Extreme ultraviolet transient gratings: A tool for nanoscale photoacoustics.

Collective lattice dynamics determine essential aspects of condensed matter, such as elastic and thermal properties. These exhibit strong dependence on the length-scale, reflecting the marked wavevector dependence of lattice excitations. The extreme ultraviolet transient grating (EUV TG) approach has demonstrated the potential of accessing a wavevector range corresponding to the 10s of nm length-scale, representing a spatial scale of the highest relevance for fundamental physics and forefront technology, previously inaccessible by optical TG and other inelastic scattering methods. In this manuscript we report on the capabilities of this technique in the context of probing thermoelastic properties of matter, both in the bulk and at the surface, as well as discussing future developments and practical considerations.

Element- and enantiomer-selective visualization of molecular motion in real-time.

Ultrafast optical-domain spectroscopies allow to monitor in real time the motion of nuclei in molecules. Achieving element-selectivity had to await the advent of time resolved X-ray spectroscopy, which is now commonly carried at X-ray free electron lasers. However, detecting light element that are commonly encountered in organic molecules, remained elusive due to the need to work under vacuum. Here, we present an impulsive stimulated Raman scattering (ISRS) pump/carbon K-edge absorption probe investigation, which allowed observation of the low-frequency vibrational modes involving specific selected carbon atoms in the Ibuprofen RS dimer. Remarkably, by controlling the probe light polarization we can preferentially access the enantiomer of the dimer to which the carbon atoms belong.

Atomic and Electronic Structure of Solid-Density Liquid Carbon.

A liquid carbon (l-C) sample is generated through constant volume heating exposing an amorphous carbon foil to an intense ultrashort laser pulse. Time-resolved x-ray absorption spectroscopy at the C K edge is used to monitor the dynamics of the melting process revealing a subpicosecond rearrangement of the electronic structure associated with a sudden change of the C bonding hybridization. The obtained l-C sample, resulting from a nonthermal melting mechanism, reaches a transient equilibrium condition with a temperature of about 14 200 K and pressure in the order of 0.5 Mbar in about 0.3 ps, prior to hydrodynamic expansion. A detailed analysis of the atomic and electronic structure in solid-density l-C based on time-resolved x-ray absorption spectroscopy and theoretical simulations is presented. The method can be fruitfully used for extending the experimental investigation of the C phase diagram in a vast unexplored region covering the 10^{3}-10^{4} K temperature range with pressures up to 1 Mbar.

Ultrafast Plasmon Dynamics in Crystalline LiF Triggered by Intense Extreme UV Pulses.

An extreme ultraviolet pump and visible-light probe transmission experiment in crystalline LiF, carried out at the Free Electron Laser facility FERMI, revealed an oscillating time dependence of the plasmon mode excited in the high-density high-temperature electron plasma. The effect is interpreted as a fingerprint of the electron-ion interaction: the ion motion, shaped by the electron dynamic screening, induces, in turn, electron density fluctuations that cause the oscillation of the plasmon frequency at the timescale of the ion dynamics. Fitting the high resolution transmission data with an RPA model for the temperature-dependent dielectric function, which includes electron self-energy and electron-ion coupling, confirms the interpretation of the time modulation of the plasmon mode.

Exploring the multiparameter nature of EUV-visible wave mixing at the FERMI FEL.

The rapid development of extreme ultraviolet (EUV) and x-ray ultrafast coherent light sources such as free electron lasers (FELs) has triggered the extension of wave-mixing techniques to short wavelengths. This class of experiments, based on the interaction of matter with multiple light pulses through the Nth order susceptibility, holds the promise of combining intrinsic ultrafast time resolution and background-free signal detection with nanometer spatial resolution and chemical specificity. A successful approach in this direction has been the combination of the unique characteristics of the seeded FEL FERMI with dedicated four-wave-mixing (FWM) setups, which leads to the demonstration of EUV-based transient grating (TG) spectroscopy. In this perspective paper, we discuss how the TG approach can be extended toward more general FWM spectroscopies by exploring the intrinsic multiparameter nature of nonlinear processes, which derives from the ability of controlling the properties of each field independently.

Nanoscale transient gratings excited and probed by extreme ultraviolet femtosecond pulses.

