Unit Cell Area Research Articles

Convoluted array elements and reduced size unit cells for frequency-selective surfaces

When the curvature of a surface that is to be made frequency selective is not small, it modifies the array lattice and element geometry, altering the transmission performance of the surface. For a given degree of curvature, small unit cells are distorted less. The transmission response of a typical array of conducting elements has a main reflection resonance at a wavelength λ1, with further nulls at shorter wavelengths. We have attempted to reduce the unit cell dimension p as much as possible for a given reflection wavelength λ1, thereby increasing its separation from grating responses. The ratio λ1/p has been used as a figure of merit. An array of linear dipoles on a square lattice of side p is a standard of comparison, a typical case giving a figure of merit of 1.6. A Jerusalem cross array gives a value of about 4.5. By convoluting the conductors of a square loop element, or by using, as the array elements, the low order generations of space filling curves, such as that described by Hilbert, we have obtained values of λ1/p in the range 7–12. The unit cell areas are lower than that of the dipole standard by factors averaging about 40.

The calculation of stacking fault energies in close-packed metals

The one-electron theory of metals is applied to the calculation of stacking fault energies in face-centered cubic metals. The extreme difficulties in calculating fault energies of the order of 0.01 eV/(interface unit-cell area) are overcome by applying the Force theorem and using the layer–Korringer–Kohn–Rostoker method to determine the charge density of isolated defects. A simple scheme is presented for accommodating deviations from charge neutrality inherent in this approach. The agreement between theoretical and experimental values for the stacking fault energy is generally good, with contributions localized to within three atomic planes of the fault, but suggest the quoted value for Rh is a significant overestimation.

Cellular distribution of prostacyclin synthase and specific prostacyclin binding sites in bovine corpora lutea of pregnancy

The cellular distribution of prostacyclin (PGI 2) synthase and specific PGI 2 binding sites was investigated by light microscope immunocytochemistry and quantitative autoradiography. The immunostaining for the enzyme was found in small (15–18 μm) and large (18–45 μm) cells as well as in non-luteal cells, arteriole smooth muscle and endothelium. There was no consistent difference between small and large luteal cells and luteal vs. non-luteal cells in the immunostaining. Vascular smooth muscle and endothelial cells, on the other hand, contained less immunostaining than the other cells. Contrary to wide-spread distribution of PGI 2 synthase, specific PGI 2 binding sites were only found in the luteal cells. On a per cell basis, large luteal cells contained more sites than small luteal cells and vice versa when expressed per unit cell area. The [ 3H]PGI 2 binding to the luteal cells was time and temperature dependent and was inhibited by excess unlabeled PGI 2 but not by its metabolite, 6-keto-PGF 1α or other eicosanoids which bind to their own receptors. In conclusion, while PGI 2 synthase is widely distributed among different cell types in bovine corpora lutea, specific binding sites which may mediate luteotropic actions of PGI 2 are only present in small and large luteal cells.

Culm Strength of Barley

Grass culms are known to differ in breaking strength, but there is little physicochemical data to explain the response. The fourth internode of four brittle and two nonbrittle barley (Hordeum vulgare L.) strains were used for physical and chemical studies of culm strength. Inner and outer culm diameters of brittle strains (3.6 +/- 0.2 and 5.0 +/- 0.1 millimeters) were not significantly different from those of nonbrittle strains (3.9 +/- 0.2 and 5.2 +/- 0.2 millimeters). Maximum bending stress, at which the culm was broken, was 192 +/- 34 g/mm(2) for brittle and 490 +/- 38 g/mm(2) for nonbrittle strains. Wall thickness and cell dimensions of epidermal, sclerenchyma, and parenchyma cells were measured in culm cross sections. The area of cell wall per unit cell area for each tissue was significantly correlated with the maximum bending stress (r = 0.93 for epidermis, 0.90 for sclerenchyma, and 0.84 for parenchyma). Cell walls of brittle culms had 6 to 64% as much cellulose content as those of nonbrittle culms. Maximum bending stress correlated significantly with cellulose content of the cell walls (r = 0.93), but not with the contents of noncellulosic compounds. The lower cellulose content of the brittle culm was significantly correlated with brittleness.

