12,548 research outputs found
The electrorheology of suspensions consisting of Na-Fluorohectorite synthetic clay particles in silicon oil
Under application of an electric field greater than a triggering electric
field kV/mm, suspensions obtained by dispersing particles of the
synthetic clay fluoro-hectorite in a silicon oil, aggregate into chain- and/or
column-like structures parallel to the applied electric field. This
micro-structuring results in a transition in the suspensions' rheological
behavior, from a Newtonian-like behavior to a shear-thinning rheology with a
significant yield stress. This behavior is studied as a function of particle
volume fraction and strength of the applied electric field, . The steady
shear flow curves are observed to scale onto a master curve with respect to
, in a manner similar to what was recently found for suspensions of laponite
clay [42]. In the case of Na-fluorohectorite, the corresponding dynamic yield
stress is demonstrated to scale with respect to as a power law with an
exponent , while the static yield stress inferred from
constant shear stress tests exhibits a similar behavior with . The suspensions are also studied in the framework of thixotropic fluids:
the bifurcation in the rheology behavior when letting the system flow and
evolve under a constant applied shear stress is characterized, and a
bifurcation yield stress, estimated as the applied shear stress at which
viscosity bifurcation occurs, is measured to scale as with to 0.6. All measured yield stresses increase with the particle
fraction of the suspension. For the static yield stress, a scaling law
, with , is found. The results are found to be
reasonably consistent with each other. Their similarities with-, and
discrepancies to- results obtained on laponite-oil suspensions are discussed
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A review of net zero energy buildings in hot and humid climates: Experience learned from 34 case study buildings
Sustainable development in the building sector requires the integration of energy efficiency and renewable energy utilization in buildings. In recent years, the concept of net zero energy buildings (NZEBs) has become a potential plausible solution to improve efficiency and reduce energy consumption in buildings. To achieve an NZEB goal, building systems and design strategies must be integrated and optimized based on local climatic conditions. This paper provides a comprehensive review of NZEBs and their current development in hot and humid regions. Through investigating 34 NZEB cases around the world, this study summarized NZEB key design strategies, technology choices and energy performance. The study found that passive design and technologies such as daylighting and natural ventilation are often adopted for NZEBs in hot and humid climates, together with other energy efficient and renewable energy technologies. Most NZEB cases demonstrated site annual energy consumption intensity less than 100 kW-hours (kWh) per square meter of floor space, and some buildings even achieved “net-positive energy” (that is, they generate more energy locally than they consume). However, the analysis also shows that not all NZEBs are energy efficient buildings, and buildings with ample renewable energy adoption can still achieve NZEB status even with high energy use intensity. This paper provides in-depth case-study-driven analysis to evaluate NZEB energy performance and summarize best practices for high performance NZEBs. This review provides critical technical information as well as policy recommendations for net zero energy building development in hot and humid climates
PPAK Wide-field Integral Field Spectroscopy of NGC 628: I. The largest spectroscopic mosaic on a single galaxy
We present a wide-field IFS survey on the nearby face-on Sbc galaxy NGC 628,
comprising 11094 individual spectra, covering a nearly circular field-of-view
of ~6 arcmin in diameter, with a sampling of ~2.7 arcsec per spectrum in the
optical wavelength range (3700--7000 AA). This galaxy is part of the PPAK IFS
Nearby Galaxies Survey, (PINGS, Rosales-Ortega et al. 2009). To our knowledge,
this is the widest spectroscopic survey ever made in a single nearby galaxy. A
detailed flux calibration was applied, granting a spectrophotometric accuracy
of \,0.2 mag.
