Detecting Backdoors in Pre-trained Encoders

Self-supervised learning in computer vision trains on unlabeled data, such as images or (image, text) pairs, to obtain an image encoder that learns high-quality embeddings for input data. Emerging backdoor attacks towards encoders expose crucial vulnerabilities of self-supervised learning, since downstream classifiers (even further trained on clean data) may inherit backdoor behaviors from encoders. Existing backdoor detection methods mainly focus on supervised learning settings and cannot handle pre-trained encoders especially when input labels are not available. In this paper, we propose DECREE, the first backdoor detection approach for pre-trained encoders, requiring neither classifier headers nor input labels. We evaluate DECREE on over 400 encoders trojaned under 3 paradigms. We show the effectiveness of our method on image encoders pre-trained on ImageNet and OpenAI's CLIP 400 million image-text pairs. Our method consistently has a high detection accuracy even if we have only limited or no access to the pre-training dataset.Comment: Accepted at CVPR 2023. Code is available at https://github.com/GiantSeaweed/DECRE

Povezanost polimorfizma pojedinačnog nukleotida gena ARID4A i kvalitete sperme kineskog vodenog bivola

ARID4A (AT-rich interaction domain 4A) is closely related to animal sperm quality traits. In the present study, the association between ARID4A gene polymorphisms of Chinese water buffalo (Bubalus bubalis) with sperm quality traits was examined, including ejaculate volume, sperm concentration, post-thaw sperm motility, and sperm abnormality of buffalo semen. Seven single-nucleotide polymorphisms (SNPs) of ARID4A gene were detected in 156 Chinese water buffaloes by Sanger sequencing and identifying overlap peaks. Among the SNPs, six were associated with at least one sperm quality trait. In brief, g.21192G>C, g.21285C>G, and g.21364A>G could be used as potential markers for selecting semen with low sperm abnormality, high ejaculate volume, sperm concentration, and sperm motility. Furthermore, 10 haplotypes (H1: -CTCGG, H2: GTGGCA, H3: GCGGCA, H4: GCTGCA, H5: GCTCGA, H6: GTGGGG, H7: GCTCCG, H8: -CGGGA, H9: GCGGCG, and H10: GTTGCA) were formed by the six SNPs through linkage disequilibrium analysis, and then 14 different combined haplotypes were collected. Correlation analysis showed that the combined H1H2 haplotype had the highest genotype frequency. Notably, the combined H1H2 haplotype had low sperm concentration, low sperm motility, and high sperm abnormality. The combined H2H3 haplotype could be used as a potential molecular marker for selecting semen with high sperm motility. In general, we illustrated a significant correlation between SNPs in ARID4A and sperm quality traits of Chinese water buffalo, which may be useful in the marker-assisted selection of buffalo breeding. This study was the first to analyze the genetic polymorphisms of ARID4A and association with sperm qualities of Chinese buffalo.Gen ARID4A (engl AT-rich interaction domain 4A) usko je povezan s kvalitetom sperme. U ovom je radu istraživana povezanost polimorfizma gena ARID4A u kineskih vodenih bivola (Bubalus bubalis) s kvalitetom sperme, uključujući volumen ejakulata, koncentraciju sperme, pokretljivost spermija nakon odmrzavanja i abnormalnost spermija u sjemenu bivola. U 156 kineskih vodenih bivola otkriveno je sedam polimorfizama pojedinačnog nukleotida (SNPs) gena ARID4A Sangerovim sekvenciranjem i identifikacijom preklopljenih vrhova. Među SNP-ovima njih je šest bilo povezano s barem jednim svojstvom kvalitete spermija. Ukratko, g. 21192G>C, g. 21285C>G i g. 21364A>G mogu se upotrijebiti kao potencijalni markeri za selekciju sjemena s niskom abnormalnošću spermija, većim volumenom ejakulata, većom koncentracijom i pokretljivošću spermija. Nadalje, šest SNP-ova formiralo je 10 haplotipova (H1: -CTCGG, H2: GTGGCA, H3: GCGGCA, H4: GCTGCA, H5: GCTCGA, H6: GTGGGG, H7: GCTCCG, H8: -CGGGA, H9: GCGGCG i H10: GTTGCA) analizom povezanosti nepodudarnosti te je ustanovljeno 14 različitih kombiniranih haplotipova. Analiza korelacije pokazala je da kombinirani haplotip H1H2 ima najveću učestalost. Kombinirani haplotip H1H2 imao je najmanju koncentraciju sperme, slabu pokretljivost seprmija i znatnu abnormalnost spermija. Kombinirani haplotip H2H3 može se upotrijebiti kao potencijalni molekularni marker za odabir sjemena s većom pokretljivošću. Općenito je pokazana znakovita korelacija između SNP-ova u ARID4A i kvalitete sperme kineskog vodenog bivola, što može biti korisno u selekciji bivola potpomognutoj markerima. Ovo je prvo istraživanje koje je analiziralo genske polimorfizme ARID4A i njihovu povezanost s kvalitetom sjemena kineskih vodenih bivola

