Cross-property connections for copper–graphite composites

Copper–graphite composite materials in the range of 0–10 vol% of carbon phase were prepared from the mixture of copper and graphite powders by hot isostatic pressing. The microstructure, mechanical (tensile strength, elongation to fracture) and physical (electrical and thermal conductivity) properties of composite samples were investigated, and the cross-property connections were calculated. It was shown that electrical and thermal conductivity cross-property (Lorenz number) is almost constant and increases only slightly (no more than 10 % increase was observed). This implies that in the investigated composition range the Lorenz number of a copper–graphite composite system behaves according to Franz–Wiedemann law for pure metals at constant temperature. On the contrary, the conductivity to tensile strength cross-property connections showed significant linear increase (over 200 % in the investigated composition range) for both electrical conductivity and thermal conductivity of composite materials. The cross-property connections of conductivity to the elongation to fracture exhibit a nonlinear dependence on the volume fraction of graphite.     

The impact of tidal stream turbines on large-scale sediment dynamics

Tidal stream turbines are exploited in regions of high tidal currents. Such energy extraction will alter the hydrodynamics of a tidal region, analogous to increasing the bed friction in the region of extraction. In addition, this study demonstrates that energy extracted with respect to tidal asymmetries due to interactions between quarter (M₄) and semi-diurnal (M₂) currents will have important implications for large-scale sediment dynamics. Model simulations show that energy extracted from regions of strong tidal asymmetry will have a much more pronounced effect on sediment dynamics than energy extracted from regions of tidal symmetry. The results show that energy extracted from regions of strong tidal asymmetry led to a 20% increase in the magnitude of bed level change averaged over the length of a large estuarine system, compared with energy extracted from regions of tidal symmetry. However, regardless of the location of a tidal stream farm within a tidal system, energy extraction reduces the overall magnitude of bed level change in comparison with non-extraction cases. This has practical application to many areas surrounding the UK, including the Irish Sea and the Bristol Channel, that exhibit strong tidal currents suitable for exploitation of the tidal stream resource, but where large variations in tidal asymmetry occur.     

Bond strength of permanent soft denture liners bonded to the denture base

The purpose of this study was to characterize denture and soft liner adhesion and to determine the adhesive and/or cohesive strength of different soft tissue liners bonded to the denture base by use of a new technique. Two groups of five permanent soft liners (dry or exposed to water for 6 months) were tested by use of a tensile mode to characterize the failure characteristics of soft liners bonded to denture base resin. The method differed from previous test methods because of the specimen's ability to align axially during the test. The results indicated significant differences in the bonding of liners to the denture base, and light-cure systems exhibited the greatest amount of stress needed for failure. Low bond strength was observed when the adhesion was poor or when the cohesive strength of the soft liner was low and lead to pure adhesive or cohesive failure. When both adhesive and cohesive bonds were strong, failure occurred at high stresses. Combinations of adhesive and cohesive failures (mixed mode) were also observed in intermediate cases.     

Applicability of a magnetic bucky gel for microextraction of mercury from complicated matrices followed by cold vapor atomic absorption spectroscopy

ABSTRACT

A new eco-friendly bucky gel nano sorbent consisting of magnetic grapheneoxide (MGO) and an ionic liquid (IL) was used based on dispersive extraction technique followed by cold vapor atomic absorption spectroscopy for determination of mercury in river water, milk, omega-3 supplements, and lipstick. The optimum conditions for extraction were 50 mg of sorbent (mass ratio IL/MGO: 26), 8 min vortexing, acetate buffer pH = 4, and for desorption 3 min vortexing of HNO₃ (1 mL). The limits of detection, quantification, preconcentration factor and extraction recovery were found at 0.57, 1.88 µg L^?1, 21 and 84%. Relative standard deviation (RSD) was 6.5% (n = 3).     

Effective management at the beginning of the school year in junior high classes.

Based on year-long process and product measures of management effectiveness, 2 groups of 13 teachers of junior high mathematics and English were identified as being more or less effective in their classroom management practices and outcomes. Observational data collected in Ss' classrooms during the 1st 3 wks of the year were then analyzed. Numerous differences were found on such classroom processes as developing rules and procedures, monitoring student compliance, maintaining a task-oriented focus, communicating information, and organizing instruction. Data indicate that the beginning of the year is a crucial time for establishing effective classroom management and that teachers' planning and decision making need to be done before school starts. The importance of teacher training in this area is noted. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of composition on friction coefficient of Cu–graphite composites

Cu–graphite composites were prepared by hot isostatic pressing from the copper and graphite powders in the range of 0–50 vol.% of graphite. The same graphite powder was copper coated and used for the preparation of coated composites with 30 and 50 vol.% of graphite. It was confirmed that with increasing concentration of graphite the coefficient of friction and wear rate of coated and uncoated composites at first decreases. When critical concentration threshold of graphite is reached the coefficient of friction of composites becomes independent on the composition while the wear rate decreases further. This threshold is not simply 20 vol.% of graphite as stated [P.K. Rohatgi, S. Ray, Y. Liu, Tribological properties of metal matrix graphite particle composites, Int. Mater. Rev. 37 (1992) 129–149.] for metal matrix composites, but it significantly depends on the composite structure: for uncoated composites, it is 12 vol.% of graphite for fine graphite powder (16 μm), while for coarse powder (25–40 μm, [S.F. Moustafa, S.A. El-Badry, A.M. Sanad, B. Kieback, Friction and wear of copper–graphite composites made with Cu-coated and uncoated graphite powders, Wear 253 (2002) 699–710.]) it is 23 vol.% of graphite. For coated composites the concentration threshold was found above 25 vol.% of graphite. The reason is that the increased number of fine copper debris within graphite rich tribolayer occurs homogeneously also at high graphite composition.     

Effects of knowledge of criterion groups on actual and expected test performance of Negro and Mexican-American eighth graders.

Examined the effects that knowledge of the criterion group had on the test performance of 102 Negro and 74 Mexican-American 8th graders. There was no evidence that comparison with 1 of 4 norm groups affected performance through either an Aptitude * Treatment interaction or through an overall treatment effect. Data on expected performance indicate a significant aptitude-treatment effect with Negro Ss only. Results suggest that knowledge of a criterion group may not consistently alter the test performance of persons from minority groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Minimal Surfaces and Architecture: New Forms

Michele Emmer discusses the relations between soap films, arts, mathematics, visual arts, architecture with very recent examples. It’s because I don’t do anything, I chatter a lot, you see, it’s already a month that I’ve got into the habit of talking a lot, sitting for days on end in a corner with my brain chasing after fancies. It is perhaps something serious? No, it’s nothing serious. They are soap bubbles, pure chimeras that attract my imagination. Fedor Dostoevsky, Crime and Punishment