Standard Theoretical Model Research Articles

Implementing Monetary Policy in a Fragmented Monetary Union

This paper shows how interbank market fragmentation disrupts monetary policy implementation. Fragmentation is defined as the situation where some banks are cut from the interbank loan market. The paper incorporates fragmentation in an otherwise standard theoretical model of monetary policy implementation, where profit maximizing banks, subject to reserve requirements, borrow and deposit funds at a central bank. It shows that in the presence of fragmentation, excess liquidity arises endogenously and the interbank rate declines below the central bank main rate. The interbank rate is then unstable. The paper documents that this is what happened in the Euro-Area since 2008. The model is also well suited to analyze unconventional monetary policy measures.

Self-written waveguides in a dry acrylamide/polyvinyl alcohol photopolymer material.

For the first time it is demonstrated that permanent optical waveguides can be self-written in a solid acrylamide/polyvinyl alcohol photopolymer material. The novel (to our knowledge) technique used to prepare the polymeric medium used is described. It is demonstrated that the resulting waveguides formed can be used to guide different wavelengths. A standard theoretical model is used to predict both the evolution of the light intensity distribution and the channel formation inside the material during the exposure. The experimental results and the numerical simulations are compared, and good agreement is obtained.

Characterizing and modeling the efficiency limits in large-scale production of hyperpolarized 129Xe.

The ability to produce liter volumes of highly spin-polarized 129Xe enables a wide range of investigations, most notably in the fields of materials science and biomedical MRI. However, for nearly all polarizers built to date, both peak 129Xe polarization and the rate at which it is produced fall far below those predicted by the standard model of Rb metal vapor, spin-exchange optical pumping (SEOP). In this work, we comprehensively characterized a high-volume, flow-through 129Xe polarizer using three different SEOP cells with internal volumes of 100, 200 and 300 cc and two types of optical sources: a broad-spectrum 111-W laser (FWHM = 1.92 nm) and a line-narrowed 71-W laser (FWHM = 0.39 nm). By measuring 129Xe polarization as a function of gas flow rate, we extracted peak polarization and polarization production rate across a wide range of laser absorption levels. Peak polarization for all cells consistently remained a factor of 2-3 times lower than predicted at all absorption levels. Moreover, although production rates increased with laser absorption, they did so much more slowly than predicted by the standard theoretical model and basic spin exchange efficiency arguments. Underperformance was most notable in the smallest optical cells. We propose that all these systematic deviations from theory can be explained by invoking the presence of paramagnetic Rb clusters within the vapor. Cluster formation within saturated alkali vapors is well established and their interaction with resonant laser light was recently shown to create plasma-like conditions. Such cluster systems cause both Rb and 129Xe depolarization, as well as excess photon scattering. These effects were incorporated into the SEOP model by assuming that clusters are activated in proportion to excited-state Rb number density and by further estimating physically reasonable values for the nanocluster-induced, velocity-averaged spin-destruction cross-section for Rb (<σcluster-Rbv> ≈4×10-7 cm3s-1), 129Xe relaxation cross-section (<σcluster-Xev> ≈ 4×10-13 cm3s-1), and a non-wavelength-specific, photon-scattering cross-section (σcluster ≈ 1×10-12 cm2). The resulting modified SEOP model now closely matches experimental observations.

Validiation of Photometric Ellipsometry for Refractive Index and Thickness Measurements

We design and build a photometric ellipsometer that can be adjusted or modified to match specific needs for different experiments. To validate our setup, we test the system with glass substrates at multiple incident angles from 30° to 70°. The experimental data can then be fitted to the standard theoretical model for ellipsometry with a single interface, allowing the amplitude ratio (tan Ψ) and the phase difference (Δ) to be evaluated as fitting parameters. As a result, we obtain the refractive indices of glass as 1.44–1.55 depending on the backing material. By the same means, it is also feasible to derive thicknesses of silicon oxide films. The resulting thicknesses are in good agreement with those determined by a commercial ellipsometer with the minimum deviation of 0.2 %.

Intangible capital in a real business cycle model

Recent empirical studies have shown that intangible capital plays an important role in explaining productivity gains that have occurred during the last two decades. By introducing intangible capital in an otherwise standard theoretical real business cycle model, this paper aims to provide a theoretical foundation of the empirical findings. Our results indicate that investment in intangible capital is pro-cyclical. Both transitory as well as permanent productivity shocks increase investment in intangible capital. However, in case of a permanent technology shock we learn that firms allocate more labor and physical capital to the creation of intangible capital which increases future profits at the cost of current profit. We also find that investment in intangible capital plays an important role in producing endogenous movements in productivity.

