Parametric and semiparametric estimation of sample selection models: an empirical application to the female labour force in Portugal

This comment corrects the errors in the estimation process that appear in Martins (2001). The first error is in the parametric probit estimation, as the previously presented results do not maximize the log-likelihood function. In the global maximum more variables become significant. As for the semiparametric estimation method, the kernel function used in Martins (2001) can take on both positive and negative values, which implies that the participation probability estimates may be outside the interval [0,1]. We have solved the problem by applying local smoothing in the kernel estimation, as suggested by Klein and Spady (1993).

The Security Council and the Legitimacy of the Use of Force: Legal, Normative, and Social Aspects.

Tal i com estableix la Carta de les Nacions Unides, el Consell de Seguretat determina l’existència d’una amenaça a la pau, un trencament de la pau o un acte d’agressió i decideix les mesures que han de fer-se servir per restaurar la pau i seguretat internacionals, també l’ús de la força. L’objectiu d’aquest article és explorar la legitimitat d’aquest ús de la força. Amb aquest objectiu, el text parteix d’una definició centrada en les seves dimensions legal, normativa i social. En segon lloc, s’analitzarà com aquestes dimensions estan representades als debats del Consell de Seguretat de la guerra d’Irak de 2003, un dels usos de la força més controvertits i que més debat ha generat als darrers anys. Finalment, l’anàlisi proposat permet treure algunes conclusions sobre les bases canviants de la legitimitat de l’ús de la força.

Primaries the unifying force

We present a formal model of intra-party politics to explain candidate selection within parties. We think of parties as heterogeneous groups of individuals who aim to implement a set of policies but who differ in their priorities. When party heterogeneity is too large, parties are in danger of splitting into smaller yet more homogeneous groups. In this context we argue that primaries can have a unifying role if the party elite cannot commit to policy concessions. Our model shows how alignment in the preferred policies of various factions within a party, the relative weight of each of these factions and the electoral system interact to create incentives for the adoption of primary elections. We discuss the existing empirical literature in the light of our theoretical predictions to provide a new, structured perspective on the adoption of primary elections.

Informal care and labour force participation among middle-aged women in Spain

Informal care is today the form of support most commonly used by those who need other peoplein order to carry out certain activities that are considered basic (eating, dressing, taking a shower,etc.), in Spain and in most other countries in the region. The possible labour opportunity costsincurred by these informal carers, the vast majority of whom are middle-aged women, have not asyet been properly quantified in Spain. It is, however, crucially important to know these quantities ata time when public authorities appear to be determined to extend the coverage offered up to nowas regards long-term care.In this context, we use the Spanish subsample of the European Community Household Panel (1994-2001) to estimate a dynamic ordered probit and so attempt to examine the effects of various typesof informal care on labour behaviour. The results obtained indicate the existence of labouropportunity costs for those women who live with the dependent person they care for, but not forthose who care for someone outside the household. Furthermore, whereas caregiving for morethan a year has negative effects on labour force participation, the same cannot be said of those who start caregiving and stop caregiving .

Declining labor force attachment and downward trends in unemployment and participation

The US labor market witnessed two apparently unrelated secular movements in thelast 30 years: a decline in unemployment between the early 1980s and the early 2000s,and a decline in participation since the early 2000s. Using CPS micro data and a stock-flow accounting framework, we show that a substantial, and hitherto unnoticed, factorbehind both trends is a decline in the share of nonparticipants who are at the margin ofparticipation. A lower share of marginal nonparticipants implies a lower unemploymentrate, because marginal nonparticipants enter the labor force mostly through unemployment,while other nonparticipants enter the labor force mostly through employment.

