Controllable electron-momentum filter in a δ-doped magnetically modulated semiconductor nanostructure

ABSTRACT

We have theoretically investigated the control of wave-vector filtering (WVF) by introducing δ-doping into a magnetically modulated nanostructure fabricated by depositing ferromagnetic stripes on top and bottom of a GaAs/Al_xGa_{1 ?x}As heterostructure. With the help of an improved transfer matrix method, the Schrödinger equation for electrons in this semiconductor nanostructure is solved exactly and the transmission efficient calculated numerically. We demonstrate that the WVF efficiency is associated closely with the weight and position of the δ-doping, which may be helpful for designing a controllable electron-momentum filter based on such a magnetically modulated semiconductor nanostructure.     

Infiltration behaviour of water in a carbon nanotube under external pressure

The wetting behaviour and associated pressure effect of water in single-walled carbon nanotubes (SWCNTs) are investigated through molecular dynamics (MD) simulations. It is found that water molecules can enter SWCNTs via surface diffusion, and the effective infiltration rate increases with pressure. The effect of pressure on infiltration rate is highly non-linear, exhibiting characteristics of both hydrophilic and hydrophobic surfaces. There exists a nominal infiltration pressure that is dependent on the SWCNT size, above which the water flux is significantly increased.     

Wentzel–Kramers–Brillouin solution of cut-off frequency for horizontal shear (SH) waves in various inhomogeneous thin films

The Wentzel–Kramers–Brillouin method is employed to study the cut-off frequencies of the horizontal shear waves in a freestanding functionally graded piezoelectric–piezomagnetic material film with the electrically and magnetically open boundary conditions. An analytical solution, which could be used in analyzing the problems of various functionally graded materials, is proven to have high precision by analytical analysis and a numerical example. The results reveal that the set of cut-off frequencies is a series of approximate arithmetic progressions. A theoretical foundation based on the relationship between the cut-off frequencies and the materials’ gradient property is established for nondestructive evaluation.     

High magnetic field induction of the formation of twinned dendrites during directional solidification of Al–4.5wt%Cu alloy

It is reported that the application of a high magnetic field is capable of inducing the formation of twinned dendrites during directional solidification of Al–4.5wt%Cu alloy. Numerical results reveal that a unidirectional thermoelectric magnetic force acts on tilted dendrites during directional solidification under a magnetic field. This force should be responsible for the formation of twinned dendrites. The work may initiate a new method for inducing twinned dendrites in Al-based alloys via an applied high magnetic field during directional solidification.     

Functional connectivity abnormalities during contextual processing in schizophrenia and in Parkinson’s disease

Functional connectivity was evaluated in patients with schizophrenia (SC) and in patients with Parkinson’s disease (PD) during the performance of a local contextual processing paradigm, to investigate the proposition that functional disconnection is involved with contextual processing deficits in these populations. To this end, we utilized event-related EEG signals, synchronization likelihood and graph theoretical analysis. Local context was defined as the occurrence of a predictive sequence of stimuli before the presentation of a target event. In the SC patients, we observed a decrease in path length (L) in the beta band, for the predictive sequence and for predicted and random targets, compared with controls. These abnormalities were associated with weaker frontal-temporal-parietal connections. In the PD patients we found longer L (theta band) for predicted targets, and higher cluster coefficients for both the predictive sequence (theta band) and predicted targets (alpha and theta bands), compared with controls. Detection of predicted targets was associated with weaker frontal-parietal connections in PD. No group differences were found for randomized standard stimuli in both SC and PD patients. These findings provide evidence of task-specific functional connectivity abnormalities within frontal networks during local contextual processing.     

价值导向元记忆中价值顺序效应初探

采用选择性记忆任务,通过价值顺序2(价值在前、价值在后)×价值高低3(低、中、高)的被试内实验设计考察价值导向元记忆的价值顺序效应。结果发现：(1)空间维度上,价值顺序在前时被试的价值导向元记忆与价值在后无显著差异(实验1);(2)时间维度上,价值顺序优先时被试价值导向元记忆水平显著高于价值随后呈现,并且价值顺序对不同学习阶段价值导向元记忆有显著影响,出现价值顺序效应(实验2)。研究结果为探讨价值顺序对元记忆的影响提供了实证依据,对教学实践有参考价值。     

Vocal emotions influence verbal memory: Neural correlates and interindividual differences

Past research has identified an event-related potential (ERP) marker for vocal emotional encoding and has highlighted vocal-processing differences between male and female listeners. We further investigated this ERP vocal-encoding effect in order to determine whether it predicts voice-related changes in listeners’ memory for verbal interaction content. Additionally, we explored whether sex differences in vocal processing would affect such changes. To these ends, we presented participants with a series of neutral words spoken with a neutral or a sad voice. The participants subsequently encountered these words, together with new words, in a visual word recognition test. In addition to making old/new decisions, the participants rated the emotional valence of each test word. During the encoding of spoken words, sad voices elicited a greater P200 in the ERP than did neutral voices. While the P200 effect was unrelated to a subsequent recognition advantage for test words previously heard with a neutral as compared to a sad voice, the P200 did significantly predict differences between these words in a concurrent late positive ERP component. Additionally, the P200 effect predicted voice-related changes in word valence. As compared to words studied with a neutral voice, words studied with a sad voice were rated more negatively, and this rating difference was larger, the larger the P200 encoding effect was. While some of these results were comparable in male and female participants, the latter group showed a stronger P200 encoding effect and qualitatively different ERP responses during word retrieval. Estrogen measurements suggested the possibility that these sex differences have a genetic basis.     

双言舌尖现象的产生机制：来自粤语-普通话双言者的证据

舌尖现象(Tip-of-the-Tongue phenomenon, TOT)是言语产生中的一种常见现象。国外研究发现, 双语者和单语者的舌尖现象差异很大。双言和双语既相似, 又存在差异。以粤语–普通话双言者为被试, 比较了普通话熟练和不熟练的被试在使用不同语言命名时的TOT产生率。结果发现：(1)粤语–普通话双言者的TOT率受普通话熟练程度影响。普通话不熟练的粤语–普通话双言者用普通话命名时产生更高的TOT率。(2)语言启动能够调节粤语–普通话双言者的普通话熟练程度与TOT产生的关系。在语言启动条件下, 普通话熟练的粤语–普通话双言者的TOT率更高。(3)粤语–普通话双言者的TOT产生机制符合部分激活理论的预言。     

强迫症诊断研究的新变化

临床实践与相关研究表明,强迫症的诊断标准已不能满足复杂的临床工作需要。首先,有关患者的自知力以及主观痛苦程度等诊断指标需要进一步修订。其次,就强迫症的核心症状而产生的争议,研究者提出应重新考虑强迫症、焦虑障碍、强迫谱系障碍和囤积障碍这四个概念之间的从属关系和诊断标准。未来研究应考虑从认知神经科学的视角探索强迫症的核心症状和病理机制,为强迫症的诊断标准提供新的依据。     

Mechanochemical synthesis for studying the melting of metallic nanoparticles: a case study of copper

Mechanochemical synthesis is a promising method for studying the size-dependent melting of metals if the size of the resulting metallic nanoparticles can be tuned effectively. Here, with Cu as an example, we show that tuning of particle sizes can be accomplished by extending the milling time at a high milling speed and following annealing of the milled samples. With the so prepared samples, the melting point depression of Cu nanoparticles and its size dependence are successfully investigated.