A large octupole magnetic trap for research with atomic hydrogen.

We describe the design and performance of a large magnetic trap for storage and cooling of atomic hydrogen (H). The trap operates in the vacuum space of a dilution refrigerator at a temperature of 1.5 K. Aiming at a large volume of the trap, we implemented the octupole configuration of linear currents (Ioffe bars) for the radial confinement, combined with two axial pinch coils and a 3 T solenoid for the cryogenic H dissociator. The octupole magnet consists of eight race-track segments, which are compressed toward each other with magnetic forces. This provides a mechanically stable and robust construction with a possibility of replacement or repair of each segment. A maximum trap depth of 0.54 K (0.8 T) was reached, corresponding to an effective volume of 0.5 l for hydrogen gas at 50 mK. This is an order of magnitude larger than ever used for trapping atoms.

Purely Spatial Quantum Diffusion of H Atoms in Solid H_{2} at Temperatures below 1 K.

We report on a direct measurement of the quantum diffusion of H atoms in solid molecular hydrogen films at T=0.7 K. We obtained a rate of pure spatial diffusion of H atoms in the H_{2} films, D^{d}=5(2)×10^{-17} cm^{2} s^{-1}, which was 2 orders of magnitude faster than that obtained from H atom recombination, the quantity used in all previous work to characterize the mobility of H atoms in solid H_{2}. We also observed that the H-atom diffusion was significantly enhanced by injection of phonons. Our results provide the first measurement of the pure spatial diffusion rate for H atoms in solid H_{2}, the only solid state system beside ^{3}He-^{4}He mixtures, where atomic diffusion does not vanish even at temperatures below 1 K.

Experimental cell with a Fabry-Pérot resonator tuned in situ for magnetic resonance studies of matrix-isolated radicals at temperatures below 1 K.

We describe the design and construction of an experimental cell for the study of free radicals in macroscopically thick films of solidified molecular and rare gases by 128 GHz Electron Spin Resonance (ESR) at temperatures below 1 K. The ESR resonator has an open Fabry-Pérot design, and its frequency can be tuned in situ by adjusting the spacing between the mirrors. The tuning mechanism consists of a piezo positioner and a stainless-steel edge-welded bellows, which can change the resonator frequency by at least 6 GHz. The films of solidified gases can be deposited either directly from a room temperature reservoir or by recondensing from a specially arranged chamber. The free radicals can be created in the solid films by dissociating matrix species by running an rf discharge in a helium vapor. We suggest that such a sample cell design can also be used for a broad range of low-temperature ESR experiments where sample cooling needs to be enhanced by the presence of superfluid helium.

Dynamic nuclear polarization and ESR hole burning in As doped silicon.

We present an experimental study of the Dynamic Nuclear Polarization (DNP) of 29Si nuclei in silicon crystals of natural abundance doped with As in the temperature range 0.1-1 K and in a strong magnetic field of 4.6 T. This ensures a very high degree of electron spin polarization, extremely slow nuclear relaxation and optimal conditions for realization of Overhauser and resolved solid effects. We found that the solid effect DNP leads to the appearance of a pattern of holes and peaks in the ESR line, separated by the super-hyperfine interaction between the donor electron and 29Si nuclei closest to the donor. On the contrary, the Overhauser effect DNP mainly affects the remote 29Si nuclei having the weakest interaction with the donor electron. This leads to the appearance of a very narrow (≈3 mG wide) hole in the ESR line. We studied relaxation of the holes after burning, which is caused by the nuclear spin diffusion. Analyzing the dynamics of the hole in the spectrum with a simple one-dimensional diffusion model leads to a value of the diffusion coefficient D = 8(3) × 10-9 G2 s-1. Our data indicate that the spin diffusion is not completely prevented even in the frozen core near the donors. The emergence of the narrow hole after the Overhauser DNP may be explained by a partial "softening" of the frozen core caused by decoupling of the donor electron and remote 29Si nuclei.

