Structural lubricity under ambient conditions.

Despite its fundamental importance, physical mechanisms that govern friction are poorly understood. While a state of ultra-low friction, termed structural lubricity, is expected for any clean, atomically flat interface consisting of two different materials with incommensurate structures, some associated predictions could only be quantitatively confirmed under ultra-high vacuum (UHV) conditions so far. Here, we report structurally lubric sliding under ambient conditions at mesoscopic (∼4,000-130,000 nm(2)) interfaces formed by gold islands on graphite. Ab initio calculations reveal that the gold-graphite interface is expected to remain largely free from contaminant molecules, leading to structurally lubric sliding. The experiments reported here demonstrate the potential for practical lubrication schemes for micro- and nano-electromechanical systems, which would mainly rely on an atomic-scale structural mismatch between the slider and substrate components, via the utilization of material systems featuring clean, atomically flat interfaces under ambient conditions

Ümitli Yaylası’nın (Gündoğmuş, Antalya) jeolojik ve jeomorfolojik özellikleri

Solution caves provide important contributions to geologists in solving the problem in the field. In the Umitli Plateau, between Manaloglu and Karacal Mountains, intensive terrain and underground karst processes are observed. The Umitli Plateau is situated in the Central Taurus which is located at the Gundogmus district, province of Antalya. 18 caves were discovered in a 2 km(2) area with the research performed in 2011. In this study, digital elevation model of the study area was plotted and the locations of the caves were processed in the digital elevation model. It has been observed that cracks and fractures are effective in the formation and development of caves that are along the faults on the side of the basin. In addition to that, the cross-section profiles of the caves have been plotted and they were examined according to the cave formation models to obtain information about the karst base level changes of the Umitli Plateau and the litho-stratigraphic characteristics of the study area

A Computational Study of Cluster Dynamics in Structural Lubricity: Role of Cluster Rotation

We present a computational study of sliding between gold clusters and a highly oriented pyrolytic graphite substrate, a material system that exhibits ultra-low friction due to structural lubricity. By means of molecular dynamics, it is found that clusters may undergo spontaneous rotations during manipulation as a result of elastic instability, leading to attenuated friction due to enhanced interfacial incommensurability. In the case of a free cluster, shear stresses exhibit a non-monotonic dependency on the strength of the tip-cluster interaction, whereby rigid clusters experience nearly constant shear stresses. Finally, it is shown that the suppression of the translational degrees of freedom of a cluster's outermost-layer can partially annihilate out-of-plane phonon vibrations, which leads to a reduction of energy dissipation that is in compliance with Stokesian damping. It is projected that the physical insight attained by the study presented here will result in enhanced control and interpretation of manipulation experiments at structurally lubric contacts

The impact of metabolic risk management on recurrence of urinary stones

Introduction: Urinary stone disease is a common urologic problem and recurrence in stone formation is a very familiar issue to urologists. Although recurrence in stone formation has been linked to metabolic abnormalities, it can be accessible by metabolic risk analysis studies.Methods: Herein, we present our experience in metabolic risk management on recurrence of urinary stones for 10 years in Akdeniz University School of Medicine department of Urology. We retrospectively analyzed Akdeniz University Urinary Stone Database between dates of January 2000 and December 2010. We found over 3500 patients who were managed by SWL (shock wave lithotripsy) or PCNL (percutaneus nephrolithotripsy) or URS (Ureterorenoscopic lithotripsy) or open surgery.Results: 525 patients’ metabolic risk analysis was ordered due to recurrent urinary stone disease. Only 134 (25.5 %) current metabolic analysis were returned. Mean patient age was 32.2 years (range: 19-82 years).Patients were 103 male and 31 female. Stone analysis results were CaOx monohydrate in 48 (35.8 %), CaOx dihydrate in 8 (5.9 %), CaOx mono and dihydrate in 70 (52.2 %), uric acid in 3, CaOx monohydrate and uricacid in 2, cystine in 2, and struvite in 1 patient, respectively. The  metabolic risk analysis showed some abnormality in 54 (40.2 %) patients.Conclusion: Although compliance to metabolic risk analysis studies is low among recurrent urinary stone formers, some significant metabolic abnormalities could be detected in those who are effectively screened.Recurrence of urinary stones in patients who are started on appropriate metabolic management can be prevented

Direct Imaging, Three-dimensional Interaction Spectroscopy, and Friction Anisotropy of Atomic-scale Ripples on MoS2_{2}

Theory predicts that two-dimensional (2D) materials may only exist in the presence of out-ofplane deformations on atomic length scales, frequently referred to as ripples. While such ripples can be detected via electron microscopy, their direct observation via surface-based techniques and characterization in terms of interaction forces and energies remain limited, preventing an unambiguous study of their effect on mechanical characteristics, including but not limited to friction anisotropy. Here, we employ high-resolution atomic force microscopy to demonstrate the presence of atomic-scale ripples on supported samples of few-layer molybdenum disulfide (MoS$_{2}$). Three-dimensional force / energy spectroscopy is utilized to study the effect of ripples on the interaction landscape. Friction force microscopy reveals multiple symmetries for friction anisotropy, explained by studying rippled sample areas as a function of scan size. Our experiments contribute to the continuing development of a rigorous understanding of the nanoscale mechanics of 2D materials.Comment: 22 pages including 4 figures in the main text, 2 figures in the supplemental informatio

Association Between Apolipoprotein E Polymorphism and Subclinic Atherosclerosis in Patients with Type 1 Diabetes Mellitus

Objective The most important cause of morbidity and mortality in type 1 diabetes mellitus (DM) is atherosclerosis. Apolipoprotein E (Apo E) polymorphism is accused of being the genetic risk factor for atherosclerosis. The aim of the present study was to determine which Apo E polymorphism was related to atherosclerosis in patients with type 1 DM

Expression of vascular endothelial growth factor and transforming growth factor alpha in rat testis during chronic renal failure

Introduction. Vascular endothelial growth factor (VEGF) is known to influence testis function. Transforming growth factor alpha (TGF-α) is expressed in the postnatal testis, and has been demonstrated to stimulate testis development. Systemic diseases such as chronic renal failure (CRF) interfere with hypothalamic-pituitary-go­nadal axis, which may cause defective steroidogenesis and gonadal functions. The aim of this study was to inve­stigate the expression and localization of VEGF and TGF-α in testicular tissues of experimental CRF model. Material and methods. Experimental CRF was induced in rats by the resection of more than 85% of renal mass. The expression of VEGF and TGF-α in testicular tissues were assessed by immunohistochemistry on paraffin sections of control, CRF-nondialysed and CRF-dialysed rats. Results. The microscopic evaluation of the testicular structure showed that CRF did not affect testicular histology. Immunohistochemical evaluation showed that VEGF was expressed in the cytoplasm of primary and secondary spermatocyte series as well as the early spermatids. Staining intensity was lower in sperma­tocytes going through the first meiotic division. TGF-α was expressed in the nuclei of spermatogonia and primary spermatocytes with stronger staining intensity in spermatogonia. The intensity of VEGF staining was similar in control and experimental animals, however, TGF-α expression was lower in the CRF group.Conclusions. The continuous expression of VEGF in spermatocytes and spermatids suggests that the applied model of CRF does not directly disrupt morphology of seminiferous epithelium, thus also spermiogenesis. However, difference between control rats and CRF group in TGF-α immunopositivity, which was localised in spermatogonial mitosis step, may suggest the interference of CRF with early stages of spermatogenesis.