We introduce a simple, discrete model of Feynman's ratchet and pawl, operating between two heat reservoirs. We solve exactly for the steady-state directed motion and heat flows produced, first in the absence and then in the presence of an external load. We show that the model can act both as a heat engine and as a refrigerator. We finally investigate the behavior of the system near equilibrium,...

Molecular diffusion processes are caused by concentration gradients in a multi-component mixture. Noticeable diffusion flux can also be induced by temperature gradients which lead to partial separation of constituent components. This cross effect between temperature and concentration is known as thermo diffusion or Soret effect. This effect can be quite important in the analysis of the distribu...

To enable assessment of risks of water management to riparian ecosystems at a regional scale, we developed a quantile-regression model of abundance of broadleaf cottonwoods (Populus deltoides and P. fremontii) as a function of flood flow attenuation. To test whether this model was transferrable to narrowleaf cottonwood (Populus angustifolia), we measured narrowleaf abundance along 39 river reac...

In this paper, we study some discretization schemes for diffusing flows in heterogeneous anisotropic porous media. We first introduce the notion of gradient scheme, and show that several existing schemes fall in this framework. Then, we construct two new gradient schemes which have the advantage of a small stencil. Numerical results obtained for real reservoir meshes, show the efficiency of the...

OBJECTIVE To analyze the urodynamic characteristics of neobladders, we conducted a pressure-flow study in patients with orthotopic urinary reservoirs. PATIENTS AND METHODS From 1986 to 1996, 90 patients underwent bladder replacement following cystectomy, using a right colonic, ileocolic, ileal, or sigmoid colonic segment. The subjects were 38 patients (31 men and 7 women) with stable urinatio...

when a dam is constructed on a river path, inevitably sedimentation of alluvial materials occurred. therefore, the initial capacity of the reservoir reduce gradually, and if don’t predict the effects of this phenomena and its proper control methods, the application of the reservoir may be affected. the findings of this thesis confirm that, the sedimentation in reservoirs and the variations of t...

many large oil and gas fields in the most productive world regions happen to be fractured. the exploration and development of these reservoirs is a true challenge for many operators. these difficulties are due to uncertainties in geological fracture properties such as aperture, length, connectivity and intensity distribution. to successfully address these challenges, it is paramount to improve ...

occurances of cyanobacterial bloom typically appear in eutrophic lakes which either have been affected by anthropogenic nutrient loading or are naturally rich in nutrients. microcystis blooms have been reported all over the world in freshwater ecosystems mainly due to increased population which results in increased the waste water production. the aim of this study was to recognize the basic re...

Failure of dams due to overtopping is among the most frequent forms of embankment failures. Owing to massive and wide spread damage to structures and loss of lives associated with a dam failure, the subject has drawn the attention of scientists. The study also becomes essential for damage assessment and for development of early warning system of people downstream of the embankment. The rate of ...

For reservoir operation, maintaining a quasi-natural flow regime can benefit river ecosystems, but may sacrifice human interests. This study took the Qingshitan Reservoir in the Lijiang River as a case, and developed an optimization model to explore a trade-off solution between social-economic interests and nature flow maintenance on a monthly base. The objective function considered irrigation,...