1,061 research outputs found
Copositivity for a class of fourth order symmetric tensors given by scalar dark matter
In this paper, we mainly discuss the analytic expression of exact
copositivity of 4th order symmetric tensor defined by the special physical
model. We first show that for the general 4th order 2-dimensional symmetric
tensor, it can be transformed into solving the quadratic polynomials, and then
we give a necessary and sufficient condition to test the copositivity of 4th
order 2-dimensional symmetric tensor. Based on this, we consider a special 4th
order 3-dimensional symmetric tensor defined by the vacuum stability for
scalar dark matter, and obtain the necessary and sufficient
condition for its copositivity.Comment: 16 page
Performance study of a novel solar solid dehumidification/regeneration bed for use in buildings air conditioning systems
In this paper, a novel solar solid dehumidification/regeneration bed has been proposed, and its three regeneration methods, i.e., simulated solar radiation regeneration, microwave regeneration, and combined regeneration of the microwave and simulated solar radiation, were experimentally investigated and compared, as well as the dehumidification performance. The degree of regeneration of the proposed system under the regeneration method combining both microwave irradiation and simulated solar radiation could reach 77.7%, which was 3.77 times higher than that of the system under the simulated solar regeneration method and 1.05 times higher than that of the system under the microwave regeneration. The maximum energy efficiency of the proposed system under the combined regeneration method was 21.7%, while it was only 19.4% for the system under microwave regeneration. All these proved that the combined regeneration method of the simulated solar and microwave radiation not only improved the regeneration efficiency of the system, but also enhanced the energy efficiency. For the dehumidification performance, the maximum transient moisture removal was 14.1 g/kg, the maximum dehumidification efficiency was 68.0% and the maximum speed of dehumidification was 0.294 g/(kgμs) when the inlet air temperature was at 26.09 °C and the air relative humidity was at 89.23%. By comparing the testing results with the semi-empirical results from the Page model, it was indicated that the Page model can predict the regeneration characteristics of the novel solar solid dehumidification/regeneration bed under the combined method of microwave and simulated solar regeneration. The results of this research should prove useful to researchers and engineers to exploit the potential of solar technologies in buildings worldwide
Experimental Study on the Effect of Using Smartphones on Pedestrian Flow in Straight Corridors
With the development of science and technology, smartphones are widely used in people’s daily lives. An interesting phenomenon is that many pedestrians use smartphones while walking in the public places, which not only harm and even kill in some cases, but also affect the pedestrian traffic safety. At present, most studies focus on the pedestrians in the normal state that they don’t use phones while walking. Few research has been done on the pedestrian flow when they use phones. Therefore, the experiment that the pedestrians use phones while walking in straight corridor was conducted to study the movement characteristics and compared with the normal one. From the trajectories, the lane formation can be found in all experiments and the trajectories when they use phones are more chaotic. When pedestrians distract themselves by using phones, they walk more slowly and the flow is lower, leading to the longer egress time to pass the corridor. The distance from the boundary is defined as the shortest distance between the pedestrians and the wall. When they use phones, they try to avoid collision with the wall and walk away from the wall, so the distance is further than the normal one. The nearest pedestrian distance is defined as the nearest distance among all pedestrians. When they use phones, they distract themselves and don’t have enough time to avoid collision with others, so the nearest pedestrians distance is closer than the normal one. Our findings maybe a new insight for pedestrian flow when they distract themselves by using the phones, talking with others and thinking deeply, which can enrich empirical data and contribute to the simulation model
Spatial scale-dependent land–atmospheric methane exchanges in the northern high latitudes from 1993 to 2004
© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 11 (2014): 1693-1704, doi:10.5194/bg-11-1693-2014.Effects of various spatial scales of water table dynamics on land–atmospheric methane (CH4) exchanges have not yet been assessed for large regions. Here we used a coupled hydrology–biogeochemistry model to quantify daily CH4 exchanges over the pan-Arctic from 1993 to 2004 at two spatial scales of 100 km and 5 km. The effects of sub-grid spatial variability of the water table depth (WTD) on CH4 emissions were examined with a TOPMODEL-based parameterization scheme for the northern high latitudes. We found that both WTD and CH4 emissions are better simulated at a 5 km spatial resolution. By considering the spatial heterogeneity of WTD, net regional CH4 emissions at a 5 km resolution are 38.1–55.4 Tg CH4 yr−1 from 1993 to 2004, which are on average 42% larger than those simulated at a 100 km resolution using a grid-cell-mean WTD scheme. The difference in annual CH4 emissions is attributed to the increased emitting area and enhanced flux density with finer resolution for WTD. Further, the inclusion of sub-grid WTD spatial heterogeneity also influences the inter-annual variability of CH4 emissions. Soil temperature plays an important role in the 100 km estimates, while the 5 km estimates are mainly influenced by WTD. This study suggests that previous macro-scale biogeochemical models using a grid-cell-mean WTD scheme might have underestimated the regional CH4 emissions. The spatial scale-dependent effects of WTD should be considered in future quantification of regional CH4 emissions.The research is funded by a DOE SciDAC
project and an Abrupt Climate Change project. This study is also
supported through projects funded by the NASA Land Use and
Land Cover Change program (NASA-NNX09AI26G), Department
of Energy (DE-FG02-08ER64599), the NSF Division of Information
& Intelligent Systems (NSF-1028291), and the NSF Carbon
and Water in the Earth Program (NSF-0630319). This research is
also in part supported by the Director, Office of Science, Office of
Biological and Environmental Research of the US Department of
Energy under Contract No. DE-AC02-05CH11231 as part of their
Earth System Modeling Program
Narrowing the wealth and income gap in Poland, China, and the United States
With the widespread of globalization, the wealth gap continues to widen globally. Due to the enormous differences in national conditions and political systems of various countries, this article selects China, the United States, and Poland as the research objects, and uses a specific time unit as the benchmark, and mainly focuses on the four directions of medical care, education, job opportunities, and pensions. A reader could understand the correlation between the wealth gap and multiple factors deeply in this article. This article analyzes the impact of income disparity on these three countries and proposes solutions to help narrow the gap between the rich and poor in these three countries
Research on Calculation of the IOL Tilt and Decentration Based on Surface Fitting
The tilt and decentration of intraocular lens (IOL) result in defocussing, astigmatism, and wavefront aberration after operation. The objective is to give a method to estimate the tilt and decentration of IOL more accurately. Based on AS-OCT images of twelve eyes from eight cases with subluxation lens after operation, we fitted spherical equation to the data obtained from the images of the anterior and posterior surfaces of the IOL. By the established relationship between IOL tilt (decentration) and the scanned angle, at which a piece of AS-OCT image was taken by the instrument, the IOL tilt and decentration were calculated. IOL tilt angle and decentration of each subject were given. Moreover, the horizontal and vertical tilt was also obtained. Accordingly, the possible errors of IOL tilt and decentration existed in the method employed by AS-OCT instrument. Based on 6–12 pieces of AS-OCT images at different directions, the tilt angle and decentration values were shown, respectively. The method of the surface fitting to the IOL surface can accurately analyze the IOL’s location, and six pieces of AS-OCT images at three pairs symmetrical directions are enough to get tilt angle and decentration value of IOL more precisely
Frosting performance of a nanoporous hydrophilic aluminum surface
© 2018 by the authors. As an efficient energy-saving piece of equipment, an air-source heat pump can not only reduce the energy consumption required for heating, but can also reduce the pollution from fossil consumption. However, when an air-source heat pump operates under low temperatures and high humidity, the heat exchanger surface of its outdoor evaporator often get covered with frost. The growth of the frost layer seriously affects the operation efficiency of the equipment and limits its engineering application. Looking for materials that can actively inhibit frost forming is a good strategy to solve the problem mentioned above. Numerous studies show that a hydrophilic surface (contact angle less than 90◦) can inhibit the normal freezing process. Manufacturing nanostructures on the surface also affect frosting performance. In this paper, nanoporous hydrophilic aluminum sheets, with contact angles of 47.8◦ (Sample 2), 35.9◦ (Sample 3), and 22.9◦ (Sample 4), respectively, were fabricated by the anodic oxidation method. The frosting performance of the nanoporous hydrophilic aluminum was studied compared with polished aluminum, with a contact angle of 60.2◦ (Sample 1). The frosting performance of the aluminum surface was systematically studied by observing the frost structure from top and side cameras and measuring the frost thickness, frost mass, and frosting rate. It was found that nanoporous hydrophilic aluminum can reduce the frost thickness and frost mass. The frost mass reduction rate of sample 2 reached a maximum of 65.9% at the surface temperature of −15 ◦C, under test conditions. When the surface temperature was −15 ◦C, the frosting rate of Sample 2 was 1.71 g/(m2·min), which was about one-third of that on sample 1 (polished aluminum). Nanoporous hydrophilic aluminum behaved better at lessening frost than polished aluminum, which revealed that manufacturing nanopores and promoting hydrophilicity can delay the formation of frost
