How space-charge behaviour at grain boundaries in electroceramic oxides is modified by two restricted equilibria.

Determining the space-charge potential at grain boundaries in oxides by various experimental methods bears the promise of providing a comprehensive, quantitative description of interfacial defect chemistry. In this study, we draw attention to the problem of unifying data measured in different temperature ranges. We focus on unifying data from elevated-temperature electrical methods, such as impedance spectroscopy and current-voltage measurements, with data from room-temperature imaging techniques, such as Scanning Probe Microscopy (SPM), Transmission Electron Microscopy (TEM), and Atom Probe Tomography (APT). By means of continuum simulations, we calculate the space-charge potential Φ0 at grain boundaries in the model electroceramic oxide acceptor-doped SrTiO3, taking into account, first, a restricted equilibrium that leads to frozen-in acceptor-dopant profiles, and subsequently, a restricted equilibrium that leads to frozen-in bulk oxygen-vacancy concentrations. Our results indicate non-trivial differences between experimental values of Φ0 obtained from electrical and from imaging methods, differences that arise from the different measurement temperatures and that are aggravated by the restricted equilibria. We also show that grain-boundary widths determined from elemental acceptor-cation profiles will not, on principle, agree with the electrical width extracted from impedance spectroscopy data.

Occurrence of Meloidogyne Arenaria in Black Pepper (Piper Nigrum L.) in the Extreme South of the State of Bahia, Brazil.

Samples of black pepper root with the presence of galls from the most southern region of the State of Bahia, Brazil, were characterized biochemically and morphologically using three criteria: i) observation of the anterior region of the males; ii) analysis of female perineal configuration and iii) polyacrylamide gel electrophoresis technique. Meloidogyne arenaria was found. This is the first report of this pathosystem in the State.

Updating predictions of dry matter intake of lactating dairy cows.

Our objective was to model dry matter intake (DMI) by Holstein dairy cows based on milk energy (MilkE), body weight (BW), change in BW (ΔBW), body condition score (BCS), height, days in milk (DIM), and parity (primiparous and multiparous). Our database included 31,631 weekly observations on 2,791 cows enrolled in 52 studies from 8 states of the United States, mostly in the Upper Midwest. The means ± standard deviations of these variables were 24 ± 5 kg of DMI, 30 ± 6 Mcal of MilkE/d, 624 ± 83 kg of BW, 0.24 ± 1.50 kg of ΔBW/d, 3.0 ± 0.5 BCS, 149 ± 6 cm height, and 102 ± 45 DIM. Data analysis was performed using a mixed-effects model containing location, study within location, diet within study, and location and cow within study as random effects, whereas the fixed effects included the linear effects of the covariates described previously and all possible 2-way interactions between parity and the other covariates. A nonlinear (NLIN) mixed model analysis was developed using a 2-step approach for computational tractability. In the first step, we used a linear (LIN) model component of the NLIN model to predict DMI using only data from mid-lactation dairy cows (76-175 DIM) without including information on DIM. In the second step, a nonlinear adjustment for DIM using all data from 0 to 368 DIM was estimated. Additionally, this NLIN model was compared with an LIN model containing a fourth-order polynomial for DIM using data throughout the entire lactation (0-368 DIM) to assess the utility of an NLIN model for the prediction of DMI. In summary, a total of 8 candidate models were evaluated as follows: 4 ways to express energy required for maintenance (BW, BW0.75, BW adjusted for a BCS of 3, and BW0.75 adjusted for a BCS of 3) × 2 modeling strategies (LIN vs. NLIN). The candidate models were compared using a 5-fold across-studies cross-validation approach repeated 20 times with the best-fitting model chosen as the proposed model. The metrics used for evaluation were the mean bias, slope bias, concordance correlation coefficient (CCC), and root mean squared error of prediction (RMSEP). The proposed prediction equation was DMI (kg/d) = [(3.7 + parity × 5.7) + 0.305 × MilkE (Mcal/d) + 0.022 × BW (kg) + (-0.689 + parity × -1.87) × BCS] × [1 - (0.212 + parity × 0.136) × exp(-0.053 × DIM)] (mean bias = 0.021 kg, slope bias = 0.059, CCC = 0.72, and RMSEP = 2.89 kg), where parity is equal to 1 if the animal is multiparous and 0 otherwise. Finally, the proposed model was compared against the Nutrient Requirements of Dairy Cattle (2001) prediction equation for DMI using an independent data set of 9,050 weekly observations on 1,804 Holstein cows. The proposed model had smaller mean bias and RMSEP and higher CCC than the Nutrient Requirements of Dairy Cattle equation to predict DMI and has potential to improve diet formulation for lactating dairy cows.

