751 research outputs found
{GAN2X}: {N}on-{L}ambertian Inverse Rendering of Image {GANs}
2D images are observations of the 3D physical world depicted with thegeometry, material, and illumination components. Recovering these underlyingintrinsic components from 2D images, also known as inverse rendering, usuallyrequires a supervised setting with paired images collected from multipleviewpoints and lighting conditions, which is resource-demanding. In this work,we present GAN2X, a new method for unsupervised inverse rendering that onlyuses unpaired images for training. Unlike previous Shape-from-GAN approachesthat mainly focus on 3D shapes, we take the first attempt to also recovernon-Lambertian material properties by exploiting the pseudo paired datagenerated by a GAN. To achieve precise inverse rendering, we devise aspecularity-aware neural surface representation that continuously models thegeometry and material properties. A shading-based refinement technique isadopted to further distill information in the target image and recover morefine details. Experiments demonstrate that GAN2X can accurately decompose 2Dimages to 3D shape, albedo, and specular properties for different objectcategories, and achieves the state-of-the-art performance for unsupervisedsingle-view 3D face reconstruction. We also show its applications in downstreamtasks including real image editing and lifting 2D GANs to decomposed 3D GANs.<br
gCoRF: Generative Compositional Radiance Fields
3D generative models of objects enable photorealistic image synthesis with 3Dcontrol. Existing methods model the scene as a global scene representation,ignoring the compositional aspect of the scene. Compositional reasoning canenable a wide variety of editing applications, in addition to enablinggeneralizable 3D reasoning. In this paper, we present a compositionalgenerative model, where each semantic part of the object is represented as anindependent 3D representation learned from only in-the-wild 2D data. We startwith a global generative model (GAN) and learn to decompose it into differentsemantic parts using supervision from 2D segmentation masks. We then learn tocomposite independently sampled parts in order to create coherent globalscenes. Different parts can be independently sampled while keeping the rest ofthe object fixed. We evaluate our method on a wide variety of objects and partsand demonstrate editing applications.<br
Topological Superfluid in one-dimensional Ultracold Atomic System with Spin-Orbit Coupling
We propose a one-dimensional Hamiltonian which supports Majorana
fermions when -wave superfluid appears in the ultracold atomic
system and obtain the phase-separation diagrams both for the
time-reversal-invariant case and time-reversal-symmetry-breaking case. From the
phase-separation diagrams, we find that the single Majorana fermions exist in
the topological superfluid region, and we can reach this region by tuning the
chemical potential and spin-orbit coupling . Importantly, the
spin-orbit coupling has realized in ultracold atoms by the recent experimental
achievement of synthetic gauge field, therefore, our one-dimensional ultra-cold
atomic system described by is a promising platform to find the
mysterious Majorana fermions.Comment: 5 papers, 2 figure
The effects of magnetic field on the d-density wave order in the cuprates
We consider the effects of a perpendicular magnetic field on the d-density
wave order and conclude that if the pseudogap phase in the cuprates is due to
this order, then it is highly insensitive to the magnetic field in the
underdoped regime, while its sensitivity increases as the gap vanishes in the
overdoped regime. This appears to be consistent with the available experiments
and can be tested further in neutron scattering experiments. We also
investigate the nature of the de Haas- van Alphen effect in the ordered state
and discuss the possibility of observing it.Comment: 5 pages, 4 eps figures, RevTex4. Corrected a silly but important typo
in the abstrac
Rashbons: Properties and their significance
In presence of a synthetic non-Abelian gauge field that induces a Rashba like
spin-orbit interaction, a collection of weakly interacting fermions undergoes a
crossover from a BCS ground state to a BEC ground state when the strength of
the gauge field is increased [Phys. Rev. B {\bf 84}, 014512 (2011)]. The BEC
that is obtained at large gauge coupling strengths is a condensate of tightly
bound bosonic fermion-pairs whose properties are solely determined by the
Rashba gauge field -- hence called rashbons. In this paper, we conduct a
systematic study of the properties of rashbons and their dispersion. This study
reveals a new qualitative aspect of the problem of interacting fermions in
non-Abelian gauge fields, i.e., that the rashbon state induced by the gauge
field for small centre of mass momenta of the fermions ceases to exist when
this momentum exceeds a critical value which is of the order of the gauge
coupling strength. The study allows us to estimate the transition temperature
of the rashbon BEC, and suggests a route to enhance the exponentially small
transition temperature of the system with a fixed weak attraction to the order
of the Fermi temperature by tuning the strength of the non-Abelian gauge field.
