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PubMed2006

Uplift, thermal unrest and magma intrusion at Yellowstone caldera.

The Yellowstone caldera, in the western United States, formed approximately 640,000 years ago when an explosive eruption ejected approximately 1,000 km3 of material. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began approximately 16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from approximately 150,000 to approximately 70,000 years ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of approximately 70 cm historically to several metres since the Pleistocene epoch, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system.

Journal Article↗
PubMed2006

A quantum Newton's cradle.

It is a fundamental assumption of statistical mechanics that a closed system with many degrees of freedom ergodically samples all equal energy points in phase space. To understand the limits of this assumption, it is important to find and study systems that are not ergodic, and thus do not reach thermal equilibrium. A few complex systems have been proposed that are expected not to thermalize because their dynamics are integrable. Some nearly integrable systems of many particles have been studied numerically, and shown not to ergodically sample phase space. However, there has been no experimental demonstration of such a system with many degrees of freedom that does not approach thermal equilibrium. Here we report the preparation of out-of-equilibrium arrays of trapped one-dimensional (1D) Bose gases, each containing from 40 to 250 (87)Rb atoms, which do not noticeably equilibrate even after thousands of collisions. Our results are probably explainable by the well-known fact that a homogeneous 1D Bose gas with point-like collisional interactions is integrable. Until now, however, the time evolution of out-of-equilibrium 1D Bose gases has been a theoretically unsettled issue, as practical factors such as harmonic trapping and imperfectly point-like interactions may compromise integrability. The absence of damping in 1D Bose gases may lead to potential applications in force sensing and atom interferometry.

Journal Article↗
PubMed2006

Detection of Earth-like planets around nearby stars using a petal-shaped occulter.

Direct observation of Earth-like planets is extremely challenging, because their parent stars are about 10(10) times brighter but lie just a fraction of an arcsecond away. In space, the twinkle of the atmosphere that would smear out the light is gone, but the problems of light scatter and diffraction in telescopes remain. The two proposed solutions--a coronagraph internal to a telescope and nulling interferometry from formation-flying telescopes--both require exceedingly clean wavefront control in the optics. An attractive variation to the coronagraph is to place an occulting shield outside the telescope, blocking the starlight before it even enters the optical path. Diffraction and scatter around or through the occulter, however, have limited effective suppression in practically sized missions. Here I report an occulter design that would achieve the required suppression and can be built with existing technology. The compact mission architecture of a coronagraph is traded for the inconvenience of two spacecraft, but the daunting optics challenges are replaced with a simple deployable sheet 30 to 50 m in diameter. When such an occulter is flown in formation with a telescope of at least one metre aperture, terrestrial planets could be seen and studied around stars to a distance of ten parsecs.

Journal Article↗
PubMed2005

Relationship of gender, body mass index, and axial length with central retinal thickness using optical coherence tomography.

BACKGROUND: Optical coherence tomography (OCT) acquires cross-sectional retinal images with high resolution using low-coherence interferometry. Few studies have studied the effect of demographic data and ocular parameters that may affect central retinal thickness. In this study, these factors were used as parameters to analyse if any significant relationship exists with central retinal thickness. METHODS: Volunteers with a best-corrected visual acuity of 6/12 or better and no evidence of ocular abnormalities or interventions were recruited from October 2001 to March 2003. Body mass index (BMI), autorefraction, and keratometry recordings were measured, followed by applanation tonometry and A-scan ultrasonography. The central retinal thickness of the right eye was analysed using a scan length of 3 cm. Another 25 eyes were selected for interobserver reproducibility. RESULTS: In all, 117 normal subjects (60 male and 57 female subjects) were recruited. The mean thickness of the central retina with a diameter of 1 mm was 203+/-23 microm for male and 189+/-20 microm for female subjects. Age, intraocular pressure, and keratometric readings were not significantly correlated with central retinal thickness. Using multiple regression, gender, BMI, axial length, and signal-to-noise ratio (P<0.05) were significantly associated with the central retinal thickness. The intraclass correlation coefficient was 0.98 for interobserver reproducibility. CONCLUSION: OCT has a high interobserver reproducibility. The male gender, larger BMI, and longer axial length are associated with a significantly thicker central retina and these parameters should be considered for assessing retinal thickening and baseline comparisons in future studies.

Adolescent↗
PubMed2003

The influence of surface forces on thin film drainage between a fluid drop and a flat solid.