Advances in developing ultrafast coherent sources operating at extreme ultraviolet (EUV) and x-ray wavelengths allow the extension of nonlinear optical techniques to shorter wavelengths. Here, we describe EUV transient grating spectroscopy, in which two crossed femtosecond EUV pulses produce spatially periodic nanoscale excitations in the sample and their dynamics is probed via diffraction of a third time-delayed EUV pulse. The use of radiation with wavelengths down to 13.3 nm allowed us to produce transient gratings with periods as short as 28 nm and observe thermal and coherent phonon dynamics in crystalline silicon and amorphous silicon nitride. This approach allows measurements of thermal transport on the ~10-nm scale, where the two samples show different heat transport regimes, and can be applied to study other phenomena showing nontrivial behaviors at the nanoscale, such as structural relaxations in complex liquids and ultrafast magnetic dynamics.

First Evidence of Purely Extreme-Ultraviolet Four-Wave Mixing.

The extension of nonlinear optical techniques to the extreme-ultraviolet (EUV), soft and hard x-ray regime represents one of the open challenges of modern science since it would combine chemical specificity with background-free detection and ultrafast time resolution. We report on the first observation of a four-wave-mixing (FWM) response from solid-state samples stimulated exclusively by EUV pulses. The all-EUV FWM signal was generated by the diffraction of high-order harmonics of the FERMI free-electron laser (FEL) from the standing wave resulting from the interference of two crossed FEL pulses at the fundamental wavelength. From the intensity of the FWM signal, we are able to extract the first-ever estimate of an effective value of ∼6×10^{-24} m^{2} V^{-2} for the third-order nonlinear susceptibility in the EUV regime. This proof of principle experiment represents a significant advance in the field of nonlinear optics and sets the starting point for a manifold of techniques, including frequency and phase-resolved FWM methods, that are unprecedented in this photon-energy regime.

Optical constants modelling in silicon nitride membrane transiently excited by EUV radiation.

We hereby report on a set of transient optical reflectivity and transmissivity measurements performed on silicon nitride thin membranes excited by extreme ultraviolet (EUV) radiation from a free electron laser (FEL). Experimental data were acquired as a function of the membrane thickness, FEL fluence and probe polarization. The time dependence of the refractive index, retrieved using Jones matrix formalism, encodes the dynamics of electron and lattice excitation following the FEL interaction. The observed dynamics are interpreted in the framework of a two temperature model, which permits to extract the relevant time scales and magnitudes of the processes. We also found that in order to explain the experimental data thermo-optical effects and inter-band filling must be phenomenologically added to the model.

Soft X-Ray Second Harmonic Generation as an Interfacial Probe.

Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (∼284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.

Characterization of ultrafast free-electron laser pulses using extreme-ultraviolet transient gratings.

The characterization of the time structure of ultrafast photon pulses in the extreme-ultraviolet (EUV) and soft X-ray spectral ranges is of high relevance for a number of scientific applications and photon diagnostics. Such measurements can be performed following different strategies and often require large setups and rather high pulse energies. Here, high-quality measurements carried out by exploiting the transient grating process, i.e. a third-order non-linear process sensitive to the time-overlap between two crossed EUV pulses, is reported. From such measurements it is possible to obtain information on both the second-order intensity autocorrelation function and on the coherence length of the pulses. It was found that the pulse energy density needed to carry out such measurements on solid state samples can be as low as a few mJ cm-2. Furthermore, the possibility to control the arrival time of the crossed pulses independently might permit the development of a number of coherent spectroscopies in the EUV and soft X-ray regime, such as, for example, photon echo and two-dimensional spectroscopy.

The role of regression performance on multimodel analysis.

In this work, we provide suggestions for designing experiments where calibration of many models is required and guidance for identifying problematic calibrations. Calibration of many conceptual models which have different representations of the physical processes in the system, as is done in cross-validation studies or multi-model analysis, often uses computationally frugal inversion techniques to achieve tractable execution times. However, because these frugal methods are usually local methods, and the inverse problem is almost always nonlinear, there is no guarantee that the optimal solution will be found. Furthermore, evaluation of each inverse model's performance to identify poor calibrations can be tedious. Results of this study show that if poorly calibrated models are included in the analysis, simulated predictions and measures of prediction uncertainty can be affected in unexpected ways. Guidelines are provided to help identify problematic regressions and correct them.

Ultrafast changes in lattice symmetry probed by coherent phonons.

The electronic and structural properties of a material are strongly determined by its symmetry. Changing the symmetry via a photoinduced phase transition offers new ways to manipulate material properties on ultrafast timescales. However, to identify when and how fast these phase transitions occur, methods that can probe the symmetry change in the time domain are required. Here we show that a time-dependent change in the coherent phonon spectrum can probe a change in symmetry of the lattice potential, thus providing an all-optical probe of structural transitions. We examine the photoinduced structural phase transition in VO(2) and show that, above the phase transition threshold, photoexcitation completely changes the lattice potential on an ultrafast timescale. The loss of the equilibrium-phase phonon modes occurs promptly, indicating a non-thermal pathway for the photoinduced phase transition, where a strong perturbation to the lattice potential changes its symmetry before ionic rearrangement has occurred.

