Storage Loop Research Articles

Characterization of high-speed writing and reading operations of the superconducting memory cell

Abstract Superconducting memory cells that use flux quanta as their storage medium can achieve ultra-fast access times with ultra-low power consumption. However, the data signal generated by a flux quantum memory (FQM) cell is usually too weak and too fast to be measured directly. Here, we present a method to characterize the real-time operation of an FQM cell. The storage loop of the FQM cell, configured with a Nb/NbN X /Nb Josephson junction, was proven the capability to store multiple flux quanta. The readout was demonstrated by a superconducting quantum interference device composed of underdamped Nb/Al-AlO X /Nb Josephson junctions. The writing and reading operations were achieved by a short pulse ranging from 0.1 ns to 2.5 ns, and a constant bit error rate of ∼2.46% was measured for the fabricated FQM cell. The method presented here can be used to study real-time operation of an FQM cell in a direct manner.

Multicolumn Nanoflow Liquid Chromatography with Accelerated Offline Gradient Generation for Robust and Sensitive Single-Cell Proteome Profiling.

Peptide separations that combine high sensitivity, robustness, peak capacity, and throughput are essential for extending bottom-up proteomics to smaller samples including single cells. To this end, we have developed a multicolumn nanoLC system with offline gradient generation. One binary pump generates gradients in an accelerated fashion to support multiple analytical columns, and a single trap column interfaces with all analytical columns to reduce required maintenance and simplify troubleshooting. A high degree of parallelization is possible, as one sample undergoes separation while the next sample plus its corresponding mobile phase gradient are transferred into the storage loop and a third sample is loaded into a sample loop. Selective offline elution from the trap column into the sample loop prevents salts and hydrophobic species from entering the analytical column, thus greatly enhancing column lifetime and system robustness. With this design, samples can be analyzed as fast as every 20 min at a flow rate of just 40 nL/min with close to 100% MS utilization time and continuously for as long as several months without column replacement. We utilized the system to analyze the proteomes of single cells from a multiple myeloma cell line upon treatment with the immunomodulatory imide drug lenalidomide.

Solar district heating system with large heat storage: Energy, exergy, economic and environmental (4E) analysis

In the context of the global energy crisis and climate change, solar district heating systems are an essential technology that can mitigate this problem. To accelerate the transition to sustainability, a proven solar district heating system and an analysis method are needed to serve as a role model. For this purpose, a techno-economic analysis method is proposed in this study. It consists of a bi-directional long short-term memory method for correcting outlier data and a balanced method for energy and exergy analyses. The solar district heating system with large-scale thermal storage in Dronninglund, Denmark, is investigated in detail. The design of this system is centered on an integrated control strategy that synchronizes the solar collector loop, the energy storage loop, and the heating load loop to improve overall efficiency. The results show an increase in solar collector efficiency to 41 %, thermal storage efficiency to 89 %, and a coefficient of performance to 1.74 for the absorption heat pump. This integration increases the system’s coefficient of performance dramatically to 2.9, with a renewable energy percentage of 77 %. Exergy analysis shows a storage exergy of 68 % and a heat pump exergy of 49 %, which suggests that the system has a highly efficient energy conversion. The annual heating demand for the industrial and residential branches is 7,450 MWh and 28,100 MWh, respectively, which are covered by solar (42 %), biomass oil (35 %), and natural gas (23 %). The economic assessment shows that the net present value could rise from −5.5 million euros over 10 years to 15.2 million euros over 40 years, indicating long-term economic advantages. The system achieves 122 kg/MWh of carbon reduction with a 0.92 carbon neutrality factor, which is carbon neutral. This study provides a compelling case for deploying large-scale solar heating systems, offering a robust analysis method and insightful findings for technological developments and economic optimizations.

