Search

Transposons are parasitic nucleic acids that threaten genome integrity in all cells. In the metazoan model organism Caenorhabditis elegans, DNA transposons are active in the soma where they are reported to exhibit mobilization rates ≅1000 fold higher than in germ cells. How and why DNA transposons might be so highly active in the C. elegans soma is a mystery. To better understand this question, we constructed reporter genes that label cells in which Tc1 has mobilized with fluorescent protein. The reporters recapitulate the known properties of DNA transposons in C. elegans and allow transposon activity to be monitored in intact, living animals. Using these reporters, we identify cytoplasmic and nuclear factors that limit transposition in the germline. Interestingly, none of these factors limit transposition in the soma. Rather, we identify a gene (nhj-1/scb-1), which we show is required for 99.9% of Tc1 mobilization events in somatic tissues, but does not influence mobilization in the germline. nhj-1/scb-1 encodes a nematode-specific component of the non-homologous end joining (NHEJ) DNA repair machinery. Mutations in the other components of the NHEJ machinery (cku-70, cku-80, and lig-4) also suppress Tc1 mobilization in the C. elegans soma by ≅1000 fold. The data show that the use of NHEJ to repair transposon-induced DNA breaks in the soma dramatically increases the rate of transposon mobilization in this tissue. And because C. elegans germ cells use homology-based repair, and not NHEJ, to fix transposon-induced breaks, we propose that the 1000-fold difference in transposon mobility reported for the C. elegans soma and germline can, in large part, be explained by tissue-specific differences in DNA repair strategy.Author SummaryTransposons are common parasitic genetic elements that threaten all genomes. For example, half of the human genome is made up of transposons. Transposon mobilization can disrupt gene function, causing disease, so transposon activity needs to be tightly regulated to prevent harm to the host. Transposons are typically less active in the soma than in the germline, because somatic transposition benefits neither host or transposon. Surprisingly, in the nematode model organism Caenorhabditis elegans, transposons are reported to be 1000-fold more active in the soma than the germline. Here, we develop a system to investigate transposon regulation in an intact live animal, and show that, in large part, tissue-specific differences in transposon activity in C. elegans is due to the use of different DNA repair pathways by these tissues, highlighting the importance of DNA repair strategy in determining outcomes of transposon excision events. Given that DNA repair factors have been linked to transposon regulation in other eukaryotes, we propose that DNA repair choice likely contributes to transposon mobilization in all eukaryotes.

This article presents the design and evaluation of robust controllers, based on linear programming, Kharitonov's theorem and Chebyshev's theorem, in order to enhance the performance of a typical structure of multistage converters present in direct current (dc) systems. In such electric power distribution systems, point-of-load converters act as a constant power load (CPL), which introduces a destabilizing nonlinear effects to their supply bus voltage. The multistage converter system uses a simplified scheme based on a cascaded converter, which is comprised of two dc–dc buck converters in a series connection. The robust controllers evaluated overcome the negative incremental impedance instability problem due to CPL, which causes a high risk of instability in interconnected converters. Thereby, the robust controllers evaluated ensure robust control performance and stability with a minor performance degradation compared to a conventional controller when the cascaded converter system is subjected to parametric uncertainties. The control methodologies evaluated are applied in both dc–dc buck converters. Assessments on the performance of the control methodologies evaluated are conducted. Experimental validations on a 160-W dc–dc cascaded converter system test board are carried out to verify the theoretical claims.

Small regulatory RNAs, such as small interfering RNAs (siRNAs) and PIWI-interacting RNAs, regulate splicing, transcription, and genome integrity in many eukaryotes. In Caenorhabditis elegans, siRNAs bind nuclear Argonautes (AGOs), which interact with homologous premessenger RNAs to recruit downstream silencing effectors, such as NRDE-2, to direct cotranscriptional gene silencing [or nuclear RNA interference (RNAi)]. To further our understanding of the mechanism of nuclear RNAi, we conducted immunoprecipitation-mass spectrometry on C. elegans NRDE-2 The major NRDE-2 interacting protein identified was the RNA helicase MTR-4 Co-immunoprecipitation analyses confirmed a physical association between NRDE-2 and MTR-4 MTR-4 colocalizes with NRDE-2 within the nuclei of most/all C. elegans somatic and germline cells. MTR-4 is required for nuclear RNAi, and interestingly, MTR-4 is recruited to premessenger RNAs undergoing nuclear RNAi via a process requiring nuclear siRNAs, the nuclear AGO HRDE-1, and NRDE-2, indicating that MTR-4 is a component of the C. elegans nuclear RNAi machinery. Finally, we confirm previous reports showing that human (Hs)NRDE2 and HsMTR4 also physically interact. Our data show that the NRDE-2/MTR-4 interactions are evolutionarily conserved, and that, in C. elegans, the NRDE-2/MTR-4 complex contributes to siRNA-directed cotranscriptional gene silencing.

