Anisotropism in Garnets

Six anisotropic garnets are studied by optical, thermal, and X-ray diffraction methods in an attempt to determine the cause of anisotropism. The garnets are all ungrandites with compositions ranging from chromian grossularite to nearly pure andradite, the composition having been estimated from indices of refraction and unit cell dimensions. In all cases the birefringence is 0.004 or less. Both positive and negative uniaxial and biaxial figures are sometimes observed. Heating of the garnets at 900°C for periods of 96 to 264 hours reduced the anisotropism in five of the six garnets studied; this observation is in agreement with previously reported studies. Precession and powder X-ray diffraction photographs show no detectable change from unheated to heated samples. Procession photographs of several sectors of a single anisotropic garnet yield identical patterns with isometric Ia3d symmetry, suggesting that anisotropism is not caused by twining. I feel the cause of anisotropism in garnets is due to a combination of strain and rate of crystal growth in the metamorphic environment. A technical garnet bibliography of over 300 papers, written from 1900 to 1960 is presented; papers on anisotropic garnets written before 1900 are also included

Theoretical studies of a hydrogen abstraction tool for nanotechnology

In the design of a nanoscale, site-specific hydrogen abstraction tool, the authors suggest the use of an alkynyl radical tip. Using ab initio quantum-chemistry techniques including electron correlation they model the abstraction of hydrogen from dihydrogen, methane, acetylene, benzene and isobutane by the acetylene radical. By conservative estimates, the abstraction barrier is small (less than 7.7 kcal mol^-1) in all cases except for acetylene and zero in the case of isobutane. Thermal vibrations at room temperature should be sufficient to supply the small activation energy. Several methods of creating the radical in a controlled vacuum setting should be feasible. The authors show how nanofabrication processes can be accurately and inexpensively designed in a computational framework

Strategic Onboarding: Tailoring Gen Z Transition for Workplace Success

Managers and human resource professionals must possess the requisite abilities of generational awareness to effectively match the distinct attributes exhibited by various age cohorts within the overarching objectives of the firm. Organizational leaders must understand the four major age groups that constitute the workforce: the Traditional Generation, the Baby Boomers, Generation X, Generation Y, also known as the Millennials, and Generation Z. A recent study conducted by McKenzie reveals that several factors, namely financial incentives, career advancement opportunities, flexibility in the workplace, and a sense of purpose at work, have a significant impact on employee retention (The Gen Z Equation, 2023). Schroth (2019) suggests that providing appropriate onboarding procedures would result in increased productivity among the Gen Z cohort in the workplace. This study’s primary focus examines Gen Z’s preferences for leadership styles, perceptions regarding organizational culture, and how these affect Gen Z’s learning approaches. The findings are utilized to generate recommendations and strategies for effectively preparing Generation Z for the workforce by implementing strategic orientation and onboarding practices

End-to-End Formal Verification of Ethereum 2.0 Deposit Smart Contract

We report our experience in the formal verification of the deposit smart contract, whose correctness is critical for the security of Ethereum 2.0, a new Proof-of-Stake protocol for the Ethereum blockchain. The deposit contract implements an incremental Merkle tree algorithm whose correctness is highly nontrivial, and had not been proved before. We have verified the correctness of the compiled bytecode of the deposit contract to avoid the need to trust the underlying compiler. We found several critical issues of the deposit contract during the verification process, some of which were due to subtle hidden bugs of the compiler.Ope

VerSum: Verifiable Computations over Large Public Logs

VerSum allows lightweight clients to outsource expensive computations over large and frequently changing data structures, such as the Bitcoin or Namecoin blockchains, or a Certificate Transparency log. VerSum clients ensure that the output is correct by comparing the outputs from multiple servers. VerSum assumes that at least one server is honest, and crucially, when servers disagree, VerSum uses an efficient conflict resolution protocol to determine which server(s) made a mistake and thus obtain the correct output. VerSum's contribution lies in achieving low server-side overhead for both incremental re-computation and conflict resolution, using three key ideas: (1) representing the computation as a functional program, which allows memoization of previous results; (2) recording the evaluation trace of the functional program in a carefully designed computation history to help clients determine which server made a mistake; and (3) introducing a new authenticated data structure for sequences, called SeqHash, that makes it efficient for servers to construct summaries of computation histories in the presence of incremental re-computation. Experimental results with an implementation of VerSum show that VerSum can be used for a variety of computations, that it can support many clients, and that it can easily keep up with Bitcoin's rate of new blocks with transactions.United States. Defense Advanced Research Projects Agency. Clean-slate design of Resilient, Adaptive, Secure Hosts (CRASH) Program (Contract N66001-10-2-4089)National Science Foundation (U.S.) (Award CNS-1053143)National Science Foundation (U.S.) (Award CNS-1413920

