529 research outputs found
Coherence of Nitrogen-Vacancy Electronic Spin Ensembles in Diamond
We present an experimental and theoretical study of electronic spin
decoherence in ensembles of nitrogen-vacancy (NV) color centers in bulk
high-purity diamond at room temperature. Under appropriate conditions, we find
ensemble NV spin coherence times (T_2) comparable to that of single NVs, with
T_2 > 600 microseconds for a sample with natural abundance of 13C and
paramagnetic impurity density ~10^15 cm^(-3). We also observe a sharp decrease
of the coherence time with misalignment of the static magnetic field relative
to the NV electronic spin axis, consistent with theoretical modeling of NV
coupling to a 13C nuclear spin bath. The long coherence times and increased
signal-to-noise provided by room-temperature NV ensembles will aid many
applications of NV centers in precision magnetometry and quantum information.Comment: 5 pages, 3 figures; v2 minor correction
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Optical magnetic imaging of living cells
Magnetic imaging is a powerful tool for probing biological and physical systems. However, existing techniques either have poor spatial resolution compared to optical microscopy and are hence not generally applicable to imaging of sub-cellular structure (e.g., magnetic resonance imaging [MRI]1), or entail operating conditions that preclude application to living biological samples while providing sub-micron resolution (e.g., scanning superconducting quantum interference device [SQUID] microscopy2, electron holography3, and magnetic resonance force microscopy [MRFM]4). Here we demonstrate magnetic imaging of living cells (magnetotactic bacteria) under ambient laboratory conditions and with sub-cellular spatial resolution (400 nm), using an optically-detected magnetic field imaging array consisting of a nanoscale layer of nitrogen-vacancy (NV) colour centres implanted at the surface of a diamond chip. With the bacteria placed on the diamond surface, we optically probe the NV quantum spin states and rapidly reconstruct images of the vector components of the magnetic field created by chains of magnetic nanoparticles (magnetosomes) produced in the bacteria, and spatially correlate these magnetic field maps with optical images acquired in the same apparatus. Wide-field sCMOS acquisition allows parallel optical and magnetic imaging of multiple cells in a population with sub-micron resolution and >100 micron field-of-view. Scanning electron microscope (SEM) images of the bacteria confirm that the correlated optical and magnetic images can be used to locate and characterize the magnetosomes in each bacterium. The results provide a new capability for imaging bio-magnetic structures in living cells under ambient conditions with high spatial resolution, and will enable the mapping of a wide range of magnetic signals within cells and cellular networks5, 6
Fourier Magnetic Imaging with Nanoscale Resolution and Compressed Sensing Speed-up using Electronic Spins in Diamond
Optically-detected magnetic resonance using Nitrogen Vacancy (NV) color
centres in diamond is a leading modality for nanoscale magnetic field imaging,
as it provides single electron spin sensitivity, three-dimensional resolution
better than 1 nm, and applicability to a wide range of physical and biological
samples under ambient conditions. To date, however, NV-diamond magnetic imaging
has been performed using real space techniques, which are either limited by
optical diffraction to 250 nm resolution or require slow, point-by-point
scanning for nanoscale resolution, e.g., using an atomic force microscope,
magnetic tip, or super-resolution optical imaging. Here we introduce an
alternative technique of Fourier magnetic imaging using NV-diamond. In analogy
with conventional magnetic resonance imaging (MRI), we employ pulsed magnetic
field gradients to phase-encode spatial information on NV electronic spins in
wavenumber or k-space followed by a fast Fourier transform to yield real-space
images with nanoscale resolution, wide field-of-view (FOV), and compressed
sensing speed-up.Comment: 31 pages, 10 figure
Enhanced solid-state multi-spin metrology using dynamical decoupling
We use multi-pulse dynamical decoupling to increase the coherence lifetime
(T2) of large numbers of nitrogen-vacancy (NV) electronic spins in room
temperature diamond, thus enabling scalable applications of multi-spin quantum
information processing and metrology. We realize an order-of-magnitude
extension of the NV multi-spin T2 for diamond samples with widely differing
spin environments. For samples with nitrogen impurity concentration <~1 ppm, we
find T2 > 2 ms, comparable to the longest coherence time reported for single NV
centers, and demonstrate a ten-fold enhancement in NV multi-spin sensing of AC
magnetic fields
Congenital dislocation of the hip: Optimal screening strategies in 2014
AbstractA prospective multi-centre nationwide study of patients with congenital dislocation of the hip (CDH) diagnosed after 3 months of age was conducted with support from the French Society for Paediatric Orthopaedics (Société Française d’Orthopédie Pédiatrique [SoFOP]), French Organisation for Outpatient Paediatrics (Association Française de Pédiatrie Ambulatoire [AFPA]), and French-Speaking Society for Paediatric and Pre-Natal Imaging (Société Francophone d’Imagerie Pédiatrique et Prénatale [SFIPP]). The results showed inadequacies in clinical screening for CDH that were patent when assessed quantitatively and probably also present qualitatively. These findings indicate a need for a communication and educational campaign aimed at highlighting good clinical practice guidelines in the field of CDH screening. The usefulness of routine ultrasound screening has not been established. The findings from this study have been used by the authors and French National Health Authority (Haute Autorité de Santé [HAS]) to develop recommendations about CDH screening. There is an urgent need for a prospective randomised multi-centre nationwide study, which should involve primary-care physicians
Magnetic field imaging with nitrogen-vacancy ensembles
Part of Focus on Diamond-Based Photonics and Spintronics
We demonstrate a method of imaging spatially varying magnetic fields using a thin layer of nitrogen-vacancy (NV) centers at the surface of a diamond chip. Fluorescence emitted by the two-dimensional NV ensemble is detected by a CCD array, from which a vector magnetic field pattern is reconstructed. As a demonstration, ac current is passed through wires placed on the diamond chip surface, and the resulting ac magnetic field patterns are imaged using an echo-based technique with sub-micron resolution over a 140 μm×140 μm field of view, giving single-pixel sensitivity \sim100\,{\rm nT}/\sqrt{{\rm Hz}} . We discuss ongoing efforts to further improve the sensitivity, as well as potential bioimaging applications such as real-time imaging of activity in functional, cultured networks of neurons.
