Disentangling production and climate signals from high-resolution Beryllium records: implications for solar and geomagnetic reconstructions

The sun is the most important energy source for the Earth’s climate system, however, influences of solar variations on climate are not fully understood. Studying past solar activity can improve our understanding of what role the sun plays in Earth’s climate. Cosmogenic radionuclides, such as 10Be in ice cores, are powerful tools to reconstruct past solar activity before the period of direct telescope observations. Because the atmospheric production rates of 10Be depend on the strengths of the solar and geomagnetic field, hence measurements of 10Be in ice can provide useful information on variabilities of these two magnetic fields back in time. However, the interpretation of 10Be data is challenged due to the influences of transport and scavenging processes on 10Be from Earth’s atmosphere to the natural archives (e.g. ice cores). Unidentified climate imprints on 10Be records could lead to errors in solar and geomagnetic reconstructions.This project aims to improve our understanding of the climate effects on 10Be through analysis of high-resolution 10Be and 7Be data, in order to improve solar and geomagnetic reconstructions. We present a well-defined seasonally resolved 10Be record for the period 1887-2002 from a NEEM firn core (NEEM07S1) in Northwestern Greenland. Through analyzing the sub-annual δ18O records at NEEM site, we identify the seasonal signals with 30% accumulation for November-April (winter) and 70% accumulation for May-October (summer). Both summer and winter 10Be data reflect the production signal induced by solar modulation of galactic cosmic rays. Superimposed on this solar signal we find that the tropopause pressure over 30°N represents an important factor influencingNEEM 10Be concentrations. Summer 10Be concentration, on average, is higher than winter, which could be attributed to the effects of stratospheric intrusion of 10Be. This stratospheric intrusion of beryllium is also supported by the study of weekly-resolved air 7Be records over Europe. Furthermore, by comparing the NEEM 10Be record with other Greenland 10Be records over the last 100 years, we identify that the 10Be values from the Dye3 ice core after 1958 are unusually low, which are resulting from a data quality issue instead of meteorological influences. This period of unusually low Dye3 10Be values can lead to a normalization problem when connecting radionuclide records to modern levels of solar modulation estimated from neutron monitor data over the past 70 years. We found that disagreements of different solar reconstructions based on Greenland and Antarctica 10Be records can be partly attributed to this data problem. Finally, we present a geomagnetic dipole moment reconstruction for the period from 11.7 ka BP (before present AD 1950) to 108 ka BP based on a new NEEM 10Be record and published GRIP 10Be and 36Cl records. With a first-order correction of cosmogenic radionuclides data using climate proxy data, the “climate correction” results lead to an improved agreement with independent reconstructions compared to simply using radionuclide data. Therefore, with this linear correction method, geomagnetic dipole moment reconstructions based on cosmogenic radionuclides data from ice cores can be extended back in time when there is a strong climate signal in radionuclides data

Sampled-Data Control of Singular Systems with Time Delays

This paper is concerned with sampled-data controller design for singular systems with time delay. It is assumed that the sampling periods are arbitrarily varying but bounded. A time-dependent Lyapunov function is proposed, which is positive definite at sampling times but not necessarily positive definite inside the sampling intervals. Combining input delay approach with Lyapunov method, sufficient conditions are derived which guarante that the singular system is regular, impulse free, and exponentially stable. Then, the existence conditions of desired sampled-data controller can be obtained, which are formulated in terms of strict linear matrix inequality. Finally, numerical examples are given to demonstrate the effectiveness and the benefits of the proposed method

Wirelessly-Controlled Untethered Piezoelectric Planar Soft Robot Capable of Bidirectional Crawling and Rotation

Electrostatic actuators provide a promising approach to creating soft robotic sheets, due to their flexible form factor, modular integration, and fast response speed. However, their control requires kilo-Volt signals and understanding of complex dynamics resulting from force interactions by on-board and environmental effects. In this work, we demonstrate an untethered planar five-actuator piezoelectric robot powered by batteries and on-board high-voltage circuitry, and controlled through a wireless link. The scalable fabrication approach is based on bonding different functional layers on top of each other (steel foil substrate, actuators, flexible electronics). The robot exhibits a range of controllable motions, including bidirectional crawling (up to ~0.6 cm/s), turning, and in-place rotation (at ~1 degree/s). High-speed videos and control experiments show that the richness of the motion results from the interaction of an asymmetric mass distribution in the robot and the associated dependence of the dynamics on the driving frequency of the piezoelectrics. The robot's speed can reach 6 cm/s with specific payload distribution.Comment: Accepted to the 2023 IEEE International Conference on Robotics and Automation (ICRA

Design of data acquisition card based on microwave auto-measurement system

This paper provides a brief introduction to the hardware configuration and the measuring principle of microwave auto-measurement system, and gives more details on the design of the data acquisition card based on the system. The card has a high accuracy which is owed to 12-bit high sampling AD converter and 12-bit multi-channel DA converter being applied, and it takes CPLD as the control core, USB as the interface, which achieves the speedy and reliable data transmission between the data acquisition card and the PC

Solar activity of the past 100 years inferred from 10Be in ice cores – implications for long-term solar activity reconstructions

Differences between 10Be records from Greenland and Antarctica over the last 100 years have led to different conclusions about past changes in solar activity. The reasons for this disagreement remain unresolved. We analyze a seasonally resolved 10Be record from a firn core (NEEM ice core project) in Northwestern Greenland for 1887-2002. By comparing the NEEM data to 10Be data from the NGRIP and Dye3 ice cores, we find that the Dye3 data after 1958 are significantly lower. These low values lead to a normalization problem in solar reconstructions when connecting 10Be variations to modern observations. Excluding these data strongly reduces the differences between solar reconstructions over the last 2000 years based on Greenland and Antarctic 10Be data. Furthermore, 10Be records from polar regions and group sunspot numbers do not support a substantial increase in solar activity for the 1937-1950 period as proposed by previous extensions of the neutron monitor data.This article is protected by copyright. All rights reserved

Model-Based Control of Planar Piezoelectric Inchworm Soft Robot for Crawling in Constrained Environments

Soft robots have drawn significant attention recently for their ability to achieve rich shapes when interacting with complex environments. However, their elasticity and flexibility compared to rigid robots also pose significant challenges for precise and robust shape control in real-time. Motivated by their potential to operate in highly-constrained environments, as in search-and-rescue operations, this work addresses these challenges of soft robots by developing a model-based full-shape controller, validated and demonstrated by experiments. A five-actuator planar soft robot was constructed with planar piezoelectric layers bonded to a steel foil substrate, enabling inchworm-like motion. The controller uses a soft-body continuous model for shape planning and control, given target shapes and/or environmental constraints, such as crawling under overhead barriers or "roof" safety lines. An approach to background model calibrations is developed to address deviations of actual robot shape due to material parameter variations and drift. Full experimental shape control and optimal movement under a roof safety line are demonstrated, where the robot maximizes its speed within the overhead constraint. The mean-squared error between the measured and target shapes improves from ~0.05 cm$^{2}$ without calibration to ~0.01 cm$^{2}$ with calibration. Simulation-based validation is also performed with various different roof shapes.Comment: Accepted to the 2022 IEEE 5th International Conference on Soft Robotics (RoboSoft). Project website: https://piezorobotcontroller.github.io/ Summary video: https://youtu.be/Md-Uo-pUaI

Sampled-Data Control for Singular Neutral System

This study is concerned with the ∞ control problem for singular neutral system based on sampled-data. By input delay approach and a composite state-derivative control law, the singular system is turned into a singular neutral system with time-varying delay. Less conservative result is derived for the resultant system by incorporating the delay decomposition technique, Wirtinger-based integral inequality, and an augmented Lyapunov-Krasovskii functional. Sufficient conditions are derived to guarantee that the resulting system is regular, impulse-free, and asymptotically stable with prescribed ∞ performance. Then, the ∞ sampled-data controller is designed by means of linear matrix inequalities. Finally, two simulation results have shown that the proposed method is effective

H

This study is concerned with the H∞ control problem for singular neutral system based on sampled-data. By input delay approach and a composite state-derivative control law, the singular system is turned into a singular neutral system with time-varying delay. Less conservative result is derived for the resultant system by incorporating the delay decomposition technique, Wirtinger-based integral inequality, and an augmented Lyapunov-Krasovskii functional. Sufficient conditions are derived to guarantee that the resulting system is regular, impulse-free, and asymptotically stable with prescribed H∞ performance. Then, the H∞ sampled-data controller is designed by means of linear matrix inequalities. Finally, two simulation results have shown that the proposed method is effective