PERFORMANCE OF A HEAT SINK WITH INTERRUPTED AND STAGGERED ELIIPITIC FINS

ABSTRACT: The power density of electronic devices has been increasing along with the rapid technology development. Cooling of electronic systems is therefore essential in controlling the component temperature and avoiding any hot spot. Heat sinks are commonly adopted in electronics cooling together with different technologies to enhance heat transfer process. Fin-based heat sinks are commonly designed so that coolants (gas or liquid) are forced to pass through the narrow straight channel. A driving fan is then needed to overcome the viscous pressure loss and maintain the coolant flow. As part of effort to improve the heat sink performance, this study simulated the details of the flow and temperature fields of heat sinks with interrupted and staggered elliptic fins cooled by forced convection. The focus of this study lies on three scenarios: Heat transfer before the flow reaches the periodic condition in the flow direction; effect of the heat sink base surface on flow and heat transfer; and conjugate heat transfer between convection and heat conduction inside the fins. In addition, studies were also conducted on the effect of the Reynolds number. The results of this paper can help design heat sinks for electronics cooling by employing the new concept of interrupted and staggered fins

Mist/Steam Heat Transfer of Multiple Rows of Impinging Jets

ABSTRACT Internal mist/steam blade cooling technology is considered the future of high-temperature gas turbine systems that burn hydrogen or synthetic gases. This paper experimentally investigates the mist/steam heat transfer of three rows of circular jet impingement in a confined channel. Fine water droplets with an average diameter of 3-µm are generated by atomizing water through small nozzles under high pressure. The circular jets have a uniform diameter of 8-mm, and the distance between adjacent jets in a row is 3 diameters. Jets in different rows are staggered and the distance between rows is 1.5 diameters. The spacing of nozzle-to-target is 2.8 diameters. Experiments were conducted with Reynolds numbers at 7,500 and 15,000 and heat fluxes ranging from 3,350 to 13,400W/m 2 . The results indicate that the wall temperature significantly decreased because of mist injection. A region of high cooling enhancement is observed and more extensive than those employing one row of circular jets or a slot jet. While the details depend on flow conditions, it is seen that the enhanced region of 3-row jets is about 5 jet diameters at Re=7,500, q"=7.54 kW/m 2 , and m l /m s =3.5%, compared to 2 jet diameters for single-row jets. The enhancement becomes negligible after a certain distance downstream. The maximum local cooling enhancement is up to 800% by injecting 3.5% of mist at low heat flux condition and 150% for high heat flux condition. The average cooling enhancement can achieve more than 100% within 2 jet-diameter distance from the stagnation line at Re=15,000 and m l /m s =1.5%

Selection of reference genes for quantitative real-time PCR analysis in cucumber (Cucumis sativus L.), pumpkin (Cucurbita moschata Duch.) and cucumber–pumpkin grafted plants

Background Quantitative real-time PCR (qRT-PCR) is a commonly used high-throughput technique to measure mRNA transcript levels. The accuracy of this evaluation of gene expression depends on the use of optimal reference genes. Cucumber–pumpkin grafted plants, made by grafting a cucumber scion onto pumpkin rootstock, are superior to either parent plant, as grafting conveys many advantages. However, although many reliable reference genes have been identified in both cucumber and pumpkin, none have been obtained for cucumber–pumpkin grafted plants. Methods In this work, 12 candidate reference genes, including eight traditional genes and four novel genes identified from our transcriptome data, were selected to assess their expression stability. Their expression levels in 25 samples, including three cucumber and three pumpkin samples from different organs, and 19 cucumber–pumpkin grafted samples from different organs, conditions, and varieties, were analyzed by qRT-PCR, and the stability of their expression was assessed by the comparative ΔCt method, geNorm, NormFinder, BestKeeper, and RefFinder. Results The results showed that the most suitable reference gene varied dependent on the organs, conditions, and varieties. CACS and 40SRPS8 were the most stable reference genes for all samples in our research. TIP41 and CACS showed the most stable expression in different cucumber organs, TIP41 and PP2A were the optimal reference genes in pumpkin organs, and CACS and 40SRPS8 were the most stable genes in all grafted cucumber samples. However, the optimal reference gene varied under different conditions. CACS and 40SRPS8 were the best combination of genes in different organs of cucumber–pumpkin grafted plants, TUA and RPL36Aa were the most stable in the graft union under cold stress, LEA26 and ARF showed the most stable expression in the graft union during the healing process, and TIP41 and PP2A were the most stable across different varieties of cucumber–pumpkin grafted plants. The use of LEA26, ARF and LEA26+ARF as reference genes were further verified by analyzing the expression levels of csaCYCD3;1, csaRUL, cmoRUL, and cmoPIN in the graft union at different time points after grafting. Discussion This work is the first report of appropriate reference genes in grafted cucumber plants and provides useful information for the study of gene expression and molecular mechanisms in cucumber–pumpkin grafted plants

