Locality-adapted kernel densities of term co-occurrences for location prediction of tweets

While geographical metadata referring to the originating locations of tweets provides valuable information to perform effective spatial analysis in social networks, scarcity of such geotagged tweets imposes limitations on their usability. In this work, we propose a content-based location prediction method for tweets by analyzing the geographical distribution of tweet texts using Kernel Density Estimation (KDE). The primary novelty of our work is to determine different settings of kernel functions for every term in tweets based on the location indicativeness of these terms. Our proposed method, which we call locality-adapted KDE, uses information-theoretic metrics and does not require any parameter tuning for these settings. As a further enhancement on the term-level distribution model, we describe an analysis of spatial point patterns in tweet texts in order to identify bigrams that exhibit significant deviation from the underlying unigram patterns. We present an expansion of feature space using the selected bigrams and show that it eventually yields further improvement in prediction accuracy of our locality-adapted KDE. We demonstrate that our expansion results in a limited increase in the size of feature space and it does not hinder online localization of tweets. The methods we propose rely purely on statistical approaches without requiring any language-specific setting. Experiments conducted on three tweet sets from different countries show that our proposed solution outperforms existing state-of-the-art techniques, yielding significantly more accurate predictions.     

Reference density trends in the major disciplines

The aim of this study was to determine whether different areas of knowledge presented different behaviour with regard to the number of references cited per journal document or if, conversely, they shared the same reference density practices. Bibliometric and bibliographic data were collected from 27,141 journals (indexed between 2001 and 2015 in the SCImago Journal & Country Rank (SJR)) and the growth rates in reference density and number of documents and journals in each category were calculated at different levels of aggregation.Our analysis identified that (a) mean reference density values in some Social Sciences and Arts and Humanities categories were equal to or higher than those in the “hard sciences”; (b) reference density growth rates in these disciplines were not as high as those in the hard sciences and, in general, did not correspond with growth rates in the number of documents produced; (c) this can be considered an indication that citation-based evaluation practices affect publication habits; and (d) no significant differences were found in mean values or growth rates between Gold Open Access and Non Gold Open Access journals.     

Gonadal hormones may predict structural bone fragility in elite female soccer player

ABSTRACT

Purpose: This study determined the impact of menstrual status on bone tissue in elite post-pubertal female soccer players over an entire season.

Methods: Fifty-one elite female soccer players participated. At baseline, forty-one were assigned to the low hormonal androgenic profile (low-HAPL) and 10 to the high hormonal androgenic profile (high-HAPL).

Results: An 8-month training program led to increased bone mineral density content (p<0.05). The low-HAPL athletes improved the Narrow neck average cortical thickness (ACT) by 1.4% and reduced the corresponding Buckling ratio (BR) by 2.6%, thus decreasing the fracture risk (p<0.05). The high-HAPL athletes decreased the Narrow neck ACT by 5.4% and increased the BR by 2.6%, increasing fracture risk (p<0.05). Differences were assigned as being “very likely beneficial” for the low-HAPL athletes, supported by very large (d=3.41) and large (d=1.58) effect sizes for the Narrow neck ACT and BR, respectively.

Conclusion: A season of soccer training has induced bone geometry improvements in adolescent females. Bone health parameters improved in the two clusters. However, high-HAPL athletes decreased its resistance to loading compare to low-HAPL athletes. Even if female players do not present clinical symptoms related to their hormonal status, sport medicine physicians should pay attention to their structural bone fragility.     

垂直密度表示研究及其应用进展

根据I-型垂直密度表示及II-型垂直密度表示,分析垂直密度表示（Vertical Density Representation,简记为VDR）的提出与Lebesgue积分创立的异曲同工之处.阐述VDR在随机数生成、概率分布构造、多元分布拟合优度检验等方面的应用.垂直密度表示是一种特殊类型的变量变换,可用以探究概率分布的内在特性.     

