Strain amplitude response and the microstructure of PA/clay nanocomposites

Polyamide 6/clay nanocomposites (PAn, where n is the mass fraction of clay) with various clay loading were prepared by melt compounding in a twin screw extruder. Exfoliation of clay in a PA matrix was confirmed by X-ray diffraction. Strain amplitude response of PAn in both melt and solution states has been investigated. In the melt state, critical strain amplitude of PAn is sensitive to strain amplitude response and decrease logarithmically with increasing clay loading. The elastic moduli (G′) of PAn are reversible under frequency loop sweeps. Comparisons of strain amplitude response in both melt and solution states have been conducted. Two different responses have been observed: strain thinning in the melt state and weak strain overshoot in the solution state. FTIR studies show that amide II band of PAn shifts toward high wavenumbers, but amide I band and N–H stretching vibration are independent of clay loading. We suggest that two types of strain amplitude response of PAn can be explained: strain thinning which is dominant in PAn caused by physical adsorption and entanglement of PA chains on nanoclays and weak strain overshoot caused by weak bonds between PA chains and nanoclays

Who Benefits from Postsecondary Occupational Education? Findings from the1980s and 1990s

Technological changes in the workplace have placed considerable pressure on the U.S. educational system to prepare students for increasingly skillbased occupations. Employers reward new hires for having the skills or credentials needed for their job, underscoring the importance of having either the requisite “tools in your toolbox,” or some basic academic preparation to continue on into postsecondary education. This stress on knowledge acquisition has contributed to a growing wage gap between high school and college graduates. Whether occupational education at the high school level, with its focus on immediate workforce entry after high school, adequately prepares students for college is a public concern. Since students who enroll in these programs are less likely to transfer to a four-year college to obtain a bachelor’s degree, occupational education is criticized for hampering their future earnings. Some of the criticisms of postsecondary occupational education could be allayed if the economic benefits were equal to (or greater than) those of other types of education. This brief investigates the economic benefits of a community college education by analyzing the effects on post-college earnings of a student’s program of study (occupational or academic), the amount of schooling accumulated with and without attaining a degree, and the type of credential earned

Structure and functional motifs of GCR1, the only plant protein with a GPCR fold?

Whether GPCRs exist in plants is a fundamental biological question. Interest in deorphanizing new G protein coupled receptors (GPCRs), arises because of their importance in signaling. Within plants, this is controversial as genome analysis has identified 56 putative GPCRs, including GCR1 which is reportedly a remote homologue to class A, B and E GPCRs. Of these, GCR2, is not a GPCR; more recently it has been proposed that none are, not even GCR1. We have addressed this disparity between genome analysis and biological evidence through a structural bioinformatics study, involving fold recognition methods, from which only GCR1 emerges as a strong candidate. To further probe GCR1, we have developed a novel helix alignment method, which has been benchmarked against the the class A – class B - class F GPCR alignments. In addition, we have presented a mutually consistent set of alignments of GCR1 homologues to class A, class B and class F GPCRs, and shown that GCR1 is closer to class A and /or class B GPCRs than class A, class B or class F GPCRs are to each other. To further probe GCR1, we have aligned transmembrane helix 3 of GCR1 to each of the 6 GPCR classes. Variability comparisons provide additional evidence that GCR1 homologues have the GPCR fold. From the alignments and a GCR1 comparative model we have identified motifs that are common to GCR1, class A, B and E GPCRs. We discuss the possibilities that emerge from this controversial evidence that GCR1 has a GPCR fol

Association of snRNA genes with coiled bodies is mediated by nascent snRNA transcripts

AbstractBackground: Coiled bodies are nuclear organelles that are highly enriched in small nuclear ribonucleoproteins (snRNPs) and certain basal transcription factors. Surprisingly, coiled bodies not only contain mature U snRNPs but also associate with specific chromosomal loci, including gene clusters that encode U snRNAs and histone messenger RNAs. The mechanism(s) by which coiled bodies associate with these genes is completely unknown.Results: Using stable cell lines, we show that artificial tandem arrays of human U1 and U2 snRNA genes colocalize with coiled bodies and that the frequency of the colocalization depends directly on the transcriptional activity of the array. Association of the genes with coiled bodies was abolished when the artificial U2 arrays contained promoter mutations that prevent transcription or when RNA polymerase II transcription was globally inhibited by α-amanitin. Remarkably, the association was also abolished when the U2 snRNA coding regions were replaced by heterologous sequences.Conclusions: The requirement for the U2 snRNA coding region indicates that association of snRNA genes with coiled bodies is mediated by the nascent U2 RNA itself, not by DNA or DNA-bound proteins. Our data provide the first evidence that association of genes with a nuclear organelle can be directed by an RNA and suggest an autogenous feedback regulation model

What Can We Learn About Postsecondary Vocational Education From Existing Data?

