1,093 research outputs found
Experimental Comparison of the Impact of Air-Side Particulate Fouling on the Thermo-Hydraulic Performance of Microchannel and Plate-Fin Heat Exchangers
Analytical prediction of stress and strain in adhesive tube-to-tube joints under thermal expansion/contraction
Adhesive joints are widely applied and studied for various industrial applications. The interest in adhesive joints has expanded to include heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems having a significant number of joints employed for manufacturing. This study investigates an analytical modeling approach for predicting joint stress and strain distribution under static loading with thermal strain. A review of modeling techniques identified the need to develop a joint analytical model under loading conditions representative of HVAC&R applications. The details of the model, governing equations, assumptions, boundary conditions, and solution techniques are first reported. The model is validated via comparison to existing results before performing parametric studies to provide insights on the influences of thermal expansion and inner tube pressure on possible failure. It is found that the joint overlap length plays an important role in stress distribution, while the adhesive thickness has less impact. Overall, the results indicate that static loading failure is not likely a concern for joints in HVAC&R systems, but the thermal strain and stress induced by temperature fluctuations must be carefully considered. This modeling effort establishes a framework that can be used to generate criteria and instructions on designing adhesive joints across different HVAC&R</p
Multi-objective Optimization of Sustainable Single-Effect Water/Lithium Bromide Absorption Cycle
A rigorous mathematical approach is developed for optimization of sustainable single-effect water/ Lithium Bromide (LiBr) absorption cooling cycles. The multi-objective formulation accounts for minimization of the chiller area as well as the environmental impact associated with the operation of the absorption cycle. The environmental impact is quantified based on the global warming potential and the Eco-indicator 99, both of which follow principles of life cycle assessment. The design task is formulated as a bi-criterion non-linear programming problem, the solution of which is defined by a set of Pareto points that represent the optimal compromise between the total area of the chiller and global warming potential. These Pareto sets are obtained via the epsilon constraint method. A set of design alternatives are provided for the absorption cycles rather than a single design; the best design can be chosen from this set based on the major constraints and benefits in a given application. The proposed approach is illustrated design of a typical absorption cooling cycle
Prediction of Air-Side Particulate Fouling of HVAC&R Heat Exchangers