Fine-Tuning Translation Kinetics Selection as the Driving Force of Codon Usage Bias in the Hepatitis A Virus Capsid

Hepatitis A virus (HAV), the prototype of genus Hepatovirus, has several unique biological characteristics that distinguish it from other members of the Picornaviridae family. Among these, the need for an intact eIF4G factor for the initiation of translation results in an inability to shut down host protein synthesis by a mechanism similar to that of other picornaviruses. Consequently, HAV must inefficiently compete for the cellular translational machinery and this may explain its poor growth in cell culture. In this context of virus/cell competition, HAV has strategically adopted a naturally highly deoptimized codon usage with respect to that of its cellular host. With the aim to optimize its codon usage the virus was adapted to propagate in cells with impaired protein synthesis, in order to make tRNA pools more available for the virus. A significant loss of fitness was the immediate response to the adaptation process that was, however, later on recovered and more associated to a re-deoptimization rather than to an optimization of the codon usage specifically in the capsid coding region. These results exclude translation selection and instead suggest fine-tuning translation kinetics selection as the underlying mechanism of the codon usage bias in this specific genome region. Additionally, the results provide clear evidence of the Red Queen dynamics of evolution since the virus has very much evolved to re-adapt its codon usage to the environmental cellular changing conditions in order to recover the original fitness.

Filamin depletion blocks endoplasmic spreading and destabilizes force-bearing adhesions

Cell motility is an essential process that depends on a coherent, cross-linked actin cytoskeleton that physically coordinates the actions of numerous structural and signaling molecules. The actin cross-linking protein, filamin (Fln), has been implicated in the support of three-dimensional cortical actin networks capable of both maintaining cellular integrity and withstanding large forces. Although numerous studies have examined cells lacking one of the multiple Fln isoforms, compensatory mechanisms can mask novel phenotypes only observable by further Fln depletion. Indeed, shRNA-mediated knockdown of FlnA in FlnB¿/¿ mouse embryonic fibroblasts (MEFs) causes a novel endoplasmic spreading deficiency as detected by endoplasmic reticulum markers. Microtubule (MT) extension rates are also decreased but not by peripheral actin flow, because this is also decreased in the Fln-depleted system. Additionally, Fln-depleted MEFs exhibit decreased adhesion stability that appears in increased ruffling of the cell edge, reduced adhesion size, transient traction forces, and decreased stress fibers. FlnA¿/¿ MEFs, but not FlnB¿/¿ MEFs, also show a moderate defect in endoplasm spreading, characterized by initial extension followed by abrupt retractions and stress fiber fracture. FlnA localizes to actin linkages surrounding the endoplasm, adhesions, and stress fibers. Thus we suggest that Flns have a major role in the maintenance of actin-based mechanical linkages that enable endoplasmic spreading and MT extension as well as sustained traction forces and mature focal adhesions.

Conduction mechanisms and charge storage in Si-nanocrystals metal-oxide-semiconductor memory devices studied with conducting atomic force microscopy

In this work, we demonstrate that conductive atomic force microscopy (C-AFM) is a very powerful tool to investigate, at the nanoscale, metal-oxide-semiconductor structures with silicon nanocrystals (Si-nc) embedded in the gate oxide as memory devices. The high lateral resolution of this technique allows us to study extremely small areas ( ~ 300nm2) and, therefore, the electrical properties of a reduced number of Si-nc. C-AFM experiments have demonstrated that Si-nc enhance the gate oxide electrical conduction due to trap-assisted tunneling. On the other hand, Si-nc can act as trapping centers. The amount of charge stored in Si-nc has been estimated through the change induced in the barrier height measured from the I-V characteristics. The results show that only ~ 20% of the Si-nc are charged, demonstrating that the electrical behavior at the nanoscale is consistent with the macroscopic characterization.

Hysteresis in a system driven by either generalized force or displacement variables: martensitic phase transition in single-crystalline Cu-Zn-Al

We report on experiments aimed at comparing the hysteretic response of a Cu-Zn-Al single crystal undergoing a martensitic transition under strain-driven and stress-driven conditions. Strain-driven experiments were performed using a conventional tensile machine while a special device was designed to perform stress-driven experiments. Significant differences in the hysteresis loops were found. The strain-driven curves show reentrant behavior yield point which is not observed in the stress-driven case. The dissipated energy in the stress-driven curves is larger than in the strain-driven ones. Results from recently proposed models qualitatively agree with experiments.