On super free fall.

Villermaux & Pomeau (J. Fluid Mech., vol. 642, 2010, p. 147) analysed the motion of the interface of an inviscid liquid column released from rest in a vertical tube whose area expands gradually downwards, with application to an inverted conical container for which experimental measurements were carried out. An error in the analysis is found and corrected in the present investigation, which provides the new governing equation for the super-accelerated interface motion down gradually varying tubes in general, and integrated results for interface trajectories, velocities and accelerations down a conical tube in particular. Interestingly, the error does not affect any of the conclusions given in the 2010 paper. Further new results are reported here such as the equation governing the centre of mass and proof that the end point acceleration is exactly that of gravity

Mechanical Characterization of Lead-Free Sn-Ag-Cu Solder Joints by High-Temperature Nanoindentation

The reliability of Pb-free solder joints is controlled by their microstructural constituents. Therefore, knowledge of the solder microconstituents’ mechanical properties as a function of temperature is required. Sn-Ag-Cu lead-free solder alloy contains three phases: a Sn-rich phase, and the intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn. Typically, the Sn-rich phase is surrounded by a eutectic mixture of β-Sn, Cu6Sn5, and Ag3Sn. In this paper, we report on the Young’s modulus and hardness of the Cu6Sn5 and Cu3Sn IMCs, the β-Sn phase, and the eutectic compound, as measured by nanoindentation at elevated temperatures. For both the β-Sn phase and the eutectic compound, the hardness and Young’s modulus exhibited strong temperature dependence. In the case of the intermetallics, this temperature dependence is observed for Cu6Sn5, but the mechanical properties of Cu3Sn are more stable up to 200°C.

A contribution to the optimal numbering of tree structures

This paper develops an automatic procedure for the optimal numbering of members and nodes in tree structures. With it the stiffness matrix is optimally conditioned either if a direct solution algorithm or a frontal one is used to solve the system of equations. In spite of its effectiveness, the procedure is strikingly simple and so is the computer program shown below.

Numerical Investigation of the Flow Features around Heave Plates Oscillating Close to a Free Surface or Seabed

Performance of heave plates used in offshore structures is strongly influenced by their added mass and damping, which are affected by proximity to a boundary. A previous paper by the authors presented numerical simulations of the flow around a circular solid disk oscillating at varying elevations from seabed [1]. The force calculated was used to evaluate the added mass and damping coefficients for the disk. The simulations suggest that as the structure moves closer to the seabed the added mass and damping coefficients (Ca and Cb) increases continuously. In order to understand the physics behind the added mass and damping trends, when a heave plate is moving near a seabed or closer to the free surface, the flow characteristics around the heave plate are examined numerically in this paper. Flow around oscillating disks is dominated by generation and development of phase-dependent vortical structures, characterized by the KC number and the distance from the seabed or free surface to the heave plate. Numerical calculations presented in this paper have comprised the qualitative analysis of the vortex shedding and the investigation of the links between such vortex shedding and, on one hand the damping coefficient, and on the other hand, pairing mechanisms such as the shedding angle.

Negative density dependence and environmental heterogeneity effects on tree ferns across succession in a tropical montane forest.

Although tree ferns are an important component of temperate and tropical forests, very little is known about their ecology. Their peculiar biology (e.g., dispersal by spores and two-phase life cycle) makes it difficult to extrapolate current knowledge on the ecology of other tree species to tree ferns. In this paper, we studied the effects of negative density dependence (NDD) and environmental heterogeneity on populations of two abundant tree fern species, Cyathea caracasana and Alsophila engelii, and how these effects change across a successional gradient. Species patterns harbor information on processes such as competition that can be easily revealed using point pattern analysis techniques. However, its detection may be difficult due to the confounded effects of habitat heterogeneity. Here, we mapped three forest plots along a successional gradient in the montane forests of Southern Ecuador. We employed homogeneous and inhomogeneous K and pair correlation functions to quantify the change in the spatial pattern of different size classes and a case-control design to study associations between juvenile and adult tree ferns. Using spatial estimates of the biomass of four functional tree types (short- and long-lived pioneer, shade- and partial shade-tolerant) as covariates, we fitted heterogeneous Poisson models to the point pattern of juvenile and adult tree ferns and explored the existence of habitat dependencies on these patterns. Our study revealed NDD effects for C. caracasana and strong environmental filtering underlying the pattern of A. engelii. We found that adult and juvenile populations of both species responded differently to habitat heterogeneity and in most cases this heterogeneity was associated with the spatial distribution of biomass of the four functional tree types. These findings show the effectiveness of factoring out environmental heterogeneity to avoid confounding factors when studying NDD and demonstrate the usefulness of covariate maps derived from mapped communities.

