Power Cycling Effects on the Structural Stability of Thermal Pastes Used in Microelectronics

2006 ◽  
Vol 977 ◽  
Author(s):  
Ijeoma Nnebe ◽  
Claudius Feger ◽  
Maurice McGlashan-Powell
Keyword(s):  
Structural Changes ◽  
Volume Fraction ◽  
Heat Spreader ◽  
Thermal Paste ◽  
Normal Forces ◽  
Power Cycling ◽  
Microelectronics Industry ◽  
Thermal Pastes ◽  
Filled Composite ◽  
Soft Composite

AbstractThermal pastes are a class of soft composite materials of great importance to the microelectronics industry. The function of these pastes is two-fold: (i) to transport heat away from the chip; and (ii) to accommodate mechanical stresses in the package arising from the mismatch in the thermal expansion between the chip and the heat spreader or sink. Due to the former requirement, thermal pastes are among some of the most highly-filled composite systems in practice (solids volume fraction > 70%). These materials are expected to withstand the significant normal forces, lateral forces, and temperature variations associated with chip operations and power off/on transitions. The structural changes and degradation of various thermal pastes during power cycling have been characterized using optical microscopy and IR thermography. Correlations between the evolving structures and variables such as thermal paste inhomogeneity and binder-particle dispersability have been successfully made and will be presented.

scholarly journals Lasting effects of prenatal exposure to Cannabis in the retina of the offspring: an experimental study in mice

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Paulo Roberto Arruda Zantut ◽  
Mariana Matera Veras ◽  
Sarah Gomes Menezes Benevenutto ◽  
Angélica Mendonça Vaz Safatle ◽  
Ricardo Augusto Pecora ◽  
...  
Keyword(s):  
Young Adult ◽  
Light Microscopy ◽  
Prenatal Exposure ◽  
Structural Changes ◽  
Volume Fraction ◽  
Clinical Care ◽  
Retinal Layer ◽  
Exposed Population ◽  
The Central Nervous System ◽  
The Impact

Abstract Background Prenatal exposure to Cannabis is a worldwide growing problem. Although retina is part of the central nervous system, the impact of maternal Cannabis use on the retinal development and its postnatal consequences remains unknown. As the prenatal period is potentially sensitive in the normal development of the retina, we hypothesized that recreational use of Cannabis during pregnancy may alter retina structure in the offspring. To test this, we developed a murine model that mimics human exposure in terms of dose and use. Methods Pregnant BalbC mice were exposed daily for 5 min to Cannabis smoke (0.2 g of Cannabis) or filtered air, from gestational day 5 to 18 (N = 10/group). After weaning period, pups were separated and examined weekly. On days 60, 120, 200, and 360 after birth, 10 pups from each group were randomly selected for Spectral Domain Optical Coherence Tomography (SD-OCT) analysis of the retina. All retina layers were measured and inner, outer, and total retina thickness were calculated. Other 37 mice from both groups were sacrificed on days 20, 60, and 360 for retinal stereology (total volume of the retina and volume fraction of each retinal layer) and light microscopy. Means and standard deviations were calculated and MANOVA was performed. Results The retina of animals which mother was exposed to Cannabis during gestation was 17% thinner on day 120 (young adult) than controls (P = 0.003) due to 21% thinning of the outer retina (P = 0.001). The offspring of mice from the exposed group presented thickening of the IS/OS in comparison to controls on day 200 (P < 0.001). In the volumetric analyzes by retinal stereology, the exposed mice presented transitory increase of the IS/OS total volume and volume fraction on day 60 (young adult) compared to controls (P = 0.008 and P = 0.035, respectively). On light microscopy, exposed mice presented thickening of the IS/OS on day 360 (adult) compared to controls (P = 0.03). Conclusion Gestational exposure to Cannabis smoke may cause structural changes in the retina of the offspring that return to normal on mice adulthood. These experimental evidences suggest that children and young adults whose mothers smoked Cannabis during pregnancy may require earlier and more frequent clinical care than the non-exposed population.

Thermal Performance of Different Carbonaceous Nanoparticles as Additives to Thermal Paste as an Interface Material

2021 ◽  
Author(s):  
Bharath Bharadwaj ◽  
Prashant Singh ◽  
Roop L. Mahajan
Keyword(s):  
Thermal Performance ◽  
Heat Dissipation ◽  
High Conductivity ◽  
The Other ◽  
Multilayer Graphene ◽  
Optimum Level ◽  
Thermal Paste ◽  
Nano Additives ◽  
Thermal Pastes ◽  
Interface Materials

