5,627 research outputs found
Simple biophysics underpins collective conformations of the intrinsically disordered proteins of the Nuclear Pore Complex
Nuclear Pore Complexes (NPCs) are key cellular transporter that control nucleocytoplasmic transport in eukaryotic cells, but its transport mechanism is still not understood. The centerpiece of NPC transport is the assembly of intrinsically disordered polypeptides, known as FG nucleoporins, lining its passageway. Their conformations and collective dynamics during transport are difficult to assess in vivo. In vitro investigations provide partially conflicting results, lending support to different models of transport, which invoke various conformational transitions of the FG nucleoporins induced by the cargo-carrying transport proteins. We show that the spatial organization of FG nucleoporin assemblies with the transport proteins can be understood within a first principles biophysical model with a minimal number of key physical variables, such as the average protein interaction strengths and spatial densities. These results address some of the outstanding controversies and suggest how molecularly divergent NPCs in different species can perform essentially the same function
Empirical regularities of opening call auction in Chinese stock market
We study the statistical regularities of opening call auction using the
ultra-high-frequency data of 22 liquid stocks traded on the Shenzhen Stock
Exchange in 2003. The distribution of the relative price, defined as the
relative difference between the order price in opening call auction and the
closing price of last trading day, is asymmetric and that the distribution
displays a sharp peak at zero relative price and a relatively wide peak at
negative relative price. The detrended fluctuation analysis (DFA) method is
adopted to investigate the long-term memory of relative order prices. We
further study the statistical regularities of order sizes in opening call
auction, and observe a phenomenon of number preference, known as order size
clustering. The probability density function (PDF) of order sizes could be well
fitted by a -Gamma function, and the long-term memory also exists in order
sizes. In addition, both the average volume and the average number of orders
decrease exponentially with the price level away from the best bid or ask price
level in the limit-order book (LOB) established immediately after the opening
call auction, and a price clustering phenomenon is observed.Comment: 11 pages, 6 figures, 3 table
The Solar--Stellar Connection
Stars have proven to be surprisingly prolific radio sources and the added
sensitivity of the Square Kilometer Array will lead to advances in many
directions. This chapter discusses prospects for studying the physics of
stellar atmospheres and stellar winds across the HR diagram.Comment: to appear in "Science with the Square Kilometer Array," eds. C.
Carilli and S. Rawlings, New Astronomy Reviews (Elsevier: Amsterdam
Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy
Studies of magnetization dynamics have incessantly facilitated the discovery
of fundamentally novel physical phenomena, making steady headway in the
development of magnetic and spintronics devices. The dynamics can be induced
and detected electrically, offering new functionalities in advanced electronics
at the nanoscale. However, its scattering mechanism is still disputed.
Understanding the mechanism in thin films is especially important, because most
spintronics devices are made from stacks of multilayers with nanometer
thickness. The stacks are known to possess interfacial magnetic anisotropy, a
central property for applications, whose influence on the dynamics remains
unknown. Here, we investigate the impact of interfacial anisotropy by adopting
CoFeB/MgO as a model system. Through systematic and complementary measurements
of ferromagnetic resonance (FMR), on a series of thin films, we identify
narrower FMR linewidths at higher temperatures. We explicitly rule out the
temperature dependence of intrinsic damping as a possible cause, and it is also
not expected from existing extrinsic scattering mechanisms for ferromagnets. We
ascribe this observation to motional narrowing, an old concept so far neglected
in the analyses of FMR spectra. The effect is confirmed to originate from
interfacial anisotropy, impacting the practical technology of spin-based
nanodevices up to room temperature.Comment: 23 pages,3 figure
Enhancing Adversarial Example Transferability with an Intermediate Level Attack
Neural networks are vulnerable to adversarial examples, malicious inputs
crafted to fool trained models. Adversarial examples often exhibit black-box
transfer, meaning that adversarial examples for one model can fool another
model. However, adversarial examples are typically overfit to exploit the
particular architecture and feature representation of a source model, resulting
in sub-optimal black-box transfer attacks to other target models. We introduce
the Intermediate Level Attack (ILA), which attempts to fine-tune an existing
adversarial example for greater black-box transferability by increasing its
perturbation on a pre-specified layer of the source model, improving upon
state-of-the-art methods. We show that we can select a layer of the source
model to perturb without any knowledge of the target models while achieving
high transferability. Additionally, we provide some explanatory insights
regarding our method and the effect of optimizing for adversarial examples
using intermediate feature maps. Our code is available at
https://github.com/CUVL/Intermediate-Level-Attack.Comment: ICCV 2019 camera-ready. Imagenet results are updated after fixing the
normalization. arXiv admin note: text overlap with arXiv:1811.0845
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