Some assembly required: assembly bias in massive dark matter halos

We study halo assembly bias for cluster-sized halos. Previous work has found little evidence for correlations between large-scale bias and halo mass assembly history for simulated cluster-sized halos, in contrast to the significant correlation found between bias and concentration for halos of this mass. This difference in behavior is surprising, given that both concentration and assembly history are closely related to the same properties of the linear-density peaks that collapse to form halos. Using publicly available simulations, we show that significant assembly bias is indeed found in the most massive halos with $M\sim 10^{15}M_\odot$, using essentially any definition of halo age. For lower halo masses $M\sim 10^{14}M_\odot$, no correlation is found between bias and the commonly used age indicator $a_{0.5}$, the half-mass time. We show that this is a mere accident, and that significant assembly bias exists for other definitions of halo age, including those based on the time when the halo progenitor acquires some fraction $f$ of the ultimate mass at $z=0$. For halos with $M_{\rm vir}\sim 10^{14}M_\odot$, the sense of assembly bias changes sign at $f=0.5$. We explore the origin of this behavior, and argue that it arises because standard definitions of halo mass in halo finders do not correspond to the collapsed, virialized mass that appears in the spherical collapse model used to predict large-scale clustering. Because bias depends strongly on halo mass, these errors in mass definition can masquerade as or even obscure the assembly bias that is physically present. More physically motivated halo definitions using splashback should be free of this particular defect of standard halo finders.Comment: 7 pages, 4 figures, to be submitted to JCA

The SLUGGS Survey: Calcium Triplet-based Spectroscopic Metallicities for Over 900 Globular Clusters

Although the colour distribution of globular clusters in massive galaxies is well known to be bimodal, the spectroscopic metallicity distribution has been measured in only a few galaxies. After redefining the calcium triplet index-metallicity relation, we use our relation to derive the metallicity of 903 globular clusters in 11 early-type galaxies. This is the largest sample of spectroscopic globular cluster metallicities yet assembled. We compare these metallicities with those derived from Lick indices finding good agreement. In 6 of the 8 galaxies with sufficient numbers of high quality spectra we find bimodality in the spectroscopic metallicity distribution. Our results imply that most massive early-type galaxies have bimodal metallicity, as well as colour, distributions. This bimodality suggests that most massive galaxies early-type galaxies experienced two periods of star formation.Comment: 23 pages, 13 figures. Accepted for publication in MNRAS. For more information about the SLUGGS Survey please see http://sluggs.swin.edu.a

Some assembly required: dedicated chaperones in eukaryotic proteasome biogenesis

The 26S proteasome is the key eukaryotic protease responsible for the degradation of intracellular proteins. Protein degradation by the 26S proteasome plays important roles in numerous cellular processes, including the cell cycle, differentiation, apoptosis, and the removal of damaged or misfolded proteins. How this 2.5-MDa complex, composed of at least 32 different polypeptides, is assembled in the first place is not well understood. However, it has become evident that this complicated task is facilitated by a framework of protein factors that chaperone the nascent proteasome through its various stages of assembly. We review here the known proteasome-specific assembly factors, most only recently discovered, and describe their potential roles in proteasome assembly, with an emphasis on the many remaining unanswered questions about this intricate process of assisted self-assembly

Some assembly required.

A creative thesis of lyric poetry. A collection exploring the struggles and beauty of childhood, relationships and desire as they play out in front of a Western Oklahoma backdrop

Some Assembly Required

\u27Some Assembly Required\u27 is a short story collection that explores the construction and deconstruction of identity within various fields of interest, generally hobbies or professions, and the type of people who do those professions or hobbies. It also explores dynamics of familial and romantic relationships

Telerobotic truss assembly

The ACCESS truss was telerobotically assembled in order to gain experience with robotic assembly of hardware designed for astronaut extravehicular (EVA) assembly. Tight alignment constraints of the ACCESS hardware made telerobotic assembly difficult. A wider alignment envelope and a compliant end effector would have reduced the problem. The manipulator had no linear motion capability, but many of the assembly operations required straight line motion. The manipulator was attached to a motion table in order to provide the X, Y, and Z translations needed. A programmable robot with linear translation capability would have eliminated the need for the motion table and streamlined the assembly. Poor depth perception was a major problem. Shaded paint schemes and alignment lines were helpful in reducing this problem. The four cameras used worked well for only some operations. It was not possible to identify camera locations that worked well for all assembly steps. More cameras or movable cameras would have simplified some operations. The audio feedback system was useful

Drawer drive for space shuttle vacuum canister

A sliding drawer type canister was designed to contain long duration exposure facility experiments which require vacuum storage before and after space exposure. The elastomeric seals require high closing loads which are generated through camming levers and transmitted through a spring loaded pressure plate. Lubrication was provided by various dry surface coatings. Higher than expected friction required some redesign after which the assembly functioned well and provided good sealing

Ground controlled robotic assembly operations for Space Station Freedom

A number of dextrous robotic systems and associated positioning and transportation devices are available on Space Station Freedom (SSF) to perform assembly tasks that would otherwise need to be performed by extravehicular activity (EVA) crewmembers. The currently planned operating mode for these robotic systems during the assembly phase is teleoperation by intravehicular activity (IVA) crewmembers. While this operating mode is less hazardous and expensive than manned EVA operations, and has insignificant control loop time delays, the amount of IVA time available to support telerobotic operations is much less than the anticipated requirements. Some alternative is needed to allow the robotic systems to perform useful tasks without exhausting the available IVA resources; ground control is one such alternative. The issues associated with ground control of SSF robotic systems to alleviate onboard crew time availability constraints are investigated. Key technical issues include the effect of communication time delays, the need for safe, reliable execution of remote operations, and required modifications to the SSF ground and flight system architecture. Time delay compensation techniques such as predictive displays and world model-based force reflection are addressed and collision detection and avoidance strategies to ensure the safety of the on-orbit crew, Orbiter, and SSF are described. Although more time consuming and difficult than IVA controlled teleoperations or manned EVA, ground controlled telerobotic operations offer significant benefits during the SSF assembly phase, and should be considered in assembly planning activities