Browsing by Author "Xu, Zhen"

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    Cascade degradation and upcycling of polystyrene waste to high-value chemicals
    Xu, Zhen; Pan, Fuping; Sun, Mengqi; Xu, Jianjun; Munyaneza, Nuwayo Eric; Croft, Zacary L.; Cai, Gangshu; Liu, Guoliang (National Academy of Sciences, 2022-08-23)
    Plastic waste represents one of the most urgent environmental challenges facing humankind. Upcycling has been proposed to solve the low profitability and high market sensitivity of known recycling methods. Existing upcycling methods operate under energy-intense conditions and use precious-metal catalysts, but produce low-value oligomers, monomers, and common aromatics. Herein, we report a tandem degradation-upcycling strategy to exploit high-value chemicals from polystyrene (PS) waste with high selectivity. We first degrade PS waste to aromatics using ultraviolet (UV) light and then valorize the intermediate to diphenylmethane. Low-cost AlCl3 catalyzes both the reactions of degradation and upcycling at ambient temperatures under atmospheric pressure. The degraded intermediates can advantageously serve as solvents for processing the solid plastic wastes, forming a self-sustainable circuitry. The low-value-input and high-value-output approach is thus substantially more sustainable and economically viable than conventional thermal processes, which operate at high-temperature, high-pressure conditions and use precious-metal catalysts, but produce low-value oligomers, monomers, and common aromatics. The cascade strategy is resilient to impurities from plastic waste streams and is generalizable to other high-value chemicals (e.g., benzophenone, 1,2-diphenylethane, and 4-phenyl-4-oxo butyric acid). The upcycling to diphenylmethane was tested at 1-kg laboratory scale and attested by industrial-scale techno-economic analysis, demonstrating sustainability and economic viability without government subsidies or tax credits.
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    First-in-man histotripsy of hepatic tumors: the THERESA trial, a feasibility study
    Vidal-Jove, Joan; Serres, Xavier; Vlaisavljevich, Eli; Cannata, Jon; Duryea, Alex; Miller, Ryan; Merino, Xavier; Velat, Manuela; Kam, Yossi; Bolduan, Ryan; Amaral, Joseph; Hall, Timothy; Xu, Zhen; Lee, Fred T., Jr.; Ziemlewicz, Timothy J. (Taylor & Francis, 2022-12-31)
    Rationale Current hepatic locoregional therapies are limited in terms of effectiveness and toxicities. Given promising pre-clinical results, a first in-human trial was designed to assess the technical effectiveness and safety profile of histotripsy, a noninvasive, non-thermal, non-ionizing focused ultrasound therapy that creates precise, predictable tissue destruction, in patients with primary and secondary liver tumors. Methods A multicenter phase I trial (Theresa Study) was performed in a single country with 8 weeks of planned follow-up. Eight of fourteen recruited patients were deemed eligible and enrolled in the study. Hepatic histotripsy, was performed with a prototype system (HistoSonics, Inc., Ann Arbor, MI). Eleven tumors were targeted in the 8 patients who all had unresectable end-stage multifocal liver tumors: colorectal liver metastases (CRLM) in 5 patients (7 tumors), breast cancer metastases in 1 (1 tumor), cholangiocarcinoma metastases in 1 (2 tumors), and hepatocellular carcinoma (HCC) in 1 (1 tumor). The primary endpoint was acute technical success, defined as creating a zone of tissue destruction per planned volume assessed by MRI 1-day post-procedure. Safety (device-related adverse events) through 2 months was a secondary endpoint. Results The 8 patients had a median age of 60.4 years with an average targeted tumor diameter of 1.4cm. The primary endpoint was achieved in all procedures. The secondary safety profile endpoint identified no device-related adverse events. Two patients experienced a continuous decline in tumor markers during the eight weeks following the procedure. Conclusions This first-in-human trial demonstrates that hepatic histotripsy effectively destroys liver tissue in a predictable manner, correlating very well with the planned histotripsy volume, and has a high safety profile without any device-related adverse events. Based on these results, the need for more definitive clinical trials is warranted.
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    Modeling SAR signals and sensors using VHDL
    Xu, Zhen (Virginia Tech, 1995)
    The purpose of radar signal processing is to extract desired data from radar signals. Testing of the radar signal processor requires that one produce a test consisting of a sequence of digitized radar sensor data. If the signal processor is modeled in VHDL then the sequence of sensor data will be applied to the model in a VHDL test bench. Generation of the sensor data and sensor models for VHDL testbenches is a labor intensive task which cannot be performed manually. This thesis concentrates on the transformation of the mathematical representations of Synthetic Aperture Radar signals and sensors into VHDL models, and provides the mathematical underpinning for the other testbench work. Cadence/Comdisco SPW is used to describe the behavioral model of the test bench, which is hierarchically constructed using the primitives in the SPW library. A parameterized VHDL model is constructed from the block diagrams in SPW to generate the test for the VHDL signal processing model under test.
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    Nanodroplet-Mediated Histotripsy for Image-guided Targeted Ultrasound Cell Ablation
    Vlaisavljevich, Eli; Durmaz, Yasemin Yuksel; Maxwell, Adam; ElSayed, Mohamed; Xu, Zhen (Ivyspring Int Publ, 2013-01-01)
    This paper is an initial work towards developing an image-guided, targeted ultrasound ablation technique by combining histotripsy with nanodroplets that can be selectively delivered to tumor cells. Using extremely short, high-pressure pulses, histotripsy generates a dense cloud of cavitating microbubbles that fractionates tissue. We hypothesize that synthetic nanodroplets that encapsulate a perfluoropentane (PFP) core will transition upon exposure to ultrasound pulses into gas microbubbles, which will rapidly expand and collapse resulting in disruption of cells similar to the histotripsy process but at a significantly lower acoustic pressure. The significantly reduced cavitation threshold will allow histotripsy to be selectively delivered to the tumor tissue and greatly enhance the treatment efficiency while sparing neighboring healthy tissue. To test our hypothesis, we prepared nanodroplets with an average diameter of 204±4.7 nm at 37°C by self-assembly of an amphiphilic triblock copolymer around a PFP core followed by cross-linkage of the polymer shell forming stable nanodroplets. The nanodroplets were embedded in agarose tissue phantoms containing a sheet of red blood cells (RBCs), which were exposed to 2-cycle pulses applied by a 500 kHz focused transducer. Using a high speed camera to monitor microbubble generation, the peak negative pressure threshold needed to generate bubbles >50 μm in agarose phantoms containing nanodroplets was measured to be 10.8 MPa, which is significantly lower than the 28.8 MPa observed using ultrasound pulses alone. High speed images also showed cavitation microbubbles produced from the nanodroplets displayed expansion and collapse similar to histotripsy alone at higher pressures. Nanodroplet-mediated histotripsy created consistent, well-defined fractionation of the RBCs in agarose tissue phantoms at 10 Hz pulse repetition frequency similar to the lesions generated by histotripsy alone but at a significantly lower pressure. These results support our hypothesis and demonstrate the potential of using nanodroplet-mediated histotripsy for targeted cell ablation.