Artificial analysis of molecular marker loci linked to tree resistance response by an artificial neural network

One of the biggest challenges that software developers face is to make an accurate estimate of the project effort. Radial basis function neural networks have been used to software effort estimation in this work using NASA dataset. This paper evaluates and compares radial basis function versus a regression model. The results show that radial basis function neural network have obtained less Mean Square Error than the regression method.

The HOSHIN KANRI TREE. Cross-Plant Lean Shopfloor Management

Shopfloor Management (SM) empowerment methodologies have traditionally focused on two aspects: goal achievement following rigid structures, such as SQDCME, or evolutional aspects of empowerment factors away from strategic goal achievement. Furthermore, SM Methodologies have been organized almost solely around the hierarchical structure of the organization, failing systematically to cope with the challenges that Industry 4.0 is facing. The latter include the growing complexity of value-stream networks, sustainable empowerment of the workforce (Learning Factory), an autonomous and intelligent process management (Smart Factory), the need to cope with the increasing complexity of value-stream networks (VSN) and the leadership paradigm shift to strategic alignment. This paper presents a novel Lean SM Method (LSM) called ?HOSHIN KANRI Tree? (HKT), which is based on standardization of the communication patterns among process owners (POs) by PDCA. The standardization of communication patterns by HKT technology should bring enormous benefits in value stream (VS) performance, speed of standardization and learning rates to the Industry 4.0 generation of organizations. These potential advantages of HKT are being tested at present in worldwide research.

Stability analysis of a free falling pararotor

The pararotor is a decelerator device based on the autorotation of a rotating wing. When it is dropped, it generates an aerodynamic force parallel to the main motion direction, acting as a decelerating force. In this paper, the rotational motion equations are shown for the vertical flight without any lateral wind component and some simplifying assumptions are introduced to obtain analytic solutions of the motion. First, the equilibrium state is obtained as a function of the main parameters. Then the equilibrium stability is analyzed. The motion stability depends on two nondimensional parameters, which contain geometric, inertia, and aerodynamic characteristics of the device. Based on these two parameters a stability diagram can be defined. Some stability regions with different types of stability trajectories (nodes, spirals, focuses) can be identified for spinning motion around axes close to the major, minor, and intermediate principal axes. It is found that the blades contribute to stability in a case of spin around the intermediate principal inertia axis, which is otherwise unstable. Subsequently, the equations for determining the angles of nutation and spin of the body are obtained, thus defining the orientation of the body for a stationary motion and the parameters on which that position depends.

Mitochondrial DNA reveals hidden diversity for tardigrades from across the Antarctic realm

Antarctica contains some of the most challenging environmental conditions on the planet due to freezing temperatures, prolonged winters and lack of liquid water. Whereas 99.7% of Antarctica is permanently covered by ice and snow, some coastal areas and mountain ridges have remained ice-free and are able to sustain populations of microinvertebrates. Tardigrades are one of the more dominant groups of microfauna in soil and limno-terrestrial habitats, but little is known of their diversity and distribution across Antarctica. Here, we examine tardigrades sampled from across an extensive region of continental Antarctica, and analyse and compare their partial mitochondrial cytochrome c oxidase subunit 1 (COI) gene sequences with those from the Antarctic Peninsula, maritime and sub-Antarctica, Tierra del Fuego and other worldwide locations in order to recognise operational taxonomic units (OTUs). From 439 new tardigrade COI sequences, we identified 98 unique haplotypes (85 from Antarctica) belonging to Acutuncus, Diphascon, Echiniscus, Macrobiotus, Milnesium and unidentified Parachela. Operational taxonomic units were delimited by Poisson tree processes and general mixed Yule coalescent methods, resulting in 58 and 55 putative species, respectively. Most tardigrades appear to be locally endemic (i.e. restricted to a single geographic region), but some (e.g. Acutuncus antarcticus (Richters, 1904)) are widespread across continental Antarctica. Our molecular results reveal: (i) greater diversity than has previously been appreciated with distinct OTUs that potentially represent undescribed species, and (ii) a lack of connectivity between most OTUs from continental Antarctica and those from other Antarctic geographical zones.

