Problem Of Amplification Research Articles

Chiral Autoamplification Meets Dynamic Chirality Control to Suggest Nonautocatalytic Chemical Model of Prebiotic Chirality Amplification.

Oxidative kinetic resolution of 1-phenylethanol in the presence of manganese complexes, bearing conformationally nonrigid achiral bis-amine-bis-pyridine ligands, in the absence of any exogenous chiral additives, is reported. The only driving force for the chiral discrimination is the small initial enantiomeric imbalance of the scalemic (nonracemic) substrate: the latter dynamically controls the chirality of the catalyst, serving itself as the chiral auxiliary. In effect, the ee of 1-phenylethanol increases monotonously over the reaction course. This dynamic control of catalyst chirality by the substrate has been unprecedented; a consistent kinetic model for this process is presented. The reported catalyzed substrate self-enantioenrichment mechanism is discussed in relation to the problem of prebiotic chirality amplification.

Low-Light Image Enhancement Based on Maximal Diffusion Values

A vast amount of pictures are taken every day by using cameras mounted on various mobile devices. Even though the clarity of such acquired images has been significantly improved due to the advance of the image sensor technology, the visual quality is hardly guaranteed under varying illumination conditions. In this paper, a novel yet simple method for low-light image enhancement is proposed via the maximal diffusion value. The key idea of the proposed method is to estimate the illumination component, which is likely to appear as the bright pixel even under the low-light condition, by exploring multiple diffusion spaces. Specifically, the illumination component can be accurately separated from the scene reflectance by selecting the maximal value at each pixel position of those diffusion spaces, and thus independently adjusted for the visual quality enhancement. That is, we propose to adopt the maximal value among diffused intensities at each pixel position, so-called maximal diffusion value, as the illumination component since illumination components buried in the dark tend to be revealed with bright intensities through the iterative diffusion process. In contrast to previous approaches that still pose difficulties to balance between over-saturated and conservative restorations, the proposed method improves the image quality without any significant distortion while successfully suppressing the problem of noise amplification. Experimental results on benchmark datasets show the efficiency and robustness of the proposed method compared to previous approaches introduced in literature.

Microphone array beamforming based on maximization of the front-to-back ratio.

Microphone arrays are typically used in room acoustic environments to acquire high fidelity audio and speech signals while suppressing noise, interference, and reverberation. In many application scenarios, interference and reverberation may mainly come from a certain region, and it is therefore necessary to develop beamformers that can preserve signals of interest while minimizing the power of signals coming from the region where interference and reverberation dominate. For this purpose, this paper first reexamines the so-called front-to-back ratio and the classical supercardioid beamformer. To deal with the white noise amplification problem and the limited directivity factor associated with the supercardioid beamformer, a set of reduced-rank beamformers are deduced by using the well-known joint diagonalization technique, which can make compromises between the front-to-back ratio and the amount of white noise amplification or the directivity factor. Then, the definition of the front-to-back ratio is extended to a generalized version, from which another set of reduced-rank beamformers and their regularized versions are developed. Simulations are conducted to illustrate the properties and advantages of the proposed beamformers.

Lifetime-aware FTL to improve the lifetime and performance of solid-state drives

Data compression techniques have been deployed in SSDs to prolong their lifetime due to the good tradeoff between data reduction and performance degradation. However, existing schemes either consume plenty of DRAM resources, or cause the read amplification problem, which may further result in significant performance degradation. In this paper, we propose a lifetime-aware FTL scheme (LAFTL) to improve both the lifetime and performance of SSDs by compressing several pages into one physical page. We then design a compression-aware page mapping table (PMT) to reduce the memory consumption, and propose a latency-aware approach to improve the performance. We conduct extensive trace-driven evaluations based on real-world workloads, and results show that our LAFTL reduces the average response time of reads by 3%–78% and ensures a minimal resource consumption in DRAM while obtaining an acceptable data reduction rate compared to other schemes.

