Estimating the Firm's Labor Supply Curve in a "New Monopsony" Framework: School Teachers in Missouri

In the context of certain dynamic models, it is possible to infer the elasticity of labor supply to the firm from the elasticity of the quit rate with respect to the wage. Using this property, we estimate the average labor supply elasticity to public school districts in Missouri. We take advantage of the plausibly exogenous variation in pre-negotiated district salary schedules to instrument for actual salary. Instrumental variables estimates lead to a labor supply elasticity estimate of about 3.7, suggesting the presence of significant market power for school districts, especially over more experienced teachers. The presence of monopsony power in this labor market may be partially explained by institutional features of the teacher labor market.labor monopsony, teachers

A broadband radio study of the average profile and giant pulses from PSR B1821-24A

We present the results of wide-band (720-2400 MHz) study of PSR B1821-24A (J1824-2452A, M28A), an energetic millisecond pulsar visible in radio, X-rays and gamma-rays. In radio, the pulsar has a complex average profile which spans >85% of the spin period and exhibits strong evolution with observing frequency. For the first time we measure phase-resolved polarization properties and spectral indices of radio emission throughout almost all of the on-pulse window. We combine this knowledge with the high-energy information to compare M28A to other known gamma-ray millisecond pulsars and to speculate that M28A's radio emission originates in multiple regions within its magnetosphere (i.e. both in the slot or outer gaps near the light cylinder and at lower altitudes above the polar cap). M28A is one of the handful of pulsars which are known to emit Giant Pulses (GPs) -- short, bright radio pulses of unknown nature. We report a drop in the linear polarization of the average profile in both windows of GP generation and also a `W'-shaped absorption feature (resembling a double notch), partly overlapping with one of the GP windows. The GPs themselves have broadband spectra consisting of multiple patches with fractional spectral width ($\Delta\nu/\nu$) of about 0.07. Although our time resolution was not sufficient to resolve the GP structure on the microsecond scale, we argue that GPs from this pulsar most closely resemble the GPs from the main pulse of the Crab pulsar, which consist of a series of narrowband nanoshots.Comment: 16 pages, 8 figures, accepted to Ap

A High-Frequency Search for Pulsars Within the Central Parsec of SgrA*

We report results from a deep high-frequency search for pulsars within the central parsec of Sgr A* using the Green Bank Telescope. The observing frequency of 15 GHz was chosen to maximize the likelihood of detecting normal pulsars (i.e. with periods of $\sim 500$\,ms and spectral indices of $\sim -1.7$) close to Sgr A*, that might be used as probes of gravity in the strong-field regime; this is the highest frequency used for such pulsar searches of the Galactic Center to date. No convincing candidate was detected in the survey, with a $10\sigma$ detection threshold of $\sim 10 \mu$Jy achieved in two separate observing sessions. This survey represents a significant improvement over previous searches for pulsars at the Galactic Center and would have detected a significant fraction ($\gtrsim 5%) of the pulsars around Sgr A*, if they had properties similar to those of the known population. Using our best current knowledge of the properties of the Galactic pulsar population and the scattering material toward Sgr A*, we estimate an upper limit of 90 normal pulsars in orbit within the central parsec of Sgr A*.Comment: 10 pages, 7 figures, accepted for publication in the ApJ

The Proper Motion of PSR J0205+6449 in 3C 58

We report on sensitive phase-referenced and gated 1.4-GHz VLBI radio observations of the pulsar PSR J0205+6449 in the young pulsar-wind nebula 3C 58, made in 2007 and 2010. We employed a novel technique where the ~105-m Green Bank telescope is used simultaneously to obtain single-dish data used to determine the pulsar's period as well as to obtain the VLBI data, allowing the VLBI correlation to be gated synchronously with the pulse to increase the signal-to-noise. The high timing noise of this young pulsar precludes the determination of the proper motion from the pulsar timing. We derive the position of the pulsar accurate at the milliarcsecond level, which is consistent with a re-determined position from the Chandra X-ray observations. We reject the original tentative optical identification of the pulsar by Shearer and Neustroev (2008), but rather identify a different optical counterpart on their images, with R-band magnitude ~24. We also determine an accurate proper motion for PSR J0205+6449 of (2.3 +- 0.3) mas/yr, corresponding to a projected velocity of only (35 +- 6) km/s for a distance of 3.2 kpc, at p.a. -38 deg. This projected velocity is quite low compared to the velocity dispersion of known pulsars of ~200 km/s. Our measured proper motion does not suggest any particular kinematic age for the pulsar.Comment: 10 pages, 7 figures; accepted for publication in MNRA

