The operation of district heating with heat pumps and thermal energy storage in a zero-emission scenario

With the decarbonisation of electricity generation, large scale heat pumps are becoming an increasingly viable prospect for district heating installations. Heat pumps couple heat demands to an intermittent electricity supply with varying electricity prices with the use of thermal energy storage providing flexibility to avoid peak electricity charges and minimise operating costs. However, the operating strategy for cost minimising in district heating system models is dependent on the size of heat pump and thermal energy storage capacity chosen and its operational conditions. Model predictive control techniques can be used to explore district heating configurations with varying forecast horizons. This study applies optimisation to a district heating operation model simulation to find low cost combinations of heat pump and thermal energy storage sizes. Physics-based representations of a district heating network and thermal energy storage are developed with ground source heat pumps and applied to a district heat load profile with hourly marginal electricity costs derived from a modelled zero-carbon electricity system as a basis for operation. Using a dynamic programming algorithm with different forecast horizons to minimise operational costs, the total costs of combinations of heat pump and thermal energy storage sizes are calculated. The operation at smaller thermal store sizes shows cycling multiple times per day, while at larger sizes these sub-daily cycles are maintained but longer multi-day cycles become more predominant. It was found that thermal energy storage equivalent of around 1% of annual demand is sufficient to minimise operating costs and enables flexibility beyond 4 days. This has important consequences for the electricity system and can facilitate the integration of variable renewable electricity

Integrating Plant Secondary Metabolites and Foraging Behavior to Enhance Animal Health in Ruminant Production Systems

Legumes and forbs contain bioactives or plant secondary compounds (PSC) with potential to enhance animal health through their antibiotic, antioxidant and immunomodulatory properties that are evident even at small dietary concentrations. In turn, ruminants can regulate their ingestion of PSC through behavioral mechanisms that allow for the efficient achievement of homeostasis. High concentrations of PSC lead to food avoidance, whereas lower content of PSC in the diet achieved through regulatory mechanisms of ingestion could promote medicinal and/or prophylactic effects in the animal and concomitant health benefits to milk and meat products. Under this context, we discuss the restructuring of rangelands and pasturelands through the strategic distribution of legume- and forb-rich patches in monotonous landscapes dominated by grasses, thus re-establishing their functionality. Such strategies can synergistically complement and provide new dimensions (prophylactic-medicinal, product quality) to the forage resources already available to livestock

CTMC calculations of electron capture and ionization in collisions of multiply charged ions with elliptical Rydberg atoms

We have performed classical trajectory Monte Carlo (CTMC) studies of electron capture and ionization in multiply charged (Q=8) ion-Rydberg atom collisions at intermediate impact velocities. Impact parallel to the minor and to the major axis, respectively, of the initial Kepler electron ellipse has been investigated. The important role of the initial electron momentum distribution found for singly charged ion impact is strongly disminished for higher projectile charge, while the initial spatial distribution remains important for all values of Q studied.Comment: 3 pages, 5 figure

Velocity-selective resonance dips in the probe absorption spectra of Rb D2 transitions induced by a pump laser

We report experimental observation of velocity-selective resonances in the Doppler-broadened probe absorption spectra of 85Rb and 87Rb D2 transitions in the presence of a strong copropagating pump laser locked to a frequency within the Doppler profile of the transition. The set of three dips having the separation of allowed hyperfine transitions can be moved along the Doppler profile by tuning the pump laser frequency indicating a resonance between the pump laser frequency and the velocity shifted probe laser frequency.Comment: 7 pages, 4 figure

Tannins in Perennial Legume and Forb Functional Forages

Feed is the greatest input cost for cattle producers. The studies summarized here employed non-bloating, tannin-containing irrigated perennial legume pastures or hay of legumes or a hydrolysable tannin-containing forb that were grown in the Mountain West USA, with non-tannin legume, grass, or feedlot treatments for comparison. Cattle grazing legume pastures or fed legume or forb hays had greater intake, gain and nitrogen retention, and in some cases, reduced enteric methane emissions compared with grass pastures or hay, and methane emissions were not different from feedlot-fed cattle

