Spectral function at high missing energies and momenta

The nuclear spectral function at high missing energies and momenta has been determined from a self-consistent calculation of the Green's function in nuclear matter using realistic nucleon-nucleon interactions. The results are compared with recent experimental data derived from ($e,e'p$) reactions on $^{12}C$. A rather good agreement is obtained if the Green's functions are calculated in a non-perturbative way.Comment: 10 pages, 3 figure

Individual and Neighborhood Impacts of Neighborhood Reinvestment's Homeownership Pilot Program

The benefits of owning versus renting a home have been extolled by policy makers for many years, and there is substantial recent research to support those views. Yet the research supporting these claims largely has been conducted on general samples of homeowners. Low- and moderate-income homeowners may have a different experience due to difficulties in keeping up with housing-related payments or a difference in the quality of the homes being purchased. A major objective of this report is to assess the impacts of home ownership on a sample of low- and moderate-income homebuyers.We also know very little about the experience of lower-income homebuyers after they purchase their homes. To what extent do low-income homebuyers experience unexpected costs associated with maintenance or repairs? What proportion of low-income buyers take out home equity loans and what do they use the funds for? What proportion of low-income homebuyers default on their loans? What do buyers feel are the greatest advantages and challenges to owning a home? Answers to these questions may provide insight into how prospective lower-income homebuyers can be better prepared for home ownership.The research described in this report involved a sample of persons who graduated from home-ownership classes taught by eight NeighborWorks organizations that participated in the Neighborhood Reinvestment Homeownership Pilot program. Neighborhood Reinvestment has encouraged its affiliated NeighborWorks organizations to offer services designed to increase access to home ownership among low- and moderate-income families. Building on Neighborhood Reinvestment's Campaign for Home Ownership, the Homeownership Pilot program was designed to assist low- and moderate-income households to obtain home ownership by providing them with counseling, down-payment assistance and affordable loans.This report is the third of three reports on the implementation, outcomes and impacts of the Homeownership Pilot program. The first report, entitled An Assessment of Neighborhood Reinvestment's Homeownership Pilot Program: A Preliminary Report (2000), covered the early implementation of the Pilot. The second report, entitled Supporting the American Dream of Home Ownership: An Assessment of Neighborhood Reinvestment's Homeownership Pilot Program (2002), covers the outcomes of the Homeownership Pilot, including the number of persons counseled and new homebuyers assisted. This final report was designed to:1. Assess the proportion of customers trained by NeighborWorks organizations who go on to buy homes, as well as the factors that predict who among those graduating from the homeownership training go on to buy homes and who do not.2. Assess both the social and financial impacts of buying a home on the program participants.3. Assess the postpurchase experience of low-income homebuyers.4. Assess the loan repayment experience of a sample of the affordable loans held by Neighborhood Housing Services of America (NHSA).5. Assess changes in the Pilot program target areas before, during and after the Pilot program was in effect

Incomplete cost pass-through under deep habits

A number of empirical studies document that marginal cost shocks are not fully passed through to prices at the firm level and that prices are substantially less volatile than costs. We show that in the relative-deep-habits model of Ravn, Schmitt-Grohe, and Uribe (2006), firm-specific marginal cost shocks are not fully passed through to product prices. That is, in response to a firm-specific increase in marginal costs, prices rise, but by less than marginal costs leading to a decline in the firm-specific markup of prices over marginal costs. Pass-through is predicted to be even lower when shocks to marginal costs are anticipated by firms. In our model, unanticipated firm-specific cost shocks lead to incomplete pass-through (or a decline in markups) of about 20 percent and anticipated cost shocks are associated with incomplete pass-through of about 50 percent. The model predicts that cost pass-through is increasing in the persistence of marginal cost shocks and U-shaped in the strength of habits. The relative-deep-habits model implies that conditional on marginal cost disturbances, prices are less volatile than marginal costs

The macroeconomics of subsistence points

This paper explores the macroeconomic consequences of preferences displaying a subsistence point. It departs from the existing related literature by assuming that subsistence points are specific to each variety of goods rather than to the composite consumption good. We show that this simple feature makes the price elasticity of demand for individual goods procyclical. As a result, markups behave countercyclically in equilibrium. This implication is in line with the available empirical evidence

Supporting the American Dream of Homeownership: An Assessment of Neighborhood Reinvestment's Home Ownership Pilot Program

