It is proved that the Cauchy problem for the Kadomtsev-Petviashvili equation (KPII) is globally w... more It is proved that the Cauchy problem for the Kadomtsev-Petviashvili equation (KPII) is globally well-posed for initial data in anisotropic Sobolev spaces $H^{s0}(mathbb{R}^2)$ with $s>-1/14$. The extension of a local solution to a solution in an arbitrary interval is carried out by means of an almost conservation property of the $H^{s0}$ norm of the solution.
Deal or No Deal? Consumer Expectations and Competition in Daily Deals
Daily deals have emerged as an integral part of the marketing mix for retail merchants and have e... more Daily deals have emerged as an integral part of the marketing mix for retail merchants and have enjoyed wide acceptance by consumers. However, there is considerable ambiguity about the effects of deals on brand evaluation, and resulting electronic word-of-mouth (eWOM). In this paper, we propose that the effects of deals on eWOM are contingent on merchant heterogeneity and whether consumers perceive merchants' marketing efforts as desperate. We empirically model the effects of daily deals on eWOM for restaurants in Washington DC over 13 months. Results show that price segment, age, and competitive deal intensity strongly moderate the effect of deals on resulting eWOM. We also show that deals have significant spillover effects on neighboring merchants who do not offer deals. We confirm these effects using three controlled lab experiments, where similar results are obtained without the possibility of deal redemption.
From an upset stomach to a life-threatening foodborne illness, getting sick is all too common aft... more From an upset stomach to a life-threatening foodborne illness, getting sick is all too common after eating in restaurants. While health inspection programs are designed to protect consumers, such inspections typically occur at wide intervals of time, allowing restaurant hygiene to remain unmonitored in the interim periods. Information provided in online reviews may be effectively used in these interim periods to gauge restaurant hygiene. In this paper, we provide evidence for how information from online reviews of restaurants can be effectively used to identify cases of hygiene violations in restaurants, even after the restaurant has been inspected and certified. We use data from restaurant hygiene inspections in New York City from the launch of an inspection program from 2010 to 2016, and combine this data with online reviews for the same set of restaurants. Using supervised machine learning techniques, we then create a hygiene dictionary specifically crafted to identify hygiene-related concerns, and use it to identify systematic instances of moral hazard, wherein restaurants with positive hygiene inspection scores are seen to regress in their hygiene maintenance within 90 days of receiving the inspection scores. To the extent that social media provides some visibility into the hygiene practices of restaurants, we argue that the effects of information asymmetry that lead to moral hazard may be partially mitigated in this context. Based on our work, we also provide strategies for how cities and policy-makers may design effective restaurant inspection programs, through a combination of traditional inspections and the appropriate use of social media.
The implementation of social distancing policies is key to reducing the impact of the current COV... more The implementation of social distancing policies is key to reducing the impact of the current COVID-19 pandemic. However, their effectiveness ultimately depends on human behavior. In the United States, compliance with social distancing policies has widely varied thus far during the pandemic. But what drives such variability? Through six open datasets, including actual human mobility, we estimated the association between mobility and the growth rate of COVID-19 cases across 3,107 U.S. counties, generalizing previous reports. In addition, data from the 2016 U.S. presidential election was used to measure how the association between mobility and COVID-19 growth rate differed based on voting patterns. A significant association between political leaning and the COVID-19 growth rate was measured. Our results demonstrate that political orientation may inform models predicting the impact of policies in reducing the spread of COVID-19.
In this work we study the initial value problem (IVP) for the fifth order KdV equations, B t u`B ... more In this work we study the initial value problem (IVP) for the fifth order KdV equations, B t u`B 5 x u`u k B x u " 0, x, t P R, k " 1, 2, in weighted Sobolev spaces H s pRq X L 2 pxxy 2r dxq. We prove local and global results. In the case k " 2 we point out the relation between decay and regularity of the solution of the IVP.
