Within-school social comparison: How students perceive the standing of their class predicts academic self-concept.

Results from prior research indicate that a student’s academic self-concept is negatively influenced by the achievement of others in his or her school (a frame of reference effect) and that this negative frame of reference effect is not or only slightly reduced by the quality, standing, or prestige of the track or school attended (a “reflected glory” effect). Going beyond prior studies, the present research used both between-school and within-school approaches to investigate frame of reference and reflected glory effects in education, incorporating students’ own perceptions of the standing of their school and class. Multilevel analyses were performed with data from 3 large-scale assessments with 4,810, 1,502, and 4,247 students, respectively. Findings from all 3 studies showed that, given comparable individual achievement, placement in high-achieving learning groups was associated with comparatively low academic self-concepts. However, students’ academic self-concept was not merely a reflection of their relative position within the class but also substantively associated with their individual and shared perceptions of the class’s standing. Moreover, the negative effects of being placed in high-achieving learning groups were weaker for high-achieving students. Overall, the studies support both educational and social psychology theorizing on social comparison. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of compression on the textural properties of porous solids

This work deals with the analysis of the effects of compression in the textural properties, the crystallinity and the packing density of porous solids. It has been found that compression produces the decrease of both, the pore volume and the interparticle voids of porous solids. The reduction of the pore volume depends on the mechanical strength of the material. Activated carbons and inorganic porous oxides with a high mechanical strength, show a relatively low reduction of their pore volume, while porous solids in which the pore walls are constituted by organic frameworks, like MOF-5, have a lower mechanical strength and thus, their porous texture is largely affected by compression. In general terms, an increasing compressive pressure produces the removal of pores in the following sequence: mesopores, broad micropores and narrow micropores. Thus, compression of porous materials could be considered as a procedure to tailor the pore volume and the pore size distribution of porous solids. The results obtained in this work allow affirming that, in the preparation of adsorbent materials, together with the development of a high specific pore volume or a specific surface area, the behaviour upon compactatation must, undoubtedly, be taken into account.     

Athletic classmates, physical self-concept, and free-time physical activity: A longitudinal study of frame of reference effects.

The systematic analysis of factors that promote or impede physical activity in children is an urgent task for educational researchers. The present study investigated the reciprocal relationship between physical self-concept, teacher-assigned grades in physical education classes, and free-time physical activity, and analyzed positive and negative consequences of being in a class with high class-average physical ability. Data from a large, representative sample of 1,095 preadolescents from 66 classrooms were examined within a longitudinal framework. Multilevel analyses showed that membership in a class with high class-average physical ability was associated with lower physical self-concept and free-time physical activity and highlighted the significant role of teacher-assigned grades in the development of physical self-concept and physical activity. Furthermore, as predicted, there were positive reciprocal effects between physical self-concept and physical activity levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chest radiographic data acquisition and quality assurance in multicenter studies

Dorsal fusion with the internal fixator has become the standard treatment of instabilities and deformities of the thoracolumbar spine. With our new device, the modular spine fixator (MSF), which has been specially designed for short-distance instrumentations, we have increasingly been treating unstable injuries of the thoracolumbar spine by one-level stabilization. Prerequisite is an accurate evaluation of the indication, including CT and MRI to assess the involvement of the intervertebral disc and the ligamental structures. The operative technique differs in some details from the procedure in more-multi-level instrumentations, especially concerning the application of the pedicle screws. The instrumentation is always combined with posterior allogenic bone grafting. Since the beginning of 1993 we also perform anterior autogenic transpedicular bone grafting. Between January 1991 and July 1995, 57 one-level stabilizations with the MSF were performed. Of the 57 patients operated on 39, 27 men and 12 women, with an average age of 41 years, have had a clinical and radiographic follow-up examination so far, on average, 27 months after the accident. Seventeen patients were completely free of pain and 17 patients (were only) sensitive to weather changes or had minor pain during great physical stress. Five patients had pain even during slight physical stress or at rest. The preoperatively measured Cobb angle was 15.1 degrees on average, after the operation 5.2 degrees, and at the time of the follow-up examination amounted to 8.1 degrees. The patients' range of motion was normal. Only five minor complications have been seen. No implant fatigue failure has been noted in this series. We derive from these results that, for correct indications, one-level stabilization can be performed successfully and should be firmly established in the operative treatment of unstable fractures of the thoracolumbar spine.     

