Essays in Public Economics

\chapter*{Abstract} In the first essay I estimate the effect of a tuition subsidy, in the form of in-state tuition for undocumented immigrants, on the college enrollment decision of non-citizen Mexican immigrants. Using data from the Current Population Survey, I capture the variable impact of the policy across age by estimating the impact on two different age groups. I also estimate the differential effect across genders. The policy increases the college enrollment among non-citizen Mexican immigrants. The subsidy is associated with a 1.5 percentage points (or 15 percent) increase in college attendance of younger immigrants aged 18 to 20 years old. Older immigrants, aged 21 and 22 years old, are more responsive: their college enrollment doubles with the introduction of the in-state tuition policy. Irrespective of age, the subsidy increases the likelihood of college attendance more for men than it does for women. Subsidizing the cost of college results in an 7.7 percentage points (or 86 percent) increase in college attendance of men while women\u27s participation drops by 72 percent. Irrespective of age, married women are more likely to drop out of college when in-state tuition is offered. The college participation of U.S. citizens is trivially impacted by the in-state tuition subsidy to undocumented students. The second essay concentrates on answering the question of whether couples strategically time their divorce so as to minimize their joint tax bill. Previous empirical literature that analyzes the changing trends in the family dynamics often rely on identifying the demographic, the sociocultural, as well as the economic factors that influence those changes. The role of the income tax code and the tax liability faced by each individual according to marital status has only recently been considered as a possible influence on the likelihood and timing of divorce. Using household data from the Panel Study of Income Dynamics, I build a parametric model of the divorce timing decision as a function of the change in the tax burden caused by whether the divorce takes place by the end of the year or not. Results provide evidence that individuals do respond to tax incentives and changes in the marriage tax penalty alters the relative value of divorcing early. A doubling of the relative marriage tax price is going to reduce the probability of accelerating the divorce by 3.2\% when the price is computed under the assumption that the spouse with the higher income gets the dependents. The effect is slightly larger (i.e. 3.7\%) when the relative marriage-tax price is computed under the assumption that the spouse with the higher income gets the dependents and also gets the \u27Head of Household\u27 filing status

3D correlative single-cell imaging utilizing fluorescence and refractive index tomography

Cells alter the path of light, a fact that leads to well-known aberrations in single cell or tissue imaging. Optical diffraction tomography (ODT) measures the biophysical property that causes these aberrations, the refractive index (RI). ODT is complementary to fluorescence imaging and does not require any markers. The present study introduces RI and fluorescence tomography with optofluidic rotation (RAFTOR) of suspended cells, quantifying the intracellular RI distribution and colocalizing it with fluorescence in 3D. The technique is validated with cell phantoms and used to confirm a lower nuclear RI for HL60 cells. Furthermore, the nuclear inversion of adult mouse photoreceptor cells is observed in the RI distribution. The applications shown confirm predictions of previous studies and illustrate the potential of RAFTOR to improve our understanding of cells and tissues.Comment: 15 pages, 5 figure

THE DEGREE OF SILTING AND THE IMPACT ON ALLUVIAL DEPOSITS IN THE RIVER BEDS OF BISTRIŢA RIVER BASIN

Since 1960 the Bistriţa River basin came under the profound influence of anthropic incidence. This river basin represents a pattern of use for hydropower potential: reservoirs (9); channels (61 km); water dams; transfers of flows; protection structures works for banks and slopes; relocation of human settlements (13 villages); gravel pits; galleries; viaducts; communication paths, etc. Bistriţa River development has led to significant changes in the structure of the hydrological regime, through the regularization of water flows and by creating significant discontinuities in the transit of silt. Lately there has been an increase in water turbidity in the highlands. Solid flows on the lower course register a continuous decrease because of the existence of reservoir. During the execution of the hydraulic structures turbidity and sediment yield increased. When brought into service intense processes of silting occurred. Analysis covers the sediment yield in Bistriţa River basin and the evolution in time of the degree of silting of reservoir. Average production of silt varies between 1.5-2 t/ha/year. Annual rate of silting in reservoirs is between 0.6% (Izvorul Muntelui) and > 2% (Pângăraţi, Racova). Racova Reservoir was decommissioned in 2011

