PubMed Health⌕ Search

Biomedical subjects

C P Sun

Publications and source records attributed to C P Sun.

13 recordsLinked to original sources
PubMed2006

Maxwell's demon assisted thermodynamic cycle in superconducting quantum circuits.

We study a new quantum heat engine (QHE), which is assisted by a Maxwell's demon. The QHE requires three steps: thermalization, quantum measurement, and quantum feedback controlled by the Maxwell demon. We derive the positive-work condition and operation efficiency of this composite QHE. Using controllable superconducting quantum circuits as an example, we show how to construct our QHE. The essential role of the demon is explicitly demonstrated in this macroscopic QHE.

Journal Article↗
PubMed2006

Decay of Loschmidt echo enhanced by quantum criticality.

We study the transition of a quantum system from a pure state to a mixed one, which is induced by the quantum criticality of the surrounding system E coupled to it. To characterize this transition quantitatively, we carefully examine the behavior of the Loschmidt echo (LE) of E modeled as an Ising model in a transverse field, which behaves as a measuring apparatus in quantum measurement. It is found that the quantum critical behavior of E strongly affects its capability of enhancing the decay of LE: near the critical value of the transverse field entailing the happening of quantum phase transition, the off-diagonal elements of the reduced density matrix describing S vanish sharply.

Journal Article↗
PubMed2006

Quantum-classical transition of photon-Carnot engine induced by quantum decoherence.

We study the physical implementation of the photon-Carnot engine (PCE) based on the cavity quantum electrodynamics system [M. O. Scully, M. Suhail Zubairy, G. S. Agarwal, and H. Walther, Science 299, 862 (2003)]. Here we analyze two decoherence mechanisms for the more practical systems of PCE, the dissipation of photon field, and the pure dephasing of the input atoms. As a result we find that (i) the PCE can work well to some extent even in the existence of the cavity loss (photon dissipation) and (ii) the short-time atomic dephasing, which can destroy the PCE, is a fatal problem to be overcome.

Journal Article↗
PubMed2005

Quantum heat engine with multilevel quantum systems.

By reformulating the first law of thermodynamics in the fashion of quantum-mechanical operators on the parameter manifold, we propose a universal class of quantum heat engines (QHE) using the multilevel quantum system as the working substance. We obtain a general expression of work for the thermodynamic cycle with two thermodynamic adiabatic processes, which are implied in quantum adiabatic processes. We also classify the conditions for a 3-level QHE to extract positive work, which is proved to be looser than that for a 2-level system under certain conditions. As a realistic illustration, a 3-level atom system with dark state configuration manipulated by a classical radiation field is used to demonstrate our central idea.

Journal Article↗
PubMed2005

Cooling mechanism for a nanomechanical [corrected] resonator by periodic coupling to a Cooper pair box.

We propose and study an active cooling mechanism for the nanomechanical resonator (NAMR) based on periodical coupling to a Cooper pair box (CPB), which is implemented by a designed series of magnetic flux pluses threading through the CPB. When the initial phonon number of the NAMR is not too large, this cooling protocol is efficient in decreasing the phonon number by 2 to 3 orders of magnitude. Our proposal is theoretically universal in cooling various boson systems of a single mode. It can be specifically generalized to prepare the nonclassical state of the NAMR.

Journal Article↗
PubMed2005

Optical selection rules and phase-dependent adiabatic state control in a superconducting quantum circuit.

We analyze the optical selection rules of the microwave-assisted transitions in a flux qubit superconducting quantum circuit (SQC). We show that the parities of the states relevant to the superconducting phase in the SQC are well defined when the external magnetic flux phi(e) = phi(0)/2; then the selection rules are the same as the ones for the electric-dipole transitions in usual atoms. When phi(e) does not = phi(0)/2, the symmetry of the potential of the artificial "atom" is broken, a so-called delta-type "cyclic" three-level atom is formed, where one- and two-photon processes can coexist. We study how the population of these three states can be selectively transferred by adiabatically controlling the electromagnetic field pulses. Different from lambda-type atoms, the adiabatic population transfer in our three-level delta atom can be controlled not only by the amplitudes but also by the phases of the pluses.

