695 research outputs found
Effects of poly(dimethylsiloxane) and inorganic fillers in halogen free flame retardant poly(ethylene-co-vinyl acetate) compound: A chemometric approach
No full textA quaternary system based on poly(ethylene-co-vinyl acetate) has been studied by Mixture Design in order to analyse the effect of additives on flame retardant properties. The FR components of the system are magnesium hydroxide (MDH), a silicon additive (Sil) based on poly(dimethylsiloxane) and a calcium borate additive (CaB). Many parameters from different flame retardant tests (LOI, UL94-V, DIN 4102 B2 and Cone Calorimeter) are selected as experimental responses and mathematical models with good quality are obtained for most of them. Principal Components Analysis (PCA) on flame retardant parameters points out no particular strong correlations among the three FR tests. The Experimental Design (DoE) approach allows minimization of the number of experiments and analysis of the influence of each component and of the interactions among them. Sil additive shows positive effects on LOI results and in the heat release rate and the fillers, mostly MDH, have positive influence on Cone Calorimeter and vertical burning test performance. Two optimal formulations have been obtained with improved stability of the residue together with LOI value in one case and Cone Calorimeter performance in the other case. © 2012 Elsevier Ltd. All rights reserved
A human CCT5 gene mutation causing distal neuropathy impairs hexadecamer assembly in an archaeal model
No full textChaperonins mediate protein folding in a cavity formed by multisubunit rings. The human CCT has eight
non-identical subunits and the His147Arg mutation in one subunit, CCT5, causes neuropathy. Knowledge
is scarce on the impact of this and other mutations upon the chaperone’s structure and functions. To make
progress, experimental models must be developed. We used an archaeal mutant homolog and demonstrated
that the His147Arg mutant has impaired oligomeric assembly, ATPase activity, and defective protein
homeostasis functions. These results establish for the first time that a human chaperonin gene defect can be
reproduced and studied at the molecular level with an archaeal homolog. The major advantage of the system,
consisting of rings with eight identical subunits, is that it amplifies the effects of a mutation as compared
with the human counterpart, in which just one subunit per ring is defective. Therefore, the slight deficit of a
non-lethal mutation can be detected and characterized
Effects of weak extremely low frequency magnetic fields on calcium/calmodulin interactions.
No full textjournal articleMechanisms by which weak electromagnetic fields may affect biological systems are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev\u27s theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev\u27s predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system. are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev\u27s theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev\u27s predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system
UVRR spectroscopic studies of valinomycin complex formation in different solvents
No full textWe investigated the complexation of valinomycin (VM) in different solvent environments with the aid of the UVRR spectroscopy. By probing the 206.5 and 229 nm excited Raman spectra, we showed that new bands are observed around 1700 and 1290 cm(-1). We assigned the 1700 cm(-1) band to the hydrogen bonded ester carbonyl stretching vibration. In a polar solvent, VM-K+ complexation shows significant intensity changes in amide and ester carbonyl stretching region. Because of the small amount of conformational interconversion, complexation has a negligible effect on other band intensities including, the amide III, CalphaH, and amide II. We also showed the effects of the solvent polarity on the solution conformation of VM. (C) 2004 Elsevier B.V. All rights reserved
Strong exciton−photon coupling with colloidal quantum dots in a tunable microcavity
No full textPolariton emission from optical cavities integrated with various luminophores has been extensively studied recently due to the wide variety of possible applications in photonics, particularly promising in terms of the fabrication of low-threshold sources of coherent emission. Tunable microcavities allow extensive investigation of the photophysical properties of matter placed inside the cavity by deterministically changing the coupling strength and controllable switching from weak to strong and ultra-strong coupling regimes. Here, we demonstrate room-temperature strong coupling of exciton transitions in CdSe/ZnS/CdS/ZnS colloidal quantum dots with the optical modes of a tunable low-mode-volume microcavity. Strong coupling is evidenced by a large Rabi splitting of the photoluminescence spectra depending on the detuning of the microcavity. A coupling strength of 154 meV has been achieved. High quantum yields, excellent photostability, and scalability of fabrication of quantum dots (QDs) pave the way to practical applications of coupled systems based on colloidal QDs in photonics, optoelectronics, and sensing.</p
