- [NMR] Position as Research Engineer / Lab Manager for the magnetic resonance lab @ IPF Dresden
- Surface-selective direct 17O DNP NMR of CeO2 nanoparticles #DNPNMR
- Site specific polarization transfer from a hyperpolarized ligand of dihydrofolate reductase
- Hyperpolarized 13C pyruvate mouse brain metabolism with absorptive-mode EPSI at 1T
- Peptide and Protein Dynamics and Low-Temperature/DNP Magic Angle Spinning NMR #DNPNMR
- [NMR] PhD position in EPR & NMR at IPF Dresden
- [NMR] ultra fast-MAS proton-detected solid-state NMR
- Fumarase activity: an in vivo and in vitro biomarker for acute kidney injury
- Tailored Polarizing Hybrid Solids with Nitroxide Radicals Localized in Mesostructured Silica Walls #DNPNMR
- U. of Ottawa NMR Facility Blog The Effect of the 2H Lock on Environmental Instability
- Rotaxane probes for protease detection by 129Xe hyperCEST NMR
- Dynamic Polarization and Relaxation of 75As Nuclei in Silicon at High Magnetic Field and Low Temperature #DNPNMR
- Delivering strong 1H nuclear hyperpolarization levels and long magnetic lifetimes through signal amplification by reversible exchange
- U. of Ottawa NMR Facility Blog HMBC vs. H2BC
- Combining DNP NMR with segmental and specific labeling to study a yeast prion protein strain that is not parallel in-register #DNPNMR
- Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples
- EPR Imaging Spin Probe Trityl Radical OX063: A Method for Its Isolation from Animal Effluent, Redox Chemistry of Its Quinone Methide Oxidation Product, and in Vivo Application in a Mouse
- [NMR] Postdoc position in liquid-state NMR methodology and hyperpolarization, Nantes, France
- Low-cost, pseudo-Halbach dipole magnets for NMR
- Atomic-Level Structure Characterization of Biomass Pre- and Post-Lignin Treatment by Dynamic Nuclear Polarization-Enhanced Solid-State NMR #DNPNMR
- [NMR] PhD position on SSNMR at the University of Lille, France #DNPNMR
- Surface-Sensitive NMR Detection of the Solid Electrolyte Interphase Layer on Reduced Graphene Oxide #DNPNMR
- Field-frequency locked X-band Overhauser effect spectrometer #DNPNMR
- Directly vs Indirectly Enhanced 13C in Dynamic Nuclear Polarization Magic Angle Spinning NMR Experiments of Nonionic Surfactant Systems
- Dynamic Nuclear Polarization Signal Amplification as a Sensitive Probe for Specific Functionalization of Complex Paper Substrates #DNPNMR
- Dynamic Nuclear Polarization of ?-Cyclodextrin Macromolecules #DNPNMR
- Hyperpolarized Multi-Metal 13C-Sensors for Magnetic Resonance Imaging
- Quantitative analysis of molecular transport across liposomal bilayer by J-mediated 13C Overhauser dynamic nuclear polarization
- The effect of Gd on trityl-based dynamic nuclear polarisation in solids
- Parallelized Ligand Screening Using Dissolution Dynamic Nuclear Polarization
- Perspectives for hyperpolarisation in compact NMR
- Dynamic Nuclear Polarization Signal Enhancement with High-Affinity Biradical Tags #DNPNMR
- Stan NMR blog Molecular Spins: a New Frontier
- Stan NMR blog Fitting of spin system parameters to NMR spectra, revisited
- One-thousand-fold enhancement of high field liquid nuclear magnetic resonance signals at room temperature
- Biosilica-Entrapped Enzymes Studied by Using Dynamic Nuclear-Polarization-Enhanced High-Field NMR Spectroscopy #DNPNMR
- Stan NMR blog NMR in XXI Century: 30 selected things to do and explore
- Stan NMR blog Is NMR Stuck?
