Circuit Geometry Research Articles

Statistical mechanics of spike events underlying phase space partitioning and sequence codes in large-scale models of neural circuits.

Cortical circuits operate in an inhibition-dominated regime of spiking activity. Recently, it was found that spiking circuit models in this regime can, despite disordered connectivity and asynchronous irregular activity, exhibit a locally stable dynamics that may be used for neural computation. The lack of existing mathematical tools has precluded analytical insight into this phase. Here we present analytical methods tailored to the granularity of spike-based interactions for analyzing attractor geometry in high-dimensional spiking dynamics. We apply them to reveal the properties of the complex geometry of trajectories of population spiking activity in a canonical model of locally stable spiking dynamics. We find that attractor basin boundaries are the preimages of spike-time collision events involving connected neurons. These spike-based instabilities control the divergence rate of neighboring basins and have no equivalent in rate-based models. They are located according to the disordered connectivity at a random subset of edges in a hypercube representation of the phase space. Iterating backward these edges using the stable dynamics induces a partition refinement on this space that converges to the attractor basins. We formulate a statistical theory of the locations of such events relative to attracting trajectories via a tractable representation of local trajectory ensembles. Averaging over the disorder, we derive the basin diameter distribution, whose characteristic scale emerges from the relative strengths of the stabilizing inhibitory coupling and destabilizing spike interactions. Our study provides an approach to analytically dissect how connectivity, coupling strength, and single-neuron dynamics shape the phase space geometry in the locally stable regime of spiking neural circuit dynamics.

Calibration technique for rotating PCB coil magnetic field sensors

A high-accuracy calibration of inductive coil sensors based on Printed Circuit Board (PCB), commonly used in rotating coil field measurements of particle accelerator magnets, is presented. The amplitude and phase of signals with and without main field suppression are compared in order to simultaneously determine both the PCB rotation radius and the transverse offset of its plane from rotation center. The accuracy of planar wire placement on the PCB boards is exploited to create loops highly precise in area which rotate at different radii. Such an area reproducibility and circuit geometry allow the suppression of the fundamental field, enabling the calibration, as well as improving signal resolution and mitigating vibration effects. Furthermore, the calibration can be performed dynamically, in-situ during measurements. Calibration accuracy is validated experimentally by referencing the PCB positions with a Coordinate Measuring Machine (CMM).

All-optical generation and ultrafast tuning of non-linear spin Hall current

Spin Hall effect, one of the cornerstones in spintronics refers to the emergence of an imbalance in the spin density transverse to a charge flow in a sample under voltage bias. This study points to a novel way for an ultrafast generation and tuning of a unidirectional nonlinear spin Hall current by means of subpicosecond laser pulses of optical vortices. When interacting with matter, the optical orbital angular momentum (OAM) carried by the vortex and quantified by its topological charge is transferred to the charge carriers. The residual spin-orbital coupling in the sample together with confinement effects allow exploiting the absorbed optical OAM for spatio-temporally controlling the spin channels. Both the non-linear spin Hall current and the dynamical spin Hall angle increase for a higher optical topological charge. The reason is the transfer of a higher amount of OAM and the enhancement of the effective spin-orbit interaction strength. No bias voltage is needed. We demonstrate that the spin Hall current can be all-optically generated in an open circuit geometry for ring-structured samples. These results follow from a full-fledged propagation of the spin-dependent quantum dynamics on a time-space grid coupled to the phononic environment. The findings point to a versatile and controllable tool for the ultrafast generation of spin accumulations with a variety of applications such as a source for ultrafast spin transfer torque and charge and spin current pulse emitter.