Pandemics of the Poor and Banking Stability

We first develop a standard theoretical model that shows that the likelihood of a collapse of the banking industry of a developing country increases, as the joint prevalence of large pandemics such as AIDS and malaria increases. We also show that the optimal bank reserves increase as the prevalence increases. In the empirical part of the paper, we consider a large dataset of developing countries, and we exhibit a strong causality effect from combined prevalence to deposit turnover, as well as a strong causality effect from an increase of combined prevalence to an increase in bank reserves. This effect is strong for tuberculosis. Those empirical facts therefore strongly support our theoretical findings.

Search for the standard model Higgs boson in the [formula omitted] channel in 9.5 fb−1 of [formula omitted] collisions at [formula omitted

We present a search for the standard model Higgs boson in 9.5 fb−1 of pp¯ collisions at s=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered contains a pair of b jets and is characterized by an imbalance in transverse energy, as expected from pp¯→ZH→νν¯bb¯ production. The search is also sensitive to the WH→ℓνbb¯ channel when the charged lepton is not identified. The data are found to be in good agreement with the expected background. For a Higgs boson mass of 125 GeV, we set a limit at the 95% C.L. on the cross section σ(pp¯→[Z/W]H), assuming standard model branching fractions, that is a factor of 4.3 times larger than the theoretical standard model value, while the expected factor is 3.9. The search is also used to measure a combined WZ and ZZ production cross section that is a factor of 0.94±0.31(stat)±0.34(syst) times the standard model prediction of 4.4 pb, with an observed significance of 2.0 standard deviations.

On the hydrogen maser oscillation threshold

In the construction and evaluation of the characteristics of a hydrogen maser, the oscillation parameter q remains an important parameter but somewhat difficult to determine precisely. Among the few techniques that exist to do such an evaluation we report on the technique using a variation of the quality factor of the microwave cavity. The results are compared to the standard theoretical model of operation of the maser accepted up to now. It is found that the technique described is extremely useful for determining the operational characteristics of such a maser. Furthermore, the experimental results and theoretical analysis are in reasonable agreement, which validates to a new level the hypothesis made in the development of the theory.

Implications of the LHC two-photon signal for two-Higgs-doublet models

We study the implications for two-Higgs-doublet models of the recent announcement at the LHC giving a tantalizing hint for a Higgs boson of mass 125 GeV decaying into two photons. We require that the experimental result be within a factor of 2 of the theoretical standard model prediction, and analyze the type I and type II models as well as the lepton-specific and flipped models, subject to this requirement. It is assumed that there is no new physics other than two Higgs doublets. In all of the models, we display the allowed region of parameter space taking the recent LHC announcement at face value, and we analyze the ${W}^{+}{W}^{\ensuremath{-}}$, $ZZ$, $\overline{b}b$, and ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ expectations in these allowed regions. Throughout the entire range of parameter space allowed by the $\ensuremath{\gamma}\ensuremath{\gamma}$ constraint, the numbers of events for Higgs decays into $WW$, $ZZ$, and $b\overline{b}$ are not changed from the standard model by more than a factor of 2. In contrast, in the lepton-specific model, decays to ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ are very sensitive across the entire $\ensuremath{\gamma}\ensuremath{\gamma}$-allowed region.

Designing Multiperson Tournaments with Asymmetric Contestants: An Experimental Study

Is the right amount of effort exerted in multiperson tournaments where contestants have two different levels of initial endowments (termed “favorites” and “underdogs”)? We develop theoretical predictions for the level of effort and the effect of varying the prize structure. We test these predictions for three-person tournaments using an economic experiment in a social environment where contest outcomes are publicly announced. We find that both favorites and underdogs overexert effort relative to the theoretical point predictions. Moreover, in the treatment with two favorites and one underdog, favorites increase their effort when the number of prizes is increased from one to two, contrary to the theory prediction. We show that a generalized model that allows for psychological losses from losing for favorites and psychological gains from winning for underdogs because of social comparisons tracks the experimental results better than the standard theoretical model. This paper was accepted by Peter Wakker, decision analysis.

Sustainable development in a natural resource rich economy: the case of Chile in 1985–2004

Searching for practical means to assessing economic growth’s sustainability, we extend a standard theoretical model to calculate “true” income measures for Chile, during the 1985–2004 period, and use estimates of natural capital depreciation to obtain genuine national saving measures. We found that, for the period, Chile’s economic growth was sustainable, even when approximately 2.5% of the income recorded by national accounts corresponded to depreciation of natural resources plus costs of atmospheric pollution. This performance can be partially explained by policies implemented to force fiscal responsibility and to assure wise public investment and expending during a natural resource driven growth. This evidence reinforces recent findings contradicting the natural resource curse, and the indirect negative effect of resource abundance over growth that would operate through the quality of institutions.

