Locational wireless and social media-based surveillance

The number of smartphones and tablets as well as the volume of traffic generated by these devices has been growing constantly over the past decade and this growth is predicted to continue at an increasing rate over the next five years. Numerous native features built into contemporary smart devices enable highly accurate digital fingerprinting techniques. Furthermore, software developers have been taking advantage of locational capabilities of these devices by building applications and social media services that enable convenient sharing of information tied to geographical locations. Mass online sharing resulted in a large volume of locational and personal data being publicly available for extraction. A number of researchers have used this opportunity to design and build tools for a variety of uses – both respectable and nefarious. Furthermore, due to the peculiarities of the IEEE 802.11 specification, wireless-enabled smart devices disclose a number of attributes, which can be observed via passive monitoring. These attributes coupled with the information that can be extracted using social media APIs present an opportunity for research into locational surveillance, device fingerprinting and device user identification techniques. This paper presents an in-progress research study and details the findings to date

Strong quantum effects in an almost classical antiferromagnet on a kagome lattice

Two ubiquitous features of frustrated spin systems stand out: massive degeneracy of their ground states and flat, or dispersionless, excitation branches. In real materials, the former is frequently lifted by secondary interactions or quantum fluctuations, in favor of an ordered or spin-liquid state, but the latter often survive. We demonstrate that flat modes may precipitate remarkably strong quantum effects even in the systems that are otherwise written off as almost entirely classical. The resultant spectral features should be reminiscent of the quasiparticle breakdown in quantum systems, only here the effect is strongly amplified by the flatness of spin-excitation branches, leading to the damping that is not vanishingly small even at $S\!\gg\!1$. We provide a theoretical analysis of excitation spectrum of the $S=5/2$ iron-jarosite to illustrate our findings and to suggest further studies of this and other frustrated spin systems.Comment: 7 pages, accepted to PR

A Grand Old Church Rose in the East: The Church of God in Christ (COGIC) in East Texas

This essay traces the history of the Church of God in Christ and its early beginnings in East Texas

Rethinking α-RuCl3

We argue that several empirical constraints strongly restrict parameters of the effective microscopic spin model describing α-RuCl3. In particular, such constraints dictate a substantial positive off-diagonal anisotropic coupling Γ′>0, not anticipated previously. The renormalization by quantum fluctuations allows to reconcile larger values of the advocated bare parameters with their earlier assessments and provides a consistent description of the field evolution of spin excitations in the paramagnetic phase. We assert that large anisotropic terms inevitably result in strong anharmonic coupling of magnons, necessarily leading to broad features in their spectra due to decays, in accord with the observations in α-RuCl3. Using duality transformations, we explain the origin of the pseudo-Goldstone mode that is ubiquitous to the studied parameter space and is present in α-RuCl3. Our analysis offers a description of α-RuCl3 as an easy-plane ferromagnet with antiferromagnetic further-neighbor and strong off-diagonal couplings, which is in a fluctuating zigzag ground state proximate to an incommensurate phase that is continuously connected to a ferromagnetic one

Charge Stripe in an Antiferromagnet: 1d Band of Composite Excitations

With the help of analytical and numerical studies of the $t$-$J_z$ model we argue that the charge stripe in an antiferromagnetic insulator should be understood as a system of holon-spin-polaron excitations condensed at the self-induced antiphase domain wall. The structure of such a charge excitation is studied in detail with numerical and analytical results for various quantities being in a very close agreement. An analytical picture of these excitations occupying an effective 1D stripe band is also in a very good accord with numerical data. The emerging concept advocates the primary role of the kinetic energy in favoring the stripe as a ground state. A comparative analysis suggests the effect of pairing and collective meandering on the energetics of the stripe formation to be secondary.Comment: 5 pages, 3 figures, proceedings of SCES'01 conference, Ann Arbor, 2001, to be published in Physica

