Estimates for the volume of a Lorentzian manifold

We prove new estimates for the volume of a Lorentzian manifold and show especially that cosmological spacetimes with crushing singularities have finite volume.Comment: 8 pages, a pdf version of the preprint can also be retrieved from http://www.math.uni-heidelberg.de/studinfo/gerhardt/LM-Volume.pdf v2: A further estimate has been added covering the case when the mean curvature is merely non-negative resp. non-positive (Theorem 1.1

Remembering Cultural Experiences: lifespan distributions, richness and content of autobiographical memories of museum visits

Little is known about our autobiographical memories for cultural events. This represents an opportunity for cultural institutions such as museums, as examination of visitor memories is one way in which they can seek to understand the long-term impact they may have on their visitors. This research applied a coding model developed from autobiographical memory theory to analysis of participants’ memories for museum visits, considering the distribution of memories across the life span, types of memories and content. Differences between visitor groups (age, visit frequency) were also considered. Findings showed a strong recency effect in the life-span distribution, suggesting the importance of social sharing in memories of cultural experience. Analysis of content showed a hierarchy of information that was present in museum memories. Knowledge acquired during the event of the visit was important, as was contextualising information whereby visitors situated the memory within their autobiographical knowledge and chronology. Emotions and thoughts were also salient. Visitor differences had minimal impact on content, with the exception of some effects that were consistent with the literature on memory and ageing. This research develops understanding of autobiographical memories for cultural experiences and provides insight to museums, with practical implications in terms of understanding visitors’ experiences

Hands-on, Shoes-off: Multisensory Tools Enhance Family Engagement Within an Art Museum

Families with young children typically struggle to engage with traditional art museum environments. This research examined the impact of multisensory tools on family engagement within Mathaf: Arab Museum of Modern Art, Qatar. Sixty families with at least one child aged 0-11 were observed during two tasks. One task required participants to look at a series of paintings to select their favorite. In another task families were given a toolkit of multisensory items to facilitate interaction with a painting. A semi-structured observational method produced quantitative and qualitative data about participant engagement and intergenerational interaction. Self-rating scores of task enjoyment were also collected. Results indicated that multisensory tools enhance family engagement with museums, artworks and with each other. Results also suggested that word-based interpretation was not necessary. We consider the potential implications of these findings in relation to family programming within art museums and museums more generally

Black Hole Criticality in the Brans-Dicke Model

We study the collapse of a free scalar field in the Brans-Dicke model of gravity. At the critical point of black hole formation, the model admits two distinctive solutions dependent on the value of the coupling parameter. We find one solution to be discretely self-similar and the other to exhibit continuous self-similarity.Comment: 4 pages, REVTeX 3.0, 5 figures include

Head-on collision of ultrarelativistic charges

We consider the head-on collision of two opposite-charged point particles moving at the speed of light. Starting from the field of a single charge we derive in a first step the field generated by uniformly accelerated charge in the limit of infinite acceleration. From this we then calculate explicitly the burst of radiation emitted from the head-on collision of two charges and discuss its distributional structure. The motivation for our investigation comes from the corresponding gravitational situation where the head-on collision of two ultrarelativistic particles (black holes) has recently aroused renewed interest.Comment: 4 figures, uses the AMSmat

On the Nature of Singularities in Plane Symmetric Scalar Field Cosmologies

The nature of the initial singularity in spatially compact plane symmetric scalar field cosmologies is investigated. It is shown that this singularity is crushing and velocity dominated and that the Kretschmann scalar diverges uniformly as it is approached. The last fact means in particular that a maximal globally hyperbolic spacetime in this class cannot be extended towards the past through a Cauchy horizon. A subclass of these spacetimes is identified for which the singularity is isotropic.Comment: 7 pages, MPA-AR-94-

Observation of critical phenomena and self-similarity in the gravitational collapse of radiation fluid

We observe critical phenomena in spherical collapse of radiation fluid. A sequence of spacetimes $\cal{S}[\eta]$ is numerically computed, containing models ($\eta\ll 1$) that adiabatically disperse and models ($\eta\gg 1$) that form a black hole. Near the critical point ($\eta_c$), evolutions develop a self-similar region within which collapse is balanced by a strong, inward-moving rarefaction wave that holds $m(r)/r$ constant as a function of a self-similar coordinate $\xi$. The self-similar solution is known and we show near-critical evolutions asymptotically approaching it. A critical exponent $\beta \simeq 0.36$ is found for supercritical ($\eta>\eta_c$) models.Comment: 10 pages (LaTeX) (to appear in Phys. Rev. Lett.), TAR-039-UN

Quantifying Aphantasia through drawing: Those without visual imagery show deficits in object but not spatial memory

Congenital aphantasia is a recently characterized variation of experience defined by the inability to form voluntary visual imagery, in individuals who are otherwise high performing. Because of this specific deficit to visual imagery, individuals with aphantasia serve as an ideal group for probing the nature of representations in visual memory, particularly the interplay of object, spatial, and symbolic information. Here, we conducted a large-scale online study of aphantasia and revealed a dissociation in object and spatial content in their memory representations. Sixty-one individuals with aphantasia and matched controls with typical imagery studied real-world scene images, and were asked to draw them from memory, and then later copy them during a matched perceptual condition. Drawings were objectively quantified by 2,795 online scorers for object and spatial details. Aphantasic participants recalled significantly fewer objects than controls, with less color in their drawings, and an increased reliance on verbal scaffolding. However, aphantasic participants showed high spatial accuracy equivalent to controls, and made significantly fewer memory errors. These differences between groups only manifested during recall, with no differences between groups during the matched perceptual condition. This object-specific memory impairment in individuals with aphantasia provides evidence for separate systems in memory that support object versus spatial information. The study also provides an important experimental validation for the existence of aphantasia as a variation in human imagery experience