Reversible H_2 Addition across a Nickel−Borane Unit as a Promising Strategy for Catalysis

We report the synthesis and characterization of a series of nickel complexes of the chelating diphosphine-borane ligands ArB(o-Ph_2PC_6H_4)_2 ([^(Ar)DPB^(Ph)]; Ar = Ph, Mes). The [^(Ar)DPB^(Ph)] framework supports pseudo-tetrahedral nickel complexes featuring η^2-B,C coordination from the ligand backbone. For the B-phenyl derivative, the THF adduct [^(Ph)DPB^(Ph)]Ni(THF) has been characterized by X-ray diffraction and features a very short interaction between nickel and the η^2-B,C ligand. For the B-mesityl derivative, the reduced nickel complex [^(Mes)DPB^(Ph)]Ni is isolated as a pseudo-three-coordinate “naked” species that undergoes reversible, nearly thermoneutral oxidative addition of dihydrogen to give a borohydrido-hydride complex of nickel(II) which has been characterized in solution by multinuclear NMR. Furthermore, [^(Mes)DPB^(Ph)]Ni is an efficient catalyst for the hydrogenation of olefin substrates under mild conditions

Diffuse panbronchiolitis in a patient with common variable immunodeficiency: a casual association or a pathogenetic correlation?

Diffuse panbronchiolitis (DPB) is an idiopathic inflammatory disease that seems to have an immunological pathogenesis and that causes a severe progressive suppurative and obstructive respiratory disorder. Common variable immunodeficiency (CVID) is the most common serious primary immunodeficiency and it is often associated with respiratory diseases. Herein, we describe a case of DPB in a 41-year-old man affected by CVID. We examined the patient's lungs, focusing on the characteristics of the inflammatory cells and of the foamy macrophagic nodules typical of DPB. Immunohistochemical typing of the lymphocytic infiltrate showed that B-cells were almost absent, matching the immunological profile of CVID. The case described is the first case reported in the literature of DPB in a patient affected by CVID. Moreover it seems to confirm the correlation between an immunodeficiency status and the development of DPB and provides more information on the accumulation of nodules of foamy macrophages in DPB

Summary of the Very Large Hadron Collider Physics and Detector Subgroup

We summarize the activity of the Very Large Hadron Collider Physics and Detector subgroup during Snowmass 96.Comment: To appear in the Proceedings of the 1996 DPF/DPB Summer Study on New Directions for High-Energy Physics, Snowmass 9

The Role of Developmental Psychobiology in the Unification of Psychology

The interdisciplinary nature of Developmental Psychobiology (DPB) means that it already unifies many perspectives in psychology. DPB explanations of the development of both individual differences and species-typical behaviors include information from cells, tissue, organ systems, family, societal groups, and sociocultural customs to explain the development of both “normal” and “abnormal” behavioral traits. DPB also contextualizes understanding of the developmental processes governing the manifestation of a behavioral trait with understanding of the adaptive functions and phylogenetic history of that trait. Thus, DPB links clinical, cognitive, social, and developmental psychology with physiology, molecular biology, evolution, ecology, and developmental biology to create explanations that are relevant for education, public health, and medicine

Constraining the cometary flux through the asteroid belt during the late heavy bombardment

In the Nice model, the late heavy bombardment (LHB) is related to an orbital instability of giant planets which causes a fast dynamical dispersion of a transneptunian cometary disk. We study effects produced by these hypothetical cometary projectiles on main-belt asteroids. In particular, we want to check whether the observed collisional families provide a lower or an upper limit for the cometary flux during the LHB. We present an updated list of observed asteroid families as identified in the space of synthetic proper elements by the hierarchical clustering method, colour data, albedo data and dynamical considerations and we estimate their physical parameters. We selected 12 families which may be related to the LHB according to their dynamical ages. We then used collisional models and N-body orbital simulations to gain insight into the long-term dynamical evolution of synthetic LHB families over 4 Gyr. We account for the mutual collisions, the physical disruptions of comets, the Yarkovsky/YORP drift, chaotic diffusion, or possible perturbations by the giant-planet migration. Assuming a "standard" size-frequency distribution of primordial comets, we predict the number of families with parent-body sizes D_PB >= 200 km which seems consistent with observations. However, more than 100 asteroid families with D_PB >= 100 km should be created at the same time which are not observed. This discrepancy can be nevertheless explained by the following processes: i) asteroid families are efficiently destroyed by comminution (via collisional cascade), ii) disruptions of comets below some critical perihelion distance (q <~ 1.5 AU) are common. Given the freedom in the cometary-disruption law, we cannot provide stringent limits on the cometary flux, but we can conclude that the observed distribution of asteroid families does not contradict with a cometary LHB.Comment: accepted in Astronomy and Astrophysic

