High-transition-temperature superconductivity in the absence of the magnetic-resonance mode

The fundamental mechanism that gives rise to high-transition-temperature (high-Tc) superconductivity in the copper oxide materials has been debated since the discovery of the phenomenon. Recent work has focussed on a sharp 'kink' in the kinetic energy spectra of the electrons as a possible signature of the force that creates the superconducting state. The kink has been related to a magnetic resonance and also to phonons. Here we report that infrared spectra of Bi2Sr2CaCu2O(8+d), (Bi-2212) show that this sharp feature can be separated from a broad background and, interestingly, weakens with doping before disappearing completely at a critical doping level of 0.23 holes per copper atom. Superconductivity is still strong in terms of the transition temperature (Tc approx 55 K), so our results rule out both the magnetic resonance peak and phonons as the principal cause of high-Tc superconductivity. The broad background, on the other hand, is a universal property of the copper oxygen plane and a good candidate for the 'glue' that binds the electrons.Comment: 4 pages, 3 figure

Two-Item Sentence Comprehension by a Dog (Canis familiaris)

Syntax use by non-human animals remains a controversial issue. We present here evidence that a dog may respond to verbal requests composed of two independent terms, one referring to an object and the other to an action to be performed relative to the object. A female mongrel dog, Sofia, was initially trained to respond to action (point and fetch) and object (ball, key, stick, bottle and bear) terms which were then presented as simultaneous, combinatorial requests (e.g. ball fetch, stick point). Sofia successfully responded to object-action requests presented as single sentences, and was able to flexibly generalize her performance across different contexts. These results provide empirical evidence that dogs are able to extract the information contained in complex messages and to integrate it in directed performance, an ability which is shared with other linguistically trained animals and may represent a forerunner of syntactic functioning

The pseudogap: friend or foe of high Tc?

Although nineteen years have passed since the discovery of high temperature superconductivity, there is still no consensus on its physical origin. This is in large part because of a lack of understanding of the state of matter out of which the superconductivity arises. In optimally and underdoped materials, this state exhibits a pseudogap at temperatures large compared to the superconducting transition temperature. Although discovered only three years after the pioneering work of Bednorz and Muller, the physical origin of this pseudogap behavior and whether it constitutes a distinct phase of matter is still shrouded in mystery. In the summer of 2004, a band of physicists gathered for five weeks at the Aspen Center for Physics to discuss the pseudogap. In this perspective, we would like to summarize some of the results presented there and discuss its importance in the context of strongly correlated electron systems.Comment: expanded version, 20 pages, 11 figures, to be published, Advances in Physic

Vocabulary Learning in a Yorkshire Terrier: Slow Mapping of Spoken Words

Rapid vocabulary learning in children has been attributed to “fast mapping”, with new words often claimed to be learned through a single presentation. As reported in 2004 in Science a border collie (Rico) not only learned to identify more than 200 words, but fast mapped the new words, remembering meanings after just one presentation. Our research tests the fast mapping interpretation of the Science paper based on Rico's results, while extending the demonstration of large vocabulary recognition to a lap dog. We tested a Yorkshire terrier (Bailey) with the same procedures as Rico, illustrating that Bailey accurately retrieved randomly selected toys from a set of 117 on voice command of the owner. Second we tested her retrieval based on two additional voices, one male, one female, with different accents that had never been involved in her training, again showing she was capable of recognition by voice command. Third, we did both exclusion-based training of new items (toys she had never seen before with names she had never heard before) embedded in a set of known items, with subsequent retention tests designed as in the Rico experiment. After Bailey succeeded on exclusion and retention tests, a crucial evaluation of true mapping tested items previously successfully retrieved in exclusion and retention, but now pitted against each other in a two-choice task. Bailey failed on the true mapping task repeatedly, illustrating that the claim of fast mapping in Rico had not been proven, because no true mapping task had ever been conducted with him. It appears that the task called retention in the Rico study only demonstrated success in retrieval by a process of extended exclusion

Is caching the key to exclusion in corvids? The case of carrion crows (Corvus corone corone)

Recently, two corvid species, food-caching ravens and non-caching jackdaws, have been tested in an exclusion performance (EP) task. While the ravens chose by exclusion, the jackdaws did not. Thus, foraging behaviour may affect EP abilities. To investigate this possibility, another food-caching corvid species, the carrion crow (Corvus corone corone), was tested in the same exclusion task. We hid food under one of two cups and subsequently lifted either both cups, or the baited or the un-baited cup. The crows were significantly above chance when both cups were lifted or when only the baited cup was lifted. When the empty cup was lifted, we found considerable inter-individual variation, with some birds having a significant preference for the un-baited but manipulated cup. In a follow-up task, we always provided the birds with the full information about the food location, but manipulated in which order they saw the hiding or the removal of food. Interestingly, they strongly preferred the cup which was manipulated last, even if it did not contain any food. Therefore, we repeated the first experiment but controlled for the movement of the cups. In this case, more crows found the food reliably in the un-baited condition. We conclude that carrion crows are able to choose by exclusion, but local enhancement has a strong influence on their performance and may overshadow potential inferential abilities. However, these findings support the hypothesis that caching might be a key to exclusion in corvids

Hawk Eyes II: Diurnal Raptors Differ in Head Movement Strategies When Scanning from Perches

