685 research outputs found
Precautionary Demand for Foreign Assets in Sudden Stop Economies: An Assessment of the New Merchantilism
Financial globalization was off to a rocky start in emerging economies hit by Sudden Stops since the mid 1990s. Foreign reserves grew very rapidly during this period, and hence it is often argued that we live in the era of a New Merchantilism in which large stocks of reserves are a war-chest for defense against Sudden Stops. We conduct a quantitative assessment of this argument using a stochastic intertemporal equilibrium framework with incomplete asset markets in which precautionary saving affects foreign assets via three mechanisms: business cycle volatility, financial globalization, and Sudden Stop risk. In this framework, Sudden Stops are an equilibrium outcome produced by an endogenous credit constraint that triggers Irving Fisher's debt-deflation mechanism. Our results show that financial globalization and Sudden Stop risk are plausible explanations of the observed surge in reserves but business cycle volatility is not. In fact, business cycle volatility has declined in the post-globalization period. These results hold whether we use the formulation of intertemporal preferences of the Bewley-Aiyagari-Hugget class of precautionary savings models or the Uzawa-Epstein setup with endogenous time preference.
Thermal Stability of Metallic Single-Walled Carbon Nanotubes: An O(N) Tight-Binding Molecular Dynamics Simulation Study
Order(N) Tight-Binding Molecular Dynamics (TBMD) simulations are performed to
investigate the thermal stability of (10,10) metallic Single-Walled Carbon
Nanotubes (SWCNT). Periodic boundary conditions (PBC) are applied in axial
direction. Velocity Verlet algorithm along with the canonical ensemble
molecular dynamics (NVT) is used to simulate the tubes at the targeted
temperatures. The effects of slow and rapid temperature increases on the
physical characteristics, structural stability and the energetics of the tube
are investigated and compared. Simulations are carried out starting from room
temperature and the temperature is raised in steps of 300K. Stability of the
simulated metallic SWCNT is examined at each step before it is heated to higher
temperatures. First indication of structural deformation is observed at 600K.
For higher heat treatments the deformations are more pronounced and the bond
breaking temperature is reached around 2500K. Gradual (slow) heating and
thermal equilibrium (fast heating) methods give the value of radial thermal
expansion coefficient in the temperature range between 300K-600K as
0.31x10^{-5}(1/K) and 0.089x10^{-5}(1/K), respectively. After 600K, both
methods give the same value of 0.089x10^{-5}(1/K). The ratio of the total
energy per atom with respect to temperature is found to be 3x10^{-4} eV/K
An Anatomy Of Credit Booms: Evidence From Macro Aggregates And Micro Data
This paper proposes a methodology for measuring credit booms and uses it to identify credit booms in emerging and industrial economies over the past four decades. In addition, we use event study methods to identify the key empirical regularities of credit booms in macroeconomic aggregates and micro-level data. Macro data show a systematic relationship between credit booms and economic expansions, rising asset prices, real appreciations, widening external deficits and managed exchange rates. Micro data show a strong association between credit booms and firm-level measures of leverage, firm values, and external financing, and bank-level indicators of banking fragility. Credit booms in industrial and emerging economies show three major differences: (1) credit booms and the macro and micro fluctuations associated with them are larger in emerging economies, particularly in the nontradables sector; (2) not all credit booms end in financial crises, but most emerging markets crises were associated with credit booms; and (3) credit booms in emerging economies are often preceded by large capital inflows but not by financial reforms or productivity gains.
Electron orbital valves made of multiply connected armchair carbon nanotubes with mirror-reflection symmetry: tight-binding study
Using the tight-binding method and the Landauer-B\"{u}ttiker conductance
formalism, we demonstrate that a multiply connected armchair carbon nanotube
with a mirror-reflection symmetry can sustain an electron current of the
-bonding orbital while suppress that of the -antibonding orbital over
a certain energy range. Accordingly, the system behaves like an electron
orbital valve and may be used as a scanning tunneling microscope to probe
pairing symmetry in d-wave superconductors or even orbital ordering in solids
which is believed to occur in some transition-metal oxides.Comment: 4 figures, 12 page
On the calculation of the D-optimal multisine excitation power spectrum for broadband impedance spectroscopy measurements
The successful application of impedance spectroscopy in daily practice requires accurate
measurements for modeling complex physiological or electrochemical phenomena in a single
frequency or several frequencies at different (or simultaneous) time instants. Nowadays, two
approaches are possible for frequency domain impedance spectroscopy measurements: (1)
using the classical technique of frequency sweep and (2) using (non-)periodic broadband
signals, i.e. multisine excitations. Both techniques share the common problem of how to
design the experimental conditions, e.g. the excitation power spectrum, in order to achieve
accuracy of maximum impedance model parameters from the impedance data modeling
process. The original contribution of this paper is the calculation and design of the D-optimal
multisine excitation power spectrum for measuring impedance systems modeled as 2R-1C
equivalent electrical circuits. The extension of the results presented for more complex
impedance models is also discussed. The influence of the multisine power spectrum on the
accuracy of the impedance model parameters is analyzed based on the Fisher information
matrix. Furthermore, the optimal measuring frequency range is given based on the properties
of the covariance matrix. Finally, simulations and experimental results are provided to validate
the theoretical aspects presented.Peer ReviewedPostprint (published version
Chemically active substitutional nitrogen impurity in carbon nanotubes
We investigate the nitrogen substitutional impurity in semiconducting zigzag
and metallic armchair single-wall carbon nanotubes using ab initio density
functional theory. At low concentrations (less than 1 atomic %), the defect
state in a semiconducting tube becomes spatially localized and develops a flat
energy level in the band gap. Such a localized state makes the impurity site
chemically and electronically active. We find that if two neighboring tubes
have their impurities facing one another, an intertube covalent bond forms.