Towards an agglomeration free Ca(OH)2/CaO thermochemical energy storage loop via nanofabricated hollow CaO microspheres with highly porous shells

The Ca(OH)₂/CaO loop offers a promising solution for seasonal thermochemical heat storage, vital for decarbonizing the heating sector thanks to its high energy density and abundant raw materials. However, cyclic hydration/dehydration of limestone-derived CaO (r-CaO) faces challenges like agglomeration and high-volume expansion, limiting its expected performances. This study focuses on fabricating hollow CaO microspheres (h-CaO) with porous shells via a facile one-pot hydrothermal synthesis method, without doping materials. These microspheres exhibit superior cyclic performance compared to r-CaO, with SEM-EDS confirming successful fabrication. Over 30 cycles in the temperature range of 400–550 °C, h-CaO achieves an average storage density of 1755 kJ/kg, peaking at 1835 kJ/kg, with kinetics twice as high as r-CaO. Most importantly, the hollow microstructure reduces dramatically the apparent volumetric expansion from 250 % to as little as 32 %, offering a potential solution to agglomeration at the reactor level and advan44cing the commercial viability of the Ca(OH)2/CaO thermochemical storage technology.

Photon number resolving detection with a single-photon detector and adaptive storage loop

Photon number resolving (PNR) measurements are beneficial or even necessary for many applications in quantum optics. Unfortunately, PNR detectors are usually large, slow, expensive, and difficult to operate. However, if the input signal is multiplexed, photon ‘click’ detectors, that lack an intrinsic PNR capability, can still be used to realize photon number resolution. Here, we investigate the operation of a single click detector, together with a storage line with tunable outcoupling. Using adaptive feedback to adjust the storage outcoupling rate, the dynamic range of the detector can in certain situations be extended by up to an order of magnitude relative to a purely passive setup. An adaptive approach can thus allow for photon number variance below the quantum shot noise limit under a wider range of conditions than using a passive multiplexing approach. This can enable applications in quantum enhanced metrology and quantum computing.

The Critical State of GaAs Photoconductive Semiconductor Switch in a Capacitive Storage Loop

The Critical State of GaAs Photoconductive Semiconductor Switch in a Capacitive Storage Loop

Sigmoid function generator using stochastic adiabatic superconductor logic

Stochastic-computing-based artificial neural networks (SC-ANNs) can be used to perform hardware- and energy-efficient neuromorphic computing. We have been developing SC-ANNs using an energy-efficient superconductor logic family, namely, adiabatic quantum-flux-parametron (AQFP) logic. AQFP logic is suitable as a building block for SC-ANNs since it can perform stochastic operations with extremely small energy dissipation. In this Letter, we propose and demonstrate a sigmoid function generator (SFG) for AQFP SC-ANNs, which we refer to as the AQFP SFG. An SFG is an important circuit in neural networks that generates outputs from the sum of weighted inputs in accordance with the sigmoid function. The AQFP SFG performs the sigmoid function using a finite state machine based on an AQFP buffer coupled to a flux storage loop. We experimentally demonstrate that the AQFP SFG generates output signals from stochastic bitstreams in accordance with the sigmoid function and that the characteristics of the sigmoid function can be controlled by a bias current. Furthermore, we show that the AQFP SFG operates with small power dissipation due to its simple structure.

Asynchronous Reversible Computing Unveiled Using Ballistic Shift Registers

Reversible logic can provide lower switching energy costs relative to all irreversible logic, including those developed by industry in semiconductor circuits, however, more research is needed to understand what is possible. Superconducting logic, an exemplary platform for both irreversible and reversible logic, uses flux quanta to represent bits, and the reversible implementation may switch state with low energy dissipation relative to the energy of a flux quantum. Here we simulate reversible shift register gates that are ballistic: their operation is powered by the input bits alone. A storage loop is added relative to previous gates as a key innovation, which bestows an asynchronous property to the gate such that input bits can arrive at different times as long as their order is clearly preserved. The shift register represents bit states by flux polarity, both in the stored bit as well as the ballistic input and output bits. Its operation consists of the elastic swapping of flux between the stored and the moving bit. This is related to a famous irreversible shift register, developed prior to the advent of superconducting flux quanta logic (which used irreversible gates). In the base design of our ballistic shift register (BSR) there is one 1-input and 1-output port, but we find that we can make other asynchronous ballistic gates by extension. The gate constitutes the first asynchronous reversible 2-input gate. Finally, for a better insight into the dynamics, we introduce a collective coordinate model. We find that the gate can be described as motion in two coordinates subject to a potential determined by the input bit and initial stored flux quantum. Aside from the favorable asynchronous feature, the gate is considered practical in the context of energy efficiency, parameter margins, logical depth, and speed.

