Publications

The asymmetric intramolecular hydroamination of allenes catalyzed by phosphinegold(I)−bis-p-nitrobenzoate complexes is described. This reaction is applicable to the enantioselective formation of vinyl pyrrolidines and piperidines in 70−99% ee.

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the hypernova SN 1997ef. However, its kinetic energy [~(4-10) ? 1051 ergs] and the mass ejected (2.5-5 M?) are smaller, resulting in a faster evolving light curve. The SN synthesized ~0.07 M? of 56Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 M?, which is also lower than that of both hypernovae SN 1997ef and SN 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by the summer of 2002, are necessary to confirm these values.

Single-phase face-centered cubic (fcc) high/medium-entropy alloys (H/MEAs) exhibit a much higher tendency to form nanoscale deformation twins than conventional fcc metals with similar low stacking fault energies (SFEs). This extraordinary propensity for nanotwin formation in H/MEAs cannot therefore be explained by their low SFEs alone. Here, using in situ compression tests of CrCoNi in comparison with Ag nanopillars inside a transmission electron microscope, we found that in the CrCoNi MEA, a high density of nanoscale twins continuously formed with an average thickness of 4.6 nm. In contrast, for similar experiments on Ag with almost identical SFE, following the nucleation of a few twins, they could further thicken to above one hundred nanometers by twin boundary migration. Molecular dynamics calculations indicated that in the highly-concentrated CrCoNi solid solution, the magnitude of the energy barriers for nucleating a stacking fault as a twin precursor in the pristine lattice and for the thickening of an existing twin both span a wide range and largely overlap with each other. Therefore, twin thickening through successive addition of atomic layers is prone to discontinuation, giving way to the nucleation of new twins at other sites where a lower energy barrier is encountered for partial-dislocation mediated fault formation.

Although aluminosilicates and metal phosphates can form porous open-framework materials such as zeolites, sulfide analogs usually form high-density phases because of the relatively small tetrahedral angle at sulfur atoms. One strategy to overcome this limitation is to use tetrahedral clusters as the building blocks to achieve porous sulfide-based networks. The preparation and crystal structures of two indium sulfide open frameworks (ASU-31 and ASU-32) built of supertetrahedral clusters around organic template and water guests are described. ASU-31, based on the sodalite-tetrahedrite network, contains cavities 25.6 angstroms in diameter, and ASU-32, based on the tetragonal CrB 4 network, contains channels with a minimum diameter of 14.7 angstroms. The organic cations can be completely exchanged with sodium ions in aqueous solution at room temperature without degradation of the crystals.

We have systematically measured the room-temperature thermal conductivity of epitaxial layers of InxGa1−xN alloys with 15 different Indium compositions ranging from 0.08 to 0.98 by time-domain thermoreflectance method. The data are compared to the estimates of the strength of phonon scattering by cation disorder. The thermal conductivity is in good agreement with the theoretical modeling results based on the mass difference for In-rich (x > 0.9) and Ga-rich (x < 0.2) compositions. At intermediate compositions (0.2 < x < 0.9), the thermal conductivity is strongly suppressed below the values expected for homogeneous alloys. We attribute this suppression of thermal conductivity to phonon scattering by nanometer-scale compositional inhomogeneities in alloys.

Understanding the origin and diversity of emission processes responsible for\nGamma-ray Bursts (GRBs) remains a pressing challenge. While prompt and\ncontemporaneous panchromatic observations have the potential to test\npredictions of the internal-external shock model, extensive multiband imaging\nhas been conducted for only a few GRBs. We present rich, early-time, multiband\ndatasets for two \\swift\\ events, GRB 110205A and GRB 110213A. The former shows\noptical emission since the early stages of the prompt phase, followed by the\nsteep rising in flux up to ~1000s after the burst ($t^{-\\alpha}$ with\n$\\alpha=-6.13 \\pm 0.75$). We discuss this feature in the context of the\nreverse-shock scenario and interpret the following single power-law decay as\nbeing forward-shock dominated. Polarization measurements, obtained with the\nRINGO2 instrument mounted on the Liverpool Telescope, also provide hints on the\nnature of the emitting ejecta. The latter event, instead, displays a very\npeculiar optical to near-infrared lightcurve, with two achromatic peaks. In\nthis case, while the first peak is probably due to the onset of the afterglow,\nwe interpret the second peak to be produced by newly injected material,\nsignifying a late-time activity of the central engine.\n

Misery is not miserly: Sadness increases the amount of money that decision makers give up to acquire a commodity. The present research investigated when and why the misery-is-not-miserly effect occurs. Drawing on William James's concept of the material self, we tested a model specifying relationships among sadness, self-focus, and the amount of money that decision makers spend. Consistent with our Jamesian hypothesis, results demonstrated that the misery-is-not-miserly effect occurs only when self-focus is high. That is, self-focus moderates the effect of sadness on spending. Moreover, mediational analyses revealed that, at sufficiently high levels, self-focus mediates (explains) the relationship between sadness and spending. Because the study used real commodities and real money, the results hold implications for everyday decisions, as well as implications for the development of theory. For example, economic theories of spending may benefit from incorporating psychological theories—specifically, theories of emotion and the self—into their models.