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41.
A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both the flexibility of clock networks and the relationships between various desirable properties such as robust entrainment, temperature compensation, and stability to environmental variations and parameter fluctuations. We use this to argue that the complexity provides the flexibility necessary to simultaneously attain multiple key properties of circadian clocks. As part of our analysis we show how to quantify the key evolutionary aims using infinitesimal response curves, a tool that we believe will be of general utility in the analysis of regulatory networks. Our results suggest that regulatory and signalling networks might be much less flexible and of lower dimension than their apparent complexity would suggest. 相似文献
42.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
43.
Near-field corrections to site attenuation 总被引:1,自引:0,他引:1
The theoretical model used for calculating normalized site attenuation for broadband antennas in ANSI C63.4-1992 and for antenna calibration in ANSI C63.5-1988 includes only the radiation terms in the electric field. The omission of the near field terms leads to errors of as much as 2.0 dB at 30 MHz for horizontally polarized antennas separated by 3 m. Corrected values of normalized site attenuation and E Dmax are presented for the 30-300 MHz frequency range 相似文献
44.
Crosstalk between microstrip transmission lines 总被引:1,自引:0,他引:1
Hill D.A. Cavcey K.H. Johnk R.T. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):314-321
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk 相似文献
45.
Younan N.H. Cox B.I. Taylor C.D. Prather W.D. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):394-398
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz 相似文献
46.
Varani L. Reggiani L. Kuhn T. Gonzalez T. Pardo D. 《Electron Devices, IEEE Transactions on》1994,41(11):1916-1925
We present a microscopic interpretation of electronic noise in semiconductor materials and two-terminal devices. The theory is based on Monte Carlo simulations of the carrier motion self-consistently coupled with a Poisson solver. Current and voltage noise operations are applied and their respective representations discussed. As application we consider the cases of homogeneous materials, resistors, n+nn + structures, and Schottky-barrier diodes. Phenomena associated with coupling between fluctuations in carrier velocity and self-consistent electric field are quantitatively investigated for the first time. At increasing applied fields hot-carrier effects are found to be of relevant importance in all the cases considered here. As a general result, noise spectroscopy is found to be a source of valuable information to investigate and characterize transport properties of semiconductor materials and devices 相似文献
47.
48.
Carroll R.D. Merritt S.W. Branciforte E.J. Tanski W.J. Cullen D.E. Sacks R.N. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):416-418
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal 相似文献
49.
We report here a series of observations-most of which the reader can experience directly-showing that distinct components of patterned visual stimuli (orthogonal lines of a different hue) vary in perception as sets. Although less frequent and often less complete, these perceptual fluctuations in normal viewing are otherwise similar to the binocular rivalry experienced when incompatible scenes are presented dichoptically. 相似文献
50.
Montanari D. Van Houdt J. Groeseneken G. Maes H.E. 《Solid-State Circuits, IEEE Journal of》1998,33(7):1090-1095
This paper presents a high-speed, small-area circuit specifically designed to identify the levels in the read out operation of a flash multilevel memory. The circuit is based on the analog computation of the Euclidean distance between the current read out from a memory cell and the reference currents that represent the different logic levels. An experimental version of the circuit has been integrated in a standard double-metal 0.7-μm CMOS process with a die area of only 140×100 μm2. Operating under a 5-V power supply, this circuit identifies the read-out current of a memory cell, and associates it with the appropriate logic level in 9 ns 相似文献