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In recent econometric work, most analyses of female labour supply consider married women, whereas the results for unmarried women are provided rather as a by-product (Burtless/Greenberg, 1982, Johnson/Pencavel, 1984, Leu/Kugler, 1986, Merz, 1990,). When the particular interest is focused on unmarried women, data of the seventies or rather simple econometric models are used (Keeley et al., 1978, Hausman, 1980, Coverman/Kemp, 1987) . Often very specific populations are examined, like for example lone mothers in Blundell/Duncan/Meghir (1992), Jenkins (1992), Staat/Wagenhals (1993) or Laisney et al. (1993). Analysing the economic behaviour of unmarried women, one is confronted with the problem that the term ‘unmarried’ is not clearly defined. It includes single, divorced, separated and widowed women. They live in different types of households, like one-person households or family households, where they occupy different economic positions as for example head of the household or relative of the head. The present work considers unmarried female heads of household. We assume that the dominant economic position as head of household, voluntarily or involuntarily occupied, forces these women to a similar behaviour independent from their family status. Thus they are taken together in the analysis from the different family statuses: single, divorced, separated and widowed. Being unmarried often is regarded as a temporary state, voluntarily or involuntarily, for example in the case of young women before marriage or in the case of divorced women after their separation. Nevertheless the demographic development shows the increased importance of unmarried women in the population during the last decades. In the USA the portion of female headed households raised from 21,1% in 1970 to 26,2% in 1980 and 29,0% in 1992 (Statistical Abstracts of the United States, 1993. Own calculations). In the FRG, female headed households constitute 26,4% of total households in 1970, 27,4% in 1980 and 30,1% in 1992 (Stat.Bundesamt, FS 1, Reihe 3, 1970, 1980, 1992). Therefore it seems an interesting topic to analyse the labour supply behaviour of unmarried female heads. Especially the question whether the labour supply of unmarried women resembles rather that of married women or of prime-age males is of particular interest. Another purpose of this analysis is to apply modern econometric panel data models with special emphasis on the problem of unbalanced panel data. Most panel data analyses are carried out using balanced panel data, which is no problem if the selection process could be ignored and if enough cases are available to guarantee efficient estimation. Especially the last point was crucial for the present analysis of unmarried females. In the available panel data sets the unmarried female heads constitute only a rather small population. Therefore the estimation techniques were modified to take missing observations of the individuals into account. The paper is organized as follows: In section 2 the underlying theoretical model of intertemporal labour supply under uncertainty is shortly presented. Section 3 deals with the econometric specification and estimation techniques where the use of unbalanced panel data is considered. Section 4 contains the data description with a particular look on the unbalancedness of the samples. In the last section 5 the empirical results are presented. We compare the estimated parameters for the unmarried women between the USA and the FRG and also analyse the differences between unmarried and married women. Moreover a comparison between different samples of unmarried women is provided.
A model for the production of quarkonium states in the midrapidity region at RHIC and LHC energy range is presented which explores well understood properties of QCD only. An increase of the quarkonium hadronisation time with the initial energy leads to a gradual change of the most important phenomena from fixed target- to collider-energies. We evaluate nuclear e ects in the quarkonium production due to medium modification of the momentum distribution of the heavy quarks produced in the hard interactions, i.e. due to the broadening of the transverse momentum distribution. Other nuclear effects, i.e. nuclear shadowing and parton energy loss, are also evaluated.
In ultra-relativistic heavy ion collisions, early stage multiple scatterings may lead to an increase of the color electric field strength. Consequently, particle production - especially heavy quark (and di-quark) production - is greatly enhanced according to the Schwinger mechanism. We test this idea via the Ultra-relativistic Quantum Molecular Dynamics model (UrQMD) for Au+Au collisions at the full RHIC energy (ps = 200 AGeV). Relative to p+p collisions, a factor of 60, 20 and 7 enhancement respectively, for (sss), (ss), and , (s) is predicted for a model with increased color electric field strength.
