bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism and evolution of cytosolic Hedgehog signal transduction
Authors: Wilson Christopher W. , Chuang Pao-Tien
Published: June 2010

Hedgehog (Hh) signaling is required for embryonic patterning and postnatal physiology in invertebrates and vertebrates. With the revelation that the primary cilium is crucial for mammalian Hh signaling, the prevailing view that Hh signal transduction mechanisms are conserved across species has been challenged. However, more recent progress on elucidating the function of core Hh pathway cytosolic regulators in Drosophila, zebrafish and mice has confirmed that the essential logic of Hh transduction is similar between species. Here, we review Hh signaling events at the membrane and in the cytosol, and focus on parallel and divergent functions of cytosolic Hh regulators in Drosophila and mammals.
doublesex/mab3 related-1 (dmrt1) is essential for development of anterior neural plate derivatives in Ciona
Authors: Tresser Jason , Chiba Shota , Veeman Michael , El-Nachef Danny , Newman-Smith Erin , Horie Takeo , Tsuda Motoyuki , Smith William C.
Published: June 2010

Ascidian larvae have a hollow, dorsal central nervous system that shares many morphological features with vertebrate nervous systems yet is composed of very few cells. We show here that a null mutation in the gene dmrt1 in the ascidian Ciona savignyi results in profound abnormalities in the development of the sensory vesicle (brain), as well as other anterior ectodermal derivatives, including the palps and oral siphon primordium (OSP). Although the phenotype of the mutant embryos is variable, the majority have a complete loss of the most anterior structures (palps and OSP) and extensive disruption of sensory structures, such as the light-sensitive ocellus, in the sensory vesicle. dmrt1 is expressed early in the blastula embryo in a small group of presumptive ectodermal cells as they become restricted to anterior neural, OSP and palp fates. Despite the early and restricted expression of dmrt1, we were unable, using several independent criteria, to observe a defect in the mutant embryos until the early tailbud stage. We speculate that the variability and late onset in the phenotype may be due to partially overlapping activities of other gene products.
Netrin-guided accessory cell morphogenesis dictates the dendrite orientation and migration of a Drosophila sensory neuron
Authors: Mrkusich Eli M. , Osman Zalina B. , Bates Karen E. , Marchingo Julia M. , Duman-Scheel Molly , Whitington Paul M.
Published: June 2010

Accessory cells, which include glia and other cell types that develop in close association with neurons, have been shown to play key roles in regulating neuron development. However, the underlying molecular and cellular mechanisms remain poorly understood. A particularly intimate association between accessory cells and neurons is found in insect chordotonal organs. We have found that the cap cell, one of two accessory cells of v'ch1, a chordotonal organ in the Drosophila embryo, strongly influences the development of its associated neuron. As it projects a long dorsally directed cellular extension, the cap cell reorients the dendrite of the v'ch1 neuron and tows its cell body dorsally. Cap cell morphogenesis is regulated by Netrin-A, which is produced by epidermal cells at the destination of the cap cell process. In Netrin-A mutant embryos, the cap cell forms an aberrant, ventrally directed process. As the cap cell maintains a close physical connection with the tip of the dendrite, the latter is dragged into an abnormal position and orientation, and the neuron fails to undergo its normal dorsal migration. Misexpression of Netrin-A in oenocytes, secretory cells that lie ventral to the cap cell, leads to aberrant cap cell morphogenesis, suggesting that Netrin-A acts as an instructive cue to direct the growth of the cap cell process. The netrin receptor Frazzled is required for normal cap cell morphogenesis, and mutant rescue experiments indicate that it acts in a cell-autonomous fashion.
HB-EGF function in cardiac valve development requires interaction with heparan sulfate proteoglycans
Authors: Iwamoto Ryo , Mine Naoki , Kawaguchi Taichiro , Minami Seigo , Saeki Kazuko , Mekada Eisuke
Published: June 2010

HB-EGF, a member of the EGF family of growth factors, plays an important role in cardiac valve development by suppressing mesenchymal cell proliferation. Here, we show that HB-EGF must interact with heparan sulfate proteoglycans (HSPGs) to properly function in this process. In developing valves, HB-EGF is synthesized in endocardial cells but accumulates in the mesenchyme by interacting with HSPGs. Disrupting the interaction between HB-EGF and HSPGs in an ex vivo model of endocardial cushion explants resulted in increased mesenchymal cell proliferation. Moreover, homozygous knock-in mice (HBΔhb/Δhb) expressing a mutant HB-EGF that cannot bind to HSPGs developed enlarged cardiac valves with hyperproliferation of mesenchymal cells; this resulted in a phenotype that resembled that of Hbegf-null mice. Interestingly, although Hbegf-null mice had abnormal heart chambers and lung alveoli, HBΔhb/Δhb mice did not exhibit these defects. These results indicate that interactions with HSPGs are essential for the function of HB-EGF, especially in cardiac valve development, in which HB-EGF suppresses mesenchymal cell proliferation.
An interview with Alex Joyner and Liz Robertson: Development editors at the helm of developmental biology societies
Authors: Amsen Eva
Published: June 2010

