13,792 research outputs found
Charged Higgs bosons in Minimal Supersymmetry: Updated constraints and experimental prospects
Full text linkWe discuss the phenomenology of charged Higgs bosons in the MSSM with minimal
flavor violation. In addition to the constrained MSSM (CMSSM) with universal
soft supersymmetry breaking mass parameters at the GUT scale, we explore
non-universal Higgs mass models (NUHM) where this universality condition is
relaxed. To identify the allowed parameter space regions, we apply constraints
from direct searches, low energy observables, and cosmology. We find that
values of the charged Higgs mass as low as GeV can be
accommodated in the NUHM models, but that several flavor physics observables
disfavor large contributions, associated with high , quite
independently of MSSM scenario. We confront the constrained scenarios with the
discovery potentials reported by ATLAS and CMS, and find that the current
exclusion by indirect constraints is similar to the expected LHC discovery
reach with 30 fb of data. Finally, we evaluate the sensitivity of the
presented discovery potential to the choice of MSSM benchmark scenario. This
sensitivity is found to be higher in the case of a light ()
charged Higgs.Comment: 33 pages, 17 figures, v2: Minor revision, agrees with published
versio
Asymmetric magnetic reconnection with a flow shear and applications to the magnetopause
Get PDFWe perform a theoretical and numerical study of anti-parallel 2D magnetic
reconnection with asymmetries in the density and reconnecting magnetic field
strength in addition to a bulk flow shear across the reconnection site in the
plane of the reconnecting fields, which commonly occurs at planetary
magnetospheres. We predict the speed at which an isolated X-line is convected
by the flow, the reconnection rate, and the critical flow speed at which
reconnection no longer takes place for arbitrary reconnecting magnetic field
strengths, densities, and upstream flow speeds, and confirm the results with
two-fluid numerical simulations. The predictions and simulation results counter
the prevailing model of reconnection at Earth's dayside magnetopause which says
reconnection occurs with a stationary X-line for sub-Alfvenic magnetosheath
flow, reconnection occurs but the X-line convects for magnetosheath flows
between the Alfven speed and double the Alfven speed, and reconnection does not
occur for magnetosheath flows greater than double the Alfven speed. We find
that X-line motion is governed by momentum conservation from the upstream
flows, which are weighted differently in asymmetric systems, so the X-line
convects for generic conditions including sub-Alfvenic upstream speeds. For the
reconnection rate, while the cutoff condition for symmetric reconnection is
that the difference in flows on the two sides of the reconnection site is twice
the Alfven speed, we find asymmetries cause the cutoff speed for asymmetric
reconnection to be higher than twice the asymmetric form of the Alfven speed.
The results compare favorably with an observation of reconnection at Earth's
polar cusps during a period of northward interplanetary magnetic field, where
reconnection occurs despite the magnetosheath flow speed being more than twice
the magnetosheath Alfven speed, the previously proposed suppression condition.Comment: 46 pages, 7 figures, abstract abridged here, accepted to Journal of
Geophysical Research - Space Physic
Ecosystem properties and principles of living systems as foundation for sustainable agriculture – Critical reviews of environmental assessment tools, key findings and questions from a course process
Get PDFWith increasing demands on limited resources worldwide, there is a growing interest in sustainable patterns of utilisation and production. Ecological agriculture is a response to these concerns.
To assess progress and compliance, standard and comprehensive measures of resource requirements, impacts and agro-ecological health are needed. Assessment tools should also be rapid, standardized, userfriendly, meaningful to public policy and applicable to management. Fully considering these requirements confounds the development of integrated methods.
Currently, there are many methodologies for monitoring performance, each with its own foundations, assumptions, goals, and outcomes, dependent upon agency agenda or academic orientation. Clearly, a concept of sustainability must address biophysical, ecological, economic, and sociocultural foundations.
Assessment indicators and criteria, however, are generally limited, lacking integration, and at times in conflict with one another. A result is that certification criteria, indicators, and assessment methods are not based on a consistent, underlying conceptual framework and often lack a management focus.
Ecosystem properties and principles of living systems, including self-organisation, renewal, embeddedness, emergence and commensurate response provide foundation for sustainability assessments and may be appropriate focal points for critical thinking in an evaluation of current methods and standards. A systems framework may also help facilitate a comprehensive approach and promote a context for meaningful discourse. Without holistic accounts, sustainable progress remains an illdefined concept and an elusive goal.
Our intent, in the work with this report, was to use systems ecology as a pedagogic basis for learning and discussion to:
- Articulate general and common characteristics of living systems.
- Identify principles, properties and patterns inherent in natural ecosystems.