New method of calculation of the surface enthalpy of solids

A new method of calculation of the surface enthalpy of solids E c in the so-called rigid lattice approximation is proposed. The formerly found [J. Solid State Chem. 57 (1985) 269, 291] empirical relationship between bond length and bond energy in oxide crystals is used for this purpose. It is sufficient to add the energies of all bonds cut in the process of surface formation over the surface unit cell and to divide the sum by double the unit cell area. The advantage of this widely applicable method consists in the fact that it is sufficient to know the structure of the considered crystal; for oxides all coefficients of the proposed equation have already been determined and listed in the quoted paper. Generalization of the method on the non-oxide (X) crystals is dependent on the determination of the respective coefficients for the element-X bonds. But at present the method is also applicable to non-oxide crystals of high symmetry (e.g. NaCl-type, CsCl-type, ZnS-type, fluorite-type). It is argued that E c may be thought of as active surface energy responsible for various aspects of the surface reactivity and cleavage, while the passive surface energy of the relaxed surface governs static phenomena. As the passive surface energy (or free energy) is not easy to be obtained either experimentally or theoretically, an attempt is made to predict the equilibrium form of crystals with Curie-Wulff plots using E c instead of the free energy. In most cases the predictions agree well with accessible literature data. Data involving cleavage planes and direct experimental determinations of the surface energy are also used in the evaluation of the proposed method. The paper is illustrated with numerical data of E hkl c calculated for a number of oxides and halides of the NaCl-type structure as well as for oxides of the rutile-type, TiO 2-anatase, V 2O 5 and MoO 3 including the reduced faces of the two latter oxides.

Broken symmetry states for two-dimensional electrons in a strong magnetic field.

A two-dimensional electron gas in a strong magnetic field and a weak periodic potential is studied in the Hartree-Fock approximation. It is shown that electron-electron interactions favor the formation of a Wigner crystal. This tendency may cause the symmetry of the externally applied potential to be broken, particularly when the area containing one electron is a multiple of the unit-cell area for the external potential. Some predictions are made for the external potential strengths below which symmetry breaking occurs.

Quantised Hall conductance in a perfect crystal

Using magnetic translation symmetry, the Hall conductance of an isolated magnetic band in units of e2/h is shown to satisfy the Diophantine equation p sigma +qm=1, where p and q are relatively prime integers giving the number of flux quanta per unit cell area, phi =p/q, and m is an integer. This equation holds for a general periodic Schrodinger Hamiltonian with an arbitrary magnetic field and is a direct consequence of the q-fold degeneracy of magnetic bands. Extension to general real phi gives the equation phi sigma H- rho =integer with sigma H the Hall conductance and rho the number of electrons per unit cell, from which sigma H is uniquely determined once rho , phi and the gap structure are given.

Transformation-Associated Increase of Adhesion, Cellular Fibronectin, and Stress Fiber Development in a Liver Epithelial Cell Line

Cytoskeletal and adhesion characteristics of DL-ethionine (CAS: 67-21-0)-transformed rat liver epithelial cells (ETC) were compared with those of nontumorigenic, untreated cells of the same cell line both at the same passage level as ETC and at an early low passage level. ETC and high-passage-level cells (HPC) showed increased cell spreading and prominent actin stress fibers compared to low-passage-level cells (LPC). The number of adhesion plaques per unit cell area was higher for ETC than for LPC. At confluence, fibronectin expression was high for ETC, moderate for HPC, and low for LPC. The observed increases in cell spreading and in actin and fibronectin expression appeared to be associated with transformation of this cell line rather than being specific responses to ethionine treatment. This conclusion is suggested by the fact that HPC, which display preneoplastic markers, are similar in many respects to ETC.

Composite von Neumann lattice

A new general subset of coherent states, which is complete and overcomplete by just one element, is introduced. It is the union of $N$ arbitrary nonintersecting von Neumann lattices whose unit-cell areas have a harmonic mean of $\mathrm{Nh}$. First applications are given in the problems of crystal electrons in rational magnetic fields, incommensurate structures in a magnetic field, and quantum dynamics.