Gold nanoparticle-mediated nucleic acid isothermal amplification with enhanced specificity

Loop-mediated isothermal amplification is a promising method in the area of nucleic acid detection. However, it suffers from a high rate of false-positive amplifications that largely restrict its application. In this study, we observed gold nanoparticles (AuNP) absorbing single-stranded DNA primers and interacting with Bst DNA polymerase via electrostatic adsorption. As a result of these interactions, the presence of the gold nanoparticles exerted a hot-start effect on the loop-mediated isothermal amplification system. Based on these results, we developed a novel AuNP-mediated nucleic acid isothermal amplification assay. This assay displays significantly enhanced specificity—the proportion of false positive decreased from 76% to 0% and from 100% to 0% for the detection of rotavirus and the β-actin gene, respectively, with the hot-start temperature of 48 °C. Moreover, our AuNP-based assay maintained good sensitivity and a satisfactory detection limit (1 × 103copies/μL) compared with the conventional assay. This approach has the potential to solve the nonspecificity problem of loop-mediated isothermal amplification, thereby promoting its real-world application, particularly, in clinical settings.

P090 Impact of chemical contamination on HLA typing accuracy obtained by real time PCR

Aim RT-PCR offers many advantages for HLA typing. Rapid turnaround time is the most appreciated for laboratories performing time-sensitive testing related to deceased donors. This technology reduces hands-on time, provides an alternative to gels, avoiding use of ethidium bromide and detects the presence of common null alleles. DNA concentration and 260/280 absorbance ratio are well-established parameters known to affect the quality of results. However, the impact of the 260/230 ratio has not been considered or properly studied. Here, we describe how 260/230 ratio can interfere with accuracy of typing obtained by RT-PCR. Methods RT-PCR typing was performed according to manufacturer instructions using LinkSeq SABR 1580 kits, K3476-AR and K3499-DR in the QuantStudio 6 Flex instrument. Samples were analyzed using Suretyper v.5.0.5 software. Results Troubleshooting samples exhibiting multiple dropout reactions, DNA quality was assessed by 260/280 and 260/230 ratios. Reagents used to isolate nucleic acids, including guanidinium thyocianate (GT), have absorbance near to 230 nm. GT is present in high concentrations in the cartridges used for DNA isolation. Downstream applications, including PCR, are known to be affected by RNA preparations exhibiting low 230/260 ratios. However, there is not much information about the impact of DNA preparations with low 230/260 ratios on typing results obtained by RT-PCR. 260/230 ratio was measured for 10 samples, where multiple reactions either failed or had weak amplifications. In all cases, ratios were less than 1. We compared with 260/230 ratios of samples with robust amplifications and all ratios were above 1.5 and above 1.7 in eight samples. The problematic DNA samples were washed with ethanol and retyped. The 260/230 ratios increased above 1.6 for all samples and the typing obtained had no amplification problems. Finally, we study the effect of the proportion between blood and elution buffer volumes loaded in the DNA isolation cartridges. We found that it could also affect the typing and established a safe range where results are not impacted. Conclusions DNA preparations containing chemical contaminants and the proportion between blood and elution buffer volumes can affect the accuracy of HLA typing results obtained by RT-PCR.

Hamiltonian approach for optimization of phase-sensitive double-pumped parametric amplifiers.

In this work we applied a Hamiltonian formalism to simplify the equations of non-degenerate nonlinear four-wave mixing to the one-degree-of-freedom Hamiltonian equations with a three-parameter Hamiltonian. Thereby, a problem of signal amplification in a phase-sensitive double-pumped parametric fiber amplifier with pump depletion was reduced to a geometrical study of the phase portraits of the one-degree-of-freedom Hamiltonian system. For a symmetric case of equal pump powers and equal signal and idler powers at the fiber input, it has been shown that the theoretical maximum gain occurs on the extremal trajectories. However, to reduce the nonlinear interaction of waves, we proposed to choose the separatrix as the optimal trajectory on the phase plane. Analytical expressions were found for the maximum amplification, as well as the length of optical fiber and the relative phase of interacting waves allowing this amplification. Using the proposed approach, we optimized of the phase-sensitive parametric amplifier. As a result, the optimal parameters of the phase-sensitive amplifier were found and the maximum possible signal amplification was realized in a broad range of signal wavelengths.

A Technical Design Approach to Soil Moisture Content Measurement

Soil moisture is an important type of data in many fields; ranging from agriculture to environmental monitoring. Three soil samples were collected at definite proportions to represent the three basic soil types (sandy, loamy and clay soils). The moisture contents of these soil samples were analyzed using the thermogravimetric method. This paper employed the use of PC-based soil moisture content measuring system in order to obtain accurate results. It works with the principle that there is an increase or decrease in soil conductivity as soil moisture increases or decreases respectively. The constructed prototype was used to test the three soil samples as well and the results were compared with that of the thermogravimetric method. The results gotten from this prototype shows the relationship between conductivity and moisture content of the soil. The system was well calibrated in order to get standard readings and conquer the problem of transistor amplification at the signal pick up stage. This therefore makes it possible to get fast an accurate results without wasting much time and energy.

