Anatomy of Welfare Reform Evaluation:Announcement and Implementation Effects

This paper formulates a simple model of female labor force decisions which embeds an in-work benefit reform and explicitly allows for announcement and implementation effects. We explore several mechanisms through which women can respond to the announcement of a reform that increases in-work benefits, including sources of intertemporal substitution, human capital accumulation, and labor market frictions. Using the model's insights and information of the precise timing of the announcement and implementation of a major UK in-work benefit reform, we estimate its effects on single mothers' behavior. We find large and positive announcement effects on employment decisions. We show that this finding is consistent with the presence of frictions in the labor market. The impact evaluations of this reform which ignore such effects produce implementation effect estimates that are biased downwards by 15 to 35 percent

Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2

We report muon-spin rotation, heat capacity, magnetization, and ac magnetic susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2. These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon depolarization persisting to about 5K above T_N is consistent with the presence of short-range magnetic order. The temperature and frequency dependence of the ac susceptibility suggests that magnetic clusters persist above 25K in the paramagnetic state and that their volume fraction decreases with increasing temperature. A frequency dependent peak in the ac magnetic susceptibility at T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this temperature. A partial magnetic phase diagram is deduced.Comment: 4 pages, 4 figure

Measurement of the 6S-7S transition polarizablility in atomic cesium and an improved test of the standard model

The ratio of the off-diagonal hyperfine amplitude to the tensor transition polarizability (Mhf/beta) for the 6S-7S transition in cesium has been measured. The value of beta=27.024(43)(expt)(67)(theory)a_0^3 is then obtained using an accurate semi-empirical value of Mhf. This is combined with a previous measurement of parity nonconservation in atomic cesium and previous atomic structure calculations to determine the value of the weak charge. The uncertainties in the atomic structure calculations are updated (and reduced) in light of new experimental tests. The result Q_W=-72.06(28)(expt) (34)(theory) differs from the prediction of the standard model of elementary particle physics by 2.5 sigma.Comment: 12 pages, 1 figur

Anomalous temperature evolution of the internal magnetic field distribution in the charge-ordered triangular antiferromagnet AgNiO2

Zero-field muon-spin relaxation measurements of the frustrated triangular quantum magnet AgNiO2 are consistent with a model of charge disproportionation that has been advanced to explain the structural and magnetic properties of this compound. Below an ordering temperature of T_N=19.9(2) K we observe six distinct muon precession frequencies, due to the magnetic order, which can be accounted for with a model describing the probable muon sites. The precession frequencies show an unusual temperature evolution which is suggestive of the separate evolution of two opposing magnetic sublattices.Comment: 4 pages, 3 figure

The optically-powerful quasar E1821+643 is associated with a 300-kpc scale FRI radio structure

We present a deep image of the optically-powerful quasar E1821+643 at 18cm made with the Very Large Array (VLA). This image reveals radio emission, over 280 kpc in extent, elongated way beyond the quasar's host galaxy. Its radio structure has decreasing surface brightness with increasing distance from the bright core, characteristic of FRI sources (Fanaroff & Riley 1974). Its radio luminosity at 5GHz falls in the classification for `radio-quiet' quasars (it is only 10^23.9 W/Hz/sr; see e.g. Kellermann et al 1994). Its radio luminosity at 151MHz (which is 10^25.3 W/Hz/sr) is at the transition luminosity observed to separate FRIs and FRIIs. Hitherto, no optically-powerful quasar had been found to have a conventional FRI radio structure. For searches at low-frequency this is unsurprising given current sensitivity and plausible radio spectral indices for radio-quiet quasars. We demonstrate the inevitability of the extent of any FRqI radio structures being seriously under-estimated by existing targetted follow-up observations of other optically-selected quasars, which are typically short exposures of z > 0.3 objects, and discuss the implications for the purported radio bimodality in quasars. The nature of the inner arcsec-scale jet in E1821+643, together with its large-scale radio structure, suggest that the jet-axis in this quasar is precessing (cf. Galactic jet sources such as SS433). A possible explanation for this is that its central engine is a binary whose black holes have yet to coalesce. The ubiquity of precession in `radio-quiet' quasars, perhaps as a means of reducing the observable radio luminosity expected in highly-accreting systems, remains to be established.Comment: Accepted by ApJ Letters; higher quality versions of figures available at http://www-astro.physics.ox.ac.uk/~km

