Focusing properties of a photonic crystal slab with multiple mechanisms in addition to negative refraction

A brief review of imaging by a photonic crystal (PC) slab with negative refraction is given. The focusing properties of the PC with multiple mechanisms in addition to negative refraction are studied by the finite-difference time-domain method. In addition to the effect of negative refraction, there are multiple mechanisms that are all attributed to the PC focusing properties, including Bragg diffraction, excitation of the surface mode, and self-collimation. The resulting field pattern is the total result of these factors. Bragg diffraction occurs in the high-frequency domain and mainly influences the quality of focusing in the optical axis direction. The excitation of the surface mode improves the resolution of focusing. Self-collimation makes the focusing position deviate from Snell's law.     

Generation of self-reproducing fractal patterns using a multiple imaging system with feedback

Abstract

We present a simple optical system for producing self-similar fractal patterns. The key component comprises three adjacent lenses, which form multiple images of a pattern displayed on a monitor. The images are recorded by a camera and displayed as the new pattern on the monitor. Iteration of this process results in an approximation to a self-similar fractal pattern which is independent of the starting image.     

Impact of negative feedback in metabolic noise propagation

Synthetic biology combines different branches of biology and engineering aimed at designing synthetic biological circuits able to replicate emergent properties useful for the biotechnology industry, human health and environment. The role of negative feedback in noise propagation for a basic enzymatic reaction scheme is investigated. Two feedback control schemes on enzyme expression are considered: one from the final product of the pathway activity, the other from the enzyme accumulation. Both schemes are designed to provide the same steady‐state average values of the involved players, in order to evaluate the feedback performances according to the same working mode. Computations are carried out numerically and analytically, the latter allowing to infer information on which model parameter setting leads to a more efficient noise attenuation, according to the chosen scheme. In addition to highlighting the role of the feedback in providing a substantial noise reduction, our investigation concludes that the effect of feedback is enhanced by increasing the promoter sensitivity for both schemes. A further interesting biological insight is that an increase in the promoter sensitivity provides more benefits to the feedback from the product with respect to the feedback from the enzyme, in terms of enlarging the parameter design space.Inspec keywords: biotechnology, enzymes, biological techniquesOther keywords: negative feedback impact, metabolic noise propagation, mathematical modelling, synthetic biological circuit, biotechnology industry, human health, environment, enzymatic reaction scheme, feedback control scheme, enzyme expression, enzyme accumulation, negative autoregulation, steady‐state average value, feedback performance, stochastic simulation algorithm, stochastic hybrid system modelling, noise attenuation, substantial noise reduction, feedback effect, parameter design space     

Amplifier based on a field-effect triode with negative current feedback

Conclusions A field-effect triode amplifier with series negative current feedback allows a voltage gain of the order of 200–300 to be obtained for a load resistance R_s1 M. The coefficient K_u begins to decrease noticeably only for a feedback resistance above 500 .The current gain reaches (8–10)·10³. Increasing the resistances R_s and R_L to hundreds of ohms has practically no effect on K_i. For a further increase of R_s and R_L the coefficient K_i decreases.The power gain reaches its maximum value (of the order of 10⁴ or more) for R_s100 and R_L=10–100 k. An increase in R_s leads to a reduction of K_pmax and to a shift of the extremum of the function K_p=f(R_L) into the range of higher values of R_L.A large input resistance of the amplifier (tens of megohms and higher) is obtained when R_s increases to 10–100 M. The maximum input resistance is obtained for R_L and R_s and may exceed values of from hundreds of megohms to several gigaohms. The minimum input resistance is hundreds of kilohms for R_L and R_s0.The minimum input resistance (5–10 k or less) is ensured for R_g and R_L0. An increase of the output resistance to hundreds of megohms or higher occurs for R_g and R_s.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 67–70, September, 1971.     