The correlation between changes in gray matter microstructure and cerebral blood flow in Alzheimer’s disease

ObjectiveTo investigate the relationship between changes in cerebral blood flow (CBF) and gray matter (GM) microstructure in Alzheimer’s disease (AD) and mild cognitive impairment (MCI).MethodsA recruited cohort of 23 AD patients, 40 MCI patients, and 37 normal controls (NCs) underwent diffusional kurtosis imaging (DKI) for microstructure evaluation and pseudo-continuous arterial spin labeling (pCASL) for CBF assessment. We investigated the differences in diffusion- and perfusion-related parameters across the three groups, including CBF, mean diffusivity (MD), mean kurtosis (MK), and fractional anisotropy (FA). These quantitative parameters were compared using volume-based analyses for the deep GM and surface-based analyses for the cortical GM. The correlation between CBF, diffusion parameters, and cognitive scores was assessed using Spearman coefficients, respectively. The diagnostic performance of different parameters was investigated with k-nearest neighbor (KNN) analysis, using fivefold cross-validation to generate the mean accuracy (mAcc), mean precision (mPre), and mean area under the curve (mAuc).ResultsIn the cortical GM, CBF reduction primarily occurred in the parietal and temporal lobes. Microstructural abnormalities were predominantly noted in the parietal, temporal, and frontal lobes. In the deep GM, more regions showed DKI and CBF parametric changes at the MCI stage. MD showed most of the significant abnormalities among all the DKI metrics. The MD, FA, MK, and CBF values of many GM regions were significantly correlated with cognitive scores. In the whole sample, the MD, FA, and MK were associated with CBF in most evaluated regions, with lower CBF values associated with higher MD, lower FA, or lower MK values in the left occipital lobe, left frontal lobe, and right parietal lobe. CBF values performed best (mAuc = 0.876) for distinguishing the MCI from the NC group. Last, MD values performed best (mAuc = 0.939) for distinguishing the AD from the NC group.ConclusionGray matter microstructure and CBF are closely related in AD. Increased MD, decreased FA, and MK are accompanied by decreased blood perfusion throughout the AD course. Furthermore, CBF values are valuable for the predictive diagnosis of MCI and AD. GM microstructural changes are promising as novel neuroimaging biomarkers of AD

Activated mouse CD4+Foxp3−CD4^+Foxp3^− T cells facilitate melanoma metastasis via Qa-1-dependent suppression of NK-cell cytotoxicity

The regulatory activities of mouse $CD^4+Foxp3^+$ T cells on various immune cells, including NK cells, have been well documented. Under some conditions, conventional $CD4^+Foxp3^−$ T cells in the periphery are able to acquire inhibitory function on other T cells, but their roles in controlling innate immune cells are poorly defined. As a potential cellular therapy for cancer, ex vivo activated $CD4^+Foxp3^−$ effector T cells are often infused back in vivo to suppress tumor growth and metastasis. Whether such activated T cells could affect NK-cell control of tumorigenesis is unclear. In the present study, we found that mitogen-activated $CD4^+Foxp3^−$ T cells exhibited potent suppressor function on NK-cell proliferation and cytotoxicity in vitro, and notably facilitated B16 melanoma metastasis in vivo. Suppression of NK cells by activated $CD4^+Foxp3^−$ T cells is cell-cell contact dependent and is mediated by Qa-1:NKG2A interaction, as administration of antibodies blocking either Qa-1 or NKG2A could completely reverse this suppression, and significantly inhibited otherwise facilitated melanoma metastasis. Moreover, activated $CD4^+Foxp3^−$ cells from Qa-1 knockout mice completely lost the suppressor activity on NK cells, and failed to facilitate melanoma metastasis when transferred in vivo. Taken together, our findings indicate that innate anti-tumor response is counter regulated by the activation of adaptive immunity, a phenomenon we term as “activation-induced inhibition”. Thus, the regulatory role of activated $CD4^+Foxp3^−$ T cells in NK-cell activity must be taken into consideration in the future design of cancer therapies

