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61.
We present a model for a synthetic gene oscillator and consider the coupling of the oscillator to a periodic process that is intrinsic to the cell. We investigate the synchronization properties of the coupled system, and show how the oscillator can be constructed to yield a significant amplification of cellular oscillations. We reduce the driven oscillator equations to a normal form, and analytically determine the amplification as a function of the strength of the cellular oscillations. The ability to couple naturally occurring genetic oscillations to a synthetically designed network could lead to possible strategies for entraining and/or amplifying oscillations in cellular protein levels. 相似文献
62.
A low-power, large-scale parallel video compression architecture for a single-chip digital CMOS camera is discussed in this paper. This architecture is designed for highly computationally intensive image and video processing tasks necessary to support video compression. Two designs of this architecture, an MPEG2 encoder and a DV encoder, are presented. At an image resolution of 640 × 480 pixels (MPEG2) and 720 × 576 (DV) and a frame rate of 25 to 30 frames per second, a computational throughput of up to 1.8 billion operations per second (BOPS) is required. This is supported in the proposed architecture using a 40 MHz clock and an array of 40 to 45 parallel processors implemented in a 0.2 m CMOS technology and with a 1.5 V supply voltage. Power consumption is significantly reduced through the single-chip integration of the CMOS photo sensors, the embedded DRAM technology, and the proposed pipelined parallel processors. The parallel processors consume approximately 45 mW of power resulting a power efficiency of 40 BOPS/W. 相似文献
63.
64.
In hamiltonian lattice gauge theory, the fermion vacuum at lowest order in 1/g2 can be determined from degenerate perturbation theory plus mean field-spin wave techniques. Using compact QED as an example, we show that: (i) chiral symmetry is spontaneously broken; and (ii) . The pseudoscalar pseudoGoldstone particles—the “pions” of this abelian theory—correspond to antiferromagnetic spin wave excitations of the fermion vacuum. 相似文献
65.
[reaction: see text] A practical and environmentally friendly organocatalytic strategy designed to mimic the DHAP aldolases has been developed and shown to be effective in the preparation of carbohydrates and aminosugars. (S)-Proline and (S)-2-pyrrolidine-tetrazole catalyzed the aldol reaction between dihydroxy acetone variants such as 1,3-dioxan-5-one and 2,2-dimethyl-1,3-dioxan-5-one with aldehydes to give the corresponding polyols in good yields with very high ees. 相似文献
66.
Boundary conditions and perturbation theory are combined to create a set of equations which, when solved, yield the reflected and transmitted wave forms in the case of a thin layer of material that is perfectly bonded between two isotropic half-spaces. The set of perturbed boundary conditions is created by first using the fully bonded boundary conditions at each of the two interfaces between the thin layer and the half-spaces. Then, by restricting the layer's thickness to be much smaller than an acoustic wavelength, perturbation theory can be used on these two sets of boundary equations, producing a set of equations which effectively treat the thin layer as a single interface via a perturbation term. With this set of equations, the full range of incident and polar angles can be considered, with results general enough to use with a layer that is anisotropic, nonlinear, or both anisotropic and nonlinear. Finally the validity of these equations is discussed, comparing the computer simulation results of this theory to results from standard methods, and looking at cases where the results (or various properties of the results) are known or can be predicted. 相似文献
67.
[reaction: see text] Titration of porphyrin-fullerene rotaxanes with DABCO or 4,4'-bipyridine led to photo- and redoxactive catenanic architectures, which upon photoexcitation undergo a sequence of short-range energy and electron transfer events to give a long-lived charge-separated radical-pair state. 相似文献
68.
Optimally Cutting a Surface into a Disk 总被引:1,自引:0,他引:1
Jeff?EricksonEmail author Sariel?Har-PeledEmail author 《Discrete and Computational Geometry》2004,31(1):37-59
We consider the problem of cutting a subset of the edges of a polyhedral manifold
surface, possibly with boundary, to obtain a single topological disk, minimizing
either the total number of cut edges or their total length. We show that this
problem is NP-hard in general, even for manifolds without boundary and for punctured
spheres. We also describe an algorithm with running time n
O(g+k), where n is
the combinatorial complexity, g is the genus, and k is the number of boundary
components of the input surface. Finally, we describe a greedy algorithm that
outputs a O(log2
g)-approximation of the minimum cut graph in O(g
2
n log n)
time. 相似文献
69.
70.