On the absence of shear from perfect Einstein rings and the stability of geometry

Concordance cosmology points to a Universe of zero mean curvature, due to the inflation mechanism which occurred soon after the Big Bang, while along a relatively small number of lower redshift light paths where lensing events are observed, space is positively curved. How do we know that global geometry and topology are robust rather than in a state of chaos? The phenomenon of cosmic shear provides an effective way of mapping curvature fluctuations, because it affects {\it any} light rays whether they intercept mass clumps or not. We discuss a range of astrophysical applications of the principal manifestation of shear - the distortion of images. It will be shown that the quickest way of testing the existence of shear in the near Universe is to look at the shape of Einstein rings. The fact that most of these rings are circular to a large extent means, statistically speaking, shear occurs at a much lower level than the expectation based upon our current understanding of the inhomogeneous Universe. While inflation may account for the mean geometry, it offers no means of stabilizing it against the fluctuations caused by non-linear matter clumping at low redshift. Either this clumping is actually much less severe, or the physical mechanism responsible for shaping the large scale curvature has been active not only during the very early epochs, but also at all subsequent times. Might it be the vital `interface' between expansion on Hubble distances and gravity on cluster scales and beneath?Comment: 16 pages, 3 figures, 18 equations. ApJ in pres

A New Approach to Probing Large Scale Power with Peculiar Velocities

We propose a new strategy to probe the power spectrum on large scales using galaxy peculiar velocities. We explore the properties of surveys that cover only two small fields in opposing directions on the sky. Surveys of this type have several advantages over those that attempt to cover the entire sky; in particular, by concentrating galaxies in narrow cones these surveys are able to achieve the density needed to measure several moments of the velocity field with only a modest number of objects, even for surveys designed to probe scales \gtwid 100\hmpc. We construct mock surveys with this geometry and analyze them in terms of the three moments to which they are most sensitive. We calculate window functions for these moments and construct a $\chi^2$ statistic which can be used to put constraints on the power spectrum. In order to explore the sensitivity of these surveys, we calculate the expectation values of the moments and their associated measurement noise as a function of the survey parameters such as density and depth and for several popular models of structure formation. In addition, we have studied how well these kind of surveys can distinguish between different power spectra and found that, for the same number of objects, cone surveys are as good or better than full-sky surveys in distinguishing between popular cosmological models. We find that a survey with $200-300$ galaxy peculiar velocities with distance errors of 15% in two cones with opening angle of $\sim 10^\circ$ could put significant constraints on the power spectrum on scales of $100-300$\hmpc, where few other constraints exist.Comment: 15 pages, 3 figures, Some revisions and different figure. Accepted for publication at ApJ letter

Equatorial locations of water on Mars: Improved resolution maps based on Mars Odyssey Neutron Spectrometer data

We present a map of the near subsurface hydrogen distribution on Mars, based on epithermal neutron data from the Mars Odyssey Neutron Spectrometer. The map’s spatial resolution is approximately improved two-fold via a new form of the pixon image reconstruction technique. We discover hydrogen-rich mineralogy far from the poles, including  ∼10 wt.% water equivalent hydrogen (WEH) on the flanks of the Tharsis Montes and  >40 wt.% WEH at the Medusae Fossae Formation (MFF). The high WEH abundance at the MFF implies the presence of bulk water ice. This supports the hypothesis of recent periods of high orbital obliquity during which water ice was stable on the surface. We find the young undivided channel system material in southern Elysium Planitia to be distinct from its surroundings and exceptionally dry; there is no evidence of hydration at the location in Elysium Planitia suggested to contain a buried water ice sea. Finally, we find that the sites of recurring slope lineae (RSL) do not correlate with subsurface hydration. This implies that RSL are not fed by large, near-subsurface aquifers, but are instead the result of either small ( < 120 km diameter) aquifers, deliquescence of perchlorate and chlorate salts or dry, granular flows

E-contact facilitated by conversational agents reduces interethnic prejudice and anxiety in Afghanistan

AIエージェントによって分断された民族間の偏見と不安を軽--対立グループのE-ContactにおけるAIエージェントの効果-- 京都大学プレスリリース. 2024-04-04.Don't matter if you're this or that: AI intervention mitigates tension among conflicting ethnic groups. 京都大学プレスリリース. 2024-05-13.Intergroup contact occurring through indirect means such as the internet has the potential to improve intergroup relationships and may be especially beneficial in high conflict situations. Here we conducted a three-timepoint online experiment to ascertain whether the use of a conversational agent in E-contact platforms could mitigate interethnic prejudices and hostility among Afghanistan’s historically segregated and persistently conflictual ethnic groups. 128 Afghans of Pashtun, Tajik, and Hazara backgrounds were assigned to one of four E-contact conditions (control with no conversational agent and three experimental groups that varied in the conversational agent settings). Participants in the experimental conditions contributed more ideas and longer opinions and showed a greater reduction in outgroup prejudice and anxiety than those in the control group. These findings demonstrate that E-contact facilitated by a conversational agent can improve intergroup attitudes even in contexts characterized by a long history of intergroup segregation and conflict

