An in-depth study of iridium catalysts for the borylation of alkyl C-H bonds is reported. Although the borylation of aryl C-H bonds can be catalyzed by iridium complexes containing phen or bpy ligands at mild temperatures and with limiting arene, the borylation of alkyl C-H bonds remains underdeveloped. We prepared a library of phenanthrolines that contain varying substitution patterns. The corresponding phen-Ir trisboryl carbon monoxide complexes were synthesized to determine the electron-donating ability of these ligands, and the initial rates for the borylation of the C-H bonds in THF and diethoxyethane <i>β</i> to oxygen catalyzed by Ir complexes containing these ligands were measured. For some subsets of these ligands, the donor ability correlated positively with the rate of C-H borylation catalyzed by the complexes containing ligands within a given subset. However, across subsets, ligands possessing similar donor properties to one another form catalysts for the borylation of alkyl C-H bonds with widely varying activity. This phenomenon was investigated computationally, and it was discovered that the stabilizing interactions between the phenanthroline ligand and the boryl ligands attached to Ir in the transition state for C-H oxidative addition could account for the differences in the activity of the catalysts that possess similar electron densities at Ir. The effect of these interactions on the borylation of secondary alkyl C-H bonds is larger than it is on the borylation of primary alkyl C-H bonds.
While PFQ algorithms can provide per-flow end-to-end delay guarantees for real-time traffic or protection among competing best-effort traffic, they have two important limitations. The first one is that, since only one parameter (a weight) is used to allocate resource for each flow, there is a coupling between delay and bandwidth allocation. When used for real-time traffic, this can result in network under-utilization. The second and less well known limitation is that, when used for best-effort traffic, PFQ algorithms favor throughputoriented applications such as FTP over delay-sensitive bursty applications such as WWW, and telnet. This is due to the memory-less instantaneous fairness property of PFQ algorithms. In a previous study [1], we proposed the Fair Service Curve (FSC) algorithm which enables more flexible delay and bandwidth allocation for real-time traffic through the use of non-linear service curves. In this paper, we show that, when used for best-effort traffic, FSC can imp...
Various forms of wafer bonding have now emerged as a serious competitor to heteroepitaxy for optoelectronic integration of dissimilar semiconductor materials. Among the types of wafer bonding, perhaps the most flexible is that which employs free-standing III–V films as created by epitaxial liftoff. For some purposes, weak Van der Waals forces provide an adequate bond between the native oxides of the III–V film and its new substrate. If the substrate is coated by palladium however, a low temperature solid-phase-topotaxial reaction occurs, producing oriented Pd4GaAs under the GaAs film. In effect, the topotaxy comes about through mechanical contact alone. The resulting metallurgical bond is an ohmic contact, a thermal contact and a robust, permanent, adherent contact.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
With an optical antenna, spontaneous emission can be stronger and faster than stimulated emission, allowing direct modulation LED's for optical interconnects. We will present the evidence for 35X spontaneous emission enhancement by an optical antenna.
BACKGROUND AND OBJECTIVES: Inadequate sleep among adolescents has negative consequences for self-regulation, emotional well-being, and risk behaviors. Using multiple assessment methods, we evaluated the adequacy of sleep among healthy adolescents from a lower socioeconomic community and expected differences by race. METHODS: A total of 250 healthy high school students enrolled in public school (mean age: 15.7 years; 57% black, 54% female) from families of low to middle class according to the Hollingshead scale participated in weeklong assessments of sleep duration and fragmentation, assessed by using actigraphy; sleep duration and perceived quality, assessed by using daily diaries; and daytime sleepiness and sleep delay, assessed by using a questionnaire. RESULTS: Students slept during the school week a mean ± SD of 6.0 ± 0.9 hours per night according to actigraphy and 6.8 ± 1.1 hours according to daily diary, and during the weekend, a mean of 7.4 ± 1.2 and 8.7 ± 1.4 hours, respectively. Black participants and male participants slept less and had more fragmented sleep; female participants reported poorer quality of sleep in their daily diaries and more daytime sleepiness. The results remained significant after adjustments for age, physical activity, smoking status, and percentile BMI. CONCLUSIONS: Most students slept less than the 8 to 9 hours suggested by the guidelines of the Centers for Disease Control and Prevention. Black male participants had the least amount of sleep, which may play a role in the substantial risks experienced by this demographic group. Our findings are consistent with recommendations that pediatricians should routinely screen their adolescent patients about their sleep, especially those from at-risk subgroups.
The use of palladium hydride electrodes (Pd black on Pd, Pt, and Au) for the measurement of pH in high temperature aqueous systems (298°–548°K) is described. The electrodes were calibrated against boric acid/lithium hydroxide buffer solutions, whose vs. temperature profiles have been calculated using known dissociation constants for the components. Linear potentialvs. pH correlations are observed for all temperatures studied. However, the gradients of the correlations deviate from the predicted Nernstian values. Furthermore, thermodynamic analyses of the systems demonstrate that above 373°K the observed potential deviates significantly from the equilibrium values calculated on the supposition that the potential‐determining reaction is . Possible reasons for the observed deviation from ideal behavior are identified.
