Kavitasyon Kabarcığı Bölünme Dinamiği

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2013Kavitasyon kabarcığı dinamiğinde, ısı iletimi, ağdalılık, kütle yayınımı ve akustik ışınım sonucu mekaniksel enerjinin önemli bir bölümü yutulmaktadır. Bu fiziksel olgulara ek olarak, kabarcığın yüksek bir basınç alanı etkisiyle aniden büzülmesiyle parçalara (fragmanlara) bölünmesi sonucu da mekaniksel enerjinin bir bölümü yutulmaktadır. Brennen [1], Rayleigh-Taylor kararsızlığı ve mikrojet oluşumu sonucu kabarcığın bölünmesi halinde yutulan mekaniksel enerjinin, yukarıdaki klasik olgulardan kaynaklanankinden çok daha fazla olabileceğini göstermiştir. Daha sonra Delale ve Tunç [2] Rayleigh-Taylor kararsızlığı sonucu oluşan bir kabarcık bölünmesi dinamiği modeli geliştirmiştir. Bu model, deney ve gözlemlerdeki sonuçları doğrulamakla birlikte, hangi koşullar altında Rayleigh-Taylor kararsızlığının kabarcık bölünmesine yol açacağı hakkında bilgi vermemektedir [3]. Bu çalışmada, Rayleigh-Taylor doğrusal kararsızlığının en kararsız modu kullanılarak, Delale-Tunç modelindeki kabarcık fragmanları dinamiğine yol açan kabarcık bölünmesinin hangi koşullar altında oluşabileceği belirlenmektedir

Modeling Progressive Failure of Bonded Joints Using a Single Joint Finite Element

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90634/1/AIAA-55313-740.pd

Homogeneous Bubble Nucleation driven by local hot spots: a Molecular Dynamics Study

We report a Molecular Dynamics study of homogenous bubble nucleation in a Lennard-Jones fluid. The rate of bubble nucleation is estimated using forward-flux sampling (FFS). We find that cavitation starts with compact bubbles rather than with ramified structures as had been suggested by Shen and Debenedetti (J. Chem. Phys. 111:3581, 1999). Our estimate of the bubble-nucleation rate is higher than predicted on the basis of Classical Nucleation Theory (CNT). Our simulations show that local temperature fluctuations correlate strongly with subsequent bubble formation - this mechanism is not taken into account in CNT

Diabetes Is the Main Factor Accounting for Hypomagnesemia in Obese Subjects

OBJECTIVE: Type 2 diabetes (T2DM) and obesity are associated with magnesium deficiency. We aimed to determine whether the presence of type 2 diabetes and the degree of metabolic control are related to low serum magnesium levels in obese individuals. METHODS: A) Case-control study: 200 obese subjects [50 with T2DM (cases) and 150 without diabetes (controls)] prospectively recruited. B) Interventional study: the effect of bariatric surgery on serum magnesium levels was examined in a subset of 120 obese subjects (40 with type 2 diabetes and 80 without diabetes). RESULTS: Type 2 diabetic patients showed lower serum magnesium levels [0.75±0.07 vs. 0.81±0.06 mmol/L; mean difference -0.06 (95% CI -0.09 to -0.04); p<0.001] than non-diabetic patients. Forty-eight percent of diabetic subjects, but only 15% of non-diabetic subjects showed a serum magnesium concentration lower than 0.75 mmol/L. Significant negative correlations between magnesium and fasting plasma glucose, HbA1c, HOMA-IR, and BMI were detected. Multiple linear regression analysis showed that fasting plasma glucose and HbA1c independently predicted serum magnesium. After bariatric surgery serum magnesium increased only in those patients in whom diabetes was resolved, but remain unchanged in those who not, without difference in loss weight between groups. Changes in serum magnesium negatively correlated with changes in fasting plasma glucose and HbA1c. Absolute changes in HbA1c independently predicted magnesium changes in the multiple linear regression analysis. CONCLUSIONS: Our results provide evidence that the presence of diabetes and the degree of metabolic control are essential in accounting for the lower levels of magnesium that exist in obese subjects

Migraine in women: the role of hormones and their impact on vascular diseases

Migraine is a predominantly female disorder. Menarche, menstruation, pregnancy, and menopause, and also the use of hormonal contraceptives and hormone replacement treatment may influence migraine occurrence. Migraine usually starts after menarche, occurs more frequently in the days just before or during menstruation, and ameliorates during pregnancy and menopause. Those variations are mediated by fluctuation of estrogen levels through their influence on cellular excitability or cerebral vasculature. Moreover, administration of exogenous hormones may cause worsening of migraine as may expose migrainous women to an increased risk of vascular disease. In fact, migraine with aura represents a risk factor for stroke, cardiac disease, and vascular mortality. Studies have shown that administration of combined oral contraceptives to migraineurs may further increase the risk for ischemic stroke. Consequently, in women suffering from migraine with aura caution should be deserved when prescribing combined oral contraceptives