UVRR spectroscopic studies of valinomycin complex formation in different solvents
No full textPMID = 1555641
Influence of Calcium Resonance-Tuned Low-Frequency Magnetic Fields on Daphnia magna
No full textA biophysical model for calculating the effective parameters of low-frequency magnetic fields was developed by Lednev based on summarized empirical data. According to this model, calcium ions as enzyme cofactors can be the primary target of low-frequency magnetic fields with different parameters tuned to calcium resonance. However, the effects of calcium-resonant combinations of static and alternating magnetic fields that correspond to Lednev’s model and differ by order in frequency and intensity were not studied. It does not allow for confidently discussing the primary targets of low-frequency magnetic fields in terms of the magnetic influence on ions-enzyme cofactors. To clarify this issue, we examined the response of freshwater crustaceans Daphnia magna to the impact of combinations of magnetic fields targeted to calcium ions in enzymes according to Lednev’s model that differ in order of magnitude. Life-history traits and biochemical parameters were evaluated. Exposure of daphnids to both combinations of magnetic fields led to a long-term delay of the first brood release, an increase in the brood size, a decrease in the number of broods, and the period between broods. The amylolytic activity, proteolytic activity, and sucrase activity significantly decreased in whole-body homogenates of crustaceans in response to both combinations of magnetic fields. The similarity in the sets of revealed effects assumes that different magnetic fields tuned to calcium ions in biomolecules can affect the same primary molecular target. The results suggest that the low-frequency magnetic fields with parameters corresponding to Lednev’s model of interaction between biological molecules and ions can remain effective with a significant decrease in the static magnetic background
Undoped CsI calorimeter for the K0 L !p0n¯n experiment at KEK-PS
No full textAn electromagnetic calorimeter consisting of 576 undoped CsI crystals has been used to search for the K0 L ! p0n¯n decay at the KEK 12-GeV proton synchrotron (E391a). The calorimeter is placed in a vacuum of lower than 10 1 Pa.Special energy & timing calibrations have been performed. The energy calibration started from a check of the linearit
for nine sample crystals using an electron beam. Then, after mounting all crystals in the E391a detector, we made an in situ calibration of the energy by using cosmic ray & punch-through muons. The gain constants obtained from both muons agree with each other with an accuracy of 2% ðsÞ. They were further refined by using gg samples from p0’s produced off an aluminum plate (5-mm thick) hit by neutral beam particles. Using the final gain constants, we obtained a K0 L mass resolution of 4.3 MeV/c2 ðsÞ for the K0 L ! p0p0p0 decay. Also, using the timing constants measured for cosmic rays, we obtained a resolution of 0.51 ns ðsÞ for the timing difference among six g’s in the K0 L !p0p0p0 decay
Change in agrochemical properties of texture-differentiated agrozem during application of green manure and organic and mineral fertilizers
No full textTime dependent dielectric breakdown in novel GaN metal-insulator-semiconductor high electron mobility transistors
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 83-84).Power electronics is expanding as we automate and electrify our households and step into mainstream electric vehicles. Recently, GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) have been increasing in popularity for high voltage power electronics applications because they combine high electron mobility with low gate leakage, increasing efficiency. This comes with the tradeoff of increased reliability concerns to be addressed before the widespread commercialization of GaN MIS-HEMTs. This thesis investigates one failure mechanism found in prototype industrial GaN MIS-HEMTs: time dependent dielectric breakdown (TDDB) of the gate insulator. TDDB occurs when a high electric field causes an accumulation of defects in the gate dielectric, forming a conducting path and rendering the device unusable. This is of major concern in GaN MIS-HEMTs because of their role as switches in high voltage circuits. In this work, we develop testing methodologies to address reticle-to-reticle variations and we estimate the lifetime of novel GaN MIS-HEMTs by performing measurements at different stress levels and temperatures in the ON and OFF-states.by Alexander I. Lednev.M. Eng.M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Scienc
- …
