Onset of channeling during DNA electrophoresis in a sparse ordered post array     

Jia Ou  Samuel J. Carpenter    Kevin D. Dorfman 《Biomicrofluidics》2010,4(1)

The “channeling hypothesis” of DNA electrophoresis in sparse, ordered arrays of posts predicts that the DNA will move through the array relatively unhindered if (i) the spacing between the posts is larger than the DNA coil and (ii) the electric field lines are straight. We tested this hypothesis by studying the electrophoretic separation of a small plasmid DNA (pUC19, 2686 base pairs) and a large, linear DNA (λ-DNA, 48 500 base pairs) in a hexagonal array of 1 μm diameter posts with a pitch of 7 μm. At low electric field strengths, these DNAs are separated due to the long-lived, rope-over-pulley collisions of λ-DNA with the posts. The resolution is lost as the electric field increases due to the onset of channeling by the λ-DNA. Using a diffusive model, we show that channeling arises at low electric fields due to the finite size of the array. This channeling is not intrinsic to the system and is attenuated by increasing the size of the array. Higher electric fields lead to intrinsic channeling, which is attributed to the disparate time scales for a rope-over-pulley collision and transverse diffusion between collisions. The onset of channeling is a gradual process, in agreement with extant Brownian dynamics simulation data. Even at weak electric fields, the electrophoretic mobility of λ-DNA in the array is considerably higher than would be expected if the DNA frequently collided with the posts.  相似文献   

A NOTE FROM THE EDITOR     

Samuel M. Taylor 《Curator: The Museum Journal》1999,42(2):69-69

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A NOTE FROM THE EDITOR     

Samuel M. Taylor 《Curator: The Museum Journal》1999,42(3):185-185

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An evaluation of the special needs referral process for low-income preschool children with emotional and behavioral problems     

John Fantuzzo  Jill Stoltzfus  Megan Noone Lutz  Helen Hamlet  Vijaykumar Balraj  Colleen Turner  Samuel Mosca 《Early childhood research quarterly》1999,14(4):465

The present study is an evaluation of the special needs referral system in a large urban Head Start program. To assess the validity of this system, two assessments were conducted. The first examined a representative sample of 105 children who were formally referred for special needs services. The Early Intervention Screening Profile (EISP) was used to indicate the distribution of problem behaviors of these special needs children. Two independent raters evaluated all cases. Reliable evaluations revealed that all of the referred children displayed speech and language problems, with 70% showing only speech problems and 30% showing speech plus emotional and behavioral problems. The second assessment examined reports of teachers’ concerns about children program-wide by obtaining a representative sample of 203 children nominated by teachers as most likely to be identified as having special needs. Teachers completed a modified EISP. Results indicated that over 70% of the children evidenced emotional and behavioral problems with no accompanying speech difficulties and 30% displayed emotional and behavioral problems plus speech problems. Implications of referral biases were discussed.  相似文献   

What are secondary students’ expectations for teachers in virtual school environments?     

Kevin Oliver  Jason Osborne  Kevin Brady 《Distance Education》2009,30(1):23-45

A recent evaluation of the new North Carolina Virtual Public School (NCVPS) in the USA revealed numerous expectations for virtual school teachers from secondary students. Specifically, students expected their teachers to actually teach rather than moderate a course shell, supplement course shells with content and projects that illustrate relevance, provide for both content and peer interaction, and respond to questions and provide feedback quickly. The data suggest a possible content‐related interaction where a limited course shell can be bolstered by a proactive teacher, but potentially flounder among teachers who do not expect or know how to supplement an online course. Data further suggest a potential communication‐related interaction where increased opportunities for student–student and student–teacher interaction could potentially decrease the actual or perceived need for individualized attention that is particularly challenging for virtual teachers to provide. These results can be used to establish teacher expectations and design professional development experiences that prepare teachers to undertake divergent roles unique to online instruction.  相似文献   

Common Assessment Framework (CAF) – early views and issues     

Roger Norgate  Maria Traill  Cara Osborne 《Educational Psychology in Practice》2009,25(2):139-150