Development editors Liz Robertson (Professor of Developmental Biology at the Sir William Dunn School of Pathology in Oxford) and Alexandra Joyner (Courtney Steel Chair in Pediatric Cancer Research and Professor in the Department of Developmental Biology at Memorial Sloan-Kettering Cancer Center in New York) are not only actively involved in research and editorial work but, as of this summer, they will both be in charge of national developmental biology societies. Liz is Chair of the British Society for Developmental Biology (BSDB), and in August 2010, Alex will become President of the Society for Developmental Biology (SDB) in North America. We caught up with both of them at the annual BSDB Spring meeting that took place at the University of Warwick in April 2010.
Development of an optimized chemical kinetic mechanism for homogeneous charge compression ignition combustion of a fuel blend of n-heptane and natural gas using a genetic algorithm
Authors: Rahimi A , Fatehifar E , Saray R Khoshbakhti
Published: June 2010

Homogeneous charge compression ignition (HCCI) is a promising technique for advanced low-temperature combustion strategies that offers a high fuel conversion efficiency and low nitrogen oxide and soot emissions. One of the major problems associated with HCCI combustion engine application is the lack of direct control for combustion timing. A proposed solution for combustion timing control is to use a binary fuel blend in which two fuels with different autoignition characteristics are blended at various ratios on a cycle-by-cycle basis. Because dual-fuel diesel—natural-gas engines have already been used, a fuel blend of n-heptane (diesel-like fuel) and natural gas (mostly methane) is one of the best available options.

The objective of this study is to optimize the chemical kinetic mechanisms available for n-heptane and natural gas to be used in a binary-fuel blend scenario. Using the genetic algorithm method, a combined mechanism was optimized and modelling results were verified against experimental results. The agreement between experimental and modelling results was found to be acceptable within the examined conditions. As a result, an optimized chemical kinetic mechanism for an n-heptane—natural-gas blend is presented.
Variable-valve-actuation-enabled high-efficiency gasoline engine
Authors: Zhang Y , Zhao H , Xie H , He B-Q
Published: June 2010

Owing to their low carbon dioxide emissions and fuel consumptions, diesel engines have gained a significant market share of passenger cars in Europe. However, gasoline engines are exclusively used to power passenger cars in the People's Republic of China and many other countries. The introduction of diesel engines to the passenger car market in many countries is unlikely to take place in the near future because of the limited diesel fuel supply, higher cost of diesel cars, and public perception of diesel vehicles. Therefore, development of high-efficiency gasoline engines is of particular importance. As part of a State Key Project of the National Basic Research Program (the 973 Program), the present authors have carried out systematic research and development of a high-efficiency gasoline engine. The engine was equipped in production with devices for mechanically variable valve lift and timing and was operated with controlled autoignition (CAI) (homogeneous charge compression ignition) combustion under part-load conditions and spark-assisted combustion between the transitional region of CAI and the normal spark ignition (SI) combustion. This paper will describe the use of devices for variable valve lift and timing in a single-cylinder engine and their control. The engine performance and emission results in the CAI operational region are presented. The ability of the engine to achieve rapid and smooth transition between CAI and SI will be illustrated. A brief discussion of the implication of the results on the calculated driving-cycle fuel consumption will be given at the end. Finally, the plan for future development of a multi-cylinder engine of variable valve actuation will be given.
Combustion characteristics and particulate emission in a natural-gas direct-injection engine: Effects of the injection timing and the spark timing
Authors: Liu Y-F , Liu B , Liu L , Zeng K , Huang Z-H
Published: June 2010

In the present study, the effects of injection timing and spark timing on combustion characteristics and particle emission were investigated. The particulate number concentration and size distribution were measured using an electrical low-pressure impactor. The combustion parameters were calculated from the cylinder pressure data. The results indicate that the combustion versus the injection timing is primarily dependent on the mixing quality of the air—fuel mixture. The particulate number concentration increases as the fuel injection is advanced but the particle size distribution is not affected significantly with different injection timings. This is probably related to the in-cylinder combustion. The initial combustion duration increases as the spark timing is advanced and the fastest rapid combustion duration is obtained at the maximum brake torque spark timing. As the fuel injection timing and spark timing are advanced, the particle number levels are increased but the particle size distribution shows few variations. Most of the particulates are in the nanoparticle size range. The amounts of nitrogen oxide and hydrocarbon emissions increase with advanced fuel injection timing and spark timing, and the carbon monoxide concentration experiences small variations under all operation conditions.
Recent Developments in the Mass Spectrometry of Atmospheric Aerosols
Authors: Baltensperger Urs , Chirico Roberto , DeCarlo Peter F. , Dommen Josef , Gaeggeler Kathrin , Heringa Maarten F. , Li Mingli , Prévôt André S.H. , Alfarra M. Rami , Gross Deborah S. , Kalberer Markus
Published: June 2010