Changes in microbubble dynamics near a boundary revealed by combined optical micromanipulation and high-speed imaging

The authors report optical observations of the change in the dynamics of one and the same ultrasound contrast agent microbubble due to the influence of interfaces and neighboring bubbles. The bubble is excited by a 2.25 MHz ultrasound burst and its oscillations are recorded with an ultrahigh-speed camera at 15 million frames per second. The position of an individual bubble relative to a rigid wall or second bubble is precisely controlled using optical tweezers based on Laguerre-Gaussian laser beams [P. Prentice et al., Opt. Express 12, 593 (2004); V. Garbin et al., Jpn. J. Appl. Phys. 44, 5773 (2005)]. This allows for repeated experiments on the very same bubble and for a quantitative comparison of the effect of boundaries on bubble behavior

Accurate evaluation of size and refractive index for spherical objects in quantitative phase imaging

Measuring the average refractive index (RI) of spherical objects, such as suspended cells, in quantitative phase imaging (QPI) requires a decoupling of RI and size from the QPI data. This has been commonly achieved by determining the object's radius with geometrical approaches, neglecting light-scattering. Here, we present a novel QPI fitting algorithm that reliably uncouples the RI using Mie theory and a semi-analytical, corrected Rytov approach. We assess the range of validity of this algorithm in silico and experimentally investigate various objects (oil and protein droplets, microgel beads, cells) and noise conditions. In addition, we provide important practical cues for future studies in cell biology.Comment: 14 pages, 10 figures, 1 tabl

Horizontal cooperation on investment: Evidence from mobile network sharing

We present a structural model to investigate the effects of horizontal cooperation on investment in the context of telecommunication networks. More specifically, we estimate the effect of network sharing in the mobile telecommunications industry on prices, network quality and consumer welfare. The presented framework allows estimating the effects of different types of sharing agreements including common ownership of shared assets in a joint venture company or collaboration via geographical separation (geo-split principle). The proposed identification strategy relies on differences in the costs of network deployment of shared versus non-shared network infrastructure, with different costs affecting operators’ optimal choice of price and network quality. We apply the structural model to estimate the effects of a network sharing agreement in the Czech Republic, using a combination of unique datasets on prices, network quality measured as average download speed and operator’s costs of network deployment. The results of our model indicate that horizontal cooperation on investments may be beneficial for consumers. Specifically, the network sharing agreement under study generated cost savings for the sharing parties, which were passed-on to consumers in the form of lower prices and higher average download speed. Our findings are of relevance to the assessment of network sharing agreements, which, considering the substantial investment cost associated with the 5G technology, are likely to play an even greater role in the telecommunications industry in the future. The findings are also of relevance to the general literature on horizontal cooperation on investments

Optical delivery of liposome encapsulated chemical stimuli to neuronal cells

Spatially confined and precise time delivery of neuroactive molecules is an important issue in neurophysiology. In this work we developed a technique for delivering chemical stimuli to cultured neurons consisting in encapsulating the molecules of interest in liposomes. These vectors were then loaded in reservoirs consisting of glass capillaries. The reservoirs were placed in the recording chamber and single liposomes were trapped and transported out by optical tweezers to the site of stimulation on cultured neurons. Finally, the release of liposome content was induced by application of UV-pulses, breaking the liposome membrane. The efficiency of encapsulation and release were first evaluated by loading the liposomes with fluorescein. In order to test the effect of the UV-induced release, liposomes with diameter ranging from 1 to 10 μm (fL to pL volumes), were filled with KCl and tested on neuronal cells. Neuronal cultures, loaded with Ca(2+) dye, were monitored by imaging intracellular Ca(2+). An efficient release from the liposomes was demonstrated by detectable calcium signals, indicating stimulated depolarization of the neuronal cells by KCl. The present technique represents an alternative method for focal chemical stimulation of cultured cells that circumvents some of the limitations of microejection and photorelease of caged compounds

