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Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short‐term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium‐term (years) and long‐term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long‐term effects of residue addition on N2O emissions. [ABSTRACT FROM AUTHOR]

File systems provide an interface for applications to obtain exclusive access to files, in which a process holds privileges to a file that cannot be preempted and restrict the capabilities of other processes. Local file systems do this by maintaining information about the privileges of current file sessions, and checking subsequent sessions for compatibility. Implementing exclusive access in this manner for distributed file systems degrades performance by requiring every new file session to be registered with a lock server that maintains global session state. We present two techniques for improving the performance of session management in the distributed environment. We introduce a distributed lock for managing file access, called a semi-preemptible lock, that allows clients to cache privileges. Under a semi-preemptible lock, a file system creates new sessions without messages to the lock manager. This improves performance by exploiting locality – the affinity of files to clients. We also present data structures and algorithms for the dynamic evaluation of locks that allow a distributed file system to efficiently manage arbitrarily complex locking. In this case, complex means that an object can be locked in a large number of unique modes. The combination of these techniques results in a distributed locking scheme that supports fine-grained concurrency control with low memory and message overhead and with the assurance that their locking system is correct and avoids unnecessary deadlocks.

Distributed file systems are often used to replicate a Web site's content among its many servers. However, for content that needs to be dynamically updated and distributed to many servers, file system locking protocols exhibit high latency and heavy network usage. Poor performance arises because the Web-serving workload differs from the assumed workload. To address the shortcomings of file systems, we introduce the publish consistency model well suited to the Web-serving workload and implement it in the producer-consumer locking protocol. A comparison of this protocol against other file system protocols by simulation shows that producer-consumer locking removes almost all latency due to protocol overhead and significantly reduces network load.

Nitrous oxide (N2O) emissions occur as a consequence of the turnover of soil nitrogen (N), but gross N transformations and N2O production are often not studied in combination, so the relationships are poorly understood. Here, we quantified gross N transformations and the N2O production pathway of alkaline fluvo-aquic soils under different fertilization regimes collected from a long-term field experiment in the North China Plain and compared them with six acidic UK soils (one was alkaline for reference) with high soil organic carbon (SOC). We found that nitrification was the dominant N2O production pathway in the alkaline Chinese soil with a contribution of nitrification to N2O emissions (N2Onit) of 81%. By contrast, denitrification was the main N2O production pathway for the acidic UK soils with the contribution of denitrification to N2O emissions (N2Oden) of 66%. Long-term manure applications significantly increased N2Oden, compared to the synthetic N and no N treatments (25% vs. 18%). The N2Onit was positively correlated with gross autotrophic nitrification rates and pH but negatively correlated with gross N mineralization, SOC, soil total N content, and C:N ratios. Our findings highlight the importance of soil pH in controlling the N2O production in cropland soils, and suggest that the increased contribution of denitrification to N2O emissions should be considered, when increasing SOC through long-term manure and straw management for carbon sequestration and soil fertility improvement. [ABSTRACT FROM AUTHOR]