Nuclear Magnetic Resonance Signature of the Spin-Nematic Phase in LiCuVO_{4} at High Magnetic Fields.

We report a ^{51}V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO_{4}, performed in pulsed magnetic fields and focused on high-field phases up to 56 T. For the crystal orientations H∥c and H∥b, we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO_{4} compound.

Entropy Evolution in the Magnetic Phases of Partially Frustrated CePdAl.

In the heavy-fermion metal CePdAl, long-range antiferromagnetic order coexists with geometric frustration of one-third of the Ce moments. At low temperatures, the Kondo effect tends to screen the frustrated moments. We use magnetic fields B to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with B employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed, the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.

Distinct high-T transitions in underdoped Ba(1-x)KxFe2As2.

In contrast with the simultaneous structural and magnetic first order phase transition T0 previously reported, our detailed investigation on an underdoped Ba(0.84)K(0.16)Fe2As2 single crystal unambiguously revealed that the transitions are not concomitant. The tetragonal (τ: I4/mmm)-orthorhombic (ϑ: Fmmm) structural transition occurs at T(S)≃110 K, followed by an adjacent long-range antiferromagnetic (AFM) transition at T(N)≃102 K. Hysteresis and coexistence of the τ and ϑ phases over a finite temperature range observed by NMR experiments confirm the first order character of the τ-ϑ transition and provide evidence that both T(S) and T(N) are strongly correlated. Our data also show that superconductivity develops in the ϑ phase below T(c)=20 K and coexists with AFM. This new observation, T(S)≠T(N), firmly establishes another similarity between the hole-doped BaFe2As2 and the electron-doped iron-arsenide superconductors.

Investigation of the superconducting gap structure in κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br by means of thermal-conductivity measurements.

We report temperature-dependent thermal-conductivity, κ, measurements on the layered quasi-two-dimensional organic superconductors κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br down to 160 mK. The results for κ-(BEDT-TTF)2Cu(NCS)2 may be consistent with a nodal superconducting (SC) gap structure as indicated by a non-negligible remnant linear contribution when [Formula: see text] is extrapolated to [Formula: see text]. For κ-(BEDT-TTF)2Cu[N(CN)2]Br, contrary to expectations, higher κ values are observed in the superconducting regime as compared to the normal, high-field state evidencing a dominant phonon contribution to κ in the superconducting state. The strong increase of κ in the normal state below T c for both samples indicates strong electron-phonon scattering. Our results highlight the need for thermal-conductivity measurements performed down to significantly lower temperatures to determine the symmetry of the SC gap.

NMR shift and relaxation measurements in pulsed high-field magnets up to 58T.

Nuclear magnetic resonance (NMR) experiments at fields up to 58T in pulsed magnets at the Dresden High Magnetic Field Laboratory are reported. The challenge to resolve NMR shifts in these time-dependent fields is addressed for the first time, and it is shown that this can indeed be accomplished with high precision with an internal reference. As a result, signal averaging is possible during a single magnetic field pulse, but also for multiple pulses. Thus, even very weak signals can in principle be recorded and their shifts can be determined. In a second set of experiments, the measurement of nuclear relaxation is investigated. Using adiabatic inversion with the inherent time dependence of the magnetic field and small-angle inspection, it is shown that relaxation measurements are possible, as well. The shift experiments were performed with (27)Al NMR on a mixture of aluminum metal and a Linde type A zeolite. For the relaxation studies, (27)Al NMR and (69)Ga NMR on the metals aluminum and gallium were preformed, respectively.

Field-stepped broadband NMR in pulsed magnets and application to SrCu2(BO3)2 at 54T.

Pulsed magnets generate the highest magnetic fields as brief transients during which the observation of NMR is difficult, however, this is the only route to unique insight into material properties up to the regime of 100T. Here, it is shown how rather broad NMR spectra can be assembled in a pulsed magnet during a single field pulse by using the inherent time dependence of the field for the recording of field-stepped free induction decays that cover a broad frequency range. The technique is then applied to (11)B NMR of the spin-dimer system SrCu2(BO3)2, a magnetic insulator known to undergo a series of field-driven changes of the magnetic ground state. At peak fields of about 54T at the Dresden High Magnetic Field Laboratory, (11)B NMR spectra spanning a total of about 9MHz width are reconstructed. The results are in good accordance with a change from a high-temperature paramagnetic state to a low-temperature commensurate superstructure of field-induced spin-dimer triplets.

The complex between retinol and retinol-binding protein is formed in the rough microsomes of liver following repletion of vitamin A-depleted rats.

