GL Model Research Articles

Optimal Portfolio Choice with Predictability in House Prices and Transaction Costs

We generalize the classic Grossman and Laroque (1990) (GL) model of optimal portfolio choice with housing and transaction costs by introducing predictability in house prices. As in the GL model, agents only move to more expensive (cheaper) houses when their wealth-to-housing ratios reach an optimal lower (upper) boundary. However, in our model, these boundaries are time-varying and depend on the dynamics of the expected growth rate of house prices. We find that households moving to a more expensive house in periods of high expected growth in house prices have significantly lower ex-ante wealth-to-housing ratios than those moving in periods of low expected growth. We also find that the share of wealth invested in risky assets is lower during periods of high expected growth in house prices and that it is higher right before moving during periods of low growth. The main implications of the model are robust to tests using household level data from the PSID and SIPP surveys. JEL Classification: G11, D11, D91, C61

Pervasiveness of Excessive Segmental Bridge Deflections: Wake-Up Call for Creep

An obsolete standard recommendation for creep design led to significant underestimation of the observed 18-year deflections of the Koror-Babeldaob (KB) Bridge in the island nation of Palau. A search for data on similar bridges revealed that 56 other large-span, prestressed concrete, segmentally erected box girders (66 by the time of proof) have been found to exhibit excessive long-time deflections. There are probably many more in existence. The observed deflections give no sign of approaching a finite bound, as implied in the empirical ACI Committee 209, CEB-fib, and GL models for creep. They were found to evolve approximately logarithmically beginning at about 1000 days after span closing. While sufficient data for the finite element creep analysis of these deflections were not obtainable, comparisons with accurate deflection solutions for the KB Bridge showed that the terminal logarithmic deflection trend can be predicted well by a simple extrapolation of the measured 1000-day deflection under the hypothesis of proportionality to the compliance function increment since the time of span closing. Comparisons of the extrapolations according to various creep models show that the underestimation of long-time deflections is much less severe for the theoretically based Model B3 than it is for the three other models, and that the terminal trend is logarithmic. A simple update of this model that gives the same mean terminal trend as the 56 bridges is devised that should allow for improving the durability of segmental bridges.

Influences of magnetic field on wave propagation in generalized thermoelastic solid with diffusion

This paper is devoted to estimation of the influence of magnetic field in an elastic solid half-space under thermoelastic diffusion. The governing equations in xz -plane are solved taking into consideration the GL model. The reflection of dilatational (P) wave and shear vertical (SV) wave splits into four waves, namely: P wave, thermal wave, mass diffusion wave and SV wave. The reflection phenomena of P and SV waves from the free surface of an elastic solid with thermoelastic diffusion, under the influence of magnetic field is considered. The expressions for the reflection coefficients for the four reflected waves are obtained. These reflection coefficients are found to depend upon the angle of incidence θ of P and SV waves, thermoelastic diffusion, magnetic field and other material parameters. The numerical values for the reflection coefficients are calculated analytically and presented graphically for various values of these parameters. Relevant results of previous investigations are deduced as special cases from this study.

Comparative study of anisotropic superconductivity in CaAlSi and CaGaSi

In order to get some insight into the origin of the anomalous angular dependence of H c2 in a layered intermetallic compound CaAlSi, electronic, superconducting, and structural properties are compared between CaAlSi and CaGaSi. The angular dependence of H c2 in CaGaSi is well described by the anisotropic GL model. Parallel to this finding, the pronounced lattice modulation accompanying the superstructure along the c-axis in CaAlSi is absent in CaGaSi. A relatively large specific heat jump at the superconducting transition in CaAlSi compared with CaGaSi indicates the presence of strong electron–phonon coupling in CaAlSi, which may cause the superstructure and the anomalous angular dependence of H c2.

THERMOELASTIC WAVE PROPAGATION IN ANISOTROPIC LAYERED MEDIA — A SPECTRAL ELEMENT FORMULATION

The generalized dynamic theory of thermoelasticity is used to investigate the propagation of plane harmonic waves in anisotropic layered media using the Spectral Finite Element Method (SFEM). Two different theories, due to Lord and Shulman (LS model) and Green and Lindsay (GL model), are considered for spectral layer element (SLE) formulation. The element is formulated in the frequency domain and the exact solution of the transformed equation is used as the interpolating polynomial of the unknown variables, which are the mechanical displacements and the thermal field. Consequently, single element captures the essential wave response of a layer of arbitrary thickness, when subjected to high frequency impact loading. This element is used to study the characteristic of the thermal wave, also known as the second sound, using nominal computational resource. The study is directed towards finding the justification of using the non-classical model of thermoelasticity and the effect of different parameters on the overall thermal and mechanical field. Stress state within a layered media with general ply-stacking is studied and the limitation of the classical theory in stress prediction is shown. Thermal wave propagation due to temperature burst and heat flux is captured and their properties are discussed.

