Mathematical retroreflectors

Retroreflectors are optical devices that reverse the direction of incident beams of light. Here we present a collection of billiard type retroreflectors consisting of four objects; three of them are asymptotically perfect retroreflectors, and the fourth one is a retroreflector which is very close to perfect. Three objects of the collection have recently been discovered and published or submitted for publication. The fourth object - notched angle - is a new one; a proof of its retroreflectivity is given.Comment: 32 pages, 19 figure

Magnetic signatures of multicomponent superconductivity in pressurized UTe2

The heavy fermion material UTe$_2$ possesses a rich phase diagram with multiple superconducting phases, several of which exhibit characteristics of odd-parity pairing. Here, we report on the pressure dependence of signatures of the superconducting transition in the temperature dependent ac magnetic susceptibility $\chi(T)$ in high quality UTe$_2$ single crystals. We resolve a single superconducting transition in $\chi(T)$ at low pressures $<$ 0.3 GPa. At higher pressure, however, a second feature emerges in $\chi(T)$, which is located at the thermodynamic phase boundary between two separate superconducting states previously identified by specific heat studies. The observation of a two-step transition in $\chi(T)$ can be understood as a consequence of the change in the London penetration depth, when UTe$_2$ switches from one superconducting phase into another

Electrical transport signatures of metallic surface state formation in the strongly-correlated insulator FeSb2

We present local and nonlocal electrical transport measurements of the correlated insulator FeSb$_2$. By employing wiring configurations that delineate between bulk- and surface-dominated conduction, we reveal the formation of a metallic surface state in FeSb$_2$ for temperatures $\lessapprox 5$~K. This result is corroborated by an angular rotation study of this material's magnetotransport, which also shows signatures of the transition from bulk- to surface-dominated conduction over the same temperature interval as the local/nonlocal transport divergence. Notable similarities with the topological Kondo insulator candidate SmB$_6$ are discussed

Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors.

A central question in the underdoped cuprates pertains to the nature of the pseudogap ground state. A conventional metallic ground state of the pseudogap region has been argued to host quantum oscillations upon destruction of the superconducting order parameter by modest magnetic fields. Here, we use low applied measurement currents and millikelvin temperatures on ultrapure single crystals of underdoped [Formula: see text] to unearth an unconventional quantum vortex matter ground state characterized by vanishing electrical resistivity, magnetic hysteresis, and nonohmic electrical transport characteristics beyond the highest laboratory-accessible static fields. A model of the pseudogap ground state is now required to explain quantum oscillations that are hosted by the bulk quantum vortex matter state without experiencing sizable additional damping in the presence of a large maximum superconducting gap; possibilities include a pair density wave.Royal Society Winton Programme for the Physics of Sustainability Engineering and Physical Sciences Research Council (EPSRC; studentship and grant numbers EP/R513180/1, EP/M506485/1 and EP/P024947/1) European Research Council under the European Unions Seventh Framework Programme (Grant Agreement numbers 337425 and 772891). EPSRC Strategic Equipment Grant EP/M000524/1 Leverhulme Trust by way of the award of a Philip Leverhulme Prize. National Key Research and Development Program of China (grant no. 2016YFA0401704). Work performed at the National High Magnetic Field Laboratory (NHMFL) supported by NSF Cooperative Agreement DMR-1157490, the State of Florida, and the Department of Energy (DOE) DOE Basic Energy Sciences project: ‘Science of 100 tesla’

High slope efficiency and high refractive index change in direct-written Yb-doped waveguide lasers with depressed claddings

We report the first Yb:ZBLAN and Yb:IOG10 waveguide lasers fabricated by the fs-laser direct-writing technique. Pulses from a Titanium-Sapphire laser oscillator with 5.1 MHz repetition rate were utilized to generate negative refractive index modifications in both glasses. Multiple modifications were aligned in a depressed cladding geometry to create a waveguide. For Yb:ZBLAN we demonstrate high laser slope efficiency of 84% with a maximum output power of 170 mW. By using Yb:IOG10 a laser performance of 25% slope efficiency and 72 mW output power was achieved and we measured a remarkably high refractive index change exceeding Δn = 2.3 × 10(-2).Guido Palmer, Simon Gross, Alexander Fuerbach, David G. Lancaster and Michael J. Withfor

An Inventory and Assessment of Sample Sources for Survey Research with Agricultural Producers in the U.S.

Researchers need probability samples to collect representative survey data about the behaviors and attitudes of agricultural producers they study in relation to the natural resources that they manage, yet obtaining accurate and complete sampling frames is challenging. We extract data from a publication database to identify the most commonly used sampling frame sources in survey research of agricultural producers in the U.S., finding that government program participant lists are used most often, while private vendor samples are increasingly being purchased. Based on our research experience, we find that for many projects, private vendors can provide the most rigorous samples. Given that survey methods remain a useful and popular method for studying the behaviors and attitudes of producers on a variety of topics, such an assessment and guide is needed for researchers and practitioners

Production of Magnetic Arsenic–Phosphorus Alloy Nanoribbons with Small Band Gaps and High Hole Conductivities

Quasi-1D nanoribbons provide a unique route to diversifying the properties of their parent 2D nanomaterial, introducing lateral quantum confinement and an abundance of edge sites. Here, a new family of nanomaterials is opened with the creation of arsenic–phosphorus alloy nanoribbons (AsPNRs). By ionically etching the layered crystal black arsenic–phosphorus using lithium electride followed by dissolution in amidic solvents, solutions of AsPNRs are formed. The ribbons are typically few-layered, several micrometers long with widths tens of nanometers across, and both highly flexible and crystalline. The AsPNRs are highly electrically conducting above 130 K due to their small band gap (ca. 0.035 eV), paramagnetic in nature, and have high hole mobilities, as measured with the first generation of AsP devices, directly highlighting their properties and utility in electronic devices such as near-infrared detectors, quantum computing, and charge carrier layers in solar cells

DNA Methylation of the ABO Promoter Underlies Loss of ABO Allelic Expression in a Significant Proportion of Leukemic Patients

Background: Loss of A, B and H antigens from the red blood cells of patients with myeloid malignancies is a frequent occurrence. Previously, we have reported alterations in ABH antigens on the red blood cells of 55% of patients with myeloid malignancies. Methodology/Principal Findings: To determine the underlying molecular mechanisms of this loss, we assessed ABO allelic expression in 21 patients with ABH antigen loss previously identified by flow cytometric analysis as well as an additional 7 patients detected with ABH antigen changes by serology. When assessing ABO mRNA allelic expression, 6/12 (50%) patients with ABH antigen loss detected by flow cytometry and 5/7 (71%) of the patients with ABH antigen loss detected by serology had a corresponding ABO mRNA allelic loss of expression. We examined the ABO locus for copy number and DNA methylation alterations in 21 patients, 11 with loss of expression of one or both ABO alleles, and 10 patients with no detectable allelic loss of ABO mRNA expression. No loss of heterozygosity (LOH) at the ABO locus was observed in these patients. However in 8/11 (73%) patients with loss of ABO allelic expression, the ABO promoter was methylated compared with 2/10 (20%) of patients with no ABO allelic expression loss (P = 0.03). Conclusions/Significance: We have found that loss of ABH antigens in patients with hematological malignancies is associated with a corresponding loss of ABO allelic expression in a significant proportion of patients. Loss of ABO allelic expression was strongly associated with DNA methylation of the ABO promoter.Tina Bianco-Miotto, Damian J. Hussey, Tanya K. Day, Denise S. O'Keefe and Alexander Dobrovi