Formation of Nuclear-Polarized Phases of H Atoms Embedded in Solid H_{2} Films.

We report on an experimental observation of two phases of hydrogen atoms in solid H_{2} films at temperatures of 0.1-0.8 K, characterized by a large enhancement of the nuclear spin polarization compared to that given by Boltzmann statistics (p=0.15 at T=0.15 K). The first phase with p=0.35(5) is formed spontaneously during sample storage in a high magnetic field (B=4.6 T). The second phase with an even higher nuclear polarization, p=0.75(7), can be achieved at T≤0.55 K by repeating sequences of dynamic nuclear polarization followed by a system relaxation. Upon warming through the range 0.55-0.65 K, the highly nuclear-polarized phase undergoes a phase transition to the spontaneously polarized phase which breaks down at T≃0.8 K, and the nuclear polarization gradually converges to the Boltzmann distribution. We discuss possible scenarios for explaining the nature of the observed phenomena.

ESR study of atomic hydrogen and tritium in solid T2 and T2:H2 matrices below 1 K.

We report on the first ESR study of atomic hydrogen and tritium stabilized in solid T2 and T2:H2 matrices down to 70 mK. The concentrations of T atoms in pure T2 approached 2 × 1020 cm-3 (0.60%) and record-high concentrations of H atoms ∼1 × 1020 cm-3 (0.33%) were reached in T2:H2 solid mixtures where a fraction of T atoms became converted into H due to the isotopic exchange reaction T + H2 → TH + H. The maximum concentrations of unpaired T and H atoms were limited by their recombination which becomes enhanced by efficient atomic diffusion due to the presence of a large number of vacancies and phonons generated in the matrices by ß-particles. Recombination also appeared in an explosive manner, both being stimulated and spontaneously in thick films where sample cooling was insufficient. We suggest that the main mechanism for H and T migration is physical diffusion related to tunneling or hopping to vacant sites in contrast to tunneling chemical exchange reactions which govern diffusion of H and D atoms created in H2 and D2 matrices by other methods.

Tunneling chemical exchange reaction D + HD → D2 + H in solid HD and D2 at temperatures below 1 K.

We report on a study of the exchange tunneling reaction D + HD → D2 + H in a pure solid HD matrix and in a D2 matrix with a 0.23% HD admixture at temperatures between 130 mK and 1.5 K. We found that the exchange reaction rates, kexHD ∼ 3 × 10-27 cm3 s-1 in the pure HD matrix, and kexD2 = 9(4) × 10-28 cm3 s-1 in the D2 matrix, are nearly independent of temperature within this range. This confirms the quantum tunnelling nature of these reactions, and their ability to proceed at temperatures down to absolute zero. Based on these observations we concluded that exchange tunneling reaction H + H2 → H2 + H should also proceed in a H2 matrix at the lowest temperatures. On the other hand, the recombination of H atoms in solid H2 and D atoms in solid D2 is substantially suppressed at the lowest temperatures as a result of a decreased probability of resonant tunneling of atoms when they approach each other.

Bose-Einstein condensation of magnons in atomic hydrogen gas.

We report on experimental observation of Bose-Einstein condensation (BEC)-like behavior of quantized electron spin waves (magnons) in a dense gas of spin-polarized atomic hydrogen. The magnons are trapped and controlled with inhomogeneous magnetic fields and described by a Schrödinger-like wave equation, in analogy to the BEC experiments with neutral atoms. We have observed the appearance of a sharp feature in the ESR spectrum displaced from the normal spin wave spectrum. We believe that this observation corresponds to a sudden growth of the ground-state population of the magnons and emergence of their spontaneous coherence for hydrogen gas densities exceeding a critical value, dependent on the trapping potential. We interpret the results as a BEC of nonequilibrium magnons which were formed by applying the rf power.

