Geographic concentration and firm survival

If localization economies are present, firms within denser industry concentrations should exhibit higher levels of performance than more isolated firms. Nevertheless, research in industrial organization that has focused on the influences on firm survival has largely ignored the potential effects from agglomeration. Recent studies in urban and regional economics suggests that agglomeration effects may be very localized. Analyses of industry concentration at the MSA or county-level may fail to detect important elements of intra-industry firm interaction that occur at the sub-MSA level. Using a highly detailed dataset on firm locations and characteristics for Texas, this paper analyses agglomeration effects on firm survival over geographic areas as small as a single mile radius. We find that greater firm density within very close proximity (within 1 mile) of firms in the same industry increases mortality rates while greater concentration over larger distances reduces mortality rates.Firm Survival, Agglomeration, Localization, and Knowledge Externalities

Research universities and regional high-tech firm start-ups and exit

If localized knowledge spillovers are present in the university setting, higher rates of both start-ups and/or survival than in the broader economy would be observed in areas that are geographically proximate to the university. Using a fully-disclosed Quarterly Census of Employment and Wages for Texas for the years 1999:3-2006:2, this paper analyzes start-ups and exit rates for high-tech firms in Texas. We find that there is evidence that the presence of a research institution will affect the likelihood of technology start-ups. However, results suggest that geographic proximity to knowledge centers does not reduce hazard rates.Entry and Survival, R & D, Regional, Urban, and Rural Analyses

Research in nonlinear structural and solid mechanics

Recent and projected advances in applied mechanics, numerical analysis, computer hardware and engineering software, and their impact on modeling and solution techniques in nonlinear structural and solid mechanics are discussed. The fields covered are rapidly changing and are strongly impacted by current and projected advances in computer hardware. To foster effective development of the technology perceptions on computing systems and nonlinear analysis software systems are presented

What blows in with the wind?

The shift toward renewable forms of energy for electricity generation in the electricity generation industry has clear implications for the spatial distribution of generating plant. Traditional forms of generation are typically located close to the load or population centers, while wind and solar-powered generation must be located where the energy source is found. In the case of wind, this has meant significant new investment in wind plant in primarily rural areas that have been in secular economic decline. This paper investigates the localized economic impacts of the rapid increase in wind power capacity at the county level in Texas. Unlike Input-Output impact analysis that relies primarily on levels of inputs to estimate gross impacts, we use traditional econometric methods to estimate net localized impacts in terms of employment, personal income, and property tax base. While we find evidence that both direct and indirect employment impacts are modest, significant increases in per capita income accompany wind power development. County and school property tax rolls also realize important benefits from the local siting of utility scale wind power

Structures and materials technology for hypersonic aerospacecraft

Major considerations in structural design of a transatmospheric aerospacecraft are discussed. The general direction of progress in structures and materials technology is indicated, and technical areas in structures and materials where further research and development is necessary are indicated. Various structural concepts under study and materials which appear to be most applicable are discussed. Structural design criteria are discussed with particular attention to the factor-of-safety approach and the probabilistic approach. Structural certification requirements for the aerospacecraft are discussed. The kinds of analyses and tests which would be required to certify the structural integrity, safety, and durability of the aerospacecraft are discussed, and the type of test facility needed to perform structural certification tests is identified

Elephants can determine ethnicity, gender, and age from acoustic cues in human voices

Animals can accrue direct fitness benefits by accurately classifying predatory threat according to the species of predator and the magnitude of risk associated with an encounter. Human predators present a particularly interesting cognitive challenge, as it is typically the case that different human subgroups pose radically different levels of danger to animals living around them. Although a number of prey species have proved able to discriminate between certain human categories on the basis of visual and olfactory cues, vocalizations potentially provide a much richer source of information. We now use controlled playback experiments to investigate whether family groups of free-ranging African elephants (Loxodonta africana) in Amboseli National Park, Kenya can use acoustic characteristics of speech to make functionally relevant distinctions between human subcategories differing not only in ethnicity but also in sex and age. Our results demonstrate that elephants can reliably discriminate between two different ethnic groups that differ in the level of threat they represent, significantly increasing their probability of defensive bunching and investigative smelling following playbacks of Maasai voices. Moreover, these responses were specific to the sex and age of Maasai presented, with the voices of Maasai women and boys, subcategories that would generally pose little threat, significantly less likely to produce these behavioral responses. Considering the long history and often pervasive predatory threat associated with humans across the globe, it is likely that abilities to precisely identify dangerous subcategories of humans on the basis of subtle voice characteristics could have been selected for in other cognitively advanced animal species

Torsional stiffness of thin-walled shells having reinforcing cores and rectangular, triangular, or diamond cross section

A theoretical investigation is presented of the torsional stiffness of thin-walled aerodynamic surfaces filled with cores which stabilize the skins. Rectangular, slender triangular, and slender diamond cross sections are considered. Results for the torsional stiffness constants are shown graphically

Advanced structures technology and aircraft safety

NASA research and development on advanced aeronautical structures technology related to flight safety is reviewed. The effort is categorized as research in the technology base and projects sponsored by the Aircraft Energy Efficiency (ACEE) Project Office. Base technology research includes mechanics of composite structures, crash dynamics, and landing dynamics. The ACEE projects involve development and fabrication of selected composite structural components for existing commercial transport aircraft. Technology emanating from this research is intended to result in airframe structures with improved efficiency and safety

Stress distributions caused by three types of loading on a circular semimonocoque cylinder with flexible rings

Equations are derived for the stress distributions caused by three types of loading on infinitely long circular, semimonocoque cylinders with flexible rings. The results are given as formula for the stringer loads and shear flows in the shell due to each type of loading. For each loading case these formulas can be used to construct tables of influence coefficients giving stringer loads and shear flows in the neighborhood of the load due to a unit magnitude of the load. (author