2,921 research outputs found
Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 3: Energy conversion subsystems and components. Part 3: Gasification, process fuels, and balance of plant
Results are presented of an investigation of gasification and clean fuels from coal. Factors discussed include: coal and coal transportation costs; clean liquid and gas fuel process efficiencies and costs; and cost, performance, and environmental intrusion elements of the integrated low-Btu coal gasification system. Cost estimates for the balance-of-plant requirements associated with advanced energy conversion systems utilizing coal or coal-derived fuels are included
Functional Sequential Treatment Allocation
Consider a setting in which a policy maker assigns subjects to treatments,
observing each outcome before the next subject arrives. Initially, it is
unknown which treatment is best, but the sequential nature of the problem
permits learning about the effectiveness of the treatments. While the
multi-armed-bandit literature has shed much light on the situation when the
policy maker compares the effectiveness of the treatments through their mean,
much less is known about other targets. This is restrictive, because a cautious
decision maker may prefer to target a robust location measure such as a
quantile or a trimmed mean. Furthermore, socio-economic decision making often
requires targeting purpose specific characteristics of the outcome
distribution, such as its inherent degree of inequality, welfare or poverty. In
the present paper we introduce and study sequential learning algorithms when
the distributional characteristic of interest is a general functional of the
outcome distribution. Minimax expected regret optimality results are obtained
within the subclass of explore-then-commit policies, and for the unrestricted
class of all policies
Conservative upper limits on WIMP annihilation cross section from Fermi-LAT -rays
The spectrum of an isotropic extragalactic -ray background (EGB) has
been measured by the Fermi-LAT telescope at high latitudes. Two new models for
the EGB are derived from the subtraction of unresolved point sources and
extragalactic diffuse processes, which could explain from 30% to 70% of the
Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely
due to the annihilation of dark matter (DM) particles in the Galactic halo, we
obtain upper limits on their annihilation cross section \sigmav.
Severe bounds on a possible Sommerfeld enhancement of the annihilation cross
section are set as well. Finally, would {\sigmav} be inversely proportional to
the WIMP velocity, very severe limits are derived for the velocity-independent
part of the annihilation cross section.Comment: Proceedings of XII Taup Conference, Munich, September 201
Fine-tuning implications for complementary dark matter and LHC SUSY searches
The requirement that SUSY should solve the hierarchy problem without undue
fine-tuning imposes severe constraints on the new supersymmetric states. With
the MSSM spectrum and soft SUSY breaking originating from universal scalar and
gaugino masses at the Grand Unification scale, we show that the low-fine-tuned
regions fall into two classes that will require complementary collider and dark
matter searches to explore in the near future. The first class has relatively
light gluinos or squarks which should be found by the LHC in its first run. We
identify the multijet plus E_T^miss signal as the optimal channel and determine
the discovery potential in the first run. The second class has heavier gluinos
and squarks but the LSP has a significant Higgsino component and should be seen
by the next generation of direct dark matter detection experiments. The
combined information from the 7 TeV LHC run and the next generation of direct
detection experiments can test almost all of the CMSSM parameter space
consistent with dark matter and EW constraints, corresponding to a fine-tuning
not worse than 1:100. To cover the complete low-fine-tuned region by SUSY
searches at the LHC will require running at the full 14 TeV CM energy; in
addition it may be tested indirectly by Higgs searches covering the mass range
below 120 GeV.Comment: References added. Version accepted for publication in JHE
Double Exponential Instability of Triangular Arbitrage Systems
If financial markets displayed the informational efficiency postulated in the
efficient markets hypothesis (EMH), arbitrage operations would be
self-extinguishing. The present paper considers arbitrage sequences in foreign
exchange (FX) markets, in which trading platforms and information are
fragmented. In Kozyakin et al. (2010) and Cross et al. (2012) it was shown that
sequences of triangular arbitrage operations in FX markets containing 4
currencies and trader-arbitrageurs tend to display periodicity or grow
exponentially rather than being self-extinguishing. This paper extends the
analysis to 5 or higher-order currency worlds. The key findings are that in a
5-currency world arbitrage sequences may also follow an exponential law as well
as display periodicity, but that in higher-order currency worlds a double
exponential law may additionally apply. There is an "inheritance of
instability" in the higher-order currency worlds. Profitable arbitrage
operations are thus endemic rather that displaying the self-extinguishing
properties implied by the EMH.Comment: 22 pages, 22 bibliography references, expanded Introduction and
Conclusion, added bibliohraphy reference
Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array
In this paper we investigate the asymptotic validity of boundary layer
theory. For a flow induced by a periodic row of point-vortices, we compare
Prandtl's solution to Navier-Stokes solutions at different numbers. We
show how Prandtl's solution develops a finite time separation singularity. On
the other hand Navier-Stokes solution is characterized by the presence of two
kinds of viscous-inviscid interactions between the boundary layer and the outer
flow. These interactions can be detected by the analysis of the enstrophy and
of the pressure gradient on the wall. Moreover we apply the complex singularity
tracking method to Prandtl and Navier-Stokes solutions and analyze the previous
interactions from a different perspective
Epidemiology of Sexually Transmitted Infections in Visitors for the London 2012 Olympic Games: A Review of Attendees at Sexual Health Services
BACKGROUND: Mass gatherings and large sporting events, such as the Olympics, may potentially pose a risk of increased sexually transmitted infection (STI) transmission and increase burden on local STI services. The objectives of this analysis were to assess whether the STI profile of Olympic visitors differed from that of the local STI clinic population and to investigate what impact these visitors had on local STI services.
