Average speaking fundamental frequency in soprano singers with and without symptoms of vocal attrition

Nineteen trained soprano singers aged 18–30 years vocalized tasks designed to assess average speaking fundamental frequency (SFF) during spontaneous speaking and reading. Vocal range and perceptual characteristics while singing with low intensity and high frequency were also assessed, and subjects completed a survey of vocal habits/symptoms. Recorded signals were digitized prior to being analyzed for SFF using the Kay Computerized Speech Lab program. Subjects were assigned to a normal voice or impaired voice group based on ratings of perceptual tasks and survey results. Data analysis showed group differences in mean SFF, no differences in vocal range, higher mean SFF values for reading than speaking, and 58% ability to perceive speaking in low pitch. The role of speaking in too low pitch as causal for vocal symptoms and need for voice classification differentiation in vocal performance studies are discussed.     

A Study of Highly Qualified Science Teachers' Career Trajectory in the Deep,Rural South: Examining a Link Between Deprofessionalization and Teacher Dissatisfaction

Science teacher retention, attrition, and migration continue to perplex educational scholars, political entities, as well as the general public. This study utilized an interpretive methodological design to generate assertions regarding career choice made by highly qualified science teachers in the deep, rural South through analysis of documents, interviews, focus groups, and observation. Generally considered “difficult to staff” because of location, socioeconomics, and demographics, Wilson County High School is an exemplar in science teacher retention and student achievement. Findings presented include how the science department at Wilson County improved student learning outcomes as well as the reasons why two of the highly qualified science teachers at this school were considering leaving the profession they love.     

Development of Surface Nano-Crystallization in Alloys by Surface Mechanical Attrition Treatment (SMAT)

Nanometer-sized grain structures that exhibit a large number of grain boundaries on the surface of a bulk material demonstrate excellent properties relative to their coarse-grained (CG) equivalents. Surface modification using surface mechanical attrition treatment (SMAT) is an option that cab be used to tailor the corrosion, tribological, mechanical, and chemical reaction properties of a surface. SMAT is an effective route to create the nanostructured surface layer. The SMAT process has unique advantages compared with the other coating and deposition techniques for surface nanocrystallization. For example, SMAT does not alter the chemical composition of the nanocrystalline surface layer in the matrix. In addition, SMAT has been demonstrated to activate the material surface layer by surface modification and enhance the atomic diffusivity. This article presents a review of the advantages offered by the SMAT technique for the creation of high performance surface layers. The influence of the created nanocrystalline layer on mechanical, physical, and chemical properties is assessed. Developments and the current status of the surface nanolayer that are formed are evaluated from a physical approach. Finally, prospects for the future development of grain refinement on the surface of a material matrix and potential applications are presented.     

通过表面机械加工调控Zr52.5Cu17.9Ni14.6Al10Ti5非晶合金的结构和韧性

作为一种新型结构材料, 非晶态合金的韧性需要进一步提高. 提高非晶态合金韧性的方法有引入枝晶相、调整其成分改变其泊松比影响其剪切带衍生、裂纹扩展等.本文通过表面机械加工的方法来调控非晶态合金的微观结构及韧性. 我们采用真空电弧熔炼、亚稳态薄板离心浇铸系统制备了Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (原子百分比) (Vit105)非晶合金板,并用表面机械研磨处理方法(surface mechanical attrition treatment, SMAT), 在Vit105板上形成纳米尺度局域类晶体序结构. 基于差示扫描量热分析、纳米压痕实验, 我们发现SMAT处理后的Vit105合金板表面附近弛豫焓更低, 微观结构更加均匀、稳定. 通过显微维氏硬度计测试, 发现SMAT处理后样品的表面附近硬度增大,硬度值分布也更均匀. 通过三点弯断裂实验, 可得到SMAT处理后合金板缺口韧度值从70.7 ± 4.7 MPa·m1/2提高到112.8 ± 3.7 MPa·m1/2. SMAT处理后合金板断裂后, 缺口前端剪切带密度比未处理的更大. Vit105合金板韧性的提高源于SMAT处理对剪切带萌生的促进作用. 该研究表明,表面机械加工可以在非晶态合金中形成局域类晶体有序结构, 影响其结构均匀性, 增大其硬度, 促进剪切带萌生, 提高其韧性. 表面机械加工作为一种新型的改变材料性能的手段, 具有广阔的应用前景.      

Analysis of Single Particle Attrition during Impact Experiments†

Particle breakage can be characterised as attrition, chipping, fracture, abrasion and wear. All these types of breakage mechanisms are the effect of the damage caused to these particles. These mechanisms can be differentiated not just on the basis of magnitude and direction of the force but also by the damage caused to the particles. The damage is measured by change in the size distribution and the change in shape of the particles. In the current research, experiments were performed on the newly developed Repeated Impact Test. The unique feature of this test is that about hundred particles can be subjected simultaneously to a monitored number of impacts, without particle‐particle interactions at regulated velocities. The preliminary experiments were performed with single crystalline particles of different shapes and sizes. After fixed number of impacts, the images of the particles were taken. The volume and shape of the particles were determined by image analysis. It was observed that the rate of attrition was very high when the particles are irregular. The rate decreased as the particles became more spherical.     

