Enhanced dynamic nuclear polarization via swept microwave frequency combs.

Dynamic nuclear polarization (DNP) has enabled enormous gains in magnetic resonance signals and led to vastly accelerated NMR/MRI imaging and spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the full electron spectrum are appealing since they allow direct participation of all electrons in the hyperpolarization process. Such methods typically entail sweeps of microwave radiation over the broad electron linewidth to excite DNP but are often inefficient because the sweeps, constrained by adiabaticity requirements, are slow. In this paper, we develop a technique to overcome the DNP bottlenecks set by the slow sweeps, using a swept microwave frequency comb that increases the effective number of polarization transfer events while respecting adiabaticity constraints. This allows a multiplicative gain in DNP enhancement, scaling with the number of comb frequencies and limited only by the hyperfine-mediated electron linewidth. We demonstrate the technique for the optical hyperpolarization of 13C nuclei in powdered microdiamonds at low fields, increasing the DNP enhancement from 30 to 100 measured with respect to the thermal signal at 7T. For low concentrations of broad linewidth electron radicals [e.g., TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl)], these multiplicative gains could exceed an order of magnitude.

Inductive measurement of optically hyperpolarized phosphorous donor nuclei in an isotopically enriched silicon-28 crystal.

We experimentally demonstrate the first inductive readout of optically hyperpolarized phosphorus-31 donor nuclear spins in an isotopically enriched silicon-28 crystal. The concentration of phosphorus donors in the crystal was 1.5×10(15) cm(-3), 3 orders of magnitude lower than has previously been detected via direct inductive detection. The signal-to-noise ratio measured in a single free induction decay from a 1 cm(3) sample (≈10(15) spins) was 113. By transferring the sample to an X-band ESR spectrometer, we were able to obtain a lower bound for the nuclear spin polarization at 1.7 K of ∼64%. The (31)P-T2 measured with a Hahn echo sequence was 420 ms at 1.7 K, which was extended to 1.2 s with a Carr Purcell cycle. The T1 of the (31)P nuclear spins at 1.7 K is extremely long and could not be determined, as no decay was observed even on a time scale of 4.5 h. Optical excitation was performed with a 1047 nm laser, which provided above-band-gap excitation of the silicon. The buildup of the hyperpolarization at 4.2 K followed a single exponential with a characteristic time of 577 s, while the buildup at 1.7 K showed biexponential behavior with characteristic time constants of 578 and 5670 s.

Ethyl trans-12-(pyridin-4-yl)-9,10-ethano-anthracene-11-carboxyl-ate.

In the title compound, C24H21NO2, the residues at the central ethyl-ene bridge are trans to each other. The dihedral angles between the pyridine and benzene rings are 67.09 (6) and 61.41 (5)°. In the crystal, centrosymmetrically related mol-ecules are linked into dimers by pairs of C-H⋯O hydrogen bonds.

1,7,8,9,10,10-Hexachloro-4-(2-phenyl-eth-yl)-4-aza-tricyclo-[5.2.1.0]dec-8-ene-3,5-dione.

In the title compound, C(17)H(11)Cl(6)NO(2), the six-membered ring of the norbornene moiety adopts a boat conformation whereas the two five-membered rings adopt envelope conformations. The phenyl ring and the ring of the succinimide moiety are almost coplanar [dihedral angle = 7.44 (14)°]. The crystal packing is stabilized by a weak inter-molecular C-H⋯O hydrogen bond.

1,7,8,9,10,10-Hexachloro-4-(thio-phen-2-ylmeth-yl)-4-aza-tricyclo-[5.2.1.0]dec-8-ene-3,5-dione.

In the title compound, C(14)H(7)Cl(6)NO(2)S, the six-membered ring of the aza-tricyclo system has a boat conformation whereas the five-membered rings have an envelope conformation. The thio-phene ring and the ring of the succinimide moiety enclose a dihedral angle of 67.2 (1)°. The crystal packing is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

Daily rhythms and sex differences in vasoactive intestinal polypeptide, VIPR2 receptor and arginine vasopressin mRNA in the suprachiasmatic nucleus of a diurnal rodent, Arvicanthis niloticus.

