Youliang Su

Sediment dynamics and hydrologic events affecting small lacustrine systems on the southern-central Tibetan Plateau – the example of TT Lake

A sedimentological, geochemical, micropaleontological, and palynological study of a lacustrine sediment record from the small TT Lake (southern-central Tibetan Plateau) shows that the background sedimentation was frequently interrupted by event-related deposits. These event-related deposits are interpreted as the result of hydrologic events that are triggered by above-average precipitation events. In total, 11 events were recorded in the TT Lake sequence. Two types can be differentiated: fluvial runoff events caused by precipitation that carried sediment in suspension into the lake and a sediment mass transport caused by torrential precipitation. The hydrologic events appear to be decoupled from long-term climate and environmental variations, but there is evidence that anthropogenic impact, in terms of pastoralism, might have favored the runoff events. The multi-proxy approach proved to be valuable and allowed for a detailed study of sedimentary processes within the lake and its watershed in order to assess their triggering processes and dynamics. The findings show the complexity of these sedimentary processes and their controlling factors, and the study aims to improve their understanding. This study is the first effort to investigate event-related deposits and sedimentary processes on the Tibetan Plateau and its triggering processes and dynamics by utilizing lacustrine sediment records.

Thermodynamic properties of tetrameric bond-alternating spin chains

Thermodynamic properties of a tetrameric bond-alternating Heisenberg spin chain with ferromagnetic-ferromagnetic-antiferromagnetic-antiferromagnetic exchange interactions are studied using the transfer-matrix renormalization group and compared to experimental measurements. The temperature dependence of the uniform susceptibility exhibits typical ferrimagnetic features. Both the uniform and staggered magnetic susceptibilities diverge in the limit T -> 0, indicating that the ground state has both ferromagnetic and antiferromagnetic long-range orders. A double-peak structure appears in the temperature dependence of the specific heat. Our numerical calculation gives a good account for the temperature and field dependence of the susceptibility, the magnetization, and the specific heat for Cu(3-Clpy)(2)(N(3))(2) (3-Clpy=3-Chloroyridine).

A 1400 year environmental magnetic record from varved sediments of Lake Xiaolongwan (Northeast China) reflecting natural and anthropogenic soil erosion

Lake sediments can provide high-quality information about human activities. In this study, we investigate a sediment core from Lake Xiaolongwan using magnetic and geochemical methods. The dominant magnetic minerals of this sediment core are stable single domain (SSD) and superparamagnetic (SP) magnetite particles. The increasing amount of SP particles reflected by the rise of magnetic susceptibility and frequency dependent magnetic susceptibility since AD 1500 can be attributed to an increasing influx in pedogenic soil, which is related to a regional-scale increase in the intensity of human activity in Northeastern China. This extends the timing of human activities, which is independent from climate changes and its effects on local ecosystems in Northeastern China significantly.

Effect of impurity resonance states on the NMR spectra of high-Tccuprates

A strong nonmagnetic impurity can induce a resonance state in the d-wave superconducting state. As far as magnetic properties are concerned, this resonance state behaves effectively like a free moment. It leads to a Curie-Weiss-like magnetic susceptibility in an intermediate temperature regime below T-c. From the impurity susceptibility, the effective moment of the resonance state is deduced and compared with experiments. The contribution of the resonance to the magnetic susceptibility can account for the main feature of the NMR spectra in overdoped high-T-c materials. In the underdoped regime, the contribution from the resonance to the magnetic susceptibility is also substantial, but the effective moment of the resonance is smaller than the total moment induced by a nonmagnetic impurity.

Effect of impurity states on the NMR spectra of high-

A strong nonmagnetic impurity can induce a resonance state in the d-wave superconducting state. As far as magnetic properties are concerned, this resonance state behaves effectively like a free moment. It leads to a Curie-Weiss-like magnetic susceptibility in an intermediate temperature regime below T-c. From the impurity susceptibility, the effective moment of the resonance state is deduced and compared with experiments. The contribution of the resonance to the magnetic susceptibility can account for the main feature of the NMR spectra in overdoped high-T-c materials. In the underdoped regime, the contribution from the resonance to the magnetic susceptibility is also substantial, but the effective moment of the resonance is smaller than the total moment induced by a nonmagnetic impurity.

T_c

The key parameters that characterize the long wavelength behaviour of correlation functions, including the Fermi momenta and the correlation length, are calculated using the transfer matrix renormalization group for the one-dimensional Kondo lattice model. The Fermi momentum varies slowly at high temperatures, but changes sharply at low temperatures in association with the formation of the Kondo singlets. By comparison with the temperature dependence of the conduction electron density, we find that the long wavelength correlations of conduction electrons are strongly affected by the localized spins at low temperatures. At high temperatures, the conduction electrons behave as for a system with a small Fermi surface. However, at low temperatures, the Fermi momentum of the conduction electrons is altered by the coupling with the localized spins.