College Students' Use of Cocaine

After experiencing a period of rapid decline between 1986 and 1994, cocaine use is once again on the rise in the United States. The increased prevalence of use among college students is particularly troubling because of its potential impact on human capital acquisition and long-term labor market success. Merging information on the price of cocaine and marijuana from the U.S. Drug Enforcement Agency with data on cocaine use from the College Alcohol Study, we investigate the demand for cocaine in the college population. We find evidence that participation in cocaine use by college students is responsive to changes in the price of cocaine and marijuana and that cocaine and marijuana are economic complements for this population. Further investigation revealed significant differences in the demand for cocaine by those less than age 21 and those at least age 21, years, with the younger age group being more responsive to changes in the price of cocaine. No difference is found, however, in the demand for cocaine across gender.     

慢性肾功能衰竭患者肱动脉弹性功能的特点

目的 :探讨慢性肾功能衰竭患者不同阶段肱动脉弹性功能的特点。方法 :采用Dynapulse 2 0 0M动脉功能测定仪检测 19例终末期肾病 (ESRD)长期维持透析患者、15例慢性肾功能衰竭 (CRF)尚未透析的患者肱动脉功能 ,并与 15例正常人对比。结果 :与正常对照组比较 ,CRF组和血透组患者的肱动脉顺应性 (BAC)、肱动脉扩张性 (BAD)明显减退 ,收缩压 (SBP)、脉压 (PP)明显增高 (P <0 0 1)。相关分析和多元线性回归表明 ,所有CRF组和血透组患者的BAC ,BAD都与PP高度负相关 (r <- 0 5 ,P <0 0 1) ,在CRF组中 ,还发现内生肌酐清除率(ccl)与BAD呈高度正相关 (r=0 76 ,P <0 0 1)。结论 :与正常对照组比较 ,CRF患者和血透患者肱动脉弹性功能明显减退 ,PP是影响其肱动脉弹性功能的主要因素 ,在CRF组 ,ccl独立于PP ,与BAD明显正相关     

Quantification of urethral function based on Griffiths' model of flow through elastic tubes

Griffiths' model of flow-through elastic tubes makes it possible to relate the elastic properties of the flow-controlling zone to the pressure/flow relation of the urethra. In this work the pressure function p(A) = P_mo + K_n Aⁿ, where A is cross-sectional area, P_mo the minimal opening pressure, and K_n and n parameters describing urethral distensibility, describes the elastic properties of the flow-controlling zone. By curve-fitting in the pressure/flow plot, the three parameters p_mo, K_n, and n can be estimated analytically. Using this model it is possible to identify three different biomechanical changes that may cause obstruction. First, p_mo may be elevated. Second, the urethra can be distended to a certain area only, corresponding to high values of K_n and n. Third, the urethra can be distended but a higher-than-normal pressure increase above P_mo is needed, K_n is high, and n is low. With this model it is possible to quantify urethral function for both scientific and clinical purposes.     

超声弹性成像逆问题求解的进一步研究

针对作者以前提出的基于有限元迭代的组织弹性模量重建即超声弹性成像逆问题求解的方法进行了进一步的研究.包括采用四边形单元代替三角形单元、尝试对组织边界的弹性模量不进行校正、考虑组织边界的弹性模量未知及含有随机噪声的情形.这些工作为组织弹性模量重建方法的实际应用奠定了基础.     

采用径向压缩的超声弹性成像逆问题求解

超声弹性成像在前列腺的应用以及血管弹性成像中,组织压缩的方向是沿径向的.本文利用极坐标下的应力-应变关系,提出一种有限元迭代的方法,进行组织弹性模量分布的重建,即弹性成像逆问题的求解.采用扇形组织模型和环形组织模型两种模型进行了计算机仿真,分别用来模拟超声弹性成像在前列腺中的应用情形和血管弹性成像的情形.仿真结果表明了该方法的可行性.     

