Rectangular Flakes Research Articles

중기 구석기시대 석기 제작기술과 내재적 발달에 대하여

One of the controversial issues in Korean Paleolithic research is establishing the technical concept of the Middle Paleolithic. In this regard, the manufacturing technique of a 65,000-year-old lithic industry excavated from the first cultural layer of the Dosan site was analyzed. As a result, a technique of selecting appropriate pebble and manufacturing flakes for blank without pre-adjustment, a technique for producing sharp rectangular flakes by hitting at the corner of raw material, a technique for making tools by precisely calculating the strike point and order and a knapping technique of large flakes were identified. While the technical elements of the Lower Paleolithic remain, it is different from the blade technique representing the Upper Paleolithic. Therefore, it can be recognized as a distinct and characteristic lithic technology of the Middle Paleolithic. However, the three techniques except the knapping technique of large flakes, contain technical elements and concepts that are common or related to the blade technique. Therefore, we cannot rule out the possibility that Upper Paleolithic inhabitants invented the blade technique by choosing and combining the essential elements from lithic technology of the previous period and also by adopting new raw materials. Thus, 65,000 years ago, lithic technology was clearly different from those of the Lower and Upper Paleolithic, but there were elements related to manufacturing techniques of both ages. In addition, considering the research results showing that the emergence of the blade technique goes up to 42,000 years ago, and that the microblade technique appeared more than 30,000 years ago, it is interpreted that the lithic technology of the Korean Peninsula has undergone a continuous and internal development process since MIS 4 stage.

Hydrothermal Synthesis and Micro-Structural, Optical and Luminescence Properties of Core-Shell Hetero Structure CdS/Zn3(PO4)2 Nanocomposite

The hydrothermal approach was used to make an inorganic semiconducting CdS/Zn3(PO4)2 nanocomposite at a mild reaction temperature of 100 ºC. The XRD data indicate peaks that correspond to CdS hexagonal structure and Zn3(PO4)2 monoclinic-phase with good crystalline character. Surprisingly, the phase shift from α-phase of Zn3(PO4)2 to γ-phase of Zn3(PO4)2 is observed under hydrothermal conditions due to the coupling of CdS with Zn3(PO4)2, as well as internal structural alterations leading to the formation of CdS/Zn3(PO4)2 nanocomposite. Debye-Scherrer and W-H methods were used to calculate average crystallite size, lattice strain and dislocation density. The average crystal lattice is 15-25 nm in size. The hexagonal spheres aggregated on rectangular flakes, indicating core-shell heterostructure, may be seen on the surface morphology of the prepared composite. Due to the quantum size effect, the absorption peak for the composite is in the visible wavelength. It also has a low optical band gap of 2.42 eV, which makes it useful for photocatalytic and photoelectrochemical applications. FT-IR spectrum shows all the fundamental vibrational modes of CdS/Zn3(PO4)2 nanocomposite. Colour coordinate values and CCT values of the prepared composites indicate that they are used for LED applications and the photoluminescence spectrum reveals a broad, intense luminescence band in the visible region with wavelengths ranging from 510 to 518 nm, in good agreement with the absorption wavelength and the CIE diagram.

Obtaining the Dimensions and Orientation of 2D Rectangular Flakes from Sectioning Experiments in Flake Composites

Recently, we developed and reported the statistical validity of two methods for determining the planar aspect ratios of two-dimensional (2D) rectangular flakes in composites from the statistics of intersection lengths: one method is based on the maximum intersection length, and the other on the average intersection length. In this work, we show that these methods are valid and robust not only for flakes having isotropic, random in-plane orientations, but for the more general situations of planar orientations ranging from unidirectional (misalignment angle ϵ=0), to partially aligned (0<ϵ<π/2), to flakes of isotropic, random-in-plane orientations (ϵ=π/2). We prove, by Monte Carlo simulations and by numerical sectioning experiments, the validity of the proposed methods for characterizing the extent of the partial alignment (the misalignment angle ϵ) of 2D rectangular flakes in composites, based again on the statistics of the intersection lengths; this information can be obtained from cross-sections of composite samples used in optical or electron microscopy or using tomographic imaging techniques. The performance of these techniques was tested using blind experiments in numerically sectioned composites which contained up to 106 individual flakes, and was found to be very good for a wide range of flake aspect ratios.

A Novel Method for the Determination of the Lateral Dimensions of 2D Rectangular Flakes.

