Animal Communication: He’s Giving Me Good Vibrations

SummaryA unique bioassay allows a substrate-borne vibration signal to be isolated and manipulated to test its role in eliciting female mate choice, which may be driving a speciation event, by a live, unrestrained male

Supporting strategic design of workplace environments with case-based reasoning

XVII+279hlm.;24c

Agent-based computational modeling of wounded epithelial cell monolayers

Computational modeling of biological systems, or ‘in silico biology’ is an emerging tool for understanding structure and order in biological tissues. Computational models of the behavior of epithelial cells in monolayer cell culture have been developed and used to predict the healing characteristics of scratch wounds made to urothelial cell cultures maintained in low and physiological [Ca2+] environments. Both computational models and in vitro experiments demonstrated that in low exogenous [Ca2+], the closure of 500mm scratch wounds was achieved primarily by cell migration into the denuded area. The wound healing rate in low (0.09mM) [Ca2+] was approximately twice as rapid as in physiological (2mM) [Ca2+]. Computational modeling predicted that in cell cultures that are actively proliferating, no increase in the fraction of cells in S-phase would be expected, and this conclusion was supported experimentally in vitro by BrdU incorporation assay. We have demonstrated that a simple rule-based model of cell behavior, incorporating rules relating to contact inhibition of proliferation and migration, is sufficient to qualitatively predict the calcium-dependent pattern of wound closure observed in vitro. Differences between the in vitro and in silico models suggest a role for wound-induced signaling events in urothelial cell cultures

The Epitheliome: agent-based modelling of the social behaviour of cells

We have developed a new computational modelling paradigm for predicting the emergent behaviour resulting from the interaction of cells in epithelial tissue. As proof-of-concept, an agent-based model, in which there is a one-to-one correspondence between biological cells and software agents, has been coupled to a simple physical model. Behaviour of the computational model is compared with the growth characteristics of epithelial cells in monolayer culture, using growth media with low and physiological calcium concentrations. Results show a qualitative fit between the growth characteristics produced by the simulation and the in vitro cell models

Ionization of Infalling Gas

H-alpha emission from neutral halo clouds probes the radiation and hydrodynamic conditions in the halo. Armed with such measurements, we can explore how radiation escapes from the Galactic plane and how infalling gas can survive a trip through the halo. The Wisconsin H-Alpha Mapper (WHAM) is one of the most sensitive instruments for detecting and mapping optical emission from the ISM. Here, we present recent results exploring the ionization of two infallling high-velocity complexes. First, we report on our progress mapping H-alpha emission covering the full extent of Complex A. Intensities are faint (<100 mR; EM <0.2 pc cm^-6 but correlate on the sky and in velocity with 21-cm emission. Second, we explore the ionized component of some Anti-Center Complex clouds studied by Peek et al. (2007) that show dynamic shaping from interaction with the Galactic halo.Comment: 4 pages, 2 figures; to appear in proceedings of "The Role of Disk-Halo Interaction in Galaxy Evolution: Outflow vs Infall?" held in Espinho, Portugal during 2008 Augus

Natural Theories of Ultra-Low Mass PNGB's: Axions and Quintessence

We consider the Wilson Line PNGB which arises in a U(1)^N gauge theory, abstracted from a latticized, periodically compactified extra dimension U(1). Planck scale breaking of the PNGB's global symmetry is suppressed, providing natural candidates for the axion and quintessence. We construct an explicit model in which the axion may be viewed as the 5th component of the U(1)_Y gauge field in a 1+4 latticized periodically compactified extra dimension. We also construct a quintessence PNGB model where the ultra-low mass arises from Planck-scale suppressed physics itself.Comment: 20 pages, fixed typo and reference

Exchange and correlation effects on drag in low density electron bilayers: Coulomb and virtual-optical-phonon-mediated electron-electron interaction

We investigate the effect of exchange and correlation (xc) in low-density electron bilayers. Along with the direct Coulomb interaction, the effective electron-electron interaction mediated by the exchange of virtual polar optical (PO) phonons is considered. We find that the introduction of xc corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. The virtual PO-phonon contribution behaves similarly to the Coulomb drag and reduces noticeably the total drag thereby resulting in a better agreement with the recent experimental findings.Comment: 5 pages, 4 figures, Int. Conf. EP2DS-1

Multiband superconductivity in NbSe_2 from heat transport

The thermal conductivity of the layered s-wave superconductor NbSe_2 was measured down to T_c/100 throughout the vortex state. With increasing field, we identify two regimes: one with localized states at fields very near H_c1 and one with highly delocalized quasiparticle excitations at higher fields. The two associated length scales are most naturally explained as multi-band superconductivity, with distinct small and large superconducting gaps on different sheets of the Fermi surface.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Using design of experiments to improve a batch chemical process

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering; in conjunction with the Leaders for Global Operations Program at MIT, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 70-71).Novartis Vaccines and Diagnostics has made a strong commitment to manufacturing seasonal influenza vaccines through their cell culture technology called Optaflu®. The goal of this project is to improve overall process yield by modifying the upstream process. The focus is on using a batch process to generate a high-density cell culture and then infecting said culture. This thesis presents the approach of using a Design of Experiment series to change a manufacturing process. Current vaccine production occurs with a fed-batch process by feeding glucose as a carbon-energy source for the final cell expansion step. This cell culture is diluted, infected, harvested, and purified for use in an influenza vaccine. Primarily, the project aims to increase cell density, using a batch process, at the infection step which should improve overall process yield. The project can therefore be broken into two main steps: batch cell growth and highdensity infection. Experiments for this project were conducted with a small-scale laboratory process that mimics the production process. The planned approach was a Design of Experiment series to screen parameters and partially optimize the cell growth process, a scale-up cell growth experiment, and finally another Design of Experiment series to explore high-density cell infection. While initial small-scale experiments showed extremely positive results, the results were not consistent and could not be replicated at a larger scale. A number of exploratory experiments were run to attempt to identify which factors inhibit high-density cell growth, particularly around scale-up, but no key parameter was identified. Given the process improvement and cost savings implications from the success of the initial small-scale experiments, this project is worth further exploration.by Andrew Hill.S.M.M.B.A

Strong subadditivity inequality for quantum entropies and four-particle entanglement

Strong subadditivity inequality for a three-particle composite system is an important inequality in quantum information theory which can be studied via a four-particle entangled state. We use two three-level atoms in $\Lambda$ configuration interacting with a two-mode cavity and the Raman adiabatic passage technique for the production of the four-particle entangled state. Using this four-particle entanglement, we study for the first time various aspects of the strong subadditivity inequality.Comment: 5 pages, 3 figures, RevTeX4, submitted to PR