Abundances and Kinematics of Extremely Metal-Deficient, Carbon-Rich Halo Stars

Original paper can be found at: http://www.astrosociety.org/pubs/cs/286.html Copyright ASPTo study the possible nucleosynthetic backgrounds of extremely metal-deficient, carbon-rich (EMDC) stars, we have conducted high-resolution spectroscopy of 26 candidate objects selected from HK-survey stars with [Fe/H]? -2.0. The aims of the analysis are: (a) to calculate abundances for the targets, including the CNO- and neutron-capture elements; (b) to monitor the radial velocities of the survey targets and another 17 bona fide EMDC stars to search for binarity

A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283

Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron capture processes: the s- and r-process. Metal-poor stars should contain fewer isotopes that form via the s-process, according to currently accepted theory. It has been shown in several investigations that theory and observation do not agree well, raising questions on the validity of either the methodology or the theory. We analyse the metal-poor star HD140283, for which we have a high quality spectrum. We test whether a 3D LTE stellar atmosphere and spectrum synthesis code permits a more reliable analysis of the iron abundance and barium isotope ratio than a 1D LTE analysis. Using 3D model atmospheres, we examine 91 iron lines of varying strength and formation depth. This provides us with the star's rotational speed. With this, we model the barium isotope ratio by exploiting the hyperfine structure of the singly ionised 4554 resonance line, and study the impact of the uncertainties in the stellar parameters. HD140283's vsini = 1.65 +/- 0.05 km/s. Barium isotopes under the 3D paradigm show a dominant r-process signature as 77 +/- 6 +/- 17% of barium isotopes form via the r-process, where errors represent the assigned random and systematic errors, respectively. We find that 3D LTE fits reproduce iron line profiles better than those in 1D, but do not provide a unique abundance (within the uncertainties). However, we demonstrate that the isotopic ratio is robust against this shortcoming. Our barium isotope result agrees well with currently accepted theory regarding the formation of the heavy-elements during the early Galaxy. The improved fit to the asymmetric iron line profiles suggests that the current state of 3D LTE modelling provides excellent simulations of fluid flows. However, the abundances they provide are not yet self-consistent. This may improve with NLTE considerations and higher resolution models.Comment: 16 pages, 10 figures, 5 tables. Accepted for publication in A&

Extending Quantum Coherence in Diamond

We experimentally demonstrate over two orders of magnitude increase in the coherence time of nitrogen vacancy centres in diamond by implementing decoupling techniques. We show that equal pulse spacing decoupling performs just as well as non-periodic Uhrig decoupling and has the additional benefit that it allows us to take advantage of "revivals" in the echo (due to the coherent nature of the bath) to explore the longest coherence times. At short times, we can extend the coherence of particular quantum states out from T_2*=2.7 us out to an effective T_2 > 340 us. For preserving arbitrary states we show the experimental importance of using pulse sequences, that through judicious choice of the phase of the pulses, compensate the imperfections of individual pulses for all input states. At longer times we use these compensated sequences to enhance the echo revivals and show a coherence time of over 1.6 ms in ultra-pure natural abundance 13C diamond.Comment: 7 pages, 7 figures; minor syntax/typo. changes and updated reference

Antiphase dynamics in a multimode semiconductor laser with optical injection

A detailed experimental study of antiphase dynamics in a two-mode semiconductor laser with optical injection is presented. The device is a specially designed Fabry-Perot laser that supports two primary modes with a THz frequency spacing. Injection in one of the primary modes of the device leads to a rich variety of single and two-mode dynamical scenarios, which are reproduced with remarkable accuracy by a four dimensional rate equation model. Numerical bifurcation analysis reveals the importance of torus bifurcations in mediating transitions to antiphase dynamics and of saddle-node of limit cycle bifurcations in switching of the dynamics between single and two-mode regimes.Comment: 7 pages, 9 figure

Molecular Gas Content of HI Monsters and Implications to Cold Gas Content Evolution in Galaxies