The mitochondrial permeability transition is required for tumor necrosis factor alpha-mediated apoptosis and cytochrome c release

This study assesses the controversial role of the mitochondrial permeability transition (MPT) in apoptosis. In primary rat hepatocytes expressing an IkappaB superrepressor, tumor necrosis factor alpha (TNFalpha) induced apoptosis as shown by nuclear morphology, DNA ladder formation, and caspase 3 activation. Confocal microscopy showed that TNFalpha induced onset of the MPT and mitochondrial depolarization beginning 9 h after TNFalpha treatment. Initially, depolarization and the MPT occurred in only a subset of mitochondria; however, by 12 h after TNFalpha treatment, virtually all mitochondria were affected. Cyclosporin A (CsA), an inhibitor of the MPT, blocked TNFalpha-mediated apoptosis and cytochrome c release. Caspase 3 activation, cytochrome c release, and apoptotic nuclear morphological changes were induced after onset of the MPT and were prevented by CsA. Depolarization and onset of the MPT were blocked in hepatocytes expressing DeltaFADD, a dominant negative mutant of Fas-associated protein with death domain (FADD), or crmA, a natural serpin inhibitor of caspases. In contrast, Asp-Glu-Val-Asp-cho, an inhibitor of caspase 3, did not block depolarization or onset of the MPT induced by TNFalpha, although it inhibited cell death completely. In conclusion, the MPT is an essential component in the signaling pathway for TNFalpha-induced apoptosis in hepatocytes which is required for both cytochrome c release and cell death and functions downstream of FADD and crmA but upstream of caspase 3.     

Tracking, grading, and student motivation: Using group composition and status to predict self-concept and interest in ninth-grade mathematics.

Assigning students to different classes on the basis of their achievement levels (tracking, streaming, or ability grouping) is an extensively used strategy with widely debated consequences. The authors developed a model of the effects of tracking on self-concept and interest that integrates the opposing predictions of "assimilation" and "contrast" effects, which specifies teacher-assigned grades as a major mediating variable, and tested it in 2 settings in which track level is clearly associated with different status-systematic tracking as a function of school type (Study 1, N = 14,341 German 9th-grade students) and separate streams within a comprehensive school system (Study 2, N = 3,243 German 9th-grade students). The results support predictions that students' math self-concept and math interest differ as a function of the achievement of their reference group, their own achievement, and their teacher-assigned grades. No systematic association between track level and math self-concept was found once individual student achievement, school-/stream-average achievement, and teacher-assigned grades were controlled. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholesterol gallstone induction in hamsters reflects strain differences in plasma lipoproteins and bile acid profiles

Because different strains of hamsters vary in their susceptibility to gallstones, the relationship between plasma lipoproteins, hepatic cholesterol, bile lipids and bile acid profile was examined during gallstone induction in strains of male Syrian hamsters from Charles River Lakeview (CHR), Biobreeder F₁B (BIO) and Harlan Sprague-Dawley (HAR). Gallstones were induced by feeding a purified diet containing 0.4 or 0.8% cholesterol for 5 wk. Basal plasma total cholesterol was similar, but the hypercholesterolemia induced by dietary challenge was significantly lower in CHR than in HAR and BIO hamsters. Cholesterol-fed CHR hamsters transported cholesterol mainly in HDL (47%), whereas VLDL-C+IDL-C predominated in BIO and HAR hamsters, and their HDL transported only 28 and 38%, respectively. HAR hamsters accumulated the most hepatic cholesterol, revealed the highest cholate/cheno ratio, the lowest glycine/taurine ratio and hydrophobicity index. HAR also developed the fewest cholesterol gallstones (23%), while 64% of CHR and 58% of BIO hamsters had cholesterol gallstones and 34% of BIO hamsters developed pigment stones. Doubling dietary cholesterol from 0.4 to 0.8% doubled the incidence of cholesterol gallstones but exerted minimal impact on other parameters compared to strain differences. Thus, different strains of hamsters vary considerably with respect to biliary cholesterol, bile acid profile and formation of cholesterol gallstones associated with differences in plasma lipoprotein profiles.     

