We discuss the motion of a hole generated in the Cu-0 plane in high-temperature superconductors at half filling. The system is described by the t-J model. Special attention is paid to the influence of spin fluctuations in the ground state on the hole motion. It is shown that they reduce the bandwidth of the excitation energy as compared to the motion within the Neel ground state. The calculations are based on a cumulant approach to dynamical correlation functions introduced recently. This approach allows for a proper treatment of the strong electronic correlations which are incorporated in the model. It also guarantees that only spin fluctuations "connected" to the hole motion can contribute to the physical quantities.
Marine ecosystem models often consider temporal dynamics on the order of months to years, and spatial dynamics over regional and global scales as a means to understand the ecology, evolution, and biogeochemical impacts of marine life. Large-scale dynamics are themselves driven over diel scales as a result of light-driven forcing, feedback, and interactions. Motivated by high-frequency measurements taken by Lagrangian sampling in the North Pacific Subtropical Gyre, we develop a hierarchical set of multitrophic community ecology models to investigate and understand daily ecological dynamics in the near-surface ocean including impacts of light-driven growth, infection, grazing, and phytoplankton size structure. Using these models, we investigate the relative impacts of viral-induced and grazing mortality for Prochlorococcus; and more broadly compare in silico dynamics with in situ observations. Via model-data fitting, we show that a multi-trophic model with size structure can jointly explain diel changes in cyanobacterial abundances, cyanobacterial size structure, viral abundance, viral infection rates, and grazer abundances. In doing so, we find that a significant component (between 5% to 55%) of estimated Prochlorococcus mortality is not attributed to either viral lysis (by T4- or T7-like cyanophage) or grazing by heterotrophic nanoflagellates. Instead, model-data integration suggests a heightened ecological relevance of other mortality mechanisms -- including grazing by other predators, particle aggregation, and stress-induced loss mechanisms. Altogether, linking mechanistic multitrophic models with high-resolution measurements provides a route for understanding of diel origins of large-scale marine microbial community and ecosystem dynamics.
Since the possibility of additional severe malformations exists for the patient and the patient's children patients should undergo careful ENT and pediatric assessment, and genetic counselling should be considered. In order to achieve good functional and esthetic results, the corrective operation must be planned carefully taking into consideration important surgical principles.
A new method of refractive corneal surgery is presented. With the q-switched Nd:YAG-laser Visulas (Zeiss-Oberkochen) we succeed in altering the optical power of the cornea of rabbits, pigs and humans. The number of applied laser spots and the distribution pattern influence the way and the amount of change of refraction. The method, clinical and histological features, complications and prospects of the Nd: YAG laser keratorhexis are described.
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