论自然资源的经济评价问题

随着工业、农业和运输业的迅速发展，自然保护和自然资源的合理利用日益成为国家最重要的经济和社会任务之一。而解决旨在资源利用最优化的自然资源经济评价问题则是经济地理学及其邻近学科的最重要的任务。本文试图从理论上论证自然资源经济评价的方法论与方法问题。首先提出$自然资源、经济评价、级差地租、总产量     

一类椭圆型变系数方程的差分格式

研究了一类二阶椭圆型变系数方程的初边值问题的求解方法,建立了一种差分格式,并且运用能量方法证明了这种格式的解的存在唯一性、收敛性和稳定性,所得结果是对相关文献中结果的一个补充。     

Assessing risk of commercial sexual exploitation among children involved in the child welfare system

The objective of this study was to assess item characteristics indicative of the severity of risk for commercial sexual exploitation among a high-risk population of child welfare system involved youth to inform the construction of a screening tool. Existing studies have discerned factors that differentiate Commercial Sexual Exploitation of Children (CSEC) victims from sexual abuse victims, yet no research has been conducted to discriminate which items in a high risk population of youth are most predictive of CSEC. Using the National Survey of Child and Adolescent Well-Being (NSCAW) cohorts I and II, we examined responses from 1063 males and 1355 females ages 11 and older, over three interview periods.A 2-parameter logistic Item Response Theory (2 PL IRT) model was employed in order to examine item performance as potential indicators for the severity of risk for CSEC. Differential Item Functioning (DIF) analysis was conducted in order to examine potential differences in item responses based on gender. Modeling strategies to assess item difficulty and discrimination were outlined and Item Characteristic Curves for the final retained items were presented. Evidence for uniform DIF were present within items that asked about runaway, any drug use, suicidality, and experiencing severe violence. Results from this study can inform the construction of a screening instrument to assess the severity of risk for experiencing CSEC.     

The differential impact of social services on young people’s resilience

Differential Impact Theory (DIT) can help explain which services and supports work best for which young people at which levels of risk exposure. As a complement to a growing understanding of how a child’s genetic and phenotypic traits influence treatment outcomes, DIT focuses attention on the relative impact of a child’s environment on psychosocial development. In this article, three principles of DIT will be discussed: (1) demands of higher level systems compel individuals to adapt; (2) the factors that influence individual change the most depend on the individual’s degree of risk exposure; and (3) the more complex the challenges an individual faces, the more complex the systems required to improve functioning. Two detailed case studies based on interviews and multiple file reviews will be used to illustrate these principles of DIT. Both case studies were drawn from a study of young people (average age 16.1 years) who were clients of multiple social services. While support for DIT requires further study, findings presented in this paper demonstrate the potential of the theory to explain the differential impact of services and supports on young people’s developmental trajectories where there has been exposure to high levels of risk. The application of DIT to service design is also discussed.     

智能监控中的运动检测算法研究

介绍了室内智能监控系统中运动检测算法的具体实现。利用帧间差分法提取运动目标,通过对差分能量和运动速度的分析判断出运动目标的大致动作。     

一种新的四阶偏微分方程的图像降噪算法

提出一种基于四阶偏微分方程的图像降噪算法——耦合梯度保真项的四阶偏微分方程的图像降噪算法,实验结果验证了算法的有效性.     

高阶微分方程的亚纯解与小函数的关系

研究了高阶微分方程f(k)+A(k-1)(z)f(k-1)+A(k-1)(z)f(k-2)+…+A1(z)f'+A0(z)f=0和f(k)+A(k-1)(z)f(k-1)+A(k-1)(z)f(k-2)+…+A1(z)f'+A0(z)f=F(z)的亚纯解f(z)与其小函数ψ(z)的关系,得到了微分方程解取小函数的点的二二级收敛指数的精确估计,其中Aj(z)是亚纯函数。     

一类含参数λ可化为线性型微分方程的可积判据

先给出一个引理,借用引理及相关的变换,提供一个定理,作为定理的特列,列出一系列更便于应用的推论,在此均列出了相应含参数λ的方程的通解的表达式。     

一种强驱动大摆幅输出缓冲器的设计

本文采用0.35 CMOS工艺,设计了一种强驱动大摆幅的输出缓冲器,该电路用5V单电源供电,能保证输入共模范围和输出信号摆幅达到电源和地,实现输入输出的Rail_to_Rail。该缓冲器在负载电容为1,负载电阻为10kΩ时开环增益为74dB,单位增益带宽为3.5MHz,相位裕度为50°,系统失调仅有3mV,静态电流只有800,输出噪声为10。当用幅度为2V,频率为100kHz的正弦波做谐波分析时,在可接受的谐波失真范围内,负载电阻可降至300Ω。     

LDPC based time-frequency double differential space-time coding for multi-antenna OFDM systems

INTRODUCTION High data rate and high quality multimedia ser- vices are required in beyond third generation (B3G) and fourth generation (4G) mobile communications. Space-time coding scheme has been proposed (Tarokh et al., 1998; 1999) to achieve higher capacity and data rate. So far, most research on space-time coding assumed that accurate channel estimations are available at the receivers. However, accurate channel estimation is difficult and too many training symbols are required in a r…