The effect of space-charge formation on the grain-boundary energy of an ionic solid.

Taking the model system of an oxide containing acceptor dopant cations and charge-compensating oxygen vacancies, we calculate at the continuum level the change in the excess grain-boundary energy of an ionic solid upon space-charge formation. Two different cases are considered for the space-charge layers: (i) only vacancies attain electrochemical equilibrium and (ii) both dopants and vacancies attain electrochemical equilibrium. The changes calculated for a specific set of grain boundaries indicate that, depending on dopant concentration, space-charge formation can decrease the excess free energy by up to 15% in the first case and by up to 45% in the second case. The possibility of the excess grain-boundary energy going to zero and the possible effects of an external electric field on the excess grain-boundary energy are also discussed. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

Family health and conditional cash transfer in Brazil and its effect on tuberculosis mortality.

BACKGROUND: Social protection can reduce poverty and act on the determinants of tuberculosis (TB). OBJECTIVE: To evaluate the impact of the Family Health Strategy (FHS) and the Bolsa Família Programme on TB-related mortality in Brazil. METHODS: This was an ecological study in which the units of analysis were Brazilian municipalities between 2001 and 2012. The principal independent variables were the levels of coverage of the primary health care system and the conditional cash transfer programme. The dependent variable was TB mortality rate (obtained from national databases). Descriptive analysis and negative binomial regression based on panel data using fixed-effects models were performed. Crude and adjusted estimates were calculated for continuous and categorical variables. RESULTS: A high FHS coverage was significantly associated with a reduction in the TB mortality rate (RR 0.80, 95%CI 0.72-0.89). An increase in the coverage of the Brazilian cash transfer programme was significantly associated with a reduction in the TB mortality rate (RR 0.87, 95%CI 0.81-0.96). CONCLUSION: FHS and the Bolsa Família conditional cash transfer programme had a positive impact on the TB mortality rate in Brazil. Public policies should include economic support combined with health promotion.

Is ReO3 a mixed ionic-electronic conductor? A DFT study of defect formation and migration in a BVIO3 perovskite-type oxide.

Density-functional-theory (DFT) calculations within the generalised gradient approximation (GGA) were used to examine the behaviour of point defects in the cubic BVIO3 perovskite-type oxide, ReO3. Energies of reduction and of hydration were calculated, and the results are compared with literature data for ABO3 perovskite oxides. The activation energies of migration were determined for O2-, H+, Li+, Na+, K+ and H3O+. An occupied A site in ReO3 is found to be beneficial to oxide-ion migration by a vacancy mechanism as well as to proton migration by a Grotthuss mechanism. Na+, K+ and H3O+ exhibit activation energies of migration higher than 2 eV, whereas Li+ is characterised by a very low migration barrier of 0.1 eV. Reasons for this behaviour are discussed. Our results suggest that H+, O2-, and especially Li+, are highly mobile ions in ReO3.

Three dimensional typological studies using scanning electron microscopy for characterization of Termitomyces pellets obtained from submerged growth conditions.

