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"Xue, Wei"
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Neural tuning and representational geometry
A central goal of neuroscience is to understand the representations formed by brain activity patterns and their connection to behaviour. The classic approach is to investigate how individual neurons encode stimuli and how their tuning determines the fidelity of the neural representation. Tuning analyses often use the Fisher information to characterize the sensitivity of neural responses to small changes of the stimulus. In recent decades, measurements of large populations of neurons have motivated a complementary approach, which focuses on the information available to linear decoders. The decodable information is captured by the geometry of the representational patterns in the multivariate response space. Here we review neural tuning and representational geometry with the goal of clarifying the relationship between them. The tuning induces the geometry, but different sets of tuned neurons can induce the same geometry. The geometry determines the Fisher information, the mutual information and the behavioural performance of an ideal observer in a range of psychophysical tasks. We argue that future studies can benefit from considering both tuning and geometry to understand neural codes and reveal the connections between stimuli, brain activity and behaviour.Developing a better understanding of neural codes should enable the links between stimuli, brain activity and behaviour to become clearer. In this Perspective, Kriegeskorte and Wei examine neural tuning and representational geometry — complementary approaches used to understand neural codes — and the relationship between them.
Journal Article
إدارة الأزمات في زمن الأوبئة : مقالات لـ 56 عالما في الإدارة
يضم هذا الكتاب خلاصة تجارب وعصارة أفكار 56 عالما، هم من أبرز علماء الإدارة في الصين، وقد حملوا على عاتقهم مسؤولية قيادة المؤسسات الصينية لسنوات عديدة، وهو كتاب مرجعي لكل المؤسسات على المستوى العالمي والتي إن حدث لها ضرر في فترات الأزمات أو الأوبئة، فلن يتوقف هذا الضرر عند ملاكها أو المنتفعين منها، بل سيمتد أثره إلى قطاعات عريضة من العمالة، وسيضرب القوة الإنتاجية ولا سيما الصادرات والواردات وغيرها من الموارد. ومن ثم فهم محاربون على الخطوط الأولى، مثلهم مثل الأطباء في أزمة انتشار فيروس كورونا المستجد، وإن كان مجال تخصص كل مختلفا منهم عن الآخر، ففريق منهم ينقذ حياة الناس، بينما الفريق الآخر ينقذ أقواتهم. ولغة الكتاب لغة سهلة وبسيطة، تنطلق أفكاره من مواقف عامة وليست من مواقف خاصة محددة، ومن هنا تعد أفكاره صالحة للتطبيق على المؤسسات الصغيرة والمتوسطة في كل مكان، والتي أصبح لزاما عليها أن تلجأ للابتكار والإبداع إن أرادت الاستمرار على قيد الحياة، وبات عليها أن تبحث وسط ركام الأزمة عن الإيجابيات التي يمكن أن تهب لها حياة جديدة وسبلا مبتكرة للخلاص.
Book
Quantification of critical particle distance for mitigating catalyst sintering
Supported metal nanoparticles are of universal importance in many industrial catalytic processes. Unfortunately, deactivation of supported metal catalysts via thermally induced sintering is a major concern especially for high-temperature reactions. Here, we demonstrate that the particle distance as an inherent parameter plays a pivotal role in catalyst sintering. We employ carbon black supported platinum for the model study, in which the particle distance is well controlled by changing platinum loading and carbon black supports with varied surface areas. Accordingly, we quantify a critical particle distance of platinum nanoparticles on carbon supports, over which the sintering can be mitigated greatly up to 900 °C. Based on in-situ aberration-corrected high-angle annular dark-field scanning transmission electron and theoretical studies, we find that enlarging particle distance to over the critical distance suppress the particle coalescence, and the critical particle distance itself depends sensitively on the strength of metal-support interactions.
Deactivation of supported metal catalysts via thermally induced sintering is a major concern in the catalysis community. Here, the authors demonstrate that enlarging particle distance to over the critical distance could suppress the particle coalescence greatly up to 900 °C.
Journal Article
Water enables mild oxidation of methane to methanol on gold single-atom catalysts
As a 100% atom-economy process, direct oxidation of methane into methanol remains as a grand challenge due to the dilemma between activation of methane and over-oxidation of methanol. Here, we report that water enabled mild oxidation of methane into methanol with >99% selectivity over Au single atoms on black phosphorus (Au
1
/BP) nanosheets under light irradiation. The mass activity of Au
1
/BP nanosheets reached 113.5 μmol g
catal
−1
in water pressured with 33 bar of mixed gas (CH
4
:O
2
= 10:1) at 90 °C under light irradiation (1.2 W), while the activation energy was 43.4 kJ mol
−1
. Mechanistic studies revealed that water assisted the activation of O
2
to generate reactive hydroxyl groups and •OH radicals under light irradiation. Hydroxyl groups reacted with methane at Au single atoms to form water and CH
3
* species, followed by oxidation of CH
3
* via •OH radicals into methanol. Considering the recycling of water during the whole process, we can also regard water as a catalyst.
