Local Loop Research Articles

Recurrent Feedback Loops in Associative Learning

In this issue of Neuron, Gao et al. (2016) report on a little-studied feedback pathway from the cerebellar nuclei back to the cerebellar cortex. They find that it contributes to associative conditioning and execution of learned movements, highlighting a role for local feedback loops in the brain.

The Effect of Local Melting of DNA on DNA Loop Formation

Statistical mechanics of double-stranded DNA (dsDNA) is well described by the wormlike chain model (WLC) which assumes a harmonic bending potential. Such smooth bending potential may no longer be valid for large bending angles to form small loops (< 100 bp). Instead, DNA may rely on rare structural transitions such as local melting (opening) of base pairs to lower the energetic cost. In theory, open base pairs called bubbles can increase the looping probability of short DNA molecules by a few orders of magnitude, but a robust experimental validation of this theoretical prediction is lacking. Here, we investigated the correlation between local melting probability and looping dynamics of dsDNA using single-molecule fluorescence resonance energy transfer (FRET). We designed two groups of short DNA molecules with low and high melting probabilities around their center and measured their looping and unlooping rates in equilibrium. Our data allow rigorous tests of meltable wormlike chain (MWLC) models at short length scales for setting the lower limit for the free energy of bubble formation.

Local Probing of Ferroelectric and Ferroelastic Switching through Stress‐Mediated Piezoelectric Spectroscopy

Strain effects have a significant role in mediating classic ferroelectric behavior such as polarization switching and domain wall dynamics. These effects are of critical relevance if the ferroelectric order parameter is coupled to strain and is therefore, also ferroelastic. Here, switching spectroscopy piezoresponse force microscopy (SS‐PFM) is combined with control of applied tip pressure to exert direct control over the ferroelastic and ferroelectric switching events, a modality otherwise unattainable in traditional PFM. As a proof of concept, stress‐mediated SS‐PFM is applied toward the study of polarization switching events in a lead zirconate titanate thin film, with a composition near the morphotropic phase boundary with co‐existing rhombohedral and tetragonal phases. Under increasing applied pressure, shape modification of local hysteresis loops is observed, consistent with a reduction in the ferroelastic domain variants under increased pressure. These experimental results are further validated by phase field simulations. The technique can be expanded to explore more complex electromechanical responses under applied local pressure, such as probing ferroelectric and ferroelastic piezoelectric nonlinearity as a function of applied pressure, and electro‐chemo‐mechanical response through electrochemical strain microscopy.

The relation between local hysteresis losses and remanent magnetic fields in HTSC films

Various critical state models have been developed to understand the hysteresis loss mechanism of high-temperature superconducting (HTSC) films. The analytic relation between the hysteresis loss and the remanent field was obtained based on Bean's critical state model for thin films in the full-penetration case. Furthermore, numerical calculation of local hysteresis loops was carried out by Kim's critical state model. In this paper, we investigated local hysteresis losses for a GdBCO coated conductor by using low-temperature scanning Hall probe microscopy and reproduced the experimental results by applying the critical state model. Because of the demagnetizing effect in thin films, analysis of local hysteresis losses can be useful approach to understand of total hysteresis losses.

Recovery of Image through Alamouti Channel with Incorporation of RSA Algorithm

In many applications, it is necessary to transmit images at a remote station, where wired Internet service is not available. In this case, wireless local loop (WLL) can help in making wireless link between one end node of the internet and remote service center. In such link, the communication is heavily affected by large and small scale fading; hence the received signal experiences huge distortion in case of forward error correction. Otherwise, huge service delay arises due to frequent negative acknowledgements. To combat the situation, we can choose Alamouti channel of full rate and fully orthogonal space-time block code (OSTBC). Our aim is to transmit images through Alamouti channel and to observe the quality of the recovered image, in context of bit error rate (BER). We have also observed the impact of fading and additive white Gaussian noise (AWGN) on the image without application of error correction or detection technique of channel coding. To ensure security, we apply the RSA algorithm on each pixel prior transmitting and decrypt them at the receiving end, where we found no impairment from the algorithm. Finally, we observe that the relative performance of the system changes digital modulation schemes.

