A review of self-assembled monolayers as potential terahertz frequency tunnel diodes

In this review, we describe the principles of the tunnel junction, self-assembled monolayer （SAM） application techniques, experimental testbed fabrication, and characterization of the films and devices. In addition, techniques for directed application, removal, and functionalization of the monolayers are discussed. Bottom-up fabrication techniques have seen increased attention because of their versatility and ease of use. These films see mechanical uses as surface modifiers and micro-scale lubricants. Advances in nanowatt electronics and ultra-low power sensors have opened up an energy harvesting niche for solutions which would have proven ineffective just some years ago. The focus of this study is the two- terminal junction which has potential applications in THz rectification for energy harvesting, medical imaging, and defense sensing. The quantum theory of operation behind these devices is touched on briefly---describing tunneling through the organic monolayers. Commentary on trends in research and potential future work are presented as well.     

Kinetic modeling of high temperature oxidation of Ni-base alloys

The rates of isothermal and cyclic oxidation and the elemental concentration profiles as a function of time of oxidation for a few Ni-base superalloys were determined through a modified Wagner’s oxidation model and the solution of coupled elemental diffusion equations. Thermodynamically calculated interfacial elemental concentrations and oxygen partial pressures for the multi-component Ni-base alloys were used as boundary conditions for the solution of Wagner’s equation and the elemental coupled diffusion equations (for Cr, Al and O). The multiple elemental diffusion and mass conservation equations were solved using a numerical procedure. The dependence of self/tracer-diffusivities of Cr, Al and O in the corundum phase on the oxygen partial pressures was deduced using a genetic algorithm based optimization procedure incorporating the experimental parabolic rate constants for several Ni-base alloys. Rates of cyclic oxidation were then deduced from the deterministic interfacial cyclic oxidation spalling model (DICOSM) developed by Smialek [1]. The calculated oxidation rates were in reasonable agreement with the experimental values for a range of multi-component Ni-base alloys.     

Cell‐Tethered Ligands Modulate Bone Remodeling by Osteoblasts and Osteoclasts

The goals of the present study are to establish an in vitro co‐culture model of osteoblast and osteoclast function and to quantify the resulting bone remodeling. The bone is tissue engineered using well‐defined silk protein biomaterials in 2D and 3D formats in combination with human cells. Parathyroid hormone (PTH) and glucose‐dependent insulinotropic peptide (GIP) are selected because of their roles in bone remodeling for expression in tethered format on human mesenchymal stem cells (hMSCs). The cell‐modified biomaterial surfaces are reconstructed from scanning electron microscopy images into 3D models for quantitative measurement of surface characteristics. Increased calcium deposition and surface roughness are found in 3D surface models of silk protein films remodeled by co‐cultures containing tethered PTH, and decreased surface roughness is found for the films remodeled by tethered GIP co‐cultures. Increased surface roughness is not found in monocultures of hMSCs expressing tethered PTH, suggesting that osteoclast‐osteoblast interactions in the presence of PTH signaling are responsible for the increased mineralization. These data point towards the design of in vitro bone models in which osteoblast‐osteoclast interactions are mimicked for a better understanding of bone remodeling.     

Interaction between a cellular protein that binds to the C-terminal region of adenovirus E1A (CtBP) and a novel cellular protein is disrupted by E1A through a conserved PLDLS motif

Adenovirus E1A proteins immortalize primary animal cells and cooperate with several other oncogenes in oncogenic transformation. These activities are primarily determined by the N-terminal half (exon 1) of E1A. Although the C-terminal half (exon 2) is also essential for some of these activities, it is dispensable for cooperative transformation with the activated T24 ras oncogene. Exon 2 negatively modulates in vitro cooperative transformation with T24 ras as well as the tumorigenic and metastatic potentials of transformed cells. A short C-terminal sequence of E1A governs the oncogenesis-restraining activity of exon 2. This region of E1A binds with a cellular phosphoprotein, CtBP, through a 5-amino acid motif, PLDLS, conserved among the E1A proteins of human adenoviruses. To understand the mechanism by which interaction between E1A and CtBP results in tumorigenesis-restraining activity, we searched for cellular proteins that complex with CtBP. Here, we report the cloning and characterization of a 125-kDa protein, CtIP, that binds with CtBP through the PLDLS motif. E1A exon 2 peptides that contain the PLDLS motif disrupt the CtBP-CtIP complex. Our results suggest that the tumorigenesis-restraining activity of E1A exon 2 may be related to the disruption of the CtBP-CtIP complex through the PLDLS motif.     

A potent cell death activity associated with transient high level expression of BCL-2

The BCL-2 proto-oncogene contains unusually long untranslated 5' and 3' sequences. Deletion of the sequences flanking the BCL-2 open reading frame dramatically increases the level of protein expression. Transient high level BCL-2 protein expression mediated by plasmid transfection or by infection with recombinant adenovirus results in potent apoptosis of several cell lines. Detailed mutational (deletion and add-back) analysis reveals that both 5'- and 3'-flanking sequences contribute to the negative modulation of protein expression from the BCL-2 open reading frame. It appears that these sequences exert the negative regulatory effect in an orientation-dependent manner. Analysis of BCL-2 RNA levels indicate that elevated levels of mRNA may be the primary cause of elevated levels of protein expression. Apoptosis induced by adenovirus vectors expressing elevated levels of BCL-2 can be readily inhibited by the caspase inhibitor z-VAD-fmk, suggesting that high levels of BCL-2 expression induce apoptosis via the caspase cascade. Mutational analysis of BCL-2 indicates that its pro-apoptotic activity is separable from its anti-apoptosis activity. Our results raise the possibility that oncogenic conversion of BCL-2 may require somatic mutations in the pro-apoptotic activity, in addition to other activating mutations that result in enhanced expression. Consistent with this hypothesis, a somatic mutation of BCL-2 observed in multiple human tumors results in reduced apoptosis activity.     

Development of nano-composite lead-free electronic solders

Inert, hybrid inorganic/organic, nano-structured chemicals can be incorporated into low melting metallic materials, such as lead-free electronic solders, to achieve desired levels of service performance. The nano-structured materials technology of polyhedral oligomeric silsesquioxanes (POSS), with appropriate organic groups, can produce suitable means to promote bonding between nano-reinforcements and the metallic matrix. The microstructures of lead-free solder reinforced with surface-active POSS tri-silanols were evaluated using scanning electron microscopy (SEM). Wettability of POSS-containing lead-free solders to copper substrate was also examined. Steady-state deformation of solder joints made of eutectic Sn-Ag solder containing varying weight fractions of POSS of different chemical moieties were evaluated at different temperatures (25°C, 100°C, and 150°C) using a rheometric solids analyzer (RSA-III). Mechanical properties such as shear stress versus simple shear-strain relationships, peak shear stress as a function of rate of simple shear strain, and testing temperature for such nano-composite solders are reported. The service reliability of joints made with these newly formulated nano-composite solders was evaluated using a realistic thermomechanical fatigue (TMF) test profile. Evolution of microstructures and residual mechanical property after different extents of TMF cycles were evaluated and compared with joints made of standard, unreinforced eutectic Sn-Ag solder.