Overestimation Problem Research Articles

Leverage, options liabilities, and corporate bond pricing

The two major problems with typical structural models are the failure to attain a positive credit spread in the very short term, and overestimation of the overall level of the credit spread. We recognize the presence of option liabilities in a firm’s capital structure and the effect they have on the firm’s credit spread. Including option liabilities and employing a regime switching interest rate process to capture the business cycle resolves the above-mentioned drawbacks in explaining credit spreads. We find that the credit spread overestimation problem in one of the structural models, Collin-Dufresne and Goldstein (J Finan 56:1929–1957, 2001), can be resolved by combining option liabilities and the regime-switching interest rate process when dealing with an investment grade bond, whereas with junk bonds, only the regime-switching interest rate process is needed. We also examine vulnerable option values, debt values, and zero-coupon bond values with different model settings and leverage ratios.

Operational land cover change detection using change vector analysis

This research study introduces the use of a change detection and classification algorithm that relies on the change vector analysis (CVA) method. Its implementation aims to ensure adequate response to operational production needs and allow optimized data processing over extended and environmentally complex areas. Automatic change class labelling relies on the use of a (3n+2)‐dimensional feature space, where n denotes the number of sensor bands. Such enhanced feature space allows for a finer and more accurate definition of change classes of the ‘from‐to’ type. Moreover, and to efficiently address the problem of change area overestimation, the proposed method takes into account specific evidence derived from the pixel's geographic neighbourhood, the latter defined as a 3×3 pixel kernel. The performance of this integrated algorithmic approach has been tested and validated in the framework of the CORINE Land Cover‐Greece 2000 and the ESA/GSE Forest Monitoring projects in three test sites located in the outskirts of the city of Ptolemais, Thasos island and the suburbs of Athens in Greece. Its implementation in such highly fragmented and dynamically changing landscape environments has resulted in qualified and accurate land cover change maps, achieving an overall level of classification accuracy of 88–96%. Compared to visual image interpretation, the method requires half the effort. In conclusion, the proposed method has proved effective and can be recommended for use in the framework of operational projects.

A novel FEM by scaling the gradient of strains with factor α (αFEM)

This paper presents a novel finite element method of quadrilateral elements by scaling the gradient of strains and Jacobian matrices with a scaling factor α (αFEM). We first prove that the solution of the αFEM is continuous for αϵ[0, 1] and bounded from both below and above, and hence is convergent. A general procedure of the αFEM has been proposed to obtain the exact or best possible solution for a given problem, in which an exact-α approach is devised for overestimation problems and a zero-α approach is suggested for underestimation problems. Using the proposed αFEM approaches, much more stable and accurate solutions can be obtained compared to that of standard FEM. The theoretical analyses and intensive numerical studies also demonstrate that the αFEM effectively overcomes the following well-known drawbacks of the standard FEM: (1) Overestimation of stiffness matrix when the full Gauss integration is used; (2) Instability problem known as hour-glass locking (presence of hour-glass modes or spurious zero-energy modes) when the reduced integration is used; (3) Volumetric locking in nearly incompressible problems when the bulk modulus becomes infinite.

Evaluation of the Moderate Resolution Imaging Spectroradiometer aerosol products at two Aerosol Robotic Network stations in China

Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products have been used to address aerosol climatic issues in many parts of the world, but their quality has yet to be determined over China. This paper presents a thorough evaluation of aerosol optical depth (AOD) data retrieved from MODIS collections 4 (C004) and 5 (C005) at two AERONET sites in northern and southeastern China. Established under the aegis of the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST‐AIRE) project, the two sites, Xianghe and Taihu, have distinct ecosystems and climate regimes, resulting in differences in retrieval performance. At the rural northeastern site (Xianghe), MODIS C004 retrievals generally overestimate AOD at 550 nm during clean days, with the largest errors occurring during winter. In the warm and humid regions of southeastern China (Taihu), MODIS C004 retrievals overestimate AOD throughout the year. The systematic error at Xianghe is primarily due to the fixed surface reflectance ratio, while as the error at Taihu is mainly caused by the choice of the single scattering albedo (SSA) for the fine model aerosols. Both problems are alleviated considerably in the C005. The comparisons between C005 retrievals and AERONET data show much higher correlation coefficient, lower offset and a slope closer to unity. Also, the variability of AOD retrieval among neighboring pixels is reduced by several factors. The strong overestimation problem at small AOD values was fixed by using dynamic reflectance ratios that vary with the vegetation index and scattering angle. However, significant uncertainties remain because of the use of highly simplified aerosol models.