Modeling Protein Loop Structure by Cyclic Coordinate Descent-based Approach.

In both predicting protein loop structure and flexible areas in a docking interface, modeling local loop conformation plays a vital role. We address the challenge with a topological manipulation method based on the cyclic coordinate descent (CCD) algorithm. The protein loop conformation sampler (LMbCCD2) presented here allows us to move some key points of the loop toward some specific positions. We test the method's performance on sets of loops, and the results show that LMbCCD2 accurately controls the loop's topology. At last we use LMbCCD2 on flexible protein-peptide docking, and it shows that LMbCCD2 can improve the accuracy of flexible peptide folding and the full docking result.

Economic Regulation of the Telecommunications Sector in South Africa: 2009-2014

South Africa's electronic communications sector regulator, the Independent Communications Authority of South Africa (ICASA), has a mixed track record in carrying out its mandate. ICASA is part of a regulatory system for the telecommunications sector, that may be characterised as dysfunctional for the following reason: ICASA is not sufficiently independent from government. While regulated entities are generally partially state owned, this does create a conflict of interest for government. Nonetheless, ICASA has had some successes, where the interests of state-owned enterprises coincide with those of consumers. Its interventions in markets for voice services during the course of Telkom Mobile's entry into the market, for example, have resulted in retail voice price reductions of more than 30%. Now that problems relating to voice services markets have largely been resolved through the call termination rate intervention, ICASA needs to shift its focus to markets for broadband services in order to ensure that South Africa becomes more competitive relative to its peers through unbundling the local loop and assigning spectrum for broadband. In order to achieve this, Telkom needs to be fully privatised in order to reduce government pressure to delay local loop unbundling (LLU) and Telkom's wholesale and retail fixed-line operations should be functionally separated. ICASA needs to be further insulated from political interference and be properly resourced through industry levies and fees. Furthermore, a single appellate body for economic regulators ought to be established in order to improve accountability of the regulators and improve outcomes in the sector.

Leader-Following Coordination of Nonlinear Agents Under Time-Varying Communication Topologies

This paper deals with the problem of synchronizing the outputs of a set of nonlinear agents that exchange information through a time-varying communication network in a leader-follower configuration. The dynamics of the individual followers may differ from each other and from that of the leader. The information exchange between the leader and (a limited fraction of) the followers as well as between neighboring followers only consists of the relative values of the output variables that are to be synchronized. The theory of output regulation for nonlinear systems is used to design decentralized controllers embedding an internal model of the leader dynamics. Then, under mild connectivity hypotheses, it is shown how synchronization between the local control loops can be achieved.

Pseudo Youla–Kucera parameterization with control of the waterbed effect for local loop shaping

This paper discusses a discrete-time loop shaping algorithm for servo enhancement at multiple wide frequency bands. Such design considerations are motivated by a large class of practical control problems such as vibration rejection, active noise control, and periodical reference tracking; as well as recent novel challenges that demand new design in the servo technologies. A pseudo Youla–Kucera parameterization scheme is proposed using the inverse system model to bring enhanced control at selected local frequency regions. Design methodologies are created to control the waterbed amplifications that come from the fundamental limitations of feedback control. Finally, simulation and experimental verification are conducted in precision control and semiconductor manufacturing.

Use of localized loops for the rehabilitation of on-demand pressurized irrigation distribution systems

Irrigation distribution systems are generally branched. They can be designed using optimization models that minimize the cost of the pipes under a number of constraints. Urban water distribution systems are generally designed as a series of interconnected closed loops which provide these systems with sufficient capability to overcome local physical failures . However, they enormously increase both the computational effort and the network cost. This research proposes an innovative approach where localized loops are used as a cost-effective solution to improve the performance of branched on-demand pressurized irrigation systems. The position of a localized loop is identified based on the overall performance improvement that can be achieved. This strategy, when necessary, also involves the increase in significantly smaller pipe diameters, where performance improvement cannot occur solely by introducing localized loops. The new approach was applied to an irrigation district in Southern Italy operating on demand. It demonstrated its effectiveness by improving the system’s overall hydraulic performance, while achieving more than 80 % cost savings, as compared to the classical rehabilitation approach. A dedicated software package that may serve, with further improvements, as a DSS platform, was developed and used to perform an accurate hydraulic performance analysis of the irrigation system.

