Low-toxic bismuth-based perovskites are prepared for the possible replacement of lead perovskite in solar cells. The perovskites have a hexagonal crystalline phase and light absorption in the visible region. A power conversion efficiency of over 1% is obtained for a solar cell with Cs3 Bi2 I9 perovskite, and it is concluded that bismuth perovskites have very promising properties for further development in solar cells.

This white paper discusses prospects for advancing hyperpolarization technology to better understand cancer metabolism, identify current obstacles to HP (hyperpolarized) 13C magnetic resonance imaging’s (MRI’s) widespread clinical use, and provide recommendations for overcoming them. Since the publication of the first NIH white paper on hyperpolarized 13C MRI in 2011, preclinical studies involving [1-13C]pyruvate as well a number of other 13C labeled metabolic substrates have demonstrated this technology's capacity to provide unique metabolic information. A dose-ranging study of HP [1-13C]pyruvate in patients with prostate cancer established safety and feasibility of this technique. Additional studies are ongoing in prostate, brain, breast, liver, cervical, and ovarian cancer. Technology for generating and delivering hyperpolarized agents has evolved, and new MR data acquisition sequences and improved MRI hardware have been developed. It will be important to continue investigation and development of existing and new probes in animal models. Improved polarization technology, efficient radiofrequency coils, and reliable pulse sequences are all important objectives to enable exploration of the technology in healthy control subjects and patient populations. It will be critical to determine how HP 13C MRI might fill existing needs in current clinical research and practice, and complement existing metabolic imaging modalities. Financial sponsorship and integration of academia, industry, and government efforts will be important factors in translating the technology for clinical research in oncology. This white paper is intended to provide recommendations with this goal in mind.

Transceive array coils, capable of RF transmission and independent signal reception, were developed for parallel, 1 H imaging applications in the human head at 7 T (300 MHz). The coils combine the advantages of high-frequency properties of transmission lines with classic MR coil design. Because of the short wavelength at the 1 H frequency at 300 MHz, these coils were straightforward to build and decouple. The sensitivity profiles of individual coils were highly asymmetric, as expected at this high frequency; however, the summed images from all coils were relatively uniform over the whole brain. Data were obtained with four-and eight-channel transceive arrays built using a loop configuration and compared to arrays built from straight stripline transmission lines. With both the four-and the eightchannel arrays, parallel imaging with sensitivity encoding with high reduction numbers was feasible at 7 T in the human head.

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A comprehensive technique was developed for using threedimensional 17 O magnetic resonance spectroscopic imaging at 9.4T for rapidly imaging the cerebral metabolic rate of oxygen consumption (CMRO2) in the rat brain during a two-min inhalation of 17 O2. The CMRO2 value (2.19 ؎ 0.14 mol͞g͞min, n ‫؍‬ 7) was determined in the rat anesthetized with ␣-chloralose by independent and concurrent 17 O NMR measurements of cerebral H2 17 O content, arterial input function, and cerebral perfusion. CMRO2 values obtained were consistent with the literature results for similar conditions. Our results reveal that, because of its superior sensitivity at ultra-high fields, the 17 O magnetic resonance spectroscopic imaging approach is capable of detecting small dynamic changes of metabolic H2 17 O during a short inhalation of 17 O2 gas, and ultimately, for imaging CMRO2 in the small rat brain. This study provides a crucial step toward the goal of developing a robust and noninvasive 17 O NMR approach for imaging CMRO2 in animal and human brains that can be used for studying the central role of oxidative metabolism in brain function under normal and diseased conditions, as well as for understanding the mechanisms underlying functional MRI.

Silicene, the silicon-based counterpart of graphene with a two-dimensional honeycomb lattice, has attracted tremendous interest both theoretically and experimentally due to its significant potential industrial applications. From the aspect of theoretical study, the widely used classical molecular dynamics simulation is an appropriate way to investigate the transport phenomena and mechanisms in nanostructures such as silicene. Unfortunately, no available interatomic potential can precisely characterize the unique features of silicene. Here, we optimized the Stillinger-Weber potential parameters specifically for a single-layer Si sheet, which can accurately reproduce the low buckling structure of silicene and the full phonon dispersion curves obtained from ab initio calculations. By performing equilibrium and nonequilibrium molecular dynamics simulations and anharmonic lattice dynamics calculations with the new potential, we reveal that the three methods consistently yield an extremely low thermal conductivity of silicene and a short phonon mean-free path, suggesting silicene as a potential candidate for high-efficiency thermoelectric materials. Moreover, by qualifying the relative contributions of lattice vibrations in different directions, we found that the longitudinal phonon modes dominate the thermal transport in silicene, which is fundamentally different from graphene, despite the similarity of their two-dimensional honeycomb lattices.

Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10-cm-diameter surface coil at 300 MHz is evaluated in a 16-cm-diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample-coil configuration. Enhancements in signal-to-noise ratio (SNR) and T* 2 contrast arising from high static magnetic field strengths are desirable for in vivo MR applications. Thus, the number of high-field human MRI systems has increased rapidly in recent years (1-10). The advent of high-field human imaging systems introduces new challenges in radiofrequency (RF) engineering (11,12). Because at high frequencies the wavelength of the RF field is comparable to or less than that of the dimension of the human body, the RF magnetic field (B 1 ) inside a sample exhibits prominent wave behavior (13-16). Additionally, the homogeneity of the B 1 field and source currents in the RF coil are strongly perturbed by sample loading (17-19). The B 1 field distribution inside a sample is important for both specific absorption rate (SAR) assessment and RF coil engineering at high frequency. However, mathematical treatment of the RF field in such systems can be extremely complicated because 1) the quasi-static approximations are no longer valid, and Maxwell's wave equation must be employed; and 2) the geometry of the human body is irregular, and electromagnetic properties of tissues are heterogeneous. Thus, computer numerical calculation becomes an effective and indispensable tool for studying interactions of the RF field with the human body at high field (20 -24). Associated with the RF field wave behavior, the distributions of the B 1 field and its circularly polarized components B ϩ and B -, which are directly responsible for the MR image intensity distribution, become distinctively different from one another. Consequently, the relationship of RF field polarization to coil configuration and sample electric properties needs to be analyzed in order to understand the resultant image intensity distribution. Computer modeling provides an effective way to study this problem, and may provide insight into complex RF field wave behavior and its dependence on the electrical properties of the sample. In this report, we present a study specifically devised to analyze high-frequency wave behavior of the RF field with the aid of numerical calculation and parallel experimental measurements. METHODSThe study was carried out using water and saline phantoms with a 10-cm-diameter sur...

The nonlinear optical properties of two novel graphene nanohybrid materials covalently functionalized with porphyrin and fullerene were investigated by using the Z-scan technique at 532 nm in the nanosecond and picosecond time scale. Results show that covalently functionalizing graphene with the reverse saturable absorption chromospheres porphyrin and fullerene can enhance the nonlinear optical performance in the nanosecond regime. The covalently linked graphene nanohybrids offer performance superior to that of the individual graphene, porphyrin, and fullerene by combination of a nonlinear mechanism and the photoinduced electron or energy transfer between porphyrin or fullerene moiety and graphene.