Testing alternative ground water models using cross-validation and other methods.

Many methods can be used to test alternative ground water models. Of concern in this work are methods able to (1) rank alternative models (also called model discrimination) and (2) identify observations important to parameter estimates and predictions (equivalent to the purpose served by some types of sensitivity analysis). Some of the measures investigated are computationally efficient; others are computationally demanding. The latter are generally needed to account for model nonlinearity. The efficient model discrimination methods investigated include the information criteria: the corrected Akaike information criterion, Bayesian information criterion, and generalized cross-validation. The efficient sensitivity analysis measures used are dimensionless scaled sensitivity (DSS), composite scaled sensitivity, and parameter correlation coefficient (PCC); the other statistics are DFBETAS, Cook's D, and observation-prediction statistic. Acronyms are explained in the introduction. Cross-validation (CV) is a computationally intensive nonlinear method that is used for both model discrimination and sensitivity analysis. The methods are tested using up to five alternative parsimoniously constructed models of the ground water system of the Maggia Valley in southern Switzerland. The alternative models differ in their representation of hydraulic conductivity. A new method for graphically representing CV and sensitivity analysis results for complex models is presented and used to evaluate the utility of the efficient statistics. The results indicate that for model selection, the information criteria produce similar results at much smaller computational cost than CV. For identifying important observations, the only obviously inferior linear measure is DSS; the poor performance was expected because DSS does not include the effects of parameter correlation and PCC reveals large parameter correlations.

Static and ELF magnetic fields enhance the in vivo anti-tumor efficacy of cis-platin against lewis lung carcinoma, but not of cyclophosphamide against B16 melanotic melanoma.

Previous works showed that exposure to static and extremely low frequency (ELF) magnetic fields (MF) over 3 mT slows down the growth kinetics of human tumors engrafted s.c. in immunodeficient mice, reducing their metastatizing power and prolonging mouse survival. In the experiments reported here, immunocompetent mice bearing murine Lewis Lung carcinomas (LLCs) or B16 melanotic melanomas were exposed to MF and treated respectively with two commonly used anti-cancer drugs: cis-diamminedichloroplatinum (cis-platin) and N,N-bis (2-chloroethyl)tetra-hydro-2H-1,3,2-oxazaphosphorin-2-amine 2-oxide (cyclophosphamide). The experiment endpoint was survival time. The survival time of mice treated with cis-platin (3mg/kg i.p.) and exposed to MF was significantly (P<0.01) longer than that of mice treated only with cis-platin or only exposed to MF, superimposing that of mice treated with 10mg/kg i.p. of the drug, showing that MF act synergically with the pharmacological treatment. On the contrary, when mice treated with cyclophosphamide (50mg/kg i.p.) were exposed to MF no synergic effects were observed, the survival curve being exactly the same as that of mice treated with the drug alone. No clinical signs or toxicity were seen in any of the mice exposed to MF alone or along with cis-platin or cyclophosphamide treatment, compared to mice given only the two known drugs.A possible explanation for the synergic effect of MF being found in mice treated with cis-platin could be that the platinum ion stimulates radical production and that MF enhance active oxygen production bringing about changes in tumor cell membrane permeability, influencing positively the drug uptake. Alternatively, or in addition to this, it has been demonstrated that the rate of conversion of cis-platin to reactive species able to bind to DNA, is increased by localized production of free radicals by MF.

Competitive enzyme immunoassay for diagnosis of human brucellosis.

The methods commonly used for human brucellosis serological testing are agglutination tests and the complement fixation test (CFT). Among the newer serological tests, primary binding assays were developed to improve sensitivity and specificity. The competitive enzyme immunoassay (CELISA) for the detection of serum antibody to Brucella is a multispecies assay which appears to be capable of differentiating vaccinal and cross-reacting antibodies from antibodies elicited by field infection in cattle. The competing monoclonal antibody used in this assay is specific for a common epitope of smooth lipopolysaccharide (S-LPS). In this study, we compared the CELISA to the classical tests for the diagnosis of human brucellosis. The CELISA cutoff value was determined to calculate its diagnostic specificity and sensitivity. A survey was performed with 911 sera. Of the sera, 341 were from an asymptomatic population that tested negative with conventional serological tests (screening and confirmatory). Based on these samples, the CELISA specificities were determined to be 99.7 and 100% with cutoff values of 28 and 30% inhibition (%I), respectively. In a further study with 393 additional sera from an asymptomatic population found negative by the conventional screening tests, the CELISA specificities were calculated to be 96.5 and 98.8% with cutoff values of 28 and 30%I. The CELISA sensitivities were determined to be 98.3 and 94.8% with cutoff values of 28 and 30%I, respectively, for sera from 116 individuals found positive by the classical tests. For the 51 culture-positive patients, CELISA was positive for 100%, the CFT was positive for 92%, and the standard tube agglutination test (TAT) was positive for 100%. The CELISA specificity was 100% for 31 sera from patients found negative by conventional serological tests but with brucellosis-like symptoms. The CELISA is fairly rapid to perform, somewhat faster than TAT, and cross-reacts less with other antigens (or antibodies) than the conventional tests. Further, the CELISA is simpler to perform that the CFT and may readily be standardized by the use of purified S-LPS antigen and monoclonal antibody for competition.

