Production of Light Nuclei at Thermal Freezeout in Heavy-Ion Collisions

We revisit the problem of the production of light atomic nuclei in ultrarelativistic heavy-ion collisions. While their production systematics is well produced by hadro-chemical freezeout at temperatures near the QCD pseudo-critical temperature, their small binding energies of a few MeV per nucleon suggest that they cannot survive as bound states under these conditions. Here, we adopt the concept of effective chemical potentials in the hadronic evolution from chemical to thermal freezeout (at typically $T_{\rm fo}$$\simeq$100\,MeV), which, despite frequent elastic rescatterings in hadronic matter, conserves the effective numbers of particles which are stable under strong interactions, most notably pions, kaons and nucleons. It turns out that the large chemical potentials that build up for antibaryons result in thermal abundances of light nuclei and antinuclei, formed at thermal freezeout, which essentially agree with the ones evaluated at chemical freezeout. Together with their transverse-momentum spectra, which also indicate a kinetic freezeout near $T_{\rm fo}$, this provides a natural explanation for their production systematics without postulating their survival at high temperatures.Comment: 5 pages, 7 figures, v2: "Note added" correcte

Break Time on the School Schedule: Evidence from Basic Education Schools in China

The mandatory 10-minute break on the basic education school schedule in China is intended to help students relieve fatigue and pressure and refresh their minds and bodies between lessons. However, instructional activities have often taken precedence over its intended purpose. This article described the current state of break time deprivation among Chinese basic education students and analyzed its causes, with a view to arousing more attention to the protection of the right of the student to rest and leisure activities at school

Conception de l’analogue topologique d’un bit magnétique

Dans ce mémoire, nous concevons l’analogue topologique d’un bit magnétique. À partir du modèle de SSH-Holstein, nous avons montré qu’une perturbation externe transi- toire entraine un changement permanent de la topologie de bande. Cela contraste avec l’ingénierie de Floquet, dans laquelle le système revient à son état d’origine lorsque la perturbation externe est désactivée. Le modèle SSH-Holstein se compose d’une chaine unidimensionnelle d’orbitales avec couplage électron-phonon de type SSH (entre les sites) et de type Holstein (sur site). Lorsque le couplage SSH domine, l’état fondamen- tal présente une instabilité et devient une onde de densité de lien. L’onde de densité de lien a deux états fondamentaux topologiquement distincts mais énergétiquement identiques, qui diffèrent par le signe de la dimérisation. Lorsque le couplage Holstein domine, le système devient une onde de densité de site. Cependant, cette dernière n’a pas de topologie de bande bien définie. Près de la frontière de phase entre les ondes de densité de lien et de site, nous avons effectué un calcul explicite du paramètre d’ordre microscopique qui favorise l’onde de densité de lien. Ses deux états fondamentaux énergétiquement identiques mais topologiquement distincts sont l’analogue des deux états d’un bit magnétique. Le problème clé est alors de montrer qu’il est possible de passer d’un état à l’autre de l’onde de densité de lien. Pour atteindre cet objectif, nous avons utilisé le formalisme de l’intégrale de chemin pour dériver l’équation du mou- vement du paramètre d’ordre. Nous avons constaté que l’équation du mouvement est profondément liée à l’anomalie chirale, et qu’il y a une analogie avec l’effet Josephson fractionnaire. Enfin, nous avons répondu par l’affirmative à la question clé et identi- fié des régimes de paramètres et de perturbations dans lesquels le bit topologique est réalisé. iAbstract: In this thesis, we design the topological analogue of a magnetic bit. Starting from the SSH-Holstein model, we showed that a transient external perturbation leads to a permanent change in the band topology. This contrasts with Floquet engineering, in which the system goes back to its original state when the external perturbation is turned off. The SSH-Holstein model consists of a one-dimensional chain of orbitals with SSH-type (inter-site) and Holstein-type (on-site) electron-phonon coupling. When the SSH coupling dominates, the ground state displays an instability and becomes a bond-density wave. The bond-density wave has two topologically distinct but energetically identical ground states, differing by the sign of the dimerization. When the Holstein coupling dominates, the system becomes a site-density wave. However, the latter has no welldefined band topology. Close to the phase boundary between the bond- and site-density waves, we performed an explicit calculation for the microscopic order parameters which favor the bond-density wave ground state. These two energetically identical but topologically distinct ground states are the analogue of the two states of a magnetic bit. The key problem is then to show that it is possible to switch between the two states of the bond-density wave. To achieve the goal, we used the path-integral formalism to derive the equation of motion of the order parameter. We found that the equation of motion is deeply related to the chiral anomaly, and that there is an analogy with the fractional Josephson effect. Finally, we provided a positive answer to the key question, and we identified parameter regimes in which the topological bit is realized

Chinese and British Teachers’ Emotional Reactions Towards Students’ Classroom Behaviours

