History versus Expectations: an Empirical Investigation

This paper provides the first empirical test of the role of history versus expectations in U.S. urban development. Starting from Paul Krugman's theoretical work in new economic geography, we test whether or not a modern city develops because of either advantageous initial conditions or by way of a self-fulfilling prophecy based on expectations of development. Using the methology developed by Granger to establish causality between two variables, but adapted to a cross-section with four time lags, we test whether asset values, that is, farmland values and housing values, anticipate urban development or vice versa. In the case of the former, we would conclude that expectations drive urban development in the U.S., and in the case of the latter we would conclude that history does. The results indicate very strongly that initial conditions, that is history, dominate the process by which one city becomes a metropolis and another languishes in the periphery.History vs. expectations; urban growth; Granger causality; economics geography

Productivity and Metropolitan Density

This paper evaluates the relationship between urban productivity and density using data on metropolitan areas. This is an alternative measure of the urban economy to the one employed by Ciccone and Hall (1996), who use data on output and education by state and employment and education by county, which excludes agricultural and mining sectors. Instead, our U.S. metropolitan area data are defined contemporaneously for the five available census years from 1950 to 1990. These data allow us to conduct both cross-sectional and panel analyses. Furthermore, since we use a model where income is a linear function of density, these data allow us to evaluate the urban system in its own right. Our results replicate the key finding of Ciccone and Hall (1996): a doubling of population density leads to about a 6% increase in productivity. Our results establish an important role for Jacobs externalities, measured by metropolitan area population.urban density; urban growth; urban productivity; Jacobs externalities; agglomeration externalities

Computer program for solving compressible nonsimilar-boundary-layer equations for laminar, transitional, or turbulent flows of a perfect gas

A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity

Finite Element Modeling and Analysis Applications in Osteogenesis Imperfecta

Understanding the biomechanics of bones in persons with osteogenesis imperfecta (OI) is a key component to further understanding the disease, optimizing treatment and quality of life, as well as injury prevention. However, it is not feasible to study bone biomechanics in vivo. Thus, modeling may play a key role in understanding how OI bones respond to the loading experienced during various activities, especially ambulation. Biomechanical modeling can provide insight into bone fracture risks, such as type and location, from single applied loads or repetitive loading. One method for obtaining this information is via a finite element analysis (FEA). FEA is a general technique for mathematically approximating solutions to boundary-value problems.1 It is a powerful computational tool with numerous applications. These numerical methods are used to obtain an output from a system of differential equations in response to boundary condition inputs in many scenarios. FEA allows for the discretization of a structure into numerous subparts (elements) for analysis. Elements represent regular strait-side geometric 2-D or 3-D shapes that enclose a finite area or volume.2 Field output variables (stress, strain, etc.) are explicitly calculated at each vertex (node) of every element.3 These outputs provide information that corresponds to bone strength and, therefore, location and risk for potential fractures

A new readily processable polyimide

As part of an effort to develop tough solvent resistance thermoplastics for potential use as structural resins on aerospace vehicles, a new processable polyimide was evaluated. The synthesis involved the reaction of a new diamine, 1,3-bis 2-(3-aminophenoxy)ethyl ether, with 3,3',4,4'-benzophenonetetracarboxylic dianhydride to form the polyamic acid and subsequent conversion of it to the polyimide. Various physical properties such as thermal stability, solvent resistance, glass transition temperature, crystalline melt temperature, melt viscosity and mechanical properties such as fracture toughness, adhesive, film and composite properties are reported. Of particular interest is the extremely high titanium to titanium tensile shear strength obtained for this polyimide

Exploration of the Neuronal Subtype Specificity of an Ethanol Responsive Gene: Glycogen Synthase Kinase 3 Beta (Gsk3b)

