Enhancement of the Anti-Stokes Fluorescence of Hollow Spherical Carbon Nitride Nanostructures by High Intensity Green Laser.

Fluorescence spectra of graphitic (g-C3N4) and spherical (s-C3N4) modifications of carbon nitride were measured as a function of green pulsed (6 ns-pulse) laser intensity. It was found that the intensity of the laser increases the maximum of the fluorescence shifts towards the anti-Stokes side of the fluorescence for s-C3N4 spherical nanoparticles. This phenomenon was not observed for g-C3N4 particles. The maximum of the anti-Stokes fluorescence in s-C3N4 nanoparticles was observed at 480 nm. The ratio of the intensity of the anti-Stokes peak (centered at 480 nm) to that of the Stokes peak (centered at 582 nm) was measured to be I484/582 = 6.4 × 10-3 at a low level of intensity (5 mW) of a green pulsed laser, whereas it rose to I484/582 = 2.27 with a high level of laser intensity (1500 mW).

Transformation of diamond to fullerene-type onions at pressure 70 GPa and temperature 2400 K.

We report the observation of a phase transition of diamond to denser than diamond carbon phase composed from 2 to 3 fullerene-type shells of onions. Raman spectra indicate the fullerene-type of the onions shells. The onions phase is a stable phase in a diamond instability zone of a phase diagram of carbon at pressure 70 GPa and temperature 2400 K. A mixture of diamond and Ni powders was heated by a laser beam under pressure in a diamond anvil cell. Both direct and catalytic diamond to onions transitions were observed during heating. The catalytic transformation includes the following steps. Melting of Ni during the laser heating at pressure 70 GPa, a 'diamond solution' (a transfer of carbon atoms from diamond) in liquid Ni and the formation of an equilibrium carbon phase from the supersaturated solution upon cooling. The catalytic process is a reverse one relative to the catalytic synthesis of diamond in a diamond stability zone at pressure around 6 GPa. The main result of our study is the presence of fullerene-type structures in the phase diagram of carbon in the region of diamond instability under high sub-Mbar pressure and wide range of temperatures.

Imaging system based on a tandem acousto-optical tunable filter for in situ measurements of the high temperature distribution.

We present, to the best of our knowledge, the first experimental demonstration of a new imaging system for in situ measurement of the two-dimensional (2D) distribution of the surface temperature of microscopic specimens. The main component of the system is an imaging tandem acousto-optical tunable filter (TAOTF) synchronized with a video camera. A set of TAOTF spectroscopic images (up to a few hundreds) is taken by the TAOTF imaging system to fit the measured spectral curves in each pixel to the Planck radiation function and determine the temperature and emissivity of the sample using the gray body approximation. It is experimentally shown that this technique provides aberration-free spectral imaging suitable for precise multispectral imaging radiometry (MIR).

Combined laser ultrasonics, laser heating, and Raman scattering in diamond anvil cell system.

We developed a multi-functional in situ measurement system under high pressure equipped with a laser ultrasonics (LU) system, Raman device, and laser heating system (LU-LH) in a diamond anvil cell (DAC). The system consists of four components: (1) a LU-DAC system (probe and pump lasers, photodetector, and oscilloscope) and DAC; (2) a fiber laser, which is designed to allow precise control of the total power in the range from 2 to 100 W by changing the diode current, for heating samples; (3) a spectrometer for measuring the temperature of the sample (using black body radiation), fluorescence spectrum (spectrum of the ruby for pressure measurement), and Raman scattering measurements inside a DAC under high pressure and high temperature (HPHT) conditions; and (4) an optical system to focus laser beams on the sample and image it in the DAC. The system is unique and allows us to do the following: (a) measure the shear and longitudinal velocities of non-transparent materials under HPHT; (b) measure temperature in a DAC under HPHT conditions using Planck's law; (c) measure pressure in a DAC using a Raman signal; and (d) measure acoustical properties of small flat specimens removed from the DAC after HPHT treatment. In this report, we demonstrate that the LU-LH-DAC system allows measurements of velocities of the skimming waves in iron at 2580 K and 22 GPa.

