Using a 77 K SQUID to measure magnetic fields for NDE

A bare HTS SQUID of commercial design was used in 77 K experiments concerning NDE. The SQUID was operated with flux-locked instrumentation to provide a noise floor of 80 pT/√Hz. The effective sensor area was measured to be approximately 70 μm² equivalent to an ideal point detector for NDE. The SQUID was used unshielded in a normal laboratory environment in a special purpose LN₂ cryostat positioned above a motorized computer-controlled scanning system. We measured magnetic fields associated with current flowing in wires and compared them with calculations. We also detected a simulated flaw in an aluminum plate using an eddy current technique and made a preliminary depth assessment by frequency sweeping. Although developments in electronic gradiometers and gradiometric SQUID's should make the use of single bare magnetometer SQUID's unnecessary, we show that these already have sufficient sensitivity for NDE research, even without flux-focusing washers or pick-up coils     

Novel large mode volume resonator

A resonator in which the dominant mode-shaping effect is diffraction from an undersized aperture is reported. The result is a large mode volume and a near diffraction-limited Gaussian output beam. The alignment sensitivity is similar to that of a positive branch unstable resonator, although the mirror configuration can vary over a large range in either the geometrically stable or unstable regimes. A pulsed Nd:YAG laser using this resonator was built and characterized in the free-running, Q-switching, and mode-locking regimes, and as a regenerative amplifier     

Brillouin light scattering investigation of FeSm/FeTaN trilayer

The static and dynamic magnetic properties of a FeTaN/FeSm/FeTaN trilayer are investigated by alternating gradient field magnetometry and Brillouin light scattering. Evidence is given for a strong in-plane uniaxial anisotropy induced by a magnetic field applied during deposition. The spin-wave spectrum consists of different modes, with either surface or bulk character. A nonreciprocal behavior of the spin-wave frequency due to the exchange field exerted on the FeTaN layer at the FeSm interface is observed.     

Magnetization reversal processes in FeSm thin films

We have investigated the in-plane magnetization reversal in FeSm thin films and discovered that it can be controlled through an induced anisotropy. For films with an induced easy direction, reversal is ultra fast and can be characterized approximately using the Fatuzzo model. In films with no pronounced induced easy axis, the reversal is much slower and can be described using a logarithmic model. We have also investigated the short time (1–50 s) dependence of the remanent coercivity and fitted to logarithmic equations. For films with no pronounced easy axis, the time dependence of the coercivity correlates with the film thickness, indicating that the switching volume scales with thickness. For films with an induced easy direction, the time dependence of the coercivity is essentially constant, independent of film thickness, indicating no scalable switching volume.     

Coverage dependent adsorption site for sulfur on Ni(111)

Angular-resolved photoemission spectra have been observed from two ordered sulfur overlayers, p(2×2) and (√3 ×√3)R30°, representing different coverages on the Ni(111) surface. Utilization of selection rules applicable to photoemission along the sample normal permits an assignment of placement and composition of the adsorbate induced bands. The spectra show dramatic changes in peak positions between these two overlayers similar in magnitude to those observed on Ni(100). The shifts in peak positions are attributed to symmetry prescribed changes in the surface unit cell relating to the character of the bond. Arguments that these changes provide evidence that the bonding site of the adsorbate atom may change with coverage are presented.     

Calculations predict rapid tunneling by carbon from the vibrational ground state in the ring opening of cyclopropylcarbinyl radical at cryogenic temperatures

B3LYP/6-31G(d) calculations have been performed on the ring opening of cyclopropylcarbinyl radical 1 to 3-buten-1-yl radical 2. The dynamics of the reaction have been computed with canonical variational transition state theory (CVT), both with and without inclusion of small-curvature tunneling (SCT). The CVT + SCT calculations predict that 1 should undergo rapid and temperature-independent ring opening to 2 at cryogenic temperatures, by tunneling from the lowest vibrational level of 1.     

Phototriggered Secretion of Membrane Compartmentalized Bioactive Agents

A strategy for the light‐activated release of bioactive compounds (BODIPY, colchicine, paclitaxel, and methotrexate) from membrane‐enclosed depots is described. We have found that membrane‐permeable bioagents can be rendered membrane impermeable by covalent attachment to cobalamin (Cbl) through a photocleavable linker. These Cbl‐bioagent conjugates are imprisoned within lipid‐enclosed compartments in the dark, as exemplified by their retention in the interior of erythrocytes. Subsequent illumination drives the secretion of the bioactive species from red blood cells. Photorelease is triggered by wavelengths in the red, far‐red, and near‐IR regions, which can be pre‐assigned by affixing a fluorophore with the desired excitation wavelength to the Cbl‐bioagent conjugate. Pre‐assigned wavelengths allow different biologically active compounds to be specifically and unambiguously photoreleased from common carriers.     

1,6-Remote stereocontrol using allylgermanes

Transmetallation of 5-hydroxy- and 5-methoxyhex-2-enyl(triethyl)germanes 8 and 9 with tin(IV) bromide is stereoselective and generates allyltin tribromides, which react with aldehydes to give (3Z)-homoallylic alcohols 3 with useful levels of 1,6-syn-stereocontrol.     

Calculations of the effects of substituents on bond localization in annelated cyclopentadienyl radicals

UB3LYP/6-31G(d) calculations have been performed in order to predict the ground states, 2A2 or 2B1, of cyclopentadienyl radicals that are mono- and bis-annelated with a wide variety of substituents. Unlike the case in the annelated cyclooctatetraenes, studied by Baldridge and Siegel, our calculations find that the sizes of the coefficients of the degenerate MOs at the annelated carbons are more important than the symmetries of the substituent's frontier orbitals in determining the mode of bond localization in the annelated cyclopentadienyl radicals.     

Which n-Venn Diagrams Can Be Drawn with Convex k-Gons?

We establish a new lower bound for the number of sides required for the component curves of simple Venn diagrams made from polygons. Specifically, for any n-Venn diagram of convex k-gons, we prove that k ≥ (2ⁿ - 2 - n) / (n (n - 2)). In the process we prove that Venn diagrams of seven curves, simple or not, cannot be formed from triangles. We then give an example achieving the new lower bound of a (simple, symmetric) Venn diagram of seven convex quadrilaterals. Previously Grunbaum had constructed a symmetric 7-Venn diagram of non-convex 5-gons ["Venn Diagrams II", Geombinatorics 2:25-31, 1992].