The primary objective of this research is to investigate whether Chinese instructors who work in the UK experience different emotions in comparison with British instructors when facing students’ disruptive behaviour. With the increase of the globalization, lager numbers of teachers are teaching abroad (Weber, 2007). Working as international teachers, this group of teachers’ built-in beliefs and cultural values may be challenged by the new cultural context in which they work (Hofstede, 1986; Volet & Ang, 1998). Moreover, according to appraisal theory, when judging an antecedent to an emotion, a person’s cultural beliefs and goals are drawn on (Lazarus, 1991; Frijda, 1986); as such, it can be assumed that, compared with local teachers, international teachers may experience different or more intense emotions due to their different beliefs and goals when they both confront the same students’ behaviours (Sutton & Wheatley 2003). In order to examine this assumption, three phases of studies (a questionnaire survey with video scenarios, a diary study and interviews) were designed. The questionnaire survey with video scenarios of classroom misbehavior contained 47 Chinese and 52 British instructors/teachers as participants and discovered that teachers from China experienced a significantly higher level of anxiety and shame than British teachers. Interestingly, there is a trend showing that British instructors perceived students’ misbehaviours were more troublesome than Chinese instructors, however, when they watched the video clips their emotional reactions to those behaviours in the classroom are less intensive than that of Chinese instructors in general. Finally, according to results from interview study, the depth of tolerance, accountability and teacher’s self-efficacy could be factors that result in these differences discovered between British and Chinese instructors

Theory of a topological analogue of the magnetic bit

In magnetic memories, the state of a ferromagnet is encoded in the orientation of its magnetization. The energy of the system is minimized when the magnetization is parallel or antiparallel to a preferred (easy) axis. These two stable directions define the logical bit. Under an external perturbation, the direction of magnetization can be controllably reversed and thus the bit flipped. Here, we theoretically design a topological analogue of the magnetic bit in the Su-Schrieffer-Heeger (SSH)-Holstein model, where we show that a transient external perturbation can lead to a permanent change in the electronic band topology.Comment: 13 pages, 5 figure

Audio Visual Speaker Localization from EgoCentric Views

The use of audio and visual modality for speaker localization has been well studied in the literature by exploiting their complementary characteristics. However, most previous works employ the setting of static sensors mounted at fixed positions. Unlike them, in this work, we explore the ego-centric setting, where the heterogeneous sensors are embodied and could be moving with a human to facilitate speaker localization. Compared to the static scenario, the ego-centric setting is more realistic for smart-home applications e.g., a service robot. However, this also brings new challenges such as blurred images, frequent speaker disappearance from the field of view of the wearer, and occlusions. In this paper, we study egocentric audio-visual speaker DOA estimation and deal with the challenges mentioned above. Specifically, we propose a transformer-based audio-visual fusion method to estimate the relative DOA of the speaker to the wearer, and design a training strategy to mitigate the problem of the speaker disappearing from the camera's view. We also develop a new dataset for simulating the out-of-view scenarios, by creating a scene with a camera wearer walking around while a speaker is moving at the same time. The experimental results show that our proposed method offers promising performance in this new dataset in terms of tracking accuracy. Finally, we adapt the proposed method for the multi-speaker scenario. Experiments on EasyCom show the effectiveness of the proposed model for multiple speakers in real scenarios, which achieves state-of-the-art results in the sphere active speaker detection task and the wearer activity prediction task. The simulated dataset and related code are available at https://github.com/KawhiZhao/Egocentric-Audio-Visual-Speaker-Localization

Chinese and British university teachers' emotional reactions to students' disruptive classroom behaviors

As globalisation increases, more teachers are teaching abroad. New teaching contexts present challenges to international teachers’ mental health. According to appraisal theory, the elicitation of an emotion is an interplay between situational (context) and dispositional (beliefs) antecedents, and people’s built-in dispositions are socially constructed and culturally shaped. Based on this premise, it can be assumed that, compared with local teachers, international teachers may experience different types or intensities of emotions due to their different beliefs and goals when they confront the same disruptive behaviours by students in the classroom. The aim of this research is to investigate Chinese teachers’ and British teachers’ emotional experiences while working in universities in the UK through a mixed methods study. The methodology that is employed in the present research is a pragmatic approach. A sequential mixed-methods design was used to examine the assumptions and discover possible explanations for the phenomenon. Study One investigated 99 participants (47 Chinese teachers and 52 British teachers) through a novel video-based survey and found that university teachers who were originally from China experienced a significantly higher level of anxiety and shame than teachers who were originally from Britain. The results show that in a new cultural context, international teachers can experience higher-level negative emotions in comparison with indigenous teachers. Study Two used semi-structured interviews to examine what factors could result in the differences discovered by Study One. The results indicated that the appraisal dimension of accountability and self-construals, shaped by cultural values, were the key factors influencing teachers’ emotional experiences. Overall, the research findings have implications for supporting international teachers’ emotional acculturation and the sustainable development of both policymakers and practitioners in foreign teaching contexts

DiffS2UT: A Semantic Preserving Diffusion Model for Textless Direct Speech-to-Speech Translation

While Diffusion Generative Models have achieved great success on image generation tasks, how to efficiently and effectively incorporate them into speech generation especially translation tasks remains a non-trivial problem. Specifically, due to the low information density of speech data, the transformed discrete speech unit sequence is much longer than the corresponding text transcription, posing significant challenges to existing auto-regressive models. Furthermore, it is not optimal to brutally apply discrete diffusion on the speech unit sequence while disregarding the continuous space structure, which will degrade the generation performance significantly. In this paper, we propose a novel diffusion model by applying the diffusion forward process in the \textit{continuous} speech representation space, while employing the diffusion backward process in the \textit{discrete} speech unit space. In this way, we preserve the semantic structure of the continuous speech representation space in the diffusion process and integrate the continuous and discrete diffusion models. We conduct extensive experiments on the textless direct speech-to-speech translation task, where the proposed method achieves comparable results to the computationally intensive auto-regressive baselines (500 steps on average) with significantly fewer decoding steps (50 steps).Comment: Accepted in EMNLP2023 main conferenc