1,048 research outputs found
Evidence from Patents and Patent Citations on the Impact of NASA and Other Federal Labs on Commercial Innovation
We explore the commercialization of government-generated technology by analyzing patents awarded to the U.S. government and the citations to those patents from subsequent patents. We use information on citations to federal patents in two ways: (1) to compare the average technological impact of NASA patents, other Federal' patents, and a random sample of all patents using measures of importance' and generality;' and (2) to trace the geographic location of commercial development by focusing on the location of inventors who cite NASA and other federal patents. We find, first, that the evidence is consistent with increased effort to commercialize federal lab technology generally and NASA specifically. The data reveal a striking NASA golden age' during the second half of the 1970s which remains a puzzle. Second, spillovers are concentrated within a federal lab complex of states representing agglomerations of labs and companies. The technology complex links five NASA states through patent citations: California, Texas, Ohio, DC/Virginia-Maryland, and Alabama. Third, qualitative evidence provides some support for the use of patent citations as proxies for both technological impact and knowledge spillovers.
Total hemispherical emittance measured at high temperatures by the calorimetric method
A calorimetric vacuum emissometer (CVE) capable of measuring total hemispherical emittance of surfaces at elevated temperatures was designed, built, and tested. Several materials with a wide range of emittances were measured in the CVE between 773 to 923 K. These results were compared to values calculated from spectral emittance curves measured in a room temperature Hohlraum reflectometer and in an open-air elevated temperature emissometer. The results differed by as much as 0.2 for some materials but were in closer agreement for the more highly-emitting, diffuse-reflecting samples. The differences were attributed to temperature, atmospheric, and directional effects, and errors in the Hohlraum and emissometer measurements (plus or minus 5 percent). The probable error of the CVE measurements was typically less than 1 percent
Quantum Moduli Spaces of String Theories
Generically, string models with supersymmetry are not expected to have
moduli beyond perturbation theory; stringy non-perturbative effects as well as
low energy field-theoretic phenomena such as gluino condensation will lift any
flat directions. In this note, we describe models where some subspace of the
moduli space survives non-perturbatively. Discrete symmetries forbid any
inherently stringy effects, and dynamical considerations control the
field-theoretic effects. The surviving subspace is a space of high symmetry;
the system is attracted to this subspace by a potential which we compute.
Models of this type may be useful for considerations of duality and raise
troubling cosmological questions about string theory. Our considerations also
suggest a mechanism for fixing the expectation value of the dilaton.Comment: 26 pages; uses harvmac. Footnote re fixing dilaton adde
High temperature radiator materials for applications in the low Earth orbital environment
Radiators must be constructed of materials which have high emittance in order to efficiently radiate heat from high temperature space power systems. In addition, if these radiators are to be used for applications in the low Earth orbital environment, they must not be detrimentally affected by exposure to atomic oxygen. Four materials selected as candidate radiator materials (304 stainless steel, copper, titanium-6% aluminum-4% vanadium (Ti-6%Al-4%V), and niobium-1% zirconium (Nb-1%Zr)) were surface modified by acid etching, heat treating, abrading, sputter texturing, electrochemical etching, and combinations of the above in order to improve their emittance. Combination treatment techniques with heat treating as the second treatment provided about a factor of two improvement in emittance for 304 stainless steel, Ti-6%Al-4%V, and Nb-1%Zr. A factor of three improvement in emittance occurred for discharge chamber sputter textured copper. Exposure to atomic oxygen in an RF plasma asher did not significantly change the emittance of those samples that had been heat treated as part of their texturing process. An evaluation of oxygen penetration is needed to understand how oxidation affects the mechanical properties of these materials when heat treated
Flexible fluoropolymer filled protective coatings
Metal oxide films such as SiO2 are known to provide an effective barrier to the transport of moisture as well as gaseous species through polymeric films. Such thin film coatings have a tendency to crack upon flexure of the polymeric substrate. Sputter co-deposition of SiO2 with 4 to 15 percent fluoropolymers was demonstrated to produce thin films with glass-like barrier properties that have significant increases in strain to failure over pure glass films which improves their tolerance to flexure on polymeric substrates. Deposition techniques capable of producing these films on polymeric substrates are suitable for durable food packaging and oxidation/corrosion protection applications
Is There A String Theory Landscape
We examine recent claims of a large set of flux compactification solutions of
string theory. We conclude that the arguments for AdS solutions are plausible.
The analysis of meta-stable dS solutions inevitably leads to situations where
long distance effective field theory breaks down. We then examine whether these
solutions are likely to lead to a description of the real world. We conclude
that one must invoke a strong version of the anthropic principle. We explain
why it is likely that this leads to a prediction of low energy supersymmetry
breaking, but that many features of anthropically selected flux
compactifications are likely to disagree with experiment.Comment: 39 pages, Latex, ``Terminology surrounding the anthropic principle
revised to conform with accepted usage. More history of the anthropic
principle included. Various references added.
Closed String Tachyons and Their Implications for Non-Supersymmetric Strings
Closed string tachyons have long been somewhat mysterious. We note that there
is often a regime in the classical moduli space in which one can systematically
compute the effective action for such fields. In this regime, the tachyon is
light, and cannot be integrated out. Instead, one must consider the combined
dynamics of gravitons, moduli, tachyons and other light fields. We compute the
action and find that the quartic term for the tachyon is positive in the field
definition where the tachyon has no derivative coupling to the radion. We study
the evolution of isotropic, homogeneous configurations and find that typically
the system is driven to regions where the calculation is no longer under
control.Comment: 10 pages, no figures, references adde
Remarks on the Racetrack Scheme
There are only a small number of ideas for stabilizing the moduli of string
theory. One of the most appealing of these is the racetrack mechanism, in which
a delicate interplay between two strongly interacting gauge groups fixes the
value of the coupling constant. In this note, we explore this scenario. We find
that quite generally, some number of discrete tunings are required in order
that the mechanism yield a small gauge coupling. Even then, there is no sense
in which a weak coupling approximation is valid. On the other hand, certain
holomorphic quantities can be computed, so such a scheme is in principle
predictive. Searching for models which realize this mechanism is thus of great
interest. We also remark on cosmology in these schemes.Comment: 20 pp, latex, discussion of calculability modifie
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