The Real‐Time Simulation of Doppler Spread in Wireless Mobile Environment by RF Circuits

The time-varying characteristic of wireless channel under the high-speed mobile environments in tunnels causes the Doppler spread to the transmitted signals, which affects the performance of wireless communication systems. The real-time Doppler effect simulation methodology directly based on Radio frequency (RF) circuits is proposed to simulate different Doppler spread effects in real environments. Mixers and a Digital-to-analog (DA) converter circuit are utilized to spread the spectrum of RF signals. A PC platform with the interface written in C# is configured to control the spectrum spread parameters. This radio channel emulator with the proposed methodology can replace the expensive fading simulating instruments with only 25.1ns system delay. Such an emulator has been applied to test the Multi-carrier wireless information local loop (McWiLL) wireless vehicle communication system in the laboratory to meet the requirement of metro Communication based train control (CBTC) system.

Alternance method of structural-parametric synthesis of cascade automatic control systems

This work is devoted to the technique of solving the problem of structural-parametric synthesis of typical controllers in a multiloop cascade automatic control system, which is developed on the basis of the alternance method of parametric optimization that provides the maximum degree of invariance of local control loops relative to external perturbations with given limitations on the peak of amplitude-frequency characteristics of closed loops of the synthesized automatic control system. The task of optimizing the subsystem for controlling the fuel oil temperature in a multiloop control system of primary oil refining on an atmospheric and vacuum crude distillation unit is considered as an example, which is of independent interest.

Graph-based models for real-time workload: a survey

This paper provides a survey on task models to characterize real-time workloads at different levels of abstraction for the design and analysis of real-time systems. It covers the classic periodic and sporadic models by Liu and Layland et al., their extensions to describe recurring and branching structures as well as general graph- and automata-based models to allow modeling of complex structures such as mode switches, local loops and also global timing constraints. The focus is on the precise semantics of the various models and on the solutions and complexity results of the respective feasibilty and schedulability analysis problems for preemptable uniprocessors.

Abstract 2367A: CSF1-dependent macrophage-stromal fibroblast interactions determine tumor stability

