Purpose
To demonstrate accurate MR image reconstruction from undersampled k‐space data using cross‐domain convolutional neural networks (CNNs)
Methods
Cross‐domain CNNs consist of 3 components: (1) a ...deep CNN operating on the k‐space (KCNN), (2) a deep CNN operating on an image domain (ICNN), and (3) an interleaved data consistency operations. These components are alternately applied, and each CNN is trained to minimize the loss between the reconstructed and corresponding fully sampled k‐spaces. The final reconstructed image is obtained by forward‐propagating the undersampled k‐space data through the entire network.
Results
Performances of K‐net (KCNN with inverse Fourier transform), I‐net (ICNN with interleaved data consistency), and various combinations of the 2 different networks were tested. The test results indicated that K‐net and I‐net have different advantages/disadvantages in terms of tissue‐structure restoration. Consequently, the combination of K‐net and I‐net is superior to single‐domain CNNs. Three MR data sets, the T2 fluid‐attenuated inversion recovery (T2 FLAIR) set from the Alzheimer's Disease Neuroimaging Initiative and 2 data sets acquired at our local institute (T2 FLAIR and T1 weighted), were used to evaluate the performance of 7 conventional reconstruction algorithms and the proposed cross‐domain CNNs, which hereafter is referred to as KIKI‐net. KIKI‐net outperforms conventional algorithms with mean improvements of 2.29 dB in peak SNR and 0.031 in structure similarity.
Conclusion
KIKI‐net exhibits superior performance over state‐of‐the‐art conventional algorithms in terms of restoring tissue structures and removing aliasing artifacts. The results demonstrate that KIKI‐net is applicable up to a reduction factor of 3 to 4 based on variable‐density Cartesian undersampling.
High energy‐density lithium‐ion batteries are in demand for portable electronic devices and electrical vehicles. Since the energy density of the batteries relies heavily on the cathode material used, ...major research efforts have been made to develop alternative cathode materials with a higher degree of lithium utilization and specific energy density. In particular, layered, Ni‐rich, lithium transition‐metal oxides can deliver higher capacity at lower cost than the conventional LiCoO2. However, for these Ni‐rich compounds there are still several problems associated with their cycle life, thermal stability, and safety. Herein the performance enhancement of Ni‐rich cathode materials through structure tuning or interface engineering is summarized. The underlying mechanisms and remaining challenges will also be discussed.
The end is Ni: Over the past two decades, nickel‐rich materials have become highly promising candidates for high‐energy cathode materials for lithium‐ion batteries. This Review brings a new perspective to Ni‐rich materials as well as providing a comprehensive account of recent progress, limits, and new utilization possibilities for these materials. ESS=energy storage systems, EV=electric vehicles, HEV=hybrid electric vehicles, Mobile=mobile appliances.
Olfactory and taste receptors are expressed primarily in the nasal olfactory epithelium and gustatory taste bud cells, where they transmit real-time sensory signals to the brain. However, they are ...also expressed in multiple extra-nasal and extra-oral tissues, being implicated in diverse biological processes including sperm chemotaxis, muscle regeneration, bronchoconstriction and bronchodilatation, inflammation, appetite regulation and energy metabolism. Elucidation of the physiological roles of these ectopic receptors is revealing potential therapeutic and diagnostic applications in conditions including wounds, hair loss, asthma, obesity and cancers. This Review outlines current understanding of the diverse functions of ectopic olfactory and taste receptors and assesses their potential to be therapeutically exploited.
Excess/unreacted lead iodide (PbI2) has been commonly used in perovskite films for the state‐of‐the‐art solar cell applications. However, an understanding of intrinsic degradation mechanisms of ...perovskite solar cells (PSCs) containing unreacted PbI2 has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI2 crystals under continuous light illumination. Unreacted PbI2 undergoes photodecomposition under illumination, resulting in the formation of lead and iodine in films. Thus, this photodecomposition of PbI2 is one of the main reasons for accelerated device degradation. Therefore, this work reveals that carefully controlling the formation of unreacted PbI2 crystals in perovskite films is very important to improve device operational stability for diverse opto‐electronic applications in the future.
Degradation of perovskite solar cells with excess PbI2 is investigated. Excess PbI2 in perovskite films undergoes photodecomposition (photolysis) under illumination, which produces lead and iodine and accelerates the degradation of PSCs.
The operational instability of perovskite solar cells (PSCs) is known to mainly originate from the migration of ionic species (or charged defects) under a potential gradient. Compositional ...engineering of the “A” site cation of the ABX3 perovskite structure has been shown to be an effective route to improve the stability of PSCs. Here, the effect of size‐mismatch‐induced lattice distortions on the ion migration energetics and operational stability of PSCs is investigated. It is observed that the size mismatch of the mixed “A” site composition films and devices leads to a steric effect to impede the migration pathways of ions to increase the activation energy of ion migration, which is demonstrated through multiple theoretical and experimental evidence. Consequently, the mixed composition devices exhibit significantly improved thermal stability under continuous heating at 85 °C and operational stability under continuous 1 sun illumination, with an extrapolated lifetime of 2011 h, compared to the 222 h of the reference device.
