scispace - formally typeset
Search or ask a question
Author

Christopher M. Sorensen

Bio: Christopher M. Sorensen is an academic researcher from Kansas State University. The author has contributed to research in topics: Light scattering & Scattering. The author has an hindex of 61, co-authored 326 publications receiving 13997 citations. Previous affiliations of Christopher M. Sorensen include Pacific Northwest National Laboratory & University of Nebraska–Lincoln.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the authors present a review of scattering and absorption of light by fractal aggregates, which are typically diffusion limited cluster aggregates with fractal dimensions of D.
Abstract: This paper presents a review of scattering and absorption of light by fractal aggregates. The aggregates are typically diffusion limited cluster aggregates (DLCA) with fractal dimensions of D

1,027 citations

Journal ArticleDOI
TL;DR: In this article, a series of samples with various sizes but the same microstructure were created by an aqueous phase coprecipitation method and the Curie temperature is modified in association with these changes.
Abstract: Manganese ferrite, ${\mathrm{MnFe}}_{2}$${\mathrm{O}}_{4}$, fine particles in the size range 5--15 nm have been prepared by an aqueous phase coprecipitation method. The freshly prepared particles are in a metastable state with regard to the cation distribution between the A and B sites of the spinel lattice. Thermomagnetic, differential scanning calorimetry and M\"ossbauer spectroscopy show that heat treatment under inert gas to 670 K irreversibly changes the cation distribution to a stable state. Heat treatment of freshly prepared samples in air to 470 K both changes the cation site distribution somewhat and, most importantly, oxidizes the ${\mathrm{Mn}}^{2+}$ to ${\mathrm{Mn}}^{3+}$. The Curie temperature is modified in association with these changes. With this knowledge, we create a series of samples with various sizes but the same microstructure. We find the following. (1) The Curie temperature decreases relative to the bulk as size decreases. The decrease is consistent with finite size scaling. (2) The fit of the spontaneous magnetization to the Bloch ${\mathit{T}}^{3/2}$ law yields a Bloch constant larger than the bulk increasing with decreasing size in proportion to the specific surface area of the particles. We find a better fit is obtained if the exponent of the temperature is increased to be in the range 1.6 to 1.8. (3) The saturation magnetization decreases with decreasing size also in proportion to the specific surface area of the particles. \textcopyright{} 1996 The American Physical Society.

486 citations

Journal ArticleDOI
TL;DR: The magnetic and structural data suggested a core-shell type of structure, where the core consists of metallic Fe and the shell is composed of Fe oxides, with the higher values corresponding to larger particles.
Abstract: The magnetic and morphological properties of fine Fe particles have been studied. Ultrafine particles of Fe were prepared using a vapor deposition technique under an argon atmosphere. The argon pressure was varied from 0.5 to 8 Torr during evaporation, and samples with a median diameter in the range 50--200 \AA{} were obtained having a log-normal distribution. The dependence of magnetic properties on particle size and temperature (10 KT300 K) were studied using superconducting-quantum-interference-device magnetometry and M\"ossbauer spectroscopy. Samples with particle diameter below 90 \AA{} showed a superparamagnetic behavior below room temperature. The saturation magnetization of the particles varied from 25 to 190 emu/g, with the higher values corresponding to larger particles. For these larger particles, a coercivity of 1.05 kOe was obtained at room temperature. The magnetic and structural data suggested a core-shell type of structure, where the core consists of metallic Fe and the shell is composed of Fe oxides.

456 citations

Journal ArticleDOI
TL;DR: In this article, the nonvolatile dodecanethiol ligand was used to control dewetting and gold nanocrystal superlattices can be formed on silicon nitride substrates with long range ordering over several microns.
Abstract: Particle−particle and particle−substrate interactions cause nanocrystals to self-assemble into superlattice structures upon drying from a colloidal suspension on a solid surface. Rapid dewetting of a volatile solvent, however, can significantly undermine the degree of ordering. We demonstrate here that by increasing the concentration of the nonvolatile dodecanethiol ligand, dewetting can be controlled and gold nanocrystal superlattices can be formed on silicon nitride substrates with long range ordering over several microns. Monolayer and bilayer superlattices can be produced by adjusting the nanocrystal concentration. The superlattice structures are robust and are not perturbed by the final dewetting of the solvent.

396 citations


Cited by
More filters
28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组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�ly.
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。

18,940 citations

Journal ArticleDOI
TL;DR: A review of gold nanoparticles can be found in this article, where the most stable metal nanoparticles, called gold colloids (AuNPs), have been used for catalysis and biology applications.
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

11,752 citations

Journal ArticleDOI
TL;DR: The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties are equally important.
Abstract: The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

6,852 citations

Journal ArticleDOI
TL;DR: This review discusses the synthetic chemistry, fluid stabilization and surface modification of superparamagnetic iron oxide nanoparticles, as well as their use for above biomedical applications.

6,207 citations