444 research outputs found
Ultra-short pulsed laser surface processing and decontamination:
No full textIn this thesis surface decontamination via USP (ultra-short pulse) laser ablation is experimentally investigated. A Raydiance laser(0.9 or 1.2 ps, 1552nm, 1-5μJ, 1-500kHz) is employed. By focusing the high peak intensity, ultra-short pulse laser beam into a small spot and scanned over the contaminated area, material removal via plasma-mediated ablation is implemented with micro-joule level pulses. Laser ablation features of different materials such as glass, PDMS polymer and blood contamination are studied. By targeting a thin film or distributed surface contaminants with the USP laser decontamination results at varies laser parameters are examined. By carefully aligning the laser focus removal at cellular level is demonstrated. Utilizing the advantages of USP laser, we successfully achieved optimum surface decontamination results on soft biological phantom and skin dermis tissue. The experiment results are evaluated by a digital microscope or SEM. The Ultra-short pulse laser ablation technique offers a promising alternative to the current surface processing and decontamination method in bio-medical applications.M.S.Includes bibliographical references (p. 63-67)by Xiaoliang Wan
Some new methods for the comparison of two linear regression models
No full textThe frequently used approach to the comparison of two linear regression models is to use the partial F test. It is pointed out in this paper that the partial F test has in fact a naturally associated two-sided simultaneous confidence band, which is much more informative than the test itself. But this confidence band is over the entire range of all the covariates. As regression models are true or of interest often only over a restricted region of the covariates, the part of this confidence band outside this region is therefore useless and to ensure 1 - ? simultaneous coverage probability is therefore wasteful of resources. It is proposed that a narrower and hence more efficient confidence band over a restricted region of the covariates should be used. The critical constant required in the construction of this confidence band can be calculated by Monte Carlo simulation. While this two-sided confidence band is suitable for two-sided comparisons of two linear regression models, a more efficient one-sided confidence band can be constructed in a similar way if one is only interested in assessing whether the mean response of one regression model is higher (or lower) than that of the other in the region. The methodologies are illustrated with two examples
Perceptions of capacity for infectious disease control and prevention to meet the challenges of dengue fever in the face of climate change: A survey among CDC staff in Guangdong Province, China
No full textAbstract not availableMichael Xiaoliang Tong, Alana Hansen, Scott Hanson-Easey, Jianjun Xiang, Scott Cameron, Qiyong Liu, Xiaobo Liu, Yehuan Sun, Philip Weinstein, Gil-Soo Han, Craig Williams, Peng B
Advancing the mechanical performance of chemically complex alloys through strategically engineered bamboo-inspired multi-stage heterostructures
No full textInnovative design in heterostructure materials has emerged as a pivotal strategy to address the strength-ductility trade-off in metals and alloys. Inspired by the hierarchical structures found in bamboo, this study engineered a bamboo-like heterogeneous microstructure in a (FeCoNi)86Al7Ti7 chemically complex alloy (CCA) through a multi-step thermomechanical processing route. The bio-inspired triple heterostructures, featuring hierarchical grain sizes and multiscale, multi-morphology precipitates, significantly enhance the balance between strength and ductility, achieving nearly 2 GPa ultra-high tensile strength while maintaining good uniform plastic deformation. During deformation, L12 nanoprecipitates contribute to precipitation strengthening through the shear mechanism, while L21 submicron precipitates within the grains do so via the Orowan looping mechanism. L21 precipitates at the grain boundaries (GBs) act as reinforcement phases in the composite material. The bamboo-like heterostructure also alters dislocation accumulation by constraining deformation between coarse and ultrafine grains, influenced by the surrounding ultrafine grains and the diverse behaviors of precipitates. This pronounced back-stress strengthening across the matrix significantly enhances the strain-hardening capacity, thereby ensuring uniform plastic deformation. Overall, this novel approach demonstrates superior mechanical properties and offers a promising strategy for overcoming the strength-ductility trade-off in advanced alloys
A lithiation/delithiation mechanism of monodispersed MSn5 (M = Fe, Co and FeCo) nanospheres
No full textA designed Sn based alloy host as a higher capacity and longer cycle life next generation lithium-ion battery, consisting of monodisperse nanospheres of intermetallic MSn5 (M = Fe, Co and FeCo) phases was synthesized by a nanocrystal conversion chemistry method using preformed Sn nanospheres as templates. The same crystal structure, identical particle surface morphology and the similar particle size distribution (30-50 nm) of these intermetallic MSn5 (M = Fe, Co and FeCo) phases are ideal for comparison of the electrochemical performance, reaction mechanism, thermodynamics and kinetics during lithiation/delithiation. Importantly, MSn5 (M = Fe, Co and FeCo) phases with defect structures Fe0.74Sn5, Co0.83Sn5 and Fe0.35Co0.35Sn5, exhibit the highest theoretical capacity of >917 mA h g(-1) among the reported M-Sn (M is electro-chemically inactive) based intermetallic anodes. The ex situ XRD and XAFS illustrate the complete reversibility of MSn5 (M = Fe, Co and FeCo) phases during lithium insertion/extraction for the first cycle. The Fe0.35Co0.35Sn5 anode can take advantage of both high capacity of Fe0.74Sn5 and long cycle life of Co0.83Sn5, providing 736 mA h g(-1) and maintaining 92.7% of initial capacity after 100 cycles with an average capacity loss of only 0.07% per cycle. The excellent electrochemical performance of the Fe0.5Co0.5Sn5 system is attributed to higher reversibility, lower reaction resistance. This work provides a novel insight toward designing and exploring an optimal Sn based alloy anode for next generation Li-ion batteries
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High-Precision Determination of Linear and Three-Dimensional Genomes of Single Cells
No full textIn human and many other metazoans, both linear genome sequence and three-dimensional nuclear structure can vary between different cells within the same organism. Variations in linear DNA reflects the mutational history of the cell, and those in three-dimensional genome folding help regulate gene expression. Single-cell genomic assays therefore provide valuable means for characterizing the composition and regulation of genomes on a cell-to-cell basis.