The European Cycle Route Network, EuroVelo

This study evaluates the challenges and opportunities of developing a cycle tourism network across Europe. It focuses on EuroVelo, a network of 12 long-distance routes managed by the European Cyclists’ Federation, which is being developed in different countries by a wide range of partners. The study reviews the market for cycle tourism in Europe and presents a EuroVelo demand modal. It reviews the carriage of cycles on trains. Finally, it evaluates the potential of the Iron Curtain Trail

Observational Tests of the Mass-Temperature Relation for Galaxy Clusters

We examine the relationship between the mass and x-ray gas temperature of galaxy clusters using data drawn from the literature. Simple theoretical arguments suggest that the mass of a cluster is related to the x-ray temperature as $M \propto T_x^{3/2}$. Virial theorem mass estimates based on cluster galaxy velocity dispersions seem to be accurately described by this scaling with a normalization consistent with that predicted by the simulations of Evrard, Metzler, & Navarro (1996). X-ray mass estimates which employ spatially resolved temperature profiles also follow a $T_x^{3/2}$ scaling although with a normalization about 40% lower than that of the fit to the virial masses. However, the isothermal $\beta$-model and x-ray surface brightness deprojection masses follow a steeper $\propto T_x^{1.8-2.0}$ scaling. The steepness of the isothermal estimates is due to their implicitly assumed dark matter density profile of $\rho(r) \propto r^{-2}$ at large radii while observations and simulations suggest that clusters follow steeper profiles (e.g., $\rho(r) \propto r^{-2.4}$).Comment: 25 pages, 10 figures, accepted by Ap

The European Cycle Route Network, EuroVelo

This update of the 2009 study evaluates the challenges and opportunities of developing a cycle tourism network across Europe. It focuses on EuroVelo, a network of 14 long distance routes managed by the European Cyclists’ Federation which is being developed in different countries by a wide range of partners. The study reviews the market for cycle tourism and presents a model of demand for EuroVelo. It also evaluates the recent developments on the Iron Curtain Trail

Reconciling LCROSS and Orbital Neutron Water Abundance Estimates in Cabeus Crater

The Lunar Prospector Neutron Spectrometer (LPNS) first revealed Cabeus crater (84.9 deg S, 35.5degW) as having the highest inferred hydrogen on the Moon. Because of the broad LPNS footprint (approximately 40 km FWHM), the apparent peak water-equivalent hydrogen (WEH) concentration is only approximately 0.25 wt%, but could be much higher in smaller areas than the spectrometer footprint. Earlier image reconstruction work suggested that areas within permanent shadow have abundances approximately 1 wt% WEH. However, the LCROSS impact yielded total water estimates, ice plus vapor, of between 3 and 10 wt%. The large disagreement between LCROSS and apparent orbital values imply that either the ice is buried, by perhaps as much as 50 to 100 cm; or the ice distribution within Cabeus is spatially inhomogeneous, or both. Modeling reveals that the areal extent of a "shallow permafrost zone" is far greater than the area of permanent shadow. Ice can be virtually stable for billions of years within a few tens of centimeters of the surface in these areas. However, the LCROSS impact took place in an area of permanent shadow. If stably-trapped volatiles can be found in locales that receive occasional, oblique sunlight, landed missions may target these sites and eventual resource exploitation may be done more easily. Are orbital neutron data consistent with areally-extensive, volatile-rich cold traps? Orbital epithermal neutron data over the northern half of Cabeus (near the LCROSS impact site) are consistent with 0.2 wt% WEH or less in the "permafrost zone" near the crater. On the other hand, pixon reconstructions that confine the hydrogen enhancements to permanent shadow result in higher abundance estimates -- around 1 wt% if homogeneously mixed. But if the PSR abundance is increased to 10 wt%, consistent with the sum of all H-bearing compounds seen by LCROSS, a much larger-than-observed reduction in neutron count rate would be seen from orbit. It is likely that volatiles are inhomogeneously distributed, due to both impact processes and emplacement history. Two possibilities may bring consistency to the orbital and LCROSS measurements. Inhomogeneous lateral distribution: Consider the extreme case of a bimodal distribution within the crater -- dry and wet. In this case the epithermal leakage flux seen from orbit is a mixture of two different values, weighted according to fractional areas. Two possible outcomes, depending on whether the inferred leakage flux for the PSR or "permafrost" areas are considered. In the first case, approximately 40% of the PSR may be "wet", the remainder dry (and LCROSS was slightly lucky). However, if the whole area of permafrost is considered, then as little as 20% of the area will be as "wet" as the LCROSS results (and LCROSS was quite lucky). Inhomogeneous depth distribution: The leakage flux of thermal and epithermal neutrons depends on depth of burial of an icy layer beneath dry ferroan anorthosite soil (FAn). For the Cabeus PSR, the pixon reconstruction values for the epithermal flux allows a range of abundance and burial depth, while that of the thermal+epi detector constrains this range. (Uncertainties in iron abundance in the FAn can have significant impact on thermal neutron leakage flux estimates.) Between 20% and 40% of the Cabeus floor may be "wet", or alternatively a 5-10 wt% "wet" layer exists between 50 and 100 cm beneath a layer of dry regolith within the PSR. But volatile abundances of 5 wt% or more, distributed uniformly and homogeneously throughout the Cabeus PSR do not agree with orbital measurement