123-419: The Russell Varian Prize was an international scientific prize awarded for a single, high-impact and innovative contribution in the field of nuclear magnetic resonance (NMR), that laid the foundation for the development of new technologies in the field. It honored the memory of Russell Varian , the pioneer behind the creation of the first commercial NMR spectrometer and
246-543: A first-class entity , rather than the specific place where the object is located at a certain time. It implements the Uniform Resource Identifier ( Uniform Resource Name ) concept and adds to it a data model and social infrastructure. A DOI name also differs from standard identifier registries such as the ISBN , ISRC , etc. The purpose of an identifier registry is to manage a given collection of identifiers, whereas
369-567: A Composite Pulse". Journal of Magnetic Resonance . 33 (2): 473–476. Bibcode : 1979JMagR..33..473L . doi : 10.1016/0022-2364(79)90265-8 . Retrieved from " https://en.wikipedia.org/w/index.php?title=Russell_Varian_Prize&oldid=1183999876 " Categories : Science and technology awards Physics awards Nuclear magnetic resonance Awards established in 2002 Awards disestablished in 2016 Hidden category: CS1 errors: periodical ignored Nuclear magnetic resonance Nuclear magnetic resonance ( NMR )
492-448: A DOI name is a handle, and so has a set of values assigned to it and may be thought of as a record that consists of a group of fields. Each handle value must have a data type specified in its <type> field, which defines the syntax and semantics of its data. While a DOI persistently and uniquely identifies the object to which it is assigned, DOI resolution may not be persistent, due to technical and administrative issues. To resolve
615-537: A DOI name, it may be input to a DOI resolver, such as doi.org . Another approach, which avoids typing or copying and pasting into a resolver is to include the DOI in a document as a URL which uses the resolver as an HTTP proxy, such as https://doi.org/ (preferred) or http://dx.doi.org/ , both of which support HTTPS. For example, the DOI 10.1000/182 can be included in a reference or hyperlink as https://doi.org/10.1000/182 . This approach allows users to click on
738-931: A Single Scan" . Proceedings of the National Academy of Sciences of the USA . 99 (25): 15858–15862. Bibcode : 2002PNAS...9915858F . doi : 10.1073/pnas.252644399 . PMC 138528 . PMID 12461169 . ^ "The Russell Varian Lecture and Prize" (PDF) . EUROMAR . Retrieved 13 December 2017 . ^ Bax, A.; Mehlkopf, A.F.; Smidt, J. (1979). "Homonuclear Broadband Decoupled Absorption Spectra". Journal of Magnetic Resonance . 35 (1): 167–169. Bibcode : 1979JMagR..35..167B . CiteSeerX 10.1.1.703.5487 . doi : 10.1016/0022-2364(79)90088-X . ^ "Major international honour for Professor of Physical Chemistry" . University of Southampton . Retrieved 13 December 2017 . ^ Levitt, M.H.; Freeman, R. (1979). "NMR Population Inversion Using
861-441: A higher chemical shift). Unless the local symmetry of such molecular orbitals is very high (leading to "isotropic" shift), the shielding effect will depend on the orientation of the molecule with respect to the external field ( B 0 ). In solid-state NMR spectroscopy, magic angle spinning is required to average out this orientation dependence in order to obtain frequency values at the average or isotropic chemical shifts. This
984-447: A lower energy when their spins are parallel, not anti-parallel. This parallel spin alignment of distinguishable particles does not violate the Pauli exclusion principle . The lowering of energy for parallel spins has to do with the quark structure of these two nucleons. As a result, the spin ground state for the deuteron (the nucleus of deuterium , the H isotope of hydrogen), which has only
1107-460: A magnetic field and when the RF was of a frequency specific to the identity of the nuclei. When this absorption occurs, the nucleus is described as being in resonance . Different atomic nuclei within a molecule resonate at different (radio) frequencies in the same applied static magnetic field, due to various local magnetic fields. The observation of such magnetic resonance frequencies of the nuclei present in
1230-401: A managed registry (providing both social and technical infrastructure). It does not assume any specific business model for the provision of identifiers or services and enables other existing services to link to it in defined ways. Several approaches for making identifiers persistent have been proposed. The comparison of persistent identifier approaches is difficult because they are not all doing
1353-530: A molecule makes it possible to determine essential chemical and structural information about the molecule. The improvements of the NMR method benefited from the development of electromagnetic technology and advanced electronics and their introduction into civilian use. Originally as a research tool it was limited primarily to dynamic nuclear polarization , by the work of Anatole Abragam and Albert Overhauser , and to condensed matter physics , where it produced one of
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#17330853958321476-573: A more stable link than directly using its URL. But if its URL changes, the publisher must update the metadata for the DOI to maintain the link to the URL. It is the publisher's responsibility to update the DOI database. If they fail to do so, the DOI resolves to a dead link , leaving the DOI useless. The developer and administrator of the DOI system is the International DOI Foundation (IDF), which introduced it in 2000. Organizations that meet
1599-544: A non-profit organization created in 1997, is the governance body of the DOI system. It safeguards all intellectual property rights relating to the DOI system, manages common operational features, and supports the development and promotion of the DOI system. The IDF ensures that any improvements made to the DOI system (including creation, maintenance, registration, resolution and policymaking of DOI names) are available to any DOI registrant. It also prevents third parties from imposing additional licensing requirements beyond those of
1722-462: A proton and a neutron, corresponds to a spin value of 1 , not of zero . On the other hand, because of the Pauli exclusion principle, the tritium isotope of hydrogen must have a pair of anti-parallel spin neutrons (of total spin zero for the neutron spin-pair), plus a proton of spin 1 / 2 . Therefore, the tritium total nuclear spin value is again 1 / 2 , just like
1845-464: A radio frequency pulse, induces an electromagnetic field (emf) in the receiver coil of the NMR spectrometer. This generates an oscillating current and a non-linear induced transverse magnetic field which returns the spin system to equilibrium faster than other mechanisms of relaxation. RD can result in line broadening and measurement of a shorter spin-lattice relaxation time ( T 1 {\displaystyle T_{1}} ). For instance,
