基于Omega涡识别理论的自适应空化流动模型

液体火箭发动机涡轮泵内存在多种空化类型,其发生机理有所不同,现有数值计算方法通常采用同一套模型预测所有类型空化,导致预测精度不足。为提高复杂空化流动的计算精度,提出了自适应空化流动模型。基于先进的Omega涡识别理论和ZGB空化模型建立了相变系数自适应调整方法,以涡轮泵内两种典型空化(附着空化和泄漏涡空化)为对象,利用翼型实验对模型进行了验证。首先对比了几种涡识别方法的差异,发现Omega方法对阈值不敏感且物理意义明确,适合作为相变系数的取值依据;分析了相变系数对附着空化和泄漏涡空化的影响规律及两种典型空化的形成机理。结果表明:自适应模型相比ZGB模型,对泄漏涡空化的预测精度在大间隙下提升了约181%,小间隙提升了约27%,对附着空化的预测更接近实验结果;附着空化是吸力面脱落涡形成的原因,间隙泄漏流场的涡带和剪切层空化是由间隙泄漏涡和分离涡共同作用形成的。

基于Omega涡识别方法的径流式水涡轮尾水管涡带特性

为了研究水涡轮尾水管的涡带特性与Omega涡识别方法对尾水管涡带的识别效果,对比了Q准则和λ_(2)准则以及Omega涡识别方法对尾水管涡带的识别效果,并基于Omega方法和降维的Omega方法分析了不同工况下尾水管的涡带特性.结果表明:对于径流式水涡轮,通过合理调整阈值,Q准则和λ_(2)准则以及Omega涡识别方法均能识别到清晰合理的尾水管涡结构,而Omega方法阈值选取区间较小且具有不敏感性;水涡轮尾水管在小流量工况时会出现较长的涡带,不利于机械的稳定性.同时运用二维Omega涡识别方法与拟涡能指标,在不同工况下对尾水管各监测面进行定量分析,确定涡量浓度高的区域,研究尾水管的能量耗散规律.结果发现,尾水管进水口到弯管之间的区域涡量浓度最高,能量耗散最大,流态最不稳定,这可为该型式水涡轮的结构优化提供理论参考与数据支撑.

从CRISPR系统到OMEGA系统:体内基因编辑技术的新突破

CRISPR/Cas系统是一种革命性的基因编辑工具,在过去的20年间已经逐渐应用于基础科学、疾病的研究与治疗、药物的开发等领域。近年来,科学家在对细菌和古生菌的基因组进行研究过程中发现了一个新的RNA引导系统——OMEGA,其转座酶IscB和TnpB分别被鉴定为CRISPR/Cas9和CRISPR/Cas12的祖先。同时,一种真核OMEGA基因编辑系统Fanzor(Fz)蛋白也在近期被报道,而TnpB被鉴定为Fz的祖先。OMEGA系统这些尺寸较小的内切酶允许腺相关病毒(AAV)的传递,在体内靶向基因编辑方面显示出更优越的特性。文章对OMEGA系统相关的RNA引导的核酸内切酶进行了综述。

TAU-OMEGA遥感辐射模型改进与参数化

大尺度地表土壤水分信息的获取对水资源管理、农业生产以及气候变化等相关研究具有重要意义。TAU-OMEGA(τ-ω)模型是利用被动微波遥感技术进行大尺度土壤水分信息提取的常用模型。由于τ-ω模型忽略了植被层的体散射作用,该模型仅适用于L波段,存在C波段适用性差及模型参数无法定量计算的问题。针对此问题,该研究在分析植被冠层对微波散射机制的基础上,通过增加反映冠层多次散射作用的辐射添加项对τ-ω模型进行了改进,成功解决了模型在C波段的适用性问题;通过理论推导,得出了模型ω参数的理论计算方法,基于模拟数据集,实现了基于冠层叶面积指数的模型ω和τ参数的计算,解决了τ-ω模型中ω参数无法根据遥感数据进行定量计算的问题。以玉米冠层为例,在C波段(6.6 GHz),改进的τ-ω模型对地表微波辐射亮温的模拟值与实测数据保持了较好的一致性,模拟误差较改进前有了极大的下降,V极化均方根误差为3.02 K,H极化均方根误差为3.94 K,结果表明了该研究提出的模型改进与参数化方案的合理性,研究结果为联合光学和被动微波遥感数据进行大尺度土壤水分反演奠定了基础。

