Hydrodynamic Modeling of Flow Reversal in Micro-channel Flow Boiling

Flow boiling in micro-channels have significantly different characteristics from flow boiling in larger channels. One particular behavior of micro-channel boiling is the instability that results in oscillations and flow reversals. This has been a unique challenge for researchers, and a satisfactory solution that eliminates the instability without a substantial performance penalty has not been found. In this study, a simple analytical model based on mass and momentum conservation is developed to identify the mechanistic conditions corresponding to the conditions of flow reversal in a boiling flow in micro-channels. The results indicate that flow reversal can occur when a rapid evaporation occurs near the inlet of the channel. The model also confirms the observations of existing studies that, if a large pressure differential in the channel is imposed in combination with a throttling section before the inlet, the flow reversal can be suppressed

A review of metal foam and metal matrix composites for heat exchangers and heat Sinks

Recent advances in manufacturing methods open the possibility for broader use of metal foams and metal matrix composites (MMCs) for heat exchangers, and these materials can have tailored material properties. Metal foams in particular combine a number of interesting properties from a heat exchanger's point of view. In this paper, the material properties of metal foams and MMCs are surveyed, and the current state of the art is reviewed for heat exchanger applications. Four different applications are considered: liquid-liquid, liquid-gas, and gas-gas heat exchangers and heat sinks. Manufacturing and implementation issues are identified and discussed, and it is concluded that these materials hold promise both for heat exchangers and heat sinks, but that some key issues still need to be solved before broad-scale application is possible

Entecavir plus tenofovir versus entecavir plus adefovir in chronic hepatitis B patients with a suboptimal response to lamivudine and adefovir combination therapy

Background/AimsWe compared the efficacies of entecavir (ETV) plus tenofovir (TDF) and ETV plus adefovir (ADV) in chronic hepatitis B (CHB) patients with genotypic resistance to lamivudine (LAM) who showed a suboptimal response to LAM and ADV combination therapy.MethodsWe reviewed 63 CHB patients with genotypic resistance to LAM who showed a suboptimal response to LAM and ADV combination therapy. Among these patients, 30 were treated with ETV + ADV and 33 were treated with ETV + TDF for 12 months.ResultsThe only baseline characteristic that differed significantly between the two groups was the ETV resistance profile. The rate of a virologic response [serum hepatitis B virus (HBV) DNA level of <20 IU/mL] was significant higher for ETV+TDF than for ETV+ADV over 12 months (57.6% vs. 23.3%, P=0.006, at 6 months; 84.8% vs. 26.7%, P<0.001, at 12 months). The probability of a virologic response was significantly increased in ETV+TDF (P<0.001, OR=54.78, 95% CI=7.15-419.54) and decreased in patients with higher baseline viral loads (P=0.001, OR=0.18, 95% CI=0.07-0.50) in multivariate analysis. No serious adverse event occurred during the study period.ConclusionsIn patients with CHB who showed a suboptimal response to LAM and ADV combination therapy, ETV+TDF was superior to ETV+ADV in achieving a virologic response regardless of the HBV resistance profile. Further large-scale and long-term follow-up prospective studies are needed to explain these results

Extrusion-Based 3D Printing of Molecular Sieve Zeolite for Gas Adsorption Applications

Extrusion based 3D printing is one of the emerging additive manufacturing technologies used for printing range of materials from metal to ceramics. In this study, we developed a customized 3D printer based on extrusion freeform fabrication technique, such as slurry deposition, for 3D printing of different molecular sieve zeolite monoliths like 3A, 4A, 5A and 13X to evaluate their performance in gas adsorption. The physical and structural properties of 3D printed zeolite monoliths will be characterized along with the gas adsorption performance. The Brunauer–Emmett–Teller (BET) test of 3D printed samples will be performed for calculation of the surface area, which will give us the capacity of gas absorption into 3D printed zeolite. The BET surface area test showed good results for Zeolite 13X compared to available literature. The surface area calculated for 3D – printed Zeolite 13X was 767m2/g and available literature showed 498 m2/g for 3D – printed Zeolite 13X. The microhardness values of 3D – printed Zeolite samples were measured using a Vicker hardness tester. The hardness value of the 3D - printed Zeolite samples increased from 8.3 ± 2 to 12.5 ± 3 HV 0.05 for Zeolite 13X, 3.3 ± 1 to 7.3 ± 1 HV 0.05 for Zeolite 3A, 4.3 ± 2 to 7.5 ± 2 HV 0.05 for Zeolite 4A, 7.4 ± 1 to 14.0 ± 0.5 HV 0.05 for Zeolite 5A, before and after sintering process, respectively. The SEM analysis was performed for 3D printed samples before and after sintering to evaluate their structural properties. The SEM analysis reveals that all 3D – printed Zeolite samples retained their microstructure after slurry preparation and also after the sintering process. The porous nature of 3D – printed Zeolite walls was retained after the sintering process