Vortices carrying an arbitrary fraction of magnetic flux quantum, neutral superfluidity and knotted solitons in two-gap Ginzburg–Landau model

We show that in two-gap superconductors there exist vortices which carry an arbitrary fraction of magnetic flux quantum and in two dimensions under certain conditions these vortices undergo a BKT transition which marks onset of quasi-long-range order only in a difference of phases of the two order parameters. In the second part of the talk we show that an U(1)× U(1) Ginzburg–Landau model or a GL model where U(1)× U(1) symmetry is weakly broken to U(1) is exactly equivalent to a version of the Faddeev's the nonlinear O(3) sigma model. This implies in particular that such a system possesses a hidden O(3) symmetry and besides that allows for the formation of knotted solitons. The second part of the talk is based on a joint work with L.D. Faddeev and A. Niem: Phys. Rev. B 65 (2002) 100512.

Updating Concrete Drying-Shrinkage Prediction Models for Local Materials

This paper addresses the need to update existing concrete drying-shrinkage prediction models to reflect local materials. The experimental program was conducted using 8 concrete mixtures of similar strength, manufactured with portland and portland pozzolan cements representing the most used concretes in Chile. Tests were conducted on 72 specimens and drying strains were measured up to 448 days of drying to study the effect of cement type, slump, maximum aggregate size, and specimen dimension on concrete shrinkage. The experimental results were compared with predictions of ACI, CEB, B3, GZ, GL, and Sakata models. All models significantly underestimated the measured shrinkage, particularly for concretes made with cement containing natural pozzolan. Cement type has a significant effect on drying shrinkage time function and magnitude. A procedure was developed to update existing prediction models. Proposed modifications to CEB relationships were derived to predict shrinkage of concrete made with locally available materials.

Analysis of Reynolds stress equations for stratified rotating homogeneous shear flow

An assessment of the Reynolds stress model of Gibson and Launder (GL model) in the prediction of rotation effects on stably stratified homogeneous shear flows has been conducted. The GL model is found to be capable of predicting the stabilizing and destabilizing effects of rotation. However, the quantitative predictions of the GL model are rather quite poor. In particular, the bifurcation diagrams of ( ε/ SK) are found not to be consistent with experimental findings. Deficiencies are traced to the pressure–strain model and the modeled dissipation equation.

Transient Disturbance in a Half Space Under Thermoelasticity with Two Relaxation Times Due to Moving Internal Heat Source

In this paper transient waves caused by a line heat source moving with a uniform velocity inside isotropic homogeneous thermoelastic half-space are studied under the GL model of generalized thermoelasticity. The problem is reduced to the solution of three differential equations by introducing the elastic vector potential and the thermoelastic scalar potential. Using Laplace and Fourier transforms solutions are obtained in transforms domain. Applying inverse transforms approximate solutions of the displacement at the boundary valid in the small time range are given. Also the approximate region valid for the solutions is given and two special cases, (i) the source is motionless and (ii) the relaxation times vanish, are studied. Numerical evaluations are presented for the medium of copper.

Chemotactic activity of oligopeptides containing an EWS motif on Tetrahymena pyriformis: the effect of amidation of the C-terminal residue.

Chemotactic properties of 3-7-mer peptides containing an EWS motive and their peptide amides synthesized and characterized by us were investigated in Tetrahymena pyriformis GL model. Analysis of the peptide acids shows that SEWS possesses exceptionally strong (660%+/-21; 430%+/-18) chemoattractant ability at 10(-12) and 10(-11) m respectively. The shorter peptide (EWS) possesses chemorepellent activity, while longer peptides display neutral (WSEWS) or moderate chemoattractant (EWSEWS and GEWSEWS) chemotactic ability. Amidation of the C-terminus can significantly modify the character of peptides: it points to the conclusion that a free alpha-COOH group at this position is required for the high efficiency of SEWS, while in the shorter (EWS) and longer peptides (WSEWS and EWSEWS) amidation can result in chemoattractant ligands. Evaluation of the structure-function relationship of these compounds establishes the significance of Glu (E) with its high surface-exposed area and negatively-charged side chain. The high discriminative ability and good chemotactic responsiveness of Tetrahymena support the theory that a chemotactic signalling mechanism working in higher levels of phylogeny is a well conserved and inducible one even in protozoa.