3D Microstructure Reconstruction of Aluminium Alloys Quenched during Solidification

In the present research the possibility of studying the solidification of aluminum alloys by using the quenching technique is analyzed. Since the quenching technique does not provide reliable information (i.e. due to an overestimation of solid fraction) when measuring the solid fraction over 2D images from samples quenched at high temperature, the overestimation problem is investigated by analyzing 3D reconstructed microstructures from quenched samples. The 3D reconstructed microstructure may provide better understanding about the cause of overestimation of solid fraction when quenching at high temperatures. Consequently, the reconstruction of the microstructure that has existed before quenching may be possible after identifying and removing the solid phase that develops during quenching. In the present research, binary aluminum alloys are solidified and quenched at different temperatures, and then 3D reconstructed images are analyzed. The possibility of reconstructing the microstructure that develops during solidification before quenching is discussed.

On maintaining pressure equilibrium between a soil CO2 flux chamber and the ambient air

Pressure equilibrium between inside a soil CO2 flux chamber and the surrounding air outside the chamber must be maintained during a measurement if measured soil CO2 flux (FCO2) is to accurately represent the rate occurring naturally outside the chamber. In previous studies a simple vent tube connecting to the chamber has often been used to maintain pressure equilibrium. This approach, however, can be effective only under calm conditions. Under windy conditions, negative pressure excursions will occur inside the chamber that are artifacts resulting from wind passing over the vent tube's external open end, a phenomenon known as the Venturi effect. This causes anomalous mass flow of CO2‐rich air from the soil into the chamber, leading to a significant overestimation of FCO2. In this present study, we found that negative chamber pressure excursions due to the Venturi effect cannot be observed unless the differential pressure measurement is made with the chamber resting on an impermeable base. Making pressure measurements with a chamber resting on porous soil can lead to the erroneous conclusion that an anomalous mass flow is not a problem precisely when it is causing serious artifacts. We also present a new vent design for a soil CO2 flux chamber capable of maintaining pressure equilibrium between inside the chamber and the ambient air outside the chamber under both calm and windy conditions. Differential pressure measurements from field experiments show that the pressures inside our newly designed vented chamber equal those outside the chamber when wind speed at a height of 0.5 m is up to 7 m s−1, thus virtually eliminating artifacts due to the Venturi effect. Our field data show that the problem of overestimation in measured FCO2 by a chamber with older vent designs under windy conditions can be avoided with our newly designed vented chamber.

Phylogenetic detection of conserved gene clusters in microbial genomes

BackgroundMicrobial genomes contain an abundance of genes with conserved proximity forming clusters on the chromosome. However, the conservation can be a result of many factors such as vertical inheritance, or functional selection. Thus, identification of conserved gene clusters that are under functional selection provides an effective channel for gene annotation, microarray screening, and pathway reconstruction. The problem of devising a robust method to identify these conserved gene clusters and to evaluate the significance of the conservation in multiple genomes has a number of implications for comparative, evolutionary and functional genomics as well as synthetic biology.ResultsIn this paper we describe a new method for detecting conserved gene clusters that incorporates the information captured by a genome phylogenetic tree. We show that our method can overcome the common problem of overestimation of significance due to the bias in the genome database and thereby achieve better accuracy when detecting functionally connected gene clusters. Our results can be accessed at database GeneChords .ConclusionThe methodology described in this paper gives a scalable framework for discovering conserved gene clusters in microbial genomes. It serves as a platform for many other functional genomic analyses in microorganisms, such as operon prediction, regulatory site prediction, functional annotation of genes, evolutionary origin and development of gene clusters.

Note: An efficient in situ method for sampling periphyton in lakes and streams

We present an efficient in situ sampling device that allows a simple and quantitative sampling of natural periphyton communities. The Brush Sampler is based on a previously developed sampler, which was improved by the addition of an external water supply, ball valve closing mechanism, and special exchangeable stiff brushes to solve previously reported problems of biomass overestimation and underestimation. The Brush Sampler was tested under ambient conditions in the field at four different sampling sites in a lentic and a lotic system and compared to the old sampler and control samples. The tests revealed a high inaccuracy of the old sampler and showed that biomass estimates (ash-free dry mass and chlorophyll-a content) obtained with the improved Brush Sampler did not significantly differ from biomass values determined from scrapings of control samples collected at the same sites. Therefore, our modified sampling device can be used as a tool for quantitative and qualitative epilithon community analyses.

