Changes In Signal Level Research Articles

Ways of ensuring effective detection of multiposition OFDM signals

The problem of processing various stages of signal detection in interference conditions was investigated, statistical processing methods were analyzed. The task of information processing is to detect the moment of change in the input signal (change in signal level, change in frequency, occurrence of a pulse signal, etc.). External interference distorts the input signal, so it can be distinguished based on the statistical difference between interference and mixing. Additional interference that distorts the input signal in the equipment of the telecommunications system is introduced during the conversion of the signal before entering the digital processing equipment. Various methods of statistical processing are studied: optimal, adaptive, non-classical optimization methods based on the principles of non-displacement, invariance, similarity, etc. The application of non-parametric methods was investigated when the functional form of the distribution of the input data was unknown and only the general difference between the presence and absence of the signal was indicated. The ranking method of signal detection processing deserves special attention. Adaptive methods are used if the distribution of input data is known with accuracy up to the array of unknown parameters. Nonparametric methods are used when the functional form of the distribution of input data is unknown, and only the general differences between the situations of the presence and absence of a signal are specified. The analysis of signal detection methods shows that one of the promising directions of research is the development of methods that use the invariant properties of the system and ensure the maximum possible storage of signal information. It was studied that the flexibility of the ranking procedure makes it possible to solve a wide range of problems in the detection of multi-position signals under conditions of non-parametric a priori uncertainty.

Добова залежність ослаблення радіосигналу Х-діапазону на трасі «геостаціонарний штучний супутник Землі – Земля»

Subject and Purpose. Statistical data on how the satellite signal level varies with changes in the characteristics of tropospheric layers and lower-troposphere hydrometeors serve designers a useful guide in the development of systems for diagnosing weather conditions and hydrometeor characteristics. The aim of the work is to generalize results from the long-term research into daily dependences of X-band radio signal attenuation between the geostationary satellite and Earth terminals. On this basis it is possible to find relationship between signal level changes at the point of reception and geophysical atmospheric agents. Methods and methodology. A receiving measuring and recording complex developed by the authors is employed for the purpose of establishing relationship between geostationary satellite signal level at the receiving point and geophysical atmospheric agents. Results. A block-diagram of the receiving measuring and recording complex is presented, its operation described. Geometric parameters of the radio signal path of propagation have been considered. Signal level measuring results obtained using a Hot Bird geostationary satellite in the period from 03 to 17 January 2019 have been generalized and interpreted. Conclusions. X-band radio signal attenuation on the path from a geostationary satellite to the Earth has a daily dependence. The radio signal level variations are not connected with alterations in spatial and technical parameters of the geostationary satellite or receiving equipment. The day and night changes in radio signal level are attributed to different daytime durations and different angles of sunbeam (including twilight) incidence on tropospheric areas associated with the receiving antenna pattern in the propagation direction, which entails changeable temperature regime and moisture content in these areas. Geophysical agents in the highest tropospheric layers insolated from far beyond the horizon can also be interpreted for long-distance tropospheric radio wave propagation in these tropospheric regions.

Several Strategies for Anti-Multiple-Access Interference of Ground Equipment in Spread Spectrum Measurement and Control

In this paper, the inter-symbol interference problem of multi-objective mode for single-station measurement of ground equipment in spread spectrum measurement and control is obtained from the autocorrelation, cross-correlation, primitive polynomial selection method and three-object code between 10-level m-sequence and Gold code. Interference test and other aspects have been analyzed and discussed. Combined with the problem of small satellite star time-sharing signal level changes causing wrong lock and long time of re-trapping, the strategy of using ground-spreading measurement and control equipment is proposed.

Non-linearity of Skin Properties in Electrotactile Applications: Identification and Mitigation.

