813 research outputs found
Adaptation in integrated assessment modeling: where do we stand?
Adaptation is an important element on the climate change policy agenda. Integrated assessment models, which are key tools to assess climate change policies, have begun to address adaptation, either by including it implicitly in damage cost estimates, or by making it an explicit control variable. We analyze how modelers have chosen to describe adaptation within an integrated framework, and suggest many ways they could improve the treatment of adaptation by considering more of its bottom-up characteristics. Until this happens, we suggest, models may be too optimistic about the net benefits adaptation can provide, and therefore may underestimate the amount of mitigation they judge to be socially optimal. Under some conditions, better modeling of adaptation costs and benefits could have important implications for defining mitigation targets. © Springer Science+Business Media B.V. 2009
A Study of Quantum Error Correction by Geometric Algebra and Liquid-State NMR Spectroscopy
Quantum error correcting codes enable the information contained in a quantum
state to be protected from decoherence due to external perturbations. Applied
to NMR, quantum coding does not alter normal relaxation, but rather converts
the state of a ``data'' spin into multiple quantum coherences involving
additional ancilla spins. These multiple quantum coherences relax at differing
rates, thus permitting the original state of the data to be approximately
reconstructed by mixing them together in an appropriate fashion. This paper
describes the operation of a simple, three-bit quantum code in the product
operator formalism, and uses geometric algebra methods to obtain the
error-corrected decay curve in the presence of arbitrary correlations in the
external random fields. These predictions are confirmed in both the totally
correlated and uncorrelated cases by liquid-state NMR experiments on
13C-labeled alanine, using gradient-diffusion methods to implement these
idealized decoherence models. Quantum error correction in weakly polarized
systems requires that the ancilla spins be prepared in a pseudo-pure state
relative to the data spin, which entails a loss of signal that exceeds any
potential gain through error correction. Nevertheless, this study shows that
quantum coding can be used to validate theoretical decoherence mechanisms, and
to provide detailed information on correlations in the underlying NMR
relaxation dynamics.Comment: 33 pages plus 6 figures, LaTeX article class with amsmath & graphicx
package
A Seesaw Mechanism in the Higgs Sector
In this letter we revisit the seesaw Higgs mechanism. We show how a seesaw
mechanism in a two Higgs doublets model can trigger the electroweak symmetry
breaking if at least one of the eigenvalues of the squared mass matrix is
negative. We then consider two special cases of interest. In the decoupling
scenario, there is only one scalar degree of freedom in the low energy regime.
In the degenerate scenario, all five degrees of freedom are in the low energy
regime and will lead to observables effects at the LHC. Furthermore, in that
scenario, it is possible to impose a discrete symmetry between the doublets
that makes the extra neutral degrees of freedom stable. These are thus viable
dark matter candidates. We find an interesting relation between the electroweak
symmetry breaking mechanism and dark matter.Comment: 10 page
Saturation of a spin 1/2 particle by generalized Local control
We show how to apply a generalization of Local control design to the problem
of saturation of a spin 1/2 particle by magnetic fields in Nuclear Magnetic
Resonance. The generalization of local or Lyapunov control arises from the fact
that the derivative of the Lyapunov function does not depend explicitly on the
control field. The second derivative is used to determine the local control
field. We compare the efficiency of this approach with respect to the
time-optimal solution which has been recently derived using geometric methods.Comment: 12 pages, 4 figures, submitted to new journal of physics (2011
A Human Development Framework for CO2 Reductions
Although developing countries are called to participate in CO2 emission
reduction efforts to avoid dangerous climate change, the implications of
proposed reduction schemes in human development standards of developing
countries remain a matter of debate. We show the existence of a positive and
time-dependent correlation between the Human Development Index (HDI) and per
capita CO2 emissions from fossil fuel combustion. Employing this empirical
relation, extrapolating the HDI, and using three population scenarios, the
cumulative CO2 emissions necessary for developing countries to achieve
particular HDI thresholds are assessed following a Development As Usual
approach (DAU). If current demographic and development trends are maintained,
we estimate that by 2050 around 85% of the world's population will live in
countries with high HDI (above 0.8). In particular, 300Gt of cumulative CO2
emissions between 2000 and 2050 are estimated to be necessary for the
development of 104 developing countries in the year 2000. This value represents
between 20% to 30% of previously calculated CO2 budgets limiting global warming
to 2{\deg}C. These constraints and results are incorporated into a CO2
reduction framework involving four domains of climate action for individual
countries. The framework reserves a fair emission path for developing countries
to proceed with their development by indexing country-dependent reduction rates
proportional to the HDI in order to preserve the 2{\deg}C target after a
particular development threshold is reached. Under this approach, global
cumulative emissions by 2050 are estimated to range from 850 up to 1100Gt of
CO2. These values are within the uncertainty range of emissions to limit global
temperatures to 2{\deg}C.Comment: 14 pages, 7 figures, 1 tabl
Availability of central α4β2* nicotinic acetylcholine receptors in human obesity
Purpose: Obesity is thought to arise, in part, from deficits in the inhibitory control over appetitive behavior. Such motivational processes are regulated by neuromodulators, specifically acetylcholine (ACh), via α4β2* nicotinic ACh receptors (nAChR). These nAChR are highly enriched in the thalamus and contribute to the thalamic gating of cortico-striatal signaling, but also act on the mesoaccumbal reward system. The changes in α4β2* nAChR availability, however, have not been demonstrated in human obesity thus far. The aim of our study was, thus, to investigate whether there is altered brain α4β2* nAChR availability in individuals with obesity compared to normal-weight healthy controls. Methods: We studied 15 non-smoking individuals with obesity (body mass index, BMI: 37.8 ± 3.1 kg/m2; age: 39 ± 14 years, 9 females) and 16 normal-weight controls (non-smokers, BMI: 21.9 ± 1.7 kg/m2; age: 28 ± 7 years, 13 females) by using PET and the α4β2* nAChR selective (−)-[18F]flubatine, which was applied within a bolus-infusion protocol (294 ± 16 MBq). Volume-of-interest (VOI) analysis was performed in order to calculate the regional total distribution volume (VT). Results: No overall significant difference in VT between the individuals with obesity and the normal-weight volunteers was found, while the VT in the nucleus basalis of Meynert tended to be lower in the individuals with obesity (10.1 ± 2.1 versus 11.9 ± 2.2; p = 0.10), and the VT in the thalamus showed a tendency towards higher values in the individuals with obesity (26.5 ± 2.5 versus 25.9 ± 4.2; p = 0.09). Conclusion: While these first data do not show greater brain α4β2* nAChR availability in human obesity overall, the findings of potentially aberrant α4β2* nAChR availability in the key brain regions that regulate feeding behavior merit further exploration
Invisible Higgs and Scalar Dark Matter
In this proceeding, we show that when we combined WMAP and the most recent
results of XENON100, the invisible width of the Higgs to scalar dark matter is
negligible(<10%), except in a small region with very light dark matter (< 10
GeV) not yet excluded by XENON100 or around 60 GeV where the ratio can reach
50% to 60%. The new results released by the Higgs searches of ATLAS and CMS set
very strong limits on the elastic scattering cross section.Comment: 4 pages, 2 figures, proceeding TAUP2011 References adde
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