Theory of the thermoelectricity of intermetallic compounds with Ce or Yb ions

The thermoelectric properties of intermetallic compounds with Ce or Yb ions are explained by the single-impurity Anderson model which takes into account the crystal-field splitting of the 4{\it f} ground-state multiplet, and assumes a strong Coulomb repulsion which restricts the number of {\it f} electrons or {\it f} holes to $n_f\leq 1$ for Ce and $n_f^{hole}\leq 1$ for Yb ions. Using the non-crossing approximation and imposing the charge neutrality constraint on the local scattering problem at each temperature and pressure, the excitation spectrum and the transport coefficients of the model are obtained. The thermopower calculated in such a way exhibits all the characteristic features observed in Ce and Yb intermetallics. Calculating the effect of pressure on various characteristic energy scales of the model, we obtain the $(T,p)$ phase diagram which agrees with the experimental data on CeRu$_{2}$Si$_2$, CeCu$_{2}$Si$_2$, CePd$_{2}$Si$_2$, and similar compounds. The evolution of the thermopower and the electrical resistance as a function of temperature, pressure or doping is explained in terms of the crossovers between various fixed points of the model and the redistribution of the single-particle spectral weight within the Fermi window.Comment: 13 pages, 11 figure

Expression of P. falciparum var Genes Involves Exchange of the Histone Variant H2A.Z at the Promoter

Plasmodium falciparum employs antigenic variation to evade the human immune response by switching the expression of different variant surface antigens encoded by the var gene family. Epigenetic mechanisms including histone modifications and sub-nuclear compartmentalization contribute to transcriptional regulation in the malaria parasite, in particular to control antigenic variation. Another mechanism of epigenetic control is the exchange of canonical histones with alternative variants to generate functionally specialized chromatin domains. Here we demonstrate that the alternative histone PfH2A.Z is associated with the epigenetic regulation of var genes. In many eukaryotic organisms the histone variant H2A.Z mediates an open chromatin structure at promoters and facilitates diverse levels of regulation, including transcriptional activation. Throughout the asexual, intraerythrocytic lifecycle of P. falciparum we found that the P. falciparum ortholog of H2A.Z (PfH2A.Z) colocalizes with histone modifications that are characteristic of transcriptionally-permissive euchromatin, but not with markers of heterochromatin. Consistent with this finding, antibodies to PfH2A.Z co-precipitate the permissive modification H3K4me3. By chromatin-immunoprecipitation we show that PfH2A.Z is enriched in nucleosomes around the transcription start site (TSS) in both transcriptionally active and silent stage-specific genes. In var genes, however, PfH2A.Z is enriched at the TSS only during active transcription in ring stage parasites. Thus, in contrast to other genes, temporal var gene regulation involves histone variant exchange at promoter nucleosomes. Sir2 histone deacetylases are important for var gene silencing and their yeast ortholog antagonises H2A.Z function in subtelomeric yeast genes. In immature P. falciparum parasites lacking Sir2A or Sir2B high var transcription levels correlate with enrichment of PfH2A.Z at the TSS. As Sir2A knock out parasites mature the var genes are silenced, but PfH2A.Z remains enriched at the TSS of var genes; in contrast, PfH2A.Z is lost from the TSS of de-repressed var genes in mature Sir2B knock out parasites. This result indicates that PfH2A.Z occupancy at the active var promoter is antagonized by PfSir2A during the intraerythrocytic life cycle. We conclude that PfH2A.Z contributes to the nucleosome architecture at promoters and is regulated dynamically in active var genes

Genomic Organization of H2Av Containing Nucleosomes in Drosophila Heterochromatin

H2Av is a versatile histone variant that plays both positive and negative roles in transcription, DNA repair, and chromatin structure in Drosophila. H2Av, and its broader homolog H2A.Z, tend to be enriched toward 5′ ends of genes, and exist in both euchromatin and heterochromatin. Its organization around euchromatin genes and other features have been described in many eukaryotic model organisms. However, less is known about H2Av nucleosome organization in heterochromatin. Here we report the properties and organization of individual H2Av nucleosomes around genes and transposable elements located in Drosophila heterochromatic regions. We compare the similarity and differences with that found in euchromatic regions. Our analyses suggest that nucleosomes are intrinsically positioned on inverted repeats of DNA transposable elements such as those related to the “1360” element, but are not intrinsically positioned on retrotransposon-related elements

The Genomic Distribution and Function of Histone Variant HTZ-1 during C. elegans Embryogenesis