We investigate the state observer design problem for thermoacoustic instabilities in a Rijke tube using an infinite dimensional perspective. The observer, whose design is based on the backstepping methodology with Volterra and full integral terms, consists of a copy of the linearized plant model plus output injection terms and relies only on a single boundary acoustic pressure sensor. The exponential convergence, in the $L_{2}$ sense, of the observed error dynamics is proved, and the analytic expression of the observer gains are derived explicitly. The results are tested in an experimental Rijke tube prototype in order to illustrate the effectiveness of the method.

The present research work aims to study the large signal stability of two parallel-connected voltage-source inverters operating with resistive droop control through bifurcation analysis. This minimal setup can be considered a prototype of a small islanded ac microgrid studying where droop control acts as a synchronization scheme between inverters. Since switching power converters are strong nonlinear circuits, bifurcation analysis helps to understand nonlinear phenomena more deeply than the standard linear approach. Plenty of complicated nonlinear phenomena have been observed through bifurcation analysis, such as multiequilibria, period-doubling bifurcation, Hopf bifurcation, quasiperiodicity, border collision, bistability, and chaos. Thereby, a set of parameters under certain conditions can influence the equilibrium point and its stability, leading to some of the aforementioned nonlinear phenomena. In this sense, the main contribution of this article is to detect the nonlinear phenomena in considering islanded ac microgrid in order to determine a safe droop parameter region for more robust microgrid operation. This information can be summarized in bifurcation diagrams leading to practical rules for choosing the control and droop parameters. Experimental results are performed to validate the main instabilities predicted by the theoretical models.

This paper proposes a Generalized Minimum Variance (GMV) controller to regulate the output of the DC-DC power converters in order to decrease the impact of the noise in the system performance. The Dual Active Bridge and the Buck converters are used to illustrate the proposed methodology. The proposed controller is designed using the stochastic augmentation methodology that provides a Proportional-Integral-Derivative (PID) controller, in the Reference Signal Tracking (RST) structure, the ability to adequately treat noise of a stochastic nature. The GMV control reduces the variance of the control signal and in turn leads to a better output characteristic. The simulation results show that the GMV controller achieve better performance in the sense of minimum variance and energy consumption in comparison with a robust PID controller.

Cascaded converters are used to satisfy the different voltage levels that loads need. Instability problems in cascaded systems may occur due to the interaction of Point-of-Load (POL) converters. POL converters exhibit the important characteristic of almost-perfect regulation at the output terminals independent of the input perturbations. However, such characteristic reflects at the input terminal as a constant power load (CPL). CPL exhibits incremental negative resistance behavior causing undesired oscillations and a high risk of instability in interconnected converters. In this paper, the cascaded converter system consists of a Dual Active Bridge (DAB) DC-DC converter that maintains a regulated DC voltage on the intermediate bus and a POL DC-DC Buck converter that acts as a CPL. Aiming to ensure system stability and effectively mitigate oscillations effects in a cascaded system, this paper proposes a Robust Feedback Linearization Control to regulate the intermediate DC bus voltage. Simulation tests are performed by using a MATLAB/Simulink simulator to show the robustness and effectiveness of the proposed controller. The simulation results show that the proposed control approach ensures robust control performance and stability with a minor performance degradation compared to a Robust Control approach, Feedback Linearization Control approach, and Classical Control approach.

In the 1990s Teixeira studied discontinuous piecewise-smooth (DPWS) dynamical systems in R 3 , whose state space is divided in two open regions by a plane acting as the switching manifold, and presenting two lines of quadratic tangency, one for each involved vector field. We call T-singularity (Teixeira singularity) the point of transverse intersection of the quadratic tangency lines that are of the invisible type. In this paper, we analyze DPWS systems that present two branches of T-singularities. In our approach we consider the cases where either a pseudo-equilibrium collides to just one of the two T-singularities or the two T-singularities (and also a pseudo-equilibrium between them) collides in a single point. As a consequence of these bifurcations, until now not covered by the literature, we can observe the birth of limit cycles, determine their stability and provide an upper limit for the number of limit cycles that occur in this scenario.