Organization of calcium pump protein dimers in the isolated sarcoplasmic reticulum membrane

The arrangement of the calcium pump protein in the isolated sarcoplasmic reticulum (SR) membrane was examined by optical diffraction of freeze-fracture electron micrographs. Several states of protein particle organization were observed: random, hexagonal and tetragonal packing, and a mixture of hexagonal and tetragonal packing. This suggests that the time-averaged positions of protein particles in the plane of the SR membrane are weakly defined. In addition, there appears to be a greater degree of local or short-range order compared to long-range order within the field of freeze-fracture particles. We utilized measurements from tetragonally or hexagonally packed arrays to determine a unit cell area occupied by each freeze-fracture particle and its associated lipid matrix. When these unit cell areas and the stereologically determined area per freeze-fracture particle were compared to the cross-sectional area occupied by a single calcium pump protein and its associated lipid, obtained by x-ray and neutron diffraction methods, we concluded that each freeze-fracture particle probably represents a dimer of pump protein molecules in the plane of the SR membrane.

Force-velocity characteristics and active tension in relation to content and orientation of smooth muscle cells in aortas from normotensive and spontaneous hypertensive rats.

Segments of abdominal aorta from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats (20-25 weeks) were compared with respect to force production and dynamic mechanical properties. The preparations were mounted in vitro for determination of optimal length (lo) for active force, and then maximally stimulated (high-K+ solution, 10 mm Ca2+, 10(-5) m noradrenaline), and fixed for electron microscopy. Muscle cellular volume per mm vessel wall was significantly (p less than 0.01) higher in SHR (0.14 +/- 0.009 mm3, n = 7) compared to WKY (0.11 +/- 0.004 mm3, n = 7). Unchanged cell length and unaltered cross-sectional area (17 micrometers2) of nucleus containing cell profiles in SHR suggest an increased number of cells in the media. No difference was found in maximum force per unit cell area between SHR (271 +/- 31, n = 7) and WKY (305 +/- 49 mN/mm2, n = 7). Cell orientation was almost circular in both groups, showing that force was measured in parallel to the cell long axis. Aortic segments were mounted in an apparatus for quick-release experiments. They were maximally stimulated and force steps were imposed at peak of contractions. The series elastic component, characterized by the initial elastic recoils at 0.75 lo, has similar stiffness values in SHR and WKY. Velocities were measured 100 msec after release. The results were fitted to Hill's equation and maximum shortening velocity (Vmax) computed. No difference in Vmax was found at 0.75 lo (WKY: 0.048 +/- 0.005; SHR: 0.042 +/- 0.006 lo/s, n = 6 for both). At 0.85 lo, the data were corrected for passive tension (40% to total). Vmax at 0.85 lo was 0.071 +/- 0.009 lo/s (n = 5) for WKY, and 0.069 +/- 0.007 lo/s (n = 5) for SHR. Similar Vmax and force per cell cross-sectional area suggest similar characteristics of actomyosin interaction in SHR and WKY aorta.

A contracted form of the trigonal purple membrane of Halobacterium halobium

A variety of procedures can be used to modify native trigonal (p3) purple membrane of Halobacterium halobium into an altered form with a smaller unit cell. X-ray powder patterns of the new form show the cell dimension a = 59·.5 Å, instead of 62·7 Å, and totally different intensities. Chemical analyses show a reduction in lipid content in this new form consistent with the smaller unit cell area. R-factor searches of the electron diffraction amplitudes, assuming the projected molecular density to be the same in the two forms, showed the molecule could be satisfactorily fitted into the modified form by a 10° rotation relative to the native. This causes the molecules to be packed more closely, both within each of the groups of three situated about the 3-fold axes as well as between the groups of three. Several new close contacts between helices result, ruling out the possibility that these helices contain amino acids with the same charge at the two aqueous surfaces. The quality of the electron diffraction pattern from the modified membranes is not yet sufficient to help in phase determination of higher resolution data by means of the molecular replacement method.

