694 research outputs found
SLED Phenomenology: Curvature vs. Volume
We assess the question whether the SLED (Supersymmetric Large Extra
Dimensions) model admits phenomenologically viable solutions with 4D maximal
symmetry. We take into account a finite brane width and a scale invariance (SI)
breaking dilaton-brane coupling, both of which should be included in a
realistic setup. Provided that the microscopic size of the brane is not tuned
much smaller than the fundamental bulk Planck length, we find that either the
4D curvature or the size of the extra dimensions is unacceptably large. Since
this result is independent of the dilaton-brane couplings, it provides the
biggest challenge to the SLED program.
In addition, to clarify its potential with respect to the cosmological
constant problem, we infer the amount of tuning on model parameters required to
obtain a sufficiently small 4D curvature. A first answer was recently given in
[arXiv:1508.01124], showing that 4D flat solutions are only ensured in the SI
case by imposing a tuning relation, even if a brane-localized flux is included.
In this companion paper, we find that the tuning can in fact be avoided for
certain SI breaking brane-dilaton couplings, but only at the price of worsening
the phenomenological problem.
Our results are obtained by solving the full coupled Einstein-dilaton system
in a completely consistent way. The brane width is implemented using a
well-known ring regularization. In passing, we note that for the couplings
considered here the results of [arXiv:1508.01124] (which only treated
infinitely thin branes) are all consistently recovered in the thin brane limit,
and how this can be reconciled with the concerns about their correctness,
recently brought up in [arXiv:1509.04201].Comment: 28 pages, 4 figure
A practice-related risk score (PRS): a DOPPS-derived aggregate quality index for haemodialysis facilities
Background. The Dialysis Outcomes and Practice Patterns Study (DOPPS) database was used to develop and validate a practice-related risk score (PRS) based on modifiable practices to help facilities assess potential areas for improving patient care.
Methods. Relative risks (RRs) from a multivariable Cox mortality model, based on observational haemodialysis (HD) patient data from DOPPS I (1996-2001, seven countries), were used. The four practices were the percent of patients with Kt/V >= 1.2, haemoglobin >= 11 g/dl (110 g/l), albumin >= 4.0 g/dl (40g/l) and catheter use, and were significantly related to mortality when modelled together. DOPPS II data (2002-2004, 12 countries) were used to evaluate the relationship between PRS and mortality risk using Cox regression.
Results. For facilities in DOPPS I and II, changes in PRS over time were significantly correlated with changes in the standardized mortality ratio (SMR). The PRS ranged from 1.0 to 2.1. Overall, the adjusted RR of death was 1.05 per 0.1 points higher PRS (P < 0.0001). For facilities in both DOPPS I and II (N = 119), a 0.2 decrease in PRS was associated with a 0.19 decrease in SMR (P = 0.005). On average, facilities that improved PRS practices showed significantly reduced mortality over the same time frame.
Conclusions. The PRS assesses modifiable HD practices that are linked to improved patient survival. Further refinements might lead to improvements in the PRS and will address regional variations in the PRS/mortality relationship
Effect of dimerization on dynamics of spin-charge separation in Pariser-Parr-Pople model: A time-dependent density matrix renormalization group study
We investigate the effect of static electron-phonon coupling, on real-time
dynamics of spin and charge transport in -conjugated polyene chains. The
polyene chain is modeled by the Pariser-Parr-Pople Hamiltonian with dimerized
nearest-neighbor parameter for short bonds and
for long bonds, and long-range electron-electron
interactions. We follow the time evolution of the spin and charge using
time-dependent density matrix renormalization group technique, when a hole is
injected at one end of the chain in its ground state. We find that spin and
charge dynamics followed through spin and charge velocities, depend both on
chain length and extent of dimerization, . Analysis of the results
requires focusing on physical quantities such as average spin and charge
polarizations, particularly in the large dimerization limit. In the
dimerization range 0.0 0.15, spin-charge dynamics is found
to have a well defined behavior, with spin-charge separation (measured as the
ratio of charge velocity to spin velocity) as well as, the total amount of
charge and spin transported in a given time, along the chain, decreasing as
dimerization increases. However, in the range 0.3 0.5, it
is observed that the dynamics of spin and charge transport becomes complicated.