Title of Document: VOX POPULI: THREE ESSAYS ON THE USE OF SOCIAL MEDIA FOR VALUE CREATION IN SERV... more Title of Document: VOX POPULI: THREE ESSAYS ON THE USE OF SOCIAL MEDIA FOR VALUE CREATION IN SERVICES Jorge Mejia Ph.D. Candidate of Information Systems, 2016 Department of Operations & Information Systems Robert H. Smith School of Business University of Maryland, College Park Directed By: Anandasivam Gopal Associate Professor of Information Systems Department of Operations & Information Systems Robert H. Smith School of Business University of Maryland, College Park Prior research shows that electronic word of mouth (eWOM) wields considerable influence over consumer behavior. However, as the volume and variety of eWOM grows, firms are faced with challenges in analyzing and responding to this information. In this dissertation, I argue that to meet the new challenges and opportunities posed by the expansion of eWOM and to more accurately measure its impacts on firms and consumers, we need to revisit our methodologies for extracting insights from eWOM. This dissertation consists of thr...
Journal of Mathematical Analysis and Applications, 2016
In this work we consider the initial value problem (IVP) associated to the two dimensional Zakhar... more In this work we consider the initial value problem (IVP) associated to the two dimensional Zakharov-Kuznetsov equation u t`B 3
We have measured group delays of the spectral components of high-frequency P-waves along two port... more We have measured group delays of the spectral components of high-frequency P-waves along two portions of the North Anatolian Fault Zone (NAFZ) in Turkey and in a region of southern Germany. Assuming that the observed dispersion is associated with attenuation in the crust and that it can be described by a continuous relaxation model, we obtained Q and the high-frequency relaxation times for those waves for each of the three regions. Individual P-wave Q values exhibit large scatter, but mean values in the NAFZ increase from about 25 to 60 over the distance range 5-90 km. Mean Q values are somewhat higher in the eastern portion of the NAFZ than in the western portion for measurements made at distances between 10 and 30 km. P-wave Q values in Germany range between about 50 and 300 over the hypocentral distance range 20-130 km. In that region we separated the effects of Q for basement rock (2-10 km depth) from that of the overlying sediment (0-2 km depth) using a least-squares method. Q varies between 100 and 500 in the upper 8-10 km of basement, with mean values for most of the distance range being about 250. Q in the overlying sediments ranges between 6 and 10. Because of large scatter in the Q determinations we investigated possible effects that variations of the source-time function of the earthquakes and truncation of the waveform may have on Q determinations. All of our studies indicate that measurement errors are relatively large and suggest that useful application of the method requires many observations, and that the method will be most useful in regions where the number of oscillations following the initial P pulse is minimized. Even though there is large scatter in our Q determinations, the mean values that we obtained in Turkey are consistent with those found in earlier studies. Our conclusions that Q is significantly higher in the basement rock of Germany than in the basement rock of Turkey and that Q is lower in western Turkey than in eastern Turkey are also consistent with results of Q studies using Lg coda.
The evolution of the particle size distribution and the surface composition of silicon carbide an... more The evolution of the particle size distribution and the surface composition of silicon carbide and titanium carbide nanoparticle (NP) dispersions were studied. The pre-dispersions were prepared using two commonly used protocols for dispersion: stirring and sonication. Two dispersants were investigated (water and Pluronic F108 1 %) at two stages: predispersion and during in vitro assays. Our data show that for each tested condition, different time-dependent results for the surface chemical composition as well as size and percentage of the agglomerates and the primary particles are observed. De-agglomeration and successive or simultaneous cleaning-wrapping cycles of the nanomaterial are observed and are related to the dispersion method and the medium as well as to the chemical stability of the NP surface. Biological response during in vitro assessment was also performed for one given pre-dispersion time condition and demonstrates that the preparation method significantly alters the results. Keywords SiC nanoparticles Á TiC nanoparticles Á Particle size distribution Á Surface composition Á Protocol of dispersion Á In vitro assays Á Effective dose Á Environmental and health effects Electronic supplementary material The online version of this article (
Background Li-ion batteries (LIB) are increasingly used worldwide. They are made of low solubilit... more Background Li-ion batteries (LIB) are increasingly used worldwide. They are made of low solubility micrometric particles, implying a potential for inhalation toxicity in occupational settings and possibly for consumers. LiCoO2 (LCO), one of the most used cathode material, induces inflammatory and fibrotic lung responses in mice. LCO also stabilizes hypoxia-inducible factor (HIF) -1α, a factor implicated in inflammation, fibrosis and carcinogenicity. Here, we investigated the role of cobalt, nickel and HIF-1α as determinants of toxicity, and evaluated their predictive value for the lung toxicity of LIB particles in in vitro assays. Results By testing a set of 5 selected LIB particles (LCO, LiNiMnCoO2, LiNiCoAlO2) with different cobalt and nickel contents, we found a positive correlation between their in vivo lung inflammatory activity, and (i) Co and Ni particle content and their bioaccessibility and (ii) the stabilization of HIF-1α in the lung. Inhibition of HIF-1α with chetomin or ...
