Nonexistence of reflexive ideals in Iwasawa algebras of Chevalley type

Let $\Phi$ be a root system and let \Phi(\Zp) be the standard Chevalley \Zp-Lie algebra associated to $\Phi$. For any integer $t\geq 1$, let $G$ be the uniform pro-$p$ group corresponding to the powerful Lie algebra p^t \Phi(\Zp) and suppose that $p\geq 5$. Then the Iwasawa algebra $\Omega_G$ has no nontrivial reflexive two-sided ideals. This was previously proved by the authors for the root system $A_1$.Comment: Minor changes made, mostly due to helpful comments from the refere

The Megamaser Cosmology Project. VII. Investigating disk physics using spectral monitoring observations

We use single-dish radio spectra of known 22 GHz H$_2$O megamasers, primarily gathered from the large dataset observed by the Megamaser Cosmology Project, to identify Keplerian accretion disks and to investigate several aspects of the disk physics. We test a mechanism for maser excitation proposed by Maoz & McKee (1998), whereby population inversion arises in gas behind spiral shocks traveling through the disk. Though the flux of redshifted features is larger on average than that of blueshifted features, in support of the model, the high-velocity features show none of the predicted systematic velocity drifts. We find rapid intra-day variability in the maser spectrum of ESO 558-G009 that is likely the result of interstellar scintillation, for which we favor a nearby ($D \approx 70$ pc) scattering screen. In a search for reverberation in six well-sampled sources, we find that any radially-propagating signal must be contributing $\lesssim$10% of the total variability. We also set limits on the magnetic field strengths in seven sources, using strong flaring events to check for the presence of Zeeman splitting. These limits are typically 200--300 mG ($1\sigma$), but our most stringent limits reach down to 73 mG for the galaxy NGC 1194.Comment: Accepted for publication in Ap

Mist Generation Behavior in Ultrasonic Atomizer for Aerosol Jet Printing

Continuous ultrasonic atomization in a closed chamber is expected to generate a mist with an equilibrium droplet concentration and size distribution. Such a mist of microdroplets with controllable mist density has been used for Aerosol Jet printing in the fabrication of a variety of additively manufactured microscale devices. Despite many unique capabilities demonstrated with the Aerosol Jet printing technology, its ultrasonic atomization behavior appears to be rather sensitive to the ink properties with gaps in our understanding of the fundamental physics underlying its operation. In this work, we investigate some basic mechanisms in the Aerosol Jet ultrasonic atomizer with a lumped-parameter kinetic coagulation model for highly concentrated mist. To mitigate the difficulty with unavailable knowledge about the complex turbulent flow inside the atomizer chamber, we present results for several orders of magnitude of the turbulent energy dissipation rates in order to examine a range of possibilities. The same approach is taken for analyzing the scavenging effect of the swirling bulk liquid. Our results also demonstrate the theoretical possibility for achieving a mist saturation condition where the mist output from the atomizer can become insensitive to process variables. As observed in experiments, such a saturated mist is highly desirable for Aerosol Jet printing with maximized and well-controlled throughput in additive manufacturing.Comment: 18 pages, 9 figure

Direct Numerical Simulation of the Sedimentation of Solid Particles with Thermal Convection

Dispersed two-phase flows often involve interfacial activities such as chemical reaction and phase change, which couple the fluid dynamics with heat and mass transfer. As a step toward understanding such problems, we numerically simulate the sedimentation of solid bodies in a Newtonian fluid with convection heat transfer. The two-dimensional Navier–Stokes and energy equations are solved at moderate Reynolds numbers by a finite-element method, and the motion of solid particles is tracked using an arbitrary Lagrangian–Eulerian scheme. Results show that thermal convection may fundamentally change the way that particles move and interact. For a single particle settling in a channel, various Grashof-number regimes are identified, where the particle may settle straight down or migrate toward a wall or oscillate laterally. A pair of particles tend to separate if they are colder than the fluid and aggregate if they are hotter. These effects are analysed in terms of the competition between the thermal convection and the external flow relative to the particle. The mechanisms thus revealed have interesting implications for the formation of microstructures in interfacially active two-phase flows

How Do UX Practitioners Communicate AI as a Design Material? Artifacts, Conceptions, and Propositions

UX practitioners (UXPs) face novel challenges when working with and communicating artificial intelligence (AI) as a design material. We explore how UXPs communicate AI concepts when given hands-on experience training and experimenting with AI models. To do so, we conducted a task-based design study with 27 UXPs in which they prototyped and created a design presentation for a AI-enabled interface while having access to a simple AI model training tool. Through analyzing UXPs' design presentations and post-activity interviews, we found that although UXPs struggled to clearly communicate some AI concepts, tinkering with AI broadened common ground when communicating with technical stakeholders. UXPs also identified key risks and benefits of AI in their designs, and proposed concrete next steps for both UX and AI work. We conclude with a sensitizing concept and recommendations for design and AI tools to enhance multi-stakeholder communication and collaboration when crafting human-centered AI experiences