A putative role for neurogenesis in neurocomputational terms: Inferences from a hippocampal model

New neurons are generated daily in the hippocampus during adult life. They are integrated into the existing neuronal circuits according to several factors such as age, physical exercise and hormonal status. At present, the role of these new neurons is debated. Computational simulations of hippocampal function allow the effects of neurogenesis to be explored, at least from a computational perspective. The present work implements a model of neurogenesis in the hippocampus with artificial neural networks, based on a standard theoretical model of biologically plausible hippocampal circuits. The performance of the model in retrieval of a variable number of patterns or memories was evaluated (episodic memory evaluation). The model increased, in a phase subsequent to initial learning, the number of granular cells by 30% relative to their initial number. In contrast to a model without neurogenesis, the retrieval of recent memories was very significantly improved, although remotes memories were only slightly affected by neurogenesis. This increase in the quality of retrieval of new memories represents a clear advantage that we attribute to the neurogenesis process. This advantage becomes more significant for higher storage loads. The model presented here suggests an important functional role of neurogenesis on learning and memory.

Laccase production in solid‐state and submerged fermentation by Pleurotus ostreatus

AbstractA solid‐state fermentation (SSF) system for production of an industrially important enzyme laccase by Pleurotus ostreatus was developed by using potato dextrose yeast extract medium and polyurethane foam as a supporting material. The maximum laccase production in the SSF system was as high as 3×105 U/L. Addition of inducers, such as copper and ferulic acid, further enhanced the laccase production in SSF. Moreover, the time required for the maximum laccase production was reduced to 6 days compared to 10 days reported earlier. The improvement achieved by the SSF system was investigated by comparing it to a submerged fermentation system (SmF), both experimentally and by using a standard theoretical model along with a parameter sensitivity analysis. Laccase production in SSF was found to be twice of that in SmF. One of the main reasons for higher laccase production in SSF compared to SmF was possibly due to the presence of higher proteolytic activity in SmF. Strong proteolytic activity in SmF presumably caused subsequent laccase degradation, which lowered the ultimate laccase production in SmF compared to SSF.

Multifractality in the Peripheral Cardiovascular System from Pointwise Hölder Exponents of Laser Doppler Flowmetry Signals

We study the dynamics of skin laser Doppler flowmetry signals giving a peripheral view of the cardiovascular system. The analysis of Hölder exponents reveals that the experimental signals are weakly multifractal for young healthy subjects at rest. We implement the same analysis on data generated by a standard theoretical model of the cardiovascular system based on nonlinear coupled oscillators with linear couplings and fluctuations. We show that the theoretical model, although it captures basic features of the dynamics, is not complex enough to reflect the multifractal irregularities of microvascular mechanisms.

Linear and nonlinear AC susceptibility studies in La(Mn 1−xCu x)O 3

The linear and nonlinear AC susceptibility as a function of temperature were measured on LaMn 1− x Cu x O 3 compounds for x = 0.05 – 0.30 . Samples with x ⩾ 0.10 exhibit paramagnetic to ferromagnetic transitions followed by low temperature spin glass like transition. The linear susceptibility exhibits strong frequency dependence and is analyzed in terms of standard theoretical model for spin glass. The magnitude and peak temperature of nonlinear susceptibility vary with AC field amplitudes. They are analyzed in terms of critical behaviour in the vicinity of spin glass transition temperature and the critical exponent is found to be 3.2.

Modeling coherent Doppler sonar in fisheries acoustics

A computer model was developed to simulate the operation of a 250-kHz coherent Doppler sonar used to detect fish movements. The backscattered signal was constructed by summing contributions from many point targets. That signal was then detected and analyzed using the same method as used in the actual Doppler system. The model results reproduce predictions for the standard deviation of Doppler velocity estimates from volume backscatter based on the standard theoretical model of coherent pulse processing [Zrnic, IEEE Trans. Aerosp. Electron. Syst. AES-13, 344–354 (1977)]. However when the signal is modified to simulate the backscatter from a swimming fish (a single strong target among many weaker targets) the modeled standard deviation is 2 to 4 times lower than predicted by theory. Furthermore, the unusually low modeled standard deviations agree with laboratory and field observations. The model results confirm that the theoretical treatment used to predict the performance of Doppler measurements of current flow, blood flow, and atmospheric phenomena does not apply to the backscatter resulting from a single strong target such as a fish.

