Surface flux pinning in superconducting amorphous (Mo0.6Ru0.4)B18

Superconducting critical current density was measured as a function of a perpendicular applied magnetic field in glassy (Mo0.6Ru0.4)82B18. The pinning force density was observed to depend linearly on 1/w, where w is the sample width measured perpendicular to both the current and field. This dependence is attributed to pinning by the sample edges. The bulk pinning contribution can be separated from the edge pinning contribution by extrapolation of the Fp vs 1/w curve. The edge contribution of the flux pinning was nearly eliminated by electrolytically polishing the sample. The contribution of the flux pinning profile due to edge pinning is analyzed in terms of the dynamic pinning model modified for edge pinning

Asset Location for Retirement Savers

This paper uses data on actual returns on taxable bonds, tax-exempt bonds, and a small sample of equity mutual funds over the 1962-1998 period to compare two asset location strategies for retirement savers. The first strategy gives priority to holding equities, through equity mutual funds, in a saver's tax-deferred account, while the second strategy gives priority to holding fixed-income investments in the tax-deferred account. We consider high-income taxable individual investors who saved in each year and invested in one of actively-managed funds in our sample. Over the thirty-seven year span that we consider, such savers would have accumulated a larger stock of wealth if they had held their equity mutual fund in their tax-deferred account than if they had held the fund in a conventional taxable form. The explanation for this apparent contradiction of the often-stated bonds in the tax-deferred account' prescription has two parts. First, many equity mutual funds impose substantial tax burdens on their investors. This raises the effective tax rate on investing in equities through mutual funds rather than in a buy-and-hold personal portfolio. Second, taxable investors who wish to hold fixed income assets can do so by holding tax-exempt bonds as well as by holding taxable bonds. The interest rate differential between taxable and tax-exempt bonds suggests that the effective tax rate on fixed income investments may be lower than the statutory tax rate for high-income investors.

Asset Location in Tax-Deferred and Conventional Savings Accounts

The optimal allocation of assets among different asset classes (such as stocks and bonds) has received considerable attention in financial theory and practice. On the other hand, investors have not been given much guidance about which assets should be located in tax-deferred retirement accounts and which in conventional savings accounts. This paper derives optimal asset allocations (which assets to hold) and asset locations (where to hold them) for a risk-averse investor saving for retirement. Locating assets optimally can significantly improve the risk-adjusted performance of retirement savings.

Planar laser-induced fluorescence imaging of OH in the exhaust of a bi-propellant thruster

Planar laser-induced fluorescence imaging of the hydroxyl radical has been performed on the flow produced by the exhaust of a subscale H2/O2 fueled bi-propellant rocket engine. Measurements were made to test the feasibility of OH (0,0) and (3,0) excitation strategies by using injection seeded XeCl and KrF excimer lasers, respectively. The flow is produced with hydrogen and oxygen reacting at a combustor chamber pressure of 5 atm which then exhausts to the ambient. The hydroxyl concentration in the exhaust flow is approximately 8 percent. Fluorescence images obtained by pumping the Q1(3) transition in the (0,0) band exhibited very high signals but also showed the effect of laser beam absorption. To obtain images when pumping the P1(8) transition in the (3,0) band it was necessary to use exceptionally fast imaging optics and unacceptably high intensifier gains. The result was single-shot images which displayed a signal-to-noise ratio of order unity or less when measured on a per pixel basis

The need to conserve farm animal genetic resources through community-based management in Africa: Should policy makers be concerned?

This paper outlines some key factors contributing to the erosion of animal genetic resources and discusses strategic options for livestock sector policy makers to counter such erosion in their respective countries.The ratification of the Convention on Biological Diversity (CBD) in 1993 represents an international consensus to conserve biodiversity including that of farm animal and plant genetic resources, which are prerequisites for food security and the improvement of agricultural productivity. In Africa, conservation of agricultural biodiversity is inbuilt into the low input - low output production strategies of smallholder farming systems. These systems are often associated with poverty in rural areas and numerous development projects have thus sought to alleviate such poverty by promoting and subsidising crossbreeding or modern reproductive technologies. However, uncontrolled crossbreeding has been and remains a serious threat to the conservation of local farm animal populations. The primary policy goal for conservation of biodiversity should focus on the diversity between and within indigenous populations of farm animals. This includes, for example, the close monitoring of crossbreeding activities with exotic breeds. The genetic and phenotypic characterisation of local breeds is a prerequisite for this purpose. Economic valuation of biodiversity in general, of breeds within given production systems and an analysis of the social welfare implications of farm animal genetic resources (FAnGR) diversity conservation although relatively complex to carry out are also important for informed policy making. Despite the difficulties involved, objectives for the conservation of a local farm animal population and opportunities to utilise its diversity to meet present and future market demands, to serve as an insurance against environmental changes such as changes in production, socio-economic, historic and cultural conditions can be identified for research and development. To improve food security through the conservation of animal genetic resources in Africa, utilisation of local farm animal genetic resources depends on the ability of communities to decide on and implement appropriate breeding strategies. This cannot be realised without enabling policies. It is for this reason policy makers need to be concerned and should take action now

External control strategies for self-propelled particles: optimizing navigational efficiency in the presence of limited resources

We experimentally and numerically study the dependence of different navigation strategies regarding the effectivity of an active particle to reach a predefined target area. As the only control parameter, we vary the particle's propulsion velocity depending on its position and orientation relative to the target site. By introducing different figures of merit, e.g. the time to target or the total consumed propulsion energy, we are able to quantify and compare the efficiency of different strategies. Our results suggest, that each strategy to navigate towards a target, has its strengths and weaknesses and none of them outperforms the other in all regards. Accordingly, the choice of an ideal navigation strategy will strongly depend on the specific conditions and the figure of merit which should be optimized

Multilevel Polar-Coded Modulation

A framework is proposed that allows for a joint description and optimization of both binary polar coding and the multilevel coding (MLC) approach for $2^m$-ary digital pulse-amplitude modulation (PAM). The conceptual equivalence of polar coding and multilevel coding is pointed out in detail. Based on a novel characterization of the channel polarization phenomenon, rules for the optimal choice of the bit labeling in this coded modulation scheme employing polar codes are developed. Simulation results for the AWGN channel are included.Comment: submitted to IEEE ISIT 201

Etching suspended superconducting hybrid junctions from a multilayer

A novel method to fabricate large-area superconducting hybrid tunnel junctions with a suspended central normal metal part is presented. The samples are fabricated by combining photo-lithography and chemical etch of a superconductor - insulator - normal metal multilayer. The process involves few fabrication steps, is reliable and produces extremely high-quality tunnel junctions. Under an appropriate voltage bias, a significant electronic cooling is demonstrated

Josephson Coupling in the Dissipative State of a Thermally Hysteretic μ\mu-SQUID

Micron-sized superconducting interference devices ($\mu$-SQUIDs) based on constrictions optimized for minimizing thermal runaway are shown to exhibit voltage oscillations with applied magnetic flux despite their hysteretic behavior. We explain this remarkable feature by a significant supercurrent contribution surviving deep into the resistive state, due to efficient heat evacuation. A resistively shunted junction model, complemented by a thermal balance determining the amplitude of the critical current, describes well all experimental observations, including the flux modulation of the (dynamic) retrapping current and voltage by introducing a single dimensionless parameter. Thus hysteretic $\mu$-SQUIDs can be operated in the voltage read-out mode with a faster response. The quantitative modeling of this regime incorporating both heating and phase dynamics paves the way for further optimization of $\mu$-SQUIDs for nano-magnetism.Comment: 10 pages, 11 figures, Revise