Implications for the Formation of Blue Straggler Stars from HST Ultraviolet Observations of NGC 188

We present results of a Hubble Space Telescope far-ultraviolet (FUV) survey searching for white dwarf (WD) companions to blue straggler stars (BSSs) in open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined binaries with properties suggestive of mass-transfer formation via Roche lobe overflow, specifically through an asymptotic giant branch star transferring mass to a main sequence secondary, yielding a BSS binary with a WD companion. In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a WD companion hot and luminous enough to be directly detected as a FUV photometric excess with HST. Comparing expected BSS FUV emission to observed photometry reveals four BSSs with WD companions above 12,000 K (younger than 250 Myr) and three WD companions with temperatures between 11,000-12,000 K. These BSS+WD binaries all formed through recent mass transfer. The location of the young BSSs in an optical color-magnitude diagram (CMD) indicates that distance from the zero-age main sequence does not necessarily correlate with BSS age. There is no clear CMD separation between mass transfer-formed BSSs and those likely formed through other mechanisms, such as collisions. The seven detected WD companions place a lower limit on the mass-transfer formation frequency of 33%. We consider other possible formation mechanisms by comparing properties of the BSS population to theoretical predictions. We conclude that 14 BSS binaries likely formed from mass transfer, resulting in an inferred mass-transfer formation frequency of approximately 67%.Comment: 13 pages, 6 figures, accepted to the Astrophysical Journa

Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer

Several possible formation pathways for blue straggler stars have been developed recently, but no one pathway has yet been observationally confirmed for a specific blue straggler. Here we report the first findings from a Hubble Space Telescope ACS/SBC far-UV photometric program to search for white dwarf companions to blue straggler stars. We find three hot and young white dwarf companions to blue straggler stars in the 7-Gyr open cluster NGC 188, indicating that mass transfer in these systems ended less than 300 Myr ago. These companions are direct and secure observational evidence that these blue straggler stars were formed through mass transfer in binary stars. Their existence in a well-studied cluster environment allows for observational constraints of both the current binary system and the progenitor binary system, mapping the entire mass transfer history.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical Journal Letter

Exact Integration of the High Energy Scale in Doped Mott Insulators

We expand on our earlier work (cond-mat/0612130, Phys. Rev. Lett. {\bf 99}, 46404 (2007)) in which we constructed the exact low-energy theory of a doped Mott insulator by explicitly integrating (rather than projecting) out the degrees of freedom far away from the chemical potential. The exact low-energy theory contains degrees of freedom that cannot be obtained from projective schemes. In particular a new charge $\pm 2e$ bosonic field emerges at low energies that is not made out of elemental excitations. Such a field accounts for dynamical spectral weight transfer across the Mott gap. At half-filling, we show that two such excitations emerge which play a crucial role in preserving the Luttinger surface along which the single-particle Green function vanishes. In addition, the interactions with the bosonic fields defeat the artificial local SU(2) symmetry that is present in the Heisenberg model. We also apply this method to the Anderson-U impurity and show that in addition to the Kondo interaction, bosonic degrees of freedom appear as well. Finally, we show that as a result of the bosonic degree of freedom, the electron at low energies is in a linear superposition of two excitations--one arising from the standard projection into the low-energy sector and the other from the binding of a hole and the boson.Comment: Published veriso

Torsion and the Gravity Dual of Parity Symmetry Breaking in AdS4/CFT3 Holography

We study four dimensional gravity with a negative cosmological constant deformed by the Nieh-Yan torsional topological invariant with a spacetime-dependent coefficient. We find an exact solution of the Euclidean system, which we call the torsion vortex, having two asymptotic AdS4 regimes supported by a pseudoscalar with a kink profile. We propose that the torsion vortex is the holographic dual of a three dimensional system that exhibits distinct parity breaking vacua. The torsion vortex represents a (holographic) transition between these distinct vacua. We expect that from the boundary point of view, the torsion vortex represents a `domain wall' between the two distinct vacua. From a bulk point of view, we point out an intriguing identification of the parameters of the torsion vortex with those of an Abrikosov vortex in a Type I superconductor. Following the analogy, we find that external Kalb-Ramond flux then appears to support bubbles of flat spacetime within an asymptotically AdS geometry.Comment: 26 pages, 4 figures; v2: minor improvements, references adde

Contribution of Implicit Memory to Adaptation of Movement Extent during Reaching against Unpredictable Spring-like Loads: Insensitivity to Intentional Suppression of Kinematic Performance