1968-541: A range of frequencies centered about the carrier frequency , with the range of excitation ( bandwidth ) being inversely proportional to the pulse duration, i.e. the Fourier transform of a short pulse contains contributions from all the frequencies in the neighborhood of the principal frequency. The restricted range of the NMR frequencies for most light spin- 1 / 2 nuclei made it relatively easy to use short (1 - 100 microsecond) radio frequency pulses to excite
2091-471: A range of frequencies, while another orthogonal coil, designed not to receive radiation from the transmitter, received signals from nuclei that reoriented in solution. As of 2014, low-end refurbished 60 MHz and 90 MHz systems were sold as FT-NMR instruments, and in 2010 the "average workhorse" NMR instrument was configured for 300 MHz. CW spectroscopy is inefficient in comparison with Fourier analysis techniques (see below) since it probes
2214-518: A sample of water in a 400 MHz NMR spectrometer will have T R D {\displaystyle T_{RD}} around 20 ms, whereas its T 1 {\displaystyle T_{1}} is hundreds of milliseconds. This effect is often described using modified Bloch equations that include terms for radiation damping alongside the conventional relaxation terms. The longitudinal relaxation time of radiation damping ( T R D {\displaystyle T_{RD}} )
2337-514: A single other intermediate atom, etc. Through-space interactions relate to actual geometric distances and angles, including effects of dipolar coupling and the nuclear Overhauser effect . Doi (identifier) A digital object identifier ( DOI ) is a persistent identifier or handle used to uniquely identify various objects, standardized by the International Organization for Standardization (ISO). DOIs are an implementation of
2460-420: A spectrum that contains many different types of information about the molecules in the sample. In multi-dimensional nuclear magnetic resonance spectroscopy, there are at least two pulses: one leads to the directly detected signal and the others affect the starting magnetization and spin state prior to it. The full analysis involves repeating the sequence with the pulse timings systematically varied in order to probe
2583-406: A static magnetic field. However, in the ordered phases of magnetic materials, very large internal fields are produced at the nuclei of magnetic ions (and of close ligands ), which allow NMR to be performed in zero applied field. Additionally, radio-frequency transitions of nuclear spin I > 1 / 2 with large enough electric quadrupolar coupling to the electric field gradient at
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#17330853958322706-419: A transaction, etc. The names can refer to objects at varying levels of detail: thus DOI names can identify a journal, an individual issue of a journal, an individual article in the journal, or a single table in that article. The choice of level of detail is left to the assigner, but in the DOI system it must be declared as part of the metadata that is associated with a DOI name, using a data dictionary based on
2829-410: Is a physical phenomenon in which nuclei in a strong constant magnetic field are disturbed by a weak oscillating magnetic field (in the near field ) and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance , when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on
2952-412: Is a key feature of NMR that the resonance frequency of nuclei in a particular sample substance is usually directly proportional to the strength of the applied magnetic field. It is this feature that is exploited in imaging techniques; if a sample is placed in a non-uniform magnetic field then the resonance frequencies of the sample's nuclei depend on where in the field they are located. This effect serves as
3075-450: Is a related technique in which transitions between electronic rather than nuclear spin levels are detected. The basic principles are similar but the instrumentation, data analysis, and detailed theory are significantly different. Moreover, there is a much smaller number of molecules and materials with unpaired electron spins that exhibit ESR (or electron paramagnetic resonance (EPR)) absorption than those that have NMR absorption spectra. On
3198-450: Is a type of Handle System handle, which takes the form of a character string divided into two parts, a prefix and a suffix, separated by a slash. The prefix identifies the registrant of the identifier and the suffix is chosen by the registrant and identifies the specific object associated with that DOI. Most legal Unicode characters are allowed in these strings, which are interpreted in a case-insensitive manner. The prefix usually takes
3321-419: Is associated with a non-zero magnetic dipole moment, μ → {\displaystyle {\vec {\mu }}} , via the relation μ → = γ S → {\displaystyle {\vec {\mu }}=\gamma {\vec {S}}} where γ is the gyromagnetic ratio . Classically, this corresponds to the proportionality between
3444-406: Is given by the equation [1]. T R D = 2 γ μ 0 η Q M 0 {\displaystyle T_{RD}={\frac {2}{\gamma \mu _{0}\eta QM_{0}}}} [1] where γ {\displaystyle \gamma } is the gyromagnetic ratio , μ 0 {\displaystyle \mu _{0}}
3567-559: Is in the initial, equilibrium (mixed) state. The precessing nuclei can also fall out of alignment with each other and gradually stop producing a signal. This is called T 2 or transverse relaxation . Because of the difference in the actual relaxation mechanisms involved (for example, intermolecular versus intramolecular magnetic dipole-dipole interactions), T 1 is usually (except in rare cases) longer than T 2 (that is, slower spin-lattice relaxation, for example because of smaller dipole-dipole interaction effects). In practice,
3690-420: Is influenced significantly by system parameters. It is notably more prominent in systems where the NMR probe possesses a high quality factor ( Q {\displaystyle Q} ) and a high filling factor , resulting in a strong coupling between the probe coil and the sample. The phenomenon is also impacted by the concentration of the nuclei within the sample and their magnetic moments, which can intensify
3813-596: Is maintained by the International DOI Foundation. The IDF is recognized as one of the federated registrars for the Handle System by the DONA Foundation (of which the IDF is a board member), and is responsible for assigning Handle System prefixes under the top-level 10 prefix. Registration agencies generally charge a fee to assign a new DOI name; parts of these fees are used to support the IDF. The DOI system overall, through
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3936-438: Is one of the techniques that has been used to design quantum automata, and also build elementary quantum computers . In the first few decades of nuclear magnetic resonance, spectrometers used a technique known as continuous-wave (CW) spectroscopy, where the transverse spin magnetization generated by a weak oscillating magnetic field is recorded as a function of the oscillation frequency or static field strength B 0 . When
4059-464: Is shown with a DOI name that leads to an Excel file of data underlying the tables and graphs. Further development of such services is planned. Other registries include Crossref and the multilingual European DOI Registration Agency (mEDRA) . Since 2015, RFCs can be referenced as doi:10.17487/rfc ... . The IDF designed the DOI system to provide a form of persistent identification , in which each DOI name permanently and unambiguously identifies