Multi-walled carbon nanotubes (MWC NTs) were dispersed in water and in a Pluronic F108 solution b... more Multi-walled carbon nanotubes (MWC NTs) were dispersed in water and in a Pluronic F108 solution by four different dispersion methods (stirring, bath sonication, stirring followed by bath sonication, and sonication probe). The effect of the dispersion methods were evaluated in terms of the particle size distribution, the agglomerates size, and the exfoliated fraction produced, as well as in terms of the surface and bulk chemical composition. Energy dispersive X-ray, X-ray photoelectron spectroscopy, and centrifugal liquid sedimentation techniques were used to characterize pristine MWCNTs and their dispersion. It is shown that, irrespective of the dispersion methods used, the MWCNTs are strongly wrapped with the biocompatible surfactant Pluronic F108, thereby modifying the external surface of the MWCNTs. Some shortening of MWCNTs and more wrapping are also observed when sonication methods are used. These observations raise questions as to the validity of results obtained in toxicology tests, in vitro and in vivo, were such methods of dispersion procedures are used.
It is proved that the Cauchy problem for the Kadomtsev-Petviashvili equation (KPII) is globally w... more It is proved that the Cauchy problem for the Kadomtsev-Petviashvili equation (KPII) is globally well-posed for initial data in anisotropic Sobolev spaces $H^{s0}(mathbb{R}^2)$ with $s>-1/14$. The extension of a local solution to a solution in an arbitrary interval is carried out by means of an almost conservation property of the $H^{s0}$ norm of the solution.
Deal or No Deal? Consumer Expectations and Competition in Daily Deals
Daily deals have emerged as an integral part of the marketing mix for retail merchants and have e... more Daily deals have emerged as an integral part of the marketing mix for retail merchants and have enjoyed wide acceptance by consumers. However, there is considerable ambiguity about the effects of deals on brand evaluation, and resulting electronic word-of-mouth (eWOM). In this paper, we propose that the effects of deals on eWOM are contingent on merchant heterogeneity and whether consumers perceive merchants' marketing efforts as desperate. We empirically model the effects of daily deals on eWOM for restaurants in Washington DC over 13 months. Results show that price segment, age, and competitive deal intensity strongly moderate the effect of deals on resulting eWOM. We also show that deals have significant spillover effects on neighboring merchants who do not offer deals. We confirm these effects using three controlled lab experiments, where similar results are obtained without the possibility of deal redemption.