The First Case of Ischemia-Free Kidney Transplantation in Humans

Background: Ischemia-reperfusion injury (IRI) has been considered an inevitable event in organ transplantation since the first successful kidney transplant was performed in 1954. To avoid IRI, we have established a novel procedure called ischemia-free organ transplantation. Here, we describe the first case of ischemia-free kidney transplantation (IFKT). Materials and Methods: The kidney graft was donated by a 19-year-old brain-dead donor. The recipient was a 47-year-old man with end-stage diabetic nephropathy. The graft was procured, preserved, and implanted without cessation of blood supply using normothermic machine perfusion. Results: The graft appearance, perfusion flow, and urine production suggested that the kidney was functioning well-during the whole procedure. The creatinine dropped rapidly to normal range within 3 days post-transplantation. The levels of serum renal injury markers were low post-transplantation. No rejection or vascular or infectious complications occurred. The patient had an uneventful recovery. Conclusion: This paper marks the first case of IFKT in humans. This innovation may offer a unique solution to optimizing transplant outcomes in kidney transplantation

Asymptotic performance analysis for EGC and SC over arbitrarily correlated Nakagami-m fading channels

The multi-branch diversity combining technique has been widely used in wireless communications systems to overcome the adverse effect of multipath fading. The three most popular diversity combining schemes are selection combining (SC), equal gain combining (EGC), and maximal ratio combining (MRC). In the performance analysis of multi-branch diversity combining, the asymptotic technique is an attractive approach to obtain compact and accurate error rate and outage probability in large signal-to-noise ratio (SNR) regions. Asymptotic performance can be obtained either in the time domain by finding the probability density function (PDF) of the instantaneous output SNR, or in the frequency domain by finding the moment generating function (MGF) of the square root of the instantaneous output SNR. In this thesis, the PDF of the instantaneous SNR at the output of selection combiner and the MGF of the square root of the instantaneous SNR at the output of equal gain combiner over arbitrarily correlated Nakagami-m fading channels are derived and used to obtain asymptotic error rate and outage probability expressions of SC and EGC, respectively. These expressions provide accurate and rapid estimation of error rates and outage probabilities. The accuracy of our analytical results is verified by computer simulation. More importantly, our analytical results provide physical insights into the transmission behavior of EGC and SC over arbitrarily correlated Nakagami-m fading channels. For instance, it is shown that the asymptotic error rates over correlated branches can be obtained by scaling the asymptotic error rates over independent branches with the factor which is the determinant of matrix M to the power m, where the elements of M are the square root of corresponding elements in the branch power covariance correlation matrix R. A similar relationship can also be found for the outage probabilities.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat

Effects of various modeling schemes on mist film cooling simulation

Abstract Numerical simulation is performed in this study to explore filmcooling enhancement by injecting mist into the cooling air with a focus on investigating the effect of various modeling schemes on the simulation results. The effect of turbulence models, dispersed-phase modeling, inclusion of different forces (Saffman, thermophoresis, and Brownian), trajectory tracking, and mist injection scheme is studied. The effect of flow inlet boundary conditions (with/without air supply plenum), inlet turbulence intensity, and the near-wall grid density on simulation results is also included. Using a 2-D slot film cooling simulation with a fixed blowing angle and blowing ratio shows a 2% mist injected into the cooling air can increase the cooling effectiveness about 45%. The RNG k-ε model, RSM and the standard k-ε turbulence model with the enhanced wall treatment produce consistent and reasonable results while the turbulence dispersion has a significant effect on mist film cooling through the stochastic trajectory calculation. The thermophoretic force slightly increases the cooling effectiveness, but the effect of Brownian force and Saffman lift is imperceptible. The cooling performance is affected negatively by the plenum in this study, which alters the velocity profile and turbulence intensity at the jet exit plane. The results of this paper can serve as the qualification reference for future more complicated studies including 3-D cooling holes, different blowing ratios, various density ratios, and rotational effect