液滴蒸发动力学研究 | 本周物理学讲座
报告人：满兴坤，北京航空航天大学
时间：5月28日（周二）16:00
单位：北京师范大学
地点：物理楼106
液滴蒸发不仅是日常生活的常见现象，也是工业制备的关键步骤。液滴蒸发的动力学研究对喷墨打印、纳米电路印刷、微电子器件制备、液滴定向输运、热传导、疾病检测等等有着重要的指导意义。 我们基于Onsager变分原理，提出了液滴蒸发动力学理论模型，成功给出了液滴蒸发后溶质在衬底上的各种环状沉积图案的形成机理和液滴定向运动的机制。在沉积图案方面：理论结果表明，可以通过调控液滴接触线与衬底的磨擦系数以及液滴蒸发速率，来实现沉积图案连续的从“咖啡环”到“火山状”再到“山状”结构的变化；针对多环沉积图案，理论上给出了实验上普遍观察到的环状结构到连续平台结构转变的条件；研究了两个相邻液滴蒸发后在衬底上形成的非对称环状结构。 两个液滴之间的蒸发速率梯度是形成非对称沉积图案的主要原因，即非对称的蒸发速率使得溶质粒子的速度不再具有轴对称性。通过控制非对称蒸发速率梯度的大小和接触线在衬底的滑移强度，我们预测了扇形和月食形的沉积图案。在液滴运动方面：一直以来 Marangoni 效应(由非均匀表面张力引起液滴内部的对流)是解释和实现液滴运动的主要物理机理。然而，这一机理却不能解释中性衬底上两个 完全相同的单组份液滴自发靠近的运动现象。基于 Onsager 变分原理，我们提出了液滴运动方程，首次给出了非均匀蒸发速率和表面张力诱导液滴运动的物 理机制。理论结果指出: 液滴会从蒸发速率快的一侧移动到蒸发速率慢的一侧 和会从表面张力小的一侧移动到表面张力大的一侧。当两者同时起作用时，液 滴则会表现出吸引、排斥、追赶等复杂运动现象。通过与实验课题组合作，我们还在实验上证实了这些理论预测。
报告人：Weitao Sun，ZHOU PEI-YUAN Center for Applied Mathematics
单位：清华大学
时间：5月28日（周二）10:30
地点：蒙民伟科技南楼S727
Granular matter, which is made of macroscopic particles, has been thought as the second most ubiquitous substance following water. The granular material can range in size from sands at micrometer to asteroids at kilometer. The most amazing characteristics is that it can form a hybrid state between fluid and solid. Unlike conventional fluid and solid, granular matter shows rich interesting dynamic behaviors, including size segregation and vortex structure formation. Some of the phenomena are believed to be associated with the dynamics of Saturn’s dense rings and the mantle convection inside a planet like the Earth. Despite granular dynamics play substantially important roles in many scientific field, the mechanism remains poorly understood. Although hydrodynamic models have been successfully applied to rapid granular flows, it may not be sufficiently general to accurately predict remarkable difference between grains and fluids behaviors, especially when the mean free path of the particle collisions is comparable to or smaller than the particle size.
In this talk, I reported the existence of a quasi-symmetric segregation-convection pattern in tightly filled granular sphere and disks rotating around a horizontal axis in experiments. The convection patterns are different from conventional fluid in that the vortex roll is segregated into alternating small-large particle bands, from inner core to the periphery. Amazingly, there exists mass transportation among the vortex rolls, which instead of destroying but maintain the segregated vortex structure. The global segregation-convection structure comes into a stable state after a quick initialization stage (a few hours). While local scale grain migration and mass circulation persists for long-term evolution (from days to a few weeks). What’s more striking is that two clear radial/tangential flux gaps emerge at a distance of about 1/3 and 0.88 radius from the disk center, which separates the granular disk into concentric rings. We realize that the formation of crust-mantle-core structure inside a planet like the Earth and the newly discovered ringlets in Saturn’s ring are in no ways as simple as the formation of gaps in a rotating granular sphere. However, the analogy is so strong that it naturally suggests a very interesting question: can vortexes and gaps be spontaneously generated in a rotating granular sphere/disk with the size of planet? This calls for a unified granular dynamics theory which would be applicable both in dilute particulate rings and in densely packed particle system.
报告人：Yuanxun Liao，University of Manchester
时间：5月28日（周二）14:00
单位：中科院物理研究所
地点：M253会议室
Coherent electron transports have been observed through a monolayer of 4nm PbS quantum dots (QD) of short-range orders. Coherent injection from Si leads to multi-dot resonant tunneling. The resonant tunneling shows ideal negative differential resistance (NDR), due to inter-dot coherence. The needle-like NDRs have peak-to-valley-current ratios above 800 and line-widths below several meV. This is attributed to the size distribution of QDs and the short-range delocalization when variable-range-hopping changing to nearest-neighbor-hopping. The ultra-high quality NDR once only achieved by gate-defined QDs at near-zero temperature now could be possible with macroscale 2D colloidal QDs at room-temperature. This amazing fact inspires a ‘laser-like’ solid electron source, which could be very useful for quantum electronics and quantum information. These findings enrich our understandings for carrier transport in QDs and expand QD applications.
