Nuclear magnetic resonance probes for the Kondo scenario for the 0.7 feature in semiconductor quantum point contact devices

We propose a probe based on nuclear relaxation and Knight shift measurements for the Kondo scenario for the "0.7 feature" in semiconductor quantum point contact (QPC) devices. We show that the presence of a bound electron in the QPC would lead to a much higher rate of nuclear relaxation compared to nuclear relaxation through exchange of spin with conduction electrons. Furthermore, we show that the temperature dependence of this nuclear relaxation is very non-monotonic as opposed to the linear-T relaxation from coupling with conduction electrons. We present a qualitative analysis for the additional relaxation due to nuclear spin diffusion (NSD) and study the extent to which NSD affects the range of validity of our method. The conclusion is that nuclear relaxation, in combination with Knight shift measurements, can be used to verify whether the 0.7 feature is indeed due to the presence of a bound electron in the QPC.Comment: Published version. Appears in a Special Section on the 0.7 Feature and Interactions in One-Dimensional Systems. 16 page

Dynamic nuclear polarization and spin-diffusion in non-conducting solids

There has been much renewed interest in dynamic nuclear polarization (DNP), particularly in the context of solid state biomolecular NMR and more recently dissolution DNP techniques for liquids. This paper reviews the role of spin diffusion in polarizing nuclear spins and discusses the role of the spin diffusion barrier, before going on to discuss some recent results.Comment: submitted to Applied Magnetic Resonance. The article should appear in a special issue that is being published in connection with the DNP Symposium help in Nottingham in August 200

Light-induced nuclear quadrupolar relaxation in semiconductors

Light excitation of a semiconductor, known to dynamically-polarize the nuclear spins by hyperfine contact interaction with the photoelectrons, also generates an intrinsic nuclear depolarization mechanism. This novel relaxation process arises from the modulation of the nuclear quadrupolar Hamiltonian by photoelectron trapping and recombination at nearby localized states. For nuclei near shallow donors, the usual diffusion radius is replaced by a smaller, quadrupolar, radius. If the light excitation conditions correspond to partial donor occupation by photoelectrons, the nuclear magnetization and the nuclear field can be decreased by more than one order of magnitude

Ni-substituted sites and the effect on Cu electron spin dynamics of YBa2Cu{3-x}NixO{7-\delta}

We report Cu nuclear quadrupole resonance experiment on magnetic impurity Ni-substituted YBa$_2$Cu$_{3-x}$Ni$_x$O$_{7-\delta}$. The distribution of Ni-substituted sites and its effect on the Cu electron spin dynamics are investigated. Two samples with the same Ni concentration $x$=0.10 and nearly the same oxygen content but different $T_c$'s were prepared: One is an as-synthesized sample (7-$\delta$=6.93) in air ($T_c$$\approx 80 K$), and the other is a quenched one (7-$\delta$=6.92) in a reduced oxygen atmosphere ($T_c$$\approx 70 K$). The plane-site $^{63}$Cu(2) nuclear spin-lattice relaxation for the quenched sample was faster than that for the as-synthesized sample, in contrast to the $^{63}$Cu(1) relaxation that was faster for the as-synthesized sample. This indicates that the density of plane-site Ni(2) is higher in the quenched sample, contrary to the chain-site Ni(1) density which is lower in the quenched sample. From the analysis in terms of the Ni-induced nuclear spin-lattice relaxation, we suggest that the primary origin of suppression of $T_c$ is associated with nonmagnetic depairing effect of the plane-site Ni(2).Comment: 7 pages, 5 figure

Выбор тактики хирургического лечения «острейшего» расслоения аорты I типа по De Bakey в условиях многопрофильного хирургического стационара