Air-to-refrigerant heat exchangers used in heating, ventilation, air-conditioning, and refrigeration systems routinely experience air-side fouling due to the presence of particulates in outdoor and indoor environments. The influence on the performance of the heat exchanger, in terms of heat transfer efficiency and pressure drop imposed, depends on the extent of air-side fouling. Fouling of a heat exchanger is determined by a variety of parameters such as the dimensions of the heat exchanger, physical properties of the airborne particulates, and airflow conditions over the heat exchange surfaces. A comprehensive model is developed to deterministically calculate the extent of fouling of a heat exchanger as a function of these parameters by accounting for each of the possible deposition mechanisms. The study enhances modeling approaches previously employed in the literature by accounting for time-dependent accumulation of particles as well as the effects of the streamwise distribution of accumulated dust on subsequent fouling; the calculations for the deposition due to several of the mechanisms are also refined to improve prediction accuracy. Particulate matter deposits already present on the surface are found to accelerate the process of fouling by decreasing available area for airflow; an existing deposit layer effectively decreases the distance that a particle must travel to collide with a surface and increases the surface area available for deposition. The modified model predictions are compared against extant experimental deposition fraction data; an improved agreement is observed compared to previous models in the literature
Bioink properties before, during and after 3D bioprinting
Bioprinting is a process based on additive manufacturing from materials containing living cells. These materials, often referred to as bioink, are based on cytocompatible hydrogel precursor formulations, which gel in a manner compatible with different bioprinting approaches. The bioink properties before, during and after gelation are essential for its printability, comprising such features as achievable structural resolution, shape fidelity and cell survival. However, it is the final properties of the matured bioprinted tissue construct that are crucial for the end application. During tissue formation these properties are influenced by the amount of cells present in the construct, their proliferation, migration and interaction with the material. A calibrated computational framework is able to predict the tissue development and maturation and to optimize the bioprinting input parameters such as the starting material, the initial cell loading and the construct geometry. In this contribution relevant bioink properties are reviewed and discussed on the example of most popular bioprinting approaches. The effect of cells on hydrogel processing and vice versa is highlighted. Furthermore, numerical approaches were reviewed and implemented for depicting the cellular mechanics within the hydrogel as well as for prediction of mechanical properties to achieve the desired hydrogel construct considering cell density, distribution and material-cell interaction
Flight performance of actively foraging honey bees is reduced by a common pathogen