There are gaps in existing understanding of fungal pellet growth dynamics. We used scanning electron microscopy (SEM) for morphological characterization of the biomass organization of Termitomyces pellets for seven species: T. microcarpus (TMI1), T. albuminosus (TAL1, TAL2), T. striatus (TSTR), T. aurantiacus (TAUR), T. heimii (THE1, THE2), T. globulus (TGLO) and T. clypeatus (TCL1, TCL2, TCL3, TCL4, TCL5). We assessed the utility of SEM for morphological and structural characterization of Termitomyces spp. in three dimensional (3D) pellet form to identify ideal pellet morphology for industrial use. Typological classification of Termitomyces species was based on furrows, isotropy, total motifs and fractal dimensions. The pellets formed were entangled and exhibited highly compacted mycelial mass with microheterogeneity and microporosity. The mean density of furrows of Termitomyces species was between 10,000 and 11,300 cm/cm2, percentage isotropy was 30-80 and total motifs varied from 300 to 2500. TGLO exhibited the highest furrow mean density, 11243 cm/cm2, which indicated a compact, cerebroid structure with complex ridges and furrows, whereas TAL2 exhibited the lowest furrow density. TMI1a exhibited a high percentage isotropic value, 74.6, TSTR exhibited the lowest, 30.9. Total motif number also was used as a typological classification parameter. Fractal values were 2.64-2.78 for various submerged conditions of Termitomyces species. TAL1 exhibited the highest fractal dimension and TAL2 the lowest, which indicates the complexity of branching patterns. Three-dimensional SEM image analysis can provide insight into pellet micromorphology and is a powerful tool for exploring topographical details of pellets.

A SIMS study of cation and anion diffusion in tantalum oxide.

Ion transport in ceramics of the low-temperature phase of tantalum pentoxide, L-Ta2O5, was examined by means of diffusion experiments and subsequent analysis of diffusion profiles with time-of-flight secondary ion mass spectrometry (ToF-SIMS). 18O/16O isotope anneals were used to investigate oxygen diffusion, and oxygen tracer diffusion coefficients were obtained for the temperature range of 623 ≤ T/K ≤ 873 at an oxygen partial pressure of pO2 = 0.2 bar and for the oxygen partial pressure range of 10-2 ≤ pO2/bar ≤ 100 at a temperature of T = 723 K. Cation diffusion in Ta2O5 was probed by using chemically similar niobium as the diffusant (in the absence of stable tantalum isotopes). Thin films of Nb2O5 were deposited onto Ta2O5 ceramics; diffusion anneals yielded niobium diffusion coefficients for the temperature range of 1073 ≤ T/K ≤ 1223 at an oxygen partial pressure of pO2 = 0.2 bar. Comparison of the measured diffusion coefficients strongly suggests that oxygen is many orders of magnitude more mobile than niobium in L-Ta2O5 at these temperatures and at pO2 = 0.2 bar. The electrical conductivity was also determined in the range 950 ≤ T/K ≤ 1200 and 10-23 ≤ pO2/bar ≤ 10-2. Considered together with the measured diffusion coefficients, the conductivity data indicate that under oxidising conditions conduction is due to oxygen ions above T = 1090-1130 K and due to electron holes below this temperature range. Point-defect models are presented that are consistent with these transport data and with conductivity data in the literature. They suggest that under oxidising conditions oxygen interstitials are the majority ionic charge carriers in L-Ta2O5. The implications for resistive switching devices are discussed.

Predicting nutrient digestibility in high-producing dairy cows.

Our objective was to determine the effects of dry matter intake (DMI), body weight (BW), and diet characteristics on total tract digestibilities of dry matter, neutral detergent fiber, and starch (DMD, NDFD, and StarchD, respectively) in high-producing dairy cows. Our database was composed of 1,942 observations from 662 cows in 54 studies from Michigan, Ohio, and Georgia. On average, cows ate 23 ± 4.5 kg of dry matter/d, weighed 669 ± 79 kg, and produced 38 ± 10 kg of milk/d. Diets were 31 ± 5% neutral detergent fiber, 27 ± 6% starch, 2.6 ± 1.2% fatty acids, and 17 ± 1.4% crude protein. Digestibility means were 66 ± 6, 42 ± 11, and 93 ± 5% for DMD, NDFD, and StarchD, respectively. Forage sources included corn silage, alfalfa, and grasses. Corn source was classified by its ruminal fermentability. Data were analyzed using a mixed effects model, including diet chemical composition, forage source, and corn source, all expressed as percentage of dry matter, except for DMI, which was expressed as percentage of BW (DMI%BW); location and 2-way interactions were fixed effects. Cow, block, period, treatment, and study were included as random effects. Best fitting candidate models were generated using backward and stepwise regression methods. Additionally, the simplest model was generated using only DMI and location as fixed effects and all random effects. Candidate models were cross-validated across studies, and the resulting predictive correlation coefficients across studies (PC) and root mean square error of prediction (RMSEP) were compared by t-test. For each nutrient, the digestibility model that resulted in the highest PC and lowest RMSEP was determined to be the best fitting model. We observed heterogeneous coefficients among the different locations, suggesting that specific location factors influenced digestibilities. The overall location-averaged best fitting prediction equations were: DMD = 69 - 0.83 × DMI%BW (PC = 0.22, RMSEP = 5.39); NDFD = 53 + 0.26 × grass %DM - 0.59 × starch %DM + 3.06 × DMI%BW - 0.46 × DMI%BW2 (PC = 0.53, RMSEP = 9.70); and StarchD = 96 + 0.19 × HFERM%DM - 0.12 × starch %DM - 1.13 × DMI%BW (PC = 0.34, RMSEP = 4.77); where HFERM%DM is highly-fermentable corn source as percentage of DM. Our results confirm that digestibility is reduced as DMI increases, albeit at a lower rate than that reported in National Research Council. Furthermore, dietary starch depresses NDFD. Whereas DMD can be predicted based on DMI only, the best predictions for NDFD and StarchD require diet characteristics in addition to DMI.