Based on recommendations from a group of NeighborWorks organization (NWO) directors, Neighborhood Reinvestment initiated the Campaign for Home Ownership in 1993. That campaign provided NWOs with both funding and technical assistance to expand homeownership opportunities in the communities they serve. Based on the experiences of organizations involved with that campaign, Neighborhood Reinvestment staff distilled a model homeownership assistance strategy they call Full-Cycle Lending. This model includes six components: partnership building, pre-purchase home-buyer education, flexible loan products, property services, post-purchase counseling and neighborhood impact. Based on the success of this first five-year Campaign, Neighborhood Reinvestment supported a second five-year campaign called the Campaign for Home Ownership 2002.In 1998 Congress authorized $25 million for a NeighborWorks Home Ownership Pilot program designed to leverage additional local support and test new strategies for assisting first-time home buyers. In less than four months, the Neighborhood Reinvestment Home Ownership Campaign staff developed and implemented specific program guidelines for the distribution of funds to local NWOs. These guidelines allowed NWOs great flexibility in the use of Pilot funds including using the funds for upgrading computers, hiring staff, developing marketing plans and programs, capitalizing loan funds, providing down payment assistance as well as other uses.Campaign staff developed guidelines for three funding categories, A, B, and C, designed to respond to the different needs of NWOs. Category A grants (up to$500,000) were to assist NWOs that were already assisting 30 or more home buyers a year increase the number of home buyers assisted. Category B grants (up to $500,000) were to assist NWOs that were already assisting a large number of new home buyers enhance the positive impacts of home ownership on their target areas by undertaking other neighborhood improvement activities as well as increasing the number of home buyers assisted. Category C grants (up to$50,000) were to assist NWOs that were assisting a relatively low number of new home buyers build their capacities to do so. A total of 35 Category A grants were made, nine Category B grants and 40 Category C grants.To assist Campaign and Pilot sites in achieving their goals, Neighborhood Reinvestment provides several types of technical assistance. The semi-annual Neighborhood Reinvestment Training Institute offers a variety of courses on developing homeownership promotion programs and home-owner education methods. Neighborhood Reinvestment has also developed an extensive array of marketing materials that can be used by Campaign and Pilot organizations. Finally, Neighborhood Reinvestment Campaign and field staff assist participating organizations with special challenges as they arise.This report is the second of three reports evaluating the outcomes, implementation process and impacts of the Pilot. The outcome evaluation was designed to document the results of the Pilot including the number of persons trained and/or counseled, the number of new home owners assisted, and the value of housing units purchased, built or rehabilitated with the assistance of the Pilot organizations. This evaluation is based on information provided to Neighborhood Reinvestment by participating NWOs. The process evaluation was designed to document and evaluate the efforts of Neighborhood Reinvestment and participating NWOs in planning and implementing the Pilot programs. This part of the evaluation is based on interviews conducted in two rounds of site visits to eight Category A and B Pilot programs -- once in the fall of 1999 and once in the spring and summer of 2001. Finally, the impact evaluation was designed to assess the influence of the Pilot on the participating NWOs and their clients. The evaluation is based on interviews with NWO staff and focus groups of new home owners assisted in the eight sites visited

Fluence Dependence of Charge Collection of irradiated Pixel Sensors

The barrel region of the CMS pixel detector will be equipped with ``n-in-n'' type silicon sensors. They are processed on DOFZ material, use the moderated p-spray technique and feature a bias grid. The latter leads to a small fraction of the pixel area to be less sensitive to particles. In order to quantify this inefficiency prototype pixel sensors irradiated to particle fluences between $4.7\times 10^{13}$ and 2.6\times 10^{15} \Neq have been bump bonded to un-irradiated readout chips and tested using high energy pions at the H2 beam line of the CERN SPS. The readout chip allows a non zero suppressed analogue readout and is therefore well suited to measure the charge collection properties of the sensors. In this paper we discuss the fluence dependence of the collected signal and the particle detection efficiency. Further the position dependence of the efficiency is investigated.Comment: 11 Pages, Presented at the 5th Int. Conf. on Radiation Effects on Semiconductor Materials Detectors and Devices, October 10-13, 2004 in Florence, Italy, v3: more typos corrected, minor changes required by the refere

Pseudogap at hot spots in the two-dimensional Hubbard model at weak coupling

We analyze the interaction-induced renormalization of single-particle excitations in the two-dimensional Hubbard model at weak coupling using the Wick-ordered version of the functional renormalization group. The self energy is computed for real frequencies by integrating a flow equation with renormalized two-particle interactions. In the vicinity of hot spots, that is points where the Fermi surface intersects the umklapp surface, self energy effects beyond the usual quasi-particle renormalizations and damping occur near instabilities of the normal, metallic phase. Strongly enhanced renormalized interactions between particles at different hot spots generate a pronounced low-energy peak in the imaginary part of the self energy, leading to a pseudogap-like double-peak structure in the spectral function for single-particle excitations.Comment: 14 pages, 7 figure

Interaction flow method for many-fermion systems

We propose an interaction flow scheme that sums up the perturbation expansion of many-particle systems by successively increasing the interaction strength. It combines the unbiasedness of renormalization group methods with the simplicity of straight-forward perturbation theory. Applying the scheme to fermions in one dimension and to the two-dimensional Hubbard model we find that at one-loop level and low temperatures there is ample agreement with previous one-loop renormalization group approaches. We furthermore present results for the momentum-dependence of spin, charge and pairing interactions in the two-dimensional Hubbard model.Comment: 14 pages, 14 figure

Tests of silicon sensors for the CMS pixel detector

The tracking system of the CMS experiment, currently under construction at the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland), will include a silicon pixel detector providing three spacial measurements in its final configuration for tracks produced in high energy pp collisions. In this paper we present the results of test beam measurements performed at CERN on irradiated silicon pixel sensors. Lorentz angle and charge collection efficiency were measured for two sensor designs and at various bias voltages.Comment: Talk presented at 6th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, September 29-October 1, 2003, Firenze, Italy. Proceedings will be published in Nuclear Instr. & Methods in Phys. Research, Section

Generalized modularity matrices

Various modularity matrices appeared in the recent literature on network analysis and algebraic graph theory. Their purpose is to allow writing as quadratic forms certain combinatorial functions appearing in the framework of graph clustering problems. In this paper we put in evidence certain common traits of various modularity matrices and shed light on their spectral properties that are at the basis of various theoretical results and practical spectral-type algorithms for community detection