目的探讨动态对比增强磁共振成像(dynamic contrast-enhanced magnetic resonance imaging,DCE-MRI)定量参数联合小视野弥散加权成像在甲状腺良恶性结节鉴别中的应用价值。材料与方法收集2022年1月至2023年10月于滨州医学院附属医院诊...目的探讨动态对比增强磁共振成像(dynamic contrast-enhanced magnetic resonance imaging,DCE-MRI)定量参数联合小视野弥散加权成像在甲状腺良恶性结节鉴别中的应用价值。材料与方法收集2022年1月至2023年10月于滨州医学院附属医院诊治并经手术病理证实为甲状腺结节的患者38例(52个结节),将其分为良性结节组和恶性结节组。术前患者均行3.0 T MRI扫描,包括常规MRI、小视野弥散加权成像(b值取0、800 s/mm^(2))和DCE-MRI检查,并测量其表观弥散系数(apparent diffusion coefficient,ADC)值和DCE-MRI定量参数,包括对比剂容积转运常数(volume transport constant,K^(trans))、速率常数(rate constant,K_(ep))、血管外细胞外间隙容积分数(extravascular extracellular volume fraction,V_(e))。对甲状腺良恶性结节组的ADC、K_(ep)、V_(e)、K^(trans)采用独立样本t检验分析,以P<0.05为差异有统计学意义,后将差异有统计学意义的变量进行逐步logistic回归模型分析,得到甲状腺良恶性结节的独立预测因素,并绘制受试者工作特征(receiver operating characteristic,ROC)曲线分析ADC、K^(trans)独立诊断模型及ADC与K^(trans)联合诊断模型的诊断效能。结果良性结节组平均ADC值、K^(trans)值、K_(ep)值分别为(1.659±0.370)×10^(-3)mm^(2)/s、(0.427±0.214)min^(-1)、(0.966±0.225)min^(-1),恶性结节组平均ADC值、K^(trans)值、K_(ep)值分别为(1.182±0.195)×10^(-3)mm^(2)/s、(0.178±0.073)min^(-1)、(0.600±0.248)min^(-1)。良性结节组的ADC、K^(trans)、K_(ep)值均高于恶性结节组,差异均有统计学意义(P<0.001)。经过独立样本t检验及逐步logistic回归分析显示,ADC值和K^(trans)差异具有统计学意义(P<0.05),是鉴别甲状腺结节良恶性的独立预测因子。单独ADC值曲线下面积(area under the curve,AUC)为0.915、单独K^(trans)值AUC为0.827。ADC值与K^(trans)联合诊断模型AUC为0.973,较二者单独应用明显增高,联合诊断模型诊断效能最高。经DeLong检验,联合诊断模型与单独K^(trans)诊断差异存在统计学意义(P<0.05)。ADC值与K^(trans)联合诊断模型在鉴别甲状腺良恶性结节中敏感度为97.3%,较ADC、K^(trans)更高,特异度为84.6%,较ADC值更高。结论ADC值和K^(trans)是鉴别甲状腺良恶性结节的重要参数,两者联合诊断可提高临床诊断准确性,为术前诊断提供重要依据。展开更多
On the basis of computational fluid dynamics,the flow field characteristics of multi-trophic artificial reefs,including the flow field distribution features of a single reef under three different velocities and the ef...On the basis of computational fluid dynamics,the flow field characteristics of multi-trophic artificial reefs,including the flow field distribution features of a single reef under three different velocities and the effect of spacing between reefs on flow scale and the flow state,were analyzed.Results indicate upwelling,slow flow,and eddy around a single reef.Maximum velocity,height,and volume of upwelling in front of a single reef were positively correlated with inflow velocity.The length and volume of slow flow increased with the increase in inflow velocity.Eddies were present both inside and backward,and vorticity was positively correlated with inflow velocity.Space between reefs had a minor influence on the maximum velocity and height of upwelling.With the increase in space from 0.5 L to 1.5 L(L is the reef lehgth),the length of slow flow in the front and back of the combined reefs increased slightly.When the space was 2.0 L,the length of the slow flow decreased.In four different spaces,eddies were present inside and at the back of each reef.The maximum vorticity was negatively correlated with space from 0.5 L to 1.5 L,but under 2.0 L space,the maximum vorticity was close to the vorticity of a single reef under the same inflow velocity.展开更多