Two-species magneto-optical trap with 40K and 87Rb

We trap and cool a gas composed of 40K and 87Rb, using a two-species magneto-optical trap (MOT). This trap represents the first step towards cooling the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is derived from laser diodes and amplified with a single high power semiconductor amplifier chip. The four-color laser system is described, and the single-species and two-species MOTs are characterized. Atom numbers of 1x10^7 40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap loss due to collisions between species is presented and future prospects for the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review

Experimental implementation of a four-level N-type scheme for the observation of Electromagnetically Induced Transparency

A nondegenerate four-level N-type scheme was experimentally implemented to observe electromagnetically induced transparency (EIT) at the $^{87}$Rb D$_{2}$ line. Radiations of two independent external-cavity semiconductor lasers were used in the experiment, the current of one of them being modulated at a frequency equal to the hyperfine-splitting frequency of the excited 5P$_{3/2}$ level. In this case, apart from the main EIT dip corresponding to the two-photon Raman resonance in a three-level $\Lambda$-scheme, additional dips detuned from the main dip by a frequency equal to the frequency of the HF generator were observed in the absorption spectrum. These dips were due to an increase in the medium transparency at frequencies corresponding to the three-photon Raman resonances in four-level N-type schemes. The resonance shapes are analyzed as functions of generator frequency and magnetic field.Comment: 3 pages, 2 figure

Legumes as a Strategy for Reducing Greenhouse Gas Emissions of Forage-Livestock Systems

Incorporation of legumes into forage systems has been a widely adopted strategy to increase pasture productivity and forage nutritive value, while reducing N inputs. Considering the population growth, and the diminishing land resources for food production, the need to increase the food supply will have to be balanced with the environmental impact of these systems, particularly their carbon footprint. Enteric methane production represents the largest source of greenhouse gas emissions from livestock. Certain forage legumes have evolved plant secondary compounds, such as tannins and other polyphenols, which have been associated with reductions in enteric methane emissions. Studies were conducted at Utah State University (USU), and at the University of Florida, North Florida Research and Education Center (UF-NFREC) to assess in vivo methane emissions in grazing cattle, using the SF6 tracer technique. At USU, cattle grazing pastures of Birdsfoot trefoil (Lotus corniculatus; BFT) emitted less methane per unit of dry matter consumed when compared with cattle fed a totally mixed ration (50% barley grain, 25% alfalfa hay, and 25% corn silage) in ad libitum amounts. However, emissions in cattle grazing BFT did not differ from those grazing the legume Cicer milkvetch (Astragalus cicer), or a traditional pasture-finishing system based on Meadow brome (Bromus riparius). At UF-NFREC, three livestock-forage systems were tested during three consecutive years to determine the effects of including the legume Rhizoma peanut (Arachis glabrata Benth.; BHR) in bahiagrass pastures (Paspalum notatum Flügge) fertilized (BH) or not (BHF) with N during the warm season. No differences were observed in methane emissions (g d-1), or in methane emission intensity. From the legumes grazed in these experiments, only BFT contains significant concentrations of tannins. Thus, the potential to mitigate livestock enteric methane emissions by grazing legumes appears to be directly related to the presence of tannins

Guiding neutral atoms around curves with lithographically patterned current-carrying wires

Laser-cooled neutral atoms from a low-velocity atomic source are guided via a magnetic field generated between two parallel wires on a glass substrate. The atoms bend around three curves, each with a 15-cm radius of curvature, while traveling along a 10-cm-long track. A maximum flux of 2*10^6 atoms/sec is achieved with a current density of 3*10^4 A/cm^2 in the 100x100-micrometer-cross-section wires. The kinetic energy of the guided atoms in one transverse dimension is measured to be 42 microKelvin.Comment: 9 page