Nonlinear current-induced forces in Si atomic wires

We report first-principles calculations of current-induced forces in Si atomic wires as a function of bias and wire length. We find that these forces are strongly nonlinear as a function of bias due to the competition between the force originating from the scattering states and the force due to bound states. We also find that the average force in the wire is larger the shorter the wire, suggesting that atomic wires are more difficult to break under current flow with increasing length. The last finding is in agreement with recent experimental data.Comment: 4 figure

Calcium Remodeling through Different Signaling Pathways in Heart Failure: Arrhythmogenesis Studies of Pyk2, Dystrophin, and β-adrenergic Receptor Signaling

Heart failure is a common clinical syndrome that ensues when the heart is no longer able to generate sufficient cardiac output to meet the demands of the body. It is one of the leading causes of death worldwide but with limited and non-ideal therapies at the moment. One reason behind this may be the complexity of significant alterations in multiple signaling pathways and concomitant structural and functional remodeling, especially Ca handling. Ca is critical in both the electrical and mechanical properties of cardiac myoctyes, and much is known about ionic currents and the normal excitation-contraction coupling process. In heart failure, distinct impaired signaling pathways induce significant alterations in how cardiac Ca handling is regulated. These alterations either directly cause certain arrhythmias or facilitate arrhythmias by association with electrical remodeling. The goal of this dissertation was to investigate the mechanisms of calcium remodeling through different signaling pathways in heart failure, and mechanisms on how the intricate and dynamic interactions between Ca handling and signaling pathways impairment facilitate arrhythmias in heart failure. To achieve this goal, a dual optical mapping system was designed to investigate electrical activity and Ca transient simultaneously. High spatio-temporal resolution mapping allows for quantifying conduction, repolarization and Ca cycling, especially on the interactions between action potential and Ca handling. In this dissertation, I investigated Ca remodeling in three different signaling pathways: stress activated signaling, cytoskeletal signaling and β adrenergic receptor signaling pathway. Proline-rich tyrosine kinase 2: Pyk2) is a non-receptor protein kinase regulated by intracellular Ca. It mediates a typical stress activated signaling pathways along with c-Src, P38 MAPK and regulates a broad range of key biological responses. By optically mapping the genetically engineered mouse model: Pyk2 knockout, I detected a protective role of Pyk2 with respect to ventricular tachyarrhythmia during parasympathetic stimulation by regulation of gene expression related to calcium handling. The mdx mouse model was introduced in the investigation of cytoskeletal signaling pathway. mdx mice is a common model for Duchenne muscular dystrophy, which is a clinical syndrome resulted from recessive of dystrophin and eventually develops into heart failure. The project suggested the association of mechanical stimulation and deficiency of dystrophin account for the cardiac mechanical defects and resulting Ca mishandling, but not either of the two above-mentioned entities alone. Ca mishandling leads to Ca cycling dispersion, which facilitates generation of arrhythmias. β Adrenergic receptor signaling pathway was investigated on explanted donor and failing human hearts. Distinct β adrenergic receptor subtypes were found to regulate remodeling differently. The association between remodeling of action potential and Ca transient provides crucial arrhythmic drivers and substrate in heart failure

Dissecting the FEAST algorithm for generalized eigenproblems

We analyze the FEAST method for computing selected eigenvalues and eigenvectors of large sparse matrix pencils. After establishing the close connection between FEAST and the well-known Rayleigh-Ritz method, we identify several critical issues that influence convergence and accuracy of the solver: the choice of the starting vector space, the stopping criterion, how the inner linear systems impact the quality of the solution, and the use of FEAST for computing eigenpairs from multiple intervals. We complement the study with numerical examples, and hint at possible improvements to overcome the existing problems.Comment: 11 Pages, 5 Figures. Submitted to Journal of Computational and Applied Mathematic

Electron-Transport Properties of Na Nanowires under Applied Bias Voltages

We present first-principles calculations on electron transport through Na nanowires at finite bias voltages. The nanowire exhibits a nonlinear current-voltage characteristic and negative differential conductance. The latter is explained by the drastic suppression of the transmission peaks which is attributed to the electron transportability of the negatively biased plinth attached to the end of the nanowire. In addition, the finding that a voltage drop preferentially occurs on the negatively biased side of the nanowire is discussed in relation to the electronic structure and conduction.Comment: 4 pages, 6 figure

Current-Induced Effects in Nanoscale Conductors

We present an overview of current-induced effects in nanoscale conductors with emphasis on their description at the atomic level. In particular, we discuss steady-state current fluctuations, current-induced forces, inelastic scattering and local heating. All of these properties are calculated in terms of single-particle wavefunctions computed using a scattering approach within the static density-functional theory of many-electron systems. Examples of current-induced effects in atomic and molecular wires will be given and comparison with experimental results will be provided when available.Comment: revtex, 10 pages, 8 figure

Single-particle and Interaction Effects on the Cohesion and Transport and Magnetic Properties of Metal Nanowires at Finite Voltages

The single-particle and interaction effects on the cohesion, electronic transport, and some magnetic properties of metallic nanocylinders have been studied at finite voltages by using a generalized mean-field electron model. The electron-electron interactions are treated in the self-consistent Hartree approximation. Our results show the single-particle effect is dominant in the cohesive force, while the nonzero magnetoconductance and magnetotension coefficients are attributed to the interaction effect. Both single-particle and interaction effects are important to the differential conductance and magnetic susceptibility.Comment: 5 pages, 6 figure

A Market-Based Approach to Facilitate the Organizational Adoption of Software Component Reuse Strategies

Despite the theoretical benefits of software component reuse (and the abundance of component-based software development on the vendor side), the adoption of component reuse strategies at the organizational level (on the client side) remains low in practice. According to research, the main barrier to advancing component-based reuse strategies into a robust industrial process is coordination failures between software producers and their customers, which result in high acquisition costs for customers. We introduce a component reuse licensing model and combine it with a dynamic price discovery mechanism to better coordinate producers’ capabilities and customer needs. Using an economic experiment with 28 IT professionals, we investigate the extent to which organizations may be able to leverage component reuse for performance improvements. Our findings suggest that implementing component reuse can assist organizations in addressing the issue of coordination failure with software producers while also lowering acquisition costs. We argue that similar designs can be deployed in practice and deliver benefits to software development in organizations and the software industry

Strategy Dynamics in Markets of Software Components

In this paper we propose a dynamic model of a software market for component reuse. We investigate the market dynamics using experiments with economically motivated human subjects. Our results suggest that the introduction of the software component market reduces production costs and increases vendor profits. The dynamic interactions in the component market helped vendors coordinate better their production decisions and resulted in production cost savings. The component market can thrive on a balance between competition and cooperation of software vendors. These experimental results could be applied with some modifications to the development of software products in general

Shot noise in parallel wires

We report first-principles calculations of shot noise properties of parallel carbon wires in the regime in which the interwire distance is much smaller than the inelastic mean free path. We find that, with increasing interwire distance, the current approaches rapidly a value close to twice the current of each wire, while the Fano factor, for the same distances, is still larger than the Fano factor of a single wire. This enhanced Fano factor is the signature of the correlation between electron waves traveling along the two different wires. In addition, we find that the Fano factor is very sensitive to bonding between the wires, and can vary by orders of magnitudes by changing the interwire spacing by less than 0.5 \AA. While these findings confirm that shot noise is a very sensitive tool to probe electron transport properties in nanoscale conductors, they also suggest that a considerable experimental control of these structures is required to employ them in electronics.Comment: 5 figure