Nucleon-antinucleon bound states in a quark rearrangement model

The possibility of deeply-bound $\text{N}\text{N}$ states is studied in a quark rearrangement annihilation plus a meson-exchange potential model. It is shown that very narrow (Γ ～- 1–10 MeV) bound states may be possible even forL = 0 with binding energies varying up to $\text{E}{}_{\mathrm{<mtext>B</mtext>}}\text{?- 800–900}\text{MeV}$ in the proposed scheme. E_B is, however, very dependent on the details of the short-range treatment of the meson-exchange part. A reasonable agreement with the present controversial data can be obtained.     

Projection-patterned etching of silicon in chlorine atmosphere with a KrF excimer laser

The formation of relief features in silicon by a one-step process that avoids resist patterning has been achieved by laser-projection-patterned etching in a chlorine atmosphere. Etching is performed with a pulsed KrF excimer laser (λ=248 nm, τ=15 ns) and deep UV projection optics having an optical resolution of 2 μm. Etching takes place in two steps. Between laser pulses, the silicon surface is covered with a monolayer of chemisorbed chlorine atoms (one Cl per Si). During the laser pulse, surface transient heating at temperatures in excess of 1250 K results in the desorption of the reaction products (mainly SiCl₂). At laser energy densities that induce surface melting, this desorption results in a saturated etch. rate of 0.06 nm per pulse, corresponding to the removal of about 0.5 Si monolayer per pulse. At densities below the melting threshold, reduced thermal and possibly a small amount of photochemical etching result in lower etch rates. Projection of a resolution test photomask onto the silicon surface shows that the size of etched features differs from the size of the projected features and strongly depends on the laser energy density. As a result of the heat spread in silicon and of the highly nonlinear character of the etching reaction, etched features smaller than the irradiated area are obtained at all fluences in the range 350–700 mJ/cm². Etched lines having a width down to about 1.3 μm were produced. Proximity effects due to heat spread were also evidenced for small projected features (<4 μm). The characteristics of the etched patterns are compared with those obtained for GaAs etching in chlorinated gases with the same experimental set-up. Significant differences in pattern resolution for Si and GaAs etching are observed. This variation in resolution is believed to result from the fact that Si has a greater thermal diffusivity than GaAs.     

Antiprotonic helium

Recent measurements of the 2p and 3d atomic levels and lifetimes in antiprotonic helium seem to indicate an inconsistency, when interpreted in terms of an optical potential based on parameters extracted from heavier antiprotonic atoms. Here it is shown that this inconsistency is removed, when the data is described in terms of a multiple scattering formalism that treats correctly the number of nucleons and their correlations in the rescattering terms.     

Studies on the Diels-Alder reaction of annulated furans: application to the synthesis of substituted phenanthrenes

In an attempt to utilize the synthetic power of the furan nucleus in the synthesis of complex natural products, we have developed an entry into annulated furan intermediates that involves an electrochemical annulation protocol. An approach to the eunicellin diterpenes based on this methodology required the use of an intermolecular Diels-Alder reaction on an annulated furan. Although well known for simple furans, there is a paucity of related examples on annulated furans. To examine the feasibility of such an approach to these diterpenes, we have studied this key cycloaddition reaction. Our studies indicate that the process can be hampered by a facile retro-Diels-Alder that is highly dependent on the dienophile employed.     

Observations on a principal components analysis of head-related transfer functions.

A recent principal components analysis (Kistler and Wightman, 1992) has shown that the transfer functions of the human external ear, for a wide range of source locations, can be expressed as weighted sums of a small number of basis vectors. Directional transfer functions obtained in this laboratory, using substantially different measurement techniques, yielded principal component basis vectors that are remarkably similar to those reported by Kistler and Wightman. When this subject population was divided in half according to the overall physical sizes of subjects, basis vectors computed for the subpopulation of smaller subjects were shifted systematically to higher frequencies relative to those computed for the subpopulation of larger subjects.     

The Mathematics Writer's Checklist: The Development of a Preliminary Assessment Tool for Writing in Mathematics

The use of writing as a pedagogical tool to help students learn mathematics is receiving increased attention at the college level ( Meier & Rishel, 1998 ), and the Principles and Standards for School Mathematics (NCTM, 2000) built a strong case for including writing in school mathematics, suggesting that writing enhances students' mathematical thinking. Yet, classroom experience indicates that not all students are able to write well about mathematics. This study examines the writing of a two groups of students in a college‐level calculus class in order to identify criteria that discriminate “;successful” vs. “;unsuccessful” writers in mathematics. Results indicate that “;successful” writers are more likely than “;unsuccessful” writers to use appropriate mathematical language, build a context for their writing, use a variety of examples for elaboration, include multiple modes of representation (algebraic, graphical, numeric) for their ideas, use appropriate mathematical notation, and address all topics specified in the assignment. These six criteria result in The Mathematics Writer's Checklist, and methods for its use as an instructional and assessment tool in the mathematics classroom are discussed.     

A harmonic oscillator model of the conformationally flexible helical polymeric molecules

The approach of the persistence vector to its asymptotic limit can be characterized by the average projection of a unit vector along the last bond onto a unit vector along the first bond. The behavior of this projection has been examined in simple, predominantly helical chains in which limited flexibility is introduced by either of two devices: occurrence in an average way of a configuration much different from that required for helix propagation, and use of a square-well potential centered at the dihedral angle utilized in a rigid helix. The manner in which flexibility is introduced determines the behavior of the angular frequency as well as the relative decay rates for oscillations and the midpoint about which oscillations occur.     

Glass transition of polymer/single-walled carbon nanotube composite films

The glass-transition temperatures (T_g's) of nanocomposites of polystyrene (PS) and single-walled carbon nanotubes were measured in the bulk and in thin films with differential scanning calorimetry and spectroscopic ellipsometry, respectively. The bulk T_g of the nanocomposites increased by approximately 3 °C and became much broader than that of PS. For the nanocomposite films thinner than 45 nm, T_g decreased with decreasing film thickness [i.e., ΔT_g(nano) < 0]. This phenomenon also occurred in thin PS films, the magnitude of the depression in PS [ΔT_g(PS)] being somewhat larger. The film thickness dependence and the differences in the magnitude of ΔT_g in the two systems were examined in light of current theory, and a quantitative comparison was made. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3339–3345, 2003     

Magnetic resonance imaging as a sensor system for multiphase mixing

Mixing in a multicomponent batch system was evaluated by magnetic resonance images. The system was a 10% carbon black powder suspended in aqueous solution. The factors in this study were surfactant type (neodol 23-5 and sodium dodecyl sulfate) at two levels: 1 and 0.1%. Water (0% surfactant) was used as the control. In addition to surfactant type and level, the third factor was mixing mode: with vortex and without vortex motion. These conditions were displayed at 180 and 60 rpm impeller speed respectively. The type of surfactant did not yield significantly different results in terms of mixing effectiveness. The rate of mixing, as characterized by first-order rate constants, was statistically different as a function of mixing mode, level of surfactant and the interaction of these factors. The extent of mixing, characterized by a normalized mean signal intensity, was also statistically different as a function of the same factors and interaction. The incorporation of air and subsequent release of air was described by the volume change of the mixture as a function of time.