408 research outputs found
Toll-managed lanes: A simplified benefit-cost analysis of seven US projects
Toll managed lanes are expressway lanes where tolls are used—often in combination with preferred access for high occupancy vehicles and other special traffic management techniques—to improve the highway's capacity, speed or reliability. Such lanes have become popular with transportation policymakers as a way of maintaining free-flowing traffic on certain sections of the highway while also, in some cases, financing the construction of new lanes in congested urban areas. This study examines whether toll-managed lanes are as beneficial as they are popular. The heart of the analysis is the application of a simplified social benefit-cost analysis (BCA) to seven projects. In brief, our results paint a complicated picture of toll-managed lane efficacy. Only two of the seven projects have benefit-cost (B/C) ratios above 1.0 using our base case assumptions about the value of travel time saved and the discount rate, although three others approach or exceed 1.0 with more optimistic but plausible assumptions. The most successful generate not only a significant savings of around 4–5 min per trip for motorists who switch to the managed lane but also smaller per-trip savings for the large majority of motorists who continue to use the general-purpose lanes. It is important to acknowledge, however, that these calculations depend upon some uncertain assumptions about the value of travel time savings and improved reliability
Fine Tuning in General Gauge Mediation
We study the fine-tuning problem in the context of general gauge mediation.
Numerical analyses toward for relaxing fine-tuning are presented. We analyse
the problem in typical three cases of the messenger scale, that is, GUT
( GeV), intermediate ( GeV), and relatively low energy
( GeV) scales. In each messenger scale, the parameter space reducing the
degree of tuning as around 10% is found. Certain ratios among gluino mass, wino
mass and soft scalar masses are favorable. It is shown that the favorable
region becomes narrow as the messenger scale becomes lower, and tachyonic
initial conditions of stop masses at the messenger scale are favored to relax
the fine-tuning problem for the relatively low energy messenger scale. Our
spectra would also be important from the viewpoint of the problem.Comment: 22 pages, 16 figures, comment adde
The Conformal Sector of F-theory GUTs
D3-brane probes of exceptional Yukawa points in F-theory GUTs are natural
hidden sectors for particle phenomenology. We find that coupling the probe to
the MSSM yields a new class of N = 1 conformal fixed points with computable
infrared R-charges. Quite surprisingly, we find that the MSSM only weakly mixes
with the strongly coupled sector in the sense that the MSSM fields pick up
small exactly computable anomalous dimensions. Additionally, we find that
although the states of the probe sector transform as complete GUT multiplets,
their coupling to Standard Model fields leads to a calculable threshold
correction to the running of the visible sector gauge couplings which improves
precision unification. We also briefly consider scenarios in which SUSY is
broken in the hidden sector. This leads to a gauge mediated spectrum for the
gauginos and first two superpartner generations, with additional contributions
to the third generation superpartners and Higgs sector.Comment: v2: 51 pages, 2 figures, remark added, typos correcte
Decision, Sensation, and Habituation: A Multi-Layer Dynamic Field Model for Inhibition of Return
Inhibition of Return (IOR) is one of the most consistent and widely studied effects in experimental psychology. The effect refers to a delayed response to visual stimuli in a cued location after initial priming at that location. This article presents a dynamic field model for IOR. The model describes the evolution of three coupled activation fields. The decision field, inspired by the intermediate layer of the superior colliculus, receives endogenous input and input from a sensory field. The sensory field, inspired by earlier sensory processing, receives exogenous input. Habituation of the sensory field is implemented by a reciprocal coupling with a third field, the habituation field. The model generates IOR because, due to the habituation of the sensory field, the decision field receives a reduced target-induced input in cue-target-compatible situations. The model is consistent with single-unit recordings of neurons of monkeys that perform IOR tasks. Such recordings have revealed that IOR phenomena parallel the activity of neurons in the intermediate layer of the superior colliculus and that neurons in this layer receive reduced input in cue-target-compatible situations. The model is also consistent with behavioral data concerning temporal expectancy effects. In a discussion, the multi-layer dynamic field account of IOR is used to illustrate the broader view that behavior consists of a tuning of the organism to the environment that continuously and concurrently takes place at different spatiotemporal scales