Exploration of the Neuronal Subtype Specificity of an Ethanol Responsive Gene: Glycogen Synthase Kinase 3 Beta (Gsk3b) Dalton Huey, Depts. of Bioinformatics, Biology & Chemistry, A. van der Vaart, G. M. Harris, and M. F. Miles, with Dr. Sarah Golding, Dept. of Biology Previous work done in our laboratory revealed that Glycogen Synthase Kinase 3 Beta (Gsk3b) functions as a hub gene in a network of genes regulated by acute ethanol in the medial prefrontal cortex (mPFC) across a mouse genetic panel. Adult mice treated with acute ethanol showed increased phosphorylation of GSK3B on the Ser9 residue in prefrontal cortex. Subsequent viral-mediated overexpression of Gsk3bin mouse mPFC caused an increase in ethanol consumption and pharmacological inhibition of GSK3B decreased ethanol consumption. However, it is unknown what neuron subtypes are driving this change in behavior. Here, we provide evidence that deletion of Gsk3bin Camk2a+ glutamatergic neurons of the mPFC results in a decrease in ethanol consumption in both continuous and intermittent access drinking paradigms. Furthermore, we have recently designed and validated a plasmid for Cre-dependent overexpression of Gsk3b, along with a Cre-dependent reporter as a control. These plasmids are planned for use in conjunction with different Cre drivers for viral-mediated expression in any cell type. Dissection of the neural circuitry of this ethanol responsive pathway can lead to a better assessment of Gsk3bas a potential target for the treatment of alcohol use disorders. Work supported by grants R01A027581 and P50AA022537 to MFM.https://scholarscompass.vcu.edu/uresposters/1313/thumbnail.jp

Recent Developments in Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is an uncommon genetic bone disease associated with brittle bones and fractures in children and adults. Although OI is most commonly associated with mutations of the genes for type I collagen, many other genes (some associated with type I collagen processing) have now been identified. The genetics of OI and advances in our understanding of the biomechanical properties of OI bone are reviewed in this article. Treatment includes physiotherapy, fall prevention, and sometimes orthopedic procedures. In this brief review, we will also discuss current understanding of pharmacologic therapies for treatment of OI

X-ray Emission from Extragalactic Jets

This review focuses on the X-ray emission processes of extra-galactic jets on scales resolvable by the sub arcsec resolution of the Chandra X-ray Observatory. It is divided into 4 parts. The introductory chapter reviews the classical problems for jets, as well as those associated directly with the X-ray emission. Throughout this section, we deal with the dualisms of low powered radio sources versus high powered radio galaxies and quasars; synchrotron models versus inverse Compton models; and the distinction between the relativistic plasma responsible for the received radiation and the medium responsible for the transport of energy down the jet. The second part collects the observational and inferred parameters for the currently detected X-ray jets and attempts to put their relative sizes and luminosities in perspective. In part 3, we first give the relevant radio and optical jet characteristics, and then examine the details of the X-ray data and how they can be related to various jet attributes. The last section is devoted to a critique of the two non-thermal emission processes and to prospects for progress in our understanding of jets.Comment: This is a version of a review article to be published (2006 Sep) in the Annual Reviews of Astronomy and Astrophysics, vol. 44, p. 463. 8 of the 12 figures have been removed from the article and are provided as separate jpg files to conserve space. There are 38 pages remaining in the text. Complete postscript and pdf versions are available at: http://hea-www.harvard.edu/~harris/Xjetreview

Motion Analysis Strategy Appropriate for 3D Kinematic Assessment of Children and Adults with Osteogenesis Imperfecta

Human motion analysis provides a quantitative means of assessing whole body and segmental motion of subjects with musculoskeletal pathologies. This chapter describes a low cost motion analysis appropriate for complete three-dimensional (3D) assessment of upper and lower extremity kinematics. The system has been designed to support lower cost outreach efforts that require accuracy and resolution on the order of classical fixed lot systems such as Vicon. The focus of this work addresses the assessment needs typically seen in adults and children with osteogenesis imperfect (OI) experiencing ambulatory and upper extremity challenges