It is important but challenging to oxidize methane by O
2
into methanol under ambient conditions. Here, the authors achieved mild oxidation of methane into methanol over Au single atoms on black phosphorus nanosheets with the help of water under light irradiation.
Journal Article
Synergizing metal–support interactions and spatial confinement boosts dynamics of atomic nickel for hydrogenations
Atomically dispersed metal catalysts maximize atom efficiency and display unique catalytic properties compared with regular metal nanoparticles. However, achieving high reactivity while preserving high stability at appreciable loadings remains challenging. Here we solve the challenge by synergizing metal–support interactions and spatial confinement, which enables the fabrication of highly loaded atomic nickel (3.1 wt%) along with dense atomic copper grippers (8.1 wt%) on a graphitic carbon nitride support. For the semi-hydrogenation of acetylene in excess ethylene, the fabricated catalyst shows extraordinary catalytic performance in terms of activity, selectivity and stability—far superior to supported atomic nickel alone in the absence of a synergizing effect. Comprehensive characterization and theoretical calculations reveal that the active nickel site confined in two stable hydroxylated copper grippers dynamically changes by breaking the interfacial nickel–support bonds on reactant adsorption and making these bonds on product desorption. Such a dynamic effect confers high catalytic performance, providing an avenue to rationally design efficient, stable and highly loaded, yet atomically dispersed, catalysts.
Synergizing metal–support interactions and spatial confinement through atomic copper grippers boost the dynamics of highly loaded atomic nickel for high activity, high thermal/chemical stability and unprecedented coke inhibition in hydrogenation reactions.
Journal Article
In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution
NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Herein, we combine electrochemical measurements,
operando
X-ray scattering and absorption spectroscopy, and density functional theory (DFT) calculations to elucidate the catalytically active phase, reaction center and the OER mechanism. We provide the first direct atomic-scale evidence that, under applied anodic potentials, MFe LDHs oxidize from as-prepared α-phases to activated γ-phases. The OER-active γ-phases are characterized by about 8% contraction of the lattice spacing and switching of the intercalated ions. DFT calculations reveal that the OER proceeds via a Mars van Krevelen mechanism. The flexible electronic structure of the surface Fe sites, and their synergy with nearest-neighbor M sites through formation of O-bridged Fe-M reaction centers, stabilize OER intermediates that are unfavorable on pure M-M centers and single Fe sites, fundamentally accounting for the high catalytic activity of MFe LDHs.
NiFe and CoFe layered double hydroxides are among the most active electrocatalysts for the alkaline oxygen evolution reaction. Here, by combining
operando
experiments and rigorous DFT calculations, the authors unravel their active phase, the reaction center and the catalytic mechanism.
Journal Article
Serendipity in dark photon searches
A
bstract
Searches for dark photons provide serendipitous discovery potential for other types of vector particles. We develop a framework for recasting dark photon searches to obtain constraints on more general theories, which includes a data-driven method for determining hadronic decay rates. We demonstrate our approach by deriving constraints on a vector that couples to the B-L current, a leptophobic
B
boson that couples directly to baryon number and to leptons via
B
-
γ
kinetic mixing, and on a vector that mediates a protophobic force. Our approach can easily be generalized to any massive gauge boson with vector couplings to the Standard Model fermions, and software to perform any such recasting is provided at
https://gitlab.com/philten/darkcast
.
Journal Article
The most active Cu facet for low-temperature water gas shift reaction
Identification of the active site is important in developing rational design strategies for solid catalysts but is seriously blocked by their structural complexity. Here, we use uniform Cu nanocrystals synthesized by a morphology-preserved reduction of corresponding uniform Cu
2
O nanocrystals in order to identify the most active Cu facet for low-temperature water gas shift (WGS) reaction. Cu cubes enclosed with {100} facets are very active in catalyzing the WGS reaction up to 548 K while Cu octahedra enclosed with {111} facets are inactive. The Cu–Cu suboxide (Cu
x
O,
x
≥ 10) interface of Cu(100) surface is the active site on which all elementary surface reactions within the catalytic cycle proceed smoothly. However, the formate intermediate was found stable at the Cu–Cu
x
O interface of Cu(111) surface with consequent accumulation and poisoning of the surface at low temperatures. Thereafter, Cu cubes-supported ZnO catalysts are successfully developed with extremely high activity in low-temperature WGS reaction.
Nanocrystals display a variety of facets with different catalytic activity. Here the authors identify the most active facet of copper nanocrystals relevant to the low-temperature water gas shift reaction and further design zinc oxide-copper nanocubes with exceptionally high catalytic activity.
Journal Article