Alkali Cation Selectivity and Fixation by Clay Minerals

AbstractTwo variables must be considered when calculating exchange free energies (ΔG°ex) for 2:1 clays: (1) anionic field strength, as expressed by equivalent anionic radius (ra), and (2) interlayer water content, as expressed by interlayer molality. For smectites that are in a state of high hydration, interlayer molality is determined by the cations undergoing exchange. Thus ΔG°ex for an exchanging cation pair can be calculated solely from measurements of ra. ra is related to layer charge per half unit cell (C) and ab unit cell area (A) by: ra = (-A/8πC)1/2. The layer charge necessary for cation fixation can be predicted by calculating the ra at which cation exchange with an illite structure expresses a AG°ex equal to that of exchange with a smectite structure. The theory can also be applied qualitatively to understand the high selectivity of illite for Cs+, the fixation of K+ rather than Na+ in shales during diagenesis, the stability of illite over muscovite in the weathering environment, and cation segregation in smectite.

Contractile and morphological properties of the portal vein in spontaneously hypertensive and wistar-kyoto rats.

In perfusion experiments, previous investigations have shown an increased responsiveness of isolated vascular beds from spontaneously hypertensive rats (SHRs) compared with Wistar-Kyoto controls (WKYs). The results have suggested that there are differences in the arterial vessels but not in the venous vessels. Here we have tested the latter part of this hypothesis by comparing the contractile and morphological properties of isolated portal veins from 18 SHRs and 18 WKYs, all 3-4 months old. We found no differences between these veins as regards: (a) maximum force response; (b) active and passive force--length relationship; (c) sensitivity to exogenous noradrenaline without and with inhibition of neuronal uptake by cocaine, and (d) cross-sectional area of the longitudinal smooth muscle layer. There was, however, evidence for difference at the cellular level, for the active force per unit cell area was 17% lower in the SHR vessels compared with that in the WKY vessels. With this exception, the results indicate that the morphological and functional differences which have been reported by others for arterial vessels from SHRs and WKYs do not prevail in the portal vein taken from rats at 3-4 months of age.

A novel low-power static I/sup 2/L RAM cell using aluminum Schottky clamps

A novel bipolar RAM cell is introduced, which combines low standby power with high-speed read and write capability. In the standby mode, the operation is entirely static at a power level of less than 1 /spl mu/W/cell. Read and write selection are performed by an increase of cell current, while discrimination is based on the fact that a cell is selected during only a certain period of time. Investigations on exploratory chips containing 4/spl times/1 arrays have demonstrated the feasibility of large arrays, and have shown a minimum read delay of 12 ns, when a sense voltage of 200 mV difference between the bit lines is used. Improvements in cell layout have led to a unit cell area of 2750 /spl mu/m/SUP 2/ using 5 /spl mu/m design rules, which would enable the realization of a 4 kbit RAM on a 15 mm/SUP 2/ chip. Read access and cycle time for this RAM are predicted to be 65 ns and 160 ns, respectively, at a peak power dissipation of 50 mW.

Optical selected-area diffraction patterns of high-resolution electron-microscope images for crystal analysis

Optical selected-area diffraction patterns made from high-resolution electron micrographs of crystals have been used as a source of diffraction information from areas as small as a single unit cell of the crystal. The intensities of the electron diffraction pattern of the specimen crystal and the optical diffraction patterns of high-resolution electron-microscope images have been discussed by electron optical image formation theory taking account of spherical aberration and defocusing of the objective electron lens and it is concluded that the optical diffraction pattern may be identical with the electron diffraction pattern if the electron micrograph is photographed under optimum conditions. Optical diffraction patterns from areas of 80, 30 and 10 Å in diameter of labradorite feldspar have been taken and the orientation of two adjoining grains, 30 Å in diameter, has been determined. The diffraction pattern from a unit-cell area has also been taken and compared with the calculated intensity.

Mechanical properties of smooth muscle cells in the walls of arterial resistance vessels.

1. Methods have been developed for measuring the dynamic mechanical response of arterial resistance vessels (i.d. 83--235 micrometer) with a time resolution of about 4 msec. 2. Observations of the microscope image of the smooth muscle cells in the walls of these vessels indicate that there is little intercellular compliance in this preparation, and that the mechanical properties of the activated preparation are a reflexion of the mechanical properties of the individual smooth muscle cells. 3. Under isometric conditions the force developed per unit cell area was about 350 mN/mm2. Under isotonic conditions the cells had a maximum velocity for shortening at 37 degrees C of about 0.17 lengths/sec. 4. Quick releases of activated vessels indicate that the instantaneous elastic characteristic of smooth muscle cells is approximately exponential. 5. The wall tension response to small (0.3%) square wave changes in circumference was proportional to the logarithm of the time following the start of each circumference change. 6. Active wall tension, deltaT, was varied by varying the Ca2+ concentration of the activating solution. Under these conditions the active dynamic stiffness, k, was proportional to deltaT, and was not temperature dependent. The active half response time, tau (the time, taken to recover half the tension change caused by a small change in circumference) was also proportional to deltaT, but here the constant of proportionality had a Q10 of about 1.8. 7. It is concluded that the quick release response and the square wave response are in part a function of the mechanical properties of the crossbridges between the contractile filaments. Calculations show that both these responses can be explained if it is assumed that there is a relatively compliant passive component in series with the crossbridges.

