444 research outputs found
Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition
The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with
coupled magnetic and structural (martensitic) phase transitions were studied
experimentally and theoretically. The magnetocaloric effect was measured by a
direct method in magnetic fields 0-26 kOe at temperatures close to the
magnetostructural transition temperature. For theoretical description of the
alloy properties near the magnetostructural transition a statistical model is
suggested, that takes into account the coexistence of martensite and austenite
domains in the vicinity of martensite transformation point.Comment: presented at ICM-2003, to appear in JMM
Diamagnetically Levitated MEMS Accelerometers
We introduce the theory and a proof-of-concept design for MEMS-based, diamagnetically-levitated
accelerometers. The theory includes an equation for determining the diamagnetic force above a
checkerboard configuration of magnets. We demonstrate both electronic probing and a rapid MEMS-based
interferometer technique for position sensing of the proof mass. Through a proof-of-concept
design, we show electrostatic-measurement sensitivity achieving 34 μg at a 0.1 V sense signal and
interferometer-measurement sensitivity achieving 6 μg for in-plane vibrations at 5 Hz. We conclude by
outlining batch-fabrication steps to produce levitated accelerometers
Evolution of the Z-Scheme of Electron Transport in Oxygenic Photosynthesis
We start with the discussion of the photosynthetic unit, based on the experiments of Emerson and
Arnold (1932a, 1932b), continue with the first two-quantum proposal by Rabinowitch (1945, 1956), Emerson's
Red drop (1943) and Emerson Enhancement Effect (1957) and various action spectra made for understanding the
roles of the photosynthetic pigments. The experimental work of Kok (1959) and the theoretical model by Hill and
Bendall (1960) were followed soon thereafter by the seminal papers of Duysens et al. (1961) and Duysens and
Amesz (1962), in which the two photosystems were shown to be connected, in series, by cytochrome, which can
be photooxidized by photo system I and photoreduced by photosystem II. Further, Witt et al. (1961) and others,
cited in this paper, made refinement of the Z-scheme
Immersed boundary-finite element model of fluid-structure interaction in the aortic root
It has long been recognized that aortic root elasticity helps to ensure
efficient aortic valve closure, but our understanding of the functional
importance of the elasticity and geometry of the aortic root continues to
evolve as increasingly detailed in vivo imaging data become available. Herein,
we describe fluid-structure interaction models of the aortic root, including
the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the
sinotubular junction, that employ a version of Peskin's immersed boundary (IB)
method with a finite element (FE) description of the structural elasticity. We
develop both an idealized model of the root with three-fold symmetry of the
aortic sinuses and valve leaflets, and a more realistic model that accounts for
the differences in the sizes of the left, right, and noncoronary sinuses and
corresponding valve cusps. As in earlier work, we use fiber-based models of the
valve leaflets, but this study extends earlier IB models of the aortic root by
employing incompressible hyperelastic models of the mechanics of the sinuses
and ascending aorta using a constitutive law fit to experimental data from
human aortic root tissue. In vivo pressure loading is accounted for by a
backwards displacement method that determines the unloaded configurations of
the root models. Our models yield realistic cardiac output at physiological
pressures, with low transvalvular pressure differences during forward flow,
minimal regurgitation during valve closure, and realistic pressure loads when
the valve is closed during diastole. Further, results from high-resolution
computations demonstrate that IB models of the aortic valve are able to produce
essentially grid-converged dynamics at practical grid spacings for the
high-Reynolds number flows of the aortic root
In photosynthesis, oxygen comes from water: from a 1787 book for women by Monsieur De Fourcroy
Abstract It is now well established that the source of oxygen in photosynthesis is water. The earliest suggestion previously known to us had come from René Bernard Wurmser (1930). Here, we highlight an earlier report by Monsieur De Fourcroy (1787), who had already discussed the broad outlines of such a hypothesis in a book on Chemistry written for women. We present here a free translation of a passage from this book, with the original text in French as an Appendix
On-line mass spectrometry: membrane inlet sampling
Significant insights into plant photosynthesis and respiration have been achieved using membrane inlet mass spectrometry (MIMS) for the analysis of stable isotope distribution of gases. The MIMS approach is based on using a gas permeable membrane to enable the entry of gas molecules into the mass spectrometer source. This is a simple yet durable approach for the analysis of volatile gases, particularly atmospheric gases. The MIMS technique strongly lends itself to the study of reaction flux where isotopic labeling is employed to differentiate two competing processes; i.e., O2 evolution versus O2 uptake reactions from PSII or terminal oxidase/rubisco reactions. Such investigations have been used for in vitro studies of whole leaves and isolated cells. The MIMS approach is also able to follow rates of isotopic exchange, which is useful for obtaining chemical exchange rates. These types of measurements have been employed for oxygen ligand exchange in PSII and to discern reaction rates of the carbonic anhydrase reactions. Recent developments have also engaged MIMS for online isotopic fractionation and for the study of reactions in inorganic systems that are capable of water splitting or H2 generation. The simplicity of the sampling approach coupled to the high sensitivity of modern instrumentation is a reason for the growing applicability of this technique for a range of problems in plant photosynthesis and respiration. This review offers some insights into the sampling approaches and the experiments that have been conducted with MIMS
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