Inconsistent phenomenon of thermoelectric load resistance for photovoltaic–thermoelectric module
Combing PV with Thermoelectric (TE) would be dominant because it can employ the solar fully spectrum to produce electricity. But the TE efficiency is significantly lower than PV efficiency and the coupling effect between them will limit the performance of PV and TE. The analyze and comparison on the different characteristics among the hybrid module, the PV alone and TE alone is significant to obtain the highest the electrical efficiency. In this paper, the attention was paid to the inconsistent phenomenon of thermoelectric load resistance for photo-voltaic–thermoelectric modules. The model of PV-TE was built and verified based on two types of PV cells. The load resistance of TE for the maximum power output was also analyzed under different working conditions for the TE alone, TE in the PV-TE and PV-TE. The results showed that the load resistance of TE for the maximum power output of the TE alone, TE in the PV-TE and PV-TE are all different. For example, the PV-TE module based on the c-Si cell attains its peak value at the load electrical resistance of TE of 0.75 Ω, while the internal electrical resistance of the TE is 0.47 Ω. The PV-TE module based on the GaAs cell shows a maximum efficiency of PV-TE with a load resistance of approximately 1.6 Ω, while the internal electrical resistance of the TE is 2.0 Ω. Referring to the load resistance of TE alone is not suitable for PV-TE maximum power output. In addition, the TE maximum power output does not correspond to the PV-TE maximum power output since the TE load resistances in these two conditions are also different. The study will provide the reference for attaining the correct load resistance for the actual maximum power output of PV-TE module
Proprioceptive Learning with Soft Polyhedral Networks
Proprioception is the "sixth sense" that detects limb postures with motor
neurons. It requires a natural integration between the musculoskeletal systems
and sensory receptors, which is challenging among modern robots that aim for
lightweight, adaptive, and sensitive designs at a low cost. Here, we present
the Soft Polyhedral Network with an embedded vision for physical interactions,
capable of adaptive kinesthesia and viscoelastic proprioception by learning
kinetic features. This design enables passive adaptations to omni-directional
interactions, visually captured by a miniature high-speed motion tracking
system embedded inside for proprioceptive learning. The results show that the
soft network can infer real-time 6D forces and torques with accuracies of
0.25/0.24/0.35 N and 0.025/0.034/0.006 Nm in dynamic interactions. We also
incorporate viscoelasticity in proprioception during static adaptation by
adding a creep and relaxation modifier to refine the predicted results. The
proposed soft network combines simplicity in design, omni-adaptation, and
proprioceptive sensing with high accuracy, making it a versatile solution for
robotics at a low cost with more than 1 million use cycles for tasks such as
sensitive and competitive grasping, and touch-based geometry reconstruction.
This study offers new insights into vision-based proprioception for soft robots
in adaptive grasping, soft manipulation, and human-robot interaction.Comment: 20 pages, 10 figures, 2 tables, submitted to the International
Journal of Robotics Research for revie
Numerical investigation on rock fragmentation under decoupled charge blasting
Blasting using decoupled charge is extensively applied in rock excavation and rock fragmentation. In this study, the rock fragmentation induced by blasting using decoupled charge is investigated by combined finite element modelling and image-processing. After calibrating the numerical model developed in LS-DYNA against the fragment morphology and fragmentation size distribution (FSD) in three air-coupling blasts and three water-coupling blasts, a series of cubic single-hole models are constructed to simulate rock cracking induced by decoupled charge blasting with various decoupling ratios, distinct coupling mediums and different decoupled charge modes. The simulated fracture networks are obtained by blanking the damaged elements whose damage level is over the threshold of crack formation, and the resulting crack patterns are image-processed using ImageJ to identify fragment size. Then, the blast-created FSDs are characterized by a three-parameter generalized extreme value function, and the FSDs with decoupling ratios, coupling mediums and different decoupled charge modes are quantitatively analyzed and compared. The results show that rock fragmentation becomes finer and the FSD range gets narrower with the decrease in decoupling ratio. Meanwhile, smaller fragment sizes and narrower FSD spans are obtained when changing coupling material from air to water and altering radial decoupling to axial decoupling.acceptedVersio
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