Agricultural Science and Technology: Tensions and Contradictions

Agricultural science and farm-based technologies have been important forces behind the dramatic rise in agricultural production in the industrial world during the 20th century, as well as in large portions of the developing world (Stanton, 1998). In the United States, mechanisation, improved seeds and breeds, chemical inputs, and other scientifically inspired production technologies and techniques are often credited with productivity gains (Dimitri, Effland & Concklin, 2005). In past decades, agricultural science and technology have contributed to the productivist goals of maximising production while seeking the greatest efficiency from inputs. However, there have always been tensions and contradictions because the distribution of risks and benefits has not been even. Despite these insights, recent shifts in the political economy of agricultural science and technology indicate a trend that favours the private sector and global markets, a 241 Leland Glenna and Elizabeth P. Ransom move that tends to exacerbate some of those underlying and persistent tensions and contradictions. We explore these issues by examining how these political-economic shifts are affecting agricultural science and technology in industrialised and developing nations

X-Ray Observations of Black Widow Pulsars

We describe the first X-ray observations of five short orbital period ($P_B < 1$ day), $\gamma$-ray emitting, binary millisecond pulsars. Four of these, PSRs J0023+0923, J1124$-$3653, J1810+1744, and J2256$-$1024 are `black-widow' pulsars, with degenerate companions of mass $\ll0.1 M_{\odot}$, three of which exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing `redback' with a near Roche-lobe filling $\sim$0.2 solar mass non-degenerate companion. Data were taken using the \textit{Chandra X-Ray Observatory} and covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and J2256$-$1024, show significant orbital variability while PSR J1124$-$3653 shows marginal orbital variability. The lightcurves for these three pulsars have X-ray flux minima coinciding with the phases of the radio eclipses. This phenomenon is consistent with an intrabinary shock emission interpretation for the X-rays. The other two pulsars, PSRs J0023+0923 and J1810+1744, are fainter and do not demonstrate variability at a level we can detect in these data. All five spectra are fit with three separate models: a power-law model, a blackbody model, and a combined model with both power-law and blackbody components. The preferred spectral fits yield power-law indices that range from 1.3 to 3.2 and blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135 shows a significant hard X-ray component, with a large number of counts above 2 keV, which is additional evidence for the presence of intrabinary shock emission and is similar to what has been detected in the low-mass X-ray binary to millisecond pulsar transition object PSR J1023+0038.Comment: 8 pages, 6 figures, 2 tables, submitted to Ap

1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds

The variable X-ray source 1E 1547.0-5408 was identified by Gelfand & Gaensler (2007) as a likely magnetar in G327.24-0.13, an apparent supernova remnant. No X-ray pulsations have been detected from it. Using the Parkes radio telescope, we discovered pulsations with period P = 2.069 s. Using the Australia Telescope Compact Array, we localized these to 1E 1547.0-5408. We measure dP/dt = (2.318+-0.005)e-11, which for a magnetic dipole rotating in vacuo gives a surface field strength of 2.2e14 G, a characteristic age of 1.4 kyr, and a spin-down luminosity of 1.0e35 ergs/s. Together with its X-ray characteristics, these rotational parameters of 1E 1547.0-5408 prove that it is a magnetar, only the second known to emit radio waves. The distance is ~9 kpc, derived from the dispersion measure of 830 pc/cc. The pulse profile at a frequency of 1.4 GHz is extremely broad and asymmetric due to multipath propagation in the ISM, as a result of which only approximately 75% of the total flux at 1.4 GHz is pulsed. At higher frequencies the profile is more symmetric and has FWHM = 0.12P. Unlike in normal radio pulsars, but in common with the other known radio-emitting magnetar, XTE J1810-197, the spectrum over 1.4-6.6 GHz is flat or rising, and we observe large, sudden changes in the pulse shape. In a contemporaneous Swift X-ray observation, 1E 1547.0-5408 was detected with record high flux, f_X(1-8 keV) ~ 5e-12 ergs/cm^2/s, 16 times the historic minimum. The pulsar was undetected in archival radio observations from 1998, implying a flux < 0.2 times the present level. Together with the transient behavior of XTE J1810-197, these results suggest that radio emission is triggered by X-ray outbursts of usually quiescent magnetars.Comment: Accepted for publication in ApJ Letter