Ultrafast quasiparticle relaxation dynamics in normal metals and heavy fermion materials

We present a detailed theoretical study of the ultrafast quasiparticle relaxation dynamics observed in normal metals and heavy fermion materials with femtosecond time-resolved optical pump-probe spectroscopy. For normal metals, a nonthermal electron distribution gives rise to a temperature (T) independent electron-phonon relaxation time at low temperatures, in contrast to the T^{-3}-divergent behavior predicted by the two-temperature model. For heavy fermion compounds, we find that the blocking of electron-phonon scattering for heavy electrons within the density-of-states peak near the Fermi energy is crucial to explain the rapid increase of the electron-phonon relaxation time below the Kondo temperature. We propose the hypothesis that the slower Fermi velocity compared to the sound velocity provides a natural blocking mechanism due to energy and momentum conservation laws.Comment: 10 pages, 11 figure

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

The femtosecond optical pump-probe technique was used to study dynamics of photoexcited electrons and coherent optical phonons in transition metals Zn and Cd as a function of temperature and excitation level. The optical response in time domain is well fitted by linear combination of a damped harmonic oscillation because of excitation of coherent $E_{2g}$ phonon and a subpicosecond transient response due to electron-phonon thermalization. The electron-phonon thermalization time monotonically increases with temperature, consistent with the thermomodulation scenario, where at high temperatures the system can be well explained by the two-temperature model, while below $\approx$ 50 K the nonthermal electron model needs to be applied. As the lattice temperature increases, the damping of the coherent $E_{2g}$ phonon increases, while the amplitudes of both fast electronic response and the coherent $E_{2g}$ phonon decrease. The temperature dependence of the damping of the $E_{2g}$ phonon indicates that population decay of the coherent optical phonon due to anharmonic phonon-phonon coupling dominates the decay process. We present a model that accounts for the observed temperature dependence of the amplitude assuming the photoinduced absorption mechanism, where the signal amplitude is proportional to the photoinduced change in the quasiparticle density. The result that the amplitude of the $E_{2g}$ phonon follows the temperature dependence of the amplitude of the fast electronic transient indicates that under the resonant condition both electronic and phononic responses are proportional to the change in the dielectric function.Comment: 10 pages, 9 figures, to appear in Physical Review

Effectiveness and cost-effectiveness of a nurse-delivered intervention to improve adherence to treatment for HIV : a pragmatic, multicentre, open-label, randomised clinical trial

This trial was funded from public money by the Netherlands Organisation for Health Research and Development (ZonMW; grant number 171002208). Aardex provided support on the development of the study website. We thank all the HIV nurses and physicians from the seven HIV clinics involved in the AIMS study for their input and collaboration (Academic Medical Centre, Slotervaart hospital, and St. Lucas-Andreas hospital, all in Amsterdam; the Leiden University Medical Centre, Leiden; HAGA hospital, The Hague; Erasmus Medical Centre, Rotterdam; and Isala clinic, Zwolle), the study participants, and the Stichting HIV Monitoring (SHM) for their support in accessing the SHM database for identifying patient inclusion criteria and developing the Markov model. Finally, we thank and remember Herman Schaalma (deceased) for his contribution to the study design and grant application.Peer reviewedPostprin

Size-Dependent Surface Plasmon Dynamics in Metal Nanoparticles

We study the effect of Coulomb correlations on the ultrafast optical dynamics of small metal particles. We demonstrate that a surface-induced dynamical screening of the electron-electron interactions leads to quasiparticle scattering with collective surface excitations. In noble-metal nanoparticles, it results in an interband resonant scattering of d-holes with surface plasmons. We show that this size-dependent many-body effect manifests itself in the differential absorption dynamics for frequencies close to the surface plasmon resonance. In particular, our self-consistent calculations reveal a strong frequency dependence of the relaxation, in agreement with recent femtosecond pump-probe experiments.Comment: 8 pages + 4 figures, final version accepted to PR

Relaxation Dynamics of Photoinduced Changes in the Superfluid Weight of High-Tc Superconductors