Crude glycerin decreases nonesterified fatty acid concentration in ewes during late gestation and early lactation.

Crude glycerin is a gluconeogenic substrate in ruminants and may help to decrease the occurrence of pregnancy toxemia. The objective in this trial was to determine the effects of feeding a diet containing crude glycerin on DMI, milk yield, milk composition, and blood metabolites in periparturient ewes and lamb performance. One hundred eighteen 90 (±1.1)-d pregnant Santa Inês ewes were used. After lambing, 32 ewes (62.8 ± 1.3 kg BW) were allotted in a randomized complete block design defined by prelambing diet, BW, BCS, lambing date, type of birth (single or twin), and sex of offspring. Diets were isonitrogenous (13.0 ± 0.3% CP, DM basis), composed of concentrate and raw sugarcane bagasse (70:30 ratio, DM basis), and fed ad libitum daily. Crude glycerin (83.6% glycerol) levels were 0 or 10% (DM basis), corresponding to the experimental diets G0 and G10, respectively. From 8 until 56 d of lactation, DMI was determined. In the same period, once a week at 1000 h, the ewes were separated from the lambs and mechanically milked after intravenous administration of 10 IU of synthetic oxytocin. Three hours after the first milking, ewes were milked again and milk yield and composition were determined. Glucose, NEFA, and ß-hydroxybutyrate (BHBA) were determined at -14, -7, 0, 7, 14, 28, and 56 d relative to lambing and insulin was determined at -14, -7, 0, and 7 d. Crude glycerin did not affect DMI (2.2 kg/d for G0 vs. 2.2 kg/d for G10; = 0.93) or milk production (171 g/3 h for G0 vs. 164 g/3 h for G10; = 0.66). However, there was a decrease ( = 0.01) in milk fat percentage (8.1% for G0 vs. 7.0% for G10) for ewes fed glycerin. Ewes fed the G10 diet had decreased ( < 0.01) NEFA concentration (0.27 mmol/L for G0 vs. 0.18 mmol/L for G10). There was an interaction between diet × time for glucose ( = 0.04), insulin ( = 0.05), and BHBA ( = 0.01); feeding glycerin increased glucose (5.61 mmol/L for G0 vs. 7.42 mmol/L for G10; < 0.01) and insulin concentrations (10.5 µIU for G0 vs. 24.5 µIU for G10; < 0.01) at parturition compared with G0. The BHBA was less ( = 0.02) on the day of lambing (0.40 mmol/L for G0 vs. 0.29 mmol/L for G10) and it was greater ( < 0.01) on d 56 for ewes fed the G10 diet (0.46 mmol/L for G0 vs. 0.61 mmol/L for G10). There was no effect of diets fed to ewes on lamb growth from birth to weaning. Crude glycerin improved energy balance of periparturient ewes, suggesting a reduced risk of developing clinical metabolic-related disorders. Crude glycerin can be added at 10% of ewes' diets without affecting DMI and milk yield.

Variables Associated with Infections of Cattle by Brucella abortus., Leptospira spp. and Neospora spp. in Amazon Region in Brazil.

