2,271 research outputs found
Single-Dirac-Cone topological surface states in TlBiSe2 class of Topological Insulators
We have investigated several strong spin-orbit coupling ternary chalcogenides
related to the (Pb,Sn)Te series of compounds. Our first-principles calculations
predict the low temperature rhombohedral ordered phase in TlBiTe2, TlBiSe2, and
TlSbX2 (X=Te, Se, S) to be topologically Kane-Mele Z2 = -1 nontrivial. We
identify the specific surface termination that realizes the single Dirac cone
through first-principles surface state computations. This termination minimizes
effects of dangling bonds making it favorable for photoemission (ARPES)
experiments. Our analysis predicts that thin films of these materials would
harbor novel 2D quantum spin Hall states, and support odd-parity topological
superconductivity. For a related work also see arXiv:1003.2615v1. Experimental
ARPES results will be published elsewhere.Comment: Accepted for publication in Phys. Rev. Lett. (2010). Submitted March
201
Ethical Control of Unmanned Systems: lifesaving/lethal scenarios for naval operations
Prepared for: Raytheon Missiles & Defense under NCRADA-NPS-19-0227This research in Ethical Control of Unmanned Systems applies precepts of Network Optional Warfare (NOW) to develop a three-step Mission Execution Ontology (MEO) methodology for validating, simulating, and implementing mission orders for unmanned systems. First, mission orders are represented in ontologies that are understandable by humans and readable by machines. Next, the MEO is validated and tested for logical coherence using Semantic Web standards. The validated MEO is refined for implementation in simulation and visualization. This process is iterated until the MEO is ready for implementation. This methodology is applied to four Naval scenarios in order of increasing challenges that the operational environment and the adversary impose on the Human-Machine Team. The extent of challenge to Ethical Control in the scenarios is used to refine the MEO for the unmanned system. The research also considers Data-Centric Security and blockchain distributed ledger as enabling technologies for Ethical Control. Data-Centric Security is a combination of structured messaging, efficient compression, digital signature, and document encryption, in correct order, for round-trip messaging. Blockchain distributed ledger has potential to further add integrity measures for aggregated message sets, confirming receipt/response/sequencing without undetected message loss. When implemented, these technologies together form the end-to-end data security that ensures mutual trust and command authority in real-world operational environments—despite the potential presence of interfering network conditions, intermittent gaps, or potential opponent intercept. A coherent Ethical Control approach to command and control of unmanned systems is thus feasible. Therefore, this research concludes that maintaining human control of unmanned systems at long ranges of time-duration and distance, in denied, degraded, and deceptive environments, is possible through well-defined mission orders and data security technologies. Finally, as the human role remains essential in Ethical Control of unmanned systems, this research recommends the development of an unmanned system qualification process for Naval operations, as well as additional research prioritized based on urgency and impact.Raytheon Missiles & DefenseRaytheon Missiles & Defense (RMD).Approved for public release; distribution is unlimited
Ab initio theory and modeling of water
Water is of the utmost importance for life and technology. However, a
genuinely predictive ab initio model of water has eluded scientists. We
demonstrate that a fully ab initio approach, relying on the strongly
constrained and appropriately normed (SCAN) density functional, provides such a
description of water. SCAN accurately describes the balance among covalent
bonds, hydrogen bonds, and van der Waals interactions that dictates the
structure and dynamics of liquid water. Notably, SCAN captures the density
difference between water and ice I{\it h} at ambient conditions, as well as
many important structural, electronic, and dynamic properties of liquid water.