An experiment is described in which a mica surface is driven towards a mercury drop immersed in aqueous electrolyte. Under appropriate conditions, hydrodynamic pressure in the aqueous film creates a classical dimple in the mercury drop. The use of optical interferometry and video recording to monitor the shape of the drop and the thickness of the aqueous film with sub-nanometre resolution yields a high density of precise data showing the formation and evolution of the dimple as the film drains. Variation of electrical potential applied to the mercury phase allows control of the surface forces acting between the drop and the mica surface, so that the effect of surface forces on the film drainage process is highlighted. It is found that the film thickness at the centre of the dimple and the lateral extent of the dimple are not significantly affected by surface forces. On the other hand, the minimum film thickness at the edge of the dimple is sensitive even to weak surface forces. Since this minimum film thickness is a major determinant of the film drainage rate, it is shown that surface forces have an important effect on the overall drainage process.

Journal Article↗
PubMed2003

Colloidal dynamics in polymer solutions: optical two-point microrheology measurements.

We present an extension of the two-point optical microrheology technique introduced by Crocker et al. [J. C. Crocker, M. T. Valentine, E. R. Weeks, T. Gisler, P. D. Kaplan, A. G. Yodh and D. A.Weitz, Phys. Rev. Lett., 2000, 85, 888] to high frequencies. The correlated fluctuations of two probe spheres held by a pair of optical tweezers within a viscoelastic medium are determined using optical interferometry. A theoretical model is developed to yield the frequency-dependent one- and two-particle response functions from the correlated motion. We demonstrate the validity of this method by determining the one- and two-particle correlations in a semi-dilute solution of polystyrene in decalin. We find that the ratio of the one- and two-particle response functions is anomalous which we interpret as evidence for a slip boundary condition caused by depletion of polymer from the surface of the particle.

Journal Article↗
PubMed2005

Phosphonate mediated surface reaction and reorganization: implications for the mechanism controlling cement hydration inhibition.

Vertical scanning interferometry and XPS show the reaction of CaCO3 with the hydration retarder nitrilo-tris-(methylene)phosphonic acid follows a pathway of dissolution of the calcium followed by precipitation of a calcium phosphonate; subsequent surface reorganization/restructuring of the calcium phosphonate exposes the underlying CaCO3 for further hydration.

Journal Article↗
PubMed2006

Mechanical manipulation of molecular lattice parameters in smectic elastomers.

Smectic liquid crystalline elastomers (SLCE) represent unique materials that combine a 1-D molecular lattice arrangement and orientational order with rubber-elasticity mediated by a polymer network. Such materials may exhibit large thermo-mechanical, opto-mechanical and electro-mechanical effects, due to the coupling of macroscopic sample geometry and microscopic structural features. It is shown that the molecular layer dimensions in the smectic phases can be influenced reversibly by macroscopic strain of the material. We present a microscopic model on the basis of experimental results obtained by mechanical dilatation measurements, optical interferometry, X-ray scattering, (13)C NMR, FTIR and polarizing microscopy data. The model gives an explanation of the controversial results obtained in different types of smectic elastomers.

Computer Simulation↗
PubMed2006

Protein-GAG interactions: new surface-based techniques, spectroscopies and nanotechnology probes.

New approaches, rooted in the physical sciences, have been developed to gain a more fundamental understanding of protein-GAG (glycosaminoglycan) interactions. DPI (dual polarization interferometry) is an optical technique, which measures real-time changes in the mass of molecules bound at a surface and the geometry of the bound molecules. QCM-D (quartz crystal microbalance-dissipation), an acoustic technique, measures the mass and the viscoelastic properties of adsorbates. The FTIR (Fourier-transform IR) amide bands I, II and III, resulting from the peptide bond, provide insight into protein secondary structure. Synchrotron radiation CD goes to much shorter wavelengths than laboratory CD, allowing access to chromophores that provide insights into the conformation of the GAG chain and of beta-strand structures of proteins. To tackle the diversity of GAG structure, we are developing noble metal nanoparticle probes, which can be detected at the level of single particles and so enable single molecule biochemistry and analytical chemistry. These new approaches are enabling new insights into structure-function relationships in GAGs and together they will resolve many of the outstanding problems in this field.

Animals↗
PubMed2005

Quantification of the effects of melittin on liposome structure.

An optical technique, dual-polarization interferometry, has been used to examine lipid structures at the solid/liquid interface. Changes in the lipid structures, in real time, were examined as a consequence of challenging them with a peptide (melittin) that is known to induce liposome rupture. This work suggests that it should be possible to obtain a better understanding of the detail of the melittin rupture process.

Fluorescence Polarization↗
PubMed2002

New approach to optical diffraction tomography yielding a vector equation of diffraction tomography and a novel tomographic microscope.

