Influences of Seaways, Atmospheric CO2 and Greenland Ice Sheet on the Pliocene Climate in the Kiel Climate Model

This thesis provides an improved understanding of the impacts of changes in the atmospheric CO2-concentration, oceanic seaways, and Greenland ice sheet (GrIS) on the Pliocene climate (5.3-2.6 million years before present; Ma B.P.). Three sets of sensitivity experiments using a coupled atmosphere–ocean–sea ice model are analyzed and assessed with multiple paleoclimate reconstructions for the Pliocene. In particular, in the first set the model sensitivity of sea surface temperature (SST) and the East Asian summer monsoon (EASM) to changes in CO2 and oceanic seaway is investigated, while in the second set the mean state, the annual cycle in the tropical Pacific and El Niño/Southern Oscillation (ENSO) is analysed. In the third set, the impact of GrIS changes on the response of the Atlantic meridional overturning circulation (AMOC) and surface climate to obliquity forcing is examined

Influences of Random Surface Waves on the Estimates of Wind Energy Input to the Ekman Layer in the Antarctic Circumpolar Current Region

Sea surface waves significantly affect the wind energy input to the Ekman layer in the upper ocean. In the study, we first incorporated the wave-induced Coriolis-Stokes forcing, the reduction of wind stress caused by wave generation, and wave dissipation into the classical Ekman model to investigate the kinetic energy balance in the wave-affected Ekman layer. Then, both the theoretical steady state solution for the idealized condition and the nonsteady state solution for the realistic ocean were derived. Total energy input to the wave-affected Ekman layer includes the wind stress energy input and the wave-induced energy input. Based on the WAVEWATCH III model, the wave spectrum was simulated to represent realistic random directional wave conditions. The wind stress energy input and the wave-induced energy input to the wave-affected Ekman layer in the Antarctic Circumpolar Current in the period from 1988 to 2010 were then calculated. The annual mean total energy input in the Antarctic Circumpolar Current region was 402.5 GW and the proportions of the wind stress energy input and the wave-induced energy input were, respectively, 85% and 15%. Particularly, total energy input in the Antarctic Circumpolar Current in the wave-affected Ekman layer model was 59.8% lower than that in the classical Ekman model. We conclude that surface waves play a significant role in the wind energy input to the Ekman layer

Theoretical Beam Hardening Correction for Industrial X-ray Computed Tomography

Beam hardening is a significant artifact that comes from the polychromatic nature of the X-ray source in computed tomography. It appears because the object tends to absorb more low-energy photons within the beam, which leads to a nonlinear relationship between attenuation and material thickness. As a result, the reconstructed image is spoiled. This work articulates an approach to promoting the correction of MeV X-ray beam hardening. In order to calculate the attenuation of the polychromatic beam, the following terms were evaluated: the energy spectra S(E) for sets of X-ray spectra with a maximum energy of 2, 4, 6 and 9 MeV were simulated using the Geant4 toolkit; the counting efficiency λ(E) was estimated based on the Lifton method; and the attenuation coefficient µ(E) was taken from the NIST database. The non-linear relationship between the attenuation and the thickness of iron was investigated. The beam hardening for each energy set was successfully corrected by polynomial fitting, transforming the polychromatic attenuation data into equivalent monochromatic data. The corrected attenuation was used to estimate the penetration capability of the X-ray source and produced a result that was consistent with what has been reported in the literature

Post-earthquake restoration of water distribution network: A resilience framework

A demand-based seismic resilience analysis framework is proposed in this paper. Four pipe recovery strategies, including random, experienced, static importance-based and dynamic importance-based strategies, are introduced and simulated using two cases to compare their effects on improving resilience level. Based on simulation analysis, the importance-based strategies perform more efficiently in improving resilience than traditional practice prioritizing pipes nearby the water factory. In addition, although the dynamic-based strategy, the best one among the four, is not globally optimal, which is verified by exhaustion and genetic algorithms, it is still a near-optimal solution due to the limited error and high computation efficiency

Differential Features of Culprit Intracranial Atherosclerotic Lesions: A Whole-Brain Vessel Wall Imaging Study in Patients With Acute Ischemic Stroke.

