On Putting Knowledge 'First'

There is a New Idea in epistemology. It goes by the name of ‘knowledge first,’ and it is particularly associated with Timothy Williamson’s book Knowledge and Its Limits. In slogan form, to put knowledge first is to treat knowledge as basic or fundamental, and to explain other states—belief, justification, maybe even content itself—in terms of knowledge, instead of vice versa. The idea has proven enormously interesting, and equally controversial. But deep foundational questions about its actual content remain relatively unexplored. We think that a wide variety of views travel under the banner of ‘knowledge first’ (and that the slogan doesn’t help much with differentiating them). Furthermore, we think it is far from straightforward to draw connections between certain of these views; they are more independent than they are often assumed to be. Our project here is exploratory and clarificatory. We mean to tease apart various ‘knowledge first’ claims, and explore what connections they do or do not have with one another. Our taxonomy is offered in §2, and connections are explored in §3. The result, we hope, will be a clearer understanding of just what the knowledge first theses are. We conclude, in §4, with some brief suggestions as to how we think the various theses might be evaluated

Giant planets around two intermediate-mass evolved stars and confirmation of the planetary nature of HIP67851 c

Precision radial velocities are required to discover and characterize planets orbiting nearby stars. Optical and near infrared spectra that exhibit many hundreds of absorption lines can allow the m/s precision levels required for such work. However, this means that studies have generally focused on solar-type dwarf stars. After the main-sequence, intermediate-mass stars (former A-F stars) expand and rotate slower than their progenitors, thus thousands of narrow absorption lines appear in the optical region, permitting the search for planetary Doppler signals in the data for these types of stars. We present the discovery of two giant planets around the intermediate-mass evolved star HIP65891 and HIP107773. The best Keplerian fit to the HIP65891 and HIP107773 radial velocities leads to the following orbital parameters: P=1084.5 d; m$_b$sin$i$ = 6.0 M$_{jup}$; $e$=0.13 and P=144.3 d; m$_b$sin$i$ = 2.0 M$_{jup}$; $e$=0.09, respectively. In addition, we confirm the planetary nature of the outer object orbiting the giant star HIP67851. The orbital parameters of HIP67851c are: P=2131.8 d, m$_c$sin$i$ = 6.0 M$_{jup}$ and $e$=0.17. With masses of 2.5 M$_\odot$ and 2.4 M$_\odot$ HIP65891 and HIP107773 are two of the most massive stars known to host planets. Additionally, HIP67851 is one of five giant stars that are known to host a planetary system having a close-in planet ($a <$ 0.7 AU). Based on the evolutionary states of those five stars, we conclude that close-in planets do exist in multiple systems around subgiants and slightly evolved giants stars, but probably they are subsequently destroyed by the stellar envelope during the ascent of the red giant branch phase. As a consequence, planetary systems with close-in objects are not found around horizontal branch stars.Comment: Accepted for publication in A&

Sand as Maxwell's demon

We consider a dilute gas of granular material inside a box, kept in a stationary state by shaking. A wall separates the box into two identical compartments, save for a small hole at some finite height $h$. As the gas is cooled, a second order phase transition occurs, in which the particles preferentially occupy one side of the box. We develop a quantitative theory of this clustering phenomenon and find good agreement with numerical simulations

Exotic magnetism in the alkali sesquoxides Rb4O6 and Cs4O6

Among the various alkali oxides the sesquioxides Rb4O6 and Cs4O6 are of special interest. Electronic structure calculations using the local spin-density approximation predicted that Rb4O6 should be a half-metallic ferromagnet, which was later contradicted when an experimental investigation of the temperature dependent magnetization of Rb4O6 showed a low-temperature magnetic transition and differences between zero-field-cooled (ZFC) and field-cooled (FC) measurements. Such behavior is known from spin glasses and frustrated systems. Rb4O6 and Cs4O6 comprise two different types of dioxygen anions, the hyperoxide and the peroxide anions. The nonmagnetic peroxide anions do not contain unpaired electrons while the hyperoxide anions contain unpaired electrons in antibonding pi*-orbitals. High electron localization (narrow bands) suggests that electronic correlations are of major importance in these open shell p-electron systems. Correlations and charge ordering due to the mixed valency render p-electron-based anionogenic magnetic order possible in the sesquioxides. In this work we present an experimental comparison of Rb4O6 and the related Cs4O6. The crystal structures are verified using powder x-ray diffraction. The mixed valency of both compounds is confirmed using Raman spectroscopy, and time-dependent magnetization experiments indicate that both compounds show magnetic frustration, a feature only previously known from d- and f-electron systems

Dynamics of inelastically colliding rough spheres: Relaxation of translational and rotational energy

