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Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars is investigated. We find that the equation of state exhibits a second stable minimum at large hyperon contents which is in accord with existing hypernuclear data. This second solution gives rise to new effects for neutron star properties which are similar to the ones proposed for the deconfinement transition to strange quark matter and absolutely stable strange stars. We find that the corresponding hyperstars can have rather small radii of R=6-8 km independent of the mass. PACS: 26.60+c, 21.65+f, 97.60.Gb, 97.60.Jd
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R ~ 8 km. PACS: 26.60+c, 21.65+f, 97.60.Gb, 97.60.Jd
This study analyses the effects of public sector sponsored vocational training (PSVT) on individuals’ unemployment duration in West Germany for the period from 1985 to 1993. The data is taken from the German Socio-Economic Panel (GSOEP). To resolve the intriguing sample selection problem, i.e. to find an adequate control group for the group of trainees, we employ matching methods. These matching methods use the individual propensity to participate in training, which is obtained by estimating a panel probit model as the main matching variable. On the basis of the matched sample a discrete time hazard rate model is utilized to assess the effects of training participation on unemployment duration. Our results indicate that a significant positive effect on reemployment chances due to PSVT can only be expected for courses with a duration of no longer than six months. No significant positive effects on post-training reemployment chances where found for courses lasting longer than six months. In fact these PSVT courses are significantly less effective at increasing reemployment chances than those lasting no longer than three months. JEL classification: C40, J20, J64
This paper provides a review of empirical evidence relating to the impact of training on employment performance. Since a central issue in estimating training effects is the sample selection problem a short theoretical discussion of different evaluation strategies is given. The empirical overview primarily focuses on non-experimental evidence for Germany. In addition selected studies for other countries and experimental investigations are discussed.
In this study we are concerned with the impact of vocational training on the individual’s unemployment duration in West Germany. The data basis used is the German Socio-Economic Panel (GSOEP) for the period from 1984 to 1994. To resolve the intriguing sample selection problem, i.e. to find an adequate control group for the group of trainees, we employ matching methods which were developed in the statistical literature. These matching methods uses as the main matching variable the individual propensity score to participate in training, which is obtained by estimating a random effects probit model. On the basis of the matched sample a discrete time hazard rate model is utilized to assess the impact of vocational training on unemployment duration. Our results indicate, that training significantly raises the transition rate of unemployed into employment in the short but not in the long run. JEL classification: C40, J20, J64
We estimate a semiparametric single-risk discrete-time duration model to assess the effect of vocational training on the duration of unemployment spells. The data basis used in this study is the German Socio-Economic-Panel (GSOEP) for West Germany for the period from 1986 to 1994. To take into account a possible selection bias actual participation in vocational training is instrumented using estimates of a randomeffects probit model for the participation in qualification measures. Our main results show that training does have a significant short term effect of reducing unemployment duration but that this effect does not persist in the long run. JEL classifications: C41, J20, J64
This paper is intended as a short survey of the most relevant methods for grouped transition data. The fundamentals of duration analysis are discussed in a continuous time framework, whereas the treatment of methods for discrete durations is limited to the peculiarity of these models. In addition, some recent empirical applications of the methods are discussed.
A sign reversal of the directed flow parameter v1 in the central rapidity region in Au+Au collisions at s = 200 AGeV is predicted. This anti-flow is shown to be linked to the expansion of the hot matter created. In line with this observation the predicted elliptic flow parameter v2 of various particle species is linked to the mean free path of these particles.
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.