Sudden and severe declines in honey bee (Apis mellifera) colony health in the US and Europe have been attributed, in part, to emergent microbial pathogens, however, the mechanisms behind the impact are unclear. Using roundabout flight mills, we measured the flight distance and duration of actively foraging, healthyβlooking honey bees sampled from standard colonies, before quantifying the level of infection by Nosema ceranae and Deformed Wing Virus complex (DWV) for each bee. Neither the presence nor the quantity of N. ceranae were at low, natural levels of infection had any effect on flight distance or duration, but presence of DWV reduced flight distance by two thirds and duration by one half. Quantity of DWV was shown to have a significant, but weakly positive relation with flight distance and duration, however, the low amount of variation that was accounted for suggests further investigation by doseβresponse assays is required. We conclude that widespread, naturally occurring levels of infection by DWV weaken the flight ability of honey bees and high levels of withinβcolony prevalence are likely to reduce efficiency and increase the cost of resource acquisition. Predictions of implications of pathogens on colony health and function should take account of sublethal effects on flight performance
Π ΠΎΠ»Ρ Ρ Π΅ΠΌΠΎΠΊΠΈΠ½ΠΎΠ² Π² ΡΠ΅ΠΊΡΡΡΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ ΠΊΠ»Π΅ΡΠΎΠΊ-ΠΏΡΠ΅Π΄ΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΎΠ² Π² ΠΎΠΏΡΡ ΠΎΠ»Π΅Π²ΡΡ Π½ΠΈΡΡ ΠΏΡΠΈ ΡΠ°ΠΊΠ΅ ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ
Π Π°Π·Π²ΠΈΡΠΈΠ΅ ΠΏΠ΅ΡΠ²ΠΈΡΠ½ΠΎΠΉ ΠΎΠΏΡΡ
ΠΎΠ»ΠΈ ΡΠΎΠΏΡΠΎΠ²ΠΎΠΆΠ΄Π°Π΅ΡΡΡ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΠΎΠΏΡΡ
ΠΎΠ»Π΅Π²ΠΎΠΉ Π½ΠΈΡΠΈ, ΠΊΠΎΡΠΎΡΠ°ΡΡΠΎΠ·Π΄Π°Π΅Ρ Π±Π»Π°Π³ΠΎΠΏΡΠΈΡΡΠ½ΡΠ΅ ΡΡΠ»ΠΎΠ²ΠΈΡ Π΄Π»Ρ Π²ΡΠΆΠΈΠ²Π°Π½ΠΈΡ ΠΈ ΠΏΡΠΎΠ»ΠΈΡΠ΅ΡΠ°ΡΠΈΠΈ ΡΠ°ΠΊΠΎΠ²ΡΡ
ΠΊΠ»Π΅ΡΠΎΠΊ. ΠΠ΄Π½ΠΈΠΌ ΠΈΠ· ΠΊΠ»ΡΡΠ΅Π²ΡΡ
ΡΠ»Π΅ΠΌΠ΅Π½ΡΠΎΠ² ΡΠ²ΠΎΠ»ΡΡΠΈΠΈ ΠΎΠΏΡΡ
ΠΎΠ»Π΅Π²ΠΎΠΉ Π½ΠΈΡΠΈ ΡΠ²Π»ΡΠ΅ΡΡΡ ΡΠ΅ΠΊΡΡΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΊΠΎΡΡΠ½ΠΎΠΌΠΎΠ·Π³ΠΎΠ²ΡΡ
ΠΊΠ»Π΅ΡΠΎΠΊ-ΠΏΡΠ΅Π΄ΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΎΠ², Π²ΠΊΠ»ΡΡΠ°Ρ ΠΊΠ»Π΅ΡΠΊΠΈ-ΠΏΡΠ΅Π΄ΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΈ ΠΌΠ°ΠΊΡΠΎΡΠ°Π³ΠΎΠ², ΠΌΠ΅Π·Π΅Π½Ρ
ΠΈΠΌΠ°Π»ΡΠ½ΡΠ΅ ΡΡΠΎΠ»ΠΎΠ²ΡΠ΅ ΠΊΠ»Π΅ΡΠΊΠΈ, ΡΠ½Π΄ΠΎΡΠ΅Π»ΠΈΠ°Π»ΡΠ½ΡΠ΅ ΠΈ Π³Π΅ΠΌΠΎΠΏΠΎΡΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΊΠ»Π΅ΡΠΊΠΈ-ΠΏΡΠ΅Π΄ΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΈ. ΠΠΈΠ³ΡΠ°ΡΠΈΡ ΡΠΏΠΎΠΌΡΠ½ΡΡΡΡ
ΠΊΠ»Π΅ΡΠΎΠΊ Π² ΠΎΠΏΡΡ
ΠΎΠ»Ρ ΡΠ΅Π³ΡΠ»ΠΈΡΡΠ΅ΡΡΡ ΡΡΠ΄ΠΎΠΌ Ρ
Π΅ΠΌΠΎΠΊΠΈΠ½ΠΎΠ², Π² ΡΠΎΠΌ ΡΠΈΡΠ»Π΅ CCL2, CXCL12, MSP (macrophage stimulating protein) ΠΈ MIF (macrophage inhibitory factor). Π¦Π΅Π»ΡΡ Π½Π°ΡΡΠΎΡΡΠ΅Π³ΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΡΠ²Π»ΡΠ»ΠΎΡΡ ΠΈΠ·ΡΡΠ΅Π½ΠΈΠ΅ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² ΠΎΠΏΡΡ
ΠΎΠ»Π΅Π²ΠΎΠΉ Π½ΠΈΡΠΈ ΠΏΡΠΈ ΡΠ°ΠΊΠ΅ ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ. ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ Π²ΠΊΠ»ΡΡΠ°Π»ΠΎ 24 Π±ΠΎΠ»ΡΠ½ΡΡ
Ρ ΠΈΠ½Π²Π°Π·ΠΈΠ²Π½ΠΎΠΉ ΠΊΠ°ΡΡΠΈΠ½ΠΎΠΌΠΎΠΉ Π½Π΅ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΈΠΏΠ° ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ. Π ΡΡΡΠΏΠ΅Π½Π·ΠΈΠΈ ΠΎΠΏΡΡ
ΠΎΠ»Π΅Π²ΡΡ