A sensitive and reproducible method for amplifying the genome of each single cell is the first step for decoding its linear DNA. In Chapter 2 we describe our single-cell whole-genome amplification assay that utilizes droplet microfluidics to produce long amplicons with accurate allele counting capability. This method has reproducibly achieved high genomic coverages of 91.0% ± 3% (average ± standard deviation) for all the cells verified to be non-replicated.
To prevent DNA self-looping, we further included 16 transposon sequences, and labeled the two complementary strands of double-stranded DNA to correct for artifacts in the detection of single-nucleotide variations (SNVs). Described in Chapter 3, this assay, termed Multiplexed End-Tagging Amplification (META) of Complementary Strands, has revealed the mutational histories of blood and neuron cells with the highest accuracy known so far. Contrary to the conventional understanding that cell types are characterized by their transcriptomes, we found that SNV patterns are cell-type dependent and can be used to define cell types by principle component analysis.
By integrating META with chromosome conformation capture, we re-constructed the genome-wide nuclear structures of single diploid human cells to an unprecedented resolution of 20kb. In Chapter 3 our method of Diploid Chromosome Conformation Capture (Dip-C) is illustrated; it has uncovered the cell-type dependent 3D genome architecture for human peripheral blood mononuclear cells. For the first time, the Waddington epigenetic landscape of human cells can be determined based on 3D genome folding, with valleys representing cell types and the width of each valley specifying cell-to-cell differences. Survey into more cell types at higher spatial resolution will help elucidate the relationships between genome structures and their functions in health and disease.Chemistry and Chemical Biolog
Enterprise, family and society: Economic development and sociocultural changes in the Pearl River Delta area of China
No full textRural economic and social development has been an important issue for many developing countries. China has experienced a unique rural development strategy since 1979. The emergence and rapid growth of rural non-agricultural enterprises in China have drawn the attention of many economists. This study aims at providing a comprehensive evaluation of the validity and the consequences of such a development strategy. The research combines historical review and anthropological depth to examine the economic and social consequences of the development of rural enterprises in a township in south China.The issues concerned in this study were: (1) had the strategy in developing rural non-agricultural enterprises met its goal in increasing household income and improving the peasants' living standards? (2) how did the transformation of economic patterns affect the family structure and the village organization during this period? (3) what were some of the socio-cultural consequences of the large-scale development of rural non-agricultural enterprises?Four administrative villages in a township were chosen to conduct participant observation and intensive interviews. Qualitative and quantitative data were gathered over a period of six months in 1989, to investigate the manner of economic transformation and the degree of social adaptation. Synchronic and diachronic analyses were combined to determine the context of socio-economic changes and the trend that will probably continue to next few decades. The field research and analysis, which combined micro analysis and macro interpretation, led into one of the most important aspects in the study of socio-economic development. Social transformation is understandable only by conjoining micro and macro analyses.The study revealed that the rural development strategy has achieved considerable success in providing vast employment opportunities and improving the rural population's living standards. Consequently, the average size of households in this township, as well as in China, has decreased due to the increased division of the family, which was encouraged by the rapid increase of living space resulting from the rise of household income. The birth control policy practiced in China also has a significant effect on the household size. The study shows that economic considerations and social ties were important factors in marriage choices. The socio-economic development in this area also resulted in the changes in recreational patterns and people's social values. The emergence of a large number of migrants has disturbed the social order. In addition, the development strategy has had an environmental impact and led to a decrease in farmland. These should be regarded as some of the adverse side-effects of the Chinese rural development strategy.Source: Dissertation Abstracts International, Volume: 52-09, Section: A, page: 3328.Advisors: Ruth Landman.Ph.D. American University 1991.Englis
RETRACTED ARTICLE: Preparation of carrierized cellulase Cellulase@MIL-88B(Fe) and its enzymatic properties