A steric engineering strategy to impede ion migration in perovskite thin films is demonstrated where ion migration is effectively hindered by localized lattice distortions induced by incorporation of oversized A site cations. The steric engineering approach improves the operational lifetime of perovskite solar cells by more than nine‐fold from 222 h to 2011 h.
This paper introduces a new multilevel converter topology for a hybrid HVDC system comprising line-commutated converter (LCC) and voltage source converter (VSC). Among the existing modular multilevel ...converter (MMC) topologies for the hybrid HVDC, a mixed MMC structure with half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) has characteristics of reduced system cost, low operation loss, but still keeping capability to cope with dc short-circuit fault. However, it is very difficult for the conventional hybrid MMC structure to balance the submodule capacitor voltages under dc-bus voltage sliding since each MMC arm is a mixture of HBSMs and FBSMs. To solve the defect of the conventional hybrid MMC structure, an asymmetric mixed MMC, in which one arm is made of series-connected HBSMs and other arm is made of FBSMs, is devised. The proposed asymmetric MMC can regulate the dc-bus voltage freely without uncontrollable submodule capacitor voltages. The problems of the conventional MMC structure and the validity of asymmetric MMC are verified by both computer simulation and experimental results.
The unique electro‐optical features of organic photovoltaics (OPVs) have led to their use in applications that focus on indoor energy harvesters. Various adoptable photoactive materials with distinct ...spectral absorption windows offer enormous potential for their use under various indoor light sources. An in‐depth study on the performance optimization of indoor OPVs is conducted using various photoactive materials with different spectral absorption ranges. Among the materials, the fluorinated phenylene‐alkoxybenzothiadiazole‐based wide bandgap polymer—poly(5,6‐bis(2‐hexyldecyloxy)benzoc1,2,5thiadiazole‐4,7‐diyl)‐alt‐(5,50‐(2,5‐difluoro‐1,4‐phenylene)bis(thiophen‐2‐yl)) (PDTBTBz‐2Fanti)‐contained photoactive layer—exhibits a superior spectrum matching with indoor lights, particularly a light‐emitting diode (LED), which results in an excellent power absorption ratio. These optical properties contribute to the state‐of‐the‐art performance of the PDTBTBz‐2Fanti:6,6‐phenyl‐C71 butyric acid methyl ester (PC71BM)‐based OPV with an unprecedented high power‐conversion efficiency (PCE) of 23.1% under a 1000 lx LED. Finally, its indoor photovoltaic performance is observed to be better than that of an interdigitated‐back‐contact‐based silicon photovoltaic (PCE of 16.3%).
Poly(5,6‐bis(2‐hexyldecyloxy)benzoc1,2,5thiadiazole‐4,7‐diyl)‐alt‐(5,50‐(2,5‐difluoro‐1,4‐phenylene)bis(thiophen‐2‐yl)) (PDTBTBz‐2Fanti)‐based organic photovoltaics (OPVs) show an exceptionally high efficiency of 23.1% under a 1000‐lx light‐emitting diode lamp.
The attachment phenomena of various hierarchical architectures found in nature have extensively drawn attention for developing highly biocompatible adhesive on skin or wet inner organs without any ...chemical glue. Structural adhesive systems have become important to address the issues of human–machine interactions by smart outer/inner organ‐attachable devices for diagnosis and therapy. Here, advances in designs of biologically inspired adhesive architectures are reviewed in terms of distinct structural properties, attachment mechanisms to biosurfaces by physical interactions, and noteworthy fabrication methods. Recent demonstrations of bioinspired adhesive architectures as adhesive layers for medical applications from skin patches to multifunctional bioelectronics are presented. To conclude, current challenges and prospects on potential applications are also briefly discussed.
Nature has inspired various developments of hierarchically structured adhesive architectures for clean, reversible attachment to skin or organs within the human body. Recent progress in biologically inspired adhesive architectures is reviewed, from their geometric, material features, fabrication methods, and various medical applications from skin patches for wound protection to integrated bioelectronics with diagnostic and therapeutic functionalities.
Recording thermal conditions, i.e., temperature and time, is of great importance for various applications. Although thermometers can measure temperature and record its temporal change with electronic ...devices, they are nondisposable and not patch‐type, restricting their uses. Here, photonic films are designed that record thermal condition through irreversible structural deformation and intuitively report it with color patterns. The photonic films are inverse opals made of negative photoresist on a solid support, where the cross‐linking density of the photoresist is regioselectively adjusted. The photonic films show a gradual blueshift of structural color upon heating due to anisotropic compression of the inverse opal, of which the rate depends on temperature and cross‐linking density. For single cross‐linking density, thermal input is quantified from the color change in the form of coupled temperature and time. With multiple cross‐linking densities in a single film, the multicolor pattern is developed, from which the temperature and time are decoupled and separately estimated for isothermal condition.
Thermal recorders are designed in a patch format using inverse opals made of negative photoresist. For thermal input, the inverse opals are irreversibly compressed along the thickness direction, leading to a blueshift of the photonic stopband. With regioselective control of UV dose, the inverse opals turn to multicolor patterns whose blueshifts decouple the temperature and time for isothermal heating.
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