Quasinormal modes of asymptotically flat rotating black holes

We study the main properties of general linear perturbations of rotating black holes in asymptotically flat higher-dimensional spacetimes. In particular, we determine the quasinormal mode (QNM) spectrum of singly spinning and equal angular momenta Myers-Perry black holes (MP BHs). Emphasis is also given to the timescale of the ultraspinning and bar-mode instabilities in these two families of MP BHs. For the bar-mode instabilities in the singly spinning MP BH, we find excellent agreement with our linear analysis and the non-linear time evolution of Shibata and Yoshino for d=6,7 spacetime dimensions. We find that d=5 singly spinning BHs are linearly stable. In the context of studying general relativity in the large dimension limit, we obtain the QNM spectrum of Schwarzschild BHs and rotating MP BHs for large dimensions. We identify two classes of modes. For large dimensions, we find that in the limit of zero rotation, unstable modes of the MP BHs connect to a class of Schwarzschild QNMs that saturate to finite values.Comment: 52 pages. 25 figure

Belowground Meristem Populations as Regulators of Grassland Dynamics

Studies of plant populations are critical for linking organism to ecosystem-level phenomena and for understanding mechanisms driving responses to global change. In perennial grasslands, the below-ground population of meristems (the bud bank) plays a fundamental role in local plant population recruitment, persistence and dynamics. We explore two aspects of the bud bank in North American grasslands. It has been hypothesized that low variability in arid biomes is explained by meristem limitation, which constrains responses to pulses of high resource availability. Our research tests this hypothesis by comparing bud-bank populations across six sites in the United States that vary 3-fold in precipitation and 4.5-fold in productivity. In addition, we are examining the effects of management practices, such as fire and grazing, on bud-bank populations using replicated long-term treatments at Konza Prairie LTER site located in north-central Kansas

Src-family tyrosine kinase activities are essential for differentiation of human embryonic stem cells

Embryonic stem (ES) cells are characterized by pluripotency, defined as the developmental potential to generate cell lineages derived from all three primary germ layers. In the past decade, great progress has been made on the cell culture conditions, transcription factor programs and intracellular signaling pathways that control both murine and human ES cell fates. ES cells of mouse vs. human origin have distinct culture conditions, responding to some tyrosine kinase signaling pathways in opposite ways. Previous work has implicated the Src family of non-receptor protein-tyrosine kinases in mouse ES cell self-renewal and differentiation. Seven members of the Src kinase family are expressed in mouse ES cells, and individual family members appear to play distinct roles in regulating their developmental fate. Both Hck and c-Yes are important in self-renewal, while c-Src activity alone is sufficient to induce differentiation. While these findings implicate Src-family kinase signaling in mouse ES cell renewal and differentiation, the role of this kinase family in human ES cells is largely unknown. Here, we explored Src-family kinase expression patterns and signaling in human ES cells during self-renewal and differentiation. Of the eleven Src-related kinases in the human genome, Fyn, c-Yes, c-Src, Lyn, Lck and Hck were expressed in H1, H7 and H9 hES cells, while Fgr, Blk, Srm, Brk, and Frk transcripts were not detected. Of these, c-Yes, Lyn, and Hck transcript levels remained constant in self-renewing human ES cells vs. differentiated EBs, while c-Src and Fyn showed a modest increase in expression as a function of differentiation. In contrast, Lck expression levels dropped dramatically as a function of EB differentiation. To assess the role of overall Src-family kinase activity in human ES cell differentiation, cultures were treated with inhibitors specific for the Src kinase family. Remarkably, human ES cells maintained in the presence of the potent Src-family kinase inhibitor A-419259 retained the morphology of domed, pluripotent colonies and continued to express the self-renewal marker TRA-1-60 despite culture under differentiation conditions. Taken together, these observations support a role for Src-family kinase signaling in the regulation of human ES cell fate, and suggest that the activities of individual Src-family members are required for the initiation of the differentiation program

