Double Relaxation via AdS/CFT

We exploit the AdS/CFT correspondence to investigate thermalization in an N=2 strongly coupled gauge theory including massless fundamental matter (quark). More precisely, we consider the response of a zero temperature state of the gauge theory under variation of an external electric field leading to a time-dependent current. The holographic dual of the above set-up is given by introducing a time-dependent electric field on the probe D7-brane embedded in an AdS_5 X S^5 background. In the dual gravity theory, due to a time-dependent electric field an apparent horizon forms on the brane which, according to AdS/CFT dictionary, is the counterpart of the thermalization process in the gauge theory. We classify different functions for time-dependent electric field and study their effect on the apparent horizon formation. In the case of pulse functions where the electric field varies from zero to zero, apart from non-equilibrium phase, we observe that two apparent horizons form on the brane. On the gauge theory side, it means that the state of the gauge theory experiences two different temperatures during the time evolution.Comment: 28 pages, 13 figures, published versio

CENP-C unwraps the human CENP-A nucleosome through the H2A C-terminal tail

Centromeres are defined epigenetically by nucleosomes containing the histone H3 variant CENP-A, upon which the constitutive centromere-associated network of proteins (CCAN) is built. CENP-C is considered to be a central organizer of the CCAN. We provide new molecular insights into the structure of human CENP-A nucleosomes, in isolation and in complex with the CENP-C central region (CENP-C-CR), the main CENP-A binding module of human CENP-C. We establish that the short alpha N helix of CENP-A promotes DNA flexibility at the nucleosome ends, independently of the sequence it wraps. Furthermore, we show that, in vitro, two regions of human CENP-C (CENP-C-CR and CENP-C-motif) both bind exclusively to the CENP-A nucleosome. We find CENP-C-CR to bind with high affinity due to an extended hydrophobic area made up of CENP-A(V)(532) and CENP-A(V)(533). Importantly, we identify two key conformational changes within the CENP-A nucleosome upon CENP-C binding. First, the loose DNA wrapping of CENP-A nucleosomes is further exacerbated, through destabilization of the H2A C-terminal tail. Second, CENP-C-CR rigidifies the N-terminal tail of H4 in the conformation favoring H4(K20) monomethylation, essential for a functional centromere

Rare BB-Decays and Heavy to Light Semileptonic Transitions in the Isgur and Wise Limit

From the experimental branching ratios for $B^- --> \rho^0 l^-\bar\nu_l$ and D^+ --> {\overl K}^{*0}({\overl K}^0) e^+ \nu_e one finds, in the Heavy Quark Limit of $HQET$, $|V_{bu}|=(8.1\pm 1.7) x 10^{-3}$, larger but consistent with the actual quoted range $(2 - 7) x 10^{-3}$. In the same framework one predicts for $R(B --> K^*\gamma)=( 2 \pm 2 ) 10^{-2}$.Comment: 9 pages, 1 Figure avalaible on request from [email protected]

Multiple classical limits in relativistic and nonrelativistic quantum mechanics

The existence of a classical limit describing interacting particles in a second-quantized theory of identical particles with bosonic symmetry is proved. This limit exists in addition to a previously established classical limit with a classical field behavior, showing that the limit $\hbar \to 0$ of the theory is not unique. An analogous result is valid for a free massive scalar field: two distinct classical limits are proved to exist, describing a system of particles or a classical field. The introduction of local operators in order to represent kinematical properties of interest is shown to break the permutation symmetry under some localizability conditions, allowing the study of individual particle properties.Comment: 13 page

Influence of the C/O ratio on titanium and vanadium oxides in protoplanetary disks

Context. The observation of carbon-rich disks have motivated several studies questioning the influence of the C/O ratio on their gas phase composition in order to establish the connection between the metallicity of hot-Jupiters and that of their parent stars. Aims. We to propose a method that allows the characterization of the adopted C/O ratio in protoplanetary disks independently from the determination of the host star composition. Titanium and vanadium chemistries are investigated because they are strong optical absorbers and also because their oxides are known to be sensitive to the C/O ratio in some exoplanet atmospheres. Methods. We use a commercial package based on the Gibbs energy minimization technique to compute the titanium and vanadium equilibrium chemistries in protoplanetary disks for C/O ratios ranging from 0.05 to 10. Our calculations are performed for pressures ranging from 1e-6 to 1e-2 bar, and for temperatures ranging from 50 to 2000 K. Results. We find that the vanadium nitride/vanadium oxide and titanium hydride/titanium oxide gas phase ratios strongly depend on the C/O ratio in the hot parts of disks (T > 1000 K). Our calculations suggest that, in these regions, these ratios can be used as tracers of the C/O value in protoplanetary disks.Comment: Accepted for publication in A&

Initial recommendations of MOOCs characteristics for academic discipline clusters

Massive Open Online Courses (known as MOOCs) have been introduced as an extensive and pervasive learning style in order to increase students’ performance. Many academics and students in Malaysian higher education institutions have begun to show their interest in applying MOOCs to deliver course material or conduct distance education in an innovative way. However, there are no guidelines available to assist the application of MOOCs; in particular, there are no guidelines to help academics develop their own MOOCs based on their area of expertise. In the education domain, usually these areas of expertise are arranged according to certain groups referred to as academic discipline clusters. This study investigates existing MOOCs characteristics and recommends specific characteristics in relation to academic discipline clusters. Content analysis was carried out by exploring MOOCs characteristics implemented successfully in six universities worldwide. This included an examination of the platforms used and the courses that applied MOOCs. Based on the results, the desirable characteristics of MOOCs are recommended with regard to academic discipline clusters, with the Universiti Teknologi Malaysia used as a case study