In all eukaryotes, histone variants are incorporated into a subset of nucleosomes to create functionally specialized regions of chromatin. One such variant, H2A.Z, replaces histone H2A and is required for development and viability in all animals tested to date. However, the function of H2A.Z in development remains unclear. Here, we use ChIP-chip, genetic mutation, RNAi, and immunofluorescence microscopy to interrogate the function of H2A.Z (HTZ-1) during embryogenesis in Caenorhabditis elegans, a key model of metazoan development. We find that HTZ-1 is expressed in every cell of the developing embryo and is essential for normal development. The sites of HTZ-1 incorporation during embryogenesis reveal a genome wrought by developmental processes. HTZ-1 is incorporated upstream of 23% of C. elegans genes. While these genes tend to be required for development and occupied by RNA polymerase II, HTZ-1 incorporation does not specify a stereotypic transcription program. The data also provide evidence for unexpectedly widespread independent regulation of genes within operons during development; in 37% of operons, HTZ-1 is incorporated upstream of internally encoded genes. Fewer sites of HTZ-1 incorporation occur on the X chromosome relative to autosomes, which our data suggest is due to a paucity of developmentally important genes on X, rather than a direct function for HTZ-1 in dosage compensation. Our experiments indicate that HTZ-1 functions in establishing or maintaining an essential chromatin state at promoters regulated dynamically during C. elegans embryogenesis

Assessing students’ perceptions of fit between secondary and higher education: a validation study of the SPFQ

Supporting first-year students to adjust to their new academic environment is a crucial task in higher education. Investigating students’ perceptions of fit between secondary and higher education could give higher education institutions valuable information for student feedback and support, when captured in a reliable and valid way. This study examines the construct validity, reliability and criterion-related validity of the Students’ Perceived Fit Questionnaire (SPFQ) by using a longitudinal dataset (N = 930, first-year students). The results of exploratory and confirmatory factor analysis supported a three-factor structure measuring students’ perceptions of: 1) the extent to which secondary education prepared them for higher education in terms of content knowledge; 2) resemblance in the teaching approach between secondary and higher education and 3) the need to adapt to their higher education study programme. Concerning the criterion-related validity, it was found that first-year students who experience similarities in teaching approach are more likely to persist in their studies. Furthermore, our results indicated that first-year students who experienced less need to adapt to their higher education study programme felt more self-efficacious regarding their own learning and, consequently, were more likely to persist in their studies

The role of memory in the acquisition of vocabulary and grammar in the first language and in English as a foreign language

Previous studies showed that phonological short-term and working memory spans are related to vocabulary and grammar learning in children learning a second language. Typically, short-term storage, as measured by simple span tasks such as non-word repetition, are connected to vocabulary learning. Grammar learning is generally linked to the working memory system. This system is often tested by complex span tasks that require participants to process and store information simultaneously. Yet, few studies have investigated the role of both memory mechanisms in native and foreign vocabulary and grammar learning longitudinally. The current study determines whether phonological short-term and verbal working memory spans contribute differentially to the acquisition of vocabulary and grammar in Dutch as a first language (L1) and in English as a foreign language (EFL). The participants for this study are monolingual Dutch children (N = 138), in grades 4 and 5 (aged 9;0-11;0), learning EFL in the classroom. An L1 and an EFL non-word repetition task were used to measure phonological short-term memory and verbal working memory was measured with a backward digit span task. Receptive vocabulary and production of grammatical knowledge was measured in Dutch and in English, as well as receptive grammar in English. The data indicated that when the same children are longitudinally followed in both L1 and EFL, only past performance is important for L1 vocabulary learning. Phonological short-term memory does not contribute to L1 vocabulary. As expected, working memory span significantly predicts L1 grammar learning. For EFL vocabulary learning, past performance is most important; L1 vocabulary has a smaller but independent role and in line with previous research, phonological short-term memory also has an independent role. For both receptive and productive EFL grammar learning, contrary to expectations, working memory span did not play a role. In contrast, EFL phonological short-term memory had a small but independent role for receptive grammar learning. EFL vocabulary had a similar role for receptive and productive grammar, which was stronger than EFL phonological short-term memory for receptive grammar. However, past performance had the largest role for both types of grammar learning. In sum, when looking at the initial stages of EFL in a formal setting, we only found a role for working memory span in L1 grammar but not in EFL. Phonological short-term memory only had a role in EFL vocabulary and receptive grammar learning, and was language specific. In all, the current data show that in addition to phonological short-term memory, past performance on vocabulary and grammar contributed significantly to vocabulary and grammar learning and that the role of vocabulary and phonological short-term memory and working memory span in grammar learning is language specific