Effects of temperature, strain rate, and vacancies on tensile and fatigue behaviors of silicon-based nanotubes

This paper adopts the Tersoff-Brenner many-body potential function to perform molecular dynamics simulations of the tensile and fatigue behaviors of hypothetical silicon-based tubular nanostructures at various temperatures, strain rates, and vacancy percentages. The tensile test results indicate that with a predicted Young's modulus of approximately $60\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, silicon nanotubes $(\mathrm{SiNTs})$ are significantly less stiff than conventional carbon nanotubes. It is observed that the presence of hydrogen has a significant influence on the tensile strength of $\mathrm{SiNTs}$. Additionally, the present results indicate that the tensile strength clearly decreases with increasing temperature and with decreasing strain rate. Moreover, it is shown that the majority of the mechanical properties considered in the present study decrease with an increasing vacancy percentage. Regarding the fatigue tests, this study uses a standard theoretical model to derive curves of amplitude stress versus number of cycles for the current nanotubes. The results demonstrate that the fatigue limit of $\mathrm{SiNTs}$ increases with a decreasing vacancy percentage and with increasing temperature.

Molecular dynamics investigation of the mechanical properties of gallium nitride nanotubesunder tension and fatigue

This study adopts a classical molecular dynamics (MD) simulation with the realistic Tersoffmany-body potential model to investigate the mechanical properties of gallium nitride(GaN) nanotubes. The investigation focuses primarily on the mechanical properties of(n,0) and (n,n) GaN nanotubes since these particular nanotubes represent two extreme cases. The presentresults indicate that under small strain conditions, mechanical properties such as Young’smodulus are insensitive to the wrapping angle. Conversely, the wrapping angle has a significantinfluence upon these mechanical properties under large strain conditions. It is demonstrated that(9,0) GaN nanotubes are far less resistant to bond rotation. Under large tensile strain conditions, due tothe unfavourable bond orientations induced by Stone–Wales (SW) transformation, the bonds in(n,0) GaN tubes quickly degenerate. Moreover, the present results suggest that the tensilestrength of a nanotube is strongly sensitive to the temperature and strain rate. Regardingthe fatigue test, this study uses a standard theoretical model to derive curves of amplitudestress versus number of cycles for the current nanotubes. The results demonstratethat the fatigue limit of GaN nanotubes increases with increasing temperature.

Electroconvection with and without the Carr-Helfrich effect in a series of nematic liquid crystals.

Experimental electroconvection (EC) investigations on four homologs with negative dielectric anisotropy epsilona and conductivity anisotropies sigmaa of various signs (the relative sigma; a=sigmaa/sigma(perpendicular) ranges from -0.6 to +0.3 ) are reported. The homolog with positive conductivity anisotropy follows the predictions of the standard theoretical model, while the homolog with negative sigmaa shows a phenomenon, i.e., nonstandard electroconvection, not described by the Carr-Helfrich mechanism but manifesting in forms of stripes mainly parallel to the initial director, thus having a morphological similarity to the rolls of the standard EC. The remaining two homologs change the sign of their conductivity anisotropy with temperature that leads to a twofold character by crossing over from standard to nonstandard electroconvection. The patterns of both the standard and nonstandard EC have been characterized and compared.

Confusion noise at far-infrared to millimetre wavelengths

We present detailed predictions for the confusion noise due to extragalactic sources in the far-infrared/(sub)millimetre channels of the ESA/ISO, NASA/Spitzer, ESA/Herschel and ESA/Planck satellites, including the contribution from clustering of unresolved SCUBA galaxies. Compared to the case of purely Poisson fluctuations, clustering is found to increase the confusion noise by 10-15 per cent for the lowest frequency (i.e. lowest angular resolution) Spitzer and Herschel channels, and by 25-35 per cent for the 175-μm ISOPHOT channel, and to dominate in the case of Planck/HFI channels at ν ≥ 143 GHz. Although our calculations make use of our recent specific evolutionary model, the results are strongly constrained by the observed counts and by data on the redshift distribution of SCUBA sources, and therefore are not expected to be heavily model-dependent. The main uncertainty arises from the poor observational definition of the source clustering properties. Two models have been used for the latter: a power law with constant slope and a redshift-independent comoving correlation length r 0 ; and the standard theoretical model for clustering evolution in a ACDM universe, with a redshift-dependent bias factor. In both cases, the clustering amplitude has been normalized to yield a unit angular correlation function at θ 0 = 1 -2 arcsec for 850-μm sources fainter than 2 mJy, consistent with earlier results by Peacock et al. This normalization yields, for the first model, r 0 ∼ 8.3 Mpc h -1 , and, for the second model, an effective mass of dark matter haloes in which these sources reside of M halo ∼ 1.8 x 10 13 M ○. h -1 . These results are consistent with independent estimates for SCUBA galaxies and for other, probably related, sources.