We study the exchange of kinetic energy between translational and rotational degrees of freedom for inelastic collisions of rough spheres. Even if equipartition holds in the initial state it is immediately destroyed by collisions. The simplest generalisation of the homogeneous cooling state allows for two temperatures, characterizing translational and rotational degrees of freedom separately. For times larger than a crossover frequency, which is determined by the Enskog frequency and the initial temperature, both energies decay algebraically like $t^{-2}$ with a fixed ratio of amplitudes, different from one.Comment: 5 pages, RevTeX, 2 eps figures, slightly expanded discussion, new figures with dimensionless units, added references, accepted for publication in PRE as a Rapid Com

We Could, but Should We? Ethical Considerations for Providing Access to GeoCities and Other Historical Digital Collections

We live in an era in which the ways that we can make sense of our past are evolving as more artifacts from that past become digital. At the same time, the responsibilities of traditional gatekeepers who have negotiated the ethics of historical data collection and use, such as librarians and archivists, are increasingly being sidelined by the system builders who decide whether and how to provide access to historical digital collections, often without sufficient reflection on the ethical issues at hand. It is our aim to better prepare system builders to grapple with these issues. This paper focuses discussions around one such digital collection from the dawn of the web, asking what sorts of analyses can and should be conducted on archival copies of the GeoCities web hosting platform that dates to 1994.This research was supported by the Natural Sciences and Engineering Research Council of Canada, the Social Sciences and Humanities Research Council of Canada, the US National Science Foundation (grants 1618695 and 1704369), the Andrew W. Mellon Foundation, Start Smart Labs, and Compute Canada

An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4 Msun giant star HIP67537

We report the discovery of a substellar companion around the giant star HIP67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP67537$\,b$: m$_b$sin$i$ = 11.1$^{+0.4}_{-1.1}$ M$_{\rm {\tiny jup}}$, $a$ = 4.9$^{+0.14}_{-0.13}$ AU and $e$ = 0.59$^{+0.05}_{-0.02}$. Considering random inclination angles, this object has $\gtrsim$ 65% probability to be above the theoretical deuterium-burning limit, thus it is one of the few known objects in the planet to brown-dwarf transition region. In addition, we analyzed the Hipparcos astrometric data of this star, from which we derived a minimum inclination angle for the companion of $\sim$ 2 deg. This value corresponds to an upper mass limit of $\sim$ 0.3 M$_\odot$, therefore the probability that HIP67537$\,b$ is stellar in nature is $\lesssim$ 7%. The large mass of the host star and the high orbital eccentricity makes HIP67537$\,b$ a very interesting and rare substellar object. This is the second candidate companion in the brown dwarf desert detected in the sample of intermediate-mass stars targeted by the EXPRESS radial velocity program, which corresponds to a detection fraction of $f$ = 1.6$^{+2.0}_{-0.5}$%. This value is larger than the fraction observed in solar-type stars, providing new observational evidence of an enhanced formation efficiency of massive substellar companions in massive disks. Finally, we speculate about different formation channels for this object.Comment: Accepted for publication to A&

Inherent Rheology of a Granular Fluid in Uniform Shear Flow

In contrast to normal fluids, a granular fluid under shear supports a steady state with uniform temperature and density since the collisional cooling can compensate locally for viscous heating. It is shown that the hydrodynamic description of this steady state is inherently non-Newtonian. As a consequence, the Newtonian shear viscosity cannot be determined from experiments or simulation of uniform shear flow. For a given degree of inelasticity, the complete nonlinear dependence of the shear viscosity on the shear rate requires the analysis of the unsteady hydrodynamic behavior. The relationship to the Chapman-Enskog method to derive hydrodynamics is clarified using an approximate Grad's solution of the Boltzmann kinetic equationComment: 10 pages, 4 figures; substantially enlarged version; to be published in PR

Colloids in light fields: particle dynamics in random and periodic energy landscapes

The dynamics of colloidal particles in potential energy landscapes have mainly been investigated theoretically. In contrast, here we discuss the experimental realization of potential energy landscapes with the help of light fields and the observation of the particle dynamics by video microscopy. The experimentally observed dynamics in periodic and random potentials are compared to simulation and theoretical results in terms of, e.g. the mean-squared displacement, the time-dependent diffusion coefficient or the non-Gaussian parameter. The dynamics are initially diffusive followed by intermediate subdiffusive behaviour which again becomes diffusive at long times. How pronounced and extended the different regimes are, depends on the specific conditions, in particular the shape of the potential as well as its roughness or amplitude but also the particle concentration. Here we focus on dilute systems, but the dynamics of interacting systems in external potentials, and thus the interplay between particle-particle and particle-potential interactions, is also mentioned briefly. Furthermore, the observed dynamics of dilute systems resemble the dynamics of concentrated systems close to their glass transition, with which it is compared. The effect of certain potential energy landscapes on the dynamics of individual particles appears similar to the effect of interparticle interactions in the absence of an external potential