You-Quan Li

The Levinthal paradox states that it would be impossible for a protein to reach its native conformation in a physically meaningful time by randomly searching over all possible conformations. So far, it has been widely assumed that this random conformational search does not occur in the folding process, for which various putative hypotheses have had to be employed in model studies. Here we show that the quantum approach, describing the folding process as a quantum walk on a definite graph, gives rise to a fast protein-folding time. In terms of the conventional lattice model describing protein conformation, we introduce a procedure to enumerate all possible structures and then determine the definite connection graphs. Evaluating the mean first-passage time, we find it is much shorter than that obtained via random searching, and the magnitude of the quantum approach is reasonably in agreement with the experimental result. Some further discussions of various characteristic average quantities are also made by comparing both cases of quantum walk and classical random walk.

We present a phenomenological model for magnetoelectricity in multiferroic materials. The distinctive feature of the model is a two-component complex order parameter that encodes the electric polarization, along with a direct coupling between the polarization and magnetic field. Our model effectively elucidates that a sufficiently strong magnetic field can destroy electric polarization. Furthermore, the transition field strength diminishes with rising temperature, following a power-law relation with the exponent being precisely worked out. At lower field strength, the electric polarization takes a spiral order in the magnetic field, with the spiral wavelength inversely proportional to the magnetic field strength. We anticipate these predictions can be experimentally tested in future studies on multiferroic materials.

Detecting a weak electric field in a strong noisy background is always an interesting but hard task. We investigate the collective effects of charged Brownian particles in the presence of a weak electric field together with a strong noisy background field by numerical simulation. We show that the pattern formed by snapshots touched by the Brownian particles on one boundary surface can manifest the direction of an applied weak electric field but will be spoiled if there exists a strong noisy background. Moreover, we find that the influence of noise can be suppressed effectively if the correlations caused by the inter-particle electric interaction are taken into account. This work is expected to provide a new angle of view: correlated random walk plays a constructive role in noise suppression.

Navigation and positioning technologies play a key role in modern human activities. Currently, navigation devices are mostly dependent on the global navigation satellite systems, for example, the global positioning system (GPS). However, it is known that GPS signals can be jammed or spoofed or otherwise fail. As the need for GPS independent navigation increases in some practical application scenarios, novel navigation techniques based on the geomagnetic field have been developed. A main task of geomagnetic navigation is to obtain the amplitude and direction of the geomagnetic field accurately. Here, we introduce an alternative scheme for vectorial measurements of the local geomagnetic field for magnetic positioning based on the biological ferric sulfide cluster, which exists in the magnetoreceptor protein/cryptochrome complex in certain avian species. We find that by observing the number of peaks and the proportional rate of spectrum on resonance, both the direction and intensity of the magnetic field can be determined. Therefore, our findings may provide a fresh insight into magnetic field measurement and also suggest further guidelines for the design and operation of satellite-free navigation systems based on the electrically tunable inorganic biological molecules.

The Ginzburg–Landau theory, which was introduced to phenomenologically describe the destruction of superconductivity by a magnetic field at the beginning, has brought up much more knowledge beyond the original one as a mean-field theory of thermodynamics states. There the complex order parameter plays an important role. Here we propose a macroscopic theory to describe the features of ferroelectrics by a two-component complex order parameter coupled to nonabelian gauge potentials that provide more freedom to reflect interplays between different measurables. Within this theoretical framework, some recently discovered empirical static and time-independent phenomena, such as vortex, anti-vortex, spiral orders can be obtained as solutions for different gauge potentials. It is expected to bring in a new angle of view with more elucidation than the traditional one that takes the polarization as order parameter.

How migratory birds can find the right way when navigating over thousands of miles is an intriguing question that has greatly interested researchers in both the fields of biology and physics for centuries. There are several putative proposals that sound intuitively plausible; all remain contested so far because these hypothetical models of magnetoreceptors that sense the geomagnetic field need either extremely high sensitivity or humankind-like intelligence to guide. Here we explore theoretically whether birds can navigate to their destination through an entirely new scenario to sense the geomagnetic field. Our proposal is based on separate peaks of the resonance-fluorescence spectrum of a four-level system derived from the ferric sulfide cluster that exists in a MagR/Cry protein complex (Drosophila CG8198) of migratory birds. As the separation of spectral peaks contains information about the geomagnetic field at both the current location and the birthland, the change of such separation cues the bird to choose the right direction to move, and double-resonance emerges once it has arrived at its destination. Our theoretical mechanism can explain previous experiments on the disorientation of migratorybirds caused by oscillating magnetic field naturally and more precisely. This work provides insight into explaining migratory navigation and motivates possible humanmade practical devices.

To report the long-term clinical outcomes of low-risk (LR) and intermediate-risk (IR) prostate cancer patients treated with low-dose-rate brachytherapy (LDR-BT) and external beam radiation therapy ...

We study the protein folding problem on the base of our quantum approach by considering the model of protein chain with nine amino-acid residues. We introduce the concept of distance space and its projections on a XY-plane, and two characteristic quantities, one is called compactness of protein structure and another is called probability ratio involving shortest path. The concept of shortest path enables us to reduce the 388 × 388 density matrix to a 2 × 2 one from which the von Neumann entropy reflecting certain quantum coherence feature is naturally defined. We observe the time evolution of average distance and compactness solved from the classical random walk and quantum walk, we also compare the features of the time-dependence of Shannon entropy and von Neumann entropy. All the results not only reveal the fast quantum folding time but also unveil the existence of quantum intelligence hidden behind in choosing protein folding pathways.