Atmospheric aerosol particles consist of a highly complex mixture of thousands of different compounds. Mass spectrometric techniques are well suited for the analysis of these particles, with each method of analysis having specific advantages and disadvantages. On-line techniques offer high time resolution and thus allow for the investigation of rapidly changing signals. They typically measure either single particles or the average non-refractory submicrometer aerosol. Off-line techniques are often coupled to chromatography or another technique separating for a specific property, which enhances their resolving power. Ultra-high resolution mass spectrometry allows for an unambiguous assignment of the elemental composition throughout the majority of the mass range typically measured in ambient aerosol samples, i.e. up to about m/z 400–600. The quantitative determination of individual compounds, or of classes of compounds, remains an important, but often unresolved, topic. Examples of applications of various mass spectrometric techniques are presented, both from laboratory and field studies.
Teaching Economics in the 21st Century
Authors: Becker William E
Published: June 2010

The desire to reverse a downward trend in the number of undergraduates majoring in economics is an impetus to advance the scholarship of teaching economics as we enter the 21st century. This article offers suggestions for changing the concepts taught and the applications used in college and university economics courses within the United States. It provides practical methods to improve the way economics is taught. The assessment of students and the evaluation of pedagogical practices are also addressed.
New Millennium Economics: How Did It Get This Way, and What Way is It?
Authors: Colander David
Published: June 2010

This paper is a discussion of the changes in the economics profession that occurred (or at least are suggested will occur) between 2000 and 2050. Structural changes include the growth of virtual universities, the movement of the center of economics out of the U.S. and the shrinking of traditional graduate economics programs as we know them today, and their replacement by public policy and specialty programs. Changes in content include an increase in simulation work, experimental work, and the replacement of a neoclassical vision with a New Millennium vision based on a complexity foundation in which patterns develop spontaneously.
Some Macroeconomics for the 21st Century
Authors: Lucas Robert E
Published: June 2010

This note describes a numerical simulation of a model of economic growth, a simplified version of Robert Tamura's (1996) model of world income dynamics, based on technology diffusion. The model makes predictions for trends in average world income growth and about the evolution of the relative income distribution that accord well with observation. The model is used to forecast the course of world income growth and income inequality over the century to come.
The Worldwide Standard of Living Since 1800
Authors: Easterlin Richard A
Published: June 2010

By many measures a revolution in living conditions is sweeping the world. Most people today are better fed, clothed, and house than their predecessors two centuries ago. They are healthier, live longer, and are better educated. Women's lives are less centered on reproduction, and political democracy has gained a foothold. Current international differences in a number of standard of living indicators are significantly correlated. Historically, however, these improvements often started at quite different times, suggesting that the determinants of change in different aspects of the standard of living are varied.
Stock Market Wealth and Consumption
Authors: Poterba James M
Published: June 2010

This paper explores the link between changes in the aggregate value of corporate stock and changes in consumer spending. It presents data on the distribution of corporate stock ownership based on the 1998 Survey of Consumer Finances. It also uses time-series evidence on the comovement of stock market wealth and various categories of consumer spending to calibrate “the wealth effect.” It concludes that in the year after a change in stock market values, consumer spending is likely to rise by between one and two cents for each dollar increase in the value of corporate stock.
Fairness and Retaliation: The Economics of Reciprocity
Authors: Fehr Ernst , Gächter Simon
Published: June 2010

This paper shows that reciprocity has powerful implications for many economic domains. It is an important determinant in the enforcement of contracts and social norms and enhances the possibilities of collective action greatly. Reciprocity may render the provision of explicit incentive inefficient because the incentives may crowd out voluntary co-operation. It strongly limits the effects of competition in markets with incomplete contracts and gives rise to noncompetitive wage differences. Finally, reciprocity it is also a strong force contributing to the existence of incomplete contracts.
Reassessing Discretionary Fiscal Policy
Authors: Taylor John B
Published: June 2010

Recent changes in policy research and in policy-making call for a reassessment of countercyclical fiscal policy. Such a reassessment indicates that countercyclical fiscal policy should focus on automatic stabilizers rather than discretionary actions. Monetary policy has been reacting more systematically to output and inflation; long expansions in the 1980s and 1990s demonstrate policy effectiveness. It is unlikely that discretionary countercyclical fiscal policy could improve things, even with less uncertainty about fiscal impacts. A discretionary countercyclical fiscal policy could make monetary policy making more difficult. Discretionary fiscal policy should focus on long-run issues, such as tax reform and social security reform.
History Lessons: Institutions, Factor Endowments, and Paths of Development in the New World
Authors: Sokoloff Kenneth L , Engerman Stanley L
Published: June 2010

The explanations offered for the contrasting records of long-run growth and development among the societies of North and South America most often focus on institutions. The traditional explanations for the sources of these differences in institutions, typically highlight the significance of national heritage or religion. We, in contrast, argue that a hemispheric perspective across the wide range of colonies established in the New World by the Europeans suggests that although there were many influences, factor endowments or initial conditions had profound and enduring effects on the long-run paths of institutional and economic development followed by the respective economies.
The Significance of Federal Taxes as Automatic Stabilizers
Authors: Auerbach Alan J , Feenberg Daniel
Published: June 2010