PACS
61.72.J- Point defects and defect clusters
78.55.Hx Other solid inorganic materials
87.50.C- Static and low-frequency electric and magnetic fields effects
85.30.Tv Field effect devices
Subjects
Electronics and devices
Condensed matter: electrical, magnetic and optical
Semiconductors
Medical physics
Biological physics
Condensed matter: structural, mechanical & thermalUnited States. Defense Advanced Research Projects AgencyNational Institute of Standards and Technology (U.S.)National Science Foundation (U.S.
Induction of microRNAs, mir-155, mir-222, mir-424 and mir-503, promotes monocytic differentiation through combinatorial regulation
Acute myeloid leukemia (AML) involves a block in terminal differentiation of
the myeloid lineage and uncontrolled proliferation of a progenitor state. Using
phorbol myristate acetate (PMA), it is possible to overcome this block in THP-1
cells (an M5-AML containing the MLL-MLLT3 fusion), resulting in differentiation
to an adherent monocytic phenotype. As part of FANTOM4, we used microarrays to
identify 23 microRNAs that are regulated by PMA. We identify four PMA-induced
micro- RNAs (mir-155, mir-222, mir-424 and mir-503) that when overexpressed
cause cell-cycle arrest and partial differentiation and when used in
combination induce additional changes not seen by any individual microRNA. We
further characterize these prodifferentiative microRNAs and show that mir-155
and mir-222 induce G2 arrest and apoptosis, respectively. We find mir-424 and
mir-503 are derived from a polycistronic precursor mir-424-503 that is under
repression by the MLL-MLLT3 leukemogenic fusion. Both of these microRNAs
directly target cell-cycle regulators and induce G1 cell-cycle arrest when
overexpressed in THP-1. We also find that the pro-differentiative mir-424 and
mir-503 downregulate the anti-differentiative mir-9 by targeting a site in its
primary transcript. Our study highlights the combinatorial effects of multiple
microRNAs within cellular systems.Comment: 45 pages 5 figure
MIR376A is a regulator of starvation-induced autophagy
Background: Autophagy is a vesicular trafficking process responsible for the degradation of long-lived, misfolded or abnormal proteins, as well as damaged or surplus organelles. Abnormalities of the autophagic activity may result in the accumulation of protein aggregates, organelle dysfunction, and autophagy disorders were associated with various diseases. Hence, mechanisms of autophagy regulation are under exploration.
Methods: Over-expression of hsa-miR-376a1 (shortly MIR376A) was performed to evaluate its effects on autophagy. Autophagy-related targets of the miRNA were predicted using Microcosm Targets and MIRanda bioinformatics tools and experimentally validated. Endogenous miRNA was blocked using antagomirs and the effects on target expression and autophagy were analyzed. Luciferase tests were performed to confirm that 3’ UTR sequences in target genes were functional. Differential expression of MIR376A and the related MIR376B was compared using TaqMan quantitative PCR.
Results: Here, we demonstrated that, a microRNA (miRNA) from the DlkI/Gtl2 gene cluster, MIR376A, played an important role in autophagy regulation. We showed that, amino acid and serum starvation-induced autophagy was blocked by MIR376A overexpression in MCF-7 and Huh-7 cells. MIR376A shared the same seed sequence and had overlapping targets with MIR376B, and similarly blocked the expression of key autophagy proteins ATG4C and BECN1 (Beclin 1). Indeed, 3’ UTR sequences in the mRNA of these autophagy proteins were responsive to MIR376A in luciferase assays. Antagomir tests showed that, endogenous MIR376A was participating to the control of ATG4C and BECN1 transcript and protein levels. Moreover, blockage of endogenous MIR376A accelerated starvation-induced autophagic activity. Interestingly, MIR376A and MIR376B levels were increased with different kinetics in response to starvation stress and tissue-specific level differences were also observed, pointing out to an overlapping but miRNA-specific biological role.
Conclusions: Our findings underline the importance of miRNAs encoded by the DlkI/Gtl2 gene cluster in stress-response control mechanisms, and introduce MIR376A as a new regulator of autophagy
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