- [NMR] PhD Position, Optically pumped DNP, University of Huddersfield (UK)
- Chemical-shift-resolved (1)(9)F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy
- A ferromagnetic shim insert for NMR magnets – Towards an integrated gyrotron for DNP-NMR spectroscopy #DNPNMR
- Chapter Sixteen - Overhauser Dynamic Nuclear Polarization Studies on Local Water Dynamics #DNPNMR
- [NMR] Joint postdoc position in biomoclecular NMR/DNP at IBS/INAC in Grenoble #DNPNMR
- [NMR] PhD position in DNP-NMR #DNPNMR
- Heteronuclear Cross-Relaxation under Solid-State Dynamic Nuclear Polarization #DNPNMR
- [NMR] PhD & Postdoc in MAS-DNP at CEA Grenoble (France)
- Singlet order conversion and parahydrogen-induced hyperpolarization of 13C nuclei in near-equivalent spin systems
- Spatial distribution of organic functional groups supported on mesoporous silica nanoparticles: a study by conventional and DNP-enhanced 29Si solid-state NMR #DNPNMR
- [NMR] Post-doctoral position in Rossini lab at Iowa State University
- Investigation of Intrinsically Disordered Proteins through Exchange with Hyperpolarized Water
- Large dose hyperpolarized water with dissolution-DNP at high magnetic field
- Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence #DNPNMR
- A combined EPR and MD simulation study of a nitroxyl spin label with restricted internal mobility sensitive to protein dynamics
- Using signal amplification by reversible exchange (SABRE) to hyperpolarise 119Sn and 29Si NMR nuclei
- Hyperpolarized Nanodiamond Surfaces #DNPNMR
- [NMR] Multiple postdoc positions in Hyperpolarized 13C MR
- [NMR] Training School on Principles and Applications of Dissolution DNP, Nov 13-17, 2017, Copenhagen
- Dynamic Nuclear Polarization and Relaxation of H and D Atoms in Solid Mixtures of Hydrogen Isotopes #DNPNMR
- [NMR] Postdoc position University of Florida / National High Magnetic Field Laboratory
- Hyperpolarized [1,4-(13)C]-diethylsuccinate: a potential DNP substrate for in vivo metabolic imaging
- [NMR] PhD & Postdoc positions on dissolution-DNP / Sami Jannin's group / Lyon
- Producing Radical-Free Hyperpolarized Perfusion Agents for In Vivo Magnetic Resonance Using Spin-Labeled Thermoresponsive Hydrogel
- Chemisorption of Water on the Surface of Silicon Microparticles Measured by DNP-Enhanced NMR #DNPNMR
- Producing Radical-Free Hyperpolarized Perfusion Agents for In Vivo Magnetic Resonance Using Spin-Labeled Thermoresponsive Hydrogel
- Dynamic nuclear polarisation via the integrated solid effect II: experiments on naphthalene-h8doped with pentacene-d14 #DNPNMR
- [NMR] EPR position in TU Dortmund (PhD)
- Studies on the MxiH protein in T3SS needles using DNP-enhanced ssNMR spectroscopy #DNPNMR
- [NMR] Postdoc position on parahydrogen-enhanced NMR available in the Levitt group
- High resolution observed in 800 MHz DNP spectra of extremely rigid type III secretion needles #DNPNMR
- Temperature dependence of cross-effect dynamic nuclear polarization in rotating solids: advantages of elevated temperatures #DNPNMR
- U. of Ottawa NMR Facility Blog Improved 1H Resolution with 14N Decoupling
- [NMR] Postdoc position at Univ. Lille, France, on high-field solid-state NMR of low-gamma quadrupolar nuclei in materials
- U. of Ottawa NMR Facility Blog PSYCHE to Evaluate 1H-19F Coupling Constants
- Application of flow sensitive gradients for improved measures of metabolism using hyperpolarized (13) c MRI
- U. of Ottawa NMR Facility Blog Pure Shift 1H NMR - PSYCHE
- Quantification of rate constants for successive enzymatic reactions with DNP hyperpolarized MR
- Hyperpolarized 13C NMR studies of glucose metabolism in living breast cancer cell cultures
- [NMR] PhD student position in hyperpolarized MRI of stroke
- Dynamic nuclear polarisation via the integrated solid effect I: theory #DNPNMR
- Insight into the Supramolecular Architecture of Intact Diatom Biosilica from DNP-Supported Solid-State NMR Spectroscopy #DNPNMR
- [NMR] MOOC on NMR, Feb. 20 to Apr. 17, 2017
- U. of Ottawa NMR Facility Blog Exchange Effects in HSQC Spectra
