1,393 research outputs found
One-dimensional wave propagation in particulate suspensions
One-dimensional small-amplitude wave motion in a two-phase system consisting of an inviscid gas and a cloud of suspended particles is analyzed using a continuum theory of suspensions. Laplace transform methods are used to obtain several approximate solutions. Properties of acoustic wave motion in particulate suspensions are inferred from these solutions
Relic density calculations beyond tree-level, exact calculations versus effective couplings: the ZZ final state
The inferred value of the relic density from cosmological observations has
reached a precision that is akin to that of the LEP precision measurements.
This level of precision calls for the evaluation of the annihilation cross
sections of dark matter that goes beyond tree-level calculations as currently
implemented in all codes for the computation of the relic density. In
supersymmetry radiative corrections are known to be large and thus must be
implemented. Full one-loop radiative corrections for many annihilation
processes have been performed. It is important to investigate whether the bulk
of these corrections can be parameterised through an improved Born
approximation that can be implemented as a selection of form factors to a
tree-level code. This paper is a second in a series that addresses this issue.
After having provided these form factors for the annihilation of the
neutralinos into fermions, which cover the case of a bino-like LSP (Lightest
Supersymmetric Particle), we turn our attention here to a higgsino-like dark
matter candidate through its annihilation into . We also investigate the
cases of a mixed LSP. In all cases we compare the performance of the form
factor approach with the result of a full one-loop correction. We also study
the issue of the renormalisation scheme dependence. An illustration of the
phenomenon of non decoupling of the heavy sfermions that takes place for the
annihilation of the lightest neutralino into is also presented.Comment: 20
Use of Discrete Choice Experiments in health economics: An update of the literature
The vast majority of stated preference research in health economics has been conducted in the random utility model paradigm using discrete choice experiments (DCEs). Ryan and Gerard (2003) have reviewed the applications of DCEs in the field of health economics. We have updated this initial work to include studies published between 2001 and 2007. Following the methods of Ryan and Gerard, we assess the later body of work, with respect to the key characteristics of DCEs such as selection of attributes and levels, experimental design, preference measurement, estimation procedure and validity. Comparisons between the periods are undertaken in order to identify any emerging trends.discrete choice experiments, health economics
Secrecy and Blocking Laws: A Growing Problem as the Internationalization of Securities Markets Continues
This Note examines the problems recently faced by the SEC in policing securities transactions effected by foreign financial institutions in jurisdictions with secrecy and blocking laws, and it proposes both a short-term solution and a long-term solution to the SEC\u27s enforcement problems. Part II of the Note outlines the problems confronting the SEC, specifically addressing the growing internationalization of securities markets and the effects on United States markets. This section also examines the problems confronting the SEC as a result of secrecy and blocking laws, and it suggests that unless new enforcement procedures are developed, these problems will increase when a fully integrated capital market system is established. Part III discusses the means the SEC currently uses to pierce secrecy and blocking laws and the difficulties and frustrations associated with the utilization of those methods. While Part IV examines the waiver-by-conduct concept and evaluates its potential effects, Part V looks at other possible alternatives. Finally, Part VI analyzes the role of secrecy and blocking laws in securities markets and the issues confronting nations that attempt to resolve these enforcement problems; Part VII concludes with a suggested approach
Why worry about awareness in choice problems? Econometric analysis of screening for cervical cancer
Cervical cancer is one of the most preventable and curable forms of cancer. Since 1991 there has been a concerted effort in Australia to recommend and encourage women to have Pap smears every two years. Part of the success of this National Cervical Screening Program can be gauged by exploring the determinants of screening for cervical cancer among high-risk women and by addressing the specific question of whether screening is associated with socio-economic status. Accessibility to health services remains a core goal in health policy in Australia but evidence on whether the goal is being met is limited. Using unit record data from the 1995 National Health Survey, an econometric model is developed for whether women have ever screened or not. A proportion of women in the sample contend that they have never heard of a Pap test. The analysis characterizes this group of women and accounts for their presence in our modellingScreening choice; Awareness; Censored probit; Cervical cancer
Positive Feedback Trading: Google Trends and Feeder Cattle Futures
What do investorsâ searches for public information reveal about their subsequent trading strategies? Does their search for information support the hypothesis of market efficiency or does it lend support to the idea that investors have behavioral biases. Using Google Trends, we find that the volume of Google searches about feeder cattle is associated with re-enforcement of momentum trading in a manner consistent with a positive feedback mechanism. Further, we find evidence that search volume for âcattleâ is associated with higher volatility and thus amplifies the positive feedback trading mechanism, while the search volume for âcornâ, a major input to cattle production, is associated with a reduction in volatility
One-loop corrections, uncertainties and approximations in neutralino annihilations: Examples
The extracted value of the relic density has reached the few per-cent level
precision. One can therefore no longer content oneself with calculations of
this observable where the annihilation processes are computed at tree-level,
especially in supersymmetry where radiative corrections are usually large.
