Prospective motion correction for brain MRI using spherical navigators.

PURPOSE: To demonstrate for the first time the feasibility of performing prospective motion correction using spherical navigators (SNAVs). METHODS: SNAVs were interleaved in a 3D FLASH sequence with an additional short baseline scan (6.8 s) for fast rotation estimation. Assessment of SNAV-based prospective motion correction was performed in six volunteers. Participant motion was guided using randomly generated stepwise prompts as well as prompts derived from real motion cases. Experiments were performed on a 3 T MRI scanner using a 32-channel head coil. RESULTS: When optimized for real-time application, SNAV-based motion estimates were computed in 25.8 ± 1.3 ms. Phantom-based quantification of rotation and translation accuracy indicated mean absolute errors of 0.10 ± 0.09° and 0.25 ± 0.14 mm, respectively. Implementing SNAV-based motion estimates for prospective motion correction led to a clear improvement in image quality with minimal increase in scan time (<5%). CONCLUSION: Optimization of SNAV processing for real-time application enables prospective motion correction with low latency and minimal scan time requirements.

Multi-dimensional cylindrical vector beam (de)multiplexing through cascaded wavelength- and polarization-sensitive metasurfaces.

Cylindrical vector beams (CVBs) exhibit great potential for multiplexing communication, owing to their mode orthogonality and compatibility with conventional wavelength multiplexing techniques. However, the practical application of CVB multiplexing communication faces challenges due to the lack of effective spatial polarization manipulation technologies for (de)multiplexing multi-dimensional physical dimensions of CVBs. Herein, we introduce a wavelength- and polarization-sensitive cascaded phase modulation strategy that utilizes multiple coaxial metasurfaces for multi-dimensional modulation of CVBs. By leveraging the spin-dependent phase modulation mechanism, these metasurfaces enable the independent transformation of the two orthogonal polarization components of CVB modes. Combined with the wavelength sensitivity of Fresnel diffraction in progressive phase modulation, this approach establishes a high-dimensional mapping relationship among CVB modes, wavelengths, spatial positions, and Gaussian fundamental modes, thereby facilitating multi-dimensional (de)multiplexing involving CVB modes and wavelengths. As a proof of concept, we theoretically demonstrate a 9-channel multi-dimensional multiplexing system, successfully achieving joint (de)multiplexing of 3 CVB modes (1, 2, and 3) and 3 wavelengths (1550 nm, 1560 nm, and 1570 nm) with a diffraction efficiency exceeding 80%. Additionally, we show the transmission of 16-QAM signals across 9 channels with the bit-error-rates below 10-5. By combining the integrability of metasurfaces with the high-dimensional wavefront manipulation capabilities of multilevel modulation, our strategy can effectively address the diverse demands of different wavelengths and CVB modes in optical communication.

Cross-connection of multiplexed cylindrical vector beams using off-axis spin-decoupled metasurfaces.

Cylindrical vector beam (CVB) multiplexing communication demands effective mode cross-connection techniques to establish communication networks. While methods like polarized grating and coordinate transformation have been developed for (de)multiplexing CVB modes, challenges persist in the cross-connection of these multiplexed mode channels, including multi-mode conversion and inhomogeneous polarization control. Herein, we present an independent off-axis spin-orbit interaction strategy utilizing spin-decoupled metasurfaces. Cross-connection is achieved by encoding conjugated Dammann optical vortex grating phases onto the two orthogonal circularly polarized components of CVBs. Experimental results demonstrate the successful interconversion of four CVB modes (CVB+1 and CVB-2, CVB+2 and CVB-4) using a Si-based metasurface with a polarization conversion efficiency exceeding 85%. This facilitates the cross-connection of 200 Gbit/s quadrature phase-shift keying signals with bit-error-rates below 10-6. Offering advantages such as ultra-compact device size, flexible control of CVB modes, and multi-mode parallel processing, this approach shows promise in advancing the networking capabilities of CVB mode multiplexing communication networks.

Cascaded partitioned phase modulation for cross-connection of orbital angular momentum mode and polarization multiplexing channels.

