Methodological issues in testing the marginal productivity theory

Previous tests of the marginal productivity theory have been criticized on several grounds reviewed by the authors. One important deficiency has been the small number of factor inputs entered in the production functions. In 1978 Gottschalk suggested a method to estimate production functions with many inputs by assuming that the production process can be split into subprocesses. This reduces the probability of multicollinearity. The authors show that the method depends on an additional assumption. Tinbergen has developed a method for avoiding this assumption. Its application to American cross-section (state) data did not alter the estimated coefficients greatly

Income distribution: Second thoughts

As a follow-up of his book on income distribution the author reformulates his version on the scarcity theory of income from productive contributions. The need to introduce into an earnings theory several job characteristics, non-cognitive as well as cognitive, and the corresponding personality traits is stressed, the latter subdivided into innate and learnable capabilities. The theory is presented in two alternative mathematical versions: one where job and person characteristics are continuous and one where they have discrete values and their frequencies assume continuous values. Although, mainly in the United States, numerous empirical inquiries have been made, job characteristics and the corresponding personal characteristics have not been included in sufficient number. I want to express my profound gratitude to Professor Robert H. Haveman, who not only published a deep-delving review article on my book Income Distribution: Analysis and Policies but also commented on an earlier text of the present article. I also owe a great debt to Professor Jan Pen who in a long series of discussions challenged a number of my concepts and figures. Finally I want to thank Dr. S. K. Kuipers for helpful comments on an earlier draft

From Oxford to Bristol and Back: The Invention of Scientific Wildlife Television

In the 1960s, two scientists from Oxford University, Niko Tinbergen and Gerald Thompson, began using film as part of their scientific practice. The BBC’s Natural History Unit (NHU) in Bristol quickly got wind of their work and started collaborating with them to develop a new approach to wildlife television making. Tinbergen, the founder of ethology, brought intellectual foundations to it, creating, with Christopher Parsons, stories of wildlife informed by the theory of evolution. Thompson provided a technological edge which enabled the Bristol NHU producers to bring a new perspective to the subject matter they were showing in their programmes. The two collaborations also led them to further define their identity as experts in wildlife television making

Apparent annual survival of staging ruffs during a period of population decline: insights from sex and site-use related differences

The ruff Philomachus pugnax, a lekkingshorebird wintering in Africa and breeding across northernEurasia, declined severely in its western range. Based on acapture-mark-resighting programme (2004–2011) in thewesternmost staging area in Friesland (the Netherlands),we investigated changes in apparent annual survival inrelation to age and sex to explore potential causes ofdecline. We also related temporal variation in apparentsurvival to environmental factors. We used the Capture-Mark-Recapture multievent statistical framework to overcomebiases in survival estimates after testing for hiddenheterogeneity of detection. This enabled the estimation ofthe probability to belong to high or low detectabilityclasses. Apparent survival varied between years but wasnot related to weather patterns along the flyway, or to floodlevels in the Sahel. Over time, a decline in apparent survivalis suggested. Due to a short data series and flag loss inthe last period this cannot be verified. Nevertheless, thepatterns in sex-specific detectability and survival lead tonew biological insights. Among highly detectable birds,supposedly most reliant on Friesland, males survived betterthan females (?/HDmales = 0.74, range 0.51–0.93;?/HDfemales = 0.51, range 0.24–0.81). Among lowdetectable birds, the pattern is reversed (?/LDmales = 0.64,range 0.37–0.89; ?/LDfemales = 0.73, range 0.48–0.93).Probably the staging population contains a mixture of sexspecificmigration strategies. A loss of staging femalescould greatly affect the dynamics of the western ruffpopulation. Further unravelling of these population processesrequires geographically extended demographicmonitoring and the use of tracking devices

High daily energy expenditure of incubating shorebirds on High Arctic tundra: a circumpolar study

1. Given the allometric scaling of thermoregulatory capacity in birds, and the cold and exposed Arctic environment, it was predicted that Arctic-breeding shorebirds should incur high costs during incubation. Using doubly labelled water (DLW), daily energy expenditure (DEE) during incubation was measured in eight shorebird species weighing between 29 and 142 g at various sites in the Eurasian and Canadian High Arctic. The results are compared with a compilation of similar data for birds at lower latitudes. 2. There was a significant positive correlation between species average DEE and body mass (DEE (kJ day−1) = 28·12 BM (g)^0·524, r^2 = 0·90). The slopes of the allometric regression lines for DEE on body mass of tundra-breeding birds and lower latitude species (a sample mostly of passerines but including several shorebirds) are similar (0·548 vs 0·545). DEE is about 50% higher in birds on the tundra than in temperate breeding areas. 3. Data for radiomarked Red Knots for which the time budgets during DLW measurements were known, indicated that foraging away from the nest on open tundra is almost twice as costly as incubating a four-egg clutch. 4. During the incubation phase in the High Arctic, tundra-breeding shorebirds appear to incur among the highest DEE levels of any time of the year. The rates of energy expenditure measured here are among the highest reported in the literature so far, reaching inferred ceilings of sustainable energy turnover rates.

Measuring energy dependent polarization in soft gamma-rays using Compton scattering in PoGOLite

Linear polarization in X- and gamma-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25-100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 hours were simulated, corresponding to a standard and a long duration flight respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.Comment: 11 pages, 12 figures; updated to match version accepted for publication in Astroparticle Physics (only minor changes

XPOL - the correlation polarimeter at the IRAM 30m telescope

XPOL, the first correlation polarimeter at a large millimeter telescope, uses a flexible digital correlator to measure all four Stokes parameters simultaneously, i.e. the total power I, the linear polarization components Q and U, and the circular polarization V. The versatility of the backend provides adequate bandwidth for efficient continuum observations as well as sufficient spectral resolution (40 kHz) for observations of narrow lines. We demonstrate that the polarimetry specific calibrations are handled with sufficient precision, in particular the relative phase between the Observatory's two orthogonally linearly polarized receivers. The many facets of instrumental polarization are studied at 3mm wavelength in all Stokes parameters: on-axis with point sources and off-axis with beam maps. Stokes Q which is measured as the power difference between the receivers is affected by instrumental polarization at the 1.5% level. Stokes U and V which are measured as cross correlations are very little affected (maximum sidelobes 0.6% (U) and 0.3% (V)). These levels critically depend on the precision of the receiver alignment. They reach these minimum levels set by small ellipticities of the feed horns when alignment is optimum (<~ 0.3"). A second critical prerequisite for low polarization sidelobes turned out to be the correct orientation of the polarization splitter grid. Its cross polarization properties are modeled in detail. XPOL observations are therefore limited only by receiver noise in Stokes U and V even for extended sources. Systematic effects set in at the 1.5% level in observations of Stokes Q. With proper precautions, this limitation can be overcome for point sources. Stokes Q observations of extended sources are the most difficult with XPOL.Comment: 31 pages, accepted for publication by Publications of the Astronomical Society of the Pacific on 2008/05/2