We present a novel method for the determination of the lateral dimensions of thin rectangular flakes, as they exist randomly dispersed in flake composites. Knowledge of flake size and shape is essential for the correct prediction of the mechanical, electrical, thermal and barrier properties of flake composites. The required information is the distribution function of lengths of the lines representing the intersection of flakes with a sectioning plane, as seen in cross-sections of composite samples used in optical or electron microscopy or obtained using tomographic imaging techniques. The key observation is that the major peak of the distribution function coincides with the short dimension S of the flake while a secondary peak corresponds to its long dimension W. These observations are explained using Monte-Carlo simulations, as well as deterministic, geometry-based modeling and probability analysis. Since the strength of the secondary peak diminishes with increasing flake aspect ratio , we develop two additional methods for the determination of W. The first finds W from the maximum intersection length; this procedure is justified by computing the relevant probability fields through Monte-Carlo simulations. The second method finds r from the average intersection length and is valid in the range . The performance of these techniques is tested and found to be very good using blind experiments in numerically sectioned specimens.

Investigation on structural and optical properties of CuO doped CdS-Zn3(PO4)2 nanocomposite for optoelectronic devices

Pure and CuO (0.3, 0.6 and 0.9 mol%) doped CdS-Zn3(PO4)2 semiconducting nanophosphors were synthesized by hydrothermal technique under mild reaction temperatures. The prepared samples were systematically investigated by Powder X-ray diffraction [XRD], Fourier Transform infra-red spectroscopy [FT-IR], Scanning electron microscopy [SEM] with EDAX, UV–Vis diffuse reflectance spectrometer [DRS] and Photoluminescence [PL] techniques. X-ray diffraction pattern shows hexagonal phase of CdS and monoclinic β-phase of Zn3(PO4)2 with good crystalline nature. The average crystallite size of nanocomposites are in the range 13 to 25 nm and found to decrease from 18 nm to 13 nm with increasing dopant concentration. FT-IR spectra indicate that the prepared samples are high in purity. The surface morphology of the samples has shown a hetero structure type morphology in which hexagonal CdS spheres network bonding accumulated on rectangular flakes. The obtained chemical composition of all the samples are identified by EDAX is in agreement with the calculated stoichiometry. The optical band gap values are determined by diffuse reflectance spectra and are found to be in the range 2.49 eV to 2.39 eV. The room temperature Photoluminescence spectra of pure CdS-Zn3(PO4)2 lattice shown a broad strong green emission peak at ~ 518 nm, while upon incorporation CuO ions in host lattice, a sharp luminescence peak around 393 nm has been observed in all the doped samples along with other peaks at 494 nm, 594 nm, 684 nm which are in the violet, blue-green-red fluorescence of UV-Visible region makes them suitable for optoelectronic device applications.

New insights into early MIS 5 lithic technological behavior in the Levant: Nesher Ramla, Israel as a case study.

Interpreting human behavioral patterns during the Middle Paleolithic in the Levant is crucial for better understanding the dispersals and evolution of Homo sapiens and their possible interactions with other hominin groups. Here, we reconstruct the technological behavior, focusing on the centripetal Levallois method at Nesher Ramla karst sinkhole, Israel. Nesher Ramla karst sinkhole is dated to the Marine Isotope stages (MIS) 6 and 5 and represents one of the oldest occurrences of the centripetal Levallois reduction strategy in the Near East. The Levallois centripetal technology is often seen as a marker of human dispersals and adaptations in the Middle Paleolithic/Middle Stone Age of Africa and the Near East. This technology is documented in East African sites as early as 300 kya and in the Levant as early as 130 kya. However, the degree of similarity between African and Levantine centripetal technology and whether it originates from the same source remain under debate. In this paper, we focus on describing the lithic organization at Unit III of Nesher Ramla (dated to MIS 5), which is dominated by the centripetal Levallois method in association with other reduction sequences. Both preferential and recurrent centripetal Levallois modes were used at the site to produce oval and rectangular flakes. Other minor reduction sequences include unidirectional convergent method for Levallois points production and a specific method for the manufacture of naturally backed knives. The lithic data from Unit III of Nesher Ramla is further used in inter-site comparisons suggesting that the mid-Middle Paleolithic sites in the Near East possess common technological characteristics, especially the use of the centripetal Levallois method as predominant reduction strategy. This trend differs from what is usually observed in Africa and Europe, where the centripetal Levallois method is modestly represented during MIS 5 and is accompanied by other, more dominant, reduction strategies.

Salt-Assisted Growth of Ultrathin GeSe Rectangular Flakes for Phototransistors with Ultrahigh Responsivity.