Biographical learning: a process for promoting person-centredness in nursing

Background: This paper explores biographical approaches to nurses’ learning. It builds on previous PhD research to consider the effects of such approaches, drawing on the experiences of learners who have recently completed biographical study, in their own words. Aims and objectives: The aim of the paper is to make sense of different forms of learning. The objectives are to identify how autobiographical approaches that involve people learning from their life stories can engage people to exert agency, or ownership, in their own lives by taking control of their learning plans. Design: This longitudinal study started with the first group of learners undertaking a biographical preparation module on an Applied BSc Health and Social Care programme. Methods: Research relating to nurses’ learning is considered, including a Swiss perspective, as well as the validity of the biographical approach to developing knowledge. The learners share stories of their learning in order to develop understanding and new insights into their own lives and those of others. Results: Different dimensions of learning including learning about self, learning to make a difference and processes of repair are revealed through the learners’ narrations. Conclusions: Engaging biographically, to make sense of different forms of learning, appears to be beneficial to more person-centred working. Implications for practice: •Introducing biographical elements into courses of study can benefit learners by helping them to make sense of who they are as learners and practitioners •Co-creating compelling spaces of learning can facilitate learners to exert agency within their own lives as well as help others to learn. By exerting agency we mean taking ownership of the learning revealed through the biographical work and taking it forward in positive ways to enhance person-centred care

Multi-Constellation GNSS: New Bounds on DOP and a Related Satellite Selection Process

GPS receivers convert the measured pseudoranges from the visible GPS satellites into an estimate of the position and clock offset of the receiver. For various reasons receivers might only track and process a subset of the visible satellites. It would be desired, of course, to use the best subset. In general selecting the best subset is a combinatorics problem; selecting m objects from a choice of n allows for n m potential subsets. And since the GDOP performance criterion is nonlinear and non-separable, finding the best subset is a brute force procedure; hence, a number of authors have described sub-optimal algorithms for choosing satellites. This paper revisits this problem, especially in the context of multiple GNSS constellations, for the GDOP and PDOP criteria. Included are a discussion of optimum constellations (based upon parallel work of these authors on achievable lower bounds to GDOP and PDOP), musings on how the non-separableness of DOP makes it impossible to rank order the satellites, and a review/discussion of subset selection algorithms. Our long term goal is the development of better selection algorithms for multi-constellation GNSS

APNT for GNSS Spoof Detection

Global Navigation Satellite Systems (GNSS) are well known to be accurate providers of position, navigation, and time (PNT) information across the globe. With capable receivers and well-populated satellite constellations, GNSS users typically believe that the position and time information provided by their GNSS receiver is perfectly accurate. More sophisticated users look beyond accuracy and are also concerned with the integrity of the GNSS information. Advances in electronics technology have enabled the creation of malicious RF interference of GNSS signals. Inexpensive jamming devices overpower or distort the GNSS receivers input so as to completely deny the GNSS user of PNT information. A second threat to GNSS integrity is spoofing, the creation of counterfeit GNSS signals. This type of attack is considered more dangerous than a jamming attack since an erroneous PNT solution is often worse than no solution at all. The detection of spoofing is the subject of this paper. A variety of approaches have been proposed in the literature to recognize spoofing; many of these are based on the RF signal alone, including multi-antenna and multi-receiver methods. Another class of spoof detection algorithm is to compare the GNSS result to data from another, non-GNSS (hence, non-spoofed) sensor. In this paper we imagine that the trusted signal is the output of an Alternative PNT (APNT) receiver. APNT refers to stand alone, non-GNSS systems that are intended to provide PNT information during periods in which GNSS is unavailable The wide recognition of the vulnerabilities of the GPS in the Volpe report spurred the search for APNT systems; examples include the development of eLoran in the U.S. and Europe, general work on signals of opportunity ranging, DME-DME positioning, and, quite recently, R-Mode in Europe (we note that none of these systems is currently operational). The intent is that an integrated receiver, either loosely or tightly coupled, would merge the two systems’ observables to yield the best PNT information possible; in practice, since the APNTs’ solutions are typically of lower accuracy than the GNSS solutions, the combined result is nearly equal to the GNSS-alone solution. The goal of this paper is to show that these APNT solutions should be used at ALL times; as a substitute for GNSS PNT when GNSS is unavailable and as an integrity check (e.g. spoof detector) when GNSS is available. At a cursory level spoof detection using APNT appears simple; just compare the two position outputs to see if they are close. This paper looks deeper, considering the questions: How can we use the time estimates to detect position spoofing? How close is close enough in this context? What is the probability of error in the decision? How do the geometries of both systems impact the test itself and its resulting performance? What happens if the receivers are providing different information