We present 12CO (J=1-0) observations of a sample of local galaxies (0.04<z<0.08) with a large neutral hydrogen reservoir, or "HI monsters". The data were obtained using the Redshift Search Receiver on the FCRAO 14 m telescope. The sample consists of 20 HI-massive galaxies with M(HI)>3e10Msun from the ALFALFA survey and 8 LSBs with a comparable M(HI) (>1.5e10Msun). Our sample selection is purely based on the amount of neutral hydrogen, thereby providing a chance to study how atomic and molecular gas relate to each other in these HI-massive systems. We have detected CO in 15 out of 20 ALFALFA selected galaxies and 4 out of 8 LSBs with molecular gas mass M(H2) of (1-11)e9Msun. Their total cold gas masses of (2-7e10Msun make them some of the most gas-massive galaxies identified to date in the Local Universe. Observed trends associated with HI, H2, and stellar properties of the HI massive galaxies and the field comparison sample are analyzed in the context of theoretical models of galaxy cold gas content and evolution, and the importance of total gas content and improved recipes for handling spatially differentiated behaviors of disk and halo gas are identified as potential areas of improvement for the modeling.Comment: 18 pages, 11 figures, 2 tables; Accepted for publication in MNRA

Limit cycle vibrations in turbomachinery

The focus is on an examination of rotordynamic systems which are simultaneously susceptible to limit cycle instability and subharmonic response. Characteristics of each phenomenon are determined as well as their interrelationship. A normalized, single mass rotor model is examined as well as a complex model of the high pressure fuel turbopump and the Space Shuttle Main Engine. Entrainment of limit cycle instability by subharmonic response is demonstrated for both models. The nonuniqueness of the solution is also demonstrated

D.I.Y. Clean Hood

The DIY Clean Hood is a low-cost, sterile, and accessible scientific workspace intended for installation in the BioElectroFluidics Lab of California Polytechnic State University’s (San Luis Obispo) Biomedical Engineering Department (BMED), under the sponsorship of Dr. Benjamin Hawkins, PhD. As normal Clean Hood, Biosafety Cabinets, and the like are generally too expensive for a university, a competitive solution to an expensive problem can assist research students and professors alike continue their own work with an inexpensive yet effective environment. Specific design elements that the customer requirements entailed for the project include a low-particle-count air filtration system, positive pressure air flow inside the vessel, and compatibility with common cleaning agents. These critical details for the DIY Clean Hood are to ensure that the cell cultures being cultivated and studied are free from any foreign contaminants or agents that could compromise the product. Unlike the original, mislabeled identification of the project as a “DIY Biosafety Cabinet”, it is not the responsibility of the Clean Hood to protect either the environment or the user of the DIY Clean Hood. Despite the non-hazardous conditions of the cells being manipulated, proper design components and features ensure sterility and effectiveness. Other notable design elements of the DIY Clean Hood include a 15 degree angled, swinging sash opening, an air filtration system utilizing a HEPA (High-Efficiency Particulate Air) filter, an installed UV light for an additional sterilization option, and a wide opening for comfortable mobility while using the Clean Hood. The project was a recipient of the Biomedical Engineering Department’s Hannah-Forbes Grant, which allows the DIY Clean Hood project an additional $500 towards any necessary purchases and bringing the total budget to$700. Due to the onset of the COVID-19 pandemic, the project required its focus to shift from a manufacturing and qualification testing standpoint to a more design and technically-centered frame, as several factors prevented the project from proceeding originally as planned. These included, but were not limited to, the closure of manufacturing and assembly facilities on the Cal Poly campus, anticipated delays in material acquisition due to non-essential items, social distancing of team members, and limited alternative build options. This decision was agreed upon in correspondence with project sponsor Dr. Hawkins, Engineering Design overseer Dr. Michael Whitt, and the members of the DIY Clean Hood Team. As a result, the DIY Clean Hood prepared a final, detailed design for the product to ensure all customer requirements were met in approaches the team thought would provide the best performance and usability; the BioElectroFluidics lab will find a team of their own in late 2020 to build the device using the enclosed detailed designs, and qualify the product with the DIY Clean Hood’s testing protocols