4182-720: Is the Bohr frequency Δ E / ℏ {\displaystyle \Delta {E}/\hbar } of the S x {\displaystyle S_{x}} and S y {\displaystyle S_{y}} expectation values. Precession of non-equilibrium magnetization in the applied magnetic field B 0 occurs with the Larmor frequency ω L = 2 π ν L = − γ B 0 , {\displaystyle \omega _{L}=2\pi \nu _{L}=-\gamma B_{0},} without change in
4305-400: Is the magnetic permeability , M 0 {\displaystyle M_{0}} is the equilibrium magnetization per unit volume, Q {\displaystyle Q} is the filling factor of the probe which is the ratio of the probe coil volume to the sample volume enclosed, Q = ω L R {\displaystyle Q={\frac {\omega L}{R}}}
4428-460: Is the magnitude of the field. This means that the spin magnetization, which is proportional to the sum of the spin vectors of nuclei in magnetically equivalent sites (the expectation value of the spin vector in quantum mechanics), moves on a cone around the B field. This is analogous to the precessional motion of the axis of a tilted spinning top around the gravitational field. In quantum mechanics, ω {\displaystyle \omega }
4551-431: Is the precession of the spin magnetization around the magnetic field at the nucleus, with the angular frequency ω = − γ B {\displaystyle \omega =-\gamma B} where ω = 2 π ν {\displaystyle \omega =2\pi \nu } relates to the oscillation frequency ν {\displaystyle \nu } and B
4674-697: Is the quality factor of the probe, and , L {\displaystyle L} , and R {\displaystyle R} are the resonance frequency, inductance, and resistance of the coil, respectively. The quantification of line broadening due to radiation damping can be determined by measuring the Δ v 1 2 {\displaystyle \Delta v_{\frac {1}{2}}} and use equation [2]. T R D − 1 = π 0.8384 Δ v 1 2 {\displaystyle T_{RD}^{-1}={\frac {\pi }{0.8384}}\Delta v_{\frac {1}{2}}} [2] Radiation damping in NMR
4797-612: Is therefore S z = mħ . The z -component of the magnetic moment is simply: μ z = γ S z = γ m ℏ . {\displaystyle \mu _{z}=\gamma S_{z}=\gamma m\hbar .} Consider nuclei with a spin of one-half, like H , C or F . Each nucleus has two linearly independent spin states, with m = 1 / 2 or m = − 1 / 2 (also referred to as spin-up and spin-down, or sometimes α and β spin states, respectively) for
4920-555: Is to use one of a number of add-ons and plug-ins for browsers , thereby avoiding the conversion of the DOIs to URLs, which depend on domain names and may be subject to change, while still allowing the DOI to be treated as a normal hyperlink. A disadvantage of this approach for publishers is that, at least at present, most users will be encountering the DOIs in a browser, mail reader , or other software which does not have one of these plug-ins installed. The International DOI Foundation ( IDF ),
5043-626: Is unnecessary in conventional NMR investigations of molecules in solution, since rapid "molecular tumbling" averages out the chemical shift anisotropy (CSA). In this case, the "average" chemical shift (ACS) or isotropic chemical shift is often simply referred to as the chemical shift. In 1949, Suryan first suggested that the interaction between a radiofrequency coil and a sample's bulk magnetization could explain why experimental observations of relaxation times differed from theoretical predictions. Building on this idea, Bloembergen and Pound further developed Suryan's hypothesis by mathematically integrating
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5166-538: Is widely used to determine the structure of organic molecules in solution and study molecular physics and crystals as well as non-crystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI). The original application of NMR to condensed matter physics is nowadays mostly devoted to strongly correlated electron systems. It reveals large many-body couplings by fast broadband detection and should not be confused with solid state NMR, which aims at removing
5289-506: The Handle System ; they also fit within the URI system ( Uniform Resource Identifier ). They are widely used to identify academic, professional, and government information, such as journal articles, research reports, data sets, and official publications . A DOI aims to resolve to its target, the information object to which the DOI refers. This is achieved by binding the DOI to metadata about
5412-527: The Maxwell–Bloch equations , a process through which they introduced the concept of "radiation damping." Radiation damping (RD) in Nuclear Magnetic Resonance (NMR) is an intrinsic phenomenon observed in many high-field NMR experiments, especially relevant in systems with high concentrations of nuclei like protons or fluorine. RD occurs when transverse bulk magnetization from the sample, following
5535-491: The indecs Content Model . The official DOI Handbook explicitly states that DOIs should be displayed on screens and in print in the format doi:10.1000/182 . Contrary to the DOI Handbook , Crossref , a major DOI registration agency, recommends displaying a URL (for example, https://doi.org/10.1000/182 ) instead of the officially specified format. This URL is persistent (there is a contract that ensures persistence in
5658-404: The square root of the number of spectra added (see random walk ). Hence the overall signal-to-noise ratio increases as the square-root of the number of spectra measured. However, monitoring an NMR signal at a single frequency as a function of time may be better suited for kinetic studies than pulsed Fourier-transform NMR spectrosocopy. Most applications of NMR involve full NMR spectra, that is,
5781-404: The z -axis is chosen to be along B 0 , and the above expression reduces to: E = − μ z B 0 , {\displaystyle E=-\mu _{\mathrm {z} }B_{0}\,,} or alternatively: E = − γ m ℏ B 0 . {\displaystyle E=-\gamma m\hbar B_{0}\,.} As a result,
5904-474: The 2020s zero- to ultralow-field nuclear magnetic resonance ( ZULF NMR ), a form of spectroscopy that provides abundant analytical results without the need for large magnetic fields , was developed. It is combined with a special technique that makes it possible to hyperpolarize atomic nuclei . All nucleons, that is neutrons and protons , composing any atomic nucleus , have the intrinsic quantum property of spin , an intrinsic angular momentum analogous to
6027-479: The DOI System. It requires an additional layer of administration for defining DOI as a URN namespace (the string urn:doi:10.1000/1 rather than the simpler doi:10.1000/1 ) and an additional step of unnecessary redirection to access the resolution service, already achieved through either http proxy or native resolution. If RDS mechanisms supporting URN specifications become widely available, DOI will be registered as
6150-413: The DOI as a normal hyperlink . Indeed, as previously mentioned, this is how Crossref recommends that DOIs always be represented (preferring HTTPS over HTTP), so that if they are cut-and-pasted into other documents, emails, etc., they will be actionable. Other DOI resolvers and HTTP Proxies include the Handle System and PANGAEA . At the beginning of the year 2016, a new class of alternative DOI resolvers
