Capabilities' Substitutability and the "S" Curve of Export Diversity

Product diversity, which is highly important in economic systems, has been highlighted by recent studies on international trade. We found an empirical pattern, designated as the "S-shaped curve", that models the relationship between economic size (logarithmic GDP) and export diversity (the number of varieties of export products) on the detailed international trade data. As the economic size of a country begins to increase, its export diversity initially increases in an exponential manner, but overtime, this diversity growth slows and eventually reaches an upper limit. The interdependence between size and diversity takes the shape of an S-shaped curve that an be fitted by a logistic equation. To explain this phenomenon, we introduce a new parameter called "substitutability" into the list of capabilities or factors of products in the tri-partite network model (i.e., the country-capability-product model) of Hidalgo et al. As we observe, when the substitutability is zero, the model returns to Hidalgo's original model but failed to reproduce the S-shaped curve. However, in a plot of data, the data increasingly resembles an the S-shaped curve as the substitutability expands. Therefore, the diversity ceiling effect can be explained by the substitutability of different capabilities

Genetic algorithms for designing digital filters

This thesis presents a method of adapting IIR filters implemented as lattice structures using a Genetic Algorithm (GA), called ZGA. This method addresses some of the difficulties encountered with existing methods of adaptation, providing guaranteed filter stability and the ability to search multi-modal error surfaces. ZGA mainly focuses on convergence improvement in respects of crossover and mutation operators. Four kinds of crossover methods are used to scan as much as possible the potential solution area, only the best of them will be taken as ZGA crossover offspring. And ZGA mutation takes the best of three mutation results as final mutation offspring. Simulation results are presented, demonstrating the suitability of ZGA to the problem of IIR system identification and comparing with the results of Standard GA, Genitor and NGA

Structural and Kinetic Studies of Drug-Resistant Mutants of HIV-1 Protease

The employment of HIV-1 protease (PR) inhibitors (PIs) in antiviral therapy has been successful in reducing mortality of HIV/AIDS patients. However, the long-term efficacy of PIs is challenged by the rapid emergence of drug-resistant mutants of PR. To understand the underlying mechanism of drug resistance, structures and activities of HIV-1 PR and its drug resistant mutants have been extensively studied. Here, PR mutants PRR8Q, PRD30N, PRI47V, PRI50V, PRI54M, PRV82A, and PRN88D/S bearing single substitutions have been investigated by crystallography and kinetics. GRL-0519 is a potent new antiviral inhibitor of HIV-1 PR that possesses tris-tetrahydrofuran (tris-THF) as the P2 ligand. The crystal structures of GRL-0519 were determined at resolutions of 1.06-1.49 Å in complex with the mutants PRR8Q, PRD30N, PRI50V, PRI54M, and PRV82A. I50V lost its interaction with inhibitor while V82Aand I54M compensated for the mutation through the main chain shift and flexibility of 80’s loop (residues 78-82), respectively. The structural changes may account for the worst inhibition of GRL-0519 for PRI50V (60-fold decrease relative to wild-type enzyme)and moderate inhibition for PRI54M and PRV82A (6-7-fold decrease). The large tris-THF group at P2 provides a good fit in the S2 subsite and may be effective against resistant virus with mutations of residues in this subsite. SQV and DRV are two clinical inhibitors that were designed to target the wild type PR and its drug resistant mutants, respectively. The crystal structures of PR mutants PRI47V, PRN88D/s in complex with DRV and mutants PRI47V and PRN88D in complex with SQV with resolutions of 1.13-1.72 Å were also analyzed. Mutation I47V gained more hydrophobic interactions with DRV and SQV. Interestingly, the structural changes did not affect the inhibition of both inhibitors for PRI47V (relative Ki is 0.7 and 1 for DRV and SQV, respectively). DRV and SQV showed 8-fold increase in Ki for PRN88D and only very subtle local changes have been observed on the structures. DRV induced 0.3 fold reduction in Ki for PRN88S and the distal structural changes have been transferred to the active site. This study provided fundamental information for understanding drug resistance and future design of potential antiviral drugs

Sample Size Calculation for Finding Unseen Species

Estimation of the number of species extant in a geographic region has been discussed in the statistical literature for more than sixty years. The focus of this work is on the use of pilot data to design future studies in this context. A Dirichlet-multinomial probability model for species frequency data is used to obtain a posterior distribution on the number of species and to learn about the distribution of species frequencies. A geometric distribution is proposed as the prior distribution for the number of species. Simulations demonstrate that this prior distribution can handle a wide range of species frequency distributions including the problematic case with many rare species and a few exceptionally abundant species. Monte Carlo methods are used along with the Dirichlet-multinomial model to perform sample size calculations from pilot data, e.g., to determine the number of additional samples required to collect a certain proportion of all the species with a pre-specified coverage probability. Simulations and real data applications are discussed

School Dropouts and Conditional Cash Transfers: Evidence from a Randomized Controlled Trial in Rural China’s Junior High Schools.

