Understanding Large Language Model Based Fuzz Driver Generation

Fuzz drivers are a necessary component of API fuzzing. However, automatically generating correct and robust fuzz drivers is a difficult task. Compared to existing approaches, LLM-based (Large Language Model) generation is a promising direction due to its ability to operate with low requirements on consumer programs, leverage multiple dimensions of API usage information, and generate human-friendly output code. Nonetheless, the challenges and effectiveness of LLM-based fuzz driver generation remain unclear. To address this, we conducted a study on the effects, challenges, and techniques of LLM-based fuzz driver generation. Our study involved building a quiz with 86 fuzz driver generation questions from 30 popular C projects, constructing precise effectiveness validation criteria for each question, and developing a framework for semi-automated evaluation. We designed five query strategies, evaluated 36,506 generated fuzz drivers. Furthermore, the drivers were compared with manually written ones to obtain practical insights. Our evaluation revealed that: while the overall performance was promising (passing 91% of questions), there were still practical challenges in filtering out the ineffective fuzz drivers for large scale application; basic strategies achieved a decent correctness rate (53%), but struggled with complex API-specific usage questions. In such cases, example code snippets and iterative queries proved helpful; while LLM-generated drivers showed competent fuzzing outcomes compared to manually written ones, there was still significant room for improvement, such as incorporating semantic oracles for logical bugs detection.Comment: 17 pages, 14 figure

Evolving Walkability of Major Cities in the People's Republic of China

Context: Walkability is an important element for assessing urban sustainability. There are increased concerns that more cities in the People's Republic of China (PRC) have become less walkable. Objectives: We aim to develop a composite walkability index. We intend to use it to evaluate the spatio-temporal evolution of the walkability of PRC cities in the context of the rapid urbanization. Methods: We developed a comprehensive walkability index that integrates five aspects of the urban built environment: dwelling density, street connectivity, land-use mix, access to public transit, and elevation variation. Using Shanghai, Hangzhou, Chongqing, and Lanzhou as cases, we evaluated the spatio-temporal patterns and changes of walkability in the context of rapid urban expansion. Results: All four cities expanded their urban land from 1990 to 2010, but that there was a higher expansion rate in 2000-2010 than in 1990-2000. For inner cities, Shanghai had the highest average walkability index, whereas Lanzhou held the lowest. In 2000-2010, however, the inner cities of Hangzhou, Chongqing, and Lanzhou and the entire cities of Shanghai and Chongqing increased their walkability index, whereas the inner city of Shanghai had decreased walkability. Furthermore, while inner cities of Shanghai and Hangzhou experienced decreased or stable walkability, inner cities of Lanzhou and Chongqing enjoyed moderate to high increases in walkability. Conclusions: The spatiotemporal changes in walkability seem to be directly associated with governmental policies at both central and local levels. The walkability index method can be widely implemented for any urban landscape because of its comprehensiveness, simplicity, and flexibility

Detecting Historical Vegetation Changes in the Dunhuang Oasis Protected Area Using Landsat Images

Abstract: Given its proximity to an artificial oasis, the Donghu Nature Reserve in the Dunhuang Oasis has faced environmental pressure and vegetation disturbances in recent decades. Satellite vegetation indices (VIs) can be used to detect such changes in vegetation if the satellite images are calibrated to surface reflectance (SR) values. The aim of this study was to select a suitable VI based on the Landsat Climate Data Record (CDR) products and the absolute radiation-corrected results of Landsat L1T images to detect the spatio-temporal changes in vegetation for the Donghu Reserve during 1986–2015. The results showed that the VI difference (ΔVI) images effectively reduced the changes in the source images. Compared with the other VIs, the soil-adjusted vegetation index (SAVI) displayed greater robustness to atmospheric effects in the two types of SR images and was more responsive to vegetation changes caused by human factors. From 1986 to 2015, the positive changes in vegetation dominated the overall change trend, with changes in vegetation in the reserve decreasing during 1990–1995, increasing until 2005–2010, and then decreasing again. The vegetation changes were mainly distributed at the edge of the artificial oasis outside the reserve. The detected changes in vegetation in the reserve highlight the increased human pressure on the reserve

Spatiotemporal Changes in Rural Settlement Land and Rural Population in the Middle Basin of the Heihe River, China

Understanding the relationship between the spatiotemporal expansion of rural settlement land and the variation of rural population is the foundation of rational and specific planning for sustainable development. Based on the integration of Landsat TM, ETM+, and OLI images and demographic data, using mathematical models, landscape indexes, and a decoupling model, the spatiotemporal changes of the rural settlement land area and its decoupling relationship with the rural registered population were analyzed for the middle basin of the Heihe River in China. During the period 1986–2014, the following changes occurred: (1) The study area experienced increases of 124.94%, 55.16%, and 1.56% in rural settlement land area, number of patches, and rural registered population, respectively; (2) Edge-expansion, dispersion, and urban encroachment were the dominant patterns of dynamic changes in the studied rural settlement land. Among these, edge-expansion was the most prevalent development pattern; it contributed more than half of the total increase in the number of patches and the total area growth; (3) The annual growth rate of the rural registered population increased from 0.7% in 1986–2002 to −0.5% in 2002–2014. By that time the rural settlement land area had undergone a gentle increase from 3.4% to 3.6%. Generally, the rural registered population and rural settlement land has experienced a shift from weakly decoupled in 1986–2009 to strongly decoupled in 2009–2014; (4) From 1986 to 2014, rural urbanization and modernization were the main causes that led to the decline in the rural registered population; however, economic growth promoted the expansion of rural settlement land during this same period. We believe that with the rapid development of urbanization, the decoupling relationship between the rural settlement land area and the reduction in the rural registered population cannot be completely reversed in the short term. It is recommended that the government should enhance the role of planning rural settlement land during the process of urbanization

