Probing the non-equilibrium transient state in magnetite by a jitter-free two-color X-ray pump and X-ray probe experiment.

We present a general experimental concept for jitter-free pump and probe experiments at free electron lasers. By generating pump and probe pulse from one and the same X-ray pulse using an optical split-and-delay unit, we obtain a temporal resolution that is limited only by the X-ray pulse lengths. In a two-color X-ray pump and X-ray probe experiment with sub 70 fs temporal resolution, we selectively probe the response of orbital and charge degree of freedom in the prototypical functional oxide magnetite after photoexcitation. We find electronic order to be quenched on a time scale of (30 ± 30) fs and hence most likely faster than what is to be expected for any lattice dynamics. Our experimental result hints to the formation of a short lived transient state with decoupled electronic and lattice degree of freedom in magnetite. The excitation and relaxation mechanism for X-ray pumping is discussed within a simple model leading to the conclusion that within the first 10 fs the original photoexcitation decays into low-energy electronic excitations comparable to what is achieved by optical pump pulse excitation. Our findings show on which time scales dynamical decoupling of degrees of freedom in functional oxides can be expected and how to probe this selectively with soft X-ray pulses. Results can be expected to provide crucial information for theories for ultrafast behavior of materials and help to develop concepts for novel switching devices.

Fermi Surface of Metallic V_{2}O_{3} from Angle-Resolved Photoemission: Mid-level Filling of e_{g}

Using angle resolved photoemission spectroscopy, we report the first band dispersions and distinct features of the bulk Fermi surface (FS) in the paramagnetic metallic phase of the prototypical metal-insulator transition material V_{2}O_{3}. Along the c axis we observe both an electron pocket and a triangular holelike FS topology, showing that both V 3d a_{1g} and e_{g}^{π} states contribute to the FS. These results challenge the existing correlation-enhanced crystal field splitting theoretical explanation for the transition mechanism and pave the way for the solution of this mystery.

An 'end-game' for sugar sweetened beverages?

OBJECTIVE: The epidemic of unhealthy weight is now in its third decade. The multitude of initiatives designed to address this issue (globally) have predominantly been ineffective as the prevalence of unhealthy weight has continued to rise. Public health professionals have proposed an 'endgame' for tobacco smoking in New Zealand by 2025, which has received widespread support. Similarly, here, to control the prevalence of unhealthy weight, we consider whether a similar approach to tobacco is justified to restrict the intake of sweetened beverages. APPROACH: This paper reviews the evidence relating sugar sweetened beverages to unhealthy weight and adverse health effects. Current initiatives aimed at reducing sugar sweetened beverage consumption both internationally and in New Zealand are reviewed. FINDINGS: Epidemiological evidence consistently links sugar-sweetened drink intake with unhealthy weight and other risk factors for cardiovascular disease, such as diabetes, gout, and raised blood pressure. Food disappearance data suggests that sugar intake continues to increase in New Zealand, and that a subtle addiction to sugar may underlie this trend. A number of successful initiatives to reduce sugary drink intake are described. IMPLICATION/CONCLUSION: We argue that an 'endgame' to the consumption of sugar-sweetened beverages be supported as a means to address the issue of unhealthy weight at a population level. Finally, a preliminary draft endgame plan is presented for consideration, dialogue and debate.

Dietary intakes of Pacific ethnic groups and European people.

OBJECTIVE: To compare dietary intakes, food servings, and cooking practices of Pacific ethnic groups with New Zealand Europeans. METHODS: Daily nutrient intakes were calculated from a self-administered food frequency questionnaire from a cross-sectional health screening study. Participants were Pacific (n=954) and New Zealand European (n=1.745) people aged 35 to 74 years. RESULTS: Total energy intakes in Samoan and Niuean men were higher than European men, while for women, total energy intakes were significantly higher in all Pacific ethnic groups compared to New Zealand European women. Pacific men and women had lower alcohol and calcium intakes compared to New Zealand Europeans, and Pacific men had higher protein and cholesterol intakes. Pacific adults reported eating more servings of fish, chicken and bread, fewer servings of cheese and breakfast cereal per month, and boiled their meat more often than European adults. CONCLUSIONS: Substantial differences in dietary habits and cooking practices exist between European and the different Pacific adult groups mainly related to the frequency of consumption of certain food/nutrient groups and greater serving sizes in Pacific compared to New Zealand European adults. Implications Strategies targeting serving sizes and frequency of consumption of specific food groups may help address the major ethnic disparities in nutrition-related health problems in New Zealand.