BACKGROUND Acute proximal aortic dissection (Stanford type A) remains the most common fatal pathology of the thoracic aorta. Despite the improvement of surgical technologies, hospital mortality after emergency surgical interventions is 17–25%, in complicated cases it can reach 80–90%.AIM OF STUDY Description of the perioperative treatment tactics adopted at the N.V. Sklifosovsky Research Institute for Emergency Medicine as well as the evolution of approaches that make it possible to obtain satisfactory hospital and long-term results in the treatment of aortic dissection.MATERIAL AND METHODS the study included 278 patients operated on from 2015 to 2021 in the acute stage of aortic dissection (less than 48 hours from the moment of manifestation of the disease). The operated patients were divided into two groups, depending on the presence of complicated forms: group A, 102 patients with uncomplicated course of the disease; group B, 176 patients with complicated course of the disease. Additionally, patients were divided depending on the level of distal reconstruction performed: group I, 83 patients, surgery was limited to prosthetics of the ascending aorta, without removing the clamp; group II, 137 patients who underwent hemi-arch surgery; group III, 58 patients, with distal reconstruction involving the aortic arch.RESULTS Total hospital mortality was 28.1%: 25.3% in group I, 29.1% in group II, 29.3% in group III. In the group of uncomplicated dissection, postoperative mortality was 18.6%, while in the group of complicated dissection it was 33.5%.CONCLUSION An integrated multidisciplinary approach with the formation of an “aortic team”, an individual approach to surgery, depending on the anatomy of the dissection and the clinical status of the patient, will improve the results of the treatment of acute aortic dissection, as the most severe and multiple organ pathology of the aorta.FINDING 1. Hospital mortality of complicated forms of dissection remains significantly higher — 33.5% versus 18.5% of uncomplicated course. 2. The most optimal method of distal reconstruction in patients with the peracute stage of dissection is an open anastomosis with the aorta using the “hemi-arch” technique. 3. If it is necessary to extend the surgical intervention on the aortic arch, a distal anastomosis in areas 0, 1, 2 with the possibility of a subsequent endovascular stage is the priority.ВВЕДЕНИЕ Острое проксимальное расслоение аорты (тип А по Stanford) остается самой частой смертельной патологией грудной аорты. Несмотря на совершенствование хирургических технологий, госпитальная летальность после экстренных оперативных вмешательств составляет 17–25%, в «осложненных» случаях она может достигать 80–90%.ЦЕЛЬ Описание периоперативной тактики лечения, принятой в НИИ скорой помощи им. Н. В. Склифосовского, а также эволюция подходов, дающих возможность получения удовлетворительных госпитальных и отдаленных результатов лечения расслоения аорты.МАТЕРИАЛ И МЕТОДЫ В исследование включены 278 пациентов, оперированных в период с 2015 по 2021 гг. в «острейшую» стадию расслоения аорты (менее 48 часов от момента манифестации заболевания). Оперированные больные были разделены на две группы, в зависимости от наличия «осложненных» форм: группа А — 102 пациента с «неосложненным» течением заболевания; группа В — 176 пациентов с «осложненным» течением заболевания. Дополнительно пациенты были разделены в зависимости от уровня выполненной дистальной реконструкции: группа I — 83 пациента, оперативное вмешательство ограничивалось протезированием восходящей аорты, без снятия зажима с аорты; группа II — 137 пациентов, которым была выполнена операция “hemi-arch”; группа III — 58 пациентов с расширением объема дистальной реконструкции на дугу аорты.РЕЗУЛЬТАТЫ Общая госпитальная летальность составила 28,1%: в I группе «зажима» — 25,3%, во II группе “hemi-arch” — 29,1%, в III группе «дуги» — 29,3%. В группе «неосложненного» расслоения послеоперационная летальность составила 18,6%, в то время как в группе «осложненного» — 33,5%.ЗАКЛЮЧЕНИЕ Комплексный мультидисциплинарный подход с формированием «аортальной команды», индивидуальный подход к хирургии в зависимости от анатомии расслоения и клинического статуса пациента позволят улучшить результаты лечения «острейшего» расслоения аорты, как наиболее тяжелой и полиорганной патологии аорты.ВЫВОДЫ 1. Госпитальная летальность «осложненных» форм расслоения остается значительно выше 33,5% против 18,5% «неосложненного» течения. 2. Наиболее оптимальным методом дистальной реконструкции у пациентов «сверхострой» стадии расслоения является наложение открытого анастомоза с аортой по методике “hemi-arch”. 3. При необходимости расширения хирургического вмешательства на дугу аорты, наложение дистального анастомоза в зонах 0, 1, 2 с возможностью последующего эндоваскулярного этапа является приоритетным направлением лечения

Oscillations and waves in solar spicules

Since their discovery, spicules have attracted increased attention as energy/mass bridges between the dense and dynamic photosphere and the tenuous hot solar corona. Mechanical energy of photospheric random and coherent motions can be guided by magnetic field lines, spanning from the interior to the upper parts of the solar atmosphere, in the form of waves and oscillations. Since spicules are one of the most pronounced features of the chromosphere, the energy transport they participate in can be traced by the observations of their oscillatory motions. Oscillations in spicules have been observed for a long time. However the recent high-resolutions and high-cadence space and ground based facilities with superb spatial, temporal and spectral capacities brought new aspects in the research of spicule dynamics. Here we review the progress made in imaging and spectroscopic observations of waves and oscillations in spicules. The observations are accompanied by a discussion on theoretical modelling and interpretations of these oscillations. Finally, we embark on the recent developments made on the presence and role of Alfven and kink waves in spicules. We also address the extensive debate made on the Alfven versus kink waves in the context of the explanation of the observed transverse oscillations of spicule axes

The human DNA glycosylases NEIL1 and NEIL3 excise psoralen-induced DNA-DNA cross-links in a four-stranded DNA structure

