The effect of the pore structure of hardened cement paste on the properties of high strength concretes

Bu çalışmada aynı Portland çimentosu ve aynı agregalar kullanılarak 4 değişik granülometri ve 5 değişik su/çimento oranında olmak üzere 20 değişik beton karışımı hazırlandı. Beton agregasının karışımında en büyük tane boyutu 16 mm’de sabit tutuldu ve karışım oranları A16-B16, B16, B16-C16 ve C16 ISO referans eğrilerine uygun olacak şekilde seçildi. Su/çimento oranları 0.26 ile 0.42 arasında ve 0.04 artımlara karşılık gelecek biçimde belirlendi. Sertleşmiş beton numuneleri üzerinde mekanik deneyler 7., 14., 28. ve 365. günlerde yapıldı. Deney sonuçları, yüksek dayanımlı betonların dayanımlarının tahmininde çimento hamurunun boşluk yapısına duyarlılıklarını gözönüne almanın normal dayanımlılarınkine göre daha büyük yarar sağlayacağını gösterdi.Anahtar Kelimeler: Duyarlı özelik, sertleşmiş çimento hamuru, su/çimento oranı.In this work, 20 mixes were prepared using the same Portland cement and the same aggregates. In the mixes, the following four different grading curves were used: A16-B16, B16, B16-C16, and C16, known as ISO reference curves. The maximum particle size of concrete aggregate was kept constant at 16 mm. Five different water/cement ratios were used from 0.26 to 0.42, in steps of 0.04. The mechanical tests on the hardened concretes were done at the following ages: 7, 14, 28, and 365 days. At these ages, the hydration degrees were also measured in the hardened cement paste specimens with the same water/cement ratios used for concrete mixes. Experimental results have shown that taking into account the sensitivities to the pore structure of the hardened cement paste provides more benefits in the strength prediction of high strength concretes than those of normal strength concretes. The compressive and tensile strengths could be adequately explained by a variable such as . The energy absorption capacities in compression were determined by calculating the area under the stress-strain curve up to peak stress. It is observed that, as the compressive strength of concrete increases the relative adsorbed energy up to peak stress decreases significantly.Keywords: Hardened cement paste, hydration degree, sensitive property, water - cement ratio.

3D Printed Polycaprolactone/Gelatin/Bacterial Cellulose/Hydroxyapatite Composite Scaffold for Bone Tissue Engineering

Three-dimensional (3D) printing application is a promising method for bone tissue engineering. For enhanced bone tissue regeneration, it is essential to have printable composite materials with appealing properties such as construct porous, mechanical strength, thermal properties, controlled degradation rates, and the presence of bioactive materials. In this study, polycaprolactone (PCL), gelatin (GEL), bacterial cellulose (BC), and different hydroxyapatite (HA) concentrations were used to fabricate a novel PCL/GEL/BC/HA composite scaffold using 3D printing method for bone tissue engineering applications. Pore structure, mechanical, thermal, and chemical analyses were evaluated. 3D scaffolds with an ideal pore size (~300 µm) for use in bone tissue engineering were generated. The addition of both bacterial cellulose (BC) and hydroxyapatite (HA) into PCL/GEL scaffold increased cell proliferation and attachment. PCL/GEL/BC/HA composite scaffolds provide a potential for bone tissue engineering applications

3D printed Artificial Cornea for Corneal Stromal Transplantation

The aim of this study is to understand the optical, biocompatible, and mechanical properties of chitosan (CS) and polyvinyl-alcohol (PVA) based corneal stroma constructs using 3D printing process. Corneal stroma is tested for biocompatibility with human adipose tissue-derived mesenchymal stem cells (hASCs). Physico-chemical and chemical characterization of the construct was performed using scanning electron microscopy (SEM), fourier transforms infrared spectroscopy (FTIR). Optical transmittance was analyzed using UV-Spectrophotometer. Results showed fabricated constructs have required shape and size. SEM images showed construct has thickness of 400 µm. The FTIR spectra demonstrated the presence of various predicted peaks. The swelling and degradation studies of 13%(wt)PVA and 13%(wt)PVA/(1, 3, 5)%(wt)CS showed to have high swelling ratios of 7 days and degradation times of 30 days, respectively. The light transmittance values of the fabricated cornea constructs decreased with CS addition slightly. Tensile strength values decreased with increasing CS ratio, but we found to support intraocular pressure (IOP) which ranges from 12 to 22 mm-Hg. Preliminary biostability studies showed that composite constructs were compatible with hASCs even after 30 days’ of degradation, showing potential for these cells to be differentiated to stroma layer in future. This study has implications for the rapid and custom fabrication of various cornea constructs for clinical applications

