Thermo-Mechanical Modeling of Carbon Nanotube Thermal Interfaces

In the last decade, much research has attempted to develop a highly conducting and mechanically reliable thermal interface material. Vertically aligned carbon nanotube arrays (CNTs) is a promising thermal interface material due to the high thermal conductivity of each CNT and the mechanical compliance of CNT arrays [1]. The computational modeling of CNTs is usually at an atomistic scale; however, atomistic simulations are computationally expensive for modeling macroscopic CNT arrays used in experiments. Coarse grain simulation techniques [2] have been developed to reduce the number of degrees of freedom and hence making large scale simulations computationally tractable. The purpose of this project is to build a nanoHUB tool for performing coarse grain simulations of vertically aligned CNT arrays. The tool simplifies the simulation process and allows for parametric studies that would help in the design optimization of CNT thermal interface materials. Geometric parameters such as CNT array height, spacing, and CNT diameter can be input from the GUI and results such as stress-strain curve and Young’s modulus of the array can be downloaded. The pressure dependence of thermal contact resistance can also be obtained from the tool. This tool is expected to be useful to experimental researchers working in the field of CNT-based thermal interfaces

Potential Role of Sugars in the Hyphosphere of Arbuscular Mycorrhizal Fungi to Enhance Organic Phosphorus Mobilization

Arbuscular mycorrhizal (AM) fungi engage in symbiosis with more than 80% of terrestrial plants, enlarging root phosphorus (P) absorption volume by producing extensive extraradical hyphae (ERH) in the soil. In addition, AM fungi recruit and cooperate with soil bacteria to enhance soil organic P mobilization and improve fungal and plant fitness through hyphal exudates. However, the role of the dominant compounds in the hyphal exudates in enhancing organic P mobilization in the mycorrhizal pathway is still not well understood. In this study, we added sugars, i.e., glucose, fructose, and trehalose, which are detected in the hyphal exudates, to the hyphal compartments (HCs) that allowed the ERH of the AM fungus to grow or not. The results showed that in AM fungus-inoculated pots, adding three sugars at a concentration of 2 mmol C kg-1 soil significantly increased the phosphatase activity and facilitated the mobilization of organic P in the HCs. The addition of fructose at a concentration of 2 mmol C kg-1 soil was the most efficient in increasing the phosphatase activity and enhancing organic P mobilization. The released inorganic P was then absorbed by the ERH of the AM fungus. The enhanced mobilization of organic P was correlated with the increase in phoD gene number and the changing bacterial community in the presence of fungal hyphae. The sugar addition enriched the relative abundance of some bacterial taxa, e.g., Betaproteobacteriales. Our study suggested that the addition of the sugars by mycorrhizae could be a pivotal strategy in managing P uptake in agricultural production, potentially directing future practices to optimize plant-fungi-bacteria interactions for improved P use efficiency.</p

Identifying teleconnections and multidecadal variability of East Asian surface temperature during the last millennium in CMIP5 simulations

We examine the relationships in models and reconstructions between the multidecadal variability of surface temperature in East Asia and two extratropical modes of variability: the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). We analyse the spatial, temporal and spectral characteristics of the climate modes in the last millennium, historical and pre-industrial control simulations of seven Coupled Model Intercomparison Project phase 5 (CMIP5)/Paleoclimate Model Intercomparison Project phase 3 (PMIP3) global climate models (GCMs) to assess the relative influences of external forcing and unforced variability. These models produce PDO and AMO variability with realistic spatial patterns but widely varying spectral characteristics. AMO internal variability significantly influences East Asian temperature in five models (MPI, HadCM3, MRI, IPSL and CSIRO) but has a weak influence in the other two (BCC and CCSM4). In most models, external forcing greatly strengthens these statistical associations and hence the apparent teleconnection with the AMO. PDO internal variability strongly influences East Asian temperature in two out of seven models, but external forcing makes this apparent teleconnection much weaker. This indicates that the AMO–East Asian temperature relationship is partly driven by external forcing, whereas the PDO–temperature relationship is largely from internal variability within the climate system. Our findings suggest that external forcing confounds attempts to diagnose the teleconnections of internal multidecadal variability. Using AMO and PDO indices that represent internal variability more closely and minimising the influence of external forcing on East Asian temperature can partly ameliorate this confounding effect. Nevertheless, these approaches still yield differences between the forced and control simulations and they cannot always be applied to paleoclimate reconstructions. Thus, we recommend caution when interpreting teleconnections diagnosed from reconstructions that contain both forced and internal variations

Biophysics at the coffee shop: lessons learned working with George Oster

Over the past 50 years, the use of mathematical models, derived from physical reasoning, to describe molecular and cellular systems has evolved from an art of the few to a cornerstone of biological inquiry. George Oster stood out as a pioneer of this paradigm shift from descriptive to quantitative biology not only through his numerous research accomplishments, but also through the many students and postdocs he mentored over his long career. Those of us fortunate enough to have worked with George agree that his sharp intellect, physical intuition and passion for scientific inquiry not only inspired us as scientists but also greatly influenced the way we conduct research. We would like to share a few important lessons we learned from George in honor of his memory and with the hope that they may inspire future generations of scientists.Comment: 22 pages, 3 figures, accepted in Molecular Biology of the Cel

