The separate computation of arcs for optimal flight paths with state variable inequality constraints

Computation of arcs for optimal flight paths with state variable inequality constraint

Evanescent character of the repulsive thermal Casimir force

The physical origin of the negative thermal correction to the Casimir force between metals is clarified. For this purpose the asymptotic behavior of the thermal Casimir force is analyzed at large and small distances in the real frequency representation. Contributions from propagating and evanescent waves are considered separately. At large distances they cancel each other in substantial degree so that only the attractive Lifshitz limit survives. At smaller separations the repulsive evanescent contribution of s-polarization dominates in the case of two metals or a metal and a high-permittivity dielectric. Common origin and order of magnitude of the repulsion in these two cases demonstrate naturalness of the controversial large thermal correction between metals.Comment: to be published in Phys. Rev.

Electrical resistivity and structural changes upon relaxation and crystallisation of (Mo_(0.6)Ru_(0.4))_(100-x)B_x metallic glasses

Crystallisation of (Mo_(0.6)Ru_(0.4))100_(-x)B_x glasses takes place in three steps: the first step corresponds to the precipitation of the sigma phase Mo_5Ru_3 which decomposes at higher temperatures, the second step is associated with the formation of an HCP solid solution of Mo in Ru, and in the last step the remaining amorphous matrix crystallises in an FCC boride. Detailed electrical resistivity measurements taken below the crystallisation temperature reveal an excess resistivity above the usual linear temperature dependence predicted by the Ziman theory. The increase in resistivity is associated with the onset of long-range compositional inhomogeneity (spinodal decomposition) and the decrease with the onset of crystallisation. The electrical behaviour for samples pre-annealed for 12 hours at various temperatures suggests that boron migration is partly responsible for this excess resistivity. The changes in the radial distribution function of (Mo_(0.6)Ru_(0.4))_(78)B_(22) during annealing at 525 ºC are also reported. The Mott s-d scattering model does not seem to be applicable to these amorphous alloys. The data suggest instead that an important contribution to the conduction comes from the d electrons

Mycobacterium tuberculosis type VII secretion system effectors differentially impact the ESCRT endomembrane damage response

Mycobacterium tuberculosis causes tuberculosis, which kills more people than any other infection. M. tuberculosis grows in macrophages, cells that specialize in engulfing and degrading microorganisms. Like many intracellular pathogens, in order to cause disease, M. tuberculosis damages the membrane-bound compartment (phagosome) in which it is enclosed after macrophage uptake. Recent work showed that when chemicals damage this type of intracellular compartment, cells rapidly detect and repair the damage, using machinery called the endosomal sorting complex required for transport (ESCRT). Therefore, we hypothesized that ESCRT might also respond to pathogen-induced damage. At the same time, our previous work showed that the EsxG-EsxH heterodimer of M. tuberculosis can inhibit ESCRT, raising the possibility that M. tuberculosis impairs this host response. Here, we show that ESCRT is recruited to damaged M. tuberculosis phagosomes and that EsxG-EsxH undermines ESCRT-mediated endomembrane repair. Thus, our studies demonstrate a battle between host and pathogen over endomembrane integrity.Intracellular pathogens have varied strategies to breach the endolysosomal barrier so that they can deliver effectors to the host cytosol, access nutrients, replicate in the cytoplasm, and avoid degradation in the lysosome. In the case of Mycobacterium tuberculosis, the bacterium perforates the phagosomal membrane shortly after being taken up by macrophages. Phagosomal damage depends upon the mycobacterial ESX-1 type VII secretion system (T7SS). Sterile insults, such as silica crystals or membranolytic peptides, can also disrupt phagosomal and endolysosomal membranes. Recent work revealed that the host endosomal sorting complex required for transport (ESCRT) machinery rapidly responds to sterile endolysosomal damage and promotes membrane repair. We hypothesized that ESCRTs might also respond to pathogen-induced phagosomal damage and that M. tuberculosis could impair this host response. Indeed, we found that ESCRT-III proteins were recruited to M. tuberculosis phagosomes in an ESX-1-dependent manner. We previously demonstrated that the mycobacterial effectors EsxG/TB9.8 and EsxH/TB10.4, both secreted by the ESX-3 T7SS, can inhibit ESCRT-dependent trafficking of receptors to the lysosome. Here, we additionally show that ESCRT-III recruitment to sites of endolysosomal damage is antagonized by EsxG and EsxH, both within the context of M. tuberculosis infection and sterile injury. Moreover, EsxG and EsxH themselves respond within minutes to membrane damage in a manner that is independent of calcium and ESCRT-III recruitment. Thus, our study reveals that T7SS effectors and ESCRT participate in a series of measures and countermeasures for control of phagosome integrity

Field equations from a surface term

As is well known, in order for the Einstein--Hilbert action to have a well defined variation, and therefore to be used for deriving field equation through the stationary action principle, it has to be amended by the addition of a suitable boundary term. It has recently been claimed that, if one constructs an action by adding this term to the matter action, the Einstein field equations can be derived by requiring this action to be invariant under active transformations which are normal to a null boundary. In this paper we re-examine this approach both for the case of pure gravity and in the presence of matter. We show that in the first case this procedure holds for more general actions than the Einstein-Hilbert one and trace the basis of this remarkable attribute. However, it is also pointed out the when matter is rigorously considered the approach breaks down. The reasons for that are thoroughly discussed.Comment: Typos corrected, minor changes to match published versio

