RESUMO
Achieving high-resolution and high signal-to-noise ratio (SNR) in vivo metabolic imaging via fast magnetic resonance spectroscopic imaging (MRSI) has been a longstanding challenge. This study combines the methods of relaxation enhancement (RE) and subspace imaging for the first time, enabling high-resolution and high-SNR in vivo MRSI of rodent brains at 9.4 T. Specifically, an RE-based chemical shift imaging sequence, which combines a frequency-selective pulse to excite only the metabolite frequencies with minimum perturbation of the water spins and a pair of adiabatic pulses to spatially localize the slice of interest, is designed and evaluated in vivo. This strategy effectively shortens the apparent T1 of metabolites, thereby increasing the SNR during relatively short repetition time ((TR) compared with acquisitions with only spatially selective wideband excitations, and does not require water suppression. The SNR was further enhanced via a state-of-the-art subspace reconstruction method. A novel subspace learning strategy tailored for 9.4 T and RE acquisitions is developed. In vivo, high-resolution (e.g., voxel size of 0.6 × 0.6 × 1.5 mm3) MRSI of both healthy mouse brains and a glioma-bearing mouse brain in 12.5 min has been demonstrated.
RESUMO
The hydrogen-deficient and oxygen-rich nature of lignocellulosic biomass prohibits effective conversions of biomass to fuels and chemicals via catalytic pyrolysis due to significant coking of the catalysts. Co-feeding of biomass feedstock with hydrogen-rich and oxygen-deficient thermoplastics could improve the process. Herein, thermal and catalytic co-pyrolysis of cellulose and polyethylene (PE) was studied via thermogravimetry combined with an online photoionization time-of-flight mass spectrometry (PI-TOF-MS). No notable synergetic effect was found in the thermal co-pyrolysis process while a considerable synergetic effect was observed during the catalytic co-pyrolysis. In the case of catalytic pyrolysis, co-feeding of cellulose with PE significantly improved the aromatic formation. Detailed reaction intermediates and products were detected by PI-TOF-MS and the process of aromatization could be ascribed to aromatization of small oxygenates and olefins, as well as Diels-Alder reaction and dehydration by HZSM-5. Moreover, this study provides a reliable tool for screening and optimizing of catalytic co-pyrolysis.
Assuntos
Celulose/química , Polietileno/química , Zeolitas/química , Biomassa , Catálise , Temperatura Alta , Íons/química , Espectrometria de Massas , Processos Fotoquímicos , Pirólise , TermogravimetriaRESUMO
An undulator-based vacuum ultraviolet (VUV) beamline (BL03U), intended for combustion chemistry studies, has been constructed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. The beamline is connected to the newly upgraded Hefei Light Source (HLSâ II), and could deliver photons in the 5-21â eV range, with a photon flux of 10(13)â photonsâ s(-1) at 10â eV when the beam current is 300â mA. The monochromator of the beamline is equipped with two gratings (200â lines mm(-1) and 400â lines mm(-1)) and its resolving power is 3900 at 7.3â eV for the 200â lines mm(-1) grating and 4200 at 14.6â eV for the 400â lines mm(-1) grating. The beamline serves three endstations which are designed for respective studies of premixed flame, fuel pyrolysis in flow reactor, and oxidation in jet-stirred reactor. Each endstation contains a reactor chamber, an ionization chamber where the molecular beam intersects with the VUV light, and a home-made reflectron time-of-flight mass spectrometer. The performance of the beamline and endstations with some preliminary results is presented here. The ability to detect reactive intermediates (e.g. H, O, OH and hydroperoxides) is advantageous in combustion chemistry research.