Publications

The late transition metal borane complexes (MeCp)Mn(CO)2(HBR2) (R = alkyl, alkoxy) and Cp*Re(CO)2(HBpin) (HBpin = pinacolborane, Cp* = pentamethylcyclopentadienyl) have been synthesized and isolated. All complexes were characterized spectroscopically, and X-ray crystal structure analyses were performed for (MeCp)Mn(CO)2(HBpin), (MeCp)Mn(CO)2(HBcat) (HBcat = catecholborane) and (MeCp)Mn(CO)2(HBCy2) (Cy = cyclohexyl). These data show that the complexes contain a borane ligand with a weakened but intact B−H bond. The borane ligand in (MeCp)Mn(CO)2(HBcat) is replaced by PhCCPh, Ph3SnH, Ph2MeSiH, CO, and excess HBpin in ligand substitution reactions. The mechanism of substitution by PhCCPh was investigated. Kinetic studies showed that the reaction is first-order in complex and that borane and PhCCPh react competitively with the 16-electron intermediate, (MeCp)Mn(CO)2. The ΔH⧧ value for borane dissociation was 24 ± 3 kcal/mol for (MeCp)Mn(CO)2(HBcat) and 21 ± 1 kcal/mol for (MeCp)Mn(CO)2(HBCy2), which provided an upper limit on the metal−borane binding energies. Dynamic NMR spectroscopy of (MeCp)Mn(CO)2(HBcat) revealed two types of rotations of the borane ligand.

Periodical signal transmission of waves through a one-dimensional array of coupled nonlinear electronic excitable cells have been investigated experimentally. Periodic wave trains give rise to a full devil’s staircase. The dependence of firing numbers defined for an excitable medium, on the amplitude and frequency of forcing, excitability of the medium, and coupling strength between cells is investigated. A nonmonotonic dependence between the locking range and the excitability has been observed for various n:m resonance regions, for different coupling strengths.

Abstract Upon several tested sulfonic acid, para‐toluene sulfonic acid shows the highest reactivity in the reaction of furfural (I) and 2‐methylfuran (II).

Continuous electroencephalogram (EEG) sleep studies were obtained on healthy full-term and preterm infants at matched conceptional ages. Studies were recorded under environmentally controlled conditions. Eighteen healthy preterm infants were matched to 18 full-term infants based on conceptional age, sex, race and socioeconomic class. The initial 3 hours of a 12-hour recording were simultaneously recorded on paper and computer. The visually scored data based on the paper recordings for sleep architecture and continuity measures were studied. Differences in each sleep organization for the preterm infants included the following: a longer ultradian sleep cycle (70 minutes vs. 53 minutes, p = 0.02) was noted. More abundant tracé alternant (34% vs. 28%, p = 0.02) and less abundant low-voltage irregular active sleep (13% vs. 17%, p = 0.05) were noted. Although no differences were observed for sleep latency and efficiency, the preterm infants had fewer numbers and shorter durations of arousals, fewer body movements and rapid eye movement (REM) (p < 0.01), particularly during quiet sleep. The extrauterine experience or the earlier birth of the preterm infant may influence specific sleep architecture and continuity measures when compared with the sleep of full-term infants who experienced a complete intrauterine gestation.

In classical sampled quantization, the signal is sampled at discrete times and at discrete values, resulting in uncertainty of the signal amplitude. However, the sampling times and the boundaries of the quantization intervals are still assumed to be known with infinite precision. The aim of this paper is to study quantization and sampling when these quantities are not known with infinite precision by considering quantized sampling in a general framework as sampling with uncertainty in time and amplitude. We define the concept of a valid quantized sample and consider a quantized sampling of a signal as a collection of valid quantized samples. We show that for continuous signals, a set of valid quantized samples generates a secondary set of valid quantized samples. We illustrate that oversampling can reduce reconstruction errors because oversampling can reduce the uncertainty in the secondary quantized samples. In particular, these secondary quantized samples have uncertainty approaching zero as oversampling increases, provided the sampling time and quantization thresholds are known with infinite precision. For a class of T-periodic bandlimited signals, this implies that the reconstruction error is a function of the oversampling ratio, the uncertainty in the sampling time, the stepsize of the quantizer, and the uncertainty in the quantization thresholds.

Paleomagnetic data from the Guadelupian (Upper Permian) Nosoni Formation of the Redding Section (RS) consistently exhibit two directional components of magnetization in addition to a late Quaternary normal weathering overprint. Six sites in ash flow tuffs and tuffaceous sedimentary rocks, spanning 200 m of section, yield data that allow precise characterization of all components. Two additional sites in calcareous mudstones were too heavily overprinted to yield stable paleomagnetic directions. Thermal demagnetization of the tuffaceous samples in 16–18 steps between natural remanent magnetization and 660°C provides a detailed data base from which to calculate directional components. Analysis of demagnetization trends identifies a prefolding reversed direction carried by both magnetite and hematite and a postfolding normal direction carried by hematite only. Petrologic considerations suggest paragenesis of these oxides in the Permian (primary magnetite and hematite) and Early‐Middle Jurassic (metamorphic hematite). Least squares analysis of progressively demagnetized vector endpoint trends between 540° and 600°C yields a formation mean direction in magnetite having D =156.4°, I =−29.7°, k = 101, α 95 =7.6°. This result is in close agreement with the composite prefolding direction ( D = 160.3°, I =−31.5°), carried by both magnetite and hematite, determined by the intersection of remagnetization circles. The postfolding hematite‐carried overprint direction calculated by the latter technique has D =352.3°, I =35.0°. Paleopoles corresponding to these two directions are located at 57.6°N, 103.0°E (magnetite formation mean) and 67.0°N, 104.1°E (hematite overprint), coinciding within error to Upper Permian and Early Jurassic (respectively) reference poles from the North American craton. These data indicate no significant rotation or latitudinal translation of the sample sites with respect to cratonic North America since the Permian. This conclusion contrasts with seemingly reliable paleomagnetic results from elsewhere in the RS, which indicate major post‐Permian clockwise rotations. These rotations are evidently specific to individual structural domains and are probably manifestations of oroclinal bending about vertical axes.

Abstract Im Hinblick auf Phänomene bei Druckwasser‐ Reaktor‐Dampfgeneratoren (Korrosion in Spalten) wurde die Magnetitbildung in Chloridlösung (0.998 M NaCl + 0.001 M FeCl,′4 H20) bei 200°C (360 psi) und 250°C (700 psi) untersucht.

Abstract We report Ir‐catalyzed, enantioselective allylic substitution reactions of unstabilized silyl enolates derived from α,β‐unsaturated ketones. Asymmetric allylic substitution of a variety of allylic carbonates with silyl enolates gave allylated products in 62–94 % yield with 90–98 % ee and &gt;20:1 branched‐to‐linear selectivity. The synthetic utility of this method was illustrated by the short synthesis of an anticancer agent, TEI‐9826.