Resonant sensors are widely employed in several applications, and resonant cavity sensors have advantages when noninvasive and non-destructive measurements are required. In this technology, the resonant frequency of the sensor is used to estimate different measurement parameters, since it varies according to the permittivity of the material under test. In this paper, a resonant frequency tracking system, combining a resonant cavity sensor and a phase-locked loop circuit, is investigated. The system has a quadrature phase detector being able to estimate both, phase and magnitude information, and is well suited for applications involving water as a material under test. A complete description of the measurement system combining experimental results with theoretical models, previously reported in the literature, is accomplished. Such theoretical models are based on the amplitude-phase dynamics and assume that the sensor is modeled as a linear resonator. Hence, a semi-empirical modeling is elaborated and the validation results precisely demonstrate the reliability of the modeling, proving to be very useful for further analysis.

The strive to increase the energy yield of photovoltaic (PV) power systems has made PV module integrated dc–dc converters (dc-MICs) a reality of modern PV plants. These converters regulate their input voltage, and their dynamic behavior is heavily influenced by the non-linear characteristic of the PV module. The regulation of the PV module voltage and average inductor current by means of a linear cascaded controller is a popular control technique, simplifying the converter dynamics, and providing inherent current limiting; however, it is prone to instability depending on the interaction between the PV source and the interfacing converter, as well as the value of the controller parameters. These factors present a clear challenge for control design; moreover, the converter transient response undesirably depends on the PV module operating point. In order to solve these issues, while maintaining regulation of PV module voltage and average inductor current, this paper proposes to adopt a non-linear controller designed with the feedback linearization control (FLC) technique. The control laws are derived and implemented in a non-inverting buck–boost dc module integrated converter, as this is a favorite topology for the PV interfacing application. A digitally controlled converter prototype is built and used to obtain experimental results, where the FLC technique is compared with a linear cascaded control technique. The results confirm the superior performance of the presented FLC technique, which is robust and able to regulate the converter input voltage with fast and consistent dynamics, regardless of the PV module or load operating conditions.

The electronic circuit of a DC–DC boost power converter under a specific sliding mode control strategy is analyzed. This circuit is modeled as a discontinuous piecewise linear three-dimensional dynamical system, whose state space is divided into two open regions by a plane acting as the switching manifold. This system displays sliding motion confined to the switching manifold and limited by two straight lines where lie the points of tangency, one for each involved linear vector field. Such tangency lines can intersect transversally on a invisible two-fold point known as Teixeira singularity. Our goal is to investigate an interesting bifurcation that occurs on the Teixeira singularity, involving both a pseudo-equilibrium point and a crossing periodic orbit. This bifurcation, named TS-bifurcation, occurs when a pseudo-equilibrium point of the discontinuous piecewise linear system, capable of moving between the attractive and repulsive sliding regions as a result of the change in a parameter, collides with the Teixeira singularity. Simultaneously, a periodic orbit arises from the Teixeira singularity crossing the switching manifold in two points. Apart from the TS-bifurcation characterization in the DC–DC converter, we have numerically detected other non-local phenomena like a saddle-node bifurcation of crossing limit cycles. Experimental results to illustrate the effects of the TS-bifurcation on the dynamics of a power electronic converter are also shown.

The non-inverting buck-boost converter has emerged as one of the most promising topologies for distributed maximum power point tracking applications. Pressure to reduce cost and volume of photovoltaic module integrated converters often compels bootstrap capacitor type gate drivers. The bootstrap technique is a simple and economical solution to create a floating power supply for high-side gate drivers. However, it comes with a major challenge, as the low-side switch must be periodically turned on , to recharge the high-side bootstrap capacitor. In the buck and the boost mode, one of the switching legs of the converter must be held with the high-side switch on , which eventually discharges the high-side capacitor. When the non-inverting buck-boost input voltage is regulated by means of a single voltage loop, recharging the bootstrap capacitor causes an undesired ripple in the PV module voltage, degrading the regulation quality. In order to mitigate this problem, this paper proposes a cascaded control technique, entailing regulation of the PV module voltage and inductor current. The cascaded controller dramatically improves the rejection of the disturbance induced by the periodic recharge of the bootstrap capacitor, thanks to the fast action of the current loop, regulating the average value of the inductor current. Converter transfer functions and controller design are derived and validated. Experimental results clearly show that the cascaded control scheme outperforms the traditional voltage control scheme, resulting in a better regulation of the PV module voltage. This main advantage comes at the cost of an additional measurement of the average inductor current.