Bias Amplification in Epidemiologic Analysis of Exposure to Mixtures

Background:The analysis of health effects of exposure to mixtures is a critically important issue in human epidemiology, and increasing effort is being devoted to developing methods for this problem. A key feature of environmental mixtures is that some components can be highly correlated, raising the issues of confounding by coexposure and colinearity. A relatively unexplored topic in epidemiologic analysis of mixtures is the impact of residual confounding bias due to unmeasured or unknown variables.Objectives:This paper examines the potential amplification of such biases when correlated exposure variables are included in regression models.Methods:We use directed acyclic graphs (DAGs) to describe different simple scenarios involving residual confounding. We derive expressions for the expected value of the resulting bias using linear models and multiple linear regression.Results:Approaches to the analysis of mixtures that involve regressing the outcome on several exposures simultaneously can in some cases amplify rather than reduce confounding bias.Discussions:The problem of bias amplification can worsen with stronger correlation between mixture components or when more mixture components are included in the model.Conclusions:Investigators must consider steps to minimize possible bias amplification in the design and analysis of epidemiologic studies of multiple correlated exposures. This may be particularly important when biomarkers of exposure are used. https://doi.org/10.1289/EHP2450

Noise robust single image super-resolution using a multiscale image pyramid

Self-learning-based single image super-resolution (SLSR) generates a high-resolution (HR) image by estimating a mapping function between patches of different resolutions. However, when handling noisy images, SLSR methods often incur a severe noise amplification problem, or suffer from image quality degradation from additional denoising procedure since noise correlation is pre-reinforced in the super-resolving process. To achieve super-resolution while preserving image quality, we propose a unified framework of super resolution and noise reduction by taking advantage of a multiscale image pyramid generated from iteratively blurring and subsampling input and output images. A salient feature of the proposed method lies in its more elaborate mapping on the basis of high-order derivatives that are readily available from the self-similarity property of the image pyramid. The proposed method is further augmented by incorporating a hybrid interpolation and denoising scheme that leverages noise decreasing property inherent in the image pyramid, thereby minimizing noise amplification in conventional SLSR. Our experiments on both synthesized and real life images demonstrate that the proposed method yields visually more appealing HR images than the conventional sequential pipeline, and improves quantitative metrics for image quality such as the peak signal-to-noise ratio and structural similarity as well.

A model and analysis for the nonlinear amplification of waves in the cochlea

A nonlinear three-dimensional model for the amplification of a wave in the cochlea is analyzed. Using the long-slender geometry of the cochlea, and the relatively high frequencies in the hearing spectrum, an asymptotic approximation of the solution is derived for linear, but spatially inhomogeneous, amplification. From this, a nonlinear WKB approximation is constructed for the nonlinear problem, and this is used to derive an efficient numerical method for solving the amplification problem. The advantage of this approach is that the very short waves needed to resolve the wave do not need to calculated as they are represented in the asymptotic solution.

Amplifying the Randomness of Weak Sources Correlated With Devices

The problem of device-independent randomness amplification against no-signaling adversaries has so far been studied under the assumption that the weak source of randomness is uncorrelated with the (quantum) devices used in the amplification procedure. In this work, we relax this assumption, and reconsider the original protocol of Colbeck and Renner using a Santha-Vazirani (SV) source. To do so, we introduce an SV-like condition for devices, namely that any string of SV source bits remains weakly random conditioned upon any other bit string from the same SV source and the outputs obtained when this further string is input into the devices. Assuming this condition, we show that a quantum device using a~singlet state to violate the chained Bell inequalities leads to full randomness in the asymptotic scenario of a large number of settings, for a restricted set of SV sources (with $0 \leq \varepsilon < (2^{(1/12)} - 1)/(2(2^{(1/12)} + 1)) \approx 0.0144$). We also study a device-independent protocol that allows for correlations between the sequence of boxes used in the protocol and the SV source bits used to choose the particular box from whose output the randomness is obtained. Assuming the SV-like condition for devices, we show that the honest parties can achieve amplification of the weak source, for the parameter range $0 \leq \varepsilon<0.0132$, against a class of attacks given as a mixture of product box sequences, made of extremal no-signaling boxes, with additional symmetry conditions. Composable security proof against this class of attacks is provided.

