Charged hydrogenic problem in a magnetic field: Non-commutative translations, unitary transformations, and coherent states

An operator formalism is developed for a description of charged electron-hole complexes in magnetic fields. A novel unitary transformation of the Hamiltonian that allows one to partially separate the center-of-mass and internal motions is proposed. We study the operator algebra that leads to the appearance of new effective particles, electrons and holes with modified interparticle interactions, and their coherent states in magnetic fields. The developed formalism is used for studying a two-dimensional negatively charged magnetoexciton $X^-$. It is shown that Fano-resonances are present in the spectra of internal $X^-$ transitions, indicating the existence of three-particle quasi-bound states embedded in the continuum of higher Landau levels.Comment: 9 pages + 2 figures, accepted in PRB, a couple of typos correcte

Shake-up Processes in a Low-Density Two-Dimensional Electron Gas: Spin-Dependent Transitions to Higher Hole Landau Levels

A theory of shake-up processes in photoabsorption of an interacting low-density two-dimensional electron gas (2DEG) in strong magnetic fields is presented. In these processes, an incident photon creates an electron-hole pair and, because of Coulomb interactions, simultaneously excites one particle to higher Landau levels (LL's). In this work, the spectra of correlated charged spin-singlet and spin-triplet electron-hole states in the first hole LL and optical transitions to these states (i.e., shake-ups to the first hole LL) are studied. Our results indicate, in particular, the presence of optically-active three-particle quasi-discrete states in the exciton continuum that may give rise to surprisingly sharp Fano resonances in strong magnetic fields. The relation between shake-ups in photoabsorption of the 2DEG and in the 2D hole gas (2DHG), and shake-ups of isolated negative X^- and positive X^+ trions are discussed.Comment: 8 pages, 8 figures. References updated, one figure added (Fig. 6). Accepted in Phys. Rev.

Cholinergic efferent synaptic transmission regulates the maturation of auditory hair cell ribbon synapses.

Spontaneous electrical activity generated by developing sensory cells and neurons is crucial for the maturation of neural circuits. The full maturation of mammalian auditory inner hair cells (IHCs) depends on patterns of spontaneous action potentials during a 'critical period' of development. The intrinsic spiking activity of IHCs can be modulated by inhibitory input from cholinergic efferent fibres descending from the brainstem, which transiently innervate immature IHCs. However, it remains unknown whether this transient efferent input to developing IHCs is required for their functional maturation. We used a mouse model that lacks the α9-nicotinic acetylcholine receptor subunit (α9nAChR) in IHCs and another lacking synaptotagmin-2 in the efferent terminals to remove or reduce efferent input to IHCs, respectively. We found that the efferent system is required for the developmental linearization of the Ca(2+)-sensitivity of vesicle fusion at IHC ribbon synapses, without affecting their general cell development. This provides the first direct evidence that the efferent system, by modulating IHC electrical activity, is required for the maturation of the IHC synaptic machinery. The central control of sensory cell development is unique among sensory systems

Cow-Calf and Vegetation Response to Heavy Rates of Stocking at the Texas Experimental Ranch.

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Winter and growing season nitrogen mineralization from fall-applied composted or stockpiled solid dairy manure

Adequate characterization of nitrogen (N) mineralization with time from manure and other organic sources is needed to maximize manure N use efficiency, decrease producer costs, and protect groundwater quality. The objective of our two-year field study at Parma, ID, was to quantify in situ N mineralization with time as affected by a one-time fall application of solid dairy manure, either composted or stockpiled. The experiment included five treatments: a non-N fertilized control, two first-year rates of stockpiled solid dairy manure (21.9 and 43.8 Mg/ha, dry wt.) and two rates (53.1 and 106.1 Mg/ha, dry wt.) of composted dairy manure (hereafter termed compost). Net N mineralization (mineralization less immobilization) was determined to a depth of 0.3 m by repeatedly measuring soil inorganic N (ammonium-N + nitrate-N) concentrations in buried polyethylene bags. Overwinter mineralization was measured between amendment incorporation in fall and sugarbeet (Beta vulgaris L.) planting the following spring. In-season mineralization was measured in situ for seven consecutive incubation periods during the c. 220-d growing season for furrow-irrigated sugarbeet. Net N mineralization often varied among amendments and from year to year through mid-season, likely due to seasonal variation in temperature, annual differences in amendment properties, and other factors. In early spring 2003 after a warmer-than-normal winter, immobilization exceeded mineralization, regardless of treatment. In-season net N mineralization peaked between mid-August and early September (DOYs 230 to 251) each year, regardless of treatment. Annual (c. 11-mo) net N mineralization in 2003 averaged 52 kg N/ha, similar among treatments. In 2004, annual net N mineralization was similar between rates within amendments and averaged 250 kg N/ha where manure treated, 150 kg N/ha where compost treated, and 106 kg N/ha where untreated. On average in 2004, 31% of compost’s annual net N mineralization occurred before the growing season and 69% during the season while essentially all of manure’s net mineralization occurred during the season. None of the amendments’ total N was, in net, mineralized in 2003 but in 2004 on average, 2% of compost’s and 16% of manure’s total N was mineralized, similar between rates within amendments. When estimating annual net N mineralization from fall-applied organic amendments, one must account for abnormal temperatures, including those overwinter

Iron under Earth's core conditions: Liquid-state thermodynamics and high-pressure melting curve

{\em Ab initio} techniques based on density functional theory in the projector-augmented-wave implementation are used to calculate the free energy and a range of other thermodynamic properties of liquid iron at high pressures and temperatures relevant to the Earth's core. The {\em ab initio} free energy is obtained by using thermodynamic integration to calculate the change of free energy on going from a simple reference system to the {\em ab initio} system, with thermal averages computed by {\em ab initio} molecular dynamics simulation. The reference system consists of the inverse-power pair-potential model used in previous work. The liquid-state free energy is combined with the free energy of hexagonal close packed Fe calculated earlier using identical {\em ab initio} techniques to obtain the melting curve and volume and entropy of melting. Comparisons of the calculated melting properties with experimental measurement and with other recent {\em ab initio} predictions are presented. Experiment-theory comparisons are also presented for the pressures at which the solid and liquid Hugoniot curves cross the melting line, and the sound speed and Gr\"{u}neisen parameter along the Hugoniot. Additional comparisons are made with a commonly used equation of state for high-pressure/high-temperature Fe based on experimental data.Comment: 16 pages including 6 figures and 5 table