Experimental cell for molecular beam deposition and magnetic resonance studies of matrix isolated radicals at temperatures below 1 K.

We present the design and performance of an experimental cell constructed for matrix isolation studies of H and D atoms in solid H2/D2 films, which are created by molecular beam deposition at temperatures below 1 K. The sample cell allows sensitive weighing of the films by a quartz microbalance (QM) and their studies by magnetic resonance techniques in a strong magnetic field of 4.6 T. We are able to regulate the deposition rate in the range from 0.01 to 10 molecular layers/s, and measure the thickness with ≈0.2 monolayer resolution. The upper QM electrode serves as a mirror for a 128 GHz Fabry-Perot resonator connected to an electron spin resonance (ESR) spectrometer. H and D atoms were created by RF discharge in situ in the sample cell, and characterized by ESR and electron-nuclear double resonance. From the magnetic resonance measurements we conclude that the films are smooth and provide homogeneous trapping conditions for embedded atoms. The current sample cell design also makes it possible to calibrate the ESR signal and estimate the average and local concentrations of H and D radicals in the film.

Dynamic nuclear polarization of high-density atomic hydrogen in solid mixtures of molecular hydrogen isotopes.

We report on magnetic resonance studies of high-density atomic hydrogen and deuterium in solid hydrogen matrices at temperatures below 1 K. Average concentrations of H atoms ≈3×10(19) cm(-3) are obtained in chemical tunneling reactions of isotope exchange with D atoms. The products of these reactions are closely located pairs of H atoms near D2 molecules with strong exchange interactions. We discovered a dynamic nuclear polarization effect on H atoms created by pumping the center of the H electron spin resonance spectrum, similar to the Overhauser effect in metals. Our results indicate that H atoms may be arranged inside molecular matrices at separations equivalent to local concentrations of 2.6×10(21) cm(-3). This opens up a way to build a metallic state of atomic hydrogen at zero pressure.

Guiding and trapping of electron spin waves in atomic hydrogen gas.

We present a high magnetic field study of electron spin waves in atomic hydrogen gas compressed to high densities of ∼10(18) cm(-3) at temperatures ranging from 0.26 to 0.6 K. We observed a variety of spin wave modes caused by the identical spin rotation effect with strong dependence on the spatial profile of the polarizing magnetic field. We demonstrate confinement of these modes in regions of strong magnetic field and manipulate their spatial distribution by changing the position of the field maximum.

Rapid screening of commercially available herbal products for the inhibition of major human hepatic cytochrome P450 enzymes using the N-in-one cocktail.

Self-administration of complementary products concurrently with conventional medication is increasingly common. The potential for cytochrome P450 (CYP) inhibition requires investigation. The N-in-one assay with ten probe substrates for nine CYPs was used with human liver microsomes to investigate ten products. CYP inhibition was measured in a single liquid chromatography-tandem mass spectrometry (LC/MS-MS) analysis. Estimated IC(50)-values were determined for the extracts that produced significant inhibition (less than 100 microg ml(-1)). Inhibition of CYP2C19 by dong quai (IC(50) = 13.7-14.3 microg ml(-1) for the methanolic extract) and CYP2D6 by goldenseal (IC(50) = 6.7 and 6.3 microg ml(-1) for the aqueous and methanolic extracts, respectively), are of particular concern as the potential for adverse interactions is high. The inhibition of CYP2C8 by horsetail (IC(50) = 93 microg ml(-1) for the aqueous extract) requires further investigation, as the potential for concurrent use with products that require CYP2C8 for metabolism is significant. CYP3A4 inhibition varied depending on the probe reaction being monitored. The earlier reported findings of inhibition by black cohosh, goldenseal and gotu kola were confirmed. The present work has shown that the N-in-one cocktail is a rapid and reliable method that can be used as an initial screen to help prioritize products that require more detailed investigations and it can also be applied to monitor product variability.

Clock shift in high field magnetic resonance of atomic hydrogen.