Abstract Tissue homeostasis is dependent on specialized ‘accessory’ cell types, which support the primary physiologic function of tissue parenchymal ‘client’ cells by performing essential accessory functions. We propose that metazoan tissues can be reduced to a minimal unit of three accessory subsets—tissue-resident macrophages, stromal fibroblasts, and endothelial cells—whose function and tissue composition is mutually dependent on CSF1R, PDGFRα, or VEGFR2 signaling from the Type III/V RTK family via their cognate growth factor ligands MCSF/IL34, PDGFα/β, or VEGFα, respectively. While each subset-specific growth factor is known to be essential for survival, proliferation, and differentiation, it is unknown to what extent growth factor supply is regulated cell extrinsically to create a stable tissue, and how accessory cell composition adapts to changes in tissue demands. Less is known of how tumor stability is disrupted by attenuation of growth-factor dependent stroma-stroma cues between tumor-associated macrophages (TAMs), cancer associated fibroblasts (CAFs), and angiogenic endothelial cells (ECs), although tumor-stromal interactions are increasingly recognized as hallmarks of the heterogeneous cancer ‘organ.’ We hypothesized that growth factor supply and demand is controlled locally and adaptively in response to sensing/reporting interactions between these accessory subsets. To test this hypothesis, we developed an in vitro model of stroma-stroma growth-factor interactions via co-culture of primary bone marrow-derived macrophages (BMDMs) and mouse embryonic fibroblasts (MEFs). Data from co-culture, conditioned media transfer and stimulation assays demonstrates a 2-loop negative feedback circuit where: 1) stromal fibroblasts upregulate CSF1, chemokine ligands and ECM components in response to soluble signals (PDGFβ, TGFβ, IL1α) produced by MCSF-starved macrophages, and 2) PDGFβ is repressed as stromal cell:macrophage ratio increases, suggesting that macrophages sense a stromal derived ‘density factor’ and repress production of growth factors for stroma fibroblasts. Furthermore, study of in vivo transplantable and spontaneous melanoma models of the minimal tissue unit, demonstrate that destabilizing the tumor equilibrium by genetic and pharmacologic ablation of tumor and subset-specific CSF1/CSR1R and other RTK signaling can decrease tumor volume, alter accessory subset (TAMs/CAFs/ECs) ratios, and attenuate subset transcription, in a manner predictable by homeostatic growth-factor control circuits. We present a novel framework for understanding how tissue—and tumor microenvironment—composition and function is regulated by adaptable local control loops between parenchyma and accessory subsets, and propose alternative mechanisms of targeting the tumor microenvironment to destabilize the tumor ‘organ.’ Citation Format: Jeremy B. Jacox, Ruslan Medzhitov. CSF1-dependent macrophage-stromal fibroblast interactions determine tumor stability. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2367A. doi:10.1158/1538-7445.AM2015-2367A

Noise canceling LNA with gain enhancement by using double feedback

In this paper we present a balun low noise amplifier (LNA) in which the gain is boosted by using a double feedback structure. The circuit is based on a conventional balun LNA with noise and distortion cancelation. The LNA is based on the combination of a common-gate (CG) stage and common-source (CS) stage. We propose to replace the load resistors by active loads, which can be used to implement local feedback loops (in the CG and CS stages). This will boost the gain and reduce the noise figure (NF). Simulation results, with a 130nm CMOS technology, show that the gain is 24dB and the NF is less than 2.7dB. The total power dissipation is only 5.4mW (since no extra blocks are required), leading to a figure-of-merit (FOM) of 3.8mW−1 using a nominal 1.2V supply. Measurement results are presented for the proposed DFB LNA included in a receiver front-end for biomedical applications (ISM and WMTS).

Multi-objective monitoring of closed-loop controlled systems using adaptive LASSO

Statistical process control detects nonrandom deviations from a normal distribution. However, most industrial processes are equipped with feedback control loops to reject such disturbances. Hence it is the failure or performance degradation that we should detect instead of mere sensor data patterns that show deviations from normal. In this paper, a multi-objective monitoring approach is proposed to monitor both the system stability and performance. First, closed-loop output data are fitted with an autoregressive moving average model with exogenous inputs (ARMA(X)), using adaptive least absolute shrinkage and selection operator (LASSO). The system stability can be monitored using the largest absolute value of the roots of AR terms. The performance of feedback controller can be monitored based on the Minimum-Variance (MV) principles. The proposed approach was applied to several simulation examples to show that the above two monitoring objects are only sensitive to the faults in processes, but not to disturbances that can be handled by the controller. The ability of the method to localized control loop failure was demonstrated using the Tennessee–Eastman benchmark problem. In addition, we found that the method was able to identify the failure of the outer loop while the inner loop is still performing in a cascade control.

Remote-sensing satellite ground station evaluation using QPSK emulator with test pattern and PRBS generation

