Objects of categories as complex numbers

In many everyday categories (sets, spaces, modules, etc.) objects can be both added and multiplied. The arithmetic of such objects is a challenge because there is usually no subtraction. We prove a family of cases of the following principle: if an arithmetic statement about the objects can be proved by pretending that they are complex numbers, then there also exists an honest proof.     

Low complexity secant quasi-Newton minimization algorithms for nonconvex functions

In this work some interesting relations between results on basic optimization and algorithms for nonconvex functions (such as BFGS and secant methods) are pointed out. In particular, some innovative tools for improving our recent secant BFGS-type and algorithms are described in detail.     

Tributyltin(IV) Butyrate: A Novel Epigenetic Modifier with ER Stress- and Apoptosis-Inducing Properties in Colon Cancer Cells

Organotin(IV) compounds are a class of non-platinum metallo-conjugates exhibiting antitumor activity. The effects of different organotin types has been related to several mechanisms, including their ability to modify acetylation protein status and to promote apoptosis. Here, we focus on triorganotin(IV) complexes of butyric acid, a well-known HDAC inhibitor with antitumor properties. The conjugated compounds were synthesized and characterised by FTIR spectroscopy, multi-nuclear (¹H, ¹³C and ¹¹⁹Sn) NMR, and mass spectrometry (ESI-MS). In the triorganotin(IV) complexes, an anionic monodentate butyrate ligand was observed, which coordinated the tin atom on a tetra-coordinated, monomeric environment similar to ester. FTIR and NMR findings confirm this structure both in solid state and solution. The antitumor efficacy of the triorganotin(IV) butyrates was tested in colon cancer cells and, among them, tributyltin(IV) butyrate (BT2) was selected as the most efficacious. BT2 induced G2/M cell cycle arrest, ER stress, and apoptotic cell death. These effects were obtained using low concentrations of BT2 up to 1 μM, whereas butyric acid alone was completely inefficacious, and the parent compound TBT was poorly effective at the same treatment conditions. To assess whether butyrate in the coordinated form maintains its epigenetic effects, histone acetylation was evaluated and a dramatic decrease in acetyl-H3 and -H4 histones was found. In contrast, butyrate alone stimulated histone acetylation at a higher concentration (5 mM). BT2 was also capable of preventing histone acetylation induced by SAHA, another potent HDAC inhibitor, thus suggesting that it may activate HDACs. These results support a potential use of BT2, a novel epigenetic modulator, in colon cancer treatment.     

Diffusion élastique des deutons polarisés par C de 20 À 30 MeV

Angular distributions of the vector polarization of deuterons elastically scattered by ¹²C have been measured at 20.5, 25.2 and 29.5 MeV. Asymmetries were measured with semiconductor telescopes. The beam polarization was determined simultaneously with a carbon polarimeter whose analysing power was calibrated by means of the d-⁴He scattering. Differential cross sections at 20.5 and 29.5 MeV are also presented. The results are analyzed in terms of the optical model. Two energy dependent average potentials are deduced.     

High conversion free-radical suspension polymerization: End groups in poly(methyl methacrylate) and their influence on the thermal stability

Suspension free-radical polymerization of vinyl monomers, carried out in the presence of alkyl mercaptans as chain-transfer agents, is analyzed. A model which accounts for the development with conversion of the polymer weight fractions having particularly tagged end groups, namely sulfur-containing and unsaturated end groups, is presented. The best current theories for diffusion-controlled polymerizations are included in the model. The sulfur content of poly(methyl methacrylate), determined as a function of conversion by a microcoulometric method, is in good agreement with the values predicted from polymerization kinetics. The rate of weight loss of the produced polymers is then related to the content of the unsaturated end groups. By comparing experimental thermal stability indexes (from thermogravimetry and isothermal heating experiments) to calculated polymer weight fractions, it is shown that the thermal stability of poly(methyl methacrylate) produced in the presence of alkyl mercaptans approximately depends on the square of the weight fraction of the polymer chains with an unsaturated end group.     

Enhanced spontaneous emission from InAs/GaAs quantum dots in pillar microcavities emitting at telecom wavelengths

Optical properties of InAs/GaAs quantum dots in micropillar cavities emitting at 1.3 microm are studied by time-resolved microphotoluminescence. The Purcell effect is observed with an enhancement of the decay rate by a factor of two for quantum dots in resonance with the cavity mode.     

Reverse mode operation polymer dispersed liquid crystal with a positive dielectric anisotropy liquid crystal

The development of electrically activated chromogenic materials is important for their potential applications in smart windows. Several previous works have reported on reverse mode operation polymer dispersed liquid crystals (PDLCs) based on negative dielectric anisotropy liquid crystals. They have a transparent OFF state, which turns opaque after the application of a suitable external electric field. Nevertheless, these devices have some limitations such as the use of large amount of expensive liquid crystals with peculiar physical‐chemical properties. In addition, a good matching between the refractive index of liquid crystal and the polymer matrix one is required. The main result of this work is the achievement of reverse mode operation devices prepared with a positive dielectric anisotropy liquid crystal and characterized by a high OFF state transmittance obtained by the onset of high intensity built‐in DC electric fields in a direct mode operation PDLC, which allows the OFF state homeotropic alignment of liquid crystal directors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Storing optical information as a mechanical excitation in a silica optomechanical resonator

We report the experimental demonstration of storing optical information as a mechanical excitation in a silica optomechanical resonator. We use writing and readout laser pulses tuned to one mechanical frequency below an optical cavity resonance to control the coupling between the mechanical displacement and the optical field at the cavity resonance. The writing pulse maps a signal pulse at the cavity resonance to a mechanical excitation. The readout pulse later converts the mechanical excitation back to an optical pulse. The storage lifetime is determined by the relatively long damping time of the mechanical excitation.     

General approach for studying first-order phase transitions at low temperatures

By combining different ideas, a general and efficient protocol to deal with discontinuous phase transitions at low temperatures is proposed. For small T's, it is possible to derive a generic analytic expression for appropriate order parameters, whose coefficients are obtained from simple simulations. Once in such regimes simulations by standard algorithms are not reliable; an enhanced tempering method, the parallel tempering-accurate for small and intermediate system sizes with rather low computational cost-is used. Finally, from finite size analysis, one can obtain the thermodynamic limit. The procedure is illustrated for four distinct models, demonstrating its power, e.g., to locate coexistence lines and the phase density at the coexistence.