Electrokinetic Control of Viscous Fingering

We present a theory of the interfacial stability of two immiscible electrolytes under the coupled action of pressure gradients and electric fields in a Hele-Shaw cell or porous medium. Mathematically, our theory describes a phenomenon of "Vector Laplacian Growth", in which the interface moves in response to the gradient of a vector-valued potential function through a generalized mobility tensor. Physically, we extend classical Saffman-Taylor problem to electrolytes by incorporating electrokinetic phenomena. A surprising prediction is that viscous fingering can be controlled by varying the injection ratio of electric current to flow rate. Beyond a critical injection ratio, stability depends only upon the relative direction of flow and current, regardless of the viscosity ratio. Possible applications include porous materials processing, electrically enhanced oil recovery, and electrokinetic remediation of contaminated soils.Comment: * Fixed a few typos * Added new discussion of possible liquid pairs * Added new reference

Memory and mutualism in species sustainability: a time-fractional Lotka-Volterra model with harvesting

We first present a predator-prey model for two species and then extend the model to three species where the two predator species engage in mutualistic predation. Constant effort harvesting and the impact of by-catch issue are also incorporated. Necessary sufficient conditions for the existence and stability of positive equilibrium points are examined. It is shown that harvesting is sustainable, and the memory concept of the fractional derivative damps out oscillations in the population numbers so that the system as a whole settles on an equilibrium quicker than it would with integer time derivatives. Finally, some possible physical explanations are given for the obtained results. It is shown that the stability requires the memory concept in the model

Freezing point depression and freeze-thaw damage by nano-fuidic salt trapping

A remarkable variety of organisms and wet materials are able to endure temperatures far below the freezing point of bulk water. Cryo-tolerance in biology is usually attributed to "anti-freeze" proteins, and yet massive supercooling ($< -40^\circ$C) is also possible in porous media containing only simple aqueous electrolytes. For concrete pavements, the common wisdom is that freeze-thaw damage results from the expansion of water upon freezing, but this cannot explain the large pressures ($> 10$~MPa) required to damage concrete, the observed correlation between pavement damage and de-icing salts, or the damage of cement paste loaded with benzene (which contracts upon freezing). In this Letter, we propose a different mechanism -- nanofluidic salt trapping -- which can explain the observations, using simple mathematical models of dissolved ions confined to thin liquid films between growing ice and charged surfaces. Although trapped salt lowers the freezing point, ice nucleation in charged pores causes enormous disjoining pressures via the rejected ions, until their removal by precipitation or surface adsorption at a lower temperatures releases the pressure and allows complete freezing. The theory is able to predict the non-monotonic salt-concentration dependence of freeze-thaw damage in concreter and provides a general framework to understand the origins of cryo-tolerance.Comment: 5 figure

Reinforced chitosan-based heart valve scaffold and utility of bone marrow-derived mesenchymal stem cells for cardiovascular tissue engineering

Recent research has demonstrated a strong correlation between the differentiation profile of mesenchymal stem cells (MSCs) and scaffold stiffness. Chitosan is being widely studied for tissue engineering applications due to its biocompatibility and biodegradability. However, its use in load-bearing applications is limited due to moderate to low mechanical properties. In this study, we investigated the effectiveness of a fiber reinforcement method for enhancing the mechanical properties of chitosan scaffolds. Chitosan fibers were fabricated using a solution extrusion and neutralization method and incorporated into porous chitosan scaffolds. The effects of different fiber/scaffold mass ratios, fiber mechanical properties and fiber lengths on scaffold mechanical properties were studied. The results showed that incorporating fibers improved scaffold strength and stiffness in proportion to the fiber/scaffold mass ratio. A fiber-reinforced heart valve leaflet scaffold achieved strength values comparable to the radial values of human pulmonary and aortic valves (220±17 kPa). Additionally, the effects of shorter fibers (2 mm) were found to be up to 3-fold greater than longer fibers (10 mm). Heparin crosslinking of fibers failed to produce additional strength or stiffness improvements to fibers. Despite this reduction in fiber mechanical properties, the heparin-modified fibers still improved the mechanical properties of the reinforced scaffolds, but to a lesser extent than the unmodified fibers. The results demonstrate that chitosan fiber-reinforcement can be used to generate tissue-matching mechanical properties in porous chitosan scaffolds and that fiber length and mechanical properties are important parameters in defining the degree of mechanical improvement