We have measured electron spin resonance line shifts due to collisions in atomic hydrogen gas compressed to densities approximately 10(18) cm(-3) in a strong magnetic field (4.6 T). The shift in a doubly polarized gas is negligible, in contrast with a mixture of two hyperfine states. This difference is explained by properly including effects of quantum statistics in atomic collisions and magnetic dipolar effects. We report on the first direct measurement of the difference between the triplet and singlet s-wave scattering lengths a(t) - a(s) = 60(10) pm, which is in agreement with existing theories.

Cold collision frequency shift in two-dimensional atomic hydrogen.

We report a measurement of the cold collision frequency shift in atomic hydrogen gas adsorbed on the surface of superfluid (4)He at T approximately < 90 mK. Using two-photon electron and nuclear magnetic resonance in 4.6 T field we separate the resonance line shifts due to the dipolar and exchange interactions, both proportional to surface density sigma. We find the clock shift Delta nu(c) = -1.0(1) x 10(-7) Hz cm(-2) x sigma, which is about 100 times smaller than the value predicted by the mean field theory and known scattering lengths in the three-dimensional case.

Contactless measurement of cow behavior in a milking robot.

We have worked on automatically measuring the behavior of dairy cows during automatic milking. A milking robot offers a unique possibility for a dynamic measurement of physical data. Four strain gauge scales were installed into a milking robot in order to measure the weight of each leg separately, and a laser distance sensor was placed next to the robot in order to measure the radial movement of the cow's body surface. The data were collected into a PC. Three video cameras were installed to observe the system, and the data were recorded digitally. From the data, the dynamic weight or load of each leg and the respiration rate of a cow could be measured. Different stages of milking were observed, and the changes in behavior during milking were analyzed. The acquired information could be used to judge a cow's restlessness and welfare--for example, leg health and stress.

Exotic behavior of hydrogen atoms in solid H2 at temperatures below 1 K.

We present the first magnetic resonance study of atomic hydrogen embedded in solid H2 films for temperatures 150-900 mK. We found that at T approximately 150 mK average concentrations of H atoms of order 10(18 cm(-3) are very stable against recombination during two weeks of observations. The distribution of the population of the two lowest hyperfine states is found to be non-Boltzmann, with a very large occupation of the ground state. We consider the possibility of formation in solid H2 of regions with high local concentrations of H atoms, where collective quantum phenomena might occur.

Is fluoroacetate-specific defluorinase a glutathione S-transferase?

Fluoroacetate-specific defluorinase (FSD) is a critical enzyme in the detoxication of fluoroacetate. This study investigated whether FSD can be classed as a glutathione S-transferase (GST) isoenzyme with a high specificity for fluoroacetate detoxication metabolism. The majority of FSD and GST activity, using 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-epoxy-3-(p-nitrophenoxy)propane (EPNP) as GST substrates, in rat liver was cytosolic. GSTT1 specific substrate, EPNP caused a slight non-competitive inhibition of FSD activity. CDNB, a general substrate of GST isoenzyme, was a more potent non-competitive inhibitor of FSD activity. The fluoroacetate defluorination activity by GST isoenzymes was determined in this study. The results showed that the GSTZ1C had the highest fluoroacetate defluorination activity of the various GST isoenzymes studied, while GSTA2 had a limited activity toward fluoroacetate. The human GSTZ1C recombinant protein then was purified from a human GSTZ1C cDNA clone. Our experiments showed that GSTZ1C catalysed fluoroacetate defluorination. GSTZ1 shares many of the characteristics of FSD; however, it accounts only for 3% of the total cytosolic FSD activity. GSTZ1C based enzyme kinetic studies has low affinity for fluoroacetate. The evidence suggests that GSTZ1 may not be the major enzyme defluorinating fluoroacetate, but it does detoxify the fluoroacetate. To clarify the identity of enzymes responsible for fluoroacetate detoxication, further studies of the overall FSD activity are needed.

