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TGF-b Downregulation by RNAi Technique in ex Vivo-Expanded HSCs on 3D DBM Scaffold
ZS Hashemi,M Forouzandeh Moghadam,M Soleimani,M Hafizi
Tehran University Medical Journal , 2012,
Abstract: Background: Bone Marrow Transplantations (BMT) are limited by low CD34+ cell counts in umbilical cord blood (UCB) and these cells need to be expanded for success in such procedures. To achieve this goal, ex vivo expansion of hematopoietic stem cells (HSCs) by enhancing their self-renewal activity on demineralized bone matrix (DBM) scaffold coated with mesenchymal progenitor cells (MPCs) and unrestricted somatic stem cells (USSCs) was recommended. TGF-b pathway is a key inhibitory factor for HSCs self-renewal. In this study ex vivo expansion and downregulation of TGF-b pathway were simultaneously performed. Methods: USSC cells were isolated from UCB and then coated on DBM scaffold as a feeder layer. UCB CD34+ cells were isolated from UCB by magnetic activated cell sorting (MACS) method and were transfected by siRNA against TGFbR2 in two-dimensional (2D) and three-dimensional (3D) cultures by co-cultivation with USSC. TGFbR2 expression levels were evaluated by quantitative real-time PCR. Cell count and flow cytometry were performed and clonogenic activity was evaluated. Results: Ex vivo expansion of CD34+ cells was significantly enhanced (41±0.7 folds) by TGFbR2 downregulation, especially in 2D than 3D cultures. Finally, 2D culture showed less TGFbR2 expression levels and higher increase in the percentage of CD34 markers by flow cytometry assay. Conclusion: The 3D siRNA delivery system would be of lower efficiency in contrast to 2D settings where the cells have less freedom and are in more contact with the feeder layer.
Dynamics of Income Distribution — A Diffusion Analysis  [PDF]
Fariba Hashemi
Theoretical Economics Letters (TEL) , 2011, DOI: 10.4236/tel.2011.12008
Abstract: The study is motivated by the observation that the distribution of income across countries varies as a function of time. It would not be unreasonable to assume that there exists a statistical equilibrium distribution of income with a certain mean and variance, towards which the ensemble of countries considered tend to converge, and there is a speed of adjustment towards this said equilibrium. In order to quantify this process, the evolution through time of income around its trend is modeled using a classic stochastic differential equation. The model describes the diffusion of shocks across space, via an income adjustment process with noise. The dynamics rely on two opposing flows: (i) a factor equalization process, and (ii) a counteracting diffusion process. It is hypothesized that these flows follow simple evolutionary laws that can be described with five parameters — parameters that can be estimated from historical data with some accuracy. The dynamic behavior of the model is analytically derived. Both the extent and speed of adjustment of income are analyzed. An empirical application of the proposed model to the evolution of the distribution of income for 25 countries in the European Union tests the validity of the proposed method and suggests that diffusion may be a preferable technique for the analysis of income dynamics.
On a Theme by Williamson: A Stochastic Model for the Evolution of Global Labor Markets since 1830  [PDF]
Fariba Hashemi
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.24065
Abstract: The cross-sectional distribution of wages has so far been neglected compared to the study of income differences across countries over time. We propose a stochastic model, built on the theory of diffusion processes, to describe the evolution of global labor markets since 1830. The model is applied to empirical data collected by Williamson, in order to describe the level and variation of cross-country wages. The empirical application validates the proposed method.


