Evaluation of the Effects of Surface Treatment Methods on the Properties of Coral Aggregate and Concrete

Coral concrete has low cost and convenient materials, making it an excellent raw material for processing. However, its lower strength limits the application of coral concrete. Surface modification is expected to increase the properties of porous coral concrete. In this study, single and compound modification treatments were applied to the surface of a coral aggregate to improve its properties for promoting the mechanical performance of coral concrete. The results showed that the micro-aggregate effect and pozzolanic activity of granulated blast furnace slag (GBFS) and the permeability and polycondensation of sodium silicate (SS) could be mutually promoted. The GBFS and SS could effectively fill the pores of the coral aggregate, enhancing the properties of the aggregate, such as density and load-bearing capacity, and reducing the water absorption and crushing index by more than 50%. GBFS and SS could intensify and accelerate the hydration of cement, and generate a large number of hard hydration products at the interfacial transition zone (ITZ), which could strengthen the bonding between the aggregate and mortar, improving the strength of the ITZ. The compressive strength of the coral concrete was significantly increased.

Racing with or Against the Machine? Evidence on the Role of Trade in Europe

Digital technologies displace labor from routine tasks, raising concerns that labor is racing against the machine. We develop an empirically tractable task-based framework to estimate the aggregate employment effects of routine-replacing technological change (RRTC), along with the labor and product demand channels through which this aggregate effect comes about, focusing on the role of inter-regional trade. While RRTC has indeed had strong displacement effects in Europe between 1999 and 2010, it has simultaneously created new jobs through increased product demand, resulting in net employment growth. However, the distribution of gains from technological progress matters for its job-creating potential.

Horizontal Differentiation and the Policy Effect of Charter Schools

While school choice may enhance competition, incentives for public schools to raise productivity may be muted if public education is imperfectly substitutable with alternatives. This paper estimates the aggregate effect of charter school expansion on education quality while accounting for the horizontal differentiation of charter programs. Our research design leverages variation following the removal of North Carolina’s statewide cap to compare test score changes for students who lived near entering charters to those farther away. We find learning gains that are driven by public schools responding to increased competition from non-horizontally differentiated charter schools, even before those charters actually open. (JEL H75, I21, I28)

Contextualizing employment outcomes in family business research: current findings and future research avenues

The empirical evidence of family business phenomenon in terms of employment outcomes is contradictory highlighting the micro–macro gap in the existing research. To address this contradiction, our study disentangles the role of context in family firms’ employment outcomes. To do so, we conduct a systematic literature review of 67 articles focusing on three employment-related outcomes—namely, growth, downsizing, and quality of labour—published in peer-reviewed journals from 1980 to 2020. Based on a two-by-two framework to classify this extant research, we unpack what we know about family firms and employment outcomes and where we can go from here. We highlight three main findings. First, current research is context-less since has mainly focused on the firm level in one context (i.e., region or country) and there is a lack of studies comparing family firms’ employment outcomes in different contexts and explicitly measuring the effects of contextual dimensions on family firms’ employment outcomes. This context-less approach could explain the conflicting results and lack of theoretical predictability about the family effect on employment across contexts. Second, the lack of understanding of the context in which family firms dwell highlights the need for future research to focus on context by theorizing about employment outcomes—that is, measuring context and its interactions with family- and job-related variables. Third, there is a need to further explore, analyse, and theorize on the aggregate effect of family firms on employment outcomes at different level of analysis (e.g., local, regional, and national).

Digitization and Pre-Purchase Information: The Causal and Welfare Impacts of Reviews and Crowd Ratings

Digitization has led to many new creative products, straining the capacity of professional critics and consumers. Yet, the digitization of retailing has also delivered new crowd-based sources of pre-purchase information. We compare the relative impacts of professional critics and crowd-based Amazon star ratings on consumer welfare in book publishing. Using various fixed effects and discontinuity-based empirical strategies, we estimate their causal impacts on sales. We use these causal estimates to calibrate a structural demand model. The aggregate effect of star ratings on consumer surplus is, in our baseline estimates, more than ten times the effect of traditional review outlets. (JEL D83, L15, L81, L82)