Germ granules are biomolecular condensates that form in germ cells of all/most animals, where they regulate mRNA expression to promote germ cell function and totipotency. In the adult Caenorhabditis elegans germ cell, these granules are composed of at least four distinct sub-compartments, one of which is the Z granule. To better understand the role of the Z granule in germ cell biology, we conducted a genetic screen for genes specifically required for Z granule assembly or morphology. Here, we show that zsp-1, which encodes a low-complexity/polyampholyte-domain protein, is required for Z granule homeostasis. ZSP-1 localizes to the outer surface of Z granules. In the absence of ZSP-1, Z granules swell to an abnormal size, fail to segregate with germline blastomeres during development, and lose their liquid-like character. Finally, ZSP-1 promotes piRNA- and siRNA-directed gene regulation and germline immortality. Our data suggest that Z granules coordinate small RNA-based gene regulation to promote germ cell function and that ZSP-1 helps/is need to maintain Z granule morphology and liquidity.

One of the most interesting typical singularity observed in 3D piecewise-smooth dynamical systems is the so called T-singularity (Teixeira Singularity). Throughout this paper, we study a Fold bifurcation involving two T-singularities that, as far as we know, has not yet been fully addressed in the literature. In this bifurcation both T-singularities collide and then disappear when a system parameter is varied. At the collision point appears a type of non-generic T-singularity. For this study we use a normal form and we apply the standard analysis for such class of systems, based on the analysis of the sliding dynamics (Filippov’s sliding vector field) and the crossing dynamics (first return map) occurring on the switching boundary. We fully describe the unfolding dynamics of the Fold bifurcation under study and also analyze the existence, stability and bifurcations of invariant manifolds in this scenario.

An important parameter in the study of multiphase flows is the volume fraction, which is defined by the ratio between the volume occupied by a specific phase and the total volume of the mixture. This is a fundamental parameter that appears in most of the flow models and frequently is applied to assist flow pattern identification routines as well as to estimate two-phase flow rates. This paper presents a water volume fraction estimation method based on electrical capacitance tomography (ECT) called electrical capacitance tomometry (ECTM). An electrode combining strategy using rotating electrodes has been implemented to transform a 12-electrode sensor into a 2-electrode sensor, simplifying the measurement hardware circuit. This strategy increases the signal-to-noise ratio and consequently improves the measurement quality. Moreover, the proposed ECTM method needs just 12 capacitance measurements and three iteration steps to converge, providing confidence in real-time applications. Simulations using COMSOL Multiphysics software and experimental results allow us to evaluate the performance of the proposed water volume fraction measurement method which presents smaller absolute errors than the conventional ECT method.

The noninverting buck–boost converter has attracted significant attention in the photovoltaic (PV) module integrated application, as it offers high efficiency while maintaining a low cost and a simple topology. When this converter is employed, special care must be taken at the transition between buck and boost operating modes, as a dead-zone in the voltage transfer function can cause abrupt perturbations in the controlled voltage, decreasing the regulation quality and ultimately lowering the power conversion efficiency. In this paper, a new dead-zone compensation technique is proposed with the scope of smoothing the transition between operating modes, eliminating the voltage ripple and improving the regulation performance, while maintaining high efficiency. The converter under analysis is studied together with its gate driving circuit, which is based on a bootstrap capacitor power supply for the high-side switches. The proposed dead-zone compensation technique is deduced by using the principle of maintaining the ideal voltage gain function across the converter operating range. The technique is analyzed, implemented and tested on a purposely built PV module integrated noninverting buck–boost converter. The experiments reveal a sensible improvement of the voltage regulation during mode transition, confirming the effectiveness of the proposed technique and its fitness for the PV application.

This paper is concerned with boundary stabilization of thermoacoustic oscillations in the Rijke tube. This system consists of a vertical tube open in both ends and a heater placed in the lower half of the tube. A speaker placed under the tube is used as actuator while a microphone placed near the top of the tube provides the pressure measurement. To study this problem we consider that the mathematical model takes the form of two interconnected compartments: one for the cold zone and other for the hot zone. The control input is applied on the left boundary condition of the cold zone. From this model we derive an irrational transfer function to design a stabilizing boundary control in the frequency domain. In particular, we derive necessary and sufficient conditions for the input-output stability through the use of Nyquist-type test. Experimental results show the effectiveness and real-life applicability of the method.

