Technical Note: Is radiation important for the high amplitude variability of the MOC in the North Atlantic?

International audienceRadiation is of fundamental importance to climate modeling and it is customary to assume that it is also important for the variability of North Atlantic Deep Water (NADW) formation and the meridional overturning cell (MOC). Numerous articles follow this scenario and incorporate radiation into the calculation. Using relatively old heat-flux maps based on measurements taken in the nineteen sixties, Sandal and Nof (2007) recently suggested that, even though the radiation terms are of the same order as the other heat-flux terms, they are not important for the variability of the NADW and the MOC. They proposed that only sensible and latent heat fluxes are important for the long-term variability of the convection, i.e., for processes such as Heinrich events, which supposedly correspond to turning convection on-and-off in the Atlantic. Here, we place this suggestion on a firmer ground by presenting new and accurate up-to-date heat flux maps that also suggest that the radiation is of no major consequence to the NADW variability. Also, we attribute the relative importance of sensible and latent heat fluxes and the contrasting negligible role of radiation to the fact that the latent and sensible heat fluxes are primarily proportional to the difference between the sea surface and the air temperature whereas the radiation is primarily proportional to the sea surface temperature, i.e., radiation is approximately independent of the atmospheric temperature. Due the small heat capacity ratio of air/water (1/4), the difference between the ocean temperature and the air temperature varies dramatically between the state of active and inactive MOC, whereas the ocean temperature by itself varies very modestly between a state of active and inactive convection

Anomalous Light Scattering by Pure Seawater

The latest model for light scattering by pure seawater was used to investigate the anomalous behavior of pure water. The results showed that water exhibits a minimum scattering at 24.6 °C, as compared to the previously reported values of minimum scattering at 22 °C or maximum scattering at 15 °C. The temperature corresponding to the minimum scattering also increases with the salinity, reaching 27.5 °C for S = 40 ps

Research on election time optimization of ZooKeeper distributed coordination service based on Raft algorithm

In distributed system, ZooKeeper is a common coordination service. Its election algorithm is one of the core algorithms in ZooKeeper cluster, which ensures the high availability and consistency of ZooKeeper. However, the time overhead in the election process can aff ect the performance of the entire cluster. In order to improve the effi ciency of ZooKeeper cluster election, this paper studies the election time optimization method of ZooKeeper cluster distributed coordination service based on Raft algorithm, analyzes the mechanism of ZooKeeper election algorithm, puts forward the main sources of election time cost, and introduces the basic principle and characteristics of Raft algorithm. And apply it to ZooKeeper election to reduce the number and complexity of election messages by pruning and batch processing technology. Finally, this paper verifi es the eff ectiveness of the optimization method through experiments, and compares it with other algorithms

Laboratory Characterization of Reservoir Stimulation and Heat Extraction with Application to EGS

Enhanced or engineered geothermal systems (EGS) could enable extraction of significant geothermal energy from hot relatively dry rock reservoirs. However, issues related to reservoir creation in different type of rocks and stress conditions, reservoir monitoring during reservoir creation and consequent production, better knowledge of the fluid/heat flow in the induced fracture, field management and optimization need be addressed before successful commercial development. As an effort to help solve these essential questions, a novel lab-scale EGS test system was developed to perform EGS simulation experiments on rock blocks under high pore pressure/elevated temperature and representative in-situ stress regimes while simultaneously recording Acoustic Emission (AE), self-potential (SP), temperature/pressure and tracers to characterize the reservoir creation, heating mining and flow characteristics of the system. The tests were performed on the 330 mm × 330 mm ×330 mm cubic igneous rock blocks. Two kinds of igneous rocks with different texture and permeability were tested with one injection hole and four producers (five-spot pattern). The great potential of EGS was demonstrated by the fact that about 50 watts of power was obtained by fluid flowing through the induced fracture with length of 8.9 cm and rock temperature less than 80oC. Analysis of the test results sheds light on the use of acoustic emission for better understanding of hydraulic fracturing. Also, self-potential analysis indicates SP response was mainly controlled by electrokinetic coupling and the impact of thermoelectric coupling on recorded SP is negligible as demonstrated in some field observations and modeling while the fluid concentration (salinity) has a great influence on the SP response compared with temperature gradient when the concentration contrast between the injection fluid and the pore fluid is large due to the streaming potential coefficient reduction by the high concentration liquid. The heat circulation test shows that it is the effective fracture area instead of the total fracture area that controls the heat mining in EGS and thus the distance between injection/production wells or the location of the producer(s) and flow path tortuosity need be optimized to increase the effective heat exchange area in reservoir stimulation practice and the heat mining should be operated in a proper way to avoid well competition when multiple producers are connected to the same injection well by natural/man-made fractures. Excessive fracture propagation and high injection pressure was avoided during circulation tests by increasing the injection rate step by step. The cooling effect of the rock matrix i.e., increased fracture conductivity and lowering of the injection pressure is clearly manifested in the circulation experiments. As the first lab-scale tracer test on EGS, the obtained result was promising. The existing of two linear tracer tail was observed in Sierra White granite test and tracer result does show a good correlation between hydraulic conductivity and the tracer concentration response. The impact of rock texture was observed. What’s more, the test result could provide some useful guide for future lab-scale tracer test deign. Low permeability rock is recommended for tracer test to minimize leakage of tracer fluid into the rock matrix and also improve the fluid recovery. Low injection rate will increase the tracer time the in the fracture while proper tracer candidate with low-concentration detectability is required. Since the in-situ permeability of most of the dry hot rocks is not high enough to support the water injection with sufficient rate, reservoir stimulation by hydraulic fracture is usually applied. Considering the comment presence of natural fractures in the underground rocks, it is of importance to analyze the interaction between the hydraulic fracture and natural fracture. Analog experiments were conducted to investigate the interaction between a natural fracture and a hydraulic fracture with focus on slippage on the natural fracture or a bedding plane discontinuity due to an approaching hydraulic fracture. The tests were conducted on 101.6 mm diameter cylinder samples with a horizontal wellbore. The test materials included PMMA, shales, and Sierra White granite. Injection pressure, deviator stress, acoustic emission and the sample deformation are monitored during the test. In all the reported tests, the displacement calculated from the measured strain across the joint clearly shows a jump subsequent to pressure breakdown, and is accompanied by increased AE activity and decreased deviator stress. The displacement jump (slippage) across the joint with decreased deviatoric stress and AE activities on the joint from show that the hydraulic fracture caused slip of the saw-cut fractures even before reaching them. Analysis of the data clearly shows the occurrence of slippage on the joint in response to an approaching hydraulic fracture. The slippage due to the increased pore pressure on the natural fracture was also observed. Before the induced fracture reached the natural fracture, different degree of slippage (0.085mm ~ 0.11 mm) was obtained from these tests with various amount of deviator stress drop (0.14 MPa~ 0.6 MPa). Expectedly, the degree of shear slip varies with natural fracture dip, and friction angle and the differential stress. It is also observed that the pore pressure increase on the natural fracture by the encroaching hydraulic fracturing triggered larger slip on the natural fracture