毽球运动对老年人下肢骨密度和骨代谢指标的影响

骨质疏松症是老年人常见的病症,近年来有逐年增高的趋势。本文探讨毽球运动对老年人下肢骨密度和骨代谢指标影响。在运动训练前后分别测试下肢骨密度（BMD）、血清骨钙素（BGP）、血清钙（Ca）,结果显示毽球组的受试者骨密度（BMD）,血清骨钙素（BGP）与非运动对照组相比明显升高。从而得出结论：毽球运动能够增强老年人骨密度,改善骨代谢指标。     

Dynamic reliability evaluation of double-layer cylindrical latticed shell under multi-support excitations

To overcome the excessive computational cost and/or bad accuracy of traditional approaches,the probabilistic density evolution method(PDEM) is introduced.The dynamic reliability of a double-layer cylindrical latticed shell is evaluated by applying PDEM and Monte Carlo Method(MCM) respectively,and four apparent wave velocities(100 m/s,500 m/s,800 m/s and 1 200 m/s) and five thresholds(0.1 m,0.2 m,0.3 m,0.4 m and 0.5 m) are taken into consideration.Only the difference between threshold and maximal deformation...     

丙烯酸与臭氧反应机理的量子化学研究

采用密度泛函理论在MPW1K／6-31＋G（d,p）水平上研究了丙烯酸分子CH2CHCOOH与臭氧O3分子的反应机理,优化了反应势能面上各驻点的几何构型,对每一个驻点能量进行零点能校正,并采用相同的基组在MPWB1K水平和BHandHLYP水平上对各驻点的构型及能量进行验证。通过同一水平的振动频率分析确认了各稳定点和过渡态,另用内禀反应坐标（IRC）对过渡态进行验证。结果表明：丙烯酸的臭氧化反应具有较高的反应活性,并且为多通道反应,多数反应通道有OH自由基生成。反应过程中有顺反异构的COOHHCOO自由基生成,二者会沿不同的反应通道进行反应,其中syn-COOHHCOO的反应活化能较高。     

LDA和GGA泛函优化锐钛矿相TiO2结构比较

采用CASTEP软件对LDA（CA—PZ）泛函和GGA泛函（包括PW91、PBE、RPBE、WC）优化锐钛矿相TiO2结构进行了比较。结果表明WC泛函得到的结果偏差最小,最接近于真实晶体的情况;其优化过程波动性最小,收敛最快、优化效率最高。LDA优化的结果较真实值普遍偏低,和通常的认为一致。除了WC外,GGA泛函优化的结果较真实值普遍偏高,而且较LDA更偏离真实值,其优化过程收敛性和优化效率也不如LDA。     

人口老龄化影响因素的实证分析

人口老龄化问题是21世纪中国所面临的严峻社会问题,已引起全社会的广泛关注,但目前我们对人口老龄化影响因素的研究还不够系统和全面。本文在对人口老龄化影响因素进行计量分析和回归分析后认为,影响人口老龄化的主要因素是生育率,而影响生育率的主要因素则是人口密度。     

两种木材基本密度及厚壁细胞长度的变异研究

通过对巨尾桉和意大利杨两种散孔材的基本密度和厚壁细胞长度在幼龄材和成熟材之间,从髓部到树皮的径向,以及在生长轮内的变异性进行研究,结果表明:两种木材的幼龄材各项性质均比成熟材低。巨尾桉的基本密度、纤维和导管分子长度差异达到极显著水平,环管管胞长度差异达显著水平。意大利杨仅纤维和导管分子长度差异分别达极显著和显著水平。基本密度在径向的变化,两种木材都是从第5轮开始随树龄增加逐渐增大,纤维长度在幼龄期都急剧增长,进入成熟期后增长缓慢。巨尾桉导管分子及环管管胞长度,幼龄期随树龄略有增长,成熟期后较为稳定。意大利杨导管的长度从髓部到第8轮增长迅速,逾此则逐步减短。初步试验表明,在生长轮内纤维、导管分子长度,因树种、植株不同,其变化规律不尽相同。