blend films showed higher dielectric constants. Moreover, they exhibited larger dielectric constants differences at the optical frequency. These results are likely bound to reduced exciton binding energy and bimolecular recombination. Besides, the overlap between the emission spectrum of donor and absorption spectra of non-fullerene acceptors allowed the energy transfer from donor to acceptors. Hence, based on the synergistic effect of dielectric property and energy transfer resulting in efficient charge separation, our finding paves an alternative path to elucidate the physical working mechanism in non-fullerene-based photovoltaic devices.

Dual Functionalization of Electron Transport Layer via Tailoring Molecular Structure for High-Performance Perovskite Light-Emitting Diodes.

Great progress in modification and optimization of emission layer (EML) in perovskite light-emitting diodes (PeLEDs) results in a significant improvement in device efficiency. However, so far, less attention has been paid to the exploration of hole/electron injection and transporting layers to maximize the utilization of charge carriers for efficient and stable PeLEDs. At present, low electron mobility of electron transport layer (ETL) causes an unbalanced charge injection, and the defects at the ETL/perovskite interface limit the formation and utilization of generated excitons. Here, a series of compounds (BPBiTP, BPBiPN, and BPBiPA) flanked by diphenyl-1H-benzo[d]imidazole end groups have been developed as ETL materials, where the bridging units (benzene, naphthalene, anthracene) are manipulated to achieve dual functionality, namely, the high charge carrier mobility and effective passivation of perovskite surface. The coordinating end groups effectively reduce the trap state at the interface of ETL and EML due to their strong nucleophilic quality. H-aggregation of anthracene units and large transfer integral in BPBiPA lead to its superior electron mobility of 8.4 × 10-4 cm2 V-1 s-1 in the solid state, over 1 order of magnitude higher than that of the typical one (TPBi). Consequently, green PeLEDs with a maximum external quantum efficiency (EQE) of 19.7%, reduced efficiency roll-off, as well as extended operational lifetime have been achieved without any outcoupling technique. Our result demonstrated that optimization of ETL materials via improving both passivation capability and electron mobility is a powerful strategy for producing high-performance PeLEDs.

Distally Based Posterior Tibial Artery Perforator Flaps for Reconstruction of the Defects in Achilles Region.

BACKGROUND: Patients with Achilles region defects remain a challenge for clinicians. The purpose of this article is to evaluate the surgical procedure to reconstruct the defects in Achilles region using distally based posterior tibial artery perforator flaps. METHODS: Between May 2015 and May 2017, 10 patients (aged from 35 to 68 years. 4 females and 6 males) with soft-tissue defects (sizes from 3 × 2 cm to 8 × 4 cm) in Achilles region received surgical therapy of posterior tibial artery perforator flap transplantation in the Affiliated Hospital of Xuzhou Medical University. RESULTS: The length of hospital stay ranged from 10 to 15 days (mean, 12 days). Local small superficial necrosis (5% of the area) was observed in only 1 case; however, it healed well after dressing was changed. All the others survived and healed well. At follow-up ranging from 12 to 24 months, all patients were satisfied with the aesthetic and functional aspects. CONCLUSIONS: Using the posterior tibial artery perforator flaps to cover the Achilles region defects is a promising, feasible, first-line, safe option and should be extensively applied in clinical therapy.

Posterior Tibial Artery Perforator Flaps Carrying Partial Gastrocnemius Muscle for Repair of Soft Tissue Defects With Dead Space in the Ankle and Foot.

BACKGROUND: Soft tissue defects with dead space in the ankle and foot remain a challenge for surgeons. The aim of the study was to evaluate the surgical technique and clinical significance of posterior tibial artery perforator flaps carrying partial gastrocnemius muscle for patients with soft tissue defects with dead space in the ankle area. METHODS: Between August 2015 and August 2017, 14 patients (2 women and 12 men) between 20 and 58 years old (median age, 42 years) were hospitalized in The First Affiliated Hospital of Soochow University. All injuries involved damage to the ankle area and formation of soft tissue defects with dead space. In all patients, posterior tibial artery perforator flaps carrying partial gastrocnemius muscle were transplanted to cover soft tissue defects with dead spaces. RESULTS: Hospitalization duration ranged from 10 to 20 days (mean, 16 days). All flaps survived and healed well. At follow-up after 6 to 24 months, all cases had recovered successfully in terms of aesthetic and functional aspects. CONCLUSIONS: Posterior tibial artery perforator flaps carrying partial gastrocnemius muscle can be an optimal reconstruction method for repairing soft tissue defects with dead space in the ankle and foot.

Air-Processed, Stable Organic Solar Cells with High Power Conversion Efficiency of 7.41.