We examined the extent to which intentionally underperforming a goal-directed reaching task impacts how memories of recent performance contribute to sensorimotor adaptation. Healthy human subjects performed computerized cognition testing and an assessment of sensorimotor adaptation, wherein they grasped the handle of a horizontal planar robot while making goal-directed out-and-back reaching movements. The robot exerted forces that resisted hand motion with a spring-like load that changed unpredictably between movements. The robotic test assessed how implicit and explicit memories of sensorimotor performance contribute to the compensation for the unpredictable changes in the hand-held load. After each movement, subjects were to recall and report how far the hand moved on the previous trial (peak extent of the out-and-back movement). Subjects performed the tests under two counter-balanced conditions: one where they performed with their best effort, and one where they intentionally sabotaged (i.e., suppressed) kinematic performance. Results from the computerized cognition tests confirmed that subjects understood and complied with task instructions. When suppressing performance during the robotic assessment, subjects demonstrated marked changes in reach precision, time to capture the target, and reaction time. We fit a set of limited memory models to the data to identify how subjects used implicit and explicit memories of recent performance to compensate for the changing loads. In both sessions, subjects used implicit, but not explicit, memories from the most recent trial to adapt reaches to unpredictable spring-like loads. Subjects did not “give up” on large errors, nor did they discount small errors deemed “good enough”. Although subjects clearly suppressed kinematic performance (response timing, movement variability, and self-reporting of reach error), the relative contributions of sensorimotor memories to trial-by-trial variations in task performance did not differ significantly between the two testing conditions. We conclude that intentional performance suppression had minimal impact on how implicit sensorimotor memories contribute to adaptation of unpredictable mechanical loads applied to the hand

Effects of experimental design and its role in interpretation of results

A total of 256 weanling pigs (PIC TR4 × 1050, initially 13.8 lb and 21 d of age) were used in a 28-d growth trial to compare allotment methods of a completely randomized design (CRD) and a randomized complete block design (RCBD). Two treatments were used to compare these designs: a negative control with no antibiotic or growth promoter and a positive control with 35 g/ton of Denagard (Novartis Animal Health), 400 g/ton of chlortetracycline, and zinc from zinc oxide at 3,000 and 2,000 ppm in Phases 1 and 2, respectively. Experimental diets were fed in 2 phases: Phase 1 from d 0 to 14 and Phase 2 from d 14 to 28. Eight replications of each dietary treatment were used for each experimental design. The first statistical model examined dietary treatment, experimental design, and the design × dietary treatment as fixed factors. With the exception of pens in the CRD having a trend for improved (P 0.11) for any responses variables, indicating that treatment means reacted similarly in each of the experimental designs. In both the CRD and the RCBD, pig weights were increased (P < 0.003) with supplementation of growth promoters on d 14 and 28. Variation of weight within pen remained the same in the CRD from d 0 to 28 at approximately 20% but increased from 3% on d 0 to 10% on d 28 for the RCBD. Dietary addition of growth promoters increased (P < 0.003) ADG and ADFI and improved F/G (P < 0.04) in both the CRD and RCBD from d 0 to 14, with lower P-values for the CRD than the RCBD. From d 14 to 28, the CRD detected an increase (P < 0.001) in ADG and ADFI with dietary addition of growth promoters, and the RCBD detected an increase (P < 0.001) only in ADFI. Over the entire 28-d trial, growth promoters increased (P < 0.001) ADG and ADFI and improved (P < 0.03) F/G in the CRD and increased (P < 0.02) ADG and ADFI in the RCBD. Lower standard errors for the difference were also estimated for ADG and F/G in the CRD than in the RCBD from d 0 to 28. The average corrected relative efficiency for each of the three periods was 2.08 for ADG, 5.05 for ADFI, and 0.80 for F/G. The gain and intake values suggest that the added variation explained by blocks in the RCBD was beneficial for achieving a more reduced estimate of σ2error compared with analyzing that particular data set as a CRD. The variance ratios of the CRD to RCBD from d 0 to 28 depict the different responses well with ADG at 0.67, ADFI at 1.70, and F/G at 0.22. When these ratios were compared with an F-test, they were well below the upper critical limit of 4.60, suggesting that the CRD offered estimates for σ2error similar to those of the RCBD. With the same estimate for σ2error, the non-centrality parameter for each design would be similar, and therefore, the increase in degrees of freedom (DF) for the error term would lead to greater power to detect differences in the CRD. Additional studies are needed to verify these results and determine whether blocking is an efficient use of error DF