Sound shielding by a piezoelectric membrane and a negative capacitor with feedback control

The design and realization of an adaptive sound-shielding system based on a method to control the effective elastic stiffness of piezoelectric materials are presented in this paper. In this system, the sound-shielding effect is achieved by a sound reflection from the piezoelectric curved membrane fixed in rigid frame and connected to an active analog circuit that behaves as a negative capacitor. The acoustic transmission loss through the curved membrane was measured for the incident sound of frequency 1.6 kHz and of acoustic pressure level 80 dB. When the negative capacitor in the system was properly adjusted, the acoustic pressure level of the transmitted sound was reduced from the initial 60 dB to 15 dB by the action of the negative capacitor. Then the system was exposed to naturally changing operational conditions, and their effect on sound-shielding efficiency was studied. It is shown that the acoustic transmission loss of the system dropped by 35 dB within 30 min from the moment of negative capacitor adjustment. Therefore, a self-adjustment of the system has been implemented by appending an additional digital control circuit to the negative capacitor. It is shown that the aforementioned deteriorating effect has been eliminated by the adjusting action of the control circuit. The long-time sustainable value of 60 dB in the acoustic transmission loss of the adaptive sound shielding system has been achieved.     

Mathematical modelling of negative feedback regulation by carboxyltransferase

Acetyl-CoA carboxylase catalyses the first committed step in fatty acid synthesis in all organisms. The chemistry is accomplished in two half-reactions: activation of biotin via carboxylation by biotin carboxylase, followed by the carboxyltransferase-catalysed transfer of the carboxyl moiety from carboxybiotin to acetyl-CoA to generate malonyl-CoA. The Escherichia coli form of the carboxyltransferase subunit was recently found to regulate its own activity and expression by binding its own mRNA. By binding acetyl-CoA or the mRNA encoding its own subunits, carboxyltransferase is able to sense the metabolic state of the cell and attenuate its own translation and enzymatic activity using a negative feedback mechanism. Here, the network of these interactions is modelled mathematically with a set of non-linear differential equations. Numerical simulations of the model show that it qualitatively and quantitatively agrees with the experimental results for both inhibition of carboxyltransferase by mRNA and attenuation of translation. The modelling of the autoregulatory function of carboxyltransferase confirms that it is more than isolated interactions, but functions as a single dynamic system.     

Heating mechanisms in a near-field optical system

A finite-difference-time-domain and two finite-difference-thermal models are used to study various heating mechanisms in a near-field optical system. It is shown that the dominant mechanism of sample heating occurs from optical power that is transferred from the probe to a metallic thin-film sample. The optical power is absorbed in the sample and converted to heat. The effects of thermal radiation from the probe 's coating and thermal conduction between the probe and the sample are found to be negligible. In a two-dimensional waveguide with TE polarization, most of the optical power is transferred directly from the aperture to the sample. In a two-dimensional waveguide with TM polarization, there is significant optical power transfer between the probe 's aluminum coating and the sample. The power transfer results in a wider thermal distribution with TM polarization than with TE polarization. Using computed temperature distributions in a Co -Pt film, we predict the relative size of thermally written marks in a three-dimensional geometry. The predicted mark size shows a 30 % asymmetry that is due to polarization effects.     

Architecture‐dependent robustness in a class of multiple positive feedback loops

Many types of multiple positive feedbacks with each having potentials to generate bistability exist extensively in natural, raising the question of why a particular architecture is present in a cell. In this study, the authors investigate multiple positive feedback loops across three classes: one‐loop class, two‐loop class and three‐loop class, where each class is composed of double positive feedback loop (DPFL) or double negative feedback loop (DNFL) or both. Through large‐scale sampling and robustness analysis, the authors find that for a given class, the homogeneous DPFL circuit (i.e. the coupled circuit that is composed of only DPFLs) is more robust than all the other circuits in generating bistable behaviour. In addition, stochastic simulation shows that the low stable state is more robust than the high stable state in homogeneous DPFL whereas the high‐stable state is more robust than the low‐stable state in homogeneous DNFL circuits. It was argued that this investigation provides insight into the relationship between robustness and network architecture.Inspec keywords: cellular biophysics, feedback, sampling methods, stochastic processesOther keywords: network architecture, low stable state, stochastic simulation, bistable behaviour, homogeneous DPFL circuit, robustness analysis, large‐scale sampling, DNFL, double negative feedback loop, double positive feedback loop, three‐loop class, two‐loop class, one‐loop class, cell architecture, bistability, multiple positive feedback loops, architecture‐dependent robustness     

Oscillator frequency stability improvement by means of negative feedback

A novel, simple method is proposed to increase the frequency stability of an oscillator. An additional negative feedback is used in combination with the positive loop of the harmonic oscillator to decrease the phase sensitivity to fluctuations of parameters other than the resonator. The main advantage of the proposed correction approach is that it does not require expensive external elements such as mixers or resonators. The validity of the method is theoretically demonstrated on a Colpitts oscillator using the control system theory approach and numerical simulations, and is experimentally verified with phase noise measurements of an actual oscillator-mockup. It is shown that the medium-term frequency stability can be easily improved by a factor of ten.     

