AFM, SEM and TEM Studies on Porous Anodic Alumina

Porous anodic alumina (PAA) has been intensively studied in past decade due to its applications for fabricating nanostructured materials. Since PAA’s pore diameter, thickness and shape vary too much, a systematical study on the methods of morphology characterization is meaningful and essential for its proper development and utilization. In this paper, we present detailed AFM, SEM and TEM studies on PAA and its evolvements with abundant microstructures, and discuss the advantages and disadvantages of each method. The sample preparation, testing skills and morphology analysis are discussed, especially on the differentiation during characterizing complex cross-sections and ultrasmall nanopores. The versatility of PAAs is also demonstrated by the diversity of PAAs’ microstructure

Factors influencing the abundance of the side population in a human myeloma cell line

2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Effect of stress relieving heat treatment on surface topography and dimensional accuracy of incrementally formed grade 1 titanium sheet parts

The forming of parts with an optimized surface roughness and high dimensional accuracy is important in many applications of incremental sheet forming (ISF). To realize this, the effect of stress relieving heat treatment of grade-1 Ti parts performed before and after forming on the surface finish and dimensional accuracy was studied. It was found that heat treatment at a temperature of 540 °C for 2 h improves the surface finish of formed parts resulting in a surface with little or no visible tool marks. Additionally, it improves the dimensional accuracy of parts after unclamping from the rig used for forming, in particular, that of parts with shallow wall angles (typically <25°). It was also noted that post-forming heat treatment improves the surface finish of parts. The surface topography of formed parts was studied using interferometry to yield areal surface roughness parameters and subsequently using secondary electron imaging. Back-scatter electron microscopy imaging results coupled with energy-dispersive X-ray (EDX) analysis showed that heat treatment prior to forming leads to tool wear as indicated by the presence of Fe in samples. Furthermore, post-forming heat treatment prevents curling up of formed parts due to compressive stresses if the formed part is trimmed

The Effects of Puerarin on Rat Ventricular Myocytes and the Potential Mechanism

Puerarin, a known isoflavone, is commonly found as a Chinese herb medicine. It is widely used in China to treat cardiac diseases such as angina, cardiac infarction and arrhythmia. However, its cardioprotective mechanism remains unclear. In this study, puerarin significantly prolonged ventricular action potential duration (APD) with a dosage dependent manner in the micromolar range on isolated rat ventricular myocytes. However, submicromolar puerarin had no effect on resting membrane potential (RMP), action potential amplitude (APA) and maximal velocity of depolarization (Vmax) of action potential. Only above the concentration of 10 mM, puerarin exhibited more aggressive effect on action potential, and shifted RMP to the positive direction. Millimolar concentrations of puerarin significantly inhibited inward rectified K+ channels in a dosage dependent manner, and exhibited bigger effects upon Kir2.1 vs Kir2.3 in transfected HEK293 cells. As low as micromolar range concentrations of puerarin significantly inhibited Kv7.1 and IKs. These inhibitory effects may due to the direct inhibition of puerarin upon channels not via the PKA-dependent pathway. These results provided direct preclinical evidence that puerarin prolonged APD via its inhibitory effect upon Kv7.1 and IKs, contributing to a better understanding the mechanism of puerarin cardioprotection in the treatment of cardiovascular diseases

Phylogeography of the South China Field Mouse (Apodemus draco) on the Southeastern Tibetan Plateau Reveals High Genetic Diversity and Glacial Refugia

The southeastern margin of the Tibetan Plateau (SEMTP) is a particularly interesting region due to its topographic complexity and unique geologic history, but phylogeographic studies that focus on this region are rare. In this study, we investigated the phylogeography of the South China field mouse, Apodemus draco, in order to assess the role of geologic and climatic events on the Tibetan Plateau in shaping its genetic structure. We sequenced mitochondrial cytochrome b (cyt b) sequences in 103 individuals from 47 sampling sites. In addition, 23 cyt b sequences were collected from GenBank for analyses. Phylogenetic, demographic and landscape genetic methods were conducted. Seventy-six cyt b haplotypes were found and the genetic diversity was extremely high (π = 0.0368; h = 0.989). Five major evolutionary clades, based on geographic locations, were identified. Demographic analyses implied subclade 1A and subclade 1B experienced population expansions at about 0.052-0.013 Mya and 0.014-0.004 Mya, respectively. The divergence time analysis showed that the split between clade 1 and clade 2 occurred 0.26 Mya, which fell into the extensive glacial period (EGP, 0.5-0.17 Mya). The divergence times of other main clades (2.20-0.55 Mya) were congruent with the periods of the Qingzang Movement (3.6-1.7 Mya) and the Kun-Huang Movement (1.2-0.6 Mya), which were known as the most intense uplift events in the Tibetan Plateau. Our study supported the hypothesis that the SEMTP was a large late Pleistocene refugium, and further inferred that the Gongga Mountain Region and Hongya County were glacial refugia for A. draco in clade 1. We hypothesize that the evolutionary history of A. draco in the SEMTP primarily occurred in two stages. First, an initial divergence would have been shaped by uplift events of the Tibetan Plateau. Then, major glaciations in the Pleistocene added complexity to its demographic history and genetic structure