Reply to "Comment on 'Deformation of biological cells in the acoustic field of an oscillating bubble' ".

In the Comment by Choi [Phys. Rev. E 82, 013901 (2010)] on two our articles [Phys. Rev. E 72, 061907 (2005); Phys. Rev. E 79, 021910 (2009)], it is claimed that (a) there is more than one natural frequency associated with the quadruple mode and (b) the quadruple mode shows resonance more closely at the characteristic frequency ω(T)/2π than at ω(K)/2π. In this Reply we would like to provide evidence supporting the conclusions made in our original articles.

Deformation of biological cells in the acoustic field of an oscillating bubble.

In this work we develop a theoretical framework of the interaction of microbubbles with bacteria in the ultrasound field using a shell model of the bacteria, following an approach developed previously [P. V. Zinin, Phys. Rev. E 72, 61907 (2005)]. Within the shell model, the motion of the cell in an ultrasonic field is determined by the motion of three components: the internal viscous fluid, a thin elastic shell, and the surrounding viscous fluid. Several conclusions can be drawn from the modeling of sound interaction with a biological cell: (a) the characteristics of a cell's oscillations in an ultrasonic field are determined both by the elastic properties of the shell the viscosities of all components of the system, (b) for dipole quadrupole oscillations the cell's shell deforms due to a change in the shell area this oscillation depends on the surface area modulus K{A} , (c) the relative change in the area has a maximum at frequency f{K} approximately 1/2pi square root[K{A}(rhoa;{3})] , where a is the cell's radius and rho is its density. It was predicted that deformation of the cell wall at the frequency f{K} is high enough to rupture small bacteria such as E . coli in which the quality factor of natural vibrations is less than 1 (Q<1). For bacteria with high value quality factors (Q>1) , the area deformation has a strong peak near a resonance frequency f{K} however, the value of the deformation near the resonance frequency is not high enough to produce sufficient mechanical effect. The theoretical framework developed in this work can be extended for describing the deformation of a biological cell under any arbitrary, external periodic force including radiation forces unduced by acoustical (acoustical levitation) or optical waves (optical tweezers).

Iron coated pottery granules for arsenic removal from drinking water.

A new media, iron coated pottery granules (ICPG) has been developed for As removal from drinking water. ICPG is a solid phase media that produces a stable Fe-Si surface complex for arsenic adsorption. Scanning electron microscopy (SEM) was used to document the physical attributes (grain size, pore size and distribution, surface roughness) of the ICPG media. Several advantages of the ICPG media such as (a) its granular structure, (b) its ability to absorb As via the F(0) coating on the granules' surface; (c) the inexpensive preparation process for the media from clay material make ICPG media a highly effective media for removing arsenic at normal pH. A column filtration test demonstrated that within the stability region (flow rate lower than 15L/h, EBCT >3 min), the concentration of As in the influent was always lower than 50 microg/L. The 2-week system ability test showed that the media consistently removed arsenic from test water to below the 5 microg/L level. The average removal efficiencies for total arsenic, As(III), and As(V) for a 2-week test period were 98%, 97%, and 99%, respectively, at an average flow rate of 4.1L/h and normal pH. Measurements of the Freundlich and Langmuir isotherms at normal pH show that the Freundlich constants of the ICPG are very close to those of ferric hydroxide, nanoscale zero-valent iron and much higher than those of nanocrystalline titanium dioxide. The parameter 1/n is smaller than 0.55 indicating a favorable adsorption process [K. Hristovski, A. Baumgardner, P. Westerhoff, Selecting metal oxide nanomaterials for arsenic removal in fixed bed columns: from nanopowders to aggregated nanoparticle media, J. Hazard. Mater. 147 (2007) 265-274]. The maximum adsorption capacity (q(e)) of the ICPG from the Langmuir isotherm is very close to that of nanoscale zero-valent indicating that zero-valent iron is involved in the process of the As removal from the water. The results of the toxicity characteristic leaching procedure (TCLP) analysis revealed that the media was non-hazardous, as shown by the ND (non-detectable) result for arsenic. The mechanism of As adsorption by ICPG has not been determined. Formation of Fe-Si complexes on the surface of the ICPG system may be responsible for the tight bonding of the As to the IGPC media.