ΠΊΠ»Π΅ΡΠΎΠΊ ΠΌΠ΅ΡΠΎΠ΄ΠΎΠΌ ΠΏΡΠΎΡΠΎΡΠ½ΠΎΠΉ ΡΠΈΡΠΎΡΠ»ΡΠΎΡΠΈΠΌΠ΅ΡΡΠΈΠΈ ΠΎΠΏΡΠ΅Π΄Π΅Π»ΡΠ»ΠΈ ΡΠΎΠ΄Π΅ΡΠΆΠ°Π½ΠΈΠ΅ ΠΊΠ»Π΅ΡΠΎΠΊ-ΠΏΡΠ΅Π΄ΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΎΠ². ΠΠΎΠ½ΡΠ΅Π½ΡΡΠ°ΡΠΈΡ Ρ
Π΅ΠΌΠΎΠΊΠΈΠ½ΠΎΠ² CCL2, CXCL12, MSP ΠΈ MIF Π² Π²Π΅Π½ΠΎΠ·Π½ΠΎΠΉ ΠΊΡΠΎΠ²ΠΈ Π±ΠΎΠ»ΡΠ½ΡΡ
ΠΎΡΠ΅Π½ΠΈΠ²Π°Π»ΠΈ Ρ ΠΏΠΎΠΌΠΎΡΡΡ ΡΠ²Π΅ΡΠ΄ΠΎΡΠ°Π·Π½ΠΎΠ³ΠΎ ΠΈΠΌΠΌΡΠ½ΠΎΡΠ΅ΡΠΌΠ΅Π½ΡΠ½ΠΎΠ³ΠΎ Π°Π½Π°Π»ΠΈΠ·Π°. ΠΠΎΡΡΠΎΠ²Π΅ΡΠ½ΡΡ
ΡΠ°Π·Π»ΠΈΡΠΈΠΉ Π² ΡΠΎΠ΄Π΅ΡΠΆΠ°Π½ΠΈΠΈ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Π½ΡΡ
ΠΊΠ»Π΅ΡΠΎΡΠ½ΡΡ
ΠΏΠΎΠΏΡΠ»ΡΡΠΈΠΉ, Π° ΡΠ°ΠΊΠΆΠ΅ ΠΊΠΎΠ½ΡΠ΅Π½ΡΡΠ°ΡΠΈΠΈ ΠΈΠ·ΡΡΠ΅Π½Π½ΡΡ
Ρ
Π΅ΠΌΠΎΠΊΠΈΠ½ΠΎΠ² ΠΌΠ΅ΠΆΠ΄Ρ ΠΏΠ°ΡΠΈΠ΅Π½ΡΠ°ΠΌΠΈ, ΡΠ°Π·Π΄Π΅Π»Π΅Π½Π½ΡΠΌΠΈ Π½Π° Π³ΡΡΠΏΠΏΡ Π²Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΎΡ Π½Π°Π»ΠΈΡΠΈΡ ΠΈΠ»ΠΈ ΠΎΡΡΡΡΡΡΠ²ΠΈΡ Π»ΠΈΠΌΡΠΎΠ³Π΅Π½Π½ΡΡ
ΠΌΠ΅ΡΠ°ΡΡΠ°Π·ΠΎΠ² ΠΈ Π½Π΅ΠΎΠ°Π΄ΡΡΠ²Π°Π½ΡΠ½ΠΎΠ³ΠΎ Π»Π΅ΡΠ΅Π½ΠΈΡ, ΠΎΠ±Π½Π°ΡΡΠΆΠ΅Π½ΠΎ Π½Π΅ Π±ΡΠ»ΠΎ. Π ΡΠΎ ΠΆΠ΅ Π²ΡΠ΅ΠΌΡ, ΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½Π° ΠΏΡΡΠΌΠ°Ρ ΠΊΠΎΡΡΠ΅Π»ΡΡΠΈΠΎΠ½Π½Π°Ρ ΡΠ²ΡΠ·Ρ ΠΌΠ΅ΠΆΠ΄Ρ ΡΠΎΠ΄Π΅ΡΠΆΠ°Π½ΠΈΠ΅ΠΌ Π³Π΅ΠΌΠΎΠΏΠΎΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΊΠ»Π΅ΡΠΎΠΊ-ΠΏΡΠ΅Π΄ΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΎΠ² Π² ΠΎΠΏΡΡ
ΠΎΠ»ΠΈ ΠΈ ΠΊΠΎΠ½ΡΠ΅Π½ΡΡΠ°ΡΠΈΠ΅ΠΉ CXCL12 ΠΈ MIF Π² ΠΊΡΠΎΠ²ΠΈ
Increased Regulatory T-Cell Activity and Enhanced T-Cell Homeostatic Signaling in Slow Progressing HIV-infected Children
Pediatric slow progressors (PSP) are rare ART-naΓ―ve, HIV-infected children who maintain high CD4 T-cell counts and low immune activation despite persistently high viral loads. Using a well-defined cohort of PSP, we investigated the role of regulatory T-cells (TREG) and of IL-7 homeostatic signaling in maintaining normal-for-age CD4 counts in these individuals. Compared to children with progressive disease, PSP had greater absolute numbers of TREG, skewed toward functionally suppressive phenotypes. As with immune activation, overall T-cell proliferation was lower in PSP, but was uniquely higher in central memory TREG (CM TREG), indicating active engagement of this subset. Furthermore, PSP secreted higher levels of the immunosuppressive cytokine IL-10 than children who progressed. The frequency of suppressive TREG, CM TREG proliferation, and IL-10 production were all lower in PSP who go on to progress at a later time-point, supporting the importance of an active TREG response in preventing disease progression. In addition, we find that IL-7 homeostatic signaling is enhanced in PSP, both through preserved surface IL-7receptor (CD127) expression on central memory T-cells and increased plasma levels of soluble IL-7receptor, which enhances the bioactivity of IL-7. Combined analysis, using a LASSO modeling approach, indicates that both TREG activity and homeostatic T-cell signaling make independent contributions to the preservation of CD4 T-cells in HIV-infected children. Together, these data demonstrate that maintenance of normal-for-age CD4 counts in PSP is an active process, which requires both suppression of immune activation through functional TREG, and enhanced T-cell homeostatic signaling
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