Reconfiguration of nondestructively readable superconductor memory by direct injection of magnetic flux to storage loop

In this study, we demonstrate a novel method for the reconfiguration of a nondestructively readable memory cell for superconductor integrated circuits. The proposed reconfiguration method involves the direct injection of flux quantum to the storage loop of the memory cell, which has been achieved using interface circuits in previous studies. By applying this method, the footprint of the superconductor memory cell can be reduced by half. We experimentally demonstrate the proof-of-concept of the investigated reconfiguration method. We expect that the memory cell reconfigured using the proposed method will be suitable for building large-scale lookup tables using superconductor circuits.

Analyses and optimization of the CFETR power conversion system with a new supercritical CO2 Brayton cycle

In this paper, the Chinese Fusion Engineering Testing Reactor (CFETR) power conversion system, with a supercritical CO2 (SCO2) Brayton cycle, is designed, analyzed and optimized. Considering the pulse operation of the reactor, a heat storage loop with high temperature molten salt and low temperature concrete is introduced. Based on the parameters of the first cooling loop, the CFETR power conversion loop is designed and studied. A new SCO2 Brayton cycle for the CFETR dual heat sources, blanket and divertor, is developed and optimized using a genetic algorithm. Compared to other simple and recompression cycles, it is shown that the new SCO2 Brayton cycle combines maximum thermal efficiency with simplicity. Exergy analyses are carried out and show that the exergy destruction rates of turbine and heat exchangers between different loops are the largest due to the large turbine power and the large temperature difference. The exergoeconomic analyses show that the fusion reactor accounts for the main cost, which is the key to the economy of fusion power generation. The following sensitivity analyses show that the hot molten salt temperature has a major influence on the system performance. Finally, several multi-criteria optimization algorithms are introduced to simultaneously optimize the three fitness functions, the cycle thermal efficiency, the system exergy efficiency and the total system product unit cost. It is found that the maximum thermal efficiency, the maximum exergy efficiency and the lowest total system product unit cost can be obtained almost simultaneously for the new CFETR power conversion system, and this optimal operation scheme is presented.

Control-oriented hybrid model of a small-scale refrigerated truck chamber

Refrigerated last-mile transport of goods has faced rapidly growing importance in recent years. Although hardware components underwent comprehensive improvements to fulfill increased efficiency demands, little was done regarding control strategies. Simple algorithms or restricted consideration of system parts for control design harshly limit attainable economic and ecological flexibilities provided by state-of-the-art hardware. Sophisticated model-based control schemes constitute a promising remedy but lack detailed and computationally reasonable models of the overall cooling application. This article introduces an appropriate dynamic, low-order model to overcome this issue. The mathematical description relies on first principles, features lumped parameters, and comprises temperature evolution and electrical power consumption, allowing for the assessment of system efficiency. Besides the explicit consideration of door openings, incorporating thermal capacities of the insulation walls and the cooling unit’s secondary storage loop stands out. Component’s switching behavior is embedded in the chosen discrete hybrid automaton modeling approach, for which 18.4h of real-world measurement data drive parameterization and validation. An overall fit to validation data of 86.2% and 88.7% for the most significant temperature quantity and total power consumption illustrates the model’s high performance and practicality for control applications, soft-sensors, and fault detection.

Nonvolatile memory cell using a superconducting-ferromagnetic π Josephson junction

Storage of a single magnetic flux quantum in a superconducting loop containing a Josephson junction represents a promising unit cell configuration for construction of a cryogenic memory of superconducting digital circuits. However, application of a DC bias current is required for operation of such a memory cell to maintain trapping of the flux quantum in the storage loop. In this work, we present a superconducting memory cell that uses a superconducting-magnetic π junction. The cell characteristics show flux quantum hysteresis centering at the zero-bias current. We develop a fabrication process that combines superconductor–ferromagnet–superconductor (SFS) junctions with superconductor–normal metal–superconductor (SNS) junctions. The critical current density of the SFS junctions shows a 0–π oscillation as a function of the ferromagnetic layer thickness. The formation of the π junction is confirmed further by the flux modulation curves of a superconducting quantum interference device made from SNS junctions with an additional SFS junction.