Interface state-based bound states in continuum and below-continuum-resonance modes with high-Q factors in the rotational periodic system

We have introduced a new approach to calculate the orbital angular momentum(OAM)of bound states in continuum(BICs)and below-continuum-resonance(BCR)modes in the rotational periodic system nested inside and outside by transforming the Bloch wave number from the translational periodic system.We extensively classify and study these BICs and BCR modes,which exhibit high-quality(high-Q)factors,in different regions relative to the interface of the system.These BICs and BCR modes with a high-Q factor have been studied in detail based on distinctive structural parameters and scattering theory.The outcomes of this research break the periodic limitation of interface state-based BICs,and realize more and higher symmetry interface state-based BICs and BCR modes.Moreover,we can control the region where light is captured by adjusting the frequency,and show that the Q factor of BICs is more closely related to the ordinal number of rings and the rotational symmetry number of the system.

钢壳沉管隧道受限空间OMEGA止水带施工技术研究及应用

沉管隧道作为现今跨海通道主要的结构形式,其管节接头的防水性和密闭性是至关重要的,直接影响工程全寿命的安全性和耐久性。OMEGA止水带为管节接头的第2道防水装置,其安装面空间狭窄,作业空间受限,和隧道内其他施工交叉影响较大。结合深中通道工程,文章详细介绍了大型钢壳沉管隧道受限空间OMEGA止水带安装施工技术,该技术具有施工简便、操作灵活、施工效率高、对其他工序影响较小等优点,可为后续沉管隧道、水下明挖隧道、地铁工程等管廊结构止水带安装提供借鉴及经验。

Omega results for coefficients of Rankin-Selberg L-functions over sparse sequences

Ω results involving the coefficients of automorphic L-functions are important research object in analytic number theory.Let f be a primitive holomorphic cusp form.Denote by λ_(f×f)(n) the nth Fourier coefficient of Rankin-Selberg L-function L(f×f,s).This paper combines Kühleitner and Nowak′s Omega theorem and the analytic properties of Rankin-Selberg L-functions to study Omega results for coefficients of Rankin-Selberg L-functions over sparse sequences,and establishes the asymptotic formula for Σ_(n≤x)λf×f(n^(m))(m=2,3).

Using fracture-based continuum modeling of coupled geomechanical-hydrological processes for numerical simulation of hydraulic fracturing

This paper describes numerical simulation of hydraulic fracturing using fracture-based continuum modeling(FBCM)of coupled geomechanical-hydrological processes to evaluate a technique for high-density fracturing and fracture caging.The simulations are innovative because of modeling discrete fractures explicitly in continuum analysis.A key advantage of FBCM is that fracture initiation and propagation are modeled explicitly without changing the domain grid(i.e.no re-meshing).Further,multiple realizations of a preexisting fracture distribution can be analyzed using the same domain grid.The simulated hydraulic fracturing technique consists of pressurizing multiple wells simultaneously:initially without permeating fluids into the rock,to seed fractures uniformly and at high density in the wall rock of the wells;followed by fluid injection to propagate the seeded fracture density hydraulically.FBCM combines the ease of continuum modeling with the potential accuracy of modeling discrete fractures and fracturing explicitly.Fractures are modeled as piecewise planar based on intersections with domain elements;fracture geometry stored as continuum properties is used to calculate parameters needed to model individual fractures;and rock behavior is modeled through tensorial aggregation of the behavior of discrete fractures and unfractured rock.Simulations are presented for previously unfractured rock and for rock with preexisting fractures of horizontal,shallow-dipping,steeply dipping,or vertical orientation.Simulations of a single-well model are used to determine the pattern and spacing for a multiple-well design.The results illustrate high-density fracturing and fracture caging through simultaneous fluid injection in multiple wells:for previously unfractured rock or rock with preexisting shallow-dipping or horizontal fractures,and in situ vertical compressive stress greater than horizontal.If preexisting fractures are steeply dipping or vertical,and considering the same in situ stress condition,well pressurization without fluid permeation appears to be the only practical way to induce new fractures and contain fracturing within the target domain.