Curcumin Inhibits Neuronal and Vascular Degeneration in Retina after Ischemia and Reperfusion Injury

Neuron loss, glial activation and vascular degeneration are common sequelae of ischemia-reperfusion (I/R) injury in ocular diseases. The present study was conducted to explore the ability of curcumin to inhibit retinal I/R injury, and to investigate underlying mechanisms of the drug effects.Different dosages of curcumin were administered. I/R injury was induced by elevating the intraocular pressure for 60 min followed by reperfusion. Cell bodies, brn3a stained cells and TUNEL positive apoptotic cells in the ganglion cell layer (GCL) were quantitated, and the number of degenerate capillaries was assessed. The activation of glial cells was measured by the expression level of GFAP. Signaling pathways including IKK-IκBα, JAK-STAT1/3, ERK/MAPK and the expression levels of β-tubulin III and MCP-1 were measured by western blot analysis. Pre-treatment using 0.01%-0.25% curcumin in diets significantly inhibited I/R-induced cell loss in GCL. 0.05% curcumin pre-treatment inhibited I/R-induced degeneration of retinal capillaries, TUNEL-positive apoptotic cell death in the GCL, brn3a stained cell loss, the I/R-induced up-regulation of MCP-1, IKKα, p-IκBα and p-STAT3 (Tyr), and down-regulation of β-tubulin III. This dose showed no effect on injury-induced GFAP overexpression. Moreover, 0.05% curcumin administered 2 days after the injury also showed a vaso-protective effect.Curcumin protects retinal neurons and microvessels against I/R injury. The beneficial effects of curcumin on neurovascular degeneration may occur through its inhibitory effects on injury-induced activation of NF-κB and STAT3, and on over-expression of MCP-1. Curcumin may therefore serve as a promising candidate for retinal ischemic diseases

Impacts of ozone on trees and crops

Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Comptes Rendus Geosciences 339 (2007): 784-798, doi:10.1016/j.crte.2007.08.008.In this review article, we explore how surface-level ozone affects trees and crops with special emphasis on consequences for productivity and carbon sequestration. Vegetation exposure to ozone reduces photosynthesis, growth, and other plant functions. Ozone formation in the atmosphere is a product of NOx that are also a source of nitrogen deposition. Reduced carbon sequestration of temperate forests resulting from ozone is likely offset by increased carbon sequestration from nitrogen fertilization. However, since fertilized croplands are generally not nitrogen-limited, capping ozone-polluting substances in the U.S., Europe, and China can reduce future crop yield loss substantially.This study was funded by the Biocomplexity Program of the U.S. National Science Foundation (ATM-0120468), the Methods and Models for Integrated Assessment Program of the U.S. National Science Foundation (DEB-9711626) and the Earth Observing System Program of the U.S. National Aeronautics and Space Administration (NAG5-10135)

On the Dynamical and Physical State of the `Diffuse Ionized Medium' in Nearby Spiral Galaxies

We have analyzed deep narrow-band H$\alpha$ images and high-resolution long-slit spectra for a sample of the nearest and brightest late-type galaxies to study the morphology, physical state, and kinematics of the `Diffuse Ionized Medium' (`DIM'). We find that the DIM covers most of the star-forming disk, and is morphologically related to the presence of the giant HII regions. In addition, the DIM and the giant HII regions differ systematically in their physical and dynamical state. The DIM is characterized by enhanced emission in the low-ionization forbidden lines ([OI], [NII], and [SII]), and even the high-ionization [OIII]$\lambda$5007 line is moderately strong in the DIM. We verify the inference made by Lehnert & Heckman that the DIM contributes significantly to the global emission-line ratios measured in late-type galaxies. We also find that the DIM is more disturbed kinematically than the gas in the giant HII regions. The intrinsic FWHMs of the H$\alpha$ and [NII]$\lambda$6584 lines range from 30 to 100 km s$^{-1}$ in the DIM compared to 20-50 km s$^{-1}$ in HII regions. The high-ionization gas in the DIM is even more kinematically disturbed than the low-ionization gas: the [OIII]$\lambda$5007 lines have intrinsic FWHMs of 70-150 km s$^{-1}$. The differing kinematics implies that `the DIM' is not a single monolithic phase of the ISM. Instead, it may consist of a `quiescent DIM' with a low ionization-state and small scale-height (few hundred pc) and a `disturbed DIM' with a high ionization state and moderate scale-height (0.5 to 1 kpc). We argue that the quiescent DIM is most likely photoionized by radiation leaking out of giant HII regions, while the disturbed DIM is most likely heated by the mechanical energy supplied by supernovae and stellar winds.Comment: 37 pages(including 7 tables) and 12 figures. To appear in the Dec 10, 1997 issue of The Astrophysical Journa