Younan Xia

Bio: Younan Xia is an academic researcher from The Wallace H. Coulter Department of Biomedical Engineering. The author has contributed to research in topics: Nanocages & Nanowire. The author has an hindex of 216, co-authored 943 publications receiving 175757 citations. Previous affiliations of Younan Xia include Washington University in St. Louis & University of Texas at Dallas.

Chalcogen Nanowires: Synthesis and Properties

Abstract: We have demonstrated a variety of solution-phase approaches for the synthesis of 1- dimensional nanostructures from chalcogens such as Se and Te. These nanostructures include uniform, single crystalline nanowires and nanorods (lateral dimensions from 10 to 1000 nm, and lengths ranging from 2 to >100 νm). These nanostructures grew via a solid-solution-solid transformation mechanism, in which Se and Te atoms were transported from the less stable source (amorphous colloids) into the more stable product (trigonal phase nanocrystallites). The nanocrystallites (or seeds) were formed either through temperature driven homogeneous nucleation or by sonochemical cavitation. As directed by the highly anisotropic crystal structure, the growth could be confined to one particular direction. These nanowires could be prepared both as dispersions in various solvents or as networked arrays on solid supports.

Engineering the optical properties of gold nanocages for biomedical applications

Abstract: The galvanic replacement reaction has been shown to be a robust method to produce a wide variety of nanostructures with complex shapes and compositions. This reaction is highly tunable, allowing for precise control of the properties of the final material. Gold nanocages, one exciting structure made with the galvanic replacement reaction, are particularly interesting for their use in biological applications such as photothermal therapy and contrast enhancement in optical imaging.

Shape Transformation via Etching and Regrowth: A Systematic Study of Pd Nanocrystals with Different Shapes and Twin Structures.

Abstract: This article describes a systematic study of the oxidative etching and regrowth behaviors of Pd nanocrystals, including single-crystal cubes bounded by {100} facets, single-crystal octahedra and tetrahedra enclosed by {111} facets; and multiple-twinned icosahedra covered by {111} facets. During etching, Pd atoms are preferentially oxidized and removed from the corners regardless of the type of nanocrystal, and the resultant Pd2+ ions are then reduced back to elemental Pd. For cubes and icosahedra, the newly formed Pd atoms are deposited on the {100} facets and twin boundaries, respectively, due to their relatively higher energies. For octahedra and tetrahedra, the Pd atoms self-nucleate in the solution phase, followed by their growth into small particles. We can control the etching rate relative to regrowth by varying the concentration of HCl in the reaction solution. As the concentration of HCl increases, 18-nm Pd cubes converted to octahedra of 23, 18, and 13 nm, respectively, in edge length. Due to the absence of regrowth, however, Pd octahedra are transformed into truncated octahedra, cuboctahedra, and spheres with decreasing sizes whereas Pd tetrahedra evolved into truncated tetrahedra and spheres. In contrast, Pd icosahedra with twin boundaries on the surface converted to asymmetric icosahedra, flower-like icosahedra, and spheres.

Synthesis, Characterization, and Utilization of Single Crystalline Nanoparticles of Silver

Abstract: This paper describes a procedure based on the Tollens’ process for preparing crystalline nanoparticles of silver with well-controlled, uniform sizes. The starting reagents are similar to those commonly used for electroless deposition of silver and are commercially available from the Peacock Laboratories (Philadelphia, PA). Only under appropriate conditions, mixing of these reagents was able to generate stable dispersions of silver colloids, rather than thin films of silver coated on surfaces of objects immersed in the solution (including the inner surface of the container). We have demonstrated the capability and feasibility of this method by forming stable dispersions of highly monodispersed, single crystalline colloids of silver with dimensions in the range of 20-50 nm.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346