Magnetic anisotropy and spin-spiral wave in V, Cr and Mn atomic chains on Cu(001) surface: First principles calculations

Recent ab intio studies of the magnetic properties of all 3d transition metal(TM) freestanding atomic chains predicted that these nanowires could have a giant magnetic anisotropy energy (MAE) and might support a spin-spiral structure, thereby suggesting that these nanowires would have technological applicationsin, e.g., high density magnetic data storages. In order to investigate how the substrates may affect the magnetic properties of the nanowires, here we systematically study the V, Cr and Mn linear atomic chains on the Cu(001) surface based on the density functional theory with the generalized gradient approximation. We find that V, Cr, and Mn linear chains on the Cu(001) surface still have a stable or metastable ferromagnetic state. However, the ferromagnetic state is unstable against formation of a noncollinear spin-spiral structure in the Mn linear chains and also the V linear chain on the atop sites on the Cu(001) surface, due to the frustrated magnetic interactions in these systems. Nonetheless, the presence of the Cu(001) substrate does destabilize the spin-spiral state already present in the freestanding V linear chain and stabilizes the ferromagnetic state in the V linear chain on the hollow sites on Cu(001). When spin-orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged, due to the weakness of SOC in 3d TM chains. Furthermore, both the orbital magnetic moments and MAEs for the V, Cr and Mn are small, in comparison with both the corresponding freestanding nanowires and also the Fe, Co and Ni linear chains on the Cu (001) surface.Comment: Accepted for publication in J. Phys. D: Applied Physic

Infrared spectroscopy of Landau levels in graphene

We report infrared studies of the Landau level (LL) transitions in single layer graphene. Our specimens are density tunable and show \textit{in situ} half-integer quantum Hall plateaus. Infrared transmission is measured in magnetic fields up to B=18 T at selected LL fillings. Resonances between hole LLs and electron LLs, as well as resonances between hole and electron LLs are resolved. Their transition energies are proportional to $\sqrt{B}$ and the deduced band velocity is $\tilde{c}\approx1.1\times10^6$ m/s. The lack of precise scaling between different LL transitions indicates considerable contributions of many-particle effects to the infrared transition energies.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let

The effect of subgroup homogeneity of efficacy on contribution in public good dilemmas

open access articleThis paper examines how to maximize contribution in public good dilemmas by arranging people into homogeneous or heterogeneous subgroups. Past studies on the effect of homo- geneity of efficacy have exclusively manipulated group composition in their experimental designs, which might have imposed a limit on ecological validity because group membership may not be easily changed in reality. In this study, we maintained the same group composi- tion but varied the subgroup composition. We developed a public good dilemmas paradigm in which participants were assigned to one of the four conditions (high- vs. low-efficacy; homogeneous vs. heterogeneous subgroup) to produce their endowments and then to decide how much to contribute. We found that individuals in homogeneous and heteroge- neous subgroups produced a similar amount and proportion of contribution, which was due to the two mediating effects that counteracted each other, namely (a) perceived efficacy rel- ative to subgroup and (b) expectation of contribution of other subgroup members. This paper demonstrates both the pros and cons of arranging people into homogeneous and het- erogeneous subgroups of efficacy

DeepJSCC-Q: Channel Input Constrained Deep Joint Source-Channel Coding

Recent works have shown that the task of wireless transmission of images can be learned with the use of machine learning techniques. Very promising results in end-to-end image quality, superior to popular digital schemes that utilize source and channel coding separation, have been demonstrated through the training of an autoencoder, with a non-trainable channel layer in the middle. However, these methods assume that any complex value can be transmitted over the channel, which can prevent the application of the algorithm in scenarios where the hardware or protocol can only admit certain sets of channel inputs, such as the use of a digital constellation. Herein, we propose DeepJSCC-Q, an end-to-end optimized joint source-channel coding scheme for wireless image transmission, which is able to operate with a fixed channel input alphabet. We show that DeepJSCC-Q can achieve similar performance to models that use continuous-valued channel input. Importantly, it preserves the graceful degradation of image quality observed in prior work when channel conditions worsen, making DeepJSCC-Q much more attractive for deployment in practical systems

Federated mmWave Beam Selection Utilizing LIDAR Data

Efficient link configuration in millimeter wave (mmWave) communication systems is a crucial yet challenging task due to the overhead imposed by beam selection. For vehicle-to-infrastructure (V2I) networks, side information from LIDAR sensors mounted on the vehicles has been leveraged to reduce the beam search overhead. In this letter, we propose a federated LIDAR aided beam selection method for V2I mmWave communication systems. In the proposed scheme, connected vehicles collaborate to train a shared neural network (NN) on their locally available LIDAR data during normal operation of the system. We also propose a reduced-complexity convolutional NN (CNN) classifier architecture and LIDAR preprocessing, which significantly outperforms previous works in terms of both the performance and the complexity