Carbonated beverages consumption among New Zealand youth and associations with BMI and waist circumference.

AIM: The primary aim of this study was to describe the carbonated beverage (soft drink) consumption patterns of New Zealand (NZ) youth and to investigate the influence that home availability of soft drinks had on their consumption. A secondary aim was to determine if there was an association between soft drink consumption and body mass index (BMI) or waist circumference. METHODS: Data from Youth '07, a nationally representative survey of the health and well-being of NZ youth, including 8,697 NZ students aged 13 to 17 years, were analysed. RESULTS: The relevant data was available for 8697 students of whom 4633 identified as NZ European. 1621 Maori, 1.098 Asian, 834 Pacific, and 504 Other. Twenty nine percent (29%) were categorised as high consumers of soft drinks (>4 times a week), 45.4% were moderate consumers (1-3 times a week), and 25.6% were low consumers (had not consumed soft drinks in the past week). Male gender, Pacific ethnicity, and high deprivation were all significantly associated with being in the high consumer group. Fifty eight percent (58%) of children who reported that soft drinks were 'usually' available at home were in the high consumption group, compared to 15.1% of children who reported that these drinks were never available at home. After adjusting for possible confounders, waist circumference was significantly associated with soft drink consumption (p<0.05), however, BMI was not. Mean soft drink consumption for boys was 3.5 times per week and was 2.0 for girls. CONCLUSION: This study provides detailed information on soft drink consumption patterns of NZ youth and highlights factors associated with high consumption. Moderating the availability of soft drinks in the home is likely to significantly reduce their consumption among NZ youth.

Speed limit of the insulator-metal transition in magnetite.

As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump-probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two-step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.

Symmetry of orbital order in Fe3O4 studied by Fe L(2,3) resonant x-ray diffraction.

We studied the symmetry of the Fe 3d wave function in magnetite below the Verwey temperature T(V) with resonant soft-x-ray diffraction. Although the lattice structure of the low-temperature phase of Fe(3)O(4) is well described by the pseudo-orthorhombic Pmca with a slight monoclinic P2/c distortion, we find that the 3d wave function does not reflect the Pmca symmetry, and its distortion toward monoclinic symmetry is by far larger than that of the lattice. The result supports a scenario in which the Verwey transition involves the ordering of t(2g) orbitals with complex-number coefficients.

Inequivalent routes across the Mott transition in V2O3 explored by X-ray absorption.

The changes in the electronic structure of V2O3 across the metal-insulator transition induced by temperature, doping, and pressure are identified using high resolution x-ray absorption spectroscopy at the V pre-K edge. Contrary to what has been taken for granted so far, the metallic phase reached under pressure is shown to differ from the one obtained by changing doping or temperature. Using a novel computational scheme, we relate this effect to the role and occupancy of the a{1g} orbitals. This finding unveils the inequivalence of different routes across the Mott transition in V2O3.

Quasiparticles at the Mott transition in V2O3: wave vector dependence and surface attenuation.

We present an angle resolved photoemission study of V2O3, a prototype system for the observation of Mott transitions in correlated materials. We show that the spectral features corresponding to the quasiparticle peak in the metallic phase present a marked wave vector dependence, with a stronger intensity along the GammaZ direction. The analysis of their intensity for different probing depths shows the existence of a characteristic length scale for the attenuation of coherent electronic excitations at the surface. This length scale, which is larger than the thickness of the surface region as normally defined for noncorrelated electronic states, is found to increase when approaching the Mott transition. These results are in agreement with the behavior of quasiparticles at surfaces as predicted by Borghi et al.

COPD prevalence is increased in lung cancer, independent of age, sex and smoking history.