The MTA: An Advanced and Versatile Thermal Simulator for Integrated Systems

Fast and accurate thermal analysis is crucial for determining the propagation of heat and tracking the formation of hotspots in integrated circuits (ICs). Existing academic thermal analysis tools primarily use compact models to accelerate thermal simulations but are limited to linear problems on relatively simple circuit geometries. The Manchester Thermal Analyzer (MTA) is a comprehensive tool that allows for fast and highly accurate linear and nonlinear thermal simulations of complex physical structures including the IC, the package, and the heatsink. The MTA is targeted for 2.5/3-D IC designs but also handles standard planar ICs. The MTA discretizes the heat equation in space using the finite element method and performs the time integration with unconditionally stable implicit time stepping methods. To improve the computational efficiency without sacrificing accuracy, the MTA features adaptive spatiotemporal refinement. The large-scale linear systems that arise during the simulation are solved with fast preconditioned Krylov subspace methods. The MTA supports thermal analysis of realistic integrated systems and surpasses the computational capabilities and performance of existing academic thermal simulators. For example, the simulation of a processor in a package attached to a heat sink, modeled by a computational grid consisting of over 3 million nodes, takes less than 3 min. The MTA is fully parallel and publicly available. 1

Regulation of the temperature in the ampoule channel with natural circulation of coolant

It has been shown by calculations that it is possible to extend considerably the capabilities for control of temperature conditions in an ampoule channel with natural coolant circulation, using the proposed hydraulic circuit layout, on samples during irradiation in the SM-3 reactor reflector cell by changing the circulation circuit geometry through the arrangement of a bypass heat removal line formed in the upper part above the flow limiter as compared to control only by changing the thermal conductivity of the gas gap in the channel body (through changing the gas pressure or composition). The ampoule channel test conditions, layout and simulation model for thermal-hydraulic analysis using the RELAP5/MOD3.2 code are presented. An investigation was conducted to study the effects of the bypass cooling circuit on the temperature conditions during irradiation of samples in an ampoule channel. The bypass flow rate change is achieved by varying the passage area of the flow limiter orifice. Options have been considered for filling the channel body gas gap with helium and a helium mixture. The calculation showed that the heat removed by the bypass line could reach 40% of the total heat released in the channel. With helium used in the channel body gap, the temperature conditions during irradiation are adjusted in a broader range (200–330 °С) than with a gas mixture of a lower thermal conductivity (279–330 °С), the major temperature variation taking place with the flow limiter orifice area being less than 0.2–0.3 cm2. Any further increase in the flow limiter orifice area does not lead to a major temperature change in the coolant flowing about the samples.

Interference effects in the Aharonov-Bohm geometries with Majorana bound states

We investigate the transport properties in an Aharonov-Bohm circuit with embedded Majorana bound states (MBSs), by considering the influence of MBS-lead coupling manners. It is found that the inter-arm quantum interference plays an important role in modulating the Andreev reflection process. This is manifested as the fact that both the conductance and Fano factor are tightly related to the circuit geometry and the local magnetic flux. The results in this work can be helpful in describing the transport characteristics of the junction with MBSs.

Numerical design of a 100 W, 38 dB gain, W-band multi-section serpentine waveguide vacuum electronic TWT

The serpentine waveguide circuit is a robust beam-wave interaction circuit for W-band TWTs. Here presented the electromagnetic properties and design methodology for W-band multi-section SWG traveling wave tube. Cold-test (in absence of electron beam) numerical design performed theoretically and further optimized/validated with standard simulation code to predict the dispersion, interaction impedance, ohmic-loss and small-signal gain. Numerical simulation for the quarter wave transformer couplers with SWG circuit geometry shown the return-loss less than −20dB for the 5% frequency band. Later, in systematic manner, hot-test (in presence of electron beam) numerical design performed for multi-section TWT by using standard particle-in-cell 3-D simulation code. The three section, 60 periods SWG TWT predicted peak radiation power 130W at target frequency 94GHz, 39.5dB saturated gain, 5.3% instantaneous 3-dB frequency bandwidth, and 6.5% electronic efficiency.