Single-Stage Hybrid Three-Level DAB Type Resonant AC–DC Converter

In order to extend the application of single-stage dual active bridge type isolated ac–dc converter and improve its current characteristics, in this article, a novel topology with a three-level half-bridge matrix converter and a resonant tank is proposed. The operation principle and steady-state characteristics are analyzed in detail based on the PWM plus phase shift modulation. Furthermore, the relationship of the equivalent three-phase shifts to realize a minimum rms value of resonant current is introduced to enhance the operation efficiency. The proposed converter reduces the voltage stress of the power switches of the ac side matrix converter to half the ac voltage, and it is helpful to reduce the power loss and cost. Especially, it is valuable to realize the excellent high-frequency power conversion in medium-voltage applications. Furthermore, the current stress of the power switches is decreased by using the resonant tank as the temporary energy storage loop. The detailed experimental results verify the correctness and feasibility of the proposed topology and theoretical analysis.

Torrefaction of cellulose, hemicelluloses and lignin extracted from woody and agricultural biomass in TGA-GC/MS: Linking production profiles of volatile species to biomass type and macromolecular composition

The production of volatile species in torrefaction of cellulose, hemicellulose and lignin extracted from woody and agricultural biomass was quantified as a function of temperature. The novel coupling of TGA to GC/MS through a heated storage loop system allowed sampling volatile species released at 11 different temperatures in a single torrefaction experiment between 200 and 300 °C, at 3 °C.min−1. The results showed that the use of extracted fractions obtained from different biomass samples led to the detection of a higher number of species (23) than in previous studies with commercial compounds, obtaining a higher degree of detail in the characterization of the production of volatile species in torrefaction. Volatile species were generally released in this study from lower temperatures than those previously reported for commercial compounds. This may be due to the better preservation of cellulose, hemicellulose and lignin properties in extracted fractions thanks to the optimized extraction procedure. Volatile species production profiles were assessed based on the formation mechanisms proposed in the literature and the production of polysaccharide-based fractions was shown to be correlated to their sugar composition. Finally, production profiles allow identifying the temperature range to enhance the production of a given volatile species in torrefaction.

Overview of Thermal Hydraulic Optimization and Verification for the EU-DEMO HCPB BOP ICD Variant

When progressing from the International Thermonuclear Experimental Reactor (ITER) to the Demonstration Fusion Reactor (DEMO), a system for transferring plasma heat exhaust to a power conversion system is necessary for the so-called Balance of Plant (BOP). During the preconceptual phase of the EU-DEMO project, different BOP concepts were investigated in order to identify the main requirements and feasible architectures to achieve that goal in the most efficient way. This paper comprises the investigations performed during the DEMO preconceptual design phase (p-CDP) and compares the different variants. The main aspect was focused on the helium-cooled pebble bed (HCPB) breeding blanket (BB) concept. After all assessments were performed, the indirect coupled design (ICD) was chosen as the reference configuration for the DEMO HCPB BOP for further development and optimization. The ICD provides decoupling using a molten salt storage loop, which accumulates thermal power during plasma pulses that are released during dwell periods. The work is supported by simulations using design codes EBSILON and MATLAB/SIMULINK, providing the basis for the next design phase.

Performance analysis of photovoltaic-thermal road assisted ground source heat pump system during non-heating season

Photovoltaic-thermal road as solar collector is a promising technology. To expand the application of photovoltaic-thermal road, a novel energy system which integrated photovoltaic-thermal road with ground source heat pump system is proposed. Focus on this system, a dynamic mathematical model during non-heating season is established and validated, and it is used to explore the system performances under two operation modes: heat collection loop and heat storage loop operate simultaneously in mode 1 while they operate independently in mode 2. Furthermore, effects of setting temperature difference in both heat collection loop and heat storage loop on system performance are investigated. It is indicated that system performance in mode 1 is better than that in mode 2. As setting temperature difference in both heat collection loop and heat storage loop are increased, the thermal energy storage, electric power generation and energy consumption are decreased. And influence of setting temperature difference on thermal energy storage is greater than that on electricity generation. The overall efficiency under mode 1 and mode 2 are 27.12–36.96% and 18.78–26.36% respectively. Considering both energy generation and energy consumption, the optimal values of setting temperature difference in heat collection loop and heat storage loop are 2 °C and 10 °C under mode 1, and that are 2 °C and 4 °C under mode 2, respectively.