Enhancing the Goos-Hänchen shift based on quasi-bound states in the continuum through material asymmetric dielectric compound gratings

Quasi-bound state in the continuum(QBIC)resonance is gradually attracting attention and being applied in Goos-Hänchen(GH)shift enhancement due to its high quality(Q)factor and superior optical confinement.Currently,symmetry-protected QBIC resonance is often achieved by breaking the geometric symmetry,but few cases are achieved by breaking the material symmetry.This paper proposes a dielectric compound grating to achieve a high Q factor and high-reflection symmetry-protectede QBIC resonance based on material asymmetry.Theoretical calculations show that the symmetry-protected QBIC resonance achieved by material asymmetry can significantly increase the GH shift up to-980 times the resonance wavelength,and the maximum GH shift is located at the reflection peak with unity reflectance.This paper provides a theoretical basis for designing and fabricating high-performance GH shift tunable metasurfaces/dielectric gratings in the future.

Static-to-kinematic modeling and experimental validation of tendon-driven quasi continuum manipulators with nonconstant subsegment stiffness

Continuum robots with high flexibility and compliance have the capability to operate in confined and cluttered environments. To enhance the load capacity while maintaining robot dexterity, we propose a novel non-constant subsegment stiffness structure for tendon-driven quasi continuum robots(TDQCRs) comprising rigid-flexible coupling subsegments.Aiming at real-time control applications, we present a novel static-to-kinematic modeling approach to gain a comprehensive understanding of the TDQCR model. The analytical subsegment-based kinematics for the multisection manipulator is derived based on screw theory and product of exponentials formula, and the static model considering gravity loading,actuation loading, and robot constitutive laws is established. Additionally, the effect of tension attenuation caused by routing channel friction is considered in the robot statics, resulting in improved model accuracy. The root-mean-square error between the outputs of the static model and the experimental system is less than 1.63% of the arm length(0.5 m). By employing the proposed static model, a mapping of bending angles between the configuration space and the subsegment space is established. Furthermore, motion control experiments are conducted on our TDQCR system, and the results demonstrate the effectiveness of the static-to-kinematic model.

Nonlinear wave dispersion in monoatomic chains with lumped and distributed masses:discrete and continuum models

The main objective of this paper is to investigate the influence of inertia of nonlinear springs on the dispersion behavior of discrete monoatomic chains with lumped and distributed masses.The developed model can represent the wave propagation problem in a non-homogeneous material consisting of heavy inclusions embedded in a matrix.The inclusions are idealized by lumped masses,and the matrix between adjacent inclusions is modeled by a nonlinear spring with distributed masses.Additionally,the model is capable of depicting the wave propagation in bi-material bars,wherein the first material is represented by a rigid particle and the second one is represented by a nonlinear spring with distributed masses.The discrete model of the nonlinear monoatomic chain with lumped and distributed masses is first considered,and a closed-form expression of the dispersion relation is obtained by the second-order Lindstedt-Poincare method(LPM).Next,a continuum model for the nonlinear monoatomic chain is derived directly from its discrete lattice model by a suitable continualization technique.The subsequent use of the second-order method of multiple scales(MMS)facilitates the derivation of the corresponding nonlinear dispersion relation in a closed form.The novelties of the present study consist of(i)considering the inertia of nonlinear springs on the dispersion behavior of the discrete mass-spring chains;(ii)developing the second-order LPM for the wave propagation in the discrete chains;and(iii)deriving a continuum model for the nonlinear monoatomic chains with lumped and distributed masses.Finally,a parametric study is conducted to examine the effects of the design parameters and the distributed spring mass on the nonlinear dispersion relations and phase velocities obtained from both the discrete and continuum models.These parameters include the ratio of the spring mass to the lumped mass,the nonlinear stiffness coefficient of the spring,and the wave amplitude.

