Thermodynamic model of the coupled valence and spin state transition in cobaltates.

A class of cobalt-based oxides exhibits a peculiar type of transition, entangling valence and spin state degrees of freedom of 4f and 3d elements. It constitutes one of the most spectacular illustrations of the interplay between charge, spin and lattice degrees of freedom in strongly correlated materials. In this work, we present a thermodynamic model capable to reproduce the main features of this transition. Our approach is based on the minimization of a free energy combining the contributions of two sublattices and the interaction between them. The coupling energies introduced in the model are related to well-known chemical pressure effects in the perovskite structure. The results of this model are compared to experimental data derived from x-ray absorption spectroscopy.

Fermi- to non-Fermi-liquid crossover and Kondo behavior in two-dimensional (Cu2/3V1/3)V2S4.

By means of a specific heat (C) and electrical resistivity ([Formula: see text]) study, we give evidence of a pronounced Fermi liquid (FL) behavior with sizable mass renormalization, [Formula: see text], up to unusually high temperatures ∼70 K in the layered system (Cu2/3V1/3)V2S4. At low temperature, a marked upturn of both C and [Formula: see text] is suppressed by magnetic field, which suggests a picture of Kondo coupling between conduction electrons in the VS2 layers and impurity spins of the V3+ ions located between layers. This picture opens the possibility of controlling electronic correlations and the FL to non-FL crossover in simple layered materials. For instance, we envisage that the coupling between layers provided by the impurity spins may realize a two-channel Kondo state.

Jumps in entropy and magnetic susceptibility at the valence and spin-state transition in a cobalt oxide.

A wide family of cobalt oxides of formulation (Pr(1-y)Ln(y))(1-x)Ca(x)CoO3 (Ln being a lanthanide) exhibits a coupled valence and spin-state transition (VSST) at a temperature T*, which involves two concomitant modifications: (i) a change in the spin state of Co(3+) from low-spin (T < T*) to a higher spin state (T > T*) and (ii) a change in the valence state of Pr, from a mixed Pr(4+)/Pr(3+) state (T < T*) to a purely trivalent state (T > T*), accompanied by an ~ 90 K is investigated by magnetization and heat capacity measurements.First, we quantitatively characterized the jumps in magnetic susceptibility (χ) and entropy (S) around T*. Then, these values were compared to those calculated as a function of the variations in the population of the different cationic species involved in the VSST. X-ray absorption spectroscopy experiments recently showed that the higher spin state above T* should be regarded as an inhomogeneous mixture between low-spin (LS) and high-spin (HS) states. In the frame of this description, we demonstrate that the jumps in both χ and S can be associated with the same change in the Co(3+) HS content around T*. This result lends further support to the relevance of the LS/HS picture for the VSST, challenging the currently dominant interpretation based on the occurrence of an intermediate-spin (IS) state of Co(3+) above T*.

Magnetocaloric effect and improved relative cooling power in (La(0.7)Sr(0.3)MnO(3)/SrRuO(3)) superlattices.

Magnetic properties of a series of (La(0.7)Sr(0.3)MnO(3)/SrRuO(3)) superlattices, where the SrRuO(3) layer thickness is varying, are examined. A room-temperature magnetocaloric effect is obtained owing to the finite size effect which reduces the T(C) of La(0.7)Sr(0.3)MnO(3) layers. While the working temperature ranges are enlarged, - ΔS(M)(max) values remain similar to the values in polycrystalline La(0.7)Sr(0.3)MnO(3). Consequently, the relative cooling powers are significantly improved, the microscopic mechanism of which is related to the effect of the interfaces at La(0.7)Sr(0.3)MnO(3)/SrRuO(3) and higher nanostructural disorder. This study indicates that artificial oxide superlattices/multilayers might provide an alternative pathway in searching for efficient room-temperature magnetic refrigerator for (nano) micro-scale systems.

Simulation of memory behaviour of a non-volatile Si3N4 structure containing si nanocrystals.

Memory hysteresis, memory window and charge retention behaviour of an Al/Si3N4/Si structure with Si nanocrystals embedded in the Si3N4 layer are studied by fitting the results of a computer simulation to the experimental ones using simple analytical expressions. It is concluded that the current through the control nitride layer during a charging voltage pulse is higher than the steady-state current. At high voltage pulses other effects, as transients, additional current mechanisms or charge injection and trapping from the metal side, has to be considered. It is also obtained that the retention behaviour of the structure were determined by the Fowler-Nordheim tunneling.

Scaling behavior in thermoelectric misfit cobalt oxides.

We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit cobalt oxides results from the addition of a spin entropy contribution to an enlarged electronic one.

