66 research outputs found
Probing molecular dynamics at the nanoscale via an individual paramagnetic center
Understanding the dynamics of molecules adsorbed to surfaces or confined to
small volumes is a matter of increasing scientific and technological
importance. Here, we demonstrate a pulse protocol using individual paramagnetic
nitrogen vacancy (NV) centers in diamond to observe the time evolution of 1H
spins from organic molecules located a few nanometers from the diamond surface.
The protocol records temporal correlations among the interacting 1H spins, and
thus is sensitive to the local system dynamics via its impact on the nuclear
spin relaxation and interaction with the NV. We are able to gather information
on the nanoscale rotational and translational diffusion dynamics by carefully
analyzing the time dependence of the NMR signal. Applying this technique to
various liquid and solid samples, we find evidence that liquid samples form a
semi-solid layer of 1.5 nm thickness on the surface of diamond, where
translational diffusion is suppressed while rotational diffusion remains
present. Extensions of the present technique could be adapted to highlight the
chemical composition of molecules tethered to the diamond surface or to
investigate thermally or chemically activated dynamical processes such as
molecular folding
Enhanced dynamic nuclear polarization via swept microwave frequency combs
Dynamic Nuclear Polarization (DNP) has enabled enormous gains in magnetic
resonance signals and led to vastly accelerated NMR/MRI imaging and
spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the
full electron spectrum are appealing since they allow direct participation of
all electrons in the hyperpolarization process. Such methods typically entail
sweeps of microwave radiation over the broad electron linewidth to excite DNP,
but are often inefficient because the sweeps, constrained by adiabaticity
requirements, are slow. In this paper we develop a technique to overcome the
DNP bottlenecks set by the slow sweeps, employing a swept microwave frequency
comb that increases the effective number of polarization transfer events while
respecting adiabaticity constraints. This allows a multiplicative gain in DNP
enhancement, scaling with the number of comb frequencies and limited only by
the hyperfine-mediated electron linewidth. We demonstrate the technique for the
optical hyperpolarization of 13C nuclei in powdered microdiamonds at low
fields, increasing the DNP enhancement from 30 to 100 measured with respect to
the thermal signal at 7T. For low concentrations of broad linewidth electron
radicals, e.g. TEMPO, these multiplicative gains could exceed an order of
magnitude.Comment: Contains supplementary inf
Influencia de la fertilización inorgánica sobre la actividad microbiana del suelo
Las mediciones se llevaron a cabo en la campaña 2010/11 en un ensayo en el establecimiento Balducchi, ubicado en la localidad de Teodelina (Santa Fe), que forma parte de la Red de Nutrición CREA Sur de Santa Fe (CREA-IPNI-ASP). En ese ensayo, bajo rotación maíz-trigo/soja, se evalúan, anualmente desde la campaña 2000/01, fertilizaciones con N, P, S y micronutrientes en las siguientes combinaciones: PS, NS, NP, NPS, NPS+Micronutrientes, y Testigo (sin adición de fertilizante) en 3 repeticiones siguiendo un diseño en bloques completos al azar.Según la información obtenida, la actividad microbiana del suelo, medida por la cuantificación del consumo de diversas fuentes de C, fue influenciada por la fertilización inorgánica. De acuerdo al ACP, el tratamiento con nutrición más balanceada (NPS+Micros) registró mayor consumo de sustratos carbonados, que los restantes tratamientos. Según algunos autores, los fertilizantes inorgánicos afectan los parámetros biológicos debido al incremento del contenido de C orgánico del suelo, que determina el crecimiento de los microorganismos, siendo el P un factor clave en el aumento de la diversidad microbiana y fertilidad del suelo. Finalmente, el rendimiento del cultivo también se incrementó en respuesta a la fertilización, en comparación con el Testigo. Existe una compleja interacción entre el nivel óptimo de fertilización, la disponibilidad de nutrientes para el crecimiento de los microorganismos y el buen desarrollo de las plantas. Esto demuestra que son necesarios más estudios para profundizar el conocimiento acerca del efecto de la fertilización inorgánica sobre las funciones metabólicas de la microbiota del suelo.Fil: Conforto, C.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; ArgentinaFil: Correa, Olga Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; ArgentinaFil: Rovea, A.. Grupo Crea Santa Fe; ArgentinaFil: Boxler, M.. Grupo Crea Santa Fe; ArgentinaFil: Rodríguez Grastorf, S.. Grupo Crea Santa Fe; ArgentinaFil: Minteguiaga, J.. Grupo Crea Santa Fe; ArgentinaFil: Meriles, Jose Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Vargas Gil, Silvina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
13C dynamic nuclear polarization in diamond via a microwave-free 'integrated' cross effect
Color-center-hosting semiconductors are emerging as promising source
materials for low-field dynamic nuclear polarization (DNP) at or near room
temperature, but hyperfine broadening, susceptibility to magnetic field
heterogeneity, and nuclear spin relaxation induced by other paramagnetic
