Cold Atomic Collisions: Coherent Control of Penning and Associative Ionization

Coherent Control techniques are computationally applied to cold (1mK < T < 1 K) and ultracold (T < 1 microK) Ne*(3s,3P2) + Ar(1S0) collisions. We show that by using various initial superpositions of the Ne*(3s,3P2) M = {-2,-1,0,1,2} Zeeman sub-levels it is possible to reduce the Penning Ionization (PI) and Associative Ionization (AI) cross sections by as much as four orders of magnitude. It is also possible to drastically change the ratio of these two processes. The results are based on combining, within the "Rotating Atom Approximation", empirical and ab-initio ionization-widths.Comment: 4 pages, 2 tables, 2 figure

Decomposing the foreclosure crisis: House price depreciation versus bad underwriting

We estimate a model of foreclosure using a data set that includes every residential mortgage, purchase-and-sale, and foreclosure transaction in Massachusetts from 1989 to 2008. We address the identification issues related to the estimation of the effects of house prices on residential foreclosures. We then use the model to study the dramatic increase in foreclosures that occurred in Massachusetts between 2005 and 2008 and conclude that the foreclosure crisis was primarily driven by the severe decline in housing prices that began in the latter part of 2005, not by a relaxation of underwriting standards on which much of the prevailing literature has focused. We argue that relaxed underwriting standards did severely aggravate the crisis by creating a class of homeowners who were particularly vulnerable to the decline in prices. But, as we show in our counterfactual analysis, that emergence alone, in the absence of a price collapse, would not have resulted in the substantial foreclosure boom that was experienced.

Adjoints of rationally induced composition operators

We give an elementary proof of a formula recently obtained by Hammond, Moorhouse, and Robbins for the adjoint of a rationally induced composition operator on the Hardy space H^2. We discuss some variants and implications of this formula, and use it to provide a sufficient condition for a rationally induced composition operator adjoint to be a compact perturbation of a weighted composition operator.Comment: 21 pages, Published Versio

Decomposing the foreclosure crisis: House price depreciation versus vad underwriting

We estimate a model of foreclosure using a data set that includes every residential mortgage, purchase-and-sale, and foreclosure transaction in Massachusetts from 1989 to 2008. We address the identification issues related to the estimation of the effects of house prices on residential foreclosures. We then use the model to study the dramatic increase in foreclosures that occurred in Massachusetts between 2005 and 2008 and conclude that the foreclosure crisis was primarily driven by the severe decline in housing prices that began in the latter part of 2005, not by a relaxation of underwriting standards on which much of the prevailing literature has focused. We argue that relaxed underwriting standards did severely aggravate the crisis by creating a class of homeowners who were particularly vulnerable to the decline in prices. But, as we show in our counterfactual analysis, that emergence alone, in the absence of a price collapse, would not have resulted in the substantial foreclosure boom that was experienced

The Effect of Boundary Conditions on Structure Formation in Fuzzy Dark Matter

We illustrate the effect of boundary conditions on the evolution of structure in Fuzzy Dark Matter. Scenarios explored include the evolution of single, ground-state equilibrium solutions of the Schr\"odinger-Poisson system, the relaxation of a Gaussian density fluctuation, mergers of two equilibrium configurations, and the random merger of many solitons. For comparison, each scenario is evolved twice, with isolation boundary conditions and periodic boundary conditions, the two commonly used to simulate isolated systems and structure formation, respectively. Replacing isolation boundary conditions by periodic boundary conditions changes the domain topology and dynamics of each scenario, by affecting the outcome of gravitational cooling. With periodic boundary conditions, the ground-state equilibrium solution and Gaussian fluctuation each evolve toward the single equilibrium solitonic core of the isolated case, but surrounded by a tail, unlike the isolated versions. The case of head-on, binary mergers illustrates additional effects, caused by the pull suffered by the system due to the infinite network of periodic images along each direction of the domain. Binary merger with angular momentum is the first scenario we found in which the tail has a polynomial profile when using a periodic domain. Finally, the 3D merger of many, randomly-placed solitonic cores of different mass makes a solitonic core surrounded by a tail with power-law-like density profile, for periodic boundary conditions, while producing a core with a much sharper fall-off in the isolated case. This suggests that the conclusion of earlier work that the ground-state equilibrium solution is an attractor for the asymptotic state is true even in 3D and for general circumstances, but only if gravitational cooling is able to carry mass and energy off to infinity, which isolation boundary conditions allow, but periodic ones do not.Comment: 17 pages, 18 figures, modifications applied in order to match the accepted version in Phys. Rev.