METHODS: Self-administered questionnaires (completed by 29,292 patients) were used to determine the visitor status of patients attending 20 STI clinics, between July 20, 2012, and September 16, 2012, in the host cities, London and Weymouth. Using routine surveillance data from the Genitourinary Medicine Clinic Activity Dataset version 2, Olympic visitors were compared with usual attendees (local residents and non-Olympic visitors) in terms of their demographic characteristics, services utilized, and STIs diagnosed using univariate and multivariate methods.
RESULTS: Compared with usual attendees, Olympic visitors were more likely to be heterosexual males (56.0% vs. 34.9%, P = 0.001), aged between 15 and 24 years of age (47.1% vs. 34.0%, P = 0.001), of white ethnicity (81.9% vs. 66.4%, P = 0.001), and born in Australasia, Asia, North America, or South America (18.8% vs. 12.0%, P = 0.006). Olympic visitors constituted 1% of new clinic attendances and were less likely to be diagnosed as having a new STI (adjusted odds ratio, 0.69; 95% confidence interval, 0.48–0.98; P = 0.040).
CONCLUSIONS: In this first multisite study to examine the effect of Olympic visitors on local sexual health services, the 2012 Olympic Games was found to have minimal impact. This suggests that a “business as usual” approach would have been sufficient
Naturalness and Fine Tuning in the NMSSM: Implications of Early LHC Results
We study the fine tuning in the parameter space of the semi-constrained
NMSSM, where most soft Susy breaking parameters are universal at the GUT scale.
We discuss the dependence of the fine tuning on the soft Susy breaking
parameters M_1/2 and m0, and on the Higgs masses in NMSSM specific scenarios
involving large singlet-doublet Higgs mixing or dominant Higgs-to-Higgs decays.
Whereas these latter scenarios allow a priori for considerably less fine tuning
than the constrained MSSM, the early LHC results rule out a large part of the
parameter space of the semi-constrained NMSSM corresponding to low values of
the fine tuning.Comment: 19 pages, 10 figures, bounds from Susy searches with ~1/fb include
Neutralino Dark Matter in BMSSM Effective Theory
We study thermal neutralino dark matter in an effective field theory
extension of the MSSM, called "Beyond the MSSM" (BMSSM) in Dine, Seiberg and
Thomas (2007). In this class of effective field theories, the field content of
the MSSM is unchanged, but the little hierarchy problem is alleviated by
allowing small corrections to the Higgs/higgsino part of the Lagrangian. We
perform parameter scans and compute the dark matter relic density. The light
Higgsino LSP scenario is modified the most; we find new regions of parameter
space compared to the standard MSSM. This involves interesting interplay
between the WMAP dark matter bounds and the LEP chargino bound. We also find
some changes for gaugino LSPs, partly due to annihilation through a Higgs
resonance, and partly due to coannihilation with light stops in models that are
ruled in by the new effective terms.Comment: 37 pages + appendi
Solid-state Marx based two-switch voltage modulator for the On-Line Isotope Mass Separator accelerator at the European Organization for Nuclear Research
A new circuit topology is proposed to replace the actual pulse transformer and thyratron based resonant modulator that supplies the 60 kV target potential for the ion acceleration of the On-Line Isotope Mass Separator accelerator, the stability of which is critical for the mass resolution downstream separator, at the European Organization for Nuclear Research. The improved modulator uses two solid-state switches working together, each one based on the Marx generator concept, operating as series and parallel switches, reducing the stress on the series stacked semiconductors, and also as auxiliary pulse generator in order to fulfill the target requirements. Preliminary results of a 10 kV prototype, using 1200 V insulated gate bipolar transistors and capacitors in the solid-state Marx circuits, ten stages each, with an electrical equivalent circuit of the target, are presented, demonstrating both the improved voltage stability and pulse flexibility potential wanted for this new modulator
- …