Muon-fluorine entangled states in molecular magnets

The information accessible from a muon-spin relaxation experiment is often limited since we lack knowledge of the precise muon stopping site. We demonstrate here the possibility of localizing a spin polarized muon in a known stopping state in a molecular material containing fluorine. The muon-spin precession that results from the entangled nature of the muon-spin and surrounding nuclear spins is sensitive to the nature of the stopping site and we use this property to identify three classes of site. We are also able to describe the extent to which the muon distorts its surroundings.Comment: 4 pages, 3 figure

Muon-spin relaxation measurements on the dimerized spin-1/2 chains NaTiSi2O6 and TiOCl

We report muon spin relaxation (muSR) and magnetic susceptibility investigations of two Ti3+ chain compounds which each exhibit a spin gap at low temperature, NaTiSi2O6 and TiOCl. From these we conclude that the spin gap in NaTiSi2O6 is temperature independent, with a value of 2*Delta=660(50)K, arising from orbital ordering at Too = 210K; the associated structural fluctuations activate the muon spin relaxation rate up to temperatures above 270K. In TiOCl we find thermally activated spin fluctuations corresponding to a spin gap 2*Delta=420(40)K below Tc1=67K. We also compare the methods used to extract the spin gap and the concentration of free spins within the samples from muSR and magnetic susceptibility data.Comment: 4 pages, 3 figure

Magnetism in Nb(1-y)Fe(2+y) - composition and magnetic field dependence

We present a systematic study of transport and thermodynamic properties of the Laves phase system Nb$_{1-y}$Fe$_{2+y}$. Our measurements confirm that Fe-rich samples, as well as those rich in Nb (for $\mid y\mid\geq 0.02$), show bulk ferromagnetism at low temperature. For stoichiometric NbFe$_2$, on the other hand, magnetization, magnetic susceptibility and magnetoresistance results point towards spin-density wave (SDW) order, possibly helical, with a small ordering wavevector $Q \sim 0.05$ \AA$^{-1}$. Our results suggest that on approaching the stoichiometric composition from the iron-rich side, ferromagnetism changes into long-wavelength SDW order. In this scenario, $Q$ changes continuously from 0 to small, finite values at a Lifshitz point in the phase diagram, which is located near $y=+0.02$. Further reducing the Fe content suppresses the SDW transition temperature, which extrapolates to zero at $y\approx -0.015$. Around this Fe content magnetic fluctuations dominate the temperature dependence of the resistivity and of the heat capacity which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point. Because the critical point is located between the SDW phase associated with stoichiometric NbFe$_2$ and the ferromagnetic order which reemerges for very Nb-rich NbFe$_2$, the observed temperature dependences could be attributed both to proximity to SDW order or to ferromagnetism.Comment: 13 pages, 20 figure

Non-Collinear Ferromagnetic Luttinger Liquids

The presence of electron-electron interactions in one dimension profoundly changes the properties of a system. The separation of charge and spin degrees of freedom is just one example. We consider what happens when a system consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall, is coupled to interacting electrons in one-dimension (more specifically a Luttinger liquid). The ferromagnetism breaks spin charge separation and the presence of the domain wall introduces a spin dependent scatterer into the problem. The absence of spin charge separation and the effects of the electron correlations results in very different behaviour for the excitations in the system and for spin-transfer-torque effects in this model.Comment: 6 pages, submitted to Journal of Physics: Conference Series for JEMS 201

Third-order many-body perturbation theory calculations for the beryllium and magnesium isoelectronic sequences

Relativistic third-order MBPT is applied to obtain energies of ions with two valence electrons in the no virtual-pair approximation (NVPA). A total of 302 third-order Goldstone diagrams are organized into 12 one-body and 23 two-body terms. Only third-order two-body terms and diagrams are presented here, owing to the fact that the one-body terms are identical to the previously studied third-order terms in monovalent ions. Dominant classes of diagrams are identified. The model potential is a Dirac-Hartree-Fock $V^{N-2}$ potential, and B-spline basis functions in a cavity of finite radius are employed in the numerical calculations. The Breit interaction is taken into account through second order of perturbation theory and the lowest-order Lamb shift is also evaluated. Sample calculations are performed for berylliumlike ions with Z = 4--7, and for the magnesiumlike ion P IV. The third-order energies are in excellent agreement with measurement with an accuracy at 0.2% level for the cases considered. Comparisons are made with previous second-order MBPT results and with other calculations. The third-order energy correction is shown to be significant, improving second-order correlation energies by an order of magnitude