Çoklu Civatalıbağlantıların Kesme Ve Eğme Yükleri Altında İncelenmesi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Bu çalışmada, çoklu cıvatalı bağlantıların kesme ve eğme yükleri altındaki davranışları incelenmiştir. Bu amaçla, 6 cıvatalı simetrik bir bağlantı ele alınmış, kesme ve eğme yüklerine maruz bırakılmıştır. Bilinen denge denklemleri ve sonlu elemanlar metodu kullanılarak iki farklı çözüm yapılmıştır. Yapılan analitik çözümlerde cıvataların sıktığı elemanlar rijit varsayılmış ve cıvata deformasyonlarına etkisi sıfır kabul edilmiştir. Sonlu elemanlar çözümlerinde ise iki farklı çözüm yapılmıştır. Birincisinde analitik çözümlerde olduğu gibi cıvataların sıktığı tüm elemanlar rijit kabul edilmiş ve analitik çözümlerle uyumuna bakılmıştır. İkinci çözümde ise cıvatalar ve bağlanan elemanlar elastik kabul edilmiş ve önceki çözümlerle farkları araştırılmıştır. Böylece analitik çözümlerdeki rijit varsayımının sonuçlar üzerindeki etkisi gösterilmiştir. Sonlu elemanlar çözümlerinde ayrıca bağlantılardaki önyükleme etkisi araştırılmıştır.In this study, bolted joints are analysed under the action of shear and bending forces. For this aim, a symmetric bolted joint including six bolts is loaded by shear and bending forces. It is solved by using well-known equilibrium equations and finite element method. In the analytical solution, the members are assumed as rigid and their effects in bolt deformations are assumed to be zero. In the finite element solutions, two different solutions have been carried out. In the first one, the members are assumed rigid as in the analytical solution. The results are compared with the results obtained from analytical solution. In the second solution, connected members are considered as elastic. The results are again compared with previous results. The preload effect has also been investigated in the finite element solutions

Comparison of soybean evapotranspirations measured by weighing lysimeter and Bowen ratio-energy balance methods

Lysimeters are considered the standard for evapotranspiration (ET) measurements. However, these units are often not replicated and are few in number at any given location. The Bowen ratio-energy balance (BREB) is a micrometeorological method often used to estimate ET because of its simplicity, robustness, and cost. In this paper, ET of irrigated soybean (Glycine max L.) was directly measured by weighing lysimeter and estimated by BREB method over a growing season in a semi-arid climate of eastern Mediterranean region. The study was conducted in Adana-Turkey du ring the summer of 2009 on a 0.12 ha area with a weighing lysimeter (2.0 × 2.0 × 2.5 m) located in the center of the field completely covered by well watered soybean where the prevailing direction of the wind and the upwind fetch was about 60 m. Cumulative evapotranspiration totals from the lysimeter and BREB methods were 354 and 405 mm, respectively. The BREB method showed a good performance for daily ET estimation when compared to values measured by lysimeter. This method, with a root mean square error (RMSE) of 0.79 mmd-1 and a 0.96 index of agreement, over-estimates lysimetric measurements by 15%. TheBREB method also performs well compared with lysimetric measurements for hourly ET, but produces overestimation of 14% with RMSE of 0.128 mmh-1, and a 0.92 index of agreement

İnce Kirişlerin Elastik Davranışlarının NIY ve RNIY Yöntemleri İle İncelemesi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2013Bu çalışmada, ince kirişlerin elastik davranışlarının incelenmesi, ağsız yöntemlerden olan Noktasal İnterpolasyon (NİY) ve Radyal Noktasal İnterpolasyon (RNİY) yöntemleri ile gerçekleştirilmiştir. Her bir yöntemde, iki farklı integrasyon tekniği kullanılmıştır. Standard olarak kullanılan Gauss integrasyon tekniği, Taylor noktasal integrasyon tekniği ile karşılaştırılmış, NİY ve RNİY üzerine etkileri araştırılmıştır. Noktasal direngenlik matrisinin elde edilmesi, Bernoulli-Euler kiriş teorisine göre gerçekleştirilmiştir. Farklı etki alanı büyüklükleri ve farklı RNİY şekil parametrelerinin çözümler üzerine etkileri ayrıca ele alınmıştır. Bir ankastre kiriş problemi, serbest uca tekil yük uygulanarak çözülmüştür. Elde edilen çözümler, ANSYS paket programı kullanılarak sonlu elemanlar yöntemiyle kıyaslanmıştır.In this study, the point interpolation method (PIM) and radial point interpolation method (RPIM) solutions of elastic thin beams are compared by using standard Gaussian integration and a nodal integration based on Taylor series expansion. The effects of integration schemes, support domain sizes and RPIM shape parameters on the convergency are also investigated. Nodal stiffness matrices are obtained using Bernoulli-Euler beam theory. A cantilever beam problem with concentrated load applied on one end is solved and the results are compared with finite element solutions in ANSYS