Diurnal and nocturnal animals differ with respect to the time of day at which the ovulatory surge in luteinizing hormone occurs. In some species this is regulated by the suprachiasmatic nucleus (SCN), the primary circadian clock, via cells that contain vasoactive intestinal polypeptide (VIP) and vasopressin (AVP). Here, we evaluated the hypothesis that chronotype differences in the timing of the luteinizing hormone surge are associated with rhythms in expression of the genes that encode these neuropeptides. Diurnal grass rats (Arvicanthis niloticus) were housed in a 12/12-h light-dark cycle and killed at one of six times of day (Zeitgeber time 1, 5, 9, 13, 17, 21; ZT 0 = lights-on). In-situ hybridization was used to compare levels of vip, avp and VIP receptor mRNA (vipr2) in the SCN of intact females, ovariectomized females, ovariectomized females given estradiol and intact males. We found a sex difference in vip rhythms with a peak occurring at ZT 13 in males and ZT 5 in intact females. In all groups avp mRNA rhythms peaked during the day, from ZT 5 to ZT 9, and had a trough in the dark at ZT 21. There was a modest rhythm and sex difference in the pattern of vipr2. Most importantly, the patterns of each of these SCN rhythms relative to the light-dark cycle resembled those seen in nocturnal rodents. Chronotype differences in timing of neuroendocrine events associated with ovulation are thus likely to be generated downstream of the SCN.

Root resorption during orthodontic tooth movements.

The aim of the study was to compare the extent of maxillary incisor root resorption during different orthodontic tooth movements using three different techniques, namely the basal intrusion arch, the three component arch, and levelling of the upper dental arch with the straightwire appliance. The radiographs of 49 subjects (20 males and 29 females) with a mean age of 14.5 years were taken at two time points: in groups 1 and 2 after the levelling phase and in group 3 immediately after placement of the archwire (T1) and in all groups after a period of 6 months (T2). The amount of root resorption of the central incisors was determined at T2. The average incisor resorption was different in the three groups, with group 2 (three component arch) showing greater resorption (0.46 mm) than groups 1 (basal arch) and 3 (straightwire) of 0.26 and 0.25 mm, respectively. Analysis of variance (ANOVA) demonstrated that differences in root resorption in the three groups were not significant. Wilcoxon paired test showed that the root resorption occurring between T1 and T2 in the three groups was not significant. There was also no significant difference among the rates of resorption in the three groups. Grouping the subjects on the basis of the extent of root resorption and the biomechanics used showed differences in the percentage of subjects with the least (<0.5 mm) and greatest (0.5-0.9 mm) amounts of root resorption between the three groups. This again showed that the technique of three component intrusion arch resulted in the greatest increase in root resorption.

Crystal structure of 4,5,6,7,8,8-hexa-chloro-2-(3,4-di-meth-oxy-pheneth-yl)-3a,4,7,7a-tetra-hydro-1H-4,7-methano-iso-indole-1,3(2H)-dione [+solvent].

In the title compound, C19H15Cl6NO4 [+solvent], the six-membered ring of the norbornene moiety adopts a boat conformation and the two five-membered rings have envelope conformations. The pyrrolidine ring makes a dihedral angle of 14.83 (12)° with the 3,4-di-meth-oxy-phenyl ring, which are attached to each other by an extended N-CH2-CH2-Car bridge. In the crystal, the structure features C-H⋯O inter-molecular hydrogen bonds, an offset π-π inter-action [inter-centroid distance = 3.564 (1) Å] and a C-Cl⋯π inter-action. The contribution of some disordered solvent to the scattering was removed using the SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18] of PLATON. The solvent contribution was not included in the reported mol-ecular weight and density.