BackgroundIntracranial atherosclerotic disease tends to affect multiple arterial segments. Using whole-brain vessel wall imaging, we sought to study the differences in plaque features among various types of plaques in patients with a recent unilateral anterior circulation ischemic stroke.Methods and resultsSixty-one patients with unilateral anterior circulation ischemic stroke were referred to undergo whole-brain vessel wall imaging (before and after contrast) within 1 month of symptom onset for intracranial atherosclerotic disease evaluations. Each plaque was classified as a culprit, probably culprit, or nonculprit lesion, according to its likelihood of causing the stroke. The associations between plaque features (thickening pattern, plaque-wall contrast ratio, high signal on T1-weighted images, plaque contrast enhancement ratio, enhancement grade, and enhancement pattern) and culprit lesions were estimated using mixed multivariable logistic regression after adjustment for maximum wall thickness. In 52 patients without motion corruption in whole-brain vessel wall imaging, a total of 178 intracranial plaques in the anterior circulation were identified, including 52 culprit lesions (29.2%), 51 probably culprit lesions (28.7%), and 75 nonculprit lesions (42.1%). High signal on T1-weighted images (adjusted odds ratio, 9.1; 95% confidence interval, 1.9-44.1; P=0.006), grade 2 (enhancement ratio of plaque ≥ enhancement ratio of pituitary) contrast enhancement (adjusted odds ratio, 17.4; 95% confidence interval, 1.8-164.9; P=0.013), and type 2 (≥50% cross-sectional wall involvement) enhancement pattern (adjusted odds ratio, 10.1; 95% confidence interval, 1.3-82.2; P=0.030) were independently associated with culprit lesions.ConclusionsHigh signal on T1-weighted images, grade 2 contrast enhancement, and type 2 enhancement pattern are associated with cerebrovascular ischemic events, which may provide valuable insights into risk stratification

East Atlantic Pattern Drives Multidecadal Atlantic Meridional Overturning Circulation Variability during the Last Glacial Maximum

The variability of the Atlantic Meridional Overturning Circulation (AMOC) and its governing processes during the Last Glacial Maximum (LGM) is investigated in the Kiel Climate Model (KCM). Under LGM conditions, multidecadal AMOC variability is mainly forced by the surface heat flux variability linked to the East Atlantic pattern (EAP). In contrast, the multidecadal AMOC variability under preindustrial conditions is mainly driven by the surface heat flux variability associated with the North Atlantic Oscillation (NAO). Stand‐alone atmosphere model experiments show that relative to preindustrial conditions, the change in AMOC forcing under LGM conditions is tightly linked to the differences in topography. Key Points Multidecadal AMOC variability during the LGM and its associated physical processes have been investigated by means of a climate model Multidecadal AMOC variability during the LGM is mainly driven by surface heat flux variability linked to the East Atlantic pattern as opposed to the North Atlantic Oscillation under preindustrial conditions Change in topography during the LGM is responsible for the change in AMOC forcin

The Research on Information Representation of Φ-OTDR Distributed Vibration Signals

This paper mainly focuses on the representable problem of Φ-OTDR distributed vibration signals. The research included a signal extraction part and a signal representation part. Firstly, in order to extract the better Φ-OTDR signal, the time-domain data should be fully preserved. The 2D-TESP method is used to extract data in this paper. There are 29 characters in the traditional TESP method. The characters’ number is reduced from 29 to 13 and the characters’ dimension is expanded from 1 to 2 in the 2D-TESP method. Secondly, in order to represent Φ-OTDR signal better, the characteristics of Φ-OTDR data and damped vibration signals are combined in the paper. The EMD method and the NMF method are combined to form the new method in the paper. Some parameters in the proposed method are optimized and adjusted by GA method. After Φ-OTDR data is represented by the proposed method, there is excellent performance both on the length dimension and on the time dimension. Lastly, some experiments are carried out according to the physical truth in this paper. The experiments are carried out in the semianechoic room. The methods of the paper have better performance. The methods are proved to be effective through these experiments