Dust cloud formation in stellar environments. II. Two-dimensional models for structure formation around AGB stars

This paper reports on computational evidence for the formation of cloud-like dust structures around C-rich AGB stars. This spatio-temporal structure formation process is caused by a radiative/thermal instability of dust forming gases as identified by Woitke et al.(2000). Our 2D (axisymmetric) models combine a time-dependent description of the dust formation process according to Gail & Sedlmayr (1988) with detailed, frequency-dependent continuum radiative transfer by means of a Monte Carlo method (Niccolini et al.2003) in an otherwise static medium (v=0). These models show that the formation of dust behind already condensed regions, which shield the stellar radiation field, is strongly favoured. In the shadow of these clouds, the temperature decreases by several hundred Kelvin which triggers the subsequent formation of dust and ensures its thermal stability. Considering an initially dust-free gas with small density inhomogeneities, we find that finger-like dust structures develop which are cooler than the surroundings and point towards the centre of the radiant emission, similar to the cometary knots observed in planetary nebulae and star formation regions. Compared to a spherical symmetric reference model, the clumpy dust distribution has little effect on the spectral energy distribution, but dominates the optical appearance in near IR monochromatic images.Comment: 16 pages, 8 figures, submitted to A&

Advances in ophthalmic drug delivery

Various strategies for ocular drug delivery are considered; from basic formulation techniques for improving availability of drugs; viscosity enhancers and mucoadhesives aid drug retention and penetration enhancers promote drug transport into the eye. The use of drug loaded contact lenses and ocular inserts allows drugs to be better placed where they are needed for more direct delivery. Developments in ocular implants gives a means to overcome the physical barriers that traditionally prevented effective treatment. Implant technologies are under development allowing long term drug delivery from a single procedure, these devices allow posterior chamber diseases to be effectively treated. Future developments could bring artificial corneas to eliminate the need for donor tissue and one-off implantable drug depots lasting the patient’s lifetime

The US-China military and defense relationship during the Obama presidency

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Deal Insurance: Representation & Warranty Insurance in Mergers & Acquisitions

Efficient contracting depends upon imposing risk on the party with superior access to information. Yet the parties in mergers and acquisitions transactions now commonly use Representation and Warranty Insurance (“RWI”) to shift this risk to a third-party insurer. Because liability and trust go together, RWI would seem to give rise to a credible commitment problem between the transacting parties, and it raises adverse selection and moral hazard problems for the insurer. This paper examines the emergence of RWI, focusing on three interrelated questions. First, how does RWI affect transactions?Second, why do transacting parties use RWI? And third, why do insurers sell RWI? The paper follows a two-fold empirical methodology. It develops data both by surveying RWI market participants—insurers, brokers, lawyers, and private equity managers—and also by analyzing a sample of over 500 acquisition agreements, approximately half of which involved RWI. Analysis of this data reveals a broad transfer of mispricing risk from buyers and sellers to insurers. RWI allows sellers to minimize risk at exit and allows buyers to control risk aversion in selecting investments. At the same time, RWI threatens to disrupt the contracting process by introducing problems of credible commitment, moral hazard, and adverse selection. Insurers’ ability to respond to these problems through shifts in the deal market and the underwriting cycle may determine whether RWI ultimately facilitates or impedes mergers and acquisitions

A Tale of Two Markets: Regulation and Innovation in Post-Crisis Mortgage and Structured Finance Markets

This Article takes the occasion of the tenth anniversary of the financial crisis to review recent developments in the structured products market, connecting the emergent pattern to post-crisis regulation. The Article tells a tale of two markets. The financial crisis stemmed from excessive risk-taking and shabby practice in the subprime home mortgage market, a market that owed its existence to the private-label, originate to securitize model. But the pre-crisis boom in private label subprime mortgage-backed securities could never have happened absent back up financing from an array of structured products and vehicles created in the capital markets—the CDOs that found their way into CDO squareds, SIVs, and synthetics, magnifying subprime credit risk and carrying it into the system’s vulnerable nodes where the bailouts occurred in 2008. The post-crisis regulatory pattern shifts the emphasis back from the end point in the causation chain (magnified risk and bailouts) to the start point (residential mortgage origination and securitization). It is only at the start point, in the world populated by consumers and their immediate counterparties, that we find anything like new prohibitions. The capital markets side of the picture is touched much more lightly. Even so, at a quick glance today’s structured products market looks like a qualitatively different place—subprime RMBS, CDOs, CDO squareds, CDO-based synthetics and SIVs are all gone. This Article takes a closer and longer look at today’s structured products market to show that the difference between now and then is more a matter of degree. The new regulatory landscape for structured products has definite borders, and it is at just those borders where the beat of financial innovation and regulatory arbitrage goes on. This activity is not centered at the banks, for there private label originate-to-securitize and investment in private label products is affirmatively discouraged by post-crisis regulation. Today’s innovation in structured products occurs at the more lightly-regulated nonbanks, which are displacing the banks at the riskier end of the residential mortgage and corporate lending markets