Design of 64-Bit Arithmetic Logic Unit Using Improved Timing Characterization Methodology for RSFQ Cell Library

Accurate timing characterization of library cells is essential for adopting the standard digital design flow using EDA tools, such as static timing analysis (STA) with timing back-annotation. For RSFQ circuits, the propagation delay of a cell is influenced by the input and output load. We have developed an automated timing characterization methodology that facilitates extraction of timing constraints and propagation delays for each cell as a function of all the possible permutations of input and output load. While being highly accurate, such a comprehensive timing characterization requires a large number of simulation runs. To significantly reduce the total number of simulation runs, we propose to analyze independently, rather than jointly, the effect of succeeding cells with standard preceding load and preceding cells with standard succeeding load. In addition, for succeeding cells with a storage loop, the delay of a cell is dependent on the state of the succeeding cell. STA tools cannot account for state-dependent timing variations. To mitigate state-dependent timing constraint violations, a state-dependent timing correction is added to the hold/set-up time. We have generated Liberty files for multiple process corners using the load dependent as well as standard load timing tables. We compare the timing accuracy for each methodology. We have designed and simulated a 64-bit ALU with 90,256 junctions with Verilog HDL and timing back-annotation across multiple process corners using Synopsys VCS tool. To validate the three timing characterization methodologies, we have evaluated their timing accuracies by comparing with full circuit simulations on representative ALU sub-blocks.

Comparison of Thermal and Flow-Based Modulation in Comprehensive Two-Dimensional Gas Chromatography—Time-of-Flight Mass Spectrometry (GC × GC-TOFMS) for the Analysis of Base Oils

Base oils are produced by refining crude oil or through chemical synthesis. They are a key component of engine oils. With an immense range of carbon numbers and boiling points, analyzing such complex mixtures is very difficult. The need to monitor industrial petroleum processing steps, as well as to identify petrochemical environmental pollutants, drives the search for improved characterization methods. Comprehensive two-dimensional gas chromatography (GC × GC) is one of the best tools for that. The modulator used in GC × GC is responsible for trapping/sampling the first dimension (1D) column analytes, then reinjecting them in the form of narrow bands onto the second dimension (2D) column for further separation. Modulators used today generally fall into two categories, thermal and flow ones. Heater-based thermal modulators trap the 1D column effluent at or above ambient temperatures. Flow-based modulators utilize storage loop(s) to collect the 1D effluent, which is subsequently flushed into the second-dimension column for further separation. A single-stage, consumable-free thermal modulator and a reverse fill/flush flow modulator were compared for the characterization of base oils. Both were evaluated on their ability to achieve separation of several conventional and synthetic engine oils components. A reverse column set, polar 1D and nonpolar 2D, allowed group-type analysis of all classes, including linear, branched, and aromatic species. The results show the ability to achieve a comprehensive separation of specific compound classes and the differentiation of engine oil types and manufacturers. Soft ionization assisted in tentative identification of two alkylated diphenylamines in each sample. The advantages and limitations of both thermal and flow modulation are presented.

Rapid Single-Flux-Quantum NOR Logic Gate Realized through the Use of Toggle Storage Loop

Rapid Single-Flux-Quantum NOR Logic Gate Realized through the Use of Toggle Storage Loop

Design and error-rate evaluation of RSFQ logic gates comprising a toggle storage loop

We propose an RSFQ digital cell with a toggle storage loop structure for logical NOT operation. Logical NOT operation is a fundamental function of digital circuitry, and hence, it had better be realized with less devices. We demonstrate a simpler and area-halved NOT gate designed as a 40 x 80 μm2 cell, which follows to cell-based design methodology. Test circuits were fabricated using a 2.5kA/cm2 Nb integration process. Measurements were executed in a liquid helium bath. We confirmed that the NOT gate comprising a toggle storage loop worked correctly. The error-rate of the NOT gate was less than 8.33 x 10−6 in the bias voltage range from 2.111 to 3.165 mV, which corresponded to the bias margin from 84.4% to 126.6% of the nominal bias voltage (2.5 mV). We also present that NOR and NAND logic gates can be configured using a toggle storage loop.