arXiv subjects

Plamen Nikolov

Publications and source records attributed to Plamen Nikolov.

18 recordsLinked to original sources

arXiv2025

Polarimetric and spectropolarimetric observations with FoReRo2: Instrument overview and standard star monitoring

In this paper, we present a description and characterisation of the 2-Channel Focal Reducer Rozhen (FoReRo2), with an emphasis on its polarimetric and spectropolarimetric observation modes. FoReRo2 is a multimode instrument mounted at the Ritchey-Chretien (RC) focus of the 2-meter Ritchey-Chretien-Coude (RCC) telescope at the Bulgarian National Astronomical Observatory (BNAO) - Rozhen. The primary targets of this instrument include novae, Be/X-ray binaries, symbiotic stars, asteroids, and comets. Standard stars with a high degree of polarisation are an essential part of the polarimetric observations. In our sample, HD 204827 shows short-term variability in the position angle (PA), making it unsuitable for calibration. HD 183143 displays intrinsic polarisation variability, but remains stable in terms of the PA. For the first time, we present a statistical study of the K and lambda_max parameters of Serkowski's law, including the mean value, standard deviation, and distribution. To demonstrate FoReRo2's polarimetric capabilities, we present several examples. The recurrent nova RS Oph shows the variability of Serkowski's K parameter, which is due to dust formation within the first few days after the 2021 outburst. These examples also include the imaging polarimetry of comet C/2019 Y4 (ATLAS) and spectropolarimetric observations of the symbiotic star Z And.

astro-ph.SR↗

arXiv2023

Entitled to Property: How Breaking the Gender Barrier Improves Child Health in India

Non-unitary household models suggest that enhancing women's bargaining power can influence child health, a crucial determinant of human capital and economic standing throughout adulthood. We examine the effects of a policy shift, the Hindu Succession Act Amendment (HSAA), which granted inheritance rights to unmarried women in India, on child health. Our findings indicate that the HSAA improved children's height and weight. Furthermore, we uncover evidence supporting a mechanism whereby the policy bolstered women's intra-household bargaining power, resulting in downstream benefits through enhanced parental care for children and improved child health. These results emphasize that children fare better when mothers control a larger share of family resources. Policies empowering women can yield additional positive externalities for children's human capital.

econ.GN↗

arXiv2022

Do Pension Benefits Accelerate Cognitive Decline in Late Adulthood? Evidence from Rural China

Economists have mainly focused on human capital accumulation rather than on the causes and consequences of human capital depreciation in late adulthood. To investigate how human capital depreciates over the life cycle, we examine how a newly introduced pension program, the National Rural Pension Scheme, affects cognitive performance in rural China. We find significant adverse effects of access to pension benefits on cognitive functioning among the elderly. We detect the most substantial impact of the program on delayed recall, a cognition measure linked to the onset of dementia. In terms of mechanisms, cognitive deterioration in late adulthood is mediated by a substantial reduction in social engagement, volunteering, and activities fostering mental acuity.

econ.GN↗

arXiv2022

Skill Downgrading Among Refugees and Economic Immigrants in Germany

Upon arrival to a new country, many immigrants face job downgrading, a phenomenon describing workers being in jobs below the ones they have based on the skills they possess. Moreover, in the presence of downgrading immigrants receiving lower wage returns to the same skills compared to natives. The level of downgrading could depend on the immigrant type and numerous other factors. This study examines the determinants of skill downgrading among two types of immigrants - refugees and economic immigrants - in the German labor markets between 1984 and 2018. We find that refugees downgrade more than economic immigrants, and this discrepancy between the two groups persists over time. We show that language skill improvements exert a strong influence on subsequent labor market outcomes of both groups.

econ.GN↗

arXiv2021

Reaping the Rewards Later: How Education Improves Old-Age Cognition in South Africa

