General implementation of the ERETIC method for pulsed field gradient probe heads

A capacitive coupling between a secondary radiofrequency (rf) channel and the gradient coil of a standard commercially available high resolution NMR spectrometer and probe head is described and used to introduce a low level exponentially damped rf signal near the frequency of the primary rf channel to serve as an external concentration standard, in analogy to the so-called ERETIC™ method. The stability of this inexpensive and simple to implement method, here referred to as the Pulse Into the Gradient (PIG) approach, is superb over a 14-h period and both gradient tailored water suppression and one-dimensional imaging applications are provided. Since the low level signal is introduced via the pulsed field gradient coil, the coupling is identical to that for a free induction signal and thus the method proves to be immune (within 5%) to sample ionic strength effects up to the 2 M NaCl solutions explored here.     

Nonlinear optical transmission properties of C60 dyads consisting of a light-harvesting diphenylaminofluorene antenna

Highly enhanced nonlinear absorption cross section values of C60(>DPAF-C2M), C60(>DPAF-C9), and C60(>DPAF-C10) dyads were detected up to 5400, 9700, and 14000 GM, respectively, in the 2.0 ps region in toluene at the concentration of 1.5 x 10(-3) M. They were correlated to a trend showing higher efficiency in light transmittance attenuation down to 39-46% for the dyads C60(>DPAF-C10) and C60(>DPAF-C9) with the increase of irradiance intensity up only to 140 GW/cm(2). The phenomena were attributed to additional enhancement on the excited-state absorption of (1)C60*(>DPAF-Cn ) in the subpicosecond to picosecond region over the two-photon absorption of C60(>DPAF-Cn ) in the femtosecond region. Its accumulative 2.0 ps absorption cross sections were estimated to be 8900 GM for (1)C60*(>DPAF-C9), roughly one order of magnitude higher than its intrinsic femtosecond 2PA cross sections.     

Spectroscopic and kinetic studies of perturbed trinuclear copper clusters: the role of protons in reductive cleavage of the O-O bond in the multicopper oxidase Fet3p

The multicopper oxidase Fet3p couples four 1e(-) oxidations of substrate to the 4e(-) reduction of O2 to H2O. Fet3p uses four Cu atoms to accomplish this reaction: the type 1, type 2, and coupled binuclear type 3 sites. The type 2 and type 3 sites together form a trinuclear Cu cluster (TNC) which is the site of O2 reduction. This study focuses on mutants of two residues, E487 and D94, which lie in the second coordination sphere of the TNC and defines the role that each plays in the structural integrity of the TNC, its reactivity with O2, and in the directional movement of protons during reductive cleavage of the O-O bond. The E487D, E487A, and D94E mutants have been studied in the holo and type 1 depleted (T1D) forms. Residue E487, located near the T3 center, is found to be responsible for donation of a proton during the reductive cleavage of the O-O bond in the peroxide intermediate and an inverse kinetic solvent isotope effect, which indicates that this proton is already transferred when the O-O bond is cleaved. Residue D94, near the T2 site, plays a key role in the reaction of the reduced TNC with O2 and drives electron transfer from the T2 Cu to cleave the O-O bond by deprotonating the T2 Cu water ligand. A mechanism is developed where these second sphere residues participate in the proton assisted reductive cleavage of the O-O bond at the TNC.     

A Learning Algorithm for the Control of Continuous Action Set-Point Regulator Systems

The convergence properties for reinforcement learning approaches, such as temporal differences and Q-learning, have been established under moderate assumptions for discrete state and action spaces. In practice, however, many systems have either continuous action spaces or a large number of discrete elements. This paper presents an approximate dynamic programming approach to reinforcement learning for continuous action set-point regulator problems, which learns near-optimal control policies based on scalar performance measures. The continuous-action space (CAS) algorithm uses derivative-free line search methods to obtain the optimal action in the continuous space. The theoretical convergence properties of the algorithm are presented. Several heuristic stopping criteria are investigated and practical application is illustrated by two example problems—the inverted pendulum balancing problem and the power system stabilization problem.     

Design of full-duplex and multifunction bidirectional CMOS transceiver for optical interconnect applications

This work presents a full-duplex and multifunction bidirectional transceiver for optical interconnect application. The transceiver utilizes a common limiting amplifier/gain stage, thus reducing total chip area and total power consumption. While providing a full-duplex bidirectional transmission with the aid of a hybrid circuit between the electrical input/output (I/O) and the optoelectronic signals from the transmitter and receiver circuits, it also allows for a half-duplex operation with the aid of a switch between the transimpedance amplifier signals and the transmitter electrical input from the I/O port. The multifunction bidirectional CMOS transceiver is designed in a 0.13 µm Si-CMOS technology, with power dissipation of 79 and 54.4 mW for the transmitter and receiver, respectively. It shows a 3-dB bandwidth of 5.58 and 5.69 GHz for the transmitter and the receiver respectively and with a 3-dB gain of 66.14 and 69.6 dB, in full-duplex mode. The transceiver operates up to 7 Gb/s in full-duplex mode.     

Asymmetric synthesis of trans-2,5-disubstituted pyrrolidines from enantiopure homoallylic amines. Synthesis of pyrrolidine (-)-197B

Iodocyclization of sulfinimine-derived enantiopure homoallylic sulfonamides affords trans-2,5-disubstituted 3-iodopyrrolidines and represents valuable methodology for the asymmetric synthesis of this important heterocyclic ring system.     

Reversible light-directed red, green, and blue reflection with thermal stability enabled by a self-organized helical superstructure

Adding external, remote, and dynamic control to self-organized superstructures with desired properties is an important leap necessary in leveraging the fascinating molecular subsystems for employment in applications. Here two novel light-driven dithienylethene chiral molecular switches possessing remarkable changes in helical twisting power during photoisomerization as well as very high helical twisting powers were found to experience photochemically reversible isomerization with thermal stability in both isotropic organic solvents and anisotropic liquid crystal media. When doped into a commercially available achiral liquid crystal host, the chiral switch was able to either immediately induce an optically tunable helical superstructure or retain an achiral photoresponsive liquid crystal phase whose helical superstructure was induced and tuned reversibly upon light irradiation. Moreover, reversible light-directed red, green, and blue reflection colors with thermal stability in a single thin film were demonstrated.     

The sequestral capture of fluoride,nitrate and phosphate by metal-doped and surfactant-modified hybrid clay materials

Toxic anions removal for increased access to potable water remains a problem that has not been adequately addressed. This study, reports the successful preparation and modification of kaolinite-papaya seed based adsorbents under vacuum (VHYCA) for the removal of Nitrate (NO₃ ^?), Fluoride (F^?) and Phosphate (PO₄ ^3?). Modified adsorbents via metal-doping using Zinc were more efficient in removing these anions from aqueous solution compared with surfactant-modified adsorbents. However, both type of adsorbents showed a higher preference for NO₃ ^? removal with Zn-VHYCA and Fe-VHYCA adsorbents having 98 and 85% removal of the anion from aqueous solution, respectively. The removal of F^? and PO₄ ^3? was best achieved by Ortho-phenylenediamine (OP) and N,N,N′,N′-Tetramethyl-1,4-phenyldiaminedihydrochloride (TPD) modified VHYCA, respectively. However, Zn-VHYCA adsorbent showed comparable results with TPD-VHYCA in the removal of PO₄ ^3? from aqueous solution. Overall, the metal-doped hybrid clay adsorbents showed better efficiency for the removal of anions than the surfactant-modified hybrid clay adsorbents.