Journal Article↗
PubMed2003

Quasi-spin-wave quantum memories with a dynamical symmetry.

For the two-mode exciton system formed by the quasi-spin-wave collective excitation of many Lambda atoms fixed at the lattice sites of a crystal, we discover a dynamical symmetry depicted by the semidirect product algebra SU2( multiply sign in circle) h(2) in the large N limit with low excitations. With the help of the spectral generating algebra method, we obtain a larger class of exact zero-eigenvalue states adiabatically interpolating between the initial state of photon-type and the final state of quasi-spin-wave exciton-type. The conditions for the adiabatic passage of dark states are shown to be valid, even with the presence of the level degeneracy. These theoretical results can lead to the proposal of a new protocol for implementing quantum memory robust against quantum decoherence.

Journal Article↗
PubMed1999

Alternative pathway of complement is activated during in vitro ventricular assist.

BACKGROUND: Although ventricular assist devices (VAD) have improved survival in selected patients, their use continues to be complicated by thromboembolism and end-organ failure. Complement activation may play a role in the pathogenesis of these complications. Previous studies have found that the complement common terminal pathway is activated during VAD circulation. C3a levels rise dramatically during VAD use. Because the C3a fragment is generated by either the alternative or classical pathway, the purpose of this study is to determine the relative importance of the respective pathways in complement activation during in vitro VAD circulation. METHODS: Six in vitro VAD circuits were simulated for 3 days using 450 mL of human blood. Temperature, activated clotting time, pH, pCO2, pO2, Ca2+, and glucose were maintained at physiologic levels. Enzyme immunoassays were used to measure concentrations of fragment Bb to indicate alternative pathway activation and fragment C4d to indicate classical pathway activation. RESULTS: Fragment Bb concentrations rise from 1.92 to 10.77 micrograms/mL during the first 6 hours of circulation. Thereafter, Bb levels plateau. C4d concentrations slowly rise from a baseline of 1.49 to 6.84 micrograms/mL in 72 hours. CONCLUSIONS: These findings suggest that both the alternative and classical pathways of complement are activated during VAD circulation. Alternative pathway activation precedes classical pathway activation during in vitro VAD circulation and may be of greater clinical importance during clinical VAD circulation.

Assisted Circulation↗
PubMed1998

Effect of lu-duo-wei on scavenging superoxide and hydroxyl radicals in vitro.

Irradiation of a riboflavin-containing system by ultraviolet light was used to produce superoxide radical (.O2-). Hydroxyl radical (.OH) was generated by the system of Fe(II)-H2O2. Using electron spin resonance and spin trapping techniques, the effect of Lu-Duo-Wei, a capsule consisting extracts of green tea, Fructus Lycii and Semen Ziziphi Spinosae, on scavenging .O2- and .OH was observed. The results showed that the efficiency of scavenging .O2- and .OH by Lu-Duo-Wei was much higher than that by tea polyphenol alone. It is suggested that the synergistic action of tea polyphenol and other components are responsible for the scavenging effect of Lu-Duo-Wei on .O2- and .OH.

Drugs, Chinese Herbal↗
PubMed1994

Biochemical and morphological changes in the lenses of selenium and/or vitamin E deficient rats.

