Seeing spin dynamics in atomic gases

The dynamics of internal spin, electronic orbital, and nuclear motion states of atoms and molecules have preoccupied the atomic and molecular physics community for decades. Increasingly, such dynamics are being examined within many-body systems composed of atomic and molecular gases. Our findings sometimes bear close relation to phenomena observed in condensed-matter systems, while on other occasions they represent truly new areas of investigation. I discuss several examples of spin dynamics that occur within spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive imaging for understanding and utilizing such dynamics.Comment: Chapter in upcoming Review Volume entitled "From Atomic to Mesoscale: The Role of Quantum Coherence in Systems of Various Complexities" from World Scientifi

Modelling the role of angiogenesis and vasculogenesis in solid tumuour growth

Recent experimental evidence suggests that vasculogenesis may play an important role in tumour vascularisation. While angiogenesis involves the proliferation and migration of endothelial cells (ECs) in pre-existing vessels, vasculogenesis involves the mobilisation of bone-marrow-derived endothelial progenitor cells (EPCs) into the bloodstream. Once blood-borne, EPCs home in on the tumour site, where subsequently they may differentiate into ECs and form vascular structures. In this paper, we develop a mathematical model, formulated as a system of nonlinear ordinary differential equations (ODEs), which describes vascular tumour growth with both angiogenesis and vasculogenesis contributing to vessel formation. Submodels describing exclusively angiogenic and exclusively vasculogenic tumours are shown to exhibit similar growth dynamics. In each case, there are three possible scenarios: the tumour remains in an avascular steady state, the tumour evolves to a vascular equilibrium, or unbounded vascular growth occurs. Analysis of the full model reveals that these three behaviours persist when angiogenesis and vasculogenesis act simultaneously. However, when both vascularisation mechanisms are active, the tumour growth rate may increase, causing the tumour to evolve to a larger equilibrium size or to expand uncontrollably. Alternatively, the growth rate may be left unaffected, which occurs if either vascularisation process alone is able to keep pace with the demands of the growing tumour. To clarify further the effects of vasculogenesis, the full model is also used to compare possible treatment strategies, including chemotherapy and antiangiogenic therapies aimed at suppressing vascularisation. This investigation highlights how, dependent on model parameter values, targeting both ECs and EPCs may be necessary in order to effectively reduce tumour vasculature and inhibit tumour growth

Building a Socio-technical Perspective of Community Resilience with a Semiotic Approach

Situated in the diversity and adversity of real-life contexts facing crisis situations, this research aims at boosting the resilience process within communities supported by digital and social technology. In this paper, eight community leaders in different parts of the world are invited to express their issues and wishes regarding the support of technology to face social challenges. Methods and artefacts based on the Organisational Semiotics (OS) and the Socially-Aware computing have been applied to analyse and consolidate this data. By providing both a systemic view of the problem and also leading to the identification of requirements, the analysis evidences some benefits of the OS-based approach to consolidate perspectives from different real-life scenarios towards building a socio-technical solution

Making, probing and understanding Bose-Einstein condensates

Contribution to the proceedings of the 1998 Enrico Fermi summer school on Bose-Einstein condensation in Varenna, Italy.Comment: Long review paper with ~90 pages, ~20 figures. 2 GIF figures in separate files (4/5/99 fixed figure

Host Specificity of Ecuadorian Bat Flies (Diptera: Streblidae)

Diptera: Streblidae are ectoparasites of bat populations found in many locations throughout the world. These ectoparasites are generally known as bat flies. They attach themselves to the wing membranes and bodies of bats to bite and feed on their blood. Using a large sample consisting of over 2,000 bats and 6,000 bat flies, I have conducted a study of the degree of host specificity of these ectoparasites. Host specificity is a measurement of the degree to which a particular parasite is restricted to its host or hosts. Here I find evidence to support more recent findings that bat flies are highly host specific. Not a single bat fly species was found to have more than four species as primary hosts or a specificity index value greater than 3.3012, and most fly species were restricted to one or two closely related host species. This is certainly considered highly host specific by parasitological standards. Research on parasite-host associations promises to increase our knowledge of both parasite and host groups, but also the myriad of ecological, evolutionary, and epidemiological properties that emerge from the intimate parasite-host relationships

Generating Schr\"{o}dinger-cat states in momentum and internal-state space from Bose-Einstein condensates with repulsive interactions

Resonant Raman coupling between internal levels induced by continuous illumination of non-collinear laser beams can create double-well momentum-space potentials for multi-level ``periodically-dressed'' atoms. We develop an approximate many-body formalism for a weakly interacting, trapped periodically-dressed Bose gas which illustrates how a tunable exchange interaction yields correlated many-body ground states. In contrast to the case of a position-space double well, the ground state of stable periodically-dressed Bose gases with repulsive interactions tends toward a Schr\"{o}dinger cat state in the regime where interactions dominate the momentum-space tunnelling induced by the external trapping potential. The dependence of the momentum-space tunnelling and exchange interaction on experimental parameters is derived. We discuss how real-time control of experimental parameters can be used to create Schr\"{o}dinger cat states either between momentum or internal states, and how these states could be dynamically controlled towards highly sensitive interferometry and frequency metrology.Comment: 7 pages, 3 figures. Submitted to PR