178 research outputs found
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Optimizing the thermal performance of building envelopes for energy saving in underground office buildings in various climates of China
This article investigates the influence of the thermal performance of building envelopes on annual energy consumption in a ground-buried office building by means of the dynamic building energy simulation, aiming at offering reasonable guidelines for the energy efficient design of envelopes for underground office buildings in China. In this study, the accuracy of dealing with the thermal process for underground buildings by using the Designer's Energy Simulation Tool (DeST) is validated by measured data. The analyzed results show that the annual energy consumptions for this type of buildings vary significantly, and it is based on the value of the overall heat transfer coefficient (U-value) of the envelopes. Thus, it is necessary to optimize the U-value for underground buildings located in various climatic zones in China. With respect to the roof, an improvement in its thermal performance is significantly beneficial to the underground office building in terms of annual energy demand. With respect to the external walls, the optimized U-values completely change with the distribution of the climate zones. The recommended optimal values for various climate zones of China are also specified as design references for public office building in underground in terms of the building energy efficiency
Local breaking of four-fold rotational symmetry by short-range magnetic order in heavily overdoped Ba(FeCu)As
We investigate Cu-doped Ba(FeCu)As with transport,
magnetic susceptibility, and elastic neutron scattering measurements. In the
heavily Cu-doped regime where long-range stripe-type antiferromagnetic order in
BaFeAs is suppressed, Ba(FeCu)As (0.145 0.553) samples exhibit spin-glass-like behavior in magnetic
susceptibility and insulating-like temperature dependence in electrical
transport. Using elastic neutron scattering, we find stripe-type short-range
magnetic order in the spin-glass region identified by susceptibility
measurements. The persistence of short-range magnetic order over a large doping
range in Ba(FeCu)As likely arises from local arrangements
of Fe and Cu that favor magnetic order, with Cu acting as vacancies relieving
magnetic frustration and degeneracy. These results indicate locally broken
four-fold rotational symmetry, suggesting that stripe-type magnetism is
ubiquitous in iron pnictides.Comment: accepted by Physical Review B Rapid Communication
Aerosolization behavior of antimicrobial resistance in animal farms: a field study from feces to fine particulate matter
Antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in animal feces can be released into the atmosphere via aerosolization, posing a high health risk to farm workers. So far, little attention has been paid to the characterization of the aerosolization process. In this study, fecal and fine particulate matter (PM2.5) samples were collected from 20 animal farms involving swine, cattle, layers, and broilers, and the ARGs, ARB, and human pathogenic bacteria (HPB) were loaded in these two media. The results showed that approximately 70% of ARGs, 60% of ARBs, and 43% of HPBs were found to be preferential aerosolization. The bioaerosolization index (BI) of target 30 ARGs varied from 0.04 to 460.07, and the highest value was detected from tetW. The highest BI values of erythromycin- and tetracycline-resistant bacteria were for Kocuria (13119) and Staphylococcus (24746), respectively, and the distribution of BI in the two types of dominant ARB was similar. Regarding the bioaerosolization behavior of HPB, Clostridium saccharolyticum WM1 was the most easily aerosolized pathogen in swine and broiler farms, and Brucella abortus strain CNM 20040339 had the highest value in cattle and layer farms. Notably, the highest BI values for ARGs, ARB, and HPB were universally detected on chicken farms. Most ARGs, ARB, and HPB positively correlated with animal age, stocking density, and breeding area. Temperature and relative humidity have significant effects on the aerosolization behavior of targets, and the effects of these two parameters on the same target are usually opposite. The results of this study provide a basis for a better understanding of the contribution of animal feces to airborne ARGs and HPBs in farms, as well as for controlling the transport of the fecal microbiome to the environment through the aerosolization pathway
Grand Canonical Adaptive Resolution Simulation for Molecules with Electrons: A Theoretical Framework based on Physical Consistency
A theoretical scheme for the treatment of an open molecular system with
electrons and nuclei is proposed. The idea is based on the Grand Canonical
description of a quantum region embedded in a classical reservoir of molecules.
Electronic properties of the quantum region are calculated at constant
electronic chemical potential equal to that of the corresponding (large) bulk
system treated at full quantum level. Instead, the exchange of molecules
between the quantum region and the classical environment occurs at the chemical
potential of the macroscopic thermodynamic conditions. T he Grand Canonical
Adaptive Resolution Scheme is proposed for the treatment of the classical
environment; such an approach can treat the exchange of molecules according to
first principles of statistical mechanics and thermodynamic. The overall scheme
is build on the basis of physical consistency, with the corresponding
definition of numerical criteria of control of the approximations implied by
the coupling. Given the wide range of expertise required, this work has the
intention of providing guiding principles for the construction of a well
founded computational protocol for actual multiscale simulations from the
electronic to the mesoscopic scale.Comment: Computer Physics Communications (2017), in pres
Structure-Property Relationship in Layered BaMn2Sb2 and Ba2Mn3Sb2O2
Layered transition-metal compounds have received great attention owing to
their novel physical properties. Here, we present the structural, electronic,
thermal, and magnetic properties of BaMn2Sb2 and Ba2Mn3Sb2O2 single crystals,
both with the layered structure analogous to high-temperature superconductors.
While the Mn moment in the MnSb4 tetrahedral environment forms G-type
antiferromagnetic (AFM) ordering in both BaMn2Sb2 (TN1~443 K) and Ba2Mn3Sb2O2
(TN1~314 K), a short-range AFM order is found in the intercalated MnO2 layer at
a much lower temperature (TN2~60 K) in Ba2Mn3Sb2O2. The directions of the
ordered moments in these two magnetic sub-lattices of Ba2Mn3Sb2O2 are
perpendicular to each other, even though the system is electrically conductive.
This indicates that the large magnetic moments in these compounds are highly
localized, leading to negligible coupling between MnSb4 and MnO2 layers in
Ba2Mn3Sb2O2. These findings provide an insight into the
structure-magnetism-based design principle for new superconductors.Comment: 15 pages, 4 figures. 2 table
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