1,411 research outputs found
Barriers to Diversification and Regional Allocation of Capital
In order to evaluate the allocational effectiveness of regional policy when harmonizing regional economic conditions firms? preferences play a pivot role. If harmonization hinders risk diversification of the firm, then instead of regional diversification of capital agglomeration of capital occurs. Hence, regional policy will not achieve its objective to equal the spatial allocation of capital. --Regional policy,agglomeration,diversification,allocation,risk aversion,prudence
Spatial allocation of capital: The role of risk preferences
This paper considers a model of spatial allocation of investment capital under uncertainty. We demonstrate that the spatial concentration of economic activity depends upon properties of risk preferences deeper than risk aversion. The degree of so-called relative prudence unambiguously decides whether or not the diversi cation of income risk favours the geographic dispersion of economic activity. In our framework we relate risk diversi cation with economic integration. Then there exists risk preferences so that spatial concentration of industry and capital is not a ected by the degree of economic integration or segmentation of the regions. We also study the impact of net return regressibility upon spatial allocation. --spatial allocation,inter-regional disparity,risk aversion,prudence,regression
Strain-induced bound states in transition-metal dichalcogenide bubbles
This is an author-created, un-copyedited version of an article published in 2D Materials. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/2053-1583/ab0113We theoretically study the formation of single-particle bound states confined by strain at the center of bubbles in monolayers of transition-metal dichalcogenides (TMDs). Bubbles ubiquitously form in two-dimensional crystals on top of a substrate by the competition between van der Waals forces and the hydrostatic pressure exerted by trapped fluid. This leads to strong strain at the center of the bubble that reduces the bangap locally, creating potential wells for the electrons that confine states inside. We simulate the spectrum versus the bubble radius for the four semiconducting group VI TMDs, MoS2, WSe2, WS2 and MoSe2, and find an overall Fock-Darwin spectrum of bubble bound states, characterised by small deviations compatible with Berry curvature effects. We analyse the density of states, the state degeneracies, orbital structure and optical transition rules. Our results show that elastic bubbles in these materials are remarkably efficient at confining photocarriersWe acknowledge funding from the Graphene Flagship, contract CNECTICT-604391, from the Comunidad de Madrid through Grant MAD2D-CM, S2013/MIT-3007, from the Spanish Ministry of Economy and Competitiveness through Grants No. RYC-2011-09345, RYC-2016-20663, FIS2015-65706-P, FIS2016-80434-P (AEI/FEDER, EU) and the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377
Helly numbers of Algebraic Subsets of
We study -convex sets, which are the geometric objects obtained as the
intersection of the usual convex sets in with a proper subset
. We contribute new results about their -Helly
numbers. We extend prior work for , , and ; we give sharp bounds on the -Helly numbers in
several new cases. We considered the situation for low-dimensional and for
sets that have some algebraic structure, in particular when is an
arbitrary subgroup of or when is the difference between a
lattice and some of its sublattices. By abstracting the ingredients of Lov\'asz
method we obtain colorful versions of many monochromatic Helly-type results,
including several colorful versions of our own results.Comment: 13 pages, 3 figures. This paper is a revised version of what was
originally the first half of arXiv:1504.00076v
Beyond Chance-Constrained Convex Mixed-Integer Optimization: A Generalized Calafiore-Campi Algorithm and the notion of -optimization
The scenario approach developed by Calafiore and Campi to attack
chance-constrained convex programs utilizes random sampling on the uncertainty
parameter to substitute the original problem with a representative continuous
convex optimization with convex constraints which is a relaxation of the
original. Calafiore and Campi provided an explicit estimate on the size of
the sampling relaxation to yield high-likelihood feasible solutions of the
chance-constrained problem. They measured the probability of the original
constraints to be violated by the random optimal solution from the relaxation
of size .
This paper has two main contributions. First, we present a generalization of
the Calafiore-Campi results to both integer and mixed-integer variables. In
fact, we demonstrate that their sampling estimates work naturally for variables
restricted to some subset of . The key elements are
generalizations of Helly's theorem where the convex sets are required to
intersect . The size of samples in both algorithms will
be directly determined by the -Helly numbers.
Motivated by the first half of the paper, for any subset , we introduce the notion of an -optimization problem, where the
variables take on values over . It generalizes continuous, integer, and
mixed-integer optimization. We illustrate with examples the expressive power of
-optimization to capture sophisticated combinatorial optimization problems
with difficult modular constraints. We reinforce the evidence that
-optimization is "the right concept" by showing that the well-known
randomized sampling algorithm of K. Clarkson for low-dimensional convex
optimization problems can be extended to work with variables taking values over
.Comment: 16 pages, 0 figures. This paper has been revised and split into two
parts. This version is the second part of the original paper. The first part
of the original paper is arXiv:1508.02380 (the original article contained 24
pages, 3 figures
Thermodynamics of quantum crystalline membranes
We investigate the thermodynamic properties and the lattice stability of
two-dimensional crystalline membranes, such as graphene and related compounds,
in the low temperature quantum regime . A key role is played by
the anharmonic coupling between in-plane and out-of plane lattice modes that,
in the quantum limit, has very different consequences than in the classical
regime. The role of retardation, namely of the frequency dependence, in the
effective anharmonic interactions turns out to be crucial in the quantum
regime. We identify a crossover temperature, , between classical and
quantum regimes, which is K for graphene. Below , the
heat capacity and thermal expansion coefficient decrease as power laws with
decreasing temperature, tending to zero for as required by the
third law of thermodynamics.Comment: 13 pages, 1 figur
Reply to 'Comment on "Thermodynamics of quantum crystalline membranes"'
In this note, we reply to the comment made by E.I.Kats and V.V.Lebedev
[arXiv:1407.4298] on our recent work "Thermodynamics of quantum crystalline
membranes" [Phys. Rev. B 89, 224307 (2014)]. Kats and Lebedev question the
validity of the calculation presented in our work, in particular on the use of
a Debye momentum as a ultra-violet regulator for the theory. We address and
counter argue the criticisms made by Kats and Lebedev to our work.Comment: 5 pages, 4 figure
Coexistence of single-mode and multi-longitudinal mode emission in the ring laser model
A homogeneously broadened unidirectonal ring laser can emit in several
longitudinal modes for large enough pump and cavity length because of Rabi
splitting induced gain. This is the so called Risken-Nummedal-Graham-Haken
(RNGH) instability. We investigate numerically the properties of the multi-mode
solution. We show that this solution can coexist with the single-mode one, and
its stability domain can extend to pump values smaller than the critical pump
of the RNGH instability. Morevoer, we show that the multi-mode solution for
large pump values is affected by two different instabilities: a pitchfork
bifurcation, which preserves phase-locking, and a Hopf bifurcation, which
destroys it.Comment: 14 pages, 7 figure
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