Influence of thermal cycling on weldments of non-ferrous materials : I - Aluminium Alloy 6061

SINCE the study of "thermal" fatigue on materials is generally concerned with repeated heating and cooling of the alloy under mechanical constraint, very little is known about the effect of thermal cycling of unrestrained materials. The materials studied to-date subjected to such "thermal", or "thermomechanical" fatigue' do not include studies of precipitation hardenable alloys.' Although, recently some work has been undertaken on the thermal cycling of a duraluminium type material,3 almost nothing is known about the effect of thermal cycling on weldments of 6061 aluminium alloy. Such studies will help in obtaining the design data concerning metallic shield to protect the main satellite structure made of plastics from radiation damage in space as well as from other relevant hazards when such scientific satellites are exposed once to the sunlit side and subsequently to very low temp-erature in the dark side during orbiting around the earth and are, consequently, subjected to thermal fatigue. The present study has been undertaken in order to find the effect of thermal cycling on mechanical properties of welded 6061 aluminium alloy

Influence of Thermal Cycling on Weldments of Non-Ferrous Metal I. Aluminium Alloy 6061

With a view to investigate the effect of thermal cycling, usually encountered by scientific earth satellites exposed once to the sunlit side, and subse-quently to very low temperature in the dark side, the cycling has been undertaken

Effect of zirconium oxide and cellulose nanoparticles addition on the flexural strength, impact strength and translucency of heat polymerized acrylic resin: an in vitro study.

Background: Polymethyl methacrylate denture base material is considered the most popular denture base material to date. The advantages of the PMMA       include low cost, biocompatibility, ease of processing, stability in the oral environment, and acceptable aesthetics. To improve the acrylic polymer’s properties for removable acrylic appliances, the significant issues to be addressed are its low mechanical properties such as impact, bending, and fatigue. Aim: This study was aimed to evaluate the effect of incorporating different concentrations of zirconium oxide and cellulose nanoparticles on flexural strength, and impact strength and translucency of heat polymerized acrylic resin. Materials and methods: A total of 180 acrylic specimens were made and divided into two groups, which comprises 90 specimens in each. Group I and Group II were reinforced with ZrO2 and cellulose nanoparticles, respectively. Each group was divided into three subgroups depending on the properties to be evaluated i.e., flexural strength, Impact strength, and Translucency, respectively. Each subgroup was further divided into three based on the concentrations (1.5 wt%, 2.5 wt% and 5.0 wt%) of the nanoparticles. The flexural strength was determined using a universal testing machine. The Izod impact tester was used to evaluate the impact strength. Translucency measured by UV visible spectrophotometer. The obtained data were analysed using one way ANOVA within the group followed by posthoc comparison by TUKEY’S method for the comparison between groups. Results: Acrylic specimens incorporated with 2.5 wt% ZrO2 exhibited more mean flexural strength, and the specimens with 2.5 wt% and 5.0 wt% cellulose nanoparticles showed the highest impact strength and translucency, respectively. One-way ANOVA showed significant differences (p=0.000) between the groups. Conclusion: PMMA incorporated with 2.5 wt% of ZrO2 NPs, 2.5 wt% and 5.0 wt% of cellulose NPs showed superior flexural strength, impact strength, and translucency, respectively.

Anomalously low dielectric constant of confined water

The dielectric constant ε of interfacial water has been predicted to be smaller than that of bulk water (ε ≈ 80) because the rotational freedom of water dipoles is expected to decrease near surfaces, yet experimental evidence is lacking. We report local capacitance measurements for water confined between two atomically flat walls separated by various distances down to 1 nanometer. Our experiments reveal the presence of an interfacial layer with vanishingly small polarization such that its out-of-plane ε is only ~2. The electrically dead layer is found to be two to three molecules thick. These results provide much-needed feedback for theories describing water-mediated surface interactions and the behavior of interfacial water, and show a way to investigate the dielectric properties of other fluids and solids under extreme confinement

National CO2 budgets (2015–2020) inferred from atmospheric CO2 observations in support of the Global Stocktake

Accurate accounting of emissions and removals of CO2 is critical for the planning and verification of emission reduction targets in support of the Paris Agreement. Here, we present a pilot dataset of country-specific net carbon exchange (NCE; fossil plus terrestrial ecosystem fluxes) and terrestrial carbon stock changes aimed at informing countries’ carbon budgets. These estimates are based on "top-down" NCE outputs from the v10 Orbiting Carbon Observatory (OCO-2) modeling intercomparison project (MIP), wherein an ensemble of inverse modeling groups conducted standardized experiments assimilating OCO-2 column-averaged dry-air mole fraction (XCO2) retrievals (ACOS v10), in situ CO2 measurements, or combinations of these data. The v10 OCO-2 MIP NCE estimates are combined with "bottom-up" estimates of fossil fuel emissions and lateral carbon fluxes to estimate changes in terrestrial carbon stocks, which are impacted by anthropogenic and natural drivers. These flux and stock change estimates are reported annually (2015–2020) as both a global 1° × 1° gridded dataset and as a country-level dataset. Across the v10 OCO-2 MIP experiments, we obtain increases in the ensemble median terrestrial carbon stocks of 3.29–4.58 PgCO2 yr-1 (0.90–1.25 PgC yr-1). This is a result of broad increases in terrestrial carbon stocks across the northern extratropics, while the tropics generally have stock losses but with considerable regional variability and differences between v10 OCO-2 MIP experiments. We discuss the state of the science for tracking emissions and removals using top-down methods, including current limitations and future developments towards top-down monitoring and verification systems