Grassland degradation can alter the structure and function of ecosystem and soil seed bank.Therefore,estimating the role of soil seed bank in vegetation regeneration of degraded grasslands is crucial.We selected grass...Grassland degradation can alter the structure and function of ecosystem and soil seed bank.Therefore,estimating the role of soil seed bank in vegetation regeneration of degraded grasslands is crucial.We selected grasslands with three levels of degradation,namely non-degraded(ND),mildly degraded(MD),and heavily degraded(HD)to analyze the effect of grassland degradation on soil seed bank,as well as the role of soil seed bank on vegetation regeneration of the alpine grasslands,China.Soil samples from each level were collected in May,before seedling emergence,in August,after completion of transient seed bank germination,and in December,after seed dispersal,to determine the seed density and species composition through germination experiment.Result showed that a total of 35 plant species was identified,including 15 species observed in both soil seed bank and above-ground vegetation.A total of 19,15,and 14 species of soil seed bank were identified in December,May,and August,respectively.The most abundant species in soil seed bank were Compositae(5 species),followed by Poaceae(4 species),and Cyperaceae(3 species).Degradation level has no significant impact on species richness and Shannon-Wiener index of soil seed bank.In addition,sampling month and grassland degradation affected soil seed bank density,in which December>May>August,and ND>MD>HD,indicating that density of transient seed bank was greater than persistent seed bank.Soil seed bank density of surface layer(0–5 cm)accounting for 42%–72%of the total density,which was significantly higher than that of deep layer(5–10 cm).Similarity of species composition between vegetation and soil seed bank was low,and it increased with degradation level(ranged from 0.14 to 0.69).We concluded that grassland degradation affects soil seed bank density more than species diversity,and soil seed bank contributed slightly to vegetation regeneration of degraded alpine grassland.Therefore,it is unlikely that degraded alpine meadow can be restored solely through soil seed bank.展开更多
随着移动通信网络的迅猛发展,其安全漏洞产生的影响更为广泛,使得安全性研究尤为重要。根据长期演进(Long Term Evolution,LTE)非接入层协议的漏洞,构建了针对网络端和终端的两种拒绝服务攻击模型,通过获取不同终端的国际移动用户标识...随着移动通信网络的迅猛发展,其安全漏洞产生的影响更为广泛,使得安全性研究尤为重要。根据长期演进(Long Term Evolution,LTE)非接入层协议的漏洞,构建了针对网络端和终端的两种拒绝服务攻击模型,通过获取不同终端的国际移动用户标识并分别伪造鉴权拒绝消息和附着请求消息对目标发起不同危害程度的拒绝服务攻击。实验结果表明,采用鉴权拒绝发起的攻击会使目标终端强制降为2G网络;而采用附着请求发起的攻击会使核心网侧中央处理器(Central Processing Unit,CPU)使用率由30%提升至80%,造成网络资源消耗巨大,导致用户很难正常接入。研究结论有助于推进非接入层协议的安全演进。展开更多
为了研究移动通信漏洞对用户速率的影响,针对空口中接入层用户设备能力信息以明文传输的特点,提出了一种在用户设备和真实网络之间中继并修改长期演进(long term evolution,LTE)信令的中间人攻击方案。该方案将目标终端吸引至中间人系统...为了研究移动通信漏洞对用户速率的影响,针对空口中接入层用户设备能力信息以明文传输的特点,提出了一种在用户设备和真实网络之间中继并修改长期演进(long term evolution,LTE)信令的中间人攻击方案。该方案将目标终端吸引至中间人系统,同时中间人系统中的终端以目标终端的国际移动用户标识(international mobile subscriber identity,IMSI)向真实网络发起注册,中间人系统中继传递目标终端和真实网络的信令,对接收到的接入层用户设备能力信息修改再转发至真实网络,从而使得目标终端的数据速率下降。测试结果表明,攻击导致目标终端的下行传输速率从64.9 Mbps降低到8.1 Mbps,上行传输速率从38.3 Mbps降低到3.5 Mbps。由于该攻击具有普遍适用性,该工作可以为移动通信网络改进提供参考。展开更多