Using the TAXSIM model for the period 1962-95, we consider the federal tax system's impact as an automatic stabilizer. Despite the many changes in the tax system, there has been relatively little change in its role as an automatic stabilizer. We estimate that individual federal taxes offset perhaps as much as 8 percent of initial shocks to GDP. We also suggest that the progressive income tax may help to stabilize output via its effect on the supply of labor, an additional effect that may even be of similar magnitude to the more traditional path of stabilization through aggregate demand.
For Love or Money—Or Both?
Authors: Folbre Nancy , Nelson Julie A
Published: June 2010

This paper explores the implications for economic analysis, societal well-being, and public policy of the movement of care services (such as child and elder care) from home to market. A broad empirical overview sets the stage for the argument that this process cannot be properly evaluated using only a priori judgments about the suitability of marketization. The context in which markets operate is crucial, and while the growth of market provision poses some risks, it also offers some potential benefits.
The Resurgence of Growth in the Late 1990s: Is Information Technology the Story?
Authors: Oliner Stephen D , Sichel Daniel E
Published: June 2010

The growth of U.S. labor productivity rebounded in the second half of the 1990s, after nearly a quarter century of sluggish gains. We assess the contribution of information technology to this rebound, using the same neoclassical framework as in our earlier work. We find that a surge in the use of information technology capital and faster efficiency gains in the production of computers account for about two-thirds of the speed-up in productivity growth between the first and second halves of the 1990s. Thus, to answer the question posed in the title of the paper, information technology largely is the story.
Gender Differences in Pay
Authors: Blau Francine D , Kahn Lawrence M
Published: June 2010

We consider the gender pay gap in the United States. Both gender-specific factors, including gender differences in qualifications and discrimination, and overall wage structure, the rewards for skills and employment in particular sectors, importantly influence the gender pay gap. Declining gender differentials in the U.S., and the more rapid closing of the gender pay gap in the U.S. than elsewhere, appear to be primarily due to gender-specific factors. However, the relatively large gender pay gap in the U.S. compared to a number of other advanced countries seems primarily attributable to the very high level of U.S. wage inequality.
Canada: Life Beyond the Looking Glass
Authors: Helliwell John F
Published: June 2010

Canada's population, a tenth that of the United States, is perched close to the U.S. northern border, tightly but asymmetrically tied to U.S. information networks. However, trade, capital and population mobility remains an order of magnitude tighter among provinces than between provinces and states. This separating effect of the national border is not primarily due to barriers, but to networks of contacts, trust and institutions that make it efficient to concentrate economic activity within national borders. This separation combines with quite different histories to explain why Canadian economic, social, education and health care policies remain distinct from U.S. policies, often closer to those in Northern Europe.
Wiring the Labor Market
Authors: Autor David H
Published: June 2010

Workers and jobs are naturally heterogeneous and the quality of their interaction when paired is difficult to forecast. The Internet promises to open new channels for worker-firm communications. What are the consequences of this opening? I discuss three labor market features that may be altered: how worker-firm matches are made; how labor services are delivered; and how local markets shape labor demand. Theory predicts these developments will produce social benefits. But the gains are unlikely to be uniform and realizing them will generate novel problems. One result may be the formation of new institutions to address issues accompanying these opportunities.
Life is not Easy: Mexico's Quest for Stability and Growth
Authors: Lustig Nora
Published: June 2010

In the wake of the debt crisis in 1982, Mexico adopted far reaching reforms but growth and stability remained elusive for many years. At present, the reforms and NAFTA seem to be finally paying off: inflation for 2000 is close to 10 percent and output per capita grew at an average of 5.4 percent during the last five years. However, altogether output per capita was only 9 percent higher in 1999 than in 1980, a great disappointment for particularly the 20 million Mexicans that live on less than $2 a day.
New Evidence and Perspectives on Mergers
Authors: Andrade Gregor , Mitchell Mark , Stafford Erik
Published: June 2010

As in previous decades, merger activity clusters by industry during the 1990s. One particular kind of industry shock, deregulation, becomes a dominant factor, accountings for nearly half of the merger activity since the late 1980s. In contrast to the 1980s, mergers in the 1990s are mostly stock swaps, and hostile takeovers virtually disappear. Over our 1973 to 1998 sample period, the announcement-period stock market response to mergers is positive for the combined merging parties, suggesting that mergers create value on behalf of shareholders. Consistent with that, we find evidence of improved operating performance following mergers, relative to industry peers.
Corporate Governance and Merger Activity in the United States: Making Sense of the 1980s and 1990s
Authors: Holmstrom Bengt , Kaplan Steven N
Published: June 2010

This paper describes and considers explanations for changes in corporate governance and merger activity in the United States since 1980. Corporate governance in the 1980s was dominated by intense merger activity distinguished by the prevalence of leveraged buyouts (LBOs) and hostility. After a brief decline in the early 1990s, substantial merger activity resumed in the second half of the decade, while LBOs and hostility did not. Instead, internal corporate governance mechanisms appear to have played a larger role in the 1990s. We conclude by considering whether these changes and the movement toward shareholder value are likely to be permanent.
The Record and Prospects of the All-Volunteer Military in the United States
Authors: Warner John T , Asch Beth J
Published: June 2010