Homeostatic Scaling of Excitability in Recurrent Neural Networks

Neurons adjust their intrinsic excitability when experiencing a persistent change in synaptic drive. This process can prevent neural activity from moving into either a quiescent state or a saturated state in the face of ongoing plasticity, and is thought to promote stability of the network in which neurons reside. However, most neurons are embedded in recurrent networks, which require a delicate balance between excitation and inhibition to maintain network stability. This balance could be disrupted when neurons independently adjust their intrinsic excitability. Here, we study the functioning of activity-dependent homeostatic scaling of intrinsic excitability (HSE) in a recurrent neural network. Using both simulations of a recurrent network consisting of excitatory and inhibitory neurons that implement HSE, and a mean-field description of adapting excitatory and inhibitory populations, we show that the stability of such adapting networks critically depends on the relationship between the adaptation time scales of both neuron populations. In a stable adapting network, HSE can keep all neurons functioning within their dynamic range, while the network is undergoing several (patho)physiologically relevant types of plasticity, such as persistent changes in external drive, changes in connection strengths, or the loss of inhibitory cells from the network. However, HSE cannot prevent the unstable network dynamics that result when, due to such plasticity, recurrent excitation in the network becomes too strong compared to feedback inhibition. This suggests that keeping a neural network in a stable and functional state requires the coordination of distinct homeostatic mechanisms that operate not only by adjusting neural excitability, but also by controlling network connectivity

Identifying Regulators for EAG1 Channels with a Novel Electrophysiology and Tryptophan Fluorescence Based Screen

Ether-à-go-go (EAG) channels are expressed throughout the central nervous system and are also crucial regulators of cell cycle and tumor progression. The large intracellular amino- and carboxy- terminal domains of EAG1 each share similarity with known ligand binding motifs in other proteins, yet EAG1 channels have no known regulatory ligands.Here we screened a library of small biologically relevant molecules against EAG1 channels with a novel two-pronged screen to identify channel regulators. In one arm of the screen we used electrophysiology to assess the functional effects of the library compounds on full-length EAG1 channels. In an orthogonal arm, we used tryptophan fluorescence to screen for binding of the library compounds to the isolated C-terminal region.Several compounds from the flavonoid, indole and benzofuran chemical families emerged as binding partners and/or regulators of EAG1 channels. The two-prong screen can aid ligand and drug discovery for ligand-binding domains of other ion channels

Expression Patterns of Genes Involved in Sugar Metabolism and Accumulation during Apple Fruit Development

Both sorbitol and sucrose are imported into apple fruit from leaves. The metabolism of sorbitol and sucrose fuels fruit growth and development, and accumulation of sugars in fruit is central to the edible quality of apple. However, our understanding of the mechanisms controlling sugar metabolism and accumulation in apple remains quite limited. We identified members of various gene families encoding key enzymes or transporters involved in sugar metabolism and accumulation in apple fruit using homology searches and comparison of their expression patterns in different tissues, and analyzed the relationship of their transcripts with enzyme activities and sugar accumulation during fruit development. At the early stage of fruit development, the transcript levels of sorbitol dehydrogenase, cell wall invertase, neutral invertase, sucrose synthase, fructokinase and hexokinase are high, and the resulting high enzyme activities are responsible for the rapid utilization of the imported sorbitol and sucrose for fruit growth, with low levels of sugar accumulation. As the fruit continues to grow due to cell expansion, the transcript levels and activities of these enzymes are down-regulated, with concomitant accumulation of fructose and elevated transcript levels of tonoplast monosaccharide transporters (TMTs), MdTMT1 and MdTMT2; the excess carbon is converted into starch. At the late stage of fruit development, sucrose accumulation is enhanced, consistent with the elevated expression of sucrose-phosphate synthase (SPS), MdSPS5 and MdSPS6, and an increase in its total activity. Our data indicate that sugar metabolism and accumulation in apple fruit is developmentally regulated. This represents a comprehensive analysis of the genes involved in sugar metabolism and accumulation in apple, which will serve as a platform for further studies on the functions of these genes and subsequent manipulation of sugar metabolism and fruit quality traits related to carbohydrates

An efficient method for thickness prediction in multi-pass incremental sheet forming

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. In the ISF process, efficient and accurate prediction of part thickness variation is still a challenging task, which is especially true for the multi-pass ISF process. The Sine law equation and the finite element method (FEM) are the two commonly used conventional prediction methods. However, these approaches are either with limited accuracy or very time consuming. For the multi-pass ISF process, the thickness prediction is even more challenging since two or more forming steps are involved. Focusing on the thickness prediction of multi-stage ISF process, this work proposes a thickness prediction model based on the geometrical calculation of intermediate shapes of the formed part and backward tracing of nodal points of the forming tool. By developing this method, the thickness distribution can be calculated through the predicted nodal displacement in the ISF process. To verify the proposed model, four different geometrical shapes, i.e., conic, parabolic conic, non-axisymmetric, and hemispherical parts, are physically formed by using a NC ISF machine. The geometric shapes and the detailed thickness distributions of the formed parts are carefully measured and compared with the prediction model developed. Good agreements between the analytical predictions, and the experimental results are obtained. This indicates the effectiveness and robustness of the developed thickness prediction approach