Chlorocatechol detection based on a clc operon/reporter gene system

A sensitive and selective sensing system for chlorocatechols (3-chlorocatechol and 4-chlorocatechol) was developed based on Pseudomonas putida bacteria harboring the plasmid pSMM50R-B'. In this plasmid, the regulatory protein of the clc operon, ClcR, controls the expression of the reporter enzyme beta-galactosidase. When bacteria containing components of the clc operon are grown in the presence of chlorocatechols, ClcR activates the clcA promoter, which is located upstream from the beta-galactosidase gene. Thus, the concentration of chlorocatechols can be related to the production of beta-galactosidase in the bacteria. The concentration of beta-galactosidase expressed in the bacteria was determined by measuring the chemiluminescence signal emitted with the use of a 1,2-dioxetane substrate. ClcR has a high specificity for chlorocatechols and provides the sensing system with high selectivity. This was demonstrated by evaluating several structurally related organic compounds as potential interfering agents. Both 3-chlorocatechol and 4-chlorocatechol can be detected with this sensing system at concentrations as low as 8 x 10(-10) and 2 x 10(-9) M, respectively, using a 2-h induction period. In the case of 3-chlorocatechol, a highly selective sensing system was developed that can detect this species at concentrations as low as 6 x 10(-8) M after a 5-min induction period; the presence of 4-chlorocatechol at concentrations as high as 2 x 10(-4) M did not interfere with this system.     

Some factors to consider in developing a quality-related feedback system

This paper reports on work which has been carried out in an attempt to identify some of the key factors in the development of a quality-related feedback system associated specifically with major installations. The main reasons why the majority of manufacturers have not developed systems to obtain data from users is due to the difficulties encountered in obtaining meaningful information. The current main sources of feedback are from technical sales representatives, customer complaints and internal feedback obtained from monitoring recurrent orders for spares. The information being generated by users of computerized maintenance systems has, to date, been little used by manufacturers to initiate quality-improving changes. However, most manufacturers said they would use such data if it was offered. It is also pointed out that designers can play a key role in improving the quality of plant and equipment by requesting feedback information in those areas where there might be design uncertainty and by giving consideration to the possibility of condition monitoring when a product is being designed.     

Automatic test equipment as a feedback link in a management control system

The Western European market for automatic test equipment (ATE) purchases is currently estimated to be of the order of $200 000 000 American dollars per annum. The case for installation of ATE stations in the production line and in maintenance workshops is usually primarily based on the requirement for a high rate of test capability (to match the product volume flow) or to Bpeed up the test because the time for manual test methods is too high relative to the product MTBF, or because of a shortage of test personnel of the requisite skill level. There are other benefits, and certain disadvantages, as listed in this paper.

It is the contention of the present authors that the enormous flow of test data offers an unusual opportunity to management which, if properly exploited, will lead to more efficient industrial production. The paper shows via a particular industrial application, that selective data processing can be used:

(a) to assess information content of the current test schedules, so that redundant measurements may be identified and eliminated;

(b) to reduce the number of test variables needing to be monitored;

(c) to forecast the onset of unacceptable quality levels thereby permitting corrective action to be taken;

(d) to highlight changes in quality levels, and by indicating the likely time of onset, to assist in detecting those events causing the change.

Thus the paper regards the provision of ATE as an opportunity to provide an extra highly effective feedback link within the management oontrol system.     