Multi-dimensional orbital angular momentum (OAM) mode multiplexing provides a promising route for enlarging communication capacity and establishing comprehensive networks. While multi-dimensional multiplexing has gained advancements, the cross-connection of these multiplexed channels, especially involving modes and polarizations, remains challenging due to the needs for multi-mode interconversion and on-demand polarization control. Herein, we propose an OAM mode-polarization cross-transformation solution via cascaded partitioned phase modulation, which enables the divergently separated OAM modes to be independently phase-imposed within distinct spatial regions, leading to the synergistic conversion operation of mode and polarization channels. In demonstrations, we implemented the cross-connection of three OAM modes and two polarization multiplexed channels, achieving the mode purity that exceeds 0.951 and polarization contrast up to 0.947. The measured mode insertion losses and polarization conversion losses are below 3.42 and 3.54 dB, respectively. Consequently, 1.2 Tbit/s quadrature phase shift keying signals were successfully exchanged, yielding the bit-error-rates close to 10-6. Incorporating with increased partitioned phase treatments, this approach shows promise in accommodating massive mode-polarization multiplexed channels, which hold the potential to augment networking capability of large-scale OAM mode multiplexing communication networks.

High-order orbital angular momentum mode-based phase shift-keying communication using phase difference modulation.

Orbital angular momentum (OAM) mode offers a promising modulation dimension for high-order shift-keying (SK) communication due to its mode orthogonality. However, the expansion of modulation order through superposing OAM modes is constrained by the mode-field mismatch resulting from the rapidly increased divergence with mode orders. Herein, we address this problem by propose a phase-difference modulation strategy that breaks the limitation of modulation orders via introducing a phase-difference degree of freedom (DoF) beyond OAM modes. Phase-difference modulation exploits the sensitivity of mode interference to phase differences, thereby providing distinct tunable parameters. This enables the generation of a series of codable spatial modes with continuous variation within the same superposed OAM modes by manipulating the interference state. Due to the inherent independence between OAM mode and phase-difference DoF, the number of codable modes increases exponentially, which facilitates establishing ultra-high-order phase shift-keying by discretizing the continuous phase difference and establishing a one-to-one mapping between coding symbols and constructed modes. We show that a phase shift-keying communication link with a modulation order of up to 4 × 104 is achieved by employing only 3 OAM modes (+1, + 2 and +3), and the decode accuracy reaches 99.9%. Since the modulation order is exponentially correlated with the OAM modes and phase differences, the order can be greatly improved by further increasing the superimposed OAM modes, which may provide new insight for high-order OAM-based SK communication.

Full-duplex cylindrical vector beam multiplexing communication using spin-dependent phase modulation metasurfaces.

Cylindrical vector beam (CVB) has recently gained attention as a promising carrier for signal multiplexing owing to its mode orthogonality. However, the full-duplex multiplexing communication has not been previously explored for the lack of effective technologies to parallelly couple and separate CVB modes. Herein, we present a full-duplex solution for CVB multiplexing communication that utilizes spin-dependent phase modulation metasurfaces. By independently phase-modulating the two spin eigenstates of CVBs with the metasurface via spin-dependent orbital interactions, and loading two binary Dammann vortex gratings, we enabled an independent and reciprocal wave vector manipulation of CVBs for full-duplex (de)multiplexing operation. To demonstrate this concept, we constructed a 16-channel (including 4 CVB modes and 4 wavelengths) full-duplex CVB multiplexing communication system and achieved the bidirectional transmission of 800 Gbit/s quadrature-phase shift-keying (QPSK) signals over a 5 km few-mode fiber. Our results demonstrate the successful multiplexing and demultiplexing of 2 radial CVB modes and 2 azimuthal CVB modes in full-duplex communication with the bit-error-rates approaching 1.87 × 10-5.

Effective magnetic susceptibility of 3D-printed porous metal scaffolds.

PURPOSE: 3D-printed porous metal scaffolds are a promising emerging technology in orthopedic implant design. Compared to solid metal implants, porous metal implants have lower magnetic susceptibility values, which have a direct impact on imaging time and image quality. The purpose of this study is to determine the relationship between porosity and effective susceptibility through quantitative estimates informed by comparing coregistered scanned and simulated field maps. METHODS: Five porous scaffold cylinders were designed and 3D-printed in titanium alloy (Ti-6Al-4V) with nominal porosities ranging from 60% to 90% using a cellular sheet-based gyroid design. The effective susceptibility of each cylinder was estimated by comparing acquired B0 field maps against simulations of a solid cylinder of varying assigned magnetic susceptibility, where the orientation and volume of interest of the simulations was informed by a custom alignment phantom. RESULTS: Magnitude images and field maps showed obvious decreases in artifact size and field inhomogeneity with increasing porosity. The effective susceptibility was found to be linearly correlated with porosity (R2  = 0.9993). The extrapolated 100% porous (no metal) magnetic susceptibility was -9.9 ppm, closely matching the expected value of pure water (-9 ppm), indicating a reliable estimation of susceptibility. CONCLUSION: Effective susceptibility of porous metal scaffolds is linearly correlated with porosity. Highly porous implants have sufficiently low effective susceptibilities to be more amenable to routine imaging with MRI.

