2,179 research outputs found
Preparation of hollow fiber membranes for gas separation
Today, immersion precipitation is the most often used process for the preparation of gas separation membranes from polymeric materials. In this process a polymer solution in the form of a thin liquid film or hollow fiber is immersed in a nonsolvent bath where the polymer precipitates and forms a membrane. \ud
The immersion precipitation process can be performed by various means. The dual bath spinning process is one specific way which can be used, e.g., for the preparation of hollow fiber membranes for gas separation. In this process hollow fibers are spun by contacting the polymer solution with two properly chosen coagulents successively. The first coagulant is used to 'extract' solvent out of the polymer solution. The contact time is short in order to create a thin layer of high polymer concentration at the interface. The second coagulent is used to quickly precipitate the polymer solution to form the membrane. With this spinning process, hollow fibers with the intrinsic selectivity of the polymer material can be easily obtained without the necessity of coating.\ud
This thesis is aimed on extending the knowledge on membrane formation and on further developing the dual bath spinning process for the preparation of gas separation hollow fibers with both high selectivity and high flux
The domination number and the least -eigenvalue
A vertex set of a graph is said to be a dominating set if every
vertex of is adjacent to at least a vertex in , and the
domination number (, for short) is the minimum cardinality
of all dominating sets of . For a graph, the least -eigenvalue is the
least eigenvalue of its signless Laplacian matrix. In this paper, for a
nonbipartite graph with both order and domination number , we show
that , and show that it contains a unicyclic spanning subgraph
with the same domination number . By investigating the relation between
the domination number and the least -eigenvalue of a graph, we minimize the
least -eigenvalue among all the nonbipartite graphs with given domination
number.Comment: 13 pages, 3 figure
The valley filter efficiency of monolayer graphene and bilayer graphene line defect model
In addition to electron charge and spin, novel materials host another degree
of freedom, the valley. For a junction composed of valley filter sandwiched by
two normal terminals, we focus on the valley efficiency under disorder with two
valley filter models based on monolayer and bilayer graphene. Applying the
transfer matrix method, valley resolved transmission coefficients are obtained.
We find that: i) under weak disorder, when the line defect length is over about
, it functions as a perfect channel (quantized conductance) and
valley filter (totally polarized); ii) in the diffusive regime, combination
effects of backscattering and bulk states assisted intervalley transmission
enhance the conductance and suppress the valley polarization; iii) for very
long line defect, though the conductance is small, polarization is indifferent
to length. Under perpendicular magnetics field, the characters of charge and
valley transport are only slightly affected. Finally we discuss the efficiency
of transport valley polarized current in a hybrid system.Comment: 6 figure
View Independent Vehicle Make, Model and Color Recognition Using Convolutional Neural Network
This paper describes the details of Sighthound's fully automated vehicle
make, model and color recognition system. The backbone of our system is a deep
convolutional neural network that is not only computationally inexpensive, but
also provides state-of-the-art results on several competitive benchmarks.
Additionally, our deep network is trained on a large dataset of several million
images which are labeled through a semi-automated process. Finally we test our
system on several public datasets as well as our own internal test dataset. Our
results show that we outperform other methods on all benchmarks by significant
margins. Our model is available to developers through the Sighthound Cloud API
at https://www.sighthound.com/products/cloudComment: 7 Page
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