Government health expenditures and health outcomes

This paper provides econometric evidence linking a country's per capita government health expenditures and per capita income to two health outcomes: under-five mortality and maternal mortality. Using instrumental variables techniques (GMM-H2SL), we estimate the elasticity of these outcomes with respect to government health expenditures and income while treating both variables as endogenous. Consequently, our elasticity estimates are larger in magnitude than those reported in literature, which may be biased up. The elasticity of under-five mortality with respect to government expenditures ranges from -0.25 to -0.42 with a mean value of -0.33. For maternal mortality the elasticity ranges from -0.42 to -0.52 with a mean value of -0.50. For developing countries, our results imply that while economic growth is certainly an important contributor to health outcomes, government spending on health is just as important a factor.     

Impact of gas bubbles generated during interstitial ablation on elastographic depiction of in vitro thermal lesions.

OBJECTIVE: Artifacts from gas bubble formation during radio frequency ablation along with the poor intrinsic contrast between normal and treated regions (zone of necrosis) are considerable problems for the visualization of the necrotic region on conventional sonography. Sonographic elastography is very effective for visualizing the zone of necrosis, but it uses the same echo signals to estimate strain as those used to form gray scale images. Thus, the impact of gas bubbles on strain images or elastograms must be investigated. METHODS: Radio frequency ablation was performed in vitro on liver tissue samples, approximately 40 x 40 x 20 mm, encased in 80-mm cubed gelatin phantoms. Elastograms generated at different instants during the ablation procedures were obtained on a real-time scanner with a 5-MHz linear array. Sequences of elastograms illustrate the growth of the thermal lesion. RESULTS: Degradation of the distal boundary of the thermal lesion was observed. The degradation was confined to the lower-fifth quadrant of the thermal lesion. However, accurate estimates of lesion areas could still be obtained by extrapolation of the thermal lesion boundary. CONCLUSIONS: Elastograms of thermal lesions in vitro can be obtained during radio frequency ablation. Some loss of thermal lesion boundary information on strain images was observed in regions where attenuation due to gas bubbles reduced the signal-noise ratio of the echo signals.     

常规超声和超声弹性成像在颈部淋巴结良恶性鉴别诊断中的价值

目的:对比实时静态超声弹性成像技术与二维灰阶、彩色多普勒等传统超声方法在判断颈部淋巴结良恶性中的诊断价值。方法:选取2012年1月—2013年12月诊治的311例颈部淋巴结肿大患者(共322个颈部淋巴结),所有淋巴结均经病理学证实良恶性。采用灰阶超声进行病灶检查,记录淋巴结的长径、短径,并计算长短径的比值。采用彩色多普勒超声对淋巴结进行血管模式分型,分为淋巴门型、中央型、周围型及混合型,并记录血流阻力指数(RI)值。对病灶行超声弹性成像,根据弹性图显示图像将感兴趣区(ROI)内病灶区与周围组织硬度相比较,并对弹性图进行分型。绘制受试者工作特征(receiver operating characteristic,ROC)曲线,评价各项指标对颈部浅表淋巴结良恶性的诊断价值。结果:322个颈部淋巴结中经病理证实良性淋巴结73个,恶性淋巴结249个。长短径比值截断值1.5789,曲线下面积0.766,准确性65.22%,敏感性61.40%,特异性78.10%。RI截断值0.655,曲线下面积0.787,准确性72.98%,敏感性73.10%,特异性72.60%。血管模式中,淋巴门型恶性病变率11.8%,中央型恶性病变率52.9%,周围型恶性病变率83.3%,混合型恶性病变率88.8%,其差异有统计学意义(P0.01)。以弹性分级≥Ⅲ级作为判断淋巴结良恶性的标准,249个恶性淋巴结中弹性分级≥Ⅲ级222个,73个良性淋巴结中弹性分级≤Ⅱ级31个,超声弹性分级诊断颈部淋巴结良恶性准确性为78.57%。长短径比值、RI、超声弹性分级用于诊断颈部淋巴结良恶性的准确性差异有统计学意义(P0.05)。结论:淋巴结长短径比值、RI、血管模式分型、超声弹性图分级对于判断颈部淋巴结的良恶性有诊断价值,超声弹性分级用于判断颈部淋巴结良恶性的准确性优于RI及长短径比值,RI优于长短径比值。血管模式分型为周围型及混合型的淋巴结恶性病变率高于中央型及淋巴门型。     

