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Practicality of Biochar Additions to Enhance Soil and Crop Productivity
David M. Filiberto,John L. Gaunt
Agriculture , 2013, DOI: 10.3390/agriculture3040715
Abstract: The benefits of biochar to soils for agricultural purposes are numerous. Biochar may be added to soils with the intention to improve the soil, displace an amount of conventional fossil fuel based fertilizers, and sequester carbon. However, the variable application rates, uncertain feedstock effects, and initial soil state provide a wide range of cost for marginally improved yield from biochar additions, which is often economically impracticable. The need for further clarity on optimizing biochar application to various crop yields is necessary if it is to gain widespread acceptance as a soil amendment.
Robust Digital Holography For Ultracold Atom Trapping
Alexander L Gaunt,Zoran Hadzibabic
Physics , 2011, DOI: 10.1038/srep00721
Abstract: We have formulated and experimentally demonstrated an improved algorithm for design of arbitrary two-dimensional holographic traps for ultracold atoms. Our method builds on the best previously available algorithm, MRAF, and improves on it in two ways. First, it allows for creation of holographic atom traps with a well defined background potential. Second, we experimentally show that for creating trapping potentials free of fringing artifacts it is important to go beyond the Fourier approximation in modelling light propagation. To this end, we incorporate full Helmholtz propagation into our calculations.
Critical Dynamics of Spontaneous Symmetry Breaking in a Homogeneous Bose gas
Nir Navon,Alexander L. Gaunt,Robert P. Smith,Zoran Hadzibabic
Physics , 2014, DOI: 10.1126/science.1258676
Abstract: We explore the dynamics of spontaneous symmetry breaking in a homogeneous system by thermally quenching an atomic gas with short-range interactions through the Bose-Einstein phase transition. Using homodyne matter-wave interferometry to measure first-order correlation functions, we verify the central quantitative prediction of the Kibble-Zurek theory, namely the homogeneous-system power-law scaling of the coherence length with the quench rate. Moreover, we directly confirm its underlying hypothesis, the freezing of the correlation length near the transition due to critical slowing down. Our measurements agree with beyond mean-field theory, and support the previously unverified expectation that the dynamical critical exponent for this universality class, which includes the $\lambda$-transition of liquid $^4$He, is $z=3/2$.
Are we winning? Improving perinatal outcomes at a deeply rural district hospital in South Africa
CB Gaunt
South African Medical Journal , 2010,
Abstract:
Derivative formulas for Bessel, Struve and Anger-Weber functions
Robert Gaunt
Mathematics , 2012,
Abstract: We derive formulas for the derivatives of general order for the functions $z^{-\nu}h_{\nu}(z)$ and $z^{\nu}h_{\nu}(z)$, where $h_{\nu}(z)$ is a Bessel, Struve or Anger-Weber function. These formulas are motivated by the occurrence of the expressions $\frac{d^n}{dz^n}(z^{-\nu}I_{\nu}(z))$ and $\frac{d^n}{dz^n}(z^{-\nu}K_{\nu}(z))$ in the study of Variance-Gamma approximations via Stein's method.
Molecular Epidemiology and Evolution of Human Respiratory Syncytial Virus and Human Metapneumovirus
Eleanor R. Gaunt,Rogier R. Jansen,Yong Poovorawan,Kate E. Templeton,Geoffrey L. Toms,Peter Simmonds
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017427
Abstract: Human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV) are ubiquitous respiratory pathogens of the Pneumovirinae subfamily of the Paramyxoviridae. Two major surface antigens are expressed by both viruses; the highly conserved fusion (F) protein, and the extremely diverse attachment (G) glycoprotein. Both viruses comprise two genetic groups, A and B. Circulation frequencies of the two genetic groups fluctuate for both viruses, giving rise to frequently observed switching of the predominantly circulating group. Nucleotide sequence data for the F and G gene regions of HRSV and HMPV variants from the UK, the Netherlands, Bangkok and data available from Genbank were used to identify clades of both viruses. Several contemporary circulating clades of HRSV and HMPV were identified by phylogenetic reconstructions. The molecular epidemiology and evolutionary dynamics of clades were modelled in parallel. Times of origin were determined and positively selected sites were identified. Sustained circulation of contemporary clades of both viruses for decades and their global dissemination demonstrated that switching of the predominant genetic group did not arise through the emergence of novel lineages each respiratory season, but through the fluctuating circulation frequencies of pre-existing lineages which undergo proliferative and eclipse phases. An abundance of sites were identified as positively selected within the G protein but not the F protein of both viruses. For HRSV, these were discordant with previously identified residues under selection, suggesting the virus can evade immune responses by generating diversity at multiple sites within linear epitopes. For both viruses, different sites were identified as positively selected between genetic groups.