Influence of Omega 3 Fatty Acid Supplementation on Phase Angle Values of People Living with HIV/AIDS with Lipodystrophy Secondary to Antiretroviral Therapy: A Randomized Clinical Trial

Objective: The measurement of phase angles is an important monitoring parameter and supplementation with omega-3 could promote benefits by modulating the electrical potential of membranes and increasing body cell mass. This study aimed to evaluate the effectiveness of omega-3 fatty acid supplementation on the phase angle of people living with HIV/AIDS. Methods: In this study, 63 individuals of all genders who were undergoing outpatient follow-up and showed lipodystrophy due to highly active antiretroviral therapy were analyzed. Our sample consisted of two groups, one that received supplementation containing 2550 mg of omega-3/day (1080 mg of eicosapentaenoic acid and 720 mg of docosahexaenoic acid) for three months (n = 32) and another that underwent nutrition guidance (n = 31). Phase angle and body cell mass were assessed for both groups and compared at the beginning of research (T0) and after our intervention (T1) for each group separately. Results: Phase angle averaged 6.45° ± 1.06 SD. The comparison between T0 and T1 showed a significant increase in phase angle and body cell mass, whereas the guidance group showed a decrease in body cell mass at T1 in relation to T0, with a significant p-value. Variance in phase angle between moments showed significant values between T0 and T1 in the supplementation group for all genders. Conclusion: Omega-3 positively modulated patients phase angle and body cell mass, but we emphasize the need for other studies that can solidify knowledge about supplementation dosage and intervention time.

Omega-3多不饱和脂肪酸在少弱精子症治疗中的研究进展

少弱精子症是男性不育常见的类型之一,但目前仍缺乏有效治疗手段。越来越多的研究显示,omega-3多不饱和脂肪酸(ω-3 PUFA)对少弱精子症具有潜在的治疗价值。本文主要对ω-3 PUFA在影响少弱精子症脂肪酸代谢与组成、炎症反应、氧化应激等方面的相关研究进行综述,以期为少弱精子症的治疗提供新的思路。

Human immunodeficiency virus cascade–continuum of care stages and outcomes in a hospital in southern Brazil

BACKGROUND The human immunodeficiency virus(HIV)continuum of care cascade illustrates the 90-90-90 goals defined by the Joint United Nations Program on HIV/acquired immunodeficiency syndrome(UNAIDS).The care cascade includes the following five steps:Diagnosis,linkage to care,retention in care,adherence to antiretroviral therapy(ART),and viral suppression.AIM To elaborate the HIV cascade of patients diagnosed with HIV at the Nossa Senhora da Conceição Hospital(HNSC)and to determine possible local causes for the loss of patients between each step of the cascade.METHODS This retrospective cohort study included patients diagnosed with HIV infection from January 1,2015 to December 31,2016 and followed up until July 31,2019.The data were analyzed by IBM SPSS software version 25,and Poisson regression with simple robust variance was used to analyze variables in relation to each step of the cascade.Variables with P<0.20 were included in multivariable analysis,and P<0.05 was considered significant.Pearson’sχ^(2) test was used to compare the groups of patients followed up at the HNSC and those followed up at other sites.RESULTS The results were lower than those expected by the UNAIDS,with 94%of patients linked,91%retained,81%adhering to ART,and 84%in viral suppression.Age and site of follow-up were the variables with the highest statistical significance.A comparison showed that the cascade of patients from the HNSC had superior results than outpatients,with a significant difference in the last step of the cascade.CONCLUSION The specialized and continued care provided at the HNSC was associated with better results and was closer to the goals set by the UNAIDS.The development of the HIV cascade using local data allowed for the stratification and evaluation of risk factors associated with the losses occurring between each step of the cascade.

孟德尔随机化探究Omega-3脂肪酸与乳腺癌发病风险的因果关系

目的利用孟德尔随机化方法分析Omega-3脂肪酸与乳腺癌发病风险的因果关联。方法对Omega-3脂肪酸与乳腺癌全基因组关联研究(GWASs)数据进行分析,筛选出与Omega-3脂肪酸相关的遗传位点作为工具变量(IVs)。使用逆方差加权(IVW)、MR-Egger、加权中位数、简单模式和加权模式等孟德尔随机化分析方法对Omega-3脂肪酸和乳腺癌发病风险间的因果关系进行评估。结果共筛选出47个与Omega-3脂肪酸强相关的SNPs作为工具变量,IVW等分析方法均显示Omega-3脂肪酸与乳腺癌的发病风险间不存在因果关联(P>0.05)。MR-Egger回归分析等方法均未检测到明显的基因水平多效性(P=0.319),表明分析结果具有较高的敏感性和稳健性。结论Omega-3脂肪酸与乳腺癌发病风险之间无因果关联。