Interior Weyl-type Solutions of the Einstein-Maxwell Field Equations

Static solutions of the electro-gravitational field equations exhibiting a functional relationship between the electric and gravitational potentials are studied. General results for these metrics are presented which extend previous work of Majumdar. In particular, it is shown that for any solution of the field equations exhibiting such a Weyl-type relationship, there exists a relationship between the matter density, the electric field density and the charge density. It is also found that the Majumdar condition can hold for a bounded perfect fluid only if the matter pressure vanishes (that is, charged dust). By restricting to spherically symmetric distributions of charged matter, a number of exact solutions are presented in closed form which generalise the Schwarzschild interior solution. Some of these solutions exhibit functional relations between the electric and gravitational potentials different to the quadratic one of Weyl. All the non-dust solutions are well-behaved and, by matching them to the Reissner-Nordstr\"{o}m solution, all of the constants of integration are identified in terms of the total mass, total charge and radius of the source. This is done in detail for a number of specific examples. These are also shown to satisfy the weak and strong energy conditions and many other regularity and energy conditions that may be required of any physically reasonable matter distribution.Comment: 21 pages, RevTex, to appear in General Relativity and Gravitatio

Teaching and Learning the Ninth Principle of the ALA Code of Ethics

In 2021 the American Library Association (ALA) Council approved a ninth principle to be added to the ALA Code of Ethics. The principle reads, “We affirm the inherent dignity and rights of every person. We work to recognize and dismantle systemic and individual biases; to confront inequity and oppression; to enhance diversity and inclusion; and to advance racial and social justice in our libraries, communities, profession, and associations through awareness, advocacy, education, collaboration, services, and allocation of resources and spaces.” This principle is in keeping with the Association for Library and Information Science Education (ALISE) Ethical Guidelines for Library and Information Science Educators: “As LIS educators, we respect and uphold academic freedom and protect the freedom to learn and to teach. We resist censorship and actively promote access to diverse points of view.” In both instances the primary thrust is equity, diversity, inclusion, decolonization, and justice. This panel addresses the ALA Code of Ethics, with special attention to the ninth principle. The panelists will address the core meaning of the principle to determine what it portends for education for library and information professionals. The principle is designed to guide action though praxis. The panelists will examine the degree to which that objective is met by the principle, as well as a set of questions related to the principle: How praxis can address systemic inequity and oppression; how diversity and inclusion manifests itself in praxis; how the advancement of racial and social justice through education can be introduced in the workplace; and how the insertion of these goals can be made into the institutions in which graduates work. The matter of the pressures in which educators work related to racial and social justice work will also be brought up. Throughout the investigation of these matters, the overarching concern of the panelists will be the insertion of the matters into the educational milieu. The panelists will bring to the fore their extensive knowledge and experience in their examination. They will not only provide analyses of the elements of the ninth principle, but will raise questions about the implementation of the principle into the education of professionals. The panel presenters and their talk titles are: (1) John Budd, The Ninth Principle and Global Ethics: The Case for Global Ethics; (2) Suliman Hawamdeh and Michele A. L. Villagran, Multiculturalism and the Role of Information Ethics in Dealing with Academic Integrity Issues; and, (3) Bharat Mehra, “White Pricks” (a.k.a. Inoculations Against Racism) to Decenter Shades of White Privilege in a Professional Association’s Leadership Networks of LIS Educators. Facilitated by John Burgess, delegate for Information Ethics SIG convenor Toni Samek, the panelists will engage the audience in a discussion of the meaning of the ninth principle, but will also have the opportunity to compare it with the ALISE guideline and to offer suggestions regarding the implementation of the tenets of the principle into education (including which kinds of curricular elements are best suited to the insertion of the ALA Code of Ethics into instruction and discussion)

Coopetition of software firms in Open source software ecosystems

Software firms participate in an ecosystem as a part of their innovation strategy to extend value creation beyond the firms boundary. Participation in an open and independent environment also implies the competition among firms with similar business models and targeted markets. Hence, firms need to consider potential opportunities and challenges upfront. This study explores how software firms interact with others in OSS ecosystems from a coopetition perspective. We performed a quantitative and qualitative analysis of three OSS projects. Finding shows that software firms emphasize the co-creation of common value and partly react to the potential competitiveness on OSS ecosystems. Six themes about coopetition were identified, including spanning gatekeepers, securing communication, open-core sourcing and filtering shared code. Our work contributes to software engineering research with a rich description of coopetition in OSS ecosystems. Moreover, we also come up with several implications for software firms in pursing a harmony participation in OSS ecosystems.Comment: This is the author's version of the work. Copyright owner's version can be accessed at https://link.springer.com/chapter/10.1007/978-3-319-69191-6_10, Coopetition of software firms in Open source software ecosystems, 8th ICSOB 2017, Essen, Germany (2017