Assessment of reynolds stress turbulence closures in the calculation of a transonic separated flow

In this study, the performances of various turbulence closure models are evaluated in the calculation of a transonic flow over axisymmetric bump. k-e, explicit algebraic stress, and two Reynolds stress models, i. e., GL model proposed by Gibson & Launder and SSG model proposed by Speziale, Sarkar and Gatski, are chosen as turbulence closure models. SSG Reynolds stress model gives best predictions for pressure coefficients and the location of shock. The results with GL model also show quite accurate prediction of pressure coefficients downstream of shock wave. However, in the predictions of mean velocities and turbulent stresses, the results are not so satisfactory as in the prediction of pressure coefficients.

On spin-up/spin-down torque reversals in disc accreting pulsars

The recent BATSE observations of the spin-up and spin-down of accreting pulsars have shown that the standard formulation for the accretion torque as proposed by Ghosh &38; Lamb may need to be revised. The observations indicate alternate spin-up and spin-down phases driven by torques of similar magnitude and typically larger than the mean torque. The variations of the torque in systems such as Cen X-3 are difficult to explain in terms of changes of the mass accretion rate. The implication is that the torque does not depend on the accretion rate as in the GL model. In this paper we argue that the observed changes in the spin rate can result from stochastic transitions between two magnetospheric states. In particular, we show that intermediate magnetospheric systems are not admissible, because of a disc-induced magnetospheric instability which exists in a star-disc magnetic interaction system. This explains why torque reversal occurs in disc accreting pulsars with similar magnitudes.

Near Infrared Spectroscopy Estimation of Feeding Value of Forage Perennial Grasses in Breeding Programmes by Global and Specific Calibrations. Estimation of Chemical Composition and Digestibility

Near infrared (NIR) spectral analysis with a NIRSystems 6500 monochromator was applied to evaluate accuracy of predictive models for forage quality in clone breeding processes of the original Bulgarian varieties over different cuts and years. The varieties were the perennial grasses: Dactylis glomerata L., Festuca arundinacea Schreb. and Bromus inermis Leyss. Global calibrations for the 418 perennial grass samples and specific calibrations for each single grass species and internal cross-validations were performed by the PLS regression method. The effect of different spectral data pre-treatments was investigated on the residual standard errors of the NIR predictive models. Among 60 calibration equations, the model with the lowest SECV value was retained for each parameter in each database. No particular data pre-treatment was really better than the other ones. Generally, the best results of the global calibrations were obtained with SNVD and MSC. For the specific calibrations, SNVD and WMSC were the best treatments. In both cases, the first or second derivatives were needed after the first pre-treatment. Chemical composition and in vitro enzymatic digestibility of clones were predicted with accuracy similar to that of classical laboratory methods. For the cell wall component contents, the standard errors of cross-validation SECV(%DM) ranged from 0.49 for ADL ( Festuca) to 2.02 for NDF ( Dactylis). The digestibilities of dry and organic matter, IVDMD and IVOMD, were estimated with SECVs from 2.6 to 3.0%, the relative intake, from 0.06 to 0.09 rel% body weight and the relative feeding value, from 4.39 to 5.64 rel%. The global calibration models offer an acceptable accuracy for the estimation of the cell wall nutrient contents, the digestibility and the nutritive value. The standard errors of prediction of specific single species calibrations with smaller numbers of terms were lower in 60% of the cases than those obtained from the best global calibrations with higher numbers of terms. On average, SECVs from specific calibrations are better than those from global calibrations, but the differences are quite small, and for the prediction of totally new samples (new crops, another year), the global calibrations will detect less outlier samples. Even with very high variability between cuts and years, NIR spectroscopy is able via ANOVA GL Models to sort clones on their feeding value and to provide relevant information for the breeding programmes.

Vortex lattice melting and the peak effect in oblique field in Bi2Sr2CaCu2O8+y

The angular dependence of local magnetization hysteresis loops has been measured in Bi2Sr2CaCu2O8+y single crystals by using micro Hall probes. It was uncovered that the angular dependences of both the melting transition and the peak field deviate from the expectation by the anisotropic GL model. In addition to the above results, we found new peak structures in hysteresis loops in oblique fields. A possible origin of this new peak structure is discussed.

Solar radiation assessment using Meteosat 4-VIS imagery

Meteosat 4-VIS high-definition imagery was used for testing solar radiation assessment over northeast Brazil during January 1991 and 1994. Actinographs of solarimetric stations in Paraíba State provided proper ground reference. A simple physical model was developed, based on two basic hypotheses: visible and infrared intervals are decoupled, and radiation transfer in the visible interval is essentially conservative. Some ideas are borrowed from the well known model of Gautier et al. for cloudiness assessment. The resulting GL model can run on a personal microcomputer, processing targets of 5 × 5 pixels for all the region. It exhibits rather good behaviour on a monthly scale, reproducing the mean diurnal cycle and assessing mean irradiation with bias and mean standard deviation lower than 10 W m −2. Fifteen-day means exhibit similar accuracy. Ground albedo is a highly important parameter of the model. As expected, the main sources of error seem to be planetary reflectance and cloudiness assessment, because of the non-lambertian reflection and the different count thresholds for each kind of cloud cover. Further studies considering longer time series of images (VIS and IR channels) as well as the anisotropic properties of finite cloud fields may improve the model.

