On Toroidal Horizons in Binary Black Hole Inspirals

We examine the structure of the event horizon for numerical simulations of two black holes that begin in a quasicircular orbit, inspiral, and finally merge. We find that the spatial cross section of the merged event horizon has spherical topology (to the limit of our resolution), despite the expectation that generic binary black hole mergers in the absence of symmetries should result in an event horizon that briefly has a toroidal cross section. Using insight gained from our numerical simulations, we investigate how the choice of time slicing affects both the spatial cross section of the event horizon and the locus of points at which generators of the event horizon cross. To ensure the robustness of our conclusions, our results are checked at multiple numerical resolutions. 3D visualization data for these resolutions are available for public access online. We find that the structure of the horizon generators in our simulations is consistent with expectations, and the lack of toroidal horizons in our simulations is due to our choice of time slicing.Comment: Submitted to Phys. Rev.

On Chiral Symmetry Restoration at Finite Density in Large N_c QCD

At large N_c, cold nuclear matter is expected to form a crystal and thus spontaneously break translational symmetry. The description of chiral symmetry breaking and translational symmetry breaking can become intertwined. Here, the focus is on aspects of chiral symmetry breaking and its possible restoration that are by construction independent of the nature of translational symmetry breaking---namely spatial averages of chiral order parameters. A system will be considered to be chirally restored provided all spatially-averaged chiral order parameters are zero. A critical question is whether chiral restoration in this sense is possible for phases in which chiral order parameters are locally non-zero but whose spatial averages all vanish. We show that this is not possible unless all chirally-invariant observables are spatially uniform. This result is first derived for Skyrme-type models, which are based on a nonlinear sigma model and by construction break chiral symmetry on a point-by-point basis. A no-go theorem for chiral restoration (in the average sense) for all models of this type is obtained by showing that in these models there exist chirally symmetric order parameters which cannot be spatially uniform. Next we show that the no-go theorem applies to large N_c QCD in any phase which has a non-zero but spatially varying chiral condensate. The theorem is demonstrated by showing that in a putative chirally-restored phase, the field configuration can be reduced to that of a nonlinear sigma model.Comment: 12 pages, 1 tabl

Representing older people: towards meaningful images of the user in design scenarios

Designing for older people requires the consideration of a range of difficult and sometimes highly personal design problems. Issues such as fear, loneliness, dependency, and physical decline may be difficult to observe or discuss in interviews. Pastiche scenarios and pastiche personae are techniques that employ characters to create a space for the discussion of new technological developments and as a means to explore user experience. This paper argues that the use of such characters can help to overcome restrictive notions of older people by disrupting designers' prior assumptions. In this paper, we reflect on our experiences using pastiche techniques in two separate technology design projects that sought to address the needs of older people. In the first case pastiche scenarios were developed by the designers of the system and used as discussion documents with users. In the second case, pastiche personae were used by groups of users themselves to generate scenarios which were scribed for later use by the design team. We explore how the use of fictional characters and settings can generate new ideas and undermine rhetorical devices within scenarios that attempt to fit characters to the technology, rather than vice versa. To assist in future development of pastiche techniques in designing for older people, we provide an array of fictional older characters drawn from literary and popular culture.</p

Extracting Atoms on Demand with Lasers

We propose a scheme that allows to coherently extract cold atoms from a reservoir in a deterministic way. The transfer is achieved by means of radiation pulses coupling two atomic states which are object to different trapping conditions. A particular realization is proposed, where one state has zero magnetic moment and is confined by a dipole trap, whereas the other state with non-vanishing magnetic moment is confined by a steep microtrap potential. We show that in this setup a predetermined number of atoms can be transferred from a reservoir, a Bose-Einstein condensate, into the collective quantum state of the steep trap with high efficiency in the parameter regime of present experiments.Comment: 11 pages, 8 figure

Martian Igneous Activity and Fluid-Based Alteration:Chronological Constraints from 40Ar/39Ar Analyses of the Nakhlites

The nakhlites are a group of mafic igneous rocks that crystallized on Mars at ca. 1.3-1.4 Ga [1-5]. They are amongst the least shocked Martian meteorites, with cumulate igneous textures (Fig. 1) and thus provide a crucial record of igneous activity and fluid-rock interaction on the red planet. Crystallization of the nakhlites. Understanding the original structure of the nakhlite source is crucial for using these stones to explore Martian igneous processes. In particular, are the different nakhlites from a single thick and differentiated lava flow/sill [6; 7], or do they instead represent magmatically related – but distinct – flows/intrusions? If the various meteorites are derived from separate units, then there will be differences in crystallization ages within the nakhlite suite – which may be identified if these differences are sufficiently large relative to the attainable precision of radioisotopic dating techniques. Some studies [e.g., 5] appear to resolve age differences between different stones, and we aim to test the single vs. multiple unit hypotheses via application of detailed 40Ar/39Ar stepheating of six nakhlites.&lt;p&gt;&lt;/p&gt; Alteration of the nakhlites, and the timing of waterrock interaction. In addition to primary magmatic minerals and glasses, the nakhlites contain secondary minerals including clays and carbonates that were precipitated by Martian aqueous fluids prior to impact ejection (Fig. 2) [8-10]. When did this alteration occur? As the clays contain potassium, they are amenable to K-Ar and 40Ar/39Ar dating. K-Ar data from Lafayette suggests the alteration phases formed between 0 to 670 Ma [11]. We consider further the timing of alteration using our 40Ar/39Ar data.&lt;p&gt;&lt;/p&gt

Cytotoxicity of withaferin A in glioblastomas involves induction of an oxidative stress-mediated heat shock response while altering Akt/mTOR and MAPK signaling pathways

Withaferin A (WA), a steroidal lactone derived from the plant Vassobia breviflora, has been reported to have anti-proliferative, pro-apoptotic, and anti-angiogenic properties against cancer growth. In this study, we identified several key underlying mechanisms of anticancer action of WA in glioblastoma cells. WA was found to inhibit proliferation by inducing a dose-dependent G2/M cell cycle arrest and promoting cell death through both intrinsic and extrinsic apoptotic pathways. This was accompanied by an inhibitory shift in the Akt/mTOR signaling pathway which included diminished expression and/or phosphorylation of Akt, mTOR, p70 S6K, and p85 S6K with increased activation of AMPKα and the tumor suppressor tuberin/TSC2. Alterations in proteins of the MAPK pathway and cell surface receptors like EGFR, Her2/ErbB2, and c-Met were also observed. WA induced an N-acetyl-L-cysteinerepressible enhancement in cellular oxidative potential/stress with subsequent induction of a heat shock stress response primarily through HSP70, HSP32, and HSP27 upregulation and HSF1 downregulation. Taken together, we suggest that WA may represent a promising chemotherapeutic candidate in glioblastoma therapy warranting further translational evaluation