Sur la résistance à la fissuration de dalles en béton de hautes performances armées

Résumé Dans cet article, les auteurs présentent les résultats d'une étude conduite sur la résistance en flexion transversale de dalles en béton de hautes performances armées, simplement appuyées sur leur contour. Trois types d'éléments ont été expérimentés, différant par leur pourcentage d'armature: inférieur au pourcentage minimal, normal, et supérieur au pourcentage maximal. Les mesures effectuées concernant la déformation superficielle et la flèche au centre de la plaque ont permis de tracer les graphes des lois de comportement local et global, déformation/pression transversale et flèche/pression transversale. Les domaines de comportement isotrope linéaire, anisotrope linéaire, non linéaire ainsi que les limites d'initiation de la microfissure et de formation des macrofissures ont pu être mis en évidence. L'influence du pourcentage d'armatures sur ces limites de comportement est semblable à celle observée en béton ordinaire: la résistance à la macrofissuration est affaiblie par des pourcentages d'armatures élevés. L'étude des mécanismes de couplage armature/béton, tenant compte des effets mécaniques (plaque multicouche) et physico-chimiques (retrait), a montré que les contraintes dues aux déformations différentielles de retrait étainent à l'origine de cette diminution de résistance.

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In this paper, the authors present the results of an experimental research program on the strength of High Strength Reinforced Concrete simply-supported slabs submitted to transverse flexure. Three kinds of structural elements have been considered, according to the values of the reinforcing rate: below the minimum rate, the average rate, beyond the maximum rate. Superficial strains and deflection have been measured at the center of the slabs, isotropic point where curvature and deflection reach their maximum. Plotted against the values of the transversally-applied pressure, these measures yield the curvature/pressure and deflection/pressure laws from which the linear isotropic, linear anisotropic and non-linear fields, along with the pressure values at the initiation of microcracking and at branching into macrocracks, can all be deduced. The effects of the reinforcement rate on the strength values at the different cracking stages are similar to those already observed on ordinary reinforced concrete plates, mainly a strong decrease of the macrocracking strength when the reinforcing rate is high. Such a decrease can be explained through the initial stresses due to differential shrinkage strains, as the study of the coupling effects between concrete and reinforcement has shown.

     

Metacognitive differences between skilled and less skilled readers: Remediating deficits through story grammar and attribution training.

Designed a metacognitive intervention program to remediate the failures of 42 4th-grade boys in using metacognitive skills to aid their reading comprehension. The program consisted of 2 components: story grammar training, designed to increase comprehension monitoring; and attribution training, designed to increase awareness of effort in efficient reading. Ss were assigned to 3 groups: 1 group received both components and the other 2 groups each received one component alone. 14 skilled 4th-grade male readers served as a contrast group. Maintenance was assessed through free and probed recall; generalization was assessed through a metareading test and an error detection and correction task. Results indicate that strategy training produced dramatic gains in comprehension. Only Ss receiving attribution training alone showed poorer performance than skilled readers. Partial support was obtained for generalization on the metareading assessment. It is concluded that strategy training improved poor readers' comprehension by providing them with metacognitive skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assault as a function of time and temperature: A moderator-variable time-series analysis.

The authors hypothesized that relations between temperature and assaults are stronger during evening hours than during other hours of the day and tested this hypothesis by obtaining 3-hr measures of assaults, temperature, and other weather variables for a 2-year interval. The hypothesis was confirmed by autoregression analyses that controlled for secular trends, seasonal differences, other weather variables, holidays, and other calendar events. In addition, as predicted by the negative affect escape model, assaults declined after reaching a peak at moderately high temperatures. The inverted U-shaped relation survived tests that controlled for secular trends, seasonality, autocorrelation, outliers, and heteroscedasticity. In addition, consistent with routine activity theory, moderator-variable regression analyses indicated that relations were strongest during evening hours and on weekends. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Screening and brief intervention for high-risk college student drinkers: Results from a 2-year follow-up assessment.

This randomized controlled trial evaluated the efficacy of a brief intervention designed to reduce the harmful consequences of heavy drinking among high-risk college students. Students screened for risk while in their senior year of high school (188 women and 160 men) were randomly assigned to receive an individualized motivational brief intervention in their freshman year of college or to a no-treatment control condition. A normative group selected from the entire screening pool provided a natural history comparison. Follow-up assessments over a 2-year period showed significant reductions in both drinking rates and harmful consequences, favoring students receiving the intervention. Although high-risk students continued to experience more alcohol problems than the natural history comparison group over the 2-year period, most showed a decline in problems over time, suggesting a developmental maturational effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sol Garfield, have you not heard about family psychotherapy?