Design of an induction motor by pre-determination of equivalent circuit parameters

The induction motor designed for the variable speed applications are different from those which are designed for constant speed applications. This paper deals with the method for the design of induction motor for variable speed applications starting from the analytical calculation of equivalent circuit parameters. Finally, the main dimensions of the motor geometries are provided by using the relation between the circuit parameters and geometries of a real induction machine. The proposed approach also minimizes the problems caused by the conventional motor design methods for the variable speed application. The effectiveness and accuracy of the proposed design can be verified through Finite Element analysis for practical design.

Effect of Circuit Geometry on Steady Flow Performance of an Automotive Turbocharger Compressor

Downsizing and turbocharging are today considered an effective way to reduce CO2 emissions in automotive gasoline engines. To this aim, a deep knowledge of turbocharger behavior could be a key solution to improve the engine-turbocharger matching calculation. The influence of the intake system geometry on the surge line position is an important aspect to guide the project of the intake manifold, enlarging the compressor stable zone. This aspect has a considerable impact on engine performance, especially during transient operation. A wide experimental investigation was carried out at the turbocharger test facility of the University of Genoa on a small turbocharger compressor. Compressor characteristic curves measured considering an automotive intake circuit are compared with standard maps provided by turbocharger's manufacturer. This information allows the optimization of 1D model implementing more realistic maps of compressor. The influence of three different layouts has been investigated varying overall circuit volume and length, keeping values in a range compatible with passenger cars packaging constraints. In the paper, the main results of the experimental campaign are presented taking into account the influence of geometry variations on compressor map and surge line position.

Enhanced responsivity resonant RF photodetectors.

The responsivity of room-temperature, semiconductor-based photodetectors consisting of resonant RF circuits coupled to microstrip buslines is investigated. The dependence of the photodetector response on the semiconductor material and RF circuit geometry is presented, as is the detector response as a function of the spatial position of the incident light. We demonstrate significant improvement in detector response by choice of photoconductive material, and for a given material, by positioning our optical signal to overlap with positions of RF field enhancement. Design of RF circuits with strong field enhancement are demonstrated to further improve detector response. The improved detector response demonstrated offers opportunities for applications in RF photonics, materials metrology, or single read-out multiplexed detector arrays.

Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer.

Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95±5% and have potential to serve as the basis of spin-logic and network implementations.

Expedited Geometry Scaling of Compact Microwave Passives by Means of Inverse Surrogate Modeling

In this paper, the problem of geometry scaling of compact microwave structures is investigated. As opposed to conventional structures [i.e., constructed using uniform transmission lines (TLs)], re-design of miniaturized circuits (e.g., implemented with artificial TLs) for different operating frequencies is far from being straightforward due to considerable cross-couplings between the circuit components. Here, we develop a simple and computationally efficient methodology for dimension scaling of the compact circuits. The proposed approach utilizes an equivalent circuit representation to identify a fast inverse model that determines the relationship between the geometry parameters of the structure at hand and its operating frequency. Upon suitable correction, the inverse model is applied to find dimensions of the scaled design at the high-fidelity (electromagnetic (EM) simulation) model level. Owing to reasonable correlations between the low- and high-fidelity models, the circuit geometry scaled to a requested operating frequency can be found using just a single EM simulation of the structure, despite possible absolute discrepancies between the models. The proposed methodology is demonstrated using two exemplary compact couplers scaled in wide ranges from 0.5 to 2 GHz and from 0.5 to 1.8 GHz, respectively. The numerical results are supported by physical measurements of the fabricated coupler prototypes.

On the reliability estimation of nano-circuits using neural networks

As the integrated circuit geometries shrink, it becomes important for the designers to take into consideration the reliability of the circuits. Different techniques can be used for reliability calculation or estimation. Some of these techniques are accurate but time-consuming while others are quick but not accurate. For example, using a set of mathematical equations for reliability estimation is very fast but not precise enough for large systems. Alternatively, Monte Carlo simulations are highly accurate, but very time-intensive. This work presents three different neural network models for estimating circuit reliability. The models provide better prediction accuracies than the mathematical technique. A reasonably large number of combinational circuits were simulated over a wide range of device reliabilities to collect the training data for the models. Multiple slices of an ISCAS-85 benchmark circuit were used to validate the models’ prediction results.

