A sustainable route from the biomass byproduct okara as a natural nitrogen fertilizer to high-content N-doped carbon sheets is demonstrated. The as-prepared unique structure exhibits high specific capacity (292 mAh g(-1) ) and extremely long cycle life (exceeding 2000 cycles). A full battery is devised for the practical use of materials with a flexible/wearable LED screen.

We developed a highly efficient photocatalyst for both H2 and O2 generation under visible-light irradiation by attaching Bi2WO6 (BWO) nanocrystals on graphene nanosheets to produce a graphene-Bi2WO6 composite (Gr-BWO-T). The composite was prepared by a sonochemical method where graphene oxide (GO) served as the support on which BWO formed in situ. Bi2WO6 nanoparticles with the size of 30-40 nm were homogeneously dispersed on the surface of graphene sheets, due to their bonding with graphene. When used as a photocatalyst under visible-light irradiation, O2 production rate reached a value up to 20.60 μmol h(-1), 4.18 times higher than that of bare BWO, resulting from the strong covalent bonding between graphene and BWO nanoparticles. The chemical bonding facilitated the electron collection and transportation and inhibited the recombination of photo-generated charge carriers, even in this system with a large amount of graphene inside (40 wt%). More interestingly, H2-production by Gr-BWO-T was also observed to be as high as 159.20 μmol h(-1). This could be ascribed to the existence of the graphene that led to decrease in conduction band potential and resulted in a more negative reduction potential than H(+)/H2. This facile sonochemical approach provides a new strategy for engineering ternary compound nanoparticles on graphene sheets, with great potential application in energy conversion.

Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a circularly polarized microwave can reverse the magnetization of a Stoner particle through synchronization. In comparison with magnetization reversal induced by a static magnetic field, it can be shown that when a proper microwave frequency is used the minimal switching field is much smaller than that of precessional magnetization reversal. A microwave needs only to overcome the energy dissipation of a Stoner particle in order to reverse magnetization, unlike the conventional method with a static magnetic field where the switching field must be of the order of magnetic anisotropy.

We report a novel method for the preparation of graphitic carbon nitride (g‐C3N4) with various morphologies through self‐assembly and calcination, which starts from the raw materials melamine, urea, and cyanuric acid. The hollow to wormlike morphologies of g‐C3N4 could be readily tailored by adjusting the molar ratio of melamine to urea; with increase in the molar ratio from 3:1 to 1:3, a morphology transformation was observed. The morphologies were tailored by self‐assembly of the aggregates by hydrogen bonding and ionic interactions. Correspondingly, an increased BET surface area from 49.6 to 97.4 m2 g−1 was observed. If used as a photocatalyst in degrading rhodamine B (RhB) under visible‐light irradiation, these g‐C3N4 samples demonstrated 7 to 13 times higher performance than conventional bulk g‐C3N4. The high performance was attributed to the unique morphology that provided not only high specific surface area but low recombination losses of photogenerated charges.

The magnetization reversal of Stoner particles is investigated from the point of view of nonlinear dynamics within the Landau-Lifshitz-Gilbert formulation. The following results are obtained. ͑1͒ We clarify that the so-called Stoner-Wohlfarth ͑SW͒ limit becomes exact when the damping constant is infinitely large. Under the limit, the magnetization moves along the steepest-energy-descent path. The minimal switching field is the one at which there is only one stable fixed point in the system. ͑2͒ For a given magnetic anisotropy, there is a critical value for the damping constant, above which the minimal switching field is the same as that of the SW limit. ͑3͒ We illustrate how fixed points and their basins change under a field along different directions. This change explains well why a nonparallel field gives a smaller minimal switching field and a short switching time. ͑4͒ The field of a ballistic magnetization reversal should be along a certain direction window in the presence of energy dissipation. The width of the window depends on both the damping constant and magnetic anisotropy. The upper and lower bounds of the direction window increase with the damping constant. The window width oscillates with the damping constant for a given magnetic anisotropy. It is zero for both zero and infinite damping. Thus, the perpendicular field configuration widely employed in the current experiments is not the best one since the damping constant in a real system is far from zero.

