Parameter trails

Successful communication is vital for the success of any design project. However, communication often fails, adversely affecting design process efficiency and product quality.understand the connections between different aspects of design and don–t know where to find out more information or who to talk to. This paper presents a new model, developed from current project planning techniques, which supports communication using parameter-specific data. It enables designers to question information, inform their colleagues pro-actively and assess the impact of changing parameter values on subsequent design tasks. Such interaction is critical in allowing designers to see how their own tasks fit into the overall product design

A functional analysis of change propagation

A thorough understanding of change propagation is fundamental to effective change management during product redesign. A new model of change propagation, as a result of the interaction of form and function is presented and used to develop an analysis method that determines how change is likely to propagate. The analysis produces a Design Structure Matrix, which clearly illustrates change propagation paths and highlights connections that could otherwise be ignored. This provides the user with an in-depth knowledge of product connectivity, which has the potential to support the design process and reduce the product's susceptibility to future change

Transient resonances in the inspirals of point particles into black holes

We show that transient resonances occur in the two body problem in general relativity, in the highly relativistic, extreme mass-ratio regime for spinning black holes. These resonances occur when the ratio of polar and radial orbital frequencies, which is slowly evolving under the influence of gravitational radiation reaction, passes through a low order rational number. At such points, the adiabatic approximation to the orbital evolution breaks down, and there is a brief but order unity correction to the inspiral rate. Corrections to the gravitational wave signal's phase due to resonance effects scale as the square root of the inverse of mass of the small body, and thus become large in the extreme-mass-ratio limit, dominating over all other post-adiabatic effects. The resonances make orbits more sensitive to changes in initial data (though not quite chaotic), and are genuine non-perturbative effects that are not seen at any order in a standard post-Newtonian expansion. Our results apply to an important potential source of gravitational waves, the gradual inspiral of white dwarfs, neutron stars, or black holes into much more massive black holes. It is hoped to exploit observations of these sources to map the spacetime geometry of black holes. However, such mapping will require accurate models of binary dynamics, which is a computational challenge whose difficulty is significantly increased by resonance effects. We estimate that the resonance phase shifts will be of order a few tens of cycles for mass ratios $\sim 10^{-6}$, by numerically evolving fully relativistic orbital dynamics supplemented with an approximate, post-Newtonian self-force.Comment: 4 pages, 1 figure, minor correction

Adiabatic instability in coupled dark energy-dark matter models

We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, which can also be thought of as a type of Jeans instability, is characterized by a negative sound speed squared of an effective coupled dark matter/dark energy fluid, and results in the exponential growth of small scale modes. We discuss the role of the instability in specific coupled CDM and Mass Varying Neutrino (MaVaN) models of dark energy, and clarify for these theories the regimes in which the instability can be evaded due to non-adiabaticity or weak coupling.Comment: 20 pages, 2 figures; final published versio

Ionization Structure and the Reverse Shock in E0102-72

The young oxygen-rich supernova remnant E0102-72 in the Small Magellanic Cloud has been observed with the High Energy Transmission Grating Spectrometer of Chandra. The high resolution X-ray spectrum reveals images of the remnant in the light of individual emission lines of oxygen, neon, magnesium and silicon. The peak emission region for hydrogen-like ions lies at larger radial distance from the SNR center than the corresponding helium-like ions, suggesting passage of the ejecta through the "reverse shock". We examine models which test this interpretation, and we discuss the implications.Comment: 4 pages, 6 figures; To appear in "Young Supernova Remnants" (11th Annual Astrophysics Conference in Maryland), S. S. Holt & U. Hwang (eds), AIP, New York (2001

Bone Morphogenetic Protein-2 Adsorption onto Poly-ɛ-caprolactone Better Preserves Bioactivity In Vitro and Produces More Bone In Vivo than Conjugation Under Clinically Relevant Loading Scenarios