From the onset of World War II until July 1973, the draft was a fact of life for male youth in the United States. Since then, America's armed forces have been staffed by volunteers. Recent recruiting difficulties have precipitated calls from some quarters for a return to conscription. This paper reviews the economic issues involved in the choice over conscription versus volunteerism and it reviews the volunteer force record in the U. S. Despite recent recruiting difficulties, the case for the volunteer force is more compelling today than it was in 1973.
Early Childhood Education Programs
Authors: Currie Janet
Published: June 2010

This paper discusses early childhood education programs: their goals; effectiveness; optimal timing, targeting, and content; and costs and benefits. Early intervention has significant short- and medium-term benefits: most notably it reduces grade repetition and special education costs, and provides quality child care. The effects are greatest for more disadvantaged children. Some model programs have produced exciting improvements in educational attainment and earnings and have reduced welfare dependency and crime. The jury is still out on the long-term effects of Head Start, but Head Start would pay for itself if it produced a quarter of the long-term gains of model programs.
Data Watch: The National Longitudinal Surveys
Authors: Pergamit Michael R , Pierret Charles R , Rothstein Donna S , Veum Jonathan R
Published: June 2010

This article describes the design features and topical coverage of the National Longitudinal Surveys (NLS). The NLS are perhaps the oldest and most widely used panel surveys of individuals in the United States. These surveys were started in the mid-1960s to exam employment issues faced by different cohorts of the U.S. population. Since then, the NLS surveys have expanded to include two new cohorts of youth. Survey topic areas include employment, education, training, family relationships, financial well-being, and health. Information on data access is also provided.
The Microsoft Case: What Can a Dominant Firm Do to Defend Its Market Position?
Authors: Klein Benjamin
Published: June 2010

This paper examines the competitive actions taken by Microsoft in its “browser war” with Netscape, most importantly Microsoft's decisions to give away Explorer free of charge, integrate Explorer into its dominant Windows operating system and pay online service providers for exclusive distribution. Consumers benefited significantly from these actions, but the fundamental economic question is whether Microsoft abused its existing market power when competing in this way. A detailed analysis of Microsoft's conduct and the economics of competition for distribution suggests that severe limits placed on Microsoft's behavior would not be welfare.
Wheat From Chaff: Meta-Analysis As Quantitative Literature Review
Authors: Stanley T.D
Published: June 2010

This paper presents and develops a quantitative method of literature reviewing and evaluating empirical research, meta-regression analysis or MRA. Economics is theory-driven. Yet, we must learn empirically if economics is to advance. MRA offers a more objective statistical method to summarize our empirical knowledge and to explain the wide study-to-study variation in economic research. MRA is used to assess the evidence for Ricardian equivalence, and its findings are contrasted to those of conventional narrative review. Furthermore, MRA establishes a platform from which to distinguish genuine empirical effect from the exploitable specification error that infests applied econometrics.
International Productivity Comparisons Built from the Firm Level
Authors: Baily Martin Neil , Solow Robert M
Published: June 2010

International productivity comparisons can be built up with micro and macro data. Studies of firms or groups of firms producing similar outputs reveal the deeper causes of differences in productivity across countries. The studies find that such differences often depend on patterns of organization within firms, the motivations of managers and the like. The intensity of domestic and international competition can have a large impact on productivity. The case of retailing illustrates the importance of industry evolution. High productivity retailing formats drive out traditional retailers, unless restrained by land-use restrictions or regulations.
Economic Education in U.S. High Schools
Authors: Walstad William B
Published: June 2010

The teaching of economics at the high school level is vital for increasing basic economic literacy. This assessment of high school economics in the United States covers seven topics: enrollments in courses; course content; the testing of students; achievement in economics courses; economics instruction in related courses; teacher preparation for economics instruction; and the contributions from organizations and economists. Significant improvements are found in the teaching, content, and testing of high school economics over the past two decades, but more work is needed because a formal course in economics is taken by less than half of high school graduates.
The Life-Cycle Model of Consumption and Saving
Authors: Browning Martin , Crossley Thomas F
Published: June 2010

A central implication of life-cycle models is that agents smooth consumption. We review the empirical evidence on smoothing at frequencies from within the year up to across a lifetime. We find that life-cycle models--particular those which incorporate realistic features of markets and goods--have more empirical successes than failures. We also show that some apparent deviations from theoretical predictions imply very small welfare losses for agents. Finally, we emphasize that the coherence of life-cycle models imposes an important discipline when incorporating new features into models.
Labor Standards: Where Do They Belong on the International Trade Agenda?
Authors: Brown Drusilla K
Published: June 2010

