Using atomistic models and molecular dynamics simulations, interlayer corrugation and resistant force in a biwalled carbon nanotube are shown to be strongly dependent upon the morphology combination of the bitube. Consequently, energy dissipation in a commensurate (e.g., armchair/armchair or zigzag/zigzag) bitube oscillator is found to be much larger than that in an incommensurate (e.g., zigzag/armchair) oscillator, resulting in a decay of oscillation amplitude within a few nanoseconds in the commensurate bitube and several tens of nanoseconds in the incommensurate bitube.

We determine the atomic-scale friction associated with a layer of Pd atoms moving across a graphite substrate from ab initio total-energy calculations. We evaluate the friction energy caused by variations of the chemical bond strength and work against an external force (load) due to variations of the bond length along the trajectory. We find only a very small dependence of the Pd-graphite interaction on the adsorption site which gives rise to a very small friction coefficient fi^ \0~^ for loads near 10"^ N. We also find ^ to increase with load in agreement with recent experiments.

This meta-analysis suggests that the DT is a valid tool to detect potential distress in cancer patients. According to our results, 4 as the optimal cut-off, is recommended. Further studies are needed to be done to examine the accuracy and optimal cut-off score in different regions globally and different cancer subtypes to guide the use of the DT for different patients.

We investigate the microscopic mechanism of energy dissipation in the friction force microscope (FFM), which is a modification of the atomic-force microscope for application to friction. Based on ab initio results for the interaction between Pd and graphite, we determine the atomic-scale modulation of the friction force and the corresponding stick-slip molion at the interface during the relative motion between these solids. We propose two idealized versions of the FF1\1 and show that the friction force depends not only on the Pd-graphite interaction potential, but even more critically on the construction parameters of such a microscope. Friction between two solids is one of the most important and complex processes which affect everyday's life. So far, the science of friction-tribology-has described this phenomenon mainly in a macroscopic and phenomenological way [1]. More recently, successful attempts have been undertaken to observe friction forces on the atomic scale [2] and to understand the underlying microscopic mechanisms in case of sliding friction without wear [3]. Independently, the availability of supercomputers has made predictive calculations [4,5] of atomic-scale friction forces possible. The recent experimental progress in nanotribology has been facilitated by the development of a modified version of the atomic-force microscope [6] (AFM) for application to friction, which is sometimes called the friction force microscope (FFM). Like the AFM, the FFM consists of an «atomically sharp" tip of a material A, suspended on a soft cantilever, which is brought into nondestructive contact with a well-defined substrate B. Measuring the vertical deflection of the cantilever is used to keep the applied load F..xl constant during the sLUface scan. An independent measurement of the cantilever deflection in the direction of

Abstract.We have studied the low frequency vibrational modes and the structural rigidity of long graphitic carbon tubules consisting of 100, 200, and 400 atoms. Our calculations have been performed using an empirical Keating Hamiltonian with parameters determined from first principles. We have found the "beam bending" mode to be one of the softest modes in these structures. The corresponding beam rigity of a " b u c k y tube" is compared to an found to exceed the highest values found in presently available materials. PACS: 36.40. +d; 81.20.Sh The successful synthesis [ 1] of macroscopic quantities of C60 clusters with a fascinating hollow "buckyball" structure [2] has ignited the interest of the scientific community in these and similar structures to an unprecedented degree. More recently, successful synthesis and identification of helical microtubules of graphitic carbon has been reported [3]. These graphite whiskers or "bucky tubes" are topological relatives of the "buckyball" [4] and might have been synthesized in direct current arc in inert gas already in the lat 50's [5]. Most interest in "bucky tubes" has concentrated on their electronic properties which can range from metallic to insulating [6]. In this paper, we present the first study of the mechanical properties of these structures. We show that these structures may be the finest and toughest fibers presently available, as was suggested recently [7].We focus our study on the low frequency vibrational eigen :modes of "bucky tubes" consisting of 100, 200, and 400 carbon atoms which reflect the rigidity of these structures. Among the man3, possible isomers [8], we consider those which can be generated by splitting the C60 "buckyball" into equal halves, and connecting the two "bucky caps" by a graphitic cylinder of variable length. All carbon atoms in the structure are three-fold coordinated. The "bucky tubes", like all members of the fullerene family, consist of a varying number of hexagonal carbon rings (distributed across the caps and the cylinder) and of twelve pentagons (on the caps). The equilibrium structure of a "bucky tube" consisting of 200 atoms is shown in Fig. la.In order to determine the structural rigidity and the vibrational eigen modes of such a complex structure, we use an elastic model with central and angular forces for the nearest neighbor bonds. Such models are currently widely used to describe properties of covalently bonded solids with directional bonding [9][10][11]. In the present study, we will use the Keating potential [9] which is attractive due to its simple form and its successful application to complex structures such as the C60 solid [12] and amorphous silicon [ 13].The Keating potential V x describes potential energy changes with respect to a relaxed reference state, and consists of a bond stretching and a bond bending term. The bond stretching term is a central nearest-neighbor two-body potential. The bond bending part of the potential is a three-body interaction term which is sensitive to changes of the angle between n...

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BACKGROUND: In patients with advanced ovarian cancer (OvCa), microscopic residual tumour nodules that remain after surgical debulking frequently escape detection by current treatment assessment methods and lead to disease recurrence. The aim of this study was to evaluate the use of high-resolution fibre-optic fluorescence imaging of the clinically approved photodynamic therapy (PDT) agent benzoporphyin-derivative monoacid ring A (BPD-MA) for detection of microscopic OvCa and for monitoring treatment response. METHODS: Our fluorescence microendoscope consists of a flexible imaging fibre coupled to a custom epi-fluorescence system optimised for imaging BPD-MA, which, after a single administration, serves as both an imaging agent and a light-activated therapeutic agent. After characterisation in an in vitro OvCa 3D model, we used the flexible imaging fibre to minimally invasively image the peritoneal cavity of a disseminated OvCa murine model using BPD-MA administered intraperitoneally (i.p.). To evaluate longitudinal changes in response to treatment, we compared sets of images obtained before and after PDT with those from untreated mice imaged at the same time points. RESULTS: By comparison with histopathology, we report an 86% sensitivity for tumour detection in vivo using the microendoscope. Using a custom routine to batch process-image data in the monitoring study, treated mice exhibited an average decrease of 58.8% in tumour volumes compared with an increase of 59.3% in untreated controls (Po0.05). CONCLUSIONS: Our findings indicate the potential of this approach as a reporter of treatment outcome that could aid in the rational design of strategies to mitigate recurrent OvCa.

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