Hyperpolarized relaxometry based nuclear T1 noise spectroscopy in diamond.

The origins of spin lifetimes in quantum systems is a matter of importance in several areas of quantum information. Spectrally mapping spin relaxation processes provides insight into their origin and motivates methods to mitigate them. In this paper, we map nuclear relaxation in a prototypical system of [Formula: see text] nuclei in diamond coupled to Nitrogen Vacancy (NV) centers over a wide field range (1 mT-7 T). Nuclear hyperpolarization through optically pumped NV electrons allows signal measurement savings exceeding million-fold over conventional methods. Through a systematic study with varying substitutional electron (P1 center) and [Formula: see text] concentrations, we identify the operational relaxation channels for the nuclei at different fields as well as the dominant role played by [Formula: see text] coupling to the interacting P1 electronic spin bath. These results motivate quantum control techniques for dissipation engineering to boost spin lifetimes in diamond, with applications including engineered quantum memories and hyperpolarized [Formula: see text] imaging.

Daily rhythms in PER1 within and beyond the suprachiasmatic nucleus of female grass rats (Arvicanthis niloticus).

Although circadian rhythms of males and females are different in a variety of ways in many species, their mechanisms have been primarily studied in males. Furthermore, rhythms are dramatically different in diurnal and nocturnal animals but have been studied predominantly in nocturnal ones. In the present study, we examined rhythms in one element of the circadian oscillator, the PER1 protein, in a variety of cell populations in brains of diurnal female grass rats. Every 4 h five adult female grass rats kept on a 12-h light/dark (LD) cycle were perfused and their brains were processed for immunohistochemical detection of PER1. Numbers of PER1-labeled cells were rhythmic not only within the suprachiasmatic nucleus (SCN), the locus of the primary circadian clock in mammals, but also in the peri-suprachiasmatic region, the oval nucleus of the bed nucleus of the stria terminalis, the central amygdala, and the nucleus accumbens. In addition, rhythms were detected within populations of neuroendocrine cells that contain tyrosine hydroxylase. The phase of the rhythm within the SCN was advanced compared with that seen previously in male grass rats. Rhythms beyond the SCN were varied and different from those seen in most nocturnal species, suggesting that signals originating in the SCN are modified by its direct and/or indirect targets in different ways in nocturnal and diurnal species.

Plastic oscillators and fixed rhythms: changes in the phase of clock-gene rhythms in the PVN are not reflected in the phase of the melatonin rhythm of grass rats.

The same clock-genes, including Period (PER) 1 and 2, that show rhythmic expression in the suprachiasmatic nucleus (SCN) are also rhythmically expressed in other brain regions that serve as extra-SCN oscillators. Outside the hypothalamus, the phase of these extra-SCN oscillators appears to be reversed when diurnal and nocturnal mammals are compared. Based on mRNA data, PER1 protein is expected to peak in the late night in the paraventricular nucleus of the hypothalamus (PVN) of nocturnal laboratory rats, but comparable data are not available for a diurnal species. Here we use the diurnal grass rat (Arvicanthis niloticus) to describe rhythms of PER1 and 2 proteins in the PVN of animals that either show the species-typical day-active (DA) profile, or that adopt a night-active (NA) profile when given access to running wheels. For DA animals housed with or without wheels, significant rhythms of PER1 or PER2 protein expression featured peaks in the late morning; NA animals showed patterns similar to those expected from nocturnal laboratory rats. Since the PVN is part of the circuit that controls pineal rhythms, we also measured circulating levels of melatonin during the day and night in DA animals with and without wheels and in NA wheel runners. All three groups showed elevated levels of melatonin at night, with higher levels during both the day and night being associated with the levels of activity displayed by each group. The differential phase of rhythms in the clock-gene protein in the PVN of diurnal and nocturnal animals presents a possible mechanism for explaining species differences in the phase of autonomic rhythms controlled, in part, by the PVN. The present study suggests that the phase of the oscillator of the PVN does not determine that of the melatonin rhythm in diurnal and nocturnal species or in diurnal and nocturnal chronotypes within a species.