Cognition, a component of human capital, is fundamental for decision-making, and understanding the causes of human capital depreciation in old age is especially important in aging societies. Using various proxy measures of cognitive performance from a longitudinal survey in South Africa, we study how education affects cognition in late adulthood. We show that an extra year of schooling improves memory performance and general cognition. We find evidence of heterogeneous effects by gender: the effects are stronger among women. We explore potential mechanisms, and we show that a more supportive social environment, improved health habits, and reduced stress levels likely play a critical role in mediating the beneficial effects of educational attainment on cognition among the elderly.

econ.GN↗

arXiv2020

Predictors of Social Distancing and Mask-Wearing Behavior: Panel Survey in Seven U.S. States

This paper presents preliminary summary results from a longitudinal study of participants in seven U.S. states during the COVID-19 pandemic. In addition to standard socio-economic characteristics, we collect data on various economic preference parameters: time, risk, and social preferences, and risk perception biases. We pay special attention to predictors that are both important drivers of social distancing and are potentially malleable and susceptible to policy levers. We note three important findings: (1) demographic characteristics exert the largest influence on social distancing measures and mask-wearing, (2) we show that individual risk perception and cognitive biases exert a critical role in influencing the decision to adopt social distancing measures, (3) we identify important demographic groups that are most susceptible to changing their social distancing behaviors. These findings can help inform the design of policy interventions regarding targeting specific demographic groups, which can help reduce the transmission speed of the COVID-19 virus.

econ.GN↗

arXiv2020

The Wage Premium of Communist Party Membership: Evidence from China

Social status and political connections could confer large economic benefits to an individual. Previous studies focused on China examine the relationship between Communist party membership and earnings and find a positive correlation. However, this correlation may be partly or totally spurious, thereby generating upwards-biased estimates of the importance of political party membership. Using data from three surveys spanning more than three decades, we estimate the causal effect of Chinese party membership on monthly earnings in in China. We find that, on average, membership in the Communist party of China increases monthly earnings and we find evidence that the wage premium has grown in recent years. We explore for potential mechanisms and we find suggestive evidence that improvements in one's social network, acquisition of job-related qualifications and improvement in one's social rank and life satisfaction likely play an important role. (JEL D31, J31, P2)

econ.GN↗

arXiv2020

The Effects of Access to Credit on Productivity Among Microenterprises: Separating Technological Changes from Changes in Technical Efficiency

Improving productivity among farm microenterprises is important, especially in low-income countries where market imperfections are pervasive and resources are scarce. Relaxing credit constraints can increase the productivity of farmers. Using a field experiment involving microenterprises in Bangladesh, we estimate the impact of access to credit on the overall productivity of rice farmers, and disentangle the total effect into technological change (frontier shift) and technical efficiency changes. We find that relative to the baseline rice output per decimal, access to credit results in, on average, approximately a 14 percent increase in yield, holding all other inputs constant. After decomposing the total effect into the frontier shift and efficiency improvement, we find that, on average, around 11 percent of the increase in output comes from changes in technology, or frontier shift, while the remaining 3 percent is attributed to improvements in technical efficiency. The efficiency gain is higher for modern hybrid rice varieties, and almost zero for traditional rice varieties. Within the treatment group, the effect is greater among pure tenant and mixed-tenant farm households compared with farmers that only cultivate their own land.

econ.GN↗

arXiv2020

Do Private Household Transfers to the Elderly Respond to Public Pension Benefits? Evidence from Rural China

Ageing populations in developing countries have spurred the introduction of public pension programs to preserve the standard of living for the elderly. The often-overlooked mechanism of intergenerational transfers, however, can dampen these intended policy effects as adult children who make income contributions to their parents could adjust their behavior to changes in their parents' income. Exploiting a unique policy intervention in China, we examine using a difference-in-difference-in-differences (DDD) approach how a new pension program impacts inter vivos transfers. We show that pension benefits lower the propensity of receiving transfers from adult children in the context of a large middle-income country and we also estimate a small crowd-out effect. Taken together, these estimates fit the pattern of previous research in high-income countries, although our estimates of the crowd-out effect are significantly smaller than previous studies in both high-income and middle-income countries.

