Crack-Like Processes Governing the Onset of Frictional Slip

We perform real-time measurements of the net contact area between two blocks of like material at the onset of frictional slip. We show that the process of interface detachment, which immediately precedes the inception of frictional sliding, is governed by three different types of detachment fronts. These crack-like detachment fronts differ by both their propagation velocities and by the amount of net contact surface reduction caused by their passage. The most rapid fronts propagate at intersonic velocities but generate a negligible reduction in contact area across the interface. Sub-Rayleigh fronts are crack-like modes which propagate at velocities up to the Rayleigh wave speed, VR, and give rise to an approximate 10% reduction in net contact area. The most efficient contact area reduction (~20%) is precipitated by the passage of slow detachment fronts. These fronts propagate at anomalously slow velocities, which are over an order of magnitude lower than VR yet orders of magnitude higher than other characteristic velocity scales such as either slip or loading velocities. Slow fronts are generated, in conjunction with intersonic fronts, by the sudden arrest of sub-Rayleigh fronts. No overall sliding of the interface occurs until either of the slower two fronts traverses the entire interface, and motion at the leading edge of the interface is initiated. Slip at the trailing edge of the interface accompanies the motion of both the slow and sub-Rayleigh fronts. We might expect these modes to be important in both fault nucleation and earthquake dynamics.Comment: 19 page, 5 figures, to appear in International Journal of Fractur

Interactions between the Nse3 and Nse4 Components of the SMC5-6 Complex Identify Evolutionarily Conserved Interactions between MAGE and EID Families

The SMC5-6 protein complex is involved in the cellular response to DNA damage. It is composed of 6-8 polypeptides, of which Nse1, Nse3 and Nse4 form a tight sub-complex. MAGEG1, the mammalian ortholog of Nse3, is the founding member of the MAGE (melanoma-associated antigen) protein family and Nse4 is related to the EID (E1A-like inhibitor of differentiation) family of transcriptional repressors.Using site-directed mutagenesis, protein-protein interaction analyses and molecular modelling, we have identified a conserved hydrophobic surface on the C-terminal domain of Nse3 that interacts with Nse4 and identified residues in its N-terminal domain that are essential for interaction with Nse1. We show that these interactions are conserved in the human orthologs. Furthermore, interaction of MAGEG1, the mammalian ortholog of Nse3, with NSE4b, one of the mammalian orthologs of Nse4, results in transcriptional co-activation of the nuclear receptor, steroidogenic factor 1 (SF1). In an examination of the evolutionary conservation of the Nse3-Nse4 interactions, we find that several MAGE proteins can interact with at least one of the NSE4/EID proteins.We have found that, despite the evolutionary diversification of the MAGE family, the characteristic hydrophobic surface shared by all MAGE proteins from yeast to humans mediates its binding to NSE4/EID proteins. Our work provides new insights into the interactions, evolution and functions of the enigmatic MAGE proteins

Migraine aura: retracting particle-like waves in weakly susceptible cortex

Cortical spreading depression (SD) has been suggested to underlie migraine aura. Despite a precise match in speed, the spatio-temporal patterns of SD and aura symptoms on the cortical surface ordinarily differ in aspects of size and shape. We show that this mismatch is reconciled by utilizing that both pattern types bifurcate from an instability point of generic reaction-diffusion models. To classify these spatio-temporal pattern we suggest a susceptibility scale having the value [sigma]=1 at the instability point. We predict that human cortex is only weakly susceptible to SD ([sigma]<1), and support this prediction by directly matching visual aura symptoms with anatomical landmarks using fMRI retinotopic mapping. We discuss the increased dynamical repertoire of cortical tissue close to [sigma]=1, in particular, the resulting implications on migraine pharmacology that is hitherto tested in the regime ([sigma]>>1), and potentially silent aura occurring below a second bifurcation point at [sigma]=0 on the susceptible scale

The effects of a constructivist learning environment on student cognition of mechanics and attitude toward science : a case study

The purpose of this project was to examine the effects of a constructivist learning environment on student cognition of mechanics and attitude toward science compared to students enrolled in a traditional lecture course. The constructivist course utilized cooperative grouping and microcomputer-based labs with very little lecture to teach mechanics. Enrollment in the course was limited to women and minorities. Case study methodology was used to collect and analyze the data. The data was both qualitative and quantitative in nature. The qualitative data consisted of formal interviews, copies of course work, a participant observation journal, and video tape of class sessions. Quantitative data consisted of student test scores from a cognitive exam, The Mechanics Baseline Test and an attitude survey, Attitude Toward Science in School Assessment

A case study of Hispanic middle school students in an ESL classroom: Discourses in academic reading instruction