文摘目的探讨动态对比增强磁共振成像(dynamic contrast-enhanced magnetic resonance imaging,DCE-MRI)定量参数联合小视野弥散加权成像在甲状腺良恶性结节鉴别中的应用价值。材料与方法收集2022年1月至2023年10月于滨州医学院附属医院诊治并经手术病理证实为甲状腺结节的患者38例(52个结节),将其分为良性结节组和恶性结节组。术前患者均行3.0 T MRI扫描,包括常规MRI、小视野弥散加权成像(b值取0、800 s/mm^(2))和DCE-MRI检查,并测量其表观弥散系数(apparent diffusion coefficient,ADC)值和DCE-MRI定量参数,包括对比剂容积转运常数(volume transport constant,K^(trans))、速率常数(rate constant,K_(ep))、血管外细胞外间隙容积分数(extravascular extracellular volume fraction,V_(e))。对甲状腺良恶性结节组的ADC、K_(ep)、V_(e)、K^(trans)采用独立样本t检验分析,以P<0.05为差异有统计学意义,后将差异有统计学意义的变量进行逐步logistic回归模型分析,得到甲状腺良恶性结节的独立预测因素,并绘制受试者工作特征(receiver operating characteristic,ROC)曲线分析ADC、K^(trans)独立诊断模型及ADC与K^(trans)联合诊断模型的诊断效能。结果良性结节组平均ADC值、K^(trans)值、K_(ep)值分别为(1.659±0.370)×10^(-3)mm^(2)/s、(0.427±0.214)min^(-1)、(0.966±0.225)min^(-1),恶性结节组平均ADC值、K^(trans)值、K_(ep)值分别为(1.182±0.195)×10^(-3)mm^(2)/s、(0.178±0.073)min^(-1)、(0.600±0.248)min^(-1)。良性结节组的ADC、K^(trans)、K_(ep)值均高于恶性结节组,差异均有统计学意义(P<0.001)。经过独立样本t检验及逐步logistic回归分析显示,ADC值和K^(trans)差异具有统计学意义(P<0.05),是鉴别甲状腺结节良恶性的独立预测因子。单独ADC值曲线下面积(area under the curve,AUC)为0.915、单独K^(trans)值AUC为0.827。ADC值与K^(trans)联合诊断模型AUC为0.973,较二者单独应用明显增高,联合诊断模型诊断效能最高。经DeLong检验,联合诊断模型与单独K^(trans)诊断差异存在统计学意义(P<0.05)。ADC值与K^(trans)联合诊断模型在鉴别甲状腺良恶性结节中敏感度为97.3%,较ADC、K^(trans)更高,特异度为84.6%,较ADC值更高。结论ADC值和K^(trans)是鉴别甲状腺良恶性结节的重要参数,两者联合诊断可提高临床诊断准确性,为术前诊断提供重要依据。
基金supported by the National Natural Science Foundation of China(No.32002442)the National Key R&D Program(No.2019YFD0902101).
文摘On the basis of computational fluid dynamics,the flow field characteristics of multi-trophic artificial reefs,including the flow field distribution features of a single reef under three different velocities and the effect of spacing between reefs on flow scale and the flow state,were analyzed.Results indicate upwelling,slow flow,and eddy around a single reef.Maximum velocity,height,and volume of upwelling in front of a single reef were positively correlated with inflow velocity.The length and volume of slow flow increased with the increase in inflow velocity.Eddies were present both inside and backward,and vorticity was positively correlated with inflow velocity.Space between reefs had a minor influence on the maximum velocity and height of upwelling.With the increase in space from 0.5 L to 1.5 L(L is the reef lehgth),the length of slow flow in the front and back of the combined reefs increased slightly.When the space was 2.0 L,the length of the slow flow decreased.In four different spaces,eddies were present inside and at the back of each reef.The maximum vorticity was negatively correlated with space from 0.5 L to 1.5 L,but under 2.0 L space,the maximum vorticity was close to the vorticity of a single reef under the same inflow velocity.
