Spherical cells

The truncated octahedron and the rhombic dodecahedron provide periodic cells that are approximately spherical and so may be more appropriate for simulations of spherical molecules. The distance between adjacent cells in the truncated octahedron or the rhombic df)decahedron is larger than the conventional cube for a system with a given number of particles and so a simulation using one of the spherical cells will require fewer particles than a comparable simulation using a cubic cell. Of the two approximately spherical cells, the truncated octahedron is often preferred as it is somewhat easier to program. The hexagonal prism can be used to simulate molecules with a cylindrical shape such as DNA. 

According to Newton s second law, the sum of the forces on a particle, ie, one spherical cell in plasma, should equal its mass, times the acceleration of the cell or particle, a. ... 

Porous membranes with selective permeabiUty to organic solvents have been prepared by the extraction of latex films prepared with moderate ratios of PVA—PVAc graft copolymer fractions. The extracted films are made up of a composite of spherical cells of PVA, PVAc microgel, and PVA—PVAc graft copolymers (113). 

This prediction is drawn according to the following model. Figure 5 illustrates that in the latex state the grafting PVA protects hydrophobic PVAc particles in water by concentrating on the surfaces of PVAc particles, but in the porous film after acetone extraction, the insoluble grafting PVAc conversely exists as an important component on the inner surface of spherical cells of PVA. 

There has been a conventional sense that the PVAc latexes prepared in the presence of PVA as a protective colloid contain the graft copolymer of PVA and PVAc, so that PVAc particles in the dried latex film are not extracted at a high ratio with solvents. In this Chapter, it has been defined without an influence by the usual sense that the porous PVA-PVAc composite can be prepared from the PVAc latex film with acetone extraction. The porous film consists of the spherical cells of PVA... 

These two considerations allowed M. Amon and C. D. Denson to avoid difficulties pertaining to the assignment of concentration gradients near the bubble wall. The authors called their model the cellular model . Setting the quantity of bubbles, they placed each bubble in correspondence with a spherical cell of surrounding liquid with a mass equal to the ratio of the entire liquid mass to the overall quantity of bubbles. This made it possible for them to solve the problem of bubble growth in this cell. 

To evaluate the effect of holdup on bubble velocity, Marrucci (M3) used a spherical cell model of radius b such that... 

When in suspension however cells tend to move at the minimum relative velocity with respect to the surrounding fluid. This means that a spherical cell will rotate at the velocity gradient of the suspension, or in proportion to it. For a spherical cell of diameter, d, the average shear rate, Yavg> on its surface is given by ... 

Some bacteria measure as large as 80 p in length others as small as 0.2 ix. However, the majority of the commonly encountered bacteria, including the disease producers, measure about 0.5 n in diameter for the spherical cells and 0.5 by 2 to 3 p for the rod forms. Bacteria producing spores are generally larger than the nonspore-producing species. The sizes of some common species in dried and stained smears are as follows Escherichia coli, 0.5 by 1 to 3... 

All of the above-mentioned examples describe organosiloxane hybrid sheet-like structures. However, cell-mimicry requires spherical structures that can form an inner space as a container. Liposomes and lipid bilayer vesicles are known as models of a spherical cell membrane, which is a direct mimic of a unicellular membrane. However, the limited mechanical stability of conventional lipid vesicles is often disadvantageous for some kinds of practical application. 

Model calculations have demonstrated that active cells are surrounded by zones containing substrate concentrations lower than those of the bulk liquid [12-14], This concentration gradient results from the dynamic interplay between the rates of substrate uptake and diffusion through the diffusion layer surrounding the cell (see [15] for details). Boone et al. [13] developed a model using spherical coordinates that allows calculation of the diffusive substrate flux to a suspended spherical cell. In their model calculations, the cell surface concentration was set to arbitrary values between zero and about half of the bulk concentration. It... 

Equation (14) also shows that for microorganisms with radii that are less than a few microns with a typical diffusion layer thickness > 10 pm, radial diffusion should predominate over linear diffusion [46], Under steady-state conditions, the area integrated cellular flux (mols-1), Q, for a small, spherical cell of surface = 4tt q, is given by ... 

