V-378A: A modified bismaleimide for advanced composites

Addition polyimides cure with no evolution of gaseous by-products at relatively low temperatures and may be cured at low pressures to yield composites with excellent hot-wet strength retention. These properaties have made them excellent candidates as matrix resins for advanced composites. However, commercially available bismaleimides are solids and difficult to handle in preimpregnated form. V-378A is an addition polyimide composed of a mixture of bismaleimides and other reactive ingredients formulated to provide good prepreg properties and handling, facile cure and excellent composite mechanical properties. Several curing mechanisms are utilized to provide the characteristics exhibited by V-378A. Part of the mechanism is free radial and takes place at ambient temperature and above. Other mechanisms are principally Diels-Alder in nature. V-378A prepregs are tacky at ambient temperature, but do not have long tacky outlife similar to some epoxies. V-378A yields composites which exhibit hot-wet strength retention which is superior to that provided by epoxy resin systems

Fractional step methods for the Navier-Stokes equations on non-staggered grids

The Navier-Stokes equations are solved on a non-staggered grid using a semi-implicit fractional step method in both iterative and non-iterative form. It is shown that the iterative scheme in standard form is second-order accurate in timei, but is very slow to integrate as a result of the non-elliptic pressure coupling at the grid scale. Inclusion of additional terms into the pressure correction equation for the iterative scheme ensures an elliptic pressure coupling at the grid scale, but introduces a first order in time error into the scheme, leading to a reduction in solution accuracy. The non-iterative scheme is shown to be second order accurate in time in standard form and to be considerably more efficient than the iterative scheme

Intrinsic hole mobility and trapping in a regio-regular poly(thiophene)

The transport properties of high-performance thin-film transistors (TFT) made with a regio-regular poly(thiophene) semiconductor (PQT-12) are reported. The room-temperature field-effect mobility of the devices varied between 0.004 cm2/V s and 0.1 cm2/V s and was controlled through thermal processing of the material, which modified the structural order. The transport properties of TFTs were studied as a function of temperature. The field-effect mobility is thermally activated in all films at T<200 K and the activation energy depends on the charge density in the channel. The experimental data is compared to theoretical models for transport, and we argue that a model based on the existence of a mobility edge and an exponential distribution of traps provides the best interpretation of the data. The differences in room-temperature mobility are attributed to different widths of the shallow localized state distribution at the edge of the valence band due to structural disorder in the film. The free carrier mobility of the mobile states in the ordered regions of the film is the same in all structural modifications and is estimated to be between 1 and 4 cm2/V s.Comment: 20 pages, 8 figure

Ultrafast harmonic mode-locking of monolithic compound-cavity laser diodes incorporating photonic-bandgap reflectors

We present the first demonstration of reproducible harmonic mode-locked operation from a novel design of monolithic semiconductor laser comprising a compound cavity formed by a 1-D photonic-bandgap (PBG) mirror. Mode-locking (ML) is achieved at a harmonic of the fundamental round-trip frequency with pulse repetition rates from 131 GHz up to a record high frequency of 2.1 THz. The devices are fabricated from GaAs-Al-GaAs material emitting at a wavelength of 860 nm and incorporate two gain sections with an etched PBG reflector between them, and a saturable absorber section. Autocorrelation studies are reported which allow the device behavior for different ML frequencies, compound cavity ratios, and type and number of intra-cavity reflectors to be analyzed. The highly reflective PBG microstructures are shown to be essential for subharmonic-free ML operation of the high-frequency devices. We have also demonstrated that the single PBG reflector can be replaced by two separate features with lower optical loss. These lasers may find applications in terahertz; imaging, medicine, ultrafast optical links, and atmospheric sensing

ReCon: Revealing and Controlling PII Leaks in Mobile Network Traffic

It is well known that apps running on mobile devices extensively track and leak users' personally identifiable information (PII); however, these users have little visibility into PII leaked through the network traffic generated by their devices, and have poor control over how, when and where that traffic is sent and handled by third parties. In this paper, we present the design, implementation, and evaluation of ReCon: a cross-platform system that reveals PII leaks and gives users control over them without requiring any special privileges or custom OSes. ReCon leverages machine learning to reveal potential PII leaks by inspecting network traffic, and provides a visualization tool to empower users with the ability to control these leaks via blocking or substitution of PII. We evaluate ReCon's effectiveness with measurements from controlled experiments using leaks from the 100 most popular iOS, Android, and Windows Phone apps, and via an IRB-approved user study with 92 participants. We show that ReCon is accurate, efficient, and identifies a wider range of PII than previous approaches.Comment: Please use MobiSys version when referencing this work: http://dl.acm.org/citation.cfm?id=2906392. 18 pages, recon.meddle.mob

What factors determine the choice of public engagement undertaken by health technology assessment decision-making organizations?