High efficiency, excellent stability, and air processability are all important factors to consider in endeavoring to push forward the real-world application of organic solar cells. Herein, an air-processed inverted photovoltaic device built upon a low-bandgap, air-stable, phenanthridinone-based ter-polymer (C150 H218 N6 O6 S4 )n (PDPPPTD) and [6,6]-phenyl-C61 -butyric acid methyl ester (PC61 BM) without involving any additive engineering processes yields a high efficiency of 6.34%. The PDPPPTD/PC61 BM devices also exhibit superior thermal stability and photo-stability as well as long-term stability in ambient atmosphere without any device encapsulation, which show less performance decay as compared to most of the reported organic solar cells. In view of their great potential, solvent additive engineering via adding p-anisaldehyde (AA) is attempted, leading to a further improved efficiency of 7.41%, one of the highest efficiencies for all air-processed and stable organic photovoltaic devices. Moreover, the device stability under different ambient conditions is also further improved with the AA additive engineering. Various characterizations are conducted to probe the structural, morphology, and chemical information in order to correlate the structure with photovoltaic performance. This work paves a way for developing a new generation of air-processable organic solar cells for possible commercial application.

Reconstruction of Soft Tissue Defects Around the Knee With Pedicled Perforator Flaps.

PURPOSE: To study the availability and effects for application of 4 kinds of perforator flaps in repairing skin and soft tissue defects in different positions around the knee joints. METHODS: The present study included 26 cases (16 males and 10 females) with soft tissue defects with ages from 7 to 82 years who came to our hospital during September 2012 to August 2016. The wound size ranged from 6 × 3 cm to 15 × 12 cm, and the exposed area ranged from 4 × 2 cm to 10 × 8 cm. Patients were treated with different perforator flaps (descending genicular artery perforator flap, sural neurocutaneous flap, lateral superior genicular artery perforator flap, and lateral popliteal artery perforator flap) and were followed up for 6 months. RESULTS: All the transplanted flaps survived well without advent events. Exposed bone, ligament, and skin and soft tissue defects healed well. In the early period, flaps were locally bloated. In the later period, the appearance of flaps was good and close to normal, with abrasion-resistant surfaces. All patients were satisfied with the flap appearance and functional recovery. No secondary necrosis, ulcers, deep infection, or nonunion of bone occurred during the follow-up. CONCLUSIONS: These 4 kinds of perforator flaps are available methods to repair the skin and soft tissue defects around the knee joints. Suitable perforator flaps should be chosen for different locations of wounds. LEVEL OF EVIDENCE: Therapeutic study, level IV.

Toward Enhancing Solar Cell Performance: An Effective and "Green" Additive.

Performance of bulk heterojunction polymer solar cells (PSCs) highly relies on the morphology of the photoactive layer involving conjugated polymers and fullerene derivatives as donors and acceptors, respectively. Herein, butylamine was found to be able to optimize the morphology of the donor/acceptor (D/A) film composed of a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Compared to the commonly used alkane dithiols and halogenated additives with high boiling points, butylamine has a much lower boiling point between 77 and 79 °C, and it is also much "greener". A specific interaction between butylamine and PCBM was demonstrated to account for the morphology improvement. Essentially, butylamine can selectively dissolve PCBM in the P3HT:PCBM blend and facilitate the diffusion of PCBM in the film fabrication processes. Atomic force microscopy and X-ray photoelectron spectroscopy investigations confirmed the formation of the P3HT-enriched top surface and the abundance of PCBM at the bottom side, i.e., the formation of vertical phase segregation, as a consequence of the specific PCBM-butylamine interaction. The D/A film with inhomogeneously distributed D and A components in the vertical film direction, with more P3HT at the hole extraction side and more PCBM at the electron extraction side, enables more efficient charge extraction in the D/A film, reflected by the largely enhanced fill factor. The power conversion efficiency of devices reached 4.03 and 4.61%, respectively, depending on the thickness of the D/A film, and these are among the best values reported for P3HT:PCBM-based devices. As compared to the devices fabricated without the introduction of butylamine under otherwise the same processing conditions, they represented 19.6 and 21.6% improvement in the efficiency, respectively. The discovery of butylamine as a new, effective additive in enhancing the performance of PSCs strongly suggests that the differential affinity of additives toward donors and acceptors likely plays a more important role in morphology optimization than their boiling point, different from what was reported previously. The finding provides useful information for realizing large-area PSC fabrication, where a "greener" additive is always preferred.

Enhanced Long-term and Thermal Stability of Polymer Solar Cells in Air at High Humidity with the Formation of Unusual Quantum Dot Networks.

Due to the practical applications of polymer solar cells (PSCs), their stability recently has received increasing attention. Herein, a new strategy was developed to largely enhance the long-term and thermal stability of PSCs in air with a relatively high humidity of 50-60% without any encapsulation. In this strategy, semiconductor PbS/CdS core/shell quantum dots (QDs) were incorporated into the photoactive blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). By replacing the initial ligands of oleic acid with halide ligands on the surface of PbS/CdS QDs via solution-phase ligand exchange, we were able to form unusual, continuous QD networks in the film of P3HT:PCBM, which effectively stabilized the photoactive layer. Air-processed PSCs based on the stabilized P3HT:PCBM film showed excellent long-term stability under high humidity, providing over 3% of power conversion efficiency (PCE) simultaneously. Around 91% of pristine PCE was retained after 30 days storage in high-humidity air without encapsulation. This constitutes a remarkable improvement compared to ∼53% retained PCE for the QD-free devices, which can be ascribed to the efficient suppression of both PCBM aggregation and oxidation of the thiophene ring in P3HT, thanks to the formation of robust QD networks. Furthermore, the presence of QD networks was able to enhance the stability of the P3HT:PCBM film against thermal stress/oxidation under high-humidity environment (50-60%) as well. The device kept 60% of pristine PCE after thermal treatment for 12 h at 85 °C in air, which is more than twice higher than that for the QD-free device. To the best of our knowledge, the work represents the first unambiguous demonstration of the formation of QD networks in the photoactive layer and of their important contribution to the stability of PSCs. This strategy is highly promising for other fullerene-based PSCs and opens a new avenue toward achieving PSCs with high PCE and excellent stability.

