Stomata are epidermal structures that modulate gas exchange between a plant and its environment. During development, stomata are specified and positioned nonrandomly by the integration of asymmetric cell divisions and intercellular signaling. The Arabidopsis mitogen-activated protein kinase kinase kinase gene, YODA , acts as part of a molecular switch controlling cell identities in the epidermis. Null mutations in YODA lead to excess stomata, whereas constitutive activation of YODA eliminated stomata. Transcriptome analysis of seedlings with altered YODA activity was used to identify potential stomatal regulatory genes. A putative transcription factor from this set was shown to regulate the developmental behavior of stomatal precursors.
In this paper, we show that Hamilton's equations can be recast into the equations of dissipative memristor circuits. In these memristor circuits, the Hamiltonians can be obtained from the principles of conservation of "charge" and "flux", or the principles of conservation of "energy". Furthermore, the dynamics of memristor circuits can be recast into the dynamics of "ideal memristor" circuits. We also show that nonlinear capacitors are transformed into nonideal memristors if an exponential coordinate transformation is applied. Furthermore, we show that the zero-crossing phenomenon does not occur in some memristor circuits because the trajectories do not intersect the i = 0 axis. We next show that nonlinear circuits can be realized with fewer elements if we use memristors. For example, Van der Pol oscillator can be realized by only two elements: an inductor and a memristor. Chua's circuit can be realized by only three elements: an inductor, a capacitor, and a voltage-controlled memristor. Finally, we show an example of two-cell memristor CNNs. In this system, the neuron's activity depends partly on the supplied currents of the memristors.
Abstract The decomposition of deformation into elastic and plastic parts is introduced in terms of transformations of the material symmetry group, due to plastic evolution, pertaining to a local undistorted state of the material. This leads naturally to the notion of dislocation density, interpreted as the torsion of the underlying material manifold. Torsion, in turn, implies that the elastic strain is incompatible, and hence that the material is residually stressed when unloaded.
Metal−organic frameworks (MOFs) have been the focus of much interest within the context of hydrogen storage and other materials applications. With static metal clusters linked by axially substituted organic spacers capable of experiencing internal rotations, MOFs are one of the most promising amphidynamic materials to investigate and exploit the dynamics of crystalline solids. In this communication we report an experimental study of the rotational dynamics of the 1,4-phenylenedicarboxylate bridge of MOF-5, which has no steric contacts that might contribute to the rotational barrier. Highly reproducible 1H T1 relaxation, high-resolution 13C CPMAS, and variable temperature quadrupolar echo 2H NMR data were obtained from high quality samples that were sealed at reduced pressure (ca. 3 mTorr). 2H NMR line shape simulation revealed an activation barrier for rotation of 11.3 ± 2.0 kcal/mol, which is lower than the 14−16 kcal/mol values reported in theoretical studies of truncated models. While our results suggest that the models used for MOF-5 are insufficient to account for the properties of the extended crystal lattice, they also suggest that the amphidynamic materials with static and dynamic components may reach the friction-free rotational motion characteristic of gas dynamics.
The ability to select an arbitrary wavelength out of a large set of wavelengths is important for future dense wavelength division multiple access (DWDM) systems. Current approaches use a spectrometer to demultiplex the wavelengths and use a switch at each wavelength to select or deselect that particular wavelength at the output. In a DWDM system with N wavelengths, N number of switches at each receiver need to be employed in order to select an arbitrary wavelength using the conventional approach. Since switches are active components, this is undesirable when N is large. A better scaling can be achieved if we can arrange a series of configurable filters in a way that half of the spectral energy is filtered out when the input spectrum is passed through each successive stage of the filter. So the first stage filters out half of the spectrum. The second stage filters out another half of the spectrum that is left from the output of the first stage, etc. Optical filters are usually interferometric devices which generate periodic complementary outputs at the same time, such as a Mach-Zehnder interferometer (MZI). The filters used at different stages could be MZIs for which the periodicity is controlled by varying the optical path differences between the two arms of the MZI. To generate more square like transmission functions, a periodic cavity structure in a form similar to a one-dimensional photonic crystal may be used.
Efforts to improve Fe-Cr-C steel by modification of heat treatment and alloying additions are described. An important result of this work is in the evaluation of toughness with austenitizing temperature. The resistance to fracture of the conventionally (870/sup 0/C) austenitized structure is greatest ahead of a rounded notch (i.e., in Charpy and K/sub A/ tests), whereas it is least ahead of a sharp crack (i.e., in K/sub Ic/ test). Therefore, the advantages of increased fracture touchness, K/sub Ic/, with increased austenitizing temperature, must be weighed against the deterioration of ductility and Charpy impact energy. However, an optimum austenitizing temperature can be chosen (in the range 1000 to 1100/sup 0/C), where a 30 to 50 percent increase occurs in fracture toughness, K/sub Ic/, with no loss of strength and little reduction in impact energy and ductility. Moreover, low alloy additions of Mn and Ni can further increase the toughness of the alloy without reduction in strength. This was possible because the strengthening in these quaternary alloys was achieved primarily through solid solution hardening and not from substructural twinning in martensite. The toughness properties obtained for Fe-4Cr-2Mn-0.26C steel are superior to conventional 4340 and 300-M steels at the 200 ksi yield strengthmore » level, and yet would be cheaper to produce in large quantities.« less
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract : The use of photogenerated base in polymer modification processes has been investigated with the study of the amine catalyzed intramolecular imidization of reactive functional groups attached to a polystyrene matrix. The monomers are prepared by reaction of 4-hydroxystyrene with suitable anhydrides such as phthalic anhydride or the corresponding diacid chlorides, followed by amidation with hexamethyldisilazane. Following their free-radical polymerization, the functionalized polystyrenes have been tested in imaging experiments involving in situ photogeneration of amine from a photoactive carbamate precursor followed by low temperature imidization. The amine catalyzed imidization occurs as a much lower temperature than the uncatalyzed process thereby allowing photopatterning. Because the imidization process results in the formation of aqueous base soluble by-products, image development may be accomplished used standard water-based developers. While the new materials themselves can be used as resists, the concepts demonstrated in this study can be used to design novel photopatternable imaging and packaging materials for microelectronics. (jg)
Ethylene influences a number of developmental processes and responses to stress in higher plants. The molecular basis for the action of ethylene was investigated in mutants of Arabidopsis thaliana that have altered responses to ethylene. One mutant line, which has a dominant mutation at a locus designated etr , lacks a number of responses to ethylene that are present in the wild-type plant. These include inhibition of cell elongation, promotion of seed germination, enhancement of peroxidase activity, acceleration of leaf senescence, and feedback suppression of ethylene synthesis by ethylene. These diverse responses, which occur in different tissues of Arabidopsis , appear to share some common element in their transduction pathways—for example, a single receptor for ethylene. Results of ethylene binding experiments in vivo indicate that this receptor may be affected by the etr mutation.
