Age structure and dynamics of Cercidiphyllum japonicum sprouts based on growth ring analysis

ArticleFOREST ECOLOGY AND MANAGEMENT. 213(1-3): 253-260 (2005)journal articl

Optical Hall Effect in the Integer Quantum Hall Regime

Optical Hall conductivity $\sigma_{xy}(\omega)$ is measured from the Faraday rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz frequency regime. The Faraday rotation angle ($\sim$ fine structure constant $\sim$ mrad) is found to significantly deviate from the Drude-like behavior to exhibit a plateau-like structure around the Landau-level filling $\nu=2$. The result, which fits with the behavior expected from the carrier localization effect in the ac regime, indicates that the plateau structure, although not quantized, still exists in the terahertz regime.Comment: 4 pages, 4 figure

Study of ortho-to-paraexciton conversion in Cu2_2O by excitonic Lyman spectroscopy

Using time-resolved $1s$-$2p$ excitonic Lyman spectroscopy, we study the orthoexciton-to-paraexcitons transfer, following the creation of a high density population of ultracold $1s$ orthoexcitons by resonant two-photon excitation with femtosecond pulses. An observed fast exciton-density dependent conversion rate is attributed to spin exchange between pairs of orthoexcitons. Implication of these results on the feasibility of BEC of paraexcitons in Cu$_2$O is discussed

Similarity and contrasts between thermodynamic properties at the critical point of liquid alkali metals and of electron-hole droplets

The recent experimental study by means of time-resolved luminescence measurements of an electron-hole liquid (EHL) in diamond by Shimano et al. [Phys. Rev. Lett. 88 (2002) 057404] prompts us to compare and contrast critical temperature T_c and critical density n_c relations in liquid alkali metals with those in electron-hole liquids. The conclusion drawn is that these systems have similarities with regard to critical properties. In both cases the critical temperature is related to the cube root of the critical density. The existence of this relation is traced to Coulomb interactions and to systematic trends in the dielectric constant of the electron-hole systems. Finally a brief comparison between the alkalis and EHLs of the critical values for the compressibility ratio Z_c is also given

Cooling Dynamics of Photoexcited Carriers in Si Studied by Using Optical Pump and Terahertz Probe Spectroscopy

We investigated the photoexcited carrier dynamics in Si by using optical pump and terahertz probe spectroscopy in an energy range between 2 meV and 25 meV. The formation dynamics of excitons from unbound e-h pairs was studied through the emergence of the 1s-2p transition of excitons at 12 meV (3 THz). We revealed the thermalization mechanism of the photo-injected hot carriers (electrons and holes) in the low temperature lattice system by taking account of the interband and intraband scattering of carriers with acoustic and optical phonons. The overall cooling rate of electrons and holes was numerically calculated on the basis of a microscopic analysis of the phonon scattering processes, and the results well account for the experimentally observed carrier cooling dynamics. The long formation time of excitons in Si after the above-gap photoexcitation is reasonably accounted for by the thermalization process of photoexcited carriers.Comment: 8 pages, 8 figures, to be published in Phys. Rev.

Electrically driven spin excitation in a ferroelectric magnet DyMnO_3

Temperature (5--250 K) and magnetic field (0--70 kOe) variations of the low-energy (1--10 meV) electrodynamics of spin excitations have been investigated for a complete set of light-polarization configurations for a ferroelectric magnet DyMnO$_3$ by using terahertz time-domain spectroscopy. We identify the pronounced absorption continuum (1--8 meV) with a peak feature around 2 meV, which is electric-dipole active only for the light $E$-vector along the a-axis. This absorption band grows in intensity with lowering temperature from the spin-collinear paraelectric phase above the ferroelectric transition, but is independent of the orientation of spiral spin plane ($bc$ or $ab$), as shown on the original $P_{\rm s}$ (ferroelectric polarization) $\parallel c$ phase as well as the magnetic field induced $P_{\rm s}\parallel a$ phase. The possible origin of this electric-dipole active band is argued in terms of the large fluctuations of spins and spin-current.Comment: New version, 11 pages including colored 8 figure

Influência do número de camadas na propriedade mecânica de espécimes fabricados com atadura gessada usados para confeccionar splints ortopédicos