Electrotactile displays can open a new sensory substitution channel to be utilized in a vast array of applications. Our Finger-Eye research used this approach to build a system for the blind to easily read any text not written in Braille. But there are still challenges in different aspects of such systems. One of the most crucial concerns, is the effects of receptor fatigue. Our tests show that during prolonged exposure of receptors to the electrical signals, their sensitivity to the signal level changes gradually and adjustments in the signal's power are required to keep the receptors is the stimulated state. This was confirmed by monitoring the electrical current passing through the skin and calculating the corresponding impedance. More interestingly, the rates of the impedance changes are different for each part of the skin, indicating inconsistent rates of receptor fatigue for each region of the skin. These electrical properties of the skin were addressed in this research for the purpose of rendering consistent sensations for the users regardless of the person or skin conditions. To solve these challenges, two methods are employed: a voltage control system based on pulse-width modulation is used to adjust the signal power; and Kalman filtering is used to predict impedance changes in advance and supply the skin with the proper signal. The result is a self-contained automated system capable of managing the signal power for any user at any given time or skin condition.

Improvement of statistical methods for detecting anomalies in climate and environmental monitoring systems

The article shows how the known statistical methods, which are widely used in solving financial problems and a number of other fields of science and technology, can be effectively applied after minor modification for solving such problems in climate and environment monitoring systems, as the detection of anomalies in the form of abrupt changes in signal levels, the occurrence of positive and negative outliers and the violation of the cycle form in periodic processes.

Gene-free methodology for cell fate dynamics during development.

Models of cell function that assign a variable to each gene frequently lead to systems of equations with many parameters whose behavior is obscure. Geometric models reduce dynamics to intuitive pictorial elements that provide compact representations for sparse in vivo data and transparent descriptions of developmental transitions. To illustrate, a geometric model fit to vulval development in Caenorhabditis elegans, implies a phase diagram where cell-fate choices are displayed in a plane defined by EGF and Notch signaling levels. This diagram defines allowable and forbidden cell-fate transitions as EGF or Notch levels change, and explains surprising observations previously attributed to context-dependent action of these signals. The diagram also reveals the existence of special points at which minor changes in signal levels lead to strong epistatic interactions between EGF and Notch. Our model correctly predicts experiments near these points and suggests specific timed perturbations in signals that can lead to additional unexpected outcomes.

Extracellular vesicles as potential biomarkers of acute graft-vs-host disease.

Acute graft-vs-host disease (GVHD) is a serious complication after allografting. We carried out an exploratory study to investigate a potential correlation of surface antigens on extracellular vesicles (EVs) and acute GVHD. EVs were extracted from serum samples from 41 multiple myeloma patients who underwent allografting. EVs were characterized by flow cytometry using a panel of 13 antibodies against specific membrane proteins that were reported to be predictive of acute GVHD. We observed a correlation between three potential biomarkers expressed on EV surface and acute GVHD onset by both logistic regression analysis and Cox proportional hazard model. In our study, CD146 (MCAM-1) was correlated with an increased risk-by almost 60%-of developing GVHD, whereas CD31 and CD140-α (PECAM-1 and PDGFR-α) with a decreased risk-by almost 40 and 60%, respectively. These biomarkers also showed a significant change in signal level from baseline to the onset of acute GVHD. Our novel study encourages future investigations into the potential correlation between EVs and acute GVHD. Larger prospective multicenter studies are currently in progress.

Allosteric proteins as logarithmic sensors

Many sensory systems, from vision and hearing in animals to signal transduction in cells, respond to fold changes in signal relative to background. Responding to fold change requires that the system senses signal on a logarithmic scale, responding identically to a change in signal level from 1 to 3, or from 10 to 30. It is an ongoing search in the field to understand the ways in which a logarithmic sensor can be implemented at the molecular level. In this work, we present evidence that logarithmic sensing can be implemented with a single protein, by means of allosteric regulation. Specifically, we find that mathematical models show that allosteric proteins can respond to stimuli on a logarithmic scale. Next, we present evidence from measurements in the literature that some allosteric proteins do operate in a parameter regime that permits logarithmic sensing. Finally, we present examples suggesting that allosteric proteins are indeed used in this capacity: allosteric proteins play a prominent role in systems where fold-change detection has been proposed. This finding suggests a role as logarithmic sensors for the many allosteric proteins across diverse biological processes.

