Analysis of Adaptive Digital Feedback Linearization Techniques

We have developed a novel digital feedback predistortion(DFBPD) linearization based on RF feedback PD for the wide bandwidth modulated signals. The wideband PD operation is carried out by combining the DFBPD and memory lookup table(LUT). To experimentally demonstrate the linearization performance of the proposed PD technique for wideband signal, a class-AB amplifier using an LDMOSFET MRF6S23140 with 140-W peak envelope power is employed at 2.345 GHz. For a forward-link 2FA wideband code-division multiple-access signal with 10 MHz carrier spacing, the proposed DFBPD with memory LUT delivers the adjacent channel leakage ratio at an 10 MHz offset of -56.8 dBc, while those of the amplifier with and without DFBPD are -43.2 dBc and -41.9 dBc, respectively, at an average output power of 40 dBm. The experimental result shows that the new DFBPD with memory LUT provides a good linearization performance for the signal with wide bandwidth.

We have developed a new adaptive digital predistortion (DPD) linearization technique based on analog feedback predistortion (FBPD). The lookup-table-based feedback input can remove the bandwidth limitation of the feedback circuit related to the loop delay, and suppress feedback oscillation by accurate digital control of the feedback signal. Moreover, the predistortion (PD) signal can be extracted very efficiently. By combining the feedback linearization and DPD linearization techniques, the performance of the predistorter is enhanced significantly compared to the conventional DPD. To clearly visualize the characteristics of digital FBPD (DFBPD), we have compared it to the conventional DPD based on the recursive least square algorithm using Matlab simulation. The results clearly show that the new method is a good linearization algorithm, better than a conventional DPD. For the demonstration, a Doherty power amplifier with 180-W peak envelope power is linearized using the proposed DFBPD. For a 2.14-GHz forward-link wideband code-division multiple-access signal, the adjacent channel leakage ratio at 2.5-MHz offset is -58 dBc, which is improved by 15 dB at an average output power of 43 dBm

The temperature effects in aging index of asphalt during UV aging process

This paper presents a now method of optimal digital PID feedback control for a linear multivariate system by using a, parameter optimization technique. The most difficult points for the design of optimal digital PID feedback control system by the modern control theory are : (1) the control structure of it is specified in advance, (2) unless all the state variables are fed back, the optimal control cannot be obtained by dynamic programming or the maximum principle. However, the optimal digital PID feedback gains are determined by using the parameter optimization technique in this paper. When there are some states which are not fed back in the control system, the optimal feedback gains depend on the initial states. First, the optimal solution is presented in the case where all the initial Btates are known. Next, it is extended to the case where the initial states are random variables and their statistical properties are known,

Effects of temperature, inoculum concentration, leaf age, and continuous and interrupted wetness on infection of olive plants by <i>Spilocaea oleagina</i>

The purpose of this study was to investigate the influence of electrolyte type, pH, temperature and aging on the viscosity property of okra gum using paracetamol as model drug. Paracetamol (125 mg/ 5 mL) suspension containing okra gum particles of undersize 180 µm as suspending agent was formulated. Similar suspension of paracetamol was formulated using tragacanth gum as a suspending agent for comparison. Effect of electrolyte type, pH, temperature and aging on the viscosity property of okra gum in paracetamol suspension was evaluated using standard methods. Addition of electrolytes, changes in pH, increase in temperature and increase in storage time were shown to decrease the viscosity of the paracetamol suspension. The effect of temperature and aging on the viscosity of the suspension formulation containing okra gum was more pronounced than on the formulation containing tragacanth gum. Conversely, the effect of alkaline pH and type of electrolyte on the viscosity of the suspension formulation containing tragacanth gum was more pronounced than on the formulation containing okra gum. On the basis of these, formulators and caregivers may consider these factors when designing or using pharmaceutical suspensions containing natural gums such as okra and tragacanth as viscosity enhancing agents.

Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20–60 °C in the next few decades. In this paper, two types of cemented gravel sand backfills, cemented rod-mill sand backfill (CRB) and cemented gobi sand backfill (CGB), were prepared and cured at various temperatures (20, 40, 60 °C) and ages (3, 7, 28 d), and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests. Results show that: 1) the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures. The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages. 2) The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB. With the increase of temperature, the compressive failure modes changed from X-conjugate shear failure to tensile failure, and the integrity of specimens was significantly improved. 3) Similarly, the shear performance of CGB is generally better than that of CRB. The temperature has a weaker effect on shear strength than age, but the shear deformation and shear plane morphology are closely related to temperature.