econ.GN↗

arXiv2020

The Importance of Cognitive Domains and the Returns to Schooling in South Africa: Evidence from Two Labor Surveys

Numerous studies have considered the important role of cognition in estimating the returns to schooling. How cognitive abilities affect schooling may have important policy implications, especially in developing countries during periods of increasing educational attainment. Using two longitudinal labor surveys that collect direct proxy measures of cognitive skills, we study the importance of specific cognitive domains for the returns to schooling in two samples. We instrument for schooling levels and we find that each additional year of schooling leads to an increase in earnings by approximately 18-20 percent. The estimated effect sizes-based on the two-stage least squares estimates-are above the corresponding ordinary least squares estimates. Furthermore, we estimate and demonstrate the importance of specific cognitive domains in the classical Mincer equation. We find that executive functioning skills (i.e., memory and orientation) are important drivers of earnings in the rural sample, whereas higher-order cognitive skills (i.e., numeracy) are more important for determining earnings in the urban sample. Although numeracy is tested in both samples, it is only a statistically significant predictor of earnings in the urban sample.

econ.GN↗

arXiv2020

Do Public Program Benefits Crowd Out Private Transfers in Developing Countries? A Critical Review of Recent Evidence

Precipitated by rapid globalization, rising inequality, population growth, and longevity gains, social protection programs have been on the rise in low- and middle-income countries (LMICs) in the last three decades. However, the introduction of public benefits could displace informal mechanisms for risk-protection, which are especially prevalent in LMICs. If the displacement of private transfers is considerably large, the expansion of social protection programs could even lead to social welfare loss. In this paper, we critically survey the recent empirical literature on crowd-out effects in response to public policies, specifically in the context of LMICs. We review and synthesize patterns from the behavioral response to various types of social protection programs. Furthermore, we specifically examine for heterogeneous treatment effects by important socioeconomic characteristics. We conclude by drawing on lessons from our synthesis of studies. If poverty reduction objectives are considered, along with careful program targeting that accounts for potential crowd-out effects, there may well be a net social gain.

econ.EM↗

arXiv2020

What Factors Drive Individual Misperceptions of the Returns to Schooling in Tanzania? Some Lessons for Education Policy

Evidence on educational returns and the factors that determine the demand for schooling in developing countries is extremely scarce. Building on previous studies that show individuals underestimating the returns to schooling, we use two surveys from Tanzania to estimate both the actual and perceived schooling returns and subsequently examine what factors drive individual misperceptions regarding actual returns. Using ordinary least squares and instrumental variable methods, we find that each additional year of schooling in Tanzania increases earnings, on average, by 9 to 11 percent. We find that on average individuals underestimate returns to schooling by 74 to 79 percent and three factors are associated with these misperceptions: income, asset poverty and educational attainment. Shedding light on what factors relate to individual beliefs about educational returns can inform policy on how to structure effective interventions in order to correct individual misperceptions.

econ.GN↗

arXiv2020

Time Delay and Investment Decisions: Evidence from an Experiment in Tanzania

Attitudes toward risk underlie virtually every important economic decision an individual makes. In this experimental study, I examine how introducing a time delay into the execution of an investment plan influences individuals' risk preferences. The field experiment proceeded in three stages: a decision stage, an execution stage and a payout stage. At the outset, in the Decision Stage (Stage 1), each subject was asked to make an investment plan by splitting a monetary investment amount between a risky asset and a safe asset. Subjects were informed that the investment plans they made in the Decision Stage are binding and will be executed during the Execution Stage (Stage 2). The Payout Stage (Stage 3) was the payout date. The timing of the Decision Stage and Payout Stage was the same for each subject, but the timing of the Execution Stage varied experimentally. I find that individuals who were assigned to execute their investment plans later (i.e., for whom there was a greater delay prior to the Execution Stage) invested a greater amount in the risky asset during the Decision Stage.

econ.GN↗

arXiv2020

One Step at a Time: Does Gradualism Build Coordination?