During the past decade, universal labor standards have become the focus of intense debate. Advocates argue from humanitarian concerns and the interests of industrialized-country labor, seeking enforcement with WTO sanctions. Opponents regard labor regulation as a matter of national sovereignty, challenge the effectiveness of trade sanctions, and prefer the ILO emphasis on dialogue, monitoring and technical advice. This paper analyzes the labor standards debate, with specific attention to the analytical underpinnings of universal rules; evidence linking weak labor protections in developing countries to industrialized country wages; and the role of labor standards in WTO negotiations.
The New Econometrics of Structural Change: Dating Breaks in U.S. Labor Productivity
Authors: Hansen Bruce E
Published: June 2010

We have seen the emergence of three major innovations in the econometrics of structural change in the past fifteen years: (1) tests for a structural break of unknown timing; (2) estimation of the timing of a structural break; and (3) tests to distinguish unit roots from broken time trends. These three innovations have dramatically altered the face of applied time series econometrics. In this paper, we review these three innovations, and illustrate their application through an empirical assessment of U.S. labor productivity in the manufacturing/durables sector.
Instrumental Variables and the Search for Identification: From Supply and Demand to Natural Experiments
Authors: Angrist Joshua D , Krueger Alan B
Published: June 2010

Instrumental variables was first used in the 1920s to estimate supply and demand elasticities and later to correct for measurement error in single equation models. Recently, instrumental variables have been widely used to reduce bias from omitted variables in estimates of causal relationships. Intuitively, instrumental variables methods use only a portion of the variability in key variables to estimate the relationships of interest; if the instruments are valid, that portion is unrelated to the omitted variables. We discuss the mechanics of instrumental variables and the qualities that make for a good instrument, devoting particular attention to instruments derived from “natural experiments.”
Applications of Generalized Method of Moments Estimation
Authors: Wooldridge Jeffrey M
Published: June 2010

I describe how the method of moments approach to estimation, including the more recent generalized method of moments (GMM) theory, can be applied to problems using cross section, time series, and panel data. Method of moments estimators can be attractive because in many circumstances they are robust to failures of auxiliary distributional assumptions that are not needed to identify key parameters. I conclude that while sophisticated GMM estimators are indispensable for complicated estimation problems, it seems unlikely that GMM will provide convincing improvements over ordinary least squares and two-stage least squares--by far the most common method of moments estimators used in econometrics--in settings faced most often by empirical researchers.
Body-on-a chip: Using microfluidic systems to predict human responses to drugs
Authors: Shuler Michael L. , Esch Mandy B.
Published: June 2010

Using an in vitro platform technology that combines microfabricated devices with cell culture, we seek to understand the response of the human body to pharmaceuticals and combinations of pharmaceuticals. Computer models of the human body guide the design of in vitro systems we call micro cell culture analogs (μCCAs) or “body-on-a-chip” devices. A μCCA device is a physical representation of a physiologically based pharmacokinetic (PBPK) model and contains mammalian cells cultured in interconnected microchambers to represent key organs linked through a circulatory system. μCCAs can provide inexpensive means for realistic, accurate, and rapid-throughput toxicological studies that do not require experimenting with animals and reveal toxic effects that can result from interactions between organs. As the natural length scale in biological systems is on the order of 10–100 μm, operating on the microscale allows us to mimic physiological relationships more accurately. We summarize proof-of-concept experiments using mixtures of drugs to treat multidrug-resistant (MDR) cancer and colon cancer. We discuss the extension of the μCCA concept to systems that connect barrier tissues with systemic circulation. Examples with models of the gastro-intestinal (GI) tract are provided.
Short-term Hypoxia Increases Tyrosine Hydroxylase Immunoreactivity in Rat Carotid Body
Authors: Kato Kouki , Yamaguchi-Yamada Misuzu , Yamamoto Yoshio
Published: June 2010

Neurochemical and morphological changes in the carotid body are induced by chronic hypoxia, leading to regulation of ventilation. In this study, we examined the time courses of changes in immunohistochemical intensity for tyrosine hydroxylase (TH) and cellular volume of glomus cells in rats exposed to hypoxia (10% O2) for up to 24 hr. Grayscale intensity for TH immunofluorescence was significantly increased in rats exposed to hypoxia for 12, 18, and 24 hr compared with control rats ( p<0.05). The transectional area of glomus cells was not significantly different between experimental groups. The TH fluorescence intensity of the glomus cells exhibited a strong negative correlation with the transectional area in control rats (Spearman's ρ = −0.70). This correlation coefficient decreased with exposure time, and it was lowest for the rats exposed to hypoxia for 18 hr ( ρ = −0.18). The histogram of TH fluorescence intensity showed a single peak in control rats. The peaks were gradually shifted to the right and became less pronounced in hypoxia-exposed rats, suggesting that a hypoxia-induced increase in TH immunoreactivity occurred uniformly in glomus cells. In conclusion, this study demonstrates that short-term hypoxia induces an increase in TH protein expression in rat carotid body glomus cells.
Spexin Expression in Normal Rat Tissues
Authors: Porzionato Andrea , Rucinski Marcin , Macchi Veronica , Stecco Carla , Malendowicz Ludwik K. , De Caro Raffaele
Published: June 2010

