Growth rates in modern speleothems from Santana Cave,Brazil, by the 210Pb-method

The Santana Cave is located at the Upper Ribeira Touristic State Park (PETAR-Parque Estadual Turístico do Alto Ribeira) in southern São Paulo State, Brazil. This paper describes ²¹⁰Pb activity concentration data in soda straw stalactites samples collected at Salão das Flores in Santana Cave that is a fossil tributary of the cave river. Non-expensive alpha counting following some analytical steps for extracting and depositing ²¹⁰Po were used for providing the ²¹⁰Pb data. In the analyzed samples, ²¹⁰Pb values of increasingly older samples fitted an exponential curve, thus suggesting that the production of ²¹⁰Pb has been constant with time. Also, the near-ideal fit indicated that the growth was uniform and there was no break in the continuous growth. The soda straw growth rates were determined from the best fit to the exponential curve through the ²¹⁰Pb activity concentration. The results of the measurements allowed estimate a longitudinal rate corresponding to 1.3 mm/yr and a lateral rate of 0.01 mm/yr, which permitted calculate times of 70 years and 317–498 years for their formation, respectively. The lateral growth rate is compatible with values from studies of chemical weathering rates held under laboratory and natural conditions.     

Time variations of 222Rn concentration and air exchange rates in a Hungarian cave

A long-term radon concentration monitoring was carried out in the Pál-v?lgy cave, Budapest, Hungary, for 1.5 years. Our major goal was to determine the time dependence of the radon concentration in the cave to characterise the air exchange and define the most important environmental parameters that influence the radon concentration inside the cave. The radon concentration in the cave air was measured continuously by an AlphaGuard radon monitor, and meteorological parameters outside the cave were collected simultaneously. The air's radon concentration in the cave varied between 104 and 7776?Bq?m(-3), the annual average value was 1884±85?Bq?m(-3). The summer to winter radon concentration ratio was as high as 21.8. The outside air temperature showed the strongest correlation with the radon concentration in the cave, the correlation coefficient (R) was 0.76.     

井旁溶洞的偶极反射声波测井响应研究*

反射声波成像测井是适应复杂地区勘探开发的一种测井新技术,能够对井旁几米至几十米内声阻抗不连续的地层界面、裂缝、溶洞、盐丘等不同地质构造进行探测评价。针对井旁存在一个不同尺度大小的溶洞时的偶极反射声波测井响应进行了数值模拟,得到了不同情况下的回波信号,探究了地层横波波长与井旁溶洞尺度之间的关系。研究结果表明,等源距阵列波形中,溶洞的回波波列有特殊的"抛物线"型形态,上提过程中距溶洞最近时,回波到时最早、幅度最大。当井旁溶洞直径逐渐增大时,回波信号幅度越强,反射横波偏移成像的结果越清晰。通过该研究,初步形成了一种反射声波测井评价井旁溶洞的方法。     

Time variations of 222Rn concentration and air exchange rates in a Hungarian cave

A long-term radon concentration monitoring was carried out in the Pál-völgy cave, Budapest, Hungary, for 1.5 years. Our major goal was to determine the time dependence of the radon concentration in the cave to characterise the air exchange and define the most important environmental parameters that influence the radon concentration inside the cave. The radon concentration in the cave air was measured continuously by an AlphaGuard radon monitor, and meteorological parameters outside the cave were collected simultaneously. The air's radon concentration in the cave varied between 104 and 7776 Bq m^?3, the annual average value was 1884±85 Bq m^?3. The summer to winter radon concentration ratio was as high as 21.8. The outside air temperature showed the strongest correlation with the radon concentration in the cave, the correlation coefficient (R) was 0.76.     

A STUDY ON ABSORPTION OF Na ATOMS ON Si(100) 2×1 SURFACES WITH DV-Xα METHOD

The Na absorption on Si(100) 2×1 surface is studied with quantum chemistry molecular cluster method. The calculated results show that the most favourable absorption site of Na is the cave site and the charge transfer of Na atom to Si is large when the Na coverage is smaller than 0.5 monolayer (ML). A Na chain is formed along the cave sites at the 0.5 ML Na coverage, the charge transfer then becomes small. The calculated density of states show that the Na atoms are metallic along the chain. At 1 ML coverage, the Na atoms occupy both the cave and pedestal sites and form a double-layer. There is a charge transfer of 0.5e from each Na atom to the Si surface. The calculated surface energy shows that the saturation absorption of Na on Si surface is 1 ML.     