6273-409: The DOI system associates metadata with objects. A small kernel of common metadata is shared by all DOI names and can be optionally extended with other relevant data, which may be public or restricted. Registrants may update the metadata for their DOI names at any time, such as when publication information changes or when an object moves to a different URL. The International DOI Foundation (IDF) oversees
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#17330853958326396-436: The DOI system have deliberately not registered a DOI namespace for URNs , stating that: URN architecture assumes a DNS-based Resolution Discovery Service (RDS) to find the service appropriate to the given URN scheme. However no such widely deployed RDS schemes currently exist.... DOI is not registered as a URN namespace, despite fulfilling all the functional requirements, since URN registration appears to offer no advantage to
6519-459: The DOI system. DOI name-resolution may be used with OpenURL to select the most appropriate among multiple locations for a given object, according to the location of the user making the request. However, despite this ability, the DOI system has drawn criticism from librarians for directing users to non-free copies of documents, that would have been available for no additional fee from alternative locations. The indecs Content Model as used within
6642-495: The IDF on users of the DOI system. The IDF is controlled by a Board elected by the members of the Foundation, with an appointed Managing Agent who is responsible for co-ordinating and planning its activities. Membership is open to all organizations with an interest in electronic publishing and related enabling technologies. The IDF holds annual open meetings on the topics of DOI and related issues. Registration agencies, appointed by
6765-597: The IDF, operates on a not-for-profit cost recovery basis. The DOI system is an international standard developed by the International Organization for Standardization in its technical committee on identification and description, TC46/SC9. The Draft International Standard ISO/DIS 26324, Information and documentation – Digital Object Identifier System met the ISO requirements for approval. The relevant ISO Working Group later submitted an edited version to ISO for distribution as an FDIS (Final Draft International Standard) ballot, which
6888-472: The IDF, provide services to DOI registrants: they allocate DOI prefixes, register DOI names, and provide the necessary infrastructure to allow registrants to declare and maintain metadata and state data. Registration agencies are also expected to actively promote the widespread adoption of the DOI system, to cooperate with the IDF in the development of the DOI system as a whole, and to provide services on behalf of their specific user community. A list of current RAs
7011-496: The NMR frequency of the spins. This oscillating magnetization vector induces a voltage in a nearby pickup coil, creating an electrical signal oscillating at the NMR frequency. This signal is known as the free induction decay (FID), and it contains the sum of the NMR responses from all the excited spins. In order to obtain the frequency-domain NMR spectrum (NMR absorption intensity vs. NMR frequency) this time-domain signal (intensity vs. time) must be Fourier transformed. Fortunately,
7134-406: The NMR response at individual frequencies or field strengths in succession. Since the NMR signal is intrinsically weak, the observed spectrum suffers from a poor signal-to-noise ratio . This can be mitigated by signal averaging, i.e. adding the spectra from repeated measurements. While the NMR signal is the same in each scan and so adds linearly, the random noise adds more slowly – proportional to
7257-550: The RF inhomogeneity of the resonant pulse). In the corresponding FT-NMR spectrum—meaning the Fourier transform of the free induction decay — the width of the NMR signal in frequency units is inversely related to the T 2 * time. Thus, a nucleus with a long T 2 * relaxation time gives rise to a very sharp NMR peak in the FT-NMR spectrum for a very homogeneous ( "well-shimmed" ) static magnetic field, whereas nuclei with shorter T 2 * values give rise to broad FT-NMR peaks even when
7380-869: The Russell Varian Prize 2011" (PDF) . EUROMAR . Retrieved 13 December 2017 . ^ Morris, G.A. (1979). "Enhancement of Nuclear Magnetic Resonance Signals by Polarization Transfer". Journal of the American Chemical Society . 101 (3): 760–762. doi : 10.1021/ja00497a058 . ^ Freeman, R.; Anderson, W.A. (1962). "Use of Weak Perturbing Radio-Frequency Fields in Nuclear Magnetic Double Resonance". Journal of Chemical Physics . 37 (9): 2053–2074. Bibcode : 1962JChPh..37.2053F . doi : 10.1063/1.1733426 . ^ Frydman, L.; Scherf, T.; Lupulescu, A. (2002). "The Acquisition of Multidimensional NMR Spectra within
7503-1202: The Theory of Relaxation Processes". IBM Journal of Research and Development . 1 : 19–31. doi : 10.1147/rd.11.0019 . ^ "2008 Russell Varian Prize to Alex Pines" . PinesLab . Lawrence Berkeley National Laboratory News Center . Retrieved 13 December 2017 . ^ Pines, A.; Gibby, M.G.; Waugh, J.S. (1972). "Proton-Enhanced Nuclear Induction Spectroscopy". Journal of Chemical Physics . 56 (4): 1776–1777. Bibcode : 1972JChPh..56.1776P . doi : 10.1063/1.1677439 . S2CID 95376682 . ^ "Russell Varian Prize 2009 Laureate" (PDF) . EUROMAR . Retrieved 13 December 2017 . ^ Overhauser, A.W. (1953). "Polarization of Nuclei in Metals". Physical Review . 92 (2): 411–415. Bibcode : 1953PhRv...92..411O . doi : 10.1103/PhysRev.92.411 . ^ Karplus, M. (1959). "Contact Electron-Spin Coupling of Nuclear Magnetic Moments". Journal of Chemical Physics . 30 (1): 11–15. Bibcode : 1959JChPh..30...11K . doi : 10.1063/1.1729860 . ^ "Announcement of
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#17330853958327626-728: The Varian, Inc. Records" . Online Archive of California . Stanford University Libraries . Retrieved 12 December 2017 . ^ "The Russel Varian Prize 2007" . EUROMAR 2006 . EUROMAR. Archived from the original on 28 August 2008 . Retrieved 12 December 2017 . ^ "Agilent Completes Varian Acquisition" . GenomeWeb . 17 May 2010 . Retrieved 17 December 2017 . ^ Reisch, M.S. (2014). "Agilent to Exit NMR Business" . Chemical & Engineering News . 92 (42): 11. doi : 10.1021/cen-09242-notw9 . Retrieved 17 December 2017 . ^ "Russel Varian Prize 2002" . EUROMAR Conference 2006 . EUROMAR. Archived from
7749-412: The above that all nuclei of the same nuclide (and hence the same γ ) would resonate at exactly the same frequency but this is not the case. The most important perturbation of the NMR frequency for applications of NMR is the "shielding" effect of the shells of electrons surrounding the nucleus. Electrons, similar to the nucleus, are also charged and rotate with a spin to produce a magnetic field opposite to