Retinol-binding protein (RBP), the plasma transport protein for vitamin A, is primarily synthesized in the rough endoplasmic reticulum of the liver. RBP then passes through the smooth endoplasmic reticulum and into the Golgi apparatus where vesicles form and transport the protein to the cell membrane. When rats were depleted of their vitamin A stores, RBP accumulated in the liver microsomes, particularly in the rough microsomes. To identify the organelle(s) where retinol initially binds to RBP, vitamin A-depleted rats were given an i.v. injection of [3H]retinol suspended in Tween 40. After intervals of 2, 3, 4, 5, 6, 8, 10, 15 and 20 min, liver fractions enriched in rough and smooth microsomes and Golgi apparatus were prepared. The retinol/RBP complex (holoRBP) was detected in the rough microsomes within 3 min post injection. HoloRBP later appeared in the smooth microsomes and Golgi fraction, and then the serum at time intervals consistent with the known secretion rate for RBP. HoloRBP was detected in the rough microsomes at all times after 3 min, whether or not the complex was present in the other subcellular fractions. Thus, the holoRBP complex can form in the rough endoplasmic reticulum of the liver.

Mercuric chloride-induced spin or ligation state changes in ferric or ferrous human cystathionine beta-synthase inhibit enzyme activity.

Cystathionine beta-synthase is a key heme and pyridoxal phosphate-dependent enzyme involved in homocysteine metabolism in humans. The role of the recently discovered heme in this protein remains an important open question. The axial ligands to the heme in both the ferrous and ferric states have been assigned as cysteine and histidine residues, respectively. In this study, we have examined the effect of ligation and spin state changes in the heme on the activity of the enzyme. Treatment of the ferric enzyme with HgCl2 results in the conversion of six-coordinate low-spin heme to five-coordinate high-spin heme and is paralleled by a loss of activity. In contrast, treatment of the ferrous enzyme with HgCl2 results in replacement of the cysteine ligand by an unidentified sixth ligand and retention of the six-coordinate state, and is also accompanied by loss of enzyme activity. Treatment of the five-coordinate HgCl2-treated enzyme with thiols, such as homocysteine, results in reversion to a six-coordinate state. Resonance Raman spectroscopy with 34S-labeled enzyme reveals the return of the endogenous thiol ligand under these conditions and rules out direct coordination by the thiolate of homocysteine to the heme.

Dean's fluorosis index: an assessment of examiner reliability.

OBJECTIVES: This report describes the interexaminer reliability achieved using Dean's Index in a study of dental fluorosis, and shows the effect on kappa values of assigning different weights to the various components of Dean's Index. METHODS: Three dentists conducted replicate fluorosis examinations on 202 children in Newburgh and Kingston, NY. Examiner reliability was assessed by computing percent agreement and weighted and unweighted kappa statistics. RESULTS: Agreement on the presence or absence of fluorosis using Dean's definition of fluorosis ranged from 92 to 97 percent and the respective kappa values ranged from 0.75 to 0.94. A comparison of subject-level severity scores for Dean's Index resulted in percent agreement ranging from 79.6 percent to 86.8 percent and kappa values ranging from 0.67 to 0.76. Weighting the kappa statistics improved agreement and reduced the differences. CONCLUSIONS: Examiners showed good to excellent agreement beyond chance in the use of the index. Subject level kappa scores were higher than tooth-level scores.

The need for dental health screening and referral programs.

School-based dental health screening and referral programs can have a tremendous impact on a community. They provide examinations to children, some of whom have never seen a dentist, and refer those in need of treatment. When coordinated with other dental health activities, these programs can also raise the overall consciousness about oral health and need for health care in children and parents alike. By their concern for dental health and encouragement to the children to participate in the screening programs and follow through on referrals, school officials can serve as role models to the children and further reinforce the importance of dental health. By conducting the screenings on a local level, the problem is seen as a community one, and is more likely to be meaningfully addressed. School officials, health personnel and teachers are instrumental in initiating and conducting these programs and are thus responsible for the benefits the children derive from the screenings.

Recommendations for fluoride use in children. A review.

Fluoride has played a significant role in the improvement of the oral health of all Americans. Because of its effectiveness, cost and frequency of exposure, water fluoridation is the preferred method of delivery. Today, many products containing fluoride are available over the counter and as prescription items. The potential for exposure to multiple sources of fluoride has increased. Therefore, practitioners should prescribe fluoride therapy based on an understanding of patients' total exposure to fluoride and the need for additional amounts.

Oral health status of second grade school children in upstate New York.

This report summarizes the results of a survey of second grade children conducted in upstate New York. The survey was designed to monitor progress toward achieving Healthy People 2000 objectives and Maternal and Child Health Services Block Grant performance measures. Data on oral health status, use of preventive measures and insurance coverage were collected on 2,474 children from 76 schools. In addition to obtaining population estimates, disparities in oral health between poor and nonpoor children were assessed. The results showed that approximately 52% of second grade children had dental caries, and 35% had untreated disease. Approximately 43% received fluoridated water, and 44% of children living in non-fluoridated areas used fluoride supplements on a regular basis. Only 25% of the children had dental sealants. The percentage of children covered by comprehensive and basic insurance plans was approximately 19% and 41%, respectively. Many of the national oral health objectives were not met primarily because of the higher rate of disease among the poor and their lower use of preventive services. These findings regarding oral health status and use of preventive services are similar to the national data.

Cognitive occupational hazards and psychopathology of the artist.

The author discusses creativity and mental health issues, with a focus on epidemiology, risk factors, and possible treatment and risk reduction. Disorders by type of artist are briefly addressed.