Frequency-modulated atomic force microscopy operation by imaging at the frequency shift minimum: the dip-df mode.

In frequency modulated non-contact atomic force microscopy, the change of the cantilever frequency (Δf) is used as the input signal for the topography feedback loop. Around the Δf(z) minimum, however, stable feedback operation is challenging using a standard proportional-integral-derivative (PID) feedback design due to the change of sign in the slope. When operated under liquid conditions, it is furthermore difficult to address the attractive interaction regime due to its often moderate peakedness. Additionally, the Δf signal level changes severely with time in this environment due to drift of the cantilever frequency f0 and, thus, requires constant adjustment. Here, we present an approach overcoming these obstacles by using the derivative of Δf with respect to z as the input signal for the topography feedback loop. Rather than regulating the absolute value to a preset setpoint, the slope of the Δf with respect to z is regulated to zero. This new measurement mode not only makes the minimum of the Δf(z) curve directly accessible, but it also benefits from greatly increased operation stability due to its immunity against f0 drift. We present isosurfaces of the Δf minimum acquired on the calcite CaCO3(101̅4) surface in liquid environment, demonstrating the capability of our method to image in the attractive tip-sample interaction regime.

The Effects of Added Hydrogen on a Helium Atmospheric-Pressure Plasma Jet Ambient Desorption/Ionization Source

We present mass spectrometric data demonstrating the effect that hydrogen has on a helium-based dielectric-barrier discharge (DBD) atmospheric-pressure plasma jet used as an ambient desorption/ionization (ADI) source. The addition of 0.9% hydrogen to the helium support gas in a 35-W plasma jet increased signals for a range of test analytes, with enhancement factors of up to 68, without proportional increases in background levels. The changes in signal levels result from a combination of changes in the desorption kinetics from the surface and increased ion production in the gas phase. The enhancement in ADI-MS performance despite the quenching of key plasma species reported in earlier studies suggests that ionization with a H2/He plasma jet is the result of an alternate mechanism involving the direct generation of ionized hydrogen.

Adaptation of differential sensitivity of auditory system neurons to amplitude modulation after abrupt change of signal level

Impulse activity of neurons of brainstem auditory nuclei (medulla dorsal nucleus and midbrain torus semicircularis) of the grass frog (Rana temporaria) was recorded under action of long amplitude-modulated tonal signals. After adaptation of neuronal response to acting stimulus (30–60 s after its onset), we performed a sharp change (by 20–40 dB) of the mean signal level with preservation of unchanged frequency and depth of modulation. We also recorded a change of density impulsation and of degree of its synchronization with the modulation period as well as the phase of maximum reaction at the modulation period and phase of the response every 2 or 4 s. In the adapted state, the sharp change of the mean level had been provided, while maintaining frequency and depth unchanged. During the adaptation to long signals with small modulation indexes the firing rate continuously decreased, but synchronization with envelope usually increased considerably. A sharp rise in the mean level resulted in an increase of firing rate, which could be accompanied either by a continuation of synchronization growth (the effect is more typical of the dorsal nucleus) or by a sharp fall in synchrony with its subsequent slow recovery (the effect is more typical of the torus semicircularis). Nature of the changes following the change of the intensity of the reaction could depend on the signal parameters (initial level, magnitude of the jump, frequency and depth of modulation). The connection between the observed physiological data and the psychophysics of differential intensity coding is discussed.