Ultrasound-based elastography: a novel approach to assess radio frequency ablation of liver masses performed with expandable ablation probes: a feasibility study

OBJECTIVE: The purpose of this study was to evaluate the technical feasibility of ultrasound-based elastography as a tool for assessing the size and shape of the coagulation necrosis caused by radio frequency ablation (RFA) probes using expandable electrodes ex vivo as well as in a patient with a liver metastasis. METHODS: A commercially available expandable RFA probe was used to create a 3-cm ablation in a piece of bovine liver. The ablation probe was used in situ to induce tissue deformation for elastography before and after ablation. Ultrasonic radio frequency data were processed to generate elasticity strain images. The appearance of the ablation zone was compared with magnetic resonance imaging and a gross section specimen. One patient with malignant metastatic disease to the liver and a clinical indication for RFA was investigated for the feasibility of percutaneous elastography of RFA using the same technique. Sonographic strain images were compared with the appearance of the nonenhancing ablation zone on contrast-enhanced computed tomography. RESULTS: Ex vivo, the ablation zone on ultrasound-based elastography was represented by an area of increased stiffness and was well demarcated from the nonablated surrounding tissue. The size and shape of the ablated zone on the strain image correlated well with the gross specimen and the magnetic resonance imaging appearance. Strain images obtained from the patient showed results similar to those of the ex vivo experiment and correlated well with the nonenhancing area of ablation on contrast-enhanced computed tomography. CONCLUSIONS: Ultrasound-based elastography may be a promising tool for displaying the ablation zone created by expandable RFA probes.     

心血管危险因素与小动脉弹性的关系

目的　探讨小动脉弹性下降的主要心血管危险因素及多种危险因素并存时对小动脉弹性的影响。方法　采用CVProfilorDO 2 0 2 0动脉脉搏分析仪测量大动脉和小动脉弹性指数 (C1和C2 ) ;用稳态模式评估法 (HOMA)评价胰岛素抵抗。依据中国健康人群动脉弹性功能参考标准把受试者分为小动脉弹性 (C2 )异常组和对照组 ;根据危险因素个数多少将C2 异常组分为 4个亚组 (0～ 3亚组 )。结果　 (1)C2 异常组的年龄、总胆固醇 (TC)、低密度脂蛋白胆固醇 (LDL C)、空腹血糖 (FBG)、收缩压 (SBP)和舒张压 (DBP)明显高于对照组 ,而C2 明显低于对照组 (P均 <0 0 5 ) ;单因素相关分析 ,年龄、TC、LDL C、FBG、SBP和DBP分别与C2 呈负相关。 (2 )随着危险因素聚集程度的增加 ,0到3亚组C2 呈依次下降趋势 (6 5± 2 6比 5 4± 2 3比 4 7± 2 7比 3 1± 1 6 ,P <0 0 0 1) ,多个危险因素并存亚组 (3亚组 )C2 下降最显著。 (3) 3亚组血浆胰岛素浓度和胰岛素抵抗指数显著高于其他亚组 (P <0 0 5 ,P <0 0 0 1)。结论　年龄、总TC、HDL C、FBG、SBP和DBP水平增加是小动脉弹性下降的主要心血管危险因素 ,它们对小动脉弹性的影响是连续的 ;多种危险因素并存时 ,可通过协同作用使小动脉弹性降低更显著 ;胰岛素抵抗可能是危险因