Rethinking Star Selection in Celestial Navigation

In celestial navigation the altitude (elevation) angles to multiple celestial bodies are measured; these measurements are then used to compute the position of the user on the surface of the Earth. Methods described in the literature include the classical “altitude-intercept” algorithm as well as direct and iterative least-squares solutions for over determined situations. While it seems rather obvious that the user should select bright stars scattered across the sky, there appears to be no established results on the level of performance that is achievable based upon the number of stars sighted nor how the “best” set of stars might be selected from those visible. This paper addresses both of these issues by examining the performance of celestial navigation noting its similarity to the performance of GNSS systems; specifically, modern results on GDOP for GNSS are adapted to this classical celestial navigation problem

GNSS Spoof Detection Using Passive Ranging

Advances in electronics technology have enabled the creation of malicious RF interference of GNSS signals. For example jamming completely denies the GNSS user of position, navigation, and time (PNT) information. While a serious concern when we expect PNT at all times, current generation GNSS receivers often warn the user when PNT is unavailable. A second threat to GNSS integrity is spoofing, the creation of counterfeit GNSS signals with the potential to confuse the receiver into providing incorrect PNT information. This type of attack is considered more dangerous than a jamming attack since erroneous PNT is often worse than no solution at all. A variety of approaches have been proposed in the literature to recognize spoofing and can vary widely based upon the assumed capabilities and a priori knowledge of the spoofer. One method is to compare the GNSS result to data from a non-GNSS sensor. At the January 2016 ION ITM these authors developed and analyzed a spoof detection algorithm based upon measurements from an active ranging system (distances, but no heading). This paper expands the class of signals viable for this spoofing detection approach to passive ranging; equivalently, to range measurements which depend upon knowledge of precise time (effectively pseudoranges)

Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces

A quantum mechanical density functional theory approach was used to investigate the structural atomic configuration, vibration mode frequencies and electronic structure of surfaces and interfaces using germanium. Initially, we investigated the H2S and H2Opassivated germanium surfaces. A supercell approach is used with the local density (LDA), generalized gradient (GGA) approximations and van der Waals (vdW) interactions. The frozen phonon method was used to calculate the vibrational mode frequencies of these surfaces. The calculated frequencies produce stretch, bond bending and wag modes. The differences between the functionals including vdW terms and the LDA or GGA are less than the differences between LDA and GGA for the vibrational mode frequencies. Some of these modes provide useful vibrational signatures of bonding of both sulfur and oxygen on germanium surfaces, which may be compared with vibrational spectroscopy measurements. A bare germanium surface is bonded to a bare silicon surface to form a Ge-Si interface. As germanium has a 4% larger lattice constant than silicon this implies there are regions on the interface where the germanium and silicon match perfectly (aligned) and are completely mismatched (misaligned). The atomic structure of the GeSi aligned interface shows the original crystal structure and the projected band structure (PBS) shows no interface states in the band gap. The GeSi misaligned structure forms a (2x1) configuration. The electronic PBS shows interface states in the band gap. To remove the interface states seen in the GeSi interface, sulfur with its six valence electrons and its flexible chemical bonds is suggested to improve the interface bonding and remove interface states. The PBS in both the aligned and misaligned GeSSi interfaces shows states around the germanium and silicon interface atomic layers and a charge density localised around the sulfur interface atoms. A sulfur terminated germanium surface results in a (1x1) configuration with surface states present in the band gap. However, a H2S terminated germanium surface results in a (2x1) configuration with symmetric Ge-Ge dimers and pushes the surface states into the bulk region, implying the presence of hydrogen results in no surface states. Including hydrogen on our GeSSi interfaces, the atomic configuration remains the same with the hydrogen molecule in the channels. However, upon looking at the PBS, states are clearly visible in the band gap and when we investigate the charge density contour plots, interface states do exist. Therefore, the presence of hydrogen here does not influence the interfaces