A splitting theorem for Kahler manifolds whose Ricci tensors have constant eigenvalues

It is proved that a compact Kahler manifold whose Ricci tensor has two distinct, constant, non-negative eigenvalues is locally the product of two Kahler-Einstein manifolds. A stronger result is established for the case of Kahler surfaces. Irreducible Kahler manifolds with two distinct, constant eigenvalues of the Ricci tensor are shown to exist in various situations: there are homogeneous examples of any complex dimension n > 1, if one eigenvalue is negative and the other positive or zero, and of any complex dimension n > 2, if the both eigenvalues are negative; there are non-homogeneous examples of complex dimension 2, if one of the eigenvalues is zero. The problem of existence of Kahler metrics whose Ricci tensor has two distinct, constant eigenvalues is related to the celebrated (still open) Goldberg conjecture. Consequently, the irreducible homogeneous examples with negative eigenvalues give rise to complete, Einstein, strictly almost Kahler metrics of any even real dimension greater than 4.Comment: 18 pages; final version; accepted for publication in International Journal of Mathematic

A Deformation of Sasakian Structure in the Presence of Torsion and Supergravity Solutions

We discuss a deformation of Sasakian structure in the presence of totally skew-symmetric torsion by introducing odd dimensional manifolds whose metric cones are K\"ahler with torsion. It is shown that such a geometry inherits similar properties to those of Sasakian geometry. As an example of them, we present an explicit expression of local metrics and see how Sasakian structure is deformed by the presence of torsion. We also demonstrate that our example of the metrics admits the existence of hidden symmetries described by non-trivial odd-rank generalized closed conformal Killing-Yano tensors. Furthermore, using these metrics as an {\it ansatz}, we construct exact solutions in five dimensional minimal (un-)gauged supergravity and eleven dimensional supergravity. Finally, we discuss the global structures of the solutions and obtain regular metrics on compact manifolds in five dimensions, which give natural generalizations of Sasaki--Einstein manifolds $Y^{p,q}$ and $L^{a,b,c}$. We also discuss regular metrics on non-compact manifolds in eleven dimensions.Comment: 38 pages, 1 table, v2: version to appear in Class. Quant. Gra

Calibrated cycles and T-duality

For Hitchin's generalised geometries we introduce and analyse the concept of a structured submanifold which encapsulates the classical notion of a calibrated submanifold. Under a suitable integrability condition on the ambient geometry, these generalised calibrated cycles minimise a functional occurring as D-brane energy in type II string theories, involving both so-called NS-NS- and R-R-fields. Further, we investigate the behaviour of calibrated cycles under T-duality and construct non-trivial examples.Comment: 43 pages. v4: formalism and T-duality part considerably expande

Sharing data from molecular simulations

Given the need for modern researchers to produce open, reproducible scientific output, the lack of standards and best practices for sharing data and workflows used to produce and analyze molecular dynamics (MD) simulations has become an important issue in the field. There are now multiple well-established packages to perform molecular dynamics simulations, often highly tuned for exploiting specific classes of hardware, each with strong communities surrounding them, but with very limited interoperability/transferability options. Thus, the choice of the software package often dictates the workflow for both simulation production and analysis. The level of detail in documenting the workflows and analysis code varies greatly in published work, hindering reproducibility of the reported results and the ability for other researchers to build on these studies. An increasing number of researchers are motivated to make their data available, but many challenges remain in order to effectively share and reuse simulation data. To discuss these and other issues related to best practices in the field in general, we organized a workshop in November 2018 (https://bioexcel.eu/events/workshop-on-sharing-data-from-molecular-simulations/). Here, we present a brief overview of this workshop and topics discussed. We hope this effort will spark further conversation in the MD community to pave the way toward more open, interoperable, and reproducible outputs coming from research studies using MD simulations

The humanistic roots of Islamic administration and leadership for education : philosophical foundations for cross-cultural and transcultural teaching

For a number of decades, a humanistic approach has been a minor but persistent one in the Western field of administrative and leadership studies, and only recently has been broadening to include other humanist traditions (Dierksmeier et al., 2011) and has yet to be fully explored in educational administration and its pedagogy and curriculum although some foundational work has been done (e.g., Samier, 2005). The focus in this chapter is on the Islamic humanist tradition as it relates to the teaching of educational administration and leadership in a Muslim context, with implications for cross-cultural and transcultural use. The second purpose of the chapter is to show the correspondences that exist between the Islamic and Western humanist traditions in terms of human values, knowledge and educational ideal, which in this chapter are argued to be close to the Western Idealist tradition and the German Bildung conception of education as well as the strong interpretive and hermeneutic foundations that originated in the Islamic tradition and which influenced the foundations of many relevant European schools of thought, particularly in the Enlightenment.The initial section of the chapter is a comparative examination of the central principles of the Islamic humanist tradition from the classical through to contemporary times with the Western humanist tradition as they relate to conceptions of the good, ethics, the construction of meaning and a set of higher order values predicated upon human dignity, integrity, empathy, well-being, and the public good (Goodman, 2003) covering a number of important scholars like Al Farabi, al Isfanhani, and Edward Said (e.g., Kraemer, 1986). In both, professions are viewed as meaningful work that allow for large measures of decision making, and are grounded in human qualities and needs including autonomy, freedom and emancipation balanced with responsibilities, obligations and duties to society. These are compared with the corresponding principles of knowledge in Western humanism which includes a strong constructivist view of reality (Makdisi, 1990). Secondly, the chapter examines the principles of good or ideal leadership and administration that humanism aims at in its preparation of officials, including those in the educational sector in both the classical Islamic tradition (Hassi, 2012) and Western approaches to humanistic administration and leadership (Czarniawska-Joerges & Guillet de Monthoux, 1994; Gagliardi & Czarniawska, 2006; Leoussi, 2000). The third section focusses on close correspondences that exist between the Islamic (Afsaruddin, 2016; al-Attas, 1980; Yasin & Jani, 2013) and Western (Aloni, 2007; Veugelers, 2011) humanist education traditions in terms of educational ideal as well as the kind of teaching practices that distinguish these traditions (Daiber, 2013; Dossett, 2014) as they apply to educational administration and leadership (Greenfield & Ribbins, 1993). The chapter concludes with a discussion of how the Islamic humanist tradition can contribute to cross-cultural and transcultural graduate teaching in international educational administration (Khan & Amann, 2013)

Helicobacter species in cancers of the gallbladder and extrahepatic biliary tract

Helicobacter species have been found in human bile and biliary tract (BT) tissue and are suspected to cause BT diseases, including gallbladder and extrahepatic cancers, collectively referred to in this work as BT cancers. We conducted a literature review of the epidemiological evidence linking the presence of Helicobacter species in bile or BT biopsies to BT cancers and benign diseases. Reports showed great variability with respect to study methods. Nine studies of BT cancers were identified, all with 30 or fewer BT cancers; eight included cancer-free control subjects and used polymerase chain reaction (PCR) as a means of Helicobacter species detection. In four of these studies, Helicobacter species were detected in patients with BT cancer significantly more frequently than in controls, at least when controls without BT diseases were used. In two studies, no Helicobacter species were detected in either cases or controls. Helicobacter species were also often detected in benign BT diseases such as gallstone disease or chronic cholecystitis. As our current knowledge relies on a few small studies that showed substantial differences, larger studies and more standardised protocols for detecting DNA and antibodies against Helicobacter species are needed to investigate a potential association with BT cancer