This study explores the profile of Common Assessment Framework (CAF) assessments and the perceptions of assessors during the early phase of its implementation. Whilst there was diversity in who completed CAFs, schools undertook the most. Headteachers and other school staff completing the assessment felt that the questions tended to be intrusive and they feared this might damage their relationship with parents. Assessments proved time consuming and completers tended to go on to become the Lead Professional. Comments suggested some people were avoiding the completion of CAFs because of fears about the increased workload. There were, however, positive views about the rigour of the process and it had tended to serve to prompt positive dialogue between agencies. There were genuine attempts to involve children in the process.  相似文献   

The validity and reliability of the GymAware linear position transducer for measuring counter-movement jump performance in female athletes     

Shannon O’Donnell  Francisco Tavares  Daniel McMaster  Samuel Chambers  Matthew Driller 《Measurement in physical education and exercise science》2018,22(1):101-107

The current study aimed to assess the validity and test–retest reliability of a linear position transducer when compared to a force plate through a counter-movement jump in female participants. Twenty-seven female recreational athletes (19 ± 2 years) performed three counter-movement jumps simultaneously using the linear position transducer and force plate for validity. In addition, 11 elite female athletes (23 ± 6 years) performed 3 counter-movement jumps with the linear position transducer on three separate days for test–retest reliability. Pearson correlations for jump height between the devices were at a high level (r = .90), with the linear position transducer overestimating jump height by 7.0 ± 2.8 cm. The reliability measured by the linear position transducer resulted in a mean intraclass correlation of .70 for jump height, .90 for peak velocity, and .91 for mean velocity. The linear position transducer was reliable for measuring counter-movement jumps in elite female athletes; however, caution should be taken for one-off jump measures as it may over-estimate jump height.  相似文献   

Preferences for Explanation Generality Develop Early in Biology But Not Physics          下载免费PDF全文

Angie M. Johnston  Mark Sheskin  Samuel G. B. Johnson  Frank C. Keil 《Child development》2018,89(4):1110-1119

One of the core functions of explanation is to support prediction and generalization. However, some explanations license a broader range of predictions than others. For instance, an explanation about biology could be presented as applying to a specific case (e.g., “this bear”) or more generally across “all animals.” The current study investigated how 5‐ to 7‐year‐olds (N = 36), 11‐ to 13‐year‐olds (N = 34), and adults (N = 79) evaluate explanations at varying levels of generality in biology and physics. Findings revealed that even the youngest children preferred general explanations in biology. However, only older children and adults preferred explanation generality in physics. Findings are discussed in light of differences in our intuitions about biological and physical principles.  相似文献   

Preschoolers Continually Adjust Their Epistemic Trust Based on an Informant's Ongoing Accuracy          下载免费PDF全文

Samuel Ronfard  Jonathan D. Lane 《Child development》2018,89(2):414-429

Children aged 4–7 years (N = 120) played four rounds of a find‐the‐sticker game. For each round, an informant looked into two cups and made a claim about which cup held a sticker. At the end of each round, children guessed the sticker's location, and then the sticker's actual location was revealed. For three of the rounds, the informant accurately reported the sticker's location. But critically, for one round—either Round 1, 2, or 3—she was inaccurate. Children continually adjusted their trust in the informant as they obtained more information about her accuracy. Relations between the informant's pattern of accuracy and children's trust were robust, neither mediated nor moderated by children inferences about her intent or traits.  相似文献   

Assessing Measurement Invariance in Multiple-Group Latent Profile Analysis     

Margarita Olivera-Aguilar  Samuel H. Rikoon 《Structural equation modeling》2018,25(3):439-452

The study of measurement invariance in latent profile analysis (LPA) indicates whether the latent profiles differ across known subgroups (e.g., gender). The purpose of the present study was to examine the impact of noninvariance on the relative bias of LPA parameter estimates and on the ability of the likelihood ratio test (LRT) and information criteria statistics to reject the hypothesis of invariance. A Monte Carlo simulation study was conducted in which noninvariance was defined as known group differences in the indicator means in each profile. Results indicated that parameter estimates were biased in conditions with medium and large noninvariance. The LRT and AIC detected noninvariance in most conditions with small sample sizes, while the BIC and adjusted BIC needed larger sample sizes to detect noninvariance. Implications of the results are discussed along with recommendations for future research.  相似文献