- DNP-Enhanced Ultrawideline Solid-State NMR Spectroscopy: Studies of Platinum in Metal-Organic Frameworks #DNPNMR
- [NMR] Faculty Position in NMR
- 19F Dynamic Nuclear Polarization and SEM in Suspensions Consisting of Fluorobenzene Derivatives and Asphaltene Extracted from MC-800 Liquid Asphalt #DNPNMR
- Rational design of dinitroxide biradicals for efficient cross-effect dynamic nuclear polarization #DNPNMR
- [NMR] Two Research Fellowships in Southampton, UK, with deadline 19 Jan 2017
- Expeditious dissolution dynamic nuclear polarization without glassing agents
- Antioxidant treatment attenuates lactate production in diabetic nephropathy
- Dissolution dynamic nuclear polarization–enhanced magnetic resonance spectroscopy and imaging: Chemical and biochemical reactions in nonequilibrium conditions #DNPNMR
- Surface Binding of TOTAPOL Assists Structural Investigations of Amyloid Fibrils by Dynamic Nuclear Polarization NMR Spectroscopy #DNPNMR
- [NMR] Tenure-track NMR position at UCSD
- Atomistic Description of Reaction Intermediates for Supported Metathesis Catalysts Enabled by DNP SENS #DNPNMR
- Dynamic Nuclear Polarization and Other Magnetic Ideas at EPFL #DNPNMR
- Rational design of dinitroxide biradicals for efficient cross-effect dynamic nuclear polarization #DNPNMR
- Correction: Theory of solid effect and cross effect dynamic nuclear polarization with half-integer high-spin metal polarizing agents in rotating solids #DNPNMR
- [NMR] Prestigous PhD fellowships
- Microwave-gated dynamic nuclear polarization #DNPNMR
- Trityl-based alkoxyamines as NMP controllers and spin-labels
- Diffusion-mediated 129Xe gas depolarization in magnetic field gradients during continuous-flow optical pumping
- High-Resolution Two-Field Nuclear Magnetic Resonance Spectroscopy
- Stan NMR blog Is NMR Stuck?
- Stan NMR blog Update of the popular Mathematical Constants page
- Nuclear spin-lattice relaxation in nitroxide spin-label EPR
- Dissolution Dynamic Nuclear Polarization capability study with fluid path
- Cross relaxation in nitroxide spin labels
- Reaction monitoring using hyperpolarized NMR with scaling of heteronuclear couplings by optimal tracking
- Theory of solid effect and cross effect dynamic nuclear polarization with half-integer high-spin metal polarizing agents in rotating solids #DNPNMR
- Stan NMR blog Fixed points of the mappings exp(z) and -exp(z) in C
- Stan NMR blog Major reorganization of Stan's Mathematics Links
- Following Metabolism in Living Microorganisms by Hyperpolarized (1)H NMR
- Phenylazide Hybrid-Silica - Polarization Platform for Dynamic Nuclear Polarization at Cryogenic Temperatures #DNPNMR
- Open Position at Bridge12: Scientist - Magnetic Resonance #DNPNMR
- Simultaneous PET/MRI with (13)C magnetic resonance spectroscopic imaging (hyperPET): phantom-based evaluation of PET quantification
- 35Cl dynamic nuclear polarization solid-state NMR of active pharmaceutical ingredients #DNPNMR
- Selective High-Resolution Detection of Membrane Protein-Ligand Interaction in Native Membranes Using Trityl-Nitroxide PELDOR
- [NMR] Symposium in Honor of Prof. Jacob Schaefer - Jan. 6, 2017
- Gyrotrons for High-Power Terahertz Science and Technology at FIR UF #DNPNMR
- Difference between Extra- and IntracellularT1Values of Carboxylic Acids Affects the Quantitative Analysis of Cellular Kinetics by Hyperpolarized NMR
- Gd(iii) and Mn(ii) complexes for dynamic nuclear polarization: small molecular chelate polarizing agents and applications with site-directed spin labeling of proteins #DNPNMR
- A compact X-Band resonator for DNP-enhanced Fast-Field-Cycling NMR #DNPNMR
- Difference between Extra- and IntracellularT1Values of Carboxylic Acids Affects the Quantitative Analysis of Cellular Kinetics by Hyperpolarized NMR
- [NMR] Summer school Theory of NMR at Schloss Windischleuba 19-25 Feb. 2017
- [NMR] Postdoc in Levitt group on hyperpolarization
- Long-lived states to sustain SABRE hyperpolarised magnetisation
- Dissolution Dynamic Nuclear Polarization capability study with fluid path
- [NMR] Postdoctoral Fellow Position at Merck
