25,990 research outputs found
Quantum fluctuations in the spiral phase of the Hubbard model
We study the magnetic excitations in the spiral phase of the two--dimensional
Hubbard model using a functional integral method. Spin waves are strongly
renormalized and a line of near--zeros is observed in the spectrum around the
spiral pitch . The possibility of disordered spiral states is
examined by studying the one--loop corrections to the spiral order parameter.
We also show that the spiral phase presents an intrinsic instability towards an
inhomogeneous state (phase separation, CDW, ...) at weak doping. Though phase
separation is suppressed by weak long--range Coulomb interactions, the CDW
instability only disappears for sufficiently strong Coulomb interaction.Comment: Figures are NOW appended via uuencoded postscript fil
UREA/ammonium ion removal system for the orbiting frog otolith experiment
The feasibility of using free urease enzyme and ANGC-101 ion exchange resin to remove urea and ammonium ion for space system waste water applications was studied. Specifically examined is the prevention of urea and ammonia toxicity in a 30-day Orbiting Frog Otolith (OFO) flight experiment. It is shown that free urease enzyme used in conjunction with ANGC-101 ion-exchange resin and pH control can control urea and amonium ion concentration in unbuffered recirculating water. In addition, the resin does not adversely effect the bullfrogs by lowering the concentration of cations below critical minimum levels. Further investigations on bioburden control, frog waste excretion on an OFO diet, a trade-off analysis of methods of automating the urea/ammonium ion removal system and fabrication and test of a semiautomated breadboard were recommended as continuing efforts. Photographs of test equipment and test animals are shown
Cow-Calf Producer Perceptions Regarding Individual Animal Traceability
This study provides valuable insights into cow-calf producer voluntary participation in the National Animal Identification System and producers’ perceptions of several issues critically impacting the success of voluntary traceability systems. Cow-calf producers believe that the most important issues to the U.S. beef industry in designing a national, individual animal traceability system are monitoring/managing disease, maintaining current foreign markets, accessing foreign markets, and increasing consumer confidence. Furthermore, producers are concerned with cost, liability, reliability of technology, failure of system to meet stated goals, and confidentiality of information associated with these systems.animal traceability, cow-calf, National Animal Identification System, voluntary adoption, Agribusiness, Community/Rural/Urban Development, Crop Production/Industries, Farm Management, Labor and Human Capital, Land Economics/Use, Livestock Production/Industries, Production Economics, Research and Development/Tech Change/Emerging Technologies, Q12, Q18, R38,
Anderson localization in Hubbard ladders
The effect of a weak random potential on two-leg Hubbard ladders is
investigated. The random potential is shown to induce Anderson localization
except for attractive enough interactions, supressing completely d-wave
superconductivity. These localization effects remain very strong even for many
ladders coupled by Josephson coupling. Both dc and ac conductivities and
localization lengths are obtained. Consequences for the superconducting ladder
compound SrCaCuO are discussed.Comment: 2 Pages, 2 Figures, Uses espcrc2.sty (included); Proceedings of the
SCES98 conference, July 1998 Paris, France; To be published in Physica
Auroral magnetosphere-ionosphere coupling: A brief topical review
Auroral arcs result from the acceleration and precipitation of magnetospheric plasma in narrow regions characterized by strong electric fields both perpendicular and parallel to the earth's magnetic field. The various mechanisms that were proposed for the origin of such strong electric fields are often complementary Such mechanisms include: (1) electrostatic double layers; (2) double reverse shock; (3) anomalous resistivity; (4) magnetic mirroring of hot plasma; and (5) mapping of the magnetospheric-convection electric field through an auroral discontinuity
Renormalization of impurity scattering in one-dimensional interacting electron systems in magnetic field
We study the renormalization of a single impurity potential in
one-dimensional interacting electron systems in the presence of magnetic field.