Studies of vibrational surface modes in ionic crystals: III. Vibrational contributions to the surface thermodynamic functions for the (001) face of LiF, MgO, NaF, NaCl, Nal, RbF, and RbCl

The temperature dependence of the vibrational contributions to surface specific heat, surface entropy, surface energy, and surface Helmholtz free energy have been calculated for the (001) face of seven crystals having the rocksalt structure. The calculations assume a perfect, unrelaxed surface and make use of shell models fitted to bulk phonon spectra determined from inelastic neutron scattering. In terms of the bulk zero-temperature Debye temperature θ 0, the surface specific heat C v s exhibits an effective power law behavior, T α, from at least T = 0.02 θ 0 up to 0.05 θ 0 in most cases (and up to 0.07 θ 0 for NaF), with α ≈ 2.5 in most cases — in contrast with the result of α = 2 in a Debye-like model. (Below 0.02 θ 0, results derived for our 15-layer films depart significantly from intrinsic surface effects because of the finite thickness.) C v s attains a maximum at a temperature T( C max s) ranging from 0.14 θ 0 to 0.20 θ 0, in contrast with the result T( C max s) = 0.21 θ 0 for the Debye-like model. The peak value C max s ranges from 0.34 k B A SUC to 0.41 k B A SUC, where A SUC is the area of the surface unit cell. The shap the peak in C v s differs characteristically between that class of crystals in which there is some overlap of the acoustical and optical bulk bands and that class in which there is an appreciable absolute gap between the acoustical and optical bulk bands; in the latter class the peak is flattened on the low side of the maximum, with the maximum pushed to somewhat higher temperature. On those points of comparison with the rather sparse existing data for surface-excess heat capacity in which the value of specific surface area is not required (e.g., the value of T( C s max)), the agreement ranges from encouraging to equivocal. On those comparisons which require the surface area of the experimental samples (e.g., the magnitude of C s max) the agreement ranges from only fair to bad. Further experimental work is needed, and great care in surface area determinations is necessary.

Trypanosoma cruzi: Interaction with vertebrate cells in vitro: II. Quantitative analysis of the penetration phase

A technique is described for quantifying the in vitro penetration of vertebrate cells by trypomastigotes of Trypanosoma cruzi. It was found that the parasites are distributed among host cells in a manner described by the negative binomial distribution. The rate at which trypomastigotes penetrate bovine embryonic skeletal muscle cells (BESM) decreased exponentially in time in this system. The rate of the exponential decrease was dependent upon the concentration of parasites, being faster for more concentrated suspensions of trypomastigotes. A significantly lower penetration rate of canine kidney and HeLa cells was found when compared to bovine embryonic skeletal muscle cells. Within a single population of BESM cells, the smaller cells were penetrated more rapidly than the larger ones per unit cell area.

Biological membrane structure. III. The lattice structure of membranous cytochrome oxidase

Membranous cytochrome oxidase forms a regular two-dimensional array, as visualized by negative staining and electron microscopy. The lattice formed by the spots in the micrographs, which are assumed to be the cytochrome oxidase protein complexes, belongs to the two-dimensional rectangular space group pg; the unit cell dimensions are 88 ± 4 × 127 ± 7 A ̊ , with two protein complexes per unit cell. By using the unit cell area in conjunction with the chemical composition of the membrane and the molecular weights and volumes of the constituents, it was possible to construct a geometrical model for the membrane which quantitatively accounts for the measurements in hand. The lipids are present as lamellar bilayer, and the protein complexes pass all the way through the bilayer.