Firm learning and growth Arkolakis, Costas; Papageorgiou, Theodore; Timoshenko, Olga A.
Review of economic dynamics,
January 2018, 2018-01-00, Letnik:
27
Journal Article
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We study the implications of introducing learning (Jovanovic, 1982) in a standard monopolistically competitive environment with firm productivity heterogeneity. Our setup predicts that firm growth ...rates decrease with age, holding size constant, and decrease with size, holding age constant, a fact that models focusing on idiosyncratic productivity shocks have difficulty matching. We characterize the planner's problem and show that relative quantities between any two firms are the same in both planner's allocation and the decentralized economy. As a result, any inefficiency is driven by a discrepancy in the firm entry and exit thresholds. We calibrate the model using Colombian plant-level data and demonstrate how policies directly affecting firm entry and exit can be welfare enhancing. In particular, age-dependent subsidies allow young firms to avoid early exit and thus benefit consumers through access to a larger number of varieties.
Product switching in a model of learning Timoshenko, Olga A.
Journal of international economics,
March 2015, 2015-03-00, 20150301, Letnik:
95, Številka:
2
Journal Article
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New exporters add and drop products with much greater frequency than old exporters. This paper explains this behavior with a model of demand learning in which an exporter's profitability on the ...demand side is determined by a time-invariant firm–destination appeal index, and transient firm–destination–year preference shocks. New exporters must learn about their appeal indices in the presence of these shocks, and respond to fluctuations in demand by adding and dropping products more frequently than older exporters because they have less information about their attractiveness to consumers. Calibrated to match cross-sectional and dynamic moments of the distribution of sales and scope, the model quantitatively accounts for two thirds of the extent of product switching. The model further predicts that in response to a decline in trade costs, existing exporters add new products and new exporters enter a destination. Counterfactual implies that the contribution of product adding to export growth resulting from a fall in trade costs is substantially larger than the contribution of exporter entry.
•The paper documents a novel fact: conditional on size, new exporters switch products more frequently than old exporters.•The paper develops a model based on demand learning to explain this behavior.•New firms switch products more frequently because they have less information about their attractiveness to consumers.•The model quantitatively accounts for approximately two thirds of the extent of product switching.•The model quantitatively accounts for up to a half of the extent of the age dependence of product switching.
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The mixing of conventional and pH-sensitive lipids was exploited to design novel stimuli-responsive liposomes (fliposomes) that could be used for smart drug delivery. We deeply ...investigated the structural properties of the fliposomes and revealed the mechanisms that are involved in a membrane transformation during a pH change. From ITC experiments we observed the existence of a slow process that was attributed to lipid layers arrangement with changing pH. Moreover, we determined for the first time the pKa value of the trigger-lipid in an aqueous milieu that is drastically different from the methanol-based values reported previously in the literature. Furthermore, we studied the release kinetics of encapsulated NaCl and proposed a novel model of release that involves the physical fitting parameters that could be extracted from the release curves fitting. We have obtained for the first time, the values of pores self-healing times and were able to trace their evolution with changing pH, temperature, the amount of lipid-trigger.
This paper explores the role of sunk costs versus learning in explaining persistence in exporting. Multiple studies attributed such persistence to sunk market-entry costs. This paper shows that ...similar patterns of exporting are also consistent with a learning mechanism and finds a strong empirical support for such a mechanism in the context of Colombian plant-level data. Second, the paper empirically discriminates between the two competing theories, and finds that once learning is controlled for, the role of sunk costs in generating export persistence is at most forty percent of what is currently estimated in the literature. Finally, while in differentiated-products industries export persistence arises primarily due to learning, in the homogeneous-products industries such persistence arises primarily due to the sunk-cost mechanism.
Crystalline silicon (Si) nanoparticles present an extremely promising object for bioimaging based on photoluminescence (PL) in the visible and near-infrared spectral regions, but their efficient PL ...emission in aqueous suspension is typically observed after wet chemistry procedures leading to residual toxicity issues. Here, we introduce ultrapure laser-synthesized Si-based quantum dots (QDs), which are water-dispersible and exhibit bright exciton PL in the window of relative tissue transparency near 800 nm. Based on the laser ablation of crystalline Si targets in gaseous helium, followed by ultrasound-assisted dispersion of the deposited films in physiological saline, the proposed method avoids any toxic by-products during the synthesis. We demonstrate efficient contrast of the Si QDs in living cells by following the exciton PL. We also show that the prepared QDs do not provoke any cytoxicity effects while penetrating into the cells and efficiently accumulating near the cell membrane and in the cytoplasm. Combined with the possibility of enabling parallel therapeutic channels, ultrapure laser-synthesized Si nanostructures present unique object for cancer theranostic applications.
