Non-Adiabatic Spin Transfer Torque in Real Materials

The motion of simple domain walls and of more complex magnetic textures in the presence of a transport current is described by the Landau-Lifshitz-Slonczewski (LLS) equations. Predictions of the LLS equations depend sensitively on the ratio between the dimensionless material parameter $\beta$ which characterizes non-adiabatic spin-transfer torques and the Gilbert damping parameter $\alpha$. This ratio has been variously estimated to be close to 0, close to 1, and large compared to 1. By identifying $\beta$ as the influence of a transport current on $\alpha$, we derive a concise, explicit and relatively simple expression which relates $\beta$ to the band structure and Bloch state lifetimes of a magnetic metal. Using this expression we demonstrate that intrinsic spin-orbit interactions lead to intra-band contributions to $\beta$ which are often dominant and can be (i) estimated with some confidence and (ii) interpreted using the "breathing Fermi surface" model.Comment: 18 pages, 9 figures; submitted to Phys. Rev.

The effect of stellar-mass black holes on the structural evolution of massive star clusters

We present the results of realistic N-body modelling of massive star clusters in the Magellanic Clouds, aimed at investigating a dynamical origin for the radius-age trend observed in these systems. We find that stellar-mass black holes, formed in the supernova explosions of the most massive cluster stars, can constitute a dynamically important population. If a significant number of black holes are retained (here we assume complete retention), these objects rapidly form a dense core where interactions are common, resulting in the scattering of black holes into the cluster halo, and the ejection of black holes from the cluster. These two processes heat the stellar component, resulting in prolonged core expansion of a magnitude matching the observations. Significant core evolution is also observed in Magellanic Cloud clusters at early times. We find that this does not result from the action of black holes, but can be reproduced by the effects of mass-loss due to rapid stellar evolution in a primordially mass segregated cluster.Comment: Accepted for publication in MNRAS Letters; 2 figures, 1 tabl

On N=8 attractors

We derive and solve the black hole attractor conditions of N=8 supergravity by finding the critical points of the corresponding black hole potential. This is achieved by a simple generalization of the symplectic structure of the special geometry to all extended supergravities with $N>2$. There are two solutions for regular black holes, one for 1/8 BPS ones and one for the non-BPS. We discuss the solutions of the moduli at the horizon for BPS attractors using N=2 language. An interpretation of some of these results in N=2 STU black hole context helps to clarify the general features of the black hole attractors.Comment: 15 page

Regioselective Reactions of Highly Substituted Arynes

The fully regioselective reactivity of four new highly substituted silyl aryl triflate aryne precursors in aryne acyl-alkylation, acyl-alkylation/condensation, and heteroannulation reactions is reported. The application of these more complex arynes provides access to diverse natural product scaffolds and obviates late-stage functionalization of aromatic rings

The Inner Galaxy resolved at IJK using DENIS data

We present the analysis of three colour optical/near-infrared images, in IJK, taken for the DENIS project. The region considered covers 17.4 square deg and lies within |l|<5 deg, |b|<1.5 deg. The adopted methods for deriving photometry and astrometry in these crowded images, together with an analysis of the deficiencies nevertheless remaining, are presented. The numbers of objects extracted in I,J and K are 748000, 851000 and 659000 respectively, to magnitude limits of 17,15 and 13. 80% completeness levels typically fall at magnitudes 16, 13 and 10 respectively, fainter by about 2 magnitudes than the usual DENIS limits due to the crowded nature of these fields. A simple model to describe the disk contribution to the number counts is constructed, and parameters for the dust layer derived. We find that a formal fit of parameters for the dust plane, from these data in limited directions, gives a scalelength and scaleheight of 3.4+-1.0 kpc and 40+-5 pc respectively, and a solar position 14.0+-2.5 pc below the plane. This latter value is likely to be affected by localised dust asymmetries. We convolve a detailed model of the systematic and random errors in the photometry with a simple model of the Galactic disk and dust distribution, to simulate expected colour-magnitude diagrams. These are in good agreement with the observed diagrams, allowing us to isolate those stars from the inner disk and bulge. After correcting for local dust-induced asymmetries, we find evidence for longitude-dependent asymmetries in the distant J and K sources, consistent with the general predictions of some Galactic bar models. We consider complementary L-band observations in a second paper.Comment: 14 pages, 33 figures, LaTeX, MNRAS accepte

Identification of the dominant precession damping mechanism in Fe, Co, and Ni by first-principles calculations

