Molecular-scale controllable conversion of biopolymers into hard carbons towards lithium and sodium ion batteries: A review

Hard carbons are widely investigated as potential anodes for lithium and sodium ion batteries owing to their internally well-tailored textures(closed pores and defects) and large microcrystalline interlayer spacing. The renewable biomass is a green and economically attractive carbon source to produce hard carbons. However, the chemical and structural complexity of biomass has plagued the understanding of evolution mechanism from organic precursors to hard carbons and the structure-property relationship.This makes it difficult to finely tune the microstructure of biomass-derived hard carbons, thus greatly restricting their high-performance applications. Most recently, the optimal utilization and controllable conversion of biomass-derived biopolymers(such as starch, cellulose and lignin) at the molecular level have become a burgeoning area of research to develop hard carbons for advanced batteries.Considering the principal source of carbonaceous materials is from biomass pyrolysis, we firstly overview the chemical structures and pyrolysis behaviors of three main biopolymers. Then, the controllable preparation of hard carbons using various physicochemical properties of biopolymers at the molecular level is systematically discussed. Furthermore, we highlight present challenges and further opportunities in this field. The Review will guide future research works on the design of sustainable hard carbons and the optimization of battery performance.

Assessment of volumetric bone mineral density of the femoral neck in postmenopausal women with and without vertebral fractures using quantitative multi-slice CT

Objective： To demonstrate the validity and reliability of volumetric quantitative computed tomography （vQCT） with multi-slice computed tomography （MSCT） and dual energy X-ray absorptiometry （DXA） for hip bone mineral density （BMD） measurements, and to compare the differences between the two techniques in discriminating postmenopausal women with osteoporosis-related vertebral fractures from those without. Methods： Ninety subjects were enrolled and divided into three groups based on the BMD values of the lumbar spine and/or the femoral neck by DXA. Groups 1 and 2 consisted of postmenopausal women with BMD changes 〈-2SD, with and without radiographically confirmed vertebral fracture （n= 11 and 33, respectively）. Group 3 comprised normal controls with BMD changes 〉-ISD （n-46）. Post-MSCT （GE, LightSpeed16） scan reconstructed images of the abdominal-pelvic region, 1.25 mm thick per slice, were processed by OsteoCAD software to calculate the following parameters： volumetric BMD values of trabecular bone （TRAB）, cortical bone （CORT）, and integral bone （INTGL） of the left femoral neck, femoral neck axis length （NAL）, and minimum cross-section area （mCSA）. DXA BMD measurements of the lumbar spine （AP-SPINE） and the left femoral neck （NECK） also were performed for each subject. Results： The values of all seven parameters were significantly lower in subjects of Groups 1 and 2 than in normal postmenopausal women （P〈0.05, respectively）. Comparing Groups 1 and 2, 3D-TRAB and 3D-INTGL were significantly lower in postmenopausal women with vertebral fracture（s） [（109.8±9.61） and （243.3±33.0） mg/cm^3, respectively] than in those without [（148.9±7.47） and （285.4±17.8） mg/cm^3, respectively] （P〈0.05, respectively）, but no significant differences were evident in AP-SPINE or NECK BMD. Conclusion： the femoral neck-derived volumetric BMD parameters using vQCT appeared better than the DXA-derived ones in discriminating osteoporotic postmenopausal women with vertebral fractures from those without, vQCT might be useful to evaluate the effect of osteoporotic vertebral fracture status on changes in bone mass in the femoral neck.

Hypoglycemic encephalopathy caused by overdose of metformin in an adolescent

To the Editor:Hypoglycemic encephalopathy is an acute brain dysfunction caused by hypoglycemia.Its clinical manifestations are complex,and sometimes its symptoms are not typical.Therefore,it can be misdiagnosed.This article shares a case of hypoglycemic encephalopathy caused by excessive ingestion of metformin for a suicide attempt in an adolescent.