Interstrand cross-links (ICLs) are highly cytotoxic DNA lesions that block DNA replication and transcription by preventing strand separation. Previously, we demonstrated that the bacterial and human DNA glycosylases Nei and NEIL1 excise unhooked psoralen-derived ICLs in three-stranded DNA via hydrolysis of the glycosidic bond between the crosslinked base and deoxyribose sugar. Furthermore, NEIL3 from Xenopus laevis has been shown to cleave psoralen- and abasic site-induced ICLs in Xenopus egg extracts. Here we report that human NEIL3 cleaves psoralen-induced DNA-DNA cross-links in three-stranded and four-stranded DNA substrates to generate unhooked DNA fragments containing either an abasic site or a psoralen-thymine monoadduct. Furthermore, while Nei and NEIL1 also cleave a psoralen-induced four-stranded DNA substrate to generate two unhooked DNA duplexes with a nick, NEIL3 targets both DNA strands in the ICL without generating single-strand breaks. The DNA substrate specificities of these Nei-like enzymes imply the occurrence of long uninterrupted three- and four-stranded crosslinked DNA-DNA structures that may originate in vivo from DNA replication fork bypass of an ICL. In conclusion, the Nei-like DNA glycosylases unhook psoralen-derived ICLs in various DNA structures via a genuine repair mechanism in which complex DNA lesions can be removed without generation of highly toxic double-strand breaks

Nuclear Magnetic Resonance Study of Ultrananocrystalline Diamonds

We report on a nuclear magnetic resonance (NMR) study of ultrananocrystalline diamond (UNCD) materials produced by detonation technique. Analysis of the 13C and 1H NMR spectra, spin-spin and spin-lattice relaxation times in purified UNCD samples is presented. Our measurements show that UNCD particles consist of a diamond core that is partially covered by a sp2-carbon fullerene-like shell. The uncovered part of outer diamond surface comprises a number of hydrocarbon groups that saturate the dangling bonds. Our findings are discussed along with recent calculations of the UNCD structure. Significant increase in the spin-lattice relaxation rate (in comparison with that of natural diamond), as well as stretched exponential character of the magnetization recovery, are attributed to the interaction of nuclear spins with paramagnetic centers which are likely fabrication-driven dangling bonds with unpaired electrons. We show that these centers are located mainly at the interface between the diamond core and shell.Comment: 25 pages, 7 figure

Mesoporous Silica Nanoparticles Loaded with Surfactant: Low Temperature Magic Angle Spinning 13C and 29Si NMR Enhanced by Dynamic Nuclear Polarization

We show that dynamic nuclear polarization (DNP) can be used to enhance NMR signals of13C and 29Si nuclei located in mesoporous organic/inorganic hybrid materials, at several hundreds of nanometers from stable radicals (TOTAPOL) trapped in the surrounding frozen disordered water. The approach is demonstrated using mesoporous silica nanoparticles (MSN), functionalized with 3-(N-phenylureido)propyl (PUP) groups, filled with the surfactant cetyltrimethylammonium bromide (CTAB). The DNP-enhanced proton magnetization is transported into the mesopores via 1H–1H spin diffusion and transferred to rare spins by cross-polarization, yielding signal enhancements εon/off of around 8. When the CTAB molecules are extracted, so that the radicals can enter the mesopores, the enhancements increase to εon/off ≈ 30 for both nuclei. A quantitative analysis of the signal enhancements in MSN with and without surfactant is based on a one-dimensional proton spin diffusion model. The effect of solvent deuteration is also investigated

Adapting Agriculture to Climate Change: A Synopsis of Coordinated National Crop Wild Relative Seed Collecting Programs across Five Continents

The Adapting Agriculture to Climate Change Project set out to improve the diversity, quantity, and accessibility of germplasm collections of crop wild relatives (CWR). Between 2013 and 2018, partners in 25 countries, heirs to the globetrotting legacy of Nikolai Vavilov, undertook seed collecting expeditions targeting CWR of 28 crops of global significance for agriculture. Here, we describe the implementation of the 25 national collecting programs and present the key results. A total of 4587 unique seed samples from at least 355 CWR taxa were collected, conserved ex situ, safety duplicated in national and international genebanks, and made available through the Multilateral System (MLS) of the International Treaty on Plant Genetic Resources for Food and Agriculture (Plant Treaty). Collections of CWR were made for all 28 targeted crops. Potato and eggplant were the most collected genepools, although the greatest number of primary genepool collections were made for rice. Overall, alfalfa, Bambara groundnut, grass pea and wheat were the genepools for which targets were best achieved. Several of the newly collected samples have already been used in pre-breeding programs to adapt crops to future challenges.info:eu-repo/semantics/publishedVersio