Leaf area index and topographical effects on turburlent diffusion in a deciduous forest

In order to investigate turbulent diffusion in a deciduous forest canopy, wind velocity measurements were conducted from late autumn of 2009 to early spring of 2010, using an observation tower 20 m in height located in the campus of Kanazawa University. Four sonic anemometers mounted on the tower recorded the average wind velocities and temperatures, as well as their fluctuations, at four different heights simultaneously. Two different types of data sets were selected, in which the wind velocities, wind bearings and atmospheric stabilities were all similar, but the Leaf Area Indexes (LAI's) were different. Vertical profiles of average wind velocities were found to have an approximately exponential profile in each case. The characteristic length scales of turbulence were evaluated by both von Karman's method and the integral time scale deduced from the autocorrelation from time-series analyses. Both methods produced comparable values of eddy diffusivity for the cases with some foliage during late autumn, but some discrepancy in the upper canopy layer was observed when the trees did not have their leaves in early spring. It was also found that the eddy diffusivities generally take greater values at higher positions, where the wind speeds are large. Anisotropy of eddy diffusivities between the vertical and horizontal components was also observed, particularly in the cases when the canopy does not have leaves, when the horizontal eddy diffusivities are generally larger than the vertical ones. On the other hand, the anisotropy is less visible when the trees have some foliage during autumn. The effects of topography on the turbulent diffusion were also investigated, including evaluation of the non-zero time-averaged vertical wind velocities. The results show that the effects are marginal for both cases, and can be neglected as far as diffusion in the canopy is concerned

Magnetization Process of One-Dimensional Quantum Antiferromagnet: The Product Wavefunction Renormalization Group Approach

The product-wavefunction renormalization group method, which is a novel numerical renormalization group scheme proposed recently,is applied to one-dimensional quantum spin chains in a magnetic field. We draw the zero-temperature magnetization curve of the spin chains, which excellently agrees with the exact solution in the whole range of the field.Comment: 14 pages, LaTeX, 5 non-embedded figures, to be published in Physics Letters

Nonequilibrium process of self-gravitating N-body systems and quasi-equilibrium structure using normalized q-expectation values for Tsallis\u27 generalized entropy

金沢大学理工研究域機械工学系To clarify the nonequilibrium processes of self-gravitating systems, we examine a system enclosed in a spherical container with reflecting walls, by N-body simulations. To simulate nonequilibrium processes, we consider loss of energy through the reflecting wall, i.e., a particle reflected at a non-adiabatic wall is cooled to mimic energy loss. We also consider quasi-equilibrium structures of stellar polytropes to compare with the nonequilibrium process, where the quasi-equilibrium structure is obtained from an extremum-state of Tsallis\u27 entropy. Consequently, we numerically show that, with increasing cooling rates, the dependence of the temperature on energy, i.e., the - curve, varies from that of microcanonical ensembles (or isothermal spheres) to a common curve. The common curve appearing in the nonequilibrium process agrees well with an - curve for a quasi-equilibrium structure of the stellar polytrope, especially for the polytrope index n ∼ 5. In fact, for n > 5, the stellar polytrope within an adiabatic wall exhibits gravothermal instability [Taruya, Sakagami, Physica A, 322 (2003) 285]. The present study indicates that the stellar polytrope with n ∼ 5 likely plays an important role in quasi-attractors of the nonequilibrium process in self-gravitating systems with non-adiabatic walls. © 2010 IOP Publishing Ltd

Numerical study on mountain waves generated by a two-dimensional mountain and their effect on the transport of Yellow Sand

金沢大学自然計測応用研究センターWe have studied the effect of ground topography, focusing on mountain waves, on the transport of Yellow Sand by two-dimensional numerical simulation. An advection-diffusion equation for scalar concentration is solved to simulate the transport of Yellow Sand. Two different models are employed: the first is a one-layer model in which the density gradient is constant in the entire domain, and the other is a two-layer model in which the density gradient changes at an altitude of 11 km. In the both models stream lines at high altitude descend greatly toward the ground along the lee side of the mountain as the atmospheric stability increases. However, in the two-layer model, trapped mountain waves become stronger than those in the one-layer model, and rotors are also generated on the ground. These become stronger for larger mountain width, and the scalar concentration rapidly diffuses there. It is found that the ground scalar concentrations for the two-layer model are generally much larger, especially in the rotors, compared with those in the one-layer model

Numberical study on trapped mountain waves and their effect on aersol diffusion

金沢大学大学院自然科学研究科金沢大学自然計測応用研究センター場所：金沢大学自然科学研究科図書館棟1階，講演会場：図書館棟1階　大会議室，ポスター会場：図書館棟1階12会議室,主催・共催：文部科学省２１世紀COE「環日本海域の環境計測と長期・短期変動予測」， 大気環境学会， 金沢大学工学

Numberical study on trapped mountain waves and their effect on aersol diffusion

金沢大学大学院自然科学研究科金沢大学自然計測応用研究センター場所：東京大学弥生講堂，共催：文部科学省２１世紀COE「環日本海域の環境計測と長期・短期変動予測」，大気環境学

