Exploring 2+2\boldsymbol{2+2} Answers to 3+1\boldsymbol{3+1} Questions

We explore potential uses of physics formulated in Kleinian (i.e., $2+2$) signature spacetimes as a tool for understanding properties of physics in Lorentzian (i.e., $3+1$) signature. Much as Euclidean (i.e., $4+0$) signature quantities can be used to formally construct the ground state wavefunction of a Lorentzian signature quantum field theory, a similar analytic continuation to Kleinian signature constructs a state of low particle flux in the direction of analytic continuation. There is also a natural supersymmetry algebra available in $2+2$ signature, which serves to constrain the structure of correlation functions. Spontaneous breaking of Lorentz symmetry can produce various $\mathcal{N} = 1/2$ supersymmetry algebras that in $3 + 1$ signature correspond to non-supersymmetric systems. We speculate on the possible role of these structures in addressing the cosmological constant problem.Comment: 22 pages, 1 figur

Observation of a Free-Shercliff-Layer Instability in Cylindrical Geometry

We report on observations of a free-Shercliff-layer instability in a Taylor-Couette experiment using a liquid metal over a wide range of Reynolds numbers, $Re\sim 10^3-10^6$. The free Shercliff layer is formed by imposing a sufficiently strong axial magnetic field across a pair of differentially rotating axial endcap rings. This layer is destabilized by a hydrodynamic Kelvin-Helmholtz-type instability, characterized by velocity fluctuations in the $r-\theta$ plane. The instability appears with an Elsasser number above unity, and saturates with an azimuthal mode number $m$ which increases with the Elsasser number. Measurements of the structure agree well with 2D global linear mode analyses and 3D global nonlinear simulations. These observations have implications for a range of rotating MHD systems in which similar shear layers may be produced.Comment: 5 pages, 4 figure

The only known egg of the Night Parrot? A molecular and morphometric assessment of an alleged egg from the Tanami Desert

The Night Parrot Pezoporus occidentalis is a much sought-after, recently ‘rediscovered’, endangered nocturnal parrot, endemic to arid Central Australia. Very little is known of its ecology, and its eggs have never been formally described. The literature on the eggs of the Night Parrot is collated here, and the provenance of an alleged Night Parrot egg found in the Tanami Desert, Northern Territory, in 1983 was assessed using DNA analysis and physical characteristics. Anecdotal reports from the late 19th–early 20th Century indicate that the Night Parrot lays a clutch of two to six roundish, white eggs. We suggest that its eggs are probably similar to and slightly larger than those of its congener, the Ground Parrot P. wallicus. The alleged Night Parrot egg was definitively identified by mitochondrial DNA analysis to be from the Brown Quail Synoicus ypsilophorus. This represents the first evidence of breeding by this species in the Tanami Desert, and lays to rest a long-standing misconception regarding the parrot

Electronic Modulation of Near-Field Radiative Transfer in Graphene Field Effect Heterostructures

Manipulating heat flow in a controllable and reversible manner is a topic of fundamental and practical interest. Numerous approaches to perform thermal switching have been reported, but they typically suffer from various limitations, for instance requiring mechanical modulation of a submicron gap spacing or only operating in a narrow temperature window. Here, we report the experimental modulation of radiative heat flow by electronic gating of a graphene field effect heterostructure without any moving elements. We measure a maximum heat flux modulation of 4 ± 3% and an absolute modulation depth of 24 ± 7 mW m^(–2) V^(–1) in samples with vacuum gap distances ranging from 1 to 3 μm. The active area in the samples through which heat is transferred is ∼1 cm^2, indicating the scalable nature of these structures. A clear experimental path exists to realize switching ratios as large as 100%, laying the foundation for electronic control of near-field thermal radiation using 2D materials

The origins of the enigmatic Falkland Islands wolf

The origins of the extinct Falkland Islands wolf (FIW), Dusicyon australis, have remained a mystery since it was first recorded by Europeans in the seventeenth century. It is the only terrestrial mammal on the Falkland Islands (also known as the Malvinas Islands), which lie ∼460 km from Argentina, leading to suggestions of either human-mediated transport or overwater dispersal. Previous studies used ancient DNA from museum specimens to suggest that the FIW diverged from its closest living relative, the South American maned wolf (Chrysocyon brachyurus) around 7 Ma, and colonized the islands ∼330 ka by unknown means. Here we retrieve ancient DNA from subfossils of an extinct mainland relative, Dusicyon avus, and reveal the FIW lineage became isolated only 16 ka (8-31 ka), during the last glacial phase. Submarine terraces, formed on the Argentine coastal shelf by low sea-stands during this period, suggest that the FIW colonized via a narrow, shallow marine strait, potentially while it was frozen over.Facultad de Ciencias Naturales y Muse

Particle Migration in Large Cross-Section Ceramic On-Demand Extrusion Components

Ceramic On-Demand Extrusion (CODE) is a direct ink writing process which allows for the creation of near theoretically dense ceramic components with large cross-sections due to oil-assisted drying. Yttria-stabilized zirconia (YSZ) colloidal pastes (∼d50 ≲ 1 µm) were used in CODE to produce dense (multi-road infill and ≳ 98% relative density), large continuous volume (\u3e 1 cm3), and high fidelity (nozzle diameters ≲ 1 mm) structural ceramic components. However, many of these printed components underwent significant particle migration after forming. The reason for this particle migration defect was investigated using the coffee-ring effect for dilute solutions and rheological methods for dense suspensions. Modifications to the colloidal paste, such as changes in solids loading, pH, or surfactant concentration were explored as to their effectiveness to mitigate the defect. Ultimately, paste formulation and printing trade-offs are discussed with respect to the post-printing defect and as to general direct-write patterning

Use of GoFundMe® to crowdfund complementary and alternative medicine treatments for cancer.

PurposeComplementary and alternative medicine (CAM) use is common amongst cancer patients. However, there is growing concern about its safety and efficacy. Online crowdfunding campaigns represent a unique avenue to understand the cancer patient's perspective for using CAM or declining conventional cancer therapy (CCT).MethodsFive hundred GoFundMe campaigns from 2012 to 2019 detailing financial need for cancer treatment were randomly selected and reviewed for endorsement of CAM use, reasons for using CAM, and reasons for declining CCT. Descriptive statistics were used to compare patient and campaign characteristics between 250 CAM users and 250 non-CAM users.ResultsCompared to non-CAM users, CAM users were more likely to be female (70% vs. 54%, p < 0.01), to report more stage IV cancer (54% vs. 12%, p < 0.01), and to have a history of delayed, missed, or misdiagnosis (10% vs. 4%, p < 0.01). Reasons for using CAM include endorsing curative/therapeutic effects 212 (85%), pain/stress reduction 137 (55%), and dissatisfaction with current or past medical treatment options 105 (42%). 87 (35%) CAM users that declined CCT reported that they wanted to try to fight off cancer using CAM first 57 (61%), that CCT was too "toxic" to the body 39 (42%), and cancer was already too advanced, so that CCT would be futile or too aggressive 25 (27%).ConclusionCancer patients on GoFundMe using CAM highly value quality of life, comfort, and autonomy. Physicians should educate themselves on CAM to set realistic expectations and provide comprehensive counseling of the risks and benefits of CAM usage to patients who choose to use CAM to either augment or completely replace CCT