Neutron-19C{}^{19}\mathrm{C} scattering: Towards including realistic interactions

Low-energy neutron-${}^{19}$C scattering is studied in the three-body $n + n + {}^{18}$C model using a realistic $nn$ potential and a number of shallow and deep $n$-${}^{18}$C potentials, the latter supporting deeply-bound Pauli-forbidden states that are projected out. Exact Faddeev-type three-body scattering equations for transition operators including two- and three-body forces are solved in the momentum-space partial-wave framework. Phase shift, inelasticity parameter, and cross sections are calculated. For the elastic $n$-${}^{19}$C scattering in the $J^\Pi=0^+$ partial wave the signatures of the Efimov physics, i.e., the pole in the effective-range expansion and the elastic cross section minimum, are confirmed for both shallow and deep models, but with clear quantitative differences between them, indicating the importance of a proper treatment of deeply-bound Pauli-forbidden states. In contrast, the inelasticity parameter is mostly correlated with the asymptotic normalization coefficient of the ${}^{19}$C bound state. Finally, in the regime of very weak ${}^{19}$C binding and near-threshold (bound or virtual) excited ${}^{20}$C state the standard Efimovian behaviour of the $n$-${}^{19}$C scattering length and cross section was confirmed, resolving the discrepancies between earlier studies by other authors [I. Mazumdar, A. R. P. Rau, V. S. Bhasin, Phys. Rev. Lett. 97 (2006) 062503; M. T. Yamashita, T. Frederico, L. Tomio, Phys. Rev. Lett. 99 (2007) 269201].Comment: 6 figure

Theoretical investigation of finite size effects at DNA melting

We investigated how the finiteness of the length of the sequence affects the phase transition that takes place at DNA melting temperature. For this purpose, we modified the Transfer Integral method to adapt it to the calculation of both extensive (partition function, entropy, specific heat, etc) and non-extensive (order parameter and correlation length) thermodynamic quantities of finite sequences with open boundary conditions, and applied the modified procedure to two different dynamical models. We showed that rounding of the transition clearly takes place when the length of the sequence is decreased. We also performed a finite-size scaling analysis of the two models and showed that the singular part of the free energy can indeed be expressed in terms of an homogeneous function. However, both the correlation length and the average separation between paired bases diverge at the melting transition, so that it is no longer clear to which of these two quantities the length of the system should be compared. Moreover, Josephson's identity is satisfied for none of the investigated models, so that the derivation of the characteristic exponents which appear, for example, in the expression of the specific heat, requires some care

Observation of a subgap density of states in superconductor-normal metal bilayers in the Cooper limit

We present transport and tunneling measurements of Pb-Ag bilayers with thicknesses, $d_{Pb}$ and $d_{Ag}$, that are much less than the superconducting coherence length. The transition temperature, $T_c$, and energy gap, $\Delta$, in the tunneling Density of States (DOS) decrease exponentially with $d_{Ag}$ at fixed $d_{Pb}$. Simultaneously, a DOS that increases linearly from the Fermi energy grows and fills nearly 40% of the gap as $T_c$ is 1/10 of $T_c$ of bulk Pb. This behavior suggests that a growing fraction of quasiparticles decouple from the superconductor as $T_c$ goes to 0. The linear dependence is consistent with the quasiparticles becoming trapped on integrable trajectories in the metal layer.Comment: 5 pages and 4 figures. This version is just the same as the old version except that we try to cut the unnecessary white space in the figures and make the whole paper look more compac