Fixed Parameter Undecidability for Wang Tilesets

Deciding if a given set of Wang tiles admits a tiling of the plane is decidable if the number of Wang tiles (or the number of colors) is bounded, for a trivial reason, as there are only finitely many such tilesets. We prove however that the tiling problem remains undecidable if the difference between the number of tiles and the number of colors is bounded by 43. One of the main new tool is the concept of Wang bars, which are equivalently inflated Wang tiles or thin polyominoes.Comment: In Proceedings AUTOMATA&JAC 2012, arXiv:1208.249

Dicke Superradiance in Solids

Recent advances in optical studies of condensed matter have led to the emergence of phenomena that have conventionally been studied in the realm of quantum optics. These studies have not only deepened our understanding of light-matter interactions but also introduced aspects of many-body correlations inherent in optical processes in condensed matter systems. This article is concerned with superradiance (SR), a profound quantum optical process predicted by Dicke in 1954. The basic concept of SR applies to a general $N$-body system where constituent oscillating dipoles couple together through interaction with a common light field and accelerate the radiative decay of the system. In the most fascinating manifestation of SR, known as superfluorescence (SF), an incoherently prepared system of $N$ inverted atoms spontaneously develops macroscopic coherence from vacuum fluctuations and produces a delayed pulse of coherent light whose peak intensity $\propto N^2$. Such SF pulses have been observed in atomic and molecular gases, and their intriguing quantum nature has been unambiguously demonstrated. Here, we focus on the rapidly developing field of research on SR in solids, where not only photon-mediated coupling but also strong Coulomb interactions and ultrafast scattering exist. We describe SR and SF in molecular centers in solids, molecular aggregates and crystals, quantum dots, and quantum wells. In particular, we will summarize a series of studies we have recently performed on quantum wells in strong magnetic fields. These studies show that cooperative effects in solid-state systems are not merely small corrections that require exotic conditions to be observed; rather, they can dominate the nonequilibrium dynamics and light emission processes of the entire system of interacting electrons.Comment: 23 pages, 26 figure

A new family of variational-form-based regularizers for reconstructing epicardial potentials from body-surface mapping

Journal ArticleWe propose a new family of regularizers for the inverse ECG problem, using a variational principle that underlies finite element approximation methods. As an alternative to traditional Tikhonov regularizers, the variational formulation has several advantages: 1)it enables a simple construction of the gradient operator (in a matrix form) over irregular meshes, which is often difficult to derive; 2) it achieves consistent regularization under multi-scale simulations by preserving the norm, which is evaluated by the resolution-independent L2-norm rather than the discrete Euclidean norm; and 3)it allows simultaneous application of multiple constraints efficiently. Our proposed method is validated by simulation on a realistic 3D model with clinical heart data, showing that the variational formulation may improve a broader range of potential-based electrocardiographic problems

Spin and Lattice Structure of Single Crystal SrFe2As2

We use neutron scattering to study the spin and lattice structure on single crystals of SrFe2As2, the parent compound of the FeAs based superconductor (Sr,K)Fe2As2. We find that SrFe2As2 exhibits an abrupt structural phase transitions at 220K, where the structure changes from tetragonal with lattice parameters c > a = b to orthorhombic with c > a > b. At almost the same temperature, Fe spins in SrFe2As2 develop a collinear antiferromagnetic structure along the orthorhombic a-axis with spin direction parallel to this a-axis. These results are consistent with earlier work on the RFeAsO (R = rare earth elements) families of materials and on BaFe2As2, and therefore suggest that static antiferromagnetic order is ubiquitous for the parent compound of these FeAs-based high-transition temperature superconductors.Comment: 14 pages with 4 figure

High-mass Starless Clumps in the inner Galactic Plane: the Sample and Dust Properties

