Diffusion-controlled on-surface synthesis of graphene nanoribbon heterojunctions

We report a new diffusion-controlled on-surface synthesis approach for graphene nanoribbons (GNR) consisting of two types of precursor molecules, which exploits distinct differences in the surface mobilities of the precursors. This approach is a step towards a more controlled fabrication of complex GNR heterostructures and should be applicable to the on-surface synthesis of a variety of GNR heterojunctions

Structure Formation and Coupling Reactions of Hexaphenylbenzene and Its Brominated Analog

The on-surface coupling of the prototypical precursor molecule for graphene nanoribbon synthesis, 6,11-dibromo-1,2,3,4-tetraphenyltriphenylene (C42Br2H26, TPTP), and its non-brominated analog hexaphenylbenzene (C42H30, HPB), was investigated on coinage metal substrates as a function of thermal treatment. For HPB, which forms non-covalent 2D monolayers at room temperature, a thermally induced transition of the monolayer’s structure could be achieved by moderate annealing, which is likely driven by π-bond formation. It is found that the dibrominated carbon positions of TPTP do not guide the coupling if the growth occurs on a substrate at temperatures that are sufficient to initiate C H bond activation. Instead, similar one-dimensional molecular structures are obtained for both types of precursors, HPB and TPTP

Structure Formation and Coupling Reactions of Hexaphenylbenzene and Its Brominated Analog

The on‐surface coupling of the prototypical precursor molecule for graphene nanoribbon synthesis, 6,11‐dibromo‐1,2,3,4‐tetraphenyltriphenylene (C(42)Br(2)H(26), TPTP), and its non‐brominated analog hexaphenylbenzene (C(42)H(30), HPB), was investigated on coinage metal substrates as a function of thermal treatment. For HPB, which forms non‐covalent 2D monolayers at room temperature, a thermally induced transition of the monolayer's structure could be achieved by moderate annealing, which is likely driven by π‐bond formation. It is found that the dibrominated carbon positions of TPTP do not guide the coupling if the growth occurs on a substrate at temperatures that are sufficient to initiate C−H bond activation. Instead, similar one‐dimensional molecular structures are obtained for both types of precursors, HPB and TPTP

Structure Formation and Coupling Reactions of Hexaphenylbenzene and Its Brominated Analog

The on-surface coupling of the prototypical precursor molecule for graphene nanoribbon synthesis, 6,11-dibromo-1,2,3,4-tetraphenyltriphenylene (C42Br2H26, TPTP), and its non-brominated analog hexaphenylbenzene (C42H30, HPB), was investigated on coinage metal substrates as a function of thermal treatment. For HPB, which forms non-covalent 2D monolayers at room temperature, a thermally induced transition of the monolayer’s structure could be achieved by moderate annealing, which is likely driven by π-bond formation. It is found that the dibrominated carbon positions of TPTP do not guide the coupling if the growth occurs on a substrate at temperatures that are sufficient to initiate C--H bond activation. Instead, similar one-dimensional molecular structures are obtained for both types of precursors, HPB and TPTP

The last giant Araucaria trees in southern Brazil

Araucaria angustifolia (Bertol.) Kuntze is a native tree species of major importance in southern Brazil. It is a regional symbol due to its iconic shape and stature in the landscape; its wood was once economically important and its seeds are an important source of food for the fauna and are presently used in regional cuisine. Despite its importance and apparent abundance, the species is facing extinction mainly as a result of unregulated exploitation and deforestation. This study catalogued the remaining individuals in order to add to the body of knowledge available on A. angustifolia, a species that has become rare across its historic range. The circumference at breast height (1.30 m), the total height, and the tree volume were measured (3,529 araucarias). We catalogued trees with a large diameter measuring them in loco over three years involving a journey of more than 6,800 km. The volumes of these old trees are very large, ranging from 38.2 m3 to 106.6 m3. The largest A. angustifolia individual is located in the state of Santa Catarina and measures 3.25 m in diameter. The giant araucarias with > 2.00 m in diameter are rare and only 13 individuals could be found in southern Brazil; a priority action at the governmental level is to recognize and preserve these monumental trees and together with a need for a public policy of drawing up specific inventories of large trees