Top-down free-energy minimization on protein potential energy landscapes

The hierarchical properties of potential energy landscapes have been used to gain insight into thermodynamic and kinetic properties of protein ensembles. It also may be possible to use them to direct computational searches for thermodynamically stable macroscopic states, i.e., computational protein folding. To this end, we have developed a top-down search procedure in which conformation space is recursively dissected according to the intrinsic hierarchical structure of a landscape's effective-energy barriers. This procedure generates an inverted tree similar to the disconnectivity graphs generated by local minima-clustering methods, but it fundamentally differs in the manner in which the portion of the tree that is to be computationally explored is selected. A key ingredient is a branch-selection algorithm that takes advantage of statistically predictive properties of the landscape to guide searches down the tree branches that are most likely to lead to the physically relevant macroscopic states. Using the computational folding of a β-hairpin-forming peptide as an example, we show that such predictive properties indeed exist and can be used for structure prediction by free-energy global minimization.

Tree rings, carbon dioxide, and climatic change

Tree rings have been used in various applications to reconstruct past climates as well as to assess the effects of recent climatic and environmental change on tree growth. In this paper we briefly review two ways that tree rings provide information about climate change and CO2: (i) in determining whether recent warming during the period of instrumental observations is unusual relative to prior centuries to millennia, and thus might be related to increasing greenhouse gases; and (ii) in evaluating whether enhanced radial growth has taken place in recent decades that appears to be unexplained by climate and might instead be due to increasing atmospheric CO2 or other nutrient fertilization. It is found that a number of tree-ring studies from temperature-sensitive settings indicate unusual recent warming, although there are also exceptions at certain sites. The present tree-ring evidence for a possible CO2 fertilization effect under natural environmental conditions appears to be very limited.

Roles of DNA polymerases V and II in SOS-induced error-prone and error-free repair in Escherichia coli

DNA polymerase V, composed of a heterotrimer of the DNA damage-inducible UmuC and UmuD\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{^{\prime}}}}\end{equation*}\end{document} proteins, working in conjunction with RecA, single-stranded DNA (ssDNA)-binding protein (SSB), β sliding clamp, and γ clamp loading complex, are responsible for most SOS lesion-targeted mutations in Escherichia coli, by catalyzing translesion synthesis (TLS). DNA polymerase II, the product of the damage-inducible polB (dinA ) gene plays a pivotal role in replication-restart, a process that bypasses DNA damage in an error-free manner. Replication-restart takes place almost immediately after the DNA is damaged (≈2 min post-UV irradiation), whereas TLS occurs after pol V is induced ≈50 min later. We discuss recent data for pol V-catalyzed TLS and pol II-catalyzed replication-restart. Specific roles during TLS for pol V and each of its accessory factors have been recently determined. Although the precise molecular mechanism of pol II-dependent replication-restart remains to be elucidated, it has recently been shown to operate in conjunction with RecFOR and PriA proteins.

The Dragon Tree in the Age of Exploration

he dragon tree, a peculiar species native to Socotra, southwest Arabia, east Africa, Morocco, Macaronesia, and the Canary islands, possesses an intriguing iconographic history. The first wave of images date from 1470 to 1550, beginning with Martin Schongauer’s 1470 engraving of The Flight into Egypt. These depictions portray the dragon tree in the context of a handful of biblical themes and with apparent symbolic import. After 1550, religious images of the dragon tree vanish abruptly and are replaced by representations of an empirical nature. Dragon tree iconography is notable for the extent to which it did and did not leave an impression on European art. In this paper I examine the inability of dragon tree images to gain the momentum required to propel them into European iconography more permanently, and the forces that may account for the abrupt change from biblical to botanical renderings.

Experiences with free and open courses using on-line multimedia resources

This paper analyzes the learning experiences and opinions obtained from a group of undergraduate students in their interaction with several on-line multimedia resources included in a free on-line course about Computer Networks. These new educational resources employed are based on the Web2.0 approach such as blogs, videos and virtual labs which have been added in a web-site for distance self-learning.