Orbital angular momentum mode diversity gain in optical communication.

Vortex beams carrying orbital angular momentum (OAM) modes show superior multiplexing abilities in enhancing communication capacity. However, the signal fading induced by turbulence noise severely degrades the communication performance and even leads to communication interruption. Herein, we propose a diversity gain strategy to mitigate signal fading in OAM multiplexing communication and investigate the gain combination and channel assignment to optimize the diversity efficiency and communication capacity. Endowing signals with distinct channel matrices and superposing them with designed channel weights, we perform the diversity gain with an optimal gain efficiency, and the signal fading is mitigated by equalizing the turbulence noise. For the tradeoff between turbulence noise tolerance and communication capacity, multiplexed channels are algorithm-free assigned for diversity and multiplexing according to bit-error-rate and outage probability. As a proof of concept, we demonstrate a 6-channel multiplexing communication, where 3 OAM modes are assigned for diversity gain and 24 Gbit/s QPSK-OFDM signals are transmitted. After diversity gain, the bit-error-rate decreases from 1.41 × 10-2 to 1.63 × 10-4 at -14 dBm, and the outage probability of 86.7% is almost completely suppressed.

Orbital angular momentum deep multiplexing holography via an optical diffractive neural network.

Orbital angular momentum (OAM) mode multiplexing provides a new strategy for reconstructing multiple holograms, which is compatible with other physical dimensions involving wavelength and polarization to enlarge information capacity. Conventional OAM multiplexing holography usually relies on the independence of physical dimensions, and the deep holography involving spatial depth is always limited for the lack of spatiotemporal evolution modulation technologies. Herein, we introduce a depth-controllable imaging technology in OAM deep multiplexing holography via designing a prototype of five-layer optical diffractive neural network (ODNN). Since the optical propagation with dimensional-independent spatiotemporal evolution offers a unique linear modulation to light, it is possible to combine OAM modes with spatial depths to realize OAM deep multiplexing holography. Exploiting the multi-plane light conversion and in-situ optical propagation principles, we simultaneously modulate both the OAM mode and spatial depth of incident light via unitary transformation and linear modulations, where OAM modes are encoded independently for conversions among holograms. Results show that the ODNN realized light field conversion and evolution of five multiplexed OAM modes in deep multiplexing holography, where the mean square error and structural similarity index measure are 0.03 and 86%, respectively. Our demonstration explores a depth-controllable spatiotemporal evolution technology in OAM deep multiplexing holography, which is expected to promote the development of OAM mode-based optical holography and storage.

[Main components in different varieties of Xihuangcao by UPLC-Q-TOF-MS and UPLC-DAD].

This study established an ultra-high performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry(UPLC-Q-TOF-MS) method to analyze the main components in different varieties of Xihuangcao and established a UPLC-DAD method to simultaneously determine the five active components(caffeic acid, rosmarinic acid, schaftoside, isoschaftoside, and oridonin).The chromatographic separation was performed on a Waters ACQUITY UPLC BEH C_(18) column(2.1 mm×100 mm, 1.7 µm) with a gradient elution of methanol(B)-water containing 0.1% formic acid(A) at a flow rate of 0.3 mL·min~(-1).The column temperature was 30 ℃.The Q-TOF-MS discriminant analysis was performed under positive electrospray ion mode and the split ratio was 1∶1. Quantitative analysis was carried out by UPLC-DAD.The determination wavelength was set at 245 nm.Thirty-two main components of Xihuangcao were separated and identified by UPLC-Q-TOF-MS, where 19 were identified in Rabdosia serra, nine in R.nervosa, 10 in R.lophanthoides, 15 in R.lophanthoides var.graciliflora, 10 in R.lophanthoides var.gerardianus, and seven in R.stracheyi.The UPLC-DVD method was developed for simultaneously determining five active components in different varieties of Xihuangcao.The standard curves for five compounds showed good linearity with correlation coefficients higher than 0.999 0.The precision, repeatability, and stability were good.The average recoveries(n=6) were between 97.01% and 102.7% with RSD<3.0%.The results of UPLC-Q-TOF-MS analysis provided a scientific basis for the use of R.stracheyi as a medicinal material of Xihuangcao and the equivalent use of R.lophanthoides var.gerardianus with R.lophanthoides var.graciliflora to some extent.The UPLC-DAD method for simultaneously determining five active components is simple, rapid, and accurate.This study can provide the basis for the quality control of different varieties of Xihuangcao.