These successful predictions of the versatile SCAN functional open the gates to
study complex processes in aqueous phase chemistry and the interactions of
water with other materials in an efficient, accurate, and predictive, ab initio
manner
Supercooled Water and the Kinetic Glass Transition II: Collective Dynamics
In this article we study in detail the Q-vector dependence of the collective
dynamics in simulated deeply supercooled SPC/E water. The evolution of the
system has been followed for 250 ns at low T, allowing a clear identification
of a two step relaxation process. We present evidence in favor of the use of
the mode coupling theory for supercooled liquid as framework for the
description of the slow alpha-relaxation dynamics in SPC/E water,
notwithstanding the fact that the cage formation in this system is controlled
by the formation of an open network of hydrogen bonds as opposed to packing
constraints, as in the case of simple liquids.Comment: rev-tex + 9 figure
An Analysis of the Environments of FU Orionis Objects with Herschel
We present Herschel-HIFI, SPIRE, and PACS 50-670 {\mu}m imaging and
spectroscopy of six FU Orionis-type objects and candidates (FU Orionis, V1735
Cyg, V1515 Cyg, V1057 Cyg, V1331 Cyg, and HBC 722), ranging in outburst date
from 1936-2010, from the "FOOSH" (FU Orionis Objects Surveyed with Herschel)
program, as well as ancillary results from Spitzer-IRS and the Caltech
Submillimeter Observatory. In their system properties (Lbol, Tbol, line
emission), we find that FUors are in a variety of evolutionary states.
Additionally, some FUors have features of both Class I and II sources: warm
continuum consistent with Class II sources, but rotational line emission
typical of Class I, far higher than Class II sources of similar
mass/luminosity. Combining several classification techniques, we find an
evolutionary sequence consistent with previous mid-IR indicators. We detect [O
I] in every source at luminosities consistent with Class 0/I protostars, much
greater than in Class II disks. We detect transitions of 13CO (J_up of 5 to 8)
around two sources (V1735 Cyg and HBC 722) but attribute them to nearby
protostars. Of the remaining sources, three (FU Ori, V1515 Cyg, and V1331 Cyg)
exhibit only low-lying CO, but one (V1057 Cyg) shows CO up to J = 23 - 22 and
evidence for H2O and OH emission, at strengths typical of protostars rather
than T Tauri stars. Rotational temperatures for "cool" CO components range from
20-81 K, for ~ 10^50 total CO molecules. We detect [C I] and [N II] primarily
as diffuse emission.Comment: 31 pages, 15 figures; accepted to Ap
A topological insulator surface under strong Coulomb, magnetic and disorder perturbations
Three dimensional topological insulators embody a newly discovered state of
matter characterized by conducting spin-momentum locked surface states that
span the bulk band gap as demonstrated via spin-resolved ARPES measurements .
This highly unusual surface environment provides a rich ground for the
discovery of novel physical phenomena. Here we present the first controlled
study of the topological insulator surfaces under strong Coulomb, magnetic and
disorder perturbations. We have used interaction of iron, with a large Coulomb
state and significant magnetic moment as a probe to \textit{systematically test
the robustness} of the topological surface states of the model topological
insulator BiSe. We observe that strong perturbation leads to the
creation of odd multiples of Dirac fermions and that magnetic interactions
break time reversal symmetry in the presence of band hybridization. We also
present a theoretical model to account for the altered surface of BiSe.
Taken collectively, these results are a critical guide in manipulating
topological surfaces for probing fundamental physics or developing device
applications.Comment: 14 pages, 4 Figures. arXiv admin note: substantial text overlap with
arXiv:1009.621
Kernel Formula Approach to the Universal Whitham Hierarchy
We derive the dispersionless Hirota equations of the universal Whitham
hierarchy from the kernel formula approach proposed by Carroll and Kodama.
Besides, we also verify the associativity equations in this hierarchy from the
dispersionless Hirota equations and give a realization of the associative
algebra with structure constants expressed in terms of the residue formulas.Comment: 18 page
High resolution Compton scattering as a Probe of the Fermi surface in the Iron-based superconductor
We have carried out first principles all-electron calculations of the
(001)-projected 2D electron momentum density and the directional Compton
profiles along the [100], [001] and [110] directions in the Fe-based
superconductor LaOFeAs within the framework of the local density approximation.
We identify Fermi surface features in the 2D electron momentum density and the
directional Compton profiles, and discuss issues related to the observation of
these features via Compton scattering experiments.Comment: 4 pages, 3 figure
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