7872-430: The angular momentum and the magnetic dipole moment of a spinning charged sphere, both of which are vectors parallel to the rotation axis whose length increases proportional to the spinning frequency. It is the magnetic moment and its interaction with magnetic fields that allows the observation of NMR signal associated with transitions between nuclear spin levels during resonant RF irradiation or caused by Larmor precession of
7995-413: The applied magnetic field. In general, this electronic shielding reduces the magnetic field at the nucleus (which is what determines the NMR frequency). As a result, the frequency required to achieve resonance is also reduced. This shift in the NMR frequency due to the electronic molecular orbital coupling to the external magnetic field is called chemical shift , and it explains why NMR is able to probe
8118-569: The average magnetic moment after resonant irradiation. Nuclides with even numbers of both protons and neutrons have zero nuclear magnetic dipole moment and hence do not exhibit NMR signal. For instance, O is an example of a nuclide that produces no NMR signal, whereas C , P , Cl and Cl are nuclides that do exhibit NMR spectra. The last two nuclei have spin S > 1 / 2 and are therefore quadrupolar nuclei. Electron spin resonance (ESR)
8241-660: The basis of magnetic resonance imaging . The principle of NMR usually involves three sequential steps: The two magnetic fields are usually chosen to be perpendicular to each other as this maximizes the NMR signal strength. The frequencies of the time-signal response by the total magnetization ( M ) of the nuclear spins are analyzed in NMR spectroscopy and magnetic resonance imaging. Both use applied magnetic fields ( B 0 ) of great strength, usually produced by large currents in superconducting coils, in order to achieve dispersion of response frequencies and of very high homogeneity and stability in order to deliver spectral resolution ,
8364-459: The characters 1000 in the prefix identify the registrant; in this case the registrant is the International DOI Foundation itself. 182 is the suffix, or item ID, identifying a single object (in this case, the latest version of the DOI Handbook ). DOI names can identify creative works (such as texts, images, audio or video items, and software) in both electronic and physical forms, performances , and abstract works such as licenses, parties to
8487-484: The chemical structure of molecules, which depends on the electron density distribution in the corresponding molecular orbitals. If a nucleus in a specific chemical group is shielded to a higher degree by a higher electron density of its surrounding molecular orbitals, then its NMR frequency will be shifted "upfield" (that is, a lower chemical shift), whereas if it is less shielded by such surrounding electron density, then its NMR frequency will be shifted "downfield" (that is,
8610-564: The classical angular momentum of a spinning sphere. The overall spin of the nucleus is determined by the spin quantum number S . If the numbers of both the protons and neutrons in a given nuclide are even then S = 0 , i.e. there is no overall spin. Then, just as electrons pair up in nondegenerate atomic orbitals , so do even numbers of protons or even numbers of neutrons (both of which are also spin- 1 / 2 particles and hence fermions ), giving zero overall spin. However, an unpaired proton and unpaired neutron will have
8733-719: The co-founder, in 1948, of Varian Associates , one of the first high-tech companies in Silicon Valley . The prize carried a monetary award of €15,000 and it was awarded annually between the years 2002 and 2015 (except for 2003) by a committee of experts in the field. The award ceremony alternated between the European Magnetic Resonance (EUROMAR) Conference and the International Council on Magnetic Resonance in Biological Systems (ICMRBS) Conference. Originally,
8856-430: The constant magnetic field B 0 ("90° pulse"), while after a twice longer time, the initial magnetization has been inverted ("180° pulse"). It is the transverse magnetization generated by a resonant oscillating field which is usually detected in NMR, during application of the relatively weak RF field in old-fashioned continuous-wave NMR, or after the relatively strong RF pulse in modern pulsed NMR. It might appear from
8979-467: The contractual obligations of the DOI system and are willing to pay to become a member of the system can assign DOIs. The DOI system is implemented through a federation of registration agencies coordinated by the IDF. By late April 2011 more than 50 million DOI names had been assigned by some 4,000 organizations, and by April 2013 this number had grown to 85 million DOI names assigned through 9,500 organizations. Fake registries have even appeared. A DOI
9102-536: The decoherence that is not refocused by the 180° pulse. In simple cases, an exponential decay is measured which is described by the T 2 time. NMR spectroscopy is one of the principal techniques used to obtain physical, chemical, electronic and structural information about molecules due to the chemical shift of the resonance frequencies of the nuclear spins in the sample. Peak splittings due to J- or dipolar couplings between nuclei are also useful. NMR spectroscopy can provide detailed and quantitative information on
9225-587: The details of which are described by chemical shifts , the Zeeman effect , and Knight shifts (in metals). The information provided by NMR can also be increased using hyperpolarization , and/or using two-dimensional, three-dimensional and higher-dimensional techniques. NMR phenomena are also utilized in low-field NMR , NMR spectroscopy and MRI in the Earth's magnetic field (referred to as Earth's field NMR ), and in several types of magnetometers . Nuclear magnetic resonance
9348-407: The detection of the kinds of nuclear–nuclear interactions that allowed for the magnetization transfer. Interactions that can be detected are usually classified into two kinds. There are through-bond and through-space interactions. Through-bond interactions relate to structural connectivity of the atoms and provide information about which ones are directly connected to each other, connected by way of
9471-551: The development of Fourier transform (FT) NMR coincided with the development of digital computers and the digital fast Fourier transform (FFT). Fourier methods can be applied to many types of spectroscopy. Richard R. Ernst was one of the pioneers of pulsed NMR and won a Nobel Prize in chemistry in 1991 for his work on Fourier Transform NMR and his development of multi-dimensional NMR spectroscopy. The use of pulses of different durations, frequencies, or shapes in specifically designed patterns or pulse sequences allows production of
9594-466: The different nuclear spin states have different energies in a non-zero magnetic field. In less formal language, we can talk about the two spin states of a spin 1 / 2 as being aligned either with or against the magnetic field. If γ is positive (true for most isotopes used in NMR) then m = 1 / 2 ("spin up") is the lower energy state. The energy difference between
