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 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.

Tax Externalities of Equity Mutual Funds

Investors holding mutual funds in taxable accounts face a classic externality. The after-tax return of their investment depends on the behavior of others. In particular, redemptions may force the mutual fund to sell some of its equity positions in order to pay off the liquidating investors. As a result, it may be forced to distribute taxable capital gains to its shareholders. On the other hand, new investors convey a positive externality upon existing investors by diluting the unrealized capital gain position of the fund. This paper's simulations show that these externalities are important determinants of the after-tax performance of equity mutual funds.

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

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.

Ion mixing to produce amorphous Mo-Ru superconducting films

Amorphous Mo55Ru45 alloy films were formed by ion mixing of multilayered samples. The ion mixed films, which contain no metalloid element, show excellent superconducting properties. The measured properties are correlated with the microstructure obtained by both x-ray diffraction and transmission electron microscopy

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