Signal Response Curves Research Articles

Fat suppression using frequency-sweep RF saturation and iterative reconstruction.

To introduce an alternative idea for fat suppression that is suited both for low-field applications where conventional fat-suppression approaches become ineffective due to narrow spectral separation and for applications with strong B0 homogeneities. Separation of fat and water is achieved by sweeping the frequency of RF saturation pulses during continuous radial acquisition and calculating frequency-resolved images using regularized iterative reconstruction. Voxel-wise signal-response curves are extracted that reflect tissue's response to RF saturation at different frequencies and allow the classification into fat or water. This information is then utilized to generate water-only composite images. The principle is demonstrated in free-breathing abdominal and neck examinations using stack-of-stars 3D balanced SSFP (bSSFP) and gradient-recalled echo (GRE) sequences at 0.55 and 3T. Moreover, a potential extension toward quantitative fat/water separation is described. Experiments with a proton density fat fraction (PDFF) phantom validated the reliability of fat/water separation using signal-response curves. As demonstrated for abdominal imaging at 0.55T, the approach resulted in more uniform fat suppression without loss of water signal and in improved CSF-to-fat signal ratio. Moreover, the approach provided consistent fat suppression in 3T neck exams where conventional spectrally-selective fat saturation failed due to strong local B0 inhomogeneities. The feasibility of simultaneous fat/water quantification has been demonstrated in a PDFF phantom. The proposed principle achieves reliable fat suppression in low-field applications and adapts to high-field applications with strong B0 inhomogeneity. Moreover, the principle potentially provides a basis for developing an alternative approach for PDFF quantification.

Sensing the ocean electric fields via a self-supported CNT sponge

A self-supported CNT sponge is composed of uniformly twisted CNTs with high aspect ratio that enables the large specific surface area and good carrier conduction to go beyond the conventional carbon-based materials, shedding light on its high electrochemical activity in salt water. Herein, we demonstrate the comparable performance of the CNT sponge as the electrode pair to the most commonly used Ag/AgCl for sensing underwater electric fields. The CNT sponge electrodes exhibit a high electrochemical reactivity in salt water with a low noise of ∼10 nV/rt(Hz)@100 Hz within a wide range of the electric field frequency (e.g., 10–105 Hz), while the frequency response approaches a constant magnitude across the same range of frequency. The performance of the CNT sponge electrodes in ocean electric field sensing is further verified by measuring the electrical signal response curve at various characteristic frequencies within a small water container, and also under a simulated source within the water pool. The high chemical stability and low costs of carbon-based CNT sponges pave the way to their potential applications.

A New Performance Optimization Method for Linear Motor Feeding System

The linear motor feeding system is a typical electromechanical coupling system. Conventional characteristic analyses of electromechanical coupling often overlook the influence of flexible deformation in critical components of the linear motor feeding system. Moreover, when employing genetic algorithms to optimize servo system PID control parameters, slow convergence, nonconvergence, or premature convergence problems may arise. To address these issues, this paper proposes a new performance optimization method for a linear motor feeding system. The method uses a combination of “multi-body theory + finite element” to accurately account for the flexible deformation of critical components of the feeding system, establishes a rigid–flexible electromechanical coupling model of the linear motor feeding system, and optimizes the PID parameters of the established model with an improved adaptive genetic algorithm. Simulation results demonstrate that, when utilizing an adaptive genetic algorithm to optimize the rigid–flexible electromechanical coupling model and a control system model that disregards flexible body deformation, the system achieves stability in 0.02 s and 0.027 s with overshoots of 13% and 27%, respectively. These outcomes confirm the accuracy and importance of considering flexible body deformation in the optimization performance of a linear motor feeding system. At the same time, the time required to reach the steady state of the rigid–flexible electromechanical coupling model optimized by the adaptive genetic algorithm is shortened from 0.035 s to 0.02 s. The sinusoidal signal response curve of the optimized system does not exhibit any peak overshoot compared with that of the nonoptimized system, and the response speed is also faster. These results demonstrate the effectiveness of the rigid–flexible electromechanical coupling model optimized by the nonlinear adaptive genetic algorithm. The displacement response curves of the linear motor feeding system under different workbench loads are obtained through experiments and compared with those obtained from simulations to verify the established model and the correctness of the proposed method.