In the transient state of d-wave superconductors, we investigate the temporal variation of photoinduced changes in the superfluid weight. We derive the formula that relates the nonlinear response function to the nonequilibrium distribution function. The latter qunatity is obtained by solving the kinetic equation with the electron-electron and the electron-phonon interaction included. By numerical calculations, a nonexponential decay is found at low temperatures in contrast to the usual exponential decay at high temperatures. The nonexponential decay originates from the nonmonotonous temporal variation of the nonequilibrium distribution function at low energies. The main physical process that causes this behavior is not the recombination of quasiparticles as previous phenomenological studies suggested, but the absorption of phonons.Comment: 18 pages, 12 figures; to be published in J. Phys. Soc. Jpn. Vol. 80, No.

AN ECOSYSTEM APPROACH TO FISHERIES IN THE SOUTHERN BENGUELA CONTEXT

The 2001 Reykjavík Declaration on Responsible Fisheries in the Marine Ecosystem and the Plan of Implementation of the 2002 World Summit on Sustainable Development highlighted the need in fisheries to look beyond considering only the target species and to consider in fisheries management the impacts of fishing on the ecosystem as a whole, as well as the impacts of the ecosystem on fisheries. This paper examines the practical implications of progressing towards ecosystem approaches by reference, in particular, to the FAO technical guidelines on the topic. It goes on to examine the major fishery types in South Africa and the southern Benguela, and to consider the probable impacts of those fisheries on target species, bycatch species and the ecosystem, as well as the indirect impacts on other ffected species. The review reveals that all fisheries have impacts beyond the target species and that an ecosystem approach is required in order to ensure the long-term sustainability of the living marine resources of the southern Benguela and the ecosystem as a whole. Finally, the likely obstacles to successful implementation of an ecosystem approach to fisheries in the southern Benguela are discussed.Afr. J. mar. Sci. 26: 9–3

Sex Hormone Binding Globulin Deficiency Due to a Homozygous Missense Mutation

Context: SHBG is known as the major sex steroid binding protein in plasma, and it regulates the bioavailability of both T and estradiol levels required for effects on target tissues. We identified a man with an undetectable SHBG concentration in combination with low total T. He presented with a 7-year history of muscle weakness, fatigue, and a low libido. Objectives: To determine the cause of the SHBG deficiency, we employed both genetic analysis of the SHBG gene and transgene SHBG expression. Results: Genetic analysis identified a novel homozygous missense mutation that was predicted to be deleterious for protein function. Transgene expression showed that the mutation resulted in a block in SHBG secretion accompanied by increased expression of the endoplasmic reticulum molecular chaperone HSPA5. The mutation results in accumulation of the mutant SHBG within the cell and failure to secrete the mutant protein. Screening of family members identified one sister who was also deficient for SHBG. Conclusions: We have identified a family with a missense mutation within the SHBG gene, which results in a complete deficiency of plasma SHBG in the homozygous state. Although total T level was low in the male patient, it did not interfere with normal gonadal development and spermatogenesis, suggesting a limited role of SHBG in sexual maturation and male physiology

Nonequilibrium Electron Interactions in Metal Films

Ultrafast relaxation dynamics of an athermal electron distribution is investigated in silver films using a femtosecond pump-probe technique with 18 fs pulses in off-resonant conditions. The results yield evidence for an increase with time of the electron-gas energy loss rate to the lattice and of the free electron damping during the early stages of the electron-gas thermalization. These effects are attributed to transient alterations of the electron average scattering processes due to the athermal nature of the electron gas, in agreement with numerical simulations

Ninth and Tenth Order Virial Coefficients for Hard Spheres in D Dimensions

We evaluate the virial coefficients B_k for k<=10 for hard spheres in dimensions D=2,...,8. Virial coefficients with k even are found to be negative when D>=5. This provides strong evidence that the leading singularity for the virial series lies away from the positive real axis when D>=5. Further analysis provides evidence that negative virial coefficients will be seen for some k>10 for D=4, and there is a distinct possibility that negative virial coefficients will also eventually occur for D=3.Comment: 33 pages, 12 figure