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91.
Many types of bacteria swim by rotating a bundle of helical filaments also called flagella. Each filament is driven by a rotary
motor and a very flexible hook transmits the motor torque to the filament. We model it by discretizing Kirchhoff’s elastic-rod
theory and develop a coarse-grained approach for driving the helical filament by a motor torque. A rotating flagellum generates
a thrust force, which pushes the cell body forward and which increases with the motor torque. We fix the rotating flagellum
in space and show that it buckles under the thrust force at a critical motor torque. Buckling becomes visible as a supercritical
Hopf bifurcation in the thrust force. A second buckling transition occurs at an even higher motor torque. We attach the flagellum
to a spherical cell body and also observe the first buckling transition during locomotion. By changing the size of the cell
body, we vary the necessary thrust force and thereby obtain a characteristic relation between the critical thrust force and
motor torque. We present a elaborate analytical model for the buckling transition based on a helical rod which quantitatively
reproduces the critical force-torque relation. Real values for motor torque, cell body size, and the geometry of the helical
filament suggest that buckling should occur in single bacterial flagella. We also find that the orientation of pulling flagella
along the driving torque is not stable and comment on the biological relevance for marine bacteria. 相似文献
92.
93.
Gerber LC Moser N Luechinger NA Stark WJ Grass RN 《Chemical communications (Cambridge, England)》2012,48(32):3869-3871
Lanthanum oxide nanoparticles were utilized to scavenge phosphate from microbial growth media for the use of targeted nutrient starvation as an antimicrobial strategy. Only in phosphate poor environments a toxic effect was observed. The effect was shown on Escherichia coli, Staphylococcus carnosus, Penicillium roqueforti, and Chlorella vulgaris. 相似文献
94.
An experimental investigation has been carried out to study the effect of test environment on transition characteristics and
the flow unsteadiness associated with the transition modes of a dual-bell nozzle. Cold-gas tests using gaseous nitrogen were
carried out in (i) a horizontal test-rig with nozzle exhausting into atmospheric conditions and, (ii) a high altitude simulation
chamber with nozzle operation under self-evacuation mode. Transient tests indicate that increasing δP
0/δt (the rate of stagnation chamber pressure change) reduces the amplitude of pressure fluctuations of the separation shock at
the wall inflection point. This is preferable from the viewpoint of lowering the possible risk of any structural failure during
the transition mode. Sea-level tests show 15–17% decrease in the transition nozzle pressure ratio (NPR) during subsequent
tests in a single run primarily due to frost formation in the nozzle extension up to the wall inflection location. Frost reduces
the wall inflection angle and hence, the transition NPR. However, tests inside the altitude chamber show nearly constant NPR
value during subsequent runs primarily due to decrease in back temperature with decrease in back pressure that prevents any
frost formation. 相似文献
95.
Integration of Singularities in FE/BE Analyses of Soil-foundation Interaction with Non-homogeneous Elastic Soils 总被引:1,自引:0,他引:1
Rudolf F. Stark 《Meccanica》2001,36(4):329-350
This paper addresses the derivation of the boundary integral equations for a non-homogeneous elastic half-space subjected to constant surface tractions on an arbitrarily shaped area on the basis of the respective Green's functions. The type of non-homogeneity considered is a power law variation of Young's modulus with depth below the surface of the half-space. Two different methods, a contour integral and an integration-free approach are presented, applicable for arbitrarily and rectangular shaped boundary elements, respectively. In the first one the divergence theorem is used in order to reduce the integration of a two-dimensional surface element to an integration over the element's confining boundary only. In the second approach no integration at all is needed since the solution is found simply by evaluating functions to be determined at the boundaries of the loaded rectangle. 相似文献
96.
97.
Multireference configuration interaction (MRCI) and complete active space second-order perturbation theory (CASPT2) calculations are performed on Fe2 and Fe? 2. Although it is not possible to definitively identify the ground states of Fe2 and Fe? 2, the calculations suggest that the ground state of Fe? 2 in 8Σ? u derived from 3d134σ2 g4σ2 u and that the states observed in photodetachment are the 9Σ? g and 7Σ? g states with a 3d134σ2 g4σ1 u occupation, but that the ground state of Fe2 is 7Δu(3d144σ2 g) and is not observed in the photo-detachment spectra. 相似文献
98.
Charles E. Carraher JR. 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1293-1356
This review emphasizes the breadth of metallic and metallic-like polymers evaluated as to thermal properties. Techniques usefully applied to particular systems are noted with the aim of suggesting their application to other systems. 相似文献
99.
The fractionation technique described in this paper was used to characterize the melting-point, monomer, and blocking distributions for polymers and copolymers. It is different from the molecular-weight fractionation technique in that the fractions are obtained by using a single solvent to extract the solid polymer below its melting point at stepwise-increasing temperatures. The reproducibility of this technique is excellent, and the technique is sufficient to distinguish pellet-to-pellet variation in a commercially available polypropylene. It was used to show the influence of preparation variables on the melting-point distributions of polyethylene and polypropylene and on the monomer and blocking distribution of copolymers, and to distinguish copolymers from blends. 相似文献
100.