基金supported by the National Natural Science Foundation of China (31960279)the Science and Technology Program of Gansu Province, China (21JR11RA018)+1 种基金the Special Project for Central Universities to Build World-class Universities/Disciplines, and Characteristic Development GuidanceProgram for Changjiang Scholars and Innovative Research Team in University of Ministry of Education, China (IRT_17R88)
文摘Grassland degradation can alter the structure and function of ecosystem and soil seed bank.Therefore,estimating the role of soil seed bank in vegetation regeneration of degraded grasslands is crucial.We selected grasslands with three levels of degradation,namely non-degraded(ND),mildly degraded(MD),and heavily degraded(HD)to analyze the effect of grassland degradation on soil seed bank,as well as the role of soil seed bank on vegetation regeneration of the alpine grasslands,China.Soil samples from each level were collected in May,before seedling emergence,in August,after completion of transient seed bank germination,and in December,after seed dispersal,to determine the seed density and species composition through germination experiment.Result showed that a total of 35 plant species was identified,including 15 species observed in both soil seed bank and above-ground vegetation.A total of 19,15,and 14 species of soil seed bank were identified in December,May,and August,respectively.The most abundant species in soil seed bank were Compositae(5 species),followed by Poaceae(4 species),and Cyperaceae(3 species).Degradation level has no significant impact on species richness and Shannon-Wiener index of soil seed bank.In addition,sampling month and grassland degradation affected soil seed bank density,in which December>May>August,and ND>MD>HD,indicating that density of transient seed bank was greater than persistent seed bank.Soil seed bank density of surface layer(0–5 cm)accounting for 42%–72%of the total density,which was significantly higher than that of deep layer(5–10 cm).Similarity of species composition between vegetation and soil seed bank was low,and it increased with degradation level(ranged from 0.14 to 0.69).We concluded that grassland degradation affects soil seed bank density more than species diversity,and soil seed bank contributed slightly to vegetation regeneration of degraded alpine grassland.Therefore,it is unlikely that degraded alpine meadow can be restored solely through soil seed bank.
文摘随着移动通信网络的迅猛发展,其安全漏洞产生的影响更为广泛,使得安全性研究尤为重要。根据长期演进(Long Term Evolution,LTE)非接入层协议的漏洞,构建了针对网络端和终端的两种拒绝服务攻击模型,通过获取不同终端的国际移动用户标识并分别伪造鉴权拒绝消息和附着请求消息对目标发起不同危害程度的拒绝服务攻击。实验结果表明,采用鉴权拒绝发起的攻击会使目标终端强制降为2G网络;而采用附着请求发起的攻击会使核心网侧中央处理器(Central Processing Unit,CPU)使用率由30%提升至80%,造成网络资源消耗巨大,导致用户很难正常接入。研究结论有助于推进非接入层协议的安全演进。
文摘为了研究移动通信漏洞对用户速率的影响,针对空口中接入层用户设备能力信息以明文传输的特点,提出了一种在用户设备和真实网络之间中继并修改长期演进(long term evolution,LTE)信令的中间人攻击方案。该方案将目标终端吸引至中间人系统,同时中间人系统中的终端以目标终端的国际移动用户标识(international mobile subscriber identity,IMSI)向真实网络发起注册,中间人系统中继传递目标终端和真实网络的信令,对接收到的接入层用户设备能力信息修改再转发至真实网络,从而使得目标终端的数据速率下降。测试结果表明,攻击导致目标终端的下行传输速率从64.9 Mbps降低到8.1 Mbps,上行传输速率从38.3 Mbps降低到3.5 Mbps。由于该攻击具有普遍适用性,该工作可以为移动通信网络改进提供参考。