Experimental infection and co-infection of dogs with Anaplasma platys and Ehrlichia canis: hematologic, serologic and molecular findings
SD Gaunt, MJ Beall, BA Stillman, L Lorentzen, PPVP Diniz, R Chandrashekar, EB Breitschwerdt
Parasites & Vectors , 2010, DOI: 10.1186/1756-3305-3-33
Abstract: Initially, transient decreases in hematocrit occurred in all groups infected with E. canis, but the mean hematocrit was significantly lower in the A. platys and E. canis co-infected group. All dogs except the controls developed marked thrombocytopenia after initial infection followed by gradually increased platelet counts by 112 days PI in groups with the single infections, while platelet counts remained significantly lower in the A. platys and E. canis co-infected group. Both sequential and simultaneous infections of A. platys and E. canis produced an enhanced humoral immune response to A. platys when compared to infection with A. platys alone. Likewise, co-infection with E. canis and A. platys resulted in a more persistent A. platys infection compared to dogs infected with A. platys only, but nearly all A. platys infected dogs became A. platys PCR negative prior to doxycycline treatment. E. canis infected dogs, whether single or co-infected, remained thrombocytopenic and E. canis PCR positive in blood for 420 days. When treated with doxycycline, all E. canis infected dogs became E. canis PCR negative and the thrombocytopenia resolved. Despite immunosuppression, neither A. platys nor E. canis DNA was PCR amplified from doxycycline-treated dogs.The results of this study demonstrate that simultaneous or sequential infection with A. platys and E. canis can alter various pathophysiological parameters in experimentally infected dogs, and because natural exposure to multiple tick-borne pathogens occurs frequently in dogs, awareness of co-infection is important in clinical practice.Ehrlichia canis is a Gram-negative, obligate intracellular bacterium which infects monocytes and is the primary causative agent of canine monocytic ehrlichiosis [1]. Rhipicephalus sanguineus transmits E. canis to dogs both transtadially and intrastadially [2]. Canine infections caused by E. canis are more commonly reported in the southern regions of the United States, however R. sanguineus is d
Quantum Joule-Thomson Effect in a Saturated Homogeneous Bose Gas
Tobias F. Schmidutz,Igor Gotlibovych,Alexander L. Gaunt,Robert P. Smith,Nir Navon,Zoran Hadzibabic
Physics , 2013, DOI: 10.1103/PhysRevLett.112.040403
Abstract: We study the thermodynamics of Bose-Einstein condensation in a weakly interacting quasi-homogeneous atomic gas, prepared in an optical-box trap. We characterise the critical point for condensation and observe saturation of the thermal component in a partially condensed cloud, in agreement with Einstein's textbook picture of a purely statistical phase transition. Finally, we observe the quantum Joule-Thomson effect, namely isoenthalpic cooling of an (essentially) ideal gas. In our experiments this cooling occurs spontaneously, due to energy-independent collisions with the background gas in the vacuum chamber. We extract a Joule-Thomson coefficient $\mu_{\rm JT} > 10^9$ K/bar, about ten orders of magnitude larger than observed in classical gases.
Observing Properties of an Interacting Homogeneous Bose--Einstein Condensate: Heisenberg-Limited Momentum Spread, Interaction Energy and Free-Expansion Dynamics
Igor Gotlibovych,Tobias F. Schmidutz,Alexander L. Gaunt,Nir Navon,Robert P. Smith,Zoran Hadzibabic
Physics , 2014, DOI: 10.1103/PhysRevA.89.061604
Abstract: We study the properties of an atomic Bose--Einstein condensate produced in an optical-box potential, using high-resolution Bragg spectroscopy. For a range of box sizes, up to $70~\mu$m, we directly observe Heisenberg-limited momentum uncertainty of the condensed atoms. We measure the condensate interaction energy with a precision of $k_B \times 100$ pK and study, both experimentally and numerically, the dynamics of its free expansion upon release from the box potential. All our measurements are in good agreement with theoretical expectations for a perfectly homogeneous condensate of spatial extent equal to the size of the box, which also establishes the uniformity of our optical-box system on a sub-nK energy scale.
A superheated Bose-condensed gas
Alexander L. Gaunt,Richard J. Fletcher,Robert P. Smith,Zoran Hadzibabic
Physics , 2012, DOI: 10.1038/nphys2587
Abstract: Our understanding of various states of matter usually relies on the assumption of thermodynamic equilibrium. However, the transitions between different phases of matter can be strongly affected by non-equilibrium phenomena. Here we demonstrate and explain an example of non-equilibrium stalling of a continuous, second-order phase transition. We create a superheated atomic Bose gas, in which a Bose-Einstein condensate (BEC) persists above the equilibrium critical temperature, $T_c$, if its coupling to the surrounding thermal bath is reduced by tuning interatomic interactions. For vanishing interactions the BEC persists in the superheated regime for a minute. However, if strong interactions are suddenly turned on, it rapidly "boils" away. Our observations can be understood within a two-fluid picture, treating the condensed and thermal components of the gas as separate equilibrium systems with a tuneable inter-component coupling. We experimentally reconstruct a non-equilibrium phase diagram of our gas, and theoretically reproduce its main features.
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