Two-dimensional (2D) GeSe is an important IVA-VIA semiconductor for future applications in electronics and optoelectronics because of its high absorption coefficient, mobility, and photoresponsivity. However, the controllable synthesis of 2D GeSe flakes is still a huge problem. Here, high-quality single-crystalline ultrathin 2D GeSe flakes are synthesized by a salt-assisted chemical vapor deposition method. The flakes tend to grow along the [010] crystal orientation presenting a rectangular shape with a thickness down to 5 nm. Then, the electrical and optoelectronic properties have been systematically investigated. A thickness-dependent Schottky barrier is shown in GeSe field-effect transistors. The p-type conductivity of GeSe is mainly caused by the Ge deficiency, which is proven by a variable-temperature experiment and theoretical calculations. In addition, the phototransistors based on as-grown GeSe flakes present an ultrahigh responsivity of 1.8 × 104 A/W and an excellent external quantum efficiency of 4.2 × 106%.

Facile synthesis of nanowire and rectangular flakes of Co3O4 onto Ni foam for high-performance asymmetric supercapacitors

In this study, Co3O4 with different morphologies (nanowires of single phase, nanowires, and rectangular flakes of both phases) for supercapacitor electrode were synthesized through a hydrothermal approach in the presence of Triton X-100 followed by annealing at 350 °C for 1 h. The different morphologies of the samples were obtained with the assistance of surfactant by adjusting the quantity of reactants. Relative to Co3O4 nanowire (Co3O4 NW) samples, the Co3O4 nanowire-flake (Co3O4 NW-F) samples exhibit excellent electrochemical performance with higher capacity of 1230.65 F g−1 at a current density of 1 A g−1, and with regard to cycling stability, they perform well in a three-electrode system during the larger specific surface area. Moreover, an asymmetric supercapacitor was assembled with Co3O4 NW-F as positive electrode and activated carbon as negative electrode; the device shows a high energy density of 61.60 W h kg−1 at a power density of 1440 W kg−1.

Closing the Nanographene Gap: Surface-Assisted Synthesis of Peripentacene from 6,6'-Bipentacene Precursors.

The thermally induced cyclodehydrogenation reaction of 6,6'-bipentacene precursors on Au(111) yields peripentacene stabilized by surface interactions with the underlying metallic substrate. STM and atomic-resolution non-contact AFM imaging reveal rectangular flakes of nanographene featuring parallel pairs of zig-zag and armchair edges resulting from the lateral fusion of two pentacene subunits. The synthesis of a novel molecular precursor 6,6'-bipentacene, itself a synthetic target of interest for optical and electronic applications, is also reported. The scalable synthetic strategy promises to afford access to a structurally diverse class of extended periacenes and related polycyclic aromatic hydrocarbons as advanced materials for electronic, spintronic, optical, and magnetic devices.

Degeneracy doubling and sublattice polarization in strain-induced pseudo-Landau levels

The degeneracy and spatial support of pseudo-Landau levels (pLLs) in strained honeycomb lattices systematically depends on the geometry -- for instance, in hexagonal and rectangular flakes the 0th pLL displays a twofold increased degeneracy, while the characteristic sublattice polarization of the 0th pLL is only fully realized in a zigzag-terminated triangle. These features are dictated by algebraic constraints in the atomistic theory, and signify a departure from the standard picture in which all qualitative differences between pLLs and Landau levels induced by a magnetic field trace back to the valley-antisymmetry of the pseudomagnetic field.

Failure processes in embedded monolayer graphene under axial compression.

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained.

The separation of Betulapopulifolia and Betulapendula and their status in Ontario

The North American Betulapopulifolia differs from the European Betulapendula in having a larger number of peltate resin glands on greyish twigs, leaves with long–caudate tips, and a dense pubescence on the adaxial surface of the pistillate scales. Furthermore, B. populifolia is a plant of acid, peaty, or sandy substrates, whereas B. pendula grows in acid to neutral or occasionally slightly alkaline substrates. The bark of B. pendula exfoliates in long thin strands, whereas in B. populifolia it exfoliates as small, very thin rectangular flakes or appears not to exfoliate at all. The basal parts of older trunks of B. pendula often develop vertical fissures, which never develop in B. populifolia. Analysis of variance suggests that the most useful quantitative characters for distinguishing the two species are scale width and the length/width ratio of the terminal one-quarter of the leaf. Several other quantitative characters are useful discriminators but are not entirely reliable by themselves. Discriminant analyses with and without qualitative characters separated a sample of North American B. populifolia from a sample of European B. pendula. The derived discriminant formula placed many members of a variable natural population from near Ottawa in an intermediate position, suggesting hybridization. The use of heavily weighted qualitative characters in the discriminant formula placed much of the hybrid population in the B. populifolia group, whereas the use of quantitative characters alone placed much of the hybrid population in the B. pendula group. As putative hybrids are being widely distributed by nurseries, the identification of the two species is likely to become increasingly problematic. Betulapendula is a widespread and naturally spreading escape from cultivation in southern Ontario, while B. populifolia is a native species confined in Ontario to the eastern portion of the province between the Ottawa and St. Lawrence rivers, with a possible outlier in Elgin County in southwestern Ontario.