In order to validate the performance of X-band (8000–8400 MHz) remote-sensing satellite receive chain, when the satellite is not in the vicinity of ground station, local loop end–end evaluation tests are mandatory to certify the RF downlink and base band receive chain performance. A customised test patterns compatible to IRS satellite series and PRBS sequence are generated, which are modulated using QPSK emulator to check and verify the satellite downlink chain performance. The design and implementation are done using novel digital techniques, and QPSK modulator is integrated with Test pattern and PRBS generator using state-of-art FPGAs. The QPSK emulator output is connected to high-speed fibre optic link which transfers the signal to near field bore-site antenna system. The test signal is thus up converted from 2557.5 MHz (S-band) frequency to required satellite carrier frequency of 8212.5 MHz; the emulated test signal is radiated from bore-site antenna, which simulates real-time satellite data transmission from space. Thus, the signal received by the parabolic dish antenna is down converted to 720 MHz, demodulated, bit synchronized, clock recovered, and frame synchronized. The evaluation of frame sync errors is done for good video data quality check. Also in the QPSK emulator, there is option of PRBS mode. Hence, using this option, the RF downlink and receive chain are evaluated for good Bit error rate (BER). The BER requirement is 1 error (tolerable) in 106 Million bits. The QPSK emulator has the provision to support different frequencies and data rates corresponding to all IRS satellite missions.

Multidimensional smooth loops with universal elasticity

Let be a universal (isotopically invariant) identity that is derived from the elasticity identity . One of the authors has previously shown that a) each local loop of dimension with identity (briefly, a loop ) is a smooth middle Bol loop of dimension ; b) smooth two-dimensional loops are Lie groups; c) up to isotopy, there exist only two three-dimensional loops : the loops and . In this paper, the loops and are extended to the multidimensional case. The fact that each smooth loop of dimension corresponds to a unique multidimensional three-web on a manifold of dimension is key to our work. In addition, the class of loops under investigation is characterized by the fact that the torsion tensor of the corresponding web has rank 1 (that is, the algebra generated by this tensor has a one-dimensional derived algebra). This enables us to express the differential equations of the problem in an invariant form. The system of equations thus obtained was found to be amenable to integration in the most general case, and the equations of the required loops have been obtained in local coordinates. Bibliography: 17 titles.

Tailoring ergodicity through selective A-site doping in the Bi1/2Na1/2TiO3–Bi1/2K1/2TiO3 system

The morphotropic phase boundary composition Bi1/2Na1/2TiO3-20 mol. % Bi1/2K1/2TiO3 was chosen as initial material to do selective A-site aliovalent doping replacing Na and K by 1 at. % La, respectively. The materials were studied macroscopically by measuring dielectric and electromechanical properties. The Na-replaced material has a lower freezing temperature Tfr, lower remanent polarization and remanent strain, and thus a higher degree of ergodicity than the K-replaced material. These results are contrasted with local poling experiments and hysteresis loops obtained from piezoresponse force microscopy. The faster relaxation of the tip-induced local polarization and the lower remanent state in bias-on and -off loops confirm the higher degree of ergodicity of the Na-replaced material. The difference in functional properties is attributed to small variations in chemical pressure achieved through selective doping. Raman results support this working hypothesis.

A 13.56 MHz Wireless Power Transfer System With Reconfigurable Resonant Regulating Rectifier and Wireless Power Control for Implantable Medical Devices

A 13.56 MHz wireless power transfer system with a 1X/2X reconfigurable resonant regulating (R $^3$ ) rectifier and wireless power control for biomedical implants is presented. Output voltage regulation is achieved through two mechanisms: 1) a local PWM loop at the secondary side controls the duty cycle of mode-switching of the rectifier between the 1X and 2X modes; and 2) a global control loop obtains the mode-switching information from the secondary side and send it back to the primary side through the wireless channel and adjusts the transmitter power of the primary coil to adapt to load and coupling variations. Two novel backscattering uplink techniques are proposed for fast and energy-efficient data feedback. The first is for general data transmission using Manchester code; and the second is for fast duty cycle feedback to cater for fast load-transient responses. Stability analysis of the entire system with the two control loops is also presented. The primary transmitter and the secondary R $^3$ rectifier are fabricated in 0.35 µm CMOS process with the digital control circuits implemented using FPGA. The measured maximum received power and receiver efficiency are 102 mW and 92.6%, respectively. For load transients, the overshoot and the undershoot are approximately 110 mV and the settling times are less than 130 µs.