Wasted Talent and Broken Dreams: The Lost Potential of Undocumented Students

The current political debate over undocumented immigrants in the United States has largely ignored the plight of undocumented children. Yet children account for 1.8 million, or 15 percent, of the undocumented immigrants now living in this country. These children have, for the most part, grown up in the United States and received much of their primary and secondary educations here. But without a means to legalize their status, they are seldom able to go on to college and cannot work legally in this country. Moreover, at any time, they can be deported to countries they barely know. This wasted talent imposes economic and emotional costs on undocumented students themselves and on U.S. society as a whole. Denying undocumented students, most of whom are Hispanic, the opportunity to go to college and join the skilled workforce sends the wrong message to Hispanics about the value of a college education-and the value that U.S. society places on their education-at a time when raising the educational attainment of the Hispanic population is increasingly important to the nation's economic health

Optical properties of tensilely strained Ge nanomembranes

Group-IV semiconductors, which provide the leading materials platform of micro- electronics, are generally unsuitable for light emitting device applications because of their indirect- bandgap nature. This property currently limits the large-scale integration of electronic and photonic functionalities on Si chips. The introduction of tensile strain in Ge, which has the effect of lowering the direct conduction-band minimum relative to the indirect valleys, is a promising approach to address this challenge. Here we review recent work focused on the basic science and technology of mechanically stressed Ge nanomembranes, i.e., single-crystal sheets with thicknesses of a few tens of nanometers, which can sustain particularly large strain levels before the onset of plastic deformation. These nanomaterials have been employed to demonstrate large strain-enhanced photoluminescence, population inversion under optical pumping, and the formation of direct-bandgap Ge. Furthermore, Si-based photonic-crystal cavities have been developed that can be combined with these Ge nanomembranes without limiting their mechanical flexibility. These results highlight the potential of strained Ge as a CMOS-compatible laser material, and more in general the promise of nanomembrane strain engineering for novel device technologies.The Ge nanomembrane fabrication and characterization efforts were supported initially by DOE under Grant DE-FG02-03ER46028, and subsequently by AFOSR under Grant FA9550-14-1-0361. The development of the photonic-crystal cavities was supported by NSF under Grant ECCS-1308534. The initial photoluminescence studies were funded by NSF under Grant DMR-0907296. The contribution from several students and research scientists involved in this research at Boston University and the University of Wisconsin-Madison (including Cicek Boztug, Francesca Cavallo, Feng Chen, Xiaorui Cui, RB Jacobson, Debbie Paskiewicz, Jose Sanchez-Perez, Pornsatit Sookchoo, Faisal Sudradjat, Xiaowei Wang, and Jian Yin) is also gratefully acknowledged. (DE-FG02-03ER46028 - DOE; FA9550-14-1-0361 - AFOSR; ECCS-1308534 - NSF; DMR-0907296 - NSF)Published versio

A further improvement of the quantitative Subspace Theorem

In 2002, Evertse and Schlickewei obtained a quantitative version of the so-called Absolute Parametric Subspace Theorem. This result deals with a parametrized class of twisted heights. One of the consequences of this result is a quantitative version of the Absolute Subspace Theorem, giving an explicit upper bound for the number of subspaces containing the solutions of the Diophantine inequality under consideration. In the present paper, we further improve Evertse's and Schlickewei's quantitative version of the Absolute Parametric Subspace Theorem, and deduce an improved quantitative version of the Absolute Subspace Theorem. We combine ideas from the proof of Evertse and Schlickewei (which is basically a substantial refinement of Schmidt's proof of his Subspace Theorem from 1972, with ideas from Faltings' and Wuestholz' proof of the Subspace Theorem.Comment: 93 page

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

"May I borrow Your Filter?" Exchanging Filters to Combat Spam in a Community

Leveraging social networks in computer systems can be effective in dealing with a number of trust and security issues. Spam is one such issue where the "wisdom of crowds" can be harnessed by mining the collective knowledge of ordinary individuals. In this paper, we present a mechanism through which members of a virtual community can exchange information to combat spam. Previous attempts at collaborative spam filtering have concentrated on digest-based indexing techniques to share digests or fingerprints of emails that are known to be spam. We take a different approach and allow users to share their spam filters instead, thus dramatically reducing the amount of traffic generated in the network. The resultant diversity in the filters and cooperation in a community allows it to respond to spam in an autonomic fashion. As a test case for exchanging filters we use the popular SpamAssassin spam filtering software and show that exchanging spam filters provides an alternative method to improve spam filtering performance

Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle, and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community.Comment: 33 pages, 7 figures; accepted in Astrophys.

Estimating the underground economy by using MIMIC models: A response to T. Breusch´s critique

Breusch (2005b) critically addresses an important and challenging question: Is it reliable to use the Multiple Indicators Multiple Causes model to estimate Shadow Economy? Breusch concludes that this approach is not suitable for the purpose. Breusch’s paper highlights the different procedures and hypotheses about the estimation of the size and development of the shadow economy in three papers: Giles and Tedds (2002a), Dell’Anno and Schneider (2003) and Bajada and Schneider (2005). In this paper, we will react and provide some answers to Breusch’s criticisms with special reference to the criticisms of the Dell’Anno and Schneider (2003) paper. According with us, the MIMIC model is still one of the best approaches to this purpose.shadow economy; MIMIC model; structural modelling.

The decay of massive closed superstrings with maximum angular momentum

We study the decay of a very massive closed superstring (i.e. \alpha' M^2>> 1) in the unique state of maximum angular momentum. This is done in flat ten-dimensional spacetime and in the regime of weak string coupling, where the dominant decay channel is into two states of masses M_1, M_2. We find that the lifetime surprisingly grows with the first power of the mass M: T =c \alpha' M. We also compute the decay rate for each values of M_1, M_2. We find that, for large M, the dynamics selects only special channels of decay: modulo processes which are exponentially suppressed, for every decay into a state of given mass M_1, the mass M_2 of the other state is uniquely determined.Comment: 22 pages, 4 figure