This paper outlines an agenda for research on postsecondary vocational education that can be carried out with existing data. We are particularly interested in encouraging research that can provide insight into the effects of the Carl D.Perkins Vocational and Technical Education Act of 1998. This act prescribes a set of performance indicators designed to promote continuous program improvement, yet some performance measures may not fully measure the educational and skills training missions of community colleges. This issue becomes especially important in light of the emerging trend of nontraditional pathways taken by students through higher education. Although fewer and fewer students proceed through higher education uninterrupted at a single institution, this ideal continues to dominate postsecondary education assessment. Helping to resolve the problems of assessment and institutional accountability within the rapidly changing landscape of postsecondary vocational education is one of the most important roles that projects using existing data could play for the National Assessment of Vocational Education. We propose a set of six projects that can help define "success" in postsecondary vocational education. We also suggest some analyses to evaluate the performance of individuals, groups of institutions, and community colleges against those standards

Beyond Student Right-to-Know Data: Factors That Can Explain Community College Graduation Rates

Policymakers, educators, and researchers recognize the importance of community colleges as open door institutions that provide a wide range of students with access to college. At the same time, competing demands for the state funds that would support community colleges have resulted in reduced public allocations and higher student tuition fees. Understandably, therefore, both state policymakers and parents are increasingly focused on the returns to their public or private investments in education, and the outcomes of community college attendance are now under greater scrutiny. To facilitate the evaluation of the colleges, there are now available data, through the Student Right-to-Know and Campus Security Act (1990), which amended the Higher Education Act, on every college’s graduation rate for fall semester cohorts of first-time, fulltime (FTFT) students in degree programs. This information is known as the Student Right-to-Know (SRK) data. A related public concern is how the outcomes of community college students can be improved. Therefore, attempts are now being made to clarify the way that specific students define success and to identify the college policies and practices that can promote success for all students. For some community college students, college completion, defined as earning a degree or certificate, is the appropriate measure of success. For other students, success is demonstrated by transferring to a baccalaureate institution. Still others are satisfied with completing courses that increase their knowledge or skill level in a particular area even though their educational experience is not considered successful as defined by traditional educational outcomes

The Characteristics of Occupational Students in Postsecondary Education

This Brief presents a profile of the enrollment, demographic, and educational characteristics, and the educational goals, of community college students in occupational programs. It compares their features with those of community college students in academic programs and with baccalaureate students. This analysis further considers the distinct features of occupational students enrolled in certificate degree programs. The Brief stands alone as a comparative description of these students, but also provides important background material for CCRC’s companion Briefs on postsecondary occupational students, Educational Outcomes of Postsecondary Occupational Students and Who Benefits from Postsecondary Occupational Education? Findings from the 1980s and 1990s

The Effects of Institutional Factors on the Success of Community College Students

Community colleges are the gateway to higher education for many students who would otherwise have limited access to college, particularly those who are from low-income households or are ethnic minorities, first generation college students, or immigrants. Yet only about one-third of all community college students receives any degree or certificate even eight years after initial college enrollment. And credit accumulation and completion rates are even lower for minority and low-income students. Meanwhile, community college student outcomes, as measures of college effectiveness, are of increasing concern for institutional accountability. The Bush administration and many legislators in Congress would like to hold postsecondary institutions to higher standards of accountability, just as they have done with elementary and secondary schools. Institutional reporting requirements to the Department of Education now include data for graduation rates overall and broken out by gender and race/ethnicity. More than half of all states take into account the performance of public colleges when determining higher education appropriations

On the recurrence times of neutron star X-ray binary transients and the nature of the Galactic Centre quiescent X-ray binaries

The presence of some X-ray sources in the Galactic Centre region which show variability, but do not show outbursts in over a decade of monitoring has been used to argue for the presence of a large population of stellar mass black holes in this region. A core element of the arguments that these objects are accreting black holes is the claim that neutron stars (NSs) in low mass X-ray binaries (LMXBs) do not have long transient recurrence times. We demonstrate in this paper that about half of the known transient LMXBs with clear signatures for NS primaries have recurrence times in excess of a decade for outbursts at the sensitivity of MAXI. We furthermore show that, in order to reconcile the expected total population of NS LMXBs with the observed one and with the millisecond radio pulsar (MSRP) population of the Galaxy, systems with recurrence times well in excess of a century for outbursts detectable by instruments like MAXI must be the dominant population of NS LMXBs, and that few of these systems have yet been discovered.Comment: 7 pages, accepted to MNRAS, small correction made to abstract from originally posted version to remove an ambiguit

The Return to a Sub-Baccalaureate Education: The Effects of Schooling, Credentials and Program of Study on Economic Outcomes

Over the last 20 years, technological changes in the workplace have placed considerable pressure on the U.S. educational system to adequately prepare students for occupations that increasingly require specific skills. However, certain educators and policy-makers have raised the question of whether vocational education at the high school level, with its focus on immediately entering the workforce after high school, adequately prepares students for college. At the postsecondary level, the debate has centered on whether vocational education restricts access to a four-year college, which may hamper future earnings. This report estimates the returns to a sub-baccalaureate education. The analyses emphasize the effect of a student's program of study, the amount of schooling accumulated with and without attaining a degree, and the type of credential earned. We test whether the earnings of degree attainers are significantly larger than those of similar students with the same amount of postsecondary education but no credential. We also examine whether economic gains from occupational education are realized not only for students who concentrated on vocational education in high school but also for special subpopulations such as older students, racial-ethnic minorities, and academically or economically disadvantaged students