An anisotropic-tolerant and error control localization algorithm in wireless sensor network

Multi-hop localization schemes are low cost, easy to implement and suitable for large-scale application. However, in practical applications, the performances of multi-hop localizations are often affected by anisotropic networks, such as irregular deployment of nodes and uneven distribution of nodes. The anisotropic problem makes the application of multi-hop localization limited, so we propose a new multi-hop approach for anisotropic network. This scheme constructs the mapping relation between hop-counts and physical distance and this algorithm views the process of location estimation as a regression prediction. In addition, we employ the geometric precision factor (Geometric Dilution Precision) to select the anchors, and effectively avoid the problem of the error amplification of the geometric relations of the anchors. Theoretical analysis and simulation results show that our proposed method can adapt to different environments, and the method has the advantages of small overhead, high precision without setting complex parameters.

An Inter-Group Swapping Based Resource Scheduling Scheme for Quasi-Single Frequency Multi-beam Mobile Satellite System

A resource scheduling scheme is proposed in this paper for multi-beam satellite system to eliminate downlink interference as well as to overcome the noise amplification problem caused by Tomlinson-Hiroshima preceding. Firstly, to analyze the noise amplification problem, Tomlinson-Hiroshima preceding (THP) is discussed. Secondly, an inter-group swapping based resource scheduling scheme is proposed to according to the principle of minimizing the maximum noise amplification factor of the same frequency users. Finally, simulations are executed to validate the proposed scheme, which suggest that compared to no-swapping scheme, the proposed scheme can successfully reduce the ratio of low SINR users and improve the minimum signal to interference and noise ratio(SINR).

High-Speed Tracking of a Nanopositioning Stage Using Modified Repetitive Control

In this paper, a modified repetitive control (MRC) based approach is developed for high-speed tracking of nanopositioning stages. First, the hysteresis nonlinearity is decomposed as a periodic disturbance over a linear system. Then, the MRC technique is utilized to account for the periodic disturbances/errors caused by the hysteresis and dynamics behaviors. The developed approach provides a simple and effective hysteresis compensation strategy, avoiding the constructions of hysteresis model and its inversion. Besides, with improved loop-shaping properties, the MRC can alleviate the nonperiodic disturbance amplification problem of the conventional repetitive control. Finally, the effectiveness and performance of the developed MRC-based approach are verified by the experimental results on a custom-built piezo-actuated stage in terms of hysteresis compensation, disturbance rejection and tracking accuracy.

Design of robust concentric circular differential microphone arrays.

Circular differential microphone arrays (CDMAs) have been extensively studied in speech and audio applications for their steering flexibility, potential to achieve frequency-invariant directivity patterns, and high directivity factors (DFs). However, CDMAs suffer from both white noise amplification and deep nulls in the DF and in the white noise gain (WNG) due to spatial aliasing, which considerably restricts their use in practical systems. The minimum-norm filter can improve the WNG by using more microphones than required for a given differential array order; but this filter increases the array aperture (radius), which exacerbates the spatial aliasing problem and worsens the nulls problem in the DF. Through theoretical analysis, this research finds that the nulls of the CDMAs are caused by the zeros in the denominators of the filters' coefficients, i.e., the zeros of the Bessel function. To deal with both the white noise amplification and deep nulls problems, this paper develops an approach that combines different rings of microphones together with appropriate radii. The resulting robust concentric circular differential microphone arrays (CCDMAs) can mitigate both problems. Simulation results justify the superiority of the robust CCDMA approach over the traditional CDMAs and robust CDMAs.