Bio-inspired knee joint: Trends in the hardware systems development

The knee joint is a complex structure that plays a significant role in the human lower limb for locomotion activities in daily living. However, we are still not quite there yet where we can replicate the functions of the knee bones and the attached ligaments to a significant degree of success. This paper presents the current trend in the development of knee joints based on bio-inspiration concepts and modern bio-inspired knee joints in the research field of prostheses, power-assist suits and mobile robots. The paper also reviews the existing literature to describe major turning points during the development of hardware and control systems associated with bio-inspired knee joints. The anatomy and biomechanics of the knee joint are initially presented. Then the latest bio-inspired knee joints developed within the last 10 years are briefly reviewed based on bone structure, muscle and ligament structure and control strategies. A leg exoskeleton is then introduced for enhancing the functionality of the human lower limb that lacks muscle power. The design consideration, novelty of the design and the working principle of the proposed knee joint are summarized. Furthermore, the simulation results and experimental results are also presented and analyzed. Finally, the paper concludes with design difficulties, design considerations and future directions on bio-inspired knee joint design. The aim of this paper is to be a starting point for researchers keen on understanding the developments throughout the years in the field of bio-inspired knee joints

A robotic test rig for performance assessment of prosthetic joints

Movement within the human body is made possible by joints connecting two or more elements of the musculoskeletal system. Losing one or more of these connections can seriously limit mobility, which in turn can lead to depression and other mental issues. This is particularly pertinent due to a dramatic increase in the number of lower limb amputations resulting from trauma and diseases such as diabetes. The ideal prostheses should re-establish the functions and movement of the missing body part of the patient. As a result, the prosthetic solution has to be tested stringently to ensure effective and reliable usage. This paper elaborates on the development, features, and suitability of a testing rig that can evaluate the performance of prosthetic and robotic joints via cyclic dynamic loading on their complex movements. To establish the rig’s validity, the knee joint was chosen as it provides both compound support and movement, making it one of the major joints within the human body, and an excellent subject to ensure the quality of the prosthesis. Within the rig system, a motorised lead-screw simulates the actuation provided by the hamstring-quadricep antagonist muscle pair and the flexion experienced by the joint. Loads and position are monitored by a load cell and proximity sensors respectively, ensuring the dynamics conform with the geometric model and gait analysis. Background: Robotics, Prosthetics, Mechatronics, Assisted Living. Methods: Gait Analysis, Computer Aided Design, Geometry Models. Conclusion: Modular Device, Streamlining Rehabilitation

Zeros of Riemann zeta-type functions

In this thesis we study two topics concerning the zeros of the zeta function and the zeros of related functions.The first topic is a proof of a generalization of Newman’s conjecture. Newman’s original conjecture, which was proved by Rodgers and Tao in 2018, states that certain deformations of the Riemann xi function have zeros off the critical line. We will show that it is possible to formulate an analogue of Newman’s conjecture for any function in the extended Selberg class, and we then prove that these analogous conjectures are true in every case. Our proof is necessarily quite different from Rogers and Tao’s proof because their work requires information about the zeros of the zeta function which is not known in the general case. Our proof also has the benefit of being simpler and more direct.The second topic is a result on the distribution of the argument of the Riemann zeta function on the critical line. In particular we will prove an unconditional lower bound on the tails of this distribution. This can equivalently be stated as a quantitative estimate for how often the number of nontrivial zeta zeros up to a given height differs greatly from the expected number of such zeros

Zeros of Riemann zeta-type functions

In this thesis we study two topics concerning the zeros of the zeta function and the zeros of related functions.The first topic is a proof of a generalization of Newman’s conjecture. Newman’s original conjecture, which was proved by Rodgers and Tao in 2018, states that certain deformations of the Riemann xi function have zeros off the critical line. We will show that it is possible to formulate an analogue of Newman’s conjecture for any function in the extended Selberg class, and we then prove that these analogous conjectures are true in every case. Our proof is necessarily quite different from Rogers and Tao’s proof because their work requires information about the zeros of the zeta function which is not known in the general case. Our proof also has the benefit of being simpler and more direct.The second topic is a result on the distribution of the argument of the Riemann zeta function on the critical line. In particular we will prove an unconditional lower bound on the tails of this distribution. This can equivalently be stated as a quantitative estimate for how often the number of nontrivial zeta zeros up to a given height differs greatly from the expected number of such zeros