Chronic obstructive pulmonary disease (COPD) is a common comorbid disease in lung cancer, estimated to affect 40-70% of lung cancer patients, depending on diagnostic criteria. As smoking exposure is found in 85-90% of those diagnosed with either COPD or lung cancer, coexisting disease could merely reflect a shared smoking exposure. Potential confounding by age, sex and pack-yr smoking history, and/or by the possible effects of lung cancer on spirometry, may result in over-diagnosis of COPD prevalence. In the present study, the prevalence of COPD (pre-bronchodilator Global Initiative for Chronic Obstructive Lung Disease 2+ criteria) in patients diagnosed with lung cancer was 50% compared with 8% in a randomly recruited community control group, matched for age, sex and pack-yr smoking exposure (n = 602, odds ratio 11.6; p<0.0001). In a subgroup analysis of those with lung cancer and lung function measured prior to the diagnosis of lung cancer (n = 127), we found a nonsignificant increase in COPD prevalence following diagnosis (56-61%; p = 0.45). After controlling for important variables, the prevalence of COPD in newly diagnosed lung cancer cases was six-fold greater than in matched smokers; this is much greater than previously reported. We conclude that COPD is both a common and important independent risk factor for lung cancer.

Antiferromagnetic-paramagnetic insulating transition in Cr-doped V(2)O(3) investigated by EXAFS analysis.

We have performed extended x-ray absorption fine-structure (EXAFS) spectroscopy on a 2.8% Cr-doped V(2)O(3) sample, with the aim of studying its structural evolution in a wide temperature range across the paramagnetic-antiferromagnetic insulating phase transition at T(c). The data were registered with two different set-ups in fluorescence and transmission geometries, for polarized and unpolarized spectra, respectively. Our idea, based on previous experiments reported in the literature, is that extended structural modifications of the nominal trigonal symmetry are present in the paramagnetic insulating phase for several tens of degrees above T(c), involving further-nearest-neighbor vanadium ions. Our data confirm that the paramagnetic insulating phase is not structurally homogeneous in a temperature range of about 30 K around T(c), where local distortions of monoclinic symmetry involving further-nearest neighbors are present. Moreover, the analysis of the absorption profile at Cr K-edge suggests that Cr ions enter the lattice randomly. We finally analyze our findings in light of current theoretical models.

Design effects associated with dietary nutrient intakes from a clustered design of 1 to 14-year-old children.

OBJECTIVE: To calculate intra-cluster and intra-household design effects and intra-class correlation coefficients for dietary nutrients obtained from a 24 h record-assisted recall. DESIGN: Children were recruited using clustered probability sampling. Randomly selected starting-point addresses were obtained with probability proportional to mesh block size. SETTING: Children aged 1-14 years in New Zealand. SUBJECTS: There were 125 children in 50 clusters, giving an average of 2.498 children per cluster. In 15 homes, there were two children for the calculation of intra-household statistics. RESULTS: Intra-cluster design effects ranged from 1.0 for cholesterol, beta-carotene, vitamin A, vitamin D, vitamin E, selenium, fructose and both carbohydrate and protein expressed as their contribution to total energy intakes to 1.552 for saturated fat, with a median design effect of 1.148. Their corresponding intra-cluster correlations ranged from 0 to 0.37, respectively. Intra-household design effects ranged from 1.0 for height to 1.839 for vitamin B(6), corresponding to intra-household correlations of 0 and 0.839. The median intra-household design effect was 1.550. Using a sampling design of two to three households per cluster for estimating dietary nutrient intakes would need, on average, a 15% increase in sample size compared with simple random sampling with a maximum increase of 55% to cover all nutrients. CONCLUSIONS: These data enable sample sizes for dietary nutrients to be estimated for both cluster and non-cluster sampling for children aged 1-14 years. The larger design effects found within households suggest that little extra information may be obtained by sampling more than one child per household.

Zener double exchange from local valence fluctuations in magnetite.

Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below T(V)=123 K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B site sublattice (approximately 80 meV) are shifted upwards in energy above T_{V} due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of Delta(5) symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above T(V).

Strain-induced bond buckling and its role in insulating properties of Cr-doped V2O3.

Structural transformations around both V and Cr atoms in (V1-xCrx)2O3 across its metal-insulator transition (MIT) at x approximately 0.01 are studied by extended x-ray absorption fine-structure technique. Our new results for Cr made possible by the use of a novel x-ray analyzer that we developed reveal the substitutional mechanism of Cr doping. We find that this system has a buckled structure with short Cr-V and long V-V bonds. This system of bonds is disordered around the average trigonal lattice ascertained by x-ray diffraction. Such local distortions can result in a long range strain field that sets in around dilute Cr atoms in microscopic regions. We suggest that such locally strained regions should be insulating even at small x. The possibility of local insulating regions within a metallic phase, first suggested by Rice and Brinkman in 1972, remains unaccounted for in modern MIT theories.