Rate of sodium chloride attrition fragment generation in a mixed‐suspension crystallizer

Attrition of crystals in industrial crystallization is the major source of secondary nucleation and has strong effects on product quality. This work describes attrition in industrial crystallizers using an empirical engineering model based on dimensionless groups describing crystal properties, suspension properties, and crystallizer geometry and operating conditions. Here the attrition rate of sodium chloride crystals in a small scale mixed‐suspension crystallizer is studied, varying the following parameters: impeller speed, parent crystal size, suspension density, draft‐tube impeller clearance, off‐bottom impeller clearance, impeller type, and impeller material. It was found that the attrition rate depends on most of the variables investigated. The direction of the dependence is predictable based on intuitive modeling. An empirical power law model based on dimensionless groups predicted by Buckingham‐Pi theory (using variables mentioned above) gives a good fit to the data.     

焙烧温度对铁基催化剂催化浆态床F-T合成反应性能的影响

 采用连续共沉淀与喷雾干燥成型技术相结合的方法制备了微球形Fe-Cu-K-SiO2催化剂,并考察了焙烧温度对催化剂的结构和织构性质的影响. 结果表明,催化剂具有较好的织构和结构热稳定性,粘结剂SiO2起到了分散和稳定α-Fe2O3晶相的作用. 随着焙烧温度的升高,催化剂的比表面积逐渐减小,α-Fe2O3晶粒逐渐增大,催化剂体相中的Cu和K原子向表面富集,且Cu向表面的迁移更明显; 同时,催化剂中的α-Fe2O3和CuO相发生了一定程度的离析,Cu的助剂作用减弱,使催化剂在合成气气氛下难于还原碳化. 催化剂在n(H2)/n(CO)=0.67,GHSV=2.0 L/(g·h),p=1.5 MPa和θ=250 ℃下的浆态床F-T合成反应评价结果表明,升高焙烧温度,催化剂的初活性和最高活性下降,但运行稳定性提高,而且有效地抑制了CH4的生成,明显促进了烃产物向高碳数方向移动. 反应600 h后卸载下的催化剂的形貌观测表明,催化剂的磨损主要是由化学磨损引起的,提高焙烧温度可明显改善其抗磨损性能,焙烧温度高于400 ℃时,催化剂具有较好的抗磨损性能.     

炭化过程对铁基费托合成催化剂强度和结构的影响

以模型费托合成Fe基催化剂为研究对象,在纯CO气氛中对催化剂进行不同时间的预处理,采用多种手段对预处理后催化剂的物理化学性质和抗磨损能力进行了表征。结果表明,在预处理初期,随着预处理时间的延长,催化剂的炭化程度显著提高,伴随着催化剂比表面积的降低和颗粒粒径的减小,而催化剂的抗磨损能力逐渐提高。当预处理时间超过72 h后,继续延长预处理时间,催化剂的炭化程度不再增加,而积炭程度逐渐增加,伴随着催化剂比表面积和颗粒粒径的增加,催化剂的质量也同时增加,并导致催化剂的抗磨损能力逐渐降低。     

Vocal problems among teachers: a review of prevalence, causes, prevention, and treatment

Voice disorders are thought to be one of the major occupational hazardsof school teaching. The resulting symptoms can affect teachers' ability to function in the classroom and prevent them from developing effective working relationships with other staff and students. Sick leave, speech pathology management, and surgical intervention can be costly. Severe voice problems can also result in a teacher permanently leaving the classroom. Despite the significant implications of voice disorders for teachers, this review of published research demonstrates that findings concerning the prevalence of voice problems in teachers and the causes and contributing factors of those voice problems are inconclusive. Similarly, previous research on the efficacy of prevention programs and treatment of voice problems in teachers provide few firm conclusions. Further research based on sound empirical data is needed, as many past studies have relied on anecdotal or self-report data. More operational definitions of what constitutes a voice disorder and the associated contributing factors should be adopted, along with the use of more instrumental measures and careful attention to methodology and appropriate statistical analyses. Only then will we have a sound basis for the development of effective prevention and education programs for teachers.     

流化催化剂磨损机制的研究进展

介绍了近年来流化催化剂的磨损机制及其耐磨性检测技术方面的研究进展,结合纳米压痕和颗粒粒度分布测试等技术分析了流化催化剂的体断裂和剥层机制,介绍了评价催化剂耐磨性的各种磨损试验方法及其磨损模型,其中流化磨损试验可直观有效地反映流化催化剂的耐磨性.指出今后需在流化模型、计算模拟和细观力学性能测试等方面进行深入研究,以满足探索催化剂磨损机理和改善其磨损测试适用性的需求.