Negative Refraction of Excitations in the Bose-Hubbard Model

Ultracold atoms in optical lattices provide a unique opportunity to study Bose- Hubbard physics. In this work we show that by considering a spatially varying onsite interaction it is possible to manipulate the motion of excitations above the Mott phase in a Bose-Hubbard system. Specifically, we show that it is possible to "engineer" regimes where excitations will negatively refract, facilitating the construction of a flat lens.Comment: 6 pages, 4 figure

Domain structures in quantum graphity

Quantum graphity offers the intriguing notion that space emerges in the low-energy states of the spatial degrees of freedom of a dynamical lattice. Here we investigate metastable domain structures which are likely to exist in the low-energy phase of lattice evolution. Through an annealing process we explore the formation of metastable defects at domain boundaries and the effects of domain structures on the propagation of bosons. We show that these structures should have observable background-independent consequences including scattering, double imaging, and gravitational lensing-like effects

Remaining Flying Time Prediction Implementing Battery Prognostics Framework for Electric UAV's

In this paper the problem of building trust in the online safety prediction of an fixed wing small electric unmanned aerial vehicles (e-UAV) for remaining flying time is addressed. A series of flight tests are described to verify the performance of the remaining flying time prediction algorithm. The estimate of remaining flying time is used to activate an alarm when the predicted remaining time falls below a threshold of two minutes. This updates the pilot to transition to the landing sequence of the flight profile. A second alarm is activated when the battery state of charge (SOC) falls below a specified safety limit threshold. This SOC threshold is the point at which the battery energy reserve would no longer safely support enough aborted landing attempts. During the test flights, the motor system is operated with the same predefined timed airspeed profile for each test. To test the robustness of the developed prediction algorithm, partial tests were performed with and remaining were performed without a simulated power train fault. To simulate a partial power train fault in the e-UAV the pilot engages a resistor bank at a specified time during the test flight. The flying time prediction system is agnostic of the pilot's activation of the fault and must adapt to the vehicle's state. The time at which the limit threshold on battery SOC is reached, it is then used to measure the accuracy of the remaining flying time predictions. This is demonstrated through comparing results from two battery models being developed. Accuracy requirements for the alarms are considered and the results discussed

Reconfigurable quantum metamaterials

By coupling controllable quantum systems into larger structures we introduce the concept of a quantum metamaterial. Conventional metamaterials represent one of the most important frontiers in optical design, with applications in diverse fields ranging from medicine to aerospace. Up until now however, metamaterials have themselves been classical structures and interact only with the classical properties of light. Here we describe a class of dynamic metamaterials, based on the quantum properties of coupled atom-cavity arrays, which are intrinsically lossless, reconfigurable, and operate fundamentally at the quantum level. We show how this new class of metamaterial could be used to create a reconfigurable quantum superlens possessing a negative index gradient for single photon imaging. With the inherent features of quantum superposition and entanglement of metamaterial properties, this new class of dynamic quantum metamaterial, opens a new vista for quantum science and technolog

3D FEM to predict residual stresses of press-braked thin-walled steel sections

Cold-formed steel sections are normally produced by cold work manufacturing processes. The amount of cold work to form the sections may have induced residual stresses in the section especially in the area of bending. Hence, these cold work processes may have significant effects on the section behaviour and load-bearing capacity. There was a lack of studies in investigating the effects of residual stresses raised by press-braking operations unlike the roll-forming operation. Therefore, a 3D finite element simulation was employed to simulate this forming process. This study investigated the magnitude of the maximum residual stresses along the length of the corner region and through-thickness residual stress variations induced by the press-braking forming process. The study concluded that residual stresses are not linear longitudinally (along the corner region). Maximum residual stresses exist near the middle surface of the plate. The comparison of the 3D-FE results with the 2D-FE results illustrate that 3D-FE has a variation in transverse and longitudinal residual stresses along the plate length. In addition, 2D-FE results overestimate the residual stresses along the corner region

An evaluation of the status of living collections for plant, environmental, and microbial research

Citation: McCluskey, K., Parsons, J. P., Quach, K., & Duke, C. S. (2017). An evaluation of the status of living collections for plant, environmental, and microbial research. Journal of Biosciences, 42(2), 321-331. https://doi.org/10.1007/s12038-017-9685-6While living collections are critical for biological research, support for these foundational infrastructure elements is inconsistent, which makes quality control, regulatory compliance, and reproducibility difficult. In recent years, the Ecological Society of America has hosted several National Science Foundation–sponsored workshops to explore and enhance the sustainability of biological research infrastructure. At the same time, the United States Culture Collection Network has brought together managers of living collections to foster collaboration and information exchange within a specific living collections community. To assess the sustainability of collections, a survey was distributed to collection scientists whose responses provide a benchmark for evaluating the resiliency of these collections. Among the key observations were that plant collections have larger staffing requirements and that living microbe collections were the most vulnerable to retirements or other disruptions. Many higher plant and vertebrate collections have institutional support and several have endowments. Other collections depend on competitive grant support in an era of intense competition for these resources. Opportunities for synergy among living collections depend upon complementing the natural strong engagement with the research communities that depend on these collections with enhanced information sharing, communication, and collective action to keep them sustainable for the future. External efforts by funding agencies and publishers could reinforce the advantages of having professional management of research resources across every discipline. © 2017 Indian Academy of Science

Hyaluronan concentration and size distribution in human knee synovial fluid: variations with age and cartilage degeneration.