No full textWe, the Editors and Publisher of Green Chemistry Letters and Reviews have retracted the following article:Erhong Zhang, Meng Wang, Xiaoliang Pan, Xinfeng Wang & Wenju Zhang (2022) Preparation of carrierized cellulase Cellulase@MIL-88B(Fe) and its enzymatic properties, Green Chemistry Letters and Reviews, 15:3, 627-637, DOI: https://doi.org/10.1080/17518253.2022.2124890Following publication, the authors requested the withdrawal of this article in 2022 due to a conflict with an associated patent. Further investigations by the Publisher, in close collaboration with the Editor-in-Chief, could not confirm a conflict with an associated patent but revealed that the article has significant overlap with a chapter of an unpublished thesis titled “Construction of an adaptive immobilized cellulase system and its enzymatic hydrolysis performance” authored by Tiantian Li in June 2022. More specifically, the overlap involves most of the data in the article which was reused without the required permissions, or the knowledge of the owners of the data.Upon query, the authors have cooperated with the investigation, but could neither demonstrate that their data was obtained appropriately, nor that their study was conducted in compliance with our editorial policies. As the reuse of data from a third-party without acquiring the required permissions is a serious breach of publishing ethics, we are retracting the article from the journal. The corresponding author listed in this publication has been informed.We have been informed in our decision-making by our editorial policies and the COPE guidelines.The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’
In situ studies of phase transitions in rapidly annealed metallic glasses and properties of obtained composites using ultrafast experimental techniques
No full textMetallic glasses (MGs) are very attractive for structural applications due to their large elastic strain, high strength and hardness, resulting from their unique atomic structure. However, MGs are brittle. Preparing metallic glass–crystal composites (MGCCs) from parent glass through thermal treatment is a useful method to induce ductility and work hardening. Thus, besides the direct applications of as-prepared MGs, the glasses can be used as a starting material to be processed, for example, by thermoplastic forming or thermal treatment to design components with desired shape and/or properties. In this view, it is of high importance to know the phase- transformation mechanisms and kinetics upon heating MGs, especially for rapid heating, which has not been sufficiently studied yet.
CuZrAl-based alloys, with near CuZr equimolar compositions, are suitable for producing MGCCs with improved plasticity owing to their good glass-forming ability and the formation of ductile B2 CuZr phase upon crystallization. However, the crystallization mechanism(s) and products have mainly been elucidated by extrapolating the available knowledge of the binary CuZr system. In the present work, a set of complementary techniques including resistive (Joule) heating, in situ high-energy synchrotron X-ray diffraction, conventional and ultrafast differential scanning calorimetry and containerless solidification during electromagnetic levitation is used to map the phase evolution ― crystallization and solid-state phase transformations ― in Cu₄₇.₅Zr₄₇.₅Al₅, Cu₄₇.₅Zr₄₈Al₄Co₀.₅ and Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MGs during isokinetic and isothermal annealing. The resistive heating devices, custom-built at the Leibniz Institute for Solid State and Materials Research Dresden – IFW Dresden, enable heating rates Φ to range from 10¹ up to 10⁵ K s⁻¹ in a vacuum.
Using the obtained experimental data, continuous-heating-transformation (CHT) diagrams for a heating rate range exceeding six orders of magnitude, covering the entire supercooled liquid region, and time-temperature-transformation (TTT) diagrams are constructed. The transformation maps reveal the competition between the Cu₁₀Zr₇, B2 CuZr and τ4 (Cu₂ZrAl) phases during crystallization. The formation of the primary phase and transformation sequence depends on the MG composition as well as on the heating rate. The critical heating rate to bypass the crystallization increases from ~30 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG to ~40 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG and to ~90 000 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, reflecting their glass-forming ability. The optimum heating rate to obtain glass–crystal composites with the predominant and desired B2 CuZr phase is evaluated to be Φ > 1 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG, Φ > 1 500 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, and Φ > 4 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG. Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG shows an increased propensity for the formation of brittle Cu₁₀Zr₇ intermetallic phase, compared to Cu₄₇.₅Zr₄₇.₅Al₅ and Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MGs. The TTT diagram for the isothermal heating of Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ shows an apparent double-nose shape which corresponds to the primary crystallization of Cu₁₀Zr₇ at lower temperatures and B2 CuZr at higher temperatures
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