In this paper, Hopf and homoclinic bifurcations that occur in the sliding vector field of switching systems in R 3 are studied. In particular, a dc–dc boost converter with sliding mode control and washout filter is analyzed. This device is modeled as a three-dimensional Filippov system, characterized by the existence of sliding movement and restricted to the switching manifold. The operating point of the converter is a stable pseudo-equilibrium and it undergoes a subcritical Hopf bifurcation. Such a bifurcation occurs in the sliding vector field and creates, in this field, an unstable limit cycle. The limit cycle is connected to the switching manifold and disappears when it touches the visible–invisible two-fold point, resulting in a homoclinic loop which itself closes in this two-fold point. The study of these dynamic phenomena that can be found in different power electronic circuits controlled by sliding mode control strategies are relevant from the viewpoint of the global stability and robustness of the control design.

In many industrial activities, the so-called multiphase flow is commonly found, which denotes the simultaneous stream of two or more distinct substances. A typical example is oil-gas and/or oil-water mixtures flowing through production pipelines in the petroleum industry. Flow behavior often determines the efficiency and safety of plants and equipment where multiphase flow is present. Therefore, monitoring of such flows and derived parameters is highly desired in many applications. In the past, a number of measurement techniques and instruments have been developed and applied [1]. Multiphase flow instrumentation relies on a number of physical principles, including common instrumentation and measurements that are based on electrical, sonic or radiation methods. This paper shows three different sensors currently being developed in Brazil, which are based on electrical measurements. They range from a simple phase concentration measurement up to multiphase flow imaging. Each instrument offers a tailored solution with potential either for field applications or for detailed multiphase flow investigation in pilot plant studies.

Mobile genetic elements threaten genome integrity in all organisms. MUT-2/RDE-3 is a ribonucleotidyltransferase required for transposon silencing and RNA interference (RNAi) inC. elegans. When tethered to RNAs in heterologous expression systems, RDE-3 can add long stretches of alternating non-templated uridine (U) and guanosine (G) ribonucleotides to the 3’ termini of these RNAs (polyUG or pUG tails). Here, we show that, in its natural context inC. elegans, RDE-3 adds pUG tails to transposon RNAs, as well as to targets of RNAi. pUG tails with more than 16 perfectly alternating 3’ U and G nucleotides convert otherwise inert RNA fragments into agents of gene silencing. pUG tails promote gene silencing by recruiting RNA-dependent RNA Polymerases (RdRPs), which use pUG-tailed RNAs as templates to synthesize small interfering RNAs (siRNAs). Cycles of pUG RNA-templated siRNA synthesis and siRNA-directed mRNA pUGylation underlie dsRNA-directed transgenerational epigenetic inheritance in theC. elegansgermline. Our results show that pUG tails convert RNAs into transgenerational memories of past gene silencing events, which, we speculate, allow parents to inoculate progeny against the expression of unwanted or parasitic genetic elements.

This paper addresses the modeling and control of a novel Forward dc-dc converter with multiplexer for active voltage cell balancing of a bank of Lithium-Ion batteries. The modeling of the converter is developed using a state-space averaging model. The control system is based on a cascade feedback linearization approach for the forward converter and an event-driven control based on the voltage of the cells. Simulation results in time-domain allow to evaluate the performance of the proposed voltage balancing system control.

In this paper we investigate the preheating temperature control problem in 3D printers based on the selective laser sintering (SLS) technology. We formulate the process as a temporal sequence of diffusion partial differential equations (PDEs), where each of these PDEs represent the temperature distribution of the layers and the control variable appears at one of the boundary conditions. We propose a full-state feedback control law, an state observer and the associated output feedback control law for the boundary input. The associated output feedback controller ensures the exponential stability of the estimation error in the ${{\mathcal{L}}_2}$ norm. The theoretical results were tested through numerical simulations and experiments. These results are promising as a method for industrial implementation of the backstepping controller.

This paper presents the design and evaluation of a robust controller, based on linear programming, Kharitonov’s theorem and Chebyshev’s theorem, in order to regulate the output voltage of the Dual Active Bridge (DAB) converter under parametric uncertainties. These robust control approach take into account all possible uncertainties in the system such as load and input voltage variations, improving the system performance. The converter is controlled by single phase-shift-modulation (PSM) with a fixed duty cycle. The proposed controller ensures robust control performance and stability with a minor performance degradation compared to an interval robust controller and a conventional controller. Simulation results are presented to validate the robustness and effectiveness of the proposed controller.