Solvents induced ZnO nanoparticles aggregation associated with their interfacial effect on organic solar cells.

ZnO nanofilm as a cathode buffer layer has surface defects due to the aggregations of ZnO nanoparticles, leading to poor device performance of organic solar cells. In this paper, we report the ZnO nanoparticles aggregations in solution can be controlled by adjusting the solvents ratios (chloroform vs methanol). These aggregations could influence the morphology of ZnO film. Therefore, compact and homogeneous ZnO film can be obtained to help achieve a preferable power conversion efficiency of 8.54% in inverted organic solar cells. This improvement is attributed to the decreased leakage current and the increased electron-collecting efficiency as well as the improved interface contact with the active layer. In addition, we find the enhanced maximum exciton generation rate and exciton dissociation probability lead to the improvement of device performance due to the preferable ZnO dispersion. Compared to other methods of ZnO nanofilm fabrication, it is the more convenient, moderate, and effective to get a preferable ZnO buffer layer for high-efficiency organic solar cells.

High-performance inverted solar cells based on blend films of ZnO Naoparticles and TiO(2) nanorods as a cathode buffer layer.

We reported the favorable cathode buffer layer based on a blend of ZnO nanoparticles (NPs) and TiO2 nanorods (NRs) applied to inverted solar cells. In addition to the high optical transmittance, the resultant blend film gave a relatively dense film with lower roughness than that of the respective single-component film. This improved the interface contact between the buffer layer and photoactive layer and therefore reduced the contact resistance and leakage current. Moreover, the combination of NRs and NPs increased the efficiency of electron transport and collection by providing both a direct path for electron transport from TiO2 NRs and a large contact area between ZnO NPs and the active layer. Consequently, both the short-circuit current density (Jsc) and fill factor (FF) in the device were improved, leading to an improvement of the device performance. The best power conversion efficiency (PCE) based on the blend film as the buffer layer reached 8.82%, which was preferable to those of a single ZnO NP film (7.76%) and a TiO2 NR-based device (7.66%).

Manipulating surface ligands of copper sulfide nanocrystals: synthesis, characterization, and application to organic solar cells.

CuS NCs were synthesized via a facile sol-gel method without post-thermal treatment. The as-prepared CuS NCs were analyzed and confirmed by XRD, HR-TEM, EDS and XPS as hexagonal covellite CuS. The average diameter of the samples was about 3nm with narrow size distribution. CuS NCs can form a thin and smooth film without ligand-exchange that can be used as hole transport layer in organic solar cell. These hydrophilic CuS NCs with pyridine ligands can be exchanged with OAm and OA rapidly at room temperature and present hydrophobic characteristic, resulting in forming oil-soluble CuS NCs. This makes it possible tuning the surface property of CuS NCs and has the potential application for different fields.

Highly efficient organic photovoltaics via incorporation of solution-processed cesium stearate as the cathode interfacial layer.

Highly efficient organic solar cells were successfully demonstrated by incorporating a solution-processed cesium stearate between the photoactive layer and metal cathode as a novel cathode interfacial layer. The analysis of surface potential change indicated the existence of an interfacial dipole between the photoactive layer and metal electrode, which was responsible for the power conversion efficiency (PCE) enhancement of devices. The significant improvement in the device performance and the simple preparation method by solution processing suggested a promising and practical pathway to improve the efficiency of the organic solar cells.

[Reversed sural neurovascular fasciocutaneous flap for reconstruction of soft tissue defects of lower limbs].

OBJECTIVE: To investigate the clinical application of the reversed sural neurovascular fasciocutaneous flap. METHODS: From January 2007 to May 2009,10 patients (6 males and 4 females) with soft tissue defects on lower limbs were treated by reversed sural neurovascular fasciocutaneous flap. The end-to-side neuroanastomosis were used to reinnervate the flap and microsurgery was used for anastomosing small saphenous vein. The age ranged from 16 to 55 years (mean, 32 years). There were 6 patient with soft tissue defects on foot, 2 patients with exposed bone after operation, 2 patients with chronic ulcer on limb. The patients were evaluated with appearance, blood supply, texture and 2-PD of the flaps. RESULTS: All the patients were followed for 6 to 24 months (mean, 15 months). The flaps in all 10 patients survived completely. The appearance, blood supply and texture of the flaps were excellent and 2-PD was 9 to 12 mm. CONCLUSION: This flap has sufficient blood supply and high survival rate. It also effectively retains the feeling of dorsolateral heeland improved quality of life.