CFD-based evolutionary algorithm for the realization of target fluid flow distribution among parallel channels

In energy and process systems, the bad fluid flow distribution (flow maldistribution) is one of the main causes of performance deterioration, equipment dysfunction, safety defaults, product quality degradation, reduced lifetime and over-cost. Flow equidistribution among numerous parallel channels is a classical goal, but is not always the optimal option according to a given objective and constraints. Target flow distribution (uniform or non-uniform) is far more difficult to achieve because it requires the precise control of flow-rate in given time for every channel. There is no such attempt in the existing literature.In this study, a CFD-based evolutionary algorithm is developed to optimize the topology of an inserted perforated baffle, for the realization of target flow distribution among parallel channels. Several 2D numerical examples with different circuit geometries and different target curves are studied and compared. Results show that the optimized distribution curves obtained by performing the evolutionary algorithm are in good agreement with the target curves, with acceptable increase in pressure drop. This optimality algorithm may be easily applied to different working conditions. In this sense, the proposed algorithm is robust, effective, general and flexible, showing its promising application in various engineering fields dealing with fluid distribution problem.

Electroresistance and field effect studies on manganite based heterostructure

Electronic properties of manganites are significantly important for various spintronic applications such as microelectronics, magnetic data storage, communication technologies, and memory devices. Influence of applied electric field on the room temperature charge transport in ZnO/La0.7Sr0.3MnO3/SrNb0.002Ti0.998O3 (SNTO) heterostructure has been investigated using field effect studies. Large negative and positive electroresistance has been observed in heterostructure under various possible circuit geometries. Field effect studies have been carried out using three different circuit geometries, namely: (i) ZnO as a control electrode (ELZ), (ii) SNTO as a control electrode (ELS), and (iii) shorted ZnO and SNTO as control electrodes (ELZS). For this, channel electric field (ECH) dependent variation in channel resistance (RC) (of manganite channel) and I-V (across manganite channel) under various control fields (EC) have been studied. Variation in barrier height (ΦB) with control field (EC) for different geometries has been discussed.

Explicitly Accounting for the Heat Sink Strengths in the Thermal Matching of Thermoelectric Devices. A Unified Practical Approach

Thermal matching of thermoelectric generators (TEGs) to their heat sinks is well known to be a critical issue in the development of efficient harvesters. It is slightly less obvious that the development of suitable novel materials would possibly take advantage of their contextualization to prospective scenarios of deployment. In this communication a novel unified analysis of the heat equation is proposed. The thermal system was embedded into a thermostat while the heat source was taken as a part of the system itself, also explicitly accounting for the heat dissipation. A continual transition of thermal matching conditions from those predicted under Dirichlet boundary conditions (BCs) to those obtained under Neumann BCs was found, depending on the strength of the heat source and on the thermal resistances of the circuit branches. In all cases it was found that, independently of the thermal or thermoelectric circuit geometry, no single material may provide optimal TEG power density for any heat source strength and branch resistance.

Source Separation for Wideband Energy Emissions Using Complex Independent Component Analysis

Complex independent component analysis is formulated for ultrawideband (UWB) incoherent fields, based on maximum-likelihood estimation with iterative natural gradient searching. It can be applied to measurements of complex power separated in contributions by propagating and reactive near-fields. A set of novel nonlinear asymmetric score functions is derived that are asymptotically matched to skewed probability density functions of incoherent energy sources departing from ideal chi-square ensemble distributions. The source decomposition is applied to two analog and digital integrated circuits. Based on the measured intensity of the emitted magnetic field, the technique is shown to enable nonlinear extraction of a set of independent spatially separated UWB sources, without knowledge of neither the detailed circuit geometry nor its on-board signals. Overcompleteness of the data set is found to have a relatively small effect on the accuracy of the estimated magnitude and location of the emission hot spots, but has a major influence on the global spatial maps and nature of the extracted sources.