Abstract With increased focus on miniature high power density electronic packages, there is a need for the development of new interface materials with lower thermal resistance. To this end, high conductivity thermal paste or similar thermal interface materials (TIMs), reinforced with superior thermal conductivity materials such as multi-walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), graphite-derived multilayer graphene (g-MLG) offer an effective strategy to provide efficient paths for heat dissipation from heat source to heat sink. In an earlier paper, we had demonstrated that multilayer graphene derived from coal (coal-MLG) synthesized using our in-house developed one-pot process, has increased presence of phenolic groups on its surfaces, which translates into better dispersion of coal-MLG in silicone thermal paste. In this paper, we first compare the thermal conductance of a high conductivity thermal paste (k = 8.9 W/mK) using coal-MLG as an additive with that realized with other nano additives — MWCNTs, GNPs, and g-MLG. The data shows that coal-MLG as an additive outperforms all the other investigated nano additives in enhancing the thermal performance of the paste. With the coal-MLG as an additive, ∼70% increase in thermal performance was observed as compared to the base thermal paste used. This increase is about 2.5 times higher than that obtained using g-MLG as an additive. We also measured the thermal performance of coal-MLG-based TIM with its different wt.% fractions. The data confirmed our hypothesis that the optimum level of the loading fraction of the additive that can be dispersed in the matrix (paste in this case) before the onset of agglomeration is higher for the coal-MLG (3%) than for the other additives (2%). The implication is further improvement thermal performance with coal-MLG. The data shows the additional thermal enhancement to ∼2X. Finally, since coal-MLG produced by our in-house process is relatively cheaper and more environmentally friendly, we believe that these results would pave the path for enhanced thermal performance with non-silicone thermal pastes at a significantly lower cost. We also expect similar benefits for the silicone-based thermal pastes.

scholarly journals Optimized design of concrete-filled steel columns

2022 ◽  
Vol 15 (1) ◽  
Author(s):  
Jéssica Salomão Lourenção ◽  
Paulo Augusto Tonini Arpini ◽  
Gabriel Erlacher ◽  
Élcio Cassimiro Alves
Keyword(s):  
Genetic Algorithm ◽  
Cost Efficiency ◽  
Optimization Problem ◽  
Optimized Design ◽  
Composite Columns ◽  
Steel Columns ◽  
Normal Forces ◽  
Steel Bars ◽  
Genetic Algorithm Method ◽  
Filled Composite

Abstract The objective of this paper is to present the formulation of the optimization problem and its application to the design of concrete-filled composite columns with and without reinforcement steel bars, according to recommendations from NBR 8800:2008, NBR 16239:2013 and EN 1994-1-1:2004. A comparative analysis between the aforementioned standards is performed for various geometries considering cost, efficiency and materials in order to verify which parameters influence the solution of the composite column that satisfies the proposed problems. The solution of the optimization problem is obtained by using the genetic algorithm method featured in MATLAB’s guide toolbox. For the examples analyzed, results show that concretes with compressive strength greater than 50MPa directly influence the solution of the problem regarding cost and resistance to normal forces.

Abstract 14309: A Novel Fibroblast Activation Inhibitor, NM922, Attenuates Maladaptive Fibrotic Remodeling to Preserve Cardiac Function Following the Onset of Heart Failure

Circulation ◽  
2015 ◽  
Vol 132 (suppl_3) ◽  
Author(s):  
Jessica M Bradley ◽  
Craig M Ziblich ◽  
Kazi N Islam ◽  
Amanda M Rushing ◽  
David J Polhemus ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cardiac Function ◽  
Structural Changes ◽  
Volume Fraction ◽  
Left Ventricular ◽  
Normal Fibroblast ◽  
Wall Thickening ◽  
Cellular Mechanisms ◽  
Collagen Formation ◽  
Failing Heart

Background: Cardiac fibroblasts are critical mediators of fibrotic remodeling in the failing heart. These maladaptive structural changes can worsen cardiac function accelerating the progression to decompensated heart failure (HF). We investigated the effects of a novel inhibitor of the conversion of normal fibroblast to the myofibroblast phenotype in the setting of pressure overload induced HF. Methods: Male C57BL/6J mice (10 wks) were subjected to transverse aortic constriction (TAC; 27 g needle) and NM922 (NovoMedix, LLC50 mg/kg/d i.p.) or VEH (DMSO + HS-15) was administered daily starting at 6 wks post TAC. Echocardiography was assessed at baseline and for 16 wks post TAC. At the 16 wk endpoint, mice were sacrificed and hearts were collected for biochemical and molecular assessment. Results: NM922 significantly attenuated TAC-induced left ventricular (LV) dilation at 16 wks post TAC (LVEDD: 3.5 ± 0.1 vs. 4.5 ± 0.2 mm, p < 0.01; LVESD: 2.5 ± 0.2 vs. 3.8 ± 0.3 mm, p < 0.01) compared to VEH. NM922 treated mice displayed reduced wall thickening (LVPWd: 1.0 ± 0.03 vs. 1.2 ± 0.05 mm; p < 0.05) at 10 wks post TAC compared to VEH. LV ejection fraction (LVEF) was preserved in NM922 treated mice at 8-16 wks post TAC compared to VEH (*p < 0.05; **p < 0.001) compared to VEH. Treatment with NM922 resulted in reductions in heart (8.5 ± 0.5 vs. 12.0 ± 0.9 mg/mm; p < 0.01) and lung (8.2 ± 0.3 vs. 11.5 ± 0.6 mg/mm; p < 0.0001) weights compared to VEH. Picrosirius Red staining revealed that NM922 reduced cardiac interstitial collagen volume fraction by 50% (p < 0.05 vs. VEH). Circulating BNP levels trended toward lower (p = 0.08) in the NM922 mice when compared to VEH. Conclusion: Chronic treatment with NM922 following the onset of cardiac hypertrophy and HF resulted in attenuated myocardial collagen formation and adverse remodeling with preservation of LVEF. Future studies are aimed at further elucidation of the molecular and cellular mechanisms by which this novel agent protects the failing heart.