Responds to S. Garfield's (see record 1981-33210-001) article appraising the progress and claims of psychotherapy over the last 40 yrs. It is argued that Garfield failed to mention the impact and existence of the psychotherapeutic modality of family therapy and that his focus on the progress and claims of psychotherapy is thus incomplete. Garfield's exclusion of family therapy is seen as characteristic of the current interface between individual psychology and family theory. It is argued that it is possible to integrate individual psychology with systems theory and associated therapies and that such an integration and progression to systems thinking is a logical and necessary step in the development of psychotherapy. (3 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of scheduling variations on the effectiveness of a group assertion-training program for women.

Explored the applicability of laboratory findings of the effects of massed vs distributed practice to an applied situation. Using a hierarchical design, 4 types of groups were compared: massed practice, distributed practice, combination massed and distributed practice assertion-training groups, and no-treatment control groups. 66 college students participated. Assertiveness was assessed by self-report measures (e.g., College Self Expression Scale), a role-play test, and peer ratings before, immediately after, and 4 wks following assertion training. Results of analyses of covariance and preplanned comparisons indicate that although assertion training produced greater increases in assertiveness than no treatment, there were no differences between the different types of assertion-training groups. Data indicate that at least for the type of program and Ss involved in the study, scheduling of sessions can be guided by the convenience of group leaders and participants without loss of effectiveness. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Growth and properties of CdxHg1−xTe crystals

It has been found that there are two main factors complicating the preparation of Cd_xHg_1–xTe. The marked difference between the liquidus and solidus curves of the CdTe-HgTe pseudo-binary system gives the expected problems of segregation of CdTe with respect to HgTe during growth but there are also problems due to the segregation of any excess Te in the melt. A 2% excess of Te can give rise to pronounced constitutional supercooling effects. To avoid this, careful control of melt stoichiometry is required. This is made difficult by the high vapour pressure of mercury over the melt, the value of which is not known with great accuracy.The conditions of melt stoichiometry required for crystal growth do not necessarily give material of the required type and resistivity and this must be adjusted after growth by annealing at a controlled mercury pressure at a fixed temperature.     

Infrared-visible sum frequency generation investigation of Cu corrosion inhibition with benzotriazole

Infrared-visible sum frequency generation spectroscopy is used to investigate the corrosion inhibitor benzotriazole (BTAH) adsorbed on Cu(100) and Cu(111) in acidic solution. Potential-dependent in situ spectra indicate that the adsorbed molecule is the benzotriazole anion (BTA-) at all potentials investigated. The Cu(100) surface is shown to form an ordered adlayer at all potentials probed, while the Cu(111) face is shown to be disordered at negative potentials, but to order with applied positive potential. The ordered adlayer is shown to consist of the BTA- in two configurations, one coordinated to the surface and Cu+ ions in solution and the other coordinated only to the surface. The BTA- coordinated to Cu+ is shown to be more stable with respect to Cl- addition than BTA- coordinated to only the surface. This study demonstrates the viability of using sum frequency generation to study corrosion inhibition in situ.     

General strategy for biosensor design and construction employing multifunctional surface-tethered components

Biosensors function by reversibly linking bioreceptor-target analyte binding with closely integrated signal generation and can either continuously monitor analyte concentrations or be returned to baseline readout values by removal of analyte. We present an approach for producing fully reversible, reagentless, self-assembling biosensors on surfaces. In the prototype biosensor, quencher-dye-labeled biotin-linked E. coli maltose binding protein (MBP) bound in a specific orientation to a NeutrAvidin-coated surface is employed as a bioreceptor. To complete sensor formation, a modular tether arm consisting of a flexible biotinylated DNA oligonucleotide, a fluorescence resonance energy-transfer (FRET) donor dye, and a distal beta-cyclodextrin (beta-CD) analyte analogue is bound in an equimolar amount to the same surface by means of DNA-directed immobilization. After self-assembly, a baseline level of FRET quenching is observed due to specific interaction between the beta-CD of the flexible tether arm and the sugar binding site of MBP, which brings the two dyes into proximity. Addition of the target analyte, the nutrient maltose, displaces the linked beta-CD-dye of the DNA-based tether arm, and a concentration-dependent change in FRET results. Biosensor sensitivity and dynamic range can be controlled by either using MBP variants having different binding constants or by binding of modulator DNA oligonucleotides that are complementary to the flexible DNA tether. The sensor can be regenerated and returned to baseline quenching levels by washing away analyte. A complex set of interactions apparently exists on the sensing surface that may contribute to sensor behavior and range. This approach may represent a general way to assemble a wide range of useful biosensors.