4Intertwined Magnetic and Nematic Orders in Semiconducting KFe0.8Ag1.2Te2
报告人：Yu Song，University of Californi
时间：5月28日（周二）15:30
单位：中科院物理研究所
地点：M253会议室
Strongly correlated materials often adopt electronic ground states that break rotational-symmetry of their underlying crystal structures, analogous to nematic liquid crystals. Such states are found in close proximity to and are an essential aspect of iron-based superconductors. Important questions in these materials concern the nature of their nematic and magnetic orders, whether the magnetism is due to local moments or itinerant electrons, and whether the nematic order is driven by the magnetic or the orbital degree of freedom. Using scattering techniques we demonstrate the presence of intertwined nematic and stripe-type magnetic orders in semiconducting KFe0.8Ag1.2Te2, a structural analogue of iron-based superconductors. A small strain induces sizeable magnetic anisotropy above the magnetic and nematic transition temperatures, indicating a large nematic susceptibility. Because KFe0.8Ag1.2Te2 is a semiconductor devoid of a Fermi surface, its magnetic and nematic orders likely arise from interactions between local moments. Such interactions should be important for systems containing Fe-pnitogen/chalcogen planes in general, including iron-based superconductors. Our results suggest several aspects of the phenomenology of iron-based superconductor result from the unique geometry of the iron-pnictogen/chalcogen planes.
5Magneto-elastocaloric effect and additive manufacturing for elastocaloric solid-state cooling
报告人：Huilong Hou，University of Marylan
时间：5月29日（周三）10:00
单位：中科院物理研究所
地点：M253会议室
Elastocaloric cooling, in which substantial temperature variations in materials respond to an application and removal of a mechanical field, is the latest discovered type in solid-state caloric cooling. In the first section of this talk, I will present a composite magneto-elastocaloric effect with an ultra-low magnetic field (0.16 T) in a compact geometry to generate a cooling temperature change as large as 4 K using a magnetostriction/superelastic alloy composite. In the second section, I will show our progress on exploring unique properties of elastocaloric alloys by use of laser directed-energy-deposition, a powder-fed additive manufacturing technique in collaboration with Ames laboratory.
报告人：Hongbin Li，Uiversity of British Columbia
时间：5月29日（周三）10:30
单位：中科院物理研究所
地点：M238会议室
Metal ions play important roles in biology. In metalloproteins, metal centers serve as active sites, as well as important structural elements to facilitate protein folding and assembly. However, it is challenging to investigate the unfolding-folding of metalloproteins due to the loss or decomposition of the metal center. Here, we combine single molecule force spectroscopy (atomic force microscopy and optical tweezers) and protein engineering techniques to investigate the unfolding-refolding mechanism of a small iron sulfur protein rubredoxin and ferredoxin. Our results revealed that the unfolding of both proteins are characterized by the initial partial unfolding of the protein followed by the rupture of the iron sulfur center and complete unraveling of the protein. However, differences in the iron chelation motif in rubredoxin and ferredoxin gave rise to distinct rupture patterns of the iron sulfur center. After complete unfolding, rubredoxin and ferredoxin were observed to refold to its holo-native form with the fully reconstituted iron sulfur center. Moreover, folding of the apo- rubredoxin was observed during the folding of rubredoxin, while apo-ferredoxin was not observed to form, revealing different roles and importance of the iron sulfur center to the holo-proteins. Our results open new avenues towards investigating the folding mechanism of metalloproteins at an unprecedented resolution.
7Detection of the Circumgalactic Medium of Nearby Galaxies via Emission Lines
报告人：Huanian Zhang，University of Arizona
时间：5月29日（周三）12:00
单位：北京大学
地点：KIAA 1st meeting room
Galaxies are surrounded by diffuse and extended gas, which is often called the circumgalactic medium (CGM) and is the least understood part of galactic ecosystems. The CGM harbors more than 60% of the total baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. Observations and simulations of the CGM suggest that it is a multi-phase medium characterized by rich dynamics and complex ionization states. The study of the CGM has so far generally come from absorption line studies of the spectra of distant objects, typically QSOs, whose lines of sight intersect lower redshift galaxy halos. However, such study is limited by statistics. Instead, I will describe a novel approach to study the CGM via emission lines, which allows for direct mapping of individual galaxies and a variety of results obtained.
报告人：李桃，西安交通大学
时间：5月29日（周三）14:30
单位：中科院物理研究所
地点：M楼253会议室
Perovskite is a family of functional materials with ABX3 structure. Barium titanite (BaTiO3) is a typical inorganic ferroelectric perovskite that possesses switchable spontaneous polarization. Ferroelectric polarizations are usually switched by electric field, but other forms of switching mechanisms have been demonstrated, such as flexoelectricity, pyroelectric effect, and change of chemical environment. In this talk, our recent works of MoS2-facilitated optical illumination induced polarization switching of BTO thin film will be reported. Based on the interplay between the photoelectric behavior of MoS2 and the build-in field in BTO, low energy UV light can cause polarization switching of BTO underneath the MoS2 flakes from upward to downward in the MoS2/BTO heterostructures. Another type of perovskites attracted much attention in recent years, the hybrid inorganic-organic perovskite materials. We recently discovered intriguing properties of this type of materials, which are ferroelasticity and the giant electrostrictive response of MAPbI3 showing compressive strain of approximately 1%. It enables the material to be used as actuators or other kinds of electromechanical systems in addition to optoelectronic applications.