Angular dependence of resistive transition in strongly anisotropic superconductors under magnetic field

Resistivity and specific heat for arbitrary field and current configurations of strongly anisotropic high- T c superconductors are studied according to the renormalized fluctuation theory and by specifically considering the 2D limit of the layered model and the anisotropic 3D GL model. It is pointed out that the theory can naturally explain phenomena peculiar to strongly anisotropic materials, such as the independence of the resistivity in arbitrary field configuration from the in-plane field component, and so-called Lorentz force-free dissipation and field independence observed in resistivity measurements in the H ⊥ c ⊥ I configuration of BSCCO.

Nonlocal Ginzburg-Landau Model for High-Temperature Superconductors in a Magnetic Field

2) The Ginzburg-Landau model is particularly useful to derive such vortex structures and to discuss the behavior near the· upper critical magnetic field H C2• However, for high-temperature superconductors, the coherence lengths are very shore)-5) and the modification of the model may be required near HC2• Experimentally, the jump of the specificheat 6 ) and the resistive transition i~ a magnetic field 7 )-9) have been observed. These behaviors are different from the conventional superconductors. In this paper, we consider the generalized phenomenological Ginzburg-Landau model in a magnetic field. We particularly investigate the nonlocal interaction. In a magnetic field, the two-dimensional degree of freedom, which is perpendicular to the magnetic field direction, is quantized and the dimensional reduction occurs near Hc2 • The behavior of the specific jump in a magnetic field has been investigated 10 )-12) for the conventional GL model by the fact of this dimensional reduction. The study of the generalization to the nonlocal interaction is motivated by two following reasons. The first is that our generalized model has a remarkable similarity to the n-compo­ nent GL model. We find that a parameter of the characteristic range of the nonlocal interaction play the role of the number of the component n. This observation leads us to develop the series expansion which is similar to lin expansion without introduc­ ing a fictitious number of n for the superconductors. The second reason is that the high-temperature superconductor has very short coherence length and therefore, the interaction of point contact should be modified particularly near H c2• The distance between the vortices near HC2 becomes 2.7~ for a triangle vortex lattice and ~(o) is about loA for YBCO. 3 )-5) It may be possible that the attractive pairing interaction has the same order range of the length. We introduce a new length of the nonlocal interaction which may depend upon the microscopic mechanism of the attractive force of the paired electrons. The renormalization group analysis reveals that the non­ local interaction is generated by the renormalization procedure. 13 ) Therefore, further

The continuum model: An experimental and theoretical challenge to the G1 model of cell cycle regulation

The dominant and current view of cell cycle regulation is that the controls for cell proliferation reside primarily in the Gl phase of the division cycle. This current or classical model is deeply ingrained in cell biology, and has been described very well [ 1, 21; therefore we will only summarize below the basic support of the Gl model. Over the past decade, however, an alternative proposal, the continuum model, has emerged that suggests that there are no Gl-specific events or controls, and that all of the evidence for the importance of the Gl phase can be explained in terms of a continuous process that occurs in all phases of the division cycle [3-71. These early reports addressed previous experimental results and explained them in terms of the continuum model. In a sense, therefore, these analyses were theoretical rather than experimental. The basic ideas of the continuum model are presented in Fig. 1. Recently there has emerged a set of experiments that has been stimulated by the ideas of the continuum model, and these experiments support the basic ideas of the continuum model. This means that the continuum model has been a stimulus to experimental tests, and therefore has an experimental as well as a theoretical base. We will describe these experiments below, and explain how they support the continuum model.

Influence of boundaries on dissipative structures in the Schl�gl model

Some comments are made concerning the multiple stationary-state patterns found in reaction-diffusion systems, including the Schlogl and Autocatalator models.

Critical Field Measurements on Superconducting Graphite-KHG Multilayers

ABSTRACTUpper critical fields of graphite-KHg multilayers with 10Å periodicity were measured as a function of angle and temperature. The Hc2 (θ, T) data were compared to the anisotropic Ginzburg-Landau model and were found to be in qualitative agreement, except at the lowest reduced temperatures, where significant deviations are found. The primary deviations from the anisotropic GL model are first, that the values of the critical field at the lowest temperatures are found to be higher than that predicted by the model, and secondly, the critical field anistropy ratio is found to be temperaturedependent. These deviations are discussed in light of more detailed models of anisotropic superconductivity.