The nature of the rashbon dispersion, and in particular the absence of the
rashbon states at large momenta, suggests a regime of parameter space where the
normal state of the system will be a dynamical mixture of uncondensed rashbons
and unpaired helical fermions. Such a state should show many novel features
including pseudogap physics.Comment: 8 pages, 6 figure
Systems theory of Smad signaling
Transforming Growth Factor-beta (TGF-beta) signalling is an important
regulator of cellular growth and differentiation. The principal intracellular
mediators of TGF-beta signalling are the Smad proteins, which upon TGF-beta
stimulation accumulate in the nucleus and regulate transcription of target
genes. To investigate the mechanisms of Smad nuclear accumulation, we developed
a simple mathematical model of canonical Smad signalling. The model was built
using both published data and our experimentally determined cellular Smad
concentrations (isoforms 2, 3, and 4). We found in mink lung epithelial cells
that Smad2 (8.5-12 x 10^4 molecules/cell) was present in similar amounts to
Smad4 (9.3-12 x 10^4 molecules/cell), while both were in excess of Smad3
(1.1-2.0 x 10^4 molecules/cell). Variation of the model parameters and
statistical analysis showed that Smad nuclear accumulation is most sensitive to
parameters affecting the rates of RSmad phosphorylation and dephosphorylation
and Smad complex formation/dissociation in the nucleus. Deleting Smad4 from the
model revealed that rate-limiting phospho-R-Smad dephosphorylation could be an
important mechanism for Smad nuclear accumulation. Furthermore, we observed
that binding factors constitutively localised to the nucleus do not efficiently
mediate Smad nuclear accumulation if dephosphorylation is rapid. We therefore
conclude that an imbalance in the rates of R-Smad phosphorylation and
dephosphorylation is likely an important mechanism of Smad nuclear accumulation
during TGF-beta signalling.Comment: To appear in IEE Proceedings Systems Biology. 12 pages of text, 36
pages tota
Primary Dendrite Distribution and Disorder During Directional Solidification of Pb-Sb Alloys
Pb-2.2 wt pct Sb and Pb-5.8 wt pet Sb alloys have been directionally solidified from a single-crystal seed with its [100] orientation parallel to the growth direction, to examine the primary dendrite distribution and disorder of the dendrite arrays. The dendrite distribution and ordering have been investigated using analysis techniques such as the Gauss-amplitude fit to the frequency distribution of nearest and higher-order spacings, minimum spanning tree (MST), Voronoi polygon, and Fourier transform (FT) of the dendrite centers. Since the arrangement of dendrites is driven by the requirement to accommodate side-branch growth along the (100) directions, the FT images of the fully developed dendrite centers contain spots which indicate this preferred alignment. A directional solidification distance of about three mushy-zone lengths is sufficient to ensure a steady-state dendritic array, in terms of reaching a constant mean primary spacing. However, local dendrite ordering continues throughout the directional solidification process. The interdendritic convection not only decreases the mean primary spacing, it also makes the dendrite array more disordered and reduces the ratio of the upper and lower spacing limits, as defined by the largest 5 pct and the smallest 5 pct of the population
Introduction to topological superconductivity and Majorana fermions
This short review article provides a pedagogical introduction to the rapidly
growing research field of Majorana fermions in topological superconductors. We
first discuss in some details the simplest "toy model" in which Majoranas
appear, namely a one-dimensional tight-binding representation of a p-wave
superconductor, introduced more than ten years ago by Kitaev. We then give a
general introduction to the remarkable properties of Majorana fermions in
condensed matter systems, such as their intrinsically non-local nature and
exotic exchange statistics, and explain why these quasiparticles are suspected
to be especially well suited for low-decoherence quantum information
processing. We also discuss the experimentally promising (and perhaps already
successfully realized) possibility of creating topological superconductors
using semiconductors with strong spin-orbit coupling, proximity-coupled to
standard s-wave superconductors and exposed to a magnetic field. The goal is to
provide an introduction to the subject for experimentalists or theorists who
are new to the field, focusing on the aspects which are most important for
understanding the basic physics. The text should be accessible for readers with
a basic understanding of quantum mechanics and second quantization, and does
not require knowledge of quantum field theory or topological states of matter.Comment: 21 pages, 5 figure
- …