What went wrong? The flawed concept of cerebrospinal venous insufficiency

In 2006, Zamboni reintroduced the concept that chronic impaired venous outflow of the central nervous system is associated with multiple sclerosis (MS), coining the term of chronic cerebrospinal venous insufficiency ('CCSVI'). The diagnosis of 'CCSVI' is based on sonographic criteria, which he found exclusively fulfilled in MS. The concept proposes that chronic venous outflow failure is associated with venous reflux and congestion and leads to iron deposition, thereby inducing neuroinflammation and degeneration. The revival of this concept has generated major interest in media and patient groups, mainly driven by the hope that endovascular treatment of 'CCSVI' could alleviate MS. Many investigators tried to replicate Zamboni's results with duplex sonography, magnetic resonance imaging, and catheter angiography. The data obtained here do generally not support the 'CCSVI' concept. Moreover, there are no methodologically adequate studies to prove or disprove beneficial effects of endovascular treatment in MS. This review not only gives a comprehensive overview of the methodological flaws and pathophysiologic implausibility of the 'CCSVI' concept, but also summarizes the multimodality diagnostic validation studies and open-label trials of endovascular treatment. In our view, there is currently no basis to diagnose or treat 'CCSVI' in the care of MS patients, outside of the setting of scientific research

The efficiency of US elastography in the differential diagnosis of thyroid nodules

Aim: To evaluate the efficiency of ultrasound elastography (USE) in the differential diagnosis of thyroid nodules. Methods: One hundred thyroid nodules in 100 patients (79 females, 21 males, age range 18-78; mean age = 45.6 years) were evaluated with real-time freehand USE, using Hitachi EUB 7500 equipment and elasticity scores were obtained. The elasticity was scored as follows: Score 1, elasticity in the entire nodule; Score 2, mainly elastic nodule with the presence of inelastic areas not constant during real time examination; Score 3, constant inelastic areas prevalently arranged at the periphery of the nodule; Score 4, constant inelastic areas prevalently arranged at the center of the nodule; Score 5, no elasticity in the nodule. Also mean strain ratio values were calculated for all nodules. Results: Eighty-four (86%) of cases were benign and sixteen (16%) were malignant. Elasticity score 3 and higher and strain ratio higher than 2.485 had statistically significant relation with malignancy (p < 0.05). Conclusions: USE including strain ratio calculations besides subjective evaluation of elasticity scores is an efficient imaging method which may contribute to the differential diagnosis of thyroid nodules

Calcium phosphate formation from sea urchin - (brissus latecarinatus) via modified mechano-chemical (ultrasonic) conversion method

This study aims to produce apatite structures, such as hydroxyapatite (HA) and fluorapatite (FA), from precursor calcium phosphates of biological origin, namely from sea urchin, with mechano-chemical stirring and hot-plating conversion method. The produced materials were heat treated at 800 °C for 4 hours. X-ray diffraction and scanning electron microscopy (SEM) studies were conducted. Calcium phosphate phases were developed. The SEM images showed the formation of micro to nano-powders. The experimental results suggest that sea urchin, Brissus latecarinatus skeleton could be an alternative source for the production of various mono or biphasic calcium phosphates with simple and economic mechano-chemical (ultrasonic) conversion method