Berk DA, Clark A, Jr., Hochmuth RM (1992) Analysis of lateral diffusion from a spherical cell surface to a tubular projection. Biophys. J. 61 1-8. 

Figure 4.8 Fat in a lamb or pork chop. Adipose tissue consists of connective tissue in which adipocytes are dispersed. Adipocytes are small spherical cells comprising 90% triacylglycerol (Chapter 7).

Palmelloid A form of colonial structure in algae where the spherical cells are united by the mucilaginous coats into indefinite mucilaginous masses. 

As can be seen from Table 1-2, which lists the diameters and volumes of several roughly spherical cells, there is a great variation in size. However, a diameter of 10-20 pm may be regarded as typical for both plants and animals. For growth of a large cell such as the ovum, many adjacent cells assist in synthesis of foodstuffs which are transferred to the developing egg cell. Plant cells are often large but usually 90% or more of the cell is filled with a vacuole or tonoplast,36 which is drawn unrealistically small in Fig. 1-6. The metabolically active protoplasm of plant cells often lies in a thin layer at their peripheries. 

There are substantially fewer MC studies of hydrates than there areMD studies. The initial MC study of hydrates was by Tester et al. (1972), followed by Tse and Davidson (1982), who checked the Lennard-Jones-Devonshire spherical cell approximation for interaction of guest with the cavity. Lund (1990) and Kvamme et al. (1993) studied guest-guest interactions within the lattice. More recently Natarajan and Bishnoi (1995) have studied the technique for calculation of the Langmuir coefficients. 

Finally, we wish to report the results for simulated cell smears. These experiments are being carried out to determine the best parameters for data acquisition, and to establish the variations of the cellular spectra from a homogeneous cell culture. Similar efforts have been undertaken before, where the cells were spin-deposited onto the microscope slides. However, for cultured cervical cancer (HeLa) cells, the resulting samples contained many cells that maintained their morphology in suspension quite well, and produced dried cells that were nearly spherical. Once dried, these cells could not be stained easily, and thus, their divisional activity could not be established after IR data acquisition. Furthermore, large spherical cells often gave spectral artifacts that made interpretation impossible.16... 

Upon coverage of longitudinally cleaved tubes with bovine endothelial cells in cell culture tests, a distinct sprouting of the initially spherical cells takes places within 24 h. SEM shows that the resulting filaments barely differ from the fibers of BC (Fig. 21). This structure also benefits the rapid endothelial colonization of BASYC . 

Fig. 3. Heat production is an important consideration for devices using electric fields in the liquid near cells. This figure shows the theoretical distribution of heat production in and around a spherical cell at the centre of a quadrupole electrode chamber in a solution of low electrical conductivity (top) and high conductivity (bottom). The heat production is given by gE2 where g is the conductivity of the solution or cell component and E is the (local) electric field strength. The contour interval is 7% of the maximum in each case. The cell is modelled as an electrically conductive sphere enveloped by an insulating but capacitive membrane.

It is assumed that the cell is symmetrical across the equatorial plane and axi-symmetrical around the axis of compression, the tj axis. This symmetry allows the compression of the cell to be fully represented by a 2D curve in the positive r and p axis. To understand the elastic membrane model, the geometry of the spherical cell under compression can be represented by Figure 10. 

Ribosomes are spherical cell structures enriched with ribonucleoprotein and with a diameter of 15-20 nm. Each ribosome is formed by two subunits of different sizes, only visible through high resolution electron microscopy. Ribosomes connected to the rough endoplasmic reticulum are involved in the biosynthesis of proteins that are temporarily stored or transported to the cell s outer environment. Proteins synthesized by ribosomes connected to membranes accumulate in the cisternae before passage to the plasma membrane for secretion. 

If f<total potential difference applied across the cell is developed across the membrane capacitance. In this limit, the induced membrane potential AV across a spherical cell is AV = 1.5 ER, where E represents the applied external field. Thus the cell samples the external field strength over its dimensions and delivers this integrated voltage to the membranes, which is a few mV at these low frequencies for cells larger than 10 ym and external fields of about 1 V/cm. These transmembrane potentials can be biologically significant. 

---