OBJECTIVE: To evaluate the effects of varying numbers of layers of plaster of Paris bandages on the mechanical properties of specimens used on the construction of orthopedic splints. METHODS: Rectangular plate-shaped and cylinder-shaped specimens were constructed and assigned to two groups simulating plaster slabs and cast and further divided into six subgroups according to the number of layers used: 3, 6, 8, 10, 12 and 14 layers. The specimens were subjected to either a three-point bending test (plates/slab) or compressive strength test (cylinders/cast). The following mechanical properties were evaluated: maximum load, elastic limit load and stiffness. Specimen weight was also calculated. Data was analyzed using Kruskal-Wallis and the least significant difference (LSD) tests. RESULTS: Pairwise comparisons of the subgroups 10x12 and 10x14 revealed significant differences for all mechanical properties (p<0.05). The results of this study suggest that when the goal is to construct appliances with high mechanical strength, regardless of weight, such as serial plaster slabs splints for stimulating tissue growth through the application of gradual load, splints made with plaster of Paris bandages with 12 or 14 layers should be preferred. For orthotic devices such as positioning orthotics, the use of 10 layers plaster bandages slab splints is advisable as they were found to have better correlation between mechanical strength and weight in comparison to those made wtih 6 or 8 layers. CONCLUSION: Based on the findings of this study, we suggest the use of 10 layers of plaster of Paris for the construction of orthopedic splints.OBJETIVO: Avaliar as propriedades mecânicas de amostras fabricadas a partir de ataduras de gesso que são utilizadas em órteses ortopédicas e que variam quanto ao número de camadas. MÉTODOS: Foram confeccionados espécimes em forma de placa retangular e em forma cilíndrica, divididos em dois grupos que simulavam splint e gesso circular, os quais foram divididos em seis subgrupos de acordo com o número de camadas utilizadas, ou seja, três, seis, oito, dez, 12 e 14 camadas. Os espécimes foram submetidos a um teste de inclinação de três pontos (placas/splint) ou teste de resistência à compressão (cilindros/gesso circular). As seguintes propriedades mecânicas foram avaliadas: carga máxima e carga no limite de elasticidade e rigidez. O peso da amostra foi calculado. Os dados foram analisados estatisticamente pelos testes de Kruskal-Wallis e diferença mínima significativa (DMS). Comparações pareadas entre os subgrupos 10x12 e 10x14 revelaram diferenças significativas para todas as propriedades mecânicas (p<0,05). RESULTADOS: Os resultados sugerem que, quando o objetivo é construir aparelhos com alta resistência mecânica, independente do peso, tais como órteses seriadas de posicionamento para simular força gradual aplicada no tecido para a melhoria da amplitude de movimento, talas de 12 ou 14 camadas devem ser preferidas. Para os aparelhos ortopédicos que irão ser submetidos a esforços de baixa intensidade, aconselha-se a utilização de dez camadas para as órteses, porque houve uma melhor correlação entre a resistência mecânica e peso para as amostras fabricadas com dez camadas de atadura gessada comparadas com aquelas confeccionadas com seis ou oito camadas. CONCLUSÂO: Baseado nos achados deste estudo, sugere-se a utilização de dez camadas na confecção de órteses ortopédicas

Observation of the spin-charge thermal isolation of ferromagnetic Ga_{0.94}Mn_{0.06}As by time-resolved magneto-optical measurement

The dynamics of magnetization under femtosecond optical excitation is studied in a ferromagnetic semiconductor Ga_{0.94}Mn_{0.06}As with a time-resolved magneto-optical Kerr effect measurement with two color probe beams. The transient reflectivity change indicates the rapid rise of the carrier temperature and relaxation to a quasi-thermal equilibrium within 1 ps, while a very slow rise of the spin temperature of the order of 500ps is observed. This anomalous behavior originates from the thermal isolation between the charge and spin systems due to the spin polarization of carriers (holes) contributing to ferromagnetism. This constitutes experimental proof of the half-metallic nature of ferromagnetic Ga_{0.94}Mn_{0.06}As arising from double exchange type mechanism originates from the d-band character of holes