We first obtain a frequency-space equation of diffraction tomography for the electric field vector, within the first-order Born approximation, using a simplified formalism resulting from using three-dimensional spatial frequencies and replacing outgoing waves by linear combinations of homogeneous plane waves. A coherent optical diffraction tomographic microscope is then described, in which a sample is successively illuminated by a series of plane waves having different directions, each scattered wave is recorded by phase-shifting interferometry, and the object is then reconstructed from these recorded waves. The measurement process in this device is analysed taking into account the illuminating wave, the wave scattered by the sample, the reference wave, and the phase relations between these waves. This analysis yields appropriate equations that take into account the characteristics of the reference wave and compensate random phase shifts. It makes it possible to obtain a high-resolution three-dimensional frequency representation in full conformity with theory. The experimentally obtained representations show index and absorptivity with a resolution limit of about a quarter of a wavelength, and have a depth of field of about 40 microm.

Animals↗
PubMed1998

[Diurnal axial eye growth rhythm in chicks is modified by diurnal light-dark cycle].

BACKGROUND: In chicks, the distance from the cornea to the posterior sclera (defined as axial eye length) grows in a diurnal rhythm: growth during the day is greater than during the night. The purpose of this study was to investigate whether this diurnal, axial eye growth rhythm is influenced by the diurnal light/dark illumination cycle. METHODS: One day after hatching, 18 White Leghorn chicks were reared under a 12 hour light/dark illumination cycle. After seven days, 12 chicks were switched to continuous light; the other 6 chicks remained under the 12 hour light/dark cycle and served as controls. Every 12 hours, at times corresponding to the onset of former light and dark phases over a period of 2 days, axial eye length was measured in the right eyes by laser Doppler interferometry with a precision of 20 microns. RESULTS: In group 1, axial eye growth during time intervals corresponding to former light phases (0.063 +/- 0.024 mm; mean +/- 95% confidence limit) and dark phases (0.040 +/- 0.017 mm) were not significantly different (one-factor ANOVA). In group 2, axial eye growth during light phases (0.065 +/- 0.028 mm) was significantly greater than during dark phases (0.015 +/- 0.023 mm; p = 0.015). Significantly, total axial eye growth during the two-day period was greater in group 1 (0.206 +/- 0.015 mm) than in group 2 (0.160 +/- 0.021 mm; p = 0.02; unpaired, two-tailed Student's t-test). CONCLUSION: The diurnal, axial eye growth rhythm is strongly attenuated following an acute switch from a 12 hour light/dark cycle to continuous light. Control chicks exhibit the normal rhythm. This observation demonstrates that the diurnal, axial eye growth rhythm is influenced by the light/dark illumination cycle. Whether the alteration of the rhythm and the increased axial growth during continuous light is caused by the increased amount of light alone or by increased light-induced form vision remains to be investigated.

Age Factors↗
PubMed2004

Correlation of femtosecond wave packets and fluorescence interference in a conjugated polymer: Towards the measurement of site homogeneous dephasing.

Probing electronic femtosecond (fs) coherence among segmental sites that are congested by static and dynamic site disorder and subject to structural relaxation is a big, experimental challenge in the study of photophysics of poly(p-phenylenevinylene). In this work, fs-wave-packet fluorescence interferometry experiments are presented that measure macroscopic coherent kernels and their phase-relaxation in the low-temperature, bottom-state regime of the density-of-states below the migrational threshold energy where downhill site-to-site transfer is marginal. By using freely propagating and tunable 70 fs excitation/probing pulses and employing narrow-band spectral filtering of wave packets, fluorescence interferograms with strongly damped beatings can be observed. The coherences formally follow the in-phase superpositions of two site-optical free-induction-decays and originate from distinct pairs of coherent doorway-states, different in energy and space, each of them being targeted, by two discrete quantum-arrival-states 1(alpha) and 1(beta), via independent, isoenergetic 0-->1 fluorescence transitions. The coherent transients are explained as site-to-site polarization beatings, caused by the interference of two fluorescence correlation signals. The numerical analysis of the damping regime, based upon second-order perturbational solutions, reveals the lower limit value of homogeneous dephasing in the range from T(2) approximately 100 fs to T(2) approximately 200 fs depending on the site-excitation energy of the bottom-states. The experiments enable to look into the formation of the relaxed state as a special molecular process of electron-phonon coupling and hence open-up a quite new perspective in the puzzle of multichromophore optical dynamics and structural relaxation in conjugated polymers.

Journal Article↗
PubMed2004

Preparation and resolution of molecular states by coherent sequences of phase-locked ultrashort laser pulses.

We study the application of nonlinear wave packet interferometry to the preparation and resolution of the overlaps of nonstationary nuclear wave functions evolving in an excited electronic state of a diatomic molecule. It is shown that possible experiments with two phase-locked ultrashort pulsepairs can be used to determine a specific vibrational wave packet state in terms of coherent states of the ground electronic state. We apply this scheme to an idealized molecule with harmonic potential energy surfaces and to the X <-- B transition states of the iodine molecule. Our results indicate that this scheme is very promising as a potential tool to quantum control.

