Propagation of Exchange Bias in CoFe/FeMn/CoFe Trilayers

CoFe/FeMn, FeMn/CoFe bilayers and CoFe/FeMn/CoFe trilayers were grown in magnetic field and at room temperature. The exchange bias field $H_{eb}$ depends strongly on the order of depositions and is much higher at CoFe/FeMn than at FeMn/CoFe interfaces. By combining the two bilayer structures into symmetric CoFe/FeMn($t_\mathrm{FeMn}$)/CoFe trilayers, $H_{eb}^t$ and $H_{eb}^b$ of the top and bottom CoFe layers, respectively, are both enhanced. Reducing $t_\mathrm{FeMn}$ of the trilayers also results in enhancements of both $H_{eb}^b$ and $H_{eb}^t$. These results evidence the propagation of exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by the FeMn antiferromagnetic order

Dynamics of Diblock Copolymers in Dilute Solutions

We consider the dynamics of freely translating and rotating diblock (A-B), Gaussian copolymers, in dilute solutions. Using the multiple scattering technique, we have computed the diffusion and the friction coefficients D_AB and Zeta_AB, and the change Eta_AB in the viscosity of the solution as functions of x = N_A/N and t = l_B/l_A, where N_A, N are the number of segments of the A block and of the whole copolymer, respectively, and l_A, l_B are the Kuhn lengths of the A and B blocks. Specific regimes that maximize the efficiency of separation of copolymers with distinct "t" values, have been identified.Comment: 20 pages Revtex, 7 eps figures, needs epsf.tex and amssymb.sty, submitted to Macromolecule

Mechanisms of MR/N024524/1Scarless Repair at Time of Menstruation: Insights From Mouse Models

The human endometrium is a remarkable tissue which may experience up to 400 cycles of hormone-driven proliferation, differentiation and breakdown during a woman's reproductive lifetime. During menstruation, when the luminal portion of tissue breaks down, it resembles a bloody wound with piecemeal shedding, exposure of underlying stroma and a strong inflammatory reaction. In the absence of pathology within a few days the integrity of the tissue is restored without formation of a scar and the endometrium is able to respond appropriately to subsequent endocrine signals in preparation for establishment of pregnancy if fertilization occurs. Understanding mechanisms regulating scarless repair of the endometrium is important both for design of therapies which can treat conditions where this is aberrant (heavy menstrual bleeding, fibroids, endometriosis, Asherman's syndrome) as well as to provide new information that might allow us to reduce fibrosis and scar formation in other tissues. Menstruation only occurs naturally in species that exhibit spontaneous stromal cell decidualization during the fertile cycle such as primates (including women) and the Spiny mouse. To take advantage of genetic models and detailed time course analysis, mouse models of endometrial shedding/repair involving hormonal manipulation, artificial induction of decidualization and hormone withdrawal have been developed and refined. These models are useful in modeling dynamic changes across the time course of repair and have recapitulated key features of endometrial repair in women including local hypoxia and immune cell recruitment. In this review we will consider the evidence that scarless repair of endometrial tissue involves changes in stromal cell function including mesenchyme to epithelial transition, epithelial cell proliferation and multiple populations of immune cells. Processes contributing to endometrial fibrosis (Asherman's syndrome) as well as scarless repair of other tissues including skin and oral mucosa are compared to that of menstrual repair

Hydrogen atom in phase space. The Kirkwood-Rihaczek representation

We present a phase-space representation of the hydrogen atom using the Kirkwood-Rikaczek distribution function. This distribution allows us to obtain analytical results, which is quite unique because an exact analytical form of the Wigner functions corresponding to the atom states is not known. We show how the Kirkwood-Rihaczek distribution reflects properties of the hydrogen atom wave functions in position and momentum representations.Comment: 5 pages (and 5 figures

Long-range forces between two excited mercury atoms and associative ionization

The long-range quadrupole-quadrupole ($\sim R^{-5}$) and leading dispersion ($\sim R^{-6}$) interactions between all pairs of excited Hg($6s6p$) $^3P_0$, $^3P_1$, $^3P_2$, and $^1P_1$ atoms are determined. The quadrupole moments are calculated using the {\it ab initio} relativistic configuration-interaction method coupled with many-body perturbation theory. The van der Waals coefficients are approximated using previously calculated static polarizabilities and expressions for the dispersion energy that are validated with similar systems. The long-range interactions are critical for associative ionization in thermal and cold collisions, and are found to be quite different for different pairs of interacting states. Based on this knowledge and the short-range parts of previously calculated potential curves, improved estimates of the chemi-ionization cross sections are obtained.Comment: accepted in Phys Rev