The dependence of charges accumulated on a quantum dot under an external voltage bias is studied. The charge is sensitive to the changes of number of filled levels and the number of conducting levels ͑channels͒. We clarify that there are two possible outcomes of applying a bias. ͑a͒ The number of conducting channels increases, but the number of filled levels decreases. ͑b͒ The number of filled levels increases or does not change while the number of conducting channels ͑levels͒ increases with the bias. In case ͑b͒, charges are generally expected to increase monotonically with the applied bias. We show, however, that this expectation may not materialize when the electron transmission coefficients depend on bias. Numerical evidences and a theoretical explanation of this negative differential capacitance, i.e., charges accumulated on a quantum dot decrease with applied bias, are presented. The capacitance of a quantum dot ͑QD͒ has been the subject of many studies.1,2 This is largely due to the fact that classical results derived from a macroscopic system are not applicable to a system of nanometer scale at which electron levels are discrete and the density of state is finite. So far, most studies have been on modifications of classical capacitance due to the finite density of states and electron tunneling, such as fluctuation of differential capacitance with respect to the gate voltage.3 However the nonlinear chargevoltage characteristics 4,5 has been less studied. A QD can be viewed as a potential well which is capable of accommodating electrons. Figure 1 is a schematic diagram of a QD connected to two external leads. The two leads can have different electrochemical potentials, and their difference is called the external bias on the dot. At nonzero bias, a tunneling current may pass through the QD while the electric charges on the QD can also vary with bias. There are three possible ways of applying a bias. Without losing generality, let us assume the electrochemical potential of the left lead L is no less than that of right lead R , i.e., L у R . The first way is to raise L while one keeps R unchanged as shown in Fig. 1͑b͒. The dashed line is electrochemical potentials of two leads at zero bias. The second way is to lower R , but L does not change. This is shown in Fig. 1͑c͒. The third way is to raise L and to lower R simultaneously as shown in Fig. 1͑d͒. Experimentally, all three ways described in Fig. 1 can be realized easily by controlling the gate voltage of the QD. Here we shall be interested in how the charge Q(V) on the QD change with the bias V. Intuitively, the behavior Q(V) depends on how a bias V is applied.An electron on the dot must occupy on one energy level. At zero temperature, there are three types of energy levels. One is the empty levels on which there are no electrons. They are the levels above L . The second type is the filled levels below R . The third type is conducting levels ͑chan-nels͒ which are between R and L , and are partially filled by electrons. In the case of Fig. 1͑b͒, as the exte...

We investigate field-driven domain wall (DW) propagation in magnetic nanowires in the framework of the Landau-Lifshitz-Gilbert equation. We propose a new strategy to speed up the DW motion in a uniaxial magnetic nanowire by using an optimal space-dependent field pulse synchronized with the DW propagation. Depending on the damping parameter, the DW velocity can be increased by about 2 orders of magnitude compared to the standard case of a static uniform field. Moreover, under the optimal field pulse, the change in total magnetic energy in the nanowire is proportional to the DW velocity, implying that rapid energy release is essential for fast DW propagation.

We study the role of periodically driven time-dependent Rashba spin-orbit coupling (RSOC) on a monolayer graphene sample. After recasting the originally 4 × 4 system of dynamical equations as two time-reversal related two-level problems, the quasienergy spectrum and the related dynamics are investigated via various techniques and approximations. In the static case, the system is gapped at the Dirac point. The rotating wave approximation (RWA) applied to the driven system unphysically preserves this feature, while the Magnus-Floquet approach as well as a numerically exact evaluation of the Floquet equation show that this gap is dynamically closed. In addition, a sizable oscillating pattern of the out-of-plane spin polarization is found in the driven case for states that are completely unpolarized in the static limit. Evaluation of the autocorrelation function shows that the original uniform interference pattern corresponding to time-independent RSOC gets distorted. The resulting structure can be qualitatively explained as a consequence of the transitions induced by the ac driving among the static eigenstates, i.e., these transitions modulate the relative phases that add up to give the quantum revivals of the autocorrelation function. Contrary to the static case, in the driven scenario, quantum revivals (suppressions) are correlated to spin-up (down) phases.