9,729 research outputs found
Single-molecule studies of unconventional motor protein myosin VI
No full textMyosin VI is one of the myosin superfamily members that are actin-based molecular motors. It has received special attention due to its distinct features as compared to other myosins, such as its opposite directionality and a much larger step size than expected given the length of its “leg”.
This dissertation presents the author‟s graduate work of several single-molecule studies on myosin VI. Special attention was paid to some of myosin VI‟s tail domains that consist of proximal tail (PT), medial tail (MT), distal tail (DT) domains and cargo-binding domain (CBD).
The functional form of myosin VI in cells is still under debate. Although full length myosin VI proteins in cytosolic extracts of cells were monomers from earlier studies, there are several reasons why it is now believed that myosin VI could exist as a dimer. If this is true and dimerization occurs, the next logical question would be which parts of myosin VI are dimerization regions? One model claimed that the CBD is the sole dimerization region. A competing model claimed that there must be another region that could be involved in dimerization, based on their observation that a construct without the CBD could still dimerize.
Our single-molecule experiment with progressively truncated myosin VI constructs showed that the MT domain is a dimerization region, supporting the latter model. Additional single-molecule experiments and molecular dynamics (MD) simulation done with our collaborators suggest that electrostatic salt bridges formed between positive and negative amino acid residues are mainly responsible for the MT domain dimerization.
After resolving this, we are left with another important question which is how myosin VI can take such a large step. Recent crystal structure showed that one of the tail domains preceding the MT domain, called the PT domain, is a three-helix bundle. The most easily conceivable way might be an unfolding of the three-helix bundle upon dimerization, allowing the protein to stretch and reach a larger distance. The single-molecule stepping data with mutant full-length construct that lacks two helices out of three in the PT domain tell that it is indeed the case.
In this dissertation, more details of myosin VI PT/MT domain experiments will be explored along with background information on the single-molecule experiment methods used in these studies.Item withdrawn by Mark Zulauf ([email protected]) on 2011-04-07T13:00:38Z
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Bending dynamics of semi-flexible particles in turbulent flows
No full textWe study the Lagrangian dynamics of semi-flexible particles in laminar as well as in homogeneous and isotropic turbulent flows by means of analytically solvable stochastic models and direct numerical simulations. The statistics of the bending angle is qualitatively different in laminar and turbulent flows and exhibits a strong dependence on the topology of the velocity field. In particular, in two-dimensional turbulence, particles are either found in a fully extended or in a fully folded configuration; in three dimensions, the predominant configuration is the fully extended one
Vi Kowalchuk
No full textPhotograph - Vi Kowalchuk, member of the Book Sub-Committee, part of the Town of Athabasca 75th Anniversary Committee, Athabasca, Alberta. The Book Sub Committee produced the book "Athabasca Landing: An Illustrated History
Cr(VI) and Cr(III)-Based Conversion Coatings on Zinc
No full textWith the aims of understanding the protective mechanism of chromate conversion coatings and developing alternatives to chromate treatments, the physical natures and corrosion properties of Cr(VI) and Cr(III) treated zinc have been investigated in this work. The Cr(VI) treatments were carried out in dichromate and sulfuric acid solution with different dipping times. The Cr(III) treatments were carried out in two commercial solutions (A and B). The thickness of the coatings was measured using ellipsometry. The morphologies and the compositions of the treated zinc have been studied by means of SEM, AFM, AES, FTIR and XPS. The drying temperature influence on the corrosion performance of the Cr(VI)âtreated zinc has been investigated. The Volta potential in treated and untreated areas has been measured using scanning Kelvin probe (SKP) and SKPFM. The corrosion behavior of the Cr(VI) and Cr(III) treated zinc has been investigated using polarization, electrochemical impedance measurements (EIS), and salt spray tests. Both Cr(VI) and Cr(III) species were detected by XPS in the outermost layer of the