9717-403: The doi.org domain, ) so it is a PURL —providing the location of an name resolver which will redirect HTTP requests to the correct online location of the linked item. The Crossref recommendation is primarily based on the assumption that the DOI is being displayed without being hyperlinked to its appropriate URL—the argument being that without the hyperlink it is not as easy to copy-and-paste
9840-400: The effect of the same couplings by Magic Angle Spinning techniques. The most commonly used nuclei are H and C , although isotopes of many other elements, such as F , P , and Si , can be studied by high-field NMR spectroscopy as well. In order to interact with the magnetic field in the spectrometer,
9963-586: The effects of radiation damping. The strength of the magnetic field is inversely proportional to the lifetime of RD. The impact of radiation damping on NMR signals is multifaceted. It can accelerate the decay of the NMR signal faster than intrinsic relaxation processes would suggest. This acceleration can complicate the interpretation of NMR spectra by causing broadening of spectral lines, distorting multiplet structures, and introducing artifacts, especially in high-resolution NMR scenarios. Such effects make it challenging to obtain clear and accurate data without considering
10086-415: The entire NMR spectrum. Applying such a pulse to a set of nuclear spins simultaneously excites all the single-quantum NMR transitions. In terms of the net magnetization vector, this corresponds to tilting the magnetization vector away from its equilibrium position (aligned along the external magnetic field). The out-of-equilibrium magnetization vector then precesses about the external magnetic field vector at
10209-629: The external magnetic field. The energy of a magnetic dipole moment μ → {\displaystyle {\vec {\mu }}} in a magnetic field B 0 is given by: E = − μ → ⋅ B 0 = − μ x B 0 x − μ y B 0 y − μ z B 0 z . {\displaystyle E=-{\vec {\mu }}\cdot \mathbf {B} _{0}=-\mu _{x}B_{0x}-\mu _{y}B_{0y}-\mu _{z}B_{0z}.} Usually
10332-419: The fields induced by radiation damping. These approaches aim to control and limit the disruptive effects of radiation damping during NMR experiments and all approaches are successful in eliminating RD to a fairly large extent. Overall, understanding and managing radiation damping is crucial for obtaining high-quality NMR data, especially in modern high-field spectrometers where the effects can be significant due to
10455-529: The first demonstrations of the validity of the BCS theory of superconductivity by the observation by Charles Slichter of the Hebel-Slichter effect. It soon showed its potential in organic chemistry , where NMR has become indispensable, and by the 1990s improvement in the sensitivity and resolution of NMR spectroscopy resulted in its broad use in analytical chemistry , biochemistry and materials science . In
10578-457: The form 10.NNNN , where NNNN is a number greater than or equal to 1000 , whose limit depends only on the total number of registrants. The prefix may be further subdivided with periods, like 10.NNNN.N . For example, in the DOI name 10.1000/182 , the prefix is 10.1000 and the suffix is 182 . The "10" part of the prefix distinguishes the handle as part of the DOI namespace, as opposed to some other Handle System namespace, and
10701-558: The full URL to actually bring up the page for the DOI, thus the entire URL should be displayed, allowing people viewing the page containing the DOI to copy-and-paste the URL, by hand, into a new window/tab in their browser in order to go to the appropriate page for the document the DOI represents. Major content of the DOI system currently includes: In the Organisation for Economic Co-operation and Development 's publication service OECD iLibrary , each table or graph in an OECD publication
10824-474: The functional groups, topology, dynamics and three-dimensional structure of molecules in solution and the solid state. Since the area under an NMR peak is usually proportional to the number of spins involved, peak integrals can be used to determine composition quantitatively. Structure and molecular dynamics can be studied (with or without "magic angle" spinning (MAS)) by NMR of quadrupolar nuclei (that is, with spin S > 1 / 2 ) even in
10947-443: The functionality of a registry-controlled scheme and will usually lack accompanying metadata in a controlled scheme. The DOI system does not have this approach and should not be compared directly to such identifier schemes. Various applications using such enabling technologies with added features have been devised that meet some of the features offered by the DOI system for specific sectors (e.g., ARK ). A DOI name does not depend on
11070-458: The increased sensitivity and resolution. The process of population relaxation refers to nuclear spins that return to thermodynamic equilibrium in the magnet. This process is also called T 1 , " spin-lattice " or "longitudinal magnetic" relaxation, where T 1 refers to the mean time for an individual nucleus to return to its thermal equilibrium state of the spins. After the nuclear spin population has relaxed, it can be probed again, since it
11193-467: The influence of radiation damping. To mitigate these effects, various strategies are employed in NMR spectroscopy. These methods majorly stem from hardware or software. Hardware modifications including RF feed-circuit and Q-factor switches reduce the feedback loop between the sample magnetization and the electromagnetic field induced by the coil and function successfully. Other approaches such as designing selective pulse sequences also effectively manage
11316-537: The integration of these technologies and operation of the system through a technical and social infrastructure. The social infrastructure of a federation of independent registration agencies offering DOI services was modelled on existing successful federated deployments of identifiers such as GS1 and ISBN . A DOI name differs from commonly used Internet pointers to material, such as the Uniform Resource Locator (URL), in that it identifies an object itself as
11439-435: The intensity of the NMR signal as a function of frequency. Early attempts to acquire the NMR spectrum more efficiently than simple CW methods involved illuminating the target simultaneously with more than one frequency. A revolution in NMR occurred when short radio-frequency pulses began to be used, with a frequency centered at the middle of the NMR spectrum. In simple terms, a short pulse of a given "carrier" frequency "contains"
11562-423: The magnet is shimmed well. Both T 1 and T 2 depend on the rate of molecular motions as well as the gyromagnetic ratios of both the resonating and their strongly interacting, next-neighbor nuclei that are not at resonance. A Hahn echo decay experiment can be used to measure the dephasing time, as shown in the animation. The size of the echo is recorded for different spacings of the two pulses. This reveals
11685-520: The nucleus may also be excited in zero applied magnetic field ( nuclear quadrupole resonance ). In the dominant chemistry application, the use of higher fields improves the sensitivity of the method (signal-to-noise ratio scales approximately as the power of 3 / 2 with the magnetic field strength) and the spectral resolution. Commercial NMR spectrometers employing liquid helium cooled superconducting magnets with fields of up to 28 Tesla have been developed and are widely used. It