Investigation into local cell mechanics by atomic force microscopy mapping and optical tweezer vertical indentation

The investigation of mechanical properties of cells represents a potential source of label free markers of cancer progression, based on measurable viscoelastic parameters. The Young modulus proved to be the most studied so far, however, even for the same cell type, the elastic modulus reported in different studies spans over a wide range of values, mainly due to the application of different experimental conditions. This complicates a reliable use of elasticity for mechanical phenotyping of cells. Here we combine two complementary techniques, Atomic Force Microscopy (AFM) and Optical Tweezers Microscopy (OTM), providing a comprehensive mechanical comparison of three human breast cell lines: normal myoepithelial (HBL-100), luminal breast cancer (MCF-7) and basal breast cancer (MDA-MB-231) cells. The elastic modulus was locally measured by AFM and OTM on single cells, using similar indentation approaches but different measurement parameters. Peak force tapping AFM was employed at nN forces and high loading rate to draw a viscoelastic map of each cell and the results indicated the region on top of the nuclei as the most meaningful. OTM was employed at those locations at pN forces and low loading rates, to measure the elastic modulus in a real elastic regime and rule out the contribution of viscous forces typical of AFM. When measured by either AFM or OTM, the cell lines elasticity trend was similar for the aggressive MDA-MB-231 cells, which were found to be significantly softer than the other two cell types in both measurements. However, when comparing HBL100 and MCF-7 cells, we found significant differences only when using OT

Real-time imaging of DNA damage in yeast cells using ultra-short near-infrared pulsed laser irradiation

Analysis of accumulation of repair and checkpoint proteins at repair sites in yeast nuclei has conventionally used chemical agents, ionizing radiation or induction of endonucleases to inflict localized damage. In addition to these methods, similar studies in mammalian cells have used laser irradiation, which has the advantage that damage is inflicted at a specific nuclear region and at a precise time, and this allows accurate kinetic analysis of protein accumulation at DNA damage sites. We show here that it is feasible to use short pulses of near-infrared laser irradiation to inflict DNA damage in subnuclear regions of yeast nuclei by multiphoton absorption. In conjunction with use of fluorescently-tagged proteins, this allows quantitative analysis of protein accumulation at damage sites within seconds of damage induction. PCNA accumulated at damage sites rapidly, such that maximum accumulation was seen approximately 50 s after damage, then levels declined linearly over 200-1000 s after irradiation. RPA accumulated with slower kinetics such that hardly any accumulation was detected within 60 s of irradiation, and levels subsequently increased linearly over the next 900 s, after which levels were approximately constant (up to ca. 2700 s) at the damage site. This approach complements existing methodologies to allow analysis of key damage sensors and chromatin modification changes occurring within seconds of damage inception

Investigating mechanosensitive channels activation in concert with the mechanical properties of red blood cells

The activity of the mechanosensitive Ca2+ permeable channels expressed in the membrane of the red blood cells (RBC) is determined both by the mechanical stimuli and the mechanical properties of the cell. Therefore, it is of most importance to correlate the triggering stimulus with the mechanical properties. In this paper, we propose an approach to determine the activation pressure of the mechanosensitive channels and concomitantly evaluate cell mechanical properties as Young’s Modulus, membrane tension and viscosity, for individual cells. Cell deformation was accomplished by micro- pipette aspiration with a controlled pressure ramp and recorded by brightfield imaging to determine the mechanical properties. The Ca2+ transient was concomitantly monitored by fluorescence imaging, to get the activation pressure. The technique was validated comparing the behavior of three pools of RBCs, probed at different intervals of time after the cell suspension preparation by the same mechanical stimuli. We found relevant changes of the activation pressure, associated with the alteration of the mechanical properties, the latest becoming significant with the passage of time. Our approach opens a new direction to investigate the correlation between mechanosensitivity and mechanical properties for individual RBCs, which can be extended to other cells, in suspension or plated, under controlled environmental conditions