Highly Dispersive Scattering From Defects In Non-Collinear Magnets

We demonstrate that point-like defects in non-collinear magnets give rise to a highly dispersive structure in the magnon scattering, violating a standard paradigm of its momentum independence. For a single impurity spin coupled to a prototypical non-collinear antiferromagnet we find that the resolvent is dominated by a distinct dispersive structure with its momentum-dependence set by the magnon dispersion and shifted by the ordering vector. This feature is a consequence of umklapp scattering off the impurity-induced spin texture, which arises due to the non-collinear ground state of the host system. Detailed results for the staggered and uniform magnetization of this texture as well as the T-matrix from numerical linear spin-wave theory are presented.Comment: 5+5 pages, 4+5 fig

Thermal conductivity in large-JJ two-dimensional antiferromagnets: Role of phonon scattering

Motivated by the recent heat transport experiments in 2D antiferromagnets, such as La$_2$CuO$_4$, where the exchange coupling $J$ is larger than the Debye energy $\Theta_{\rm D}$, we discuss different types of relaxation processes for magnon heat current with a particular focus on coupling to 3D phonons. We study thermal conductivity by these in-plane magnetic excitations using two distinct techniques, Boltzmann formalism within the relaxation-time approximation and memory-function approach. Within these approaches, a close consideration is given to the scattering of magnons by both acoustic and optical branches of phonons. A remarkable accord between the two methods with regards to the asymptotic behavior of the effective relaxation rates is demonstrated. Additional scattering mechanisms, due to grain boundaries, impurities, and finite correlation length in the paramagnetic phase, are discussed and included in the calculations of the thermal conductivity $\kappa(T)$. Again, we demonstrate a close similarity of the results from the two techniques of calculating $\kappa(T)$. Our complementary approach strongly suggests that scattering from optical or zone-boundary phonons is important for magnon heat current relaxation in a high temperature window of $\Theta_D\lesssim T \ll J$.Comment: 21+ pages, 16 figure

Damped Topological Magnons in the Kagom\'{e}-Lattice Ferromagnets

We demonstrate that interactions can substantially undermine the free-particle description of magnons in ferromagnets on geometrically frustrated lattices. The anharmonic coupling, facilitated by the Dzyaloshinskii-Moriya interaction, and a highly-degenerate two-magnon continuum yield a strong, non-perturbative damping of the high-energy magnon modes. We provide a detailed account of the effect for the $S=1/2$ ferromagnet on the kagom\'e lattice and propose further experiments.Comment: 4.5 p + 4 figs main, 8 p + 16 figs supplemental, typos correcte

Verification of primitive Sub-Ghz RF replay attack techniques based on visual signal analysis

As the low-cost options for radio traffic capture, analysis and transmission are becoming available, some security researchers have developed open-source tools that potentially make it easier to assess the security of the devices that rely on radio communications without the need for extensive knowledge and understanding of the associated concepts. Recent research in this area suggests that primitive visual analysis techniques may be applied to decode selected radio signals successfully. This study builds upon the previous research in the area of sub-GHz radio communications and aims to outline the associated methodology as well as verify some of the reported techniques for carrying out radio frequency replay attacks using low-cost materials and freely available software

Heat Transport in Spin Chains with Weak Spin-Phonon Coupling

The heat transport in a system of $S=1/2$ large-$J$ Heisenberg spin chains, describing closely Sr$_2$CuO$_3$ and SrCuO$_2$ cuprates, is studied theoretically at $T\ll J$ by considering interactions of the bosonized spin excitations with optical phonons and defects. Treating rigorously the multi-boson processes, we derive a microscopic spin-phonon scattering rate that adheres to an intuitive picture of phonons acting as thermally populated defects for the fast spin excitations. The mean-free path of the latter exhibits a distinctive $T$-dependence reflecting a critical nature of spin chains and gives a close description of experiments. By the naturalness criterion of realistically small spin-phonon interaction, our approach stands out from previous considerations that require large coupling constants to explain the data and thus imply a spin-Peierls transition, absent in real materials.Comment: 5+ pages main text, 4+ pages supplemental, 4+2 figures, adiabatic approximation to the published versio