Real-Time monitoring of intracellular wax ester metabolism

BackgroundWax esters are industrially relevant molecules exploited in several applications of oleochemistry and food industry. At the moment, the production processes mostly rely on chemical synthesis from rather expensive starting materials, and therefore solutions are sought from biotechnology. Bacterial wax esters are attractive alternatives, and especially the wax ester metabolism of Acinetobacter sp. has been extensively studied. However, the lack of suitable tools for rapid and simple monitoring of wax ester metabolism in vivo has partly restricted the screening and analyses of potential hosts and optimal conditions.ResultsBased on sensitive and specific detection of intracellular long-chain aldehydes, specific intermediates of wax ester synthesis, bacterial luciferase (LuxAB) was exploited in studying the wax ester metabolism in Acinetobacter baylyi ADP1. Luminescence was detected in the cultivation of the strain producing wax esters, and the changes in signal levels could be linked to corresponding cell growth and wax ester synthesis phases.ConclusionsThe monitoring system showed correlation between wax ester synthesis pattern and luminescent signal. The system shows potential for real-time screening purposes and studies on bacterial wax esters, revealing new aspects to dynamics and role of wax ester metabolism in bacteria.

Stereolithographic Bone Scaffold Design Parameters: Osteogenic Differentiation and Signal Expression

Scaffold design parameters including porosity, pore size, interconnectivity, and mechanical properties have a significant influence on osteogenic signal expression and differentiation. This review evaluates the influence of each of these parameters and then discusses the ability of stereolithography (SLA) to be used to tailor scaffold design to optimize these parameters. Scaffold porosity and pore size affect osteogenic cell signaling and ultimately in vivo bone tissue growth. Alternatively, scaffold interconnectivity has a great influence on in vivo bone growth but little work has been done to determine if interconnectivity causes changes in signaling levels. Osteogenic cell signaling could be also influenced by scaffold mechanical properties such as scaffold rigidity and dynamic relationships between the cells and their extracellular matrix. With knowledge of the effects of these parameters on cellular functions, an optimal tissue engineering scaffold can be designed, but a proper technology must exist to produce this design to specification in a repeatable manner. SLA has been shown to be capable of fabricating scaffolds with controlled architecture and micrometer-level resolution. Surgical implantation of these scaffolds is a promising clinical treatment for successful bone regeneration. By applying knowledge of how scaffold parameters influence osteogenic cell signaling to scaffold manufacturing using SLA, tissue engineers may move closer to creating the optimal tissue engineering scaffold.

Acoustic measurements of clay-size particles

Knowledge of sediment concentration is important in the study of streams and rivers. The work presented explores using high frequency (20 MHz) acoustic signal attenuation to measure the concentration of fine sediment particles (0.2-5.0 microm) in a fluvial environment. A small laboratory tank with a pitch-catch transducer configuration measured a 35 dB change in signal level over a wide range of kaolinite and bentonite concentrations (1-14 g/l) over a range of distances (180-357 mm). The data suggest that a fixed distance of 180 mm between the transducers will be capable of measuring the entire range of concentrations.

Use of Diagnostic Accuracy as a Metric for Evaluating Laboratory Proficiency with Microarray Assays Using Mixed-Tissue RNA Reference Samples

Effective use of microarray technology in clinical and regulatory settings is contingent on the adoption of standard methods for assessing performance. The MicroArray Quality Control project evaluated the repeatability and comparability of microarray data on the major commercial platforms and laid the groundwork for the application of microarray technology to regulatory assessments. However, methods for assessing performance that are commonly applied to diagnostic assays used in laboratory medicine remain to be developed for microarray assays. A reference system for microarray performance evaluation and process improvement was developed that includes reference samples, metrics and reference datasets. The reference material is composed of two mixes of four different rat tissue RNAs that allow defined target ratios to be assayed using a set of tissue-selective analytes that are distributed along the dynamic range of measurement. The diagnostic accuracy of detected changes in expression ratios, measured as the area under the curve from receiver operating characteristic plots, provides a single commutable value for comparing assay specificity and sensitivity. The utility of this system for assessing overall performance was evaluated for relevant applications like multi-laboratory proficiency testing programs and single-laboratory process drift monitoring. The diagnostic accuracy of detection of a 1.5-fold change in signal level was found to be a sensitive metric for comparing overall performance. This test approaches the technical limit for reliable discrimination of differences between two samples using this technology. We describe a reference system that provides a mechanism for internal and external assessment of laboratory proficiency with microarray technology and is translatable to performance assessments on other whole-genome expression arrays used for basic and clinical research.