Regulation of oscillation dynamics in biochemical systems with dual negative feedback loops

Feedback controls are central to cellular regulation. Negative-feedback mechanisms are well known to underline oscillatory dynamics. However, the presence of multiple negative-feedback mechanisms is common in oscillatory cellular systems, raising intriguing questions of how they cooperate to regulate oscillations. In this work, we studied the dynamical properties of a set of general biochemical motifs with dual, nested negative-feedback structures. We showed analytically and then confirmed numerically that, in these motifs, each negative-feedback loop exhibits distinctly different oscillation-controlling functions. The longer, outer feedback loop was found to promote oscillations, whereas the short, inner loop suppresses and can even eliminate oscillations. We found that the position of the inner loop within the coupled motifs affects its repression strength towards oscillatory dynamics. Bifurcation analysis indicated that emergence of oscillations may be a strict parametric requirement and thus evolutionarily tricky. Investigation of the quantitative features of oscillations (i.e. frequency, amplitude and mean value) revealed that coupling negative feedback provides robust tuning of the oscillation dynamics. Finally, we demonstrated that the mitogen-activated protein kinase (MAPK) cascades also display properties seen in the general nested feedback motifs. The findings and implications in this study provide novel understanding of biochemical negative-feedback regulation in a mixed wiring context.     

Enhanced negative refractive index control in a 5-level system

In this paper we demonstrate that for a five-level atomic system in a dense gas interacting with two low-intensity fields by adjusting the ratio of the two magnetic amplitudes associated with the fields the effects of atomic coherence can be simply controlled. Furthermore, a negative index of refraction can be achieved over a wide wavelength range with minimal absorption.     

Takens-Bogdanov bifurcation in a two-component nonlinear optical system with diffractive feedback

Abstract

We analyse the conditions for stationary and oscillatory instabilities in a system consisting of two nonlinear Kerr-type elements. For the nonlinearities of the opposite sign, there is a degenerate point in the parameter space where both instabilities have equal thresholds and the same spatial frequency. In a vicinity of this point the dynamics are extremely sensitive to variation in control parameters, demonstrating a complex superposition of steady and time-periodic solutions. We relate this behaviour to the theory of the Taken-Bogdanov bifurcation.     

Statistical monitoring performance for startup operations in a feedback control system

Previously, it has been held that statistical process control (SPC) and engineering process control (EPC) were two distinct domains for process improvement. However, we specifically consider the impact for integrating the two approaches on a first‐order dynamic system with ARIMA disturbances. We show how to model and analyze this system over a range of practical conditions. Our work results in a set of response surfaces that characterize the performance of the integrated design. We also compare these results to the case where the SPC and EPC policies are applied separately. In general, we find that the EPC approach performs best in terms of minimizing error, but that we can reduce the number and magnitude of adjustments using the integrated monitoring and control approach. This work also further supports our earlier findings that the integrated design is effective on complex dynamic systems during the initial transient or startup period. Copyright © 2001 John Wiley & Sons, Ltd.     

Theoretical study on polarization dynamics of VCSELs with negative optoelectronic feedback

We investigate theoretically the polarization dynamics of vertical-cavity surface-emitting lasers (VCSELs) subjected to negative optoelectronic feedback. As we vary the feedback delay and strength, the VCSEL exhibits interesting nonlinear dynamics in the two-linear polarized directions. The output instability and negative current modulation induced by delayed feedback can also cause polarization switching (PS) to happen. In addition, we investigate the case when the free-running VCSEL emits in the modulated-elliptical state and find that the laser experiences in succession the elliptical polarization, the x-mode polarization, and the mixed-mode polarization states with an increasing feedback strength.     

Deformation mechanisms in negative Poisson's ratio materials: structural aspects

Poisson's ratio in materials is governed by the following aspects of the microstructure: the presence of rotational degrees of freedom, non-affine deformation kinematics, or anisotropic structure. Several structural models are examined. The non-affine kinematics are seen to be essential for the production of negative Poisson's ratios for isotropic materials containing central force linkages of positive stiffness. Non-central forces combined with pre-load can also give rise to a negative Poisson's ratio in isotropic materials. A chiral microstructure with noncentral force interaction or non-affine deformation can also exhibit a negative Poisson's ratio. Toughness and damage resistance in these materials may be affected by the Poisson's ratio itself, as well as by generalized continuum aspects associated with the microstructure.