Coherent Control and Entanglement in the Attosecond Electron Recollision Dissociation of D2+

We examine the attosecond electron recollision dissociation of D2+ recently demonstrated experimentally [H. Niikura et al., Nature (London) 421, 826 (2003)] from a coherent control perspective. In this process, a strong laser field incident on D2 ionizes an electron, accelerates the electron in the laser field to eV energies, and then drives the electron to recollide with the parent ion, causing D2+ dissociation. A number of results are demonstrated. First, a full dimensional Strong Field Approximation (SFA) model is constructed and shown to be in agreement with the original experiment. This is then used to rigorously demonstrate that the experiment is an example of coherent pump-dump control. Second, extensions to bichromatic coherent control are proposed by considering dissociative recollision of molecules prepared in a coherent superposition of vibrational states. Third, by comparing the results to similar scenarios involving field-free attosecond scattering of independently prepared D2+ and electron wave packets, recollision dissociation is shown to provide an example of wave-packet coherent control of reactive scattering. Fourth, this analysis makes clear that it is the temporal correlations between the continuum electron and D2+ wave packet, and not entanglement, that are crucial for the sub-femtosecond probing resolution demonstrated in the experiment. This result clarifies some misconceptions regarding the importance of entanglement in the recollision probing of D2+. Finally, signatures of entanglement between the recollision electron and the atomic fragments, detectable via coincidence measurements, are identified

Effect of surface activated poly(dimethylsiloxane) on fibronectin adsorption and cell function

Cell function on biomaterials may depend on surface chemistry and concentration (as well as conformation) of protein molecules. To understand the interplay between these two effects, fibronectin (Fn) was physi-sorbed on a smooth, activated poly(dimethylsiloxane), films spun cast on silicon wafers. Contact angle goniometry, ellipsometry, Atomic force microscopy and Rutherford backscattering spectrometry were used to characterize the nanoscale roughness and thickness of the films. The films were activated by exposure to 30 min ultraviolet ozone radiation. Water contact angle measurements indicated higher hydrophobicity (\u3e 100o) prior to surface activation. Tapping mode AFM scans showed that the activation process produced a rougher substrate (Ra \u3e 0.50 nm). Fibronectin surface coverage after incubating PDMS in 2.5µg/mL of Fn was significantly higher than on non-activated surface, possibly due to favorable hydrophobic interactions between PDMS and Fn. To investigate the effect of surface activation on MC3T3-E1 osteoblast-like cells, cell spreading on PDMS and activated PDMS (30 min) coated with 2.5 µg/mL Fn was studied. Cells plated on the activated Fn-coated PDMS, for 15 min, in DMEM (with serum) showed higher cell attachment. Cell spreading after 72 h plating was clearly favored on the hydrophilic substrates as well. The increase in cell area is attributed to favorable conformational changes in absorbed Fn molecules on these substrates

Heterotic-Heterotic String Duality and Multiple K3 Fibrations

A type IIA string compactified on a Calabi-Yau manifold which admits a K3 fibration is believed to be equivalent to a heterotic string in four dimensions. We study cases where a Calabi-Yau manifold can have more than one such fibration leading to equivalences between perturbatively inequivalent heterotic strings. This allows an analysis of an example in six dimensions due to Duff, Minasian and Witten and enables us to go some way to prove a conjecture by Kachru and Vafa. The interplay between gauge groups which arise perturbatively and nonperturbatively is seen clearly in this example. As an extreme case we discuss a Calabi-Yau manifold which admits an infinite number of K3 fibrations leading to infinite set of equivalent heterotic strings.Comment: 13 pages, LaTe

Entanglement and Timing-Based Mechanisms in the Coherent Control of Scattering Processes

The coherent control of scattering processes is considered, with electron impact dissociation of H$_2^+$ used as an example. The physical mechanism underlying coherently controlled stationary state scattering is exposed by analyzing a control scenario that relies on previously established entanglement requirements between the scattering partners. Specifically, initial state entanglement assures that all collisions in the scattering volume yield the desirable scattering configuration. Scattering is controlled by preparing the particular internal state wave function that leads to the favored collisional configuration in the collision volume. This insight allows coherent control to be extended to the case of time-dependent scattering. Specifically, we identify reactive scattering scenarios using incident wave packets of translational motion where coherent control is operational and initial state entanglement is unnecessary. Both the stationary and time-dependent scenarios incorporate extended coherence features, making them physically distinct. From a theoretical point of view, this work represents a large step forward in the qualitative understanding of coherently controlled reactive scattering. From an experimental viewpoint, it offers an alternative to entanglement-based control schemes. However, both methods present significant challenges to existing experimental technologies