An eigenanalysis-based method for blind channel identification and equalisation

Subspace (SS) methods are effective approaches for blind channel identification, for they achieve a good performance with a relatively short data lengths and work well at low signal-to-noise ratio (SNR). However, they require accurate channel order estimation, which is difficult in a noisy environment. Although linear prediction (LP) methods can handle the problem of channel order overestimation, their performance degrades dramatically when SNR is low. In this letter, we proposed a blind channel identification and equalisation algorithm, based on the eigenanalysis of shifted correlation matrices of the received data and their associated properties. The algorithm is robust to channel order overestimation and not sensitive to noise as well. Furthermore, the algorithm does not require the computation of the correlation matrix pseudo-inverse, as with linear prediction algorithms, nor are the whole noise or signal eigen vectors necessary to achieve identification as with the subspace algorithm, so it is computationally efficient. Copyright © 2005 AEIT.

연결 성분 간 간격 측정에 의한 필기체 수표 금액 문장에서의 단어 추출

본 논문에서는 연결 성분간의 공간적 간격에 기반하여 수표 영상 내의 필기체 문장 금액에서 단어를 효율적으로 추출하기 위한 방법을 제안한다. 인접한 연결 성분간의 거리측정을 위한 기존의 방식들은 과대추정 또는 과소추정 문제로 인한 단어 분리 오류를 초래할 수 있으나 본 논문에서는 이러한 문제를 줄이기 위해 각 측정 방식들을 수정 보완하였다. 또한 본 논문에서는 서로 다른 형태의 세 가지 거리 측정법들을 효과적으로 결합하여 각 개별 측정법이 가지는 단점을 상호 보완하고 전체 단어 추출 성능을 좀더 향상시킬 수 있는 4-클래스 군집화에 기반한 결합 방법을 새로이 제안하였다. 분장 금액에 대한 단어 추출 실험 결과로부터 수정된 각 거리 측정법이 대응되는 기존의 측정법에 비해 2-3% 정도 향상된 단어 분리율을 보임을 확인하였다. 또한 제안된 4-클래스 군집화에 기반한 결합 방식은 각 측정 방식에서 개별적으로 발생하는 에러뿐만 아니라 두 개의 방식에서 동시에 나타나는 에러도 효율적으로 감소시킴으로서 전체 단어 분리 성능을 향상 시킬수 있었다. We have proposed an efficient method of word separation in a handwritten legal amount on bank check based on the spatial gaps between the connected components. The previous gap measures all suffer from the inherent problem of underestimation or overestimation that causes a deterioration in separation performance. In order to alleviate such burden, we have developed a modified version of each distance measure. Also, 4 class clustering based method of integrating three different types of distance measures has been proposed to compensate effectively the errors in each measure, whereby further improvement in performance of word separation is expected. Through a series of word separation experiments, we found that the modified distance measures show a better performance with over 2 - 3% of the word separation rate than their corresponding original distance measures. In addition, the proposed combining method based on 4-class clustering achieved further improvement by effectively reducing the errors common to two of three distance measures as well as the individual errors.

Accurate polymer polarizabilities with exact exchange density-functional theory

The long-standing problem of the large overestimation of polymer polarizabilities in density-functional theory is reexamined and largely solved using an exact exchange method. We have built an accurate optimized effective potential as the sum of a fixed potential and a linear combination of basis sets based on our direct optimization method. This effective potential properly develops a linear counteracting depolarization field, and it significantly improves recent results from approximate optimized potentials. The controversial case of hydrogen chains is now correctly described and the failure of the local density approach is attributed to the large self-interaction error in systems with a non-integer number of electrons.