Using the bosonization technique and Bethe ansatz solutions, we determine the
renormalization group flow diagram for the amplitudes of scattering of up- and
down-spin electrons by the impurity in a quantum wire at low electron density
and in the Hubbard model at less than half filling. In the absence of magnetic
field the repulsive interactions are known to enhance backscattering and make
the impurity potential impenetrable in the low-energy limit. On the contrary,
we show that in a strong magnetic field the interaction may suppress the
backscattering of majority-spin electrons by the impurity potential in the
vicinity of the weak-potential fixed point. This implies that in a certain
temperature range the impurity becomes almost transparent for the majority-spin
electrons while it is impenetrable for the minority-spin ones. The impurity
potential can thus have a strong spin-filtering effect.Comment: 11 pages, 2 figures; v2: a typo corrected and a reference added; v3:
published version, Sec.II revised with an additional explanatory subsection,
comments on the case of more than half-filling added, typos corrected, a
reference update
On the metal-insulator transition in the two-chain model of correlated fermions
The doping-induced metal-insulator transition in two-chain systems of
correlated fermions is studied using a solvable limit of the t-J model and the
fact that various strong- and weak-coupling limits of the two-chain model are
in the same phase, i.e. have the same low-energy properties. It is shown that
the Luttinger-liquid parameter K_\rho takes the universal value unity as the
insulating state (half-filling) is approached, implying dominant d-type
superconducting fluctuations, independently of the interaction strength. The
crossover to insulating behavior of correlations as the transition is
approached is discussed.Comment: 7 pages, 1 figur
Immunohistochemische Untersuchung zur Expression von Mastzelltryptase an Beckenkammbiopsien bei Mastozytose
In der vorliegenden Studie wurden Knochenmarkpräparate von insgesamt 57 Patienten berücksichtigt, wobei 24 keine systemische Mastozytose, und 33 eine systemische Mastozytose in den konventionellen Färbungen aufwiesen. Durch die Mastzelltryptase, eine Serinprotease, die fast ausschließlich in menschlichen Mastzellen vorkommt und in allen Stadien der Mastzelle gebildet wird, ist ein sehr spezifischer Nachweis von Mastzellen und damit der systemischen Mastozytose möglich. Bei der Korrelation von konservativen Färbungen an Beckenkammbiopsien bei Patienten mit systemischer Mastozytose und ohne systemische Mastozytose aus dem Zeitraum zwischen 1993 und 2003, und den neu angefertigten, immunohistochemischen Färbungen der Mastzelltryptase, findet sich eine Übereinstimmung der Diagnosen in 97 Prozent bei Patienten mit systemischer Mastozytose, und in 95,8 Prozent bei Patienten ohne systemische Mastozytose
Global dust model intercomparison in AeroCom phase I
This study presents the results of a broad intercomparison of a total of 15 global aerosol models within the AeroCom project. Each model is compared to observations related to desert dust aerosols, their direct radiative effect, and their impact on the biogeochemical cycle, i.e., aerosol optical depth (AOD) and dust deposition. Additional comparisons to Angström exponent (AE), coarse mode AOD and dust surface concentrations are included to extend the assessment of model performance and to identify common biases present in models. These data comprise a benchmark dataset that is proposed for model inspection and future dust model development. There are large differences among the global models that simulate the dust cycle and its impact on climate. In general, models simulate the climatology of vertically integrated parameters (AOD and AE) within a factor of two whereas the total deposition and surface concentration are reproduced within a factor of 10. In addition, smaller mean normalized bias and root mean square errors are obtained for the climatology of AOD and AE than for total deposition and surface concentration. Characteristics of the datasets used and their uncertainties may influence these differences. Large uncertainties still exist with respect to the deposition fluxes in the southern oceans. Further measurements and model studies are necessary to assess the general model performance to reproduce dust deposition in ocean regions sensible to iron contributions. Models overestimate the wet deposition in regions dominated by dry deposition. They generally simulate more realistic surface concentration at stations downwind of the main sources than at remote ones. Most models simulate the gradient in AOD and AE between the different dusty regions. However the seasonality and magnitude of both variables is better simulated at African stations than Middle East ones. The models simulate the offshore transport of West Africa throughout the year but they overestimate the AOD and they transport too fine particles. The models also reproduce the dust transport across the Atlantic in the summer in terms of both AOD and AE but not so well in winter-spring nor the southward displacement of the dust cloud that is responsible of the dust transport into South America. Based on the dependency of AOD on aerosol burden and size distribution we use model bias with respect to AOD and AE to infer the bias of the dust emissions in Africa and the Middle East. According to this analysis we suggest that a range of possible emissions for North Africa is 400 to 2200 Tg yr-1 and in the Middle East 26 to 526 Tg yr-1
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