- [NMR] MR Imaging and Spectroscopy Research Staff Scientist position at the U.S. National High Magnetic Field Laboratory / University of Florida
- Evidence of spin-temperature in dynamic nuclear polarization: an exact computation of the EPR spectrum #DNPNMR
- Finite element modeling of (129)Xe diffusive gas exchange NMR in the human alveoli
- Selective Protein Hyperpolarization in Cell Lysates Using Targeted Dynamic Nuclear Polarization #DNPNMR
- [NMR] Deadline 25 October: Two Research Fellow positions and one PhD studentship at University of Southampton #DNPNMR
- Multidimensional solid-state NMR spectroscopy of plant cell walls #DNPNMR
- Renal MR angiography and perfusion in the pig using hyperpolarized water
- [NMR] PhD Position, Biological Solid-state NMR, Univ. Leipzig
- Molecular Rationale for Improved Dynamic Nuclear Polarization of Biomembranes
- Two Research Fellow positions and one PhD studentship at University of Southampton #DNPNMR
- Filterable Agents for Hyperpolarization of Water, Metabolites, and Proteins
- IVAN (International Varian-Agilent NMR users group) Introduction
- Milli-tesla NMR and spectrophotometry of liquids hyperpolarized by dissolution dynamic nuclear polarization
- Hydration Dynamics of a Peripheral Membrane Protein #DNPNMR
- Impact of Ho3+-doping on 13C dynamic nuclear polarization using trityl OX063 free radical #DNPNMR
- Heteronuclear DNP of protons and deuterons with TEMPOL #DNPNMR
- Room-temperature electron spin relaxation of nitroxides immobilized in trehalose: Effect of substituents adjacent to NO-group
- [NMR] Post-doctoral position in MAS-DNP at Aix-Marseille University (France) #DNPNMR
- Hyperpolarization of Frozen Hydrocarbon Gases by Dynamic Nuclear Polarization at 1.2 K #DNPNMR
- [NMR] Postdoctoral Position in Biomolecular Solid-State NMR at USC, Los Angeles
- Structural analysis of a signal peptide inside the ribosome tunnel by DNP MAS NMR #DNPNMR
- Molecular Rationale for Improved Dynamic Nuclear Polarization of Biomembranes #DNPNMR
- 500-fold enhancement of in situ (13)C liquid state NMR using gyrotron-driven temperature-jump DNP #DNPNMR
- [NMR] Post-doctoral position in MAS-DNP, Lyon, France #DNPNMR
- Cubic three-dimensional hybrid silica solids for nuclear hyperpolarization
- Structural biology applications of solid state MAS DNP NMR #DNPNMR
- On The Potential of Dynamic Nuclear Polarization Enhanced Diamonds in Solid-State and Dissolution 13 C NMR Spectroscopy #DNPNMR
- Dynamics of 4-oxo-TEMPO-d16-(15)N nitroxide-propylene glycol system studied by ESR and ESE in liquid and glassy state in temperature range 10-295K
- Dynamic nuclear polarization at 40 kHz magic angle spinning #DNPNMR
- Solvent responsive catalyst improves NMR sensitivity via efficient magnetisation transfer #DNPNMR
- Silica materials with wall-embedded nitroxides provide efficient polarization matrices for dynamic nuclear polarization NMR #DNPNMR
- Single spin magnetic resonance
- Low-field thermal mixing in [1-(13)C] pyruvic acid for brute-force hyperpolarization
- A triarylmethyl spin label for long-range distance measurement at physiological temperatures using T1 relaxation enhancement #DNPNMR
- Orphan Spin Polarization: A Catalyst for High-Throughput Solid-State NMR Spectroscopy of Proteins
- Assessment of a Heuristic Model for Characterization of Magnetic Nanoparticles as Contrast Agent in MRI
- Nuclear magnetic resonance studies of DNP-ready trehalose obtained by solid state mechanochemical amorphization #DNPNMR
- bcTol: a highly water-soluble biradical for efficient dynamic nuclear polarization of biomolecules
- Creating a hyperpolarised pseudo singlet state through polarisation transfer from parahydrogen under SABRE
- [NMR] Research Associate in Dynamic Nuclear Polarisation NMR - Nottingham # DNPNMR
- Analysis of the SABRE (Signal Amplification by Reversible Exchange) Effect at High Magnetic Fields
- Immobilization of soluble protein complexes in MAS solid-state NMR: Sedimentation versus viscosity
- Do twisted laser beams evoke nuclear hyperpolarization?