A Semi-Active Vibration Isolator For 3D Printing On Shipboard

In the recent years, additive manufacturing (AM) (aka 3D printing)-has become a viable alternative to traditional manufacturing due to its unique advantages, such as enabling the fabrication of complex geometries at reduced weight and costs as well as allowing on-site fabrication for maintenance and repair. One specific application area of the AM is the navy vessels. During extended voyages, the navy vessels likely require the convenience of on-site fabrication of the malfunctioned parts. However, the shipboard equipment suffers from a broad range of external excitations arising not only from the waves but also from the vessel’s engines, which poses a concern for the quality of the 3D printed parts. Thus, efficient vibration isolation systems are needed for quality production. To this end, in this study, a novel semi-active vibration isolation system called Magnetorheological-based Semi-Active Vibration Isolator (MR-SAVI for short) was proposed. A comprehensive design methodology for the MR-SAVI, including both analytical and simulation modeling, was presented. A sophisticated optimization program was created to find the optimal values of the significant design parameters. The results were discussed, and future recommendations were made for the fabrication and characterization of the device

Analisis Laba Kotor Penjualan Cat Pada Toko Timur Jaya Di Muara Jawa

Penjualan merupakan salah satu faktor dominan yang berperan penting dalam USAha untuk mempertahankan dan meningkatkan USAha yang sedang dijalankan. Setiap pengusaha yang menjual barang atau jasanya harus jeli untuk menganalisis hambatan serta peluang penjualan dalam persaingan pasar.Yang menjadi permasalahan dalam penelitian ini adalah manakah diantara Cat tembok Avitex, Komilex dan Cat tembok Aries yang memberikan sumbangan laba Kotor terbesar untuk penjualan cat pada Toko Timur di Muara Jawa.Dasar teori Manajemen Pemasaran yang menguraikan pengertian Manajemen Pemasaran dan membahas Analisa biaya pemasaran yang dilanjutkan dengan pembahasan manajemen penjualan dan konsep penjualan yang dirangkaikan dengan pembahasan Akuntansi Keuangan meliputi Harga Pokok Penjualan, Pengertian Laba, Analisis Laba Kotor dan Laporan Laba Rugi.Hipotesis dalam penelitian ini diduga bahwa penjualan Cat tembok Avitex memberikan sumbangan laba kotor yang lebih besar dibandingkan dengan penjualan Cat tembok Komilex dan Cat tembok Aries pada Toko Timur Jaya di Muara Jawa.Berdasarkan hasil analisis dan pembahasan diperoleh Jenis/merk Avitex yang menghasilkan laba Kotor terbesar dari ketiga jenis/ merk cat tembok yang dijual yaitu sebesar Rp. 7.007.000,- dengan Harga Pokok sebesar Rp. 96.733.000,- kemudian Cat tembok Komilex dengan laba kotor sebesar Rp 3.555.000,- dengan Harga Pokok Penjualan sebesar Rp. 55.365.000,- dan jenis/merk Aries dengan laba Kotor sebesar Rp. 1.551.000,- dengan Harga Pokok Penjualan sebesar Rp. 45.676.000.Besarnya laba kotor, dan Harga Pokok Penjualan pada Cat tembok Avitex yang tinggi dikarenakan : lebih banyak memiliki pilihan warna – warni cemerlang yang lagi trend pada saat ini, walaupun memiliki harga penjualan lebih tinggi, dari kedua jenis/merk cat yang dijual pada Toko Timur Jaya di Muara Jawa. Hipotesis pertama yang diajukan dalam penelitian ini adalah bahwa penjualan Cat Avitex, Komilex dan Aries memberikan sumbangan laba kotor pada Toko Timur Jaya diterima. Hipotesis kedua bahwa cat Avitex memberikan sumbangan Laba Kotor yang lebih besar dibanding cat Komilex dan cat Aries, terbukti dan dapat diterima