The frequency of Neospora spp., Leptospira spp. and Brucella abortus infections in adult cattle was determined in herds of the State of Pará, Brazil, which is an important region for cattle production located in the Amazon region. A total of 3466 adult female cattle from 176 herds were tested, leading to a frequency of seropositive animals of 14.7%, 3.7% and 65.5% and a herd positivity of 87.4%, 41.3% and 98.8% for infections caused by Neospora spp., B. abortus and Leptospira spp., respectively. The five most frequently diagnosed serologic responses to Leptospira spp. were those against serovars hardjo, wolfii, grippotyphosa, hebdomadis and shermani. The following associations were found: practice of artificial insemination, large farm size, large herd size, large number of dogs and high number of total abortions per year with the presence of antibodies against serovar hardjo; positive results to serovar grippotyphosa with the presence of dogs; inappropriate disposal of aborted foetuses with positivity to serovar hebdomadis. Serovar grippotyphosa was also associated with number of episodes of abortions. Neospora spp. positive herds were associated with episodes of abortion and B. abortus infection with the disposal of dead animals and aborted foetuses on pastures and with the use of artificial insemination. In conclusion, the high frequency of brucellosis, leptospirosis and neosporosis in the region may be a consequence of social, natural and raising conditions as: (i) climate conditions that favour the survival and spread of pathogens in the environment; (ii) farms located in regions bordering forest areas; (iii) farms in areas of difficult access to the veterinary service; (iv) extensive beef herds raised at pastures with different age and productive groups inter-mingled; and (v) minimal concerns regarding hygiene practices and disease prevention measures.

Identification and antifungal susceptibility of fungi isolated from dermatomycoses.

BACKGROUND: Dermatomycoses are superficial fungal infections of the skin, hair and nails that affect more than 20-25% of the people worldwide. These infections can be caused by yeasts, dermatophytes and non-dermatophyte filamentous fungi (NDFF) and are considered a public health problem. Despite this, few studies have investigated the prevalence and antifungal susceptibility of causative agents of dermatomycoses in the developing world. OBJECTIVES: The aims of this study were to identify and determine the antifungal susceptibility profile of yeast and filamentous fungi isolated from dermatomycoses in Uberaba, Minas Gerais, Brazil. METHODS: Specimens were obtained from patients with clinically diagnosed and laboratory confirmed dermatomycosis between July 2009 and July 2011. Fungal identification was based on classical methods and antifungal susceptibility testing was performed by broth microdilution method. RESULTS: Of the 216 fungal isolates, 116 (53.8%) were yeasts, 70 (32.4%) dermatophytes and 30 (13.8%) NDFF. Onychomycosis was the most common clinical condition. Candida parapsilosis (24.1%) and Trichophyton rubrum (17.1%) were the fungi most frequently isolated. Voriconazole, ketoconazole and itraconazole were the most potent antifungal agents against yeast, whereas terbinafine, voriconazole and itraconazole had a high in vitro activity against dermatophytes. Overall, the antifungal agents had little or no activity against NDFF and the highest minimum inhibitory concentrations were those against Fusarium spp. CONCLUSION: Yeasts, particularly C. parapsilosis, play an important role as causative agents of dermatomycosis in our region. Our results suggest that the antifungal susceptibility testing coupled with proper identification of the fungi may be useful to assist clinicians in determining the appropriate therapy for dermatomycoses.

Ionic conduction in the SrTiO3|YSZ|SrTiO3 heterostructure.

Employing previously published experimental data, we analyse the enhanced conductivity of the heterostructure comprising yttria-stabilised zirconia (YSZ) and SrTiO3. We confirm that the heterostructure's conductivity arises from SrTiO3, and we conclude that it is exclusively ionic below T ∼ 540 K. The calculated excess conductance from space-charge layers is found to be negligible.

Activation volume tensor for oxygen-vacancy migration in strained CeO2 electrolytes.