- Studying the Conformation of a Silaffin-Derived Pentalysine Peptide Embedded in Bioinspired Silica using Solution and Dynamic Nuclear Polarization Magic-Angle Spinning NMR
- Towards Overhauser DNP in supercritical CO2
- Correlating Synthetic Methods, Morphology, Atomic-Level Structure, and Catalytic Activity of Sn-? Catalysts
- High-field dissolution dynamic nuclear polarization of [1-(13)C]pyruvic acid
- Tailoring of Polarizing Agents in the bTurea Series for Cross-Effect Dynamic Nuclear Polarization in Aqueous Media
- Further Characterization of 394-GHz Gyrotron FU CW GII with Additional PID Control System for 600-MHz DNP-SSNMR Spectroscopy #DNPNMR
- [NMR] Postdoctoral position in biological MAS ssNMR #NMR #SSNMR
- Solid Effect DNP in a Rapid-melt setup #DNPNMR
- Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods
- U. of Ottawa NMR Facility Blog NMR and Food Chemistry - Maple Syrup
- Waveguide transition with vacuum window for multiband dynamic nuclear polarization systems #DNPNMR
- HP-Xe to go: Storage and transportation of hyperpolarized 129Xenon
- Combined Hyperthermia and Photodynamic Therapy Using a Sub-THz Gyrotron as a Radiation Source
- [NMR] Two PhD positions in Solid State NMR in Nijmegen #DNPNMR #HYPERPOLARIZATION
- Determination of long-range scalar (1)H-(1)H coupling constants responsible for polarization transfer in SABRE #DNPNMR
- Constant-variable flip angles for hyperpolarized media MRI #DNPNMR
- A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization #DNPNMR
- Polarization enhancement technique for nuclear quadrupole resonance detection #DNPNMR
- Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP
- [NMR] PhD Position at PSI, Switzerland f#DNPNMR
- [NMR] Post-doctoral position in hyperpolarization available at the University of Florida, associated with the NHMFL.