&amp;lt;p&amp;gt;Our understanding of ecosystem responses to climate change is hampered by a poor understanding of the environmental drivers of autumn leaf phenology in temperate and boreal forests. Specifically, the interplay between climate and day length in regulating autumn senescence is still poorly understood. In our recent experiment on European beech seedlings, we studied the effects of radiation (shading) and temperature throughout the vegetation season on autumn leaf senescence dates. We found that the effects of temperature and radiation differ before and after summer solstice, with pre-solstice cooling delaying leaf senescence dates by 10.2 &amp;amp;#177; 2.5 days and pre-solstice shading having little effect. By contrast, cooling after the summer solstice tended to advance leaf senescence, while post-solstice shading delayed senescence dates by 6.5 &amp;amp;#177; 2.8 days. These findings suggest a pre-solstice effect of temperature linked to growth (sink) processes of trees, whereas radiation appears to directly affect senescence through ageing effects on leaves. These findings can help to constrain uncertainties in the length of the vegetation season and annual carbon uptake, thereby helping to deepen knowledge on the interactions between climate and ecosystem dynamics.&amp;lt;/p&amp;gt;

The equivalent representation in the delta domain of the digital optimal compensation problem is provided and computed in this article. This problem concerns finding digital optimal full and reduced-order output feedback controllers for linear time-varying and time-invariant systems with white stochastic parameters. It can subsequently be solved in the delta domain using the strengthened optimal projection equations that we recently formulated in this domain as well. If the sampling rate becomes high, stating and solving the problem in the delta domain becomes necessary because the conventional discrete-time problem formulation and solution become ill-conditioned. In this article, by means of several numerical examples and compensator implementations, we demonstrate this phenomenon. To compute and quantify the improved performance when the sampling rate becomes high, a new delta-domain algorithm is developed. This algorithm computes the performance of arbitrary digital compensators for linear systems with white stochastic parameters. The principle application concerns nonconservative robust digital perturbation feedback control of nonlinear systems with high sampling rates.

A digital feedback automatic gain control (DFAGC) with the constant settling time is presented for the stability of the Phase Locked Loop in the QPSK demodulation. The DFAGC consists of an exponential gain controlled amplifier and a logarithmic amplifier, which gets the constant gain settling time independent of the input signal amplitude. This scheme allows using the linear system theory directly analyze the DAGC performance. So the mathematical model and the backward difference equation are given to investigate the settling time, and the transfer function given to obtain the transient response and the DFAGC tracking performance. Finally, it is verified by simulations that the analysis results closely coincide with the settling time and the DFAGC characteristic in high SNR, and the linear system theory analysis method concisely gives the insight of the proposed scheme.

This paper studies optimal tracking performance issues for multi-input-multi-output linear time-invariant systems under networked control with limited bandwidth and additive colored white Gaussian noise channel. The tracking performance is measured by control input energy and the energy of the error signal between the output of the system and the reference signal with respect to a Brownian motion random process. This paper focuses on two kinds of network parameters, the basic network parameter-bandwidth and the additive colored white Gaussian noise, and studies the tracking performance limitation problem. The best attainable tracking performance is obtained, and the impact of limited bandwidth and additive colored white Gaussian noise of the communication channel on the attainable tracking performance is revealed. It is shown that the optimal tracking performance depends on nonminimum phase zeros, gain at all frequencies and their directions unitary vector of the given plant, as well as the limited bandwidth and additive colored white Gaussian noise of the communication channel. The simulation results are finally given to illustrate the theoretical results.