Cr(VI) coatings, while no Cr(VI) species was found in the Cr(III) coatings. AES depth profile results show that chromium oxides are the main components in the Cr(VI) coatings. Zinc oxide is mainly located at the chromium oxides / zinc interface. The Cr(III) coating is a mixture of chromium oxides and zinc oxide. Both the Cr(VI) and the Cr(III) treatments can supply corrosion protection to zinc. The corrosion resistance of the Cr(III)-B coating is greater than that of the Cr(III)-A coating. However, the inhibition of the corrosion of zinc by Cr(VI) coating is more effective than by the Cr(III) coatings. The inhibition of the corrosion of zinc by the Cr(VI) and the Cr(III) treatments is discussed, and future research topics are suggested.Mechanical, Maritime and Materials Engineerin
Xây dựng thang đo hành vi công dân tổ chức của nhân viên trong ngành khách sạn theo mô hình 3 chân (a three-leg model)
No full textIn the hospitality industry, the job characteristics of frontline employees are distinctively characterized by high levels of interaction while serving customers. In addition to organizational citizenship behavior directed towards colleagues and the organization, organizational citizenship behavior oriented towards customers significantly enhances positive customer experiences, which is a core factor contributing to the enterprise’s success. This study applies a three-leg model to develop a scale for measuring employees’ organizational citizenship behavior directly serving customers in the Danang City, Vietnam, hotel industry. The author employs a qualitative research method to gain deeper insights into the scale; subsequently, quantitative research is utilized to evaluate the scale. The research findings indicate that the three-leg model achieves a high level of compatibility, wherein the organizational citizenship behavior of hotel employees can be measured through 18 observed variables across three aspects: organizational citizenship behavior directed towards the organization (06 items), organizational citizenship behavior directed towards colleagues (06 items), and organizational citizenship behavior directed towards customers (06 items).Với ngành khách sạn, đặc điểm công việc của nhân viên tuyến đầu mang tính riêng biệt bởi dịch vụ đòi hỏi từ sự tương tác cao giữa khách hàng và nhân viên. Bên cạnh hành vi công dân tổ chức hướng đến đồng nghiệp và tổ chức, hành vi công dân tổ chức hướng đến khách hàng có ảnh hưởng đáng kể đến việc nâng cao trải nghiệm tích cực của khách hàng, là nhân tố cốt lõi đem lại hình ảnh thương hiệu cho khách sạn. Nghiên cứu này vận dụng mô hình 3 chân (a three-leg model) để xây dựng thang đo hành vi công dân tổ chức của nhân viên trong bối cảnh ngành khách sạn tại thành phố Đà Nẵng, Việt Nam. Để có những hiểu biết rõ ràng và thấu đáo hơn về thang đo, tác giả sử dụng phương pháp nghiên cứu định tính; tiếp theo, sử dụng nghiên cứu định lượng nhằm đánh giá thang đo. Kết quả nghiên cứu cho thấy mô hình 3 chân đạt được sự tương thích cao, trong đó hành vi công dân tổ chức của nhân viên trong ngành khách sạn có thể đo lường qua 18 mục hỏi ở 03 khía cạnh là hành vi công dân tổ chức hướng đến tổ chức (06 mục hỏi), hành vi công dân tổ chức hướng đến đồng nghiệp (06 mục hỏi) và hành vi công dân tổ chức hướng đến khách hàng (06 mục hỏi)
8-isorpostanes – markers for oxidative stress in obstructive sleep apnea patients with systolic dysfunction
No full textRadostina Vlaeva Cherneva,1 Ognian Borisov Georgiev,1 Daniela Stoichkova Petrova,1 Emil Ivanov Manov,2 Sylvia Rumenova Ruseva,3 Vanio Ivanov Mitev,3 Julia Ivanova Petrova4 1Department of Internal Medicine, Division of Pulmonary Medicine, Medical University of Sofia, Sofia, Bulgaria; 2Department of Internal Medicine, Division of Cardiology, Medical University of Sofia, Sofia, Bulgaria; 3Department of Medical Chemistry and Biochemistry, Laboratory of Synthesis and Analysis of Bioactive Substances, Medical University of Sofia, Sofia, Bulgaria; 4Department of Neurology, Medical University of Sofia, Sofia, Bulgaria Objective: Increased oxidative stress is considered to be an independent risk factor for cardiovascular diseases, but remains disputed in obstructive sleep apnea (OSA). Among oxidative stress markers, isorpostanes are considered to be the most sensitive and specific. Aims: The aim of the study was to compare urinary isorpostanes in patients with OSA and systolic dysfunction to patients with OSA and preserved ejection fraction (EF) and determine their role as markers for increased oxidative stress and early cardiac damage. Materials and methods: Urinary 8F2-isorpostanes were measured in 30 patients with OSA and mild systolic