Protein-tyrosine phosphatase activity in human adipocytes is strongly correlated with insulin-stimulated glucose uptake and is a target of insulin-induced oxidative inhibition.

Protein-tyrosine phosphatases (PTPases), in particular PTP1B, have been shown to modulate insulin signal transduction in liver and skeletal muscle in animal models; however, their role in human adipose tissue remains unclear. The uptake of (14)C-D-glucose in response to 10 or 100 nmol/L insulin was measured in isolated subcutaneous adipocytes from subjects with a mean age of 44 years (range, 26 to 58) and mean body mass index (BMI) of 35.6 (range, 29.7 to 45.5). The endogenous activity of total PTPases and specifically of PTP1B in immunoprecipitates was measured in cell lysates under an inert atmosphere with and without added reducing agents. Using nonlinear regression analysis, higher BMI was significantly correlated with lower adipocyte glucose uptake (r = 0.73, P =.01) and with increased endogenous total PTPase activity (r = 0.64, P =.04). Correlation with waist circumference gave similar results. The endogenous total PTPase activity also strongly correlated with insulin-stimulated glucose uptake (R =.89, P <.0001); however, the activity of PTP1B was unrelated to the level of glucose uptake. Consistent with the insulin-stimulated oxidative inhibition of thiol-dependent PTPases reported for 3T3-L1 adipocytes and hepatoma cells, treatment of human adipocytes with 100 nmol/L insulin for 5 minutes lowered endogenous PTPase activity to 37% of control (P <.001), which was increased 25% by subsequent treatment with dithiothreitol in vitro. Cellular treatment with diphenyleneiodonium (DPI), an NADPH oxidase inhibitor that blocks the cellular generation of H(2)O(2) and reduces the insulin-induced reduction of cellular PTPase activity, also diminished insulin-stimulated glucose uptake by 82% (P =.001). These data suggest that total cellular PTPase activity, but not the activity of PTP1B, is higher in more obese subjects and is negatively associated with insulin-stimulated glucose transport. The insulin-stimulated oxidative inhibition of PTPases may also have an important permissive role in the transmission of the insulin signal to glucose transport in human adipocytes.

Differential regulation of adiponectin secretion from cultured human omental and subcutaneous adipocytes: effects of insulin and rosiglitazone.

Adiponectin is an adipocyte-derived plasma protein with insulin-sensitizing and antiatherosclerotic properties. Because adipose tissue depots differ in the strength of their association with the adverse metabolic consequences of obesity, we studied the secretion of adiponectin in vitro from paired samples of isolated human omental and sc adipocytes and its regulation by insulin and rosiglitazone. Cells were incubated for 12 or 24 h with and without treatment with 100 nM insulin, 8 micro M rosiglitazone, or both combined; adiponectin secreted into the culture medium was measured by a RIA with a human adiponectin standard and normalized for cellular DNA content. Secretion of adiponectin by omental cells was generally higher than sc cells and showed a strong negative correlation with body mass index (r = -0.78;P = 0.013). In contrast, secretion from the sc cells was unrelated to body mass index. Compared with sc-derived adipocytes, adiponectin secretion from omental cells was increased by insulin or rosiglitazone alone and was up to 2.3-fold higher following combined treatment with insulin and rosiglitazone, whereas secretion from sc adipose cells was unaffected by these treatments. These data suggest that reduced secretion from the omental adipose depot may account for the decline in plasma adiponectin observed in obesity. Furthermore, enhanced adiponectin secretion from fat cells derived from the visceral compartment in response to rosiglitazone alone or in combination with insulin may play a role in some of the systemic insulin-sensitizing and antiinflammatory properties of the thiazolidinediones.

Premedical enrichment program at East Carolina University School of Medicine.

The Summer Program for Future Doctors, which started in 1978 at East Carolina University School of Medicine, prepares underrepresented-minority (URM), disadvantaged, and nontraditional students for admission to medical school. The annual eight-week program, sponsored by the school's Academic Support and Counseling Center and funded by the school, is a two-pronged program targeting both premedical and pre-matriculating students. The program has 24 openings per year, with priority accorded to students matriculating at the medical school the following fall. The program covers learning strategies, test-taking skills, reading and comprehension tests, MCAT preparation, contemporary issues in the medical environment, scientific writing, communication skills, and medical school applications. Students who have demonstrated strong performances and consistent improvement in the summer program are likely to gain admission to medical school and perform satisfactorily, especially in their first year. Data collected from 1994-1997 indicate that of the 69 participants, 51 (74%) had applied to medical school, and 24 (47%) of them had been admitted, with 15 of these (63%) being URMs. In these four years of the program, there were twice as many women as men among the 69 participants, of which 60% were African Americans, 20% whites, 13% Asian Americans/Pacific Islanders, 3% Native Americans, and 2% Hispanics. Although most of these participants pursued medical education, 12 chose other health professions; 13 students were in or had completed graduate school in basic science programs; and seven had not yet completed their under graduate degrees, although most planned to apply to medical school within the next few years.

