实验物理创造教学与传统教学的比较

对实验物理创造教学与实验物理传统教学进行了比较,以求有助于从根本上理解和把握实验物理创造教学的实质。     

MAC protocol with delay-aware adaptive round time for split light-trail

Light-trail (LT) has been considered as an attractive solution for optical networks to support emerging services such as video-on-demand, pseudo-wires, and data-centers. The media access control (MAC) protocol is essential for LT networks because LT is a shared-medium. Recently, in order to enhance the throughput, a regular LT can be split into several sub-LTs at the split nodes where traffic undergoes optical-electronic-optical conversation. To deal with the split LT, a novel MAC protocol named Delay-aware adaptive round time for split LT (DAARTS) is developed on the basis of DAART MAC protocol and the schemes of splitting LT. To estimate the performance of the developed MAC protocol, ART, DAART and DAARTS protocols are simulated and compared in the scenarios of three different traffic patterns. Simulation results show that, for traffic 1 and traffic 2, DAARTS has stable throughput performance and can obtain almost 40.83% and 106.64% throughput improvement compared with DAART, respectively. In other words, DAARTS can further enhance the throughput of LT networks.     

Janus Metastructure Based on Magnetized Plasma Material with and Logic Gate and Multiple Physical Quantity Detection

In this paper, a Janus metastructure (JMS) is proposed that can act both as a logic gate and detect multiple physical quantities. By adjusting the incident angle of electromagnetic waves, arranging the dielectrics asymmetrically, and using the anisotropy of the plasma, the Janus function can be obtained, which gives the metastructure a multiscale property. Sharp transmission peak (TP) is generated by located defect mode resonance. The AND logic gate on the positive and negative scales can be realized by judging the TP value. By locking the point frequency of the TP, the refractive index, magnetic field strength, incident angle, and plasma density can be detected simultaneously on the two scales in the GHz range, which is rarely studied. Good sensing performances are also owned, and the corresponding optimal sensitivities are 0.095 (2πc/d)/RIU, 9.42 × 10⁻³ (2πc/d)/T, 1.48 × 10⁻³ (2πc/d)/°, and 0.035 (2πc/d) m³/10¹⁹, respectively. Compared with the traditional sensors, the proposed JMS equipped with two scales not only can realize the logic gate but also measure multiple physical quantities, which has a certain application potential.     

正项级数Cauchy判别法的改进

探讨了正项级数敛散性的判别方法。改进和推广了经典的Cauchy判别法,获得了一般形式的Cauchy判别法。     

Hydrogen-bond-induced quantum interference in single-molecule junctions of regioisomers

Solvents can play a significant role in tuning the electrical conductance of single-molecule junctions. In this respect, protic solvents offer the potential to form hydrogen bonds with molecular backbones and induce electrostatic gating via their dipole moments. Here we demonstrate that the effect of hydrogen bond formation on conductance depends on whether transport through the junction is controlled by destructive quantum interference (DQI) or constructive quantum interference (CQI). Furthermore, we show that a protic solvent can be used to switch the conductance of single-molecule junctions between the two forms of quantum interference. To explore this possibility, two regioisomers (BIT-Zwitterion and BIT-Neutral) were synthesized and their single-molecule conductances in aprotic and protic solvents were investigated using a scanning-tunneling-microscope-based break junction technique, combined with density functional theory and quantum transport theory. We find that the protic solvent twists the geometry of BIT-Zwitterion by introducing intermolecular hydrogen bonds between the solvent and target molecule. Moreover, it increases the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecule by imposing different electrostatic gating on the delocalized HOMO and localized LUMO, leading to a lower conductance compared to that in aprotic solvent. In contrast, the conductance of BIT-Neutral increases due to a transformation from DQI to CQI originating from a change from a planar to a folded conformation in the protic solvent. In addition, the stacking between the two folded moieties produces an extra through-space transport path, which further contributes to conductance. This study demonstrates that combinations of protic solvents and regioisomers present a versatile route to controlling quantum interference and therefore single-molecule conductance, by enabling control of hydrogen bond formation, electrostatic gating and through-space transport.

We demonstrate that the effect of solvent–molecule interaction through hydrogen bonding on junction conductance depends on whether transport through the junction is controlled by destructive or constructive quantum interference.     

B(C6F5)3催化合成二吲哚甲烷类化合物的研究

以硼试剂B(C₆F₅)₃为催化剂, 吲哚类化合物与芳香醛为底物, 经过脱除一分子水的过程, 简洁有效地制得了一系列二吲哚基甲烷类化合物. 该方法的模板反应在最优条件下可以实现快速转化, 底物范围适用性较广泛, 可以适用一系列取代基和官能团. 该研究发展了无过渡金属参与条件下直接制备二吲哚甲烷类化合物的简单策略, 其反应副产物为水, 反应条件温和, 可以实现目标化合物的有效合成.     

Evolution of Routes for Asymmetric Total Synthesis of Cyclocitrinol Enabled by Type Ⅱ [5+2] Cycloaddition

Main observation and conclusion The asymmetric total synthesis of an unusual C25 steroid containing a unique bicyclo[4.4.1]undecene A/B ring system,resulting in...     

Constructive Quantum Interference in Single-Molecule Benzodichalcogenophene Junctions

Heteroatom substitution into the cores of alternant, aromatic hydrocarbons containing only even-membered rings is attracting increasing interest as a method of tuning their electrical conductance. Here, the effect of heteroatom substitution into molecular cores of non-alternant hydrocarbons, containing odd-membered rings, is examined. Benzodichalcogenophene (BDC) compounds are rigid, planar π-conjugated structures, with molecular cores containing five-membered rings fused to a six-membered aryl ring. To probe the sensitivity or resilience of constructive quantum interference (CQI) in these non-bipartite molecular cores, two C₂-symmetric molecules (I and II) and one asymmetric molecule (III) were investigated. I (II) contains S (O) heteroatoms in each of the five-membered rings, while III contains an S in one five-membered ring and an O in the other. Differences in their conductances arise primarily from the longer S−C and shorter O−C bond lengths compared with the C−C bond and the associated changes in their resonance integrals. Although the conductance of III is significantly lower than the conductances of the others, CQI was found to be resilient and persist in all molecules.     

Enhancing single-molecule conductance of platinum (Ⅱ) complexes through synergistic aromaticity-assisted structural asymmetry

Seeking the strategies of designing highly conductive molecular structures is one of the core researches in molecular electronics.As asymmetric structure has manifested feasible properties in comprehensive fields, we introduce the structures of asymmetric platinum(Ⅱ) complexes into the charge transport study at single-molecule scale for the first time. The single-molecule conductance measurement results reveal that, in platinum(Ⅱ)-aryloligoynyl structures, the conductance of asymmetrically coordinated complexes is obviously higher than that of the symmetric isomers with the same molecular length, while the conductance is almost identical in symmetric and asymmetric platinum(Ⅱ)-oligoynyl complexes. Theoretical study uncovers that, upon connecting to the oligoynyl structure, the aromatic group effectively extends the π-system of the whole conductive backbone and gathers the HOMO population mainly on the longer oligoynyl ligand, which reduces the energy barrier in electron transport and enhances the conductance through HOMO energy lifting. This result provides feasible strategy for achieving high conductive molecular devices.