dysfunction (EF = 45.7% ± 6.17%) and compared to 15 patients with OSA and normal EF (EF = 60.3% ± 6.3%). Univariate regression analysis was performed to find predictors of left systolic dysfunction. Correlations between 8-isorpostanes, anthropometric, metabolic, and sleep study characteristics were explored. In addition, in 19 patients the effect of bilevel positive airway pressure (BiPAP) therapy was evaluated during a 3 month follow-up. Markers of hemodynamic stress, N-terminal prohormone of brain natriuretic peptide and oxidative stress, measured by 8-isorpostanes were compared before and after the follow-up. Results: Urinary levels of 8-isorpostanes were significantly higher in the group with mild systolic dysfunction in comparison to the controls with preserved EF (0.149 versus 0.049 pg/µL, P = 0.023). The regression analysis did not define them as predictors for left systolic dysfunction. Their urinary concentration correlated best to the average desaturation index (P = 0.043). Urinary 8-isorpostanes decreased as a result of BiPAP therapy after three months of follow-up (0.164 versus 0.098 pg/µL, P = 0.011). Conclusion: Urinary isorpostanes are reliable markers for chronic intermittent hypoxia and oxidative stress in OSA patients. They may be of clinical application for the early detection of patients at risk for cardiovascular damage and could help in the monitoring of the restoration of oxidative balance. Keywords: 8-isorpostanes, oxidative stress, LV systolic dysfunction, OS
Vi editor for MC56000 computer system
No full textVi is a powerful editor on MASSCOMP 5600 system. It has numerous facilities: easy editing, lots of options, indenting, to edit the files without exiting vi, easy moving of between files and so on.(Author
Towards Cr(VI)-free anodization of aluminum alloys for aerospace adhesive bonding applications: A review
No full textFor more than six decades, chromic acid anodizing (CAA) has been the central process in the surface pre-treatment of aluminum for adhesively bonded aircraft structures. Unfortunately, this electrolyte contains hexavalent chromium (Cr(VI)), a compound known for its toxicity and carcinogenic properties. To comply with the new strict international regulations, the Cr(VI)-era will soon have to come to an end. Anodizing aluminum in acid electrolytes produces a self-ordered porous oxide layer. Although different acids can be used to create this type of structure, the excellent adhesion and corrosion resistance that is currently achieved by the complete Cr(VI)-based process is not easily matched. This paper provides a critical overview and appraisal of proposed alternatives to CAA, including combinations of multiple anodizing steps, pre- and post anodizing treatments. The work is presented in terms of the modifications to the oxide properties, such as morphological features (e.g., pore size, barrier layer thickness) and surface chemistry, in order to evaluate the link between fundamental principles of adhesion and bond performance.[Figure not available: see fulltext.]Accepted Author Manuscript(OLD) MSE-6(OLD) MSE-
Automated essay assessment: an evaluation on paperrater’s reliability from practice / Nguyen Vi Thong
No full textFrom a perspective of a PaperRater user, the author attempts to investigate the reliability of the
program. Twenty-four freshman students and one writing teacher at Dalat University - Vietnam
were recruited to serve the study. The author also served as one scorer. The scores generated by
PaperRater and the two human scorers were analyzed quantitatively and qualitatively. The
statistical results indicate that there is an excellent correlation between the means of scores
generated by three scorers. With the aid of SPSS and certain calculation, it is shown that
PaterRater has an acceptable reliability which implies that the program can somehow assist in
grading students’ papers. The semi-structured interview at the qualitative stage with the teacher
scorer helped point out several challenges that writing teachers might encounter when assessing
students’ prompts. From her perspective, it was admitted that with the assistance of PaperRater,
the burden of assessing a bunch of prompts at a short time period would be much released.
However, how the program can be employed by teachers should be carefully investigated.
Therefore, this study provides writing teachers with pedagogical implications on how
PaperRater should be used in writing classrooms. The study is expected to shed new light on the
possibility of adopting an automated evaluation instrument as a scoring assistant in large
writing classrooms
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