Negative specific heat in self-gravitating N -body systems enclosed in a spherical container with reflecting walls

金沢大学理工研究域機械工学系金沢大学環日本海域環境研究センターエコテクノロジー研究部門Gravity-dominated systems have a negative specific heat. We investigate the negative specific heat of self-gravitating systems enclosed in a spherical container with reflecting walls by means of N -body simulations. To simulate nonequilibrium processes, a particle reflected at a nonadiabatic wall is cooled to mimic energy loss by reflecting walls, while an adiabatic wall is employed for microcanonical ensembles. We show that a negative specific heat occurs not only in the microcanonical ensemble but also in certain nonequilibrium processes with the nonadiabatic wall. With increasing cooling rates, the dependence of temperature T on energy ε, i.e., the ε- T curve, gradually deviates from the microcanonical ensemble and approaches a certain common curve at a low-energy region. The common curve agrees with an ε- T curve for stellar polytropes, especially for the polytrope index of n∼5. We show that the stellar polytrope should be related to the present nonequilibrium process appearing in the self-gravitating system with the nonadiabatic wall. In the nonequilibrium process, a rapid change in velocity at the nonadiabatic wall significantly affects the velocity and density profiles. In particular, the greater the cooling rate, the greater the local velocity gradient at a low-energy region. © 2009 The American Physical Society

Corrigendum to: "Numerical irreversibility in self-gravitating small N-body systems" [Physica A 387 (2008) 2267-2278]

金沢大学理工研究域機械工学

バイモーダル励起による同軸噴流制御に関する研究

金沢大学理工研究域本研究は、空力騒音による作業環境悪化と公害問題の立場から、騒音源である渦の挙動を調べ、同軸噴流における騒音低減の最適条件(ノズル形状、加振条件)を明らかにすることを目的とし、その有効な手段と考えられる噴流のバイモーダル励起の可能性を探る。まず、せん断層の干渉を調べるために平面噴流の片側に平板を取り付けた結果、(1)2次元噴流においても軸対称の同軸噴流と同様に2つのせん断層内の渦列が干渉し、自励振動が生じ、乱れ強さやエントレイメントが増加すること。(2)正弦波的に加振を与えた場合に周波数に依存して渦合体の位置が変化し、さらに平板長さも影響し非加振時の渦構造と様相が異なることを示した。次に、同軸噴流において環状噴流または中心円形噴流に正弦波的に振動を加えた実験やその位相の影響を調べ、空気噴流実験において、(3)内側噴流を加振した場合は内側混合領域だけでなく、外側混合領域にも影響を与え、外側噴流を加振した場合よりも乱れの大きい領域が拡大する。(4)位相φ=45°で両側の噴流を加振した場合に最も乱れが大きくなり、流量増加が見られた。水噴流実験において、(5)PIVによる計測で自然渦周波数の0.5倍で加振した場合、渦合体が促進されて乱れや噴流の広がりが増加する。(6)片側の噴流のみを加振した場合、それぞれのせん断層内の渦合体に影響を及ぼし、ノズル出口近傍の流れの様相が変化する。しかし、両側の噴流を加振した場合は内側噴流を加振した場合とほぼ同じであった。これら研究結果は、日本機械学会年次大会・流体工学部門講演会で発表し、2000年8月のFLUCOME2000国際学会で発表する。研究課題/領域番号:10750120, 研究期間(年度):1998 – 1999出典：「バイモーダル励起による同軸噴流制御に関する研究」研究成果報告書　課題番号10750120（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-10750120/)を加工して作

Transition of velocity distributions in collapsing self-gravitating N-body systems

By means of N-body simulations, we study the evolution of gravity-dominated systems from an early relaxation to a collapse, focusing on the velocity distributions and thermodynamic properties. To simulate the dynamical evolution, we consider self-gravitating small N-body systems enclosed in a spherical container with adiabatic or semipermeable walls. It is demonstrated that in the early relaxation process, the velocity distribution is non-Gaussian and q-Gaussian, since the system is in quasiequilibrium states (here q is the Tsallis entropic parameter). Thereafter, the velocity distribution undergoes higher non-Gaussian distributions, especially when the core forms rapidly in the collapse process; i.e., q tends to be larger than that for the quasiequilibrium state, since the velocity distribution further deviates from Gaussian. However, after the core forms sufficiently, the velocity distribution gradually relaxes toward a Gaussian-like distribution. Accordingly, the velocity distribution evolves from a non-Gaussian distribution through a higher non-Gaussian distribution to a Gaussian-like distribution; i.e., the velocity distribution does not monotonically relax toward a Gaussian-like distribution in our collapse simulations. We clearly show such a transition of the velocity distribution, based not only on the Tsallis entropic parameter but also on the ratio of velocity moments. We also find that a negative specific heat occurs in a collapse process with mass and energy loss (such as the escape of stars from globular clusters), even if the velocity distribution is Gaussian-like. © 2012 American Physical Society