3,117 research outputs found
Nominal stylized facts of U. S. business cycles
The authors investigate the basic nominal stylized facts of business cycles in the United States, using monthly data from 1960:1 to 1993:4 and the methodology suggested by Kydland and Prescott (1990). They make comparisons among simple sum and Divisia aggregates, using the Thornton and Yue (1992) series of Divisia monetary aggregates, and they investigate the robustness of the results to relevant nonstochastic stationarity-inducing transformations.Business cycles
Indirect Network Effects and Adoption Externalities
The conventional wisdom is that indirect network effects, unlike direct network effects, do not give rise to externalities. In this paper we show that under very general conditions, indirect network effects lead to adoption externalities. In particular we show that in markets where consumption benefits arise from hardware/software systems, adoption externalities will occur when there are (i) increasing returns to scale in the production of software, (ii) free-entry in software, and (iii) consumers have a preference for software variety. The private benefit of the marginal hardware purchaser is less than the social benefit since the marginal hardware purchaser does not internalize the welfare improving response of the software industry, particularly the increase in software variety, on inframarginal purchasers when the market for hardware expands.Network Externalities, Network Effects
Enhancement of magnetic fields arising from galactic encounters
Galactic encounters are usually marked by a substantial increase of
synchrotron emission of the interacting galaxies compared to the typical
emission from similar isolated galaxies. This is believed to be associated with
an increase of the star formation rate and the associated turbulent magnetic
fields. The regular magnetic field is usually believed to decrease. We consider
a simple, however rather realistic, mean-field galactic dynamo model where the
effects of small-scale generation are represented by random injections of
magnetic field from star forming regions. We represent an encounter by the
introduction of large-scale streaming velocities and by an increase in
small-scale magnetic field injections. The latter describes the effect of an
increase of the star formation rate caused by the encounter. We demonstrate
that large-scale streaming, with associated deviations in the rotation curve,
can result in an enhancement of the anisotropic turbulent (ordered) magnetic
field strength, mainly along the azimuthal direction, leading to a significant
temporary increase of the total magnetic energy during the encounter; the
representation of an increase in star formation rate has an additional strong
effect. In contrast to expectations, the large-scale (regular) magnetic field
structure is not significantly destroyed by the encounter. It may be somewhat
weakened for a relatively short period, and its direction after the encounter
may be reversed. The encounter causes enhanced total and polarized emission
without increase of the regular magnetic field strength. The increase of
synchrotron emission caused by the large-scale streaming can be comparable to
the effect of the increase of the star formation rate, depending on the choice
of parameters.The effects of the encounter on the total magnetic field energy
last only slightly longer than the duration of the encounter (ca. 1 Gyr).Comment: 9 pages, 11 figures minor changes in response to referee's
comments+linguistic/stylistic change
Learning Generative Models across Incomparable Spaces
Generative Adversarial Networks have shown remarkable success in learning a
distribution that faithfully recovers a reference distribution in its entirety.
However, in some cases, we may want to only learn some aspects (e.g., cluster
or manifold structure), while modifying others (e.g., style, orientation or
dimension). In this work, we propose an approach to learn generative models
across such incomparable spaces, and demonstrate how to steer the learned
distribution towards target properties. A key component of our model is the
Gromov-Wasserstein distance, a notion of discrepancy that compares
distributions relationally rather than absolutely. While this framework
subsumes current generative models in identically reproducing distributions,
its inherent flexibility allows application to tasks in manifold learning,
relational learning and cross-domain learning.Comment: International Conference on Machine Learning (ICML
Overcoming The Challenges of Establishing A Student-Managed Fixed Income Fund
Student-managed funds (SMFs) offer unique educational opportunities. In a typical SMF, students select common stocks and manage a real portfolio, gaining practical money management experience. Until recently, establishing a fixed income SMF has been unworkable for most academic institutions. Fixed income exchange traded funds (ETFs) are relatively new financial offerings that allow non-institutional investors the ability to trade shares of an entire bond portfolio as a single security. By combining different ETFs into a fund of funds, it is possible for students to implement various bond portfolio management strategies - a valuable learning opportunity previously unavailable to most business students
Gauge-independent Renormalization of the N2HDM
The Next-to-Minimal 2-Higgs-Doublet Model (N2HDM) is an interesting benchmark
model for a Higgs sector consisting of two complex doublet and one real singlet
fields. Like the Next-to-Minimal Supersymmetric extension (NMSSM) it features
light Higgs bosons that could have escaped discovery due to their singlet
admixture. Thereby, the model allows for various different Higgs-to-Higgs decay
modes. Contrary to the NMSSM, however, the model is not subject to
supersymmetric relations restraining its allowed parameter space and its
phenomenology. For the correct determination of the allowed parameter space,
the correct interpretation of the LHC Higgs data and the possible distinction
of beyond-the-Standard Model Higgs sectors higher order corrections to the
Higgs boson observables are crucial. This requires not only their computation
but also the development of a suitable renormalization scheme. In this paper we
have worked out the renormalization of the complete N2HDM and provide a scheme
for the gauge-independent renormalization of the mixing angles. We discuss the
renormalization of the soft breaking parameter and
the singlet vacuum expectation value . Both enter the Higgs self-couplings
relevant for Higgs-to-Higgs decays. We apply our renormalization scheme to
different sample processes such as Higgs decays into bosons and decays into
a lighter Higgs pair. Our results show that the corrections may be sizeable and
have to be taken into account for reliable predictions
The formation of regular interarm magnetic fields in spiral galaxies
Observations of regular magnetic fields in several nearby galaxies reveal
magnetic arms situated between the material arms. The nature of these magnetic
arms is a topic of active debate. Previously we found a hint that taking into
account the effects of injections of small-scale magnetic fields generated,
e.g., by turbulent dynamo action, into the large-scale galactic dynamo can
result in magnetic arm formation. We now investigate the joint roles of an
arm/interarm turbulent diffusivity contrast and injections of small-scale
magnetic field on the formation of large-scale magnetic field ("magnetic arms")
in the interarm region. We use the relatively simple "no-" model for the
galactic dynamo. This involves projection on to the galactic equatorial plane
of the azimuthal and radial magnetic field components; the field component
orthogonal to the galactic plane is estimated from the solenoidality condition.
We find that addition of diffusivity gradients to the effect of magnetic field
injections makes the magnetic arms much more pronounced. In particular, the
regular magnetic field component becomes larger in the interarm space compared
to that within the material arms.The joint action of the turbulent diffusivity
contrast and small-scale magnetic field injections (with the possible
participation of other effects previously suggested) appears to be a plausible
explanation for the phenomenon of magnetic arms.Comment: 9 pages, 9 figure
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