Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures

Role of culturally protected forests in biodiversity conservation in Southeast China

Culturally protected forests (CPFs), preserved and managed by local people on the basis of traditional practices and beliefs, have both social and ecological functions. We investigated plant species richness and diversity within the tree layer, shrub layer and herb layer in three types of CPFs (community forests, ancestral temple forests, cemetery forests) as well as nearby forests without cultural protection (NCPFs) in Southeast China. A total of 325 species belonging to 85 families and 187 genera were recorded in CPFs, including 17 protected species in China Species Red List and IUCN Red List, which accounted for 17 % of counties' endangered species. Compared with NCPFs, the tree layer of CPFs had larger DBH and lower species density, especially in the cemetery forests. CPFs had higher alpha diversity values generally, particularly in the tree layer. The differences in tree layer were substantial, and CPFs covered nearly 85.4 % of the tree species in the surveyed sites. The similarities between CPFs and NCPFs were higher in the herb and shrub layers than in the tree layer. These differences of species diversity may be attributed to differences in resource use and management between CPFs and NCPFs. Our field investigation results suggested that local CPFs harbor many plant species, high biodiversity, and contribute to the conservation of a substantial proportion of the local species pool

Exchange bias in a nanocolumnar Ni80Fe20/alpha-Fe2O3 thin film

A Ni80Fe20/alpha-Fe2O3 thin film has been deposited using a dual ion-beam deposition technique where the alpha-Fe2O3 is formed in situ by O-2 bombardment of pure Fe. AC susceptibility results indicate moment fluctuations at temperatures above 150 K. This behavior combined with the thermal fluctuation driven temperature dependence of the negative field coercivity indicates that the alpha-Fe2O3 nanocolumnar crystallite magnetism evolves from static single domain moments to superparamagnetic moments with warming. 25 kOe field cooling establishes exchange bias with an onset temperature of 50 K. The positive (H-c2) and negative (H-c1) field coercivities exhibit very different temperature dependencies, with H-c1(T) well described by a thermally activated coherent domain wall reversal model, while H-c2(T) is essentially constant except for the lowest temperatures. These results point towards different domain reversal mechanisms in positive and negative fields

First microwave map of the Moon with Chang'E-1 data: The role of local time in global imaging

Among recent lunar orbiters, only the Chinese Chang'E-1 (CE-1) was equipped with a passive microwave radiometer (MRM) to measure the natural microwave emission from the lunar surface. The microwave emission, characterized by a frequency-dependent brightness temperature (TB), is related to the physical temperature and dielectric properties of the lunar surface. By measuring the brightness temperature at different frequencies, detailed thermal behavior and properties of the lunar surface can be retrieved. Using CE-1's microwave data, we present here a set of microwave maps of the Moon constructed through a rescaling of TB to noontime or midnight. The adopted processing technique helps to reduce the effect of mixing up the temporal and spatial variations introduced by the satellite's localized measurements which cover different locations of the globe at different lunar . local times. The resulting maps show fine structures unseen in previous microwave maps that disregarded the local time effect. We discussed the new features revealed and their possible connections with the lunar geology. © 2012

Tuning the exchange bias in NiFe/Fe-oxide bilayers by way of different Fe-oxide based mixtures made with an ion-beam deposition technique

We have investigated the structural and magnetic properties of ion-beam deposited polycrystalline NiFe (25 nm)/Fe-oxide (35 nm) bilayers. A film prepared with an assist beam O-2 to At gas ratio of 0% during deposition had a bottom layer that consisted of pure b.c.c.. Fe (a = 2.87 angstrom) whereas films prepared with 19%O-2/Ar and 35%O-2/Ar had either Fe3O4(a = 8.47 angstrom) or alpha-Fe2O3 (a = 5.04 angstrom, c = 13.86 angstrom) bottom layers, respectively. Cross-sectional transmission electron microscopy revealed a smooth interface between the top nano-columnar NiFe and bottom nano-columnar Fe-oxide layer for all films. At room temperature, the observed coercivity (H-c similar to 25 Oe) for a film prepared with 19%O-2/Ar indicates the existence of a magnetically hard ferrimagnetic Fe3O4 phase that is enhancing the plain NiFe (H-c similar to 2 Oe) by way of exchange coupling. A significant amount of exchange bias is observed below 50 K, and at 10 K the size of exchange bias hysteresis loops shift increases with increasing oxygen in the films. Furthermore, the strongest exchange coupling (H-ex similar to 135 Oe at 10 K) is with alpha-Fe2O3 (35%O-2/Ar) as the bottom film layer. This indicates that the pure antiferromagnetic phases work better than ferrimagnetic phases when in contact with ferromagnetic NiFe. H-ex(T) is well described by an effective AF domain wall energy that creates an exchange field with a (1 - T/T-crit) temperature dependence. H-c(T) exhibits three distinct regimes of constant temperature that may indicate the existence of different AF spin populations that couple to the FM layer at different temperatures

Anomalous positive exchange bias in Ni80Fe20/NixFe1-xO thin-film bilayers induced by ion-beam deposition effects

We present results on a Ni80Fe20/NixFe1-xO thin-film bilayer that shows a positive exchange bias loop shift of similar to 90 Oe at 10 K under zero-field-cooled conditions. Zero-field-cooled and field-cooled hysteresis loops were double shifted at temperatures below 200 K. This behavior is due to the presence of a range of antiferromagnetic crystallite sizes in addition to multiple magnetic phases (e.g., FeO, Fe2O3, and NiO). Furthermore, the positive exchange bias loop shift decreases linearly with increasing temperature, with a compensation temperature T-comp similar to 220 K, after which negative exchange bias is measured. This temperature dependence of the exchange bias reflects the competition between the Ni80Fe20 ferromagnet and antiferromagnetic Fe oxide and NiO phases as well as a range of local blocking temperatures. We attribute the appearance of a positive exchange bias loop shift at low temperatures to temperature-dependent changes in the interfacial pinning and exchange coupling due to a complex NixFe1-xO structure from energetic ion-beam bombardment effects during the film deposition. (C) 2006 American Institute of Physics

Exchange bias dependence on interface spin alignment in a Ni80Fe20/(Ni,Fe)O thin film

A Ni80Fe20/(Ni,Fe)O thin film exhibits a positive exchange bias when cooled in a zero field and a negative exchange bias when field cooled. With transmission electron microscopy and electron energy loss spectrometry, the composition and magnetic structure has been ascertained and a distribution of magnetization easy axes about the interface extrapolated. The results indicate that the positive exchange bias is from antiferromagnetic interface moments perpendicular to their ferromagnetic counterparts. With field cooling the alignment is put into a parallel configuration resulting in a negative exchange bias