Renato Torre

Structural relaxation in supercooled water by time-resolved spectroscopy

Water has many kinetic and thermodynamic properties that exhibit an anomalous dependence on temperature, in particular in the supercooled phase. These anomalies have long been interpreted in terms of underlying structural causes, and their experimental characterization points to the existence of a singularity at a temperature of about 225 K. Further insights into the nature and origin of this singularity might be gained by completely characterizing the structural relaxation in supercooled water. But until now, such a characterization has only been realized in simulations that agree with the predictions of simple mode-coupling theory; unambiguous experimental support for this surprising conclusion is, however, not yet available. Here we report time-resolved optical Kerr effect measurements that unambiguously demonstrate that the structural relaxation of liquid and weakly supercooled water follows the behaviour predicted by simple mode-coupling theory. Our findings thus support the interpretation of the singularity as a purely dynamical transition. That is, the anomalous behaviour of weakly supercooled water can be explained using a fully dynamic model and without needing to invoke a thermodynamic origin. In this regard, water behaves like many other, normal molecular liquids that are fragile glass-formers.

Placental Enlargement in Women with Primary Maternal Cytomegalovirus Infection Is Associated with Fetal and Neonatal Disease

BACKGROUND Serological testing for primary maternal cytomegalovirus (CMV) infection during pregnancy is not routine, but ultrasound studies are routine. Therefore, we evaluated placental thickening in women with primary CMV infection during pregnancy. METHODS The study included 92 women with primary CMV infection during pregnancy and 73 CMV-seropositive pregnant women without primary CMV infection. Neonatal CMV transmission was determined by CMV culture of urine samples. Thirty-two women were treated with CMV hyperimmune globulin to either prevent or treat intrauterine CMV infection. Maximal placental thickness was measured by longitudinal (nonoblique) scanning with the ultrasound beam perpendicular to the chorial dish. Programmed placental ultrasound evaluations were performed from 16 to 36 weeks of gestation. RESULTS At each measurement between 16 and 36 weeks of gestation, women with primary CMV infection who had a fetus or newborn with CMV disease had placentas that were significantly thicker than those of women with primary CMV infection who did not have a diseased fetus or newborn (P<.0001); the latter group, in turn, had placentas that were significantly thicker than those of seropositive control subjects (P<.0001). For both women with and women without diseased fetuses or newborns, receipt of hyperimmune globulin after primary CMV infection was associated with statistically significant reductions in placental thickness (P<.001). Placental vertical thickness values, which are predictive of primary maternal infection, were observed at each measurement from 16 to 36 weeks of gestation, and cutoff values ranged from 22 mm to 35 mm, with the best sensitivity and specificity at 28 and 32 weeks of gestation. CONCLUSIONS Primary maternal CMV infection and fetal or neonatal disease are associated with sonographically thickened placentas, which respond to administration of hyperimmune globulin. These observations suggest that many of the manifestations of fetal and neonatal disease are caused by placental insufficiency.

Evidence of two distinct local structures of water from ambient to supercooled conditions

The liquid and supercooled states of water show a series of anomalies whose nature is debated. A key role is attributed to the formation of structural aggregates induced by critical phenomena occurring deep in the supercooled region; the nature of the water anomalies and of the hidden critical processes remains elusive. Here we report a time-resolved optical Kerr effect investigation of the vibrational dynamics and relaxation processes in supercooled bulk water. The experiment measures the water intermolecular vibrations and the structural relaxation process in an extended temperature range, and with unprecedented data quality. A mode-coupling analysis of the experimental data enables to characterize the intermolecular vibrational modes and their interplay with the structural relaxation process. The results bring evidence of the coexistence of two local configurations, which are interpreted as high-density and low-density water forms, with an increasing weight of the latter at low temperatures.

Vibrational Spectroscopy and Dynamics of Water.

We present an overview of recent static and time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state, as well as of crystalline and amorphous ice forms. The structure and dynamics of the complex hydrogen-bond network formed by water molecules in the bulk and interphases are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed, from conventional infrared and Raman spectroscopy to femtosecond pump-probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. Additionally, we discuss novel approaches, such as two-dimensional sum-frequency generation, three-dimensional infrared, and two-dimensional Raman terahertz spectroscopy. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges. Furthermore, we outline future perspectives of vibrational spectroscopy for water researches.

Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO(3) waveguide and covering the 0.1-6 THz frequency range. We show that even a small fraction (<100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.

Regression of fetal cerebral abnormalities by primary cytomegalovirus infection following hyperimmunoglobulin therapy

To assess the effects of maternal and intra‐amniotic hyperimmunoglobulin (HIG) infusions among cytomegalovirus (CMV) infected fetuses with ultrasound abnormalities following a primary CMV infection.

Prenatal diagnosis of fetal cytomegalovirus infection after primary or recurrent maternal infection

OBJECTIVE To determine the reliability of prenatal diagnosis of cytomegalovirus infection in women with primary or recurrent infection. METHODS Amniotic fluid (AF) samples from 117 pregnant women were evaluated for cytomegalovirus culture and cytomegalovirus-DNA detection. Neonatal and postnatal samples also were examined to confirm or exclude transmission of maternal-fetal cytomegalovirus infection. RESULTS Of 25 women with primary cytomegalovirus infection, 13 (52%) had cytomegalovirus-positive AF samples by polymerase chain reaction (PCR), nine of which also were diagnosed by culture. All eight neonates born to mothers whose AF was cytomegalovirus-positive by PCR and culture were cytomegalovirus infected, and three were symptomatic. One aborted fetus had cytomegalovirus-DNAemia. Of four women with cytomegalovirus-positive AF samples by PCR only, two delivered asymptomatic cytomegalovirus-infected neonates and two aborted (one fetus had cytomegalovirus encephalopathy). Of 45 mothers with recurrent infection, two with AF cytomegalovirus-positive by PCR and culture, and another with cytomegalovirus-positive AF samples by PCR only, aborted cytomegalovirus-DNA-positive fetuses. Of the other seven women with cytomegalovirus-positive AF samples by PCR only, two delivered asymptomatic cytomegalovirus-infected neonates, two delivered neonates cytomegalovirus-positive by PCR only (one was symptomatic), and three delivered infants cytomegalovirus-negative by PCR and culture. All 47 mothers with nonactive cytomegalovirus infection and cytomegalovirus-negative AF samples had uninfected neonates. Polymerase chain reaction was superior to viral culture in sensitivity and negative predictive value (100% compared with 57% and 94%, respectively) but was lower in specificity and positive predictive value (97% and 83%, respectively, compared with 100%). CONCLUSION Prenatal diagnosis of fetal cytomegalovirus infection should include PCR in addition to viral culture, particularly for congenital cytomegalovirus infections following maternal recurrence.

Amniotic fluid nitric oxide and uteroplacental blood flow in pregnancy complicated by intrauterine growth retardation

Objective To examine the correlation between placental nitric oxide production and uteroplacental blood flow.

Nanosecond time scale dynamics of pseudo-nematic domains in the isotropic phase of liquid crystals

Abstract The slow reorientational dynamics of isotropic methoxybenzylidene-butylaniline (MBBA) were measured, using a transient grating optical Kerr effect experiment, over a wide temperature range (49.4°–119.7°C). The range of validity of the Landau—de Gennes theory for hydrodynamic relaxation in ordered fluids is determined. The results are compared to previous experiments on pentylcyanobiphenyl (5CB). Both liquid crystals conform to the Landau—de Gennes theory until the pseudo-nematic domain correlation length falls below three molecular lengths.

Diffusive and oscillatory dynamics of liquid iodobenzene measured by femtosecond optical Kerr effect

The dynamics of liquid iodobenzene are studied by means of time resolved heterodyne detected optical Kerr effect in a wide temperature range (263–371 K). In the picosecond regime the relaxation is characterized by a biexponential decay, attributed to the rotational diffusion of an anisotropic rotator. The temperature dependence of the two relaxation times agrees only in part with the prediction of the hydrodynamic theory. The subpicosecond dynamics is essentially oscillatory in nature; the Raman spectra obtained by Fourier transform of the time domain data show the contribution of two intramolecular low-frequency vibrations, and that of the intermolecular dynamics. The intermolecular spectra at different temperatures are interpreted on the basis of the Brownian oscillator model, and consist of the superposition of overdamped and underdamped modes. The intermolecular spectrum of the liquid shows a close resemblance with the low-frequency Raman spectrum of crystalline iodobenzene, and suggests an interpreta...