Purification of intact nuclear lamina and identification of novel laminlike proteins in Raji, a cell line devoid of lamins A and C.

Research on the structure of the nuclear lamina and the nuclear matrix of cells devoid of lamins A and C has been hampered by the fact that intact residual nuclear structures are difficult to isolate from such cells. In this paper, we show that some extraction parameters, such as buffer composition and the nature of the detergent used to remove nuclear membranes, are critical for achieving isolation of whole nuclear residual structures from the lymphoblastic cell line Raji, used as a model for cells without lamins A and C. Electron microscopic analysis shows that the nuclear lamina of Raji cells is formed by a network of intermediate-size filaments interrupted with circular discontinuities. Both lamins B1 and B2, and lamin D/E, are present in this structure. In addition, a group of 45-kDa proteins or intermediate filament protein--reacting proteins (IFA-RPs), located uniquely in the lamina, were found to exhibit the same immunological and chemical characteristics as lamins. Although they behave like nuclear lamins, microsequencing analysis of the IFA-RPs has revealed no homology with known lamins. These IFA-RPs may contribute to the formation of the nuclear lamina filament network in the absence of lamins A and C.

A comprehensive quality management approach.

Value analysis and shared governance are two management concepts relatively new to the health care industry. Operating together, they complement each other and can result in a comprehensive "quality management" plan. An example of this model in a purchasing decision illustrates the benefits that can result from use of this collaborative, multidisciplinary approach.

Structure of the gene coding for the mouse TRiC-P5 subunit of the cytosolic chaperonin TRiC.

TRiC is a cytoplasmic chaperonin involved in actin and tubulin folding. It is formed by six to nine different but related proteins of 52 to 65 kDa arranged in two hetero-oligomeric rings. We have cloned the gene coding for the mouse TRiC-P5 subunit (also called CCT gamma) using a XbaI-DraIII fragment of the mTRiC5 cDNA. The mouse genome contains one TRiC5 gene and one TRiC5 pseudogene located on chromosomes 3F and 5B, respectively. The 2-kb transcript of TRiC5 is encoded by 14 exons distributed within 25 kb of genomic DNA. The largest exon is 312 bp and the smallest exon is 51 bp. We have used primer extension to demonstrate multiple transcription start points for the TRiC5 gene. This is consistent with the lack of any obvious TATA box upstream of the transcription start points.

The cytosolic chaperonin subunit TRiC-P5 begins to be expressed at the two-cell stage in mouse embryos.

The cytosolic chaperonin TRiC is a large protein complex involved in the folding of newly synthesized actin and tubulin. The fertilization of the mouse oocyte is followed by a remodelling of the actin and tubulin filaments. The TRiC subunit TCP1 is expressed only from the 4-cell stage on, even though actin and tubulin are synthesized in the previous stages. We investigated the onset of synthesis of another subunit, TRiC-P5, during early mouse embryogenesis. We report that TRiC-P5 is synthesized at the 2-cell stage in an alpha-amanitin sensitive manner. Thus, it is expressed before TCP1 and is one of the first proteins to be synthesized after zygotic genome activation.

Neuron specificity of the neurofilament light promoter in transgenic mice requires the presence of DNA unwinding elements.

Three reporter genes, the chloramphenicol acetyltransferase (CAT), the lacZ, and the intronless NF-L DNA, were used to test the activity of the proximal promoter region (-292 bp) of the human neurofilament light (hNF-L) gene in transgenic mice. Surprisingly, the hNF-L/CAT construct was highly sensitive to position effect, and its expression was found at low levels in several tissues of adult transgenic mice (Beaudet, L., Charron, G., Houle, D., Tretjakoff, I. Peterson, A., and Julien, J.-P. (1992) Gene (Amst.) 116, 205-214). In contrast, the hNF-L/lacZ or the hNF-L/intronless constructs were expressed exclusively in the nervous system during embryonic development and in adult animals. The DNA sequences analysis of the different reporter genes revealed the presence of matrix attachment regions (MARs) within the 3'-untranslated regions of all three transgenes. DNA unwinding elements were found within the MARs of lacZ and hNF-L gene constructs but not in the CAT gene construct. When this element was removed from the lacZ construct, expression of the hNF-L/lacZ transgene became susceptible to position effect and was no longer tissue-specific. These results indicate that DNA unwinding elements are essential for position effect independence conferred by MARs to the hNF-L basal promoter.