On the Design of Frequency-Invariant Beampatterns With Uniform Circular Microphone Arrays

This paper deals with two critical issues about uniform circular arrays (UCAs): frequency-invariant response and steering flexibility. It focuses on some optimal design of frequency-invariant beampatterns in any desired direction along the sensor plane. The major contributions are as follows. 1) We explain how to include the steering information in the desired directivity pattern. 2) We show that the optimal approximation of the beamformer's beampattern with a UCA from a least-squares error perspective is the Jacobi–Anger expansion. 3) We develop an approach to the design of any desired symmetric directivity pattern, where the deduced beampattern is almost frequency invariant and its main beam can be pointed to any wanted direction in the sensor plane. 4) With the proposed approach, we derive an explicit form of the white noise gain (WNG) and the directivity factor (DF), and explain clearly the white noise amplification problem at low frequencies and the DF degradation at high frequencies. The analysis also indicates that increasing the number of microphones can always improve the WNG. We show that the proposed method is a generalization of circular differential microphone arrays. The relationship between the proposed method and the so-called circular harmonics beamformers is also discussed.

Computing the binding affinity of a ligand buried deep inside a protein with the hybrid steered molecular dynamics

Computing the ligand-protein binding affinity (or the Gibbs free energy) with chemical accuracy has long been a challenge for which many methods/approaches have been developed and refined with various successful applications. False positives and, even more harmful, false negatives have been and still are a common occurrence in practical applications. Inevitable in all approaches are the errors in the force field parameters we obtain from quantum mechanical computation and/or empirical fittings for the intra- and inter-molecular interactions. These errors propagate to the final results of the computed binding affinities even if we were able to perfectly implement the statistical mechanics of all the processes relevant to a given problem. And they are actually amplified to various degrees even in the mature, sophisticated computational approaches. In particular, the free energy perturbation (alchemical) approaches amplify the errors in the force field parameters because they rely on extracting the small differences between similarly large numbers. In this paper, we develop a hybrid steered molecular dynamics (hSMD) approach to the difficult binding problems of a ligand buried deep inside a protein. Sampling the transition along a physical (not alchemical) dissociation path of opening up the binding cavity---pulling out the ligand---closing back the cavity, we can avoid the problem of error amplifications by not relying on small differences between similar numbers. We tested this new form of hSMD on retinol inside cellular retinol-binding protein 1 and three cases of a ligand (a benzylacetate, a 2-nitrothiophene, and a benzene) inside a T4 lysozyme L99A/M102Q(H) double mutant. In all cases, we obtained binding free energies in close agreement with the experimentally measured values. This indicates that the force field parameters we employed are accurate and that hSMD (a brute force, unsophisticated approach) is free from the problem of error amplification suffered by many sophisticated approaches in the literature.

Local seismic site amplification: effects of obliquely incident antiplane motions

Seismic site amplification studies are generally used to assess the effects of local geology and soil conditions on ground motion characteristics. Although extensive reviews on site amplification phenomena associated with stratigraphic effects can be found in the specialized literature, it should be pointed out that most of the practical applications have been limited to the study of vertically propagating shear horizontal (SH) waves, i.e., to the 1-D soil amplification problem. Furthermore, little attention, if any, has been devoted to the study of the effects of non-vertically incident SH waves on surface accelerograms and on the earthquake response of structures. In the present work, the study is extended to an investigation of 2-D site amplification of non-vertically propagating seismic shear waves in multilayered viscoelastic soil deposits. Sensitivity analyses of the effects of non-vertical incidence on site amplification functions are performed based on site geotechnical data collected from post-seismic investigations of the 1980 El-Asnam earthquake. Analytical results are discussed in terms of seismic site transfer functions, spectral ratios, surface acceleration time histories, and structural response spectra for different values of wave incidence angle. Both bedrock and rock outcropping cases are examined.

Reduced-Order Robust Superdirective Beamforming With Uniform Linear Microphone Arrays

Sensor arrays for audio and speech signal acquisition are generally required to have frequency-invariant beampatterns to avoid adding spectral distortion to the broadband signals of interest. One way to obtain frequency-invariant beampatterns is via superdirective beamforming. However, traditional superdirective beamformers may cause significant white noise amplification (particularly at low frequencies), making them sensitive to uncorrelated white noise. To circumvent the problem of white noise amplification, a method was developed to find the superdirective beamforming filter with a constraint on the white noise gain (WNG), leading to the so-called WNG-constrained superdirective beamformer. But this method damages the frequency invariance of the beampattern. In this paper, we develop a flatness-constrained robust superdirective beamformer. We divide the overall beamformer into two subbeamformers, which are convolved together: one subbeamformer forms a lower order superdirective beampattern while the other attempts to improve the WNG. We show that this robust approach can improve the WNG while limiting the frequency dependency of the beampattern at the same time.