Attachment and Proliferation of Osteoblasts on Lithium-Hydroxyapatite Composites

The biocompatibility and bioactivity properties of hydroxyapatites (HAs) modified through lithium addition were investigated. Hydroxyapatites obtained from bovine bone were mixed with lithium carbonate (Li), in the proportions of 0.25, 0.50, 1.00, and 2.00% wt, and sintered at 900°, 1000°, 1100°, 1200°, and 1300°C, creating LiHA samples. The osteoblast culture behavior was assessed in the presence of these LiHA compositions. The cellular interactions were analyzed by evaluating the viability and cellular proliferation, ALP production and collagen secretion. The cytotoxic potential was investigated through measurement of apoptosis and necrosis induction. The process of cellular attachment in the presence of the product of dissolution of LiHA, was evaluated trough fluorescence analysis. The physical characteristics of these materials and their cellular interactions were examined with SEM and EDS. The results of this study indicate that the LiHA ceramics are biocompatible and have variable bioactivities, which can be tailored by different combinations of the concentration of lithium carbonate and the sintering temperature. Our findings suggest that LiHA 0.25% wt, sintered at 1300°C, combines the necessary physical and structural qualities with favorable biocompatibility characteristics, achieving a bioactivity that seems to be adequate for use as a bone implant material

A gastrointestinal stromal tumor with mesenteric and retroperitoneal invasion

<p>Abstract</p> <p>Background</p> <p>Gastrointestinal stromal tumors are rare visceral sarcomas arising in the gastrointestinal tract wall. In this report we present a case of gastrointestinal stromal tumors with mesenteric and retroperitoneal invasion, describe and discuss its computed tomography findings.</p> <p>Case presentation</p> <p>A 57-years-old male patient has been complaining of abdominal distention, weight lose, and hematuria. During physical examination, significant distention and multiple palpable tumor masses were identified on the abdomen. Abdominal computed tomography showed multiple, well-defined, soft tissue masses with homogenous and heterogeneous pattern, in the mesenteric and retroperitoneal areas. Unlike specific features of gastrointestinal stromal tumor, renal obstruction and atypical central calcification without chemotherapy that has not been yet described were seen in this case. Computed tomography did not reveal liver metastases and/or the lymph nodes with pathological size. Ultrasonography-guided true-cut^®biopsy was made, histopathologic and immunohistochemical analyses demonstrated stromal tumor which, C-KIT (+). The patient underwent left ureterectomy, left nephrectomy and total colectomy. Postoperative histopathological analyses revealed lower grade malignant GISTs. As of 17 months after the surgery, he is alive and free of recurrence.</p> <p>Conclusion</p> <p>When intraabdominal, multiple, large (>5 cm), well-circumscribed, homogenous or heterogeneous mass lesions without ascites, omental caking and lymph nodes metasteses were seen, gastrointestinal stromal tumors should be considered in the differential diagnosis.</p

Getting aligned on representational alignment

Biological and artificial information processing systems form representations that they can use to categorize, reason, plan, navigate, and make decisions. How can we measure the extent to which the representations formed by these diverse systems agree? Do similarities in representations then translate into similar behavior? How can a system's representations be modified to better match those of another system? These questions pertaining to the study of representational alignment are at the heart of some of the most active research areas in cognitive science, neuroscience, and machine learning. For example, cognitive scientists measure the representational alignment of multiple individuals to identify shared cognitive priors, neuroscientists align fMRI responses from multiple individuals into a shared representational space for group-level analyses, and ML researchers distill knowledge from teacher models into student models by increasing their alignment. Unfortunately, there is limited knowledge transfer between research communities interested in representational alignment, so progress in one field often ends up being rediscovered independently in another. Thus, greater cross-field communication would be advantageous. To improve communication between these fields, we propose a unifying framework that can serve as a common language between researchers studying representational alignment. We survey the literature from all three fields and demonstrate how prior work fits into this framework. Finally, we lay out open problems in representational alignment where progress can benefit all three of these fields. We hope that our work can catalyze cross-disciplinary collaboration and accelerate progress for all communities studying and developing information processing systems. We note that this is a working paper and encourage readers to reach out with their suggestions for future revisions.Comment: Working paper, changes to be made in upcoming revision