Prospects for Power Generation of the Doublet Supercritical Geothermal System in Reykjanes Geothermal Field, Iceland

Supercritical geothermal resources are in the preliminary exploration stage as a new type of clean energy and there are no practical utilization projects. The IDDP-2 well at Reykjanes geothermal field in Iceland encountered supercritical geothermal conditions in 2017, with a maximum temperature of 535 °C. The system is still in the field experiment stage and no exploitation work has been carried out. Hence, a hypothetical doublet geothermal system was simulated based on IDDP-2 to study the power generation potential and favorable operating conditions for future development of supercritical geothermal resources. A multiphase flow model is established to predict the fluid and heat flow characteristics. Furthermore, sensitivity and economic analyses were performed to evaluate the expected commercial and environmental benefits of the supercritical geothermal system. The results show that the system’s evolution could be briefly divided into three stages according to the temperature variation. The power generation ranges between 5.4 MW~16.5 MW, and the levelized cost of electricity (LCOE) is 0.02 $/kWh. In addition, the system can reduce CO2 emissions, which are 1.2~7.75 Mt less than that of fossil fuel plants with the same installed capacity. The results prove the great development potential and commercial competitiveness of the supercritical geothermal system

Numerical Modeling of Reactive Transport and Self-Sealing Processes in the Fault-Controlled Geothermal System of the Guide Basin, China

Strong chemical reactions in the geothermal systems may cause sealing of fractures, which reduces the permeability in the reservoir and subsequently affects the heat production. However, it is difficult to reveal the sealing range in a deeply buried reservoir based on a limited number of downhole logs. This study recreated the sealing processes of the fault-controlled geothermal system in the Guide Basin, China, by reactive transport modeling. The modeling domain was discretized based on multiple interacting continua (MINC) approach, to address the nonequilibrium heat transport processes between the matrix and conduit in the fractured fault damage zone. Once the model was validated by observations of major ions in spring water and downhole temperature logs in the discharge area, it was used to determine the coupled processes of fluid, heat, and chemical transport in the reservoir and the resultant sealing ranges. It was found that the dissolution of albite and K-feldspar leads to the precipitation of smectite-Ca and illite in the middle and bottom of the fault under the condition of high concentration of Ca2+ and Mg2+ in the recharge water. Calcite veins were formed in discharge zone, because the horizontal fast flow in shallow subsurface zone supplied abundant Ca2+ and HCO3-. As a consequence, the permeability in the discharge zone reduced by 15% when compared to the original permeability of 100 mD. Moreover, another three self-sealing areas were formed near the recharge zone, the deep upgradient zone, and the downgradient area where the fast upward fluid flow occurred. Self-sealing subsequently prevented the deep circulation of the flow and heat absorption, which tends to make the fault-controlled geothermal system inactive

Prospects for Power Generation of the Doublet Supercritical Geothermal System in Reykjanes Geothermal Field, Iceland

Supercritical geothermal resources are in the preliminary exploration stage as a new type of clean energy and there are no practical utilization projects. The IDDP-2 well at Reykjanes geothermal field in Iceland encountered supercritical geothermal conditions in 2017, with a maximum temperature of 535 °C. The system is still in the field experiment stage and no exploitation work has been carried out. Hence, a hypothetical doublet geothermal system was simulated based on IDDP-2 to study the power generation potential and favorable operating conditions for future development of supercritical geothermal resources. A multiphase flow model is established to predict the fluid and heat flow characteristics. Furthermore, sensitivity and economic analyses were performed to evaluate the expected commercial and environmental benefits of the supercritical geothermal system. The results show that the system’s evolution could be briefly divided into three stages according to the temperature variation. The power generation ranges between 5.4 MW~16.5 MW, and the levelized cost of electricity (LCOE) is 0.02 $/kWh. In addition, the system can reduce CO2 emissions, which are 1.2~7.75 Mt less than that of fossil fuel plants with the same installed capacity. The results prove the great development potential and commercial competitiveness of the supercritical geothermal system