FhuF, an iron-regulated protein of Escherichia coli with a new type of [2Fe-2S] center

We previously used fhuF as a sensitive reporter gene of the iron status of Escherichia coli. In this report, the fhuF gene was identified as open reading frame f262b at 99.2 min on the genome sequence map of E. coli K-12. The FhuF protein was labeled with a His-tag and then purified to electrophoretic homogeneity. Based on sulfur determinations and M?ssbauer and EPR spectroscopy, FhuF was identified as a [2Fe-2S] protein. The g values (gx = 1.886, gy = 1.961, gz = 1.994) and some of the M?ssbauer parameters of FhuF obtained [oxidized protein as isolated: delta EQ,4.2K = 0.474 mm s-1; Fe3+ (reduced protein): delta EQ = 0.978 mm s-1] are not typical of common [2Fe-2S] proteins and indicate that FhuF has unusual structural properties. The primary sequence of FhuF does not show any sequence similarities to known [2Fe-2S] proteins. By site-directed mutagenesis, each of the six cysteines of FhuF was replaced by serine. EPR of the six reduced mutant proteins revealed that the terminal cysteine residues 244, 245, 256, and 259 form the [2Fe-2S]Cys4 cluster. Mutants having the Cys-to-Ser replacement at positions 244, 245, 256, or 259 did not complement a fhuF mutant. The motif Cys-Cys-Xaa10-Cys-Xaa2-Cys in FhuF differs considerably from the motif Cys-Xaa2-Cys-Xaa9-15-Cys-Xaa2-Cys found in other [2Fe-2S] proteins. The unusual Cys-Cys terminal group of the cluster may explain the atypical EPR and M?ssbauer spectroscopic properties of the FhuF protein; possibly the tetrahedral symmetry at the ferric ion site is distorted. The phenotype of fhuF mutants and the structural features of the FhuF protein suggest that FhuF is involved in the reduction of ferric iron in cytoplasmic ferrioxamine B.     

On the mechanism underlying the action of D-600 on slow inward current and tension in mammalian myocardium

D-600 the methoxy derivative of verapamil, is said to affect the force of cardiac contraction and the slow inward current (LSi) specifically by reducing the membrane conductance for Ca2+ (gsi). However, it is apparent that many effects of D-600 cannot be adequately explained solely by an effect on gsi. We studied the effects of D-600 on membrane current and tension of cat papillary muscle, using a conventional single sucrose gap voltage clamp technique. The results indicate that D-600 not only reduces the maximal Ca conductance but also, depending on concentration and duration of exposure, alters both the kinetics of the Ca-carrying system and the amplitude of the steady state outward current. No changes in the steady state activation and inactivation variables or in the rate of Isi inactivation were found. However, a substantial increase in the time to peak Lsi, as much as 7 times normal, was observed after exposure to D-600 (0.5 X 10(-6) to 2.0 X 10(-6) M) for at least 20 minutes. Because approximately only 75% of the reduction in Lsi induced by D-600 could be attributed to change in the maximum value of gsi (gsi), we conclude that the change in time to peak and about 25% of the reduction in Isi must be due to a change in the activation kinetics of the Ca-carrying system, Calculations suggest that the time to 70% activation of gsi can be prolonged to as much as 10 times normal by prolonged exposure to negatively inotropic concentrations of D-600.