This case study examined student teacher interaction that took place in one ESL middle school classroom with 29 Latino/a students learning to read in English. Observations in classrooms and interviews with teachers were conducted over a ten month period, one complete school year. Students were also tested in their reading comprehension in Spanish at the beginning of the school year. These results were compared with results on English entrance exams and with the results on English reading tests at the end of the school year. The important and main themes were those of the ESL teachers’ preparation of the students in reading and writing throughout the school year for the spring term project and a juried poster presentation, and the students’ self-reflection contained in responses to teacher initiated prompts. The principal artifact mediating learning was the interactive computer software programs provided by the school. The qualitative results suggest that students’ strong identification with family and the immigrant circumstances may provide discourse dissonances that interfere with motivation and the development of self-directed learning. The results of testing showed that a student’s year-end results in English reading were predicted by the beginning level of English reading skills. A lesser, but still significant finding, was that L1 Spanish reading performance was a predictor of L2 English reading performance

Simultaneous tone on tone masking : an investigation of monaural and dichotic overshoot

Transient elevations in the threshold of a signal presented within milliseconds of onset and Just prior to the offset of a masker are called "overshoot." Overshoot was investigated by manipulating three independent variables frequency of the signal, temporal delay of the signal, and mode of stimuli presentation (monaural or dichotic). The masker was always a 60 dB SPL, 250 msec, 1000 Hz pure tone, while the 10 msec signal was one of 8 pure tone frequencies centered around the masker from 400 to 1600 Hz. The signal onset was delayed by one of 4 temporal intervals: +2, +20, +125, and +238 msec. Thresholds were taken for both dichotic and monaural presentation of stimuli. A 2x4x8 Repeated Measures design was used, and an ANOVA provided the statistical analysis. Significant main effects for all three independent variables were found, as well as a significant frequency by mode of presentation interaction. The results confirmed previous research on the effects of signal temporal delay and mode of presentation of stimuli. The absence of frequency selective characteristics of overshoot in the dichotic condition conflicted with research by Zwislocki et al. (1967, 1968). The results were discussed in terms of Scholl's neural sharpening hypothesis

Binary nematic mixtures of 4,4'-dialkoxyazoxybenzene homologs

Four phase diagrams of binary mixtures of nematogenic dialkoxyazoxybenzenes were constructed by determining the melting range and nematic-isotropic (N-I) transition range of various compositions of the binary systems. The components included 4,4'-dimethoxy- (la), 4,4'-diethoxy- (lb), 4,4'-di-n- butyloxy- (lc) and 4,4'-di-n-hexyloxyazoxybenzene (ld). All mixtures give nematic mesophases in which the molecular order is intermediate relative to the nematic mesophase of the pure components. The eutectic mixtures generally exhibit the widest nematic range. The noneutectic mixtures having N-I transition temperatures higher than the corresponding eutectic mixture often exhibit nematic ranges greater than the eutectic mixture due to their ability to be supercooled. Binary mixtures from these systems and also pure 1c were used as stationary liquid phases in gas-liquid partition chromatography (glpc) to determine the selectivity of their nematic mesophases toward the positional isomers m- and p-xylene. This selectivity is an indication of the molecular order within the mesophase. The molecular order of the pure compounds was found to be in the same order as that of their N-I transition temperatures. The results from the mixtures, however, demonstrate that the N-I transition temperature is only a rough indication of order

The development of a framework for an articulation plan for the transfer of credits from two- to four-year public educational institutions in North Carolina

It was the purpose of this study to develop a framework for an articulation plan to transfer credits for courses from two- to four-year public educational institutions in North Carolina. In 1981, 109,951 students were enrolled in the 58 institutions in the North Carolina Community College System. The problem precipitating the study was the lack of a plan whereby these students could transfer credits to institutions in the North Carolina University System. Only those students following a prescribed program of study in the College Transfer programs in the 23 community colleges in the system could transfer credits to the University System. A search was made of the education professional literature, and the articulation plans for higher education in other states were studied. Data were solicited through the use of a questionnaire mailed to the chief administrative officer of the two-year public postsecondary institutions in all 50 states. The 43 states (86 percent) from which data were received enrolled approximately 97 percent of students attending public two-year postsecondary educational institutions in the United States as of October, 1981. The states rated their plans using criteria developed by the researcher based on information gathered from the literature

The impacts of experiential learning on leadership identity in female college graduates

The purpose of this study was to gain a clearer understanding of how undergraduate Experiential Learning facilitates leadership identity among female college students. The higher education research literature focuses on the leadership development of White males primarily, without examining the Experiential Learning component of a college education with regard to leadership outcomes. Most studies on leadership in higher education use a quantitative approach with leadership survey instruments. Using an interpretive research paradigm and building on previous research literature examining leadership identity in college students, the researcher asked six female college graduates about the role of Experiential Learning in their leadership identity. The students' four year-end legacy papers from their leadership program were examined as well. The data revealed that Undergraduate Leadership, Volunteer Service, Study Abroad, and Internships had a positive impact on leadership outcomes for the participants. Ultimately, this study revealed that this style of learning did facilitate leadership identity in female students who might not otherwise have reached full leadership identity due to their initial perceptions of leaders as being central, positional, and authoritative rather than approaching leadership as shared, collaborative, and relational