From an upset stomach to a life-threatening foodborne illness, getting sick is all too common aft... more From an upset stomach to a life-threatening foodborne illness, getting sick is all too common after eating in restaurants. While health inspection programs are designed to protect consumers, such inspections typically occur at wide intervals of time, allowing restaurant hygiene to remain unmonitored in the interim periods. Information provided in online reviews may be effectively used in these interim periods to gauge restaurant hygiene. In this paper, we provide evidence for how information from online reviews of restaurants can be effectively used to identify cases of hygiene violations in restaurants, even after the restaurant has been inspected and certified. We use data from restaurant hygiene inspections in New York City from the launch of an inspection program from 2010 to 2016, and combine this data with online reviews for the same set of restaurants. Using supervised machine learning techniques, we then create a hygiene dictionary specifically crafted to identify hygiene-related concerns, and use it to identify systematic instances of moral hazard, wherein restaurants with positive hygiene inspection scores are seen to regress in their hygiene maintenance within 90 days of receiving the inspection scores. To the extent that social media provides some visibility into the hygiene practices of restaurants, we argue that the effects of information asymmetry that lead to moral hazard may be partially mitigated in this context. Based on our work, we also provide strategies for how cities and policy-makers may design effective restaurant inspection programs, through a combination of traditional inspections and the appropriate use of social media.
The implementation of social distancing policies is key to reducing the impact of the current COV... more The implementation of social distancing policies is key to reducing the impact of the current COVID-19 pandemic. However, their effectiveness ultimately depends on human behavior. In the United States, compliance with social distancing policies has widely varied thus far during the pandemic. But what drives such variability? Through six open datasets, including actual human mobility, we estimated the association between mobility and the growth rate of COVID-19 cases across 3,107 U.S. counties, generalizing previous reports. In addition, data from the 2016 U.S. presidential election was used to measure how the association between mobility and COVID-19 growth rate differed based on voting patterns. A significant association between political leaning and the COVID-19 growth rate was measured. Our results demonstrate that political orientation may inform models predicting the impact of policies in reducing the spread of COVID-19.
In this work we study the initial value problem (IVP) for the fifth order KdV equations, B t u`B ... more In this work we study the initial value problem (IVP) for the fifth order KdV equations, B t u`B 5 x u`u k B x u " 0, x, t P R, k " 1, 2, in weighted Sobolev spaces H s pRq X L 2 pxxy 2r dxq. We prove local and global results. In the case k " 2 we point out the relation between decay and regularity of the solution of the IVP.
Title of Document: VOX POPULI: THREE ESSAYS ON THE USE OF SOCIAL MEDIA FOR VALUE CREATION IN SERV... more Title of Document: VOX POPULI: THREE ESSAYS ON THE USE OF SOCIAL MEDIA FOR VALUE CREATION IN SERVICES Jorge Mejia Ph.D. Candidate of Information Systems, 2016 Department of Operations & Information Systems Robert H. Smith School of Business University of Maryland, College Park Directed By: Anandasivam Gopal Associate Professor of Information Systems Department of Operations & Information Systems Robert H. Smith School of Business University of Maryland, College Park Prior research shows that electronic word of mouth (eWOM) wields considerable influence over consumer behavior. However, as the volume and variety of eWOM grows, firms are faced with challenges in analyzing and responding to this information. In this dissertation, I argue that to meet the new challenges and opportunities posed by the expansion of eWOM and to more accurately measure its impacts on firms and consumers, we need to revisit our methodologies for extracting insights from eWOM. This dissertation consists of thr...
Journal of Mathematical Analysis and Applications, 2016
In this work we consider the initial value problem (IVP) associated to the two dimensional Zakhar... more In this work we consider the initial value problem (IVP) associated to the two dimensional Zakharov-Kuznetsov equation u t`B 3
We have measured group delays of the spectral components of high-frequency P-waves along two port... more We have measured group delays of the spectral components of high-frequency P-waves along two portions of the North Anatolian Fault Zone (NAFZ) in Turkey and in a region of southern Germany. Assuming that the observed dispersion is associated with attenuation in the crust and that it can be described by a continuous relaxation model, we obtained Q and the high-frequency relaxation times for those waves for each of the three regions. Individual P-wave Q values exhibit large scatter, but mean values in the NAFZ increase from about 25 to 60 over the distance range 5-90 km. Mean Q values are somewhat higher in the eastern portion of the NAFZ than in the western portion for measurements made at distances between 10 and 30 km. P-wave Q values in Germany range between about 50 and 300 over the hypocentral distance range 20-130 km. In that region we separated the effects of Q for basement rock (2-10 km depth) from that of the overlying sediment (0-2 km depth) using a least-squares method. Q varies between 100 and 500 in the upper 8-10 km of basement, with mean values for most of the distance range being about 250. Q in the overlying sediments ranges between 6 and 10. Because of large scatter in the Q determinations we investigated possible effects that variations of the source-time function of the earthquakes and truncation of the waveform may have on Q determinations. All of our studies indicate that measurement errors are relatively large and suggest that useful application of the method requires many observations, and that the method will be most useful in regions where the number of oscillations following the initial P pulse is minimized. Even though there is large scatter in our Q determinations, the mean values that we obtained in Turkey are consistent with those found in earlier studies. Our conclusions that Q is significantly higher in the basement rock of Germany than in the basement rock of Turkey and that Q is lower in western Turkey than in eastern Turkey are also consistent with results of Q studies using Lg coda.