11808-405: The nucleus must have an intrinsic angular momentum and nuclear magnetic dipole moment . This occurs when an isotope has a nonzero nuclear spin , meaning an odd number of protons and/or neutrons (see Isotope ). Nuclides with even numbers of both have a total spin of zero and are therefore not NMR-active. In its application to molecules the NMR effect can be observed only in the presence of
11931-430: The object to which it is associated (although when the publisher of a journal changes, sometimes all the DOIs will be changed, with the old DOIs no longer working). It also associates metadata with objects, allowing it to provide users with relevant pieces of information about the objects and their relationships. Included as part of this metadata are network actions that allow DOI names to be resolved to web locations where
12054-462: The object's location and, in this way, is similar to a Uniform Resource Name (URN) or PURL but differs from an ordinary URL. URLs are often used as substitute identifiers for documents on the Internet although the same document at two different locations has two URLs. By contrast, persistent identifiers such as DOI names identify objects as first class entities: two instances of the same object would have
12177-425: The object, such as a URL where the object is located. Thus, by being actionable and interoperable , a DOI differs from ISBNs or ISRCs which are identifiers only. The DOI system uses the indecs Content Model to represent metadata . The DOI for a document remains fixed over the lifetime of the document, whereas its location and other metadata may change. Referring to an online document by its DOI should provide
12300-454: The objects they describe can be found. To achieve its goals, the DOI system combines the Handle System and the indecs Content Model with a social infrastructure. The Handle System ensures that the DOI name for an object is not based on any changeable attributes of the object such as its physical location or ownership, that the attributes of the object are encoded in its metadata rather than in its DOI name, and that no two objects are assigned
12423-1199: The original on 30 March 2012 . Retrieved 13 December 2017 . ^ "Russel Varian Prize 2004" . EUROMAR Conference 2006 . EUROMAR . Retrieved 13 December 2017 . ^ Hahn, E.L. (1950). "Spin Echoes" . Physical Review . 80 (4): 580–594. Bibcode : 1950PhRv...80..580H . doi : 10.1103/PhysRev.80.580 . S2CID 46554313 . ^ "Russel Varian Prize 2005" . EUROMAR Conference 2006 . EUROMAR . Retrieved 13 December 2017 . ^ Bloembergen, N.; Purcell, E.M.; Pound, R.V. (1947). "Nuclear Magnetic Relaxation" . Nature . 160 (4066): 475–476. Bibcode : 1947Natur.160..475B . doi : 10.1038/160475a0 . hdl : 1874/7413 . PMID 20265559 . S2CID 4002836 . Retrieved 14 December 2017 . ^ "Russel Varian Prize 2006" . EUROMAR Conference 2006 . EUROMAR . Retrieved 13 December 2017 . ^ Waugh, J.S.; Wang, C.H.; Huber, L.M.; Vold, R.L. (1968). "Multiple-Pulse NMR Experiments" . Journal of Chemical Physics . 48 (2): 662–670. Bibcode : 1968JChPh..48..662W . doi : 10.1063/1.1668698 . ^ Redfield, A.G. (1957). "On
12546-439: The oscillation frequency matches the nuclear resonance frequency, the transverse magnetization is maximized and a peak is observed in the spectrum. Although NMR spectra could be, and have been, obtained using a fixed constant magnetic field and sweeping the frequency of the oscillating magnetic field, it was more convenient to use a fixed frequency source and vary the current (and hence magnetic field) in an electromagnet to observe
12669-647: The oscillations of the spin system are point by point in the time domain. Multidimensional Fourier transformation of the multidimensional time signal yields the multidimensional spectrum. In two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR), there will be one systematically varied time period in the sequence of pulses, which will modulate the intensity or phase of the detected signals. In 3D-NMR, two time periods will be varied independently, and in 4D-NMR, three will be varied. There are many such experiments. In some, fixed time intervals allow (among other things) magnetization transfer between nuclei and, therefore,
12792-406: The other hand, ESR has much higher signal per spin than NMR does. Nuclear spin is an intrinsic angular momentum that is quantized. This means that the magnitude of this angular momentum is quantized (i.e. S can only take on a restricted range of values), and also that the x, y, and z-components of the angular momentum are quantized, being restricted to integer or half-integer multiples of ħ ,
12915-544: The populations of the energy levels because energy is constant (time-independent Hamiltonian). A perturbation of nuclear spin orientations from equilibrium will occur only when an oscillating magnetic field is applied whose frequency ν rf sufficiently closely matches the Larmor precession frequency ν L of the nuclear magnetization. The populations of the spin-up and -down energy levels then undergo Rabi oscillations , which are analyzed most easily in terms of precession of
13038-453: The presence of magnetic " dipole -dipole" interaction broadening (or simply, dipolar broadening), which is always much smaller than the quadrupolar interaction strength because it is a magnetic vs. an electric interaction effect. Additional structural and chemical information may be obtained by performing double-quantum NMR experiments for pairs of spins or quadrupolar nuclei such as H . Furthermore, nuclear magnetic resonance
13161-467: The primary purpose of the DOI system is to make a collection of identifiers actionable and interoperable, where that collection can include identifiers from many other controlled collections. The DOI system offers persistent, semantically interoperable resolution to related current data and is best suited to material that will be used in services outside the direct control of the issuing assigner (e.g., public citation or managing content of value). It uses
13284-1659: The prize was sponsored by Varian, Inc. and later by Agilent Technologies , after the latter acquired Varian, Inc. in 2010. The prize was discontinued in 2016 after Agilent Technologies closed its NMR division. Russell Varian Prize Awardees [ edit ] 2002 Jean Jeener . Contribution: Multi-dimensional Fourier NMR spectroscopy . Jeener, J. (September 1971). Lecture . Ampère International Summer School II. Basko Polje, Yugoslavia. 2004 Erwin L. Hahn . Contribution: Spin echo phenomena and experiments. 2005 Nicolaas Bloembergen . Contribution: Nuclear magnetic relaxation . 2006 John S. Waugh . Contribution: Average Hamiltonian theory. 2007 Alfred G. Redfield. Contribution: Relaxation Theory. 2008 Alexander Pines . Contribution: Cross-polarization method for NMR in solids. 2009 Albert W. Overhauser . Contribution: Nuclear Overhauser effect (NOE). 2010 Martin Karplus . Contribution: Karplus equation . 2011 Gareth A. Morris . Contribution: INEPT pulse sequence . 2012 Ray Freeman and Weston A. Anderson. Contribution: Double resonance. 2013 Lucio Frydman . Contribution: Ultrafast NMR. 2014 Ad Bax . Contribution: Homonuclear broad band decoupled absorption spectra. 2015 Malcolm Levitt . Contribution: Composite pulses. See also [ edit ] List of physics awards References [ edit ] ^ The Russel Varian Prize and Lecture . Elsevier . Retrieved 12 December 2017 . {{ cite book }} : |website= ignored ( help ) ^ "Guide to