Background Relatively little is known about the degree of inter-specific variability in visual scanning strategies in species with laterally placed eyes (e.g., birds). This is relevant because many species detect prey while perching; therefore, head movement behavior may be an indicator of prey detection rate, a central parameter in foraging models. We studied head movement strategies in three diurnal raptors belonging to the Accipitridae and Falconidae families. Methodology/Principal Findings We used behavioral recording of individuals under field and captive conditions to calculate the rate of two types of head movements and the interval between consecutive head movements. Cooper\u27s Hawks had the highest rate of regular head movements, which can facilitate tracking prey items in the visually cluttered environment they inhabit (e.g., forested habitats). On the other hand, Red-tailed Hawks showed long intervals between consecutive head movements, which is consistent with prey searching in less visually obstructed environments (e.g., open habitats) and with detecting prey movement from a distance with their central foveae. Finally, American Kestrels have the highest rates of translational head movements (vertical or frontal displacements of the head keeping the bill in the same direction), which have been associated with depth perception through motion parallax. Higher translational head movement rates may be a strategy to compensate for the reduced degree of eye movement of this species. Conclusions Cooper\u27s Hawks, Red-tailed Hawks, and American Kestrels use both regular and translational head movements, but to different extents. We conclude that these diurnal raptors have species-specific strategies to gather visual information while perching. These strategies may optimize prey search and detection with different visual systems in habitat types with different degrees of visual obstruction

Array algorithms for H^2 and H^∞ estimation

Currently, the preferred method for implementing H^2 estimation algorithms is what is called the array form, and includes two main families: square-root array algorithms, that are typically more stable than conventional ones, and fast array algorithms, which, when the system is time-invariant, typically offer an order of magnitude reduction in the computational effort. Using our recent observation that H^∞ filtering coincides with Kalman filtering in Krein space, in this chapter we develop array algorithms for H^∞ filtering. These can be regarded as natural generalizations of their H^2 counterparts, and involve propagating the indefinite square roots of the quantities of interest. The H^∞ square-root and fast array algorithms both have the interesting feature that one does not need to explicitly check for the positivity conditions required for the existence of H^∞ filters. These conditions are built into the algorithms themselves so that an H^∞ estimator of the desired level exists if, and only if, the algorithms can be executed. However, since H^∞ square-root algorithms predominantly use J-unitary transformations, rather than the unitary transformations required in the H^2 case, further investigation is needed to determine the numerical behavior of such algorithms

Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states

In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced1. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within CuO2 unit cell. We analyze spectroscopic-imaging scanning tunneling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8+{\delta} and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90o -rotational symmetry within every CuO2 unit cell.Comment: See the Nature website for the published version. High-resolution version of figures, supplementary information and supplementary movies are available at http://eunahkim.ccmr.cornell.edu/KimGroup/highlights.htm

Nanofibrous Scaffolds Incorporating PDGF-BB Microspheres Induce Chemokine Expression and Tissue Neogenesis In Vivo

Platelet-derived growth factor (PDGF) exerts multiple cellular effects that stimulate wound repair in multiple tissues. However, a major obstacle for its successful clinical application is the delivery system, which ultimately controls the in vivo release rate of PDGF. Polylactic-co-glycolic acid (PLGA) microspheres (MS) in nanofibrous scaffolds (NFS) have been shown to control the release of rhPDGF-BB in vitro. In order to investigate the effects of rhPDGF-BB release from MS in NFS on gene expression and enhancement of soft tissue engineering, rhPDGF-BB was incorporated into differing molecular weight (MW) polymeric MS. By controlling the MW of the MS over a range of 6.5 KDa–64 KDa, release rates of PDGF can be regulated over periods of weeks to months in vitro. The NFS-MS scaffolds were divided into multiple groups based on MS release characteristics and PDGF concentration ranging from 2.5–25.0 µg and evaluated in vivo in a soft tissue wound repair model in the dorsa of rats. At 3, 7, 14 and 21 days post-implantation, the scaffold implants were harvested followed by assessments of cell penetration, vasculogenesis and tissue neogenesis. Gene expression profiles using cDNA microarrays were performed on the PDGF-releasing NFS. The percentage of tissue invasion into MS-containing NFS at 7 days was higher in the PDGF groups when compared to controls. Blood vessel number in the HMW groups containing either 2.5 or 25 µg PDGF was increased above those of other groups at 7d (p<0.01). Results from cDNA array showed that PDGF strongly enhanced in vivo gene expression of the CXC chemokine family members such as CXCL1, CXCL2 and CXCL5. Thus, sustained release of rhPDGF-BB, controlled by slow-releasing MS associated with the NFS delivery system, enhanced cell migration and angiogenesis in vivo, and may be related to an induced expression of chemokine-related genes. This approach offers a technology to accurately control growth factor release to promote soft tissue engineering in vivo

The Feasibility, Appropriateness, Meaningfulness, and Effectiveness of Parenting and Family Support Programs Delivered in the Criminal Justice System: A Systematic Review

Children whose parents are involved in the criminal justice system (CJS) are at increased risk of developing social, emotional, and behavioural difficulties and are more likely than their peers to become involved in the CJS themselves. Parenting behaviour and parent-child relationships have the potential to affect children’s outcomes with positive parenting practices having the potential to moderate some of the negative outcomes associated with parental involvement in the CJS. However, many parents in the CJS may lack appropriate role models to support the development of positive parenting beliefs and practices. Parenting programs offer an opportunity for parents to enhance their parenting knowledge and behaviours and improve relationships with children. Quantitative and qualitative evidence pertaining to the implementation and effectiveness of parenting programs delivered in the CJS was included. Five databases were searched and a total of 1145 articles were identified of which 29 met the review inclusion criteria. Overall, programs were found to significantly improve parenting attitudes; however, evidence of wider effects is limited. Additionally, the findings indicate that parenting programs can be meaningful for parents. Despite this, a number of challenges for implementation were found including the transient nature of the prison population and a lack of parent-child contact. Based on these findings, recommendations for the future development and delivery of programs are discussed