Electronic structure and magnetic properties of Gd-doped and Eu-rich EuO

The effects of Gd doping and O vacancies on the magnetic interaction and Curie temperature of EuO are studied using first-principles calculations. Linear response calculations in the virtual crystal approximation show a broad maximum in the Curie temperature as a function of doping, which results from the combination of the saturating contribution from indirect exchange and a decreasing contribution from the f-d hopping mechanism. Non-Heisenberg interaction at low doping levels and its effect on the Curie temperature are examined. The electronic structure of a substitutional Gd and of an O vacancy in EuO are evaluated. When the 4f spins are disordered, the impurity state goes from single to double occupation, but correlated bound magnetic polarons are not ruled out. At higher vacancy concentrations typical for Eu-rich EuO films, the impurity states broaden into bands and remain partially filled. To go beyond the homogeneous doping picture, magnetostructural cluster expansions are constructed, which describe the modified exchange parameters near Gd dopants or O vacancies. Thermodynamic properties are studied using Monte Carlo simulations. The Curie temperature for Gd-doped EuO agrees with the results of the virtual crystal approximation and shows a maximum of about 150 K. At 3.125% vacancy concentration the Curie temperature increases to 120 K, consistent with experimental data for Eu-rich film samples.Comment: 15 pages, 13 figures, under review in Physical Review

SUMOylation of NaV1.2 channels mediates the early response to acute hypoxia in central neurons.

The mechanism for the earliest response of central neurons to hypoxia-an increase in voltage-gated sodium current (INa)-has been unknown. Here, we show that hypoxia activates the Small Ubiquitin-like Modifier (SUMO) pathway in rat cerebellar granule neurons (CGN) and that SUMOylation of NaV1.2 channels increases INa. The time-course for SUMOylation of single NaV1.2 channels at the cell surface and changes in INa coincide, and both are prevented by mutation of NaV1.2-Lys38 or application of a deSUMOylating enzyme. Within 40 s, hypoxia-induced linkage of SUMO1 to the channels is complete, shifting the voltage-dependence of channel activation so that depolarizing steps evoke larger sodium currents. Given the recognized role of INa in hypoxic brain damage, the SUMO pathway and NaV1.2 are identified as potential targets for neuroprotective interventions

Enhanced relativistic harmonics by electron nanobunching

It is shown that when an few-cycle, relativistically intense, p-polarized laser pulse is obliquely incident on overdense plasma, the surface electrons may form ultra-thin, highly compressed layers, with a width of a few nanometers. These electron "nanobunches" emit synchrotron radiation coherently. We calculate the one-dimensional synchrotron spectrum analytically and obtain a slowly decaying power-law with an exponent of 4/3 or 6/5. This is much flatter than the 8/3 power of the BGP (Baeva-Gordienko-Pukhov) spectrum, produced by a relativistically oscillating bulk skin layer. The synchrotron spectrum cut-off frequency is defined either by the electron relativistic $\gamma$-factor, or by the thickness of the emitting layer. In the numerically demonstrated, locally optimal case, the radiation is emitted in the form of a single attosecond pulse, which contains almost the entire energy of the full optical cycle.Comment: to appear in Physics of Plasma

Facebook surveillance of former romantic partners: Associations with post-breakup recovery and personal growth

Copyright @ 2012 Mary Ann Liebert, Inc.This article has been made available through the Brunel Open Access Publishing Fund.Previous research has found that continuing offline contact with an ex-romantic partner following a breakup may disrupt emotional recovery. The present study examined whether continuing online contact with an ex-partner through remaining Facebook friends and/or engaging in surveillance of the ex-partner's Facebook page inhibited postbreakup adjustment and growth above and beyond offline contact. Analysis of the data provided by 464 participants revealed that Facebook surveillance was associated with greater current distress over the breakup, more negative feelings, sexual desire, and longing for the ex-partner, and lower personal growth. Participants who remained Facebook friends with the ex-partner, relative to those who did not remain Facebook friends, reported less negative feelings, sexual desire, and longing for the former partner, but lower personal growth. All of these results emerged after controlling for offline contact, personality traits, and characteristics of the former relationship and breakup that tend to predict postbreakup adjustment. Overall, these findings suggest that exposure to an ex-partner through Facebook may obstruct the process of healing and moving on from a past relationship

K2P channels and their protein partners.

A decade since their discovery, the K2P channels are recognized as pathways dedicated to regulated background leakage of potassium ions that serve to control neuronal excitability. The recent identification of protein partners that directly interact with K2P channels (SUMO, 14-3-3 and Vpu1) has exposed new regulatory pathways. Reversible linkage to SUMO silences K2P1 plasma membrane channels; phosphorylation of K2P3 enables 14-3-3 binding to affect forward trafficking, whereas it decreases open probability of K2P2; and, Vpu1, an HIV encoded partner, mediates assembly-dependent degradation of K2P3. An operational strategy has emerged: tonic inhibition of K2P channels allows baseline neuronal activity until enhanced potassium leak is required to suppress excitability