Potential Landscapes, Bifurcations, and Robustness of Tristable Networks.

Bistable switches that produce all-or-none responses have been found to regulate a number of natural cellular decision making processes, and subsequently synthetic switches were designed to exploit their potential. However, an increasing number of studies, particularly in the context of cellular differentiation, highlight the existence of a mixed state that can be explained by tristable switches. The criterion for designing robust tristable switches still remains to be understood from the perspective of network topology. To address such a question, we calculated the robustness of several 2- and 3-component network motifs, connected via only two positive feedback loops, in generating tristable signal response curves. By calculating the effective potential landscape and following its modifications with the bifurcation parameter, we constructed one-parameter bifurcation diagrams of these models in a high-throughput manner for a large combinations of parameters. We report here that introduction of a self-activatory positive feedback loop, directly or indirectly, into a mutual inhibition loop leads to generating the most robust tristable response. The high-throughput approach of our method further allowed us to determine the robustness of four types of tristable responses that originate from the relative locations of four bifurcation points. Using the method, we also analyzed the role of additional mutual inhibition loops in stabilizing the mixed state.

Misconduct at the Lab? A Performance Task Case Study for Teaching Data Analysis and Critical Thinking

A distractor-rich performance task case study was developed to teach undergraduate analytical chemistry students about standard addition while reinforcing their grasp of data analysis and quality control principles. The performance task presents students with an e-mail from a fictional district attorney that asks them to investigate allegations of data falsification in a crime lab and determine whether fabricated, falsified, or faulty analyses may have impacted one particular court case. It also asks students to suggest changes to the lab’s quality assurance practices. Correct analysis of the task scenario requires students to recognize that the accused analyst systematically overestimated analyte levels when they incorrectly assumed that their standard addition data fell within the linear region of their method’s signal-response curve. The task is also designed to help students to grow in their professional awareness as chemists, critical thinking, and communication skills. This is because students are e...

Phosphate sink containing two-component signaling systems as tunable threshold devices.

Synthetic biology aims to design de novo biological systems and reengineer existing ones. These efforts have mostly focused on transcriptional circuits, with reengineering of signaling circuits hampered by limited understanding of their systems dynamics and experimental challenges. Bacterial two-component signaling systems offer a rich diversity of sensory systems that are built around a core phosphotransfer reaction between histidine kinases and their output response regulator proteins, and thus are a good target for reengineering through synthetic biology. Here, we explore the signal-response relationship arising from a specific motif found in two-component signaling. In this motif, a single histidine kinase (HK) phosphotransfers reversibly to two separate output response regulator (RR) proteins. We show that, under the experimentally observed parameters from bacteria and yeast, this motif not only allows rapid signal termination, whereby one of the RRs acts as a phosphate sink towards the other RR (i.e. the output RR), but also implements a sigmoidal signal-response relationship. We identify two mathematical conditions on system parameters that are necessary for sigmoidal signal-response relationships and define key parameters that control threshold levels and sensitivity of the signal-response curve. We confirm these findings experimentally, by in vitro reconstitution of the one HK-two RR motif found in the Sinorhizobium meliloti chemotaxis pathway and measuring the resulting signal-response curve. We find that the level of sigmoidality in this system can be experimentally controlled by the presence of the sink RR, and also through an auxiliary protein that is shown to bind to the HK (yielding Hill coefficients of above 7). These findings show that the one HK-two RR motif allows bacteria and yeast to implement tunable switch-like signal processing and provides an ideal basis for developing threshold devices for synthetic biology applications.

Research on Computer Information Processing Technology Based on Signal Autocorrelation Domain

The paper establishes signal correlation processing mathematical model according to Ordinary differential equations with boundary value, which is introduced into the analysis on basketball virtual simulation sliding technique, and it designs the signal autocorrelation computer processing system. In order to verify the reliability and practicality of the system in the basketball technology analysis, this paper extracts the temperature signal using the FLUENT software, it obtains the isotherm diagram and temperature distribution cloud picture, verifies the effectiveness of the system. Finally, it verifies the practicality system in basketball technology analysis, taking analysis of back gliding speed rhythm of basketball as an example, and it gets the basketball shuffle rhythm control 3D signal response curves, which provides technical reference for basketball players.