Background: One strategy to reconstruct large bone defects is to prefabricate a vascularized flap by implanting a biomaterial scaffold with associated biologics into the latissimus dorsi and then transplanting this construct to the defect site after a maturation period. This strategy, similar to all clinically and regulatory feasible biologic approaches to surgical reconstruction, requires the ability to quickly (<1?h within an operating room) and efficiently bind biologics to scaffolds. It also requires the ability to localize biologic delivery. In this study, we investigated the efficacy of binding bone morphogenetic protein-2 (BMP2) to poly-?-caprolactone (PCL) using adsorption and conjugation as a function of time. Methods: BMP2 was adsorbed (Ads) or conjugated (Conj) to PCL scaffolds with the same three-dimensional printed architecture while altering exposure time (0.5, 1, 5, and 16?h), temperature (4°C, 23°C), and BMP2 concentration (1.4, 5, 20, and 65??g/mL). The in vitro release was quantified, and C2C12 cell alkaline phosphatase (ALP) expression was used to confirm bioactivity. Scaffolds with either 65 or 20??g/mL Ads or Conj BMP2 for 1?h at 23°C were implanted subcutaneously in mice to evaluate in vivo bone regeneration. Micro-computed tomography, compression testing, and histology were performed to characterize bone regeneration. Results: After 1?h exposure to 65??g/mL BMP2 at 23°C, Conj and Ads resulted in 12.83±1.78 and 10.78±1.49??g BMP2 attached, respectively. Adsorption resulted in a positive ALP response and had a small burst release; whereas conjugation provided a sustained release with negligible ALP production, indicating that the conjugated BMP2 may not be bioavailable. Adsorbed 65??g/mL BMP2 solution resulted in the greatest regenerated bone volume (15.0±3.0?mm3), elastic modulus (20.1±3.0?MPa), and %bone ingrowth in the scaffold interior (17.2%±5.4%) when compared with conjugation. Conclusion: Adsorption may be optimal for the clinical application of prefabricating bone flaps due to BMP2 binding in a short exposure time, retained BMP2 bioactivity, and bone growth adhering to scaffold geometry and into pores with healthy marrow development.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140249/1/ten.tec.2014.0377.pd

Radion Potential and Brane Dynamics

We examine the cosmology of the Randall-Sundrum model in a dynamic setting where scalar fields are present in the bulk as well as the branes. This generates a mechanism similar to that of Goldberger-Wise for radion stabilization and the recovery of late-cosmology features in the branes. Due to the induced radion dynamics, the inflating branes roll towards the minimum of the radion potential, thereby exiting inflation and reheating the Universe. In the slow roll part of the potential, the 'TeV' branes have maximum inflation rate and energy as their coupling to the radion and bulk modes have minimum suppresion. Hence, when rolling down the steep end of the potential towards the stable point, the radion field (which appears as the inflaton of the effective 4D theory in the branes) decays very fast, reheats the Universe .This process results decayin a decrease of brane's canonical vacuum energy $\Lambda_4$. However, at the minimum of the potential $\Lambda_4$ is small but not neccessarily zero and the fine-tuning issue remains .Density perturbation constraints introduce an upper bound when the radion stabilizies. Due to the large radion mass and strong suppression to the bulk modes, moduli problems and bulk reheating do not occur. The reheat temperature and a sufficient number of e-folding constraints for the brane-universe are also satisfied. The model therefore recovers the radiation dominated FRW universe.Comment: 16 pages, 3 figures,extraneous sentences removed, 2 footnotes added, some typos correcte

Bounds on negative energy densities in flat spacetime

We generalise results of Ford and Roman which place lower bounds -- known as quantum inequalities -- on the renormalised energy density of a quantum field averaged against a choice of sampling function. Ford and Roman derived their results for a specific non-compactly supported sampling function; here we use a different argument to obtain quantum inequalities for a class of smooth, even and non-negative sampling functions which are either compactly supported or decay rapidly at infinity. Our results hold in $d$-dimensional Minkowski space ($d\ge 2$) for the free real scalar field of mass $m\ge 0$. We discuss various features of our bounds in 2 and 4 dimensions. In particular, for massless field theory in 2-dimensional Minkowski space, we show that our quantum inequality is weaker than Flanagan's optimal bound by a factor of 3/2.Comment: REVTeX, 13 pages and 2 figures. Minor typos corrected, one reference adde