Implementing full one-loop corrections to all annihilation processes that would
be needed in a scan over parameters is a daunting task. On the other hand one
may ask whether the bulk of the corrections are taken into account through
effective couplings of the neutralino that improve the tree-level calculation
and would be easy to implement. We address this issue by concentrating in this
first study on the neutralino coupling to i) fermions and sfermions and ii) Z.
After constructing the effective couplings we compare their efficiency compared
to the full one-loop calculation and comment on the failures and success of the
approach. As a bonus we point out that large non decoupling effects of heavy
sfermions could in principle be measured in the annihilation process, a point
of interest in view of the latest limit on the squark masses from the LHC. We
also comment on the scheme dependencies of the one-loop corrected results
A database of sources of information on mineral reaction kinetics
The rate and magnitude of geochemical reactions can be described by two main processes; thermodynamics which determines the end point of reaction (i.e. approach to equilibrium conditions), and kinetics which determines how rapidly the reaction proceeds. There have been many studies that have investigated equilibrium conditions and have generated a wealth of data. However, for many systems the rate at which the end point of the reaction is reached is of equal, and possibly greater importance (e.g. the behaviour of waste products stored within the geosphere or during weathering).
Predictive geochemical computer modelling is becoming increasingly important for investigating many different scenarios relatively rapidly. Although such models are capable of modelling rate-controlled dissolution and precipitation, there is no standard database of kinetic functions. As a consequence, it is sometimes difficult to locate sources of information to aid modelling.
The overall aim of this report, is to provide information on literature sources of mainly mineral reaction rate data. It is hoped that this will facilitate predictive modelling exercises, or laboratory experimental studies addressing gaps in data coverage. Information on the sources of literature information has been produced in the form of an EndNote electronic database (see Appendix I). This study does not however, go as far as extracting and tabulating all the individual data points within these references
Results of laboratory carbonation experiments on Nirex Reference Vault Backfill cement
Some repository concepts envisage the use of large quantities of cementitious materials â both
for repository construction and as a buffer/backfill. However, some wastes placed within a
subsurface repository will contain a significant amount of organic material that may degrade to
produce carbon dioxide. This will react with cement buffer/backfill to produce carbonate
minerals such as calcite, which will reduce the ability of the buffer/backfill to maintain highly
alkaline conditions and as a consequence its ability to limit radionuclide migration. The reaction
may also alter the physical properties of the buffer/backfill. The work involved in this study
investigates these processes through elevated pressure laboratory experiments conducted at a
range of likely future in situ repository conditions. These will provide information on the
reactions that occur, with results serving as examples with which to test predictive modelling
codes. This report details a series of batch experiments to study carbonation of Nirex Reference
Vault Backfil (NRVB) cement.
Thirty-two static batch experiments were pressurised with either CO2, or with N2 for ânonreactingâ
comparison tests at 20°C or 40°C, and 40 or 80 bar. Twenty-six of these were left to
react for durations of between 10-40 days, with six more left to react for a year. The aim of them
was to help investigate mineralogical and fluid chemical changes due to the diffusional ingress
of CO2 into unconfined NRVB samples measuring 2.5 cm in diameter and 5 cm long.
All the cement samples showed rapid reaction with CO2, manifested by a colour change from
grey to light brown. Petrographic analysis of the reacted cement revealed that this colour change
reflected the breakdown and dissolution of primary calcium ferrite and calcium alumina-ferrite
(CAF) cement clinker phases (e.g. brownmillerite, Ca2(Al,Fe)2O5 to form calcium carbonates
and finely-disseminated free ferric oxide (probably hematite, Fe2O3), as a result of reaction with
CO2 to give a ârustyâ colour. It should be noted that his is not an oxidation reaction as the iron is
present as Fe3+ in the original cement phases.
The cement blocks remained intact, even after prolonged exposure to CO2-rich fluids.
Carbonation was associated with an increase in weight of up to 8.5% during CO2 uptake, though
the samples did not change in overall size. There is potential therefore, for carbonation to
immobilise 14CO2 if that were present. Free-phase CO2 gave slightly more reaction than dissolved
CO2, possibly because of its higher concentration and greater ability to penetrate the samples. In
terms of major reactions during carbonation, these were the breakdown of portlandite, calcium
silicate hydrate (CSH) phases, calcium aluminate (or calcium aluminate hydrate) phases, and
ettringite-like phases, and the formation of carbonate phases and silica gel. Carbonation also
revealed that heterogeneity within the cement samples had a major impact on migration
pathways and extent of carbonation. This heterogeneity may have been a result of casting, and
was only observed in some of the samples studied. It led to faster carbonation in some areas, and
may account for some of the differences observed in the reacted cement samples. Such
heterogeneity may be present within a repository, and should be taken into account when
assessing repository performance
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