scholarly journals Structural Changes in a-Si:H Films Deposited on the Edge of Crystallinity

1999 ◽  
Vol 557 ◽  
Author(s):  
A.H. Mahan ◽  
J. Yang ◽  
S. Guha ◽  
D.L. Williamson
Keyword(s):  
Low Temperature ◽  
Glow Discharge ◽  
Structural Changes ◽  
Amorphous Matrix ◽  
Volume Fraction ◽  
Peak Frequency ◽  
X Ray Diffraction ◽  
X Ray

AbstractUsing infrared, H evolution and x-ray diffraction (XRD), the structure of high H dilution, glow discharge deposited a-Si:H films ‘on the edge of crystallinity’ is examined. From the Si-H wag mode peak frequency and the XRD results, we postulate the existence of very small Si crystallites contained within the as-grown amorphous matrix, with the vast majority of the bonded H located on these crystallite surfaces. Upon annealing at ramp rates of 8-15°C/min, a H evolution peak at ~400°C appears, and film crystallization is observed at temperatures as low as 500°C, both of which are far below those observed for a-Si:H films grown without H dilution using similar rates. While the crystallite volume fraction is too small to be detected by XRD in the as-grown films, these crystallites enable the crystallization of the remainder of the amorphous matrix upon moderate annealing, thus explaining the existence of the low temperature H evolution peak.

Hardness evolution of Al–Cr–N coatings under thermal load

2008 ◽  
Vol 23 (11) ◽  
pp. 2880-2885 ◽  
Author(s):  
Herbert Willmann ◽  
Paul H. Mayrhofer ◽  
Lars Hultman ◽  
Christian Mitterer
Keyword(s):  
Thermal Load ◽  
Structural Changes ◽  
Single Phase ◽  
Volume Fraction ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Al Content ◽  
Annealing Temperatures ◽  
Transmission Electron

Microstructure and hardness evolution of arc-evaporated single-phase cubic Al0.56Cr0.44N and Al0.68Cr0.32N coatings have been investigated after thermal treatment in Ar atmosphere. Based on a combination of differential scanning calorimetry and x-ray diffraction studies, we can conclude that Al0.56Cr0.44N undergoes only small structural changes without any decomposition for annealing temperatures Ta ⩽ 900 °C. Consequently, the hardness decreases only marginally from the as-deposited value of 30.0 ± 1.1 GPa to 29.4 ± 0.9 GPa with Ta increasing to 900 °C, respectively. The film with higher Al content (Al0.68Cr0.32N) exhibits formation of hexagonal (h) AlN at Ta ⩾ 700 °C, which occurs preferably at grain boundaries as identified by analytical transmission electron microscopy. Hence, the hardness increases from the as-deposited value of 30.1 ± 1.3 GPa to 31.6 ± 1.4 GPa with Ta = 725 °C. At higher temperatures, where the size and volume fraction of the h-AlN phase increases, the hardness decreases to 27.5 ± 1.0 GPa with Ta = 900 °C.

Soft composite based hyperelastic model for anisotropic tissue characterization

2020 ◽  
Vol 54 (28) ◽  
pp. 4525-4534 ◽  
Author(s):  
Arnab Chanda ◽  
Subhodip Chatterjee ◽  
Vivek Gupta
Keyword(s):  
Fiber Orientation ◽  
Strain Energy ◽  
Soft Tissues ◽  
Volume Fraction ◽  
Deformation Gradient ◽  
Model Parameters ◽  
Hyperelastic Model ◽  
Fiber Matrix ◽  
Soft Composite