We examine the effect of mechanical strain on the migration of oxygen vacancies in fluorite-structured ceria by means of density functional theory calculations. Different strain states (uniaxial, biaxial and isotropic) and strain magnitudes (up to ± 7%) are considered. From the calculations we extract the complete activation volume tensor for oxygen-vacancy migration in CeO(2), that is, all diagonal ΔV(mig,kk) and off-diagonal ΔV(mig,kl) tensor elements. These individual tensor elements are found, crucially, to be independent of strain state; they do, however, depend on stress (ΔV(mig,kk)) or effective pressure (ΔV(mig,kl)). Armed with knowledge of all tensor elements we predict strain states for which oxygen-ion transport in ceria is maximized. In general, with our approach the effect of an arbitrary strain state on the migration barrier for mass transport in a solid can be calculated quantitatively.

Femtosecond dynamics of the collinear-to-spiral antiferromagnetic phase transition in CuO.

We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic reorientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.

Clinical characteristics and outcomes of patients with acute lung injury and ARDS.

BACKGROUND: Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are critical illnesses associated with significant morbidity and mortality. AIMS: This was designed to assess various etiologies of ALI/ARDS, to determine the correlation between the diagnostic criteria and need of mechanical ventilation, and to correlate biochemical factors with the outcome of patients. SETTINGS AND DESIGN: An observational, prospective study was conducted in a medical intensive care unit (MICU) of a tertiary care hospital, for a period of 1 year. MATERIALS AND METHODS: This study encompassed 58 consecutive cases of ALI/ARDS admitted to a MICU as per AECC guidelines. Patients excluded were with cardiac failure, chronic kidney diseases with fluid overload, and age below 12 years. STATISTICAL ANALYSIS: The data were analysed applying χ2 -test, multivariate logistic regression analysis of significance, using computer-based program SPSS. RESULTS: There were more males (74%) than females, and presentation was more common in the younger age group, with a total mortality of 57%. Factors attributable for ALI/ARDS were malaria in 16 patients (27.6%), leptospirosis in 12 (20.7%), malaria with dengue in 3 (5.2%), undiagnosed fever in 16 (27.6%), pneumonia in 8 (13.8%), urinary tract infection in 2 (3.4%), and pancreatitis in 1 (1.7%) patient. Out of 41 patients with PaO 2 /FiO 2 <200, 40 patients required invasive ventilation, and out of 17 patients with PaO 2 /FiO 2 >200, 11 patients though initially managed on noninvasive ventilation (NIV) subsequently required invasive ventilation, and remaining six were successfully managed on NIV. Out of 41 patients requiring mechanical ventilation, 36 had LIS >2.5, whereas only 3 out of 17 patients with LIS <2.5 required mechanical ventilation. CONCLUSION: Malaria, leptospirosis, and undiagnosed fever were the main etiologies followed by pneumonia, urinary tract infections, and pancreatitis. Both the PaO 2 /FiO 2 ratio and lung injury score (LIS) at the time of admission were significant predictors of the outcome and of necessity of mechanical ventilation. PaO 2 /FiO 2 was a better predictor of duration of stay at the intensive care unit than the LIS. Sepsis, acidosis, hypotension, and multiorgan failure were individual predictors of mortality in patients with ALI/ARDS while age, sex, anemia, thrombocytopenia, renal failure, hepatic failure, and X-ray picture were not predictors of the outcome.

Observation of orbital currents in CuO.

Orbital currents are proposed to be the order parameter of the pseudo-gap phase of cuprate high-temperature superconductors. We used resonant x-ray diffraction to observe orbital currents in a copper-oxygen plaquette, the basic building block of cuprate superconductors. The confirmation of the existence of orbital currents is an important step toward the understanding of the cuprates as well as materials lacking inversion symmetry, such as magnetically induced multiferroics. Although observed in the antiferromagnetic state of cupric oxide, we show that orbital currents can occur even in the absence of long-range magnetic moment ordering.

Ultrafast structural phase transition driven by photoinduced melting of charge and orbital order.

We use femtosecond x-ray diffraction to probe directly the structural dynamics of a charge ordered and orbitally ordered thin film of La0.42Ca0.58MnO3 initiated by an ultrafast optical pulse. At low excitation fluences we observe the displacive excitation of a coherent optical A(g) phonon. Under high excitation conditions we observe a complete phase transition within 1 ps via the disappearance of a superlattice reflection. The initial step of the phase transition occurs on a time scale significantly faster than the 200 fs time resolution of our experiment.