Coupling between feedback loops in autoregulatory networks affects bistability range, open-loop gain and switching times

Biochemical regulatory networks governing diverse cellular processes such as stress-response, differentiation and cell cycle often contain coupled feedback loops. We aim at understanding how features of feedback architecture, such as the number of loops, the sign of the loops and the type of their coupling, affect network dynamical performance. Specifically, we investigate how bistability range, maximum open-loop gain and switching times of a network with transcriptional positive feedback are affected by additive or multiplicative coupling with another positive- or negative-feedback loop. We show that a network's bistability range is positively correlated with its maximum open-loop gain and that both quantities depend on the sign of the feedback loops and the type of feedback coupling. Moreover, we find that the addition of positive feedback could decrease the bistability range if we control the basal level in the signal-response curves of the two systems. Furthermore, the addition of negative feedback has the capacity to increase the bistability range if its dissociation constant is much lower than that of the positive feedback. We also find that the addition of a positive feedback to a bistable network increases the robustness of its bistability range, whereas the addition of a negative feedback decreases it. Finally, we show that the switching time for a transition from a high to a low steady state increases with the effective fold change in gene regulation. In summary, we show that the effect of coupled feedback loops on the bistability range and switching times depends on the underlying mechanistic details.

Characterization of Signal Response of Lead Absorber Coupled Transition Edge Sensor Gamma-Ray Microcalorimeters

We are developing bulk lead absorber coupled transition edge sensor gamma-ray detectors that can be applied to positron annihilation spectroscopy at 511 keV. We observe a double exponential decay in the signal response curves of our detectors. Here, we characterize this signal response using three gamma-ray detectors with different thermal conductance values.

Soot and thin-filament pyrometry using a color digital camera

A simple and compact temperature and soot volume fraction diagnostic technique based on ratio pyrometry has been studied. Two different consumer digital single lens reflex cameras were evaluated for use as pyrometers. The incandescence from soot and a SiC filament was imaged at the three wavelengths of each camera’s color filter array (CFA). After characterization of the detector’s signal response curves, temperatures were calculated by two-color ratio pyrometry using a lookup table approach. A SiC filament with known emissivity was shown to provide an absolute light intensity calibration, which further allows the soot volume fraction to be determined. Measurements were carried out on four different flames with varying levels of soot loading. The filament-derived gas temperature and soot temperature measurements have been compared with computational results and overall good agreement has been shown. Soot volume fraction measurements have been compared with previous LII results, with excellent agreement for both cameras tested.

A synthetic genetic circuit whose signal-response curve is temperature-tunable from band-detection to sigmoidal behaviour

Programming new cellular functions by using synthetic gene circuits is a key goal in synthetic biology, and an important element of this process is the ability to couple to the information processing systems of the host cell using synthetic systems with various signal-response characteristics. Here, we present a synthetic gene system in Escherichia coli whose signal-response curve may be tuned from band detection (strongest response within a band of input concentrations) to a switch-like sigmoidal response, simply by altering the temperature. This change from a band-detection response to a sigmoidal response has not previously been implemented. The system allows investigation of a range of signal-response behaviours with minimal effort: a single system, once inserted into the cells, provides a range of response curves without any genetic alterations or replacement with other systems. By altering its output, the system may couple to other synthetic or natural genetic circuits, and thus serve as a useful modular component. A mathematical model has also been developed which captures the essential qualitative behaviours of the circuit.

Agglomeration of particles during coal combustion in multistage spouted fluidized tower

An experimental platform of spray agglomeration has been designed and built for removing small fly ash particles (PM10) from coal combustion. Systematic experiments were conducted in a multistage spouted tower using kinds of agglomerant solutions. The particle concentration increases greatly from the first stage to the second stage of the tower. With the increase of flue gas flow rate the oscillation of impulse signal response curves increases and the internal circulation of the tower intensifies. The influencing factors such as the surfactant, PH value, flow rate of the agglomerant solutions and inlet flue gas temperature were analyzed. SEM was used to analyze the microstructure of the particles. Final results indicate that the special shape of a multistage spouted fluidized tower has significant influences on the effect of agglomeration. The findings from this work will be helpful to form the basis, and provide guidance for, further studies on the control of fine particles such as PM2.5 or even smaller.