报告人：Chris Parkes，University of Manchester
时间：5月29日（周三）14:30
单位：中科院高能物理所
地点：主楼C305会议室
The LHCb experiment has recently completed its initial operating period (2010-2018), and has published over 450 scientific papers. Highlights of the physics output of the experiment will be reviewed, with an emphasis on recent results such as the discovery of charm CP violation, lepton flavour universality anomalies and observation of pentaquark states. The next era is now starting for LHCb. The Upgrade I experiment is being installed over the next two years for operation from 2021. This will allow a significant increase of instaneous luminosity and improve efficiencies and flexibility through the introduction of a fully software based trigger at 40MHz. Beyond this the collaboration is planning further upgrades, with a range of novel technological developments considered including “5D" calorimetry and CMOS and other silicon based tracking systems and many opportunities for involvement in the research, design and construction activities.
报告人：C. S. Lam，McGill/UBC
时间：5月29日（周三）14:30
单位：中科院理论物理所
地点：ITP South (New) Building 6420
n-gluon tree diagrams can be formally expressed as a Mobius-invariant integral over (n-3) complex variables. In order for this CHY formalism to describe the complete Yang-Mills theory, a similar formula must be found for off-shell gluons, namely, all tree-level Green's functions in momentum space. This is a non-trivial task because space-time local interaction and its propagation, as well as local gauge invariance demanded by the Yang-Mills theory, must be directly incorporated into a Mobius-invariant integral of momenta and polarization. I will discuss how this can be done.
报告人：Min-Kai Lin，ASIAA , Taiwan
时间：5月30日（周四）14:00
单位：清华大学
地点：蒙民伟科技南楼S727
Planets appears commonplace in the Universe. However, the details of their formation remains a puzzle. The building blocks of planets are planetesimals, themselves formed from small dust grains immersed in a gaseous protoplanetary disk (PPD) surrounding young stars. Thus, understanding the dust-gas dynamics in PPDs lays the foundation to any theory of planet formation. I will present recent work on dust-gas dynamics in PPDs and discuss implications for planet formation. I first describe the problem of dust sedimentation in PPDs. This process is widely considered as a necessary step towards planetesimal formation. However, turbulence in the disk can stir up dust particles, thereby prevent planetesimal formation. I will discuss how dust can overcome turbulence and sediment by accounting for two-way drag forces between gas and dust. I will then describe how newly born protoplanets continue to interact with its surrounding disk. Such disk-planet interactions may be responsible for substructures such as rings and gaps now commonly observed in real PPDs. I show that planets interacting with a dusty disk can differ significantly from the more frequently studied case of pure gas disks. This may be important for shaping the final architecture of planetary systems. Finally, I will give a preview of upcoming projects that combine disk-planet interaction and dust settling in the context of PPD substructures.
报告人：Yuanning Gao，PKU School of Physics
时间：5月30日（周四）16:00
单位：北京大学
地点：KIAA-PKU Auditorium
Colliders (and accelerators) have been drive engines for discovering elementary particles and the fundamental laws of the nature. With the Large Hadron Collider (LHC) our reach to the microscopic world has been deepened to a scale as short as 10^-18 m. The observation of the Higgs boson completes the standard model. Yet there are still many outstanding questions to be answered. In this lecture, the role of the Higgs boson and the history of its discovery will be reviewed. Focused on the CEPC project, proposals for the future colliders will be introduced and their scientific and social impacts will be discussed.
13New directions on searches for new Gauge Bosons at the LHC
报告人：Ricardo Eusebi，Texas A & M University
时间：5月30日（周四）16:00
单位：清华大学
地点：物理系理科楼郑裕彤讲堂
Over the past years the multipurpose detectors of CMS and ATLAS at the Large Hadron Collider have gathered an enormous amount of data. This data has been, and continues to be, meticulously analyzed to extract precision parameters that characterize the inner workings of the Standard Model, and also to probe for theories beyond that of the Standard Model. While to this day the discovery of new physics is eluding these experiments, there are a some interesting hints emerging from the LHCb, Belle and BaBar experiments. In this talk I will describe some of the new directions we are taking on the search for new physics at the LHC, and on some aspects of the technical upgrade of the CMS detector to extend the sensitivity of the data we will collect in the years to come.
更多报告信息：中国物理学会期刊网学术讲座列表
2.量子十问之六：量子计算，这可是一个颠覆性的新技术 | 郭光灿
7.物理学：A Source of Power for Man
9.杨-米尔斯理论说了啥？为什么说这是杨振宁超越他诺奖的贡献？
相关内容
微信扫码咨询专知VIP会员