East Asian Economic Growth—An Evolutionary Perspective  [PDF]
Fariba Hashemi
Journal of Service Science and Management (JSSM) , 2011, DOI: 10.4236/jssm.2011.43033
Abstract:
The High Performing Asian Economies have been the fastest growing economies anywhere, anytime. This phenomenal growth experience has stimulated extensive research on its determinants. What is less known however, is dynamics of the distribution of income. This paper considers a statistical model to describe convergence of cross-country incomes across the High Performing Asian Economies. The empirical results illustrate that diffusion is a potential technique for the analysis of spatial dynamics of economic growth.
Stochastic Convergence in Regional Economic Activity  [PDF]
Fariba Hashemi
Journal of Mathematical Finance (JMF) , 2011, DOI: 10.4236/jmf.2011.13016
Abstract: A stochastic model is presented, based on a double process of temporal drift and random disturbance, to fit the evolution of cross-country distribution of income and economic activity. Instead of assuming a steady state as is standard practice, a long run stationary equilibrium distribution is hypothesized, around which economic activity fluctuates. An empirical application comparing dynamics of growth in Asia and Europe tests the validity of the proposed method. In particular, results point out that the distribution of income and economic activity is approaching a long run equilibrium at a faster rate in the case of Asia, and that the dispersion of the distribution is shrinking over time above all in the case of Europe. Main implications are supportive of the convergence hypothesis, and suggest that diffusion may be a potential technique for the analysis of growth dynamics.
Industry dynamics in biotechnology  [PDF]
Fariba Hashemi
Advances in Bioscience and Biotechnology (ABB) , 2012, DOI: 10.4236/abb.2012.31006
Abstract: The field of modern biotechnology is thought to have largely begun in 1980, when the United States Supreme Court ruled that a genetically-modified microorganism could be patented. The growth of the Biotechnology industry has stimulated extensive research on its determinants. One of the areas which has attracted a fair amount of attention is the distribution of firm size within an industry. What is less known however, is the dynamics of firm size. This paper considers a statistical model to describe the spatial dynamics of firm size across the biotechnology industry. It is found that firm size fluctuates around its long run stationary equilibrium according to a temporal drift and random disturbance. The empirical results illustrate that diffusion is a potential technique for the analysis of spatial dynamics of firm size.
Industry Dynamics in Pharmaceuticals  [PDF]
Fariba Hashemi
Pharmacology & Pharmacy (PP) , 2012, DOI: 10.4236/pp.2012.31001
Abstract: Pharmaceuticals is a relatively large and mature industry, and of growing significance. The industry has stimulated extensive research on determinants of its growth and development. Specifically, the distribution of firm size has attracted significant attention, due to tis relevance as an indicator of degree of industrial concentration. A large part of this literature has focused, since the early contributions, on the explanation of the shape of firm size distribution in the industry at a given point in time by reference to steady state arguments. The dynamics in question have been relatively neglected however. The main objective of this paper is to help fill this gap. It is shown that interesting issues arise when one considers how firm structure evolves over time, rather than simply attending to equilibrium implications of processes. Information on the shape and time-evolution of the size distribution of firms over an extended period of time can be used to make inferences about an underlying process; specifically, on which characteristics lead to which kinds of dynamics. To that end, we propose a diffusion model to examine the spatial dynamics of firm size. Instead of assuming a steady state as is standard practice, we consider that firm size fluctuates around its long run stationary equilibrium, according to a double process of temporal drift and random disturbance. An empirical application to real data from the Pharmaceutical industry helps fill a second gap in the literature, as only a few diffusion studies have employed real statistical data when analyzing firm size dynamics. Our empirical application confirms results presented elsewhere and offers some new insights.
Dynamics of firm size in healthcare industry  [PDF]
Fariba Hashemi
Health (Health) , 2012, DOI: 10.4236/health.2012.43024
Abstract: Healthcare is one of the world’s fastest growing industries consisting of broad services offered by various hospitals, physicians, nursing homes, diagnostic laboratories, pharmacies and supported by drugs, pharmaceuticals, chemicals, medical equipment, manufacturers and suppliers. The industry is highly fragmented, comprising of various ancillary sectors namely medical equipment and supplies, pharmaceutical, healthcare services, biotechnology, and alternative medicines. The present study focuses on the pharmaceutical and biotechnology segments of the healthcare industry, and presents a stochastic analysis of the evolution over time of firm size. A dynamic model is proposed that attempts to predict the evolutionary process of firm size distribution based on industry and product characteristics. A validation exercise, applying the model to pharmaceutical and the biotechnology industries finds that the predictions from the model are very close to the actual trajectories of firm size distributions within these industries at the global level. The results show interestingly, that the drivers of firm size dynamics are industry level characteristics that can be estimated from historical data with some accuracy. Specifically, it is found that firm size distributions are approaching a long-run equilibrium at a faster rate in the case of the pharmaceutical industry and that the dispersion of the distributions are shrinking over time above all for the biotechnology industry.
On a Theme by Heckscher-Ohlin: A Diffusion Model for Spatial Dynamics in Factor Prices  [PDF]
Fariba Hashemi
Technology and Investment (TI) , 2012, DOI: 10.4236/ti.2012.33017
Abstract: An analytical study is presented for the cross-sectional distribution of factor prices over time and across space. A drift-diffusion model is proposed to describe the dynamic process governing the fluctuations around the equilibrium distribution. The model is mechanical and descriptive in nature, and illustrates that the growth distribution of factor prices can be generated by a single stochastic process that builds upon the theory of diffusion processes. An empirical application of the proposed model, to the evolution of the distribution of incomes for 186 countries, recorded from 1993 up to 2007, illustrates the applicability of the proposed method and suggests that diffusion may be a preferable technique for the analysis of the spatial dynamics in factor prices.
Migrated Exploding Reflectors in Evaluation of Finite Difference Solution for Inhomogeneous Seismic Models  [PDF]
Maryam Nejati, Hosein Hashemi
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.412A120
Abstract:

Earth is inhomogeneous, which means its elastic characteristics change with depth. The seismic method employs the propagation of waves throughout the earth to locate different structures and stratigraphy. Understanding the wave propagation is an important matter in exploration seismology; therefore modeling of seismic wave is an important tool. To validate the interpreted earth model out of the seismic data, seismic synthetic seismograms should be generated in a process named “seismic forward modeling”. Finite difference method is used as one of the most common numerical modeling techniques. In this paper the accuracy of finite difference method in seismic section modeling is explored on different modeled data set of heterogeneous earth. It is shown that finite difference method completes with migration to reposition the events in their correct location. Two different migration methods are used and various velocities are also tested to determine an appropriate migration velocity. Finally the validly of finite difference modeling is examined using a 2D structural similarity index technique.

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