Recent anecdotal reports suggest that dropout rates may be higher and actually increasing over time in poor rural areas. There are many reasons not to be surprised that there is a dropout problem, given the fact that China has a high level of poverty among the rural population, a highly competitive education system and rapidly increasing wages for unskilled workers. The overall goal of this study is to examine if there is a dropout problem in rural China and to explore the effectiveness that a Conditional Cash Transfer (CCT) program could have on dropouts (and mechanism by which the CCT might affect drop outs). To meet this objective, we conducted a randomized controlled trial (RCT) of a CCT using a sample of 300 junior high school students in a nationally-designated poor county in Northwest China. Using our data, we found that the annual dropout rate in the study county was high, about 7%. We find, however, that a CCT program reduces drop outs by 60%; the dropout rate is 13.3% in the control group and 5.3 % in the treatment group. The program is most effective in the case of girls, younger students and the poorest performing students.

Cautions of Using Allele-Based Tests Under Heterosis

Abstract: In genetic studies, heterotic effects are commonly assessed as dominant, additive, or recessive effects for a given genetic marker. However, the distorting effect of heterosis on statistical tests is non-trivial. An inheritance model needs to be carefully chosen to achieve highest testing power. We assess this through simulations via allele- and genotype-based tests. Chi-square test statistics for different inheritance models are formulated as a function of relative risks and allele frequencies. The results indicate that testing power from the commonly used allele-based tests can be substantially diminished by heterosis. Assessing the existence of heterosis is thus recommended to avoid false negative findings

Precise Tide-independent Bathymetric Survey and Application to the Inshore Monitoring of Seabed Evolution

Due to the influences of tidal water level, vessel attitude and wave motion, the traditional bathymetric method of reducing depths by the tidal level makes it difficult to meet precise engineering requirements in the vertical direction. Therefore a precise method, termed a tide-independent bathymetric survey, is presented in this paper. In this method, the quality of the sounding and positioning solution, the influences of time offset and vessel attitude as well as height transformation are considered by taking a series of measurements. The tide-independent method has been used for inshore monitoring of the seabed sediments. The statistical parameters acquired by comparing the traditional method with the tide-independent method used in the monitoring show that the latter is accurate and credible.Debido a las influencias del nivel del agua de las mareas, la actitud de los buques y el movimiento de las alas, el metoda batimetrico tradicional de reduccion de profundidades mediante los niveles de las mareas dificulta el cumplimiento de los requerimientos precisos de ingenieroa en la direccion vertical. Asf pues, en este articulo se presenta un metoda preciso, denominado levantamiento batimetrico independiente de las mareas. En este metoda, la calidad de los sondeos y la solucion del posicionamiento, las influencias del desfase horario y de la actitud de la nave, asl como la transformacion de las altura son consideradas mediante la toma de una serie de mediciones. El metoda independiente de las mareas ha sido utilizado para el control costero de los sedimentos del fonda del mar. Los parametres estadisticos adquiridos comparando el metoda tradicional con el metoda independiente de las mareas utilizado en el control muestran que este ultimo es exacto y creible.En raison de l'influence du niveau de la maree, de l'attitude du navire et du mouvement de l'eau, la methode bathymetrique traditionnelle de reduction des profondeurs par le niveau de l'eau rend difficile la satisfaction d'exigences precises d'ingenierie dans la direction verticale. Cet article presente done une methode precise, appelee leve bathymetrique independant des marees. Dans cette methode, la qualite du systeme de sondages et de determination de la position, les influences des decalages temporels et l'attitude du navire ainsi que la transformation de la hauteur sont pris en compte dans une serie de mesures. La methode independante des marees a ete utilisee pour le controle cotier des sediments du fond de la mer. Les parametres statistiques obtenus en comparant la methode traditionnelle a la methode independante des marees utilisee montre que cette derniere est exacte et credible