Interaction of hen production type, age, and temperature on laying pattern and egg quality

Aims: A preliminary epidemiological study, for COVID-19, for the period January to 31 March 2020, was undertaken for the six major global regions, covering 173 infected countries. Factors that were considered to affect the human-to-human transmission of the SARS-CoV-2 virus: the effect of average monthly country temperature and median age, were investigated. Methods: Documented case infections were accessed from the WHO website . Temperature, median age, COVID-19 testing data were obtained from relevant sites. Standard statistical data analysis was used to investigate any relationships. Results: The optimum temperature range for viral infection with SARS-CoV-2 appears to be ± -2,71°C up to 10,50˚C based on about 91% of the total infections occurring at this range. Transmission does appear to occur at a fairly wide temperature range of ± -26˚C up to +33°C. Relatively more cases seem to occur in human subjects at median age of 40,1 ± 5,0 years (56,6%), as noted for Europe, compared to younger subjects of age 20,1 ± 4,3 (0,5%), for Africa. Conclusions: The virus appears to be fairly stable, and of varying transmission, at extreme conditions of low and high temperature. There may be a seasonal behavior regarding its occurrence in line with a recent finding. Keywords: Enveloped virus; SARS-CoV-2; COVID-19; temperature; median age; Case Infection Rate (CIR); seasonal

Environmental effects on the mechanical behaviour of pultruded jute/glass fibre-reinforced polyester hybrid composites

Mobility impairments in older adults have been well documented, and much information is gleaned from comparison with gait of younger adults. However, many impairments likely begin in middle age and progress gradually till they become acute issues in older adults. If such changes can be spotted early, then one can intervene early. Physical therapy and movement sciences, unlike cardiac science, have always intervened after the inception of gait impairments rather than promoting prevention in younger adults.Gait research and clinical tests use indoor walking even though much ecological locomotion also happens outdoors. Clinical tests, in particular, are designed for identifying acute gait issues in older adults. These tests are unlikely to identify subtle gait changes in middle age because these adults will neither reach their physiological limits nor exhaust their compensatory mechanisms during indoor walking. Therefore, this thesis investigated whether changes in the gait of middle-aged men and women will be apparent while walking outdoors on various terrains. Gait quality was quantified using kinematic variability measures, and sex differences were also assessed given the asymmetric impacts of falls for men vs women.Portable inertial measurement units (IMUs) were used to measure ankle kinematics when healthy young and middle-aged men and women walked outdoors on various concrete and grass surfaces of different slopes at their self-selected comfortable speed. Statistical models tested for surface, age and sex differences in gait variability. Study 1 focused on task and sex effects in young adults. Study 2 investigated task and age effects in young and middle-aged adults. To quantify performance, novel metrics were introduced to measure gait variability. This dissertation applies the spatio-temporal index (STI) – a metric commonly used in the speech sciences – to the analysis of gait. This thesis introduces two new derivatives, STIref and <b>Δ</b>STI, that partitioned the variability into a feedforward and a feedback plus noise component, respectively. STIref quantified one feature – the average local roughness – of the ankle acceleration, which is a peripheral consequence of the feedforward motor command. <b>Δ</b>STI quantified the residual, including the magnitude of the feedback-driven step-to-step corrections and neuromotor and external noise evident in the ankle accelerations.In healthy young adults, the feedback-driven corrections and noise component (<b>Δ</b>STI) increased substantially on slopes and on more irregular grassy surfaces. The feedforward component (STIref) was slightly higher in men, likely due to morphological differences. Despite reported differences in fall rates, the variability measures used in this study did not identify differences in the gait of young men and women. The same patterns were evident in middle-aged individuals, and there was no change in these metrics with age. Therefore, a key finding was that a feature of the feedforward component of gait control is relatively invariant, whereas young and middle-aged individuals navigate different terrains mainly through feedback-driven step-to-step corrections. Another key finding was that variability was inversely related to the self-selected walking speed on different surfaces. Individuals may have slowed down on harder terrains so that they have time to implement the step-to-step corrections. Therefore, a plausible explanation of the null age effect in the data is that middle aged adults adapted to the terrains by modulating speed. As motor capacities start to decline in middle-age, individuals adapt to maintain key functions.In conclusion, differences in gait were evident on different surfaces, but the tasks used in this work did not tax the middle-aged adults to reveal gait deficits, especially because individuals were free to select their walking speed. The novel metrics were highly sensitive to terrain but not sensitive to sex differences and early aging. However, the results indicate the path forward: controlling walking speed or increasing task difficulty will be essential to identify gait differences in middle age. The STI-based metrics dissociate the feedforward contributions to gait from the feedback and noise components and provide testable predictions that can be validated with future work.