- Static DNP-NMR Spectroscopy to Characterize Active Pharmaceutical Ingredients #DNPNMR
- Rotaxane-mediated suppression and activation of cucurbit[6]uril for molecular detection by (129)Xe hyperCEST NMR
- Dynamic nuclear polarization in a magnetic resonance force microscope experiment
- Identifying low-coverage surface species on supported noble metal nanoparticle catalysts by DNP-NMR #DNPNMR
- Dynamic nuclear polarization of biocompatible (13)C-enriched carbonates for in vivo pH imaging #DNPNMR
- Multiscale computational modeling of (13)C DNP in liquids #DNPNMR
- [NMR] PhD position #DNPNMR
- [NMR] Inaugural Workshop for Nottingham DNP MAS NMR Facility, UK #DNPNMR
- Magnetic resonance imaging of (1)H long lived states derived from parahydrogen induced polarization in a clinical system #DNPNMR
- Dynamic Nuclear Polarization Enhanced MAS NMR Spectroscopy for Structural Analysis of HIV-1 Protein Assemblies #DNPNMR
- Essentials of Dynamic Nuclear Polarization #DNPNMR
- Conceptual and instrumental progress in dissolution DNP #DNPNMR
- Nuclear hyperpolarization comes of age #DNPNMR
- Dynamic Nuclear Polarization enhanced NMR at 187GHz/284MHz using an Extended Interaction Klystron amplifier #DNPNMR
- Ultra-low temperature MAS-DNP #DNPNMR
- Symmetry constraints on spin dynamics: Application to hyperpolarized NMR
- U. of Ottawa NMR Facility Blog Non-uniform Sampling (NUS)
- Advanced instrumentation for DNP-enhanced MAS NMR for higher magnetic fields and lower temperatures
- [NMR] AMPERE biological solid-state NMR school in Palma de Mallorca October 2016 #DNPNMR #NMR
- [NMR] Preclinical MRI Staff Scientist Position at The Weizmann Institute
- Optimizing water hyperpolarization and dissolution for sensitivity-enhanced 2D biomolecular NMR
- Magnetic resonance imaging of DNP enhancements in a rotor spinning at the magic angle
- Liquid state DNP at high magnetic fields: Instrumentation, experimental results and atomistic modelling by molecular dynamics simulations
- Basic facts and perspectives of Overhauser DNP NMR
- [NMR] PhD fellowship #DNPNMR
- Development and testing of hyperpolarized 13C MR calibrationless parallel imaging
- Dissolution DNP for in vivo preclinical studies
- [NMR] Summer school Theory of NMR at Colditz 4-10 Sept. 2016
- NP 2016 summerschool August 22-26, organized by the EPFL and the PSI #DNPNMR
- Optimizing dissolution dynamic nuclear polarization
- U. of Ottawa NMR Facility Blog CEST - Chemical Exchange Saturation Transfer
- On the present and future of dissolution-DNP
- Instrumentation for solid-state dynamic nuclear polarization with magic angle spinning NMR
- The phenomenology of optically pumped 13C NMR in diamond at 7.05 T: Room temperature polarization, orientation dependence, and the effect of defect concentration on polarization dynamics
- A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument
- U. of Ottawa NMR Facility Blog Inept
- Low-temperature dynamic nuclear polarization with helium-cooled samples and nitrogen-driven magic-angle spinning
- Meet Bridge12 at ENC in Pittsburgh #DNPNMR
- Perspectives on DNP-enhanced NMR spectroscopy in solutions
- DNP 2016 summerschool August 22-26, Tramelan, Switzerland, #DNPNMR
- Solid effect DNP polarization dynamics in a system of many spins
- Dynamic nuclear polarization by frequency modulation of a tunable gyrotron of 260GHz
- Spin polarization transfer mechanisms of SABRE: A magnetic field dependent study
- Stan NMR blog Major reorganization of Stan's Mathematics Links
- EUROMAR 2016, July 3-7 in Aarhus, Denmark
- U. of Ottawa NMR Facility Blog Solid-State 13C NMR of Chicken Eggshells
- DNP 2016 Summer School organized by the EPFL #DNPNMR
- Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly (13)C-Isotope-Labeled Photosynthetic Reaction Center
- A New Tool for NMR Crystallography: Complete (13)C/(15)N Assignment of Organic Molecules at Natural Isotopic Abundance Using DNP-Enhanced Solid-State NMR
- Long-lived spin states as a source of contrast in magnetic resonance spectroscopy and imaging
- Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization
- Dynamic nuclear polarization by frequency modulation of a tunable gyrotron of 260GHz
- Transport and imaging of brute-force (13)C hyperpolarization
- [nmr] postdoc position: Metabolic imaging using hyperpolarized 13c mr
- Strategy for Enhancement of (13)C-Photo-CIDNP NMR Spectra by Exploiting Fractional (13)C-Labeling of Tryptophan
- Surface ligand-directed pair-wise hydrogenation for heterogeneous phase hyperpolarization
- Low field photo-CIDNP in the intramolecular electron transfer of naproxen-pyrrolidine dyads
- Effects of biradical deuteration on the performance of DNP: towards better performing polarizing agents
- [NMR] Postdoc positions in Hyperpolarized 13C MR