Charge reduction experimental investigation of CO2 single-phase flow in a horizontal micro-channel with constant heat flux conditions

The use of carbon dioxide as alternative refrigerant in refrigeration plants and heat pumps has been focused recently. Through the specific properties of CO₂, the use of very compact heat exchangers is relevant and the technology of micro-channel heat exchangers rises as a suitable solution. The experimental investigation of CO₂ flow in a single micro-channel with an inner diameter of 529 μm is planned with an original test section. This test section is initially dedicated for further CO₂ two-phase flow analysis. The local heat transfer coefficients are estimated with micro-thermocouples stuck on the micro-channel wall. The pressure drop is also measured. This paper presents the first results in single-phase pressure drop and heat transfer and exhibits promising coming data in two-phase flow pressure drop and heat transfer for mass velocity between 200 kg/m²/s and 1400 kg/m²/s and working saturation temperature between −10 °C and 5 °C. The results stress on the good accuracy of suitable classical laws to predict pressure drop and heat transfer in single-phase flow in micro-channel.     

High Throughput‐Per‐Footprint Inertial Focusing

Matching the scale of microfluidic flow systems with that of microelectronic chips for realizing monolithically integrated systems still needs to be accomplished. However, this is appealing only if such re‐scaling does not compromise the fluidic throughput. This is related to the fact that the cost of microelectronic circuits primarily depends on the layout footprint, while the performance of many microfluidic systems, like flow cytometers, is measured by the throughput. The simple operation of inertial particle focusing makes it a promising technique for use in such integrated flow cytometer applications, however, microfluidic footprints demonstrated so far preclude monolithic integration. Here, the scaling limits of throughput‐per‐footprint (TPFP) in using inertial focusing are explored by studying the interplay between theory, the effect of channel Reynolds numbers up to 1500 on focusing, the entry length for the laminar flow to develop, and pressure resistance of the microchannels. Inertial particle focusing is demonstrated with a TPFP up to 0.3 L/(min cm²) in high aspect‐ratio rectangular microfluidic channels that are readily fabricated with a post‐CMOS integratable process, suggesting at least a 100‐fold improvement compared to previously demonstrated techniques. Not only can this be an enabling technology for realizing cost‐effective monolithically integrated flow cytometry devices, but the methodology represented here can also open perspectives for miniaturization of many biomedical microfluidic applications requiring monolithic integration with microelectronics without compromising the throughput.     

Modeling the behavior of persons with mild cognitive impairment or Alzheimer’s for intelligent environment simulation

User Modeling and User-Adapted Interaction - Intelligent environments may improve the independence and quality of life of persons with mild cognitive impairment (MCI) or Alzheimer’s disease...     

A fast and practical bit-vector algorithm for the Longest Common Subsequence problem

This paper presents a new practical bit-vector algorithm for solving the well-known Longest Common Subsequence (LCS) problem. Given two strings of length m and n, nm, we present an algorithm which determines the length p of an LCS in O(nm/w) time and O(m/w) space, where w is the number of bits in a machine word. This algorithm can be thought of as column-wise “parallelization” of the classical dynamic programming approach. Our algorithm is very efficient in practice, where computing the length of an LCS of two strings can be done in linear time and constant (additional/working) space by assuming that mw.     

Thermoelectric transport in graphene and 2D layered materials

ABSTRACT

In early 90s, Hicks and Dresselhaus proposed that low dimensional materials are advantages for thermoelectric applications due to the sharp features in their density-of-states, resulting in a high Seebeck coefficient and, potentially, in a high thermoelectric power factor. Two-dimensional (2D) materials are the latest class of low dimensional materials studied for thermoelectric applications. The experimental exfoliation of graphene, a single-layer of carbon atoms in 2004, triggered an avalanche of studies devoted to 2D materials in view of electronic, thermal, and optical applications. One can mix and match and stack 2D layers to form van der Waals hetero-structures. Such structures have extreme anisotropic transport properties. Both in-plane and cross-plane thermoelectric transport in these structures are of interest. In this short review article, we first review the progress achieved so far in the study of thermoelectric transport properties of graphene, the most widely studied 2D material, as a representative of interesting in-plane thermoelectric properties. Then, we turn our attention to the layered materials, in their cross-plane direction, highlighting their role as potential structures for solid-state thermionic power generators and coolers.     

Deposition rate and morphology of carbon nanotubes at different positions in a CVD reactor

Carbon nanotubes (CNTs) were synthesized through the catalytic decomposition of a ferrocene-xylene mixture in a horizontal chemical va- por deposition reactor. The deposition rate of CNTs along the axial direction was measured. The morphology of CNTs was observed by scan- ning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the deposition rate of CNTs along the axial direction first increased and later decreased, the position achieving the maximum deposition rate was influenced by the operating conditions. The morphologies of CNTs also changed along the axial direction.     

Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering

Injection of cell‐laden scaffolds in the form of mesoscopic particles directly to the site of treatment is one of the most promising approaches to tissue regeneration. Here, a novel and highly efficient method is presented for preparation of porous microbeads of tailorable dimensions (in the range ≈300–1500 mm) and with a uniform and fully interconnected internal porous texture. The method starts with generation of a monodisperse oil‐in‐water emulsion inside a flow‐focusing microfluidic device. This emulsion is later broken‐up, with the use of electric field, into mesoscopic double droplets, that in turn serve as a template for the porous microbeads. By tuning the amplitude and frequency of the electric pulses, the template droplets and the resulting porous bead scaffolds are precisely produced. Furthermore, a model of pulsed electrodripping is proposed that predicts the size of the template droplets as a function of the applied voltage. To prove the potential of the porous microbeads as cell carries, they are tested with human mesenchymal stem cells and hepatic cells, with their viability and degree of microbead colonization being monitored. Finally, the presented porous microbeads are benchmarked against conventional microparticles with nonhomogenous internal texture, revealing their superior performance.     

Fair multi-agent task allocation for large datasets analysis

MapReduce is a design pattern for processing large datasets distributed on a cluster. Its performances are linked to the data structure and the runtime environment. Indeed, data skew can yield an unfair task allocation, but even when the initial allocation produced by the partition function is well balanced, an unfair allocation can occur during the reduce phase due to the heterogeneous performance of nodes. For these reasons, we propose an adaptive multi-agent system. In our approach, the reducer agents interact during the job and the task reallocation is based on negotiation in order to decrease the workload of the most loaded reducer and so the runtime. In this paper, we propose and evaluate two negotiation strategies. Finally, we experiment our multi-agent system with real-world datasets over heterogeneous runtime environment.     

CHOOSE: Towards a metamodel for enterprise architecture in small and medium-sized enterprises

Enterprise architecture (EA) is a coherent whole of principles, methods, and models that are used in the design and realization of an enterprise’s organizational structure, business processes, information systems, and IT infrastructure. Recent research indicates the need for EA in small and medium-sized enterprises (SMEs), important drivers of the economy, as they struggle with problems related to a lack of structure and overview of their business. However, existing EA frameworks are perceived as too complex and, to date, none of the EA approaches are sufficiently adapted to the SME context. Therefore, this paper presents the CHOOSE metamodel for EA in SMEs that was developed and evaluated through action research in an SME and further refined and validated through case study research in five other SMEs. This metamodel is based on the essential dimensions of EA frameworks and is kept simple so that it may be applied in an SME context. The final CHOOSE metamodel includes only four essential concepts (i.e. goal, actor, operation, object), one for each most frequently used EA focus. As an example, an extract is included from the specific model that was created for the SME used in our action research. Finally, the CHOOSE metamodel is evaluated according to the dimensions essential in EA and the requirements for EA in an SME context.