The Landau-Lifshitz equation reliably describes magnetization dynamics using a phenomenological treatment of damping. This paper presents first-principles calculations of the damping parameters for Fe, Co, and Ni that quantitatively agree with existing ferromagnetic resonance measurements. This agreement establishes the dominant damping mechanism for these systems and takes a significant step toward predicting and tailoring the damping constants of new materials.Comment: 4 pages, 1 figur

Topological phase for entangled two-qubit states and the representation of the SO(3)group

We discuss the representation of the $SO(3)$ group by two-qubit maximally entangled states (MES). We analyze the correspondence between $SO(3)$ and the set of two-qubit MES which are experimentally realizable. As a result, we offer a new interpretation of some recently proposed experiments based on MES. Employing the tools of quantum optics we treat in terms of two-qubit MES some classical experiments in neutron interferometry, which showed the $\pi$-phase accrued by a spin-$1/2$ particle precessing in a magnetic field. By so doing, we can analyze the extent to which the recently proposed experiments - and future ones of the same sort - would involve essentially new physical aspects as compared with those performed in the past. We argue that the proposed experiments do extend the possibilities for displaying the double connectedness of $SO(3)$, although for that to be the case it results necessary to map elements of $SU(2)$ onto physical operations acting on two-level systems.Comment: 25 pages, 9 figure

Neonatal White Matter Maturation Is Associated With Infant Language Development

Background: While neonates have no sophisticated language skills, the neural basis for acquiring this function is assumed to already be present at birth. Receptive language is measurable by 6 months of age and meaningful speech production by 10-18 months of age. Fiber tracts supporting language processing include the corpus callosum (CC), which plays a key role in the hemispheric lateralization of language; the left arcuate fasciculus (AF), which is associated with syntactic processing; and the right AF, which plays a role in prosody and semantics. We examined if neonatal maturation of these fiber tracts is associated with receptive language development at 12 months of age. Methods: Diffusion-weighted imaging (DWI) was performed in 86 infants at 26.6 ± 12.2 days post-birth. Receptive language was assessed via the MacArthur-Bates Communicative Development Inventory at 12 months of age. Tract-based fractional anisotropy (FA) was determined using the NA-MIC atlas-based fiber analysis toolkit. Associations between neonatal regional FA, adjusted for gestational age at birth and age at scan, and language development at 12 months of age were tested using ANOVA models. Results: After multiple comparisons correction, higher neonatal FA was positively associated with receptive language at 12 months of age within the genu (p < 0.001), rostrum (p < 0.001), and tapetum (p < 0.001) of the CC and the left fronto-parietal AF (p = 0.008). No significant clusters were found in the right AF. Conclusion: Microstructural development of the CC and the AF in the newborn is associated with receptive language at 12 months of age, demonstrating that interindividual variation in white matter microstructure is relevant for later language development, and indicating that the neural foundation for language processing is laid well ahead of the majority of language acquisition. This suggests that some origins of impaired language development may lie in the intrauterine and potentially neonatal period of life. Understanding how interindividual differences in neonatal brain maturity relate to the acquisition of function, particularly during early development when the brain is in an unparalleled window of plasticity, is key to identifying opportunities for harnessing neuroplasticity in health and disease

d=4 Attractors, Effective Horizon Radius and Fake Supergravity

We consider extremal black hole attractors (both BPS and non-BPS) for N=3 and N=5 supergravity in d=4 space-time dimensions. Attractors for matter-coupled N=3 theory are similar to attractors in N=2 supergravity minimally coupled to Abelian vector multiplets. On the other hand, N=5 attractors are similar to attractors in N=4 pure supergravity, and in such theories only 1\N-BPS non-degenerate solutions exist. All the above mentioned theories have a simple interpretation in the first order (fake supergravity) formalism. Furthermore, such theories do not have a d=5 uplift. Finally we comment on the "duality" relations among the attractor solutions of N\geq2 supergravities sharing the same full bosonic sector.Comment: 1+47 pages, 2 Tables. v2: Eqs. (2.3),(2.4) and Footnote 3 added; minor cosmetic changes; to appear in PR

Orthogonal Synthesis of Indolines and Isoquinolines via Aryne Annulation

Described in this report is the development of two unique methodologies exploiting the reactivity of arynes. Reaction of N-carbamoyl-functionalized enamine derivatives with benzyne affords substituted indolines. An orthogonal reactivity is uncovered when related enamine derivatives are modified as amides, such that isoquinolines are formed as the product of condensation with benzyne. This latter transformation is applied to a concise total synthesis of the opiate alkaloid papaverine