Novel micro-cavity substrates for improving the Raman signal from submicrometer size materials.

A novel and simple method for improving the detection limit of conventional Raman spectra using a micro-Raman system and picoliter volumes is presented. A micro-cavity in a reflecting metal substrate uses various mechanisms that collectively improve the entire Raman spectrum from the sample. A micro-cavity with a radius of several micrometers acts as a very effective device that provides multiple excitation of the sample with the laser and couples the forward-scattered Raman photons toward the collection optics in the back-scattered Raman geometry. One of the important features of the micro-cavity substrate is that it enhances the entire Raman spectrum of the molecules under investigation and maintains the relative intensity ratios of the various Raman bands. This feature of maintaining the overall integrity of the Raman features during signal enhancement makes the micro-cavity substrate ideal for forensic science applications for chemical detection of residual traces and other applications requiring low sample concentrations. The spectra measured in these cavities are also observed to be highly reproducible and reliable. A simple method for fabricating micro-cavity substrates with precise sizes and shapes is described. It is further shown that micro-cavities coated with nanofilms of gold take advantage of both surface-enhanced Raman scattering (SERS) and micro-cavity methods and also significantly improve sample detection limits.

Mechanical properties of single cells by high-frequency time-resolved acoustic microscopy.

In this paper, we describe a new, high-frequency, time-resolved scanning acoustic microscope developed for studying dynamical processes in biological cells. The new acoustic microscope operates in a time-resolved mode. The center frequency is 0.86 GHz, and the pulse duration is 5 ns. With such a short pulse, layers thicker than 3 microm can be resolved. For a cell thicker than 3 microm, the front echo and the echo from the substrate can be distinguished in the signal. Positions of the first and second pulses are used to determine the local impedance of the cell modeled as a thin liquid layer that has spatial variations in its elastic properties. The low signal-to-noise ratio in the acoustical images is increased for image generation by averaging the detected radio frequency signal over 10 measurements at each scanning point. In conducting quantitative measurements of the acoustic parameters of cells, the signal can be averaged over 2000 measurements. This approach enables us to measure acoustical properties of a single HeLa cell in vivo and to derive elastic parameters of subcellular structures. The value of the sound velocity inside the cell (1534.5 +/- 33.6 m/s) appears to be only slightly higher than that of the cell medium (1501 m/s).

Imaging of focal contacts of chicken heart muscle cells by high-frequency acoustic microscopy.

A study of the adhesion of embryonic chicken heart muscle cells was conducted with a newly developed time-resolved acoustic microscope, which operates in the GHz-frequency range. The interpretation of the acoustical images of the heart muscle cells was done in combination with the fluorescence optical microscopy. A comparison between the acoustical images of chicken heart muscle cells and optical images of the same cells after staining showed that the actin fibers end inside the dark streaks in the acoustical images and thus represent the focal contacts (FCs). For cell biology applications, this demonstrates (a) the use of SAM as a tool for studying the dynamics of the FCs of living cells without any chemical staining and (b) that the combination of acoustic and optical microscopes allows interpretation of the acoustical images by using the wide variety of techniques available in optical microscopy.

Combining Brillouin spectroscopy and laser-SAW technique for elastic property characterization of thick DLC films.

Surface Brillouin spectroscopy (SBS) has been widely used for elastic property characterization of thin films. For films thicker than 500 nm, however, the wavelength of surface acoustic wave in the frequency range available for SBS is smaller than film thickness, and the SBS measures only the Rayleigh wave of the film. The laser-SAW technique, on the other hand, measures only the low-frequency portion of the surface acoustic wave dispersion and can estimate only one elastic modulus of the film (typically Young's modulus). In this work, we have combined the two methods to determine both Young's modulus and Poisson's ratio of a diamond-like carbon (DLC) film. It was found that reasonable estimates can be obtained for the longitudinal wave velocity, shear wave velocity, and Young's modulus of the film. The Poisson's ratio, however, still has a relatively large measurement error.