Effects of teratogenic exposures to Zn2+, Cd2+, Ni2+, Co2+, and Cu2+ on metallothionein and metallothionein-mRNA contents of Xenopus embryos.

Xenopus laevis embryos were analyzed for metallothionein by silver-saturation assay and metallothionein-mRNA by reverse transcriptase/polymerase chain reaction following exposures to the following metal chlorides at levels that caused > 95% malformations and < 7% mortality: Zn2+ (300 microM); Cd2+ (18 microM); Ni2+ (56 microM); Co2+ (1,800 microM); and Cu2+ (5.6 microM). At the beginning of the exposure (stages 8), metallothionein-mRNA and metallothionein levels averaged 2.0 x 10(6) copies/embryo and 19 pmol/embryo, respectively. In control embryos at stages 26, 36, 42, and 46, metallothionein-mRNA content averaged 9, 37, 104, and 97 copies x 10(6)/embryo, and metallothionein content averaged 6, 11, 15, and 18 pmol/embryo. In Zn(2+) -exposed embryos at the same stages, metallothionein-mRNA content averaged 116*, 11,400*, 3,210*, and 14 copies x 10(6)/embryo and metallothionein content averaged 10, 18*, 46*, and 90* pmol/embryo; in Cd(2+)-exposed embryos, metallothionein-mRNA content averaged 22, 7,170*, 1,783*, and 240 copies x 10(6)/embryo and metallothionein content averaged 8, 14, 33*, and 56* pmol/embryo, respectively (*P < 0.05 versus controls). Exposure-response curves (Cd2+, 1-18 microM; Zn2+, 3-300 microM) indicated that Cd2+ was 3- to 5-times more potent than Zn2+, based on metallothionein-mRNA response at stage 36 and metallothionein response at stage 46. In Ni(2+)-, Co(2+)-, or Cu(2+)-exposed embryos, metallothionein-mRNA and metallothionein contents did not differ significantly from controls.(ABSTRACT TRUNCATED AT 250 WORDS)

[Severe depression and risk factors in Buenos Aires]. / Depresión grave y factores de riesgo en Buenos Aires.

A study on prevalence of depression and its risk factors in 18 year old males with residence in the city of Buenos Aires was performed in 1991 during a mass medical examination of aptitude for the Military Service. An anonyme, self administered questionnaire was given to 553 youngsters in a probability sample. From findings in that study it was deemed necessary a deepen analysis on severe depression and its possible associations with ideas of suicide. Prevalence at severe depression was 4.5% and strong association was found with sadness in depression was 4.5% and strong association was found with sadness in childhood (RR 12.73), boredom (RR 10.56), retiring (RR 8.28) and nervousness (RR 3.89) as well as drugs abuse by brothers (RR 3.48) and family conflicts (RR 2.43). Possibility of having ideas of suicide is thirty three times more when depression exists. The attributable risk of suicide due to severe depression is 75%. Keeping in mind this health problem in youngsters might help to establish collective and individual strategic measures toward prevention.

Depresión grave y factores de riesgo en Buenos Aires. / [Severe depression and risk factors in Buenos Aires]

A study on prevalence of depression and its risk factors in 18 year old males with residence in the city of Buenos Aires was performed in 1991 during a mass medical examination of aptitude for the Military Service. An anonyme, self administered questionnaire was given to 553 youngsters in a probability sample. From findings in that study it was deemed necessary a deepen analysis on severe depression and its possible associations with ideas of suicide. Prevalence at severe depression was 4.5

and strong association was found with sadness in depression was 4.5

and strong association was found with sadness in childhood (RR 12.73), boredom (RR 10.56), retiring (RR 8.28) and nervousness (RR 3.89) as well as drugs abuse by brothers (RR 3.48) and family conflicts (RR 2.43). Possibility of having ideas of suicide is thirty three times more when depression exists. The attributable risk of suicide due to severe depression is 75

. Keeping in mind this health problem in youngsters might help to establish collective and individual strategic measures toward prevention.

