Experimental demonstration of painting arbitrary and dynamic potentials for Bose-Einstein condensates

There is a pressing need for robust and straightforward methods to create potentials for trapping Bose-Einstein condensates which are simultaneously dynamic, fully arbitrary, and sufficiently stable to not heat the ultracold gas. We show here how to accomplish these goals, using a rapidly-moving laser beam that "paints" a time-averaged optical dipole potential in which we create BECs in a variety of geometries, including toroids, ring lattices, and square lattices. Matter wave interference patterns confirm that the trapped gas is a condensate. As a simple illustration of dynamics, we show that the technique can transform a toroidal condensate into a ring lattice and back into a toroid. The technique is general and should work with any sufficiently polarizable low-energy particles.Comment: Minor text changes and three references added. This is the final version published in New Journal of Physic

Monitoring global vegetation

An attempt is made to identify the need for, and the current capability of, a technology which could aid in monitoring the Earth's vegetation resource on a global scale. Vegetation is one of our most critical natural resources, and accurate timely information on its current status and temporal dynamics is essential to understand many basic and applied environmental interrelationships which exist on the small but complex planet Earth

Control of threshold voltage in E-mode and D-mode GaN-on-Si metal-insulator-semiconductor heterostructure field effect transistors by in-situ fluorine doping of atomic layer deposition Al2O3 gate dielectrics

We report the modification and control of threshold voltage in enhancement and depletion mode AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors through the use of in-situ fluorine doping of atomic layer deposition Al2O3. Uniform distribution of F ions throughout the oxide thickness are achievable, with a doping level of up to 5.5 × 1019 cm−3 as quantified by secondary ion mass spectrometry. This fluorine doping level reduces capacitive hysteretic effects when exploited in GaN metal-oxide-semiconductor capacitors. The fluorine doping and forming gas anneal also induces an average positive threshold voltage shift of between 0.75 and 1.36 V in both enhancement mode and depletion mode GaN-based transistors compared with the undoped gate oxide via a reduction of positive fixed charge in the gate oxide from +4.67 × 1012 cm−2 to −6.60 × 1012 cm−2. The application of this process in GaN based power transistors advances the realisation of normally off, high power, high speed devices

A Study of Feasibility of State Water User Fees for Financing Water Development

Water user fees imposed by a state on major water uses is a possible new alternative source of state water development funds. A fee, similar to an excise tax, might be charged for the use of the water resource per se, which in a number of states is declared to be the property of the public of the state. States generally have not employed such fees as a source of operating funds for water agencies or of development capital. Only in the area of water based recreation-fishing, coating, camping, etc.—have states extensively employed user fees. The revenues from these fees, however, are used only to defray management and operating expenses associated with these activities. The implementation of user-fee financing would result in some shifts of financing burden connected with water programs from the general taxpayers of the state to specific water users. Although this approach has not been utilized by states to a significant extent, the “user pay” principle is well established in economic theory. The theory indicated that user fees would be an economically more efficient and equitable source for financing water development than general tax revenues. In the design of fee structures for major water uses, several characteristics of fees are appropriate to consider. Five which were identified in this study are as follows: equity, economic efficiency, allocational effectiveness, administrative simplicity, and revenue generating potential. These were used to evaluate different structures for extracting fees from the user. These rate design considerations may relate only indirectly to a state system of user fees since the state fees envisioned in this study in many cases may be only an add-on or surcharge to a basic charge imposed by a local entity, such as a municipality or an irrigation district. Revenue generating potential, the last of the five characteristics listed, was of primary interest in this study. Estimates of revenue potential for four major water uses—irrigation, municipal, industrial, and recreations—were made with a formula developed in this study for this purpose. Gross estimates of potential from public supply and irrigation uses were made for several selected states, and somewhat more detailed estimates were made for the four major uses in Utah. The calculations indicated that substantial amounts of funds could be generated with only modest increases in current charges. A preliminary assessment of legal and administrative implications of implementing water user fees in the State of Utah was made in this study. The results indicated that some fee alternatives probably could be implemented by administrative action; others would require legislative approval. Constitutional issues related to some alternatives would have to be resolved by the state supreme court. New uses associated with developing Utah’s vast energy resources appear to offer a particularly promising prospect for instituting a user fee program with minimal legal complications

Bypassing the requirement for aminoacyl-tRNA by a cyclodipeptide synthase enzyme

C. J. H. and C. M. C. are funded by the Wellcome trust (210486/Z/18/Z), ES is funded by the Cunningham trust (PhD-CT-18-41).Cyclodipeptide synthases (CDPSs) produce a variety of cyclic dipeptide products by utilising two aminoacylated tRNA substrates. We sought to investigate the minimal requirements for substrate usage in this class of enzymes as the relationship between CDPSs and their substrates remains elusive. Here, we investigated the Bacillus thermoamylovorans enzyme, BtCDPS, which synthesises cyclo(L-Leu–L-Leu). We systematically tested where specificity arises and, in the process, uncovered small molecules (activated amino esters) that will suffice as substrates, although catalytically poor. We solved the structure of BtCDPS to 1.7 Å and combining crystallography, enzymatic assays and substrate docking experiments propose a model for how the minimal substrates interact with the enzyme. This work is the first report of a CDPS enzyme utilizing a molecule other than aa-tRNA as a substrate; providing insights into substrate requirements and setting the stage for the design of improved simpler substrates.Publisher PDFPeer reviewe

Goal-oriented a posteriori error estimation for the travel time functional in porous media flows

In this article we consider the a posteriori error estimation and adaptive mesh refinement for the numerical approximation of the travel time functional arising in porous media flows. The key application of this work is in the safety assessment of radioactive waste facilities; in this setting, the travel time functional measures the time taken for a non-sorbing radioactive solute, transported by groundwater, to travel from a potential site deep underground to the biosphere. To ensure the computability of the travel time functional, we employ a mixed formulation of Darcy's law and conservation of mass, together with Raviart-Thomas H(div) conforming finite elements. The proposed a posteriori error bound is derived based on a variant of the standard Dual-Weighted-Residual approximation, which takes into account the lack of smoothness of the underlying functional of interest. The proposed adaptive refinement strategy is tested on both a simple academic test case and a problem based on the geological units found at the Sellafield site in the UK

EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6

We present a study of the high-energy diffuse emission observed toward Orion by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory. The total exposure by EGRET in this region has increased by more than a factor of two since a previous study. A simple model for the diffuse emission adequately fits the data; no significant point sources are detected in the region studied ($l = 195^\circ$ to $220^\circ$ and $b = -25^\circ to -10^\circ$) in either the composite dataset or in two separate groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion is found to be $(1.65 \pm 0.11) \times 10^{-26} {s sr}^{-1}$ for E > 100 MeV, and the differential emissivity is well-described as a combination of contributions from cosmic-ray electrons and protons with approximately the local density. The molecular mass calibrating ratio is $N(H_2)/W_{CO} = (1.35 \pm 0.15) \times 10^{20} cm^{-2} (K km/s)^{-1}$.Comment: 16 pages, including 5 figures. 3 Tables as three separate files. Latex document, needs AASTEX style files. Accepted for publication in Ap