The age of the stellar populations shows a negative gradient from the inner
(older) to the outer (younger) regions. We found an inversion of this gradient
in the central ~1 kpc region, where a somewhat younger stellar population is
present within a ring at this radius. This structure is associated with a
circumnuclear star-forming region at ~ 500 pc, also found in similar spiral
galaxies. From the study of the integrated and spatially resolved ionized gas
we found a moderate SFR of ~ 2.4 Msun yr. The oxygen abundance shows a a
clear gradient of higher metallicity values from the inner part to the outer
part of the galaxy, with a mean value of 12~+~log(O/H) ~ 8.7. At some specific
regions of the galaxy, the spatially resolved distribution of the physical
properties show some level of structure, suggesting real point-to-point
variations within an individual \hh region. Our results are consistent with an
inside-out growth scheme, with stronger star formation at the outer regions,
and with evolved stellar populations in the inner ones.Comment: 31 pages, 22 Figuras, Accepted for Publishing in MNRAS (corrected
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Determination of the electronic structure of bilayer graphene from infrared spectroscopy results
We present an experimental study of the infrared conductivity, transmission,
and reflection of a gated bilayer graphene and their theoretical analysis
within the Slonczewski-Weiss-McClure (SWMc) model. The infrared response is
shown to be governed by the interplay of the interband and the intraband
transitions among the four bands of the bilayer. The position of the main
conductivity peak at the charge neutrality point is determined by the
interlayer tunneling frequency. The shift of this peak as a function of the
gate voltage gives information about less known parameters of the SWMc model,
in particular, those responsible for the electron-hole and sublattice
asymmetries. These parameter values are shown to be consistent with recent
electronic structure calculations for the bilayer graphene and the SWMc
parameters commonly used for the bulk graphite.Comment: (v2) 11 pages, 7 figures; Important typo fixes and bibliography
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On the origin of multiple ordered phases in PrFe4P12
The nature of multiple electronic orders in skutterudite PrFe_4P_{12} is
discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction
of \Gamma_3 symmetry. The high-field phase can be reproduced qualitatively
provided (i) ferro-type interactions are introduced between the dipoles as well
as between the octupoles of localized f-electrons, and (ii) separation is
vanishingly small between the \Gamma_1-\Gamma_4^{(1)} crystalline electric
field (CEF) levels. The high-field phase can have either the same ordering
vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on
the parameters. In the latter case, distortion of the crystal perpendicular to
the (111) axis is predicted. The corresponding anomaly in elastic constants
should also appear. The electrical resistivity is calculated with account of
scattering within the CEF quasi-quartet. It is found that the resistivity as a
function of the direction of magnetic field shows a sharp maximum around the
(111) axis at low temperatures because of the level crossing.Comment: 16 pages, 5 figure
Boosting the Figure Of Merit of LSPR-based refractive index sensing by phase-sensitive measurements
Localized surface plasmon resonances possess very interesting properties for
a wide variety of sensing applications. In many of the existing applications
only the intensity of the reflected or transmitted signals is taken into
account, while the phase information is ignored. At the center frequency of a
(localized) surface plasmon resonance, the electron cloud makes the transition
between in- and out-of-phase oscillation with respect to the incident wave.
Here we show that this information can experimentally be extracted by
performing phase-sensitive measurements, which result in linewidths that are
almost one order of magnitude smaller than those for intensity based
measurements. As this phase transition is an intrinsic property of a plasmon
resonance, this opens up many possibilities for boosting the figure of merit
(FOM) of refractive index sensing by taking into account the phase of the
plasmon resonance. We experimentally investigated this for two model systems:
randomly distributed gold nanodisks and gold nanorings on top of a continuous
gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5
for the respective nanoparticles
Electronic density of states derived from thermodynamic critical field curves for underdoped La-Sr-Cu-O
Thermodynamic critical field curves have been measured for
over the full range of carrier concentrations
where superconductivity occurs in order to determine changes in the normal
state density of states with carrier concentration. There is a substantial
window in the plane where the measurements are possible because the
samples are both thermodynamically reversible and the temperature is low enough
that vortex fluctuations are not important. In this window, the data fit
Hao-Clem rather well, so this model is used to determine and
for each temperature and carrier concentration. Using N(0) and the ratio of the
energy gap to transition temperature, , as fitting
parameters, the curves give over the
whole range of . Values of N(0) remain rather constant in the optimum-doped
and overdoped regime, but drops quickly toward zero in the underdoped regime.
Study of relativistic nuclear collisions at AGS energies from p+Be to Au+Au with hadronic cascade model
A hadronic cascade model based on resonances and strings is used to study
mass dependence of relativistic nuclear collisions from p+Be to Au+Au at AGS
energies (\sim 10\AGeV) systematically. Hadron transverse momentum and
rapidity distributions obtained with both cascade calculations and Glauber type
calculations are compared with experimental data to perform detailed discussion
about the importance of rescattering among hadrons. We find good agreement with
the experimental data without any change of model parameters with the cascade
model. It is found that rescattering is of importance both for the explanation
of high transverse momentum tail and for the multiplicity of produced
particles.Comment: 27 pages, 30 figure
(4-Methylphenyl)[1-(4-methylphenyl)-3-(5-nitro-2-furyl)-1H-pyrazol-4-yl]methanone
In the title pyrazole compound, C22H17N3O4, an intramolecular C—H⋯O contact generates a seven-membered ring, producing an S(7) ring motif. The furan and pyrazole rings are essentially planar [maximum deviations = 0.004 (1) and 0.004 (2) Å, respectively] and are almost coplanar, making a dihedral angle of 3.75 (10)°. One of the methylphenyl groups is inclined to the pyrazole ring, as indicated by the dihedral angle of 48.41 (9)°. In the crystal structure, molecules are linked into chains along [10] by C—H⋯O contacts. The crystal structure is further stabilized by π–π interactions [centroid–centroid distance = 3.4437 (10) Å]
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