Zigzag domain wall mediated reversal in antiferromagnetically coupled layers

The Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between two magnetic layers leads to many important technological applications. Here, the interaction between changing antiferromagnetic RKKY coupling and domain structure is studied in a sample consisting of two 5 nm thick CoFeB layers separated by a wedge of Cu up to 4 nm thick. Magnetic reversal occurs via the propagation of a zigzag domain wall front along the wedge. The modification of domain patterns created in the reversal of a coupled layers in the presence of antiferromagnetic RKKY coupling and coupling gradients is demonstrated. Firstly, the coupling leads to a smaller amplitude of the zigzag wall, which is aligned perpendicular to the easy axis, followed by elongation of the walls at higher coupling strength. The antiferromagnetic RKKY coupling, while not strong enough to cause antiparallel alignment of the layers, is argued to lead to coupling between the spins in the domain walls in the two layers, lowering their energy and driving the reversal behavior of the film

Multi-bit operations in vertical spintronic shift registers

Spintronic devices have in general demonstrated the feasibility of non-volatile memory storage and simple Boolean logic operations. Modern microprocessors have one further frequently used digital operation: bit-wise operations on multiple bits simultaneously. Such operations are important for binary multiplication and division and in efficient microprocessor architectures such as reduced instruction set computing (RISC). In this paper we show a four-stage vertical serial shift register made from RKKY coupled ultrathin (0.9 nm) perpendicularly magnetised layers into which a 3-bit data word is injected. The entire four stage shift register occupies a total length (thickness) of only 16 nm. We show how under the action of an externally applied magnetic field bits can be shifted together as a word and then manipulated individually, including being brought together to perform logic operations. This is one of the highest level demonstrations of logic operation ever performed on data in the magnetic state and brings closer the possibility of ultrahigh density all-magnetic microprocessors

Conformational Closure of the Catalytic Site of Human CD38 Induced by Calcium

First identified on the surface of lymphoids as a type II transmembrane protein, CD38 has now been established to have dual functions not only as a receptor but also as a multifunctional enzyme, catalyzing the synthesis of and hydrolysis of a general calcium messenger molecule, cyclic ADP-ribose (cADPR). The receptorial functions of CD38 include the induction of cell adhesion, differentiation, apoptosis, and cytokine production upon antibody ligation. Here we determined the crystal structure of calcium-loaded human CD38 at 1.45 Å resolution which reveals that CD38 undergoes dramatic structural changes to an inhibited conformation in the presence of calcium. The structural changes are highly localized and occur in only two regions. The first region is part of the active site and consists of residues 121-141. In the presence of calcium, W125 moves 5 Å into the active site and forms hydrophobic interactions with W189. The movement closes the active site pocket and reduces entry of substrates, resulting in inhibition of the enzymatic activity. The structural role of calcium in inducing these conformational changes is readily visualized in the crystal structure. The other region that undergoes calcium-induced changes is at the receptor region, where a highly ordered helix is unraveled to a random coil. The results suggest a novel conformational coupling mechanism, whereby protein interaction targeted at the receptor region can effectively regulate the enzymatic activity of CD38. © 2008 American Chemical Society.link_to_subscribed_fulltex

Inferring Public and Private Information from Trades and Quotes

We propose a new model that uses nonsynchronous, ultra-high frequency data to analyze the sequential impact of trades and quotes on the price process. Private information is related to the impact of trades and public information to the impact of quotes. The model is extended to include various other factors that affect public and private information. For 20 active Nasdaq stocks, private information causes, on average, 9.43% of daily stock price movements. Additionally, quotes are more informative when (1) many dealers set the best price and (2) traditional market makers rather than Electronic Communication Networks set the best price. Copyright 2006 by the Eastern Finance Association.

Excess Volatility and UK Investment Trusts

The issue of whether or not asset prices are more volatile than the underlying fundamentals is an empirical question with implications for market efficiency. Recent research suggests that the volatility of closed end fund returns in the USA is significantly higher than the returns on assets held by the funds. This has been attributed to noise trading as closed-end fund shares are predominantly held by individual investors. This study demonstrates that UK investment trust returns exhibit similar excess volatility in spite of the prevalence of institutional investors. However, big investment trusts in terms of market capitalisation show greater excess volatility than small trusts. Although most of the excess volatility appears to be idiosyncratic, investor sentiment index is the most important variable associated with residual returns. Copyright Blackwell Publishers Ltd, 2005.