Isotope Climatic Record Over The Last 2.5 KA from Dome C, Antarctica, Ice cores

Data on climatic changes over thousands of years is needed for a better understanding of the shorter term variations which are of interest to man. For this purpose we measured the isotope composition (δD‰) of two adjacent ice cores drilled in the Dome C area. The time scale was established using the remarkably constant mean annual accumulation rate (37 kg m−2) determined by various techniques. The detailed isotope records were smoothed to filter out the δ value fluctuations not directly related to local temperature changes. With respect to conditions over the last 2.5 ka, the combined smoothed δ curve indicates a cooler climate from about 1800 to 1200 AD and a slightly warmer period from about 1200 to 700 AD. These periods may well correspond to the suggested world-wide Little Ice Age and medieval warm phase. Using the present δD‰/T°C measured at the surface, the maximum amplitude for these two periods, after smoothing with a low pass filter of 512 a, is approximately -0.35 and +0.3°C, respectively.

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Controlling Chaos by Bounded Self-Controlling Function Using Butterworth Filter Feedback

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.541-542.1216 ◽

2014 ◽

Vol 541-542 ◽

pp. 1216-1221

Author(s):

Lin Du ◽

Fei Lei Jia

Keyword(s):

Maximum Amplitude ◽

Sigmoid Function ◽

Pass Filter ◽

Low Pass Filter ◽

Input Signals ◽

Low Pass ◽

Large Maximum ◽

Effectiveness And Efficiency ◽

Feedback Control Strategy ◽

Invariance Theorem

Using the bounded sigmoid function and two-order Butterworth low-pass filter, a self-controlling feedback method for regulate the motion of a chaotic system is presented in this paper. It is shown that such controller has the advantage of being easy to implement based on the measurable input signals. A rigorous stability proof is provided from LaSalle Invariance theorem. Furthermore, the effectiveness and efficiency of the proposed feedback control strategy is illustrated by means of the numerical simulations of two-well Duffing Vander Pol oscillator. Finally, the result reveals that the enough large maximum amplitude results in a more possible regular domain in parameter space of the controlled oscillator.

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Local artifacts in ice core methane records caused by layered bubble trapping and in-situ production: a multi-site investigation

10.5194/cp-2015-183 ◽

2016 ◽

Author(s):

R. H. Rhodes ◽

X. Faïn ◽

E. J. Brook ◽

J. R. McConnell ◽

O. J. Maselli ◽

...

Keyword(s):

Transport Model ◽

Accumulation Rate ◽

Ice Core ◽

Ice Cores ◽

Analytical Techniques ◽

Site Investigation ◽

Pass Filter ◽

Low Pass Filter ◽

Bubble Trapping

Abstract. Superimposed on the coherent and major atmospheric changes in trace gases revealed by ice core records, local high frequency, non-atmospheric features can now be resolved due to improvement s in resolution and precision of analytical techniques. These are signals that could not have survived the low-pass filter effect that firn diffusion exerts on the atmospheric history and therefore do not result from changes in the composition of the atmosphere at the surface of the ice sheet. Using continuous methane (CH4) records obtained from five polar ice cores, we characterize these non-atmospheric signals and explore their origin. Isolated samples, enriched in CH4 in the Tunu13 (Greenland) record are linked to the presence of melt layers. Melting can enrich the methane concentration due to preferential dissolution of methane relative to nitrogen, but we find that an additional in-situ process is required to generate the full magnitude of these anomalies. Furthermore, in the all ice cores studied there is evidence of reproducible, decimetre-scale CH4 variability. Through a series of tests, we demonstrate that this sign al is an artifact of layered bubble trapping in a heterogeneous-density firn column; we term this phenomenon ‘trapping noise’. The magnitude of CH4 trapping noise increases with atmospheric CH4 growth rate and seasonality of density contrasts, and decreases with accumulation rate. Firn air transport model simulations, accounting for layered bubble trapping, are in agreement with our empirical data. Significant annual periodicity is present in the CH4 variability of two Greenland ice cores, suggesting that layered gas trapping at these sites is controlled by regular, seasonal variations in the physical properties of the firn.

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Modelling the firn thickness evolution during the last deglaciation: constrains on sensitivity to temperature and impurities

10.5194/cp-2016-91 ◽

2016 ◽

Author(s):

Camille Bréant ◽

Patricia Martinerie ◽

Anaïs Orsi ◽

Laurent Arnaud ◽

Amaëlle Landais

Keyword(s):

Accumulation Rate ◽

Ice Cores ◽

Ice Age ◽

Age Difference ◽

Last Deglaciation ◽

High Accumulation ◽

Temperature Changes ◽

Gas Trapping ◽

Different Temperatures ◽

The Last Deglaciation

Abstract. The transformation of snow into ice is a complex phenomenon difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger that the surrounding ice. The resulting gas-ice age difference is essential to document the phasing between CO2 and temperature changes especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ15N of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with δ15N measurements in several sites of East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ15N suggests a reduced firn thickness compared to the Holocene. We present here modifications of the LGGE firn densification model, which significantly reduce the model-data mismatch for the gas trapping depth evolution over the last deglaciation, while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the activation energy to temperature and impurities in the firn densification rate calculation. The temperature influence reflects the existence of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ15N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. However, the inclusion of impurities effects deteriorates the agreement between modelled and measured δ15N evolution in Greenland and Antarctic sites with high accumulation.

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Theoretical and Experimental Study on Nonlinear Failure of an MEMS Accelerometer under Dual Frequency Acoustic Interference

Sensors ◽

10.3390/s21030945 ◽

2021 ◽

Vol 21 (3) ◽

pp. 945

Author(s):

Peng Guo ◽

Jiayu Zhang ◽

Lihui Feng ◽

Jianmin Cui ◽

Chaoyang Xing

Keyword(s):

Mathematical Model ◽

Damping Ratio ◽

Maximum Amplitude ◽

Dual Frequency ◽

Maximum Acceleration ◽

Pass Filter ◽

Low Pass Filter ◽

Low Pass ◽

The Mathematical Model ◽

Frequency Sweeping

In order to quantitatively study the interfered output of the accelerometer under an acoustic injection attack, a mathematical model for fitting and predicting the accelerometer output was proposed. With ADXL103 as an example, an acoustic injection attack experiment with amplitude sweeping and frequency sweeping was performed. In the mathematical model, the R-squared coefficient was R2 = 0.9990 in the acoustic injection attack experiment with amplitude sweeping, and R2 = 0.9888 with frequency sweeping. Based on the mathematical model, the dual frequency acoustic injection attack mode was proposed. The difference frequency signal caused by the nonlinear effect was not filtered by the low-pass filter. At a 115 dB sound pressure level, the maximum acceleration bias of the output was 4.4 m/s2 and the maximum amplitude of fluctuation was 4.97 m/s2. Two kinds of methods of prevention against acoustic injection attack were proposed, including changing the damping ratio of the accelerometer and adding a preposition low-pass filter.

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