Human settlement and changes in the distribution of river systems in the Minqin Basin over the past 2000 years in Northwest China

Introduction: Arid area is an important base for human settlement, however, long and drastic human activities have altered the drainage patterns in the arid watersheds significantly, causing serious ecological consequences. This study, through a case study of the Minqin Basin, a microcosm of the artificial oases in the arid northwest China, used the multi-types of data to recover the spatial distribution of human settlement and drainage patterns during historical period and analyze the relationship between them over the past 2000 years. Outcomes: Before the Han Dynasty (121 BC), the utilization of water resources in the Minqin Basin was in the primitive stage and the drainage pattern maintained the natural state. From the Han (121 BC- 220) to the Wei-Jin Dynasties (220- 316), the utilization of water resources intensified unprecedentedly, but the natural shape of the river systems was still maintained. In the following 1,000 years or so, the drainage pattern was in the state of “following its own course” due to the small human population. In the Ming Dynasty (1368-1644), with the alteration of the main rivers, the water resource utilization increased obviously, but the human reclamations were mainly confined to the southern part of the basin. In the Qing Dynasty (1644-1911), the reclamation of the Liulin Lake area significantly changed the drainage patterns, resulted in the drastically northward expansion of human settlement. Since the foundation of the People’s Republic of China (PRC) in 1949, the artificial water system completely replaced the natural water system and intensified the ecological problems in the basin. Discussion: The changes over the past 2000 years show the drastic impacts of human activities on the alterations of the drainage patterns and related ecological problems in the arid Northwest China. Conclusion: Rehabilitation of such ecological impairments requires both ecological restoration projects and changes in human paradigm and behavior over multiple temporal and spatial scales

CrnnCrispr: An Interpretable Deep Learning Method for CRISPR/Cas9 sgRNA On-Target Activity Prediction

CRISPR/Cas9 is a powerful genome-editing tool in biology, but its wide applications are challenged by a lack of knowledge governing single-guide RNA (sgRNA) activity. Several deep-learning-based methods have been developed for the prediction of on-target activity. However, there is still room for improvement. Here, we proposed a hybrid neural network named CrnnCrispr, which integrates a convolutional neural network and a recurrent neural network for on-target activity prediction. We performed unbiased experiments with four mainstream methods on nine public datasets with varying sample sizes. Additionally, we incorporated a transfer learning strategy to boost the prediction power on small-scale datasets. Our results showed that CrnnCrispr outperformed existing methods in terms of accuracy and generalizability. Finally, we applied a visualization approach to investigate the generalizable nucleotide-position-dependent patterns of sgRNAs for on-target activity, which shows potential in terms of model interpretability and further helps in understanding the principles of sgRNA design

Driving Factors of Recent Vegetation Changes in Hexi Region, Northwest China Based on a New Classification Framework

Since other factors (soil properties, topography, etc.) under natural conditions are relatively invariant over one or two decades, climate variables (precipitation and temperature) and human activities are the two fundamental factors driving vegetation changes in global or large-scale areas. However, the combined effects of either single climatic factor and human activities on vegetation changes and the role of human activities itself in a specific region has not been fully discussed. In this study, the Hexi region, a typical dryland consisting of three inland river basins in northwest China was selected as a case area. A new classification framework combining Pearson correlation analysis and residual trend approach was proposed to assess their individual and conjoint contributions of climate variables and human activities in areas of significant vegetation changes. Our results indicated that most of vegetation covered areas in the Hexi region experienced significant changes during the period 2001−2017, and vegetation improvements were widespread except the interior of oases; significant changes in vegetation caused by human activities, precipitation, the interactions of precipitation and human activities, temperature, the interactions of temperature and human activities, the interactions of temperature and precipitation, and the interactions of the three factors accounted for 50.46%, 16.39%, 19.90%, 4.33%, 2.32%, 2.11%, and 4.49% of the total change areas, respectively. Generally, the influence of temperature was relatively weaker than that of precipitation, and the contributions of the interactions of climate variables and human activities on vegetation changes were greater than that of climate contributions alone. Moreover, the results of various investigations, according to the trends and the time of vegetation changes, indicate that decreasing trends of the normalized difference vegetation index (NDVI) in the Hexi region were chiefly attributed to the adjustments of agricultural planting structure while the comprehensive treatment programs implemented in river basins supported a large proportion of vegetation improvements

Spatio-Temporal Changes of Oases in the Hexi Corridor over the Past 30 Years

In recent decades, the oases in the Hexi Corridor have gone through a tremendous transformation, which has caused a series of social and environmental problems. We aim to explore quantitatively the characteristics of the oasis expansion and their dynamic mechanism(s) in the Hexi Corridor, and their implications and impact on current and future policies. The spatial distribution pattern and dynamic changes experienced by the oases are examined using Landsat imagery. Their spatio-temporal changes are analyzed using the grid-transformed model and the dynamic-degree model. The model drivers are analyzed based on data from statistics yearbooks and field surveys. The total area of oases in the Hexi Corridor has expanded tremendously during the last 30 years from 10,709 km2 to 14,950 km2, almost 40% of the original value. Oasis evolution patterns of ‘unchanged’, ‘expanding’, ‘shrinking’, and ‘oscillating’ are observed at different periods in the three basins. In terms of area, almost half of the oases experienced some change, where most of the changes took place in the ecotone between oases and deserts, and the interior of oases due to the reclamation of abandoned land. Oasis expansion is mainly determined by the human instincts for survival and well-being, which are generally governed by population growth, agricultural policies and economic development. These changes reflect the need to find a balance in the relationship between ecological protection and increasing the well-being of local residents, because unreasonable or excessive development and utilization will cause damage to the local ecological environment