Mobile Kink Solitons in a Van der Waals Charge-Density-Wave Layer

Kinks, point-like geometrical defects along dislocations, domain walls, and DNA, are stable and mobile, as solutions of a sine-Gordon wave equation. While they are widely investigated for crystal deformations and domain wall motions, electronic properties of individual kinks have received little attention. In this work, electronically and topologically distinct kinks are discovered along electronic domain walls in a correlated van der Waals insulator of 1$T$-TaS$_2$. Mobile kinks and antikinks are identified as trapped by pinning defects and imaged in scanning tunneling microscopy. Their atomic structures and in-gap electronic states are unveiled, which are mapped approximately into Su-Schrieffer-Heeger solitons. The twelve-fold degeneracy of the domain walls in the present system guarantees an extraordinarily large number of distinct kinks and antikinks to emerge. Such large degeneracy together with the robust geometrical nature may be useful for handling multilevel information in van der Waals materials architectures.Comment: 12 pages, 4 figure

Passive vibration on the legs reduces peripheral and systemic arterial stiffness

Intermittent leg exercise (10 × 1-min sets) with whole-body vibration (WBV) decreases brachial-ankle pulse-wave velocity (baPWV)1 and leg PWV (legPWV) but not aortic PWV.2 As baPWV is an index of systemic arterial stiffness3 mainly influenced by aortic PWV (∼58%) and legPWV (∼23%),4 previously published results1, 2 suggest that WBV affects baPWV through peripheral but not central PWV. The post-exercise decrease in PWV is associated with vasodilation in the exercised limb.5, 6 Similarly, intermittent WBV (3 × 3-min sets)7 or passive vibration (PV)8 has been shown to increase blood flow in the vibrated limb after only 1-min post vibration. Interestingly, 10 min of continuous PV was found to increase arm skin blood flow after 5-min post vibration,9 indicating a direct relationship between the duration of exposure and vasorelaxation. We hypothesized that PV on the legs may decrease legPWV and baPWV more than aortic PWV. The purpose of our study was to examine PWV responses following continuous PV of lengthy duration

Impact of passive vibration on pressure pulse wave characteristics

The augmentation index (AIx), a marker of wave reflection, decreases following acute leg exercise. Passive vibration (PV) causes local vasodilation that may reduce AIx. This study investigated the effects of acute PV on wave reflection and aortic hemodynamics. In a crossover fashion 20 (M=9, F=11) healthy young (22±3 year) participants were randomized to 10 min PV or no vibration control (CON) trials. Subjects rested in the supine position with their legs over a vibration platform for the entire session. Radial waveforms were obtained by applanation tonometry before and after 3 min (Post-3) and 30 min (Post-30) of PV (∼5.37 G) or CON. No change in parameters was found at Post-3. We found significant time-by-trial interactions (P\u3c0.01) at Post-30 for augmented pressure, AIx and second systolic peak pressure (P2), such that these parameters significantly (P\u3c0.05) decreased (−2.3±3.0 mm Hg, −7.2±6.9% and −1.5±3.5 mm Hg, respectively) after PV but not after CON. These findings suggest that acute PV applied to the legs decreases AIx owing to a decrease in wave reflection magnitude (P2). Further research is warranted to evaluate the potential clinical application of PV in populations at an increased cardiovascular risk who are unable to perform conventional exercise