Spexin is a highly conserved peptide which was recently identified through the bioinformatics approach. Immunohistochemical analysis of its expression has not yet been performed. Thus, in this study, we examined spexin location in a wide range of rat organs by both RT-PCR and IHC. RT-PCR identified spexin mRNA in all tissues examined. Spexin immunoreaction was mainly cytoplasmic. Spexin was immunohistochemically detected, although with different staining intensities, in epithelia and glands of skin and respiratory, digestive, urinary, and reproductive systems. Smooth muscle cells showed weak immunostaining, and connective tissue was negative. In the central nervous system, neuronal groups showed different intensities for reaction product. Immunoreaction was also found in ganglionic cells of both trigeminal and superior cervical ganglia and in photoreceptor, inner nuclear, and ganglionic layers of the retina. In the endocrine system, spexin immunoreaction was detected in the hypothalamic paraventricular and supraoptic nuclei; adenohypophysis, thyroid, and parathyroid glands; adrenal cortex and medulla (mainly ganglionic cells); Leydig cells; and thecal, luteal, and interstitial cells of the ovary. Because of its widespread expression, spexin is probably involved in many different physiological functions; in particular, location of spexin in neurons and endocrine cells suggests its roles as neurotransmitter/neuromodulator and endocrine factor.
Industrial Composting of Poly(Lactic Acid) Bottles
Authors: Danyluk Casey , Erickson Ryan , Burrows Samuel , Auras Rafael
Published: June 2010

In order to better understand the end of life scenario potential of poly(lactic acid) (PLA) packaging to reduce waste through composting when properly disposed, this study aimed to determine the rate at which 473 mL (16 oz) PLA bottles with and without associated high density polyethylene (HDPE) caps and polypropylene (PP) labels decomposed in an industrial compost pile. Temperature, moisture content, and pH levels of the compost pile were recorded throughout the study to determine their effects on the rate of decomposition and to ensure optimal conditions were met. Analyses performed at weeks 2, 4, and 8 showed that from week 2, a 94 % reduction of mass and weight average molecular weight occurred, along with a complete loss of structural integrity. PLA bottles without caps and labels were considered to be decomposed completely by week 4, while the bottles with the HDPE caps and PP labels showed plastic residues until week 8. The caps and labels acted as a barrier that slowed the rate of biodegradation. This study showed that PLA bottles can be composted in industrial composting facilities in 30–45 days, and it is recommended to remove all caps and labels. The results further indicated that if a proper infrastructure is put in place to allow large scale composting of PLA, this packaging polymer could have a significant impact on reducing municipal solid waste.
Herodotus and the Map of Aristagoras
Authors: Branscome David
Published: June 2010

Herodotus uses the encounter between the Milesian tyrant Aristagoras and the Spartan king Cleomenes (5.49–51) to further his authorial self-presentation. He contrasts his own aims and methods as an inquirer with those of Aristagoras, who becomes a “rival” inquirer for Herodotus in this passage. Seeking military aid from Cleomenes for the Ionian Revolt, Aristagoras points to his bronze map of the world and gives an ethnographical and geographical account of the peoples and land of Asia, from Ionia to Susa. Aristagoras accordingly takes on many of the characteristics of Herodotus himself, including the use of shared ethnographical language. Aristagoras' ethnographical account is marred, however, by a rhetorical strategy that depicts the Asians as wealthy, but weak adversaries. While careful not to criticize Aristagoras' map itself, Herodotus is able to exploit Aristagoras' verbal description of his map to illustrate his own forthcoming account of the Persian Royal Road (5.52–54), which Herodotus assures readers is even more “accurate” than Aristagoras' account had been (5.54.1). Aristagoras is “deceiving” Cleomenes “well,” says Herodotus, until he tells the “truth” about the length of the journey to Susa (5.50.2). Telling the truth is a mistake for the deceiver Aristagoras, but an obligation for the inquirer Herodotus.
Demolished Houses, Monumentality, and Memory in Roman Culture
Authors: Roller Matthew B.
Published: June 2010

This article examines the tradition of punitive house demolition during the Roman Republic, but from a sociocultural rather than institutional-legal perspective. Exploiting recent scholarship on the Roman house, on exemplarity, and on memory sanctions, I argue that narratives of house demolition constitute a form of ethically inflected political discourse, whose purpose is to stigmatize certain social actors as malefactors of a particular sort (“aspiration to kingship” being the central instance). The demolition itself is symbolically resonant, and the resultant stigma is propagated by subsequent monuments—various structures, toponyms, narratives, etc.—that attach to the housesite. These monuments are thought to bear the trace of what went before, hence transmit an account of the alleged malefactor's deed and disgrace. Far from obliterating the doer of misdeeds, then, the discourse of punitive house demolition fixes him in cultural memory as a negative exemplum.
Development, embryonic genome activity and mitochondrial characteristics of bovine–pig inter-family nuclear transfer embryos
Authors: Lagutina Irina , Fulka Helena , Brevini Tiziana A L , Antonini Stefania , Brunetti Dario , Colleoni Silvia , Gandolfi Fulvio , Lazzari Giovanna , Fulka Josef , Galli Cesare
Published: June 2010