The intermittent behavior and hierarchical clustering of the cosmic mass field

The hierarchical clustering model of the cosmic mass field is examined in the context of intermittency. We show that the mass field satisfying the correlation hierarchy $\xi_n\simeq Q_n(\xi_2)^{n-1}$ is intermittent if $\kappa < d$, where $d$ is the dimension of the field, and $\kappa$ is the power-law index of the non-linear power spectrum in the discrete wavelet transform (DWT) representation. We also find that a field with singular clustering can be described by hierarchical clustering models with scale-dependent coefficients $Q_n$ and that this scale-dependence is completely determined by the intermittent exponent and $\kappa$. Moreover, the singular exponents of a field can be calculated by the asymptotic behavior of $Q_n$ when $n$ is large. Applying this result to the transmitted flux of HS1700 Ly$\alpha$ forests, we find that the underlying mass field of the Ly$\alpha$ forests is significantly intermittent. On physical scales less than about 2.0 h$^{-1}$ Mpc, the observed intermittent behavior is qualitatively different from the prediction of the hierarchical clustering with constant $Q_n$. The observations, however, do show the existence of an asymptotic value for the singular exponents. Therefore, the mass field can be described by the hierarchical clustering model with scale-dependent $Q_n$. The singular exponent indicates that the cosmic mass field at redshift $\sim 2$ is weakly singular at least on physical scales as small as 10 h$^{-1}$ kpc.Comment: AAS Latex file, 33 pages,5 figures included, accepted for publication in Ap

Superoxide dismutase downregulation in osteoarthritis progression and end-stage disease

Oxidative stress is proposed as an important factor in osteoarthritis (OA). To investigate the expression of the three superoxide dismutase (SOD) antioxidant enzymes in OA. SOD expression was determined by real-time PCR and immunohistochemistry using human femoral head cartilage. SOD2 expression in Dunkin–Hartley guinea pig knee articular cartilage was determined by immunohistochemistry. The DNA methylation status of the SOD2 promoter was determined using bisulphite sequencing. RNA interference was used to determine the consequence of SOD2 depletion on the levels of reactive oxygen species (ROS) using MitoSOX and collagenases, matrix metalloproteinase 1 (MMP-1) and MMP-13, gene expression. All three SOD were abundantly expressed in human cartilage but were markedly downregulated in end-stage OA cartilage, especially SOD2. In the Dunkin–Hartley guinea pig spontaneous OA model, SOD2 expression was decreased in the medial tibial condyle cartilage before, and after, the development of OA-like lesions. The SOD2 promoter had significant DNA methylation alterations in OA cartilage. Depletion of SOD2 in chondrocytes increased ROS but decreased collagenase expression. This is the first comprehensive expression profile of all SOD genes in cartilage and, importantly, using an animal model, it has been shown that a reduction in SOD2 is associated with the earliest stages of OA. A decrease in SOD2 was found to be associated with an increase in ROS but a reduction of collagenase gene expression, demonstrating the complexities of ROS function

Why do ultrasoft repulsive particles cluster and crystallize? Analytical results from density functional theory

We demonstrate the accuracy of the hypernetted chain closure and of the mean-field approximation for the calculation of the fluid-state properties of systems interacting by means of bounded and positive-definite pair potentials with oscillating Fourier transforms. Subsequently, we prove the validity of a bilinear, random-phase density functional for arbitrary inhomogeneous phases of the same systems. On the basis of this functional, we calculate analytically the freezing parameters of the latter. We demonstrate explicitly that the stable crystals feature a lattice constant that is independent of density and whose value is dictated by the position of the negative minimum of the Fourier transform of the pair potential. This property is equivalent with the existence of clusters, whose population scales proportionally to the density. We establish that regardless of the form of the interaction potential and of the location on the freezing line, all cluster crystals have a universal Lindemann ratio L = 0.189 at freezing. We further make an explicit link between the aforementioned density functional and the harmonic theory of crystals. This allows us to establish an equivalence between the emergence of clusters and the existence of negative Fourier components of the interaction potential. Finally, we make a connection between the class of models at hand and the system of infinite-dimensional hard spheres, when the limits of interaction steepness and space dimension are both taken to infinity in a particularly described fashion.Comment: 19 pages, 5 figures, submitted to J. Chem. Phys; new version: minor changes in structure of pape

The role of marine reserves in achieving sustainable fisheries (One contribution of 15 to a Theme Issue 'Fisheries: a Future?')

Many fishery management tools currently in use have conservation value. They are designed to maintain stocks of commercially important species above target levels. However, their limitations are evident from continuing declines in fish stocks throughout the world. We make the case that to reverse fishery declines, safeguard marine life and sustain ecosystem processes, extensive marine reserves that are off limits to fishing must become part of the management strategy. Marine reserves should be incorporated into modern fishery management because they can achieve many things that conventional tools cannot. Only complete and permanent protection from fishing can protect the most sensitive habitats and vulnerable species. Only reserves will allow the development of natural, extended age structures of target species, maintain their genetic variability and prevent deleterious evolutionary change from the effects of fishing. Species with natural age structures will sustain higher rates of reproduction and will be more resilient to environmental variability. Higher stock levels maintained by reserves will provide insurance against management failure, including risk-prone quota setting, provided the broader conservation role of reserves is firmly established and legislatively protected. Fishery management measures outside protected areas are necessary to complement the protection offered by marine reserves, but cannot substitute for it