Omega蠕变寿命评估方法及应用

传统高温过热蒸汽管及过热炉管蠕变寿命评估多采用等温外推、Larson-Miller参数和θ参数等寿命评估方法,此类寿命评估方法常通过开展多组高应力蠕变测试进行短时外推,不仅耗时长、取样破坏性大、寿命评估存在分散性,而且此方法没有考虑材料的老化与损伤,长时外推结果置信度下降。1986年,美国材料学会(MPC)发起了用于评估工作在蠕变范围内部件剩余寿命的O-mega工程,目前该评估方法已被编入API 579 Fitness-For-Service标准中。通过介绍Omega寿命评估方法,并对1Cr0.5MoV和1.25Cr0.5MoSi两种材料开展Omega蠕变分析,再将Omega方法预测的材料蠕变断裂时间与实际断裂时间进行对比,发现Omega方法在评定蠕变寿命评估方面更具优越性。

基于Omega网的新型自路由多播网络

介绍了一种新型的基于Omega网构造的多播网络模型FiO,由1个Omega-1网和4个Omega网串连,并适当改变中间连接方式构成,其硬件代价为O(5/2NlogN).同时,本文在FiO网络模型上提出了一种对换设置找中间状态的自路由方法实现多源点多播,算法初始设置时间为O(N),通信时间达到O(logN).由于Omega网本身的构造简单,所以该网络有利于硬件集成,同时在处理多播能力上较以前的网络模型也有显著提高,所以该网络有较好的实用价值和发展潜力.

番木瓜proteinase omega基因启动子的克隆及功能初步研究

采用PCR技术从番木瓜基因组中克隆了proteinase omega基因的部分序列及其5′侧翼序列。序列分析表明,克隆到的基因序列与GenBank中的序列同源性为96%,长1039bp的5′端侧翼序列在GenBank数据库中没有同源片段。预测5′端侧翼序列有两处基础启动子区域,转录起始位点(TSS)分别为是A,T。在基础启动子区域都存在TATA-box,上游发现多处CAAT-box,G-box,I-box等顺式作用元件和AT富含区。构建了植物表达载体并用基因枪轰击番木瓜的叶组织,GUS基因瞬间表达结果表明,该长1039bp的5′端侧翼序列具有驱动GUS基因在乳管中表达的功能。该启动子的发现对进一步研究启动子的功能和开发番木瓜作为生物反应器具有重要意义。

沉管隧道接头OMEGA止水带损坏分析及修复技术

研究目的:管段接头是沉管隧道的薄弱环节,相比管段本身,极易损坏和老化,特别是建在软土地基上的沉管隧道,常因差异沉降导致接头受损,严重影响沉管隧道的使用寿命。为满足百年运营的要求,就需在运营过程中进行管段接头修复。因此,需要提出一套可靠性高、实施方便并且具有推广性的修复方案。同时,从预防的角度需要针对接头受损原因提出预防措施。研究结论:(1)综合监测数据与现场观测结果分析还原出上海外环沉管隧道OMEGA止水带的三阶段损坏过程;(2)依托该工程提出一套接头修复方案,方案包含沉降控制、接头限位和OMEGA止水带修复三部分,配合分步更换OMEGA止水带的施工筹划,最大程度降低接头修复工程对交通的干扰;(3)针对接头各阶段损坏的原因,提出三类预防建议:增添限位块和注浆孔的设计建议,合理计划岸边地面用途的规划建议以及观测沉降及时注浆的运营维护建议;(4)本文中的修复方案及预防措施可为未来铁路及公路沉管隧道工程提供参考。

Omega沸石的改性研究

为改善Omega沸石热及水热稳定性的缺陷 ,以水热焙烧结合化学脱铝的方法对Omega沸石进行了脱铝改性 ,并考察了改性沸石的结构稳定性及裂化性能。结果表明 ,改性处理后 ,脱铝Omega沸石的结构水热稳定性提高 ,80 0℃水热处理 4h ,结晶保留度可从 38%提高到 6 0 % ;结构富含中孔 ;中强酸所占比例增加 ;对重油的转化能力增加。