Base station antenna near-field radiation pattern distortion analysis

When estimating the potential radiation hazard of a base station antenna system, one often relies on the antenna far-field radiation pattern, while the estimation often refers to the antenna near-field zone. It is widely accepted that this leads to overestimation of the field amplitudes. Some recent works suggest the use of modified analytical models to avoid the overestimation problem. However, all of these references refer only to a single antenna in the free space. This work shows that potential near-field radiation pattern distortion due to conductive objects in the close proximity of the antenna (like in multiple- antenna configuration) makes many models inapplicable. In that case, in the directions outside the mainlobe of the antenna, sidelobes are shifted and changed in an unpredictable manner. The nulls are either shifted, or filled so they do not really exist. The mainlobe itself can get an additional gain of a few dB in unpredictable directions. This suggests that even the use of the far-field pattern can sometimes lead to underestimation of the field. Considering that many real antennas have some conductive object nearby, especially in multiple antenna configurations, this work suggests that for truly conservative, worst-case electromagnetic field estimation, far-field pattern should be used for the mainlobe, with the uncertainty of a few dB. For all other directions, the protective envelope should be used as the radiation pattern, with the gain in all directions equal to the highest sidelobe gain. No nulls should be considered to exist in the near field radiation pattern.

Adjusted Coefficients of Determination for Logistic Regression

This article proposes two adjusted coefficients of determination for logistic regression for measuring the strength of association between the outcome variable and the predictors as an extension of a similar concept in linear regression. The proposed adjusted coefficients correct the overestimation problem of the unadjusted coefficients and are especially useful when the sample size is small or the number of predictors is large. An R program is provided on the Internet.

Application of time-dependent current-density-functional theory to nonlocal exchange-correlation effects in polymers

We provide a successful approach towards the solution of the longstanding problem of the large overestimation of the static polarizability of conjugated oligomers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory enables us to describe ultranonlocal exchange-correlation effects within a local current description. Recently a brief account was given of the application of the Vignale–Kohn current-functional [G. Vignale and W. Kohn, Phys. Rev. Lett. 77, 2037 (1996)] to the axial polarizability of oligomer chains [M. van Faassen, P. L. de Boeij, R. van Leeuwen, J. A. Berger, and J. G. Snijders, Phys. Rev. Lett. 88, 186401 (2002)]. With the exception of the model hydrogen chain, our results were in excellent agreement with best available wavefunction methods. In the present work we further outline the underlying theory and describe how the Vignale–Kohn functional was implemented. We elaborate on earlier results and present new results for the oligomers of polyethylene, polysilane, polysilene, polymethineimine, and polybutatriene. The adiabatic local density approximation gave good results for polyethylene, which were slightly modified by the Vignale–Kohn functional. In all other cases the Vignale–Kohn functional gave large improvements upon the adiabatic local density approximation. The Vignale–Kohn results were in agreement with best available data from wave function methods. We further analyze the hydrogen chain model for different bond length alternations. In all these cases the Vignale–Kohn correction upon the adiabatic local density approximation was too small. Arguments are given that further improvements of the functional are needed.

Ultranonlocality in time-dependent current-density-functional theory: application to conjugated polymers.

We solve the long-standing problem of the large overestimation of the static polarizability of conjugated polymers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation (xc) effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory enables a local current description of ultranonlocal xc effects using the Vignale-Kohn functional [G. Vignale and W. Kohn, Phys. Rev. Lett. 77, 2037 (1996)]. Except for the model hydrogen chain, our results are in excellent agreement with the best available correlated methods.

Arctic stratus cloud properties and their effect on the surface radiation budget: Selected cases from FIRE ACE

To study Arctic stratus cloud properties and their effect on the surface radiation balance during the spring transition season, analyses are performed using data taken during three cloud and two clear days in May 1998 as part of the First ISCCP Regional Experiment (FIRE) Arctic Cloud Experiment (ACE). Radiative transfer models are used in conjunction with surface‐ and satellite‐based measurements to retrieve the layer‐averaged microphysical and shortwave radiative properties. The surface‐retrieved cloud properties in Cases 1 and 2 agree well with the in situ and satellite retrievals. Discrepancies in Case 3 are due to spatial mismatches between the aircraft and the surface measurements in a highly variable cloud field. Also, the vertical structure in the cloud layer is not fully characterized by the aircraft measurements. Satellite data are critical for understanding some of the observed discrepancies. The satellite‐derived particle sizes agree well with the coincident surface retrievals and with the aircraft data when they were collocated. Optical depths derived from visible‐channel data over snow backgrounds were overestimated in all three cases, suggesting that methods currently used in satellite cloud climatologies derive optical depths that are too large. Use of a near‐infrared channel with a solar infrared channel to simultaneously derive optical depth and particle size appears to alleviate this overestimation problem. Further study of the optical depth retrieval is needed. The surface‐based radiometer data reveal that the Arctic stratus clouds produce a net warming of 20 W m−2 in the surface layer during the transition season suggesting that these clouds may accelerate the spring time melting of the ice pack. This surface warming contrasts with the net cooling at the top of the atmosphere (TOA) during the same period. An analysis of the complete FIRE ACE data sets will be valuable for understanding the role of clouds during the entire melting and refreezing process that occurs annually in the Arctic.