Prevalencia de bocio en varones de 18 años en la provincia de Neuquen, 1991 / Prevalence of goiter in 18 years old males in Neuquen province

El bocio endémico, causa de disminución del desarrollo físico y mental, cretinismo, sordera y mudez, es un problema de salud pública, que ha sido identificado en la Argentina en áreas montañosas del noroeste ya desde fines del siglo XIX. Su prevención mediante yodación de la sal de mesa se inició en la provincia de Mendoza en 1953, y en 1964 se creó el Plan Nacional de Prevención en el Ministerio de Salud. En 1965 se realizó el primer estudio epidemiológico con cobertura nacional en 9 provincias, en nuestra probabilísticas de varones jóvenes durante el examen médico de aptitud para el Servicio Militar. Se hallaron tasas de sprevalencia cercanas a 50 por ciento en áreas tales como la provincia montañosa del Neuquén en la Cordillera de los Andes y en Corrientes, llanuras rodeadas por grandes ríos. La yodación de la sal de mesa se hizo obligatoria por ley en 1967 y alcanzó una amplia cobertura en 1970. Después de 24 años de uso continuo de la sal enriquecida se realizó un nuevo estudio para evaluar la evolución de la endemia en varones jóvenes en Neuquén en 1991 y en Corrientes en 1992, con métodos de muestreo, examenes clínico y análisis de datos similares a los de 1965. Este informe se refiere al estudio en Neuquén. La tasa de prevalencia de bocio disminuyó desde 46,5 por ciento en 1965 a 10,7 por ciento en 1991, más alta el área rural (16,9 por ciento ) que urbana (9,8 por ciento ), con la forma difusa más frecuente que la nodular en 1965 (4,9 por ciento ) que en 1991 (1,7 por ciento ). También se halló más prevalencia en quienes consumían sal no enriquecida de salina (26,4 por ciento ) que en quienes consumían sal con iodo (10,3 por ciento ). Todas las diferencias fueron estadísticamente significativas con p<0,05. La persistencia de bocio aún en áreas urbanas y en quienes cosumen sal yodada hace pensar en la posible influencia de factores bocígenos en el suelo, agua y alimentos locales, tema que merece nuevos estudios.

Prevalencia de bocio en varones de 18 años en la provincia de Neuquen, 1991 / Prevalence of goiter in 18 years old males in Neuquen province

El bocio endémico, causa de disminución del desarrollo físico y mental, cretinismo, sordera y mudez, es un problema de salud pública, que ha sido identificado en la Argentina en áreas montañosas del noroeste ya desde fines del siglo XIX. Su prevención mediante yodación de la sal de mesa se inició en la provincia de Mendoza en 1953, y en 1964 se creó el Plan Nacional de Prevención en el Ministerio de Salud. En 1965 se realizó el primer estudio epidemiológico con cobertura nacional en 9 provincias, en nuestra probabilísticas de varones jóvenes durante el examen médico de aptitud para el Servicio Militar. Se hallaron tasas de sprevalencia cercanas a 50 por ciento en áreas tales como la provincia montañosa del Neuquén en la Cordillera de los Andes y en Corrientes, llanuras rodeadas por grandes ríos. La yodación de la sal de mesa se hizo obligatoria por ley en 1967 y alcanzó una amplia cobertura en 1970. Después de 24 años de uso continuo de la sal enriquecida se realizó un nuevo estudio para evaluar la evolución de la endemia en varones jóvenes en Neuquén en 1991 y en Corrientes en 1992, con métodos de muestreo, examenes clínico y análisis de datos similares a los de 1965. Este informe se refiere al estudio en Neuquén. La tasa de prevalencia de bocio disminuyó desde 46,5 por ciento en 1965 a 10,7 por ciento en 1991, más alta el área rural (16,9 por ciento ) que urbana (9,8 por ciento ), con la forma difusa más frecuente que la nodular en 1965 (4,9 por ciento ) que en 1991 (1,7 por ciento ). También se halló más prevalencia en quienes consumían sal no enriquecida de salina (26,4 por ciento ) que en quienes consumían sal con iodo (10,3 por ciento ). Todas las diferencias fueron estadísticamente significativas con p<0,05. La persistencia de bocio aún en áreas urbanas y en quienes cosumen sal yodada hace pensar en la posible influencia de factores bocígenos en el suelo, agua y alimentos locales, tema que merece nuevos estudios.