Curcumin attenuates Adriamycin-resistance of acute myeloid leukemia by inhibiting the lncRNA HOTAIR/miR-20a-5p/WT1 axis.

Acute myeloid leukemia (AML) is a common subtype of leukemia, and a large proportion of patients with AML eventually develop drug resistance. Curcumin exerts cancer suppressive effects and increases sensitivity to chemotherapy in several diseases. This study aimed to investigate the mechanism by which curcumin affects the resistance of AML to Adriamycin by regulating HOX transcript antisense RNA (HOTAIR) expression. Cell viability, colony-formation, flow cytometry, and Transwell assays were used to assess cell proliferation, apoptosis, and migration. A dual-luciferase reporter assay was used to verify the interaction between microRNA (miR)-20a-5p and HOTAIR or Wilms' tumor 1 (WT1). RT-qPCR and Western blotting assays were performed to detect gene and protein expression. The results showed that curcumin suppressed the resistance to Adriamycin, inhibited the expression of HOTAIR and WT1, and promoted the expression of miR-20a-5p in human acute leukemia cells (HL-60) or Adriamycin-resistant HL-60 cells (HL-60/ADR). Furthermore, curcumin suppressed proliferation and promoted apoptosis of HL-60/ADR cells. Overexpression of HOTAIR reversed the regulatory effect of curcumin on apoptosis and migration and restored the effect of curcumin on inducing the expression of cleaved caspase3, Bax, and P27. In addition, HOTAIR upregulated WT1 expression by targeting miR-20a-5p, and inhibition of miR-20a-5p reversed the regulation of Adriamycin resistance by curcumin in AML cells. Finally, curcumin inhibited Adriamycin resistance by suppressing the HOTAIR/miR-20a-5p/WT1 pathway in vivo. In short, curcumin suppressed the proliferation and migration, blocked the cell cycle progression of AML cells, and sensitized AML cells to Adriamycin by regulating the HOTAIR/miR-20a-5p/WT1 axis. These findings suggest a potential role of curcumin and HOTAIR in AML treatment.

Optical diffractive deep neural network-based orbital angular momentum mode add-drop multiplexer.

Vortex beams have application potential in multiplexing communication because of their orthogonal orbital angular momentum (OAM) modes. OAM add-drop multiplexing remains a challenge owing to the lack of mode selective coupling and separation technologies. We proposed an OAM add-drop multiplexer (OADM) using an optical diffractive deep neural network (ODNN). By exploiting the effective data-fitting capability of deep neural networks and the complex light-field manipulation ability of multilayer diffraction screens, we constructed a five-layer ODNN to manipulate the spatial location of vortex beams, which can selectively couple and separate OAM modes. Both the diffraction efficiency and mode purity exceeded 95% in simulations and four OAM channels carrying 16-quadrature-amplitude-modulation signals were successfully downloaded and uploaded with optical signal-to-noise ratio penalties of ∼1 dB at a bit error rate of 3.8 × 10-3. This method can break through the constraints of conventional OADM, such as single function and poor flexibility, which may create new opportunities for OAM multiplexing and all-optical interconnection.

Intra-symbol frequency-domain averaging for turbulence mitigation in optical orbital angular momentum multiplexing.

Optical vortex beams (VBs) possessing helical phase-front have attracted considerable attention in multiplexing communication for their orthogonal orbital angular momentum (OAM) modes. However, the mode-crosstalk and signal jitter caused by turbulence fluctuation are two main challenges in OAM multiplexing communication. Here, we introduce an intra-symbol frequency-domain averaging technology (ISFA) for turbulence mitigation. By equalizing the distorted multiplexing signals, ISFA mitigates the amplitude and phase jitter of received signals without adding system complexity and information redundancy. The experimental results show that VBs are successfully demultiplexed, and the transmission rate reaches 48 Gbit/s. After ISFA, the bit-error-rate of QPSK-OFDM signals is reduced from 1.10 × 10-3 to 6.31 × 10-4, and the error-vector-magnitude (EVM) is reduced from 31.69% to 26.29% under the turbulence strength of Cn2 = 1×10-13m-2/3 and equivalent transmission distance of 200 m. By combining ISFA with MIMO diversity gain, the EVM can be further reduced from 46.70% to 26.70%. These indicate that ISFA is available for turbulence mitigation and compatible with MIMO technology, which may have perspective potential in improving the performance of OAM multiplexing communication.

