Sinteran hidroksiapatit dalam atmosfera nitrogen untuk peningkatan sifat mikrokekerasan

Hidroksiapatit (HA) adalah sejenis kalsium fosfat yang merupakan komposisi kepada kebanyakan fasa mineral tulang dan enamel gigi. HA bersifat bioserasi dan berkonduksi osteo selain mempunyai afiniti biologi dan kimia yang bagus untuk tisu tulang. Dengan ciri tersebut, HA diguna secara luas sebagai graf tulang dan bahan salut bagi implan tisu keras manusia. Walau bagaimanapun, kerapuhan dan keliatan patah yang rendah HA tersinter menghadkan penggunaannya dalam aplikasi bebanan yang tinggi. Kajian ini tertumpu kepada mengenal pasti kesan atmosfera sinteran dengan gas nitrogen (N2) ke atas sifat mekanik HA untuk aplikasi pergigian. Serbuk nano HA dicirikan dengan menggunakan mikroskop elektron pancaran. Cakera silinder HA dihasilkan dengan kaedah penekanan ekapaksi. Kemudian, cakera silinder HA dikenakan tekanan isostatik sejuk dan disinter dalam dua atmosfera sinteran yang berbeza iaitu sinteran dalam gas N2 dan sinteran dalam udara pada suhu 1300°C. Ketumpatan, mikrostruktur, kestabilan fasa dan mikrokekerasan HA tersinter dicirikan. Secara keseluruhan, sinteran dengan menggunakan gas N2 menyebabkan pertumbuhan saiz butiran yang lebih besar dengan ketumpatan relatif dan mikrokekerasan yang lebih tinggi jika dibandingkan dengan atmosfera sinteran dalam udara. Dalam kajian ini, HA yang disinter dengan menggunakan gas N2 pada suhu 1300°C menunjukkan mikrostruktur yang lebih tumpat, ketumpatan relatif (94%) dan mikrokekerasan (4.07 GPa) yang lebih tinggi jika berbanding dengan sinteran dalam udara tanpa penguraian HA. Kesimpulannya, penggunaan atmosfera sinteran dengan menggunakan gas N2 pada suhu 1300°C dapat meningkatkan sifat kekerasan Vickers nanokomposit HA dengan mikrostruktur yang padat

Bump Energy for Durability Prediction of Coil Spring Based on Local Regularity Analysis

This paper aims to study the identification of bumps in vibrational signals and develop bump-energy-based durability predictive models for a suspension coil spring. The bump energy of the loading signal is affected by high frequency noises and can lead to inaccurate results. Therefore, it is necessary to eliminate high frequency noise during bump identification. Local regularity analysis was employed to determine the singular points in road signals. Bump signals were then reconstructed from these singular points. Subsequently, bump-energy-based models were developed by correlating with the fatigue lives estimated using the Coffin–Manson, Morrow and Smith–Watson–Topper strain-life models. The results show that the bump signals extracted from the road excitations had a frequency band within 0–50 Hz, indicating that the high frequency noises had been successfully removed during extraction of the bumps. The bump-energy-based models predicted a fatigue life ranging from 3.98x104 to 4x109 cycles within a 95% confidence interval, where the Coffin–Manson-based model showed the highest fatigue life. This is because the Coffin–Manson model did not consider the mean stress effects. When compared with the experimental results, the Coffin–Manson-based model indicates the highest accuracy, given its highest R2 of 0.948. The bump-energy-based models developed in this study contributed an accurate durability prediction of coil springs

Identification of Gene Networks and Pathways Associated with Guillain-Barré Syndrome

BACKGROUND: The underlying change of gene network expression of Guillain-Barré syndrome (GBS) remains elusive. We sought to identify GBS-associated gene networks and signaling pathways by analyzing the transcriptional profile of leukocytes in the patients with GBS. METHODS AND FINDINGS: Quantitative global gene expression microarray analysis of peripheral blood leukocytes was performed on 7 patients with GBS and 7 healthy controls. Gene expression profiles were compared between patients and controls after standardization. The set of genes that significantly correlated with GBS was further analyzed by Ingenuity Pathways Analyses. 256 genes and 18 gene networks were significantly associated with GBS (fold change ≥2, P<0.05). FOS, PTGS2, HMGB2 and MMP9 are the top four of 246 significantly up-regulated genes. The most significant disease and altered biological function genes associated with GBS were those involved in inflammatory response, infectious disease, and respiratory disease. Cell death, cellular development and cellular movement were the top significant molecular and cellular functions involved in GBS. Hematological system development and function, immune cell trafficking and organismal survival were the most significant GBS-associated function in physiological development and system category. Several hub genes, such as MMP9, PTGS2 and CREB1 were identified in the associated gene networks. Canonical pathway analysis showed that GnRH, corticotrophin-releasing hormone and ERK/MAPK signaling were the most significant pathways in the up-regulated gene set in GBS. CONCLUSIONS: This study reveals the gene networks and canonical pathways associated with GBS. These data provide not only networks between the genes for understanding the pathogenic properties of GBS but also map significant pathways for the future development of novel therapeutic strategies

Improvement of colloidal stability in colloidal processing for highly translucent, nanosized zirconia

This study aimed to improve the colloidal stability of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) suspension through colloidal processing to obtain highly translucent Y-TZP. Agglomeration is often the main complication in the processing of nanosized Y-TZP as it deteriorates mechanical and optical properties. Thus, colloidal processing is necessary to mitigate the agglomeration in Y-TZP. The colloidal stability of Y-TZP suspension plays a key role for the success of colloidal processing. In this study, colloidal processing was conducted at several stages, namely, dispersant addition, pH adjustment and sedimentation. Changes in particle size and zeta potential at various stages were recorded. The suspensions were then slip-casted to form green bodies. Green bodies were sintered and characterized for density and translucency. The results showed that dispersant addition followed by pH adjustment effectively dispersed soft agglomerates by introducing electrosteric stabilization, whereas sedimentation successfully segregated hard agglomerates and contributed excellent colloidal stability. With high colloidal stability, the translucency of Y-TZP was improved by approximately 30%. This study demonstrated different colloidal processing stages and proved that high colloidal stability and fine particle size are vital to produce highly translucent Y-TZP