The activities of glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R), superoxide dismutase (SOD) and the contents of malondialdehyde (MDA) and free radicals were measured, and the morphological changes were observed in the lens of control rats, selenium-deficient (SeD) and/or vitamin E deficient (VED) rats. The activities of GSH-Px in the lens of SeD rats decreased significantly. The GSH-Px activities of lens were positively related to erythrocytes selenium level. There was a free radical at g = 2.0015 in the rat lens of all groups, but the content of free radicals in the lens of SeD group was significantly higher than that of the control group. The free radical content of lens was negatively related to erythrocytes selenium level, as well as the GSH-Px activities in the lens. In vitro, ultraviolet radiation caused the generation of another kind of free radical (g = 2.0097) in the lens of all groups, but the amount of the free radical in the lens of the SeD group was also significantly higher than that of the control group. The activities of SOD and GSSG-R in VED rat lens were significantly decreased. The amount of MDA in the lens of SeD and/or VED rats were significantly increased. The results showed that the decrease of antioxidative capability in the lenses of SeD and/or VED rats accelerated the lipid peroxidation and generation of free radicals. Although only early morphological changes in SeD and/or VED rat lens were observed, it is considered that selenium and vitamin E deficiency may be involved in the occurrence of cataract.

Animals↗
PubMed1992

Age-related change of free radical generation in liver and sex glands of rats.

Many investigations have been made on age-related changes of lipid peroxidation in tissue homogenates and subcellular fractions. However, to date there are few reports on the age-related change of free radicals in living organs during aging. In our study, we investigated free radical concentration in liver and sex glands of different aged rats by using electron spin resonance (ESR) technique. A significant reduction of free radicals in liver and sex glands of old aged rats was observed when compared with those of young or middle-aged ones. The decrease of free radical generation during aging is discussed.

Aging↗
PubMed1991

Beneficial effects of N-acetylcysteine and cysteine in stunned myocardium in perfused rat heart.

1. The objective of this study was to evaluate the effects of three sulphydryl (SH) compounds, N-acetylcysteine (NAC), cysteine (Cys) and cystamine, on functional recovery and ventricular arrhythmias (VF) in stunned myocardium in the isolated perfused heart of the rat. 2. Hearts (n = 7-8 per group) were perfused by the Langendorff procedure for 20 min to stabilize and then assigned to one of five groups: saline, sham, NAC, Cys and cystamine. After the stabilizing period, the drugs (at 3.6 microM min-1) or their vehicle (saline) were infused into coronary vessels throughout the experimental period. Ten min after administration of drugs, the left anterior descending coronary artery (LAD) was ligatured for 20 min and then untied to reperfuse for 30 min. In the sham group, a ligature was placed around the LAD but not tied. 3. NAC and Cys had a significant effect in attenuating myocardial stunning: the percentage recovery of rate-pressure product measured 30 min after reperfusion as an index of heart function, was improved with the NAC (98.3 +/- 4.5) and Cys groups (104.0 +/- 6.5) compared with the saline (only 73.6 +/- 3.8, P < 0.01) group. Cystamine did not show these beneficial effects. This may be due to the difference in chemical structure between NAC, Cys and cystamine since the latter does not have a free SH group with a disulphide bond formed. This phenomenon suggests that a free SH group is essential for the protective effects of compounds like NAC and Cys in myocardial injury. 4. NAC and Cys prevented the fall in coronary flow during the LAD occlusion and enhanced coronary flow during reperfusion but cystamine did not have such a beneficial effect. 5. The incidence of VF in the saline, cystamine, Cys and NAC groups was 6/8 (75.0%), 4/7 (57.1%), 3/8 (37.5%) and 2/7 (28.6%), respectively, and no significant differences (P > 0.05) were noted between the saline- and drug-treated groups. 6. An in vitro study with electron spin resonance indicated that Cys effectively scavenged the hydroxyl radical (-OH) generated by Fenton's reaction but did not scavenge superoxide generated in an irradiated riboflavin system. NAC and cystamine showed a scavenging effect on -OH to a certain extent but this effect did not reach statistical significance (P > 0.05 vs saline). 7. Our results demonstrate that NAC and Cys treatment before ischaemia and reperfusion can reduce myocardial stunning. This beneficial effect may be mainly due to their ability to preserve and enhance coronary flow during coronary occlusion and reperfusion and in part due to scavenging -OH and/or replenishing intracellular glutathione. The results also indicate that the condition of coronary perfusion can produce a great impact on postischaemic ventricular performance.

Acetylcysteine↗