13407-480: The reduced Planck constant . The integer or half-integer quantum number associated with the spin component along the z-axis or the applied magnetic field is known as the magnetic quantum number , m , and can take values from + S to − S , in integer steps. Hence for any given nucleus, there are a total of 2 S + 1 angular momentum states. The z -component of the angular momentum vector ( S → {\displaystyle {\vec {S}}} )
13530-543: The resonant absorption signals. This is the origin of the counterintuitive, but still common, "high field" and "low field" terminology for low frequency and high frequency regions, respectively, of the NMR spectrum. As of 1996, CW instruments were still used for routine work because the older instruments were cheaper to maintain and operate, often operating at 60 MHz with correspondingly weaker (non-superconducting) electromagnets cooled with water rather than liquid helium. One radio coil operated continuously, sweeping through
13653-411: The same DOI name. DOI name resolution is provided through the Handle System , developed by Corporation for National Research Initiatives , and is freely available to any user encountering a DOI name. Resolution redirects the user from a DOI name to one or more pieces of typed data: URLs representing instances of the object, services such as e-mail, or one or more items of metadata. To the Handle System,
13776-537: The same DOI name. Because DOI names are short character strings, they are human-readable, may be copied and pasted as text, and fit into the URI specification. The DOI name-resolution mechanism acts behind the scenes, so that users communicate with it in the same way as with any other web service; it is built on open architectures , incorporates trust mechanisms , and is engineered to operate reliably and flexibly so that it can be adapted to changing demands and new applications of
13899-431: The same thing. Imprecisely referring to a set of schemes as "identifiers" does not mean that they can be compared easily. Other "identifier systems" may be enabling technologies with low barriers to entry, providing an easy to use labeling mechanism that allows anyone to set up a new instance (examples include Persistent Uniform Resource Locator (PURL), URLs, Globally Unique Identifiers (GUIDs), etc.), but may lack some of
14022-549: The simpler, abundant hydrogen isotope, H nucleus (the proton ). The NMR absorption frequency for tritium is also similar to that of H. In many other cases of non-radioactive nuclei, the overall spin is also non-zero and may have a contribution from the orbital angular momentum of the unpaired nucleon . For example, the Al nucleus has an overall spin value S = 5 / 2 . A non-zero spin S → {\displaystyle {\vec {S}}}
14145-470: The spin magnetization around the effective magnetic field in a reference frame rotating with the frequency ν rf . The stronger the oscillating field, the faster the Rabi oscillations or the precession around the effective field in the rotating frame. After a certain time on the order of 2–1000 microseconds, a resonant RF pulse flips the spin magnetization to the transverse plane, i.e. it makes an angle of 90° with
14268-421: The strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla , the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. High-resolution nuclear magnetic resonance spectroscopy
14391-401: The two states is: Δ E = γ ℏ B 0 , {\displaystyle \Delta {E}=\gamma \hbar B_{0}\,,} and this results in a small population bias favoring the lower energy state in thermal equilibrium. With more spins pointing up than down, a net spin magnetization along the magnetic field B 0 results. A central concept in NMR
14514-400: The value of T 2 *, which is the actually observed decay time of the observed NMR signal, or free induction decay (to 1 / e of the initial amplitude immediately after the resonant RF pulse), also depends on the static magnetic field inhomogeneity, which may be quite significant. (There is also a smaller but significant contribution to the observed FID shortening from
14637-414: The z-component of spin. In the absence of a magnetic field, these states are degenerate; that is, they have the same energy. Hence the number of nuclei in these two states will be essentially equal at thermal equilibrium . If a nucleus with spin is placed in a magnetic field, however, the two states no longer have the same energy as a result of the interaction between the nuclear magnetic dipole moment and
14760-664: Was accepted on July 24, 1951. Varian Associates developed the first NMR unit called NMR HR-30 in 1952. Purcell had worked on the development of radar during World War II at the Massachusetts Institute of Technology 's Radiation Laboratory . His work during that project on the production and detection of radio frequency power and on the absorption of such RF power by matter laid the foundation for his discovery of NMR in bulk matter. Rabi, Bloch, and Purcell observed that magnetic nuclei, like H and P , could absorb RF energy when placed in
14883-510: Was approved by 100% of those voting in a ballot closing on 15 November 2010. The final standard was published on 23 April 2012. DOI is a registered URI under the info URI scheme specified by IETF RFC 4452 . info:doi/ is the infoURI Namespace of Digital Object Identifiers. The DOI syntax is a NISO standard, first standardized in 2000, ANSI/NISO Z39.84-2005 Syntax for the Digital Object Identifier. The maintainers of
15006-744: Was first described and measured in molecular beams by Isidor Rabi in 1938, by extending the Stern–Gerlach experiment , and in 1944, Rabi was awarded the Nobel Prize in Physics for this work. In 1946, Felix Bloch and Edward Mills Purcell expanded the technique for use on liquids and solids, for which they shared the Nobel Prize in Physics in 1952. Russell H. Varian filed the "Method and means for correlating nuclear properties of atoms and magnetic fields", U.S. patent 2,561,490 on October 21, 1948 and
15129-614: Was started by http://doai.io. This service is unusual in that it tries to find a non-paywalled (often author archived ) version of a title and redirects the user to that instead of the publisher's version . Since then, other open-access favoring DOI resolvers have been created, notably https://oadoi.org/ in October 2016 (later Unpaywall ). While traditional DOI resolvers solely rely on the Handle System, alternative DOI resolvers first consult open access resources such as BASE (Bielefeld Academic Search Engine). An alternative to HTTP proxies
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