Stationary untrapped boundary conditions in general relativity

A class of boundary conditions for canonical general relativity are proposed and studied at the quasi-local level. It is shown that for untrapped or marginal surfaces, fixing the area element on the 2-surface (rather than the induced 2-metric) and the angular momentum surface density is enough to have a functionally differentiable Hamiltonian, thus providing definition of conserved quantities for the quasi-local regions. If on the boundary the evolution vector normal to the 2-surface is chosen to be proportional to the dual expansion vector, we obtain a generalization of the Hawking energy associated with a generalized Kodama vector. This vector plays the role for the stationary untrapped boundary conditions which the stationary Killing vector plays for stationary black holes. When the dual expansion vector is null, the boundary conditions reduce to the ones given by the non-expanding horizons and the null trapping horizons.Comment: 11 pages, improved discussion section, a reference added, accepted for publication in Classical and Quantum Gravit

Perturbation Calculation of the Axial Anomaly of a Ginsparg-Wilson lattice Dirac operator

A recent proposal suggests that even if a Ginsparg-Wilson lattice Dirac operator does not possess any topological zero modes in topologically-nontrivial gauge backgrounds, it can reproduce correct axial anomaly for sufficiently smooth gauge configurations, provided that it is exponentially-local, doublers-free, and has correct continuum behavior. In this paper, we calculate the axial anomaly of this lattice Dirac operator in weak coupling perturbation theory, and show that it recovers the topological charge density in the continuum limit.Comment: 25 pages, v2: calculation up to O(g^4) for nonabelian gauge backgroun

Dazl Functions in Maintenance of Pluripotency and Genetic and Epigenetic Programs of Differentiation in Mouse Primordial Germ Cells In Vivo and In Vitro

Mammalian germ cells progress through a unique developmental program that encompasses proliferation and migration of the nascent primordial germ cell (PGC) population, reprogramming of nuclear DNA to reset imprinted gene expression, and differentiation of mature gametes. Little is known of the genes that regulate quantitative and qualitative aspects of early mammalian germ cell development both in vivo, and during differentiation of germ cells from mouse embryonic stem cells (mESCs) in vitro.We used a transgenic mouse system that enabled isolation of small numbers of Oct4DeltaPE:GFP-positive germ cells in vivo, and following differentiation from mESCs in vitro, to uncover quantitate and qualitative phenotypes associated with the disruption of a single translational regulator, Dazl. We demonstrate that disruption of Dazl results in a post-migratory, pre-meiotic reduction in PGC number accompanied by aberrant expression of pluripotency genes and failure to erase and re-establish genomic imprints in isolated male and female PGCs, as well as subsequent defect in progression through meiosis. Moreover, the phenotypes observed in vivo were mirrored by those in vitro, with inability of isolated mutant PGCs to establish pluripotent EG (embryonic germ) cell lines and few residual Oct-4-expressing cells remaining after somatic differentiation of mESCs carrying a Dazl null mutation. Finally, we observed that even within undifferentiated mESCs, a nascent germ cell subpopulation exists that was effectively eliminated with ablation of Dazl.This report establishes the translational regulator Dazl as a component of pluripotency, genetic, and epigenetic programs at multiple time points of germ cell development in vivo and in vitro, and validates use of the ESC system to model and explore germ cell biology

Generalized mirror symmetry and trace anomalies

We consider compactification of M-theory on X7 with betti numbers (b_0, b_1, b_2, b_3, b_3, b_2, b_1, b_0) and define a generalized mirror symmetry (b_0, b_1, b_2, b_3) goes to (b_0, b_1, b_2 -rho/2, b_3+rho/2)$ under which rho = 7b_0-5b_1+3b_2 -b_3 changes sign. Generalized self-mirror theories with rho=0 have massless sectors with vanishing trace anomaly (before dualization). Examples include pure supergravity with N \geq 4 and supergravity plus matter with N \leq 4.Comment: 19 pages late

Interaction-induced shift of the cyclotron resonance of graphene using infrared spectroscopy

We report a study of the cyclotron resonance (CR) transitions to and from the unusual $n=0$ Landau level (LL) in monolayer graphene. Unexpectedly, we find the CR transition energy exhibits large (up to 10%) and non-monotonic shifts as a function of the LL filling factor, with the energy being largest at half-filling of the $n=0$ level. The magnitude of these shifts, and their magnetic field dependence, suggests that an interaction-enhanced energy gap opens in the $n=0$ level at high magnetic fields. Such interaction effects normally have limited impact on the CR due to Kohn's theorem [W. Kohn, Phys. Rev. {\bf 123}, 1242 (1961)], which does not apply in graphene as a consequence of the underlying linear band structure.Comment: 4 pages, 4 figures. Version 2, edited for publication. Includes a number of edits for clarity; also added a paragraph contrasting our work w/ previous CR expts. in 2D Si and GaA