Nonuniversality of the dispersion interaction: analytic benchmarks for van der Waals energy functionals

We highlight the non-universality of the asymptotic behavior of dispersion forces, such that a sum of inverse sixth power contributions is often inadequate. We analytically evaluate the cross-correlation energy Ec between two pi-conjugated layers separated by a large distance D within the electromagnetically non-retarded Random Phase Approximation, via a tight-binding model. For two perfect semimetallic graphene sheets at T=0K we find Ec = C D^{-3}, in contrast to the "insulating" D^{-4} dependence predicted by currently accepted approximations. We also treat the case where one graphene layer is replaced by a thin metal, a model relevant to the exfoliation of graphite. Our general considerations also apply to nanotubes, nanowires and layered metals.Comment: 4 pages, 0 fig

Enhanced dispersion interaction between quasi-one dimensional conducting collinear structures

Recent investigations have highlighted the failure of a sum of $R^{-6}$ terms to represent the dispersion interaction in parallel metallic, anisotropic, linear or planar nanostructures [J. F. Dobson, A. White, and A. Rubio, Phys. Rev. Lett. 96, 073201 (2006) and references therein]. By applying a simple coupled plasmon approach and using electron hydrodynamics, we numerically evaluate the dispersion (non-contact van der Waals) interaction between two conducting wires in a collinear pointing configuration. This case is compared to that of two insulating wires in an identical geometry, where the dispersion interaction is modelled both within a pairwise summation framework, and by adding a pinning potential to our theory leading to a standard oscillator-type model of insulating dielectric behavior. Our results provide a further example of enhanced dispersion interaction between two conducting nanosystems compared to the case of two insulating ones. Unlike our previous work, this calculation explores a region of relatively close coupling where, although the electronic clouds do not overlap, we are still far from the asymptotic region where a single power law describes the dispersion energy. We find that strong differences in dispersion attraction between metallic and semiconducting / insulating cases persist into this non-asymptotic region. While our theory will need to be supplemented with additional short-ranged terms when the electronic clouds overlap, it does not suffer from the short-distance divergence exhibited by purely asymptotic theories, and gives a natural saturation of the dispersion energy as the wires come into contact.Comment: 10 pages, 5 figures. Added new extended numerical calculations, new figures, extra references and heavily revised tex

Cascading blackout overall structure and some implications for sampling and mitigation

Cascading blackouts can be thought of as initiating events followed by propagating events that progressively weaken the power system. We briefly discuss the implications for assessing cascading risk by proper sampling from the various sources of uncertainty and for mitigating cascading risk by reducing both the initiating events and their propagation

Mechanism of Lck Activation in Driving Leukemia Cell Proliferation

Leukemia is a type of cancer that develops in blood-forming tissues of the immune system. These tissues can include the bone marrow or sites within the lymphatic system such as the lymph nodes. Leukemia progresses from a mutational event within a white blood cell. Often this mutation alters the cell’s normal life cycle, resulting in uninhibited cell division and growth. With this uncontrolled cell proliferation, mutated white blood cells accumulate and begin interfering with the functioning of healthy cells. Scientists are unsure of the exact mechanisms required for leukemia development. However, recently scientists identified four characteristic mutations in the protein tyrosine kinase, Lck, found specifically in the CTV-1 leukemia cell line. Lck is suspected to play an important regulatory role in immune system cell growth. In this honors project, I introduced these mutations into the Lck gene and produced the wildtype and the mutant enzymes. By comparing the mutated enzyme’s activity to the wild-type enzyme’s activity, we can potentially better understand how a mutation in Lck could stimulate cell proliferation. One of the mutations is an insertion mutation located in the linker region of the Lck’s structure. It is a potentially interesting alteration that could result in the enzyme’s constitutive activation. This inability for the enzyme to be turned off not only demonstrates how mutated Lck could be contributing to cancer progression but also reveals valuable knowledge about the functional importance of the linker region in Lck

ENGL64.05: Cultural Analytics

Syllabus for ENGL 64.05 "Cultural Analytics," taught Fall 2019 at Dartmouth College

A study of chemical stabilization of the swell properties of Putman soil

The theory of chemical stabilization of a swelling clay was reviewed. The effect of several chemicals on the engineering properties of Putnam soil was investigated using the Atterberg tests. Strength of concentration of chemical additives versus preferred structural orientation of treated Putnam was investigated using sedimentation procedures similar to those used in the hydrometer analysis of fine grained soil sizes. Swell tests were conducted under a static load of 1.25 psi on untreated Putnam, Putnam in combination with sodium carbonate, and Putnam treated with calcium hydroxide. These tests were conducted at varying initial moisture contents and dry densities. It was found from the swell tests that the measured swell of Putnam under the load used was uniquely related to the initial moisture content of the sample --Abstract, page ii