A STUDY ON ABSORPTION OF Na ATOMS ON Si(100) 2×1 SURFACES WITH DV-Xα METHOD

The Na absorption on Si(100) 2×1 surface is studied with quantum chemistry molecular cluster method. The calculated results show that the most favourable absorption site of Na is the cave site and the charge transfer of Na atom to Si is large when the Na coverage is smaller than 0.5 monolayer (ML). A Na chain is formed along the cave sites at the 0.5 ML Na coverage, the charge transfer then becomes small. The calculated density of states show that the Na atoms are metallic along the chain. At 1 ML coverage, the Na atoms occupy both the cave and pedestal sites and form a double-layer. There is a charge transfer of 0.5e from each Na atom to the Si surface. The calculated surface energy shows that the saturation absorption of Na on Si surface is 1 ML.     

井外溶洞储层的偶极横波反射特征研究*

溶洞型储层是油气田中比较典型的储层之一,其非均质性强,勘探开发难度较大,偶极横波远探测技术是目前探测井外溶洞的有效方法。碳酸盐岩溶洞模型正演模拟对于现场的油气勘探和资料解释具有指导性作用。该文建立了几种比较典型的溶洞模型,并通过有限差分方法对溶洞储层的偶极三维反射声场进行了研究,发现在小源距范围内可以接收到来自溶洞后壁较强的反射波,随着源距的增大,该反射波逐渐减弱至消失;对于缝洞结合体的反射波场,来自裂缝的反射波能量要强于来自溶洞的反射波,且来自裂缝的反射波会掩盖溶洞前壁的反射波信息,这对后期的成像处理带来了困难。最后进一步研究了偶极远探测技术在溶洞方位识别以及尺寸大小估算中的应用。     

Turbulence decay rate as a measure of flow dimensionality

The dimensionality of turbulence in fluid layers determines their properties. We study electromagnetically driven flows in finite-depth fluid layers and show that eddy viscosity, which appears as a result of three-dimensional motions, leads to increased bottom damping. The anomaly coefficient, which characterizes the deviation of damping from the one derived using a quasi-two-dimensional model, can be used as a measure of the flow dimensionality. Experiments in turbulent layers show that when the anomaly coefficient becomes high, the turbulent inverse energy cascade is suppressed. In the opposite limit turbulence can self-organize into a coherent flow.     

A fluid generalization of membranes

In a certain sense a perfect fluid is a generalization of a point particle. This leads to the question as to what is the corresponding generalization for extended objects. Here the lagrangian formulation of a perfect fluid is much generalized by replacing the product of the co-moving vector which is a first fundamental form by higher dimensional first fundamental forms; this has as a particular example a fluid which is a classical generalization of a membrane; however there is as yet no indication of any relationship between their quantum theories.     

Flow and fracture in drying nanoparticle suspensions

Drying aqueous suspensions of monodisperse silica nanoparticles can fracture in remarkable patterns. As the material solidifies, evenly spaced cracks invade from the drying surface, with individual cracks undergoing intermittent motion. We show that the growth of cracks is limited by the advancement of the compaction front, which is governed by a balance of evaporation and flow of fluid at the drying surface. Surprisingly, the macroscopic dynamics of drying show signatures of molecular-scale fluid effects.     

Particle in cell simulation of relativistic Buneman instability in a current-carrying plasma

Abstract

Non-linear evolution of the relativistic Buneman instability in a current-carrying plasma is investigated by a particle in cell simulation. These simulations show that as the time progresses, some electrons are trapped in phase space holes and thus counter-streaming and plateau can be formed. Moreover, the electron and ion density profiles indicate a periodic pattern of the density steepening. This density distribution is similar to the generation of the grating-like patterns which strongly depends on the initial electron velocity and saturation time. It is also shown that the electric field profile has the sawtooth form; charged particles can be accelerated by this field. Finally, it is found that increasing the electron velocity increases the saturation time and consequently the growth rate decreases which is in good agreement with the result obtained by the fluid model.     