The evolution of the particle size distribution and the surface composition of silicon carbide an... more The evolution of the particle size distribution and the surface composition of silicon carbide and titanium carbide nanoparticle (NP) dispersions were studied. The pre-dispersions were prepared using two commonly used protocols for dispersion: stirring and sonication. Two dispersants were investigated (water and Pluronic F108 1 %) at two stages: predispersion and during in vitro assays. Our data show that for each tested condition, different time-dependent results for the surface chemical composition as well as size and percentage of the agglomerates and the primary particles are observed. De-agglomeration and successive or simultaneous cleaning-wrapping cycles of the nanomaterial are observed and are related to the dispersion method and the medium as well as to the chemical stability of the NP surface. Biological response during in vitro assessment was also performed for one given pre-dispersion time condition and demonstrates that the preparation method significantly alters the results. Keywords SiC nanoparticles Á TiC nanoparticles Á Particle size distribution Á Surface composition Á Protocol of dispersion Á In vitro assays Á Effective dose Á Environmental and health effects Electronic supplementary material The online version of this article (
Background Li-ion batteries (LIB) are increasingly used worldwide. They are made of low solubilit... more Background Li-ion batteries (LIB) are increasingly used worldwide. They are made of low solubility micrometric particles, implying a potential for inhalation toxicity in occupational settings and possibly for consumers. LiCoO2 (LCO), one of the most used cathode material, induces inflammatory and fibrotic lung responses in mice. LCO also stabilizes hypoxia-inducible factor (HIF) -1α, a factor implicated in inflammation, fibrosis and carcinogenicity. Here, we investigated the role of cobalt, nickel and HIF-1α as determinants of toxicity, and evaluated their predictive value for the lung toxicity of LIB particles in in vitro assays. Results By testing a set of 5 selected LIB particles (LCO, LiNiMnCoO2, LiNiCoAlO2) with different cobalt and nickel contents, we found a positive correlation between their in vivo lung inflammatory activity, and (i) Co and Ni particle content and their bioaccessibility and (ii) the stabilization of HIF-1α in the lung. Inhibition of HIF-1α with chetomin or ...
Multi-walled carbon nanotubes (MWC NTs) were dispersed in water and in a Pluronic F108 solution b... more Multi-walled carbon nanotubes (MWC NTs) were dispersed in water and in a Pluronic F108 solution by four different dispersion methods (stirring, bath sonication, stirring followed by bath sonication, and sonication probe). The effect of the dispersion methods were evaluated in terms of the particle size distribution, the agglomerates size, and the exfoliated fraction produced, as well as in terms of the surface and bulk chemical composition. Energy dispersive X-ray, X-ray photoelectron spectroscopy, and centrifugal liquid sedimentation techniques were used to characterize pristine MWCNTs and their dispersion. It is shown that, irrespective of the dispersion methods used, the MWCNTs are strongly wrapped with the biocompatible surfactant Pluronic F108, thereby modifying the external surface of the MWCNTs. Some shortening of MWCNTs and more wrapping are also observed when sonication methods are used. These observations raise questions as to the validity of results obtained in toxicology tests, in vitro and in vivo, were such methods of dispersion procedures are used.
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