7,642 research outputs found
Evaluation of a locally homogeneous flow model of spray combustion
A model of spray combustion which employs a second-order turbulence model was developed. The assumption of locally homogeneous flow is made, implying infinitely fast transport rates between the phase. Measurements to test the model were completed for a gaseous n-propane flame and an air atomized n-pentane spray flame, burning in stagnant air at atmospheric pressure. Profiles of mean velocity and temperature, as well as velocity fluctuations and Reynolds stress, were measured in the flames. The predictions for the gas flame were in excellent agreement with the measurements. The predictions for the spray were qualitatively correct, but effects of finite rate interphase transport were evident, resulting in a overstimation of the rate development of the flow. Predictions of spray penetration length at high pressures, including supercritical combustion conditions, were also completed for comparison with earlier measurements. Test conditions involved a pressure atomized n-pentane spray, burning in stagnant air at pressures of 3, 5, and 9 MPa. The comparison between predictions and measurements was fair. This is not a very sensitive test of the model, however, and further high pressure experimental and theoretical results are needed before a satisfactory assessment of the locally homogeneous flow approximation can be made
Thinking Globally About Universities and Extension: The Convergence of University-Based and Centralized Extension Systems in China
The U.S. university-based extension system model has been successful nationally, but not adopted globally. Various historical factors rendered the U.S. system a less attractive option for emerging post-WWII nations. However, current changes in education and extension landscapes are creating new opportunities for the globalization of U.S. Extension. Specifically, both the U.S. and Chinese extension systems now face the common challenge of delivering meaningful university-based extension under shifting conditions. This commonality creates opportunities for exploring long-term, synergistic university-based extension systems and potentially achieving associated benefits worldwide
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Cooperative Carbon Dioxide Adsorption in Alcoholamine- and Alkoxyalkylamine-Functionalized Metal-Organic Frameworks.
A series of structurally diverse alcoholamine- and alkoxyalkylamine-functionalized variants of the metal-organic framework Mg2 (dobpdc) are shown to adsorb CO2 selectively via cooperative chain-forming mechanisms. Solid-state NMR spectra and optimized structures obtained from van der Waals-corrected density functional theory calculations indicate that the adsorption profiles can be attributed to the formation of carbamic acid or ammonium carbamate chains that are stabilized by hydrogen bonding interactions within the framework pores. These findings significantly expand the scope of chemical functionalities that can be utilized to design cooperative CO2 adsorbents, providing further means of optimizing these powerful materials for energy-efficient CO2 separations
NMR determination of Van Hove singularity and Lifshitz transitions in nodal-line semimetal ZrSiTe
We have applied nuclear magnetic resonance spectroscopy to study the
distinctive network of nodal lines in the Dirac semimetal ZrSiTe. The low-
behavior is dominated by a symmetry-protected nodal line, with NMR providing a
sensitive probe of the diamagnetic response of the associated carriers. A sharp
low- minimum in NMR shift and provides a quantitative measure
of the dispersionless, quasi-2D behavior of this nodal line. We also identify a
van Hove singularity closely connected to this nodal line, and an associated
-induced Lifshitz transition. A disconnect in the NMR shift and line width
at this temperature indicates the change in electronic behavior associated with
this topological change. These features have an orientation-dependent behavior
indicating a field-dependent scaling of the associated band energies.Comment: 7 pages, 4 figure
Anisotropy of magnetothermal conductivity in Sr2RuO4
The dependence of in-plane and interplane thermal conductivities of Sr2RuO4
on temperature, as well as magnetic field strength and orientation, is
reported. We found no notable anisotropy in the thermal conductivity for the
magnetic field rotation parallel to the conducting plane in the whole range of
experimental temperatures and fields, except in the vicinity of the upper
critical field Hc2, where the anisotropy of the Hc2 itself plays a dominant
role. This finding imposes strong constraints on the possible models of
superconductivity in Sr2RuO4 and supports the existence of a superconducting
gap with a line of nodes running orthogonal to the Fermi surface cylinder.Comment: published in Phys. Rev. Lett. 4pages, 4 eps figures, LaTe
Free field realization of the exceptional current superalgebra \hat{D(2,1;\a)}_k
The free-field representations of the D(2,1;\a) current superalgebra and
the corresponding energy-momentum tensor are constructed. The related screening
currents of the first kind are also presented.Comment: Latex file, 10 page
Tuning a Circular p-n Junction in Graphene from Quantum Confinement to Optical Guiding
The motion of massless Dirac-electrons in graphene mimics the propagation of
photons. This makes it possible to control the charge-carriers with components
based on geometrical-optics and has led to proposals for an all-graphene
electron-optics platform. An open question arising from the possibility of
reducing the component-size to the nanometer-scale is how to access and
understand the transition from optical-transport to quantum-confinement. Here
we report on the realization of a circular p-n junction that can be
continuously tuned from the nanometer-scale, where quantum effects are
dominant, to the micrometer scale where optical-guiding takes over. We find
that in the nanometer-scale junction electrons are trapped in states that
resemble atomic-collapse at a supercritical charge. As the junction-size
increases, the transition to optical-guiding is signaled by the emergence of
whispering-gallery modes and Fabry-Perot interference. The creation of tunable
junctions that straddle the crossover between quantum-confinement and
optical-guiding, paves the way to novel design-architectures for controlling
electronic transport.Comment: 16 pages, 4 figure
Pilot Scheme of Health Policy in Stroke Adjuvant Acupuncture Therapy for Acute and Subacute Ischemic Stroke in Taiwan
To reduce the health care burden of strokes, the Taiwan Department of Health launched the Pilot Scheme of the Health Policy in Stroke Adjuvant Acupuncture Therapy (HPSAAT) in 2006. This cross-sectional, hospital-based, match-controlled study at Chang Gung Memorial Hospital-Kaohsiung Medical Center during 2006∼2008 retrospectively evaluated the clinical characteristics of acute and subacute ischemic stroke patients who electively joined the HPSAAT. The study also evaluated the safety and clinical benefits of adjuvant acupuncture in treating acute and subacute ischemic stroke patients.
Twenty-six HPSAAT participants and 52 age-sex matched random controls were enrolled. The stroke baseline of the HPSAAT participants was more severe than the non-HPSAAT controls. Although the stroke severity closely correlates to mortality and comorbidity, this study noted no significant complications in the HPSAAT participants during the acupuncture treatment course. Adjuvant acupuncture was considered safe at the acute and subacute stages of ischemic stroke. Due to uneven baseline severity, the clinical benefits in reducing neurological deficits and functional recovery were not concluded in this study
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