This finding opens an intriguing possibility for tunnel junctions, as well as
the functionalization of suitably doped carbon nanotubes by selectively forming
chemical bonds with ligands at the impurity site. If the intertube bond density
is high enough, a highly packed bundle of interlinked single-wall nanotubes can
form.Comment: 4 pages, 4 figures; major changes to the tex
Tubular structures of GaS
In this Brief Report we demonstrate, using density-functional tight-binding theory, that gallium sulfide (GaS) tubular nanostructures are stable and energetically viable. The GaS-based nanotubes have a semiconducting direct gap which grows towards the value of two-dimensional hexagonal GaS sheet and is in contrast to carbon nanotubes largely independent of chirality. We further report on the mechanical properties of the GaS-based nanotubes
Nanoscale Processing by Adaptive Laser Pulses
We theoretically demonstrate that atomically-precise ``nanoscale processing"
can be reproducibly performed by adaptive laser pulses. We present the new
approach on the controlled welding of crossed carbon nanotubes, giving various
metastable junctions of interest. Adaptive laser pulses could be also used in
preparation of other hybrid nanostructures.Comment: 4 pages, 4 Postscript figure
Diseño y optimización de una mezcla de compota, elaborada a partir de pulpa de guayaba, chalarina y oca
Este estudio tuvo como objetivo diseñar y optimizar una mezcla de compota, elaborada a partir de pulpa de guayaba, chalarina y oca. Para ello, se utilizaron frutas de guayaba, chalarina y tubérculos de oca recién cosechados, a los que se extrajeron las pulpas sin presencia de cáscara, pepas y materias extrañas. Seguidamente, las pulpas fueron escaldadas a 90 °C por 5 min y fueron mezcladas en proporciones de 0-100 %, de acuerdo al Diseño de Mezclas Simplex Centroide. La optimización se realizó teniendo en cuenta las variables de respuesta aceptabilidad y diferencial de color (ΔE). Las mezclas elaboradas con altos porcentajes de pulpa de guayaba y chalarina y bajos porcentajes de pulpa de oca mostraron una mayor aceptabilidad. La mezcla con un 66,66 % de pulpa de guayaba, 16,66 % de pulpa de chalarina y 16,66% de pulpa de oca presentó la mayor aceptabilidad de los panelistas. Las mezclas con altos porcentaje de pulpa de guayaba y chalarina y con proporciones iguales de las pulpas de guayaba, chalarina y oca (33,33 %/ 33,33 %/ 33,33 %) presentaron altos valores de ΔE. Los modelos cuadráticos para la aceptabilidad y ΔE exhibieron un mejor ajuste de los datos (R2 ajustado > 0,70), en comparación con los modelos lineales. La mezcla de pulpas óptimas fue la elaborada con 75 % de pulpa de guayaba y 25 % de pulpa de oca. Esto indica que las mezclas elaboradas con pulpa de guayaba y oca fueron las más aceptadas por los panelistas y presentaron el mayor ΔE
Bundling up carbon nanotubes through Wigner defects
We show, using ab initio total energy density functional theory, that the
so-called Wigner defects, an interstitial carbon atom right besides a vacancy,
which are present in irradiated graphite can also exist in bundles of carbon
nanotubes. Due to the geometrical structure of a nanotube, however, this defect
has a rather low formation energy, lower than the vacancy itself, suggesting
that it may be one of the most important defects that are created after
electron or ion irradiation. Moreover, they form a strong link between the
nanotubes in bundles, increasing their shear modulus by a sizeable amount,
clearly indicating its importance for the mechanical properties of nanotube
bundles.Comment: 5 pages and 4 figure
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