The best results of inter-species somatic cell nuclear transfer (iSCNT) in mammals were obtained using closely related species that can hybridise naturally. However, in the last years, many reports describing blastocyst development following iSCNT between species with distant taxonomical relations (inter-classes, inter-order and inter-family) have been published. This indicates that embryonic genome activation (EGA) in xeno-cytoplasm is possible, albeit very rarely. Using a bovine–pig (inter-family) iSCNT model, we studied the basic characteristics of EGA: expression and activity of RNA polymerase II (RNA Pol II), formation of nucleoli (as an indicator of RNA polymerase I (RNA Pol I) activity), expression of the key pluripotency geneNANOGand alteration of mitochondrial mass. In control embryos (obtained by IVF or iSCNT), EGA was characterised by RNA Pol II accumulation and massive production of poly-adenylated transcripts (detected with oligo dT probes) in blastomere nuclei, and formation of nucleoli as a result of RNA Pol I activity. Conversely, iSCNT embryos were characterised by the absence of accumulation and low activity of RNA Pol II and inability to form active mature nucleoli. Moreover, in iSCNT embryos,NANOGwas not expressed, and mitochondria mass was significantly lower than in intra-species embryos. Finally, the complete developmental block at the 16–25-cell stage for pig–bovine iSCNT embryos and at the four-cell stage for bovine–pig iSCNT embryos strongly suggests that EGA is not taking place in iSCNT embryos. Thus, our experiments clearly demonstrate poor nucleus–cytoplasm compatibility between these animal species.
Fractures and Traumatic Brain Injuries: Abuse Versus Accidents in a US Database of Hospitalized Children
Authors: Leventhal John M. , Martin Kimberly D. , Asnes Andrea G.
Published: June 2010

OBJECTIVE:

The goal was to use a national database to determine the incidence of abusive traumatic brain injuries (TBIs) and/or fractures and the frequency of abuse versus accidents among children <36 months of age.

METHODS:

We used the 2006 Kids' Inpatient Database and classified cases into 3 types of injuries, that is, (1) TBI only, (2) TBI and fracture, or (3) fracture only. Groups 2 and 3 were divided into 3 patterns, that is, (1) skull fractures, (2) skull and nonskull fractures, or (3) nonskull fractures. For each type and pattern, we compared abuse, accidental falls, other accidents, and motor vehicle accidents.

RESULTS:

The incidence of TBIs and/or fractures attributable to abuse was 21.9 cases per 100 000 children <36 months of age and 50.0 cases per 100 000 children <12 months of age. In the abuse group, 29.9% of children had TBIs only, 28.3% TBIs and fractures, and 41.8% fractures only. Abused children were younger and were more likely to be enrolled in Medicaid. For TBI only, falls were more common than abuse in the first 2 months of life but abuse was more common from 2 to 7 months. For TBI and skull fracture, falls were more common during the first year of life. For skull fracture only, almost all injuries were attributable to falls.

CONCLUSIONS:

There was overlap in TBIs and fractures attributable to abuse. Among <12-month-old children, TBIs and/or fractures attributable to abuse occurred in 1 of 2000. Falls occurred more commonly than abuse, even among very young children.
Respiratory Morbidity and Lung Function in Preterm Infants of 32 to 36 Weeks' Gestational Age
Authors: Colin Andrew A. , McEvoy Cynthia , Castile Robert G.
Published: June 2010

Normal lung development follows a series of orchestrated events. Premature birth interrupts normal in utero lung development, which results in significant alterations in lung function and physiology. Increasingly, there are reports documenting the broad range of complications experienced by infants aged 34 to 36 weeks' gestational age (GA). Our objective was to summarize the evidence demonstrating respiratory system vulnerability in infants aged 34 to 36 weeks' GA and to review the developmental and physiologic principles that underlie this vulnerability. A comprehensive search for studies that reported epidemiologic data and respiratory morbidity was conducted on the PubMed, Medline, Ovid Biosis, and Embase databases from 2000 to 2009 by using medical subject headings “morbidity in late preterm infants,” “preterm infants and lung development,” “prematurity and morbidity,” and “prematurity and lung development.” Because the number of studies exclusive to infants aged 34 to 36 weeks' GA was limited, selected studies also included infants aged 32 to 36 weeks' GA. Of the 24 studies identified, 16 were retrospective population-based cohort studies; 8 studies were observational. These studies consistently revealed that infants born at 32 to 36 weeks' GA, including infants of 34 to 36 weeks' GA, experience substantial respiratory morbidity compared with term infants. Levels of morbidity were, at times, comparable to those observed in very preterm infants. The developmental and physiologic mechanisms that underlie the increased morbidity rate and alterations in respiratory function are discussed. We also present evidence to demonstrate that the immaturity of the respiratory system of infants 34 to 36 weeks' GA at birth results in increased morbidity in infancy and leads to deficits in lung function that may persist into adulthood.