The Goldbeter-Koshland Switch in the First-Order Region and Its Response to Dynamic Disorder

In their classical work (Proc. Natl. Acad. Sci. USA, 1981, 78:6840–6844), Goldbeter and Koshland mathematically analyzed a reversible covalent modification system which is highly sensitive to the concentration of effectors. Its signal-response curve appears sigmoidal, constituting a biochemical switch. However, the switch behavior only emerges in the ‘zero-order region’, i.e. when the signal molecule concentration is much lower than that of the substrate it modifies. In this work we showed that the switching behavior can also occur under comparable concentrations of signals and substrates, provided that the signal molecules catalyze the modification reaction in cooperation. We also studied the effect of dynamic disorders on the proposed biochemical switch, in which the enzymatic reaction rates, instead of constant, appear as stochastic functions of time. We showed that the system is robust to dynamic disorder at bulk concentration. But if the dynamic disorder is quasi-static, large fluctuations of the switch response behavior may be observed at low concentrations. Such fluctuation is relevant to many biological functions. It can be reduced by either increasing the conformation interconversion rate of the protein, or correlating the enzymatic reaction rates in the network.

An entire feature extraction method of metal oxide gas sensors

A phase space entire (PSE) feature extraction method for metal oxide gas sensors was proposed in this paper. This method extracts six features from the response curve in phase space. The difference from other feature extraction methods such as extracting phase space integral (PSI), which also use phase space, is that the sensor response curves could be completely described and well reconstructed with the six features by a sensory response feedback process. The proposed method PSE was compared with the PSI extracting method and a common signal maximum (SM) extracting method in a dataset. The dataset was consisted of 264 measurements of 11 volatile organic compounds (VOCs) of four concentrations by six TGS gas sensors. The six features were first extracted from each response curve of all samples, and then all response curves were reconstructed by the six features. The mean sensory response feedback error of the reconstructed response curves from the original signal response curves was 5.4%, which indicated that PSE could extract the entire signal of response curves. Meanwhile, Fisher discriminant analysis (FDA) was used in the comparison of the three feature extraction methods. The correct recognition rates of FDA with SM, PSI and PSE were 90.9%, 81.1% and 100%, respectively. The results show that PSE is an efficient entire feature extraction method.

White‐marker imaging—Separating magnetic susceptibility effects from partial volume effects

By applying dephasing gradients, local magnetic field inhomogeneitiescan selectively visualized with positive contrast, such as those created by magnetically labeled cells. This is known as "white-marker imaging." In white-marker imaging, subvoxel signal variations are also visualized as a result of partial volume (PV) effects and may compromise the identification of magnetic structures (e.g., magnetically-labeled cells). This study presents the theory and proof-of-principle experiments of a strategy to eliminate PV effects during white-marker imaging. The strategy employs the asymmetry of the signal response curves for non-PV effects as a function of externally applied gradients. In the case of PV effects, subtraction of the symmetrical signal responses eliminates their contribution. In vitro experimental images were made using a spherical phantom with cylindrical elements. In vivo images of the brain were obtained at a location that included air cavities (susceptibility effects) and the circle of Willis (PV effect). The results show that PV effects were eliminated in the in vitro experiments and were virtually absent under in vivo conditions.

Control of Streptococcus pyogenes virulence: Modeling of the CovR/S signal transduction system

The CovR/S system in Streptococcus pyogenes (Group A Streptococcus, or GAS), a two-component signal transduction/transcription regulation system, controls the expression of major virulence factors. The presence of a negative feedback loop distinguishes the CovR/S system from the majority of bacterial two-component systems. We developed a deterministic model of the CovR/S system consisting of eight delay differential equations. Computational experiments showed that the system possessed a unique stable steady state. The dynamical behavior of the system showed a tendency for oscillations becoming more pronounced for longer but still biochemically realistic delays resulting from reductions in the rates of translation elongation. We have devised an efficient procedure for computing the system's steady state. Further, we have shown that the signal–response curves are hyperbolic for the default parameter values. However, in experiments with randomized parameters we demonstrated that sigmoidality of signal–response curves, implying a response threshold, is not only possible, but seems to be rather typical for CovR/S-like systems even when binding of the CovR response regulator protein to a promoter is non-cooperative. We used sensitivity analysis to simplify the model in order to make it analytically tractable. The existence and uniqueness of the steady state and hyperbolicity of signal–response curves for the majority of the variables was proved for the simplified model. Also, we found that provided CovS was active, the system was insensitive to changes in the concentration of any other phosphoryl donor such as acetyl phosphate.

