Effect of Image Forces on Polyelectrolyte Adsorption at a Charged Surface

The adsorption of flexible and highly charged polyelectrolytes onto oppositely charged planar surfaces is investigated by means of Monte Carlo simulations. The effect of image forces stemming from the dielectric discontinuity at the substrate interface is considered. The influence, at fixed polyelectrolyte volume fraction, of chain length and surface-charge density is also considered. A detailed structural study, including monomer and fluid charge distributions, is provided. It is demonstrated that image forces can considerably reduce the degree of polyelectrolyte adsorption and concomitantly inhibit the charge inversion of the substrate by polyelectrolytes.Comment: 19 pages - 7 eps figs - RevTex 4 - submitted for publicatio

High Fidelity State Transfer Over an Unmodulated Linear XY Spin Chain

We provide a class of initial encodings that can be sent with a high fidelity over an unmodulated, linear, XY spin chain. As an example, an average fidelity of ninety-six percent can be obtained using an eleven-spin encoding to transmit a state over a chain containing ten-thousand spins. An analysis of the magnetic field dependence is given, and conditions for field optimization are provided.Comment: Replaced with published version. 8 pages, 5 figure

Scorpion: Close Air Support (CAS) aircraft

The objective is to outline the results of the preliminary design of the Scorpion, a proposed close air support aircraft. The results obtained include complete preliminary analysis of the aircraft in the areas of aerodynamics, structures, avionics and electronics, stability and control, weight and balance, propulsion systems, and costs. A conventional wing, twin jet, twin-tail aircraft was chosen to maximize the desirable characteristics. The Scorpion will feature low speed maneuverability, high survivability, low cost, and low maintenance. The life cycle cost per aircraft will be 17.5 million dollars. The maximum takeoff weight will be 52,760 pounds. Wing loading will be 90 psf. The thrust to weight will be 0.6 lbs/lb. This aircraft meets the specified mission requirements. Some modifications have been suggested to further optimize the design

Clearinghouse Default Resources: Theory and Empirical Analysis

Clearinghouses insure trades. Acting as a central counterparty (CCP), clearinghouses consolidate financial exposures across multiple institutions, aiding the efficient management of counterparty credit risk. In this thesis, we study the decision problem faced by for-profit clearinghouses, focusing on primary economic incentives driving their determination of layers of loss-absorbing capital. The clearinghouse's loss-allocation mechanism, referred to as the default waterfall, governs the allocation and management of counterparty risk. This stock of loss-absorbing capital typically consists of initial margins, default funds, and the clearinghouse's contributed equity. We separate the overall decision problem into two distinct subproblems and study them individually. The first is the clearinghouse's choice of initial margin and clearing fee requirements, and the second involves its choice of resources further down the waterfall, namely the default funds and clearinghouse equity. We solve for the clearinghouse's equilibrium choices in both cases explicitly, and address the different economic roles they play in the clearinghouse's profit-maximization process. The models presented in this thesis show, without exception, that clearinghouse choices should depend not only on the riskiness of the cleared position but also on market and participants' characteristics such as default probabilities, fundamental value, and funding opportunity cost. Our results have important policy implications. For instance, we predict a counteracting force that dampens monetary easing enacted via low interest rate policies. When funding opportunity costs are low, our research shows that clearinghouses employ highly conservative margin and default funds, which tie up capital and credit. This is supported by the low interest rate environment following the financial crisis of 2007--08. In addition to low productivity growth and return on capital, major banks have chosen to accumulate large cash piles on their balance sheets rather than increase lending. In terms of systemic risk, our empirical work, joint with the U.S. Commodity Futures Trading Commission (CFTC), points to the possibility of destabilizing loss and margin spirals: in the terminology of Brunnermeier and Pedersen (2009), we argue that a major clearinghouse's behavior is consistent with that of an uninformed financier and that common shocks to credit quality can lead to tightening margin constraints

Reassessing the Duration of the Second Stage of Labor in Relation to Maternal and Neonatal Morbidity.

OBJECTIVE: To assess the morbidity associated with continuing the second-stage duration of labor, weighing the probability of spontaneous vaginal birth without morbidity compared with birth with serious maternal or neonatal complications. METHODS: In a retrospective cohort, we analyzed singleton, vertex births at 36 weeks of gestation or greater without prior cesarean delivery (n=43,810 nulliparous and 59,605 multiparous women). We calculated rates of spontaneous vaginal birth and composite serious maternal or neonatal complications. Results were stratified by parity (nulliparous or multiparous) and epidural status (yes or no). Competing risks models were created for 1) spontaneous vaginal birth with no morbidity, 2) birth with maternal or neonatal morbidity, and 3) no spontaneous vaginal birth and no morbidity, and our main interest was in comparing number 1 against number 2. RESULTS: Rates of spontaneous vaginal birth without morbidity were slightly higher after the first half hour (greater than 0.5-1.0 hours) for nulliparous women, after which rates decreased with increasing second-stage duration. For multiparous women, rates of spontaneous vaginal birth without morbidity decreased with increasing second-stage duration. For illustration, for a nulliparous woman with an epidural at 3.0 hours of the second stage of labor who extended by another 1.0 hour, her likelihood of delivering by spontaneous vaginal birth was 31.4% compared with her likelihood of birth with any serious complication in the subsequent hour, which was 7.6%. The percentage of cesarean deliveries for nonreassuring fetal heart rate tracing were higher for women without compared with women with an epidural. CONCLUSION: Rates of spontaneous vaginal birth without serious morbidity steadily decreased for increasing second-stage duration except for the first half hour for nulliparous women. We did not observe an inflection point at a particular hour mark for either spontaneous vaginal delivery without morbidity or births with morbidity. Our findings will assist in decision-making for extending second-stage duration

Comparison of two efficient methods for calculating partition functions

In the long-time pursuit of the solution to calculate the partition function (or free energy) of condensed matter, Monte-Carlo-based nested sampling should be the state-of-the-art method, and very recently, we established a direct integral approach that works at least four orders faster. In present work, the above two methods were applied to solid argon at temperatures up to $300$K, and the derived internal energy and pressure were compared with the molecular dynamics simulation as well as experimental measurements, showing that the calculation precision of our approach is about 10 times higher than that of the nested sampling method.Comment: 6 pages, 4 figure