Simple Model for Wet Granular Materials with Liquid Clusters

We propose a simple phenomenological model for wet granular media to take into account many particle interaction through liquid in the funicular state as well as two-body cohesive force by a liquid bridge in the pendular state. In the wet granular media with small liquid content, liquid forms a bridge at each contact point, which induces two-body cohesive force due to the surface tension. As the liquid content increases, some liquid bridges merge, and more than two grains interact through a single liquid cluster. In our model, the cohesive force acts between the grains connected by a liquid-gas interface. As the liquid content increases, the number of grains that interact through the liquid increases, but the liquid-gas interface may decrease when liquid clusters are formed. Due to this competition, our model shows that the shear stress has a maximum as a function of the liquid-content.Comment: 6 pages, 8 figures. Discussion is updated. Accepted for publication in EP

Cost–Benefit Analysis of a Trans-Arctic Alternative Route to the Suez Canal: A Method Based on High-Fidelity Ship Performance, Weather, and Ice Forecast Models

Climate change in recent years has produced viable shipping routes in the Arctic. However, critical uncertainties related to maritime operations in the Arctic make it difficult to predict ship speeds in ice and, thus, the voyage time and fuel costs. Cost–benefit analysis of alternative Arctic routes based on accurate environmental condition modeling is required. In this context, this paper presents a holistic approach that considers the major voyage-related costs of a trans-Arctic route as an alternative to the conventional routes via the Suez Canal Route (SCR) for existing merchant ships. This tool is based on high-fidelity models of ship performance, metocean forecasting, and a voyage optimization algorithm. Case studies are performed based on a general cargo vessel in operation to quantify realistic expenses inclusive of all the major operational, fuel, and voyage costs of the specific voyages. A comparison is made between the total costs of the trans-Arctic route and SCR for different seasons, which proves the economic feasibility of the trans-Arctic route. Overall, this work can provide valuable insights to help policymakers as well as shipbuilders, owners, and operators to assess the potential cost-effectiveness and sustainability of future Arctic shipping, thereby better developing future strategies

Epinephrine and clonidine do not improve intrathecal sufentanil analgesia after total hip replacement†

Background. We compared analgesia after intrathecal sufentanil alone, sufentanil with epinephrine 200µg and sufentanil with clonidine 30 µg in patients after total hip replacement, the endpoints being onset and duration of action. Methods. We performed a randomized double‐blind study of 45 patients for elective total hip arthroplasty using continuous spinal anaesthesia. As soon as a pain score higher than 3 on a 10 cm visual analogue scale was reported, sufentanil 7.5 µg alone, sufentanil 7.5 µg + epinephrine 200 µg or sufentanil 7.5 µg + clonidine 30 µg in 2 ml normal saline was given intrathecally. Pain scores, rescue analgesia (diclofenac and morphine) and adverse effects (respiratory depression, postoperative nausea and vomiting, itching) were observed for 24h after surgery. Results. Time to a pain score of 3 [281 (36) vs 288 (23) vs 305 (30) min] were similar in all three groups. Adverse effects and analgesic requirements during the first 24h were also similar. Conclusion. After total hip replacement, all three analgesic regimens gave good analgesia with comparable onset and duration of action, and minor adverse effects. Br J Anaesth 2002; 89: 562-

Inherent Inhomogeneities in Tunneling Spectra of BSCCO Crystals in the Superconducting State

Scanning Tunneling Spectroscopy on cleaved BSCCO(2212) single crystals reveal inhomogeneities on length-scales of $\sim$30 $\AA$. While most of the surface yields spectra consistent with a d-wave superconductor, small regions show a doubly gapped structure with both gaps lacking coherence peaks and the larger gap having a size typical of the respective pseudo-gap for the same sample.Comment: 4 pages, 4 figure

Anomalous Thermal Diffusivity of Amorphous Semiconductor Superlattices

Since the development of amorphous semiconductor superlattice films, the great interesting in fundamental and technological is attracted by their special properties and applications. The optical and electronic properties of the films have been studied by conventional spectroscope, photoluminescence and photoconductance techniques etc. Some anomalous phenomena, such as, the quantum size effect and the permenent photoconductivity (PPC) effect, have been discovered [1–2]. Recently the investigations of the characteristics and parameters of amorphous semiconductor superlattice films by photoacoustic and photothermal techniques are being got attention [3,4]. In this paper, we describe the study of the thermal diffusivity of a series samples of amorphous semiconductor superlattices a-Si:H/a-SiNx:H. The thermal diffusivity of the samples is experimentally measured by using mirage detection technique [5,6]. Up to date, the mirage detection method has been used successfully to determine the thermal diffusivity of both transparent and opaque materials. Specially it is available to measure directly the thermal parameters of thin films which are usually difficalt to be, evaluated. In the theoretical calculation, one dimensional model with “ the thormal resistors in series “ and ” the weighted average ” is used. Comparing the experimental and theoretical results, we find that both are in good agreement for the most of the samples. However, some anomalous thermal diffusivity phenomena have been observed in some special samples

Shear strength properties of wet granular materials

We investigate shear strength properties of wet granular materials in the pendular state (i.e. the state where the liquid phase is discontinuous) as a function of water content. Sand and glass beads were wetted and tested in a direct shear cell and under various confining pressures. In parallel, we carried out three-dimensional molecular dynamics simulations by using an explicit equation expressing capillary force as a function of interparticle distance, water bridge volume and surface tension. We show that, due to the peculiar features of capillary interactions, the major influence of water content over the shear strength stems from the distribution of liquid bonds. This property results in shear strength saturation as a function of water content. We arrive at the same conclusion by a microscopic analysis of the shear strength. We propose a model that accounts for the capillary force, the granular texture and particle size polydispersity. We find fairly good agreement of the theoretical estimate of the shear strength with both experimental data and simulations. From numerical data, we analyze the connectivity and anisotropy of different classes of liquid bonds according to the sign and level of the normal force as well as the bond direction. We find that weak compressive bonds are almost isotropically distributed whereas strong compressive and tensile bonds have a pronounced anisotropy. The probability distribution function of normal forces is exponentially decreasing for strong compressive bonds, a decreasing power-law function over nearly one decade for weak compressive bonds and an increasing linear function in the range of tensile bonds. These features suggest that different bond classes do not play the same role with respect to the shear strength.Comment: 12 page

Effective Area-Elasticity and Tension of Micro-manipulated Membranes

We evaluate the effective Hamiltonian governing, at the optically resolved scale, the elastic properties of micro-manipulated membranes. We identify floppy, entropic-tense and stretched-tense regimes, representing different behaviors of the effective area-elasticity of the membrane. The corresponding effective tension depends on the microscopic parameters (total area, bending rigidity) and on the optically visible area, which is controlled by the imposed external constraints. We successfully compare our predictions with recent data on micropipette experiments.Comment: To be published in Phys. Rev. Let