We study b¯b and c¯c production and the influence of nuclear shadowing at LHC and RHIC energies. We find a significant reduction in the production cross section of both charm and bottom at RHIC and LHC. Bound states such as and J/psi are suppressed by this reduction in the charm production cross sections. Therefore, J/psi suppression may not be useful as a signature for the quark gluon plasma. PACS: 12.38.Mh, 25.75.-q, 24.85.+p, 14.65.Dw
We compute bremsstrahlung arising from the acceleration of individual charged baryons and mesons during the time evolution of high-energy Au+Au collisions at the Relativistic Heavy Ion Collider using a microscopic transport model. We elucidate the connection between bremsstrahlung and charge stop- ping by colliding artificial pure proton on pure neutron nuclei. From the inten- sity of low energy bremsstrahlung, the time scale and the degree of stopping could be accurately extracted without measuring any hadronic observables. PACS: 25.75.-q, 13.85.Qk
This paper provides an empirical assessment of hypotheses that identify causes of demand side constraints of individual labour supply. In a comparative study for the USA and the FRG we focus on analysing the effect of productivity gaps (industry wage growth beyond productivity growth), industry investment intensity and regional labour market conditions on individual employment probabilities. Furthermore, we investigate whether demand side constraints of labour supply can be caused by a spill over from commodity markets. Efficiency wage theory and the theory of inter-industry wage differentials are utilised to derive identifying restrictions that are applicable to the labour supply models for both countries. The econometric contribution of the paper is the derivation and application of a two step estimation method for the class of simultaneous random effects double hurdle models, of which the labour supply model employed in this paper is a special case. To provide the empirical basis for the comparative study, the Panel Study of Income Dynamics and the German Socio-Economic Panel are linked to the OECD’s International Sectoral Database. JEL classification: C33, C34, J64, O57
By using the background field method of QCD in a path integral approach, we derive the equation of motion for the classical chromofield and for the gluon in a system containing the gluon and the classical chromofield simul- taneously. This inhomogeneous field equation contains a current term, which is the expectation value of a composite operator including linear, square and cubic terms of the gluon field. We also derive identities which the current should obey from the gauge invariance. We calculate the current at the leading order where the current induced by the gluon is opposite in sign to that induced by the quark. This is just the feature of the non-Abelian gauge field theory which has asymptotic freedom. Physically, the induced current can be treated as the displacement current in the polarized vacuum, and its e ect is equivalent to redefining the field and the coupling constant. PACS: 12.38.-t,12.38.Aw,11.15.-q,12.38.Mh
A generic property of a first-order phase transition in equilibrium, and in the limit of large entropy per unit of conserved charge, is the smallness of the isentropic speed of sound in the mixed phase . A specific prediction is that this should lead to a non-isotropic momentum distribution of nucleons in the reaction plane (for energies < 40A GeV in our model calculation). On the other hand, we show that from present effective theories for low-energy QCD one does not expect the thermal transition rate between various states of the effective potential to be much larger than the expansion rate, questioning the applicability of the idealized Maxwell/Gibbs construction. Experimental data could soon provide essential information on the dynamics of the phase transition.
Modelling consumer behaviour in a profile design using a three equation generalised Tobit model
(1997)
We propose the application of a three equation generalised Tobit to model different aspects of consumer behaviour in a full profile study design. The model takes into account that consumer behaviour can be measured by preference scores, purchase probability and purchase volume. We aim to avoid the drawbacks of traditional conjoint analysis where the latter two aspects are disregarded. Starting from a full profile design, we develop the appropriate questionnaire layout, the econometric model, the likelihood function and tests. The model is applied in a market entry study for an innovative medicament after a reform of Germany´s public health system in 1993-1994. JEL Classification: C35,M31,L65
Equation of state of baryon rich quark matter is studied within the SU(3) Nambu Jona-Lasinio model with flavour mixing interaction. Possible bound states (strangelets) and chiral phase transitions in this matter are investigated at various values of strangeness fraction rs. The model predictions are very sensitive to the ratio of vector and scalar coupling constants, ¾ = GV /GS. At ¾ = 0.5 and zero temperature the maximum binding energy (about 15 MeV per baryon) takes place at rs C 0.4. Such strangelets are negatively charged and have typical life times < 10 7 s. The calculations are carried out also at finite temperatures. They show that bound states exist up to temperatures of about 15 MeV. The model predicts a first order chiral phase transition at finite baryon densities. The parameters of this phase transition are calculated as a function of rs.