Robert J. Levis

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Inactivation of currents carried by Ba2+ and Ca2+, as well as intramembrane charge movement from L-type Ca2+ channels were studied in guinea pig ventricular myocytes using the whole-cell patch clamp technique. Prolonged (2 s) conditioning depolarization caused substantial reduction of charge movement between -70 and 10 mV (charge 1, or charge from(More)
Intramembrane charge movement was recorded in guinea pig ventricular myocytes at 19-22 degrees C using the whole-cell patch clamp technique. From a holding potential of -110 mV, the dependence of intramembrane charge moved on test voltage (Q(V)) followed the sum of two Boltzmann components. One component had a transition voltage (V) of -48 mV and a total(More)
To understand the nature of the transmission process of excitation-contraction (EC) coupling, the effects of the anion perchlorate were investigated on the voltage sensor (dihydropyridine receptor, DHPR) and the Ca release channel (ryanodine receptor, RyR) of the sarcoplasmic reticulum (SR). The molecules, from rabbit skeletal muscle, were either separated(More)
We used strong-field laser pulses that were tailored with closed-loop optimal control to govern specified chemical dissociation and reactivity channels in a series of organic molecules. Selective cleavage and rearrangement of chemical bonds having dissociation energies up to approximately 100 kilocalories per mole (about 4 electron volts) are reported for(More)
Nonlinear optics experiments measuring phase shifts induced in a weak probe pulse by a strong pump pulse must account for coherent effects that only occur when the pump and probe pulses are temporally overlapped. It is well known that a weak probe beam experiences a greater phase shift from a strong pump beam than the pump beam induces on itself. The(More)
Simultaneous spatial and temporal focusing pulses are created using parametric pulse shaping and characterized with scanning SEA TADPOLE. Multiple foci are created with optically-controlled longitudal and transverse spatial positions. The characterized foci are in agreement with the predictions of a Fourier optics model. The measurements reveal significant(More)
High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Because of reduced quantum diffusion of the radiating electron wave function, the(More)
A nonresonant femtosecond laser pulse, with an intensity of 10(13) Wcm(-2), vaporizes proteins and biomolecules intact, regardless of molecular structure, size or electronic structure for subsequent electrospray ionization and transfer into a mass spectrometer. Rapid, direct analysis from dried sample, aqueous solution and cellular material is demonstrated(More)
Time-dependent Hartree-Fock theory has been used to study the electronic optical response of a series of linear polyene cations (+1 and +2) in strong laser fields. The interaction of ethylene, butadiene, and hexatriene, with pulsed and CW fields corresponding to 8.75 x 10(13) W/cm(2) and 760 nm, have been calculated using the 6-31G(d,p) basis set.(More)
We demonstrate electrospray post-ionization mass spectrometry with an Yb fiber laser producing 500 fs, 50 μJ pulse-bursts, enabling protein, peptide and lipid identification and imaging for the pharmaceutical and biomedical realm.