It is observed that for large values, spin-charge separation is
suppressed and the injected hole fails to travel the entire length of the
chain.Comment: Published in Phys. Rev. B; preprint format of published versio
Conflicts in the Niger Delta: Analysis of Causes, Impacts and Resolution Strategies
Conflict in the Niger Delta holds profound implications for the democratic and developmental transformation of Nigeria. The analysis of the causes and impacts of the oil conflict in the region, and of strategies to resolve it, requires an understanding of the traditionally and constitutionally enshrined resource rights of the marginalised inhabitants. Patterns of resource appropriation by multinational oil companies and the mismanagement of resource revenue by federal government, and the associated environmental pollution, remain a legacy of the topdown approaches that have been employed in an attempt to resolve conflicts in the Niger Delta. These approaches have largely failed to effectively address the complex issues affecting the indigenes and have even triggered further dissention amongst various local communities. Using grounded theory as a research method, this thesis explores the grassroots approach to conflict resolution in the Niger Delta region as a socio-political paradigm for developing substantive content for the resolution of conflict in this oil-rich region of Nigeria. Drawing on history and using social and conflict theories, the paper investigates the potential for the bottom-up approach to be applied to the conflict resolution paradigm, in order to advance a sustainable peace process and promote economic, political and social transformation in Nigeria – and, in particular, the Niger Delta regio
Model-driven Enterprise Systems Configuration
Enterprise Systems potentially lead to significant efficiency gains but require a well-conducted configuration process. A promising idea to manage and simplify the configuration process is based on the premise of using reference models for this task. Our paper continues along this idea and delivers a two-fold contribution: first, we present a generic process for the task of model-driven Enterprise Systems configuration including the steps of (a) Specification of configurable reference models, (b) Configuration of configurable reference models, (c) Transformation of configured reference models to regular build time models, (d) Deployment of the generated build time models, (e) Controlling of implementation models to provide input to the configuration, and (f) Consolidation of implementation models to provide input to reference model specification. We discuss inputs and outputs as well as the involvement of different roles and validation mechanisms. Second, we present an instantiation case of this generic process for Enterprise Systems configuration based on Configurable EPCs
New Constraints on General Slepton Flavor Mixing
We explore the phenomenological implications on charged lepton flavor
violating (LFV) processes from slepton flavor mixing within the Minimal
Supersymmetric Standard Model. We work under the model-independent hypothesis
of general flavor mixing in the slepton sector, being parametrized by a
complete set of dimensionless delta^AB_ij (A,B = L,R; i,j = 1, 2, 3)
parameters. The present upper bounds on the most relevant LFV processes,
together with the requirement of compatibility in the choice of the MSSM
parameters with the recent LHC and (g-2) data, lead to updated constraints on
all slepton flavor mixing parameters. A comparative discussion of the most
effective LFV processes to constrain the various generation mixings is
included.Comment: 42 pages, 19 figures. Minor changes, version to appear in PR
Timber roof structure for outdoor auditorium in Parque Paraiso, San Blas (Madrid)
p. 468-475A timber shell structure is designed to provide covering for an outdoor auditorium in
Madrid (Spain). The covering comprises five independent overlapped marquees with
similar shape but diverse dimensions. The surface geometry of each marquee is defined by a hyperbolic paraboloid, with its boundaries delimited by elliptical curves in horizontal
projection. Structural section for the timber shell is a composite section with several
staggered layers of straight sawn timber planks, arranged in two orthogonal directions
following the straight skew lines of the hyperbolic paraboloid. Over them two continuous
top layers are arranged which provides bracing for the structure and support for the
waterproofing material. Each layer is laid over the previous one, bolted and glued with
polyurethane adhesive. Special characteristics of the design analysis and detailed erection process are described. The designed solution provides lightweight roofing with a powerful and original image, short construction time and reasonable budget.Anton, A.; Meijide, AG.; Corbal, JJ. (2009). Timber roof structure for outdoor auditorium in Parque Paraiso, San Blas (Madrid). Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/653
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