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Biomedical subjects

E A Shapiro

Publications and source records attributed to E A Shapiro.

18 recordsLinked to original sources
PubMed2004

Phase control of rotational wave packets and quantum information.

Lasers can create rotational wave packets in gas-phase molecules which periodically revive as field-free, aligned distributions. We control the wave packet evolution with relatively weak laser pulses at fractional revivals which modify the phase between wave packet components. We demonstrate two phase control effects in oxygen: coherently switching revivals off and on, and doubling the revival frequency. When viewed as a quantum logic system, these effects correspond to a Hadamard and a T operation.

Journal Article↗
PubMed2004

Coarse-grained controllability of wavepackets by free evolution and phase shifts.

We describe an approach to controlling wavepacket dynamics and a criterion of wavepacket controllability based on discretized properties of the wavepacket's localization on the orbit. The notion of "coarse-grained control" and the coarse-grained description of the controllability in infinite-dimensional Hilbert spaces are introduced and studied using the mathematical apparatus of loop groups. We prove that 2D rotational wavepackets are controllable by only free evolution and phase kicks by AC Stark shift implemented at fractional revivals. This scheme works even if the AC Stark shifts can have only a smooth coordinate dependence, correspondent to the action of a linearly polarized laser field.

Journal Article↗
PubMed2004

Coherent control of rotational wave-packet dynamics via fractional revivals.

We show (i) how the evolution of a wave packet created from an initial thermal ensemble can be controlled by manipulating interferences during the wave packet's fractional revivals and (ii) how the wave-packet evolution can be mapped onto the dynamics of a few-state system, where the number of states is determined by the amount of information one wants to track about the wave packet in the phase space. We illustrate our approach by (i) switching off and on field-free molecular axis alignment induced by a strong laser pulse and (ii) converting alignment into field-free orientation, starting with rotationally cold or hot systems.

Journal Article↗
PubMed2003

Quantum logic approach to wave packet control.

We study control of wave packets with a finite accuracy, approaching it as quantum information processing. For a given control resolution, we define the analogs of several quantum bits within the shape of a single wave packet. These bits are based on wave packet symmetries. Analogs of one- and two-bit gates can be implemented using only free wave packet evolution and coordinate-dependent ac Stark shifts applied at the moments of fractional revivals. As in quantum computation, the gates form a logarithmically small set of basis operations which can be used to approximate any unitary transformation desired for quantum control of the wave packet dynamics. Numerical examples show the application of this approach to control vibrational wave packet revivals.

Journal Article↗
PubMed1987

[Na+ and K+ binding by glycerinated muscle fibers with reciprocal cation concentrations in the medium].

The binding of Na+ and K+ by glycerinated muscle fibres was observed at reserve concentrations of NaCl in the medium. Under external concentrations of Na+ of K+ up to 0.4-0.5 mM, a constant fraction (0.15-0.25 mmoles/kg dry weight of the fibres) bound by glycerinated fibres was revealed. With the increase of NaCl or KCl concentration in the medium up to 10 mM the concentration of bound cations increased too. The parameters of Na+ and K+ sorption by glycerinated models were calculated. The values of Na+ and K+ binding limits were 4.4 and 1.8 mmole/kg dry weight of the fibres and those of affinity, 3.2 and 4.1 kcal/mol, respectively. The binding of one cation took place in conditions when its concentration was 10,000-20,000 fold less than that of the other cation. This points to the fact that Na+ and K+ binding is highly specific and is carried out by different centres. It is suggested that myosin ATPase is a substratum binding Na+ and K+ in glycerinated muscle fibres at reverse ratio concentrations of these cations in the medium.

Animals↗
PubMed1985

[Na+ and K+ binding by glycerinated muscle fibers at equal concentrations of the chlorides of these cations in the medium].

The Na+ and K+ equilibrium distribution between the medium and glycerinated muscle fibres of the frog has been investigated under equal concentrations of NaCl and KCl in solutions. Concentrations of NaCl and KCl varied from 0.5-1.5 mkM till 50 mM. Ion strength (0.11) was constant owing to the imidazol--HCl buffer. The binding of Na+ and K+ by model fibres occurred in accordance with the Langmur equation. Two kinds of cation-binding sites were found. The one with a low limiting ion sorption (A infinity approximately 1.3 mmol/kg dry weight of fibres) and high affinities (-delta F0 approximately 4.3 kcal/mol) was saturated at 0.5 mM concentrations (Na+ = K+) in the medium, and the other--with A infinity exceeding the previous one by an order and low -delta F0 (2.5 kcal/mol) was discovered at Na+, K+-1-10 mM. At ion concentrations equal to 0.5-1 mM the Langmur-binding is disturbed. At Na+-K+ less than or equal to 1 mM Na+ bound:K+ bound approximately to 1:1. At higher concentrations of cations Na+ bound:K+ bound approximately equal to 3:2. It is concluded that at least part of the sites in model fibres is capable of interacting only with Na+, but not with K+. It is supposed that at equal concentrations of Na+ and K+ in the medium the cations are bound by Na+, K+-ATPase of glycerinated muscle fibres.

Animals↗
PubMed1976

[Cooperative sorbtion of trypaflavin by glycerinized muscle fibers. I. Adsorption isotherm and changes in the fluorescence polarization of the sorbed dye].

The equilibrium binding of a fluorescent cationic dye Tripaflavine (TPF) by frog's glicerinated mucle fibres is described by a S-shaped isotherm: the Langmuir sorption at low dye concentrations in the medium (0.84-10-5--3.38-10-5 M) is followed by the cooperative binding with the increase of concentration (8.45-10-5--338.0-10-5 M). The appearance of new TPF binding centres, alteration in fluorescence anisotropy of sorbed dye as well as inactivation of myosine ATPase of model fibres at high concentrations indicate that the cooperative phase of sorption is characterized by changes in the structure of contractile proteins.

Acriflavine↗