Extending the working range of immunoanalysis by exploitation of two monoclonal antibodies.

A newly established rat monoclonal antibody (mAb) for isoproturon, namely, IOC 10G7, is described. This mAb shows a standard curve for isoproturon in phosphate-buffered saline with a test midpoint of 5.5 +/- 1.8 microg/L (n = 15). In combination with the formerly developed mAb IOC 7E1, IOC 10G7 can be exploited to extend the working range for the analysis of isoproturon. Both antibodies were formatted into a competitive enzyme-linked immunosorbent assay (ELISA), using the same enzyme-tracer. MAb IOC 7E1 and mAb IOC 10G7 have different affinities for the target compound, but the signal-response curves of the single antibodies overlap. Cross-reactivity (CR) patterns of both antibodies are comparable, showing the highest CR for the metabolite 1-(4-isopropylphenyl)-3-methylurea (IOC 10G7, 9%; IOC 7E1, 19%). The system described here includes the combined, but individual, usage of both assays on one microtiter plate, as well as the strategy for mixing the two antibodies for the utilization in one assay. When standards are performed in Milli-Q water, the working range for isoproturon with the individual ELISAs using mAb IOC 7E1 is from 0.01 to 1 microg/L (test midpoint = 0.11 +/- 0.03 microg/L; n = 17) and with IOC 10G7, it is 1-100 microg/L (test midpoint = 10.3 +/- 1.6 microg/L; n = 32). The working range with mixed antibodies is usually on the order of 0.03-30 microg/L (test midpoint = 0.5 +/- 0.2 microg/L; n = 17). These strategies (mAbs individually and mixed) cover a range of 4 and 3 orders of magnitude, respectively. As a demonstration, water samples of different origins and an extract of mixed sediment were analyzed. The advantages of these strategies are discussed.

The optical detection of individual DNA-conjugated gold nanoparticle labels after metalenhancement

The detection of DNA using nanoparticles as labels is an interesting alternative to thestandard fluorescence technique. It requires simpler detection equipment, resulting inhigher stability and lower costs. Besides easier detection, metal enhancement allows ahigher sensitivity of detection. The signal-response curve for labelled DNA before andafter silver enhancement was studied, applying both atomic force microscope(AFM) and optical (reflection/transmission) measurements. The dynamic rangeand the sensitivity were determined for nanoparticle labelling with and withoutmetal enhancement. Nanoparticle concentrations down to the fM range could bedetected. The ultimate limit of detection, the identification of individual labels, isdemonstrated for the optical readout. Therefore, AFM images of the particleswere correlated with the optical signal of individual or clustered particles. Wedemonstrate that the optical signal allows the identification of single particles.

Absorption and Rayleigh scattering and resonance Rayleigh scattering spectra of [HgX2]n nanoparticles

The composition and existing species of the reaction production of Hg 2+ and X - . (X= Cl, Br and I) under different conditions, and their absorption, Rayleigh scattering (RS) and resonance Rayleigh scattering (RRS) spectra have been studied. The results show that the products exist in the form of nanoparticles as [HgX 2 ] n aggregates under suitable conditions, and their average diameters increase with the increase of X- diameters. The diameters of [HgCl 2 ] n , [HgBr 2 ] n and [HgI 2 ] n are less than 4 nm, equal to 9 nm and 70 nm respectively. There are bathchromic shifts gradually with the increase of X- diameters in their absorption spectra. The absorption bands of [HgCl 2 ] n and [HgBr 2 ] n locate at ultraviolet region. However, the absorption band of [HgI 2 ] n is obvious in visible light region. Among three particles, only [HgI 2 ] n exhibits a strong RRS and its scattering peak is at 580 nm. The main reasons leading to the enhancement of resonance scattering are the large size of nanoparticle, the formation of the interface and the location of light scattering in the absorption band. There are three important factors affecting resonance scattering spectrum: the quanta colored effect and molecular absorption spectrum of [HgI 2 ] n nanoparticle as well as instrumental factors which mainly include the light source’s emission spectral characteristics and the signal response curve of detector.