ANALYSIS OF MECHANICAL SYSTEMS USING INTERVAL COMPUTATIONS APPLIED TO FINITE ELEMENT METHODS

This paper addresses the problem of mechanical systems in which parameters are uncertain and bounded. Interval calculation is used to find an envelope of transfer functions for mechanical systems modelled with finite elements. Within this context, a new formulation has been developed for finite element problems involving bounded parameters, to avoid the problems of overestimation. An iterative algorithm is introduced, which leads to a conservative solution for linear mechanical problems. A method to ensure the convergence of this algorithm is also proposed. This new algorithm has been tested on simple mechanical systems, and leads to a conservative envelope of the transfer functions.

Effect of cake thickness and particle polydispersity on prediction of permeate flux in microfiltration of particulate suspensions by a hydrodynamic diffusion model

We present a modification of the concentration polarization model with shear-induced diffusion which corrects the problem of flux overestimation at the membrane inlet and takes into account the presence of a particle cake layer of a finite thickness and the effect of particle polydispersity. The resistance of the cake is calculated from the Kozeny–Carman equation, while the cake porosity and particle concentration on the cake surface are determined from permeametric experiments. The model calculates the local cake thickness, its mean porosity and specific resistance, the shear rate and permeate flux as a function of distance from the inlet by equating the flux through the cake given by Darcy’s law and the flux given by the concentration polarization model. The cake is assumed to form at a distance from the inlet when the hydraulic flux through the clean membrane starts to exceed the flux predicted by the concentration polarization model. The characteristic particle diameter for diffusion and the mean particle diameter in the cake were determined by comparing predictions of the model with a set of experimental data on microfiltration of CaCO 3 suspensions through 0.1 μm pore size hollow fibers. The mean diffusion diameter, at 8.2 μm, was found, from the model, to be larger than the mean surface-volume diameter (4.65 μm), while the cake was found to be predominantly formed of smaller particles (mean diameter = 1–2 μm). This result was confirmed by granulometric analysis of the cake formed on the membrane. The predictions of our model are very close to those from the Romero and Davis model (J. Membr. Sci. 39 (1988) 157–185). With these particle diameters, our model correctly predicts the variations of permeate flux with transmembrane pressure, velocity and particle concentration when the comparison is made with different experimental data. This model, which describes only external fouling, should be more realistic than previous models when the cake thickness is not negligible in comparison with the membrane lumen.

Development of Two-Dosemeter Algorithm for Better Estimation of Effective Dose Equivalent and Effective Dose

An optimal algorithm, which suitably combines two dosemeter readings, one dosemeter on the chest and the other on the back, for better estimation of effective dose equivalent (HE) and effective dose (E), was developed by utilising hundreds of broad parallel photon beam irradiation geometries. The developed algorithm, weighting front (chest) and back dosemeter readings by 0.58 and 0.42, respectively, was found to be superior to other currently available algorithms, neither underestimating HE or E by more than 14%, nor overestimating by more than a few tens of a per cent for a broad range of frontal and dorsal incident beams. Like other algorithms, however, this algorithm tends to overestimate HE and E significantly for the lateral, overhead and underfoot beam directions. This study also suggests that this overestimation problem significantly decreases when one uses typical commercial dosemeters instead of isotropic-responding dosemeters.

Stated Preferences, Real Behaviour and Anchoring: Some Empirical Evidence

We compare different contingent valuation question formats with each other and with observed behaviour for a non-monetary estimation task, the expected number of kilometers travelled by automobile. Open-ended questions, open-ended follow-up questions, dichotomous choice (DC) questions, and double-bound DC questions are included. The single and double-bound DC questions result in an estimated mean about twice as high as the actual value and the open-ended mean. The DC question overestimation seems to be due to an anchoring effect leading to ‘yea-saying’ behaviour. Our results about the difference between DC questions and open-ended questions is consistent with the pattern observed in contingent valuations studies of the willingness to pay. Our results indicates that DC questions seem to be associated with a general overestimation problem that is present even for simple non-monetary estimation tasks.