均匀液滴氧发生器液流破断的线性分析

 在均匀液滴氧发生器的研究过程中，液滴的形成是关键技术。利用压电换能器对液流施加扰动，初始扰动沿液流表面呈指数增长，直到将液流夹断生成液滴。通过理论分析，发现在影响液流表面增长率的诸多参数中，碱性过氧化氢溶液(BHP)表面张力的增加和液体分配板板孔直径的减小能够增大扰动增长率，其他参数的改变对增长率的影响非常小。通过分析还发现，BHP液体的喷射流速不同，要取得最大增长率的外界扰动频率也随之变化，外界施加扰动的频率随液流喷射流速的增大而增大。这些结果为均匀液滴氧发生器的实验研究提供有力的参考依据。     

The osgood criterion and finite‐time cosmological singularities

In this paper, we apply Osgood's criterion from the theory of ordinary differential equations to detect finite‐time singularities in a spatially flat FLRW universe in the context of a perfect fluid, a perfect fluid with bulk viscosity, and a Chaplygin and anti‐Chaplygin gas. In particular, we applied Osgood's criterion to demonstrate singularity behaviour for Type 0/big crunch singularities as well as Type II/sudden singularities. We show that in each case the choice of initial conditions is important as a certain number of initial conditions leads to finite‐time, Type 0 singularities, while other precise choices of initial conditions which depend on the cosmological matter parameters and the cosmological constant can avoid such a finite‐time singularity. Osgood's criterion provides a powerful and yet simple way of deducing the existence of these singularities, and also interestingly enough, provides clues of how to eliminate singularities from certain cosmological models.     

Rayleigh-Taylor instability experiments with precise and arbitrary control of the initial interface shape

In a Rayleigh-Taylor instability a dense fluid sits metastably atop a less dense fluid, a configuration that can be stabilized using a magnetic field gradient when one fluid is highly paramagnetic. On switching off the magnetic field, the instability occurs as the dense fluid falls under gravity. By affixing appropriately shaped magnetically permeable wires to the outside of the cell, one may impose arbitrarily chosen and well-controlled initial perturbations on the interface. This technique is used to examine both the linear and nonlinear growth regimes for which the perturbation amplitudes, growth rates, and nonlinear growth coefficients are obtained.     

Surface tension effects in the zero gravity inflow of a drop into a fluid

As a drop of fluid is deposited on the surface of a miscible fluid (that we call the solvent), it undergoes a strong pulling due to its surface rupture and it acquires a kinetic energy independently of gravity. For the drop and the solvent being of the same fluid we observe a drop injection at an initial velocity which scales as the square root of the surface tension of the drop against air. Once injected, the drop develops a transverse instability giving rise to an expanding ring. Viscosity terminates the process and stops the ring. We show that the final ring height follows a scaling law whereas two asymptotical scaling regimes can be identified for the ring radius. Received 31 August 1999     

Still a bridge too far? Biolinguistic questions for grounding language on brains

In this paper we discuss how Fibonacci growth patterns are apparent in the structure of human language. We moreover show how familiar dynamics yielding these sorts of patterns in nature may be taken to apply, at some level of abstraction, for the human faculty of language. The overall picture casts doubts on any simplistic treatment of language behavior, of the sort stemming from classical behaviorism in psychology (which is again popular in contemporary computational models). Instead, it appears to be more profitable to study language as a complex dynamic system, emerging in human brains for physical reasons which are yet to be fully comprehended, but which in the end disfavor any dualistic approach to the study of mind in general, and the human mind in particular.     

Numerical analysis of fluid flow through a cylinder array using a lattice Boltzmann model

In this paper we present a detailed computational study of an incompressible Newtonian fluid flow across a periodic array of two-dimensional cylinders which is a simplest non-trivial representation of a porous media. A two-dimensional Lattice Boltzmann Method is used to solve the governing Navier－Stokes equation taking into account of viscous dissipation effects and influence of nonlinear fluid drag. Both the flow fields and the Darcy－Forchheimer drag coefficient as a function of the solid volume fraction are calculated for a wide range of flow Reynolds numbers. The predictions were compared with the results from conventional numerical and empirical models for verification. Apart from confirming that inertial effects can cause a significant deviation from Darcy's law for large velocities the results also show that the characteristics of the vorticity field vary considerably as the Reynolds number increases, which will have major implications to the transport of passive particulate substances within the pores and their removal rate.     

Collisional granular flow as a micropolar fluid

We show that a micropolar fluid model successfully describes collisional granular flows on a slope. A micropolar fluid is the fluid with internal structures in which coupling between the spin of each particle and the macroscopic velocity field is taken into account. It is a hydrodynamical framework suitable for granular systems which consists of particles with macroscopic size. We demonstrate that the model equations can quantitatively reproduce the velocity and the angular velocity profiles obtained from the numerical simulation of the collisional granular flow on a slope using a simple estimate for the parameters in the theory.