Shape and Size of Particles Scaled from Concrete Surfaces during Salt Frost Testing and Rapid Freeze/thaw in Water

Thickness (T), Length (L), Width (W) and size distribution of scaled concrete particles in frost testing were measured. T (mm) increases with particle size surprisingly similarly for different concrete qualities and frost test methods. 2T/(L+W) reduces as function of size and is lowest for the largest particles of the salt scaling test: 0.1 – 0.15 but increases if large aggregate particles scale. Particle size distributions from salt frost testing peak for particles of 1-2 mm. The particles are flakier compared to particles from freeze/thaw in water which also have flatter size distribution no matter type of concrete or degree of damage. Scaling in water is not so efficiently reduced by air voids despite protecting very efficiently against internal damage and scaling in salt frost testing. Comparisons with T predicted by the glue spall model (≈3/4 × ice thickness) and the air void dependent (≈3× critical air void spacing) model proposed by Fagerlund are difficult due to the size dependent flake thickness. Image analysis could well describe shape. Further studies of concrete flake thickness scaled at varying thickness of ice layers are proposed.

2D layered SiP as anisotropic nonlinear optical material

Two-dimensional (2D) material of silicon phosphide (SiP) has recently been shown as a promising optical material with large band gap, fast photoresponse and strong anisotropy. However, the nonlinear optical properties of 2D SiP have not been investigated yet. Here, the thickness-dependent in-plane anisotropic third-harmonic generation (THG) from the mechanically exfoliated 2D layered SiP flakes is reported. The crystal orientation of the SiP flake is determined by the angle-resolved polarized Raman spectroscopy. The angular dependence of the THG emission with respect to the incident linear polarization is found to be strongly anisotropic with the two-fold polarization dependence pattern. Furthermore, the effect of the SiP flake thickness on the THG power is analyzed.

High-performance n-type black phosphorus transistors with type control via thickness and contact-metal engineering

Recent work has demonstrated excellent p-type field-effect switching in exfoliated black phosphorus, but type control has remained elusive. Here, we report unipolar n-type black phosphorus transistors with switching polarity control via contact-metal engineering and flake thickness, combined with oxygen and moisture-free fabrication. With aluminium contacts to black phosphorus, a unipolar to ambipolar transition occurs as flake thickness increases from 3 to 13 nm. The 13-nm aluminium-contacted flake displays graphene-like symmetric hole and electron mobilities up to 950 cm2 V−1 s−1 at 300 K, while a 3 nm flake displays unipolar n-type switching with on/off ratios greater than 105 (107) and electron mobility of 275 (630) cm2 V−1 s−1 at 300 K (80 K). For palladium contacts, p-type behaviour dominates in thick flakes, while 2.5–7 nm flakes have symmetric ambipolar transport. These results demonstrate a leap in n-type performance and exemplify the logical switching capabilities of black phosphorus.

Were Bifaces used as Mobile Cores by Clovis Foragers in the North American Lower Great Lakes Region? An Archaeological Test of Experimentally Derived Quantitative Predictions

The notion that Paleoindians used bifaces as “mobile cores” is widespread in Late Pleistocene lithic research, although it can be difficult to test empirically. Here, we use experimental replication to establish two quantitative predictions that would be indicative of biface-core transport. If bifaces are being used as mobile cores, then we should see among a group of sites of varying toolstone procurement distances (a) a negative relationship between toolstone procurement distance and the mean unifacial tool maximum-thickness value from each site; and (b) a negative relationship between toolstone procurement distance and the variability (standard deviation) of maximum flake thickness values from each site. We then test these predictions against data from six Clovis sites of varying toolstone procurement distance in the Lower Great Lakes region. The results show that both sets of data possess a strong, positive relationship with increasing toolstone procurement distance, which is inconsistent with the notion that biface-cores were transported. Since the Clovis presence in the Lower Great Lakes is widely acknowledged to be a colonization pulse, we conclude that the lack of biface-core transport there is an economizing and risk-mitigating behavior consistent with the models of Kuhn (1994) and Meltzer (2002, 2003, 2004).