Obtaining Atomic Matrix Elements from Vector Tune-Out Wavelengths using Atom Interferometry

Accurate values for atomic dipole matrix elements are useful in many areas of physics, and in particular for interpreting experiments such as atomic parity violation. Obtaining accurate matrix element values is a challenge for both experiment and theory. A new technique that can be applied to this problem is tune-out spectroscopy, which is the measurement of light wavelengths where the electric polarizability of an atom has a zero. Using atom interferometry methods, tune-out wavelengths can be measured very accurately. Their values depend on the ratios of various dipole matrix elements and are thus useful for constraining theory and broadening the application of experimental values. Tune-out wavelength measurements to date have focused on zeros of the scalar polarizability, but in general the vector polarizability also contributes. We show here that combined measurements of the vector and scalar polarizabilities can provide more detailed information about the matrix element ratios, and in particular can distinguish small contributions from the atomic core and the valence tail states. These small contributions are the leading error sources in current parity violation calculations for cesium.Comment: 11 pages, 3 figure

Assessing consistency of fish survey data : uncertainties in the estimation of mackerel icefish (Champsocephalus gunnari) abundance at South Georgia

Acknowledgments The authors wish to thank the crews, fishermen and scientists who conducted the various surveys from which data were obtained, and Mark Belchier and Simeon Hill for their contributions. This work was supported by the Government of South Georgia and South Sandwich Islands. Additional logistical support provided by The South Atlantic Environmental Research Institute with thanks to Paul Brickle. Thanks to Stephen Smith of Fisheries and Oceans Canada (DFO) for help in constructing bootstrap confidence limits. Paul Fernandes receives funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland), and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. We also wish to thank two anonymous referees for their helpful suggestions on earlier versions of this manuscript.Peer reviewedPostprin

Impact mitigating capabilities of a spray-on elastomer coating applied to concrete

Structural protection against the effects of a nearby explosive detonation is an area of growing importance. Spray-on elastomer coatings are of interest as a practical and low cost protective solution. Recent research has demonstrated the effectiveness of such coatings for blast mitigation. However, there are two loading scenarios of concern for these applications: blast pressures and fragment impacts. To date, there remains a need to understand the merits of this protective solution for impact indentation of concrete structural elements. In this work, we examine whether, and by what mechanism, an elastomer coating can offer protection in this case. A series of quasi-static indentation and dynamic impact experiments are performed using a 0.1 kg circular cylindrical (i.e. blunt) projectile. It is demonstrated that the coating displays a significant protective capability over the full range of impact velocities considered, c. 45 - 150 m/s. The coating remains intact until impacted at a velocity of c. 120 m/s when it fails by a ductile, tearing mechanism, forming a plug which undergoes large elastic contraction after projectile penetration. A finite element model of the impact indentation of uncoated and coated concrete cubes is developed and validated against the experiments. Focusing on the early time steps and damage initiation in the concrete, the numerical model is used to interrogate the mechanism by which the elastomer achieves its mitigating effect. It is found that the way in which the elastomer alters the stress distribution in the concrete, and its time evolution, is key to its performance. These findings provide a basis for optimising protective coatings for concrete structural elements.George and Lillian Schiff Foundation, University of Cambridg

Application of NASTRAN/COSMIC in the analysis of ship structures to underwater explosion shock

The application of NASTRAN/COSMIC in predicting the transient motion of ship structures to underwater, non-contact explosions is discussed. Examples illustrate the finite element models, mathematical formulations of loading functions and, where available, comparisons between analytical and experimental results

Design of elastomer coatings for concrete impact damage mitigation

Practical, cost-effective strategies are of interest for the protection of vulnerable infrastructure against dynamic load events such as blast and fragment impact. Recent research has established that spray-on elastomer coatings can provide a significant impact mitigating effect when applied to concrete structural elements [1]. However, to date, no practical design guidelines exist to support efficient implementation of this retrofit solution. In this work, an analytical model is proposed for the impact indentation of an elastomer-coated concrete structural element. Design maps are produced, predicting the critical projectile impact velocities for elastomer failure and concrete failure, taking the coating thickness and elastomer modulus as the key design variables. The analytical predictions provide a close match to experimental and finite element analysis (FEA) results [1,2]. Spanning a realistic range of elastomer moduli, representative of typical spray application polymers, a regime change is predicted that depends only on the elastomer modulus, Ee. For Ee &lt; 50 MPa, elastomer failure is predicted to occur first. In this regime, there is a much higher sensitivity to Ee compared with the elastomer thickness, he. For Ee &gt; 50 MPa, the concrete is predicted to fail first and in this regime, the critical velocities are most sensitive to he compared with Ee.</p