Cylindrical vector beam sorter with spin-dependent spiral transformation.

Here, we propose and experimentally demonstrate a cylindrical vector beam (CVB) sorter based on a spin-dependent spiral transformation. By exploiting the spin-orbital interaction of the geometric phase, a pair of conjugated spiral transformations are applied to modulate the two orthogonal circularly polarized components of the CVB, which are converted into the same linear phase gradient from opposite azimuthal phase gradients. Since the orthogonal spin components of CVBs with different polarization orders carry different phase gradients, under the convergence of a convex lens, the coaxially transmitted CVBs can be sorted with spatially separated positions, and the increased phase gradient provided by the spiral transformation yields the high resolution. We show that five CVB modes from -2 to +2 are successfully sorted with a separation efficiency of 3.65. As a proof-of-concept, we demonstrate a two-channel CVB multiplexing communication with a bit error rate approaching 10-6. In addition to providing an avenue for CVB demultiplexing, our results show potential applications in mode filtering and mode routing in all-optical interconnection.

Cylindrical vector beam multiplexing for radio-over-fiber communication with dielectric metasurfaces.

Radio-over-fiber (ROF) technology, loading microwave signal on light beams, has attracted considerable attention in wireless access network for its superiority in processing high-frequency microwave signals. Multiplexing for achieving high-capacity density, however, remains elusive in ROF communication because the optical microwave occupies large bandwidth. Here, we introduce a cylindrical vector beam (CVB) multiplexing for ROF communication with dielectric Pancharatnam-Berry phase-based metasurfaces (PBMs). CVBs, a structured light beam possessing spatially nonuniform polarization distribution and carrying vector mode, provide an additional multiplexing dimension for optical communication with the advantages of weak scintillation in free-space and low mode injure in few-mode-fiber. Exploiting the spin-orbit interaction of the PB phase, we construct PBMs to manipulate CVBs, which show broadband working wavelengths ranging from C- to L-band. After 3 m free-space propagation, two multiplexed CVBs carrying 100 GHz microwave are successfully demultiplexed, and the 100 GHz ROF communication with 12 Gbit/s QPSK-OFDM signals is realized. The crosstalk of the multiplexed CVBs is less than -15.13 dB, and the bit-error-rates (BERs) are below 3.26 × 10-5. With 5 km few-mode-fiber transmission, the CVBs are also demultiplexed with the BERs of 6.51 × 10-5. These results indicate that CVB is not only capable of free-space transmission but also available for few-mode-fiber transmission, which might pave new avenues for the multiplexing of ROF communications.

Cage Based Crystalline Covalent Organic Frameworks.

The first two cage based crystalline covalent organic frameworks, cage-COF-1 and cage-COF-2, were constructed from a prism-like three-aldehyde-containing molecular cage. The cage contains two horizontal phloroglucinol and three vertical triazine moieties forming three identical V-shaped cavities. By reacting with p-phenylenediamine and 4,4'-biphenyldiamine, the two cage-COFs were formed with a hexagonal skeleton and possess a unique structure. Due to the pillared cage nodes, the linkers are hanging with their π-surfaces but not C-H sites exposed to the pore, and enjoy certain rotational dynamics as suggested by 13C CP/MAS NMR. The antidirection of the diimine linkages leads to rippled layers which pack in unique ABC mode through alternate stacking of the cage twosided faces in both AB and AC layers. Such packing forms trigonal channels along c axis which are interconnected in ab plane due to the large open space created across the hanging linkers, resembling the porous characteristics of 3D COFs. The cage-COFs have a permanent porosity and can adsorb CO2 facilitated by the intrinsic cage cavities that serve as prime adsorption sites. The unprecedented cage-COFs not only merge the borderline of 2D and 3D COFs but also bridge porous organic cages to extended crystalline organic frameworks.

Deep learning based atmospheric turbulence compensation for orbital angular momentum beam distortion and communication.