defects set practical constraints difficult to circumvent. Here, we explore an
alternate route to color-center-assisted DNP using nitrogen-vacancy (NV)
centers in diamond coupled to substitutional nitrogen impurities, the so-called
P1 centers. Working near the level anti-crossing condition - where the P1
Zeeman splitting matches one of the NV spin transitions - we demonstrate
efficient microwave-free 13C DNP through the use of consecutive magnetic field
sweeps and continuous optical excitation. The amplitude and sign of the
polarization can be controlled by adjusting the low-to-high and high-to-low
magnetic field sweep rates in each cycle so that one is much faster than the
other. By comparing the 13C DNP response for different crystal orientations, we
show that the process is robust to magnetic field/NV misalignment, a feature
that makes the present technique suitable to diamond powders and settings where
the field is heterogeneous. Applications to shallow NVs could capitalize on the
greater physical proximity between surface paramagnetic defects and outer
nuclei to efficiently polarize target samples in contact with the diamond
crystal
Probing molecular dynamics at the nanoscale via an individual paramagnetic centre
We demonstrate a protocol using individual nitrogen-vacancy centres in diamond to observe the time evolution of proton spins from organic molecules located a few nanometres from the diamond surface. The protocol records temporal correlations among the interacting protons, and thus is sensitive to the local dynamics via its impact on the nuclear spin relaxation and interaction with the nitrogen vacancy. We gather information on the nanoscale rotational and translational diffusion dynamics by analysing the time dependence of the nuclear magnetic resonance signal. Applying this technique to liquid and solid samples, we find evidence that liquid samples form a semi-solid layer of 1.5-nm thickness on the surface of diamond, where translational diffusion is suppressed while rotational diffusion remains present. Extensions of the present technique could be exploited to highlight the chemical composition of molecules tethered to the diamond surface or to investigate thermally or chemically activated dynamical processes such as molecular folding
Wide dynamic range magnetic field cycler: Harnessing quantum control at low and high fields
We describe the construction of a fast field cycling device capable of
sweeping a 4-order-of-magnitude range of magnetic fields, from ~1mT to 7T, in
under 700ms. Central to this system is a high-speed sample shuttling mechanism
between a superconducting magnet and a magnetic shield, with the capability to
access arbitrary fields in between with high resolution. Our instrument serves
as a versatile platform to harness the inherent dichotomy of spin dynamics on
offer at low and high fields - in particular, the low anisotropy, fast spin
manipulation, and rapid entanglement growth at low field as well as the long
spin lifetimes, spin specific control, and efficient inductive measurement
possible at high fields. Exploiting these complementary capabilities in a
single device open up applications in a host of problems in quantum control,
sensing, and information storage, besides in nuclear hypepolarization,
relaxometry and imaging. In particular, in this paper, we focus on the ability
of the device to enable low-field hyperpolarization of 13C nuclei in diamond
via optically pumped electronic spins associated with Nitrogen Vacancy (NV)
defect centers
Caracterización física y obtención de parámetros de fluidización de germen de trigo
El germen de trigo es el embrión del grano de trigo, presenta un elevado contenido de tocoferoles y proteínas y ácidos grasos y proteínas de alta calidad. A su vez, contiene enzimas con elevada actividad que limitan su periodo de aptitud a unos pocos días. El objetivo del presente trabajo fue caracterizar físicamente las partículas de germen de trigo para determinar los parámetros de diseño para un proceso de fluidificación térmica con aire. Los ejes principales de las partículas fueron determinados mediante análisis de imágenes y sus dimensiones y parámetros geométricos fueron calculados. La densidad de lecho fijo y la porosidad del lecho fueron determinadas. Los estudios fluido-dinámicos nos permitieron determinar los coeficientes, laminar (277,46±17,48) y turbulento (7,79±0,69) de la ecuación de Ergun y la velocidad de mínima fluidificación (0,35±0,02 m/s).Wheat germ is the embryo of de wheat seed, it contains a high tocopherol and protein content, and high quality proteins and fatty acids. Also, wheat germ has a considerable enzymatic activity that limits its shelf life. The aims of the study were to physically characterize wheat germ particles to determine their design parameters of thermal fluidization process with air. The principal axes of the particle were measured by image analysis, and their dimensions and geometric parameters were calculated. The fixed bed density and the void fraction were measured. The fluid-dynamic studies allowed us to determine laminar (277.46±17.48) and turbulent (7.79±0.69) coefficients of the Ergun equation and the minimum fluidization velocity (0.35±0.02 m/s).Centro de Investigación y Desarrollo en Criotecnología de Alimento
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