Testing a two‐loop pattern of the substorm current wedge (SCW2L)

Recent quantitative testing of the classical (region 1 sense) substorm current wedge (SCI) model revealed systematic discrepancies between the observed and predicted amplitudes, which suggested us to include additional region 2 sense currents (R2 loop) earthward of the dipolarized region (SCW2L model). Here we discuss alternative circuit geometries of the 3‐D substorm current system and interpret observations of the magnetic field dipolarizations made between 6.6RE and 11RE, to quantitatively investigate the SCW2L model parameters. During two cases of a dipole‐like magnetotail configuration, the dipolarization/injection front fortuitously stopped at r ~ 9RE for the entire duration of ~ 30 min long SCW‐related dipolarization within a unique, radially distributed multispacecraft constellation, which allowed us to determine the locations and total currents of both SCW2L loops. In addition, we analyzed the dipolarization amplitudes in events, simultaneously observed at 6.6RE, 11RE and at colatitudes under a wide range of magnetograph conditions. We infer that the ratio I2/I1 varies in the range 0.2 to 0.6 (median value 0.4) and that the equatorial part of the R2 current loop stays at r>6.6RE in the case of a dipole‐like field geometry (BZ0>75 nT at 6.6RE prior to the onset), but it is located at r<6.6RE in the case of a stretched magnetic field configuration (with BZ0<60 nT). Since the ground midlatitude perturbations are sensitive to the combined effect of the R1 and R2 sense current loops with the net current roughly equal to I1−I2, the ratio I2/I1 becomes an important issue when attempting to monitor the current disruption intensity from ground observations.

Radio-Frequency Tank Circuit for DNA Sequencing

DNA sequencing by now is a ubiquitous technique in biology and medicine. Nanopore sequencers turn out to be a promising approach for high-speed sequencing of long DNA-strands while cutting costs by many orders of magnitude.We present a resonant RLC-circuit operating at radio frequency (Bhat, Soft Nanoscience Letters (2013)). DNA is driven through a nanopore which causes a shift in the resonance of the circuit. The nanopore is embedded within a resonant CPW structure, a so-called tank circuit that enables the measurement of extremely small capacitance changes caused by the transition of the macromolecule through the pore. In contrast to existing nanopore-sequencing technologies, such a design does not rely on a molecular motor to slow down the translocating DNA. Furthermore, the presented method is not limited by the length or a specific design of the pore, allowing a plethora of pore modifications and designs to be used.Finite element simulation techniques provide an insight into the behavior of different tank-circuit geometries. We present several studies on how the circuit geometry can be modified to increase the sensitivity. Additionally, different concepts for amplification of the atto-Farad signal levels are discussed (Ramachandran et al., Applied Physics Letter 99 (2011)), a degree of sensitivity sufficient for resolving the different DNA bases and paving the way for DNA sequencing in the MHz regime.

Experimental Realization of Josephson Junctions for an Atom SQUID

We report the creation of a pair of Josephson junctions on a toroidal dilute gas Bose-Einstein condensate (BEC), a configuration that is the cold atom analog of the well-known dc superconducting quantum interference device (SQUID). We observe Josephson effects, measure the critical current of the junctions, and find dynamic behavior that is in good agreement with the simple Josephson equations for a tunnel junction with the ideal sinusoidal current-phase relation expected for the parameters of the experiment. The junctions and toroidal trap are created with the painted potential, a time-averaged optical dipole potential technique which will allow scaling to more complex BEC circuit geometries than the single atom-SQUID case reported here. Since rotation plays the same role in the atom SQUID as magnetic field does in the dc SQUID magnetometer, the device has potential as a compact rotation sensor.