A basis for new approaches to the chemotherapy of AIDS: novel genes in HIV-1 potentially encode selenoproteins expressed by ribosomal frameshifting and termination suppression.

Several previously unnoticed genes in the human immunodeficiency virus type 1 (HIV-1), potentially encoding selenoproteins, have been discovered by analyzing the genomic RNA structure and its relation to novel open reading frames. We have found a number of new potential RNA pseudoknots, including one in the long terminal repeat, several that coincide with highly conserved enzyme active site sequences in the pol coding region, and one in the env coding region. These pseudoknots can potentially direct the synthesis of selenocysteine (SeC) containing--1 frameshift fusion proteins. This is possible because we have found potential SeC insertion sequences (SECIS) in the RNA of HIV and other retroviruses; such structures are known to be necessary and sufficient for the incorporation of SeC at UGA "stop" codons anywhere in a eukaryotic mRNA. In several locations, UGA codons in the -1 reading frame are highly conserved across a broad spectrum of primate immunodeficiency viruses. Due to the degeneracy of the genetic code, this conservation cannot be explained by evolutionary selection of the pol gene protein sequence alone. Such observations, combined with the conservation of the associated reading frames, strongly suggest that these are real genes, and thus that the pseudoknots are also real. A protease pseudoknot-directed -1 frameshift fusion protein contains a highly conserved SeC codon and has significant similarities to a number of DNA binding proteins, including papillomavirus E2 proteins, suggesting it may be a virally encoded repressor of HIV transcription when cleaved by protease from the rest of the gag-pol gene product. A reverse transcriptase (RT) frameshift fusion protein replaces the RT active site with a highly conserved SeC-containing module. An integrase frameshift fusion protein contains the N-terminal integrase DNA-binding domain and a potential ATP-binding "GKS" motif; it has significant similarities to several helicases, but no SeC codons. A potential frameshift fusion protein from env has one SeC codon, but not in a highly conserved position. SeC incorporation could extend the nef gene product by 33 residues through the C-terminal UGA codon without frameshifting, potentially leading to substantial SeC utilization in infected cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Imaging the long-range dipolar field in structured liquid state samples.

We describe imaging experiments in which the pattern of the dipolar field generated by spatially modulated nuclear magnetization is directly visualized in simply structured phantoms. Two types of experiment have been carried out at 11.7 T using (1)H NMR signals. In the first, the field from a single spin species is imaged via its own NMR signal. In the second, the NMR signal from one spin species is used to image the field generated by a second species. The field patterns measured in these experiments correspond well with those calculated using simple theoretical expressions for the dipolar field. The results also directly demonstrate the spatial sensitivity of the signal generated using dipolar field effects, indicating that the range of the field depends upon the inverse of the spatial frequency with which the magnetization is modulated.

ADRF differential cross polarization spectroscopy of synthetic calcium phosphates and bone mineral.

An adiabatic demagnetization in the rotating frame (ADRF) differential cross polarization (DCP), or inversion recovery cross polarization (IRCP), technique has been developed to study synthetic calcium phosphates and bone mineral. ADRF of the protons followed by a remagnetization of the phosphorus-31 spins results in an equalization of the dipolar and phosphorus Zeeman nuclear spin temperatures. By shifting the phase of the phosphorus RF by 180 degrees during the forward cross polarization it is possible to invert the temperature of this reservoir and initiate reverse cross polarization. Transient Strombotne-Hahn oscillations were observed on inverting the temperature. The presence of these oscillations complicates the determination of a null point on the basis of cross polarization times. It is necessary to shift the phase of the RF only after a Zeeman spin temperature can be defined, and to use an RF field strength that is slightly smaller than the equivalent S-spin local dipolar field in order to produce a zero crossing after the transient oscillations have decayed.

