5,166 research outputs found
Forecasting, uncertainty, and public project appraisal
Uncertainty in project planning and appraisal is still topical in the World Bank and other lending and development agencies although it is certainly not a new issue. It is appropriate to reconsider the issue now because more than a decade of active research on risk analysis has transpired without, however, the seeming emergence of agreed procedures and practice. In particular, the implications for what information price forecasters should provide for risky project appraisers have yet to be clarified. In Section 2, theoretical arguments about the proper role of uncertainty in appraisal are reviewed, and this section is closed by discussion of the various'practical'methods that have been proposed, in and outside the World Bank. Further procedures for quantifying uncertainty in both forecasting and appraisal are considered in Section 3. Section 4 presents a set of procedures that seem workable and retain some theoretical defensibility. These are illustrated through an example. Finally, conclusions and implications are drawn out in Section 5.Economic Theory&Research,Environmental Economics&Policies,Health Economics&Finance,Statistical&Mathematical Sciences,Insurance&Risk Mitigation
Effectiveness of summer applications of Trifluralin
Non-Peer Reviewe
The (p,d) Reaction at E_p=121 MeV
This work was supported by National Science Foundation Grant PHY 75-00289 and Indiana Universit
The (p,t) Reaction at Higher Energy
This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit
Generic theory of colloidal transport
We discuss the motion of colloidal particles relative to a two component
fluid consisting of solvent and solute. Particle motion can result from (i) net
body forces on the particle due to external fields such as gravity; (ii) slip
velocities on the particle surface due to surface dissipative phenomena. The
perturbations of the hydrodynamic flow field exhibits characteristic
differences in cases (i) and (ii) which reflect different patterns of momentum
flux corresponding to the existence of net forces, force dipoles or force
quadrupoles. In the absence of external fields, gradients of concentration or
pressure do not generate net forces on a colloidal particle. Such gradients can
nevertheless induce relative motion between particle and fluid. We present a
generic description of surface dissipative phenomena based on the linear
response of surface fluxes driven by conjugate surface forces. In this
framework we discuss different transport scenarios including self-propulsion
via surface slip that is induced by active processes on the particle surface.
We clarify the nature of force balances in such situations.Comment: 22 pages, 1 figur
The MSSM fine tuning problem: a way out
As is well known, electroweak breaking in the MSSM requires substantial
fine-tuning, mainly due to the smallness of the tree-level Higgs quartic
coupling, lambda_tree. Hence the fine tuning is efficiently reduced in
supersymmetric models with larger lambda_tree, as happens naturally when the
breaking of SUSY occurs at a low scale (not far from the TeV). We show, in
general and with specific examples, that a dramatic improvement of the fine
tuning (so that there is virtually no fine-tuning) is indeed a very common
feature of these scenarios for wide ranges of tan(beta) and the Higgs mass
(which can be as large as several hundred GeV if desired, but this is not
necessary). The supersymmetric flavour problems are also drastically improved
due to the absence of RG cross-talk between soft mass parameters.Comment: 28 pages, 9 PS figures, LaTeX Published versio
Site investigation for the effects of vegetation on ground stability
The procedure for geotechnical site investigation is well established but little attention is currently given to investigating the potential of vegetation to assist with ground stability. This paper describes how routine investigation procedures may be adapted to consider the effects of the vegetation. It is recommended that the major part of the vegetation investigation is carried out, at relatively low cost, during the preliminary (desk) study phase of the investigation when there is maximum flexibility to take account of findings in the proposed design and construction. The techniques available for investigation of the effects of vegetation are reviewed and references provided for further consideration. As for general geotechnical investigation work, it is important that a balance of effort is maintained in the vegetation investigation between (a) site characterisation (defining and identifying the existing and proposed vegetation to suit the site and ground conditions), (b) testing (in-situ and laboratory testing of the vegetation and root systems to provide design parameters) and (c) modelling (to analyse the vegetation effects)
Can the Pioneer anomaly be of gravitational origin? A phenomenological answer
In order to satisfy the equivalence principle, any non-conventional mechanism
proposed to gravitationally explain the Pioneer anomaly, in the form in which
it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave
out of consideration its impact on the motion of the planets of the Solar
System as well, especially those orbiting in the regions in which the anomalous
behavior of the Pioneer probes manifested itself. In this paper we, first,
discuss the residuals of the right ascension \alpha and declination \delta of
Uranus, Neptune and Pluto obtained by processing various data sets with
different, well established dynamical theories (JPL DE, IAA EPM, VSOP). Second,
we use the latest determinations of the perihelion secular advances of some
planets in order to put on the test two gravitational mechanisms recently
proposed to accommodate the Pioneer anomaly based on two models of modified
gravity. Finally, we adopt the ranging data to Voyager 2 when it encountered
Uranus and Neptune to perform a further, independent test of the hypothesis
that a Pioneer-like acceleration can also affect the motion of the outer
planets of the Solar System. The obtained answers are negative.Comment: Latex2e, 26 pages, 6 tables, 2 figure, 47 references. It is the
merging of gr-qc/0608127, gr-qc/0608068, gr-qc/0608101 and gr-qc/0611081.
Final version to appear in Foundations of Physic
A pulsed, low-temperature beam of supersonically cooled free radical OH molecules
An improved system for creating a pulsed, low-temperature molecular beam of
OH radicals has been developed. We use a pulsed discharge to create OH from
HO seeded in Xe during a supersonic expansion, where the high-voltage pulse
duration is significantly shorter than the width of the gas pulse. The pulsed
discharge allows for control of the mean speed of the molecular packet as well
as maintains a low temperature supersonic expansion. A hot filament is placed
in the source chamber to initiate the discharge for shorter durations and at
lower voltages, resulting in a translationally and rotationally colder packet
of OH molecules
Naturally Rehearsing Passwords
We introduce quantitative usability and security models to guide the design
of password management schemes --- systematic strategies to help users create
and remember multiple passwords. In the same way that security proofs in
cryptography are based on complexity-theoretic assumptions (e.g., hardness of
factoring and discrete logarithm), we quantify usability by introducing
usability assumptions. In particular, password management relies on assumptions
about human memory, e.g., that a user who follows a particular rehearsal
schedule will successfully maintain the corresponding memory. These assumptions
are informed by research in cognitive science and validated through empirical
studies. Given rehearsal requirements and a user's visitation schedule for each
account, we use the total number of extra rehearsals that the user would have
to do to remember all of his passwords as a measure of the usability of the
password scheme. Our usability model leads us to a key observation: password
reuse benefits users not only by reducing the number of passwords that the user
has to memorize, but more importantly by increasing the natural rehearsal rate
for each password. We also present a security model which accounts for the
complexity of password management with multiple accounts and associated
threats, including online, offline, and plaintext password leak attacks.
Observing that current password management schemes are either insecure or
unusable, we present Shared Cues--- a new scheme in which the underlying secret
is strategically shared across accounts to ensure that most rehearsal
requirements are satisfied naturally while simultaneously providing strong
security. The construction uses the Chinese Remainder Theorem to achieve these
competing goals
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