Publication highlights 2011-12
Hans-Benjamin Braun has published a topical review "Topological effects in nanomagnetism: from superparamagnetism to chiral quantum solitons", where he shows how progress has been made to extend the micromagnetics formalism to include thermal and quantum fluctuations in order to describe recent experimental developments in nanoscale magnetism. (Adv. Physics 61, 1-116 (2012); doi: 10.1080/00018732.2012.663070)
Peter Hogan published a paper on "Collisions of Shock Waves in General Relativity", in which he demonstrated that dark energy is a product of collisions of gravitational shock waves. (Pogr. Theor. Phys. 126, 1157 (2011); doi: 10.1143/PTP.126.1157). His book "Equations of Motion in General Relativity" published a year ago has already received several very positive reviews (http://dx.doi.org/10.1088/0264-9381/29/5/059002).
Anna Cannon took part in Fermi/Integral collaboration, which detected two separate gamma-ray (photon energy > 100 MeV) flares from Crab Nebula source by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Their observations were reported in Science 331, 739-742 (2011) (doi: 10.1126/science.1199705).
Sheila McBreen took part in a team at Fermi Gamma-Ray Burst Monitor that observed simultaneously the thermal and non-thermal components of Gamma-Ray emission from GRB 100724B. The results imply either a very high efficiency for the non-thermal process or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux (Astrophys. J. Lett. 727 L33 (2011); doi:10.1088/2041-8205/727/2/L33).
John Quinn, teamed with partners from VERITAS collaboration, reported the detection of pulsed gamma rays from the Crab pulsar at energies above 100 GeV with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) array of atmospheric Cherenkov telescopes. This detection cannot be explained on the basis of current pulsar models. The photon spectrum of pulsed emission between 100 mega–electron volts and 400 GeV is described by a broken power law that is statistically preferred over a power law with an exponential cutoff. It is unlikely that the observation can be explained by invoking curvature radiation as the origin of the observed gamma rays above 100 GeV. Their findings require that these gamma rays be produced more than 10 stellar radii from the neutron star (Science 334, 69-72 (2011); doi: 10.1126/science.1208192).
Frances Lordan and James Rice published a paper "Site selective surface enhanced Raman on nanostructured cavities" (Appl. Phys. Lett. 99, 033104 (2011); doi:10.1063/1.3615282), where
they studied angle dependence of the surface enhanced Raman signal obtained from dye placed on plasmon active nanocavity arrays. Their results show that Raman intensities as a function of angle depend on the location of the dye on the array; this was interpreted to arise from the presence of different plasmon polariton modes in these sites.
The Nanoscale Function Group led by Suzi Jarvis published several papers on biosystems studied with atomic force microscopy. In particular, they performed direct submolecular-scale imaging of model raft membranes using ultrahigh resolution AFM (J. Am. Chem. Soc. 133, 18296–18303 (2011), doi: 10.1021/ja2068142). They characterized the heterogeneous nature of crystalline hydration layers at the membrane–fluid interface. The association of crystalline hydration layers with raft membranes would significantly affect the mechanism and kinetics of both inter-raft interactions and those between rafts and external biomolecules, and therefore this finding has important implications for membrane biology. Another paper using ultrahigh resolution AFM addressed the effects of salts on lipid ordering in biomembranes (Eur. Biophys. J. - Biophys. Lett. 40, 329-338, (2011), DOI: 10.1007/s00249-010-0650-7).
The spectroscopy group (Rebekah D’Arcy, Padraig Dunne, and Gerry O’Sullivan) collaborated successfully with Japanese colleagues to characterize the emission spectrum and temporal history of a pure potassium plasma. They found that temporal behavior of this emission strongly follows the recombination phase in the laser-produced plasma and it was reproduced by a hydrodynamic simulation of the potassium plasma which accounted for atomic processes (Appl. Phys. Lett. 98, 091503 (2011); doi:10.1063/1.3560304). Another spectacular work concerned a development of a new efficient extreme ultraviolet (EUV) source for operation at λ =6.7nm by optimizing the optical thickness of gadolinium (Gd) plasmas (Appl. Phys. Lett. 99, 191502 (2011); doi:10.1063/1.3660275)
Brian Vohnsen, Sara Castillo and Diego Rativa proposed to use a large apex-angle axicon for common-path interferometric wavefront. Their approach is a variant of point-diffraction interferometry bearing similarities to pyramidal wavefront sensing. It has been confirmed that the axicon can be used for wavefront sensing, although its refraction may ultimately complicate and limit its operational range. (Optics Lett. 36, 846-848 (2011); doi: 10.1364/OL.36.000846)
Peter Hogan and Shane O'Farrell used explicit perturbations of isotropic cosmological models which describe simple gravitational waves to provide an answer to the question: in what sense can an energy-momentum-stress tensor similar to that describing the cosmic microwave background radiation (neglecting anisotropies) be associated with an isotropic background of gravitational radiation? (Gen. Relativity Gravitation 43, 1625-1638; doi: 10.1007/s10714-011-1144-3)
Éadaoin McClean and Dominic Zerulla worked on polymer based solar cells, which are particularly attractive because of their mechanical flexibility and potential for low-cost fabrication. Through finite-difference time-domain calculations, it was possible to optimize the overall spectral response of the cell yielding surface plasmon resonances at predetermined wavelengths. The improved solar cell design resulted in a system with increased absorption, allowing for the desired reduction in active layer thickness while also enhancing the performance of the cell over a wide wavelength range (Appl. Phys. Lett. 99, 093307 (2011); doi:10.1063/1.3633349).
Simone Meloni and Giovanni Ciccotti worked on combining rare events techniques to study phase changes nanoparticles. They introduced a combined Restrained MD/Parallel Tempering approach to study the difference in free energy as a function of a set of collective variables between two states in presence of metastabilities in the manifold orthogonal to the one spanned by the chosen collective variables. The results show that the method permits to get over the hidden metastabilities (J. Stat. Phys. 145, 812-830 (2011); doi: 10.1007/s10955-011-0390-9)
Pengfei Huo and David Coker developed an approach for treating dissipative, non-adiabatic quantum dynamics in general model systems at finite temperature based on linearizing the density matrix evolution in the forward-backward path difference for the environment degrees of freedom. The approach can capture both short time coherent quantum dynamics and long time thermal equilibration in an application to excitation energy transfer in a model photosynthetic light harvesting complex. (J. Chem. Phys. 135, 201101 (2011); doi: 10.1063/1.3664763)
For the complete list of publications of School of Physics in 2010-2011 click here.