Convergence acceleration of implicit schemes in the presence of high aspect ratio grid cells

The performance of Navier-Stokes codes are influenced by several phenomena. For example, the robustness of the code may be compromised by the lack of grid resolution, by a need for more precise initial conditions or because all or part of the flowfield lies outside the flow regime in which the algorithm converges efficiently. A primary example of the latter effect is the presence of extended low Mach number and/or low Reynolds number regions which cause convergence deterioration of time marching algorithms. Recent research into this problem by several workers including the present authors has largely negated this difficulty through the introduction of time-derivative preconditioning. In the present paper, we employ the preconditioned algorithm to address convergence difficulties arising from sensitivity to grid stretching and high aspect ratio grid cells. Strong grid stretching is particularly characteristic of turbulent flow calculations where the grid must be refined very tightly in the dimension normal to the wall, without a similar refinement in the tangential direction. High aspect ratio grid cells also arise in problems that involve high aspect ratio domains such as combustor coolant channels. In both situations, the high aspect ratio cells can lead to extreme deterioration in convergence. It is the purpose of the present paper to address the reasons for this adverse response to grid stretching and to suggest methods for enhancing convergence under such circumstances. Numerical algorithms typically possess a maximum allowable or optimum value for the time step size, expressed in non-dimensional terms as a CFL number or vonNeumann number (VNN). In the presence of high aspect ratio cells, the smallest dimension of the grid cell controls the time step size causing it to be extremely small, which in turn results in the deterioration of convergence behavior. For explicit schemes, this time step limitation cannot be exceeded without violating stability restrictions of the scheme. On the other hand, for implicit schemes, which are typically unconditionally stable, there appears to be room for improvement through careful tailoring of the time step definition based on results of linear stability analyses. In the present paper, we focus on the central-differenced alternating direction implicit (ADI) scheme. The understanding garnered from this analyses can then be applied to other implicit schemes. In order to systematically study the effects of aspect ratio and the methods of mitigating the associated problems, we use a two pronged approach. We use stability analyses as a tool for predicting numerical convergence behavior and numerical experiments on simple model problems to verify predicted trends. Based on these analyses, we determine that efficient convergence may be obtained at all aspect ratios by getting a combination of things right. Primary among these are the proper definition of the time step size, proper selection of viscous preconditioner and the precise treatment of boundary conditions. These algorithmic improvements are then applied to a variety of test cases to demonstrate uniform convergence at all aspect ratios

Unifying Parsimonious Tree Reconciliation

Evolution is a process that is influenced by various environmental factors, e.g. the interactions between different species, genes, and biogeographical properties. Hence, it is interesting to study the combined evolutionary history of multiple species, their genes, and the environment they live in. A common approach to address this research problem is to describe each individual evolution as a phylogenetic tree and construct a tree reconciliation which is parsimonious with respect to a given event model. Unfortunately, most of the previous approaches are designed only either for host-parasite systems, for gene tree/species tree reconciliation, or biogeography. Hence, a method is desirable, which addresses the general problem of mapping phylogenetic trees and covering all varieties of coevolving systems, including e.g., predator-prey and symbiotic relationships. To overcome this gap, we introduce a generalized cophylogenetic event model considering the combinatorial complete set of local coevolutionary events. We give a dynamic programming based heuristic for solving the maximum parsimony reconciliation problem in time O(n^2), for two phylogenies each with at most n leaves. Furthermore, we present an exact branch-and-bound algorithm which uses the results from the dynamic programming heuristic for discarding partial reconciliations. The approach has been implemented as a Java application which is freely available from http://pacosy.informatik.uni-leipzig.de/coresym.Comment: Peer-reviewed and presented as part of the 13th Workshop on Algorithms in Bioinformatics (WABI2013

Aluminium metallisation for interdigitated back contact silicon heterojunction solar cells

Back contact silicon heterojunction solar cells with an efficiency of 22 were manufactured, featuring a simple aluminium metallisation directly on the doped amorphous silicon films. Both the open circuit voltage and the fill factor heavily depend on the parameters of the annealing step after aluminium layer deposition. Using numerical device simulations and in accordance with the literature, we demonstrate that the changes in solar cell parameters with annealing can be explained by the formation of an aluminium silicide layer at temperatures as low as 150 C, improving the contact resistance and thus enhancing the fill factor. Further annealing at higher temperatures initialises the crystallisation of the amorphous silicon layers, yielding even lower contact resistances, but also introduces more defects, diminishing the open circuit voltag