- Use these findings as foci in a dialogue about attributes of sustainability to:
a. develop a model for communicating scientific rationale.
b. critically evaluate environmental assessment tools for application in land-use.
c. propose appropriate criteria for a comprehensive assessment and expanded definition of ecological land use
A theoretical analysis of the chemical bonding and electronic structure of graphene interacting with Group IA and Group VIIA elements
Get PDFWe propose a new class of materials, which can be viewed as graphene
derivatives involving Group IA or Group VIIA elements, forming what we refer to
as graphXene. We show that in several cases large band gaps can be found to
open up, whereas in other cases a semimetallic behavior is found. Formation
energies indicate that under ambient conditions, sp and mixed sp/sp
systems will form. The results presented allow us to propose that by careful
tuning of the relative concentration of the adsorbed atoms, it should be
possible to tune the band gap of graphXene to take any value between 0 and 6.4
eV.Comment: 5 pages, 4 figures. Transferred to PR
HIGH INHERITANCE ELONGATE STROMATOLITIC MOUNDS FROM THE TRANSVAAL DOLOMITE
Get PDFElongate mound·like structures up to 10 metres across and 40 metres in length are
described. Characteristic features of the mounds are their high inheritance and
considerable relief which, along with the absence of sub-aerial exposure features, the
fine-grained nature of the carbonate, and their vertical persistence, are taken to suggest a
subtidal origin. Marine currents are considered adequate to account for their elongation
Correlated quantum dynamics of graphene
Full text linkPhase-space representations are a family of methods for dynamics of both
bosonic and fermionic systems, that work by mapping the system's density matrix
to a quasi-probability density and the Liouville-von Neumann equation of the
Hamiltonian to a corresponding density differential equation for the
probability. We investigate here the accuracy and the computational efficiency
of one approximate phase-space representation, called the fermionic Truncated
Wigner Approximation (fTWA), applied to the Fermi-Hubbard model. On a many-body
2D system, with hopping strength and Coulomb tuned to represent the
electronic structure of graphene, the method is found to be able to capture the
time evolution of first-order (site occupation) and second-order (correlation
functions) moments significantly better than the mean-field, Hartree-Fock
method. The fTWA was also compared to results from the exact diagonalization
method for smaller systems, and in general the agreement was found to be good.
The fully parallel computational requirement of fTWA scales in the same order
as the Hartree-Fock method, and the largest system considered here contained
198 lattice sites
Two-Impurity Kondo Model: Spin-Orbit Interactions and Entanglement
Full text linkMotivated by proposals to employ RKKY-coupled spins as building blocks in a
solid-state quantum computer, we analyze how the RKKY interaction in a 2D
electron gas is influenced by spin-orbit interactions. Using a two-impurity
Kondo model with added Dresselhaus and Rashba spin-orbit interactions we find
that spin-rotational invariance of the RKKY interaction - essential for having
a well-controllable two-qubit gate - is restored when tuning the Rashba
coupling to have the same strength as the Dresselhaus coupling. We also discuss
the critical properties of the two-impurity Kondo model in the presence of
spin-orbit interactions, and extract the leading correction to the block
entanglement scaling due to these interactions.Comment: Proceedings of StatPhys 24 satellite conference in Hanoi; 9 pages, 4
figure
Impact of chosen cutoff on response rate differences between selective serotonin reuptake inhibitors and placebo
Get PDFResponse defined as a 50% reduction in the sum score of the Hamilton Depression Rating Scale (HDRS-17-sum) is often used to assess the efficacy of antidepressants. Critics have, however, argued that dichotomising ratings with a cutoff close to the median may lead to scores clustering on either side, the result being inflation of miniscule drug-placebo differences. Using pooled patient-level data sets from trials of three selective serotonin reuptake inhibitors (SSRIs) (citalopram, paroxetine and sertraline) (n = 7909), and from similar trials of duloxetine (n = 3478), we thus assessed the impact of different cutoffs on response rates. Response criteria were based on (i) HDRS-17-sum, (ii) the sum score of the HDRS-6 subscale (HDRS-6-sum) and (iii) the depressed mood item. The separation between SSRI and placebo with respect to response rates increased when HDRS-17-sum was replaced by HDRS-6-sum or depressed mood as effect parameter and was markedly dependent on SSRI dose. With the exception of extreme cutoff values, differences in response rates were largely similar regardless of where the cutoff was placed, and also not markedly changed by the exclusion of subjects close to the selected cutoff (e.g., \ub110%). The observation of similar response rate differences between active drugs and placebo for different cutoffs was corroborated by the analysis of duloxetine data. In conclusion, the suggestion that using a cutoff close to the median when defining response has markedly overestimated the separation between antidepressants and placebo may be discarded
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