467 research outputs found
Effect of diet restriction on work performance and weight loss of local Zebu and Friesian X Boran crossbred oxen
Reports results of an experiment conducted to determine the effect of diet restriction on work performance and body weight in crossbred and local oxen worked as singles in farmers' fields around Debre Zeit, Ethiopia, during the normal cultivation season
Shot noise in tunneling transport through molecules and quantum dots
We consider electrical transport through single molecules coupled to metal
electrodes via tunneling barriers. Approximating the molecule by the Anderson
impurity model as the simplest model which includes Coulomb charging effects,
we extend the ``orthodox'' theory to expand current and shot noise
systematically order by order in the tunnel couplings. In particular, we show
that a combined measurement of current and shot noise reveals detailed
information of the system even in the weak-coupling limit, such as the ratio of
the tunnel-coupling strengths of the molecule to the left and right electrode,
and the presence of the Coulomb charging energy. Our analysis holds for
single-level quantum dots as well.Comment: 8 page
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Measurements of cross sections and resonance structures following electron-impact excitation/ionization of Na-like Kr and Xe
We report high-resolution measurements of electron impact excitation and ionization cross sections for the Na-like ions Kr{sup 25+} and Xe{sup 43+}. Ions with ionization states centered on the Na-like configurations were produced in an electron beam ion trap (EBIT) using electrons with energies below the L shell ionization thresholds. The Na-like ions were exposed to an electron beam with an energy between 3 and 7 keV. The Na- and Ne-like ions were then extracted and their intensities measured as a function of the electron beam energy. Theoretical ionization cross sections were calculated using relativistic distorted wave methods. Complex resonance structures that appear in the computed cross sections are observed in the experimental results. These results are the first experimental observation of resonant-excitation-double-autoionization (REDA) in highly charged high-Z ions
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Enhanced groundwater flow on and below Vera Rubin ridge, the Murray Formation, Gale Crater: Evidence from thermochemical modeling
NASAs Mars Science Laboratory Curiosity rover has been exploring Vera Rubin ridge (VRR), part of the Murray formation in Gale crater, Mars, between sol 1809 and 2302. Evidence for Fe-oxides and phyllosilicates in mineralogical and geochemical data for this region was returned by Curiosity [1-5]. We applied thermochemical modeling to con-strain the formation conditions of the phyllosilicate-hematite assemblage identified on and below VRR. Average alteration compositions for the Murray formation on and below VRR were derived using CheMin and APXS data. These compositions were reacted with Gale Portage Water (GPW) between 25100 C and for 10% and 50% Fe3+/Fetot of the host rock [6]. Here we summarize models run at 50 C and 10% Fe3+/Fetot for alteration compositions derived from Murray host rock compositions
Stakeholder engagement in the study and management of invasive alien species
Invasive alien species are a major driver of global environmental change and a range of management interventions are needed to manage their effects on biodiversity, ecosystem services, human well-being and local livelihoods. Stakeholder engagement is widely advocated to integrate diverse knowledge and perspectives in the management of invasive species and to deal with potential conflicts of interest. We reviewed the literature in the ISI Web of Science on stakeholder engagement (the process of involving stakeholders (actors) in decision making, management actions and knowledge creation) in invasion science to assess and understand what has been done (looking at approaches and methodologies used, stakeholders involved, and outcomes from engagement) and to make recommendations for future work. Research on stakeholder engagement in invasion science has increased over the last decade, helping to improve scientific knowledge and contributing towards policy formulation and co-implementation of management. However, many challenges remain and engagement could be made more effective. For example, most studies engage only one stakeholder group passively using questionnaires, primarily for assessing local knowledge and perceptions. Although useful for management and policy planning, these stakeholders are not active participants and there is no two-way flow of knowledge. To make stakeholder
involvement more useful, we encourage more integrative and collaborative engagement to (1) improve co-design, co-creation and co-implementation of research and management actions; (2) promote social learning and provide feedback to stakeholders; (3) enhance collaboration and partnerships beyond the natural sciences and academia (interdisciplinary and transdisciplinary collaboration); and (4) discuss some practical and policy suggestions for improving stakeholder engagement in invasion science research and management. This will help facilitate different stakeholders to work better together, allowing problems associated with biological invasions to be tackled more holistically and successfully
Scaling anomaly in cosmic string background
We show that the classical scale symmetry of a particle moving in cosmic
string background is broken upon inequivalent quantization of the classical
system, leading to anomaly. The consequence of this anomaly is the formation of
single bound state in the coupling interval \gamma\in(-1,1). The inequivalent
quantization is characterized by a 1-parameter family of self-adjoint extension
parameter \omega. It has been conjectured that the formation of loosely bound
state in cosmic string background may lead to the so called anomalous
scattering cross section for the particles, which is usually seen in molecular
physics.Comment: 4 pages,1 figur
Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation
The fully nonlinear response of a many-level tunneling system to a strong
alternating field of high frequency is studied in terms of the
Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent
tunneling current is calculated exactly and its resonance structure is
elucidated. In particular, it is shown that under certain reasonable conditions
on the physical parameters, the Fourier component is sharply peaked at
, where is the spacing between
two levels. This frequency multiplication results from the highly nonlinear
process of photon absorption (or emission) by the tunneling system. It is
also conjectured that this effect (which so far is studied mainly in the
context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from
[email protected], submitted to Phys.Rev.
Resummation of the Divergent Perturbation Series for a Hydrogen Atom in an Electric Field
We consider the resummation of the perturbation series describing the energy
displacement of a hydrogenic bound state in an electric field (known as the
Stark effect or the LoSurdo-Stark effect), which constitutes a divergent formal
power series in the electric field strength. The perturbation series exhibits a
rich singularity structure in the Borel plane. Resummation methods are
presented which appear to lead to consistent results even in problematic cases
where isolated singularities or branch cuts are present on the positive and
negative real axis in the Borel plane. Two resummation prescriptions are
compared: (i) a variant of the Borel-Pade resummation method, with an
additional improvement due to utilization of the leading renormalon poles (for
a comprehensive discussion of renormalons see [M. Beneke, Phys. Rep. vol. 317,
p. 1 (1999)]), and (ii) a contour-improved combination of the Borel method with
an analytic continuation by conformal mapping, and Pade approximations in the
conformal variable. The singularity structure in the case of the LoSurdo-Stark
effect in the complex Borel plane is shown to be similar to (divergent)
perturbative expansions in quantum chromodynamics.Comment: 14 pages, RevTeX, 3 tables, 1 figure; numerical accuracy of results
enhanced; one section and one appendix added and some minor changes and
additions; to appear in phys. rev.
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