On lower ramification subgroups and canonical subgroups

Let p be a rational prime, k be a perfect field of characteristic p and K be a finite totally ramified extension of the fraction field of the Witt ring of k. Let G be a finite flat commutative group scheme over O_K killed by some p-power. In this paper, we prove a description of ramification subgroups of G via the Breuil-Kisin classification, generalizing the author's previous result on the case where G is killed by p>2. As an application, we also prove that the higher canonical subgroup of a level n truncated Barsotti-Tate group G over O_K coincides with lower ramification subgroups of G if the Hodge height of G is less than (p-1)/p^n.Comment: 23 pages; Theorem 1.3 adde

Vibrational thermodynamics: coupling of chemical order and size effects

The effects of chemical order on the vibrational entropy have been studied using first-principles and semi-empirical potential methods. Pseudopotential calculations on the Pd_3V system show that the vibrational entropy decreases by 0.07k_B upon disordering in the high-temperature limit. The decrease in entropy contradicts what would be expected from simple bonding arguments, but can be explained by the influence of size effects on the vibrations. In addition, the embedded-atom method is used to study the effects of local environments on the entropic contributions of individual Ni and Al atoms in Ni_3Al. It is found that increasing numbers of Al nearest neighbours decreases the vibrational entropy of an atom when relaxations are not included. When the system is relaxed, this effect disappears, and the local entropy is approximately uniform with increasing number of Al neighbours. These results are explained in terms of the large size mismatch between Ni and Al. In addition, a local cluster expansion is used to show how the relaxations increase the importance of long-range and multisite interactions

CM cycles on Shimura curves, and p-adic L-functions

Let f be a modular form of weight k>=2 and level N, let K be a quadratic imaginary field, and assume that there is a prime p exactly dividing N. Under certain arithmetic conditions on the level and the field K, one can attach to this data a p-adic L-function L_p(f,K,s), as done by Bertolini-Darmon-Iovita-Spiess. In the case of p being inert in K, this analytic function of a p-adic variable s vanishes in the critical range s=1,...,k-1, and therefore one is interested in the values of its derivative in this range. We construct, for k>=4, a Chow motive endowed with a distinguished collection of algebraic cycles which encode these values, via the p-adic Abel-Jacobi map. Our main result generalizes the result obtained by Iovita-Spiess, which gives a similar formula for the central value s=k/2. Even in this case our construction is different from the one found by Iovita-Spiess

Shell and glass beads from the tombs of Kindoki, Mbanza Nsundi, Lower Congo

The ancient Kingdom of Kongo originated in Central Africa in the 14th century. In the 15th century, the Portuguese organized tight contacts with the Bakongo. From then on European goods gained new significance in the local culture and even found their way into funerary rites. Among the most important grave goods in the Kingdom of Kongo were shell and glass beads. They occur in many tombs and symbolize wealth, status, or femininity. At the burial site of Kindoki, linked with the former capital of Kongo’s Nsundi province, a great number of shell and glass beads were found together with symbols of power in tombs attributed primarily to the first half of the 19th century. Determining the origin of these beads and their use in the Kongo Kingdom leads to interesting insights into the social and economic organization of the old Bakongo society, their beliefs, and the symbolic meaning of the beads

Dieudonne crystals and Wach modules for p-divisible fgroups

Let $k$ be a perfect field of characteristic $p>2$ and $K$ an extension of $F=\mathrm{Frac} W(k)$ contained in some $F(\mu_{p^r})$. Using crystalline Dieudonn\'e theory, we provide a classification of $p$-divisible groups over $\mathscr{O}_K$ in terms of finite height $(\varphi,\Gamma)$-modules over $\mathfrak{S}:=W(k)[[u]]$. Although such a classification is a consequence of (a special case of) the theory of Kisin--Ren, our construction gives an independent proof and allows us to recover the Dieudonn\'e crystal of a $p$-divisible group from the Wach module associated to its Tate module by Berger--Breuil or by Kisin--Ren

One Dimensional Oxygen Ordering in YBa2Cu3O(7-delta)

A model consisting of oxygen-occupied and -vacant chains is considered, with repulsive first and second nearest-neighbor interactions V1 and V2, respectively. The statistical mechanics and the diffraction spectrum of the model is solved exactly and analytically with the only assumption V1 >> V2. At temperatures T ~ V1 only a broad maximum at (1/2,0,0) is present, while for ABS(delta - 1/2) > 1/14 at low enough T, the peak splits into two. The simple expression for the diffraction intensity obtained for T << V1 represents in a more compact form previous results of Khachaturyan and Morris[1],extends them to all delta and T/V2 and leads to a good agreement with experiment. [1] A.G.Khachaturyan and J.W.Morris, Jr., Phys.Rev.Lett. 64,76(1990)Comment: 13 pages,Revtex,3 figures available upon request but can be plotted using simple analytical functions,CNEA-CAB 92/04

Asteroseismology of close binary stars

In this review paper, we summarise the goals of asteroseismic studies of close binary stars. We first briefly recall the basic principles of asteroseismology, and highlight how the binarity of a star can be an asset, but also a complication, for the interpretation of the stellar oscillations. We discuss a few sample studies of pulsations in close binaries and summarise some case studies. This leads us to conclude that asteroseismology of close binaries is a challenging field of research, but with large potential for the improvement of current stellar structure theory. Finally, we highlight the best observing strategy to make efficient progress in the near future.Comment: Invited Review Talk at S240 of the IAU: To appear in: Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, Eds W. Hartkopf, E. Guinan, P. Harmanec. 10 pages, 4 figure

CO oxidation on Pd(100) at technologically relevant pressure conditions: A first-principles kinetic Monte Carlo study

The possible importance of oxide formation for the catalytic activity of transition metals in heterogenous oxidation catalysis has evoked a lively discussion over the recent years. On the more noble transition metals (like Pd, Pt or Ag) the low stability of the common bulk oxides suggests primarily sub-nanometer thin oxide films, so-called surface oxides, as potential candidates that may be stabilized under gas phase conditions representative of technological oxidation catalysis. We address this issue for the Pd(100) model catalyst surface with first-principles kinetic Monte Carlo (kMC) simulations that assess the stability of the well-characterized (sqrt{5} x sqrt{5})R27 surface oxide during steady-state CO oxidation. Our results show that at ambient pressure conditions the surface oxide is stabilized at the surface up to CO:O2 partial pressure ratios just around the catalytically most relevant stoichiometric feeds (p(CO):p(O2) = 2:1). The precise value depends sensitively on temperature, so that both local pressure and temperature fluctuations may induce a continuous formation and decomposition of oxidic phases during steady-state operation under ambient stoichiometric conditions.Comment: 13 pages including 5 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm