436 research outputs found
The Potential Role of Addition Coupled Electron Transfer (ACET) in Single Atom Catalysis: The Hydrogen Transfer from Metalloporphyrin to Imine is an ACET
No full textThe formal hydrogen transfer from single atom catalyst to unsaturated compounds is of great interest in the catalysis research. With the hydrogen transfer from metalloporphyrin hydride (MPcH, M = Fe, Co) to imines as an example, we have shown that this reaction is an addition coupled electron transfer (ACET) reaction instead of a hydride transfer, by combining density functional theory (DFT), multireference calculations, intrinsic reaction coordinate analysis and substituent effect study. The ACET mechanism is universe in both low-polar solvent (dichloromethane) and high-polar protic solvent (2-propanal). The barrier versus Hammett substituent constant relationship under dichloromethane solvation features a volcano-like shape, in which both electron-withdrawing and electron-donating groups accelerates the reaction. While the structure-reactivity relationship cannot be rationalized by either substituent constant σp or the spin delocalization constant σJJ, it can be successfully explained by a theoretical model of ACET proposed by us for the first time in this work. This work shows that ACET may be ubiquitous in single atom catalyzed addition reactions
ACET is a highly potent and specific kainate receptor antagonist: Characterisation and effects on hippocampal mossy fibre function
No full textKainate receptors (KARs) are involved in both NMDA receptor-independent long-term potentiation (LTP) and synaptic facilitation at mossy fibre synapses in the CA3 region of the hippocampus. However, the identity of the KAR subtypes involved remains controversial. Here we used a highly potent and selective GluK1 (formerly GluR5) antagonist (ACET) to elucidate roles of GluK1-containing KARs in these synaptic processes. We confirmed that ACET is an extremely potent GluK1 antagonist, with a Kb value of 1.4+/-0.2 nM. In contrast, ACET was ineffective at GluK2 (formerly GluR6) receptors at all concentrations tested (up to 100 microM) and had no effect at GluK3 (formerly GluR7) when tested at 1 microM. The X-ray crystal structure of ACET bound to the ligand binding core of GluK1 was similar to the UBP310-GluK1 complex. In the CA1 region of hippocampal slices, ACET was effective at blocking the depression of both fEPSPs and monosynaptically evoked GABAergic transmission induced by ATPA, a GluK1 selective agonist. In the CA3 region of the hippocampus, ACET blocked the induction of NMDA receptor-independent mossy fibre LTP. To directly investigate the role of pre-synaptic GluK1-containing KARs we combined patch-clamp electrophysiology and 2-photon microscopy to image Ca2+ dynamics in individual giant mossy fibre boutons. ACET consistently reduced short-term facilitation of pre-synaptic calcium transients induced by 5 action potentials evoked at 20-25Hz. Taken together our data provide further evidence for a physiological role of GluK1-containing KARs in synaptic facilitation and LTP induction at mossy fibre-CA3 synapses
Efficient AC electrothermal flow (ACET) on-chip for enhanced immunoassays
No full textBiochemical reaction rates in microfluidic systems are known to be limited by the diffusional transport of reagents, leading often to lowered sensitivity and/or longer detection times in immunoassays. Several methods, including electrically powering electrodes to generate AC electrothermal flow (ACET) on-chip, have been adopted to enhance the mass transport of the reagents and improve microfluidic mixing. Here, we report a novel ACET electrode design concept for generating in-plane microfluidic mixing vortices that act over a large volume close to the reaction surface of interest. This is different from the traditional ACET parallel electrode design that provides rather local vertical mixing vortices directly above the electrodes. Both numerical simulation and experimental studies were performed to validate the new design. Moreover, numerical simulation was carried out to show the effects of experimental factors such as the reaction kinetics (association constant) and the reagent concentration on the ACET-enhanced surface-based assays. As a proof of concept, the new design for the ACET-enhanced immunoassays was used to improve the immunostaining signal of the HER2 (human epidermal growth factor receptor 2) cancer biomarker on breast cancer cells. Finally, the concept of scaling up the design has been validated by experiments (immunoassays on breast cancer cells for different ACET power and different assay times). In particular, we show that larger ACET in-plane designs can agitate and mix the fluid over large microfluidic volumes, which further enhances the immunoassay's output. We have achieved a 6-times enhancement in the assay signal with a 75% reduction in assay time.LMIS
ACEt: An R Package for Estimating Dynamic Heritability and Comparing Twin Models
No full textEstimating dynamic effects of age on the genetic and environmental variance components in twin studies may contribute to the investigation of gene-environment interactions, and may provide more insights into more accurate and powerful estimation of heritability. Existing parametric models for estimating dynamic variance components suffer from various drawbacks such as limitation of predefined functions. We present ACEt, an R package for fast estimating dynamic variance components and heritability that may change with respect to age or other moderators. Building on the twin models using penalized splines, ACEt provides a unified framework to incorporate a class of ACE models, in which each component can be modeled independently and is not limited by a linear or quadratic function. We demonstrate that ACEt is robust against misspecification of the number of spline knots, and offers a refined resolution of dynamic behavior of the genetic and environmental components and thus a detailed estimation of age-specific heritability. Moreover, we develop resampling methods for testing twin models with different variance functions including splines, log-linearity and constancy, which can be easily employed to verify various model assumptions. We evaluated the type I error rate and statistical power of the proposed hypothesis testing procedures under various scenarios using simulated datasets. Potential numerical issues and computational cost were also assessed through simulations. We applied the ACEt package to a Finnish twin cohort to investigate age-specific heritability of body mass index and height. Our results show that the age-specific variance components of these two traits exhibited substantially different patterns despite of comparable estimates of heritability. In summary, the ACEt R package offers a useful tool for the exploration of age-dependent heritability and model comparison in twin studies.Academy of Finland (Grant 265240
Tuberculosis Control Laws--United States, 1993; Recommendations of the Advisory Council for the Elimination of Tuberculosis (ACET)
No full textBecause of its communicable nature and because there are many state laws specific to the control of tuberculosis (TB), TB is managed differently than other airborne infectious diseases [corrected]. Many of these laws predate the current public health recommendations for the prevention and control of TB. In 1989, CDC published A Strategic Plan for the Elimination of Tuberculosis in the United States that was developed by the Advisory Committee (now Council) for the Elimination of Tuberculosis (ACET). The Plan called for the establishment of a national goal of TB elimination (i.e., achieving a case rate of < 1 per million population) by the year 2010. One of the methods for improving disease containment in the Plan was for the use of quarantine measures for nonadherent patients. The Plan called for revision of state and local laws to "facilitate the cure of persons with infectious tuberculosis". The issue of outdated state TB laws was also identified as a problem in the National Action Plan to Combat Multidrug-resistant Tuberculosis. In response to this issue, CDC conducted a survey of state TB control laws and ACET developed recommendations to address discrepancies between previously published recommendations and guidelines for the control of TB and state TB control laws. In order to address these discrepancies, states updating TB control laws should incorporate current recommendations and guidelines from CDC, ACET, and the American Thoracic Society. State laws should permit policies and practices to be rapidly reviewed and amended as new data becomes available and new recommendations and guidelines are published.The following CDC staff members prepared this report: Brian M. Willis, Office of the General Counsel Office of the Director; Lawrence Paul Schwartz, Division of Tuberculosis Elimination National Center for Prevention Services; Sarah B. Knowlton, Office of the General Counsel Office of the Director.Includes bibliographical references (p. 12-13)
Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys
No full textThe applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q ≈ 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature
Dynamics of non-ergodic ferromagnetic/antiferromagnetic ordering and magnetocalorics in antiperovskite Mn3SnC
No full textWe investigated the time dependence of the magnetic configuration at the mixed magnetic magnetostructural transition in Mn3SnC. The non-ergodic nature of the transition involves the stabilization of a final magnetic configuration that involves additional AF ordering which is not present when the transition is initiated and develops only in time. We show the presence of the non-ergodicity over a time scale of about 1 hour by field and time-dependent magnetization studies. Two charac-
teristic times related to the transition are observed. We also study the equilibrium thermodynamics under ergodic conditions by heat capacity studies and determine the entropy-change and the adiabatic temperature-change around the transition. We find agreement between the indirect and direct methods in determining the adiabatic temperature change and discuss the influence of non-ergodic properties on the magnetocaloric effects
Neutron diffraction and symmetry analysis of the martensitic transformation in Co-doped Ni2MnGa
No full textMartensitic transformations are strain driven displacive transitions governing the mechanical and physical properties in intermetallic materials. This is the case in Ni2MnGa, where the martensite transition is at the heart of the striking magnetic shape memory and magnetocaloric properties. Interestingly, the martensitic transformation is preceded by a premartensite phase, and the role of this precursor and its influence on the martensitic transition and properties is still a matter of debate. In this work we report on the influence of Co doping (Ni50-xCoxMn25Ga25 with x=3 and 5) on the martensitic transformation path in stoichiometric Ni2MnGa by neutron diffraction. The use of the superspace formalism to describe the crystal structure of the modulated martensitic phases, joined with a group theoretical analysis, allows unfolding the different distortions featuring the structural transitions. Finally, a general Landau thermodynamic potential of the martensitic transformation, based on the symmetry analysis, is outlined. The combined use of phenomenological and crystallographic studies highlights the close relationship between the lattice distortions at the core of the Ni2MnGa physical properties and, more in general, on the properties of the martensitic transformations in the Ni-Mn based Heusler systems
Intermartensitic transitions and phase stability in Ni<inf>50</inf>Mn<inf>50-x</inf>Sn<inf>x</inf> Heusler alloys
No full textNi–Mn based Heusler alloys are of considerable interest due to their multifunctional properties such as
magnetic shape memory, magnetocaloric effect and spintronics. The reason for these multifunctional
properties is the presence of a first order martensitic transition and its strong coupling to the magnetization.
In this work, one of the outstanding class of martensitic Heuslers, Ni–Mn–Sn, is investigated in
relation to magneto-structural phase transitions and the stability of the various crystallographic structures
under varying temperature. Temperature-dependent X-ray diffraction, resistance and magnetization
measurements on Ni50Mn50xSnx alloys are performed in a broad valence electron concentration
range 7:91 6 ðe=aÞ 6 8:34 (5:1 6 x 6 20:3 at:%). The results reveal that in addition to the austenite–
martensite transition, further intermartensitic transitions take place with decreasing temperature.
Depending on the composition, we observe that the parent martensite phase tends to transform to L10
martensite as the ground state phase when the temperature is lowered. A phase diagram of
Ni50Mn50xSnx is constructed to include intermartensitic phase transition boundaries
Magnetic properties and the inverse magnetocaloric effect in Mn3Ga1-xPtxC and Mn3Ga(C,N) at the magnetostructural transition
No full textMagnetic properties and the inverse magnetocaloric effect in Mn3Ga1-xPtxC at the magnetostructural transitionÖ. Cakir1, M. Acet 2(1) Physics department, Yildiz Technical University, 34210 Istanbul,Turkey, (2) Physics Dept., Duisburg Essen University, 47048 Duisburg, GermanyThe ferromagnetic to antiferromagnetic transition on decreasing temperature in the antiperovskite Mn3Ga1-xPtxC is accompanied by a structural distortion which leads to thermal hysteresis. This magnetostructural transition occurs in the temperature range 150 ≤ T ≤ 170 K and has a thermal hysteresis-width of about 4-10 K as observed from magnetization measurements. The transition shifts to lower temperature under higher applied fi elds. This shift is accompanied by a fi eld-induced reverse transformation from the antiferromagnetic to the ferromagnetic state, giving rise to the inverse magnetocaloric effect. We study the inverse magnetocaloric effect, both by determining the entropy change from magnetization isotherms and by direct adiabatic temperature-change measurement around the transition. We further study the properties of the effect of the thermal hysteresis on the inverse magnetocaloric effect.</p
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