Glycomic analysis of gastric carcinoma cells discloses glycans as modulators of RON receptor tyrosine kinase activation in cancer
Background Terminal a2-3 and a2-6 sialylation of glycans precludes further chain elongation, leading to the biosynthesis of cancer relevant epitopes such as sialyl-Lewis X (SLe X ). SLe X overexpression is associated with tumor aggressive phenotype and patients' poor prognosis. Methods MKN45 gastric carcinoma cells transfected with the sialyltransferase ST3GAL4 were established as a model overexpressing sialylated terminal glycans. We have evaluated at the structural level the glycome and the sialoproteome of this gastric cancer cell line applying liquid chromatography and mass spectrometry. We further validated an identified target expression by proximity ligation assay in gastric tumors. Results Our results showed that ST3GAL4 overexpression leads to several glycosylation alterations, including reduced O-glycan extension and decreased bisected and increased branched N-glycans. A shift from a2-6 towards a2-3 linked sialylated N-glycans was also observed. Sialoproteomic analysis further identified 47 proteins with significantly increased sialylated N-glycans. These included integrins, insulin receptor, carcinoembryonic antigens and RON receptor tyrosine kinase, which are proteins known to be key players in malignancy. Further analysis of RON confirmed its modification with SLe X and the concomitant activation. SLe X and RON co-expression was validated in gastric tumors. Conclusion The overexpression of ST3GAL4 interferes with the overall glycophenotype of cancer cells affecting a multitude of key proteins involved in malignancy. Aberrant glycosylation of the RON receptor was shown as an alternative mechanism of oncogenic activation. General significance This study provides novel targets and points to an integrative tumor glycomic/proteomic-profiling for gastric cancer patients' stratification. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.We acknowledge the support from the European Union, Seventh Framework Programme, Gastric Glyco Explorer initial training network: grant number 316929. IPATIMUP integrates the i3S Research Unit, which is partially supported by FCT, the Portuguese Foundation for Science and Technology. This work is funded by FEDER funds through the Operational Programme for Competitiveness Factors-COMPETE (FCOMP-01-0124-FEDER028188) and National Funds through the FCT-Foundation for Science and Technology, under the projects: PEst-C/SAU/LA0003/2013, PTDC/BBB-EBI/0786/2012, and PTDC/BBB-EBI/0567/2014 (to CAR). This work was also supported by"Glycoproteomics" project grant number PCIG09-GA-2011-293847(to DK) and the Danish Natural Science Research Council and a generous grant from the VILLUM Foundation to the VILLUM Center for Bioanalytical Sciences at the University of Southern Denmark (to MRL). Grants were received from FCT, POPH (Programa Operacional Potencial Humano) and FSE (Fundo Social Europeu): SFRH/BPD/75871/2011 to AM; SFRH/BPD/111048/2015 to JAF; SFRH/BPD/96510/2013 to CG. The UPLC instrument was obtained with a grant from the Ingabritt and Arne Lundbergs Research Foundation (to NK). C.J. was supported by the Knut and Alice Wallenberg Foundation. The mass spectrometer (LTQ) was obtained by a grant from the Swedish Research Council (342-2004-4434) (to NK)
Non-supersymmetric heterotic model building
We investigate orbifold and smooth Calabi-Yau compactifications of the
non-supersymmetric heterotic SO(16)xSO(16) string. We focus on such Calabi-Yau
backgrounds in order to recycle commonly employed techniques, like index
theorems and cohomology theory, to determine both the fermionic and bosonic 4D
spectra. We argue that the N=0 theory never leads to tachyons on smooth
Calabi-Yaus in the large volume approximation. As twisted tachyons may arise on
certain singular orbifolds, we conjecture that such tachyonic states are lifted
in the full blow-up. We perform model searches on selected orbifold geometries.