Coherent peaks and minimal probing depth in photoemission spectroscopy of Mott-Hubbard systems.

We have measured hard x-ray photoemission spectra of pure vanadium sesquioxide (V(2)O(3)) across its metal-insulator transition. We show that, in the metallic phase, a clear correlation exists between the shakedown satellites observed in the vanadium 2p and 3p core-level spectra and the coherent peak measured at the Fermi level. Comparing experimental results and dynamical mean-field theory calculations, we estimate the Hubbard energy U in V(2)O(3) (4.20+/-0.05 eV). From our bulk-sensitive photoemission spectra we infer the existence of a critical probing depth for investigating electronic properties in strongly correlated solids.

Purification, crystallization and preliminary X-ray analysis of Mycobacterium tuberculosisfolylpolyglutamate synthase (MtbFPGS).

The gene encoding Mycobacterium tuberculosis FPGS (MtbFPGS; Rv2447c) has been cloned and the protein (51 kDa) expressed in Escherichia coli. The purified protein was crystallized either by the batch method in the presence of adenosine diphosphate (ADP) and CoCl2 or by vapour diffusion in the presence of ADP, dihydrofolate and CaCl2. X-ray diffraction data to approximately 2.0 and 2.6 A resolution were collected at the Stanford Synchrotron Radiation Laboratory (SSRL) for crystals grown under the respective conditions. Both crystals belong to the cubic space group P2(1)3, with a unit-cell parameter of 112.6 and 111.8 A, respectively. Structure determination is proceeding.

Filling of the mott-hubbard gap in the high temperature photoemission spectrum of (V0.972Cr0.028)2O3.

Photoemission spectra of the paramagnetic insulating phase of (V0.972Cr0.028)2O3, taken in ultrahigh vacuum up to the unusually high temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH) insulator that has not been observed previously. With increasing T the MH gap is filled by spectral weight transfer, in qualitative agreement with high-T theoretical calculations combining dynamical mean field theory and band theory in the local density approximation.

Universality and critical behavior at the Mott transition.

We report conductivity measurements of Cr-doped V2O3 using a variable pressure technique. The critical behavior of the conductivity near the Mott insulator to metal critical endpoint is investigated in detail as a function of pressure and temperature. The critical exponents are determined, as well as the scaling function associated with the equation of state. The universal properties of a liquid-gas transition are found. This is potentially a generic description of the Mott critical endpoint in correlated electron materials.

Short-term repeatability of a food frequency questionnaire in New Zealand children aged 1-14 y.

OBJECTIVE: To evaluate the repeatability of a children's food frequency questionnaire (FFQ) by gender, ethnicity, and age group. DESIGN: A 117-item FFQ asking about food intake patterns over the past 4 weeks was developed using food records from 428 children (204 boys and 224 girls) and the reproducibility on average 13 days apart was tested in 130 children (78 boys and 52 girls). Children were recruited using clustered probability sampling (n=103), and a convenience sample of 25 Maori children. SETTING: Children aged 1-14 y from Auckland, Feilding and Shannon, New Zealand. SUBJECTS: There were 71 Maori, 20 Pacific, and 39 Other children. RESULTS: Spearman correlations between the two FFQs ranged from 0.50 for bread to 0.82 for fruit, with a median of 0.76 for spreads and nonmilk drinks, and Cronbach's coefficient alpha's ranged from 0.59 for bread to 0.92 for nonmilk drinks, with a median of 0.85 for mixed meat dishes. There were no significant differences between the two administrations, apart from reporting higher intakes of vegetables and snacks & sweets in the first FFQ. Correlation coefficients tended to be slightly higher in boys than in girls, and in Other ethnic groups compared to Maori and Pacific children. Correlations were slightly higher for the 1-4 y age group, intermediate in the 10-14 y age group, and lowest in the 5-9 y-old age group. CONCLUSIONS: Overall, the FFQ described here shows similar or better repeatability in New Zealand children of all major ethnic groups compared to other child or adolescent FFQs.