30 research outputs found
A Self Consistent Reaction Field Calculation of the Fluorobenzonitrile Radical Ions
A self consistent reaction field study has been carried out at the MINDO/3 level, in order to explain the decomposition of the species in solution.Publicado on line en 2014.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
Surveying Standard Model Flux Vacua on
We consider the SU(2)LxSU(2)R Standard Model brane embedding in an
orientifold of T6/Z2xZ2. Within defined limits, we construct all such Standard
Model brane embeddings and determine the relative number of flux vacua for each
construction. Supersymmetry preserving brane recombination in the hidden sector
enables us to identify many solutions with high flux. We discuss in detail the
phenomenology of one model which is likely to dominate the counting of vacua.
While Kahler moduli stabilization remains to be fully understood, we define the
criteria necessary for generic constructions to have fixed moduli.Comment: 30 pages, LaTeX, v2: added reference
Sigma-model for Generalized Composite p-branes
A multidimensional gravitational model containing several dilatonic scalar
fields and antisymmetric forms is considered. The manifold is chosen in the
form M = M_0 x M_1 x ... x M_n, where M_i are Einstein spaces (i > 0). The
block-diagonal metric is chosen and all fields and scale factors of the metric
are functions on M_0. For the forms composite (electro-magnetic) p-brane ansatz
is adopted. The model is reduced to gravitating self-interacting sigma-model
with certain constraints. In pure electric and magnetic cases the number of
these constraints is m(m - 1)/2 where m is number of 1-dimensional manifolds
among M_i. In the "electro-magnetic" case for dim M_0 = 1, 3 additional m
constraints appear. A family of "Majumdar-Papapetrou type" solutions governed
by a set of harmonic functions is obtained, when all factor-spaces M_k are
Ricci-flat. These solutions are generalized to the case of non-Ricci-flat M_0
when also some additional "internal" Einstein spaces of non-zero curvature are
added to M. As an example exact solutions for D = 11 supergravity and related
12-dimensional theory are presented.Comment: 33 pages, Latex. Some corrections and rearrangements are mad
Hermes: a Fast, Fault-Tolerant and Linearizable Replication Protocol
Today's datacenter applications are underpinned by datastores that are
responsible for providing availability, consistency, and performance. For high
availability in the presence of failures, these datastores replicate data
across several nodes. This is accomplished with the help of a reliable
replication protocol that is responsible for maintaining the replicas
strongly-consistent even when faults occur. Strong consistency is preferred to
weaker consistency models that cannot guarantee an intuitive behavior for the
clients. Furthermore, to accommodate high demand at real-time latencies,
datastores must deliver high throughput and low latency.
This work introduces Hermes, a broadcast-based reliable replication protocol
for in-memory datastores that provides both high throughput and low latency by
enabling local reads and fully-concurrent fast writes at all replicas. Hermes
couples logical timestamps with cache-coherence-inspired invalidations to
guarantee linearizability, avoid write serialization at a centralized ordering
point, resolve write conflicts locally at each replica (hence ensuring that
writes never abort) and provide fault-tolerance via replayable writes. Our
implementation of Hermes over an RDMA-enabled reliable datastore with five
replicas shows that Hermes consistently achieves higher throughput than
state-of-the-art RDMA-based reliable protocols (ZAB and CRAQ) across all write
ratios while also significantly reducing tail latency. At 5% writes, the tail
latency of Hermes is 3.6X lower than that of CRAQ and ZAB.Comment: Accepted in ASPLOS 202
Autonomic Network-layer Multicast Service
providing consistent service quality across the Internet remains a challenge. Multicast applications further exacerbate that problem as the number of participants -- clients, providers and administrative domains -- and the level of heterogeneity in a single session is increased. Recently the increasing complexity of managing and operating the Internet has sparked off interest in autonomous networking