The naturally persistent flow of hundreds of dust particles is experimentally achieved in a dusty plasma system with the asymmetric sawteeth of gears on the electrode. It has also demonstrated that the direction of the dust particle flow can be controlled by changing the plasma conditions of the gas pressure or the plasma power. Numerical simulations of dust particles verify the experimental observations of the flow rectification of dust particles. Both experiments and simulations suggest that the asymmetric electric potential and the collective effect are two keys in this dusty plasma ratchet.A dusty plasma (or complex plasma) consists of micron-sized dust particles immersed in plasma environments such as the ionosphere, the semiconductor manufacture and the laboratory [1,2]. These dust particles are highly charged so that they can be strongly coupled [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Due to the various heating mechanisms in plasmas, such as the plasma instability [17] and the spatial/temporal particle charge fluctuation, the kinetic energy of these dust particles can reach from several eV [10] to tens eV [18,19] or even higher.Realizing the manipulation of those energetic dust particles can lead to further scientific insights and applications such as the particle separation and the energy collection. Turning the random motion of these dust particles into the directional motion will definitely pave the way for this manipulation. The Feynman ratchet model provides a strategy to rectify the nonequilibrium fluctuations into the directional motion of particles [20,21]. Here, we demonstrate a dusty plasma ratchet to experimentally realize a rectification of dust particles in a radio-frequency (rf) plasma, i.e., the dust particles are rectified into a directional flow by the Feynman ratchet strategy. Remarkably, we can experimentally control the direction of particle flow by regulating the gas pressure or the rf power of the plasma. We further explore the rectification mechanisms of the dusty plasma ratchet by performing numerical simulations.Experiments. -A circular resin gear (named inner gear) with asymmetric sawtooth is placed concentrically with another circular resin gear (named outer gear) on a horizontal lower electrode, as shown in Fig. 1(a). The sizes of the inner and outer gears are 9 mm in height, 11.75 and 23 mm in radius, 1.5 and 4 mm in depth, respectively *

L-Selenomethionine (SeMet), the predominant form of selenium acquired from the diet by humans, has been used as a supplement, and exhibit some important functions like cancer prevention and antioxidative defense. Its interactions with Pt(II) anticancer drugs have been characterized, but its redox reactions with platinum(IV) anticancer prodrugs have not been exploited. In this work, the oxidation of SeMet by Pt(IV) anticancer model compounds trans-[PtX2(CN)4](2-) (X = Cl, Br) was characterized. A stopped-flow spectrometer was used to record the rapid scan spectra and to follow the reaction kinetics over a wide pH range. An overall second-order rate law was derived: -d[Pt(IV)]/dt = k'[Pt(IV)][SeMet], where k' pertains to the observed second-order rate constants. The k'-pH profiles showed that k' increased only about 6 times even though the solution pH was varied from 0.25 to 10.5. The redox stoichiometry was determined as Δ[Pt(IV)]/Δ[SeMet] = 1 : (1.07 ± 0.07), suggesting that SeMet was oxidized to selenomethionine selenoxide. The selenoxide together with its hydrated form was identified explicitly by high resolution mass spectral analysis. A reaction mechanism was proposed which encompassed three parallel rate-determining steps relying on the protolytic species of SeMet. Rate constants of the rate-determining steps were obtained from the simulations of the k'-pH profiles. Activation parameters were determined for the reactions of the zwitterionic form of SeMet with the Pt(IV) complexes. A bridged electron transfer process is delineated in the rate-determining steps and several lines of evidence support the bridged electron transfer mode. Strikingly, reduction of [PtX2(CN)4](2-) by SeMet is 3.7 × 10(3)-5.7 × 10(4) times faster than that by L-methionine. Some potential biological consequences resulting from the strikingly fast reduction are discussed.

Platinum(iv) complexes with a heterocyclic ligand and an ancillary ligand have been investigated and applied for the formation of disulfide bonds in peptides.

In this study, l-methionine selenoxide (MetSeO) was used as an oxidant for the construction of peptide disulfide bonds. Excellent yields for various disulfide-containing peptides were achieved via the MetSeO oxidation method in different solvents and on a resin. Most importantly, the construction of disulfide bonds can be performed in the trifluoroacetic acid cocktail used for the cleavage of peptides from the resin, which obviates the steps of peptide purification and lyophilization. This facilitates and simplifies the synthesis of disulfide-containing peptides. Kinetic and mechanistic studies of the reaction between MetSeO and dithiothreitol (DTT, a model compound of dicysteine-containing peptide) show that the reaction is first order in both [MetSeO] and [DTT], and a reaction mechanism is proposed that can help us gain insights into the reaction of the oxidative synthesis of disulfide bonds via MetSeO oxidation.

• qDCE-MRI parameters are useful for discriminating between malignant and benign breast lesions. • K , K and MaxSlope were independent predictors of breast malignancy. • qDCE-MRI has a better diagnostic ability than morphology and kinetic analysis. • qDCE-MRI can be used to improve the diagnostic accuracy of breast malignancy.

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Cardiac SPECT images are known to suffer from both cardiac and respiratory motion blur. In this work, we investigate a 4D reconstruction approach to suppress the effect of respiratory motion in gated cardiac SPECT imaging. In this approach, the sequence of cardiac gated images is reconstructed with respect to a reference respiratory amplitude bin in the respiratory cycle. To combat the challenge of inherent high imaging noise, we utilize the data counts acquired during the entire respiratory cycle by making use of a motion-compensated scheme, in which both cardiac motion and respiratory motion are taken into account. In our evaluation study, we first use Monte Carlo simulated imaging data wherein the ground truth is known for quantitative comparison. We then demonstrate the proposed approach on eight sets of clinical acquisitions, in which the subjects exhibit different degrees of respiratory motion blur. The quantitative evaluation results show that 4D reconstruction with respiratory correction could effectively reduce the effect of motion blur and lead to a more accurate reconstruction of the myocardium. The mean-squared-error of the myocardium is reduced by 22%, and the LV resolution is improved by 21%. Such improvement is also demonstrated with the clinical acquisitions, where the motion blur is markedly improved in the reconstructed LV wall and blood pool. The proposed approach is also noted to be effective on correcting the spill-over effect in the myocardium from nearby bowel or liver activities.

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