Purpose: Public engagement in health technology assessment (HTA) is increasingly considered crucial for good decision-making. Determining the “right” type of engagement activity is key in achieving the appropriate consideration of public values. Little is known about the factors that determine how HTA organizations decide on their method of public engagement, and there are a number of possible factors that might shape these decisions. This paper seeks to understand the potential drivers of public engagement choice from an organizational perspective. Design/Methodology/: The published HTA literature is reviewed alongside existing frameworks of public engagement in order to elucidate key factors influencing the choice of public engagement process undertaken by HTA organizations. A conceptual framework is then developed to illustrate the factors identified from the literature that appear to influence public engagement choice. Findings: Determining the type of public engagement to be undertaken in HTA is based on multiple factors, some of which are not always explicitly acknowledged. These factors include: perceived complexity of the policymaking issue, perceived impact of the decision, transparency and opportunities for public involvement in governance, as well as time and resource constraints. The influence of these factors varies depending on the context, indicating that a one size fits all approach to public engagement may not be effective. Originality/value: Awareness of the various factors that might influence the type of public engagement undertaken would enable decision-makers to reflect on their choices and be more accountable and transparent about their choice of engagement process in eliciting public values and preferences in a HTA organization.SW was in receipt of an Australian Postgraduate Awar

Test of mode coupling theory for a supercooled liquid of diatomic molecules.I. Translational degrees of freedom

A molecular dynamics simulation is performed for a supercooled liquid of rigid diatomic molecules. The time-dependent self and collective density correlators of the molecular centers of mass are determined and compared with the predictions of the ideal mode coupling theory (MCT) for simple liquids. This is done in real as well as in momentum space. One of the main results is the existence of a unique transition temperature T_c, where the dynamics crosses over from an ergodic to a quasi-nonergodic behavior. The value for T_c agrees with that found earlier for the orientational dynamics within the error bars. In the beta- regime of MCT the factorization of space- and time dependence is satisfactorily fulfilled for both types of correlations. The first scaling law of ideal MCT holds in the von Schweidler regime, only, since the validity of the critical law can not be confirmed, due to a strong interference with the microscopic dynamics. In this first scaling regime a consistent description within ideal MCT emerges only, if the next order correction to the asymptotic law is taken into account. This correction is almost negligible for q=q_max, the position of the main peak in the static structure factor S(q), but becomes important for q=q_min, the position of its first minimum. The second scaling law, i.e. the time-temperature superposition principle, holds reasonably well for the self and collective density correlators and different values for q. The alpha-relaxation times tau_q^(s) and tau_q follow a power law in T-T_c over 2 -- 3 decades. The corresponding exponent gamma is weakly q-dependent and is around 2.55. This value is in agreement with the one predicted by MCT from the value of the von Schweidler exponent but at variance with the corresponding exponent gammaComment: 14 pages of RevTex, 19 figure

A predictive model for kidney transplant graft survival using machine learning

Kidney transplantation is the best treatment for end-stage renal failure patients. The predominant method used for kidney quality assessment is the Cox regression-based, kidney donor risk index. A machine learning method may provide improved prediction of transplant outcomes and help decision-making. A popular tree-based machine learning method, random forest, was trained and evaluated with the same data originally used to develop the risk index (70,242 observations from 1995-2005). The random forest successfully predicted an additional 2,148 transplants than the risk index with equal type II error rates of 10%. Predicted results were analyzed with follow-up survival outcomes up to 240 months after transplant using Kaplan-Meier analysis and confirmed that the random forest performed significantly better than the risk index (p<0.05). The random forest predicted significantly more successful and longer-surviving transplants than the risk index. Random forests and other machine learning models may improve transplant decisions.Comment: This work has been published: Pahl ES, Street WN, Johnson HJ, Reed AI. "A Predictive Model for Kidney Transplant Graft Survival Using Machine Learning." 4th International Conference on Computer Science and Information Technology (COMIT 2020), November 28-29, 2020, Dubai, UAE. ISBN: 978-1-925953-30-5. Volume 10, Number 16.10.5121/csit.2020.10160

The New Element Californium (Atomic Number 98)

Definite identification has been made of an isotope of the element with atomic number 98 through the irradiation of Cm{sup 242} with about 35-Mev helium ions in the Berkeley Crocker Laboratory 60-inch cyclotron. The isotope which has been identified has an observed half-life of about 45 minutes and is thought to have the mass number 244. The observed mode of decay of 98{sup 244} is through the emission of alpha-particles, with energy of about 7.1 Mev, which agrees with predictions. Other considerations involving the systematics of radioactivity in this region indicate that it should also be unstable toward decay by electron capture. The chemical separation and identification of the new element was accomplished through the use of ion exchange adsorption methods employing the resin Dowex-50. The element 98 isotope appears in the eka-dysprosium position on elution curves containing berkelium and curium as reference points--that is, it precedes berkelium and curium off the column in like manner that dysprosium precedes terbium and gadolinium. The experiments so far have revealed only the tripositive oxidation state of eka-dysprosium character and suggest either that higher oxidation states are not stable in aqueous solutions or that the rates of oxidation are slow. The successful identification of so small an amount of an isotope of element 98 was possible only through having made accurate predictions of the chemical and radioactive properties