Synthesis of bio-functional nanomaterials in reactive plasma discharges

Plasma processing technologies have been extensively used as surface modification platforms in many biomedical applications. Particularly, plasma polymerization (PP) is a versatile deposition technology which has the potential to deliver biocompatible interfaces for a myriad of medical devices. To successfully translate new materials for specific clinical applications, the plasma process needs to be scalable and incorporate appropriate control feedback strategies. However, the plasma medium in PP is exceptionally complex and identifying the main physical quantities that allow a suitable formulation and description of the interface growth mechanisms is challenging. The first part of the thesis reports the design and optimization of a single step ion assisted PP process to create plasma-activated coatings (PAC) that meet the extreme mechanical demands for cardiovascular implants and in particular stents. An ideal working window in the parameter space is identified, and found suitable for the synthesis of PAC interfaces that are mechanically robust, hemocompatibility and allow one step covalent protein immobilization without the need for chemical processes. This window is identified by combining plasma optical emission spectroscopy (OES) with a comprehensive macroscopic process description that isolates key coating growth mechanisms. During process scalability, OES diagnostics revealed the formation of plasma polymer nanoparticles (nanoP3), usually known as plasma dust, in parallel with the deposition of PAC coatings. The second part of the thesis reports the demonstration of carbonaceous plasma nanoparticles for nanomedicine applications. By controlling nanoparticle formation and collection, nanoP3 were engineered with unique immobilization capabilities facilitating multifunctional nanocarriers. The unique surface chemistry of nanoP3, allowing a robust immobilization of the cargo without the need for intermediate functionalization strategies, has great potential to overcome major limitations of currently proposed platforms. As many of the favorable characteristics of nanoP3 are inherent to the fabrication process, this work proposes PP as a nanoparticle synthesis route with valuable potential for broad clinical and commercial applications

Understanding the effect of ultra-low nanofiller loadings on optically-transparent polycarbonate

The use of fillers in materials engineering has long been used to improve material properties such as strength, stiffness and toughness. However, these enhancements tend to occur at the detriment to optical transparency in transparent polymeric materials. Nano-sized fillers or nanofillers are thought to maintain the transparency of such materials due to their small size. Moreover because of their smaller size, nanofillers have larger interfacial areas and can therefore provide increased interaction sites (providing fine dispersion in the medium). [Continues.

TRANSIENT AND MECHANICAL PROPERTIES OF POLY(PHTHALALDEHYDE) AND THE VARIABLE FREQUENCY MICROWAVE CURING OF HIGH-PERFORMANCE THERMOSETS

Research presented in this thesis is split into two parts. The first section involves tuning the transient and mechanical properties of poly(phthaldehyde) to form a flexible, liquefiable transient material that can depolymerize upon the flick of a metaphorical switch. Such materials can be useful for devices designed to vanish into their surroundings once used. This application-based research required further understanding of how plasticizer additives work to not only make flexible films in an efficient manner, but how they can also serve to decrease the freezing point of o-phthalaldehyde, poly(phthaldehyde)’s monomer unit, upon degradation such that said devices can effectively disappear. Chapter 1 section 1.1 introduces how poly(phthalaldehyde) works as a transient material, and Chapter 1 section 1.2 describes some important fundamental concepts pertaining to how plasticizers can efficiently provide flexibility to polymers and how they work to reduce poly(phthaldehyde)’s freezing point upon depolymerization. Chapter 2 describes an initial approach used to successfully make flexible poly(phthaldehyde) films, and Chapter 3 describes an improved approach utilizing fundamental principles discussed in Chapter 1 section 1.2. Lastly, challenges regarding flexible poly(phthaldehyde)’s low strength are discussed. The second section involves studying the variable frequency microwave curing of epoxy and cyanate ester resins. Such resins are used for a broad range of applications, including microelectronic packaging, circuit board substrates, lightweighting, high- temperature performance parts, etc. Regardless of the application some thermosets, particularly those that possess a high glass transition temperature, require elevated temperatures above 100°C and cure times above 2 hours for complete cure. Variable frequency microwave heating as an alternative to conventional, thermal heating has been proposed as a method for reducing cure times and temperatures. However, proposed and sometimes conflicting microwave heating phenomena described by scientists and engineers are still not very well understood. Thus, the overarching goal of this section is to better understand and use microwave-heating mechanisms that can be useful in reducing thermoset cure times. This involves using a microwave field’s ability selectively heat reactive species (i.e. a catalyst) at the microscopic level, which can occur when two different materials of dissimilar dielectric parameters are mixed. Chapter 4 briefly summarizes important fundamentals of matter-interactions with microwave electromagnetic fields, and how it pertains to selective heating phenomena. Chapter 5 and 6 describe the microwave curing of high glass transition temperature, homogeneous epoxy and cyanate esters respectively. Chapter 7 describes microwave enhanced curing of cyanate ester resin upon the addition of graphene and reduced graphene oxide, two microwave-absorbing, catalytic fillers. Finally, the problems regarding quantifying selective heating phenomena and dielectric property characterization are described.Ph.D