In particular, we construct an explicit example of a Standard Model-like theory
with three generations and a single Higgs field.Comment: 1+30 pages latex, 11 tables; v2: references and minor revisions
added, matches version published in JHE
Simplifying one-loop amplitudes in superstring theory
We show that 4-point vector boson one-loop amplitudes, computed in ref.[1] in
the RNS formalism, around vacuum configurations with open unoriented strings,
preserving at least N=1 SUSY in D=4, satisfy the correct supersymmetry Ward
identities, in that they vanish for non MHV configurations (++++) and (-+++).
In the MHV case (--++) we drastically simplify their expressions. We then study
factorisation and the limiting IR and UV behaviour and find some unexpected
results. In particular no massless poles are exposed at generic values of the
modular parameter. Relying on the supersymmetric properties of our bosonic
amplitudes, we extend them to manifestly supersymmetric super-amplitudes and
compare our results with those obtained in the D=4 hybrid formalism, pointing
out difficulties in reconciling the two approaches for contributions from N=1,2
sectors.Comment: 38 pages plus appendice
Sparticle Spectrum of Large Volume Compactification
We examine the large volume compactification of Type IIB string theory or its
F theory limit and the associated supersymmetry breakdown and soft terms. It is
crucial to incorporate the loop-induced moduli mixing, originating from
radiative corrections to the Kahler potential. We show that in the presence of
moduli mixing, soft scalar masses generically receive a D-term contribution of
the order of the gravitino mass m_{3/2} when the visible sector cycle is
stabilized by the D-term potential of an anomalous U(1) gauge symmetry, while
the moduli-mediated gaugino masses and A-parameters tend to be of the order of
m_{3/2}/8pi^2. It is noticed also that a too large moduli mixing can
destabilize the large volume solution by making it a saddle point.Comment: 29 page
Neutron Majorana mass from exotic instantons
We show how a Majorana mass for the Neutron could result from
non-perturbative quantum gravity effects peculiar to string theory. In
particular, "exotic instantons" in un-oriented string compactifications with
D-branes extending the (supersymmetric) standard model could indirectly produce
an effective operator delta{m} n^t n+h.c. In a specific model with an extra
vector-like pair of `quarks', acquiring a large mass proportional to the string
mass scale (exponentially suppressed by a function of the string moduli
fields), delta{m} can turn out to be as low as 10^{-24}-10^{-25} eV. The
induced neutron-antineutron oscillations could take place with a time scale
tau_{n\bar{n}} > 10^8 s, that could be tested by the next generation of
experiments. On the other hand, proton decay and FCNC's are automatically
strongly suppressed and are compatible with the current experimental limits.
Depending on the number of brane intersections, the model may also lead to the
generation of Majorana masses for R-handed neutrini. Our proposal could also
suggest neutron-neutralino or neutron-axino oscillations, with implications in
UCN, Dark Matter Direct Detection, UHECR and Neutron-Antineutron oscillations.
This suggests to improve the limits on neutron-antineutron oscillations, as a
possible test of string theory and quantum gravity.Comment: 35 pages, 11 figures. More comments on neutron-neutralino mixin
Spontaneous breaking of SU(3) to finite family symmetries: a pedestrian's approach
Non-Abelian discrete family symmetries play a pivotal role in the formulation
of models with tri-bimaximal lepton mixing. We discuss how to obtain symmetries
such as A4, semidirect product of Z7 and Z3, and Delta(27) from an underlying
SU(3) gauge symmetry. Higher irreducible representations are required to
achieve the spontaneous breaking of the continuous group. We present methods of
identifying the required vacuum alignments and discuss in detail the symmetry
breaking potentials.Comment: 21 page
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