The role of expectations in the FRB/US macroeconomic model

In the past year, the staff of the Board of Governors of the Federal Reserve System began using a new macroeconomic model of the U.S. economy referred to as the FRB/US model. This system of mathematical equations, describing interactions among economic measures such as inflation, interest rates, and gross domestic product, is one of the tools used in economic forecasting and the analysis of macroeconomic policy issues at the Board. The FRB/US model replaces the MPS model, which, with periodic revisions, had been used at the Federal Reserve Board since the early 1970s. A key feature of the new model is that expectations of future economic conditions are explicit in many of its equations. Because of this clear delineation of expectations, the FRB/US model can be used to study issues that would be difficult or impossible to study with the MPS model. For example, the new model can show how the economy's response to specific events, such as a reduction in defense spending, may vary considerably with the speed at which the public recognizes that the event has occurred or will occur.Econometric models ; Federal Reserve System ; Forecasting

Unbound Universe

Astronom

Some contractible open manifolds and coverings of manifolds in dimension three

AbstractMcMillan has shown that every irreducible, contractible, open 3-manifold is the monotone union of handlebodies (only 0- and 1-handles) and that there are uncountably many such manifolds. Work by Myers and Wright shows that no irreducible, contractible, open 3-manifold different from R3 can nontrivially cover any 3-manifold when the handlebodies all have genus one or have bounded genus. We describe a family of irreducible, contractible, open 3-manifolds that we call composite Whitehead manifolds. These manifolds have the property that when written as the monotone union of handlebodies, the handlebodies must have unbounded genus. We show that there are uncountably many composite Whitehead manifolds that nontrivially cover open 3-manifolds but do not cover a compact 3-manifold. We also show that there exist uncountably many composite Whitehead manifolds which cannot nontrivially cover any 3-manifold. It is a famous unsolved problem if any irreducible, contractible, open 3-manifold different from R3 can cover a compact 3-manifold. It is unlikely that any composite Whitehead manifold covers a compact manifold, but our techniques are not strong enough to answer this question

Chemical Abundance Constraints on White Dwarfs as Halo Dark Matter

We examine the chemical abundance constraints on a population of white dwarfs in the Halo of our Galaxy. We are motivated by microlensing evidence for massive compact halo objects (Machos) in the Galactic Halo, but our work constrains white dwarfs in the Halo regardless of what the Machos are. We focus on the composition of the material that would be ejected as the white dwarfs are formed; abundance patterns in the ejecta strongly constrain white dwarf production scenarios. Using both analytical and numerical chemical evolution models, we confirm that very strong constraints come from Galactic Pop II and extragalactic carbon abundances. We also point out that depending on the stellar model, significant nitrogen is produced rather than carbon. The combined constraints from C and N give $\Omega_{WD} h < 2 \times 10^{-4}$ from comparison with the low C and N abundances in the Ly$\alpha$ forest. We note, however, that these results are subject to uncertainties regarding the nucleosynthesis of low-metallicity stars. We thus investigate additional constraints from D and $^4$He, finding that these light elements can be kept within observational limits only for \Omega_{WD} \la 0.003 and for a white dwarf progenitor initial mass function sharply peaked at low mass (2$M_\odot$). Finally, we consider a Galactic wind, which is required to remove the ejecta accompanying white dwarf production from the galaxy. We show that such a wind can be driven by Type Ia supernovae arising from the white dwarfs themselves, but these supernovae also lead to unacceptably large abundances of iron. We conclude that abundance constraints exclude white dwarfs as Machos. (abridged)Comment: Written in AASTeX, 26 pages plus 4 ps figure

Glaucoma: Past and Present Management Techniques

This article reviews the clinical signs and diagnostic modalities appropriate for glaucoma. Classification of this disease and currently recommended treatment options are discussed

An Assessment of the Use of Structural Deformation as a Method of Determining Area of Fire Origin

Current methodologies of origin investigation have yet to include the structural deformations seen in steel buildings as a viable indicator of the area of origin of a given fire. As many steel structures are of relatively large size, it is often difficult to determine the area of origin using the typical dig and sift methods advocated in NFPA 921, especially if the extent of the fire was large and there were no witnesses as to the origin of the fire. As has been investigated for years, the performance of steel is highly affected by the application of heat. The science of predicting the deformations of steel members is such that an investigator may be able to “reverse engineer” the fire to get an idea of its relative growth rate and length of combustion even if it is not possible to compute a heat release rate curve. The information derived from careful analysis of the deformations may also yield valuable input for use in computer fire modeling. Using several example cases, this paper explores the methodology that can be applied in order to use the structural deformations as a viable tool to determine the point of origin of large, single story steel framed structures

Virus prevalence and genetic diversity across a wild bumblebee community

Viruses are key population regulators, but we have limited knowledge of the diversity and ecology of viruses. This is even the case in wild host populations that provide ecosystem services, where small fitness effects may have major ecological impacts in aggregate. One such group of hosts are the bumblebees, which have a major role in the pollination of food crops and have suffered population declines and range contractions in recent decades. In this study, we investigate the diversity of four recently discovered bumblebee viruses (Mayfield virus 1, Mayfield virus 2, River Liunaeg virus and Loch Morlich virus), and two previously known viruses that infect both wild bumblebees and managed honeybees (Acute bee paralysis virus and Slow bee paralysis virus) from isolates in Scotland. We investigate the ecological and environmental factors that determine viral presence and absence. We show that the recently discovered bumblebee viruses were more genetically diverse than the viruses shared with honeybees. Coinfection is potentially important in shaping prevalence: we found a strong positive association between River Liunaeg virus and Loch Morlich virus presence after controlling for host species, location and other relevant ecological variables. We tested for a relationship between environmental variables (temperature, UV radiation, wind speed and prevalence), but as we had few sampling sites, and thus low power for site-level analyses, we could not conclude anything regarding these variables. We also describe the relationship between the bumblebee communities at our sampling sites. This study represents a first step in the description of predictors of bumblebee infection in the wild

On the distribution of initial masses of stellar clusters inferred from synthesis models

The fundamental properties of stellar clusters, such as the age or the total initial mass in stars, are often inferred from population synthesis models. The predicted properties are then used to constrain the physical mechanisms involved in the formation of such clusters in a variety of environments. Population synthesis models cannot, however, be applied blindy to such systems. We show that synthesis models cannot be used in the usual straightforward way to small-mass clusters (say, M < few times 10**4 Mo). The reason is that the basic hypothesis underlying population synthesis (a fixed proportionality between the number of stars in the different evolutionary phases) is not fulfilled in these clusters due to their small number of stars. This incomplete sampling of the stellar mass function results in a non-gaussian distribution of the mass-luminosity ratio for clusters that share the same evolutionary conditions (age, metallicity and initial stellar mass distribution function). We review some tests that can be carried out a priori to check whether a given cluster can be analysed with the fully-sampled standard population synthesis models, or, on the contrary, a probabilistic framework must be used. This leads to a re-assessment in the estimation of the low-mass tail in the distribution function of initial masses of stellar clusters.Comment: 5 pages, 1 figure, to appear in ``Young Massive Star Clusters - Initial Conditions and Environments'', 2008, Astrophysics & Space Science, eds. E. Perez, R. de Grijs, R. M. Gonzalez Delgad