Raman spectroscopy is used to probe free charge carriers in layers of silicon nanowires (SiNWs) formed by metal‐assisted chemical etching of crystalline silicon (c‐Si) wafers followed by additional ...doping with boron. One‐phonon Raman spectra of the boron‐doped SiNWs are strongly modified due to the Fano effect that allowed us to determine the free carrier concentration in the nanowires in the range from 1019 to 1020 cm−3, depending on the doping conditions. The micro‐Raman mapping was used to determine the depth profile of charge carrier density along nanowires, which decreases toward the SiNWs/c‐Si interface. The obtained results are discussed in view of possible applications of the Raman spectroscopy for express‐diagnostics of doped Si nanostructures for photonics and thermoelectric applications.
Determination of the free hole concentration in boron‐doped silicon nanowires by Raman spectroscopy.
Increased expression of COX-2 or VEGF-C has been correlated with progressive disease in certain cancers. Present study utilized several human breast cancer cell lines (MCF-7, T-47D, Hs578T and ...MDA-MB-231, varying in COX-2 expression) as well as 10 human breast cancer specimens to examine the roles of COX-2 and prostaglandin E (EP) receptors in VEGF-C expression or secretion, and the relationship of COX-2 or VEGF-C expression to lymphangiogenesis. We found a strong correlation between COX-2 mRNA expression and VEGF-C expression or secretion levels in breast cancer cell lines and VEGF-C expression in breast cancer tissues. Expression of LYVE-1, a selective marker for lymphatic endothelium, was also positively correlated with COX-2 or VEGF-C expression in breast cancer tissues. Inhibition of VEGF-C expression and secretion in the presence of COX-1/2 or COX-2 inhibitors or following downregulation of COX-2 with COX-2 siRNA established a stimulatory role COX-2 in VEGF-C synthesis by breast cancer cells. EP1 as well as EP4 receptor antagonists inhibited VEGF-C production indicating the roles of EP1 and EP4 in VEGF-C upregulation by endogenous PGE2. Finally, VEGF-C secretion by MDA-MB-231 cells was inhibited in the presence of kinase inhibitors for Her-2/neu, Src and p38 MAPK, indicating a requirement of these kinases for VEGF-C synthesis. These results, for the first time, demonstrate a regulatory role of COX-2 in VEGF-C synthesis (and thereby lymphangiogenesis) in human breast cancer, which is mediated at least in part by EP1/EP4 receptors.
•Extractive distillation of the ternary azeotropic mixtures was studied.•The flowsheets with partially thermally coupled columns were investigated.•Their applicability estimates for all types of the ...ternary mixtures VLE diagrams.•The feasible flowsheets were found of the mixture with unique VLE diagram.
An application is considered of the extractive distillation flowsheets with partially thermally coupled columns for the separation of ternary azeotropic mixtures with the different type of vapor–liquid equilibrium diagrams. The feasible extractive distillation flowsheets with such columns are identified for all types of the ternary azeotropic mixture vapor–liquid equilibrium diagrams. The manifold of flowsheets is the search space to identify the optimal arrangement for the separation of the individual mixture. An applicability analysis of all possible extractive distillation flowsheets for all types of vapor–liquid equilibrium diagram decreases the number of feasible configurations for the selection of the optimal extractive distillation sequence for the mixture with unique vapor–liquid equilibrium diagram separation. For example, in the case of benzene–cyclohexane–toluene mixture distillation with N-methylpyrrolidone as an entrainer, only 10 extractive distillation flowsheets instead of 22 potential ones must be analyzed, calculated and optimized for the identification of the best extractive distillation arrangement.
The application of wavelet transform to the analysis of the extended X-ray absorption fine structure (EXAFS) from perovskite-type compounds is presented on the example of the Re L
3-edge in ReO
3 and ...Co K-edge in LaCoO
3. We propose a modified wavelet transform procedure, which allows better discrimination of the overlapped contributions into the EXAFS signal.
Prostate cancer is the second most common type of cancer among men. The main method of its treatment is androgen deprivation therapy, which has a wide range of side effects. One of the solutions to ...this challenge is the targeted delivery of drugs to prostate cancer cells. In this study, we performed the synthesis of a novel small-molecule PSMA-targeted conjugate based on abiraterone. Cytotoxicity, the induction of intracellular reactive oxygen species, and P450-cytochrome species inhibition were investigated for this conjugate PSMA-abiraterone. The conjugate demonstrated a preferential effect on prostate tumor cells, remaining inactive at up to 100 µM in human fibroblast cells. In addition, it revealed preferential efficacy, specifically on PSMA-expressing lines with a 65% tumor growth inhibition level on 22Rv1 (PSMA+) xenografts after 14-fold oral administration of
at a single dose of 500 mg/kg (7.0 g/kg total dose) was observed. This compound showed significantly reduced acute toxicity with comparable efficacy compared to
.
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