Anterior-posterior patterning and segmentation of the vertebrate head.

Segmentation of the vertebrate head emerges out of earlier processes that establish the anterior-posterior (A-P) axis. Recent genetic studies and comparisons across species have led to a better understanding of the links between A-P patterning and segmentation. These point to similar signals acting on both head and trunk, such as retinoic acid and fibroblast growth factors. These form interacting networks of diffusible morphogen gradients that pattern both hindbrain rhombomeres and mesodermal somites. New computational models, particularly for retinoic acid, have revealed how morphogen gradients are established and made robust to changes in signaling levels. However, the orientations of these gradients, as well as how they interact to generate segments, differ remarkably between germ layers and body regions. Thus, the vertebrate head is, in part, built through modifications of the same processes that link A-P patterning and segmentation in the trunk, but fundamental differences in how these processes are deployed lend further doubt to the notion that head and trunk segments are homologous.

Model of Incoming Waves at Base Station to Evaluate the Performance of Intersector Soft Handover

A propagation model is needed to evaluate the performance of handover in mobile-communication systems. Generally, the received signal level from base stations (BSs) is calculated assuming path loss, and a lognormal (shadow)-fading model is used for evaluating intercell handover. The lognormal fading was assumed to be uncorrelated between cells. However, since the correlation between sectors is not clarified, an appropriate shadow-fading model to evaluate intersector handover has not yet been proposed. To obtain shadow-fading characteristics between neighboring sectors, the change in signal level and the direction of arrival of incoming waves at a BS must be clarified. This paper proposes a simple model of incoming waves to evaluate the performance of intersector handover. The validity of the proposed model is confirmed by comparing the difference between signal levels in BS sectors that are calculated using the proposed model and the measured power azimuth spectrum.

Satellite propagation channel modelling using photogrammetry and hidden Markov model approach

In a typical satellite-earth propagation path, the field strength of the received signal level changes with respect to time and space according to the changing morphology of the environment. It has been shown that the switching between different attenuation levels can be represented as a Markov stochastic process using the assumption that the channel properties are quasi-stationary in small periods of time. A hidden Markov model is introduced to replace the often used channel fading models, such as Rice, Loo and Rayleigh distributions. Three sets of parameters are trained to simulate the state transition and observation conditional probability density function among three basic propagation states that are categorised according to the environmental images. The simulated data were compared to the real RF measurement of satellite signals in several propagation properties, such as the cumulative fading distribution, level cross rate and error probability performance, at typical user environments. With the help of observation sets and their conditional probability densities, the proposed propagation channel simulator can model the satellite propagation properties with better accuracy than three-state Markov transition models.

Acoustic behaviour of current ultrasound contrast agents

A general law gives the approximate change in signal level obtained in a particular imaging mode when a suitable contrast agent is added. It also shows that reduction of background signals is essential to overcome limitations found mainly in conventional (linear) ultrasound contrast imaging. Contrast agents contain stabilized microbubbles with very helpful non-linear properties. Acoustic methods for non-destructive and destructive testing of microbubbles are briefly discussed. In the main part, the linear and non-linear acoustic behaviour of various types of contrast agent are described. The latter is useful for new applications in diagnostic ultrasound.

Coherent gust detection by wavelet transform

Abstract The spectrum is commonly used to characterize the energy content and the longitudinal scale of turbulence in the wind field. However, this incoherent signal model is not always sufficient to identify intermittent coherent structures in the wind that may be responsible for wind damage. These periods of gusts may be viewed as coherent structures occurring in an otherwise incoherent signal. In this paper, we describe a method for using wavelet transforms to detect coherent structures in the wind field. To detect coherent gusts, we use the Haar wavelet since the Haar analyzing function detects the magnitude and length scale of sustained changes in signal level. A statistical technique is developed to separate coherent structures in the wavelet transform from fluctuations due to incoherent noise.