Soft tissues are complex anisotropic composite systems comprising of multiple differently oriented layers of fiber embedded within a soft matrix. To date, soft tissues have been mainly characterized using simplified linear elastic material models, isotropic viscoelastic and hyperelastic models, and transversely isotropic models. In such models, the effect of fiber volume fraction (FVF), fiber orientation, and fiber-matrix interactions are missing, inhibiting accurate characterization of anisotropic tissue properties. The current work addresses this literature gap with the development of a novel soft composite based material framework to model tissue anisotropy. In this model, the fiber and matrix are considered as separate hyperelastic materials, and fiber-matrix interaction is modeled using multiplicative decomposition of the deformation gradient. The effect of the individual contribution of the fibers and matrix are introduced into the numerical framework for a single soft composite layer, and fiber orientation effects are incorporated into the strain energy functions. Also, strain energy formulations are developed for multiple soft composite layers with varying fiber orientations and contributions, describing the biomechanical behavior of an entire anisotropic tissue block. Stress-strain relationships were derived from the strain energy equations for a uniaxial mechanical test condition. To validate the model parameters, experimental models of soft composites tested under uniaxial tension were characterized using the novel anisotropic hyperelastic model (R2 = 0.983). To date, such a robust anisotropic hyperelastic composite framework has not been developed, which would be indispensable for experimental characterization of tissues and for improving the fidelity of computational biological models in future.

scholarly journals STEREOLOGICAL EVALUATION OF BRAIN MAGNETIC RESONANCE IMAGES OF SCHIZOPHRENIC PATIENTS

2013 ◽  
Vol 32 (3) ◽  
pp. 145
Author(s):  
Amani Abdelrazag Elfaki ◽  
Abdelrazag Elfaki ◽  
Tahir Osman ◽  
Bunyamin Sahin ◽  
Abdelgani Elsheikh ◽  
...  
Keyword(s):  
White Matter ◽  
Magnetic Resonance ◽  
Structural Changes ◽  
Volume Fraction ◽  
Brain Structures ◽  
Magnetic Resonance Images ◽  
Brain Images ◽  
Schizophrenic Patients ◽  
The Mean ◽  
Mr Brain

Advances in neuroimaging have enabled studies of specific neuroanatomical abnormalities with relevance to schizophrenia. This study quantified structural alterations on brain magnetic resonance (MR) images of patients with schizophrenia. MR brain imaging was done on 88 control and 57 schizophrenic subjects and Dicom images were analyzed with ImageJ software. The brain volume was estimated with the planimetric stereological technique. The volume fraction of brain structures was also estimated. The results showed that, the mean volume of right, left, and total hemispheres in controls were 551, 550, and 1101 cm³, respectively. The mean volumes of right, left, and total hemispheres in schizophrenics were 513, 512, and 1026 cm³, respectively. The schizophrenics’ brains were smaller than the controls (p < 0.05). The mean volume of total white matter of controls (516 cm³) was bigger than the schizophrenics’ volume (451 cm³), (p < 0.05). The volume fraction of total white matter was also lower in schizophrenics (p < 0.05). Volume fraction of the lateral ventricles was higher in schizophrenics (p < 0.05). According to the findings, the volumes of schizophrenics’ brain were smaller than the controls and the volume fractional changes in schizophrenics showed sex dependent differences. We conclude that stereological analysis of MR brain images is useful for quantifying schizophrenia related structural changes.

Biodegradable polyhydroxybutyrate as a polyol for elastomeric polyurethanes

2012 ◽  
Vol 66 (9) ◽  
Author(s):  
Lucy Vojtová ◽  
Vojtěch Kupka ◽  
Jan Žídek ◽  
Jaromír Wasserbauer ◽  
Petr Sedláček ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Volume Fraction ◽  
Stress Strain ◽  
Strain Behavior ◽  
Feed Stock ◽  
Measured Stress ◽  
Strain Data ◽  
Polyether Polyol ◽  
Filled Composite

AbstractIn the proposed work, new elastomeric bio-polyol based polyurethanes (bio-PUs) with specific mechanical properties were prepared by a one-shot process without the presence of a solvent. Commercial non-degradable polyether polyol derived from petrochemical feed stock was partly (in the amount of 1 mass %, 5 mass %, and 10 mass %) substituted by the biodegradable polyhydroxybutyrate (PHB). Morphology of elastomeric PU composites was evaluated by scanning electron microscopy and mechanical properties of the prepared samples were obtained by both tensile measurements and prediction via the Mooney-Rivlin equation. Electron microscopy proved that the prepared materials have the character of a particle filled composite material, where PHB particles are regular with their size of about 1–2 μm in diameter. Tensile measurements demonstrated that the Young’s modulus, tensile stress at break, and tensile strain at break of each sample increase with the increase of the volume fraction of the filler. From the measured stress-strain data, the first and the second term of the Mooney-Rivlin equation were calculated. The obtained constants were applied to recalculate the stress-strain curves. It was found that the Mooney-Rivlin equation corresponds well with the stress-strain behavior of the prepared specimens.

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