Vortex Lattices in Active Nematics with Periodic Obstacle Arrays

We numerically model a two-dimensional active nematic confined by a periodic array of fixed obstacles. Even in the passive nematic, the appearance of topological defects is unavoidable due to planar anchoring by the obstacle surfaces. We show that a vortex lattice state emerges as activity is increased, and that this lattice may be tuned from ``ferromagnetic'' to ``antiferromagnetic'' by varying the gap size between obstacles. We map the rich variety of states exhibited by the system as a function of distance between obstacles and activity, including a pinned defect state, motile defects, the vortex lattice, and active turbulence. We demonstrate that the flows in the active turbulent phase can be tuned by the presence of obstacles, and explore the effects of a frustrated lattice geometry on the vortex lattice phase.Comment: 6 + 8 pages, 4 + 3 figure

Friction mediated phase transition in confined active nematics

Using a minimal continuum model, we investigate the interplay between circular confinement and substrate friction in active nematics. Upon increasing the friction from low to high, we observe a dynamical phase transition from a circulating flow phase to an anisotropic flow phase in which the flow tends to align perpendicular to the nematic director at the boundary. We demonstrate that both the flow structure and dynamic correlations in the latter phase differ from those of an unconfined, active turbulent system and may be controlled by the prescribed nematic boundary conditions. Our results show that substrate friction and geometric confinement act as valuable control parameters in active nematics.Comment: 6+7 pages, 4+3 figure

Theory and Application of Dissociative Electron Capture in Molecular Identification

The coupling of an electron monochromator (EM) to a mass spectrometer (MS) has created a new analytical technique, EM-MS, for the investigation of electrophilic compounds. This method provides a powerful tool for molecular identification of compounds contained in complex matrices, such as environmental samples. EM-MS expands the application and selectivity of traditional MS through the inclusion of a new dimension in the space of molecular characteristics--the electron resonance energy spectrum. However, before this tool can realize its full potential, it will be necessary to create a library of resonance energy scans from standards of the molecules for which EM-MS offers a practical means of detection. Here, an approach supplementing direct measurement with chemical inference and quantum scattering theory is presented to demonstrate the feasibility of directly calculating resonance energy spectra. This approach makes use of the symmetry of the transition-matrix element of the captured electron to discriminate between the spectra of isomers. As a way of validating this approach, the resonance values for twenty-five nitrated aromatic compounds were measured along with their relative abundance. Subsequently, the spectra for the isomers of nitrotoluene were shown to be consistent with the symmetry-based model. The initial success of this treatment suggests that it might be possible to predict negative ion resonances and thus create a library of EM-MS standards.Comment: 18 pages, 7 figure

Eagle Mountain To Big Fossil Creek Diversion Tarrant, County, Texas

The City of Fort Worth is proposing to construct the Eagle Mountain to Big Fossil Diversion Pipeline in northern Tarrant County. Alan Plummer Associates, Inc. is handling the environmental permitting for the construction of the pipeline. AR Consultants, Inc. was contracted to conduct a cultural resource survey, which included archival research, to determine the presence of prehistoric and historic archaeological sites along the route and make recommendations about eligibility for the National Register of Historic Places (NRHP) and State Antiquities Landmark (SAL) designation. Four survey areas were identified, totaling approximately 3.1 kilometers of the approximately 9-km-long route. The westernmost survey area of the pipeline crosses Dosier Creek on the northside of Boat Club Road. The central segment out of the four survey areas is parallel to Park Drive and was investigated due to the presence of structures shown on historic maps within the 100-foot survey corridor. The longest segment in the east is parallel an intermittent tributary flowing northeast into Big Fossil Creek, while the final survey area approaches Big Fossil Creek in its floodplain. Survey of the approximately 25 acres was conducted on January 09, 2018. One site, 41TR309, was recorded and represents the remains of a historic farmstead. The site is not recommended eligible for NRHP or SAL. No other cultural resources were identified on or below the surface during the survey. Based on the results of the survey, ARC concludes that further cultural resource investigations for this project are unwarranted, and requests that the Texas Historical Commission (THC) concur with this recommendation. However, if buried cultural materials are discovered during construction, the Archeology Division of the THC should be notified. The records will be curated at the Center for Archaeological Studies at Texas State University in San Marcos

Archeological Survey Of The Proposed Sanger Outfall Pipeline Denton County, Texas

The City of Sanger is proposing to construct the 3.06-kilometer-long Sanger Outfall Pipeline in Denton County, Texas. Alan Plummer Associates, Inc. contracted with AR Consultants, Inc. to survey a 100-foot-wide corridor along the proposed route. AR Consultants, Inc. hypothesized that there would be low potential for both prehistoric and historic cultural resources. These hypotheses were based on the location of the pipeline route in the narrow Ranger Branch floodplain and lack of mapped historic structures remaining in the project area. Fieldwork was conducted on May 31, 2018 under Texas Antiquities permit 8338, during which 19 shovel tests were excavated and a total of 11 acres were surveyed. No historic or prehistoric cultural resources were noted within the survey corridor. As such, AR Consultants, Inc. recommends that no further cultural resource investigations are necessary for this project, and requests that the Texas Historical Commission concur with this recommendation. Project documents will be curated at the Center for Archaeological Studies, Texas State University, San Marcos

Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577

We located interstellar organics from a CR1 chondrite with NanoSIMS and analyzed FIB-extracted sections with XANES. D-rich material appears not associated with a functional group, whereas 15N-rich matter shows some affinity to nitrile functionality

Characteristics of a Nonvolatile SRAM Memory Cell Utilizing a Ferroelectric Transistor

The SRAM cell circuit is a standard for volatile data storage. When utilizing one or more ferroelectric transistors, the hysteresis characteristics give unique properties to the SRAM circuit, providing for investigation into the development of a nonvolatile memory cell. This paper discusses various formations of the SRAM circuit, using ferroelectric transistors, n-channel and p-channel MOSFETs, and resistive loads. With varied source and supply voltages, the effects on the timing and retention characteristics are investigated, including retention times of up to 24 hours

HiPEP Ion Optics System Evaluation Using Gridlets

Experimental measurements are presented for sub-scale ion optics systems comprised of 7 and 19 aperture pairs with geometrical features that are similar to the HiPEP ion optics system. Effects of hole diameter and grid-to-grid spacing are presented as functions of applied voltage and beamlet current. Recommendations are made for the beamlet current range where the ion optics system can be safely operated without experiencing direct impingement of high energy ions on the accelerator grid surface. Measurements are also presented of the accelerator grid voltage where beam plasma electrons backstream through the ion optics system. Results of numerical simulations obtained with the ffx code are compared to both the impingement limit and backstreaming measurements. An emphasis is placed on identifying differences between measurements and simulation predictions to highlight areas where more research is needed. Relatively large effects are observed in simulations when the discharge chamber plasma properties and ion optics geometry are varied. Parameters investigated using simulations include the applied voltages, grid spacing, hole-to-hole spacing, doubles-to-singles ratio, plasma potential, and electron temperature; and estimates are provided for the sensitivity of impingement limits on these parameters

Correlated analyses of D- and 15N-rich carbon grains from CR2 chondrite EET 92042

Extract from introduction: Insoluble organic matter (IOM) and matrix from primitive carbonaceous chondrites carry isotope enrichments (?D?20000', ?15N?3200�) that are comparable to those in interplanetary dust particles [1, this work]. Hence, primitive organics that formed in the protosolar cloud (PSC) – or maybe in the cold outer regions of the protoplanetary disk – survived accretion and planetary processing on the asteroids, the parent bodies of the chondrites