Characterization of the fluoroacetate detoxication enzymes of rat liver cytosol.

Two forms of fluoroacetate-specific defluorinase (FSD) were purified from rat hepatic cytosol. The first form, FSD1 (molecular weight 38 kDa), contained 81% of the total cytosolic fluoroacetate defluorination activity and did not bind to the glutathione-affinity, orange A or mono P columns used in the purification procedures. The second form, FSD2 (molecular weight 27 kDa), contained only 13% of the fluoroacetate defluorination activity, had a pI = 7.8, and exhibited a high glutathione S-transferase (GST)-like activity towards dichloroacetic acid. The FSD1 proteins were identified from peptide mass data and best matched with rat sorbitol dehydrogenase (SDH) (short form), although pure sheep liver SDH enzyme did not possess defluorination activity when subsequently investigated. The FSD2 protein was identified from peptide mass data and best matched with the amino acid sequence of mouse and human Zeta 1 of glutathione S-transferase (GSTZ1) and showed a high GSTZ1 specific activity. This study suggests that the major FSD component (FSD1) represents a new and unique dehalogenating or dehydrogenating enzyme present in rat liver cytosol. The minor FSD component (FSD2) is due to the GSTZ1 present in rat liver cytosol. However, it is not yet clear that FSD1 is indeed SDH and FSD2 is indeed GSTZ1, due to sequence homology being less than 60 and 45%, respectively.

Binding of aflatoxin B1 to cell wall components of Lactobacillus rhamnosus strain GG.

The surface of Lactobacillus rhamnosus strain GG (LGG) has previously been shown to bind aflatoxin B(1) (AFB(1)) effectively, it being a food-borne carcinogen produced by certain species of Aspergillus fungi. To establish which components of the cell envelope are involved in the AFB(1) binding process, exopolysaccharides and a cell wall isolate containing peptidoglycan were extracted from LGG and its AFB(1) binding properties were tested. LGG was also subjected to various enzymatic and chemical treatments and their effects on the binding of AFB(1) by LGG were examined. No evidence was found for exopolysaccharides, cell wall proteins, Ca(2+) or Mg(2+) being involved in AFB(1) binding. The AFB(1) binding activity of the cell wall isolate indicates that AFB(1) binds to the cell wall peptidoglycan of LGG or compounds tightly associated with the peptidoglycan.

Selective in vitro binding of dietary mutagens, individually or in combination, by lactic acid bacteria.

Specific strains of lactic acid bacteria possessing antimutagenic properties are suggested to remove mutagenic contaminants of foods through binding and an investigation of their substrate specificity is required. The ability of Lactobacillus rhamnosus strains GG and LC-705 in viable and non-viable (heat- and acid-treated) forms to remove both dietary mutagens and other aromatic dietary substrates from solution was studied using HPLC. Overall, removal increased in the order: caffeine = vitamin B12 =folic acid < ochratoxin A < aflatoxin B1 = PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) < Trp-P-1 (3-amino-1, 4-dimethyl-5H-pyrido[4,3-b]indole) (p < 0.05). Aflatoxin B1, Trp-P-1 and PhIP were removed in high amounts (77-95%) and ochratoxin A was removed in moderate amounts (36-76%). By contrast, only minimal amounts of caffeine, vitamin B12 andfolic acid were removed (9-28%). The significant removal of selected mutagens, but not other substrates, suggests these strains may be useful for dietary detoxification. Since exposure to multiple mutagens is likely, the removal of aflatoxin B1 and Trp-P-1 from a mixture of these substrates was also investigated. Removal of AFB1 significantly increased (p < 0.05) in the presence of Trp-P-1, while removal of Trp-P-1 significantly decreased (p < 0.05) in the presence of AFB1. Overall, no significant differences in removal were found between bacterial strains or between viable, heat- and acid-treated bacteria.