Journal Article↗
PubMed2004

Phase-stabilized two-dimensional electronic spectroscopy.

Two-dimensional (2D) spectroscopy is a powerful technique to study nuclear and electronic correlations between different transitions or initial and final states. Here we describe in detail our development of inherently phase-stabilized 2D Fourier-transform spectroscopy for electronic transitions. A diffractive-optic setup is used to realize heterodyne-detected femtosecond four-wave mixing in a phase-matched box geometry. Wavelength tunability in the visible range is accomplished by means of a 3 kHz repetition-rate laser system and optical parametric amplification. Nonlinear signals are fully characterized by spectral interferometry. Starting from fundamental principles, we discuss the origin of phase stability and the precise calibration of excitation-pulse time delays using movable glass wedges. Automated subtraction of undesired scattering terms removes experimental artifacts. On the theoretical side, the response-function formalism is extended to describe molecules with three electronic levels, and the shape of 2D spectral features is discussed. As an example for this technique, experimental 2D spectra are shown for the dye molecule Nile Blue in acetonitrile at 595 nm, recorded for a series of population times. Simulations explore the influence of different model parameters and qualitatively reproduce the experimental results. We show that correlations between different electronically excited states can be determined from the spectra. The technique described here can be used to measure the third-order response function of complex systems covering several electronic transitions.

Journal Article↗
PubMed2004

Sublimation enthalpy of dye molecules measured using fluorescence.

We present an in-flight fluorescence detection scheme for molecular beams which is applied to determine the enthalpy of sublimation of dye molecules. We investigate tetraphenylporphyrin (TPP), porphine, and nile red, which are believed to be suitable candidates for molecular de Broglie wave interferometry. The measured values are H(sub)(TPP)=142+/-3 kJ/mol, H(sub)(porphine)=87+/-3 kJ/mol, and H(sub)(nile red)=66+/-2 kJ/mol. For TPP, sublimation enthalpies differ in the literature by more than a factor of 2. Our measurements confirm a value at the lower end of this scale. We discuss changes in the character of the molecular flow with the source temperature as a prime reason for discrepancies in the published data.

Journal Article↗
PubMed2005

Nanosecond freezing of water under multiple shock wave compression: continuum modeling and wave profile measurements.

Using real time optical transmission and imaging measurements in multiple shock wave compression experiments, water was shown to solidify on nanosecond time scales [D. H. Dolan and Y. M. Gupta, J. Chem. Phys. 121, 9050 (2004)]. Continuum modeling and wave profile measurements, presented here, provide a complementary approach to examine the freezing of shocked water. The water model consisted of thermodynamically consistent descriptions of liquid and solid (ice VII) water, relationships for phase coexistence, and a time-dependent transition description to simulate freezing dynamics. Continuum calculations using the water model demonstrate that, unlike single shock compression, multiple shock compression results in pressure-temperature conditions where the ice VIII phase is thermodynamically favored over the liquid phase. Wave profile measurements, using laser interferometry, were obtained with quartz and sapphire windows at a peak pressure of 5 GPa. For water confined between sapphire windows, numerical simulations corresponding to a purely liquid response are in excellent agreement with the measured wave profile. For water confined between quartz windows (to provide a nucleating surface), wave profile measurements demonstrate a pure liquid response for an incubation time of approximately 100 ns followed by a time-dependent transformation. Analysis of the wave profiles after the onset of transformation suggests that water changes from a metastable liquid to a denser phase, consistent with the formation of a high-pressure ice phase. Continuum analyses and simulations underscore the need for multiple time scales to model the freezing transition. Findings from the present continuum work are extremely consistent with optical results reported previously. These studies constitute the first comprehensive investigation reported for freezing of a liquid at very short time scales.

Journal Article↗
PubMed2006

Implementation of quantum gate operations in molecules with weak laser fields.

We numerically propose a way to perform quantum computations by combining an ensemble of molecular states and weak laser pulses. A logical input state is expressed as a superposition state (a wave packet) of molecular states, which is initially prepared by a designed femtosecond laser pulse. The free propagation of the wave packet for a specified time interval leads to the specified change in the relative phases among the molecular basis states, which corresponds to a computational result. The computational results are retrieved by means of quantum interferometry. Numerical tests are implemented in the vibrational states of the B state of I2 employing controlled-NOT gate, and 2 and 3 qubits Fourier transforms. All the steps involved in the computational scheme, i.e., the initial preparation, gate operation, and detection steps, are achieved with extremely high precision.

Journal Article↗