91 research outputs found
PATENTS, R&D AND LAG EFFECTS: EVIDENCE FROM FLEXIBLE METHODS FOR COUNT PANEL DATA ON MANUFACTURING FIRMS
Hausman, Hall and Griliches (1984) and Hall, Griliches and Hausman (1986) investigated whether there was a lag in the patent-R&D relationship for the U.S. manufacturing sector using 1970¿s data. They found that there was little evidence of anything but contemporaneous movement of patents and R&D. We reexamine this important issue employing new longitudinal patent data at the firm level for the U.S. manufacturing sector from 1982 to 1992. To address unique features of the data, we estimate various distributed lag and dynamic multiplicative panel count data models. The paper also develops a new class of count panel data models based on series expansion of the distribution of individual effects. The empirical analyses show that, although results are somewhat sensitive to different estimation methods, the contemporaneous relationship between patenting and R&D expenditures continues to be rather strong, accounting for over 60% of the total R&D elasticity. Regarding the lag structure of the patents-R&D relationship, we do find a significant lag in all empirical specifications. Moreover, the estimated lag effects are higher than have previously been found, suggesting that the contribution of R&D history to current patenting has increased from the 1970¿s to the 1980¿s.Innovative activity, Patents and R&D, Individual effects, count panel data methods.
Detection limits of organic compounds achievable with intense, short-pulse lasers
Many organic molecules have strong absorption bands which can be accessed by ultraviolet short pulse lasers to produce efficient ionization. This resonant multiphoton ionization scheme has already been exploited as an ionization source in time-of-flight mass spectrometers used for environmental trace analysis. In the present work we quantify the ultimate potential of this technique by measuring absolute ion yields produced from the interaction of 267 nm femtosecond laser pulses with the organic molecules indole and toluene, and gases Xe, N2 and O2. Using multiphoton ionization cross sections extracted from these results, we show that the laser pulse parameters required for real-time detection of aromatic molecules at concentrations of one part per trillion in air and a limit of detection of a few attomoles are achievable with presently available commercial laser systems. The potential applications for the analysis of human breath, blood and tissue samples are discussed
Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam
The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration (μ 500 MeV) with an intense laser pulse (a0>10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy >30 MeV
Deep HST Observations of Star Clusters in NGC 1275
We present an analysis of compact star clusters in deep HST/WFPC2 images of
NGC 1275. B and R band photometry of roughly 3000 clusters shows a bimodality
in the B-R colors, suggesting that distinct old and young cluster populations
are present. The small spread in the colors of the blue clusters is consistent
with the hypothesis that they are a single age population, with an inferred age
of 0.1 to 1 Gyr. The luminosity function shows increasing numbers of blue
clusters to the limit of our photometry, which reaches several magnitudes past
the turnover predicted if the cluster population were identical to current
Galactic globulars seen at a younger age. The blue clusters have a spatial
distribution which is more centrally peaked than that of the red clusters. The
individual clusters are slightly resolved, with core radii <~ 0.75 pc if they
have modified Hubble profiles. We estimate the specific frequencies of the old
and young populations and discuss the uncertainties in these estimates. We find
that the specific frequency of the young population in NGC 1275 is currently
larger than that of the old population and will remain so as the young
population evolves, even if the majority of the low mass clusters are
eventually destroyed. If the young population formed during a previous merger,
this suggests that mergers can increase the specific frequency of globulars in
a galaxy. However, the presently observed young population likely contains too
few clusters to have a significant impact on the overall specific frequency as
it will be observed in the future.Comment: 26 pages, 9 figures, to be published in the Astronomical Journa
The James Webb Space Telescope
The James Webb Space Telescope (JWST) is a large (6.6m), cold (50K),
infrared-optimized space observatory that will be launched early in the next
decade. The observatory will have four instruments: a near-infrared camera, a
near-infrared multi-object spectrograph, and a tunable filter imager will cover
the wavelength range, 0.6 to 5.0 microns, while the mid-infrared instrument
will do both imaging and spectroscopy from 5.0 to 29 microns. The JWST science
goals are divided into four themes. The End of the Dark Ages: First Light and
Reionization theme seeks to identify the first luminous sources to form and to
determine the ionization history of the early universe. The Assembly of
Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars,
metals, morphological structures, and active nuclei within them evolved from
the epoch of reionization to the present day. The Birth of Stars and
Protoplanetary Systems theme seeks to unravel the birth and early evolution of
stars, from infall on to dust-enshrouded protostars to the genesis of planetary
systems. The Planetary Systems and the Origins of Life theme seeks to determine
the physical and chemical properties of planetary systems including our own,
and investigate the potential for the origins of life in those systems. To
enable these observations, JWST consists of a telescope, an instrument package,
a spacecraft and a sunshield. The telescope consists of 18 beryllium segments,
some of which are deployed. The segments will be brought into optical alignment
on-orbit through a process of periodic wavefront sensing and control. The JWST
operations plan is based on that used for previous space observatories, and the
majority of JWST observing time will be allocated to the international
astronomical community through annual peer-reviewed proposal opportunities.Comment: 96 pages, including 48 figures and 15 tables, accepted by Space
Science Review
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