Almost Commuting Orthogonal Matrices

We show that almost commuting real orthogonal matrices are uniformly close to exactly commuting real orthogonal matrices. We prove the same for symplectic unitary matrices. This is in contrast to the general complex case, where not all pairs of almost commuting unitaries are close to commuting pairs. Our techniques also yield results about almost normal matrices over the reals and the quaternions.Comment: 13 pages, 3 figure

General criterion for oblivious remote state preparation

A necessary and sufficient condition is given for general exact remote state preparation (RSP) protocols to be oblivious, that is, no information about the target state can be retrieved from the classical message. A novel criterion in terms of commutation relations is also derived for the existence of deterministic exact protocols in which Alice's measurement eigenstates are related to each other by fixed linear operators similar to Bob's unitaries. For non-maximally entangled resources, it provides an easy way to search for RSP protocols. As an example, we show how to reduce the case of partially entangled resources to that of maximally entangled ones, and we construct RSP protocols exploiting the structure of the irreducible representations of Abelian groups.Comment: 5 pages, RevTe

Microscopic dynamics of charge separation at the aqueous electrochemical interface

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na$^+$I$^-$, or classical ions, and the products of water autoionization, H$_3$O$^+$OH$^-$, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. Despite this, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free energy barrier to charge separation and a smaller flux over that barrier at the interface, results in a rate of dissociation that is 40x slower relative to the bulk. For water ions, a slightly higher free energy barrier is offset by a higher flux over the barrier from longer lived hydrogen bonding patters at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface.Comment: 6 pages, 3 figures + S

Documentation Related to a 1991 Observation of Sturgeon in the Rio Grande – Río Bravo, USA (Texas) and Mexico (Coahuila)

This digital archive provides a compilation of previously unpublished information regarding a 1991 observation of a live sturgeon (Family Acipenseridae) in the Rio Grande-Río Bravo of the USA and Mexico. Though a few specimens collected in the 19th century support occurrence of sturgeon in this river basin, lack of credible, recent records has often led to this species not being recognized as part of the basin’s native fish fauna, and certainly not part of its modern fish community. The second and third authors of this document manage the Fishes of Texas Project (Hendrickson, Dean A., & Cohen, Adam E. (2015). Fishes of Texas Project Database (version 2.0). Texas Advanced Computing Center, University of Texas at Austin. http://doi.org/10.17603/C3WC70) and knew of the unpublished 1991 observation of sturgeon reported here. They requested the content provided here from first author (Platania) who provided what follows below (verbatim as received in April 2018) and permission to archive it for public access.Integrative Biolog

Exciton Trapping Is Responsible for the Long Apparent Lifetime in Acid-Treated MoS2

Here, we show that deep trapped "dark" exciton states are responsible for the surprisingly long lifetime of band-edge photoluminescence in acid-treated single-layer MoS2. Temperature-dependent transient photoluminescence spectroscopy reveals an exponential tail of long-lived states extending hundreds of meV into the band gap. These sub-band states, which are characterized by a 4 microsecond radiative lifetime, quickly capture and store photogenerated excitons before subsequent thermalization up to the band edge where fast radiative recombination occurs. By intentionally saturating these trap states, we are able to measure the "true" 150 ps radiative lifetime of the band-edge exciton at 77 K, which extrapolates to ~600 ps at room temperature. These experiments reveal the dominant role of dark exciton states in acid-treated MoS2, and suggest that excitons spend > 95% of their lifetime at room temperature in trap states below the band edge. We hypothesize that these states are associated with native structural defects, which are not introduced by the superacid treatment; rather, the superacid treatment dramatically reduces non-radiative recombination through these states, extending the exciton lifetime and increasing the likelihood of eventual radiative recombination

Towards synthetic biological approaches to resource utilization on space missions.

This paper demonstrates the significant utility of deploying non-traditional biological techniques to harness available volatiles and waste resources on manned missions to explore the Moon and Mars. Compared with anticipated non-biological approaches, it is determined that for 916 day Martian missions: 205 days of high-quality methane and oxygen Mars bioproduction with Methanobacterium thermoautotrophicum can reduce the mass of a Martian fuel-manufacture plant by 56%; 496 days of biomass generation with Arthrospira platensis and Arthrospira maxima on Mars can decrease the shipped wet-food mixed-menu mass for a Mars stay and a one-way voyage by 38%; 202 days of Mars polyhydroxybutyrate synthesis with Cupriavidus necator can lower the shipped mass to three-dimensional print a 120 m(3) six-person habitat by 85% and a few days of acetaminophen production with engineered Synechocystis sp. PCC 6803 can completely replenish expired or irradiated stocks of the pharmaceutical, thereby providing independence from unmanned resupply spacecraft that take up to 210 days to arrive. Analogous outcomes are included for lunar missions. Because of the benign assumptions involved, the results provide a glimpse of the intriguing potential of 'space synthetic biology', and help focus related efforts for immediate, near-term impact

Single-particle levitation system for automated study of homogeneous solute nucleation

We present an instrument that addresses two critical requirements for quantitative measurements of the homogeneous crystal nucleation rate in supersaturated aqueous solution. First, the need to perform repeated measurements of nucleation incubation times is met by automating experiments to enable programmable cycling of thermodynamic conditions. Second, the need for precise and robust control of the chemical potential in supersaturated aqueous solution is met by implementing a novel technique for regulating relative humidity. The apparatus levitates and weighs micron-sized samples in an electric field, providing access to highly supersaturated states. We report repeated observations of the crystal nucleation incubation time in a supersaturated aqueous sodium chloride droplet, from which we infer the nucleation rate

Modular multilevel converter with modified half-bridge submodule and arm filter for dc transmission systems with DC fault blocking capability

Although a modular multilevel converter (MMC) is universally accepted as a suitable converter topology for the high voltage dc transmission systems, its dc fault ride performance requires substantial improvement in order to be used in critical infrastructures such as transnational multi-terminal dc (MTDC) networks. Therefore, this paper proposes a modified submodule circuit for modular multilevel converter that offers an improved dc fault ride through performance with reduced semiconductor losses and enhanced control flexibility compared to that achievable with full-bridge submodules. The use of the proposed submodules allows MMC to retain its modularity; with semiconductor loss similar to that of the mixed submodules MMC, but higher than that of the half-bridge submodules. Besides dc fault blocking, the proposed submodule offers the possibility of controlling ac current in-feed during pole-to-pole dc short circuit fault, and this makes such submodule increasingly attractive and useful for continued operation of MTDC networks during dc faults. The aforesaid attributes are validated using simulations performed in MATLAB/SIMULINK, and substantiated experimentally using the proposed submodule topology on a 4-level small-scale MMC prototype