Use of CO2 as Heat Transmission Fluid to Extract Geothermal Energy: Advantages and Disadvantages in Comparison with Water

ABSTRACT Use of CO 2 as heat transmission fluid to extract geothermal energy is currently considered as a way to achieve CO 2 resource utilization and geological sequestration. As a novel heat transmission fluid, the thermophysical property of CO 2 is quite different from water. It has many advantages, such as larger mobility and buoyancy resulted from the lower density and viscosity. This will reduce the consumption of driving pressure of the circulation, and save the energy consumption of external equipment. The cycle even can be achieved by siphon phenomenon under a negative circulating pressure difference. However, there are still some disadvantages for CO 2 as a kind of heat transmission fluid, such as small heat capacity, leading to carry less heat at the same mass flow rate. At the same time, if temperature and pressure change, it will cause a more complex flow and thermodynamic processes because of the lager expansion and compression coefficient for CO 2 . Lager compressibility makes it possible to get high temperature at the bottom of the injection well, but lager expansion coefficient makes the temperature drops rapidly during the extraction process. Therefore, how to scientifically control the production pressure to guarantee the temperature at the head of production well to be high enough and then improve the efficiency of heat extraction is the key problem to be further studied and solved. Here, a classic idealized "five-spot" model coupled with wellbores is set up according to the geological and geothermal conditions and parameters of the central depression of Songliao basin. Our purpose is to (1) explore the flow and thermodynamics process of supercritical CO2 as heat transmission fluid, analyze the heat recovery mechanism, (2) compare the heat extraction efficiency of CO2 with water, and evaluate the advantages and disadvantages using CO2, (3) optimize the temperature and pressure of injection and production and other parameters for CO2, and (4) determine the favorable range of temperature and pressure of geothermal reservoirs, and provide a theoretical basis for the selection of heat transmission fluid. Results from this work may be useful for future field design of a CO 2 -geothermal system

An Approximate Solution for Predicting the Heat Extraction and Preventing Heat Loss from a Closed-Loop Geothermal Reservoir

Approximate solutions are found for a mathematical model developed to predict the heat extraction from a closed-loop geothermal system which consists of two vertical wells (one for injection and the other for production) and one horizontal well which connects the two vertical wells. Based on the feature of slow heat conduction in rock formation, the fluid flow in the well is divided into three stages, that is, in the injection, horizontal, and production wells. The output temperature of each stage is regarded as the input of the next stage. The results from the present model are compared with those obtained from numerical simulator TOUGH2 and show first-order agreement with a temperature difference less than 4°C for the case where the fluid circulated for 2.74 years. In the end, a parametric study shows that (1) the injection rate plays dominant role in affecting the output performance, (2) higher injection temperature produces larger output temperature but decreases the total heat extracted given a specific time, (3) the output performance of geothermal reservoir is insensitive to fluid viscosity, and (4) there exists a critical point that indicates if the fluid releases heat into or absorbs heat from the surrounding formation

Assessment of Energy Production in the Deep Carbonate Geothermal Reservoir by Wellbore-Reservoir Integrated Fluid and Heat Transport Modeling

Geothermal energy is clean and independent to the weather and seasonal changes. In China, the huge demanding of clean energy requires the geothermal energy exploitation in the reservoir with depth larger than 1000 m. Before the exploitation, it is necessary to estimate the potential geothermal energy production from deep reservoirs by numerical modeling, which provides an efficient tool for testing alternative scenarios of exploitation. We here numerically assess the energy production in a liquid-dominated middle-temperature geothermal reservoir in the city of Tianjin, China, where the heat and fluid transport in the heterogeneous reservoir and deep wellbores are calculated. It is concluded that the optimal injection/production rate of the typical geothermal doublet well system is 450 m3/h, with the distance between geothermal doublet wells of 850 m. The outflow temperature and heat extraction rate can reach 112°C and 43.5 MW, respectively. Through decreasing injection/production rate lower than 450 m3/h and optimizing layout of the injection well and production well (avoiding the high permeability zone at the interwell sector), the risk of heat breakthrough can be reduced. If the low permeability zone in the reservoir is around injection well, it usually leads to abnormal high wellhead pressure, which may be solved by stimulation technique to realize stable operation. The methodology employed in this paper can be a reference for a double-well exploitation project with similar conditions