Visual Function and Brief Cognitive Assessment for Multiple Sclerosis (BICAMS) in Optic Neuritis Clinically Isolated Syndrome Patients

BACKGROUND: In this study, we hypothesized that clinically isolated syndrome–optic neuritis patients may have disturbances in neuropsychological functions related to visual processes. METHODS: Forty-two patients with optic neuritis within 3 months from onset and 13 healthy controls were assessed at baseline and 6 months with MRI (brain volumes, lesion load, and optic radiation lesion volume) and optical coherence tomography (OCT) (peripapillary retinal nerve fiber layer [RNFL], ganglion cell and inner plexiform layers [GCIPLs], and inner nuclear layer). Patients underwent the brief cognitive assessment for multiple sclerosis, high-contrast and low-contrast letter acuity, and color vision. RESULTS: At baseline, patients had impaired visual function, had GCIPL thinning in both eyes, and performed below the normative average in the visual-related tests: Symbol Digit Modalities Test and Brief Visuospatial Memory Test-Revised (BVMT-R). Over time, improvement in visual function in the affected eye was predicted by baseline GCIPL (P = 0.015), RNFL decreased, and the BVMT-R improved (P = 0.001). Improvement in BVMT-R was associated with improvement in the high-contrast letter acuity of the affected eye (P = 0.03), independently of OCT and MRI metrics. CONCLUSION: Cognitive testing, assessed binocularly, of visuospatial processing is affected after unilateral optic neuritis and improves over time with visual recovery. This is not related to structural markers of the visual or central nervous system

Non-parametric combination of multimodal MRI for lesion detection in focal epilepsy

One third of patients with medically refractory focal epilepsy have normal-appearing MRI scans. This poses a problem as identification of the epileptogenic region is required for surgical treatment. This study performs a multimodal voxel-based analysis (VBA) to identify brain abnormalities in MRI-negative focal epilepsy. Data was collected from 69 focal epilepsy patients (42 with discrete lesions on MRI scans, 27 with no visible findings on scans), and 62 healthy controls. MR images comprised T1-weighted, fluid-attenuated inversion recovery (FLAIR), fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor imaging, and neurite density index (NDI) from neurite orientation dispersion and density imaging. These multimodal images were coregistered to T1-weighted scans, normalized to a standard space, and smoothed with 8 mm FWHM. Initial analysis performed voxel-wise one-tailed t-tests separately on grey matter concentration (GMC), FLAIR, FA, MD, and NDI, comparing patients with epilepsy to controls. A multimodal non-parametric combination (NPC) analysis was also performed simultaneously on FLAIR, FA, MD, and NDI. Resulting p-maps were family-wise error rate corrected, threshold-free cluster enhanced, and thresholded at p < 0.05. Sensitivity was established through visual comparison of results to manually drawn lesion masks or seizure onset zone (SOZ) from stereoelectroencephalography. A leave-one-out cross-validation with the same analysis protocols was performed on controls to determine specificity. NDI was the best performing individual modality, detecting focal abnormalities in 38% of patients with normal MRI and conclusive SOZ. GMC demonstrated the lowest sensitivity at 19%. NPC provided superior performance to univariate analyses with 50% sensitivity. Specificity in controls ranged between 96 and 100% for all analyses. This study demonstrated the utility of a multimodal VBA utilizing NPC for detecting epileptogenic lesions in MRI-negative focal epilepsy. Future work will apply this approach to datasets from other centres and will experiment with different combinations of MR sequences

Design of Polyamine-Grafted Starches for Nucleotide Analogue Delivery: In Vitro Evaluation of the Anticancer Activity

Nucleotide analogues are a therapeutic class that is very promising and currently used in clinics, notably against viral infectious diseases and cancer. However, their therapeutic potential is often restricted by a poor stability in vivo, the induction of severe side effects, and limited passive intracellular diffusion due to their hydrophilicity. Polysaccharide-based polymers (e.g., starch) have considerable advantages, including a lack of toxicity and the absence of antigenicity. The aim of this study was to develop new cationic starches able to form complexes with nucleotide analogues, thus protecting them and increasing their cell uptake. At the same time, the material should demonstrate good biocompatibility and low cytotoxicity. Different polyamines, (TREN, TEPA, and spermine) were grafted to starch to evaluate the impact of side-chain properties. The resulting cationic starch derivatives were characterized (e.g., degree of modification) and compared in their ability to form polyplexes with ATP as a model nucleotide. Among the tested candidates, the formulation of starch–TEPA and ATP with an N/P ratio of 2 led to nanoparticles with a size of 429 nm, a PdI of 0.054, and a ζ potential of −9 mV. MTT and LDH assays on A549 cell line showed low toxicity for this polymer. Confocal microscopy study proved that the cell internalization was an incubation-time- and energy-dependent process. Most important, starch–TEPA complexed with ddGTP showed significant biological activity on A549 cancer cells compared to that of plain ddGTP at the same concentration

