Higher triplet state of fullerene C70 revealed by electron spin relaxation

Spin-lattice relaxation timesT1 of photoexcited triplets 3C70 in glassy decalin were obtained from electron spin echo inversion recovery dependences. In the range 30–100 K, the temperature dependence of T1 was fitted by the Arrhenius law with an activation energy of 172 cm−1. This indicates that the dominant relaxation process of 3C70 is described by an Orbach-Aminov mechanism involving the higher triplet state t2 which lies 172 cm−1 above the lowest triplet state t1. Chemical modification of C70fullerene not only decreases the intrinsic triplet lifetime by about ten times but also increases T1 by several orders of magnitude. The reason for this is the presence of a low-lying excited triplet state in 3C70 and its absence in triplet C70 derivatives. The presence of the higher triplet state in C70 is in good agreement with the previous results from phosphorescence spectroscopy

A fast electrochemical actuator in the non-explosive regime

Microfluidic systems require a compact, energy-efficient and microtechnology-compatible actuator that pushes the liquid through the channels. Electrochemical devices are promising candidates, but they suffer from a long response time due to slow gas recombination. An actuator with a millisecond response time was demonstrated recently. A micron-sized chamber of the device with two titanium electrodes is sealed by a polydimethylsiloxane membrane. A series of microsecond voltage pulses of alternating polarity is applied to the electrodes. Nanobubbles generated in the chamber push the membrane up, but disappear quickly due to spontaneous combustion of hydrogen and oxygen. In this work, operation of the device is investigated in detail. The pulses with a frequency from 100 to 500 kHz are used for actuation. It is demonstrated that higher frequency and higher amplitude of the pulses provide larger deflection of the membrane, but finally the deflection is saturated. The stroke of 8-9 mu m can be achieved. In a cyclic operation regime the actuator is driven by series of pulses. If the time interval between the series is too short, the gas accumulates in the chamber. The membrane lifts during several cycles and then oscillates in the lifted position. In this regime the operating frequency as high as several hundred hertz can be achieved. The higher the frequency, the higher is the lift. The stroke also increases with the frequency, making a higher value more beneficial. Destruction of the electrodes is not observed, but the oxidation of titanium with time suppresses the gas production and decreases the membrane deflection. At a high frequency of the pulses the oxidation goes slower, but still significantly affects the performance. The oxidation of the electrodes is recognized as the main problem of the device. Methods to solve the problem are proposed

Peculiarities and evolution of Raman spectra of multilayer Ge/Si(001) heterostructures containing arrays of low-temperature MBE-grown Ge quantum dots of different size and number density: Experimental studies and numerical simulations

Ge/Si(001) multilayer heterostructures containing arrays of low-temperature self-assembled Ge quantum dots and very thin Si$_x$Ge$_{1-x}$ layers of varying composition and complex geometry have been studied using Raman spectroscopy and scanning tunneling microscopy. The dependence of Raman spectra on the effective thickness of deposited Ge layers has been investigated in detail in the range from 4 to 18 \r{A}. The position and shape of both Ge and SiGe vibrational modes are of great interest since they are closely related to the strain and composition of the material that plays a role of active component in perspective optoelectronic devices based on such structures. In this work, we present an explanation for some peculiar features of Raman spectra, which makes it possible to control the quality of the grown heterostructures more effectively. A dramatic increase of intensity of both the Ge$-$Ge and Si$-$Ge bands for the structure containing Ge layers of 10 \r{A} and anomalous shift and broadening of the Si$-$Ge band for structures comprising Ge layers of 8 and 9 \r{A} thick were observed. In our model, the anomalous behavior of the Raman spectra with the change of thickness of deposited Ge is connected with the flatness of Ge layers as well as transitional SiGe domains formed via the stress-induced diffusion from {105} facets of quantum dots. The conclusions are supported by the STM studies and the numerical calculations.Comment: 17 pages, 11 figure

Structural mechanisms of formation of adiabatic shear bands

The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the size of grains is ~300nm. Rotational deformation modes give rise to the high angular disorientations of grains. The development of plastic shear instability regions has been simulated numerically. For this purpose, we use a recently developed theory, in which the influence of microshears on the deformation properties of materials has been studied by the methods of statistical physics and thermodynamics of irreversible processes. The results of theoretical and experimental studies suggest that one of the mechanisms of the plastic shear instability and localization of plastic strain at high-velocity perforation is related to structural and kinetic transitions in microshear ensembles.&nbsp

Search for composite and exotic fermions at LEP 2

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermio

Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP

Promptly decaying lightest neutralinos and long-lived staus are searched for in the context of light gravitino scenarios. It is assumed that the stau is the next to lightest supersymmetric particle (NLSP) and that the lightest neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector at centre-of-mass energies from 161 to 183 \GeV are analysed. No evidence of the production of these particles is found. Hence, lower mass limits for both kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is found to be greater than 71.5 GeV/c^2. In the search for long-lived stau, masses less than 70.0 to 77.5 \GeVcc are excluded for gravitino masses from 10 to 150 \eVcc . Combining this search with the searches for stable heavy leptons and Minimal Supersymmetric Standard Model staus a lower limit of 68.5 \GeVcc may be set for the stau mas

Novel Photosensitizers Trigger Rapid Death of Malignant Human Cells and Rodent Tumor Transplants via Lipid Photodamage and Membrane Permeabilization

BACKGROUND: Apoptotic cascades may frequently be impaired in tumor cells; therefore, the approaches to circumvent these obstacles emerge as important therapeutic modalities. METHODOLOGY/PRINCIPAL FINDINGS: Our novel derivatives of chlorin e(6), that is, its amide (compound 2) and boronated amide (compound 5) evoked no dark toxicity and demonstrated a significantly higher photosensitizing efficacy than chlorin e(6) against transplanted aggressive tumors such as B16 melanoma and M-1 sarcoma. Compound 5 showed superior therapeutic potency. Illumination with red light of mammalian tumor cells loaded with 0.1 µM of 5 caused rapid (within the initial minutes) necrosis as determined by propidium iodide staining. The laser confocal microscopy-assisted analysis of cell death revealed the following order of events: prior to illumination, 5 accumulated in Golgi cysternae, endoplasmic reticulum and in some (but not all) lysosomes. In response to light, the reactive oxygen species burst was concomitant with the drop of mitochondrial transmembrane electric potential, the dramatic changes of mitochondrial shape and the loss of integrity of mitochondria and lysosomes. Within 3-4 min post illumination, the plasma membrane became permeable for propidium iodide. Compounds 2 and 5 were one order of magnitude more potent than chlorin e(6) in photodamage of artificial liposomes monitored in a dye release assay. The latter effect depended on the content of non-saturated lipids; in liposomes consisting of saturated lipids no photodamage was detectable. The increased therapeutic efficacy of 5 compared with 2 was attributed to a striking difference in the ability of these photosensitizers to permeate through hydrophobic membrane interior as evidenced by measurements of voltage jump-induced relaxation of transmembrane current on planar lipid bilayers. CONCLUSIONS/SIGNIFICANCE: The multimembrane photodestruction and cell necrosis induced by photoactivation of 2 and 5 are directly associated with membrane permeabilization caused by lipid photodamage