Atmospheric transmission distortion is one of the main challenges hampering the practical application of a vortex beam (VB) which carries orbital angular momentum (OAM). In this work, we propose and investigate a deep learning based atmospheric turbulence compensation method for correcting the distorted VB and improving the performance of OAM multiplexing communication. A deep convolutional neural network (CNN) model, which can automatically learn the mapping relationship of the intensity distributions of input and the turbulent phase, is well designed. After trained with loads of studying samples, the CNN model possesses a good generalization ability in quickly and accurately predicting equivalent turbulent phase screen, including the untrained turbulent phase screens. The results show that through correction, the mode purity of the distorted VB improves from 39.52% to 98.34% under the turbulence intensity of Cn2 = 1 × 10-13. Constructing an OAM multiplexing communication link, the bit-error-rate (BER) of the transmitted signals in each OAM channel is reduced by almost two orders of magnitude under moderate-strong turbulence, and the demodulated constellation diagram also converges well after compensated by the CNN model.

Spatial phase and polarization retrieval of arbitrary circular symmetry singular light beams using orthogonal polarization separation.

Circular symmetry singular light beams (CS-SLBs) possessing spatially variant field distributions have drawn extensive attention because of their unique optical properties. However, the extraction of spatial phase and polarization distributions is always a significant but difficult issue in CS-SLB applications. Here, we propose and experimentally investigate an orthogonal polarization separation (OPS) method to retrieve the spatial phase and polarization distributions of arbitrary CS-SLBs. Theoretically, the CS-SLB, including the vortex beam (VB), cylindrical vector beam (CVB), and cylindrical vector vortex beam (CVVB), can be decomposed into two orthogonal circularly polarized sub-VBs. Therefore, once the spatial phase distributions and initial phase difference of the two components are obtained, the phase and polarization distributions of the CS-SLB can be retrieved, and its type can also be identified. Based on this analysis relationship, we first separated the CS-SLB into two circularly polarized sub-VBs and designed an astigmatic phase iterative algorithm to restore their spatial phase information. After retrieving the phases of the two components, we have experimentally obtained the spatial phase and polarization distributions of three typical CS-SLBs, including VBs, CVBs, and CVVBs. These results demonstrate that this method provides a feasible way to retrieve the variant field distributions of CS-SLBs and may have great application prospects in optical imaging, optical communication, etc.

Single multi-echo GRE acquisition with short and long echo spacing for simultaneous quantitative mapping of fat fraction, B0 inhomogeneity, and susceptibility.

Multi-echo gradient echo (mGRE) sequences have been widely adapted in clinical and scientific practice for different purposes to their capability of performing Dixon MRI, generating multi-contrast images and extracting multi-parametric maps. This work aims to extend mGRE-based techniques for imaging whole head, where further technical developments are required due to the co-existence of fat and large B0 inhomogeneity in regions such as the skull base and neck. Specifically, bipolar mGRE data were acquired with a single sequence that contains both a short echo-spacing (ΔTE) echo train to capture water-fat and B0 phase shifts (for proton density fat-fraction (FF) and B0 mapping) and a longer ΔTE echo train (and long echo times) to capture subtle susceptibility variations and R2* information. The mGRE images covering the whole head (spatial resolution 1.0 × 1.0 × 2.0 mm3) were acquired in 5 min. An automated processing pipeline was implemented to use the FF and B0 maps determined from the short-TE train to compensate for the effects of fat, remove the background phase for whole-head quantitative susceptibility mapping, and reduce the difficulty of spatial phase unwrapping of the long echo-time data. Data from healthy volunteers imaged on a 3 T scanner along with phantom validation are presented. Co-registered quantitative multi-parametric maps (FF, B0 inhomogeneity, R2*, local frequency shift and quantitative susceptibility) and multi-contrast images covering the whole head were successfully generated in processing times of several minutes.

Molecular Barrel by a Hooping Strategy: Synthesis, Structure, and Selective CO2 Adsorption Facilitated by Lone Pair-π Interactions.

A sophisticated molecular barrel 5 was efficiently constructed by hooping a 63-membered loop around a D3h-symmetric, shape-persistent bis(tetraoxacalix[2]arene[2]triazine) core. The hooping strategy involved 3-fold ring-closing metathesis (RCM) reactions of six branched olefin arms which were preanchored on the inner core. Through hooping, the loop tightens the cage structure and significantly enhances its stability toward nucleophilic decomposition. The X-ray crystal structure showed the molecular barrel bears three enclosed fan-shaped cavities as divided by the triazine rings and each of the cavities can hold a solvent CHCl3 or CH2Cl2 molecule. With the intrinsic porosity, the amorphous solids of 5 exhibit considerable CO2 uptake with an exceptionally large isosteric enthalpy. Lone pair (lp)-π interactions between the electron-deficient triazine rings and CO2 could contribute to the strong adsorption as supported by IR studies and DFT modeling.