Design of polyamines-grafted starches for nucleotide analogues delivery: in vitro evaluation of the anticancer activity

Nucleotide analogues are a therapeutic class really promising and currently used in clinic notably against viral infectious diseases and cancer. However, their therapeutic potential is often restricted by a poor stability in vivo, the induction of severe side effects and a limited passive intracellular diffusion due to their hydrophilicity. Polysaccharide-based polymers (e. g. starch) have considerable advantages including a lack of toxicity and absence of antigenicity. The aim of this study was to develop new cationic starches able to form complexes with nucleotide analogues: to protect them and increase their cell uptake. The material should demonstrate good biocompatibility and low cytotoxicity. Different oligoamines, (TREN, TEPA and spermine) were covalently grafted to starch: the resulting cationic starch derivatives were characterized (e.g. degree of modification) and compared in their properties to form polyplexes with ATP as a model nucleotide. Among the tested candidates, the formulation of starch-TEPA and ATP with a N/P ratio = 2 led to nanoparticles with a size of 429 nm, a PdI of 0.054 and a zeta potential of -9 mV. MTT and LDH assays on A549 cell line showed a low toxicity of this cationic starch. Confocal microscopy studies proved that the cell internalization was an incubation time and energy dependent process. Most important, starch-TEPA complexes with ddGTP (0.3 mg/mL) showed a significant biological activity on A549 cancer cells (&gt; 90 %) compared to plain ddGTP (~ 21 %) at the same concentration, revealing a real promising system to deliver intracellularly nucleotide analogues

A deep learning network from downsampled diffusion-weighted MRI k-space to image-space

Advanced Magnetic Resonance Imaging (MRI) techniques, such as Diffusion Weighed Imaging, usually require long acquisition times and an open challenge is to reduce the acquisition time more and more in order to allow their use in the clinical routine. Downsampling k-space is a way to speed up MRI, but this can generate artefacts in the resulting images when reconstructing them with standard Fourier transform methods. Here, we used deep learning to perform the inverse Fourier transform from k-space to the Diffusion Weighted (DW) images. and used it to assess the quality of images obtained from significantly reduced k-space acquisition strategies. The hypothesis is that a deep learning algorithm would preserve data quality, learned from the fully sampled k-space association. We tested our deep learning algorithm by reducing the number of acquired k-space rows by 30%, which would correspond to a total acquisition time reduction. We considered different types of k-space downsampling. All the trained networks were able to map the relationship between k-space and DW images, reducing artefacts. In conclusion, this work paves the way to designing acquisition strategies for fast diffusion imaging

Whole-brain diffusion tensor imaging predicts 6-month functional outcome in acute intracerebral haemorrhage

Introduction: Small vessel disease (SVD) causes most spontaneous intracerebral haemorrhage (ICH) and is associated with widespread microstructural brain tissue disruption, which can be quantified via diffusion tensor imaging (DTI) metrics: mean diffusivity (MD) and fractional anisotropy (FA). Little is known about the impact of whole-brain microstructural alterations after SVD-related ICH. We aimed to investigate: (1) association between whole-brain DTI metrics and functional outcome after ICH; and (2) predictive ability of these metrics compared to the pre-existing ICH score. Methods: Sixty-eight patients (38.2% lobar) were retrospectively included. We assessed whole-brain DTI metrics (obtained within 5 days after ICH) in cortical and deep grey matter and white matter. We used univariable logistic regression to assess the associations between DTI and clinical-radiological variables and poor outcome (modified Rankin Scale > 2). We determined the optimal predictive variables (via LASSO estimation) in: model 1 (DTI variables only), model 2 (DTI plus non-DTI variables), model 3 (DTI plus ICH score). Optimism-adjusted C-statistics were calculated for each model and compared (likelihood ratio test) against the ICH score. Results: Deep grey matter MD (OR 1.04 [95% CI 1.01–1.07], p = 0.010) and white matter MD (OR 1.11 [95% CI 1.01–1.23], p = 0.044) were associated (univariate analysis) with poor outcome. Discrimination values for model 1 (0.67 [95% CI 0.52–0.83]), model 2 (0.71 [95% CI 0.57–0.85) and model 3 (0.66 [95% CI 0.52–0.82]) were all significantly higher than the ICH score (0.62 [95% CI 0.49–0.75]). Conclusion: Our exploratory study suggests that whole-brain microstructural disruption measured by DTI is associated with poor 6-month functional outcome after SVD-related ICH. Whole-brain DTI metrics performed better at predicting recovery than the existing ICH score