Genetics of substance use disorders: a review

Substance use disorders (SUDs) are prevalent and result in an array of negative consequences. They are influenced by genetic factors (h2 = ~50%). Recent years have brought substantial progress in our understanding of the genetic etiology of SUDs and related traits. The present review covers the current state of the field for SUD genetics, including the epidemiology and genetic epidemiology of SUDs, findings from the first-generation of SUD genome-wide association studies (GWAS), cautions about translating GWAS findings to clinical settings, and suggested prioritizations for the next wave of SUD genetics efforts. Recent advances in SUD genetics have been facilitated by the assembly of large GWAS samples, and the development of state-of-the-art methods modeling the aggregate effect of genome-wide variation. These advances have confirmed that SUDs are highly polygenic with many variants across the genome conferring risk, the vast majority of which are of small effect. Downstream analyses have enabled finer resolution of the genetic architecture of SUDs and revealed insights into their genetic relationship with other psychiatric disorders. Recent efforts have also prioritized a closer examination of GWAS findings that have suggested non-uniform genetic influences across measures of substance use (e.g. consumption) and problematic use (e.g. SUD). Additional highlights from recent SUD GWAS include the robust confirmation of loci in alcohol metabolizing genes (e.g. ADH1B and ALDH2) affecting alcohol-related traits, and loci within the CHRNA5-CHRNA3-CHRNB4 gene cluster influencing nicotine-related traits. Similar successes are expected for cannabis, opioid, and cocaine use disorders as sample sizes approach those assembled for alcohol and nicotine.

Pediatric sarcoma survivorship: A call for a developmental cascades approach

Survivors of pediatric sarcomas often experience greater psychological and psychosocial difficulties than their non-afflicted peers. We consider findings related to poorer outcomes from a developmental cascade perspective. Specifically, we discuss how physical, neurocognitive, psychological, and psychosocial costs associated with pediatric sarcomas and their treatment function transactionally to degrade well-being in long-term pediatric sarcoma survivors. We situate the sarcoma experience as a broad developmental threat – one stemming from both the presence and treatment of a life-imperiling disease, and the absence of typical childhood experiences. Ways in which degradation in one developmental domain spills over and effects other domains are highlighted. We argue that the aggregate effect of these cascades is two-fold: first, it adds to the typical stress involved in meeting developmental milestones and navigating developmental transitions; and second, it deprives survivors of crucial coping strategies that mitigate these stressors. This position suggests specific moments of intervention and raises specific hypotheses for investigators to explore.

International financial organisations and global child mortality rates

This paper makes a contribution to the sociology and political economy of "successful societies" by investigating how children’s health across the world is impacted by multilateral financial organisations. In particular, I assess the causal effect of domestic policy reforms mandated by the International Monetary Fund (IMF) on child mortality rates across 176 countries between 1990 and 2017 using instrumental variables. I find that IMF programmes cause up to 90 excess under-5 deaths per 1,000 live births (95% CI: 50–130). This aggregate effect appears to be driven by large-scale privatisation reforms, which cause up to 132 excess child deaths per 1,000 live births (95% CI: 72–191).

Analysis of the Aggregate Effect on the Compressive Strength of Concrete Using Dune Sand

In this study, the compressive strengths of concrete were investigated based on water content and aggregate volume fractions, comprising dune sand (DS), crushed sand (CS), and coarse aggregate (CA), for different ages. Experimental data were used to analyze the effects of the volume fraction changes of aggregates on the compressive strength. The compressive strength of concrete increases until the volumetric DS to fine aggregate (FA) ratio (DS/FA ratio) reaches 20%, after which it decreases. The relationship between changes in compressive strength and aggregate volume fractions was analyzed considering the effect factor of each aggregate on the compressive strength and at 2 conditions: (1) 0 < DS < CS < CA and (2) 0 < CA < CS < DS. For condition (1), when the effect factor of CA = 1, those of DS and CS were within 0.04–0.83 and 0.72–0.92, respectively, for all mixtures. For condition (2), when the effect factor of DS = 1, those of CS and CA were within 0.68–0.80 and 0.02–0.79, respectively.

Free Riding in Products with Positive Network Externalities: Empirical Evidence from a Large Mobile Network

We study the effect of peer influence on products that exhibit positive network externalities to non-adopters, i.e., products that benefit adopters' friends even if they do not adopt. Contrary to products that exhibit positive network externalities upon adoption, this structure of incentives likely results in negative peer influence: the more friends that adopted the product, the smaller the incentives to adopt. We measure this effect empirically by using observational data from a large mobile carrier serving 5.7 million users. We estimate the effect of peer influence across five different products of this type. A naive approach to do so results in a positive estimate for peer influence due to unobserved homophily. We follow two approaches to address this issue. First, we suggest using the number of friends that end up adopting the product as a proxy for unobserved user fixed effects. Second, we control for homophily by applying a shuffle test, i.e., we compare the effect of peer influence from the original data with the effect obtained from comparable randomly generated data without peer influence. We get negative estimates from both approaches, which provides robustness to our findings. Finally, we show that even for these products, the effect of peer influence associated with the first friends that adopt the product is positive, which arises because they still convey useful information about reducing uncertainty. The negative effect of peer influence arises only for the subsequent friends that adopt the product. These friends are unlikely to convey new information about the product, but each of them decreases the economic incentive to adopt, resulting in a negative aggregate effect of peer influence.