Pulse error compensating symmetric magic-echo trains.

We present improved line-narrowing sequences for dipolar coupled spin systems, based on a train of magic-echoes which are compensated for the effects of finite pulse widths and utilize symmetry properties of supercycles. Sequences are introduced for spectroscopy and imaging by proper choice of a phase alternating scheme. Using a 16 pulse time-suspension magic-echo cycle, the highest level of line-narrowing achieved was 2.7 Hz for the [100] direction of a single crystal of calcium fluoride, a reduction in linewidth by 4 orders of magnitude.

Fat emulsification measured using NMR transverse relaxation.

This paper presents a novel method of measuring the droplet size in oil-in-water emulsions. It is based on changes in the NMR transverse relaxation rate due to the effect of microscopic magnetic susceptibility differences between fat droplets and the surrounding water. The longitudinal and transverse relaxation rates of a series of emulsions with constant oil volume fraction and five different mean droplet sizes, in the range 0.4-20.9 microm, were measured in vitro at 37 degrees C using EPI. While the longitudinal relaxation rate 1/T(1) did not change significantly, 1/T(2) was observed to increase with mean droplet size. The measured changes in 1/T(2) were found to be in good agreement with results predicted from proton random walk simulations, and were also consistent with analytical solutions based on an outer sphere relaxation model. Measurements of 1/T(2) on emulsions with a higher oil volume fraction, and on emulsions of a fixed size where the water phase was doped with gadolinium to modulate the susceptibility difference between the phases, also showed the predicted behavior. As part of this study the susceptibility difference between olive oil and water was measured to be 1.55 ppm.

Direct measurement of porous media local hydrodynamical permeability using gas MRI.

The concept of hydraulic permeability is at the core of modeling single phase or multi-phase flow in heterogeneous porous media, as it is the spatial distribution of the permeability that primarily governs the behavior of fluid flow in the medium. To date, the modeling of fluid flow in porous media has been hampered by poor estimates of local permeability. Magnetic Resonance Imaging is well known for its ability to measure non-invasively the local density and flow rate of different fluids saturating porous media [1,2]. In this paper we demonstrate the first non-invasive method for the direct measurement of a single projection of the local permeability tensor of a porous medium using gas-phase MRI. The potential for three-dimensional imaging of the medium permeability is also discussed. The limitations of the method are listed and results are presented in a model porous medium as well as in a real oil reservoir rock.

Measuring spatially resolved gas transport and adsorption in coal using MRI.

The storage and transport of gases in coal is of tremendous importance in the utilisation of coalbeds, and in particular the recovery of methane. There is also increasing interest in the use of coal mines as sites for carbon dioxide sequestration to alleviate the potentially harmful effects of global warming. This paper demonstrates the use of magnetic resonance imaging to investigate the spatiotemporal dynamics of gas transport in coal. The presence of significant structural heterogeneities in the coal was observed. Dynamical effects displayed a broad range of time constants ranging from minutes to days.

Method for measuring local hydraulic permeability using magnetic resonance imaging.

The hydraulic permeability of a porous medium characterizes the ease with which a fluid may be driven through it, and is defined via the classical Darcy law. A method for noninvasive, nondestructive measurement of one projection of the local permeability tensor of a porous medium, using gas phase magnetic resonance imaging, is presented. Results are shown for one-dimensional experiments on dry porous rocks. The limitations of the method are explored, and the extension to three-dimensional imaging of the permeability is discussed.

Scald burns in children caused by hot drinks--the importance of the type of cup.

A prospective study of 36 consecutive scald injuries in children caused by hot beverages is reported. Almost a third of these were deep dermal or full skin thickness and the highest percentage resulted in injury to the upper chest region. The study further investigates the cooling characteristics in four different types of cup. These studies clearly show the potential for significant disfigurement from this type of injury for up to 11 min from the time the drink is poured. The need for greater public awareness in relation to hot drinks is highlighted.