国家预印本平台

Frontier LLM providers cache a prompt's processed prefix so that a follow-up request sharing it pays ~10% of the input price and skips most of the prefill latency. Agentic workloads systematically destroy this benefit: the agent sends a request, runs a tool or waits for approval for minutes, and by the time the follow-up is sent the cached prefix has been evicted, so the agent pays the full prefill again. A client-side keepalive, replaying the prefix on a timer during the pause, prevents this, and it is individually rational: across Anthropic, OpenAI, Google, and DeepSeek we show that a keepalive holds the prefix warm through gaps where idle baselines are evicted, cutting the post-pause request cost by up to 12.5x. The strategic question is the ping frequency, and it has a clean answer: keepalive cost falls monotonically in the interval, so the economical choice is the largest interval safely under the provider's TTL, about 4 minutes at Anthropic's 5-minute TTL rather than the 30-second convention, and the strategy breaks even against a re-prefill at idle ~tau(w/r - 1) (~46 min for Anthropic, ~36 min for OpenAI and DeepSeek). Because the benefit is real and bounded only by each user's own bill, rational adoption is universal adoption; and since cache residency is priced per read rather than per token-hour, a keepalive-saturated tier gives LRU eviction nothing to rank. We argue this externality will push providers to meter cache residency directly, and one already does. We derive the operator's policy until then.

The recent growth in data availability in football has increased the risk of incorrect use of data-driven models, making guidelines on their validation and application necessary. The Expected Threat (xT) model is an accessible option for football organisations that start building in-house methods, yet little is known about how to assess its quality. The aim of this study is twofold: to examine how the model quality depends on the number of game states and the number of training points, and to translate these results into guidelines for constructing and applying the model. Using the Markov chain underlying the model, we perform theoretical analyses and simulations to study the estimation error. These show that the estimation error is approximately lognormal for a given number of training points and game states. Additionally, we combine the simulations with expert consultation to establish the estimation error beyond which player evaluations based on the Expected Threat model become unreliable for scouting applications. From this, we derive rules of thumb to ensure the quality of an Expected Threat model before application, and we illustrate through an example how a validated model can be applied in practice. Because the approach generalises to Expected Possession Value models, this paper illustrates a framework to systematically quantify model quality, despite the ground truth being unobservable in football analytics.

塔里木盆地地形复杂，暖季降水预报的不确定性显著。为了深入认识中国气象局区域高分辨率数值模式（CMA-MESO）在塔里木盆地的降水预报性能，基于2023—2024年暖季CMA-MESO预报数据与地面观测资料，采用多种降水检验指标，系统评估了该模式对塔里木盆地暖季降水的预报偏差。结果表明：CMA-MESO总体上能较好地模拟盆地暖季降水的空间分布特征。随着海拔升高，TS评分上升，而PC评分下降。降水频率预报偏差幅度在亚高海拔区最为显著，正偏差中心带集中分布在昆仑山西段迎风坡，24 h和1 h降水频率预报最大偏差分别为44.1%和11.6%。TS评分的日变化显著，并呈昼高夜低的特征，这种昼夜偏差在低海拔区最为显著。从降水强度的变化看，CMA-MESO模式对24 h和1 h有效降水的TS评分分别为34.4%和8.8%，但随着降水强度的增加，预报性能迅速下降。值得注意的是，1 h降水预报的概率密度偏差主要集中在0.1~2 mm，针对性订正该区间预报可更有效地降低整体降水频率偏差。研究结果可为CMA-MESO在干旱区复杂地形下的降水预报改进及防灾减灾业务提供科学依据。

构建未来不同情景土地利用变化下生态安全格局，为流域尺度生态经济可持续发展的规划和决策提供支持。利用FLUS模型模拟石羊河流域2035年土地利用格局，涵盖自然发展、耕地保护与生态保护三种情景，采用InVEST模型量化产水量、土壤保持和碳储量服务功能，应用“绿额分配”经验方法计算粮食生产服务功能，并基于层次分析法建立综合生态系统服务指数（CES），利用形态学空间格局分析模型（MSPA）及电路理论构建石羊河流域生态安全格局。石羊河流域2020年综合生态系统服务指数CES均值为0.2362，自然发展、耕地保护、生态保护情景下CES 均值分别达 0.2402、0.2415、0.2435，流域生态系统服务总体水平实现提升；2020 年现状年流域生态源地总面积7218.3 km2，现状和未来三种情景下生态廊道数量依次为55条、49条、52条、53条，基于生态源地及廊道空间分布规律构建石羊河流域“一带、三区、多点”总体生态安全格局，同步制定生态系统适应性管理与保护策略。研究成果可为石羊河流域生态空间的管控与优化提供科学参考。

土壤盐碱化是我国面临的重要土地退化问题，也是制约干旱、半干旱区农业可持续发展的主要问题。盐碱地土壤结构不良、肥力差、生物活力低等障碍，导致作物生长困难、土地产能低。优化土壤结构和提升肥力是盐碱地改良的核心，也直接关系到盐碱地的农业利用潜力。本研究以中重度盐碱地适生先锋植物草木樨（Melilotus suaveolens）为对象，通过对节水滴灌种植下盐碱地土壤结构、土壤肥力的变化分析，探究现代节水滴灌种植模式下盐碱地生物改良效果。结果表明：草木樨种植后，0 ~20 cm 表层土壤容重显著下降（P=0.015）、土壤水稳定性团聚体粒径变化不明显；土壤耕层盐分降低了4 .469 g·kg-1，八大离子中除HCO-3外，其余离子在土壤0 ~20 cm 耕层均呈下降趋势；0 ~60 cm 土层全氮含量显著提高（P=0.03），但全钾含量减少，有机质、硝态氮和铵态氮含量减少，全磷含量变化不明显。草木樨作为两年生的耐盐先锋植物，在第一年生长季即表现出较好的增肥改土作用。研究表明，西北内陆干旱区新垦中重度盐碱地种植豆科耐盐先锋植物草木樨，可起到快速培肥和改土的效果。