Improved Fine-Grained Representation Learning with Data Transformation

University of Technology Sydney. Faculty of Engineering and Information Technology.Fine-grained recognition is challenging in computer vision and artificial intelligence. It aims to identify under subcategories of given images but suffers from small inter-class variance and large intra-class variance along with multiple object scales and complex background, leading to a more complex problem space. Recently, deep neural networks have extensively promoted the development of fine-grained recognition. However, the existing methods still suffer from several issues, including data limitation, model interpretation, and performance. In this thesis, we propose several data-transformation models to address these challenges. First, we develop a unified framework (MGN-CNN) based on a mixture of experts to promote diversity among experts by combing a gradually-enhanced learning strategy and a KullbackLeibler divergence based constraint. The strategy learns new experts on the dataset with prior knowledge from former experts and adds them to the model sequentially. At the same time, the introduced constraint forces the experts to produce diverse prediction distributions. These drive the experts to learn the task from different aspects, making them specialized in various subspace problems. Second, we propose Intra-class Part Swapping (InPS) that produces new data by performing attention-guided content swapping on input pairs from the same class. Compared with previous approaches, InPS avoids introducing noisy labels and ensures a likely holistic structure of objects in generated images. We demonstrate InPS outperforms the most recent augmentation approaches in both fine-grained recognition and weakly object localization. Finally, we explore fine-grained zero-shot learning and introduce a novel structure-aware feature generation scheme, termed SA-GAN, to explicitly account for the topological structure in learning both the latent space and the generative networks. This topology-preserving mechanism enables our method to significantly enhance the generalization capability on unseen-classes and consequently improve the classification performance

Light Scattering by Pure Seawater: Effect of Pressure

The Zhang et al. model [Optics Express,17, 5698-5710 (2009)] for calculating light scattering by seawater doesnot account for pressure, which should, theoretically, affect molecular scattering. While negligible in nearsurface waters, the error associated with this approximation could be significant when backscattering is mea-sured directly in the deep ocean, by deep CTD casts or biogeochemical-Argo floats, for example. We updated theparameterization in the Zhang et al. model using (1) the Millard and Seaver equation for the refractive index ofseawater [Deep Sea Research Part A,37, 1909-1926 (1990)] and (2) the Feistel equation for Gibbs free energyfor seawater thermodynamics [Deep-Sea Research I,55, 1639-1671 (2008)]. As these equations include theeffect of pressure as well as salinity and temperature, our new parameterization allows us to investigate thepotential effect of pressure on scattering. Increasing pressure suppresses the random motion of molecules, re-ducing the fluctuations in both density and concentration, which in turn causes an overall decrease in lightscattering by seawater. For pure water and seawater with a salinity of 34 PSU, the decreases are approximately13% and 12%, respectively, with a 100-MPa (approximately the pressure of seawater at 10000 m) increase inpressure. Below the thermocline and/or halocline where temperature and salinity change slowly, the steadyincrease of pressure is the dominant factor affecting the light scattering by seawater. At depths where back-scattering is typically dominated by molecular scattering by seawater, particulate backscattering would beunderestimated if the effect of pressure on molecular scattering were not considered

Crew Scheduling Considering both Crew Duty Time Difference and Cost on Urban Rail System

Urban rail crew scheduling problem is to allocate train services to crews based on a given train timetable while satisfying all the operational and contractual requirements. In this paper, we present a new mathematical programming model with the aim of minimizing both the related costs of crew duty and the variance of duty time spreads. In addition to iincorporating the commonly encountered crew scheduling constraints, it also takes into consideration the constraint of arranging crews having a meal in the specific meal period of one day rather than after a minimum continual service time. The proposed model is solved by an ant colony algorithm which is built based on the construction of ant travel network and the design of ant travel path choosing strategy. The performances of the model and the algorithm are evaluated by conducting case study on Changsha urban rail. The results indicate that the proposed method can obtain a satisfactory crew schedule for urban rails with a relatively small computational time