BackgroundOne potential mechanism for early superficial cartilage wear in normal joints is alteration of the lubricant content and quality of synovial fluid. The purpose of this study was to determine if the concentration and quality of the lubricant, hyaluronan, in synovial fluid: (1) was similar in left and right knees; (2) exhibited similar age-associated trends, whether collected postmortem or antemortem; and (3) varied with age and grade of joint degeneration.MethodsHuman synovial fluid of donors (23-91 years) without osteoarthritis was analyzed for the concentrations of protein, hyaluronan, and hyaluronan in the molecular weight ranges of 2.5-7 MDa, 1-2.5 MDa, 0.5-1 MDa, and 0.03-0.5 MDa. Similarity of data between left and right knees was assessed by reduced major axis regression, paired t-test, and Bland-Altman analysis. The effect of antemortem versus postmortem collection on biochemical properties was assessed for age-matched samples by unpaired t-test. The relationships between age, joint grade, and each biochemical component were assessed by regression analysis.ResultsJoint grade and the concentrations of protein, hyaluronan, and hyaluronan in the molecular weight ranges of 2.5-7 MDa, 1-2.5 MDa, and 0.5-1 MDa in human synovial fluid showed good agreement between left and right knees and were similar between age-matched patient and cadaver knee joints. There was an age-associated decrease in overall joint grade (-15 %/decade) and concentrations of hyaluronan (-10.5 %/decade), and hyaluronan in the molecular weight ranges of 2.5-7 MDa (-9.4 %/decade), 1-2.5 MDa (-11.3 %/decade), 0.5-1 MDa (-12.5 %/decade), and 0.03-0.5 MDa (-13.0 %/decade). Hyaluronan concentration and quality was more strongly associated with age than with joint grade.ConclusionsThe age-related increase in cartilage wear in non-osteoarthritic joints may be related to the altered hyaluronan content and quality of synovial fluid

Runway Incursion Prevention System: Demonstration and Testing at the Dallas/Fort Worth International Airport

A Runway Incursion Prevention System (RIPS) was tested at the Dallas-Ft. Worth International Airport (DFW) in October 2000. The system integrated airborne and ground components to provide both pilots and controllers with enhanced situational awareness, supplemental guidance cues, a real-time display of traffic information, and warning of runway incursions in order to prevent runway incidents while also improving operational capability. A series of test runs was conducted using NASA s Boeing 757 research aircraft and a test van equipped to emulate an incurring aircraft. The system was also demonstrated to over 100 visitors from the aviation community. This paper gives an overview of the RIPS, DFW flight test activities, and quantitative and qualitative results of the testing

Adolescents' contraception continuation in Switzerland: a prospective observational study.

Securing the adherence over time to contraception by adolescent girls is a challenge. Until now little was known about this topic in Switzerland. The aim of our study was to determine contraceptive continuation rates among adolescents in this country and assess possible predictive factors for discontinuation. A prospective observational cohort study of 12- to 19-year-old girls starting contraception was performed. Patients were interviewed again after 1 year by phone, email or postal mail. A total of 204 patients were included, of whom 85.8% chose a combined oestrogen-progestogen pill. The answer rate 1 year later was 71%. Among these, continuation of the initially prescribed contraceptive method was observed in 73.1%. Factors statistically affecting the continuation rate were the initial contraceptive method, the place of residence and sexual activity after 1 year. Classification of contraceptive methods in decreasing order of continuation rate was the following: long acting reversible contraception (LARC) methods, oestrogen-progestogen pills, injections, progestogen pills, patches and rings. Major reasons reported for stopping the prescribed contraceptive method were ending sexual relations (54.3%), developing side effects (34.3%) or changing to another contraceptive method (22.9%). Neither age, nationality, smoking, occupation, nor the legal representative's knowledge of the contraception influenced adherence. Contraceptive continuation rate was high among the adolescent population studied. The only predictive factor of discontinuation was the contraceptive method. Our study also reveals that respecting teenagers' confidentiality is essential as it does not negatively impact the continuation rate. The significant impact of the type of contraception on continuation rates stresses the importance of individualised counselling

Verification Test of Automated Robotic Assembly of Space Truss Structures

A multidisciplinary program has been conducted at the Langley Research Center to develop operational procedures for supervised autonomous assembly of truss structures suitable for large-aperture antennas. The hardware and operations required to assemble a 102-member tetrahedral truss and attach 12 hexagonal panels were developed and evaluated. A brute-force automation approach was used to develop baseline assembly hardware and software techniques. However, as the system matured and operations were proven, upgrades were incorporated and assessed against the baseline test results. These upgrades included the use of distributed microprocessors to control dedicated end-effector operations, machine vision guidance for strut installation, and the use of an expert system-based executive-control program. This paper summarizes the developmental phases of the program, the results of several assembly tests, and a series of proposed enhancements. No problems that would preclude automated in-space assembly or truss structures have been encountered. The test system was developed at a breadboard level and continued development at an enhanced level is warranted