We report a sample of 463 high-mass starless clump (HMSC) candidates within $-60\deg<l<60\deg$ and $-1\deg<b<1\deg$. This sample has been singled out from 10861 ATLASGAL clumps. All of these sources are not associated with any known star-forming activities collected in SIMBAD and young stellar objects identified using color-based criteria. We also make sure that the HMSC candidates have neither point sources at 24 and 70 \micron~nor strong extended emission at 24 $\mu$m. Most of the identified HMSCs are infrared ($\le24$ $\mu$m) dark and some are even dark at 70 $\mu$m. Their distribution shows crowding in Galactic spiral arms and toward the Galactic center and some well-known star-forming complexes. Many HMSCs are associated with large-scale filaments. Some basic parameters were attained from column density and dust temperature maps constructed via fitting far-infrared and submillimeter continuum data to modified blackbodies. The HMSC candidates have sizes, masses, and densities similar to clumps associated with Class II methanol masers and HII regions, suggesting they will evolve into star-forming clumps. More than 90% of the HMSC candidates have densities above some proposed thresholds for forming high-mass stars. With dust temperatures and luminosity-to-mass ratios significantly lower than that for star-forming sources, the HMSC candidates are externally heated and genuinely at very early stages of high-mass star formation. Twenty sources with equivalent radius $r_\mathrm{eq}<0.15$ pc and mass surface density $\Sigma>0.08$ g cm$^{-2}$ could be possible high-mass starless cores. Further investigations toward these HMSCs would undoubtedly shed light on comprehensively understanding the birth of high-mass stars.Comment: 16 pages, 15 figures, and 5 tables. Accepted for publication in ApJS. FITS images for the far-IR to sub-mm data, H2 column density and dust temperature maps of all the HMSC candidates are available at https: //yuanjinghua.github.io/hmscs.html. Codes used for this work are publicly available from https://github.com/yuanjinghua/HMSCs_ca

B2: Presence of Immunosuppressive Drugs affect Innate Immune Response and Monocyte Differentiation in Lung Transplant Patients

Lung transplant patients are administered Immunosuppressive Drugs (ISDs) to prevent transplant rejection, but this also puts them at constant risk of infection due to the decreased ability of the immune system to respond to subsequent infections by viruses, bacteria etc. Purpose This paper focuses on the effect of ISDs on the innate immune response. We are using different parts of viruses and bacteria and allowing them to represent the organism as a whole. Methods As representatives of the innate immune system, we are going to be testing monocyte, macrophage, and dendritic cell lineages. We are hypothesizing that the presence of ISDs dampens the immune system response to viruses/bacteria as well as that in the presence of ISDs, there is decreased differentiation of the monocytes into macrophages. We used PCR and Flow cytometry to help interpret the data. PCR allowed us to recognize innate immune transcriptional changes of the cells that were treated with ISDs in comparison to the control. We used the Flow Cytometer to test monocyte differentiation into macrophages. Results The results showed that there were certain innate immune genes that showed increase in expression, some showed decrease, while others showed no change in the presence of ISDs. It was also concluded that the presence of ISDs actually induced differentiation of Monocytes into Macrophages. Conclusion This information can be used to manipulate the immune systems of lung transplant patients to better respond to specific subsequent infections even in the presence of Immunosuppressive Drugs while still maintaining the integrity of the transplant

Electronic Origin of High Temperature Superconductivity in Single-Layer FeSe Superconductor

The latest discovery of high temperature superconductivity signature in single-layer FeSe is significant because it is possible to break the superconducting critical temperature ceiling (maximum Tc~55 K) that has been stagnant since the discovery of Fe-based superconductivity in 2008. It also blows the superconductivity community by surprise because such a high Tc is unexpected in FeSe system with the bulk FeSe exhibiting a Tc at only 8 K at ambient pressure which can be enhanced to 38 K under high pressure. The Tc is still unusually high even considering the newly-discovered intercalated FeSe system A_xFe_{2-y}Se_2 (A=K, Cs, Rb and Tl) with a Tc at 32 K at ambient pressure and possible Tc near 48 K under high pressure. Particularly interesting is that such a high temperature superconductivity occurs in a single-layer FeSe system that is considered as a key building block of the Fe-based superconductors. Understanding the origin of high temperature superconductivity in such a strictly two-dimensional FeSe system is crucial to understanding the superconductivity mechanism in Fe-based superconductors in particular, and providing key insights on how to achieve high temperature superconductivity in general. Here we report distinct electronic structure associated with the single-layer FeSe superconductor. Its Fermi surface topology is different from other Fe-based superconductors; it consists only of electron pockets near the zone corner without indication of any Fermi surface around the zone center. Our observation of large and nearly isotropic superconducting gap in this strictly two-dimensional system rules out existence of node in the superconducting gap. These results have provided an unambiguous case that such a unique electronic structure is favorable for realizing high temperature superconductivity