This study investigates a potential mechanism to promote coordination. With theoretical guidance using a belief-based learning model, we conduct a multi-period, binary-choice, and weakest-link laboratory coordination experiment to study the effect of gradualism - increasing the required levels (stakes) of contributions slowly over time rather than requiring a high level of contribution immediately - on group coordination performance. We randomly assign subjects to three treatments: starting and continuing at a high stake, starting at a low stake but jumping to a high stake after a few periods, and starting at a low stake while gradually increasing the stakes over time (the Gradualism treatment). We find that relative to the other two treatments, groups coordinate most successfully at high stakes in the Gradualism treatment. We also find evidence that supports the belief-based learning model. These findings point to a simple mechanism for promoting successful voluntary coordination.

econ.TH↗

arXiv2020

Short-Run Health Consequences of Retirement and Pension Benefits: Evidence from China

This paper examines the impact of the New Rural Pension Scheme (NRPS) in China. Exploiting the staggered implementation of an NRPS policy expansion that began in 2009, we use a difference-in-difference approach to study the effects of the introduction of pension benefits on the health status, health behaviors, and healthcare utilization of rural Chinese adults age 60 and above. The results point to three main conclusions. First, in addition to improvements in self-reported health, older adults with access to the pension program experienced significant improvements in several important measures of health, including mobility, self-care, usual activities, and vision. Second, regarding the functional domains of mobility and self-care, we found that the females in the study group led in improvements over their male counterparts. Third, in our search for the mechanisms that drive positive retirement program results, we find evidence that changes in individual health behaviors, such as a reduction in drinking and smoking, and improved sleep habits, play an important role. Our findings point to the potential benefits of retirement programs resulting from social spillover effects. In addition, these programs may lessen the morbidity burden among the retired population.

econ.GN↗

arXiv2018

Implications of the Small Spin Changes Measured for Large Jupiter-Family Comet Nuclei

Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P) and 25 (162P) minutes per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally-driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesise that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids.

astro-ph.EP↗

arXiv2016

ESpeRo: Echelle Spectrograph Rozhen

In this paper we describe the echelle spectrograph of the 2 meter telescope of the Rozhen National Astronomical Observatory. The spectrograph is a cross-dispersed, bench-mounted, fiber-fed instrument giving a resolution from $\sim$30000 to $\sim$45000. The spectral range obtained in one single image is from 3900 to 9000 Å. We describe the parameters of the fiber injection and the guiding unit, of the spectrograph itself, and of the detector. The identified orders and the resulting resolving power are presented. The opportunity to increase of the resolution by using a narrower slit is discussed and the corresponding loss of flux is calculated. The expected signal-to-noise ratio for a set of stars of different magnitudes was derived. Some of the first results obtained with ESpeRo are shortly described.

astro-ph.IM↗

arXiv2016

Imaging polarimetry and spectropolarimetry of comet C/2013 R1 (Lovejoy)

We have obtained imaging polarimetry of the comet C/2013 R1 (Lovejoy) with 2-Channel-Focal-Reducer Rozhen instrument at 2m Ritchey-Chrétien-Coudé telescope of the Bulgarian National Astronomical Observatory Rozhen in two dust continuum filters covering wavelength intervals clear from molecular emissions and centred at $4430Å$ in (blue filter) and at $6840Å$ in (red filter). In imaging mode we measured the degree of linear polarisation $17.01\pm0.09$% in the blue and $18.81\pm0.02$% in the red, which is in a very good agreement with measurements of other comets at the similar phase angle. We have also obtained polarisation maps in both filters. We found a strong correlation between the spatial distribution of the polarisation and the dust colour. Spectropolarimetry of the nucleus region shows an increase of the polarisation with wavelength, and a depolarisation in the spectral regions with gas emission lines, most noticeable in C$_2$ emission band, which shows a polarisation of $6.0\pm1.1$%.

astro-ph.EP↗