We present a global variational approach to the L2-gradient flow of the area functional of cartesian surfaces through the study of the so-called weighted energy-dissipation (WED) functional. In particular, we prove a relaxation result which allows us to show that minimizers of the WED converge
in a quantitatively prescribed way to gradient-flow trajectories of the relaxed area functional. The result is then extended
to general parabolic quasilinear equations arising as gradient flows of convex functionals with linear growth. 相似文献
The crack opening displacement (COD) in annealed soda-lime (float) glass has been measured with an electronic speckle pattern interferometry (ESPI) apparatus using coherent laser light. Specimens, naturally pre-cracked with a particular technique, were loaded under strain-driven bending until crack propagated; at regular intervals loading was paused to let the crack reach subcritical equilibrium and the COD measured. By using a post-processing algorithm comparing four images lighted with phase-shifted laser beams, surface displacements could be measured at a resolution of .Glass transparency has allowed to see through that the propagating crack front is not sharp but curved, jagged and merged in an opaque neighborhood. Numerical simulations show that the measured CODs cannot be reproduced if cohesive surface forces à la Barenblatt-Dugdale bridge the crack lips; instead a plastic-like region must form in a bulk neighborhood of the tip, where inelastic strains are associated with volume increase rather than deviatoric distortion. For this, a Gurson-Tvergaard model of porous plasticity, accounting for the formation of microvoids/microcracks, has been found more efficient than classical von Mises plasticity. This study confirms the formation at the crack tip of a process zone, whose occurrence in brittle materials like glass is still a subject of controversy. 相似文献
The classical basic concepts of cyclic processes and the efficiency of heat engines are used here to conjecture about the laws of thermodynamics for open systems that can exchange matter with a surrounding environment. An ideal chemomechanical elastic bar is envisioned that changes its stiffness while undergoing a chemical transformation which is, in turn, influenced by the axial strain of the bar. Stable equilibrium states are identified as minimizers of the total energy, which is assumed to be nonconvex in type. If the bar is loaded and then alternatively placed in environments at chemical potentials either ??i or ??s>??i, a reversible cycle analogous to the classical Carnot cycle may be traced. In this case, the environmental ??chemical potential?? plays the role of the temperature and the ??chemical work?? the role of heat. For the system, the main form of interaction with the exterior, other than mechanical work, is the exchange of mass of a component at different environmental chemical potentials. It is then possible to obtain an elementary theory of chemical engines in which efficiency estimates (in terms of environmental chemical potentials) and related pertinent issues can be discussed. This model may serve as a basis for analyzing coupled chemo-mechanical processes occurring in materials such as ionized gels for possible applications as actuators, and to interpret complex phenomena in biological systems, such as the chemical kinetics of smooth muscles. 相似文献
Ruthenium anticancer drugs have attracted an increasing interest in the last 20 years and two of them have entered clinical trials. Compared to platinum drugs, the complexes based on ruthenium are often identified as less toxic and capable of overcoming the resistance induced by platinum drugs in cancer cells. These activities were attributed to the transportation to tumour cells by transferrin and to the selective activation to more reactive species by the reducing environment of solid tumours as compared to healthy tissues. Ruthenium anticancer drugs have been almost always designed to mimic platinum drugs, particularly for targeting DNA. Indeed, none of the above properties has never been clearly demonstrated even for the ruthenium drugs that entered clinical trials. The suggestion for the future is to change the perspective when designing new chemical entities, abandoning the philosophy that guided the actual panel of ruthenium drugs and to look further into the fine mechanism by which the most relevant ruthenium complexes available kill the target tumour cells, then focusing on targets selective of tumour cells and responsible for cell growth and malignancy. 相似文献
In our Dalton Transactions Perspective article entitled, 'Metal-based antitumour drugs in the post genomic era', (Dalton Trans., 2006, 1929-1933) we discussed metal-based drugs in light of past decades of research. We concluded that the post-genomic era would dictate a change in the direction of the field with knowledge of the genome increasingly allowing protein targets to be identified and not simply assuming that DNA is the only relevant target of metal-based drugs. Since our article was published new insights into the mode of action of metal-based drugs have emerged making some older findings increasingly relevant to current drug design. In this article we discuss these developments in terms of what we believe should be the future direction for the field. 相似文献
We continue the study of U(1) vortices with cholesteric vacuum structure. A new class of solutions is found which represent global vortices of the internal spin field. These spin vortices are characterized by a non-vanishing angular dependence at spatial infinity, or winding. We show that despite the topological Z2 behavior of SO(3) windings, the topological charge of the spin vortices is of the Z type in the cholesteric. We find these solutions numerically and discuss the properties derived from their low energy effective field theory in 1+1 dimensions. 相似文献
Both metal complexes and organic molecules are widely used for the treatment of various diseases including cancer - in addition to surgery and radiotherapy. Recent years have witnessed a surge of interest in the application of organometallic compounds to treat cancer and other diseases. Indeed, the unique properties of organometallic compounds, intermediate between those of classical inorganic and organic materials provide new opportunities in medicinal chemistry. In this review, based on the award lecture at ICBOMC’10, we describe a class of ruthenium(II)-arene complexes that are weakly cytotoxic in vitro, but show selective antimetastatic activity in vivo. These compounds, [Ru(η6-p-arene)Cl2(pta)] termed RAPTA, interact strongly with proteins, with the ability to discriminate binding to different proteins, but show a relatively low propensity to bind DNA, which is considered to be the main target of many metal-based drugs. The basic RAPTA structure is quite stable in physiological environments, and studies have shown that aquation of the chloride bonds occurs, it may not be an essential step for anticancer drug activity - direct substitution with biomolecular targets is also possible. Based on the favorable physicochemical properties of RAPTA compounds, combined with their highly promising pharmacological properties, the structure represents an ideal scaffold for rational drug design. Thus far, strategies to overcome drug resistance, by interference with critical enzymes responsible for drug deactivation, and tumor targeting, by tethering to human serum albumin via hydrolyzable linkers, have been demonstrated. However, many more approaches can be envisaged. In any case, the net result are a type of hybrid compounds, that occupy a niche somewhere between classical cisplatin-type anticancer agents that are widely applied to many tumor types and targeted therapies based on organic structures used to inhibit specific enzymes. As such, should these compounds prove themselves in the clinic it is not inconceivable that they could be rapidly refined to form personalized chemotherapies. 相似文献
The ability of a MgCl2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu2 with HCl gave high activity with TiCl4 but low activity with (n‐PrCp)2ZrCl2. High polymerization activities with the zirconocene were only obtained with supports of type MgCl2/AlRn(OEt)3−n prepared from the reaction of AlR3 with MgCl2 · 1.1EtOH. These supports are characterized by additional peaks in the X‐ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species.